Deposition of Selenium and Other Constituents in Reservoir Bottom Sediment of the Solomon River Basin, North-Central Kansas

Abstract

The Solomon River drains approximately 6,840 square miles of mainly agricultural land in north-central Kansas. The Bureau of Reclamation, U.S. Department of the Interior, has begun a Resource Management Assessment (RMA) of the Solomon River Basin to provide the necessary data for National Environmental Policy Act (NEPA) compliance before renewal of long-term water-service contracts with irrigation districts in the basin. In May 1998, the U.S. Geological Survey (USGS) collected bottom-sediment cores from Kirwin and Webster Reservoirs, which are not affected by Bureau irrigation, and Waconda Lake, which receives water from both Bureau and non-Bureau irrigated lands. The cores were analyzed for selected physical properties, total recoverable metals, nutrients, cesium-137, and total organic carbon.

Spearman's rho correlations and Kendall's tau trend tests were done for sediment concentrations in cores from each reservoir. Selenium, arsenic, and strontium were the only constituents that showed an increasing trend in concentrations for core samples from more than one reservoir. Arsenic and selenium are of concern because of the potential for adverse biological effects. The USEPA threshold effects level (TEL) for arsenic in sediment of 7.24 mg/kg was exceeded in each reservoir. Selenium does not have a regulatory guideline although 4.0 mg/kg in sediment is frequently cited for the potential for bioaccumulation and this level was not exceeded in any sample and only equaled in one sample in Webster Reservoir. Strontium also has no regulatory guideline and is considered non-toxic. The USEPA probable effects level (PEL) was not exceeded for any constituent analyzed.

Concentrations and trends for these three constituents were compared to information on historical irrigation to determine any causal effect. Increases in selenium, arsenic, and strontium concentrations can not be completely explained by Bureau irrigation. However, mean selenium, arsenic, and strontium concentrations in sediment from all three reservoirs may be related to total irrigated acres (Bureau and non-Bureau irrigation) in the basin. Selenium, arsenic, and strontium loads were calculated for Webster Reservoir to determine if annual loads deposited in the reservoir were increasing along with constituent concentrations. Background selenium, arsenic, and strontium loads in Webster Reservoir are significantly larger than post-background loads.

Additional information on Reservoir Sediment in Kansas can be found at: http://ks.water.usgs.gov/studies/ressed/

Christensen, V.G., 2000, Deposition of selenium and other constituents in reservoir bottom sediment of the Solomon River basin, north-central Kansas [abst.], in Water quality restoration and protection, 17th Annual Water and the Future of Kansas Conference, Manhattan, Kansas, March 1, 2000, Proceedings: Manhattan, Kansas Water Resources Research Institute, p. 11.