Browsing by Author "von Schiller, Daniel"

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    Drivers of nitrogen transfer in stream food webs across continents
    Norman, Beth C.; Whiles, Matt R.; Collins, Sarah M.; Flecker, Alexander S.; Hamilton, Steve K.; Johnson, Sherri L.; Rosi, Emma J.; Ashkenas, Linda R.; Bowden, William B.; Crenshaw, Chelsea L.; Crowl, Todd; Dodds, Walter K.; Hall, Robert O.; El-Sabaawi, Rana; Griffiths, Natalie A.; Marti, Eugenia; McDowell, William H.; Peterson, Scot D.; Rantala, Heidi M.; Riis, Tenna; Simon, Kevin S.; Tank, Jennifer L.; Thomas, Steven A.; von Schiller, Daniel; Webster, Jackson R. (2017-12)
    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 <1% to 43%) than N transfer efficiencies from primary consumers to predators (mean 80%, range 5% to >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.
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    Respiration regimes in rivers: Partitioning source-specific respiration from metabolism time series
    Bertuzzo, Enrico; Hotchkiss, Erin R.; Argerich, Alba; Kominoski, John S.; Oviedo-Vargas, Diana; Savoy, Philip; Scarlett, Rachel; von Schiller, Daniel; Heffernan, James B. (Wiley, 2022-09)
    Respiration in streams is controlled by the timing, magnitude, and quality of organic matter (OM) inputs from internal primary production and external fluxes. Here, we estimated the contribution of different OM sources to seasonal, annual, and event-driven characteristics of whole-stream ecosystem respiration (ER) using an inverse modeling framework that accounts for possible time-lags between OM inputs and respiration. We modeled site-specific, dynamic OM stocks contributing to ER: autochthonous OM from gross primary production (GPP); allochthonous OM delivered during flow events; and seasonal pulses of leaf litter. OM stored in the sediment and dissolved organic matter (DOM) transported during baseflow were modeled as a stable stock contributing to baseline respiration. We applied this modeling framework to five streams with different catchment size, climate, and canopy cover, where multi-year time series of ER and environmental variables were available. Overall, the model explained between 53% and 74% of observed ER dynamics. Respiration of autochthonous OM tracked seasonal peaks in GPP in spring or summer. Increases in ER were often associated with high-flow events. Respiration associated with litter inputs was larger in smaller streams. Time lags between leaf inputs and respiration were longer than for other OM sources, likely due to lower biological reactivity. Model estimates of source-specific ER and OM stocks compared well with existing measures of OM stocks, inputs, and respiration or decomposition. Our modeling approach has the potential to expand the scale of comparative analyses of OM dynamics within and among freshwater ecosystems.