School of Life Sciences, Arizona State University, Tempe, Arizona 85287, USA.
Ecology. 2009 Nov;90(11):3062-73. doi: 10.1890/08-1742.1.
Atmospheric nitrogen (N) deposition to lakes and watersheds has been increasing steadily due to various anthropogenic activities. Because such anthropogenic N is widely distributed, even lakes relatively removed from direct human disturbance are potentially impacted. However, the effects of increased atmospheric N deposition on lakes are not well documented. We examined phytoplankton biomass, the absolute and relative abundance of limiting nutrients (N and phosphorus [P]), and phytoplankton nutrient limitation in alpine lakes of the Rocky Mountains of Colorado (USA) receiving elevated (> 6 kg N x ha(-1) x yr(-1)) or low (< 2 kg N x ha(-1) x yr(-1)) levels of atmospheric N deposition. High-deposition lakes had higher NO3-N and total N concentrations and higher total N : total P ratios. Concentrations of chlorophyll and seston carbon (C) were 2-2.5 times higher in high-deposition relative to low-deposition lakes, while high-deposition lakes also had higher seston C:N and C:P (but not N:P) ratios. Short-term enrichment bioassays indicated a qualitative shift in the nature of phytoplankton nutrient limitation due to N deposition, as high-deposition lakes had an increased frequency of primary P limitation and a decreased frequency and magnitude of response to N and to combined N and P enrichment. Thus elevated atmospheric N deposition appears to have shifted nutrient supply from a relatively balanced but predominantly N-deficient regime to a more consistently P-limited regime in Colorado alpine lakes. This adds to accumulating evidence that sustained N deposition may have important effects on lake phytoplankton communities and plankton-based food webs by shifting the quantitative and qualitative nature of nutrient limitation.
由于各种人为活动，大气氮（N）沉积到湖泊和流域的量一直在稳步增加。由于这种人为 N 广泛分布，即使是远离直接人为干扰的湖泊也可能受到影响。然而，增加的大气 N 沉积对湖泊的影响并没有得到很好的记录。我们研究了科罗拉多落矶山脉高山湖泊中的浮游植物生物量、限制养分（N 和磷[P]）的绝对和相对丰度以及浮游植物的养分限制，这些湖泊接受了较高（> 6 kg N x ha(-1) x yr(-1)）或较低（< 2 kg N x ha(-1) x yr(-1)）水平的大气 N 沉积。高沉积湖泊的 NO3-N 和总 N 浓度以及总 N：总 P 比值较高。与低沉积湖泊相比，高沉积湖泊的叶绿素和悬浮物碳（C）浓度高 2-2.5 倍，而高沉积湖泊的悬浮物 C:N 和 C:P（但不是 N:P）比值也较高。短期富营养化生物测定表明，由于 N 沉积，浮游植物养分限制的性质发生了定性转变，高沉积湖泊中初级 P 限制的频率增加，而对 N 和 N 和 P 联合富化的响应的频率和幅度降低。因此，大气 N 沉降的增加似乎已经将养分供应从相对平衡但主要是 N 缺乏的状态转变为科罗拉多高山湖泊中更一致的 P 限制状态。这增加了越来越多的证据表明，持续的 N 沉积可能通过改变养分限制的数量和质量性质，对湖泊浮游植物群落和以浮游生物为基础的食物网产生重要影响。
