干旱区生态环境知识资源中心

Stream solute signals arise from the convolution of catchment delivery, hydraulic transport, and biogeochemical processing. Drawing inference from such signals requires analytical or experimental tools to isolate the signal attributable to stream processing. We used Lexan (R) chambers open to the air and inserted into the sediment (benthic chambers) and high-frequency in situ sensors to measure metabolism and nutrient processing rates for a small (0.36 m(2)) footprint across a variety of benthic cover types. We estimated gross primary production (GPP) and ecosystem respiration (ER) based on high-resolution dissolved 0 2 measurements, and we estimated N retention via both autotrophic assimilation (U-A) and dissimilatory removal (U-D) from high-resolution NO3- measurements. We observed marked spatial variation in metabolism and nutrient retention, principally in response to autotroph cover and light during thirty-three 1-wk deployments in Gum Slough, a spring-fed river (discharge approximate to 1.5 m(3)/s) in northern Florida. Spatially weighted mean chamber rates were commensurate with, but slightly underpredicted, open-channel measurements. Moreover, the stoichiometry (i.e., molar C : N from GPP and U-A) matched expectations based on tissue stoichiometry and autotroph composition. Our approach enabled disaggregated measurements of metabolic processing across heterogeneous riverine settings, albeit principally where sediments were sufficiently fine-grained to limit hydraulic exchange (assessed here with a Cl- tracer). In addition, the small chamber volume allowed manipulation of myriad environmental factors, including solute concentrations via both active enrichment, or, in our case, passive depletion. We observed negligible GPP and minimal U-A responses to NO3- depletion, in contrast to strong U-D responses.