QUANTIFYING STREAM PHOSPHORUS DYNAMICS AND TOTAL SUSPENDED SEDIMENT EXPORT IN FORESTED WATERSHEDS IN VERMONT

Globally the quantity of reactive phosphorus (P) in soils, streams and groundwater has greatly increased throughout the 20^th and early 21^st centuries. This phenomenon is problematic in Vermont, evidenced by the repeated cyanobacteria blooms in shallow bays in Lake Champlain. While many studies have focused on P dynamics in agricultural watersheds, there is limited information on P dynamics in forested watersheds. Current remediation plans under the Lake Champlain TMDL call for substantial reductions in P loadings from forested areas of the basin. However, the lack of information and knowledge regarding forest P dynamics limits management and remediation plans. This study was conducted in three small forested watersheds, ranging in size from 2.5 to 8.3 square kilometers that have been managed under varying practices, including logging and maple sugaring. All three of the watersheds drain into Missisquoi Bay, a shallow bay in Lake Champlain that consistently has seasonal algal blooms. Streams were instrumented with pressure transducers to measure stage and a stream discharge rating curve was developed. Water samples were collected from May through November using ISCO Automated Samplers.A total of twenty storm events were captured, along with periodic baseflow sampling, and used to characterize P concentrations and calculate seasonal P loadings. Preliminary results indicate that there is a strong positive correlation between sediment concentration and total phosphorus concentrations (r² ranging from .69 to .90). Soluble reactive P was highest in the middle of the summer (~20 µg P/L), but relatively low throughout the sampling period. The ultimate goal of this project is to gain a better understanding of the variability of P and total suspended sediment outputs within forested catchments of Lake Champlain tributaries.