Evaluation of Potamogeton pectinatus as a tool for phosphorus removal

This study examined the potential of transplanted Potamogeton pectinatus (sago pondweed) to be used as an effective tool to remove phosphorus from a hypereutrophic lake. Field studies showed growing P. pectinatus from tubers in-lab and then transplanting into enclosed structures within Crystal Lake, Minnesota, promoted positive plant growth and phosphorus uptake. While planted within Crystal Lake, mean increases per plant were found in shoot length (11.21 mm SE±15.70), in root length (89.95 mm SE± 16.20), and in total dry weight (0.45 g SE±0.11). Furthermore, water depth was found to be significantly important (p>0.05) in promoting positive growth. Plants transplanted into shallower water had greater mean shoot and root lengths as well as a higher mean total dry weight than plants planted in deeper water. Overall, plants assimilated a mean of 6.67 mg (SE±1.77) of phosphorus per plant into plant tissues. Expanding on these data, modeling was conducted to see if P. pectinatus alone could be transplanted and reduce all current in-lake and incoming total phosphorus (TP) concentrations below the Western Cornbelt Ecoregion (WCBE) TP standard for lakes. Modeling showed that at best on an annual basis, P. pectinatus alone could only remove 10.4% of the in-lake water TP concentrations and 31.8% of the incoming TP load needed to be removed annually. If no more phosphorus were to enter Crystal Lake and water TP concentrations were to remain the same as they were at the time of sampling, it could take P. pectinatus up to 218 years to remove all in-lake phosphorus and up to 87 years to reduce incoming phosphorus loads to below the WCBE TP standard for lakes. Although P. pectinatus can be successfully transplanted and uptake phosphorus, using P. pectinatus alone to reduce phosphorus levels within Crystal Lake is not feasible. Potamogeton pecinatus should not be used as an individual method for reducing TP concentrations within a lake, but rater as a tool used in conjunction with other efforts to reduce TP levels within a lake.