Williamson Craig E, Overholt Erin P, Pilla Rachel M, Leach Taylor H, Brentrup Jennifer A, Knoll Lesley B, Mette Elizabeth M, Moeller Robert E
Department of Biology, Miami University, Oxford, OH 45056, USA.
Lacawac Sanctuary, Lake Ariel, PA 18436, USA.
Sci Rep. 2015 Dec 22;5:18666. doi: 10.1038/srep18666.
Increases in terrestrially-derived dissolved organic matter (DOM) have led to the browning of inland waters across regions of northeastern North America and Europe. Short-term experimental and comparative studies highlight the important ecological consequences of browning. These range from transparency-induced increases in thermal stratification and oxygen (O2) depletion to changes in pelagic food web structure and alteration of the important role of inland waters in the global carbon cycle. However, multi-decadal studies that document the net ecological consequences of long-term browning are lacking. Here we show that browning over a 27 year period in two lakes of differing transparency resulted in fundamental changes in vertical habitat gradients and food web structure, and that these responses were stronger in the more transparent lake. Surface water temperatures increased by 2-3 °C in both lakes in the absence of any changes in air temperature. Water transparency to ultraviolet (UV) radiation showed a fivefold decrease in the more transparent lake. The primary zooplankton grazers decreased, and in the more transparent lake were largely replaced by a two trophic level zooplankton community. These findings provide new insights into the net effects of the complex and contrasting mechanisms that underlie the ecosystem consequences of browning.
源自陆地的溶解有机物质（DOM）增加，导致北美东北部和欧洲各地区内陆水域褐变。短期实验和比较研究突出了褐变的重要生态后果。这些后果包括透明度导致的热分层增加和氧气（O2）消耗，以及远洋食物网结构的变化和内陆水域在全球碳循环中重要作用的改变。然而，缺乏记录长期褐变净生态后果的数十年研究。在此，我们表明，在两个透明度不同的湖泊中，27年的褐变导致了垂直栖息地梯度和食物网结构的根本变化，而且这些反应在透明度较高的湖泊中更为强烈。在气温没有任何变化的情况下，两个湖泊的地表水温度都升高了2-3摄氏度。透明度较高的湖泊对紫外线（UV）辐射的透明度下降了五倍。主要的浮游动物食草动物减少，在透明度较高的湖泊中，主要被一个两级浮游动物群落所取代。这些发现为构成褐变生态系统后果基础的复杂且相互矛盾的机制的净效应提供了新的见解。
