Gary O. Dick

Aquatic vegetation community structure response to hydrilla management with triploid grass carp, herbicide, and native vegetation planting

Abstract Schad AN, Dick GO. Aquatic vegetation community structure response to hydrilla management with triploid grass carp, herbicide, and native vegetation planting. Lake Reserve Manage. 34:417–425. To aid conservation managers conducting hydrilla (Hydrilla verticillata (L.f.) Royle) management, we evaluated changes in aquatic vegetation community structure and dominance in dioecious hydrilla-infested ponds by applying several management tools and monitoring vegetation changes on an annual basis over a 4 yr period. The study was conducted in fully vegetated (dioecious hydrilla and native macrophytes) 0.3 ha mesocosm ponds using 4 levels of triploid grass carp (Ctenopharyngodon idella Valenciennes) stocking densities (0–129 per vegetated hectare), a one-time second-year herbicide treatment to reduce standing biomass of hydrilla and other submersed aquatic vegetation (SAV), and native plantings to provide the basis for replacing hydrilla as it was controlled. Grass carp stocking density had an inverse relationship with coverage of total vegetation, hydrilla, volunteer SAV, and volunteer emergents. All vegetation categories recovered from the one-time herbicide application, although this was suppressed by higher densities of grass carp. Grass carp did not significantly affect planted growth forms (SAV, floating-leaved, and emergent), with increases in mean coverage in all treatments through time, although coverage was lowest at the highest grass carp density. Vegetation dominance shifted from hydrilla to native in both control and low grass carp density treatments, with most SAV eliminated from treatments stocked with more than 72 per hectare.

Secondary production and seasonal development of epiphytic Enallagma civile Hagen, 1861 (Odonata: Coenagrionidae) in a newly constructed urban wetland floodway ecosystem

ABSTRACT Secondary production and seasonal development of the damselfly Enallagma civile Hagen, 1861 were determined as part of an epiphytic macroinvertebrate study in the Dallas Floodway Extension Trinity River Project Lower Chain of Wetlands, Dallas, TX, USA. These wetlands were constructed to mitigate flooding of the Trinity River, but also provided quality wildlife habitat and removal of wastewater effluent contaminants. Variations in life history were observed between two macrophytes and three different wetlands of varying age, effluent source, and vegetation establishment. Mean annual production of E. civile was 1393 mg/m2/year, standing stock biomass was 1376 mg/m2/year, cohort production/biomass (P/B) ratio was 4.30/year, and annual P/B was 10.18/year. These values are in the upper range of known Odonata production values from a lentic system. Enallagma civile biomass growth rates were observed to be higher from populations on the better established macrophyte (Potamogeton nodosus Poiret, 1816) and in the longest established wetland.