Terrestrial-Aquatic Linkages I: Changing Patterns of Sediment Delivery From Agricultural Watersheds
Tuesday, August 6, 2013: 8:00 AM-11:30 AM
101G, Minneapolis Convention Center
Robert D. Dietz, University of Minnesota
Shawn P. Schottler, St. Croix Watershed Research Station, Science Museum of Minnesota; and
James E. Almendinger, St. Croix Watershed Research Station, Science Museum of Minnesota
Daniel R. Engstrom, St. Croix Watershed Research Station, Science Museum of Minnesota
Agricultural practices, conservation efforts, and climatic variability can each influence patterns of sediment delivery to aquatic systems. Agriculture – specifically row-crop cultivation – is associated with increased exports of sediment into aquatic environments and can lead to impairment of aquatic habitat. Many lakes and streams are impaired by high suspended sediment loads, but the extent to which agricultural practices have contributed to these problems, or to which conservation efforts have alleviated them, is often unclear due to short timescales of investigation and the challenge of separating land-use signals from superimposed climatic signals. Retirement of agricultural lands and emplacement of conservation buffers are expected to reduce fluxes of sediments into surface waters, but recent research has yielded conflicting results, with some studies suggesting that conservation programs have achieved broad sediment reductions and other studies indicating little or no improvement. Furthermore, significant disparities exist between the results from plot-scale and watershed-scale research as well as between findings from empirical and model-based studies.
The goal of this session – the first of two sessions focused on material fluxes across terrestrial-aquatic boundaries (see “Terrestrial-aquatic Linkages II: Movement of Nutrients and Carbon”) – is to better understand the long-term influences of land-use and climatic changes on sediment inputs to aquatic environments, through examination of both monitoring studies and paleoenvironmental investigations conducted at watershed scales. The session will be of interest to aquatic ecologists, paleolimnologists, and individuals who work at the nexus of ecological research and conservation management. Key questions include: What is the magnitude and timing of change in suspended sediments and associated water quality in relation to documented land use changes and how might this compare to natural/climatic variability? Are land conservation practices indeed reducing fluxes of eroded sediment and, if so, by what extent? The first half of the session will focus on sediment loading to fluvial systems in the Midwestern USA, opening with talks that elucidate the problem of high suspended sediment concentrations in rivers flowing through agricultural catchments and providing broader context for understanding connections between land-use, sediment sources, and water quality. We then continue to speakers who will discuss evidence for reductions (or lack thereof) in sediment supply from catchments where cultivated lands have been converted to natural vegetation. In the second half, presenters will describe historical patterns of sediment accumulation in lakes (Minnesota and Iowa, USA), as determined from dated sediment cores, and their relationships with regional land-use history.