Acid deposition, resulting from the atmospheric transport of acidifying compounds emitted during the combustion of fossil fuels, has historically resulted in stream acidification in many headwater streams in the eastern United States, including streams in Shenandoah National Park (SHEN). Though restrictions on these emissions were established by an amendment to the Clean Air Act in 1990, reductions in stream acidification have not been observed in all regions of SHEN due to variations in the geological composition of SHEN watersheds. Before the implementation of these restrictions, fish assemblages were strongly controlled by a stream’s acid neutralizing capacity (ANC), which is the ability of a watershed to buffer acid inputs. This study investigated changes in the relationship between fish assemblages and ANC within SHEN 21 years after implementation of more stringent restrictions on the emission of sulfur and nitrogen oxides in 1995. Results indicated that recovery trends in water chemistry were observed in some SHEN watersheds; however, fish species richness and total fish biomass continue to be influenced by the legacy of acid deposition in acid sensitive watersheds. Temporal trend analysis indicated little change in ANC within acid sensitive watersheds and minor decreases in stream sulfate concentrations. These findings indicate a persistent impact from previously deposited sulfur oxides and the continued influence of these compounds on fish assemblages within SHEN. Though no further loss of fish species, and in some cases, increases in species richness, suggest the early stages of recovery, many SHEN streams remain as susceptible to acidification as they were over two decades ago, highlighting the need for continued regulation of acidifying emissions and conservation efforts in headwater streams.

历史上，由于化石燃料燃烧过程中排放的酸化化合物在大气中的迁移，导致酸沉积，导致美国东部许多上游水流（包括谢南多厄国家公园（SHEN）的水流）被水流酸化。尽管1990年通过的《清洁空气法》修正案规定了对这些排放的限制，但是由于SHEN流域的地质组成变化，并未在SHEN的所有地区都观察到溪流酸化的降低。在实施这些限制之前，鱼群受到溪流的酸中和能力（ANC）的强烈控制，这是分水岭缓冲酸输入的能力。这项研究调查了在1995年实行更严格的硫和氮氧化物排放限制后，沉21年来鱼群与ANC之间关系的变化。结果表明，在某些SHEN流域中观察到水化学的恢复趋势。然而，鱼类种类的丰富度和鱼类总生物量继续受到酸敏感流域中酸沉积的影响。时间趋势分析表明，对酸敏感的流域内ANC几乎没有变化，而溪流中硫酸盐的浓度则略有下降。这些发现表明，先前沉积的硫氧化物会持续产生影响，并且这些化合物对SHEN内鱼类组合的持续影响。尽管鱼类种类没有进一步的损失，在某些情况下，鱼类种类的丰富度有所提高，