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On behalf of the Task Force, EPA’s Office of Water requested that the Science Advisory Board (SAB) evaluate the state-of-the-science regarding hypoxia in the Gulf of Mexico and potential nutrient mitigation and control options in the Mississippi-Atchafalaya River basin. In response to this request, the SAB established the SAB Hypoxia Advisory Panel (SAB Panel). The Office of Water asked the SAB Panel to focus its evaluation on the following issues and questions.
1. Characterization of Hypoxia – The development, persistence and areal extent of hypoxia is thought to result from interactions in physical, chemical and biological oceanographic processes along the northern Gulf continental shelf; and changes in the Mississippi River basin that affect nutrient loads and fresh water flow.
A. Address the state-of-the-science and the importance of various processes in the formation of hypoxia in the Gulf of Mexico. These issues include:
i. increased volume or funneling of fresh water discharges from the Mississippi River;
ii. changes in hydrologic or geomorphic processes in the Gulf of Mexico and the Mississippi River basin;
iii. increased nutrient loads due to coastal wetlands losses, upwelling or increased loadings from the Mississippi River basin;
iv. increased stratification, and seasonal changes in magnitude and spatial distribution of stratification and nutrient concentrations in the Gulf;
v. temporal and spatial changes in nutrient limitation or co-limitation, for nitrogen or phosphorus, as significant factors in the development of the hypoxic zone;and
vi. the implications of reduction of phosphorus or nitrogen without concomitant reduction of the other.
B. Comment on the state of the science for characterizing the onset, volume, extent and duration of the hypoxic zone.
2. Characterization of Nutrient Fate, Transport and Sources -- Nutrient loads, concentrations, speciation, seasonality and biogeochemical recycling processes have been suggested as important causal factors in the development and persistence of hypoxia in the Gulf. The Integrated Assessment (CENR 2000) presented information on the geographic locations of nutrient loads to the Gulf and the human and natural activities that contribute nutrient loadings.
A. Given the available literature and information (especially since 2000), data and models on the loads, fate and transport and effects of nutrients, evaluate the importance of various processes in nutrient delivery and effects. These may include:
i. the pertinent temporal (annual and seasonal) characteristics of nutrient loads/fluxes throughout the Mississippi River basin and, ultimately, to the Gulf of Mexico;
ii. the ability to determine an accurate mass balance of the nutrient loads throughout the basin;and
iii. nutrient transport processes (fate/transport, sources/sinks, transformations, etc.) through the basin, the deltaic zone, and into the Gulf.
B. Given the available literature and information (especially since 2000) on nutrient sources and delivery within and from the basin, evaluate capabilities to:
i. predict nutrient delivery to the Gulf, using currently available scientific tools and models; and
ii. route nutrients from their various sources and account for the transport processes throughout the basin and deltaic zone, using currently available scientific tools and models.
3. Scientific Basis for Goals and Management Options -- The Task Force has stated goals of reducing the 5-year running average areal extent of the Gulf of Mexico hypoxic zone to less than 5,000 square kilometers by the year 2015, improving water quality within the basin and protecting the communities and economic conditions within the basin. Additionally, nutrient loads from various sources in the Mississippi River basin have been suggested as the major driver for the formation, extent and duration of the Gulf hypoxic zone.
A. Are these goals supported by present scientific knowledge and understanding of the hypoxic zone, nutrient loads, fate and transport, sources and control options?
i. Based on the current state-of- the-science, should the reduction goal for the size of the hypoxia zone be revised?
ii. Based on the current state-of-the-science, can the areal extent of Gulf hypoxia be reduced while also protecting water quality and social welfare in the basin?
B. Based on the current state-of- the-science, what level of reduction in causal agents (nutrients/discharge) will be needed to achieve the current reduction goal for the size of the hypoxic zone?
C. Given the available literature and information (especially since 2000) on technologies and practices to reduce nutrient loss from agriculture, runoff from other non-point sources and point source discharges, discuss options (and combinations of options) for reducing nutrient flux in terms of cost, feasibility and any other social welfare considerations. These options may include:
i. the most effective agricultural practices, considering maintenance of soil sustainability and avoiding unintended negative environmental consequences;
ii. the most effective actions for other non-point sources; and
iii. the most effective technologies for industrial and municipal point sources.
In all three areas, please address research and information gaps (expanded monitoring, documentation of sources and management practices, effects of practices, further model development and validation, etc.) that should be addressed prior to the next 5-year review.
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