Suchergebnisse

Estimating changes in organic matter flow from resource to consumer using trophic basis of production (TBP) is a way to examine resource limitation effects on ecosystem function. We examined diet shifts and production of insect detritivores to assess changes with reduced detrital inputs to a forested headwater stream. Organic matter was excluded for 7 years using a canopy net. Small and large wood were removed from the stream after the 3rd and 5th year, respectively. Detritivore production declined after 3 years of litter exclusion. After wood removal, production of detritivores declined again. Steepest declines in Pycnopsyche gentilis production occurred within year 1. Tipula spp. and Tallaperla spp. production declined after wood removal. Diets shifted from leaves to wood to fine particulate organic matter (FPOM) for Tipula spp. and Tallaperla spp., but not for P. gentilis. Resource flows to detritivores shifted in the exclusion stream from leaves to wood to FPOM after leaf standing crops declined and wood removal. Small wood was an important food resource. TBP results showed shifts in food resource use by two detritivores with terrestrial input reduction. These findings suggest that maintaining diverse riparian inputs of organic matter is important for detritivore productivity in forested headwater watersheds. ; National Science FoundationNational Science Foundation (NSF) [DEB-9207498, DEB-9629268, DEB-0212315] ; We thank the technicians and students that assisted with this study. Special thanks to C. Wallace for digitizing many insect gut contents. S. Golladay, A. Rosemond, D. Batzer, M. Moretti, and two anonymous reviewers provided helpful comments that improved this paper. W. Swank, J. Vose, and B. Kloeppel at Coweeta Hydrologic Laboratory provided site support. The National Science Foundation (Grants DEB-9207498, DEB-9629268, and DEB-0212315) funded this research. ; Public domain authored by a U.S. government employee

Catchments with minimal disturbance usually have low dissolved inorganic nitrogen (DIN) export, but disturbances and anthropogenic inputs result in elevated DIN concentration and export and eutrophication of downstream ecosystems. We studied streams in the southern Appalachian Mountains, USA, an area dominated by hardwood deciduous forest but with areas of valley agriculture and increasing residential development. We collected weekly grab samples and storm samples from nine small catchments and three river sites. Most discharge occurred at baseflow, with baseflow indices ranging from 69% to 95%. We identified three seasonal patterns of baseflow DIN concentration. Streams in mostly forested catchments had low DIN with bimodal peaks, and summer peaks were greater than winter peaks. Streams with more agriculture and development also had bimodal peaks; however, winter peaks were the highest. In streams draining catchments with more residential development, DIN concentration had a single peak, greatest in winter and lowest in summer. Three methods for estimating DIN export produced consistent results. Annual DIN export ranged from less than 200 g ha(-1) year(-1) for the less disturbed catchments to over 2,000 g ha(-1) year(-1) in the catchments with the least forest area. Land cover was a strong predictor of DIN concentration but less significant for predicting DIN export. The two forested reference catchments appeared supply limited, the most residential catchment appeared transport limited, and export for the other catchments was significantly related to discharge. In all streams, baseflow DIN export exceeded stormflow export. Morphological and climatological variation among watersheds created complexities unexplainable by land cover. Nevertheless, regression models developed using land cover data from the small catchments reasonably predicted concentration and export for receiving rivers. Our results illustrate the complexity of mechanisms involved in DIN export in a region with a mosaic of climate, geology, topography, soils, vegetation, and past and present land use. ; U.S. Forest ServiceUnited States Department of Agriculture (USDA)United States Forest Service; National Science FoundationNational Science Foundation (NSF) [DEB0823293] ; U.S. Forest Service; National Science Foundation, Grant/Award Number: DEB0823293 ; Public domain authored by a U.S. government employee

In this study, we document a functional regime shift in stream inorganic nitrogen (N) processing indicated by a major change in N export from a forested watershed. Evidence from 36 years of data following experimental clearcut logging at Coweeta Hydrologic Laboratory, NC, suggests that forest disturbance in this area can cause elevation of dissolved inorganic N (DIN) loss lasting decades or perhaps longer. This elevation of N export was apparently caused by an initial pulse of organic matter input, reduced vegetation uptake, increased mineralization of soil organic N, and N fixation by black locust-associated bacteria following clearcut logging. In forested reference watersheds at Coweeta, maximum DIN concentration occurs in summer when base flow is low, but the clearcut watershed shifted to a pattern of maximum winter DIN concentration. The seasonal pattern of DIN concentration and export from reference watersheds can be explained by terrestrial and in-stream processes, but following clearcutting, elevated DIN availability saturated both terrestrial and in-stream uptake, and the N export regime became dominated by hydrologic transport. We suggest that the long-term elevation of stream DIN concentration and export along with the changes in seasonality of DIN export and the relationship between concentration and discharge represent a functional regime shift initiated by forest disturbance. ; USDA Forest ServiceUnited States Department of Agriculture (USDA)United States Forest Service; Southern Research StationUnited States Department of Agriculture (USDA)United States Forest Service; Coweeta Hydrologic Laboratory; National Science FoundationNational Science Foundation (NSF); NSFNational Science Foundation (NSF) [DEB0823293] ; We thank Bobbie Niederlehner for help with the statistical analyses. Many of the ideas in this paper resulted from discussions with Drs. Rhett Jackson, Durrell Scott, Stephen Schoenholtz, Jeb Barrett, Kevin McGuire, Brian Strahm, Mary Beth Adams, Sheila Christopher, and Charley Kelly. We also appreciate the helpful comments from two anonymous reviewers. The WS 7 study was supported by the USDA Forest Service, Southern Research Station, Coweeta Hydrologic Laboratory, and by a series of grants from the National Science Foundation. This analysis of long-term data was supported by NSF grant DEB0823293 to the Coweeta LTER program at the University of Georgia and by Coweeta Hydrologic Laboratory. ; Public domain authored by a U.S. government employee

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

Studies of trophic-level material and energy transfers are central to ecology. The use of isotopic tracers has now made it possible to measure trophic transfer efficiencies of important nutrients and to better understand how these materials move through food webs. We analyzed data from thirteen N-15-ammonium tracer addition experiments to quantify N transfer from basal resources to animals in headwater streams with varying physical, chemical, and biological features. N transfer efficiencies from primary uptake compartments (PUCs; heterotrophic microorganisms and primary producers) to primary consumers was lower (mean 11.5%, range 100%). Total N transferred (as a rate) was greater in streams with open compared to closed canopies and overall N transfer efficiency generally followed a similar pattern, although was not statistically significant. We used principal component analysis to condense a suite of site characteristics into two environmental components. Total N uptake rates among trophic levels were best predicted by the component that was correlated with latitude, DIN:SRP, GPP:ER, and percent canopy cover. N transfer efficiency did not respond consistently to environmental variables. Our results suggest that canopy cover influences N movement through stream food webs because light availability and primary production facilitate N transfer to higher trophic levels. ; National Science FoundationNational Science Foundation (NSF) [NSF-DEB 1052399, DBI-1401954]; Department of Energy's Office of Science, Biological and Environmental Research; U.S. DOEUnited States Department of Energy (DOE) [DE-AC05-00OR22725]; U.S. Department of EnergyUnited States Department of Energy (DOE) [DE-AC05-00OR22725] ; We thank everyone who participated in the individual tracer experiments used in this analysis. We are grateful for the leadership and friendship of the late Pat Mulholland, whose legacy continues to inspire. This manuscript is the product of a workshop funded by a National Science Foundation grant (NSF-DEB 1052399) to M. R. Whiles and W. K. Dodds. Partial support during manuscript preparation to N. A. Griffiths was from the Department of Energy's Office of Science, Biological and Environmental Research. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. DOE under contract DE-AC05-00OR22725. This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. S. M. Collins was supported by a National Science Foundation Postdoctoral Research Fellowship in Biology (DBI-1401954). ; Public domain authored by a U.S. government employee