SHORT-TERM AND LONG-TERM EFFECTS OF HYDRO-RAKING ON THE TROPHIC LEVEL OF LAKE WAPALANNE AND POTENTIAL OF VETIVER GRASS FOR PHOSPHORUS REMOVAL

Similar to other natural and man-made lakes in New Jersey, Lake Wapalanne in the Stokes State Forest is suffering from eutrophication due to significant input of nutrients. The lake has two distinct lobes (southern and northern) that are interconnected by a channel. Over the past decade, the southern lobe became shallow and started suffering from massive algal blooms. Hydro-raking was performed in 2009 to remove aquatic vegetation and unconsolidated bottom debris from the southern lobe, resulting in partial dredging of lake sediments. Because of this, sediment bound phosphorus (P) was released back to water, promoting further algal growth. This study determined the short term (11 months) and long term effects (6 years) of hydro-raking on the trophic level of Lake Wapalanne, and also evaluated the potential of a fast-growing, high biomass grass, vetiver in removing P from lake water. Basic water quality parameters, such as pH (6.3-8.5), conductivity (37.8-47.3 µS), and dissolved oxygen (5.7-6.5) levels were also measured. Results indicated that based on P content, the southern lobe of Lake Wapalanne was eutrophic prior to hydro-raking (in 2009). After 11 months of hydro-raking (in 2010), total P contents of water collected from various sections of Lake Wapalanne were higher than the samples collected prior to hydro-raking, indicating eutrophication and super-eutrophication, resulting in further algal blooms. Inorganic algaecide was applied in 2010 to control the blooms. After 5 years of hydro-raking (in 2014), P contents of water samples revealed that the dissolved P migrated towards the northern lobe, consistent with the flow direction of the lake. Phosphorus data from water samples collected this year (2015) revealed that the entire lake has become eutrophic. Laboratory study is ongoing to determine the potential of vetiver grass in removing P from the lake water, which may indicate if the lake can be sustainably restored in the future via floating treatment wetlands of vetiver.