Hypoxia in aquatic systems refers to waters where the dissolved oxygen concentration is below 2 mg/L. Most organisms avoid, or become physiologically stressed in, waters with oxygen below this concentration. Hypoxia can also kill marine organisms which cannot escape the low-oxygen water, affecting commercial harvests and the health of impacted ecosystems. While hypoxia can occur naturally, it is often a symptom of environments stressed by human impact such as from excess nutrient enrichment from point and non-point sources. Over half of the U.S. estuaries now experience natural or human-induced hypoxic conditions at some time each year and evidence suggests that the frequency and duration of hypoxic events have increased over the last few decades.
The importance and national scale of hypoxia and nutrient pollution in U.S. waters is evidenced by the reauthorization of the Harmful Algal Bloom and Hypoxia Research and Control Act (HABHRCA) and two national reports which describe the need and identify priorities for research related to nutrient inputs, eutrophication and hypoxia in U.S. coastal waters (i.e. Priority Topics for Nutrient Pollution in Coastal Waters: An Integrated National Research Program for the United States and An Assessment of Coastal Hypoxia and Eutrophication in U.S. Waters). The recently released reports by the U.S. Commission on Ocean Policy and the Pew Oceans Commission Report both identify non-point source pollution in coastal ecosystems as one of the nation’s most widespread pollution problems and the greatest pollution threat to coastal marine life.
Over the past three decades, the U.S. has made substantial progress in reducing water pollution from industrial and municipal facilities. But control of what is called “nonpoint” pollution - such as nutrient, bacterial, and chemical pollution from agricultural fields and from urban areas - remains a continuing challenge. CSCOR-sponsored scientists and their partners in government, academia and industry are seeking ways to better understand links between nutrient over-enrichment and eutrophication and their impacts on human health and estuaries.
An example of the key role which CSCOR is playing to address nutrient enrichment can be found in the Gulf of Mexico where a large area of low oxygen bottom water, known as the “Dead Zone”, is a recurrent feature during the summer. The “Dead Zone” immediately became a focal point for considerable scientific and policy attention because of its enormous size and implications for watershed management for more than 40% of the continental United States. Employing a combination of field, monitoring, and modeling studies, within an ecosystem management framework, CSCOR-sponsored research has enabled NOAA to provide key information and tools to coastal managers to help manage and mitigate the size and impact of the annual hypoxic zone in the Gulf of Mexico (see NGOMEX program). CSCOR is now expanding the program to address hypoxia in other coastal, estuarine, and Great Lake regions around the U.S.
CSCOR also has other studies examining the effects of multiple stressors from human activities on natural systems. The Barataria watershed in the Gulf of Mexico is a significant estuary with a large fisheries yield and is currently experiencing large habitat changes and anticipates a doubled nitrogen loading. The watershed is located next to, and exchanges water with, the Mississippi River — the largest river in North America— whose watershed is shifting to a new management regime to reduce its nitrogen load. This long-term, ecosystem scale, study will quantify ecosystem responses to multiple stressors with several indicators being developed to assess the health and sustainability of the coastal wetlands when subject to varying degrees of nutrient inputs.
CSCOR’s intent is to provide timely and high-quality scientific results that can be used in an adaptive management program that connects monitoring, data analysis, and model predictions with management actions to restore and protect coastal ecosystems. CSCOR-sponsored research has enabled NOAA to provide key information and tools to coastal managers to help manage and mitigate the size and impact of the annual hypoxic zone in the Gulf of Mexico. Ongoing research efforts are helping to develop a hierarchical suite of indicators of estuarine habitat health and sustainability which can be used to help evaluate the effectiveness of various estuarine mitigation and restoration strategies.
Using information and tools developed by CSCOR-sponsored research, coastal managers can now better address the national problems of hypoxia and nutrient pollution and help protect and restore valuable coastal ecosystems. Several examples are described below: