Scientific Tools for Assessing Eutrophication in Northeast Estuaries

Sound scientific research is the basis for the nitrogen reduction efforts in Northeast National Estuary Programs (NEPs), and many of them support, coordinate, or facilitate such research in their estuaries. Long-term water quality monitoring is an essential part of many efforts because such time-series data can provide information on spatial and temporal changes in water quality to facilitate ongoing adaptive management. Water quality monitoring is often conducted by regional or state agencies, but is also carried out by universities and citizens’ groups. While largely based on ship or shore-based surveys, the use of automated instruments by regional networks of the NOAA Integrated Ocean Observing System (IOOS) and related systems is becoming more important. These networks can now reliably supply routine meteorological and physical oceanographic data, however, the use of automated instruments for nutrient measurements and nucleic acid detection of specific organisms is just beginning. Aircraft and satellite remote sensing can also be used to monitor long-term changes in marshes, seagrass, harmful algal blooms, and other parameters. Additionally, an array of models from simple nutrient-loading models to 3D coupled hydrodynamic-biogeochemical models is used to determine loading thresholds and ecosystem impacts. Such scientific information has proven vital for developing successful nitrogen reduction strategies in both Northeast US and other estuaries. In Long Island Sound (LIS), comprehensive water quality and hypoxia monitoring and the System Wide Eutrophication Model (SWEM) have been crucial to nitrogen reduction efforts. As a result of wastewater treatment plant upgrades under the 2000 Total Maximum Daily Load (TMDL), annual nitrogen inputs to LIS have been reduced by 40 million pounds (18 million kg), inorganic nitrogen concentrations in LIS have decreased, and bottom water hypoxia in 2015 covered the second smallest area in the past 28 years. However, further nitrogen reduction steps are needed, and more sophisticated scientific tools will be required to assess their progress and facilitate future adaptive management.