Stream Corridor Soil Phosphorus Availability in a Forested-Agricultural Mixed Land Use Watershed

Abstract

Watershed land use affects nutrient and sediment export, particularly through streambank erosion, which can add to P export and contribute to eutrophication in downstream waterbodies. We characterized P of soils from four different land uses (32 sites) along streams in the Missisquoi River basin (Vermont, USA)-silage corn (Zea mays L.), hay meadow, emergent wetlands, and forest-and their corresponding streambanks. We measured total P (TP), pH 4.8 NH4-acetate P, degree of P saturation (DPS), and soluble P. The latter three measurements were used as predictors of potential P bioavailability. Forest soils were relatively low in TP, whereas soils in corn, hay, and wetland were elevated (>1000 mg kg−1). With the exception of forests, the TP of the corresponding streambanks of each land use was statistically significantly lower than in the interior of the land use, while still higher than those in forests, suggesting a possible influence of land use on its adjacent streambank. The pH 4.8 NH4-acetate P was low in nonagricultural land uses and all streambanks of different land uses, but higher than optimum for soils in cornfields and hayfields. The DPS averaged 36% in the cornfields, but <21% in all of the streambanks. Mean soluble P was 0.14 mg kg−1 for corn- and hay-associated streambanks with a DPS <10% but was as high as 3.2 mg kg−1 in the agricultural fields. The combination of low bioavailable P measurements indicates that most streambank soils are likely low contributors to P enrichment downstream. However, the elevated TP in some agricultural streambank soils suggests an accumulation of legacy P.