Apportionment of suspended sediment sources in an agricultural watershed using sediment fingerprinting

Abstract

Sediment fingerprinting techniques can provide valuable information on sources of suspended sediment to facilitate effective targeting of best management practices. Research was conducted in the Pleasant Valley watershed (50km2) in South Central Wisconsin to identify sources of suspended sediment during cropping season and snowmelt periods at a subwatershed scale. Results show that both stream banks and agriculture are important sources of suspended sediment. The contribution from agriculture and stream banks to suspended sediment at the watershed outlet ranged from 45 to 97% and from 3 to 47%, respectively. During periods of high sediment loading agriculture was the important source of suspended sediment at the majority of sites within this watershed, with the exception of snowmelt runoff, when stream banks were the dominant source of suspended sediment at the watershed outlet. The average annual erosion rates in croplands and pasture land-use determined from the Revised Universal Soil Loss Equation 2 (RUSLE 2) ranged from 0 to 0.00509tm−2yr−1, indicating significant variability among fields. Conservation practices in this watershed should be targeted to stream banks or agriculture (prioritize fields based on RUSLE 2 average annual erosion rates) depending on the dominant source of suspended sediment within a subwatershed. The results of this study show that both temporal and spatial variability in suspended sediment sources should be considered to develop management strategies and sampling only at the watershed outlet or capturing a few storms might not be sufficient to target locations for best management practices.