Geologic and Cultural Effects Upon Water Quality of the Hillsdale Reservoir, Miami County, Kansas
Authors:   , Zahner Thomas 
Published: February 2023

The Hillsdale Reservoir in northwest Miami County, Kansas is used as a source of water, for recreation, and for flood control. An intensive study to determine the effects that geology and culture in the watershed have on water quality in the reservoir was completed, utilizing field reconnaissance and water analyses. Completed in 1980, Hillsdale Reservoir has a multipurpose capacity of 9.4 x107 m3 and a watershed that encompasses 373 km2. Topographic maps and field reconnaissance revealed that the watershed is characterized by gently rolling hills and a dendritic flow pattern, with a stream gradient of 1.5 m/km to the south. The major streams in the Hillsdale Reservoir watershed are Big Bull and Little Bull creeks, which are tributaries of the Marais des Cygnes River. The watershed is extensively vegetated and its gentle slopes result in slow movement of surface flow. The stratigraphy of the watershed proper consists of repetitive Pennsylvanian cyclothemal limestones and shales with very poor water transporting characteristics. The shales in the study area have an average porosity of 6% and a hydraulic conductivity of approximately 5 x 10.8 m/day. The limestones, with initial porosity of less than 5 %, display considerable secondary porosity in the form of solution cavities; they have a hydraulic conductivity of 1 to 5 m/day. The Pennsylvanian strata in the study area have a dip of approximately 1Â° NW. The overall geologic character of the watershed is not conducive to groundwater flow nor to expedient surface water flow. The meager transport of water in the study area has resulted in high levels of nutrients in the upper reaches of the watershed, large quantities of dissolved solids in the surface flow, and large macrophyte populations along the streams flowing through the watershed. Cultural sources of nutrients and contaminants were also identified in the watershed of the Hillsdale Reservoir. The point sources of pollution include three wastewater treatment plant outlets, a mobile home park waste lagoon, and a limestone quarry. The greatest point source contributor of pollution is the Johnson County Industrial Airport wastewater treatment plant, whose effluent contains as much as 297 mg/l biological oxygen demand and 438 mg/l total suspended solids. Nonpoint sources of pollution in the watershed are cropland, urban development, pastureland and feedlots, and precipitation. Water samples for the reservoir and watershed were analyzed in the field by a Hach DR/3 portable spectrophotometer and in the laboratory by a Bausch and Lomb atomic absorption spectrophotometer. The field analyses were run for the concentrations of nitrite, nitrate, phosphate, silica, sulfate, and fluoride; conductivity, turbidity, and alkalinity tests were also run in the field. The lab analyses were run for the concentrations of calcium, magnesium, sodium, potassium, iron, copper, and lead. It was determined that copper and lead cannot be properly analyzed with the atomic absorption spectrometer. The results of this study were compared to analyses done in 1985 and 1987 by the Kansas Department of Health and Environment (KDHE) to see if any trends could be observed. Increases in nitrogen (as nitrite and nitrate) and phosphorus (as phosphate), two important plant nutrients, were observed since the 1985 and 1987 testings. An increase in the availability of these two nutrients will result in an overabundance of oxygen demanding plants and organic debris. High levels of iron, calcium, and manganese present in the Hillsdale Reservoir indicate a low level of free oxygen. Toxic substances and pesticides are presently not found in large quantities in the Hillsdale Reservoir, but increases in the concentrations of these substances could result in a further decrease in water quality. Presently, the reservoir displays the characteristics of a border-line eutrophic lake, and continued influx of contaminants and nutrients from the many sources of pollution within the watershed will result in further degradation of water quality of the Hillsdale Reservoir.