Norwegian Institute for Water Research, Gaustadalleen 21, 0349 Oslo, Norway.
Sci Total Environ. 2013 Feb 1;444:73-84. doi: 10.1016/j.scitotenv.2012.11.034. Epub 2012 Dec 23.
Eutrophication and acidification are among the major stressors on freshwater ecosystems in northern Europe and North America, but possible consequences of interactions between pH and nutrients on ecological status assessment and species richness patterns have not previously been assessed. Using data from 52 river sites throughout Norway, we investigated the combined effects of pH and nutrients on benthic algae assemblages, specifically 1) taxa-specific couplings between nutrient and acidity traits, 2) the degree of consistency between different biotic indices, separately for nutrients and acid conditions, 3) the impact of pH on nutrient indices and phosphorus on indices of acid conditions, and 4) the impact of pH and phosphorus supply on diatom and non-diatom taxon richness. We found that 1) acid-tolerant taxa are generally associated with nutrient-poor conditions, with only a few exceptions; this is probably more a consequence of habitat availability than reflecting true ecological niches; 2) correlation coefficients between nutrient indices and TP, as well as acid conditions indices and pH were barely affected when the confounding factor was removed; 3) the association of acid-tolerant taxa with nutrient-poor conditions means that the lowest possible nutrient index at a site, as indicated by benthic algae, is lower at acid than at circumneutral sites. Although this may be an artifact of the datasets from which taxa-specific indicator values were derived, it could lead to a drift in nutrient indices with recovery from acidification; 4) the response of non-diatom taxon richness follows a complex pattern with a synergistic interaction between nutrient supply and pH. In contrast, diatom richness follows a simple additive pattern; this suggests structural differences between diatoms and non-diatom benthic algae in their response to nutrient supply and pH; diatom taxon richness tended to increase with nutrient supply, while non-diatom richness decreased.
富营养化和酸化是北欧和北美淡水生态系统的主要压力因素之一，但 pH 值和养分之间相互作用对生态状况评估和物种丰富度模式的可能影响以前尚未得到评估。本研究使用来自挪威 52 个河流站点的数据，调查了 pH 值和养分对底栖藻类组合的综合影响，具体包括：1）养分和酸度特征之间的特定分类群耦合；2）分别针对养分和酸条件，不同生物指数之间的一致性程度；3）pH 值对养分指数和磷对酸条件指数的影响；4）pH 值和磷供应对硅藻和非硅藻分类丰富度的影响。研究结果表明：1）耐酸类群通常与贫营养条件相关，只有少数例外；这可能更多是由于栖息地的可用性，而不是反映真实的生态位；2）去除混杂因素后，养分指数与 TP、酸条件指数与 pH 值之间的相关系数几乎没有受到影响；3）耐酸类群与贫营养条件相关，这意味着底栖藻类指示的一个站点的最低可能养分指数在酸性条件下比在近中性条件下更低。尽管这可能是从分类特定指示值数据集中得出的一种假象，但随着酸化的恢复，养分指数可能会发生漂移；4）非硅藻分类群丰富度的响应呈现出复杂的模式，与养分供应和 pH 值之间存在协同相互作用。相比之下，硅藻丰富度遵循简单的加性模式；这表明硅藻和非硅藻底栖藻类在对养分供应和 pH 值的响应方面存在结构差异；硅藻分类群丰富度倾向于随养分供应的增加而增加，而非硅藻丰富度则减少。
