May Linda, Spears Bryan M, Dudley Bernard J, Hatton-Ellis Tristan W
Centre for Ecology & Hydrology, Bush Estate, Penicuik, Midlothian, Scotland, UK EH26 0QB.
J Environ Monit. 2010 Jan;12(1):338-46. doi: 10.1039/b912827a. Epub 2009 Oct 19.
Llangorse Lake is the largest natural lake in South Wales, UK, and is of European conservation importance. The site has a long history of eutrophication problems and, in recent years, significant efforts have been made to meet water quality restoration targets at this site by reducing the input of phosphorus (P) from external sources. Although the lake has improved substantially in quality since the late 1970s, it is still not meeting its ecological targets. Phosphorus concentrations have remained high and there has been little reduction in algal biomass. Management decisions to reduce P input were originally based on the widely held assumption that shallow lakes are P-limited in summer. However, this study clearly shows that this is not always the case; Llangorse Lake, at least, is strongly nitrogen (N) limited over the summer months. As a result, bio-available P released from the sediments cannot be used by the phytoplankton population. So, it accumulates in the water column, causing very high concentrations to occur in late summer. This puts the lake at very high risk of developing algal blooms when N availability increases, usually in early autumn. The study also found that the hydrology of the lake was strongly affected by sub-surface flow. This suggested that nutrients and water could be delivered to the lake from areas beyond the topographically defined surface water catchment. These findings have widespread implications for the successful management of external inputs to lakes, which currently tends to focus on management of the surface water catchment only. The results are discussed in relation to the restoration and management of nitrogen-limited lakes, and of those that are significantly affected by sub-surface flow.
兰戈斯湖是英国南威尔士最大的天然湖泊，具有欧洲层面的保护意义。该湖长期存在富营养化问题，近年来，人们为实现该湖水质恢复目标付出了巨大努力，通过减少外部磷（P）的输入来改善水质。尽管自20世纪70年代末以来，该湖水质已有显著改善，但仍未达到其生态目标。磷浓度依然很高，藻类生物量几乎没有减少。最初，减少磷输入的管理决策是基于一个广泛存在的假设，即浅水湖泊在夏季受磷限制。然而，本研究清楚地表明情况并非总是如此；至少兰戈斯湖在夏季的几个月里严重受氮（N）限制。因此，沉积物中释放的生物可利用磷无法被浮游植物群落利用。于是，它在水柱中积累，导致夏末时浓度极高。当氮的可利用性增加时（通常在初秋），这使该湖极易出现藻华。该研究还发现，该湖的水文状况受到地下水流的强烈影响。这表明营养物质和水可能从地形界定的地表水集水区以外的区域输送到该湖。这些发现对湖泊外部输入的成功管理具有广泛影响，目前湖泊外部输入管理往往只侧重于地表水集水区的管理。本文结合氮限制湖泊以及受地下水流显著影响的湖泊的恢复和管理对研究结果进行了讨论。
