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Review of the Edwards Aquifer Habitat Conservation Plan: Report 3 (2018)

Chapter: 3 Will the Biological Objectives Meet the Biological Goals?

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Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
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3

Will the Biological Objectives Meet the Biological Goals?

This chapter addresses the first part of the Committee’s statement of task, that is, whether the biological objectives can meet the biological goals for the listed species in the Edwards Aquifer system. As discussed previously, the biological objectives are different for each species, although they generally have three components: flow, water quality, and habitat. This chapter addresses whether the combined effects of the flow objective, the water quality objective, and the habitat objective achieve the biological goals for the fountain darter, Texas wild rice, the Comal Springs riffle beetle (CSRB), and the San Marcos salamander.

The Habitat Conservation Plan (HCP) contains a flow objective for each species that differs between the two systems. For the Comal system, the flow objective is to maintain a long-term average total discharge (50 years including the Drought of Record) above 225 cubic feet per second (cfs) with a minimum of 30 cfs that is not to exceed six months in duration, followed by at least 80 cfs for three months. For the San Marcos system, the flow objective is to maintain a long-term average total discharge above 140 cfs with a minimum of 45 cfs that is not to exceed six months in duration, followed by at least 80 cfs for three months. The water quality objective is the same in both systems: daily average water quality cannot deviate by more than 10 percent from historically recorded water quality conditions (long-term average) within the Edwards Aquifer. The conditions are measured at the spring openings for species that dwell near or in the springs (e.g., the CSRB) and in the river systems for the other species (e.g., the fountain darter). Texas wild rice and the San Marcos salamander do not have a water quality objective. Finally, it should be noted that the fountain

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

darter has a more detailed water quality objective than the other species, which is that instantaneous water temperature must be maintained below 25°C and instantaneous dissolved oxygen (DO) maintained above 4 mg/L. The habitat objective varies by species and in some cases is worded similarly to a minimization and mitigation (M&M) measure.

UNDERSTANDING THE RATINGS

The statement of task specified that, to the extent possible, the Committee should determine the likelihood that the biological objectives will achieve the biological goals. The Committee developed a rubric of four possible ratings: highly likely, likely, somewhat likely, and unlikely. The rating highly likely corresponds to minimal or no concerns about achieving biological goals, likely implies that the objective is expected to achieve biological goals, somewhat likely implies that the objective may reach the goals but there are significant concerns, and an unlikely rating is given where the objective is not expected to reach biological goals. Because the effort to determine the ratings was spread among Committee members with expertise in different species, an extensive discussion occurred to ensure consistency of ratings across the species. The ratings were based on the collective and consensus opinion of the Committee using the available evidence on how the collection of objectives for a species would achieve the biological goals for that species. The Committee did not parse the likelihoods in any further detail (e.g., whether a specific objective will achieve a specific goal) than a single overall determination per species.

Several assumptions about the ratings require explanation. First, the likelihood rating is specifically about whether the objectives will meet the biological goals in the HCP and is not a judgment about the likelihood of success of the restoration actions under way or planned or the effectiveness of other management actions. Second, the rating refers to the likelihood of success over the lifetime of the HCP, and not the annual probability of success. Third, there are two drivers that move determinations down from the highest rating of success (highly likely) and up (to higher success) away from the lowest rating of success (unlikely). One driver is the inferences possible from the available information, data, and past performance. The other driver results from lack of information or uncertainty in how objectives will achieve goals and from unknown future conditions.

The language is nuanced because the discussion becomes how much certainty is associated with the likelihoods, which are already in the form of probability statements. For example, there is extensive information on fountain darters and Texas wild rice, and so the determinations are offered with a relatively high degree of confidence. In contrast, for the CSRB and the San Marcos salamander, much less is known, which prevents determi-

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

nations of the more definitive likelihoods (highly likely and unlikely) and pushes the determination to middle probabilities. Thus, to say “highly likely” or “unlikely” requires a higher degree of certainty.

For each species the determinations of the Committee are stated first, followed by the evidence and reasoning that led to the determination. Finally, the actions that could be taken to move the determination for a species up to a higher rating are discussed.

FOUNTAIN DARTER

The biological goals for the fountain darter are to maintain specific areal amounts of various types of submersed aquatic vegetation (SAV) in several river reaches (the long-term biological goal, or LTBG, reaches) and to maintain specific fountain darter densities (number/area) in each SAV type. The biological objectives are (1) to meet certain minimum flow requirements in the Comal or San Marcos systems, (2) to maintain surface water quality within 10 percent of historical conditions for many parameters at various locations (except for DO and temperature; see above), and (3) to restore native SAV.

Determination and Information Used

Will the biological objectives for the fountain darter achieve the biological goals? The Committee determined that, based on the available information, it is likely that the biological objectives will meet the biological goals for the fountain darter. The determination of likely is offered with a high level of confidence because it is based on evidence rather than based on a lack of information causing uncertainty to drive down the determination. The fountain darter differs from some of the other organisms of interest because it is well studied in the two systems, and extensive data and models (suitability, population dynamics) are available. (There is also a large body of available information for Texas wild rice.)

The Committee used many documents available from the Edwards Aquifer Authority (EAA). Some of the key sources were the recent SAV report (BIO-WEST and Watershed Systems Group, 2016), including the creation of the restoration reaches, inclusion of Texas wild rice as fountain darter habitat, discussion of the Texas wild rice expansion, and the time schedule of future restoration. The HCP (EARIP, 2012), Hardy (2009), Hardy et al. (2010), and Variable Flow Study reports (BIO-WEST, 2007) were consulted for the rationales and derivation of the biological objectives. The report that documented the development and preliminary simulations of the fountain darter population model highlighted known information and critical unknowns (Grant et al., 2017). In addition, the Committee re-

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

lied on the many informative presentations made by EAA staff during Committee meetings, and the Committee did some simple analyses of the data.

Evidence That the Objectives Are Achieving the Goals

Given that fountain darters are highly associated with SAV (see Figure 2-2), that flows are a major driver of local conditions (water velocities, depths, health of the SAV), and that fountain darters need relatively stable water quality conditions, the use of the three components (habitat, flow, and water quality) of the biological objectives makes good ecological sense. In addition, the goals and objectives were derived, in a logical manner, from empirical data available at the time of the HCP. The flow objectives were derived from habitat suitability modeling of each system. Habitat suitability modeling is an accepted method for determining minimum flows that support fish habitat, often used as part of Instream Flow Incremental Methodology in the licensing of hydropower facilities whose operations affect flows (Tharme, 2003; Lamb et al., 2004; NRC, 2015).

Evidence that the habitat, flow, and water quality objectives can meet the goals for fountain darters can be gleaned from past performance. This is the argument that the objectives have been successful to date, and so they would be expected to be successful into the future. EAA has been able to remove nonnative SAV and successfully plant native SAV in the LTBG reaches. For example, 3,595 m2 of invasive plants were removed from the San Marcos system in 2017, out of a total target vegetated area in the San Marcos of 6,200 m2 (Blanton and Associates, 2018). Nonnative SAV removal is obviously contributing to a substantial proportion of needed area available for active planting of native SAV, which in 2017 totaled almost 46,000 individual plants. Furthermore, during the last 15 years the average fountain darter densities in key SAV types have not shown persistent downward trends (Figure 3-1).

Although the scientific basis of the water quality component (i.e., 10 percent deviation, minimum DO, maximum temperature) is not well documented (as discussed in the last section of this chapter), the available data show that good water quality conditions have been generally maintained. Figure 3-2 shows a wide range in ambient daytime DO with highest densities of fountain darters between ~ 6 and 9 mg/L but certainly reasonable densities down to about 5 mg/L. The mean fountain darter abundance is 19.7 individuals/trap (median density = 10; 25th, 75th = 4, 24, respectively). Figures 3-3 and 3-4 show that DO is under 4 mg/L at most 2.5 percent of the time, and that temperatures over 25°C are observed only 2.5 percent of the time. Furl (2017) showed that conductivity and pH are frequently outside the 10 percent bounds, and yet the density goals for fountain darters are being met. The water quality component can be viewed as necessary

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×
Image
FIGURE 3-1 Average fountain darter densities by submerged aquatic vegetation type for each year in the Comal (top) and San Marcos (bottom) systems. The data are from EAA biomonitoring using the drop-net method for sampling fountain darters. Only SAV types with at least three to four measurements per year per SAV type and measurements spanning roughly April to November were included. The right-hand y-axis applies to bryophytes in the top panel and to Hydrilla in the bottom panel. SOURCE: Committee manipulation of Edwards Aquifer Authority data.
Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×
Image
FIGURE 3-2 Abundance of fountain darters, captured in 2-m2 drop nets, plotted against the ambient dissolved oxygen (DO) in mg/L at time of sampling. SOURCE: Committee manipulation of Edwards Aquifer Authority data.

but not sufficient; good water quality is needed but alone would not likely result in increased fountain darter abundance.

Recently, the EAA used the nonstandard optional adaptive management process to adjust their restoration activities related to the fountain darter. This is noteworthy for two reasons. First, it shows that the adaptive management process is a viable mechanism for changing the restoration in response to new information. This adds a degree of flexibility and robustness and thereby increases our confidence that the objectives can be effectively and efficiently modified to ensure that the goals are met in the future. Second, a solution was identified that addressed the immediate issues that arose that would have prevented the goals from being met. The solution was to add reaches (i.e., restoration reaches) so that habitat created

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×
Image
FIGURE 3-3 Range of dissolved oxygen (DO) observed during the drop-net sampling. This shows that DO is less than 4 mg/L at most 2.5 percent of time. N = 965. No nighttime data are available. SOURCE: Committee manipulation of Edwards Aquifer Authority data.
Image
FIGURE 3-4 Range of temperature observed during the drop-net sampling. A temperature over 25°C is observed only 2.5 percent of the time. N = 965. Note that there is clearly an error in the dataset: the point indicating a water temperature of 2.4°C. SOURCE: Committee manipulation of Edwards Aquifer Authority data.
Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

in these new reaches would contribute to the target number of fountain darters required (which is unchanged). In addition, Texas wild rice is now being credited as fountain darter habitat. These actions demonstrate that adaptive management, which always sounds good on paper, can actually be successfully used in practice by the EAA. Such management actions have been challenging to implement in other systems undergoing restoration, so this demonstration that the adaptive management process is working is noteworthy and adds reassurance that the objectives can achieve the goals in the future.

Another piece of evidence that the objectives can meet the goals was maintenance of general habitat conditions and achievement of the flow objective during the recent drought and flood years (2013–2014 and 2015). While there were reach-specific responses to these events (e.g., in the Old Channel), there were no systemwide massive losses of habitat (see Blanton and Associates, 2018, App. K2, Fig. 18) nor did EAA report any obvious sharp changes in fountain darter densities by SAV type. While achieving the objectives is a question of the effectiveness of the M&M measures, it is relevant here because the flow objective is described in the HCP as addressing uncertainty issues related to the habitat objective. If the flow objective had not been met under the recent extreme conditions, then this would leave the habitat objective more vulnerable to not meeting the goals.

Finally, as discussed above, there do not seem to be any obvious temporal trends in fountain darter densities by SAV type (Figure 3-1). Detection of persistent declines would suggest that the population was decreasing or that the additional habitat was simply diluting the fountain darter in its habitat rather than causing an increase in fountain darter population abundance. Some caution is needed because of the possibility of false negatives (i.e., low power prevents detection when a trend is occurring). Further analysis on the ability to detect events and trends in the fountain darter monitoring data (i.e., power analysis—see Green, 1989; Fairweather, 1991) would enable a determination of what magnitude of trends is detectable and shed some light on the likelihood of false negatives.

Notable Concerns

Habitat Objectives. The recent addition of the restoration reaches raises some concerns about the capacity of the two systems for further adaptation. It is clear that the LTBG reaches in both systems have finite capacity for desired SAV. At some point, the systems will run out of options for good habitat reaches, which may affect the ability of the objectives to achieve the goals. The two systems are relatively small in size and have other activities occurring (e.g., recreation), and so there is a finite capacity for restoring good habitat reaches in both systems.

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

Achieving the biological goals of numbers of fountain darters (square meters times density) relies on the philosophy common in habitat restoration that habitat is limiting the population of interest. Otherwise, the new habitat simply results in a spatial redistribution of existing fountain darters. This is a very common debate in other systems, often referred to as “production versus attraction” (Grossman et al., 1997; Osenberg et al., 2002). Even under the best conditions of the habitat being the bottleneck, one should not assume that the responses will be proportional; that is, a 50 percent increase in habitat would not be expected to cause a 50 percent increase in the total population. It depends on how habitat affects growth, mortality, and reproduction over the fountain darter’s life cycle. A sign that habitat is not limiting the fountain darter population would be decreasing median densities in some reaches as individuals move to a new habitat (i.e., become diluted).

Colonization of new habitat is based on dispersal and connectivity. The Comal and San Marcos systems are relatively small and linear in arrangement, and so connectivity is likely high and thus there is the potential (pathways available) for individuals to find the new habitat. However, EAA studies have shown that fountain darters are highly localized in their movement patterns and show relatively little net displacement over the order of days to weeks (BIO-WEST, 2014; Grant et al., 2017). This confined home range can limit individuals in finding new habitats. Whether dispersal becomes more limiting as less preferred (and maybe less connected) habitats are added remains a question. Data can be analyzed from the monitoring program to show that dispersal is not a limiting factor to fountain darters inhabiting new habitats.

Habitat stability is at risk from extreme events (droughts, floods) and other resets, such as dam repairs, changes in recreational access, possible plant diseases, and invasive species. As SAV restoration is anticipated to take until 2027, it is possible that some of these events may occur over the next nine years. These risks are recognized by the EAA (BIO-WEST and Watershed Systems Group, 2016). There is also the possibility of unanticipated effects in the future. For example, during development of the HCP, it was not anticipated that Texas wild rice would expand as it did, nor was it considered habitat in the calculations of fountain darter abundance. Despite these risks, the responses of SAV to the recent drought and floods are encouraging and support a high degree of stability.

A final caution is warranted because of the method used to compute median fountain darter densities to show compliance with the biological goals. The EAA uses cumulative median densities of fountain darter, which are very insensitive to any year-to-year changes (see Box 2-1).

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

Flow Objectives. The flow objectives were designed, in part, to protect against uncertainty in how the habitat objective would perform. The flow objectives were derived from habitat suitability index (HSI) modeling. However, the analyses were done almost 10 years ago and the systems have changed since then, so some of the interpretations of the results should be confirmed. Although HSI modeling is widely used, it is often criticized for several of its key assumptions (Mathur et al., 1985; Gore, 1989; Railsback, 2016). A major assumption is that actual species abundance will track how habitat quality and quantity vary in space and time. HSI results are best interpreted as the capacity or potential for abundance, rather than how the population abundance will respond.

The HSI analyses used to derive the flow objectives included some questionable methodological decisions. First, simulations were steady-state flows, and so temporal variation in flows was not directly assessed. Given the small size of the two systems, inferring how dynamically varying flows affect fountain darter habitat by piecing together results from steady-state flows is reasonable for average conditions but less robust for extreme low and high flows. Third, the HSI modeling for the fountain darter was correlated with velocity, depth, and vegetation type. The vegetation maps were assumed invariant under all conditions, including velocity, depth, and temperature, which is reasonable for short-term predictions but more questionable over multiple years when vegetation responds to changing flows. Furthermore, the specific suitability relationships can be refined based on new data and statistical fitting methods (e.g., Ahmadi-Nedushan et al., 2006). The Committee mentions these issues for completeness and does not consider any to be of critical importance to the determination of likely. The use of older data could be addressed by revisiting the HSI analyses, as suggested in NRC (2015).

Water Quality Objectives. The water quality objectives help to create a stable environment needed by the fountain darter, but one could question some aspects of the DO and temperature objectives. DO is measured during the daytime; nighttime values would be lower. For both DO and temperature, the use of minimum DO and maximum temperature are reasonable, but some caution arises when the long term (decades) is considered because of warming trends. The biological basis for the objectives, especially the 10 percent deviations, should be confirmed using empirical data.

Conclusion and Actions Needed to Improve the Rating

The evidence in support of the biological objectives meeting the biological goals is based on empirical observations and the cumulative input (including the development of the HCP) from many experts and stakeholders.

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

Examination of past performance showed successful removals and planting of SAV, no obvious drops in fountain darter densities, stable water quality, and a successful adaptive management action demonstrating flexibility in the process. The cautionary evidence is mostly related to the use of older information in the HSI modeling, lack of certain analyses that would increase confidence (described below), and uncertainty about future options to expand restoration in new reaches and how the systems and fountain darters will respond to future conditions. In the case of fountain darters, substantial data and information from monitoring, process studies in the field and lab, and modeling have led to a conclusion about the likelihood of success that is offered with relatively high confidence.

There are several actions the EAA could take to move the determination of likely toward very likely. First, the EAA can show that flows and habitat conditions during the Variable Flow Study are reasonable for today and into the future. The study was done almost 10 years ago, and the conditions in both systems have changed and both systems have experienced extreme events. Second, update the HSI modeling to reflect the current state of the systems and to explore scenarios such as the Drought of Record and flooding. Third, expand fountain darter monitoring to the restoration reaches to confirm that target densities are being met. Fourth, analyze the fountain darter data for temporal trends in population abundances that reflect each year and only each year. Presentations to date of fountain darter abundance time series have used either monitoring data that may not be quantitative enough (the dip-net data) or quantitative data (drop-net data) that show only cumulative median fountain darter densities. In addition, a power analysis on the abundance time series could help guide the interpretation of false negatives (no detection of downward trend when there is actually a decrease).

TEXAS WILD RICE

The long-term biological goals for Texas wild rice were determined by (1) an evaluation of the maximum occupied area of Texas wild rice that has been present in the San Marcos River in each segment over time, (2) analysis of the physical habitat modeling carried out by Hardy (2009) and Hardy et al. (2010), and (3) the 1996 FWS recovery plan goals (FWS, 1996). The biological goals for Texas wild rice are to maintain a range of areal coverage in four reaches of the San Marcos River and to maintain a range of percentages of the coverage in a given reach (see Table 2-2 for details). The biological objectives are (1) to meet certain minimum flow requirements in the San Marcos system, (2) to maintain minimum areal coverage in the four river reaches during the Drought of Record, and (3)

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

recreation awareness, with control in high-quality habitat areas when flow is below 100 cfs.

Determination and Information Used

The Committee determined that, based on available data, it is likely that the biological objectives will be able to meet the biological goals for Texas wild rice in the San Marcos River. This determination was based partially on information the Committee garnered from the impressive amount of available data as well as from oral presentations by EAA staff, discussions of existing conditions and M&M measures implemented in the river by City of San Marcos staff, and site visits to the river. In addition, relevant scientific literature was consulted, along with a voluminous collection of regulatory documents and raw data. This information has provided a historical review of Texas wild rice distribution in the San Marcos River from the time of its initial scientific description in 1933 (confirming it as a unique new species) through the 2017 HCP Annual Report (Blanton and Associates, 2018).

Evidence That the Objectives Are Achieving the Goals

The most persuasive evidence that the objectives will be able to meet the long-term goals is the gain in Texas wild rice coverage in recent years (Table 3-1). The recent SAV report (BIO-WEST and Watershed Systems Group, 2016), as well as the most recent HCP Annual Report (Blanton and Associates, 2018) give strong evidence that many of the measures that have been taken in the San Marcos basin are working. This suggests increased resilience in this ecosystem, which was once in precarious condition. The only exception is downstream of I-35 in 2017, where there may be water quality issues (addressed below). The gain in Texas wild rice coverage comes despite a near record drought in 2013–2014 as well as recent flooding. Although not every section of the San Marcos River saw a spectacular resurgence of Texas wild rice, some areas, such as the City Park reach and Spring Lake, were remarkable, with the coverage of Texas wild rice increasing threefold in a single year. This bodes well for achievement of the long-term goals in future years, and it is the foremost reason that it was decided that they were likely to be met by 2027.

Notable Concerns

Flow Objective. The flow objective for Texas wild rice was designed to protect against an extended period of drought. The origins of the flow objective include Hardy (2009), who constructed a detailed grid to represent

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

TABLE 3-1 Texas Wild Rice 2016 and 2017 Areal Coverage, Change in Areal Coverage 2013–2017, and Change in Areal Coverage 2016–2017, per Long-term Biological Goal and Restoration Reach

Reach Total Area (m2)
2016 2017 Change
2013–2017 2016–2017
Spring Lake 47.1 184.1 184.1 137.0
Spring Lake Dam 887.3 1,389.3 1,190.8 502.0
Sewell Park 1,185.8 1,811a 1,144.7 625.2
Below Sewell to City Park 2,429.0 2,810a 1,598.0 381.0
City Park 1,561.5 2,247.0 1,863.0 685.5
Hopkins Street to Snake Island 1,168.57a
Cypress Island to Rio Vista Dam 238.0 246.9 246.9 8.9
I-35 (upper and lower) 276.0 512.1 512.1 236.1
Below I-35 55.61a

aBIO-WEST data mapped July 2017.

SOURCE: Blanton and Associates (2018).

the factors that can affect Texas wild rice habitat, as part of an effort to conduct a habitat suitability analysis. Hardy (2009) ended up using only two parameters to assess the physical habitat: water depth and velocity. Using these two parameters, Hardy calculated the habitat suitability for a range of San Marcos River discharges. This exercise revealed that the optimal discharge was around 135 cfs, with declines in habitat suitability on either side of this discharge. Although avoiding explicit suggestion of what flow rate should be adopted to sustain Texas wild rice during droughts, Hardy (2009) did caution that a flow rate of 30 cfs is a concern. Hardy et al. (2010) updated the habitat suitability analysis for Texas wild rice, again using only water depth and velocity as the primary parameters. As for the fountain darters, the habitat suitability modeling may be out of date now because it was completed almost 10 years ago and the systems have changed.

Water Quality Objective. For unknown reasons, there was no term in the existing habitat suitability model that Hardy (2009) developed for Texas wild rice to assess water quality issues. This is somewhat surprising since temperature was part of the fountain darter habitat suitability modeling. The sensitivity of C3 plants to high temperatures in aquatic environments was mentioned briefly in Hardy (2009), and he was likely aware of

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

its overall importance. The realization that there are multiple modes of photosynthesis (first mentioned in the scientific literature by Hatch and Slack, 1966) has been increasingly used to explain differences in stress responses in a variety of higher plant groups over the last several decades (Ehleringer et al., 1997; Sage, 2004; Christin and Osbourne, 2014). Chapter 2 briefly outlined the problems that aquatic plants experience in accessing CO2 when they are exposed to prolonged temperatures exceeding 25°C if their primary photosynthetic mechanism is C3 rather than C4. Temperature stress has two important effects on C3 species (including Texas wild rice). The first effect is an internal decline in plant growth, and the second is that nonnative C4 species are not affected and can easily outcompete them—especially in a karst environment (Wang et al., 2017). During average- and high-flow years, the spring waters emanating from the Edwards Aquifer have ample cooling capacity. However, during droughts and if water temperature rises, Texas wild rice photosynthesis will slow considerably. The invasive weedy C4 species, such as Hydrilla, will then accelerate their uptake of CO2 and eventually drive pH up to 8 or beyond. In this pH range, C4 species can rely on bicarbonate as their prime carbon substrate, whereas C3 species cannot (Spence and Maberly, 1985). The latter first become carbon limited and ultimately carbon starved as pH climbs to 8 and beyond. Thus, without temperature being among the biological objectives, the HCP may lack an important driver that could limit Texas wild rice growth under stress conditions whenever severe droughts occur in the San Marcos system.

Habitat Objective. The main habitat objective is recreation awareness, with control in high-quality habitat areas when flow is below 100 cfs. Despite the high level of recreation in the San Marcos River, there has been a very thoughtful approach in addressing the various impacts of recreation in this system. The Committee was particularly impressed by the incorporation of SCUBA diving for students at Spring Lake with the objective in assisting with the aquatic gardening annually.

The recent decision to remove nonnative SAV species from the system should have a positive effect on Texas wild rice populations by reducing competition of very aggressive species that can take up carbon when pH exceeds 7.5. Field plots should be used to confirm this, by means of a Before-After-Control-Impact (BACI) experimental design and/or a mesocosm approach with water from the San Marcos River (Smith et al., 1993). Along with these positive developments is the recent approval (using the adaptive management process) to count Texas wild rice coverage as fountain darter habitat in the San Marcos River, thereby eliminating a source of conflict in the goals of the HCP. This should eliminate the situation where Texas wild rice was essentially pitted against the other SAV species in terms of coverage.

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

Conclusion and Actions Needed to Improve the Rating

The evidence in support of the rating is based on empirical observations of Texas wild rice coverage gain, even in the face of recent floods and droughts. In addition, the decision to remove nonnative SAV has a long-term benefit for Texas wild rice because it will lessen the risks that nonnative SAV species will be more competitive when pH is higher than 8 in this system. Finally, adaptive management has led to now including Texas wild rice as fountain darter habitat. The cautionary evidence is related to the absence of a defined water quality objective. As with the fountain darter, monitoring and successful restoration of Texas wild rice to date have led to a conclusion offered with relatively high confidence.

The main action that the EAA could take to move the determination of likely toward very likely would be to create a water quality objective for Texas wild rice, especially during low-flow conditions. If a water quality objective were to be created for Texas wild rice, an upper value for temperature in the San Marcos River could be chosen by local experts after consulting the existing scientific literature. A good starting point for initial discussions might be 25°C. Also, it will be important to continue to remove nonnative SAV, and there may be value in making this a stated biological objective for Texas wild rice. Note that temperature becomes less important once nonnatives have been removed from the system.

COMAL SPRINGS RIFFLE BEETLE

The biological goals for the CSRB are to maintain specific beetle density (number/lure) in three locations (Spring Run 3, the western shoreline of Landa Lake, and the Spring Island area) and to maintain silt-free gravel and cobble substrate in the same three locations. The biological objectives are (1) to meet certain minimum flow requirements in the Comal system, (2) to maintain spring water quality within 10 percent of historical conditions at the three locations, and (3) to restore riparian habitat adjacent to spring openings at Spring 3 and the western shoreline to reduce siltation.

Determination and Information Used

The Committee determined that, based on the available information, it is somewhat likely that the biological objectives will meet the biological goals for the CSRB. This determination was based on the fact that there are substantial needs for additional information related to quantitative monitoring of CSRB populations. Furthermore, mechanisms to evaluate the efficacy of riparian restoration in eliminating silt at spring openings are limited and not currently in place. Finally, there is some question about the validity

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

of the flow objective for two of the reaches in the Comal system that are monitored to determine compliance with the CSRB biological goals.

To reach their determination, the Committee made use of biomonitoring data for the CSRB and reviewed evidence that riparian restoration activities are working. It considered how well the flow objective reflects the habitat suitability modeling done for the CSRB as found in Hardy (2009) and Hardy et al. (2010). And it reviewed Appendix D from the HCP (EARIP, 2012), the Variable Flow Study reports (BIO-WEST, 2007), and numerous reports on the CSRB from the Applied Research Program (see Table 5-3 in NASEM, 2017).

Evidence That the Objectives Are Achieving the Goals

Chapter 2 discussed the limitations of quantitative sampling of the CSRB, in terms of the enormous variation in the number of samples collected each year, as well as the lack of a standard protocol for sampling until very recently. Given these sampling limitations and the high number of zero samples recorded, it is not surprising that the biomonitoring data show no particular trends over the last 12 years (Figure 3-5). Hence, unlike

Image
FIGURE 3-5 Biomonitoring data for Comal Springs riffle beetle from all three long-term biological goal reaches, 2004–2016. The y-axis is number of beetles per lure, with a maximum value of 50, such that not all data are shown. SOURCE: Furl (2017).
Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
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with Texas wild rice, the monitoring data do not provide evidence that the objectives can meet the biological goals for the CSRB.

Notable Concerns

Flow Objective. The flow objective for the CSRB is the same as for the fountain darter. The flow objective was developed to sustain flow sufficient to maintain habitat, and therefore populations of the listed species, which in the case of the Comal system are the fountain darter and the CSRB. The habitat suitability modeling done for the fountain darter played a significant role in determining the flow objectives in the Comal system; hence, the criticism of that HSI modeling discussed previously (see Fountain Darter section) is also applicable here. Nonetheless, it is also important to consider the extent to which the flow objectives take into consideration the habitat suitability modeling done for the CSRB.

As discussed in Appendix D of the HCP (EARIP, 2012), the habitat suitability modeling for the CSRB was done at three major springs in the Comal system (Spring Runs 1, 2, and 3). Habitat suitability for the CSRB was modeled to be a function of surface water depth and velocity, with the optimal water depth ranging from 0.02 to 2.0 feet and velocities up to 2 feet per second (Hardy, 2009). Hardy (2009) estimated a 30 percent reduction in CSRB habitat for Spring Run 1 at flows < 150 cfs, while the other runs would not experience a loss in estimated habitat until flows were < 125 cfs (Figure 3-6). There was no estimated suitable CSRB habitat at flow rates less than 30, 65, and 100 cfs for Spring Runs 1, 2 and 3, respectively. However, there are no data showing how different flow rates affect habitat suitability in the other two reaches used for LTBG monitoring (western shoreline of Landa Lake and Spring Island area).

Other assumptions went into establishing the Comal flow objectives, including the historical evidence of the CSRB surviving the Drought of Record when all major spring runs ceased to flow for five months. It is assumed that repopulation of the major spring runs came from emigration of the CSRB from smaller springs in Landa Lake that remained wetted during the Drought of Record. Although only the LTBG reaches are used for assessing if CSRB biological objectives are being achieved, it has been estimated that approximately 50 percent of CSRB habitat exists in other areas of Landa Lake that are less likely to become dry at extreme low flows (e.g., < 30 cfs) (EARIP, 2012, App. D). This additional habitat is expected to act as a refugium and ultimately sources of the CSRB in cases of extended low, or zero, flow at the main springs. There is also the hypothetical potential for the CSRB to survive prolonged periods of drought by retreating into spring openings and relying on subsurface habitats.

According to Hardy (2009), a minimum of 30-cfs spring flow would

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×
Image
FIGURE 3-6 Simulated suitable habitat for the Comal Springs riffle beetle in three Comal Spring runs at various spring flow rates. SOURCES: EARIP (2012, App. D) and Hardy (2009).

only provide suitable CSRB habitat at Spring 1, with no habitat available at the other two main springs. Indeed, at 100 cfs and 60 cfs, CSRB habitat is eliminated in Spring 2 and Spring 3, respectively. So, while the long-term objective of 225 cfs is likely to achieve the biological goals of the CSRB, it is more difficult to determine if the minimum flow of 30 cfs not to exceed six months, followed by 80 cfs for three months, would be adequate. At flows less than 100 cfs, potential CSRB surface habitat is eliminated at Springs 2 and 3, and it is unknown how long these springs will remain dry if overall flow is further reduced for nine months. Based on this limited information, the 30 cfs minimum flow for six months followed by 80 cfs for three months may be appropriate to achieve the biological goals of the CSRB. This assessment is also dependent on how well the habitat suitability modeling actually predicts CSRB populations, an issue discussed earlier for the fountain darter.

There is an important disconnect between the habitats for which the habitat suitability modeling was done (Spring Runs 1, 2, and 3) and the habitats where CSRB populations are currently monitored for meeting the long-term biological goals (Spring Run 3, western shoreline of Landa Lake, and Spring Island area). The HSI model used to support the flow objectives for Comal has not been repeated for the western shoreline of Landa Lake and Spring Island. Furthermore, Figure 3-6 shows that suitable habitat in

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

Spring 3 is eliminated well above the 30-cfs minimum, suggesting that for at least one of the monitored locations the minimum flow objective is unlikely to achieve the biological goals. Additional studies are needed to validate the habitat suitability models of Hardy (2009) in the areas where CSRB populations are monitored, to better determine the likelihood of meeting the CSRB biological goals.

Water Quality Objective. The water quality objective is to maintain aquifer water quality from the spring openings within 10 percent of historical conditions in the three LTBG reaches. The known habitat of the CSRB is immediately within and adjacent to spring openings that receive continuous subterranean flow, the quality of which has not varied significantly over time. Thus, it could be argued that the water quality objective is not particularly relevant to meeting the biological goals for the CSRB. However, there are at least three distinct scenarios that could cause water quality of the springs to deviate by more than 10 percent. One would be a toxic chemical spill that enters the aquifer, thereby affecting spring water quality. The second would be a catastrophic riparian bank collapse that buries spring openings in the LTBG reaches. Although these two scenarios are unlikely to occur, they should be considered in long-term HCP planning. The third scenario that might cause spring water quality to deviate by more than 10 percent is chronic erosion from riparian areas sufficient to cover and bury spring openings with sediment in a way that changes temperature and DO conditions (this is discussed in greater detail in the Habitat Objective section below). Based on current water quality monitoring and laboratory studies, the temperature and oxygen values at the spring openings are rarely outside the tolerance thresholds for the CSRB (Nowlin et al., 2016; BIO-WEST, 2017). As discussed earlier for the fountain darter, the water quality objectives are necessary, but not sufficient, to ensure that the biological goals are met.

Habitat Objective. A riparian zone restoration program was implemented in 2013 to improve CSRB habitat in Spring Run 3 and the western shoreline. The restoration activities have been implemented each year with minor modifications annually to reduce fine-sediment accumulation. In 2016, the activities included removal and/or treatment of exotic vegetation and replanting the shoreline with native vegetation; the construction and maintenance of erosion structures to limit runoff; and sediment and vegetation monitoring. As discussed in greater detail in Chapter 4, while there is documented success of nonnative riparian plant removal, there is also substantial sediment capture by the erosion structures, calling into question the ability of this objective to meet the biological goal of silt-free substrate unless there is continuous maintenance of the erosion control structures.

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

Furthermore, there have been no quantitative assessments for measuring sedimentation at the CSRB spring openings, so it is difficult to assess how riparian restoration activities will affect CSRB biological goals.

Conclusion and Actions Needed to Improve the Rating

There has been considerable recent research on the CSRB that has revealed important information on some life history traits using laboratory colonies and conditions, physiological tolerances to abiotic conditions such as temperature and oxygen, and habitat and trophic relationships with detritus from riparian buffers. In addition, the new standard operating procedure for the cotton-lure sampling method is an important step in improving the monitoring of CSRB populations. Although this surge in understanding of the basic natural history and biology of the CSRB is to be lauded, there remain informational needs that would increase the potential for the biological objectives to achieve the goals. Based on the limitations associated with (1) the lack of quantitative monitoring of CSRB populations, (2) determining whether riparian restoration can actually eliminate silt at spring openings, and (3) the lack of habitat suitability modeling in the LTBG reaches, collectively the biological objectives are somewhat likely to achieve the long-term biological goals of the CSRB.

The following actions could be taken to move the rating from somewhat likely to likely. First, as has been mentioned in previous reports of the Committee (NRC, 2015; NASEM, 2017) and in Chapter 2, improvements to the sampling of the CSRB are critical in order to better understand what the true beetle population is in the monitored reaches. Second, it is highly recommended that a plan be developed to quantitatively monitor CSRB habitat sedimentation associated with continuing riparian restoration efforts. Finally, if the habitat suitability modeling was repeated in the LTBG reaches, it would increase confidence in the ability of the flow objectives to meet those goals.

SAN MARCOS SALAMANDER

The biological goals for the San Marcos salamander are to maintain specific salamander populations (number/m2) in three locations (hotel site, riverbed site, and Spring Lake Dam site) and to maintain silt-free gravel and cobble substrate in the same three locations. Maintaining silt-free gravel is assumed to be crucial for ensuring suitable habitat for San Marcos salamanders, which use interstitial spaces within the gravel to seek refuge and forage. The biological objectives are (1) to meet certain minimum flow requirements in the San Marcos system that are the same as those for the fountain darter and Texas wild rice, (2) aquatic gardening at the riverbed

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

and hotel sites, and (3) regulation of human recreation activity at the spillway site. The latter two are odd because as stated they are virtually identical to certain M&M measures. Note that there is no water quality component of the biological objective for San Marcos salamanders.

Determination and Information Used

The Committee determined that, based on the available information, it is somewhat likely that the biological objectives will meet the biological goals for the San Marcos salamander. Like the CSRB, biological data that could provide evidence are lacking for this species. Much of the current scientific information on the species is based on observations and experiments with captive individuals. This lack of information precluded us from assigning a more definitive likelihood. Also, there is no stated water quality objective for the San Marcos salamander, although water quality is suspected to be an important factor in the long-term persistence of the species.

To reach this determination, the Committee considered the biomonitoring data for San Marcos salamanders; historical monitoring of the species (an interpretation of those results) within the San Marcos springs system and a short reach of the San Marcos River downstream from Spring Lake Dam spillway (Tupa and Davis, 1976; Nelson, 1993; FWS, 1996); progress to date implementing numerous recreation-associated M&M measures in Spring Lake and just below the dam spillway; and various reports already cited for the other species.

Evidence for and Against the Objectives Achieving the Goals

Like the CSRB, evidence in the form of positive trends in abundance is not as easy to come by for San Marcos salamanders as it is for fountain darters and Texas wild rice. According to the HCP, both the habitat (extent of silt-free gravel) and population (minimum median salamander densities) biological goals “must be met concurrently to be deemed successful” (EARIP, 2012, pp. 4-34, 4-35). Unfortunately, determining if the goal of maintaining ≥ 90 percent silt-free gravel at each of the sampling reaches is being met is not possible; neither the HCP annual reports nor the biomonitoring reports present any data or summaries of the extent of silt-free gravel at the three reaches. Also conspicuously absent is any mention of the aquatic gardening efforts, though, according to the HCP, this management action is conducted quite frequently.

Assessing the population-based goal is more straightforward because annual estimates of salamander densities have been conducted continuously. On the basis of estimated densities of salamanders among the three sites through 2016, the EAA appears to be generally meeting its goals. Although

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

density estimates at each of the sites vary considerably among sampling periods within and among years (some single estimates greatly exceed the targets and others fall well short of them), the measured density values during more than 15 years of consecutive sampling remain very close to the targets (Figure 3-7). However, with regard to salamander sampling, the 2017 annual biomonitoring report states “The estimates created from this work are valuable for comparing between trips, but any estimates of total population size derived from this work should be viewed with caution” (BIO-WEST, 2018). That is, there is no way to know if trends in salamander numbers over time within the three reaches are an indicator of true population trends.

Flow Objective. As it pertains to San Marcos salamanders, the flow objective will help to maintain the appropriate extent of silt-free gravel (≥ 90%) at the three sites where salamander monitoring occurs. In addition to supporting silt-free gravel, adequate spring flow also facilitates growth of SAV that provides food and shelter for San Marcos salamanders.

Unlike the situation with the fountain darter, HSI modeling was not conducted to assess potential impacts of spring flow variability on San Marcos salamanders. Nonetheless, San Marcos salamanders can retreat into subterranean refuges at spring vents during periods of extremely low spring flow, such as the Drought of Record (see Chapter 2 of this report). Given this feature of their natural history, and the fact that they are largely limited to Spring Lake, they are likely more resilient to reduced spring flow than fountain darters. Therefore, the flow objective for fountain darters should be adequate for San Marcos salamanders. As with fountain darters, protection and maintenance of salamander habitat in Spring Lake during excessively high-flow events is uncertain and needs to be considered.

Habitat Objectives. Regulation of recreation at the spillway site is one of the habitat objectives for the San Marcos salamander. Of all the listed species, San Marcos salamanders arguably are the least likely to be negatively impacted by recreation from spring and river users because of the salamander’s limited extent. The species is primarily confined to Spring Lake, although some individuals (roughly half the densities observed at Spring Lake sites) are found in the very upper reach of the San Marcos River, to ~50 meters below the Spring Lake Dam spillway. Access to Spring Lake proper is highly regulated and managed, but people often access the river at the dam spillway. People currently are only allowed in Spring Lake to take SCUBA classes, view the lake from glass-bottom boats, and tour the lake on paddleboards, canoes, and kayaks. All human recreation in the lake is organized and managed by the Meadows Center for Water and the Environment operated by Texas State University. More important would

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×
Image
FIGURE 3-7 San Marcos salamander densities at the three long-term biological goal sampling sites, 2002–2016. The y-axis is number per square meter. SOURCE: Committee manipulation of Edwards Aquifer Authority data.
Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

be to better regulate recreational access to the 50-meter reach of the San Marcos River just below Spring Lake Dam to eliminate bank erosion and direct disturbance of salamander habitat. Recreational impacts here are far greater than within Spring Lake. Restricting public access to this short section of the upper San Marcos River would curtail human-caused bank erosion and eliminate disturbance to rocks and other salamander habitat, which should facilitate the maintenance of silt-free gravel and possibly increase salamander densities.

The other habitat objective, called aquatic gardening, refers to the hand removal of algae and SAV around spring vents at the hotel area and riverbed area in Spring Lake. In addition to removing vegetation, trained divers will “fin the area around the springs to remove accumulated sediment.” The process of aquatic gardening is important to meeting the biological goal of silt-free gravel.

Although it is not explicitly identified in the HCP as an objective, an implicit habitat objective for the San Marcos salamander is the management of riparian areas along a short stretch of the San Marcos River just downstream from Spring Lake Dam. Impacts of recreational use, which contributes to riverbank erosion and increased siltation, in this short section of the San Marcos River is greatest during periods of low flow. During high-flow conditions, water depth is greater and underwater hazards (e.g., remains of an old dam) discourage recreationist use. During low-flow conditions, the hazards are exposed and this leads to human use of the site. People access the river and physically disturb the location by moving rocks “to create structures, dams, underwater rock art, and artificial channels” (Blanton and Associates, 2018, App. D, Fig. 18). Such perturbation certainly has the potential to impact salamander habitat; thus, protection of this area via bank stabilization and exclusion of recreationists is an important measure at this site.

Water Quality Objective. A water quality objective is glaringly absent for the San Marcos salamander. Maintaining suitable water quality (e.g., temperature, DO, nutrients, and pesticide/herbicide residues) has been identified by numerous authors as essential for long-term persistence of San Marcos salamanders. Research has determined critical thermal maximum (CTmax) and oxygen consumption rates for the species (see Chapter 2), but nothing is known about effects of nutrients and environmental contaminants. Such studies should be considered as part of the Applied Research Program. Equally important is determining the effects of altered water quality on the invertebrate prey species upon which San Marcos salamanders depend. And, as noted for the CSRB, consideration of catastrophic events, such as a toxic chemical spill that enters the Edwards Aquifer, should be addressed in long-term HCP planning.

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
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Conclusion and Actions Needed to Improve the Rating

Considering the lack of detailed biological data for the San Marcos salamander in the peer-reviewed literature, historical estimates of population size, recent estimates of densities at the three sampling reaches, and lack of information on the effects of aquatic gardening and the extent of silt-free substrates, the Committee deems the biological objectives somewhat likely to achieve the long-term biological goals for San Marcos salamanders.

There are several actions the EAA could take to move this assessment to likely. The first is to develop a water quality objective for San Marcos salamanders, which should be informed by and concordant with water quality objectives for the other covered species. The second action is to better regulate recreational access to the 50-meter reach of the San Marcos River just below Spring Lake Dam to eliminate bank erosion and direct disturbance of salamander habitat. Third is to quantify, monitor, and report the extent and outcomes of aquatic gardening and maintenance of silt-free gravel at the salamander study-reaches. A final action would be to report on the variation associated with San Marcos salamander density estimates and augment the current sampling protocol with a new method to estimate proportion of area occupied and detection probability of San Marcos salamanders (see Chapter 2).

WATER QUALITY COMPONENT OF THE BIOLOGICAL OBJECTIVE

Found in several places within the HCP is the objective for maintaining water quality within 10 percent of historical conditions. This objective is given for fountain darters in both the Comal and San Marcos systems and for the CSRB, Peck’s Cave amphipod, Comal Springs dryopid beetle, and Texas blind salamander. In the case of the latter four organisms, the water quality under consideration is that of the aquifer water measured at the spring openings, while for the fountain darter the water being considered is the river water in both systems. Note that this water quality objective is actually the sole biological goal for the Texas blind salamander, the Comal Springs dryopid beetle, and the Peck’s Cave amphipod because there are no population metrics that can be used for these organisms (given the difficulties with sampling these species).

The Water Quality Monitoring Work Group report (EAHCP, 2016) spends some time determining which datasets to use for setting historical levels, but it is insufficient in explaining why those levels (or divergences from those levels) actually matter. The report suggests that many of the criteria and thresholds are based on State Water Quality levels and are not necessarily tied to either the listed species or other important species, such

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

as SAV. There is little description of how the 10 percent rule came to be applied to the fountain darter (or other taxa). Furthermore, the Committee could find no publication that actually lists all of the water quality parameters being considered and their historical values.

The water quality objective appears to be a conservative approach to identifying potential conditions of concern; it could be described as an early warning indicator of potential water quality issues. The objective was defined, however, without the benefit of historical data on the actual variations in water quality measures. As such, the objective should be recognized as an interim objective that should be informed and updated by the actual variations in water quality that occur that do not lead to significant negative consequences for the listed species. Admittedly this is an imperfect standard but one that recognizes that there are variations in water quality that at least on a short-term basis exceed the objective of a 10 percent deviation in specific water quality parameters with no apparent effect on the listed species. Moreover, there are water quality parameters, such as pH and DO, for which a 10 percent deviation is inherently misleading. A 10 percent deviation in hydrogen ion concentration is unlikely to be consistently measurable while a 10 percent deviation in the logarithmic pH scale at near neutral conditions is in reality a change by a factor of 5 in hydrogen ion concentration. For oxygen, a 10 percent deviation is of little consequence until the oxygen reaches critically low levels that lead to organism stress or death. There is little clarity for most organisms as to how a 10 percent deviation in the water quality objective is to be applied and little information as to critical water quality levels that lead to adverse effects on the listed species.

A better approach to the water quality objective would be to relate observed variations in water quality to adverse effects on organisms and use that information to define the objective. For example, one could look to statistical techniques described by Harding et al. (2014) and Sutula et al. (2017) using such approaches as quantile regression or conditional probability analysis. Batiuk et al. (2009) provide an overview of setting DO criteria that also considers spatial challenges that may be critical, as well as duration and threshold conditions. In the absence of adverse effects, the observed variations in water quality would be a conservative indication of variations that can be safely experienced by the listed species. To maintain conservatism, a statistical measure, such as a variation in a specific water quality parameter within 95 percent of the distribution of historical observations of that parameter that do not lead to apparent adverse effects might be employed. It is therefore recommended that the historical data in all available water quality parameters be analyzed, the distribution of observations that are not believed to lead to adverse effects be defined, and the biological objective for that water quality parameter be updated to reflect that analysis.

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

CONCLUSIONS AND RECOMMENDATIONS

It is likely that the biological objectives will meet the biological goals for the fountain darter. Fountain darters are clearly associated with SAV and there have been no recent downward trends in fountain darter densities by habitat type or systemwide changes in SAV coverage, despite the drought and flood years of 2013–2014 and 2015, respectively. The flow objectives are consistent with the habitat suitability modeling for fountain darters, and adaptive management was used successfully to adjust the long-term biological goals. The rating could be improved by repeating the habitat suitability modeling using more recent data; by further examining fountain darter median densities over time, by vegetative habitat type, and abundance indices both within reaches and systemwide; and by performing a power analysis on fountain darter data to guide the interpretation of false negatives.

It is likely that the biological objectives will meet the biological goals for Texas wild rice. This conclusion is based on empirical observations of gains in the coverage of Texas wild rice, even in the face of recent floods and droughts; on the compatibility of the flow objective with the habitat suitability model for Texas wild rice; and on the adaptive management changes that now include Texas wild rice as fountain darter habitat. As with the fountain darter, monitoring and successful restoration of Texas wild rice to date have led to conclusions offered with relatively high confidence. The rating could be improved by repeating the habitat suitability modeling using more recent data, by creating a defined water quality objective for Texas wild rice, and by adding a habitat objective to continue to remove nonnative SAV.

It is somewhat likely that the biological objectives will meet the biological goals for the Comal Springs riffle beetle. This conclusion is based on the limitations associated with (1) the lack of quantitative monitoring of CSRB populations, (2) determining whether riparian restoration can actually eliminate or significantly reduce siltation at spring openings, and (3) the lack of habitat suitability modeling for the CSRB in the monitored reaches. To improve the rating, the following actions should be undertaken. First, it is important to continue to standardize and move toward quantitative sampling of the CSRB in order to better understand what the true beetle populations are in the monitored reaches. Second, it is highly recommended that a plan be developed to quantitatively monitor CSRB habitat sedimentation associated with continuing riparian restoration efforts. The lack of data that link riparian erosion to spring orifice sedimentation represents a significant omission important to achieving the biological goals. Finally, if the habitat suitability modeling were repeated in the LTBG reaches, it would increase confidence in the ability of the flow objectives to meet the biological goals.

Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
×

It is somewhat likely that the biological objectives will meet the biological goals for the San Marcos salamander. A robust monitoring program that could provide evidence of upward trends in abundance is lacking for this species. Much of the current scientific information on the species is based on observations and experiments with captive individuals. There is no water quality objective for the salamander or information on the effects of aquatic gardening. The rating could be improved by creating a water quality objective for San Marcos salamanders, better regulating recreational access to the 50-meter reach of the San Marcos River just below Spring Lake Dam, quantifying the outcomes of aquatic gardening and maintenance of silt-free gravel at the salamander study reaches, and augmenting the current sampling protocol with a new method to estimate proportion of area occupied and detection probability of San Marcos salamanders. Controlling access just below Spring Lake Dam and quantifying the maintenance of silt-free gravel should be made high priorities because they could be implemented soon and will help ensure that the stated salamander goals are met.

There are many documented occurrences of water quality parameters deviating more than 10 percent from their historical average with no noticeable impacts on the listed species. This calls into question the water quality objectives for the fountain darter and the CSRB. Historical data on all available water quality parameters should be analyzed and the distribution of observations that are not believed to lead to adverse effects should be defined, so that the water quality objective for each parameter can be updated.

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Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
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Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
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Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
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Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
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Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
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Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
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Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
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Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
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Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
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Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
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Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
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Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
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Suggested Citation:"3 Will the Biological Objectives Meet the Biological Goals?." National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. doi: 10.17226/25200.
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The Edwards Aquifer in south-central Texas is the primary source of water for one of the fastest growing cities in the United States, San Antonio, and it also supplies irrigation water to thousands of farmers and livestock operators. It is also the source water for several springs and rivers, including the two largest freshwater springs in Texas that form the San Marcos and Comal Rivers. The unique habitat afforded by these spring-fed rivers has led to the development of species that are found in no other locations on Earth. Due to the potential for variations in spring flow caused by both human and natural causes, these species are continuously at risk and have been recognized as endangered under the federal Endangered Species Act (ESA). In an effort to manage the river systems and the aquifer that controls them, the Edwards Aquifer Authority (EAA) and stakeholders have developed a Habitat Conservation Plan (HCP). The HCP seeks to effectively manage the river-aquifer system to ensure the viability of the ESA-listed species in the face of drought, population growth, and other threats to the aquifer.

This report is the third and final product of a three-phase study to provide advice to the EAA on various aspects of the HCP that will ultimately lead to improved management of the Edwards Aquifer. This final report focuses on the biological goals and objectives found in the HCP for each of the listed species.

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