Issues in Ecology Number 7 al12000 Nutrient Pollution of Coastal Rivers,Bays,and Seas by Robert Howarth,Donald Anderson.James Cloem.Chris Elfring.Charles Hopkinson. Brian Lapointe,Tom Malone.Nancy Marcus,Karen McGlathery.Andrew Sharpley.and Dan Walker INTRODUCTION This article summarize es the ecological damage c b nutrient po sys why N i Antipolution laws enacted and enforced over the s have incr of the United States.While the ghting this effort has oreatly reduced point-source pollution of to materials.oxvgen-consuming organic materials (BOD).and e 0% Alte to some exter phosphorus(P)from industrial and municipa 199 effluent pipes.no comparable attempt has been made to re. and nd Nitrogen strict the input of nitrogen(N)from municipal effluent.nor to control the flows of N and p that enter waterways from ECOLOGICAL DAMAGE dispersed or nonpoint sources such as agricultural and urban FROM NUTRIENT POLLUTION runoff or windbomne deposits.As a consequence.inputs of nonpoint pollutants.particularly N.have increased dramati- Nutrient over-enrichment has a range of effects on cally.Today.pollution from the nutrients N and P represents s on ecologica the largest source of degradation in coastal waters.which sity-the variety include some of the richest and most productive habitats in in the ecosvstem the oceans.Roughly half of the global fishe es catch occurs Fertilizino lakes.rivers.or coastal waters with pre in or is dependent upon coastal waters of the world. viously scarce nutrients such as N or P usually boosts the Nutrient pollution is also called nutrient over- enrich primary productivity of these systems-that is,the produc bo P are vital to plant growth. tion of algae (phytoplankton)that forms the base of the range plag uing nea aquatic food web(Figure 2).This excessive.nutrient-induced increase in the production of organic matter is called eutrophi cation.and eutrophication is linked to a number of problems the en in aquatic ecosystems. As the mass of algae in the water L grows,the water may become murkier:and particularly as the the algae die and decompose.periods of oxygen depletion Atlantic (hypoxi oxia)occur mor ng al ate 8a can c xyge uts nd p radation of coasta night changes i utr has confirmed that N over others and on, tems. De communiti lating water quality. brown tid because of public cor n water ula ing N inputs to aquatic systems severely under-regulated. 351mp9 suhtle cha s in the pla nity and The National Academies'National Research Council othe cological factors wth and (NRC)recently reviewed the causes and consequences of this t of fish ecies and lo red fisher neglected pollution problem in a report entitled “ean Coral reefs and suh ed nlant co Coastal Waters:Understanding and Reducing the Effects of beds can be harmed by loss of light from reduced water clar Nutrient Pollution."All of the authors of this article partici ity.or from nutrient-induced gro ths of nuisance seaw eeds pated as members,staff,or invited experts- in the work Some coastal ecosystems are more susceptible to of the NRC Committee on Causes and Management of Coastal nutrient over-enrichment than others because a host of addi Eutrophication and contributed to the NRC report.This ar- tional factors can influence the extent of plant productivity ticle is intended to bring the findings and recommendations These factors include how much light is available.how exten made in that report to a broader audience of non-specialists sively algae are grazed by zooplankton and benthic suspen 2 Issues in Ecology Number 7 Fall 2000 INTRODUCTION Antipollution laws enacted and enforced over the past 40 years have increasingly restricted discharge of toxic substances into coastal waters of the United States. While this effort has greatly reduced point-source pollution of toxic materials, oxygen-consuming organic materials (BOD), and to some extent phosphorus (P) from industrial and municipal effluent pipes, no comparable attempt has been made to re￾strict the input of nitrogen (N) from municipal effluent, nor to control the flows of N and P that enter waterways from dispersed or nonpoint sources such as agricultural and urban runoff or windborne deposits. As a consequence, inputs of nonpoint pollutants, particularly N, have increased dramati￾cally. Today, pollution from the nutrients N and P represents the largest source of degradation in coastal waters, which include some of the richest and most productive habitats in the oceans. Roughly half of the global fisheries catch occurs in or is dependent upon coastal waters of the world. Nutrient pollution is also called nutrient over-enrich￾ment because both N and P are vital to plant growth. A wide range of problems plaguing near-shore waters world￾wide, from fish kills to some coral reef destruction, can be linked directly or indirectly to excessive nutrient inputs. In the United States, for example, more than 60 percent of coastal rivers and bays are moderately to severely degraded by nutrient pollution. Although such problems occur in all coastal states, the situation is particularly acute in the mid Atlantic states, southeast, and Gulf of Mexico (Figure 1). While inputs of both N and P contribute to the deg￾radation of coastal rivers, bays, and seas, recent research has confirmed that N is particularly damaging to these sys￾tems. This contrasts with findings from freshwater lakes, where P has been demonstrated to be more critical in regu￾lating water quality. Because of public concern over readily apparent fouling in lakes and rivers, water quality regula￾tions over the past 30 years have focused largely on P, leav￾ing N inputs to aquatic systems severely under-regulated. The National Academies’ National Research Council (NRC) recently reviewed the causes and consequences of this neglected pollution problem in a report entitled Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. All of the authors of this article partici￾pated as members, staff, or invited experts in the work of the NRC Committee on Causes and Management of Coastal Eutrophication and contributed to the NRC report. This ar￾ticle is intended to bring the findings and recommendations made in that report to a broader audience of non-specialists. This article summarizes the ecological damage caused by nutrient pollution in coastal systems, discusses why N is of particular concern in these systems, and outlines the sources of N inputs to the coast. By highlighting the problem of nutrient pollution in coastal rivers, bays, and seas, this ar￾ticle builds upon two earlier volumes in the Issues in Ecology series: Human Alteration of the Global Nitrogen Cycle: Causes and Consequences (1997) and Nonpoint Pollution of Surface Waters with Phosphorus and Nitrogen (1998). ECOLOGICAL DAMAGE FROM NUTRIENT POLLUTION Nutrient over-enrichment has a range of effects on coastal systems, but in general, it brings on ecological changes that decrease the biological diversity the variety of living organisms in the ecosystem. Fertilizing lakes, rivers, or coastal waters with pre￾viously scarce nutrients such as N or P usually boosts the primary productivity of these systems that is, the produc￾tion of algae (phytoplankton) that forms the base of the aquatic food web (Figure 2). This excessive, nutrient-induced increase in the production of organic matter is called eutrophi￾cation, and eutrophication is linked to a number of problems in aquatic ecosystems. As the mass of algae in the water grows, the water may become murkier; and particularly as the algae die and decompose, periods of oxygen depletion (hypoxia and anoxia) occur more frequently. Even living al￾gae can contribute to oxygen depletion due to their oxygen consumption at night. These changes in nutrients, light, and oxygen favor some species over others and cause shifts in the structure of phytoplankton, zooplankton, and bottom-dwell￾ing (benthic) communities. For instance, blooms of harmful algae such as red and brown tide organisms become more frequent and extensive, sometimes resulting in human shell￾fish poisonings and even marine mammal deaths. Oxygen depletion can cause fish kills and create dead zones. Just as important, subtle changes in the plankton community and other ecological factors may trigger reduced growth and recruitment of fish species and lowered fishery production. Coral reefs and submerged plant communities such as seagrass beds can be harmed by loss of light from reduced water clar￾ity, or from nutrient-induced growths of nuisance seaweeds. Some coastal ecosystems are more susceptible to nutrient over-enrichment than others because a host of addi￾tional factors can influence the extent of plant productivity. These factors include how much light is available, how exten￾sively algae are grazed by zooplankton and benthic suspen￾Nutrient Pollution of Coastal Rivers, Bays, and Seas by Robert Howarth, Donald Anderson, James Cloern, Chris Elfring, Charles Hopkinson, Brian Lapointe, Tom Malone, Nancy Marcus, Karen McGlathery, Andrew Sharpley, and Dan Walker