In the last year the Aquatic Plant Management Group has expanded its’ interest in basic research, trying to understand what are the mechanisms involved in the spread of invasive species and weeds and to the evaluate the different methods of control. Both approaches are essential in order to obtain the best results against these species at the lowest environmental and economic costs. Some of the biological research has focused on the effects of aquatic plant management on stream metabolism. This work was carried out at CEH’s recently acquired experimental area (the Lambourn Observatory) at Boxford. During the course of weed cutting in the summer months, the primary in-stream production was compared before and after. The preliminary results show a decrease in the process of gross production and respiration, but an increase in net production, with a change from the heterotrophic to autotrophic. The outcome will be elaborated upon during the presentation. We have also been looking at the relationship between nutrients and biomass in Floating pennywort (Hydrocotyle ranunculoides), which has now been reported in around 150 sites in the southern England and south Wales. This study was undertaken at the Pevensey Levels and the overall results show that the biomass of the plants is positively correlated with high levels of nutrients; meanwhile, the root length and the ratio between above and below biomass decrease. Concerning chemical control we have continued with experiments in Witham 4th and Black Sluice IDB areas on the impacts of the herbicide diquat, mentioned previously in this meeting. This year it has been observed that dissolved oxygen declined for a period of about two weeks, which was also the case last year, recovering but never reaching the initial level. Given that diquat and other herbicides are being withdrawn, however, we are not intending to focus on the impact of chemical controls on non-target species, and will instead be looking at alternative herbicides to take their place
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