A Comparison of Agricultural vs. Forested Basins: Carbon and Nutrient Cycling Within the Hyporheic Ecotone of StreamsEPA Grant Number: R824786
Title: A Comparison of Agricultural vs. Forested Basins: Carbon and Nutrient Cycling Within the Hyporheic Ecotone of Streams
Investigators: White, David
Current Investigators: White, David , Hendricks, Susan P. , Johnston, Timothy C. , Kipphut, George , Spencer, William E.
Institution: Murray State University
EPA Project Officer: Hiscock, Michael
Project Period: November 1, 1996 through October 1, 1998
Project Amount: $300,000
RFA: Water and Watersheds (1995) Recipients Lists
Research Category: Water and Watersheds , Water
Description:The hyporheic ecotone, the biologically and chemically active interface between groundwater and surface water, functions as a sink and source of dissolved organic matter and nutrients to maintain stream productivity. Increased sedimentation coupled with highly variable discharge and nutrient inputs in agricultural basins may impair hyporheic function, explaining differences in productivity between more pristine and human-dominated basins. Most of our present knowledge of hyporheic ecotones comes from a very limited number of high gradient, relatively pristine streams in summer months at base flow. The overall objective of this research therefore is to characterize the function of hyporheic ecotones in pristine versus agricultural streams. Research focuses on 3rd order reaches of two basins, one a forested ecosystem (Panther Creek = PC), the other an agricultural basin (Ledbetter Creek = LC). Selected studies also will occur in 1st and 2nd order tributaries of both basins.
The overall objectives are being met by: (1) determining surface, groundwater, and hyporheic dynamics, (2) following changes in surface and subsurface conditions during and after seasonal sedimentation events (i.e., storms), and (3) spatially and temporally comparing selected chemical and biological processes which may be directly affected by hyporheic storage and release, e.g., methane production, benthic algal structure and function, and bacterial abundance, activity, and diversity. Monthly and event related surface water monitoring of 3 sites began in each basin in December 1995. The two basins respond differently for a number of physical and chemical parameters that may be attributed to land use, e.g., turbidity at base flow in LC ranged from 3-10 NTU increasing to > 100 NTU following a 5 cm rain, while PC ranged from 0-4 NTU at base flow increasing to 14 NTU following the same rain. The size and structure of the hyporheic ecotone is being examined using wells and piezometers at the 3rd order sites. Both basins were instrumented this year. Hyporheic patterns (as shown in the graph for dissolved organic carbon) coupled with experimental tracer releases (bromide) are allowing us to determine not only the size of subsurface storage zones, but also nutrient and carbon flux rates. These studies will continue through the next year in both basins. Nutrient flux and sediment respiration experiments will begin in October 1996 using specially designed black and clear chambers. Bacterial studies will occur in conjunction with chamber experiments and will include secondary production (3H-thymidine) and diversity estimates (RNA extractions) for both basins. Benthic algae sampling arrays fixed to aluminum stubs have been installed in both basins. Random samples are collected weekly to determine colonization rates and community structure. The macroinvertebrate community (the hyporheos) is being examined seasonally. Initial results have shown that the PC community is much more diverse and richer and that the LC community tends to lack filter-feeding taxa.
One immediate product has been the creation of a Windows PC version of the widely use OTIS solute transport model which allows us to calculate tracer storage within the stream bed and exchange with surface waters.