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Climate, Clams, and a Changing Watershed: A time series analysis to quantify the impact of management and climate on water quality in the Potomac Estuary
Harris, L., R. Murphy, R. Woodland, R. Sabo, K. Eshleman, H. Walker, AND D. Liang. Climate, Clams, and a Changing Watershed: A time series analysis to quantify the impact of management and climate on water quality in the Potomac Estuary. Coastal and Estuarine Research Federation (CERF) 24th Biennial Conference, Providence, RI, November 05 - 09, 2017.
A combination of natural factors effect water quality variations in the tidal fresh section of the Potomac estuary including: climate variations, stream flow, variations in cloud cover; and factors affecting water column stratification including tides and wind. Atmospheric deposition of nitrogen, resulting from human activities, and human loading of nitrogen (N), and phosphorus (P) from a combination of point and non-point sources have also stimulated excess phytoplankton production, and contributed to loss of dissolved oxygen in the bottom waters of the tidal Potomac. A variety of management actions have been taken to reduce loads of N and P from the Potomac watershed, directly into the Potomac estuary, and to the larger Chesapeake Bay system. We present an innovative computational method, to quantitatively tease apart natural components of variations in water quality that can be associated with inter-annual variations in forcing functions that have non-linear, and seasonally specific effects on water quality variations in the tidal fresh Potomac. An additional component of variations in water clarity and quality can be attributed to varying abundance of clams, who’s filtration capacity can significantly affect water clarity and quality. Once these naturally varying factors affecting water quality variations are accounted for, it is easier to discern the effects of various management actions that have been taken to reduce point and non-point source loads of N & P, and restore and protect this important estuary.
The Potomac River is the largest tributary of the Chesapeake Bay and has been a key study site in water quality research, beginning with work to address public health concerns such as safe drinking water and waterborne disease during periods of population growth and urbanization at the turn of the 19th century. An updated analysis of the Potomac is timely because a number of management actions have taken place since the early 2000s. These include upgrades at the Blue Plain Wastewater Treatment Plant to biological nitrogen reduction practices that have greatly reduced point sources from this large facility, dramatic declines in NOx emissions over the Potomac airshed, changes in agricultural practices in the watershed, and shifts in climate. Here we present our approach of applying General Additive Models to unravel the complex impacts of nutrient and freshwater inputs from the watershed, as well as within-estuary processes driven by climatic conditions, as they relate to two key water quality criteria. The results of this analysis permit us to present a narrative that connects dynamics in the watershed to ecological processes within the tidal Potomac in an effort to assess how management actions related to nutrient loadings impact chlorophyll-a and dissolved oxygen concentrations.