Virginia Institute of Marine Science
While ecosystem health is improving in many estuaries worldwide following nutrient reductions, inconsistent trends in water clarity often remain. The Chesapeake Bay, a eutrophic estuary with a highly populated watershed, is a crucial testbed for these concerns. Improved efforts are needed to understand why some measurements of downstream estuarine water clarity appear to be uncorrelated with watershed management actions, and multiple metrics of clarity are needed to address this issue. To complement in situ measurements, satellite remote sensing provides an additional tool with which to assess long-term change in water clarity. In this study, remote sensing reflectance (Rrs) from the Moderate Resolution Imaging Spectroradiometer on satellite Aqua was evaluated from 2003 to 2020 at multiple wavelengths for surface waters of the Chesapeake Bay. Trends show an overall long-term decrease in Rrs in the upper estuary for all wavelengths, yet an increase in Rrs in the lower estuary for green wavelengths. Trends in band ratios show long-term decreasing red-to-green and red-to-blue ratios, yet long-term increasing green-to-blue ratios. Seasonally, trends in band ratios were relatively consistent throughout the year and along-estuary, whereas single band reflectance trends varied seasonally and along-estuary. In the lower Bay, Septembers showed the strongest decreasing trends in red reflectance, while early spring and summer had the most pronounced increasing trends in green reflectance. These trends suggest that the system has experienced a long-term reduction in suspended solids concentration and light attenuation without a systematic reduction in chlorophyll-a concentration.
Chesapeake Bay; estuaries; MODIS-Aqua; remote sensing oceanography; remote sensing reflectance; water clarity
Turner, Jessica S.; Friedrichs, Carl T.; and Friedrichs, Marjorie A.M., Long-Term Trends in Chesapeake Bay Remote Sensing Reflectance: Implications for Water Clarity (2021). JGR Oceans, 126(12), e2021JC017959.