@article {KNZ001324, title = {The influence of land use on stream biofilm nutrient limitation across eight North American ecoregions}, journal = {Canadian Journal of Fisheries and Aquatic Sciences}, volume = {66}, year = {2009}, pages = {1081 -1094}, abstract = {

Nutrient diffusing substrata were used to determine the influence of inorganic nitrogen (N) and phosphorus (P) availability on community respiration (CR), gross primary production (GPP), and chlorophyll a (chl a) on inorganic and organic substrata. We incubated substrata in nine streams each in a total of eight ecoregions (n = 72 streams) located in a range of native vegetation, agriculture, and urban land-use types. On organic substrata, CR was nutrient-limited in 94\% of reference streams but showed significant nutrient limitation in only 60\% and 65\% of agricultural and urban streams, respectively. The relative magnitude of nutrient limitation for CR on organic substrata decreased with increasing percent modified land use in the basin (agriculture + urban). On inorganic and organic substrata, GPP and chl a were rarely nutrient-limited across all ecoregions and land-use types, although the magnitude of nutrient limitation increased with increasing light availability. The effect of human land use on nutrient limitation of biofilm CR, GPP, and chl a was influenced by ecoregion, yet heterotrophic biofilms were consistently most sensitive to nutrient enrichment across ecoregions. Both heterotrophic and autotrophic biofilm constituents should be considered to fully understand stream ecosystem responses to nutrient enrichment.

}, keywords = {LTER-KNZ}, doi = {10.1139/F09-065}, url = {http://www.nrcresearchpress.com/doi/10.1139/F09-065}, author = {Johnson, L.T. and Tank, J.L. and W. K. Dodds} } @article {KNZ001251, title = {Nitrate removal in stream ecosystems measured by 15N addition experiments: Denitrification}, journal = {Limnology and Oceanography}, volume = {54}, year = {2009}, pages = {666 -680}, abstract = {

We measured denitrification rates using a field 15NO3\− tracer-addition approach in a large, cross-site study of nitrate uptake in reference, agricultural, and suburban-urban streams. We measured denitrification rates in 49 of 72 streams studied. Uptake length due to denitrification (SWdenn) ranged from 89 m to 184 km (median of 9050 m) and there were no significant differences among regions or land-use categories, likely because of the wide range of conditions within each region and land use. N2 production rates far exceeded N2O production rates in all streams. The fraction of total NO3\− removal from water due to denitrification ranged from 0.5\% to 100\% among streams (median of 16\%), and was related to NH4+ concentration and ecosystem respiration rate (ER). Multivariate approaches showed that the most important factors controlling SWden were specific discharge (discharge / width) and NO3\− concentration (positive effects), and ER and transient storage zones (negative effects). The relationship between areal denitrification rate (Uden) and NO3\− concentration indicated a partial saturation effect. A power function with an exponent of 0.5 described this relationship better than a Michaelis-Menten equation. Although Uden increased with increasing NO3\− concentration, the efficiency of NO3\− removal from water via denitrification declined, resulting in a smaller proportion of streamwater NO3\− load removed over a given length of stream. Regional differences in stream denitrification rates were small relative to the proximate factors of NO3\− concentration and ecosystem respiration rate, and land use was an important but indirect control on denitrification in streams, primarily via its effect on NO3\− concentration.

}, keywords = {LTER-KNZ}, doi = {10.4319/lo.2009.54.3.0666}, url = {https://aslopubs.onlinelibrary.wiley.com/doi/abs/10.4319/lo.2009.54.3.0666}, author = {Mulholland, P.J. and Hall, R.O. and Sobota, D.J. and W. K. Dodds and Findlay, S.E.G. and Grimm, N.B. and Hamilton, S.K. and W.H. McDowell and O{\textquoteright}Brien, J.M. and Tank, J.L. and L.R. Ashkenas and Cooper, L.W. and Dahm, C.N. and Gregory, S.V. and Johnson, S.L. and Meyer, J.L. and Peterson, B.J. and Poole, G.C. and Valett, H.M. and Webster, J.R. and Arango, C.P. and Beaulieu, J.J. and Bernot, M.J. and Burgin, A.J. and Crenshaw, C.L. and Helton, A.M. and Johnson, L.T. and Niederlehner, B.R. and Potter, J.D. and Sheibley, R.W. and Thomas, S.M.} } @article {KNZ001250, title = {Nitrate removal in stream ecosystems measured by 15N addition experiments: Total uptake}, journal = {Limnology and Oceanography}, volume = {54}, year = {2009}, pages = {653 -665}, abstract = {

We measured uptake length of 15NO3\− in 72 streams in eight regions across the United States and Puerto Rico to develop quantitative predictive models on controls of NO3\− uptake length. As part of the Lotic Intersite Nitrogen eXperiment II project, we chose nine streams in each region corresponding to natural (reference), suburban-urban, and agricultural land uses. Study streams spanned a range of human land use to maximize variation in NO3\− concentration, geomorphology, and metabolism. We tested a causal model predicting controls on NO3\− uptake length using structural equation modeling. The model included concomitant measurements of ecosystem metabolism, hydraulic parameters, and nitrogen concentration. We compared this structural equation model to multiple regression models which included additional biotic, catchment, and riparian variables. The structural equation model explained 79\% of the variation in log uptake length (SWtot). Uptake length increased with specific discharge (Q/w) and increasing NO3\− concentrations, showing a loss in removal efficiency in streams with high NO3\− concentration. Uptake lengths shortened with increasing gross primary production, suggesting autotrophic assimilation dominated NO3\− removal. The fraction of catchment area as agriculture and suburban-urban land use weakly predicted NO3\− uptake in bivariate regression, and did improve prediction in a set of multiple regression models. Adding land use to the structural equation model showed that land use indirectly affected NO3\− uptake lengths via directly increasing both gross primary production and NO3\− concentration. Gross primary production shortened SWtot, while increasing NO3\− lengthened SWtot resulting in no net effect of land use on NO3\− removal.

}, keywords = {LTER-KNZ}, doi = {10.4319/lo.2009.54.3.0653}, url = {https://aslopubs.onlinelibrary.wiley.com/doi/abs/10.4319/lo.2009.54.3.0653}, author = {Hall, R.O. Jr. and Tank, J.L. and Sobota, D.J. and Mulholland, P.J. and O{\textquoteright}Brien, J.M. and W. K. Dodds and Webster, J.R. and Valett, H.M. and Poole, G.C. and Peterson, B.J. and Meyer, J.L. and W.H. McDowell and Johnson, S.L. and Hamilton, S.K. and Grimm, N.B. and Gregory, S.V. and Dahm, C.N. and Cooper, L.W. and L.R. Ashkenas and Thomas, S.M. and Sheibley, R.W. and Potter, J.D. and Niederlehner, B.R. and Johnson, L.T. and Helton, A.M. and Crenshaw, C.M. and Burgin, A.J. and Bernot, M.J. and Beaulieu, J.J. and Arango, C.P.} }