@article {KNZ002017, title = {Using path analysis to determine interacting effects of biotic and abiotic factors on patch-scale biogeochemical rates in a prairie stream}, journal = {Aquatic Sciences}, volume = {82}, year = {2020}, abstract = {

Biogeochemical rates within streams vary with ecosystem properties including the distribution of fishes. While many studies investigate the singular effect of fishes on ecosystem components, there is a limited understanding of how fish presence interacts with other ecosystem properties to affect ecosystem structure and function. Here, we used path analyses to elucidate direct and indirect effects of fish presence, and other ecosystem properties on ecosystem respiration (ER), gross primary production (GPP), and ammonium uptake. Experimental responses of fish removal on patch scale (300 cm2) benthic rates of ER, GPP, and ammonium uptake were measured at two sites in a prairie stream. The effect of fish was determined by comparing substrata from field exclosures with fish absent to substrata exposed to fish. Total path model-explained variance was greatest for ER (R2\ =\ 0.55) and least for ammonium uptake (R2\ =\ 0.36) and GPP (R2\ =\ 0.34). Fish decreased algal biomass and directly increased all biogeochemical rates. The relative importance of the different abiotic ecosystem properties varied by process; however, FBOM and substrata size were important for most rates. This study provides evidence for predominantly direct effects of fish on both stream structure and function in a prairie stream. Our results emphasize that interactions between biotic and abiotic factors should be considered when determining drivers of biogeochemical activity. We suggest that simple linear food webs that consist of top\–down or bottom\–up control are not always sufficient to describe animal effects on ecosystem rates.

}, keywords = {LTER-KNZ}, doi = {10.1007/s00027-020-0702-8}, url = {http://link.springer.com/10.1007/s00027-020-0702-8}, author = {Trentman, M.T. and W. K. Dodds and K. B. Gido and R{\"u}egg, J. and Ruffing, C.M.} } @article {KNZ001775, title = {Dissolved organic carbon concentration and flux in a grassland stream: spatial and temporal patterns and processes from long-term data}, journal = {Biogeochemistry}, volume = {125}, year = {2015}, pages = {393 - 408}, abstract = {

Dissolved organic carbon (DOC) in streams is a critical component of the global carbon cycle, but little is known about long-term patterns in DOC concentration and export in grassland streams. Here we present the results of a 15-year dataset collected from multiple sites in the Kings Creek watershed on Konza Prairie, KS, USA. DOC concentrations ranged from 0.15 to 15.97 mg L\−1, with a mean of 1.19 mg L\−1 (standard deviation 1.01 mg L\−1). Sites differed in their DOC concentrations as a function of the year of study and the season. Generally, headwaters had greater DOC concentrations, and DOC decreased downstream. The lowest concentrations were found in a groundwater spring in the watershed. Concentrations showed no trend over the study and were not correlated with discharge. However, annual export (mean: 0.29 kg ha\−1 year\−1; range: 0.00\–9.09 kg ha\−1 year\−1) was highly correlated with annual runoff, and annual runoff explained over 80 \% of the variation in export. Export from Kings Creek was 30 times lower than the literature-reported mean for grasslands and 137 times less than export averaged across all biomes. Neither fire nor bison, two forces that maintain prairies, were statistically related to DOC concentrations. Main drivers of DOC concentrations are likely leaching from terrestrial organic material in soils and the accumulations in dry streambeds during drought periods as well as instream autotrophic production. Downstream declines in DOC concentrations suggest instream processing. Grassland streams probably have modest effects on the global carbon budget due to instream processing and low precipitation. Changes in precipitation may have large effects on carbon export from grassland streams.

}, keywords = {LTER-KNZ, carbon cycle, Carbon export, long-term study, prairie streams}, doi = {10.1007/s10533-015-0134-z}, url = {https://link.springer.com/article/10.1007\%2Fs10533-015-0134-z}, author = {R{\"u}egg, J. and Eichmiller, J.J. and Mladenov, N. and W. K. Dodds} } @article {KNZ001777, title = {Quantifying ambient nitrogen uptake and functional relationships of uptake versus concentration in streams: a comparison of stable isotope, pulse, and plateau approaches}, journal = {Biogeochemistry}, volume = {125}, year = {2015}, pages = {65 - 79}, abstract = {

Nutrient releases and spiraling metrics are frequently used to quantify the downstream transport of nutrients and to better understand the effects of anthropogenic inputs to downstream waters. Ambient uptake rates in streams can be measured through stable isotope enrichments, while pulse and plateau additions can estimate such rates via extrapolation and modeling techniques, respectively. Data from these releases can be used to estimate ambient uptake rates from nutrient additions and possibly determine the functional relationships between nutrient concentrations and uptake rates. Here, we compared estimated ambient rates calculated from established pulse and plateau approaches, results obtained from new modeling approaches, and rates at ambient concentrations from stable isotope enrichments. Comparative releases of NH4Cl and 15NH4Cl were conducted in four experimental reaches across the grassland Kings Creek and urban Campus Creek, KS. Nutrient uptake was predominantly linear with increasing ammonium. Estimated ambient uptake rates varied among sites, release methods, and data analysis approaches. However, plateau ambient rates from new modeling approaches matched closely with measured ambient rates from isotope enrichments at three sites, suggesting that modeled plateau data may be best for a first look at determining nutrient uptake rates at an individual site. Limitations and benefits of each approach vary; however, baseflow discharge may be a key driver when choosing a method. If possible, multiple methods should be attempted at each location and under each novel set of conditions to determine the best approach prior to designing and implementing a more extensive series of measurements.

}, keywords = {LTER-KNZ, Ammonium uptake, nutrient spiraling, TASCC, uptake length}, doi = {10.1007/s10533-015-0112-5}, url = {https://link.springer.com/article/10.1007\%2Fs10533-015-0112-5}, author = {Trentman, M.T. and W. K. Dodds and Fencl, J.S. and Gerber, K. and Guarneri, J. and Hitchman, S.M. and Peterson, Z. and R{\"u}egg, J.} }