We have been collecting water quality data on Antipoison Creek for about 11 months now, sampling for nitrate-nitrites (NO23), phosphates (PO4), ammonium (NH4), and chlorophyll. Our data collection extends from last September to this May (with sampling ongoing). Last month, Gary, Libby and I visited with Dr. Lora Harris, an associate professor at the University of Maryland’s Center for Environmental Science (UMCES), who specializes in systems ecology and ecosystem modeling, to get input on how to analyze our water quality data.
Dr. Harris gave us several suggestions, one of which was to create a Nitrogen Loading Model (NLM) for Antipoison Creek, to determine if the creek is primarily fed by nitrogen coming in from the Chesapeake Bay, or from the watershed (land-based activity and runoff, groundwater leaching, and atmospheric deposition). Harris described the NLM as a type of box model, showing inputs and outputs in and from a watershed. (See Figure 1, from the NLM instruction manual below).
The Nitrogen Loading Model, created by Mark J. Brush (VIMS), Lora A. Harris (UMCES), Juliette C. Giordano (VIMS), and Joanna K. York (UDEL) allows a user to put in data on land use and activity in a specific watershed- for us, Antipoison Creek. The model pulls in miscellaneous information on the watershed, such as atmospheric deposition, loads from point sources, and surface area of the creek. It also pulls in data on non-agricultural and agricultural land cover, as well as the fertilization rate and agricultural yield of each crop grown in the watershed.
Using a mix of applications including a GIS operating system (QGIS) and GoogleEarth, as well as a number of sources on Antipoison Creek and Lancaster County, we came up with estimates for the needed parameters. Once all the inputs were entered, and the model generated kilograms of nitrogen for groundwater input, wastewater input, direct atmospheric deposition onto water surface, and a total annual load of nitrogen (kg) entering the watershed, we contacted Dr. Brush to discuss our procedure and results.
Now that we have an annual watershed load for nitrogen to the estuary, we must determine if Antipoison Creek has a greater flux of nitrogen coming from the watershed and emptying out into the Bay, or if the Bay is primarily feeding the creek with an influx of nitrogen.
We will be working with Dr. Brush on this next step, as well as a more in-depth paper to share our work on the NLM model.
Source: Brush, M.J., L.A. Harris, J.C.P. Giordano, and J.K. York. 2015. Delmarva Coastal Bays Nitrogen Loading Model. Virginia Institute of Marine Science, Gloucester Point, VA. Available at: http://www.vims.edu/research/departments/bio/programs/semp/models/index.php.