The Intersection of Science and Management: Improving the Scientific Foundation for Nutrient Criteria Development II
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
NB14E-01 INVITED 15:30h
Eutrophication and Trophic State in Rivers and Streams
Given the heterotrophic nature of many natural streams, I propose that trophic state be divided into autotrophic and heterotrophic state. This division requires consideration of external carbon and inorganic nutrients and facilitates a stoichiometric view of lotic trophic structure. Empirical results suggest that phosphorus and nitrogen are the most important nutrients regulating autotrophic state in flowing waters, and that benthic algal biomass is positively correlated to gross primary production. Published estimates of reference nutrient concentrations and nutrient to algal biomass correlations were used to characterize reference distributions of autotrophic state. Mean benthic chlorophyll exceeds 100 mg per square meter less than 30 percent of the time when nutrients are less than the upper third of the expected reference concentrations. A similar analysis suggested that reference nutrient conditions lead to sestonic chlorophyll concentrations above those considered typical of eutrophic lakes less than half the time. Less is known about heterotrophic state, but autotrophic state is probably more variable in small pristine streams than heterotrophic state because autotrophic state is more influenced by canopy (light). Nutrient enrichment often stimulates primary producers and microbial consumers of allochthonous organic materials, so nitrogen and phosphorus enrichment can influence both heterotrophic and autotrophic state.
NB14E-02 INVITED 15:45h
Watershed Classification as a Tool to Partition Variance in Nutrient- Biological Response Relationships
Refining effects-based nutrient water quality criteria requires the partitioning of variation in nutrient-response relationships, including responses related to algae and dissolved oxygen, among stream types. In addition to nutrients, algal accrual rate can be limited by shading, herbivory, and the instream flow regime. For example, moderate flow rates can stimulate nutrient uptake, while frequent spates can scour algal biomass. Furthermore, algal accrual affects instream dissolved oxygen through primary production and instream respiration. To better understand the effects of nutrients on Upper Midwest streams, all subwatersheds at the HUC12 scale have been characterized for climatic, soils, geomorphology, andland-use/land-cover variables expected to control flow regime, and subjected to a nonparametric cluster analysis to identify unique hydrologic classes. A regional database also has been constructed comprising historical monitoring data for stream hydrology, water quality, habitat, algal biomass, and algal, macro-invertebrate, and fish community composition. Relationships between nutrients and minimum dissolved oxygen levels, BOD, periphyton or plankton biomass, and between nutrients and aquatic community metrics are being examined for differences in sensitivity across the identified watershed classes. This abstract does not necessarily reflect EPA policy.
http://www.epa.gov/med/research_topics.html
NB14E-03 INVITED 16:00h
Biotic Response in Lotic Environments to Wide Range of Nutrient Levels, with an Emphasis on Diatoms
The Wisconsin Department of Natural Resources has proposed agricultural performance standards, TMDLs, and phosphorus criteria enforcement as tools to reduce eutrophication in Wisconsin's rivers. Watershed-level to ecoregional differences in nutrient effects may affect the response of water quality to nutrient reduction. Objectives of this project included determining the relationships between watershed and regional characteristics and nutrient concentrations on stream biological integrity, refining phosphorus criteria for Wisconsin, and developing a nutrient index of biological integrity. Samples were taken from 241 wadeable streams from which habitat and fish data had been collected within 5 years. Periphyton and macroinvertebrate samples were sampled once. Diatom data were used to develop a Diatom Nutrient Index based on autecological data and a Diatom Siltation Index based on the sum of epipelic taxa in counts. Relationships between nutrient concentrations and diatom community structure were examined using percentile rankings for total phosphorus (TP) and total nitrogen (TN). Best water quality as indicated by diatoms occurred in sites with either TP or TN at the 50th percentile or below (TP ≤ 0.07 mg L-1; TN ≤ 1.7 mg L-1). These nutrient levels appeared to be a threshold above which headwater stream diatom community structure was relatively stable.
NB14E-04 INVITED 16:15h
Using algal indicators to diagnose nutrient enrichment in the Northwestern Glaciated Plains
The relationships among nutrients, benthic algal community, and aquatic plant biomass were examined in 21 different streams in Montana's Hi-line region, in the Northwestern Glaciated Plains ecoregion. We examined habitat, physical and chemical characteristics, aquatic macrophytes, and benthic algae in the stream segments. Based on multiple lines of evidence, nitrogen was the primary limiting nutrient in the Hi-line region. Correlation analysis indicated that annual total nitrogen concentration in the stream significantly increased with agricultural land use (r = 0.55). Diatom pollution indices and trophic indices also increased with rising nutrient concentrations and agricultural land use. Both structure and function of valued ecological attributes responded to the nitrogen gradient. Loss of sensitive taxa was observed with increased nutrient concentrations. Floating and benthic algal biomass was positively correlated with NO2+3 concentrations in the water column. Benthic algal and aquatic macrophyte biomass also increase with diatom-inferred trophic status. The relationships indicate diatoms can be better indicators for algal community structure and primary productivity change than water chemistry in this system. Based on our results, both a reference approach and a stressor-response approach could be used to define nutrient criteria for this ecoregion.
NB14E-05 INVITED 16:30h
Development of numeric nutrient criteria in Florida
Building on the success of the recently adopted numeric phosphorus criterion for the Florida Everglades, the Florida Department of Environmental Protection (FDEP) is developing numeric nutrient criteria for all Florida freshwaters. FDEP is currently pursuing a reference site-based approach for streams and lakes. Least disturbed reference lakes and streams have been delineated based on landuse patterns (Landscape Development Intensity Index) and the knowledge of local experts. As a means of reducing and explaining the overall variance among reference lakes or reference streams, FDEP is evaluating different types of natural waterbodies (e.g., Florida ecoregions based on geography, physiography, etc.). The goal of these evaluations is to subdivide natural waterbodies into homogenous groups. It is anticipated that criteria will be statistically derived, for each homogenous waterbody group, from the frequency distribution of reference site nutrient concentrations and will likely be expressed as the long-term level required to preserve the least-disturbed condition in that waterbody type. Furthermore, FDEP is pursuing the development and evaluation of biological indices (vegetation, algae, macroinvertebrates) that may be used in conjunction with the reference nutrient concentration distribution approach in establishing nutrient criteria or verifying waterbody impairment status relative to the nutrient criteria.
http://www.dep.state.fl.us/water/wqssp/nutrients
NB14E-06 INVITED 16:45h
Abundance of Macroalgae in Florida Springs: Understanding the Role of Nutrients.
In the last 4 decades Florida springs have experienced a large increase in nutrient concentrations. High nutrient levels are blamed for excess growth of thick algal mats in many springs. Reach-scale benthic algal assessments were conducted to characterize spatial extent and thickness of macroalgae and periphyton at 60 sites within 28 springs, where physico-chemical data were also collected. Diatom indicators were developed using the weighted average approach to infer nutrient conditions. Algal-nutrient relations were determined with % cover and thickness of all macroalgae and each common taxon independently and with measured and diatom-inferred nutrient concentrations. The most common taxa of macroalgae were a blue green alga Lyngbya wollei found at 57 % sites and a green alga Vaucheria sp. found at 55 % sites. Over half of the bottoms of Florida springs, on average, were covered by macroalgae. Analyses indicated a threshold in Vaucheria sp. cover response at 0.6 mg TN/L, but no such response was observed for Lyngbya wollei which seems to have a high tolerance for low nutrient concentrations. Further laboratory experiments were conducted to determine phosphorus and nitrogen limitation of Vaucheria sp. and Lyngbya wollei growth rates and to confirm limiting nutrient concentrations for growth of the macroalgae.