Satellite remote sensing of chlorophyll a in support of nutrient management in the Neuse and Tar-Pamlico River (North Carolina) estuaries

- The MERIS chl a data product was used to conduct a retrospective analysis.
- Large areas of NC estuaries exceed the state water quality standard of 40 μg/L.
- MERIS allowed for estimating the estuarine area impaired by chlorophyll.
- On a daily basis thousands of estuarine hectares is impaired.

The North Carolina Environmental Management Commission (EMC) has adopted as a water quality standard that chlorophyll a concentration should not exceed 40 μg/L in sounds, estuaries and other slow-moving waters. In 1996, nutrient load reductions were placed into North Carolina (NC) law to reduce the extent and duration of algal blooms in the Neuse and Tar River estuaries (Session Law 1995, Section 572). The chlorophyll a criterion was used as the endpoint to manage total nitrogen concentrations, and compliance would be achieved if chl a exceedances occurred in fewer than 10% of the samples collected in a specified area and time (known as the 10/40 criterion).In 2009, discussions were held between the North Carolina Department of Environmental and Natural Resources (NCDENR) and US Environmental Protection Agency (EPA) concerning the practicality of using satellite-derived chl a concentrations to monitor water quality, enforce water quality-related environmental regulations, and understand the environmental impacts of the watershed land-use practices on coastal waters.In this study, the MERIS chlorophyll a data product was used to conduct a retrospective analysis of the NC standard for water quality and Total Maximum Daily Load (TMDL) for total nitrogen in the Neuse and Tar-Pamlico River estuaries from 2006 to 2009. From daily MERIS images, compliance and chlorophyll exceedances in the Neuse and Tar-Pamlico River estuaries were assessed at daily and aggregated to annual time scales.