Dunlap Bottoms is located in southeastern Morris County, KS. The wetland was restored from cropland to a wet meadow under the Wetlands Reserve Program as part of the Agricultural Act of 2014. It was donated to Emporia State University in 2008. During restoration, islands were built from soils dredged to make shallow impoundments. The impoundments were created to
Dunlap Bottoms was used as a field study location to determine the differences in Oxidation-Reduction Potential (ORP), pH, and sediment type in higher and lower elevation areas.
Impoundment built at Dunlap Bottoms along with furrows from the restored cropland. Photo by J.S. Aber and J. Abel
Dunlap Bottoms impoundment after a precipitation event in late April 2016. Photo by B. Longwell.
Oxidation-reduction potential (ORP) is the tendency of a substance to oxidize or reduce another substance. Oxidizing a substance will involve a loss of an electron while reducing will involve the gain of an electron (Emerson, 2008). Changes in ORP can be attributed to changes in soil moisture content. Areas with an increased soil moisture are more likely to be in reduced conditions.
The ORP in the wetland soils was measured using an ORP probe made with platinum wire. A reference probe was made using electroplated silver wire. The reference cell was placed inside a glass frit and filled with 4 M KCl. The platinum wire was placed directly into the soil. Both were connected to a voltmeter to measure the voltage difference in mV, indicating the ORP value (Wafer, et al., 2004). Negative values indicate reducing conditions and positive values indicate oxidating conditions. The values found in low, wet areas averaged in 50 mV while values in high, drier areas averaged 110 mV.
Oxidation-Reduction Potential
Sediment Type and pH
Soil samples were taken using a backsaver soil probe to a depth of 10 cm. A total of ten soil samples were taken throughout the Dunlap Bottoms study location. The sediments were observed on site to determine soil type. The sediment type of both, low and high areas, were thick, silty clay sediment.
The collected soil samples were taken to the lab to analyze pH. To measure pH, soils samples were dried at 105°C for 72 hours. Dried samples were crushed using a grinder. Ground samples were sieved using 2 mm soil sieve. Samples were grinded to a fine powder with a mortar and pestle. 10 g of each sample was mixed throughly with 25 mL of dionized water and let stand for 20 minutes. A lab calibrated pH meter was used to measure the pH in each sample.
The pH for high areas was compared to the pH values found in low areas. The average pH for all the samples was 6.81. There was not a significant difference in pH values for high and low areas as the average for the low areas 6.78 and the average for high areas was 6.87.
A platinum soil probe and silver electroplated reference probe were used to complete the ORP analysis. Photo by K. Schwinghamer.
Backsaver soil probe used to collect soil samples. Photo by K. Schwinghamer.
Dunlap Bottoms
Conclusion
The positive value for the low, wet areas can be attributed to the fact the these locations are dry for a majority of the year. During wet seasons, these areas fill with water due to the underlying, impermeable clay. The higher, dry areas were created when the impoundments were built. These man made areas are dry year-round giving a higher, positive value than the lower areas.
Typical wetland soils have pH values in the range of 5-8 (Mullen, 2011). The pH values found at Dunlap Bottoms were near the neutral pH of 7. This is due to high levels of limestone in the which react with water to form a buffer zone. The dissolution of limestone adds calcium and carbonate ions to the system. The addition of carbonate shifts the equilbrium as the carbonate reacts with water to form bicarbonate. The bicarbonate will then undergo hydrolysis, forming a weak acid, carbonic acid. Carbonic acid will dissociate to form bicarbonate which will dissociate to form carbonate. The reactions explained above are repeated, creating a buffer zone and a neatral pH (Fetter, 1998).
Soil samples after drying in the oven for 72 hours. Photo by B. Longwell.
Soil slurry made with grinded soil and dionized water. Photo by B. Longwell.