The Influence of Drainage on Biogeochemical Cycling of Carbon in Agricultural Ecosystems
Principal Investigators: Jennifer King, Assistant Professor, Department of Soil, Water, and Climate; Jacques Finlay, Assistant Professor, Department of Ecology, Evolution, and Behavior; David Mulla, Professor, Department of Soil, Water, and Climate University of Minnesota
Additional Staff: Brent Dalzell, Post-Doctorial Researcher, University of Minnesota
USGS-WRRI 104B/ CAIWQ Competitive Grants Program
March 2007 - February 2008
Dissolved organic matter (DOM) in streams represents the biogeochemical transition between upland source and its fate via burial in sediments or respiration as CO2 in the atmosphere. The ultimate fate DOM is determined by qualitative characteristics of DOM which are controlled by processes such as microbial and fungal degradation in soils and its selective transport through soil mineral phases. The role of selective transport is especially likely to influence the quality of DOM in agricultural ecosystems owing to the predominance of drainage ditches and subsurface tile drainage systems which are employed to reduce uncertainty and improve yield in row crop agriculture. Agricultural land use represents over 60% of land cover in the Mississippi River Basin, yet our understanding of landscape-scale controls of dissolved organic carbon export is generally limited to historic (pre-settlement) land cover patterns. The abundance and quality of DOM in agricultural waterways can also influence water quality by affecting denitrification rates. While the effects of improved drainage practices are relatively well-understood with respect to export of non-point source pollutants such as nitrate, phosphorous, and sediment, their influence on biogeochemical cycling of carbon and its interaction with water quality is poorly understood.
Our long term objective is to understand and quantify how artificial drainage influences environmental quality and the biogeochemical cycling of carbon, nitrogen, and phosphorous, which are increasingly impacted by human activities. The objective of this study is to understand how different spacing and depths of agricultural tile drainage systems affect the nature and extent of organic carbon export. This research is critical for understanding how past and future land use changes influence biogeochemistry at the landscape scale. Our proposed study will investigate how subsurface tile drainage practices affect biogeochemical cycling of carbon and will address the relative lack of understanding of DOM dynamics at the field scale. We propose to address two primary objectives:
Objective 1: Determine the effect of depth and spacing of subsurface tile drainage in agricultural ecosystems on the magnitude of dissolved organic carbon export. Our working hypothesis is that increased tile drainage intensity will increase dissolved organic carbon fluxes mainly through control of water discharge.
Objective 2: Determine the influence of subsurface tile drainage systems on qualitative characteristics of DOM that will, in turn, affect the fate of DOM. Our working hypothesis is that DOM exported from systems with deeper drainage will exhibit lower molecular weight that drainage which followed a shallower flow path. We also expect that DOM in drainage will become less bioavailable with increasing contact time with mineral soil (e.g. deeper drainage).
Results of this research will enable us to identify how agricultural drainage influences the quality and quality of DOM export. Knowledge of how subsurface tile drainage systems influence the export of DOM is critical for understanding the role that agricultural ecosystems play in biogeochemical carbon cycling in agricultural landscapes. This knowledge of carbon cycling dynamics is also essential for understanding the movement of nitrogen across the landscape, due to the tight coupling of carbon and nitrogen cycling.
Dalzell, B.J. 2008. Climate change as a factor in export of dissolved organic matter from agricultural watersheds. Invited Oral Presentation. Global Climate Change and Agriculture: Interactions, Land−Use Patterns, and Educational Connections Symposium, 93rd Annual Meeting of the Ecological Society of America. August 3−8, 2008. Milwaukee, WI.