2015 Summer Patrick Henry Building Virginia Water Resources 


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Sara Lubkin (SL): It’s a beautiful day on Virginia’s York River. The sun is shining, the water is sparkling, but this view isn’t as peaceful as it seems. Lurking on the surface of the water, you’ll see signs of Virginia’s algal monster -  an overgrowth of algae known as a harmful algal bloom. 


Cassandra Morgan (CM): Since algal cells grow best in warm, slow-moving, nutrient-rich water, the peak period for bloom growth is Mid-June through late September. During this period, dense aggregations of algae discolor the water and produce unpleasant odors. Many species also produce toxins that can kill fish and cause health effects in wildlife and in humans. 


SL: Because of the potential risks that blooms pose to human health, natural resources, environmental quality, and the economy, the state of Virginia works with marine research institutions to monitor algal blooms in the Chesapeake Bay Watershed. Our team is working with scientists from the Virginia Institute of Marine Science and Old Dominion University who are studying bloom toxicity and bloom initiation triggers in the Lower Chesapeake, including the York River and James River.


CM: VIMs monitors blooms on the York River with 7 fixed sample stations and a fixed path sample boat. Samples from the James River are collected by the Hampton Roads Sanitation District during routine water quality monitoring. However, it takes weeks to process the samples, and collection methods are limited both in geographic range and temporal scope. 
 
SL: Remote sensing of chlorophyll would allow both real-time monitoring of the entire lower Chesapeake Bay and the ability to compare chlorophyll levels over time. Chlorophyll data is available from the MODIS satellite, but only at a 1.4 km scale. This doesn’t provide the resolution needed for monitoring Virginia’s rivers. Landsat provides better resolution, but a tool for modeling chlorophyll is not readily available.
        
CM: Imagery was obtained for May - October of 2011 through 2014, the peak period for bloom growth. We downloaded Landsat Surface Reflectance products for Landsat 8, Path 14 Row 34 from the United States Geological Survey’s Earth Explorer System. We obtained daily Aqua MODIS Level 2 chlorophyll data for the Chesapeake Bay Watershed from the National Oceanic and Atmospheric Administration CoastWatch’s East Coast Node. 


SL: In situ chlorophyll measurements were downloaded from the Virginia Estuarine and Coastal Observing System or VECOS. The water quality data served as cross reference measurement for remote sensing data. Bathymetry was also provided by VECOS.


CM: In order to create a chlorophyll estimation tool, we cross calibrated Landsat data from the 2013 bloom season with CoastWatch MODIS chlorophyll-a estimations for corresponding dates. The Landsat band data was filtered through a 1.4 kilometer moving window to match the MODIS scale.  MODIS chlorophyll-a values were joined to bathymetry measurements and the values of each smoothed masked Landsat spectral reflectance band.  This provided the information we needed for our regression equations. 


SL: Regression equations were calculated using R software.Several regression methods were tested. We chose the equations with the highest R-squared values. The resulting regression formulae were used to produce rough estimates of chlorophyll using ArcGIS. The equations were then used to create a tool in ArcGIS model builder that will be provided to our partners. This will allow our partners to independently process Landsat 8 data to show chlorophyll estimates at a 30 meter resolution. 


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CM: Next term, the model will be tested and the tool will be refined. Once completed, the tool will allow our partners to improve their current tracking and monitoring techniques by allowing data to be available in a quicker timeframe


SL: Remote sensing of chlorophyll will allow our partners to assess the timing, magnitude, duration and frequency of Harmful Algal Blooms in the lower Chesapeake Bay watershed and better predict the environmental and water quality conditions that favor bloom development. This understanding will help the state of Virginia to develop policies that will protect the water and keep the Chesapeake Bay healthy and beautiful.