Aquatic systems disturbances

The primary pathway of Hg to aquatic systems is considered to be atmospheric transport and subsequent deposition, which has caused an accumulation of Hg in watershed soils (Mason, et al., 1994). Recent work has shown that watershed disturbance such as clear cutting results in the increased export of Hg from the watershed to aquatic systems (Porvari, et al., 2003) and others have found agricultural and urbanized land use to be important factors influencing Hg export (Fitzgibbon, et al., 2008 Mason Sullivan, 1998). Thus the recovery of aquatic systems from anthropogenic Hg may depend on watershed characteristics which will differ among watersheds. Therefore we compared time to recovery to watershed attributes (e.g., %urban, susceptibility to erosion, watershed to lake area ratio, etc...) to test the hypothesis that the rate of recovery from Hg enrichment is influenced by watershed controlled pathways and stressors. 

Bio-control using pathogens holds promise mostly in non-cropland situations because of the slow pace of control of weeds and the wider window for control as compared with the shorter window of the cropping season and associated disturbances under cropland situations. However, in aquatic systems they appear to be more realistic, due to the absence of such cropping barriers and enhanced mode of dispersal in water. Among the wetland weeds, Echinochloa crusgalli and Cyperus rotundas are being... 

Niemi GJ, DeVore P, Detenbeck N, Taylor D, Lima A, Pastor J, Yount JD, Naiman RJ. 1990. Overview of case studies on recovery of aquatic systems from disturbance. Environ Managment 14 571-587. 

Studies investigating the effects of pesticides on crustaceans should be of high priority. Crustaceans are very important consumers and prey in various aquatic systems and there are delicate relationships between crustacean plankton prey and fish predators in the pelagic zone that can and have been shown to be disturbed. It is known that pesticides are present in surface waters and it is especially urgent to study the effects of insecticides on freshwater species and species that are present in estuaries and coastal waters with high risks of contamination due to vicinity to the sources. In acute toxicity tests crustaceans were much more (often 10-times more) sensitive to insecticides than fish (Maltby et al. 2005), and some of the chemicals probably affect behaviors at very low concentrations. As there are very few studies done on pesticide effects on crustacean chemoreception it is not possible to compare their sensitivity with fish, but it is likely that there are differences. The few crustaceans studied concerning effects of copper indicate that they are less sensitive to the metal compared with fish. 

Hydropower use for electricity generation is responsible for a wide array of enviromnental disturbances to river systems. Over the past decades, aquatic science research has been successful in identifying a considerable number of relationships that exist between plant operation and ecosystem quality. This increase in scientific knowledge was, however, not matched by a corresponding reduction in environmental impacts stemming from hydropower. One of the major reasons for this situation is that political, economic, and social aspects are neglected in purely scientific assessments of environmental impacts. 

In view of mans inability to adapt to major environmental changes, pollution is equated with disturbance of ecological balance and loss of stability. Increasing the chemical diversity (number of components and phases) makes an equilibrium system more resistant toward external influences imposed on the system. In an ecosystem, its members are interlocked by various feedback loops (homeostasis) and thus adapted to coexistence for mutual advantage increased diversity makes the system less subject to perturbations and enhances its survival. Because various kinds of disturbance cause similar patterns of change in aquatic ecosystems and affect their stability in a predictable way, general measures of pollution control beyond those of waste treatment can be outlined which mitigate the conflict between resource exploitation and protection of natural waters. 

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