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Early 1970s

Figure 10.8. Comparison of inputs to the saline Hudson River estuary of total nitrogen and of labile organic matter (expressed as carbon) per area of estuary in the early 1970s and in the 1990s. Over this time period, improvements in wastewater treatment led to large decreases in organic carbon loads from sewage and smaller decreases in nitrogen loads. On the other hand, gross primary production by phytoplankton increased dramatically, as climatic changes resulted in lower flows of freshwater down the Hudson during some summers. The lower flows increased the residence time of surface waters in the saline estuary, and allowed phytoplankton to use the still high nitrogen loads to bloom. In the 1990s, the higher freshwater flows down the Hudson River kept residence times in the estuary short and, consequently, phytoplankton production low. Overall, the inputs of labile organic matter to the estuary actually increased between the 1970s and the 1990s.

1990s

Early 1970s

Figure 10.8. Comparison of inputs to the saline Hudson River estuary of total nitrogen and of labile organic matter (expressed as carbon) per area of estuary in the early 1970s and in the 1990s. Over this time period, improvements in wastewater treatment led to large decreases in organic carbon loads from sewage and smaller decreases in nitrogen loads. On the other hand, gross primary production by phytoplankton increased dramatically, as climatic changes resulted in lower flows of freshwater down the Hudson during some summers. The lower flows increased the residence time of surface waters in the saline estuary, and allowed phytoplankton to use the still high nitrogen loads to bloom. In the 1990s, the higher freshwater flows down the Hudson River kept residence times in the estuary short and, consequently, phytoplankton production low. Overall, the inputs of labile organic matter to the estuary actually increased between the 1970s and the 1990s.

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