The presence of excessive amounts of biologically reactive nitrogen in coastal bays and estuaries has been recognized as a major environmental issue. For the most part, this is due to its role in enhancing phytoplankton growth that, in turn, can lead to algal blooms, oxygen consumption in seawater and on the seabed, altered patterns of primary productivity, changes in species composition, and shading effects on macrophytes and seagrass beds. Of particular concern is the occurrence and magnitude of harmful algal blooms, for which nutrient over-enrichment could be the primary or an important co-factor. Nitrogen sources to coastal waters and estuaries are diverse and include wastewater effluents, certain industrialdischarges, surface water runoff, groundwater discharge, the atmosphere, and influx from the coastal ocean. Atmospheric deposition can be a relatively major source of nitrogen to estuaries, particularly in areas where other nitrogen sources are relatively small. There are very few estuaries for which a balance sheet of nitrogen input and export has been developed. This is due to a lack of coherent monitoring programs that can provide a continuum of observations from the watershed to the coastal ocean, and in different environmental matrices to calculate or simulate source attribution of analytes of concern. The apparent complexity of nitrogen's role in promoting eutrophication has occasionally rekindled debate on the comparative influences of nitrogen and phosphorus on primary productivity in coastal and marine waters, particularly where mixing between surface and deeper waters is more pronounced. Corollary to this debate is the question of whether nitrogen is the scarcest of the nutrients in coastal bays and estuaries and whether a singular focus on nitrogen controls would be fruitful.43,16 Occasional reviews of nitrogen limitation of algal growth and nitrogen to phosphorus ratios in marine and freshwater environments suggest that nitrogen limitation can occur when the N:P ratio is less than 20, and phosphorus limitation when the ratio is more than 50, rather than whether the system is marine or freshwater.44,19 Even after years of focused research on the consequences of nitrogen over-enrichment in U.S. coastal waters and estuaries, several key issues remain, including the magnitude, spatial, and temporal extent of eutrophication and associated water quality and habitat impairments attributable to increasing nitrogen inputs to estuaries and coastal waters.
|Original language||English (US)|
|Number of pages||7|
|Specialist publication||EM: Air and Waste Management Association's Magazine for Environmental Managers|
|State||Published - Dec 1 2007|
All Science Journal Classification (ASJC) codes
- Environmental Engineering
- Waste Management and Disposal