The efficacy and ecological impacts of herbicide and cutting regimes on the submerged plant communities of four British rivers. I. A comparison of management efficacies.
Abstract
In field trials in 4 UK rivers, the Coln, the Mouse Water, the Windrush and the Petteril, all of which supported macrophyte communities that included Ranunculus subgenus Batrachium the efficacies of management techniques were quantitatively evaluated by plant biomass sampling and mapping of permanent transects. Labour-intensive cutting treatment in two of the rivers removed most of the Ranunculus from the centres of the channels. In the Petteril, the cut was sufficiently late to prevent regrowth, but in the Windrush a significant regrowth was evident 6 weeks after the cut. Diquat-alginate was very effective in removing Ranunculus from the moderately calcareous Petteril and Mouse Water however the herbicide effects were significant only for the Petteril. Ranunculus plants were removed or damaged for considerable distances downstream of the point of herbicide application. Less susceptible species, such as filamentous algae and Potamogeton natans, showed herbicide damage only in the treated areas. Max. concn of diquat residues detected in these rivers exceeded 1.0 mg/litre for at least 40 min. The herbicide appeared to be ineffective in the Windrush, but in the Coln, of similar size and calcium content, a large proportion of the Ranunculus was removed. Differences in the plant species compositions, lengths of river treated, and water turbidity may have led to the differences in the efficacy of the herbicide. Adsorption and inactivation of diquat ions by suspended clay particles may have been responsible for the low concn and short persistence of diquat in the Windrush.