Inorganic and Organic Phosphorus in Sediments in the Walnut Creek Watershed of Central Iowa, USA

Rahutomo, Suroso; Kovar, JohnL.; Thompson, MichaelL.

Inorganic and Organic Phosphorus in Sediments in the Walnut Creek Watershed of Central Iowa, USA

2018

Rahutomo, Suroso | Kovar, JohnL. | Thompson, MichaelL.

The dynamics of phosphorus (P) reactions in stream water are important because of their potential to trigger eutrophication. This study aimed to explore the nature of P in sediments associated with Walnut Creek, Jasper County, Iowa. The Walnut Creek watershed supports row crop production, grazing, and riparian buffer zones. 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 collected near Walnut Creek (classified as bank, in-stream, and floodplain deposits) were sequentially extracted for P. 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 to 1134, 5 to 85, and 60 to 823 mg kg⁻¹, respectively. Among the sample groups, the highest concentrations of TP, P-M₃, and Pₒₓ were measured in in-stream deposits. Total P was significantly correlated with Fe oxides, clay, and soil organic matter, especially in the bank and floodplain deposits. Because of the potential release of P from these sediments, we can speculate that changes in land use within the riparian areas may, at least initially, have little direct effect on soluble or particulate P loads in Walnut Creek.

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