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Microbial Enzyme Stoichiometry and Nutrient Limitation in US Streams and Rivers
HILL, B. H., C. M. ELONEN, L. R. SEIFERT, A. A. MAY, AND E. TARQUINIO. Microbial Enzyme Stoichiometry and Nutrient Limitation in US Streams and Rivers . ECOLOGICAL INDICATORS. Elsevier Science Ltd, New York, NY, 18(1):540-551, (2012).
We analyzed water and sediment chemistry, catchment land cover, and extracellular enzymes (ecoenzymes) activities related to microbial C, N, and P acquisition in more than 2100 1st- 10th order streams. Streams were selected from a probability design to represent the entire population of streams in the conterminous United States. Streams and their catchments were aggregated into nine ecoregions representing coastal and interior plains, eastern and western mountains, the Laurentian Great Lakes basin, or xeric western lowlands. There were significant ecoregions differences for all of the water chemistry variables: ANC, DOC, TN and TP were all lowest in the mountain streams; SO4, TN and TP were highest in plains streams. Sediment chemistry also varied across ecoregions. Biofilm and sediment ecoenzyme activity exhibited ecoregional trends correlated with stream and sediment chemistry and with catchment land cover. Oxidases (enzymes that degrade recalcitrant C) represented 80-90% of the biofilm ecoenzyme activity and >95% of the sediment ecoenzyme activity. Hydrolytic ecoenzymes (those which hydrolyze glycoside, peptide and ester bonds to release, C, N, P, S) were better correlated with the chemical variables and this was reflected in the relative apportionment of ecoenzyme activity toward C, N, and P acquisition. Across the nine ecoregions, biofilm hydrolytic ecoenzyme activity related to C acquisition ranged from 27-40%; N acquisition ranged from 22-33%; and P acquisition ranged from 32-48%. Sediment hydrolytic ecoenzyme activity devoted to C acquisition ranged from 43-56%; N acquisition ranged from 25-32%; and P acquisition ranged from 19-31%. Stream water chemistry indicated potential N-limitation ranged from 4-46%; and P-limitation based on water chemistry ranged from 46-89%. N-limitation based on sediment chemistry ranged from 78-96%; P-limitation ranged from 3-16%. Biofilm ecoenzyme activity indicated that N-limitation ranged from 6-26%; P-limitation ranged from 24-63%. N-limitation based on sediment ecoenzymes ranged from 40-70%; sediment ecoenzyme P-limitation ranged from 26-57%. Ecoenzymatic stoichiometry provides a biological perspective on the influence of catchment scale anthropogenic disturbances resulting in an imbalance of nutrients being transported from those catchments. Ecoenzymatic activities represent the interface between microbial demands for, and environmental supplies of, C, N, and P, effectively linking ecological stoichiometric theory with the concept of threshold elemental ratios. The relative activities of the functional classes of ecoenzymes provide both a measure of nutrient availability and ecosystem metabolism that may be used to assess large-scale phenomena such as regional impacts of climate change or anthropogenic disturbances.
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Record Details:Record Type: DOCUMENT (JOURNAL/PEER REVIEWED JOURNAL)
Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL HEALTH AND ENVIRONMENTAL EFFECTS RESEARCH LAB
MID-CONTINENT ECOLOGY DIVISION
WATERSHED DIAGNOSTICS RESEARCH