Betsy M. Summers,
University of New Mexico, Department of Civil, Construction & Environmental Engineering
Globally, aridlands comprise one third of the terrestrial land mass, however, limited research has been conducted on the streams and rivers that drain these regions. This is particularly true for measurements of whole stream metabolism (gross primary production – GPP, ecosystem respiration – ER), a knowledge of which is fundamental for understanding and managing these systems. Aridland rivers are characterized by flashy hydrographs, high turbidity levels, variable flow, and overallocated water resources, all of which create temporally and spatially complex ecosystems with likely impacts to metabolism. Two years of whole-stream metabolism estimates were generated at three sites spanning 93 river km along the Middle Rio Grande to assess the variability in GPP and ER across and within sites at daily and seasonal timescales. This river varies longitudinally in discharge, geomorphology, and anthropogenic impacts. Differences in substrate type and geomorphology across sites resulted in spatially and temporally variable patterns in whole stream metabolism. At the upstream site, GPP peaked (daily – 2.2 gO2 m-2 d-1, monthly average – 1.6 gO2 m-2 d-1) in-phase with light availability and turbidity during summer. At the middle site, GPP peaked either in the fall, or at multiple points through the summer/fall (daily and monthly peak values of 2.9 gO2 m-2 d-1 and 1.7 gO2 m-2 d-1, respectively), depending on discharge. At the most downstream site, GPP predictably peaked during fall (daily and monthly peak values of 2.2 gO2 m-2 d-1 and 1.2 gO2 m-2 d-1, respectively) when both discharge and turbidity were low. Autotrophy was common at the middle site, which has coarse cobble substrate, while heterotrophy was associated with the fine-grained sand and silt substrates found at the upper and lower sites. In this aridland river, a combination of discharge, turbidity, geomorphology, and substrate type are key determinants of daily GPP and trophic conditions.
David J. Van Horn, Department of Biology, University of New Mexico
Justin K. Reale, U.S. Army Corps of Engineers
Ricardo González-Pinzón, Department of Civil, Construction & Environmental Engineering, University of New Mexico
Alison P. Appling, U.S. Geological Survey
Rebecca J. Bixby, Department of Biology, University of New Mexico
Mark C. Stone, Department of Civil, Construction & Environmental Engineering, University of New Mexico
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