Above: Under reduced lighting, Mote Chemist Susan Launay measures a sample for chlorophyll filtration and analysis.
“We’ve provided a way to model water clarity more reliably at depths where we want seagrasses to be, to determine if the criteria for light are being met,” said Dr. Kellie Dixon, the senior scientist at Mote who developed the new, Charlotte Harborspecific optical model. “If seagrasses are retreating, we need to know if that is due to a change in water clarity — for instance, from freshwater with brown color or runoff carrying fertilizer and other nutrient sources into Charlotte Harbor.” Dixon continued: “If you’re trying to monitor water clarity by measuring light in the field, a lot can go wrong — for instance, your boat can tip sideways and reflect unwanted light where you’re trying to measure. However if you collect a jug of water, then laboratory analyses can accurately detect color, chlorophyll and turbidity, and we can use that to model light.” To create the new Optical Model, Dixon analyzed years of the most reliable water quality and light-sensor data from Charlotte Harbor. Now Charlotte Harbor-based scientists can plug in their own water quality data into the model to calculate clarity with more accuracy and precision than ever. “This is a wonderful tool for monitoring water clarity,” said Judy Ott, program scientist with CHNEP. “Kellie fine-tuned existing modeling work to account for the details of how light is absorbed as it goes around the water column, for waves distorting the light and for the angle of the sun. This is the first time we’ve had a good enough tool to go back in time, to use our water quality data going back to the ‘60s and calculate water clarity historically.” Dixon’s model is also the first to represent how Charlotte Harbor’s water quality affects the individual wavelengths within sunlight, such as blue, green and red. That’s important: seagrasses need specific wavelengths of light. Ott said that fine-tuning water clarity information helps to finetune management. “Seagrass growth depends, in part, on the percentage of light available; they may grow deeper if the water is clear enough. In Charlotte Harbor, our targets for seagrasses and estuary health are based on water quality and clarity. If we anticipate changes in water flow or quality, we can use the optical
12 MOTE MAGAZINE | ANNUAL 2016-2017
Above: Mote Intern Thije Zuidewind collects a water sample from the surface for later laboratory analyses.
model to estimate how that will affect water clarity, which will let us focus on projects most protective and restorative of our resources.” To see how water clarity fares from year to year, the public can visit the Water Clarity Report Card on the Charlotte Harbor Water Atlas website presented by CHNEP and the University of South Florida: www.chnep.wateratlas.usf.edu/water-clarity/ Water quality data, used to model clarity, are collected each month by the Coastal Charlotte Harbor Monitoring Network. Partners including CHNEP, the Florida Fish and Wildlife Conservation Commission, City of Cape Coral, Florida Department of Environmental Protection, Lee and Charlotte counties collect and analyze about 65 randomized samples each month across Charlotte Harbor, from Lemon Bay through Estero Bay. Field scientists continue to monitor light in the water with increasingly sophisticated gear, which in turn, helps to check and refine models such as Dixon’s. Dixon has previously calibrated the Optical Model for other Florida estuaries. Next, she hopes the model will shed more light on water clarity trends in Mote’s underwater “backyard,” Sarasota Bay.