Review of the St. Johns River Water Supply Impact Study Report 1 (2009) / Chapter Skim
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4 Ecological Assessments
4 Ecological Assessments
Pages 43-71
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From page 43... ...
Johns River as a consequence of changes in river stage induced by additional water withdrawals. The floodplains have swampy herbaceous wetlands with deep organic soils, and withdrawals could increase the number of days that organic wetland soils are exposed to air.
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From page 44... ...
Johns River as a result of the proposed additional water withdrawals. Oxidation of airexposed organic soils degrades high molecular weight (insoluble)
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From page 45... ...
The Phase I report did not make a persuasive case that changes in CDOM concentrations or loadings under conditions of additional water withdrawals would have significant ecological or water quality impacts. If water flow rates decrease and CDOM loadings remain constant (or increase)
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From page 46... ...
Johns River under the conditions likely to be engendered by enhanced consumptive-use water withdrawals. Finally, the committee is not convinced that the Phase I studies have provided a sufficient predicate for the laboratory and in situ studies proposed for Phase II.
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From page 47... ...
Johns River system. Summary Although the biogeochemistry workgroup identified and ranked several potential effects of additional water withdrawals on biogeochemical processes, their analysis did not use local release rates of constituents from flooded and exposed organic soils.
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From page 48... ...
First, additional water withdrawals may increase the likelihood, duration, and areal extent of water column density stratification and induce bottom water hypoxia in the lower St. Johns River under low flow conditions, which was not discussed in the Phase I report.
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From page 49... ...
. Under conditions of increased water withdrawals, CDOM concentrations could increase if export of CDOM from riparian wetlands remains constant (or possibly increases)
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From page 50... ...
Thus, the Phase II efforts should emphasize the importance of both nitrogen and phosphorus and the effects of water withdrawals in the context of a dual nutrient management strategy (Paerl, 2009)
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From page 51... ...
Examine available data for insight about the effects of hydrologic alterations from water withdrawals on benthic macroinvertebrates. The Phase I report reviewed past work in the watershed, began analysis of an existing data base, and briefly described several conceptual models to guide thinking about how to study and understand the effects of water withdrawal on the trophic organization of benthic invertebrates.
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From page 52... ...
The potential impacts of water withdrawals for these early life history stages were not addressed adequately in the Phase I report, a subject that might be addressed jointly with the plankton workgroup during Phase II. Questions that could be address include: what proportion of the species in the St.
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From page 53... ...
The committee strongly supports the development of indicators beyond individual species in the WSIS, and commends the benthos team's commitment to use of more integrative measures of biological condition to judge the effects of water withdrawals. In addition to the study of functional or trophic groups, the Phase II work plan suggests the exploration of a broader array of measures to characterize biological condition (SJRWMD, 2009c, page 58)
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From page 54... ...
Much of the detail of those efforts is yet to be defined, a fact that makes it difficult to offer specific recommendations on the next steps to be taken in the process. LITTORAL ZONE The proposed surface water withdrawals from the St.
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From page 55... ...
The District predicted that projected future water withdrawals could have dramatic consequences on SAV in some areas, especially where V americana populations now fluctuate in the lower St.
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From page 56... ...
Water Quality Monitoring and Data Analysis The hydrologic modeling in Phase II is expected to provide more spatially explicit predictions on the salinity increases of the littoral zone. In Phase II, three separate water quality monitoring programs are to be continued that will provide important data for verifying the model output.
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From page 57... ...
The exposure of fishes to potential effects from water intake structures will vary based on their life history characteristics in relation to the location of the intake structures. The District identified 22 species that it considers good "indicators of impact" due to water withdrawals (although the 22 species listed in Table 1 of the Phase I report and discussed in the associated text do not exactly match the species with potential impacts identified in bold in Appendix A)
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From page 58... ...
Entrainment and Impingement The District recognizes the importance of understanding the potential effects of entrainment and impingement from surface water withdrawals. Its hypothesis is that given the relatively low intake velocities of the proposed withdrawals, adult and juvenile fish entrainment or impingement probably will not be significant enough to elicit broad-based community changes.
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From page 59... ...
Many other species are important in the maintenance of a sustainable and diverse fish fauna in the St. Johns River system in the face of expanded water withdrawals and should be carefully examined.
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From page 60... ...
Furthermore, the FIM sampling may not be spatially and temporally defined enough to capture the data needed to address water withdrawals and subsequent movement of the saltwater upstream. These concerns, which relate to where the data are collected and how those sites relate to changing patterns of salt intrusion, water level fluctuations (particularly under low flow conditions)
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From page 61... ...
and thus to water withdrawals. Indeed, a program could be developed that integrates the FFWCC fish and decapod data and the benthic macroinvertebrate and aquatic vegetation components using an approach similar to that of Peebles and colleagues from the University of South Florida.
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From page 62... ...
Johns River. An understanding of their ecologies and how their distributions and abundances will be affected by proposed water withdrawals is central to the evaluation of natural resource effects that comprises the bulk of the WSIS.
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From page 63... ...
integrate existing fish data sets with benthic macroinvertebrate and SAV data to address impacts to fish assemblages, and (3) comprehensively study the impact of a 4-cm water level drop to the spawning and feeding habitat in the middle and upper St.
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From page 64... ...
WETLANDS AND WETLAND-DEPENDENT SPECIES Changes in hydrology can alter the structure and function of wetlands. Therefore, the wetlands workgroup is examining the potential impacts of the proposed surface water withdrawals to wetland vegetation and a few species of wetland-dependent fauna.
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From page 65... ...
The Phase II work plan indicates that the transect data will be used to accomplish this through appropriate data analysis. Identifying Sensitive Wetland Areas To cope with the distribution of wetland types found in the watershed, the wetlands workgroup divided the river into nine segments (see Figure 3-3)
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From page 66... ...
SOURCE: SJRWMD. from water withdrawals to all wetlands in the segment.
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From page 67... ...
• A stressor layer was created to represent water level lowering or other environmental changes, including changes in salinity. • Where sensitive areas overlapped with areas impacted by stressors, some likelihood of effects was assigned.
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From page 68... ...
It is unlikely that there will be impacts due to water withdrawals.
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From page 69... ...
An integrative method such as sediment elevation tables may provide information that is better able to reveal the impacts of hydrologic change than, for example, the soil analysis planned for Phase II. This proposed analysis involves the collection of soil samples at 150 locations throughout the basin to characterize the dominant soils in each river segment, particularly the organic soils vulnerable to drawdown.
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From page 70... ...
, an index developed to assess the impact of human disturbance on vegetation communities. This index, akin to a plant-based Index of Biotic Integrity, assigns a repeatable and quantitative value to vegetation community composition and could be used to detect shifts in vegetation community composition that might occur with water withdrawals.
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From page 71... ...
The District plans during Phase II to produce DEMs for the portions of the watershed where data are available. It will also be important for the workgroup to better define the criteria used to determine the likelihood of impacts of water withdrawals to each wetland segment.
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