This study implemented the Universal Soil Loss Equation (USLE) utilizing Geographic Information Systems to assess soil erosion risk, plus the spatial correlation to the economic value of non-point pollution sources from the Rock River watershed, expecting small farms to pollute more due to lack of regulatory oversight. The study area drains extensive agricultural lands into Missisquoi Bay, a frequently eutrophicated segment of Lake Champlain, located between the state of Vermont, U.S.A and the province of Quebec, Canada. High phosphorous loads via sediment exacerbate algal blooms, which in turn diminishes recreational potential and degrades the drinking supply for over 200,000 residents. Data processing of USLE variables was performed in the form of raster layers. The rainfall-runoff factor was calculated from a twenty year mean annual precipitation data clipped to the study area as were as other factors. The topographic factors were derived from a digital elevation model. Estimation of the soil erodibility factor was based on soil properties recompiled from previous surveys by the National Resource Conservation Center. The land cover factor was estimated to site-specific conditions based on literature papers utilizing compatible National Land Cover Database indexes. The conservation factor was set to 1 due to lack of data.
Results/Conclusions
Annual sediment load totaled to a mean value of 28, 614 tons or a loading rate of 77.5 tons/ha, spatially situated on the steepest regions, and a mean loading value of 3.1 tons/ha*yr-1. Utilizing 11.2 tons/ha as the threshold for sustainable erosion, 368 ha or 4.02% of the study area, is at risk. Critical source areas (CSAs) for sediment loading were overlaid alongside total phosphorus load (TP) and property value (PV) data. When the median sediment loading values were compared to PVs, properties with prices of $2,981/acre are most likely to have highest sediment loads. The highest TP load for CSAs, was associated to properties of $1,097/acre, the lowest price group, but high TP rates could also be observed in the highest PV groups, which may be explained by low-price, marginal lands or high price, food-productive farmlands with excessive nutrient inputs. Further insight into other causes of erosion vulnerability are needed in order to determine whether small farms could have caused more erosion due to their reduced potential for investing in best management practices or due to the lack of regulatory enforcement. Future estimates of prime soil loss from cropland could be a powerful tool to incentivize soil conservation practices.