Patricia M. Dooris

Implications of lake augmentation on growth of hydrilla

Abstract The growth of hydrilla (Hydrilla verticillata Royle) in lake water, Floridan aquifer waten and mixtures of the two water samples was studied. The water was sampled from Lake Hobbs that has been previously identified as a lake that has not been augmented with water from the Floridan Aquifer. Evidence is presented that adding water from the deep wells enhances growth of hydrilla.

Aeration as a tool to improve water quality and reduce the growth of hydrilla

Abstract Aeration of artificial, model lake systems was studied as a tool to improve water quality and to control the growth of a nuisance aquatic weed, Hydrilla verticillata (L.F.) Royle, which has been recognized as a plant pest since the mid-1960s. Aeration decreased the growth of Hydrilla by 20% fresh weight and 18% dry weight on average after 21 days. The effect was due to the oxygenation of the water and not the mechanical effect of the bubbles, as verified by studies using pure nitrogen. Aeration also affected water quality. Inorganic carbon decreased; nitrate-nitrite-nitrogen decreased, more slowly in test systems than in control systems; dissolved oxygen increased to saturation within 24 h and pH increased 0.5–1.5 unit over the period of study. Phosphate-phosphorus concentration was unaffected. The concentrations of zinc, calcium and iron decreased as well. The effect of aeration upon Hydrilla growth appears to be correlated with a decrease of iron. After 7 days, iron concentrations decreased to less than 20 ppb. Iron toxicity is proposed as the mechanism responsible for creating a limiting condition for Hydrilla growth.

Hydrilla‐growth inhibiting substances from aqueous extracts of lake sediments. Effect of temperature.

Abstract Aqueous extracts of peat‐like sediments from Lake Starvation, Hillsborough County, Florida, inhibit the growth of Hydrilla verticillata in laboratory systems. The extracts were obtained by autoclaving sediment in water, and it may be that this process degrades the sediment. Evidence is presented that the total organic content of the extract obtained is not substantially different from solutions obtained at much lower temperatures. Therefore, the use of autoclaving in the preparation of sediment extract would appear to produce a material similar to that possibly produced in the environments of selected lakes.

Effect of hydrilla‐growth inhibiting extracts upon the growth of scenedesmus obliquus

Abstract The noxious, submersed aquatic plant Hydrilla verticillata has not thrived in certain lakes, including Lake Starvation, northwest Hillsborough County, Florida. Aqueous extracts of sediment from that lake were inhibiting the growth of hydrilla in the laboratory (Co, organic carbon, ca. 0.4 ppm). In contrast, similar concentrations of active fractions did not inhibit the growth of the freshwater alga S. obliquus, though at higher concentrations, cultures were stimulated (6–12 ppm, Co), and inhibition was noted for the highest concentration studied (18 ppm Co, 0.01 ppm Fe).