Browsing by Author "Rabalais, Nancy N."
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Item Characterization of Hypoxia(NOAA Coastal Ocean Program, 1999-05) Rabalais, Nancy N.; Turner, R. Eugene; Justic, Dubravko; Dortch, Quay; Wiseman, William J., Jr.Nutrient overenrichment from human activities is one of the major stresses affecting coastal ecosytems. There is increasing concern in many areas around the world that an oversupply of nutrients from multiple sources is having pervasive ecological effects on shallow coastal and estuarine areas. These effects include reduced light penetration, loss of aquatic habitat, harmful algal blooms, a decrease in dissolved oxygen (or hypoxia), and impacts on living resources. The largest zone of oxygen-depleted coastal waters in the United States, and the entire western Atlantic Ocean, is found in the northern Gulf of Mexico on the Louisiana-Texas continental shelf. This zone is influenced by the freshwater discharge and nutrient flux of the Mississippi River system. This report describes the seasonal, interannual, long-term variability in hypoxia in the northern Gulf of Mexico and its relationship to nutrient loading. It also documents the relative roles of natural and human-induced factors in determining the size and duration of the hypoxic zone.Item Long-Term Effects of Offshore Oil and Gas Development: An Assessment and A Research Strategy(Louisiana Universities Marine Consortium, 1985-06) Rabalais, Nancy N.; Boesch, Donald F.The ultimate purpose of this project has been to develop recommendations for the design of an environmental research and monitoring program to quantify and evaluate the significance of subtle and long-term effects of offshore oil and gas development activities. To accomplish this the participants decided that extensive background must be developed to support the conclusions and recommendations. Hence, voluminous technical papers are included in addition to the overall assessment and research plan in Chapter 1.Item Nitrogen in Aquatic Ecosystems(2002) Rabalais, Nancy N.Aquatic ecosystems respond variably to nutrient enrichment and altered nutrient ratios, along a continuum from fresh water through estuarine, coastal, and marine systems. Although phosphorus is considered the limiting nutrient for phytoplankton production in freshwater systems, the effects of atmospheric nitrogen and its contribution to acidification of fresh waters can be detrimental. Within the estuarine to coastal continuum, multiple nutrient limitations occur among nitrogen, phosphorus, and silicon along the salinity gradient and by season, but nitrogen is generally considered the primary limiting nutrient for phytoplankton biomass accumulation. There are well-established, but nonlinear, positive relationships among nitrogen and phosphorus flux, phytoplankton primary production, and fisheries yield. There are thresholds, however, where the load of nutrients to estuarine, coastal and marine systems exceeds the capacity for assimilation of nutrient-enhanced production, and water-quality degradation occurs. Impacts can include noxious and toxic algal blooms, increased turbidity with a subsequent loss of submerged aquatic vegetation, oxygen deficiency, disruption of ecosystem functioning, loss of habitat, loss of biodiversity, shifts in food webs, and loss of harvestable fisheries.Item Nutrient Enhanced Coastal Ocean Productivity in the Northern Gulf of Mexico - Understanding the Effects of Nutrients on a Coastal Ecosystem(National Oceanic and Atmospheric Administration National Ocean Service, 1999-04) Wiseman, William J., Jr.; Rabalais, Nancy N.; Dagg, Michael J.; Whitledge, Terry E.This publication is a synthesis of the findings and management implications of research sponsored by the National Oceanic and Atmospheric Administration's (NOAA) Coastal Ocean Program (COP) through its Nutrient Enhanced Coastal Ocean Productivity (NECOP) study. Enhanced nutrient enrichment from anthropogenic sources is one of the major stresses imposed on the sea. This is particularly true in the northern Gulf of Mexico where the nation's largest river discharges into an otherwise oligotrophic sea. This report contains six chapters devoted to syntheses of specific topics important to understanding the oceanography of the area and the cumulative impact of river-borne nutrients on the coastal ecosystem.