A team of researchers from Virginia Tech (VT), University of Maryland Eastern Shore (UMES), Penn State (PSU), and USDA published a new climate change study in Science of the Total Environment this past May. The goal of the study was to better understand nutrient exports from agricultural landscapes under the effects of climate change. The research team included VT researchers Moges Wagena (lead author), Andrew Sommerlot, Daniel Fuka, and Zachary Easton.

Their study looked at a sub-watershed of the Mahantango Creek in east-central PA, which drains to the Susquehanna River. They used the Soil and Water Assessment Tool-Variable Source Area (SWAT-VSA) model forced by seven downscaled regional climate models (RCMs) in order to understand the effects of climate change on hydrology, water quality, nutrient cycling, and greenhouse gas emissions.

Their models showed that climate change impacts on temperature and precipitation would lead to increased winter and spring flow and decreased late spring and summer flow. They also showed increases in nitrate, dissolved phosphorous, total phosphorous, and sediments, as well as slight increases in nitrous oxide and di-nitrogen emissions during the non-summer months and decreases in the summer dry period. Their models also predict decreases in dissolved phosphorous, total phosphorous, sediment, and nitrate in the drier summer months due to greater evapotranspiration from hotter temperatures.

Five out of the seven climate models predicted increased precipitation, with six of the seven predicting higher precipitation intensity as well. Increased precipitation will lead to increased surface runoff in the winter and spring, causing an 8% increase in sediment yields from agricultural fields. The team also found that nitrous oxide and di-nitrogen emissions would be highest from October to March.

Surprisingly, the climate models predicted a slight decrease in annual flow overall, with increased spring/winter flows offset by significant decreases in summer/fall flows. Decreased flows, together with increases in water temperatures, could lead to reduced dissolved oxygen and instream habitat, and increased algal blooms. Increased flow after the fall crop harvest could lead to increased sediment loads due to the lack of vegetation to help slow the water and filter sediments.

The team suggests that farmers will need to focus on the timing of fertilizer applications so that crops are in the growing stage as soon as the fertilizer is applied. Management strategies like this will help use fertilizers most effectively and reduce nutrient export into the local watershed.