The Catskill Mountains have been adversely impacted by decades of acid deposition, however, since the early 1990s, levels have decreased sharply as a result of decreases in emissions of sulfur dioxide and nitrogen oxides. This study examines trends in acid deposition, stream-water chemistry, and soil chemistry in the southeastern Catskill Mountains. We measured significant reductions in acid deposition and improvement in stream-water quality in 5 streams included in this study from 1992 to 2014. The largest, most significant trends were for sulfate (SO42−) concentrations (mean trend of −2.5 μeq L−1 yr−1); hydrogen ion (H+) and inorganic monomeric aluminum (Alim) also decreased significantly (mean trends of −0.3 μeq L−1 yr−1 for H+ and −0.1 μeq L−1 yr−1 for Alim for the 3 most acidic sites). Acid neutralizing capacity (ANC) increased by a mean of 0.65 μeq L−1 yr−1 for all 5 sites, which was 4 fold less than the decrease in SO42− concentrations. These upward trends in ANC were limited by coincident decreases in base cations (−1.3 μeq L−1 yr−1 for calcium + magnesium). No significant trends were detected in stream-water nitrate (NO3−) concentrations despite significant decreasing trends in NO3− wet deposition. We measured no recovery in soil chemistry which we attributed to an initially low soil buffering capacity that has been further depleted by decades of acid deposition. Tightly coupled decreasing trends in stream-water silicon (Si) (−0.2 μeq L−1 yr−1) and base cations suggest a decrease in the soil mineral weathering rate. We hypothesize that a decrease in the ionic strength of soil water and shallow groundwater may be the principal driver of this apparent decrease in the weathering rate. A decreasing weathering rate would help to explain the slow recovery of stream pH and ANC as well as that of soil base cations.

Rare earth elements (REEs) are used in various fields, resulting in their accumulation in the environment. This accumulation has affected the survival and distribution of crops in various ways. Acid rain is a serious global environmental problem. The combined effects on crops from these two types of pollution have been reported, but the effects on crop root nitrogen assimilation are rarely known. To explore the impact of combined contamination from these two pollutants on crop nitrogen assimilation, the soybean seedlings were treated with simulated environmental pollution from acid rain and a representative rare earth ion, lanthanum ion (La³⁺), then the indexes related to plant nitrogen assimilation process in roots were determined. The results showed that combined treatment with pH 4.5 acid rain and 0.08 mM La³⁺ promoted nitrogen assimilation synergistically, while the other combined treatments all showed inhibitory effects. Moreover, acid rain aggravated the inhibitory effect of 1.20 or 0.40 mM La³⁺ on nitrogen assimilation in soybean seedling roots. Thus, the effects of acid rain and La³⁺ on crops depended on the combination levels of acid rain intensity and La³⁺ concentration. Acid rain increases the bioavailability of La³⁺, and the combined effects of these two pollutants were more serious than that of either pollutant alone. These results provide new evidence in favor of limiting overuse of REEs in agriculture. This work also provides a new framework for ecological risk assessment of combined acid rain and REEs pollution on soybean crops.

Acid rain is a serious environmental problem in China, caused by the urbanization and industrialization. We used recent acid rain and urban pollutant emissions data from the eastern coastal Jiangsu province to analyze the spatial distribution of acid rain. Further, we analyzed the regional air pollution data of the commission discharge atmospheric research database (EDGAR) regional air pollution data and developed a back-trajectory model for the cluster analysis of the air mass transfer characteristics of acid rain. The results show that from 2007 to 2013 the precipitation pH were high in northern and low in southern parts of Jiangsu Province. The average precipitation pH in the northwest and northeast parts were higher than 5.6; the frequency of acid rain in the area south of the Huaihe River accounted for more than 50% of total rainfall samples. Precipitation conductive in the northwest and southwest was greater than 60 μs/cm. The SO2, NOX, and PM10 were lower in the northern part and higher in the southern part. The northern part has higher pH and lower emission of precursors. One likely source for high ammonium and calcium concentration is local soil. From the northwest air mass, the acid rain appeared to have the highest average pH and the air mass from the southwest had the highest percentage of acid rain. The local emission (SO2, NOX, and Dust) reduction from 2005 led the haze and the acid rain problems mitigated to a good trend. The haze day increase and acid rain decrease due to the NH4+, and Ca2+ increase, and the long-distance transmission and the alkaline pollutant played an important role in Jiangsu' acid rain problem and haze since 2009.