ABSTRACT

Lake Gaston, located on the border of Virginia and North Carolina, is colonized by several aquatic invasive species including hydrilla which cover over 15% of the lake. Hydrilla forms dense mats, and restricts swimming, boating, and suppresses property values. Hydrilla also displaces natural vegetation, reduces habitat quality for fish, provides breeding habitat for mosquitoes, impedes commercial navigation, reduces drainage and increases flooding, and blocks intakes for hydroelectric turbines and potable water. Few management tools are available for aquatic weeds. Proper selection and integration of management techniques requires accurate vegetation surveys. In Lake Gaston, private contractors are hired yearly to generate vegetation maps at a cost of $30,000 to $40,000. The accuracy of these maps could be increased or the cost of production decreased by utilizing trained volunteers. Volunteer scouts (Lake Gaston residents) were trained in the identification of seven aquatic plant species, (including hydrilla) and the use of handheld GPS units. Fourteen volunteers worked alone or in groups of two to scout weeds during the months of October and November. Scouts sampled in areas of their own choosing, and used their own boats (both motor boats and kayaks). Volunteers recorded GPS coordinates using a specialized computer program written by one of the volunteers. The scouts measured water clarity and depth, as well as presence or absence of hydrilla and 6 other aquatic weeds. Over 97 man-hours of labor were spent scouting an estimated 57 miles of shoreline (approximately 17% of total lakeshore) from at least 1,180 distinct sampling points. Data points were overlaid on existing topographic maps for relatively detailed documentation of hydrilla presence or absence in certain areas. Volunteers recorded the locations of floating mats of hydrilla, grass carp sightings, length of hydrilla shoots, whether the area had been treated with herbicides, and condition of the plants collected. Current efforts will be extended through 2008 with additional volunteers expected. Volunteers will be surveyed to determine time investment of each volunteer. The data collected from this research may serve as a complement (to ground-truth) data collected by the independent contractors. Future efforts could include assigning part of the lake to contractors in an effort to reduce scouting costs. It is also expected that the location of hydrilla growth could be tracked using the GPS data and comparing growth from year to year to determine long-term spread or control.