酸沉降对缙云山湖水化学的影响

Effects of acid deposition on the hydrochemistry of Jinyunshan Lake

关键词:  酸雨  MK检验  大气沉降  湖水化学

Key words:  acid rain  MK test  atmospheric deposition  lake water chemistry

摘要:

为了解我国典型酸雨区酸沉降时间变化特征以及对水化学特征的影响，利用2001—2020年东亚酸沉降监测网（EANET）的湿沉降与湖泊监测数据，使用MK检验分析缙云山酸沉降和湖水化学长期变化特征，使用Spearman相关系数明确酸沉降对湖水化学特征的影响。结果表明：2001—2020年，缙云山酸雨问题已得到改善，但降水pH值在3.94—5.15，平均值为4.41，酸雨问题依然严峻。硫和溶解无机氮（dissolved inorganic nitrogen，DIN）沉降通量分别为32.85 kg·hm⁻²·a⁻¹和22.55 kg·hm⁻²·a⁻¹，酸雨类型已由“硫酸型”转变为“硫酸-硝酸混合型”。湖水pH值的范围在5.25—7.50，平均值为5.86，酸化频率为30%。湖水pH值与降水pH值之间的相关性（r=0.56，P＜0.01）表明酸沉降对湖水酸化有一定作用。因此，对于酸化水体的治理须考虑大气沉降因素，只有协同治理大气污染才能根治水生生态系统的退化现象。

Abstract:

Background, aim, and scope Acid deposition is an environmental problem caused by acid-causing precursors such as SO₂ and NO_x emitted into the atmosphere by manmade or natural activities and then deposited on the surface. It has a critical impact on ecosystems, such as soil and water acidification, changes in the ecosystem’s structure, and reduced productivity. In this study, we clarify the effects of acid deposition on water acidification and hydrochemistry to provide a scientific basis for the management of aquatic ecosystems. Materials and methods Using the monitoring data of EANET in Jinyunshan (JYS) and Chongqing (2001—2020), the temporal changes of acid deposition and water chemistry were investigated, and the effects of acid deposition on the chemical characteristics of lake water were analyzed using the MK mutation test method in combination with the Spearman correlation analysis. Results It shows that the pH value of precipitation fluctuated between 3.94 and 5.15, with an average of 4.41. The acidification of precipitation in JYS is critical. The pH value of JYS lake water varied from 5.25 to 7.50, with an average of 5.86, which is weakly acidic. The pH value of lake water was significantly correlated with the pH value of precipitation (r=0.56, P＜0.01). The sulfur deposition flux was between 10.86 kg·hm⁻²·a⁻¹ and 53.92 kg·hm⁻²·a⁻¹, with an average of 32.85 kg·hm⁻²·a⁻¹; the dissolved inorganic nitrogen (DIN) sedimentation amount was between 15.08 kg·hm⁻²·a⁻¹ and 30.16 kg·hm⁻²·a⁻¹, with an average of 22.55 kg·hm⁻²·a⁻¹. Discussion The pH of precipitation showed a “five-year change” characteristic, indicating that the five-year regulation plan implemented by the state has achieved significant results; the acidity of precipitation was affected by atmospheric SO₂ emissions. While the acidity of precipitation in JYS has been improved and stabilized, it is still strong. The high concentration of SO₄^2- and the lack of a way to neutralize it are the main reasons for the acid deposition in JYS. The correlation and time trend of precipitation pH with lake water pH showed that acid deposition plays a critical role in lake water acidification, and there is a lagging effect of lake SO₄^2- and NH₄⁺ concentrations on atmospheric SO₄^2- and NH₄⁺ deposition. The concentration of SO₄^2- in the lake water and the weak neutralization effect of Ca²⁺ and Mg²⁺ on acid-causing ions are the causes of why the acidity of JYS lake water was higher than that of other watersheds. The deposition type of JYS changed from sulfur deposition to sulfur-nitrogen mixed deposition. Conclusions Acid deposition has a significant impact on water acidification. Thus, it is very important to achieve a synergistic control of nitrogen and sulfur. Recommendations and perspectives This study shows the implications of acid deposition on aquatic ecosystems, and atmospheric deposition factors must be considered for the treatment of acidified water bodies.