Diversity of lake life is harmed by water pollution
LOE POOL (An Logh in Cornish) near Helston is not only a beautiful and mysterious place, but also a place of many rarities.
It's a perfect example of a ria, a drowned river valley, a process that began at the end of the last Ice Age about 10,000 to 12,000 years ago.
Although there's still debate as to when Loe Bar, at the sea end, was formed, what is not in dispute is Loe Pool's regional and national importance. It's the largest area of natural fresh water in Cornwall and its designations are impressive. It falls within the south coast/western section of the Cornwall Area of Outstanding Natural Beauty (AONB); it's designated a Site of Special Scientific Interest (SSSI) by Natural England; it's considered a classical geological conservation review site; and it's on the Penrose Estate, owned and managed by the National Trust. Loe Bar is a perfect and rare example of a shingle bar and of international geological importance in its own right.
But Loe Pool and its catchment also falls within a particular designation: a nitrate vulnerable zone.
NVZs were adopted by the European Union in 1991 to cover all land draining on to waters vulnerable to nitrate pollution or, to give it its scientific name, eutrophication. This occurs when the natural balance of a body of water is disturbed by the addition of excess ingredients not normally occurring. For example, fertilisers added to soils can then run off into waterways, adding large quantities of nitrates: hence NVZs.
Nitrates and phosphates are a cause for concern. Phosphates bind very strongly to the soil matrix and can enter the water when soil run-off occurs, while nitrates leach very easily when it rains. If they run off into a body of water it becomes hypoxic, or oxygen- depleted, and aquatic organisms suffer and die. At the last assessment in September, 2010, the water in Loe Pool was found to be in poor condition, unchanged from the previous assessment. Fertiliser run-off from agriculture was given as one cause, but research has confirmed sewage treatment works are the main contributors of phosphates and nitrates to the pool.
So why should we be worried about eutrophication? Nothing in nature works in isolation; everything is part of the food chain, there's no cause without effect and this is especially important in a protected and designated area such as Loe Pool. The algal blooms that occur at Loe Pool deplete the oxygen and shade out natural light, making it harder for life to survive. Both the pool and the bar provide habitat found nowhere else in Cornwall, with rare species of higher plants and many rare and local insect species. The area is also an important overwintering site to around 80 bird species.
In the past Loe Pool supported a luxurious growth of water plants, but the long history of metalliferous mining and more recent eutrophication has taken its toll. Today there are few plants in the lake itself besides the water lilies planted in Victorian times. A few rare species such as six-stamened waterwort are hanging on, hoping for cleaner water.
The shingle bar supports many local plant species such as yellow horned sea poppy. The sandhill rustic moth is a seldom-seen nocturnal species, and two specimens of an unknown sub-species, leechi, were discovered on the bar in 1974. It remains the only known population in the world, and is the subject of a policy in Cornwall's biodiversity action plan (BAP) and listed in the Red Data Book of Cornwall and the Isles of Scilly as in need of special protection.
Last week there was an article here on farming and how farmers were custodians of our AONB landscape and its biodiversity, yet they also have to carry out the vital role of providing the food we need. In order to do this they need recognition and support to carry out this difficult dual role.
The Loe Pool Catchment Forum, a grouping of organisations with an interest and a role to play in Loe Pool, is working to improve water quality in the catchment for the benefit of the pool and the local community and will write in a future column here about their work and how we can all play our part to bring Loe Pool back to a clean, clear body of water full of plants and wildlife.