Nitrogen Budgets of Estuarine Systems

P loads were statistically related to population density and runoff per unit land area, (2) N and P loads were closely correlated to each other despite different biogeochemistries, (3) loads to coastal waters had increased by a factor of about three since the 1970s. Estimates of future loads to estuaries and the coastal ocean suggest another doubling by 2050 (e.g., Kroeze and Seitzinger, 1998 Chapter 18 by Seitzinger and Harrison, this volume). 

The anthropogenic rates of N-loading to adjacent estuarine systems are clearly much higher 37% of the sample exceeded 50 g N m year, almost an order of magnitude greater than most adjacent land areas. 

Compared to N inputs, the internal loss terms of estuarine N-budgets are not as well documented. In general, internal losses include burial of PN in accreting sediment colunms and denitrification in either the water colunm or sediments (see also Devol, this volume). A few nutrient budgets have estimated N-extraction in the harvest of fish and shellfish biomass and fish migration from estuaries. 

Estimates of long-term PN burial (Table 18.2) illustrate a substantial range in rates from very small values (0.05—0.2 g N m year ) in the deepest systems to 

Ecosystem N-burial rate (g N N-burial rate (mmol N  

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