The effects of vegetation removal by grass carp and herbicides on the water chemistry of four Florida lakes

Abstract

1. Four lakes in central Florida each received a different weed control treatment consisting of herbicide and/or different stocking ratios of grass carp {Clenopharyrigodo/i idella Val.)-2. Submersed vegetation was eliminated by grass carp within 6 months In Lake Orienta and within 14 months in Clear Lake. Because Little Lake Fairview. treated with herbicide and a smaller stocking ratio of grass carp, retained abundant vegetation levels over the first two study years, grass carp which had been introduced initially were replaced with a greater number of fish at the beginning of the third year. Submersed vegetation was subsequently eliminated in this lake within 10 tnonths. Aquatic vegetation was reduced but not eliminated in Lake Mann which was treated with herbicide only.3. Where macrophytes were removed there tended to be increased bottom dissolved oxygen, higher and more stable total alkalinity values, increased turbidity, lowered transparency,, higher specific conductivity and increased chlorophyll levels. Significant increases in pH were probably due lo low water levels resulting from a severe drought rather than weed control. Low water also affected specific conductivity. Annual means for nutrients did not differ significantly between years in the four lakes.

Biology and management of grass carp (Ctenopharyngodon idella, Cyprinidae) for vegetation control: a North American perspective

“…Alkalinity and chlorophyll a values increased significantly after stocking, while Secchi disc readings declined as a result of an increased algal standing crop. Small et al (1985) obtained similar results with respect to alkalinity, chlorophyll a, turbidity and transparency after grass carp introduction in four central Florida lakes. Maceina et al (1992) reported that 1 year after grass carp introductions in Lake Conroe, Texas, Secchi disc readings declined from 1.5 m to 1.0 m (p < 0.05).…”

Limnological changes in a pond ecosystem caused by grass carp (Ctenopharyngodon idella Val.) low stocking density

“…g. and Cer. d. ( Most of the significant changes in water chemistry were reported from long-lasting experiments in American lakes (Mitzner, 1978;Small et al, 1985;Maceina et al, 1992) or from the Danube River branch (Tomajka, 1995), especially following the total eradication of macrophytes. Studies dealing with indirect changes in water bodies after grass carp stocking are usually complicated by problems with experimental design mentioned in the introduction.…”

“…In spite of the extensive use of grass carp for controlling the aquatic macrophytes, most of the experiments studying indirect consequences following from grass carp stocking compared a few ponds/lakes stocked with grass carp with ponds/ lakes without fish before and after they were stocked with grass carp (Fowler and Robson, 1978;Lembi et al, 1978;Mitzner, 1978;Small et al, 1985;Maceina et al, 1992;Kirkagac and Demir, 2004). None of the studies used real control pond(s) which would indicate changes both in space (the initial difference between the ponds chosen for stocking with grass carp and control pond(s)) and in time, caused especially by weather, water level fluctuations or fish stock of other fish in all ponds.…”

Management, Operation and Maintenance of Irrigation and Drainage Systems

“…This is how this fish obtained the name "grass carp" (Sutton et al 1987). Numerous studies have shown, with the exception of overstocking and cleaning out all vegetative cover of other desirable fish, grass carp do not adversely impact the ecology of a water system (Leslie and Kobylinski 1985;Chapman et al 1987;Small et al 1985;Mitchell et al 1984;and Canfield et al 1983).…”