Summertime Hypoxia and Water Quality Improvements in Narragansett Bay, RI
Spatial surveys of dissolved oxygen (DO) and water column properties are used to assess the extent of hypoxia in mid and upper Narragansett Bay, RI. Following a major fish kill in the summer of 2003 attributed to hypoxic conditions driven by excess nutrient discharges from waste water treatment facilities (WWTFs), the WWTFs were mandated to decrease total nitrogen (TN) loading by half during summer months. Excess TN fuels a cycle of biological production that then decays, drawing down DO levels in the waters below the pycnocline, especially when the water column is stratified in summer months. Major decreases in TN occurred between 2004-2006 and 2011-2013 so that currently the WWTF TN contribution to the Bay has decreased by about 70%. The spatial surveys sample about 70 stations to quantify the area of the bay where bottom water is hypoxic (<2.9 mg/l). The % hypoxic area is an integrated and reliable indicator because of the geographical distribution of stations and the number of surveys (58) over the period from 2005-2015. We find that the area of hypoxia varies between about 2% and 60% inter-annually and within seasons but seems to have decreased since 2010. Much of the seasonal-scale variability is correlated to “wet summers” where above average river flux is correlated with greater areas of hypoxia.
David Murray received a B.S. in Geology with Honors in 1978 from the University of Rhode Island, and an M.S. in 1983 and a Ph.D. in 1987 in Geological Oceanography from Oregon State University. He began his career at Brown as a post-doc in 1986 with research interests in Cenozoic climate change with a focus on the evolution of the Indian Ocean monsoon system. After 12 years of grant-funded research projects, he became the manager for the technical and curricular programs in Environmental Science housed in MacMillan Hall. He still maintains an active research program, serving as the Director of the Environmental Chemistry Facility and is a co-investigator with Warren Prell on projects concerning environmental change in Narragansett Bay and the surrounding watershed.
Warren Prell received a B.A. in 1966 with Honors from Hanover College, and a Ph.D. in 1974 from Columbia University. He became director of oceanographic and geologic programs for the NYC Energy Research and Development Authority before being appointed as Assistant Professor in the Department of Geological Sciences at Brown in 1975. He was promoted to full professor in 1989, and was appointed to the Henry L. Doherty Chair in Oceanography in 1990.