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' TN and organic matter (BOD) loadings averaged over area of entire saline estuary.

2 GPP estimates are for mesohaline estuary and are based on measured data for 1970s and 1990s and are estimated based on nutrient loading for pre-European settlement and potential future.

3 Potential future assumes complete conversion to nutrient-reduction treatment for sewage treatment, elimination of CSO discharges, and a significant reduction in nitrogen loading from upriver tributaries. See text for further details on derivation of estimates.

' TN and organic matter (BOD) loadings averaged over area of entire saline estuary.

2 GPP estimates are for mesohaline estuary and are based on measured data for 1970s and 1990s and are estimated based on nutrient loading for pre-European settlement and potential future.

3 Potential future assumes complete conversion to nutrient-reduction treatment for sewage treatment, elimination of CSO discharges, and a significant reduction in nitrogen loading from upriver tributaries. See text for further details on derivation of estimates.

(Fig. 10.6; Boyer et al., 2002). A nitrogen flux of 100 kg N km-2 y-1 from the landscape contributes atotalloadto the estuary of 3.5 x 103 tonsNy-1 for a watershed the size of Hudson basin, suggesting that human activity up to the 1990s has increased nitrogen loading to the Hudson estuary twelve-fold (Tables 10.2,10.5). Per area of estuary, the pristine nitrogen loading would have corresponded to an input of 23 g N m-2 y-1 (Table 10.5). Note that this estimated nitrogen loading to the Hudson estuary under pristine conditions is in fact higher than the current loading to Chesapeake Bay and is only slightly less than the current loading to Delaware and Narragansett Bays. Again, this reflects the very high ratio of watershed area to estuarine surface area for the Hudson in comparison to other large estuaries.

While the export of nitrogen from the landscape in the temperate zone can be well predicted from the net anthropogenic inputs of nitrogen, export of phosphorus is quite dependent upon the amount of phosphorus in the parent soil, which is highly variable across regions. As a result, there is no consistent estimate of a baseline flux of phosphorus from pristine watersheds, as there is for nitrogen (NRC, 2000). For the Hudson, we can estimate what the pre-European phosphorus input to the estuary may have been by evaluating changes in erosion. In the pristine landscape (i.e., 100 percent forested), most of the phosphorus input to the Hudson would likely have been bound to particles. Currently, inputs of sediment to the Hudson estuary from erosion in the watershed are ten-fold higher than if the basin were entirely forested (Swaney et al.,

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