ABSTRACT

Pickerel Lake (Minnesota, USA) is a shallow, polymictic lake that has had eutrophication problems for decades. Although excess nutrient loading has been a problem in the past, the dominance of common carp (Cyprinus carpio) was considered to be a substantial factor driving and sustaining eutrophic conditions. To remove carp and restore the fish community, the lake was treated with rotenone in late 2009 and then restocked with native species. All water quality variables improved after carp removal, with mean values (May–Sep) for chlorophyll a, total phosphorus, and turbidity decreasing by 80% to 93% and Secchi disk transparency increasing nearly 600% when comparing means of pre- to post-treatment years. Macrophyte coverage also improved, from means of 4.6% before treatment to 90% after treatment, indicating a shift from an algal- to a macrophyte-dominated system. Sediment phosphorus (P) storage increased significantly after carp removal as well, with labile (releasable) forms of P increasing in the upper 10 cm of sediment in all cores (n = 7). The decrease in water column P equaled the increase in labile sediment P forms after treatment, indicating carp were a key driver of P transport from sediment to water. The results of this study indicate that an ecological (i.e., both abiotic and biotic) approach is needed when managing eutrophic lakes because management of nutrients alone will not likely be adequate to restore water quality in systems dominated by carp or other large benthic feeding fish.

摘要

皮克雷尔湖（美国明尼苏达州）是一个浅水混合湖，几十年来一直存在富营养化问题。尽管过去营养过剩一直是一个问题，但鲤鱼（Cyprinus carpio）的优势被认为是驱动和维持富营养化状况的重要因素。为了去除鲤鱼并恢复鱼类群落，该湖于 2009 年底用鱼藤酮处理，然后用本地物种重新放养。去除鲤鱼后，所有水质变量均得到改善，叶绿素a 的平均值（5 月至 9 月）, 总磷和浊度下降 80% 至 93% 和 Secchi 圆盘透明度增加近 600% 与前后处理年的平均值相比。大型植物覆盖率也有所提高，从处理前的 4.6% 提高到处理后的 90%，表明从藻类到大型植物主导系统的转变。去除鲤鱼后沉积物磷 (P) 的储存量也显着增加，所有岩心 ( n = 7)。水柱 P 的减少等于处理后不稳定沉积物 P 形式的增加，表明鲤鱼是 P 从沉积物向水中运输的关键驱动力。这项研究的结果表明，在管理富营养化湖泊时需要采用生态（即非生物和生物）方法，因为仅管理养分可能不足以恢复以鲤鱼或其他大型底栖鱼类为主的系统的水质。