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Adapting a Dynamic Land Model, LM3V, to Simulate Nitrogen Exports and Transformations in the Susquehanna River

Speaker: Minjin Lee, Graduate Student
Series: EEWR Brown Bag Seminars
Location: Engineering Quad E225
Date/Time: Friday, February 22, 2013, 12:00 p.m. - 1:00 p.m.

Abstract:

Biologically available nitrogen (N) in terrestrial ecosystems has significantly increased via anthropogenic nutrient inputs. This has caused severe water quality problems associated with cultural eutrophication. Climate variability also plays a great role in the water quality by affecting the distribution of high and low flow extremes. Therefore, it is imperative to develop a comprehensive model that treats how climate variability result in detrimental effects on the N pollutions for optimal nutrient loading controls.

We have modified the Princeton-GFDL LM3V land model, which includes terrestrial N cycle, to assess the human influences on the N cycle, how they are linked to different weather patterns, and how much N is exported to river systems. We incorporated a first-order denitrification mechanism in the land and added aquatic biochemical processes in the river component of hydrology. By coupling biogeographical, biophysical, and biogeochemical dynamics, the model captures key N mechanisms in the climate-plant-soil-river system.

In this study, we have downscaled and applied the modified LM3V model to the Susquehanna River, the largest of the watersheds in the northeastern U.S, using a historically reconstructed scenario of land use change and anthropogenic nitrogen inputs. The denitrification module was most sensitive to soil moisture among the reduction factors. In general, the model had an ability to produce temporal patterns of stream discharges and N loads, though overall flows and loads were under-estimated especially in the wet period. Simulated and reported N budgets in terrestrial and aquatic ecosystems were in a good agreement. Analysis of four different climate scenarios suggests that series of dry years increase river exports in the next year by accumulating N in the soil storage. These results suggest that the modified LM3V model can be used to determine N sources to streams and estimate nitrogen exports to sensitive environments like the Chesapeake Bay.