Suchergebnisse

The water-quality effects of low-density rural land-use activities are understudied but important because of large rural land coverage. We review and synthesize spatially extensive studies of oligotrophic mountain streams in the rural Southern Appalachian Mountains, concluding that rural land-use activities significantly degrade water quality through altered and mostly enhanced landscape-stream connections, despite high forest retention. Some connections (insolation, organic inputs, root-channel interactions, stream-field connectivity, individual landowner discharges) are controlled by near-stream land-use activities, whereas others (reduced nitrogen uptake and cycling, enhanced biological nitrogen fixation, nutrient subsidy, runoff from compacted soils, road runoff delivery) are controlled by basin-wide land use. These connections merge to alter basal resources and shift fish, salamander, and invertebrate assemblages toward species tolerant of higher turbidity and summer temperatures and those more competitive in mesotrophic systems. Rural water quality problems could be mitigated substantially with well-known best management practices, raising socioecological governance questions about best management practice adoption. ; National Science Foundation through the LTER program [DEB-1637522] ; Published version ; Thomas Prebyl created the land cover map. The Coweeta LTER and Coweeta Hydrologic Laboratory technicians, students, and investigators who worked on the synthesized projects are too numerous to name, but we thank all of them for their help. Jason Meador and Kelder Monar from Mainspring Conservation Trust provided input about their conservation programs, such as Shade Your Stream. Fred Benfield, John Maerz, Cathy Pringle, and Paul Bolstad helped conceptualize and frame this synthesis. This work was supported by multiple grants from the National Science Foundation through the LTER program, the last of which was grant no. DEB-1637522. ; Public domain authored by a U.S. government employee

Streams and rivers are important conduits of terrestrially derived carbon (C) to atmospheric and marine reservoirs. Leaf litter breakdown rates are expected to increase as water temperatures rise in response to climate change. The magnitude of increase in breakdown rates is uncertain, given differences in litter quality and microbial and detritivore community responses to temperature, factors that can influence the apparent temperature sensitivity of breakdown and the relative proportion of C lost to the atmosphere vs. stored or transported downstream. Here, we synthesized 1025 records of litter breakdown in streams and rivers to quantify its temperature sensitivity, as measured by the activation energy (E-a, in eV). Temperature sensitivity of litter breakdown varied among twelve plant genera for which E-a could be calculated. Higher values of E-a were correlated with lower-quality litter, but these correlations were influenced by a single, N-fixing genus (Alnus). E-a values converged when genera were classified into three breakdown rate categories, potentially due to continual water availability in streams and rivers modulating the influence of leaf chemistry on breakdown. Across all data representing 85 plant genera, the E-a was 0.34 +/- 0.04 eV, or approximately half the value (0.65 eV) predicted by metabolic theory. Our results indicate that average breakdown rates may increase by 5-21% with a 1-4 C rise in water temperature, rather than a 10-45% increase expected, according to metabolic theory. Differential warming of tropical and temperate biomes could result in a similar proportional increase in breakdown rates, despite variation in E-a values for these regions (0.75 +/- 0.13 eV and 0.27 +/- 0.05 eV, respectively). The relative proportions of gaseous C loss and organic matter transport downstream should not change with rising temperature given that E-a values for breakdown mediated by microbes alone and microbes plus detritivores were similar at the global scale. ; US Long Term Ecological Research (LTER) Network through award DEB from National Science Foundation (NSF)National Science Foundation (NSF) [0936498]; NSF EFNational Science Foundation (NSF) [1064998]; NSF DBINational Science Foundation (NSF) [1216512]; Department of Energy's Office of Science, Biological and Environmental Research; US DOEUnited States Department of Energy (DOE) [DE-AC05-00OR22725] ; We thank many authors who graciously provided requested information that was not included in published literature and three anonymous reviewers who provided suggestions that improved the clarity of the manuscript. The US Long Term Ecological Research (LTER) Network provided financial support for this project, through an award (DEB#0936498) from the National Science Foundation (NSF). JSK was supported by NSF EF#1064998. MA was supported by NSF DBI#1216512. NAG was supported by the Department of Energy's Office of Science, Biological and Environmental Research. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the US DOE under contract DE-AC05-00OR22725. ; Public domain authored by a U.S. government employee

Streams play a key role in the global carbon cycle. The balance between carbon intake through photosynthesis and carbon release via respiration influences carbon emissions from streams and depends on temperature. However, the lack of a comprehensive analysis of the temperature sensitivity of the metabolic balance in inland waters across latitudes and local climate conditions hinders an accurate projection of carbon emissions in a warmer future. Here, we use a model of diel dissolved oxygen dynamics, combined with high-frequency measurements of dissolved oxygen, light and temperature, to estimate the temperature sensitivities of gross primary production and ecosystem respiration in streams across six biomes, from the tropics to the arctic tundra. We find that the change in metabolic balance, that is, the ratio of gross primary production to ecosystem respiration, is a function of stream temperature and current metabolic balance. Applying this relationship to the global compilation of stream metabolism data, we find that a 1 degrees C increase in stream temperature leads to a convergence of metabolic balance and to a 23.6% overall decline in net ecosystem productivity across the streams studied. We suggest that if the relationship holds for similarly sized streams around the globe, the warming-induced shifts in metabolic balance will result in an increase of 0.0194 Pg carbon emitted from such streams every year. ; National Science Foundation (NSF)National Science Foundation (NSF) [EF-1258994]; NSFNational Science Foundation (NSF) [EF-1065255, EF-1065286, EF-1065055, EF-1065682, EF-1065267, EF-1064998, EF-1065377]; Northern Australian Environmental Resources Hub of the National Environmental Science Program; Scale, Consumers and Lotic Ecosystem Rates project ; The authors thank K. Gido for his contribution in obtaining funding and designing the field experiments. K. Gido, J. Drake, C. Osenberg and J. Minucci provided comments on earlier versions of this paper. Georgia Advanced Computing Resource Center provided the computing facility. This study was supported by the National Science Foundation (NSF, grant EF-1258994) and is part of the Scale, Consumers and Lotic Ecosystem Rates project supported by NSF grant EF-1065255. Data collection at each site was supported by NSF grants EF-1065286, EF-1065055, EF-1065682, EF-1065267, EF-1064998 and EF-1065377, and the Northern Australian Environmental Resources Hub of the National Environmental Science Program. ; Public domain authored by a U.S. government employee