| Popis: |
Lough Doon is a dual basin lake in the west of Ireland, split into an upper and lower basin that are morphometrically and physiochemically similar. Zebra mussels [Dreissena polymorpha (Pallas, 1771)] were introduced in the lower basin in 1998 and are now well established there. A survey in July 2007 involving scuba dive transects and dredging revealed a population of 5.5 × 10 8 zebra mussels (4.9 × 10 5 kg) in the lower basin, while just 3 zebra mussels were recorded in the upper basin. To assess the effects of Dreissena infestation on suspended solids, algal production and nutrient concentrations, near-surface water samples from Lough Doon were analysed from January−July 2007 (n = 12) for selected chemical and biological parameters. Sampling revealed marked differences in seston load between the two basins, with the infested lower basin exhibiting significantly reduced concentrations of suspended solids, chlorophyll-a and phytoplankton biovolumes and, conversely, greater Secchi transparency. Total phosphorus concentrations were lower in the lower basin but concentrations of ammonium and, particularly, nitrate were significantly higher. Inter-basin differences in Lough Doon mirror the post-invasion changes observed in other, larger European and North American lakes and reflect the effectiveness of coupled filter feeding-excretion by zebra mussels in reducing seston load and converting particulate nutrients into soluble forms. The data provide initial evidence that modest zebra mussel populations can significantly alter water chemistry in a small well-mixed lough, with implications for water quality management as the zebra mussel continues its rapid range extension in Ireland. |
