The Intersection of Science and Management: Improving the Scientific Foundation for Nutrient Criteria Development III
Presiding: J R Stevenson, Michigan State University; C R Bauer, U.S. Environmental Protection Agency Region 5; D Tillman, U.S. Environmental Protection Agency, Office of Research and Development; D Pfeifer, U.S. Environmental Protection Agency Region 5
NB21E-01 08:30h
Use Of Statistical Modeling To Assist Phosphorous Criteria For Midwestern Streams
Statistical models of complex ecosystems often struggle with limited generality and weak evidence for causality. Science designed to support nutrient criteria must deal with these problems as well. To help provide a scientific basis for nutrient criteria in Illinois streams we are creating regression models with the widest possible scope and are testing experimentally for evidence of causation. Our analyses employ long term data sets, contemporary observations, and experimental tests of phosphorous dose-responses. Response variables include algal biomass, fish and invertebrate diversity and dissolved oxygen. Analyses conducted on long term data from functionally independent watersheds (N=84) revealed non-linear relationships between both fish and mussel species richness, and P and NH3-N. Nutrient-biodiversity relationships were not apparent in smaller streams and collinearity between P and NH3-N limits inference of any causal relationships. A multivariate model developed from intensive sampling within a single stream demonstrated a clear relationship between phosphorous, canopy cover, current velocities and alga growth (R2=0.552; p<0.001). However, extensive empirical observations across stream ecosystems showed no relationship between phosphorous and algae growth. Our data do not yet support use of an extensive statistical model for phosphorous criteria across the state of Illinois.
NB21E-02 08:45h
High Resolution Monitoring of Algal Growth Dynamics in a Hypereutrophic River in the Central Valley, California
The lower San Joaquin River in California's Central Valley experiences periods of hypoxia during the late summer and fall that is detrimental to aquatic organisms and migration of fall-run chinook salmon and steelhead trout. Hypoxia is attributable, in part, to excess nutrients from urban waste water and agricultural runoff, which contribute to growth of high concentrations of phytoplankton. This study examined spatial and temporal growth patterns that control algal loading using continuous fluorescence measurements at three sites along a 50 km section of the lower San Joaquin River between April and October. A strong diel fluorescence signal was observed and associated grab samples verified that fluorescence was an accurate measure of chlorophyll. Peak chlorophyll concentrations occurred between 18:00 and 20:00 and minimum concentrations between 10:00 and 12:00. Maximum concentrations were nearly two times greater than minimum concentrations although this ratio varied temporally and spatially. Although the mechanism for the diel chlorophyll signal is not very well understood several parameters including temperature, irradiance, turbidity, residence time, stream depth, and zooplankton grazing were considered within the scope of this study. This study highlights the importance of considering high resolution sampling on algal loading rates within heavily impacted riverine systems.
NB21E-03 09:00h
Response of Periphyton to Seasonal Changes in Nutrient Concentrations in Central Illinois Agricultural Streams
Headwater streams in central Illinois have been dredged and channelized to drain surrounding agricultural fields and has led to extensive erosion and eutrophication. Restoration of these systems through farmer implementation of Best Management Practices (BMPs) may be one solution. Examination of algal population dynamics may be useful in assessment of BMP effectiveness. We have monitored two small headwater streams, Bray Creek and Frog Alley, for a suite of physicochemical parameters focusing on dissolved oxygen, nitrogen, and phosphorus for three years. Nutrient concentrations suggested potential nutrient limitation by nitrates during late summer and phosphorus limitation in early summer. To determine seasonal algal dynamics with seasonally varying nutrient limitation in agricultural headwater streams, we used nutrient diffusing substrata (NDS). NDS with agar (controls) or amended with either nitrogen, phosphorus, or both were deployed for 21-24 days in both streams each month for a year. Slight nutrient limitation was observed in Bray Creek during August and November while phosphorus was limiting in September (P<0.05). We suggest agricultural streams are more dynamic than previously thought and algal populations may be seasonally nutrient limited and with consequent effects on dissolved oxygen concentrations.
NB21E-04 09:15h
Scientifically Derived Phosphorus Loading Objective and Adaptive Watershed Management for Lake Simcoe, Canada
The recruitment failure of native cold-water fish in Lake Simcoe, Canada, has been attributed to a three-fold increase in phosphorus (P) loading from pre-settlement rates and consequent oxygen depletion in the hypolimnion and spawning shoal degradation. These water quality concerns led to a multi-agency partnership, the Lake Simcoe Environmental Management Strategy, whose goals include reducing phosphorus loading to the lake and restoring a self-sustaining cold-water fishery. A targeted end-of-summer hypolimnetic dissolved oxygen concentration (DO) was related to phosphorus loading rate through a series of intermediary relationships among trophic state variables using an empirical modeling approach to derive a phosphorus loading objective. The proposed P loading target of 75 metric tons/year is predicted to generate a P concentration of 0.01 mg/L and an end-of-summer hypolimnetic DO of 5 mg/L. The 5mg/L target is considered a significant interim step towards the goal of 7mg/L, a threshold above which cold-water fish recruitment should no longer be impaired. This model is presently being evaluated using data collected from 1980 to 2004 and will be compared to a three-dimensional mechanistic lake model. An adaptive watershed management approach is employed to meet the phosphorus loading target, linking scientific assessments to implementation activities and incorporating community education.
NB21E-05 09:30h
Factors Affecting the Distribution of Wild Rice (Zizania palustris) and the Surrounding Macrophyte Community.
A recent decline in wild rice wetlands is cause for concern due to its importance as a food source, refuge for wildlife, and cultural significance. Sixty wetlands in Wisconsin and Minnesota (USA) were sampled, with approximately equal numbers displaying dense, moderate and sparse wild rice production. Chemical, physical, and watershed parameters were measured as well as macrophyte densities. Data were analyzed using multivariate statistics (CCA). Moderate levels of phosphorus appear beneficial to the overall success of wild rice, while free-floating macrophytes show an overwhelming positive response to higher levels of P. The distribution of macrophytes bordering wild rice beds is correlated to pH,with Potamogeton robbinsii and filamentous green algae responding most strongly to its increase. Healthy stands of wild rice exhibit a narrow circum-neutral range of pH (6.1-8.0)which is significantly different from the greater range exhibited by sparse wild rice wetlands (6.5-8.5). This pattern was paralleled when considering depth which suggests that deeper wetlands may be more susceptible to wild rice loss. Management of existing wild rice wetlands should focus monitoring on pH, depth, phosphorus concentrations and shore development. We are currently using this data base to locate the best reintroduction sites for wild rice.