In Harmful Algal Blooms – Part 1, I discussed what a harmful algal bloom is and why we care about blooms. I wrote about the dangers that HABs pose to public health and the economy and explained why it is important to monitor and study HABs.
Members of the Virginia Harmful Algal Bloom Task Force use a combination of fixed stations, continuous sampling, and periodic dataflow cruises to monitor water quality in the Chesapeake Bay watershed. This map shows monitoring stations in Virginia.
Data for each of these stations is available at the Virginia Estuarine and Coastal Observing System (VECOS) website. It looks as if Virginia’s rivers are well-covered, but if you go to the site and take a look at this data, you will notice that many of these sites are no longer active due to funding cuts.
Current monitoring consists of fixed stations and periodic dataflow cruises operated by the Virginia Institute of Marine Science and Old Dominion University. Most of this monitoring focuses on the James River and the York River. Sanitation districts, like the Hampton Roads Sanitation District, do automated continuous sampling in their service areas. This monitoring is on-going, but it doesn’t provide a complete picture of HAB activity.
The first obstacle is that processing all these samples takes time. Harmful algal bloom species have to be separated out of water samples that contain hundreds or thousands of other microorganisms through a complex series of DNA tests. Information isn’t available until weeks or months after a bloom occurs. By then, it may be too late to determine what factors contributed to the bloom.
The second problem is that using dataflow cruises for real-time monitoring is expensive. So, boat cruises are restricted to areas of high concern. This means that blooms in other parts of the Chesapeake Bay watershed may be overlooked.
This makes it difficult to get the environmental and water quality information needed to understand and predict HAB occurrences. It also makes it difficult to get real time information about HAB activity in the Chesapeake Bay watershed.
What if there was a less expensive option?
Last summer, I participated in the NASA DEVELOP program at the Patrick Henry Building in Richmond. Our team, Cassandra Morgan and I, worked on a method to monitor harmful algal blooms using satellite data.
Satellites can take pictures of HABs like this Landsat 8 true color image.
While, you can see the bloom in this picture, it’s hard to determine exactly which areas are in the bloom. However, phytoplankton uses chlorophyll-A to harvest the energy of the sun. VIMS and ODU detect harmful algal blooms by measuring levels of chlorophyll-A. What if we could detect chlorophyll-A in the water using remote sensing? We could then use chlorophyll measurements as a proxy for HABs.
NASA’s MODIS Aqua satellite collects information about water, including chlorophyll-A levels. Chlorophyll-A maps are available at no charge from NOAA CoastWatch’s East Coast Node.
This is a MODIS chlorophyll map for the same day.
You can see that there are high levels of chlorophyll in the James River, Upper Chesapeake, Potomac and Mobjack Bay.
The problem is that MODIs aqua chlorophyll products have a 1.4 kilometer resolution. So, they don’t give a lot of detail – especially in narrow rivers like the York.
Landsat 8 has a 30 meter resolution. But, there are no publicly available Landsat chlorophyll-A products. It was Cassandra and my job to create this product.
We started by downloading Landsat 8 images (Path 14, Row 34) from May through September 2011-2014. We looked for images without too much cloud cover. We masked out the land and the clouds and filtered these images through a 1.4 km moving window to match the MODIS resolution. We chose the day with the best overlap between MODIS and Landsat and joined MODIS the chlorophyll-a values to each smoothed, masked Landsat band. We also added bathymetric measurements
Once we had this data in one table, we were able to export it to “R” and run a series of regressions. We tested 78 separate equations. The best five equations were used to create tools using ArcGIS model builder (r-squared values .57 to .62). Here is an image of chlorophyll in the Bay created with one of those tools.
We were now able to show chlorophyll-A estimates at 30 meter resolution.
Cassandra and I created a preliminary model for chlorophyll-A during our summer term. This term, NASA DEVOLOP teams at Langley Research Center and Wise County are testing the model on additional dates and validating the equations using VECOS water quality data. They are also creating easy-to-use ArcGIS tools that will allow VIMS and ODU to quickly assess the extent of algal blooms in the Chesapeake Bay.
These tools will save time and money by allowing VIMS and ODU to better target their monitoring efforts. The tools will also allow researchers to collect information about environmental factors associated with HABs.