Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2016
Publication Date: 10/5/2016
Citation: Rice, C., Bialek Kalinski, K.M., Hapeman, C.J., Mccarty, G.W. 2016. Role of riparian areas in atmospheric pesticide deposition and its potential effect on water quality. Journal of the American Water Resources Association. 52:1109-1120.
Interpretive Summary: Riparian buffer areas adjacent to agricultural fields are known for their ability to mitigate hydrologic losses of nutrients and other contaminants. The vegetation in these areas can physically impede the runoff from fields (decreasing potential stream contamination) and/or utilize the excess nutrients from runoff and groundwater flows. Riparian areas can also scavenge volatilized pollutants, including pesticides, from the air. Once the residues are removed from the air and are trapped on the riparian area vegetation, they can potentially be washed off during rain events and be delivered to the local stream, but little is known about these processes. Therefore, in this study, we examined the role of various riparian area processes in capturing volatized pesticide residues from the air, and then their role in depositing the residues to the riparian area floor and ultimately flowing to the local stream. Stemflow is rain that lands on leaves and flows down the smaller to larger branches and then down the trunk of the tree to the riparian floor. Throughfall is rain that passes through the canopy and may or may not touch leaves on its way down to the riparian floor. Four years of stemflow, throughfall, and precipitation from an instrumented agricultural field in and around the adjacent riparian area were collected and analyzed. Results showed that volatilized residues are readily captured by the riparian area, especially on the perimeter of the riparian area. While concentrations in stemflow were greater than throughfall concentrations, the total mass of pesticides delivered to the riparian floor is much larger in throughfall. Results also revealed that weather conditions and the chemical characteristics affected pesticide fate and transport. Analysis of previous work and the results of this study suggested that producers and land managers will need to consider the width of the riparian buffer areas to minimize delivery of pesticides to local streams.
Technical Abstract: Riparian buffers are known to mitigate hydrologic losses of nutrients and other contaminants as they exit agricultural fields. The vegetation of riparian buffers can also trap atmospheric contaminants, but these pollutants can subsequently be delivered via rain to the riparian buffer floor. These processes, however, are poorly understood especially for pesticide residues. Therefore, we conducted a four-year study examining the stemflow and throughfall within and precipitation outside a riparian buffer which was adjacent to a cultured Zea mays field. Stemflow is rain contacting the tree canopy traveling down smaller to larger branches and down the tree trunk, whereas throughfall is rain that may or may not contact leaves and branches and falls to the floor. Stemflow concentrations were larger than throughfall concentrations and accounted for 5-15% of the atrazine and 6-66% of the metolachlor depositional flux under the canopy. Larger depositional fluxes were measured when leaves were more fully emerged and temperatures and humidity were elevated. Rain collected outside the riparian buffer on the field side and on the back side revealed that the trees trapped the pesticide residues. Enhanced herbicide loading to the riparian buffer stream was found to be linked to tree canopy deposition and subsequent washoff during rain events. These results indicate that during low overland-flow precipitation events, the tree canopy can be a dominant pesticide source to surface waters.