Petrin Zlatko, Laudon Hjalmar, Malmqvist Björn
Department of Ecology and Environmental Science, Umeå University, 90187 Umeå, Sweden.
Sci Total Environ. 2008 May 15;394(2-3):321-30. doi: 10.1016/j.scitotenv.2008.01.055. Epub 2008 Mar 4.
Anthropogenic acidification caused by aerial deposition of acidifying substances is known to have detrimental effects on freshwater biota, including reductions in species diversity and ecosystem functioning. However, such impairment is not found in systems acidified to a similar extent by natural processes. A proposed explanation for this difference is that freshwater organisms have had far more time to evolve and adapt to natural than anthropogenic acidification. Thus, where acidity is natural, adaptation may account for diverse and functional communities. Here, we investigated whether adaptations--that were previously implied to occur on small spatial scales--may explain the species richness patterns on a much larger geographical scale, apply to ecological functioning, and are relevant in Sweden, where natural acidity is geologically relatively recent. Therefore, we compared differences in species diversity and ecosystem process rates between 24 acidic and circumneutral streams in northern Sweden, where acidity is natural, and southern Sweden, where acidity is largely anthropogenic. In agreement with our predictions, the difference in macroinvertebrate species richness between acidic and circumneutral streams was threefold larger in the region where acidity was anthropogenic than where it was natural, albeit marginally non-significantly. In contrast, no such trend was found for the rates of decomposition by microbes and leaf-feeding macroinvertebrates, possibly due to functional redundancy. The structure of species assemblages differed between acidic and circumneutral sites and between the regions. Our results agree with the notion that freshwater biota are adapted to natural acidity, but competing explanations including other differences in water chemistry and differences in the biogeographical colonization histories may also account for part of the observed patterns. Since naturally acidic environments similar to those in northern Sweden are widespread, we predict that diverse and functionally efficient freshwater communities that are well adapted to such conditions are more common than currently recognized.
由酸化物质的大气沉降导致的人为酸化已知会对淡水生物群产生有害影响，包括物种多样性和生态系统功能的降低。然而，在由自然过程酸化到类似程度的系统中并未发现这种损害。对此差异的一种解释是，淡水生物有更多时间进化并适应自然酸化而非人为酸化。因此，在酸度是自然形成的地方，适应性可能解释了多样化且功能健全的群落。在此，我们研究了先前被认为在小空间尺度上发生的适应性是否可以解释更大地理尺度上的物种丰富度模式，是否适用于生态功能，以及在瑞典是否相关，在瑞典自然酸度在地质上相对较新。因此，我们比较了瑞典北部24条酸性和近中性溪流（那里的酸度是自然形成的）与瑞典南部（那里的酸度主要是人为造成的）之间物种多样性和生态系统过程速率的差异。与我们的预测一致，在酸度是人为造成的地区，酸性和近中性溪流之间大型无脊椎动物物种丰富度的差异比酸度是自然形成的地区大三倍，尽管略微不显著。相比之下，微生物和以叶为食的大型无脊椎动物的分解速率未发现这种趋势，可能是由于功能冗余。酸性和近中性地点之间以及不同地区之间的物种组合结构不同。我们的结果与淡水生物群适应自然酸度的观点一致，但包括水化学的其他差异和生物地理殖民历史差异在内的其他解释也可能部分解释了观察到的模式。由于与瑞典北部类似的自然酸性环境很普遍，我们预测适应此类条件的多样化且功能高效的淡水群落比目前所认识的更为常见。
