Assessing the responses of aquatic macrophytes to the application of a lanthanum modified bentonite clay, at Loch Flemington, Scotland, UK

Published source details Gunn I.D.M., Meis S., Maberly S.C. & Spears B.M. (2014) Assessing the responses of aquatic macrophytes to the application of a lanthanum modified bentonite clay, at Loch Flemington, Scotland, UK. Hydrobiologia, 737, 309-320.
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Summary

Action: Add chemicals to reduce nutrient levels

A before-and-after study in 2009–2011 of a shallow lake in Scotland, UK (Gunn et al. 2014) reported that adding Phoslock® to reduce the amount of phosphorous in the water increased the overall coverage of submerged vegetation and the abundance of characteristic species, but had no clear effect on submerged macrophyte richness. Results summarized for this study are not based on assessments of statistical significance. In the two years after intervention, submerged vegetation covered 80% of the lake bed (vs 30–40% in the year before). This increase was linked to a reduction in phytoplankton abundance (before: 51 µg chl a/L; after: 12–25 µg chl a/L) and an increase in the maximum depth at which submerged vegetation could grow (before: 1.2–1.8 m; after: 1.9–2.0 m). The number of submerged macrophyte species in the lake did not clearly change over time. This was true overall (before: 12; after: 11–12 species) and for species characteristic of the natural target community (before: 4; after: 3 species). However, the abundance of the characteristic species increased: they were present at only 16% of survey points before intervention, but 28–36% after. The study also reports data on the abundance of individual macrophyte species. For example, the invasive Canadian waterweed Elodea canadensis was the most common species both before (at 62% of survey points) and after (51–52%) intervention. Methods: In March 2010, Phoslock® (25 tonnes) was added to Loch Flemington (15 ha, maximum depth 2.9 m) to address excessive release of phosphorous from the lake sediments. Nutrient levels had been elevated for several decades. Vegetation was surveyed in summer before (2009) and after (2010–2011) intervention: around the strandline, on foot in wadeable areas, and with a boat. The original paper also includes historical data for some metrics (not included in this summary).

Action: Use cutting/mowing to control problematic plants

A replicated study in 2010 in a shallow lake in Scotland, UK (Gunn et al. 2014) reported that clear-cut patches of Canadian waterweed Elodea canadensis were not colonized by any other macrophyte species within one growing season. Canadian waterweed abundance did remain significantly lower in clear-cut patches (6–38% volume inhabited) than uncut plots (37–71% volume inhabited). Other macrophyte species were present elsewhere in the lake. Methods: Ten 4-m² plots were established on the bottom of Loch Flemington, in patches of Canadian waterweed (≤2 m deep). In summer 2010, a diver cut and removed Canadian waterweed from five of the plots. The other five plots were left undisturbed. The plots were surveyed until October 2010, to identify any plant species other than Canadian waterweed and visually estimate the volume of submerged vegetation.