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Agricultural land use alters the seasonality and magnitude of stream metabolism
Citation:
Griffiths, N. A., J. L. Tank, T. V. Royer, S. S. Roley, E. J. Rosi-Marshall, M. R. Whiles, J. J. Beaulieu, AND L. T. Johnson. Agricultural land use alters the seasonality and magnitude of stream metabolism. LIMNOLOGY AND OCEANOGRAPHY. American Society of Limnology and Oceanography, Lawrence, KS, 58(4):1513-1529, (2013).
Impact/Purpose:
To inform the public.
Description:
Streams are active processors of organic carbon; however, spatial and temporal variation in the rates and controls on metabolism are not well quantified in streams draining intensively-farmed landscapes. We present a comprehensive dataset of gross primary production (GPP) and ecosystem respiration (ER) in open-canopy, nutrient-rich streams draining row-crop agriculture in the midwestern United States. We used two approaches to characterize temporal and spatial variation in whole-stream metabolism: 1) continuous measurements in one agricultural stream for one year, and 2) periodic daily measurements in 6 agricultural streams on 6 dates spanning summer, autumn, and winter. Continuous measurements revealed high rates of GPP (range: 0.1 to 22.0 g O2 m-2 d-1) and ER (range: -0.9 to -34.8 g O2 m-2 d-1) that varied seasonally with light availability and temperature, respectively. GPP and ER were correlated during periods of high autotrophic production, suggesting autotrophic respiration comprised a large portion of ER; however, GPP:ER ratio exceeded 1 for only 4% of the year. While there were distinct temporal patterns in metabolism in one agricultural stream, rates of GPP and ER were similar among 6 streams when assessed via periodic daily measurements. Furthermore, 26% of all periodic daily measurements were autotrophic with GPP:ER >1. However, these periodic measurements were collected under baseflow conditions and may have overestimated the extent of autotrophy in agricultural streams. Continuous metabolism measurements have the advantage of capturing daily, seasonal, and episodic variation in rates that may not be quantified via periodic measurements. As fluvial ecosystems are important components of regional and global carbon budgets, accurate estimates of metabolism obtained through continuous monitoring are needed to quantify carbon fluxes from these ecosystems.
