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Review of the St. Johns River Water Supply Impact Study: Report 2
Pages 1-11

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From page 1...
... Committee to Review the St. Johns River Water Supply Impact Study, which is providing ongoing advice to the St.
From page 2...
... These activities include modeling of the relevant river basins, determining what criteria should be used to evaluate the environmental impacts of water withdrawals, evaluating the extent of those impacts, coordinating with other ongoing projects, and issuing a final report. The NRC committee will review scientific aspects of the WSIS, including hydrologic and water quality modeling, how river withdrawals for drinking water will affect minimum flows and levels in the two rivers, the impact of removing old and introducing new wastewater streams into the rivers, the cumulative impacts of water withdrawals on several critical biological targets, and the effects of sea level rise.
From page 3...
... stated that "it would be useful for the District to assemble basic water budget information for the drainage basin and its major subunits." Subsequently, the District provided water budgets for a few locations in the lower and middle river basin, showing the contributions of upper basin water, rainfall, evaporation, tributaries, springs, diffuse groundwater (from the Upper Floridan aquifer) , and reverse flow to the water budget for the wettest and driest four-month seasons.
From page 4...
... There is some concern that feedback from the ecological groups to the hydrologic modeling has not been shown formally in the conceptual models, but the District indicated that these feedbacks do exist. District staff mentioned that the hydrologic data needs of all the ecological workgroups are being compiled, and the committee hopes to review this when available.
From page 5...
... With respect to the recommendation to consider density-dependent flow, District scientists stated that sufficient data are not available to perform this type of analysis. It is probable that river salinity contributed by the upper Floridan Aquifer will not substantially increase with the small change in river stage that would result from water withdrawal.
From page 6...
... Existing biological monitoring protocols, such as the Floristic Quality Index, could be useful for the latter, but their implementation will require some data collection by the District to determine how to best use these methods for assessing possible impacts of water withdrawals. Finally, the committee still believes that an integrative method to measure soil subsidence, such as Sediment Elevation Tables, is worth considering as a field-based tool to assess the effects of altered hydrology (for example, if dewatering caused the oxidation and subsidence of organic soils, potentially leading to nutrient release)
From page 7...
... release rates from drying soils that would yield data reflective of environmental conditions, and the committee re-emphasizes that recommendation here. Second, the committee expressed concern that the equation being used by District scientists to estimate changes in nutrient fluxes from wetland soils as a result of desiccation is simplistic because it assumes that the changes are solely due to changes in oxidation rates.
From page 8...
... Although the importance of salinity is widely recognized, the committee is concerned that salinity provides a narrow window through which to understand potential changes in invertebrate assemblages that may occur in response to water withdrawals. Discussion by the submersed aquatic vegetation (SAV)
From page 9...
... They have continued with their efforts to project the impacts of water withdrawals on SAV in the littoral zone by understanding species responses to salinity. One particularly cogent set of experiments involved detection of stress enzymes, and the results from this matched extremely well with the overall salinity relationships largely derived from the literature in the draft Phase 1 document (SJRWMD, 2008)
From page 10...
... The District's plan to understand the extent of areas dewatered by potential water withdrawals is to use the newly acquired LIDAR data to construct better DEMs across the range, in consultation with the wetlands workgroup. However, the fish workgroup suspects that these DEMs will be at too coarse a scale to observe alterations in the distribution and abundance of many fish species in wetland areas brought about by water withdrawal.
From page 11...
... The committee has frequently reviewed District graphs meant to compare model results with actual observations. In most of the cases observed by the committee, the predicted and observed values share a common x-axis, which can give a false sense of the predictability of the simulation, especially in terms of ability of the model to predict individual values.


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