Integrating Biological Data into TMDL Assessments: Refining a Model to Determine Biologically Meaningful Target Levels for Dissolved Oxygen
Principal Investigator: Leonard Ferrington Jr., Professor, Department of Entomology, University of Minnesota
USGS-WRRI 104B/ CAIWQ Competitive Grants Program
March 2008 - February 2009
Reduced levels of dissolved Oxygen (DO) can have severe and unacceptable consequences for productivity and biological diversity in surface waters. The Minnesota Pollution Control Agency has identified 64 stream/river segments with unacceptable DO conditions in their 2008 draft TMDL listing document (available on-line). All require development of a TMDL strategy to restore and protect productivity and diversity of aquatic organisms. Quantitative models are required in order to determine target levels of DO that wil1 protect pre-determined percentages of aquatic organisms. This proposal is designed to continue developing models for integrating and interpreting data derived from a newly tested rapid bioassessment technique developed for assessing Chironormidae and using them as surrogates to measure biological conditions in streams that are listed for TMDL based on reduced DO conditions. Species thermal preferenda will be developed and related to thermal patterns in stream segments that are controlled by groundwater/surface water interactions. In this project 20 stream segments from the MPCA 2008 draft list that are all warm-water segment, are listed for reduced DO, and have TMDL start dates of 2006, 2007 or 2008 will be modeled. All streams occur in the Upper Mississippi, Minnesota River, Saint Croix River or Lake Superior drainage units. These models will serve to inform decisions about target levels for DO developed in the TMDL program and are constructed to allow predictions of the percentage of species that will be protected. The approach used to analyze data from this research project is patterned on concepts formulated by Posthuma et al. 2001 (and papers contained within) and is based on species sensitivities distributions derived from field data. This modeling approach relies on relationships of daily mean temperature to equilibrium saturation DO concentrations. The utility of the model derives from the ability to pre-determine a percentage of the chironomid community that is defined as the potentially affected fraction (PAP). In this modeling approach, the PAP is the percent of the total species that could potentially be affected (or extirpated) if water temperatures exceed their individual species preferenda during their emergence periods. Once the patterns of thermal preferenda are quantified, it will be possible to identify taxa that are extirpated, but should be present based on thermal regime, and develop predictive statements about species that should re-colonize a given stream if the TMDL results in improved DO conditions. This project will enable these species to be identified, and they can then be considered as species that will be indicators of improving DO conditions. This will enable and independent measure of improvement in biological conditions in addition to relying on physical and chemical indicators.