Review of the St. Johns River Water Supply Impact Study Final Report (2012) / Chapter Skim
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3 Review of Environmental Workgroup Reports
3 Review of Environmental Workgroup Reports
Pages 37-95
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From page 37... ...
As noted earlier, some activities within the drainage basin, such as the Upper Basin projects, produced model output with water flows and levels greater than those in the baseline case. The workgroups prioritized withdrawal scenarios by deviation from base conditions, and the scenario with the largest deviations generally was 37
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From page 38... ...
The conceptual models -- basically box and arrow diagrams -- were intended to show plausible cause-effect relationships between key environmental drivers and changes in some ecosystem attribute relevant to the ecosystem component of interest (e.g., phytoplankton, benthos, fish)
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From page 39... ...
Examples of the District's conceptual and hydroecological models are included in discussions of the workgroup reports in subsequent sections of this chapter, and Figure 3-2 is a flow diagram that illustrates the general approach the District used in conducting its analyses. The workgroups were given a mandate to characterize potential environmental effects of water withdrawals using three criteria: persistence, strength, and diversity.
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From page 40... ...
Subsequent sections of this chapter describing the individual workgroup reports generally follow a common outline. The conceptual model developed by the workgroup is presented first, along with any hypotheses or key questions that drove their analyses.
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From page 41... ...
Conceptual Model A conceptual model illustrating the effects of water withdrawals on wetland plant communities was developed to investigate possible responses to alterations in wetland hydroperiod and salinity (Figure 3-3)
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From page 42... ...
. The wetlands workgroup generated four hypotheses from the conceptual model and identified specific hydrological criteria to test each: H1: Changes in inundation depth and duration, relative to baseline, will lead to changes in the extent of wetlands in the landscape.
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From page 43... ...
The second step used a combination of stage exceedence curves to relate the distribution of plant communities along the elevational gradient of the floodplain and a GIS-based analysis to display the spatial extent of wetlands in the targeted river reaches and how wetland community composition, wetland area, and boundaries between wetland community types might be affected by water withdrawals. This analysis was done using a combination of a DEM based on LiDAR data, generation of exceedence curves using elevation and plant community information from MFL transects, and a "Hydroperiod Tool." The latter tool performed GIS-based analysis that provided estimates of daily water depth over an area by subtracting the ground surface elevation (DEM)
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From page 44... ...
Johns River so that the potential changes in plant communities could be predicted. Results The screening level assessment identified river segments most at risk for impacts based on changes in average annual water levels and salinity using the Full1995NN scenario, which shows maximum change from the base condition (Base1995NN)
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From page 45... ...
Water withdrawals were found to lead to the dewatering of portions of the floodplain and subsequent movement of wetland boundaries along the hydrological gradient from riverbank to upland. Shallow marshes were found to be one of the most affected community types, and under this modeled "worst case" scenario, the total length of shallow marsh on the County Line MFL transect in segment 8, for example, decreased by up to 69.4 percent, while the extent of wet prairies increased by 76 percent (see Table 3-2)
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From page 46... ...
Ratings for the response variables that were directly assessed in segments 2 and 8 were based solely on ecological effects; i.e., the workgroup did not combine its ratings with the uncertainty associated with modeled output of the withdrawal scenarios from the H&H workgroup. Conversely, an abbreviated uncertainty analysis, based only on results of the H&H workgroup or arrived at deductively, was done for response variables in river segments where little to no change in river hydrology was predicted.
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From page 47... ...
Critique The wetlands workgroup produced a solid analysis of potential impacts of water withdrawals to the St. Johns River.
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From page 48... ...
. The model portrays the linkages between increased water withdrawals and changes in water levels and wetland soil inundation, leading to changes in oxidation of soil organic matter (SOM)
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From page 49... ...
how much additional release of the constituents of interest would occur from SOM as a result of water withdrawals; (3) how much of the additional material gets exported from the wetlands to lakes; and (4)
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From page 50... ...
results from the H&H workgroup, in combination with detailed land elevation data produced in Phase II for the wetlands workgroup. At the outset of the WSIS Phase II studies, the biogeochemistry workgroup developed a sampling program to collect soil samples and cores from 86 wetland sites in various segments along the St.
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From page 51... ...
Johns River (Figure 3-1) , the workgroup concluded that water withdrawals from the St.
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From page 52... ...
Segments 1-4 were considered not to be susceptible to impacts because water levels in those segments are controlled by sea level, and segment 9 and the portion of segment 8 above the Lake Washington weir also were considered not susceptible to impacts because all proposed withdrawal points are downstream of the weir, which isolates upstream segments from downstream water level changes. The workgroup also concluded that forested wetlands were not likely to be affected by water withdrawals because an analysis by the wetlands workgroup indicated that these wetlands occur primarily along tributaries or seeps and are not likely to be affected by water levels in the main channel of the river.
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From page 53... ...
Overall, measured release rates for nutrients and DOC from Lake Poinsett wetland soils were low, indicating that the soils were recalcitrant to oxidation upon exposure to air. The workgroup provided supporting evidence for the low release rates in the form of carbon-tonitrogen (C:N)
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From page 54... ...
Finally, the uncertainty in conclusions for segment 8, the only segment for which the workgroup conducted a complete analysis, was regarded as "medium." Critique Although the general approach used in the screening assessment to rank the vulnerability of river segments to impacts of withdrawals on biogeochemical processes was reasonable, it relied on an important assumption that may not have been accurate, namely, that decomposition/oxidation rates of the wetland soils in different segments are similar. The biogeochemistry workgroup found that sediments in the portion of segment 8 where they focused their studies (i.e., Lake Poinsett)
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From page 55... ...
Overall, the metrics used in the screening assessment -- wetland area, river flow, and average water level decrease (Table 3-4) -- led to the conclusion that the segment 8/Lake Poinsett wetlands were the most susceptible region, but in the Committee's view, they are not sufficient to dismiss the potential importance of withdrawal impacts on downstream segments.
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From page 56... ...
model the relationships between bloom characteristics and hydrology, and (3) determine whether water withdrawals would cause or exacerbate adverse effects of algal blooms.
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From page 57... ...
FIGURE 3-5 Conceptual model for the plankton workgroup. SOURCE: Coveney et al.
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From page 58... ...
was designed to evaluate the potential effects of marine phytoplankton blooms using dinoflagellates as a surrogate group. The workgroup used best professional judgment to select a threshold for dinoflagellate biovolume of 1,000×103 μm3 mL-1, beyond which bloom conditions were considered to exist.
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From page 59... ...
Johns River, was used to provide a second, relatively independent assessment of water withdrawals on metric #3 (bloom maximum chl a) for segment 3.
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From page 60... ...
effects of water withdrawals on bloom maximum chl a in segment 3 independent of the empirical model. The model was not able to capture the magnitude of extreme algal blooms but did appear to capture the timing and frequency of bloom events.
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From page 61... ...
Some of the most effective models include both quantitative and qualitative components to predict ecosystem responses to anthropogenic alterations in environmental conditions. Given the large number of variables and the stochastic nature of ecosystems, quantitative predictions in most cases represent an informed or "best guess." It is within this framework that the plankton workgroup had the difficult task of predicting phytoplankton responses for a range of water withdrawal scenarios.
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From page 62... ...
Moreover, in calculating the effects of water withdrawals on mass loadings to the system by N2 fixation, the workgroup assumed that only water flows would change and nutrient concentrations would remain the same as in the historical data used to generate 1996-2005 estimates and predictive model. The Committee views this situation as highly unlikely, and consequently views the predictions for this metric to be subject to high uncertainty.
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From page 63... ...
The littoral zone workgroup eventually formulated two main hypotheses that are illustrated in the central panels of the conceptual model: FIGURE 3-6 Conceptual model showing effects of hydrologic and other drivers on the submersed aquatic vegetation (SAV) community in the St.
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From page 64... ...
SAV habitat could potentially increase in the deeper areas of the freshwater lakes, provided that both CDOM and increased turbidity associated with phytoplankton blooms did not increase in the water column as a consequence of the withdrawals. Methods The assessment of potential changes in the SAV community of the littoral zone from water withdrawals was based largely on output of the hydrological models under various water withdrawal scenarios, which was provided by the H&H workgroup.
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From page 65... ...
. Salinity Exposure Model To assess the potential impacts of water withdrawals on Vallisneria habitat in the estuarine portion of the St.
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From page 66... ...
. Table 3-7 summarizes the negligible stage and salinity effects of the two "worst-case" withdrawal scenarios on segments 2 and 3 (FwOR1995PS)
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From page 67... ...
The hydrologic model output was designated as very low uncertainty for Lake Poinsett and low uncertainty for Lake Harney, such that the overall stage analysis is considered to have medium uncertainty. Uncertainty regarding the salinity analysis was lower because of the strong understanding of the mechanism, strong supporting evidence, and strong quantitative predictive model relating salinity exposure to SAV stress and mortality.
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From page 68... ...
This secondary effect of the proposed water withdrawals could be as much a problem as salinity and water levels in determining the fate of SAV in the St. Johns River ecosystem.
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From page 69... ...
In contrast to the conceptual models of most other ecological workgroups, the freshwater benthos model does not include any hydroecological model to predict the magnitude of changes in benthic conditions as a function of hydrologic (or other) changes resulting from water withdrawals.
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From page 70... ...
They combined this information with data on water levels along the Lake Poinsett MFL transect to make predictions about the potential effect of water withdrawals on benthos.
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From page 71... ...
The workgroup predicted that there would be no effect of withdrawals on benthos at average water levels, although withdrawals may have an effect at lower water levels. The workgroup noted that stage reductions of 0.10 m, which were predicted to occur frequently at Lake Poinsett under the extreme withdrawal scenario, could have more substantial effects on the benthic macroinvertebrate community.
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From page 72... ...
The workgroup superimposed the predicted water level reductions at Lake Poinsett given the extreme withdrawal scenario onto the minimum, median, and maximum land surface elevations of marshes along the transect. They found that withdrawals are likely to have negligible effects on crayfish and apple snail habitat at higher water levels (because water would still be above the maximum measured land elevation)
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From page 73... ...
High variability in the data prevented the workgroup from separating the effects of hydrology from seasonal and other possible water quality effects. The Committee's concerns are somewhat lessened by the knowledge that the likely future withdrawal scenario will reduce water levels by much less than the extreme scenarios evaluated by the workgroup.
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From page 74... ...
, as revealed by the analyses of the fish workgroup. Estuarine Benthos Conceptual Model During Phase II of the WSIS, the benthos workgroup developed a conceptual model for the effects of water withdrawals on estuarine benthic communities and selected estuarine populations (see Figure 3-8)
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From page 75... ...
(2011) , the workgroup used a weighted Spearman rank correlation to relate multivariate ordinations of community structure with measured water quality variables (temperature, salinity, pH, dissolved oxygen)
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From page 76... ...
Of the 14 taxa with optimal mean salinity delineations, nine were at the genus or species level of identification. The benthic workgroup compared the worst-case withdrawal scenario (FwOR1995NN)
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From page 77... ...
as a result of water withdrawals is thus a concern for estuarine benthic community structure. Segment 2 is the main area where salinity increases could affect benthic taxa, particularly aquatic insects, which generally are stenohaline (i.e., have narrow salinity tolerances)
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From page 78... ...
Table 3-9 shows the results for effects on estuarine benthos for the FwOR1995NN and the FwOR2030PS scenarios, using the same three metrics as the freshwater analysis: community changes, population changes, and changes to target taxa. For both of these water withdrawal scenarios, the overall response was found to be negligible to minor, and changes in community structure, total abundance, and abundance of white shrimp and blue crab populations all were minor in this scenario.
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From page 79... ...
, which are really not populations but groups of similar species that cannot be identified. Finally, there were no connections in the conceptual model or in the text between the effects of water withdrawals on estuarine benthos and effects on vertebrate groups (e.g., birds, snakes)
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From page 80... ...
FISH Freshwater Fish Assemblages Conceptual Model A conceptual model for the effects of water withdrawals on freshwater fish assemblages, as well as potential direct and indirect effects on other ecological processes and conditions, is shown in Figure 3-9. The model portrays the linkages between changes in water levels, flow, floodplain inundation and frequency, and entrainment/impingement impacts, leading to changes in various vital fish metrics at different levels of organization.
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From page 81... ...
to the Base1995NN scenario indicated that from Lake Harney downstream, the mean, mean 30-day low, and mean 30-day high water levels would change
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From page 82... ...
would occur and would impact fish floodplain habitat use upstream of Lake Harney. To examine changes in the timing and duration of flood events due to water withdrawals, the fish workgroup compared the Base1995NN scenario to the other predicted scenarios by month at Lake Poinsett.
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From page 83... ...
The workgroup carefully examined impacts to fish along seven MFL transects and at Lake Poinsett in appropriate scales relative to the projected water level reductions. They were able to quantify different responses due to water withdrawals based on geography.
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From page 84... ...
The models portray the linkages between increased water withdrawals and changes in water levels, flow, and changes in spatial coverage and distribution of salinity zones leading to changes in various biological vital metrics of selected fishes. As with the freshwater component, the Committee views the conceptual model as reasonable and appropriate.
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From page 85... ...
Each monthly sampling trip was a single data point in the regression with the center-of-abundance being calculated for all samples within each trip. Pseudospecies were selected initially based on having > 100 individuals by gear type and at least 5 percent frequency of occurrence in all samples, and mean daily flow data used were lagged at 30-day intervals from 30 to 360 days.
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From page 86... ...
Given the large number and variability in the pseudospecies considered, it is difficult to make gross generalizations about the impacts of water withdrawals
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From page 87... ...
Nonetheless, the fish workgroup produced a level-of-effects table found below as Table 3-10. The table shows the effects of the Full1995NN scenario, which was deemed to have the largest overall effect on fish assemblages.
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From page 88... ...
To accomplish this, species were assigned to one of four "wildlife hydrologic types," groupings of species with similar hydrologic requirements and so, it is assumed, similar responses to hydrologic change. Conceptual Model A conceptual model depicting the potential effects of water withdrawals on wetland wildlife species was developed to investigate possible responses to alterations in hydroperiod and salinity (Figure 3-11)
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From page 89... ...
. workgroup predicted that changes in water depth would lead to changes in wildlife abundance as mediated by the changes in wetland type and area (shown as an input from the wetlands workgroup)
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From page 90... ...
Results The screening level assessment of hydrologic change by river segment was used to identify groups of estuarine species that may be affected by water withdrawals in river segments 1 and 2, and freshwater wildlife in segments 6, 7 and 8. A partial assessment was also made for some categories of the freshwater species in segments 2 and 3.
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From page 91... ...
Overall, the AQ and OBL wildlife groups were predicted to persist if water withdrawals occur, partly due to compensation from the upper basin projects. Habitat shifts due to sea level rise, on the other hand, may lead to a shift from freshwater to estuarine habitats in the lower reaches of the river with consequent impacts to freshwater species there.
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From page 92... ...
Thus, the analysis is an integration of a very thorough literature review along with the results of the H&H modeling effort and input from the wetlands, benthic invertebrate, and fish workgroups. Effects due to salinity changes in the lower reaches of the river were predicted to be much greater than impacts from lower water levels in the upper basin.
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From page 93... ...
2011. Water Supply Impact Study Littoral Zone Working Group Draft Final Report: Assessment of Impacts from Water Withdrawals.
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From page 94... ...
2011. Water Supply Impact Study Benthic Macroinvertebrate Working Group Draft Final Report: Assessment of Impacts from Water Withdrawals.
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From page 95... ...
2004. Photooxidation and its effects on the carboxyl content of dissolved organic matter in two coastal rivers in the southeastern United States.
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