Modeling phosphorus sequestration and release in an Upper Klamath Basin wetland

Graduation date: 2012Upper Klamath Lake (UKL) and Agency Lake (AL) in southern Oregon are both hypereutrophic, in large part due to natural and anthropogenic loading of phosphorus (P), resulting in annual blooms of blue-green algae. Reduction of P loading to the lake is considered crucial to reduce the blue-green algae blooms, maintain water quality, and increase the fish populations within the lake. Restoration of fringe wetlands is one potential way to reduce external P loading to the lake. However, upon the initial period of flooding, restored wetlands have been found to also be a source of P into the lake, as a result of P resuspension due to years of soil disturbance.\ud We adapted a mass balance model of the biological P uptake and release to examine how P wetland dynamics change over the course of a year in restored wetlands in the Upper Klamath Basin. Our analyses focused on 1) comparing the P release and sequestration processes over each season, 2) examining whether wetlands around the lakes act as a net source or sink of P to UKL, 3) investigating wetland management strategies to determine if there is any one that is most successful at sequestering P, and 4) if release and sequestration of P in restored wetlands contribute to the P dynamics of the broader ecosystem in the UKL.\ud Results from this model indicate resuspension of P in the wetlands is high throughout the year, yet outflow only occurs during the first 16 days of the summer, and macrophyte uptake and sedimentation of P are most important in sequestering P.\ud Additionally, our findings indicate that two of the modeled management strategies are successful at preventing P from reaching the lakes, and that wetlands around the lake act as a net sink of P to UKL over time. However, the reduction or termination of external loading is not likely to reduce the algal blooms in the lakes, as the amount of P recycled from the lake sediments each year far exceeds the capabilities of the current wetlands