By Bethany Rossiter
Higher than normal temperatures experienced earlier this year, may have contributed to the return of blanket weed on parts of Loe Pool this summer. The largest area of this blanket weed has been observed in Carminowe Creek, with it blanketing the rocks on the lake bed, and growing up to 20m from the shoreline. Although, it was not the more toxic blue-green algae, that was originally feared; the current trend of increasing temperatures, resulting from climate change, may contribute to the increase in the chances of the toxic algae from returning. However, whilst blanket weed doesn’t pose any health risks to the public or livestock around the pool, it could result in issues related to eutrophication.
When a body of water starts to receive too much nutrients, in the form of nitrates and phosphates, some plant species, such as algaes and blanket weed, will start to grow too much and can take over the lake. The process of an increase in nutrient levels of water is referred to as eutrophication(1).
Eutrophication, and the resulting growth in blanket weed, can make it very hard for aquatic species to be able to reach the surface of the water to gain oxygen(1). It can also act like a net, restricting the movement of larger fish species, as well causing the deoxygenation (removal of oxygen) of the lake as the blanket weed dies and begins to decompose(1).
Management of this accumulation of blanket weed can be tackled in two main ways: removing the actual blanket weed from Loe Pool, and treating the cause of the mass growth of it in the first place.
Removal of the blanket weed can be done by hand- through raking the majority of the weed out of the pool, using weed grappling hooks, or loading it into a boat- to remove material harder to reach from shore. Some factors should be taken into consideration whilst this work as carried out such as; how much nutrients will be removed from the system in the process, as well as how to reduce the risk of killing the small invertebrate nymphs, small amphibians or fish that may have been living within the weed. To give these creatures a chance to return to the pool, the weed should be left on the shoreline.
Whilst the above will solve the problem for now, the best way to prevent the return of blanket weed or the other toxic forms of algae from returning in the future, is to try to reduce the inputs of phosphates and nitrates into the Cober catchment. Efforts to do so have been underway in the upper Cober and sometimes the lower Cober as well; and will continue to make progress in improving agricultural methods and reducing the run off from the surrounding farms into the river Cober. More information and research into this can be found here.
Field Studies Council (FSC): Life in Freshwater, Pollution in Lentic Waters, website accessed 15th August 2019,<https://www.lifeinfreshwater.org.uk/Web%20pages/ponds/Pollution.htm>