NUTRIENT CONCENTRATIONS IN TRIBUTARIES TO SPRING LAKE, MCDONOUGH COUNTY, ILLINOIS

Water samples from the Spring Lake watershed tributaries were collected in an effort to determine locations in the watershed that are highest in production of the nutrients nitrate and phosphate. Excessive phosphorous in Spring Lake was identified as a problem by the Illinois EPA and the Spring Lake Watershed committee in their “Spring Lake Watershed Plan, July 2005.” However, this same report states that the locations of high concentrations of phosphorous in the watershed are unknown. We hope to see if there is any correlation between the nutrient levels and either the watershed area and/or the land use upstream of the sampling location.

The water sample’s pH, temperature, and specific conductance were measured in the field with meters. Pocket colorimeters, one each for nitrate nitrogen (NO₃-N) and orthophosphate, were used into the field to immediately measure the concentrations of unfiltered samples. Thus far, seven locations have been sampled seven times between late September and early November, 2011.

At the seven locations the phosphate concentration ranges from 0.08 - 3.3 mg/L. The nitrate ranges from 0.01- 4.5 mg/L. The location (#6) with the highest individual measurements of both phosphate and nitrate is located about 0.2 miles away from a rural high school that discharges wastewater into an agricultural drainage tile. The mean phosphate ranges from 0.25-1.0 mg/L. The mean nitrate level ranges from 0.57-3.1 mg/L. Location 5 exhibited the highest mean nitrate (3.1 mg/L) and the most consistent concentrations, with standard deviations of 0.037 mg/L and 0.050 mg/L phosphate and nitrate respectively. Location 6 exhibited the highest mean phosphate (1.0 mg/L) but had the highest standard deviation for both phosphate (0.61 mg/L) and nitrate (1.7 mg/L) concentrations. This may be due to the fact that location 6 drains the smallest watershed area currently being tested and, as mentioned earlier, may be influenced by a nearby school.

Continued sampling in 2012 and the addition of more sampling locations within the watershed will be undertaken to identify seasonal changes in concentration and further investigate any possible correlation between watershed area and land use with regards to the phosphate and nitrate levels.