
Eurasian water milfoil (Myriophyllum spicatum) has been documented to negatively impact the ecosystem it invades due to its rapid growth rate and its ability to reproduce through fragmentation. It often outcompetes native vegetation and becomes dominant plant species, and further alters the ecosystem composition. This study investigated the impacts of invasive Eurasian water milfoil on benthic macroinvertebrate communities. Three lakes located in Stokes State Forest, Sussex County, New Jersey were selected for this study. Lake Ocquittunk (LO) is dominated with invasive Eurasian milfoil, Lake Wapalanne (LW) with native spiny coontail (Ceratophyllum echinatum), and Sawmill Pond (SP) with a mix of both native and introduced plant species. Ten sites were randomly selected in each lake. One bethic sample (16.5 cm x 16.0 cm) was collected from each site using an Eckman Drege. Macroinvertebrates from samples were identified and counted. LW was found to have the highest density of 600 macroinvertebrates, the highest taxonomic richness of 17 orders, and the highest Shannon-wiener diversity index value of 2.11. LO was found to have the lowest density of 167, the second highest amount of taxonomic groups of 14 orders, and the second highest Shannon-wiener diversity index value of 1.77. SP was recorded to have the second highest density of 453, the fewest taxonomic groups of 13 orders, and the lowest Shannon-wiener index value of 1.61. The results of this study indicated the invasive Eurasian water milfoil negatively impacted the benthic macroinvertebrate communities.
Lake Wapalanne is a manmade lake, approximately 5.4 hectares, fed primarily by a small stream, with controlled outflow at a broad-crested weir. Located at the eastern edge of the Appalachian Ridge and Valley physiographic province in northwestern New Jersey, Lake Wapalanne and its watershed lie within a forested landscape, surrounded by 6500 hectares of protected land. The lake’s location, small size, simplified inflow and outflow, and minimal external impacts provide a research environment ideal for studying present and future hydrologic lake dynamics. Quantifying the water budget for this small lake improves upon the existing understanding of regional surface water and groundwater interactions. Between July 13th and August 3rd we developed a hydrologic budget for Lake Wapalanne. We quantified precipitation, evapotranspiration, stream inflow and outflow, groundwater seepage, and lake water storage using direct and indirect methods. We installed a weather station to collect precipitation, evapotranspiration, and additional weather data used to calculate evaporation with the Penman-Shuttleworth equation. To develop a rating record between water depth and stream discharge, we installed water level loggers at the inlet and outlet streams and within the lake. To determine inlet and outlet discharge rates we used the midpoint method at 60% depth to measure velocity; we used a broad-crested weir equation to verify the outlet stream discharge. We measured groundwater using seepage meters and piezometers installed at various locations in the lake. To determine changes in lake water storage, we completed a bathymetry survey using a total station and used ArcGIS spatial analyst software to create relationships between depth, area, and volume. The water budget was computed in Excel with all variables quantified on a 15-minute interval.
Our initial results indicate that the average total precipitation and evapotranspiration were 0.2 cm/day and 0.4 cm/day respectively. For a more detailed report of lake evaporation see Jordan et al. 2011, this conference. Inflow and outflow discharges were 1290 and 2350 m3/day respectively, or, expressed as an equivalent depth over the lake's surface area, 2.4 and 4.3 cm/day. The change in lake storage was minimal. Interpolated groundwater discharge into the lake was 2.4 cm/day; however, preliminary groundwater results indicate lake water is seeping into the ground. Additional groundwater data and quantification of overland flow is necessary to refine the hydrologic budget for Lake Wapalanne. This study is part of an ongoing NSF Research Experience for Undergraduates (REU) project that encompasses additional topics of lake research, including algal, phosphorous and sediment analyses. These results and methods create a baseline water budget for future efforts to use and expand upon, and have water resource implications as nearby lakes and reservoirs provide drinking water to over five million people.
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