Quantifying Phosphorus Content in Riparian Buffers of Different Land Use

Excess phosphorus (P) loading to freshwater systems can lead to eutrophication, resulting in a loss of ecosystem services. Lake Champlain has historically exhibited negative effects of eutrophication due to P overloading from non-point sources. Reducing P inputs to the Lake is critical, as lake-related tourism contributes nearly 4 billion dollars to the economies of Vermont, New York and Quebec each year. Riparian buffers help protect adjacent water bodies from runoff by sequestering sediment and excess nutrients. To better understand how P retention in riparian buffers is influenced by soil saturation and adjacent land use, we explored differences in P content between riparian buffers located in forested and agricultural watersheds. Within each land use type, we focused on two paired riparian buffers with contrasting soil saturation levels (one wet transect and one dry transect). At each of the four sites, soil pits were dug along a transect perpendicular to the streambank and were placed strategically to capture convergent and divergent landscape positions. Soil samples were collected from each horizon within 0-45cm of the soil profile. We measured soil test P, soluble P, degree of phosphorus saturation (DPS), and trace elements in each soil sample.

No significant differences in soil test P content were detected among the four riparian transects. In contrast, soluble P content varied significantly between the agricultural (median = 0.46 mg P/kg soil) and forested (median = 0.30 mg P/kg soil) transects. Degree of P saturation also differed significantly between the agricultural (median = 1.7%) and forested (median = 9.0%) transects. Linear regression analysis indicated that in the agricultural soils DPS levels greater than 20% may result in desorption of soluble P, subsequently generating P runoff. Our results suggest DPS and soluble P may be better indicators of potential P runoff than soil test P. Accurately quantifying P in riparian soils is necessary to evaluate their potential to store and transform nutrients that have potentially harmful consequences for Lake Champlain.