Water quality assessment and ecoregional comparison of a reservoir in east-central Indiana

Abstract

Popovičová, J. 2009. Water quality assessment and ecoregional comparison of a reservoir in east-central Indiana. Lake Reserv. Manage. 25:155–166.

This study assessed water quality of a reservoir in an agricultural watershed of east-central Indiana, examined the effects of a thermal and oxygen regime on cycling of nutrients, and compared the results to ecoregional data and reference guidelines. Two locations were monitored biweekly from May through September 2007 for pH, temperature, dissolved oxygen, alkalinity, Secchi disk transparency (SD), chlorophyll a, and nutrient concentrations. The reservoir did not stratify during the monitoring season, although both anoxia and reoxygenation of the hypolimnion were observed. These conditions affected nitrogen (N) and phosphorus (P) cycling because nitrification was found to occur in the hypolimnion, and both internal load and water column mixing affected the concentrations and distribution of P. The reservoir was characterized as a eutrophic water body based on SD, total N and chlorophyll a concentrations, while total P concentrations classified the reservoir as slightly hypereutrophic (TSI = 73). This P overload has shifted the system toward N-limiting conditions (molar TN:TP = 18). Comparison of trophic parameters to Ecoregion 55 data placed this reservoir within the 75th percentile, and all parameters exceeded the U.S. Environmental Protection Agency ecoregional reference guidelines. I discuss a potential restoration of this water body to comply with the ecoregional nutrient criteria and to avoid future deterioration associated with N limitation.

Key words:

• ecoregional comparison
• eutrophication
• mixing
• nutrient cycling

Acknowledgments

The author is grateful to Diana Fiallos Celi for her work on field monitoring and laboratory analyses. This project was funded by Ball State University (BSU), Indiana Academy of Science, and a Lilly V grant.

Notes

†Epilimnion.

^††Hypolimnion.

⁺Soluble reactive phosphorus.

⁺⁺Euphotic zone.

*Depth difference significant at p< 0.05.

**Depth differences significant at p< 0.01.

***Depth differences significant at p< 0.001.

†data from Jones and Sauter (2005).

*data from Jones and Medrano (2006).

⁺calculated from Kratzer and Brezonik (1981).

^††calculated from Carlson (1977).

†epilimnetic values from July and August for the ecoregion (data from Jones and Medrano 2006); data in parentheses denote minimum and maximum.

*reference guidelines for Ecoregion 55; median value from 4 seasons—25th percentile % for each season (U.S. EPA 2000).

⁺reference guidelines for Ecoregion VI (U.S. EPA 2000).

^††July and August epilimnetic values.

**nitrate + nitrite.