Our project began in 2015 with the selection of sample sites that would give us a mix of land-use and land-cover types throughout the state of Ohio. We selected three reservoirs – Indian Lake, Hoover Reservoir, and Burr Oak Lake – due to the variation in forested, agricultural, and urban areas in their watershed land cover. We then identified stream sites in each watershed that were not only representative of the watershed as a whole, but also represent variability in potential nutrient inputs from headwater streams all the way to the mouths of the major rivers flowing into each reservoir. In 2018, we were able to expand the project to include additional catchments in Indiana (Lake Monroe and Patoka Lake) and Kentucky (Taylorsville Lake and Barren River Lake). Indian Lake’s watershed is dominated by agriculture. Burr Oak, Monroe and Patoka’s watersheds are dominated by forest. Barren River, Taylorsville, and Hoover are a mix of urban, forest and agriculture land use.
With land access and collection permits in hand from private landowners, local municipalities, state, and federal government, we completed our first round of sampling in summer of 2016. Samples were collected to examine biota (Figure 2), chemical water quality, and hydrogeomorphology. These parameters are three times a year, in the summer, fall, and spring. In addition to our three major sampling events, we also collect water-quality samples on a quarterly basis throughout the year to track seasonal changes in nutrient fluxes.
To date, we have begun to see an interesting pattern in nutrient concentrations in our reservoirs and streams. Within stream sites, those in the watershed flowing into Burr Oak Lake have the lowest total phosphorus, orthophosphate, total nitrogen and nitrate levels (Figure 3), with little difference between streams associated with Hoover Reservoir and Indian lake. However, this pattern was not seen in the lakes, especially for phosphorus. Total phosphorus was similar in all three lakes, while orthophosphate was similar for Burr Oak Lake and Hoover Reservoir (Figure 3).
In addition to examining the concentration of phosphorus within the Ohio River watershed, we are also using a novel technique to try to trace orthophosphate – phosphate readily taken up by plants and animals – from its sources. Orthophosphate is a molecule made up of phosphorus and oxygen atoms. We are using oxygen atoms within orthophosphate as a tracer and examining the abundance and ratio of oxygen isotopes within orthophosphate. Since oxygen isotope values observed in rivers and reservoirs reflect their sources, this approach will enable us to target both land-use types and point sources that most contribute to phosphorus loads. So far, we have seen distinct ranges of oxygen isotope values within the three reservoirs being examined – a promising sign!
Additional information can be found in our Presentations and Reports below.
This research is supported by the US Environmental Protection Agency (83926901) and Ohio Corn and Small Grains Marketing Programs.
This website was developed under Assistance Agreement No. RD839269 awarded by the U.S. Environmental Protection Agency to Drs. S. Mazeika P. Sullivan, Lauren Pintor, and Kaiguang Zhao. It has not been formally reviewed by EPA. The views expressed in this document are solely those of study team and do not necessarily reflect those of the Agency. EPA does not endorse any products or commercial services mentioned in this publication.