Review of the Edwards Aquifer Habitat Conservation Plan Report 1 (2015) / Chapter Skim
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3 Ecological Modeling
3 Ecological Modeling
Pages 76-113
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From page 76... ...
, and other factors that degrade water quality. Three of the species covered by the Incidental Take Permit -- the fountain darter, the Comal Springs riffle beetle, and Texas wild rice -- are designated as indicator species, whose protection under the Habitat Conservation Plan (HCP)
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From page 77... ...
Texas Wild Rice Within the HCP there are biological goals, a habitat suitability analysis, and a description of biomonitoring in the San Marcos system, all for Texas wild rice. However, the HCP also places great importance on SAV because of its role in providing fountain darter habitat.
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From page 78... ...
. The sections below focus only on Texas wild rice, while the section on ecological modeling later in the chapter focuses exclusively on SAV.
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From page 79... ...
While there are hard-scaped access points in all adjacent city parks, numerous ad hoc access trails created by recreationists contribute to bank erosion. The HCP targets the entire San Marcos River for recreation awareness, and four segments TABLE 3-1 Long-Term Biological Goal for Texas Wild Rice in Four Segments of the San Marcos River Reach Percentage of River Segment Areal Coverage (m2)
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From page 80... ...
. Habitat Suitability Analysis for Texas Wild Rice Over the last 15 years, there have been several efforts to determine habitat suitability criteria for Texas wild rice (Bartsch et al., 2000; Hardy, 2009; Hardy et al., 2010)
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From page 81... ...
Habitat suitability criteria for water depth and velocity were used in the following equation to determine overall habitat suitability for Texas wild rice in various sections of the San Marcos River (Hardy, 2009) : Overall suitability = depth suitability × velocity suitability where depth suitability and velocity suitability are determined by taking their respective values for the hydraulic simulation results at a node and using linear interpolation between the defined suitability values from the habitat suitability index curves.
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From page 82... ...
Furthermore, the model predicted little to no Texas wild rice habitat in Spring Lake, which is expected because there is no flow in the lake above the threshold for Texas wild rice. Similarly, in the lower San Marcos River, the model predicted poor habitat because of deep water, which agrees with the lack of Texas wild rice in that area.
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From page 83... ...
ECOLOGICAL MODELING 83 FIGURE 3-1 Spatial distribution of predicted Texas wild rice computational cell suitability ranges versus the 1989 to 2008 spatial distribution of Texas wild rice stands (red dots) in the Rio Vista to Cape's Dam section.
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From page 84... ...
Currently, the habitat suitability analysis is the only ecological model for Texas wild rice. Given the lack of plans for a more rigorous Texas wild rice ecological model, the Committee recommends continuing and improving upon the habitat suitability effort.
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From page 85... ...
, and three representative reaches in the San Marcos system (the Spring Lake Dam, City Park, and I-35 Reaches) (Figure 3-4)
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From page 86... ...
Surface water quality will be maintained within a 10 percent deviation of all monitored parameters, except temperature and dissolved oxygen, from the average recorded water quality measured at 15 locations during the EAA Variable Flow Study. This water quality objective is based on the assumption that a 10 percent deviation in average conditions would
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From page 87... ...
for Each Habitat Type in Comal and San Marcos Springs COMAL SPRINGS Coverage (m2) Bryophytes Hygrophila Ludwigia Cabomba Fil.
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From page 88... ...
Water temperatures less than 25°C and dissolved oxygen concentrations greater than 4.0 mg/L will be maintained to ensure fountain darter survival, reproduction, and recruitment. As with Texas wild rice, along with the habitat-based long-term biological goals and the associated restoration and water quality management objectives, the HCP also identifies flow-related objectives to help ensure maintenance of fountain darter populations (see Table 3-5)
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From page 89... ...
Dissolved oxygen simulations were considered questionable because sediment oxygen demand and plant respiration were not explicitly included in the model. As for the Texas wild rice analysis, the predicted weighted usable areas by region (groups of segments)
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From page 90... ...
. TABLE 3-6 Habitat Suitability of Fountain Darter by Vegetation and Substrate Type Vegetation/Substrate classification Code HSI Value Vegetation/Substrate classification Code HSI Value Clay 1 0.05 Acmella oppositifolia 27 0.25 Silt 2 0.05 Arundo donax 28 0.05 Sand 3 0.05 Ceratopteris thalictroides 75-100% 29 0.06 Gravel 4 0.05 Ceratopteris thalictroides 50-75% 29.1 0.06 Cobble 5 0.10 Echinochloa sp 30 0.05 Small Boulder 6 0.05 Heteranthera dubia 75-100% 31 0.80 Large Boulder 7 0.05 Heteranthera dubia 50-75% 31.1 0.80 Bedrock 8 0.05 Hydrocotyle sp 75-100% 32 0.20 Large Woody Debris 9 0.05 Hydrocotyle sp 50-75% 32.1 0.20 Concrete 10 0.05 Juncus texanus 75-100% 33 0.05 Artificial Wood 11 0.05 Juncus texanus 50-75% 33.1 0.05 Metal 12 0.05 Justicia americana 75-100% 34 0.00 Hydrilla verticillata 75-100% cover 13 0.29 Justicia americana 50-75% 34.1 0.00 Hydrilla verticillata 50-75% cover 13.1 0.29 Iris pseudocoris 35 0.60 Hygrophila polysperma 75-100% cover 14 0.93 Ludwigia sp 75-100% 36 0.56 Hygrophila polysperma 50-75% cover 14.1 0.93 Ludwigia sp 50-75% 36.1 0.56 Colocasia esculenta 75-100% cover 15 0.60 Myriophyllum sp 75-100% 37 0.80 Colocasia esculenta 50-75% cover 15.1 0.60 Myriophyllum sp 50-75% 37.1 0.80 Potamogeton illinoensis 75-100% 16 0.01 Nasturtium officinale 75-100% 38 0.00 Potamogeton illinoensis 50-75% 16.1 0.11 Nasturtium officinale 50-75% 38.1 0.00 Zizania texana 75-100% 17 0.11 Nuphar advena 39 0.20 Zizania texana 50-75% 17.1 0.11 Nuphar advena 39.1 0.20 Zizania texana <50% mono with substrate 17.2 0.11 Ricinus 40 1.00 Sagittaria platyphylla 75-100% 18 0.16 Typha lattifolia 41 0.60 Sagittaria platyphylla 50-75% 18.1 0.16 Utricularia gibba 42 0.00 Cabomba caroliniana 75-100% 19 0.54 Vallisneria americana 75-100% 43 0.13 Cabomba caroliniana 50-75% 19.1 0.54 Vallisneria americana 50-75% 43.1 0.13 Ceratophyllum demersum 75-100% 20 0.02 Xanthosoma sagittifollium 44 0.01 Ceratophyllum demersum 50-75% 20.1 0.02 Cynodon dactylon 45 0.05 Submergent Vegetation Mix 21 0.50 Salix nigra 46 0.05 Emergent Vegetation Mix 22 0.20 Limnophila sessiflora 47 0.20 Submergent/Emergent vegetation mix 23 0.25 Chara sp 48 1.00 Floating vegetation 24 0.00 Algae 49 1.00 Floating/Submergent vegetation mix 25 0.25 Zizianopsis 50 0.11 Unclassified 26 0.50 Moss 51 0.50 SOURCE: Hardy et al.
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From page 91... ...
implementation of the HCP-Phase 2. Unlike the Hardy efforts, habitat suitability in this analysis was related only to spring flows and vegetation type.
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From page 92... ...
92 REVIEW OF THE EDWARDS AQUIFER HABITAT CONSERVATION PLAN FIGURE 3-7 Weighted usable area (WUA) for fountain darter at various discharges within the Comal River.
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From page 93... ...
. The HCP's apparent reliance on the third habitat suitability analysis to assess the effects of various spring flow scenarios on fountain darter abundances is questionable because of methodological and interpretation issues.
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From page 94... ...
at 90 percent or more of the area throughout the representative sample reaches. Due to the paucity of data for CRSB in the San Marcos system, it is not possible to establish specific long-term habitat-based biological goals.
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From page 95... ...
presents a habitat suitability analysis for the CRSB, with suitability being a function of water depth and velocity. This was followed by an updated analysis in Hardy et al.
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From page 96... ...
Two management objectives are "aquatic gardening" (i.e., use of a harvester boat and hand cutting of vegetation by divers in the Riverbed area of Spring Lake) and recreational control similar to that used for Texas wild rice.
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From page 97... ...
provide habitat as input to the fountain darter ecological model, and possibly (2) predict SAV (and Texas wild rice)
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From page 98... ...
The grid will either be the same 2-dimensional grid that was used in the habitat suitability analyses (see Box 3-1) and is being used in the fountain darter model, or it will be an aggregated version of that grid (e.g., 0.25 m2 averaged for 1-m2 resolution)
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From page 99... ...
Representing density-dependence realistically is important because it affects how SAV responds to changes in environmental conditions. A second critical issue is the treatment of flow and water quality effects on SAV dynamics.
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From page 100... ...
If the modeling team takes the route of using a generic species or a functional grouping of species, it will not be straightforward to compare model predictions to species-specific field data. Also, the fine spatial scale thought to be needed for compatibility with the fountain darter model may not be ideal for simulating SAV biomass dynamics over seasons and among years.
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From page 101... ...
It is recommended that continued efforts focus on Texas wild rice restoration, mitigation, public awareness and improving the existing habitat suitability analyses. Fountain Darter The fountain darter modeling effort that is replacing the habitat suitability analyses is truly a population modeling approach.
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From page 102... ...
The model is in the planning stages and so some variables, like velocity and vegetation type, are inputted as placeholders for use later to relate to growth, mortality, reproduction, or movement. The proposed approach uses a spatially explicit, individual-based methodology to simulate the growth, mortality, reproduction, and movement of individuals; the sum over individuals is then the population-level outputs.
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From page 103... ...
. A major question to be addressed with this model that cannot be addressed with habitat suitability analysis is the decline and recovery of fish over multiple years given patterns of drought, flood, and other hydrological conditions.
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From page 104... ...
The development of the population model would also be an opportunity to revisit the influence diagrams found in the HCP and, as discussed later, develop more rigorous formal conceptual models for how factors affect darter population dynamics and how management actions directly and indirectly affect their vital rates. The proposed modeling approach is a scientifically sound way to address the limitations of habitat suitability analyses, and a spatially explicit IBM has many attractive features, along with challenges in terms of model formulation, calibration, and validation.
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From page 105... ...
Comal Springs Riffle Beetle In 2013, the HCP Ecosystem Modeling Team completed a literature review of the CSRB and other riffle beetle species (EA HCP Ecosystem Modeling Team, 2013) with the intention of determining what is known about these species and how it could be used for exploring new modeling approaches for the CSRB and its habitat.
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From page 106... ...
Also, the HCP states that more extensive work is required to evaluate and assess water quality tolerances of the CSRB. At the present time, the primary measure of habitat quality for the beetle found in the HCP is qualitatively (and possibly only anecdotally)
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From page 107... ...
, and all available management actions are linked within a common framework. It is timely to assess the state-ofknowledge about the Comal and San Marcos ecosystems, given the new
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From page 108... ...
. It should be a top priority for the EAA to develop a conceptual model, or a series of models of increasing resolution, that show how water quality and quantity, other biota, and restoration and mitigation activities are expected to interact with the indicator species, as well as with all covered species.
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From page 109... ...
not included in the habitat suitability analysis, especially over a longer term, as several years to decades may be required for their roles to become evident. They stated that "for the target organisms and the habitats within which they live to achieve recovery and persist over the long term, additional information is needed to understand, anticipate, and manage these factors as much as possible." An added benefit of the conceptual models would be to highlight these other important factors, determine whether and how they can be incorporated into the ongoing ecological models for SAV and the fountain darter, and allow the EAA to prioritize the research and monitoring required to support model development.
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From page 110... ...
Given the absence of a planned ecological model for Texas wild rice, the current habitat suitability analysis should be treated as an hypothesis and tested for robustness throughout the San Marcos River. The EAA should consider designing minimization and mitigation measures for Texas wild rice in a manner to provide experimental analysis of the habitat suitability results.
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From page 111... ...
Habitat suitability analyses are tied closely to data, they are easy to explain, and the reporting of the amount of high quality habitat has intuitive appeal. Although the habitat suitability approach does not convey fish abundance like the population modeling, the latter requires more data, greater mechanistic understanding, and is more challenging to explain.
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From page 112... ...
and Texas Wild Rice (Zizania texana) in Spring Lake and the San Marcos River System.
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From page 113... ...
2010. Evaluation of the Proposed Edwards Aquifer Recovery Implementation Program Drought of Record Minimum Flow Regimes in the Comal and San Marcos River Systems.
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