Long-term trends in estuarine nutrients and chlorophyll, and short-term effects of variation in watershed discharge
نویسندگان
چکیده
For up to 18 yr we monitored salinity and the concentrations of nutrients, organic matter, plant pigments, and suspended particles in the Rhode River (a subestuary of Chesapeake Bay, USA) to examine long-term trends and relabonships to watershed discharges. There was no clear evldence of increasing eutrophlcation. Chlorophyll concentration did not show a long-term trend, although pheopigments increased. Total suspended particles and forms of P, N, and C showed either a decrease or no trend, except for dissolved ammonium, which increased slightly in one segment of the estuary. The largest and most consistent trend was a decrease in dissolved organic N. We also analyzed correlations between watershed flow and concentrations at weekly and seasonal time scales, resolving the different influences of the Susquehanna kver and local watersheds. In some cases, nitrate was posihvely correlated with either local or Susquehanna flow depending on season, location in the estuary, and time scale At both weekly and seasonal time scales, chlorophyll was positively correlated with Susquehanna flow in spring in one segment of the estuary. At the seasonal time scale, chlorophyll in summer was correlated with Susquehanna flow of the previous spring. These results and the pattern of fluctuation in the ratio of dissolved inorganic N : P support the hypothesis that chlorophyll concentrations in spring are controlled by nitrate inputs from the Susquehanna, while in summer they are controlled by the regeneration of inorganic N from organic matter produced in the spring.
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