Citation:

Campbell, P., J. Bash, Chris Nolte, T. Spero, E. Cooter, K. Hinson, AND L. Linker. Implications of Climate and Emissions Changes on Atmospheric Nitrogen Deposition to the Chesapeake Bay Watershed. Sixth Interagency Conference on Research in the Watersheds (ICRW), Shepherdstown, WV, July 23 - 26, 2018.

Impact/Purpose:

Presented at the Sixth Interagency Conference on Research in the Watersheds (ICRW)

Description:

Atmospheric deposition remains one of the largest loadings of nutrients to the Chesapeake Bay Watershed (CBW). The interplay between future climate and emission changes, however, will cause shifts in the future nutrient deposition abundance and regime (e.g., oxidized vs. reduced nitrogen (N)). In this work we dynamically downscale the Community Earth System Model version 1.0 under Representative Concentration Pathway 4.5 (RCP4.5) using the Weather Research and Forecasting (WRF) model version 3.8.1. The WRF fields are then used to drive the Community Multiscale Air Quality (CMAQ) model version 5.2 coupled to the agro-economic Environmental Policy Integrated Climate (EPIC) model to explore the relative impacts of emission and climate changes on atmospheric nutrient deposition to the CBW for a current (CURR: 1995 – 2004) and a future period (FUT: 2045 – 2054). The regional emission projections in CMAQ are based on federal and state regulations promulgated in 2015, which use baseline and projected emission years 2011 and 2040, respectively. Evaluation of the downscaled WRF/CMAQ CURR simulations in the CBW show a good agreement in average 2-meter temperature (CBW avg. mean bias ~ +1.5 K) and precipitation (CBW avg. mean bias ~ +12.4 mm) compared to reanalysis data sets, with a warmer (CBW relative change ~ +14%) and wetter (CBW relative change ~ +4%) FUT period under RCP4.5. An approximate WRF/CMAQ CURR comparison against surface observations of wet deposition (WDEP) of inorganic PM2.5 species also shows good agreement, except for larger underpredictions in WDEP of PM2.5 nitrate. Climate and deposition changes impact the EPIC agroecosystem changes, leading to increases in FUT ammonia (NH3) fertilizer application and crop soil content, which in turn affects the CMAQ bi-directional NH3 surface exchange in the CBW. These changes along with widespread decreases anthropogenic nitrogen oxides (NOx) emissions (U.S. avg ~ -51%), but increases in agricultural NH3 emissions (U.S. avg. ~ + 2%) projected in the FUT period leads to a shift towards relative decreases in total oxidized N deposition (CBW seasonal avg. ~ -40 to -50%), along with increases in total reduced N deposition (CBW seasonal avg. up to ~ +20%) that are dominated by NH3 dry deposition changes. The reductions in future emissions are the largest factor in reducing the total atmospheric N deposition; however, the impacts of land use changes on nutrient deposition need further evaluation. As sources of atmospheric reactive N from the burning of fossil fuels (oxidized N) decline, the emissions, transport, and fate of atmospheric reactive N from agriculture (reduced N) are altered and will likely become the dominant form of atmospheric N loading to the Chesapeake Bay. Results from this work aid in developing effective policies to protect ecosystems from excess N deposition in the face of climate change.

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