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Document Type

Research

Keywords

gully bank soil losses, gully bank phosphorus losses, loafing areas, riparian pasture management, soil phosphorus, stream bank soil losses, stream bank phosphorus losses

Abstract

Gully and stream banks can be major sources of sediment and nutrients to surface waters, both major water quality problems in the United States. Sediment may also carry phosphorus to surface waters, the primary limiting nutrient causing eutrophication. Overgrazing can induce gully and stream bank erosion by reducing vegetation cover that weakens bank soil resistance to stream water flow. This study examines stream and gully bank erosion adjacent to continuous (CP), rotational (RP) and intensive rotational (IP) pastures, grazed by beef cattle in southeast Iowa. Stream and gully bank erosion were measured by: a) surveying the extent of the severely eroding bank areas of the stream reaches running through the pasture management site and the gullies intersecting the specific stream reach and b) randomly establishing pin plots on subsets of the surveyed eroding stream and gully banks. Soil loss for the gullies and stream banks for each site were estimated as the product of the mean bank erosion rate, bulk density and the total severely eroding bank area. Total phosphorus (TP) losses from the gully and stream banks were estimated by multiplying the total soil loss by the TP concentration of the gully and stream bank soils. Soil samples were collected from the gully banks and bed, stream banks, loafing areas and surface riparian areas to estimate TP soil concentrations. The high TP concentrations of the loafing area soils compared to the other sampled locations and their proximity to the stream indicated that these areas could be significant sources of both sediment and TP to surface waters. The gully bank soil and TP losses ranked as follows: CP (207 Mg km-1 of soil; 70 kg km-1 of TP) > RP (89 Mg km-1 of soil; 40 kg km-1 of TP) > IP (28 Mg km-1 of soil; 12 kg km-1 of TP). The stream banks had a different ranking for soil losses: RP (323 Mg km-1 of soil) > CP (282 Mg km-1 of soil)> IP (170 Mg km-1 of soil) and TP losses: RP (129 kg km-1 of TP) >IP (86 kg km-1 of TP) > CP (83 kg km-1 of TP). It was expected that moving from CP, the traditional pasture management practice in Iowa, to RP and IP would reduce stream and gully bank erosion but this was not always the case. Assuming that the only sources of soil and TP losses in each site were stream and gully banks, then stream banks would contribute 76%, 85% and 86% of the total soil loss and 73%, 84% and 87% of the TP from the CP, RP and IP, respectively. These results indicate that stream banks were a more substantial source of sediment and TP in these streams than gully banks.

Publication Date

January-December 2009

Journal Title

Journal of the Iowa Academy of Science

Volume

116

Issue

1-4

First Page

1

Last Page

8

Copyright

© 2010 by the Iowa Academy of Science, Inc.

Language

EN

File Format

application/pdf