Location: Agroecosystems Management ResearchTitle: Inorganic and organic phosphorus in sediments in the Walnut Creek Watershed of central Iowa, USA
|RAHUTOMO, SUROSO - Iowa State University|
|THOMPSON, MICHAEL - Iowa State University|
Submitted to: Water, Air, and Soil Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2018
Publication Date: 2/17/2018
Citation: Rahutomo, S., Kovar, J.L., Thompson, M.L. 2018. Inorganic and organic phosphorus in sediments in the Walnut Creek Watershed of central Iowa, USA. Water, Air, and Soil Pollution. 229:72. https://doi.org/10.1007/s11270-018-3721-5.
Interpretive Summary: Phosphorus (P) exists in many forms in soils, sediments, and waters. Various extraction procedures have been developed to assess the distribution of P among the different fractions. Soil is initially extracted with a “weak” extracting solution in the first step followed by “stronger” extracting solutions in subsequent steps. The amounts of P extracted can then be used to predict biological availability or the potential for environmental degradation. We collected soil and sediment samples from 25 locations near and within Walnut Creek in Jasper County, Iowa. Among the sample groups, the highest concentrations of extractable phosphorus were found in the stream sediments. Because of the potential release of P from the stream sediments, we can speculate that changes in land use within the riparian areas may, at least initially, have little effect on P loads in Walnut Creek. The results of this work will contribute useful information to crop and cattle producers, local environmental groups, Cooperative Extension and NRCS personnel interested in improving water quality in watersheds with significant agricultural production.
Technical Abstract: The dynamics of phosphorus (P) reactions in stream water have received much attention due to their potential to trigger eutrophication. This study aimed to explore the dynamics of P in Walnut Creek, Jasper County, Iowa. The Walnut Creek watershed supports a variety of land uses (row crop production, grazing, and riparian buffer zones), and the alluvial cross section is composed of a sequence of sediments that contribute differentially to the amounts and forms of P entering the stream. Twenty-five sediment samples from Walnut Creek watershed (classified into three groups: bank, in-stream, and floodplain deposits) were sequentially extracted for P. The distribution of P among organic and inorganic solid phases varied among the riparian soils and stream sediments. Across all 25 samples, the inorganic P (Pi) fractions followed the order: Fe bound Pi > Ca bound Pi > reductant soluble Pi > Al bound Pi > soluble and loosely bound Pi. For the organic (Po) fractions, the order was nonlabile Po > fulvic acid bound Po > humic acid bound Po > labile Po > moderately labile Po. The ranges of total P (TP), Mehlich-3 extractable P (P-M3), and ammonium oxalate extractable P (Pox) were 386-1,134, 5-85, and 60-823 mg kg-1, respectively. Among the sample groups, the highest concentrations of TP, P-M3, and Pox were found in the in-stream deposits. Total P was significantly correlated with Fe oxides, clay, and soil organic matter, especially in the bank and floodplain deposits. From these results, we can speculate that changes in land use within the riparian areas may, at least initially, have little effect on P loads in Walnut Creek.