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Ohio EPA Study Sets the Stage for State Nutrient Criteria Development

The Ohio EPA, with assistance from the U.S. Geological Survey (USGS) Ohio Water Science Center in Columbus, Ohio, has embarked on a study designed to determine a link between nutrient concentration (total phosphorus [TP] and/or total inorganic nitrogen [TIN]) and algal biomass, habitat quality, and the health of fish and benthic macroinvertebrate communities. The study will also examine the role that habitat quality and flow conditions have on variations in nutrient effects. A pilot study was launched in 2003, with plans of having four sampling seasons to collect data to supplement pre-existing stream and river data for 1,788 sites sampled between 1981 and 2001 for similar parameters (though chlorophyll a, a proxy for algal abundance, was not sampled for any of this pre-existing data). They have already had successful field seasons in 2004 and 2005, sampling from a total of 53 sites of varying habitat quality, anthropogenic enrichment and sizes (including wadeable streams, large and small rivers, and headwaters). Study results will be used to develop nutrient water quality standards for Ohio rivers and streams.

What approach has this study taken in helping to set nutrient criteria?

Study sites are selected from river basins already involved in surveys from TMDL development; a few streams selected are the location of USGS gauging stations, which are used to capture flow data. To capture any potential effects from excess algal abundance, samples are collected during late summer or early fall, Ohio's low-flow seasons. Samples collected are analyzed for the following causal variables: 4-6 samples per site of NOx, NH3, TKN, and TP, and one habitat sample per site, including physical stream habitat, riparian width, solar irradiance, and flow regime. In addition to chlorophyll a (one water column and one periphyton sample per site), fish (one sample per site), and benthic macroinvertebrates (one sample per site), response variables being analyzed include 4-6 samples per site of turbidity, and hourly DO. Fish health is being measured by an index of biological integrity (IBI), and benthic macroinvertebrate health is being measured by an invertebrate community index (ICI). A qualitative habitat evaluation index (QHEI) is being used to assess physical characteristics.

Data are entered into a stream database that was established in 2004. Data for causal variables can then be plotted against response variables and water quality standards to help establish targets for nutrient criteria development (Figure 1). After all the data have been analyzed, results will be used to develop criteria for a decision tree structure to assist in water quality rule development (Figure 2).

What are some of the preliminary results for the study?

A few trends have emerged from 2004 and 2005 data:

• Data from the 2004 and 2005 sampling seasons suggest that TP shows a slightly stronger correlation with DO than TIN; however, nitrogen and phosphorus concentrations have been highly correlated in water column grab samples at most sampling stations. This finding supports this same conclusion that was drawn from the historical data.
• TP is also a better predictor of biological integrity than TIN, which is consistent with TP being a limiting nutrient for streams.
• Headwaters and nonwadeable streams behave similarly in terms of nutrient enrichment. This implies that these waterbody types can be combined into one strata ("smaller streams") for the purposes of nutrient criteria development.
• The health of fish communities has an association with minimum and daily fluctuations of DO (note that DO varied between study seasons due to higher than normal levels of precipitation in 2004 and lower levels of precipitation in 2005).
• The amount of chlorophyll a was correlated with nutrient concentrations and canopy cover, with canopy cover and land use (urban and agricultural uses) having more influence on variations in chlorophyll a levels than nutrients.

Future plans?

Two more sampling seasons are planned for 2006 and 2007. Ohio EPA anticipates rule making for criteria for headwaters and wadeable streams to commence in 2008. Criteria will be set around stream size initially and, depending on the outcome of 2006 and 2007 data, ecoregion-based criteria may also be developed. Ohio EPA hopes to sample from 50 more sites before beginning rule making for nutrients for these smaller streams. Rule making for lakes will also commence in 2008, and will be based on reference data compiled by US EPA and Ohio EPA. Rules for the small stream category plan to be submitted in 2009. More data collection will be needed beyond 2007 for large rivers to develop criteria for those waterbodies; they hope to collaborate with USGS in this effort using funds available for a taxonomic analysis of periphyton samples and the development of a diatom-based biotic index Criteria will be based on a suite of causal variables, such as TP and TIN, and response variables such as chlorophyll a and DO.

What have been some challenges in conducting this study?

The effect of nutrient enrichment on running waters is one of the more difficult questions facing resource managers and aquatic ecologists, and therefore requires considerable effort to understand. One of the biggest challenges has been to reprioritize existing internal resources. Fortunately, the extramural funding from US EPA has allowed USGS to partner with Ohio EPA to augment data collection.

For more information on this study and Ohio EPA's nutrient criteria development timeline, please contact Bob Miltner at Bob.Miltner@epa.state.oh.us.