Geoscience Reference
In-Depth Information
Excess nutrients reach surface-water resources in direct discharges from
point sources (for example, municipal wastewater-treatment plants) and from
diffuse non-point sources (for example, nutrient runoff from farmland, urban,
and suburban areas and air pollution). Because the nutrient-use efficiency of
crops is less than 100%, farmers need to apply more nutrients to their fields than
the plants need for healthy growth. The challenge for all farmers is to add fertil-
izer at the optimal time and rate and then to keep the nutrients in the field. Con-
comitant with the substantial increases in agronomic yields that have allowed
agriculture and fish production to meet the food needs of 7 billion people has
been a need for higher rates of application of fertilizers, which have exacerbated
runoff, limited the effectiveness of strategies for remediating eutrophication, and
resulted in production of nitrous oxide as a byproduct of nitrification and denitri-
fication processes. (Nutrient sources for the Chesapeake Bay and the Gulf of
Mexico are shown in Figure 2-1.) Addressing the nutrient loading will require
increased scientific understanding, including new information on pollution
sources, on emerging technologies that could be used in agriculture and in
wastewater treatment, on water quality conditions, and on the response of eco-
systems to increasing nutrient loads and shifting stochiometry. Such scientific
understanding can be gained only through integrated research.
The Chesapeake Bay, North America's largest estuary, offers a highly
instructive example of contributions made by EPA and allied researchers to a
more fundamental understanding of the physical processes that lead to the ef-
fects of nutrient pollution. Substantial reductions in nutrient discharges from
sewage-treatment plants, factories, and other point sources of pollution have
been achieved in the bay watershed since the 1970s but are insufficient to
meet water-quality goals. The challenges faced by the Chesapeake Bay eco-
system are shared by many other ecosystems, but the differences among them
make the required research and the effective tools for addressing the chal-
lenges more complex. For example, 500 km to the north of the Chesapeake
Bay lies Narragansett Bay. Although smaller than its southern cousin, it shares
many historical and ecologic characteristics; but the challenges faced today by
the Narragansett Bay (where EPA's Atlantic Ecology Division Laboratory is
located) have developed in very different ways. The region has historically
been dominated by agricultural activity, but that is no longer the case. Today,
Narragansett Bay suffers from excess nitrogen inputs, largely from upstream
wastewater-treatment facilities (Pryor et al. 2007). The upper reaches of the
bay have been closed to shellfishing and swimming for decades. In 2004,
Rhode Island mandated a minimum standard for effluent nitrogen from the
wastewater facilities within its jurisdiction, yet the science suggests that with-
out concomitant reductions in nitrogen from wastewater facilities upstream on
the Blackstone River in Massachusetts and reduction in nitrogen inputs that
result directly and indirectly from air pollution, restoring the waters of the
upper bay will be difficult (see Figure 2-2). Narragansett Bay, as a result of
the large influence of sewered effluents, should be one of the easiest places to
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