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1 Understanding Nutrient Over-Enrichment: An Introduction
Pages 11-36

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From page 11...
... Introduction and Overview
From page 12...
... 4. Congress and the White House-these entities set policy and delegate specific legal and administrative powers to federal agencies.
From page 13...
... However, there is growing evidence that events such as the deaths of unusually large numbers of sea lions and manatees, unusual patterns of coral reef destruction, widespread fish kills, outbreaks of certain shellfish poisonings, disappearance of seagrasses, and the occurrence of the so-called "dead zone" in the Gulf of Mexico actually have much more in common than originally thought. All of these events reflect both subtle and not-sosubtle changes in the relative and absolute abundance of certain organisms near the very base of the food web.
From page 14...
... . This is of particular importance when changes in the total or relative abundance of organisms have adverse impacts on the environmental quality of biologically rich coastal waters.
From page 15...
... One of the most common is eutrophication that is, the process of increasing organic enrichment of an ecosystem where the increased supply of organic matter causes changes to that system (Nixon 1995~. In coastal ecosystems, eutrophication can lead to excessive, and sometimes toxic, production of algal biomass (including red and brown tides)
From page 16...
... and the Environmental Protection Agency (EPA) are primarily responsible for research, policymaking, and management related to eutrophication, in part through the tools provided by the Clean Air, Clean Water, and Coastal Zone Management Acts (Box 1-1~.
From page 18...
... However, nutrient over-enrichment and eutrophication pose an extremely complex and variable problem that occurs at a number of scales. The complexity of sources, fates, and effects of nutrients coupled with associated socioeconomic and political issues mean that solutions will require coordinated local, state, regional, and national efforts and the involvement of an extremely varied range of stakeholders.
From page 19...
... The remainder of the report, Sections II and III, provides a detailed treatment of the topics necessary to understand nutrient over-enrichment and plan actions to combat it. Section II, which includes Chapters 3, 4, 5, and 6, serves as a primer on nutrient enrichment and its impacts, including discussions of sources of nutrients and water body susceptibility.
From page 20...
... (1999) concluded that "Nearly all estuarine waters now exhibit some symptoms of eutrophication, though the scale, intensity, and impact may vary widely, the level of nutrient inputs required to produce the symptoms also varies." This conclusion reflects, in part, the reality that coastal water bodies vary in susceptibility to nutrient loading (Box 1-2~.
From page 22...
... in ~ ~ ~ s s O ~ ~ —~ ~0 an ~ '~ ~ CLEAN COASTAL WATERS
From page 23...
... Eutrophication As noted earlier, eutrophication is the process of increasing organic enrichment of an ecosystem where the increased rate of supply of organic matter causes changes to that system (Nixon 1995; see Chapter 4~. In moderation, increasing organic matter can sometimes be beneficial, such as when an increased rate of primary production leads to greater fishery production and, ultimately, increased harvests (Nixon 1988; Hansson and
From page 24...
... Loss of Seagrasses and the Habitat They Form Most coastal waters are shallow enough that benthic plant communities contribute significantly to primary production as long as sufficient light penetrates the water column to the seafloor. In good conditions, dense populations of seagrasses and perennial macroalgae can grow and attain rates of net primary production that are as high as the most productive terrestrial ecosystems (Charpy-Roubaud and Sournia 1990~.
From page 25...
... In temperate systems, perennial seagrasses largely obtain their nutrient requirements by using stored nitrogen pools, internal recycling, and nutrient sources in the sediment (Pedersen and Borum 1996~. As a result, excess nutrient enrichment rarely stimulates these populations.
From page 26...
... The impacts of these phenomena include mass mortalities of wild and farmed fish and shellfish; human illness or even death from contaminated shellfish or fish; alterations of marine trophic structure through adverse effects on larvae and other life history stages of commercial fisheries species; and death of marine mammals, seabirds, and other animals. HABs and related phenomena such as Pfiesteria outbreaks have attracted intense public and political attention (Box 1-5~.
From page 28...
... 1990~. Another type of HAB impact occurs when marine animals are killed by algal species that release toxins and other compounds into the water, or that kill without toxins by physically damaging gills or by creating low oxygen conditions as bloom biomass decays.
From page 29...
... In addition to the toxic impacts shown, harmful microalgal and macroalgal species have caused whale and other marine mammal mortalities, occasional anoxia, habitat destruction, and a general decline in coastal aesthetics in many coastal areas during the last 20 years. Neurotoxic shellfish poisoning = NSP, paralytic shellfish poisoning = PSP, and amnesic shellfish poisoning = ASP (Anderson 1995~.
From page 30...
... The world's major coral reef ecosystems are distributed in nutrient-poor surface waters in the tropics and subtropics. Coral reefs are a paradox because their high gross productivity and biodiversity occur in waters with very low concentrations of dissolved and particulate nutrients.
From page 31...
... Nitrogen is of paramount importance in both causing and controlling eutrophication in coastal marine ecosystems (Box 1-6~. Other elements particularly silicon and iron may also be of importance in regulating HAB occurrences in coastal waters and in determining some of the consequences of eutrophication, but their importance with respect to nutrient over-enrichment in coastal waters is secondary to nitrogen.
From page 33...
... When human activity drastically alters the distribution or relative abundance of the various compounds containing these element forms, they alter the overall biogeochemical cycle of Airshed 1 1 Large Coastal Upstream Watersheds Watersheds Smaller Streams Coastal Water Body r Exchange ~ Open Ocean | FIGURE 1-3 Schematic showing general sources of nutrients and main routes of transport to coastal waters.
From page 34...
... 1997~. By 1995, however, the global use of inorganic nitrogen fertilizer was again growing rapidly, with much of the growth driven by use in China.
From page 36...
... 1999~. Thus, the rate at which humans have altered nitrogen availability globally far exceeds the rate at which humans have altered the global carbon cycle.


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