Agricultural land use alters the seasonality and magnitude of stream metabolism

Abstract

We present a comprehensive data set 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: continuous measurements in one agricultural stream for 1 yr, and periodic daily measurements in six agricultural streams on six dates spanning summer, autumn, and winter. Continuous measurements revealed high rates of GPP (range: 0.1 to 22.0 g O 2 m 22 d 21 ) and ER (range: 20.9 to 234.8 g O 2 m 22 d 21 ) that varied seasonally with light availability and temperature. GPP and ER were correlated during periods of high autotrophic production, suggesting that autotrophic respiration comprised a large portion of ER; however, the 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 six streams when assessed via periodic daily measurements, and 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. Overall, the open canopy and elevated nutrients of agricultural streams resulted in higher rates of GPP and ER compared with more pristine systems. Estimates of metabolism are needed from underrepresented systems to accurately quantify carbon fluxes from fluvial ecosystems.

Land use affects temporal variation in stream metabolism

“…Our findings support 2 important tenets: 1) Riparian buffers are likely to moderate the negative effects of land use on stream function (e.g., Bunn et al 1999). 2) Calculation of stream C budgets requires, at minimum, seasonal measurements, especially in disturbed streams (e.g., Griffiths et al 2013).…”

“…The lack of a relationship between ER and temperature and the nonsignificant effect of land use on ER in winter further suggests that seasonal variability in ER at the study sites is driven by autotrophic productivity . Griffiths et al (2013) also observed strong seasonality in the ecosystem metabolism of agricultural streams dominated by autotrophic productivity, which was associated with water temperature and light availability. Increased seasonal variation associated with land use has implications for ecosystem health assessment and could be used to inform targeted monitoring.…”

The influence of riparian vegetation and season on stream metabolism of Valley Creek, Minnesota

“…Beaulieu et al 2013;Dodds et al 2013;Griffiths et al 2013;Yates et al 2013;Gonz alez-Pinz on et al 2014;Hotchkiss & Hall 2014;Roley et al 2014), including the interaction between these factors depending on the type of riparian zone of the stream ). We found spatial variation in stream metabolism in Valley Creek, as hypothesized, with GPP, ER and NEP being lower at the forested location versus the open location.…”

Agricultural Best Management Practice Abundance and Location does not Influence Stream Ecosystem Function or Water Quality in the Summer Season

“…Our study also examined metabolism over a two-week period in summer. Temporal differences associated with seasonality have been seen to alter the magnitude of stream metabolism, with greatest rates generally occurring from spring through autumn [50]. However, the greater light intensity and duration, and resultant increase in water temperature in the summer months can promote a greater activity of both photosynthetic and heterotrophic organisms facilitating higher metabolic rates.…”