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Ecologist Lora Harris heads Potomac project to determine status of water quality
Dr. Lora Harris heads Potomac project to determine status of water quality
Chesapeake Biological Laboratory ecologist Lora Harris is the principle investigator on a project involving research cruises on the Potomac River, the Chesapeake Bay's largest tributary.
Harris has been studying the impact of releases of nitrogen and phosphorus from the Blue Plains Wastewater Treatment Plant, which is located on the shore of the Potomac. These two elements are particularly important nutrients which can promote excessive growth of phytoplankton in lakes, estuaries and the ocean.
“The levels of these two nutrients in releases from Blue Plains have changed greatly over the last 30 years,” Harris said. “Blue Plains was the largest point-source of nutrient pollution in the area."
in the 1980s, phosphorous was largely removed from the Blue Plains effluent, and the water quality in the Potomac improved. Then in the 1990s, Blue Plains was ordered to clean up nitrogen releases as part of the Environmental Protection Agency’s efforts to restore water quality in Chesapeake Bay.
This required installing a third stage of treatment known as biological nitrogen reduction, or BNR; a billion-dollar project.
“Today, Blue Plains is the largest BNR facility in the world," Harris noted. “But now they're being asked to take out even more nitrogen. So much, in fact, that the next set of upgrades will cost another billion dollars.”
With support from the treatment facility, Harris has been studying the Potomac River ecosystem to understand what the removals over the last 35 years have done to improve the water quality in the Potomac, and how their newest upgrade may impact the water quality, once it comes online.
Harris and her team, which includes several graduate students as well as collaborators from the Horn Point Laboratory and the University of Maryland's College Park campus, are particularly interested in carbon production and nitrogen recycling. These processes are good indicators of ecosystem efficiency.
In addition to collecting samples from their cruises on the RV Rachel Carson, the team also looked at samples collected by the Maryland Department of Natural Resources. "We did what is probably the most spatially synoptic survey of sediment nitrogen cycling ever done," Harris said.
The data collected from this research is used to create models that can help make management decisions.
One of Harris' graduate students recently completed a project that used data collected by the Chesapeake Bay Program to look at carbon production before Blue Plains installed their BNR facility, versus after the installation. She then developed a model that ranked which explanatory variables are most predictive of carbon production (known as primary production). Excessive primary production in estuaries can lead to low oxygen levels in the water, or “dead zones”, a chronic problem in Chesapeake Bay waters.
The model showed that Blue Plains was the main cause of primary production prior to their BNR installation, whereas after the BNR installation, the main variables affecting carbon production included nutrient loading from the watershed above Chain bridge--which drains the rest of the Potomac--and temperature, but not Blue Plains.
In other words, the model revealed that adding the BNR facility did have an effect on carbon production, which has global implications for the future impacts of wastewater plant upgrades. In a time when assessments of restoration for Chesapeake Bay sometimes report discouraging progress, these results also provide encouragement for managers attempting to improve water quality.
Other questions being investigated by Harris' team include how diversity in the plankton community affects primary production rates, and whether oyster aquaculture or restoration in the Potomac could affect the nitrogen levels.