Riparian Land-use Impacts on Stream Bank Soil and Phosphorus Loss via Surface Runoff.
Mustafa Tufekcioglu1, Richard Schultz2, Thomas Isenhart2, George Zaimes3, and James R. Rusell Sr.1. (1) Iowa State Univ, Ames, IA 50011, (2) Iowa State Univ, Dept. of Natl Res. Ecology & Management, Ames, IA 50011-3221, (3) Univ of Arizona, School of Natural Resources, 310 Bio Sciences East, Tucson, AZ 85721
Overland flow is a major pathway of sediment and phosphorus transport to surface waters. We studied the impacts of stocking densities (cow-calf pair ha-1) on the amounts of sediment and phosphorus in surface runoff derived from stream bank critical source areas (CSA). Fifty-four rainfall simulations were conducted on stream-side loafing areas, stream access points (CSA) and other lengths of stream banks in central, northeast, and southeast Iowa. Runoff samples were analyzed for suspended sediment and total phosphorus. Soil bulk density and antecedent soil moisture samples were collected around rainfall simulation plots to identify differences in compaction, infiltration and surface runoff between stocking densities. Suspended sediment and total P from access and loafing areas within 15 m wide strips on both side of the stream, accounted for up to 72% (86 kg ha-1) and 55% (78g ha-1) of total sediment and phosphorus, respectively, even though they accounted for only 2.7% of the total area in the 15 m wide strips. The other 97.3% of the area contributed 45% (64 g ha-1) of the total P. Significant correlations were found between stocking densities and both suspended sediment and total P loss suggesting that low stocking densities can reduce sediment and total P export to streams from the CSAs. However, the results also suggest that riparian areas are inherently attractive corridors for cattle because they provide good forage and areas of shade that regardless of stocking densities still show significant negative impacts on sediment and total P transport to streams. From an environmental perspective, the most effective way to reduce sediment and total P loads from these areas would be to restrict animal entrance to the channel with fencing.