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Figure 8-22 Long-term trends in fishery resources of the Potomac estuary based on Index of Biotic Integrity (IBI). Source: Jordan, 1992.

are indirectly influenced by SAV abundance, necessary to provide nursery habitat for juvenile fish (Fewlass, 1991). The quality of river habitat for fish has increased with the resurgence of SAV habitat in comparison to areas characterized by the absence of SAV beds. During 1984-1986, years characterized by a rapid increase in the distribution of SAV beds (primarily Hydrilla) (see Figure 8-16), fishery surveys near Washington, DC, clearly showed an increase in species diversity; abundance increased from 79 to 196 fish per net haul over the same 2-year period (MWCOG, 1989). The relationship of SAV and fishery data from the tidal Potomac is consistent with data reported by Kemp et al. (1984) for the Choptank River on the eastern shore of Maryland (see Figure 8-21).

S^y and Ecological Resources The evidence is clear from observations in Chesapeake Bay and the tidal Potomac River that the presence of SAV beds is critical for a healthy and diverse aquatic ecosystem. The presence of SAV beds has the following positive ecological impacts:

• Increases habitat and food resource availability

• Increases species diversity and abundance

• Increases fishery resources

• Increases waterfowl populations

• Increases recreational opportunities (fishing, hunting, bird-watching)

• Enhances water quality

• Removes nutrients

• Allows particulate material to settle out

• Reoxygenates water column by photosynthesis

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