The efficacy and ecological impacts of the management of submerged vegetation in flowing water

Fox, Alison Mary (1987) The efficacy and ecological impacts of the management of submerged vegetation in flowing water. PhD thesis, University of Glasgow.

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Freshwater macrophytes are an essential component of a lotic ecosystem. In large quantities they can cause problems in watercourses, by increasing the risks of flooding and obstructing fishing. The rapidly-acting, contact herbicide diquat has been formulated with sodium alginate to produce a viscous aquatic herbicide which may be used for specific placement in static and flowing water. Factors which influence the efficacy of diquat-alginate and the ecological consequences of its use, have been studied using three approaches. 1) Small-scale laboratory experiments were used to investigate the effects of: Herbicide exposure period Calcium concentration Water temperature on the efficacy of the herbicide. Increased concentrations of calcium (100-300mg l-1) reduced the activity of the herbicide. 2) Field trials to compare watercourse management by use of diquat-alginate and weed cutting, were carried out in four rivers and a canal. The herbicide was very effective in removing Ranunculus in the swiftly-flowing, moderately calcareous (60-80mg l-1) and shallow R. Petteril and Mouse Water. Plants were removed,or damaged, for considerable distances downstream of the point of herbicide application. Less susceptible species, such as filamentous algae, Potamogeton natans and Sparganium emersum, only showed localised damage. 3) Beds of Ranunculus were established and grown over-winter in large-scale recirculating channels. Two herbicide trials were carried out in the summer, with diquat-alginate directly applied to half of one channel. In the first trial the loss of Ranunculus from the untreated channel was almost as great as from the one treated with diquat-alginate at 0.51 100m-2 , but the percentage of decayed tissue was significantly less. Blooms of filamentous and blue-green algae in the untreated channel probably caused mechanical damage to the Ranunculus. The algae were regularly removed in the second trial and the herbicide (1.01 100m-2 ) was very effective in reducing the biomass of Ranunculus. Directly treated plants were damaged more quickly than those receiving an indirect dose of diquat residues. The removal of an inert solute from the channel, by dilution, was modelled and tested. Diquat residues showed an initially greater loss from the channel than would have been predicted by dilution alone. This would have been due to uptake and adsorption by plants and other substrates, and the incomplete release of diquat ions from the alginate. After four hours the delayed release of diquat resulted in a slower loss rate than predicted by dilution. The macroinvertebrates on the Ranunculus were not directly affected by the herbicide. There was no evidence that the diurnal fluctuations of chemical parameters, such as pH and dissolved oxygen concentrations, were influenced by the decay of herbicide treated Ranunculus plants. The remaining algae probably buffered any effects that decaying macrophytes might have been expected to have on the water chemistry.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Ecology, Water resources management
Date of Award: 1987
Depositing User: Enlighten Team
Unique ID: glathesis:1987-76629
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 14:01
Last Modified: 19 Nov 2019 14:01

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