Objective: To investigate the reasons of natural extinction of Oncomelania hupensis snails by comparing the difference of the water chemical properties between the snail-breeding marshland and non-snail marshland in Eastern Dongting Lake areas.
Methods: Three adjoining marshlands in Eastern Dongting Lake areas were selected, one was a snail-breeding marshland, the second was a non-snail marshland, and the third was a boundary zone between them. During the periods of water-rising season, wet season and water-falling season, the water samples from the bottom of 0.5 m were collected by the systematic random sampling method (200 m × 200 m grid method). In addition, the water samples below the surface of 0.5 m were also collected in the wet season. The physicochemical indexes of the sampling water were detected.
Results: According to the Surface Water Environmental Quality Standard (GB 3838-2002), the water quality indicators which were less than the detection limit were Cr, Cd, Zn, Hg, Cu, S－ and CN－ during the three sampling seasons. The pollutants which were slightly higher than Grade III but lower than Grade IV (Hg ≤ 1 μg/L, TP ≤ 0.1 mg/L) were Hg and TP. The pollutants below the Grade III included As and F－. The temperature and pH values were within the Grade III. The oxygen consumption indicators covering DO, COD and BOD in the water-rising season and wet season were within the Grade III, while the value of BOD was beyond the scope of Grade III but was between Grade Ⅳ (≤ 6 mg/L) and Grade V (≤ 10 mg/L) in the water-falling season. The differences of the water pollution indexes between the snail-breeding marshland and non-snail marshland were statistically significant, and these indexes included F－, As and pH in the water-rising season (P < 0.05); pH, BOD and Fat the surface layer in the wet season (P < 0.05); F－ at the bottom in the wet season (P < 0.05); TP and F－ in the water-falling season. Moreover, the above-mentioned indexes in the non-snail marshland of Qianliang Lake were higher than those in the snail-breeding marshland of Junshan Park. Thus, F－ was the only index which had statistical differences in every sampling season, and the concentration of F－ at the non-snail marshland was also higher than that at the snail-breeding marshland. In the water-rising season, the pH value at the non-snail marshland exceeded the suitable range for the growth of snails (6.8 to 7.8).
Conclusions: In the Eastern Dongting Lake area, the high concentration of F－ and pH of water may be responsible for the natural extinction of O. hupensis snails.
［摘要］ 目的 比较东洞庭湖区钉螺自然消亡洲滩和有螺洲滩水体化学性质差异, 探究钉螺自然消亡的原因。方法 选取东洞庭湖区钱粮湖钉螺自然消亡洲滩、君山公园有钉螺孳生洲滩, 以及两者交界地带建兴农场洲滩作为研究现场。 在涨水期、丰水期以及退水期, 分别采用系统随机抽样法 (200 m × 200 m 网格法) 采集距水底 0.5 m 处的底层水样, 其中在 丰水期还同时采集水面以下 0.5 m 处的表层水样, 检测水体中的一般理化指标。结果 以《地表水环境质量标准》 (GB 3838–2002) 为参考, 3 次采样水样检测含量都小于检出限的指标有铬 (Cr) 、铅 (Cd) 、锌 (Zn) 、汞 (Hg) 、铜 (Cu) 、硫化物 (S－) 及氰化物 (CN－) ; 含量略高于Ⅲ类标准但低于Ⅳ类水质标准的污染物有 Hg 和总磷 (TP) ; 低于Ⅲ类水质标准限值的污染 物有砷 (As) 和氟化物 (F－) ; 常规指标中, 水温和 pH 值都在Ⅲ类水质标准范围。耗氧量指标溶解氧 (DO) 、化学耗氧量 (COD) 和生化耗氧量 (BOD) 在涨水期和丰水位期都处于Ⅲ类水质标准范围, 但退水期 BOD 值超出了Ⅲ类标准范围, 处于 Ⅳ类 (≤ 6 mg/L) 与Ⅴ类水质标准 (≤ 10 mg/L) 之间。有螺洲滩与无螺洲滩涨水期 F－含量、As 含量、pH 值差异均有统计学 意义 (P 均 < 0.05), 丰水期表层水 pH 值、BOD 值、F－含量差异均有统计学意义 (P 均 < 0.05), 丰水期底层水 F－含量差异有 统计学意义 (P < 0.05), 退水期 TP 和 F－含量差异均有统计学意义 (P 均 < 0.05) 。其中每次采集的水样检测差异均有统计 学意义的指标仅有 F－含量; 在涨水期无螺洲滩 pH 值超出了适合钉螺生长的 pH 值范围 (6.8～7.8) 。结论 在东洞庭湖, 水体酸碱度以及水体中 F－含量偏高可能与钉螺自然消亡有关, 但仍待进一步研究。.
Keywords: Chemical contaminant; Dongting Lake area; Natural extinction; Oncomelania snail.