5/21/2015  |   13:30 - 13:45   |  102C

SPATIAL PATTERNS OF GPP AND R IN A BOREAL STREAM NETWORK Patterns of primary production (GPP) and respiration (ER) in stream networks will depend, in part, on patterns of availability of limiting resources. Resource competition theory suggests that resource ratios determine competitive advantage between two species. This theory has been extended to competition between freshwater heterotrophs and autotrophs, though competition is altered by light availability. In the boreal forest, stream DOC and nutrient concentrations are linked with permafrost distribution. Watersheds with extensive permafrost have higher DOC and lower inorganic nitrogen concentrations than watersheds with little permafrost. We evaluated patterns in metabolism across a boreal forest stream network in relation to light, DOC, and nutrient availability to assess what factors best describe patterns of GPP and ER. We measured whole-stream metabolism in nine stream reaches draining watersheds that varied in permafrost extent. We predict that competition between heterotrophs and autotrophs will be dependent on light and DOC availability. It is important that we understand patterns of metabolism in boreal stream networks, because changes in light and DOC availability are likely to occur with climate induced changes in fire regimes and permafrost thaw.

Christina Baker (Primary Presenter/Author), University of Alaska Fairbanks, clbaker5@alaska.edu;


Jeremy B. Jones (Co-Presenter/Co-Author), University of Alaska Fairbanks, jbjonesjr@alaska.edu;


Tamara Harms (Co-Presenter/Co-Author), University of California Riverside, tharms@ucr.edu;

5/21/2015  |   13:45 - 14:00   |  102C

ABIOTIC VARIABLES CONTROL STREAM METABOLISM IN A NUTRIENT LIMITED MONTANE RIVER NETWORK Stream metabolism (GPP and ER) is an integrated measure of ecosystem function that takes into account allochthonous and autochtonous sources. Understanding the drivers and the spatial and temporal variability of available energy is critical for developing watershed restoration strategies that take advantage of hot spots and peak times of GPP and ER. We measured metabolism in 13 reaches continuously for one year at representative sites across a montane river network in Washington, USA. We hypothesized that 1) abiotic factors (nutrients, light, temperature, flow and geomorphology) rather than biotic factors (grazing, spawning, riparian inputs) are a first order control on GPP and ER, and 2) most reaches are heterotrophic through most of the year. Results were consistent with our hypothesis. Light, temperature, and flow were main drivers for both GPP and ER, nitrogen was important for GPP and geomorphology for ER. Conversely, most sites were heterotrophic except in April and July coinciding with leafing, longer photoperiod and warmer temperatures. Findings are relevant because they explore spatial and temporal variation in metabolism at the watershed scale.

Francine Mejia (Primary Presenter/Author), U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, Cascadia Field Station, fmejia@usgs.gov;


J. Ryan Bellmore (Co-Presenter/Co-Author), USGS Forest and Rangeland Ecosystem Science Center, Corvallis, OR, jbellmore@usgs.gov;


Joseph Benjamin (Co-Presenter/Co-Author), USGS Forest and Rangeland Ecosystem Science Center, Corvallis, OR, jbenjamin@usgs.gov;


Adrianne Zuckerman (Co-Presenter/Co-Author), University of Idaho, Moscow, ID, adriannez@gmail.com;


Grace Watson (Co-Presenter/Co-Author), Methow Salmon Recovery Foundation, Twisp, WA, grace@methowsalmon.org;


Michael Newsom (Co-Presenter/Co-Author), US Bureau of Reclamation, Portland, OR, mnewsom@usbr.gov;


Alexander Fremier (Co-Presenter/Co-Author), Washington State University, Pullman, WA, alex.fremier@wsu.edu;

5/21/2015  |   14:00 - 14:15   |  102C

EIGHT-YEAR SEASONAL TIME SERIES OF KLAMATH RIVER METABOLISM Gross primary production (GPP) and ecosystem respiration (ER) control dissolved oxygen in rivers and they describe resource availability at the base of the foodweb. Long-term studies of patterns and controls on GPP and ER in rivers are limited. We calculated daily ecosystem metabolism on the Lower Klamath River from 2007–2014 during the May–November water-quality monitoring season, resulting in approximately 1,150 daily measurements of GPP and ER. Daily GPP predicted ER across the dataset (r²=0.42), with the strength of the relationship varying among years. During base-flow periods, daily GPP ranged from 3–20 g O₂ m^-2 d^-1, but at higher flows GPP decreased with increasing discharge, with ER following similar patterns. Seasonal mean GPP and ER were not related to annual discharge metrics, despite inclusion of extreme high- and low-flow years in our study. Mean July–August GPP ranged from 8–17 g O₂ m^-2 d^-1. Summer GPP decreased after year-3 of our study, following decreases in total phosphorus and total nitrogen concentrations. While discharge likely controls within year variation in GPP and ER, base-flow variation may be driven by nutrients.

Laurel Genzoli (Primary Presenter/Author), University of Montana, laurel.genzoli@umontana.edu;


Robert O. Hall (Co-Presenter/Co-Author), Flathead Lake Biological Station, University of Montana, bob.hall@flbs.umt.edu;

5/21/2015  |   14:15 - 14:30   |  102C

COMPUTATIONAL CONSIDERATIONS OF WHOLE STREAM METABOLISM Modeling whole stream metabolism based on diel dissolved oxygen (DO) cycle involves estimating multiple parameters in an ordinary differential equation. This often poses statistical and computational challenges. Numerical approximation, especially the simple Euler method, is often employed in solving differential equation in stream ecology literatures. In addition, DO, light and temperature are measured on a discrete basis. We often have to make interpolation between measurement time when estimating metabolism. However, the error and uncertainty associated with such approximation and interpolation has seldom been explicitly evaluated. Here, we use representative datasets to demonstrate how much difference the approximation and interpolation lead to in parameter estimates. Our analysis demonstrates that numeric approximation in solving differential equation could lead to major difference in stream metabolism estimates, especially with long measurement interval. Different interpolations of light and temperature also resulted in difference in metabolism estimates but to a less extend. We conclude that it is important to always use accurate numeric solution to differential equation in metabolism estimates.

Chao Song (Primary Presenter/Author), Taizhou University, songchaonk@163.com ;


Ford Ballantyne (Co-Presenter/Co-Author), University of Georgia, fb4@uga.edu;

5/21/2015  |   14:30 - 14:45   |  102C

TO CONSTRAIN OR NOT TO CONSTRAIN: FORCING METABOLISM PARAMETERS TO ECOLOGICALLY FEASIBLE VALUES Gross primary production (GPP) and ecosystem respiration are fundamental ecosystem attributes. Significant advancement in sensor technologies has provided opportunities to estimate these parameters in aquatic ecosystems using high-frequency dissolved oxygen data. However, in low productivity systems, metabolism models generate daily parameter values that are not ecologically realistic (e.g., negative GPP). Analysis of metabolism data from Trout Lake, an oligotrophic study lake of the North Temperate Lakes Long-Term Ecological Research Program in northern Wisconsin, indicates that unrealistic model predictions occur on 40-60% of the days.. We compared model estimates of primary production generated from oxygen data with those measured concurrently using the traditional 14C approach to assess whether constraining model metabolism parameters to realistic values or filtering dissolved oxygen data to remove noise improved metabolism estimates. We found that both pre-filtering the data to remove noise and constraining the parameters to realistic values increased the strength of relationships between metabolism estimates based dissolved oxygen and those based on 14C.

Noah Lottig (Primary Presenter/Author), University of Wisconsin Center for Limnology, nrlottig@wisc.edu;