Analysis of Chickasaw Creek Concentrations and Loads
Summary of Major Findings, 2009-2011
R. Peter Richards, Senior Research Scientist, National Center for Water Quality Research, Heidelberg University
Summed on a water year basis (October 1 – September 30), 2009 and 2010 had below average precipitation (29.6” and 32.3”). 2011 had much above average precipitation at 47.6”. Out of 55 years of record, these three years ranked 48th, 44th, and 3rd respectively, with 81%, 88%, and 130% of the average precipitation of 36.7”. Precipitation drives discharge and strongly influences concentrations and loads, so these statistics are important in understanding some aspects of the concentration and load patterns described below.
Parameters analyzed were flow, suspended solids, total phosphorus, dissolved reactive phosphorus, nitrate nitrogen, total Kjeldahl nitrogen, and chloride. Over the three year period Oct. 1, 2008 to Sept. 30, 2011, 1,413 samples were analyzed. At least one sample was available to characterize 857 of the 1095 days in the study period.
Concentrations of particulate parameters (suspended solids, particulate phosphorus, and total Kjeldahl nitrogen), were generally comparable in Chickasaw Creek to those in Rock Creek and Lost Creek, two comparison watersheds in Northwest Ohio. Concentrations of dissolved parameters (dissolved reactive phosphorus, nitrite nitrogen, and chloride) are substantially higher in Chickasaw Creek than in Rock Creek and Lost Creek.
Moderate to high concentrations, particularly of the dissolved constituents, are often seen in Chickasaw Creek under conditions of moderate to low flow. This is not true of Rock Creek and Lost Creek.
In Chickasaw Creek during the three-year study period, daily average total phosphorus concentrations exceeded the Ohio EPA draft Warm Water Habitat standard (0.1 mg/L) on more than 89% of the days sampled, and nitrate nitrogen exceeded the draft standard for dissolved nitrogen (1.0 mg/L) on nearly 73% of the days sampled. The corresponding figures for Rock Creek were 33% and 44%, respectively.
A greater percentage of the total phosphorus in Chickasaw Creek is in the form of dissolved reactive phosphorus than is the case in Rock and Lost Creeks. Dissolved reactive phosphorus is more potent in supporting algal growth than other forms of phosphorus included in the total phosphorus analysis.
Loads are very unevenly distributed in time, with most of the annual loading occurring on only a few days with high flows. These conditions are associated with rainfall and/or snowmelt. Recent application of fertilizer or manure to the surface of agricultural fields can make loads even higher, though data are not available to indicate how frequently this happened during the study period.
On a per-acre basis, daily loads of suspended solids from Chickasaw Creek were generally less than loads from Rock Creek. Loads of total phosphorus and total Kjeldahl nitrogen were approximately equal. Loads of dissolved reactive phosphorus, nitrate nitrogen, and chloride from Chickasaw Creek were on average 2 to 4 times those from Rock Creek.
WY2011 was a very wet year. The result was much greater discharge and loads from Chickasaw Creek than occurred in WY2009 and WY2010. However, flow-weighted mean concentrations were somewhat lower than in these years. This may be due to changing practices in the watershed, or it may be due to the depletion of readily available supplies of these materials in the watershed.
Given the high nutrient loads in 2011, Grand Lake might have been expected to have a worse year for algal blooms than in 2010. That this was not the case suggests that remedial actions in the lake have had some success in reducing in-lake concentrations which feed algal growth.