Balogh Steven J, Huang Yabing, Offerman Heather J, Meyer Michael L, Johnson D Kent
Metropolitan Council Environmental Services, 2400 Childs Road, St. Paul, MN 55106, USA.
Sci Total Environ. 2003 Mar 20;304(1-3):305-13. doi: 10.1016/S0048-9697(02)00577-6.
Total mercury (THg) concentrations in streams draining cultivated watersheds in Minnesota, USA are strongly correlated with total suspended sediment (TSS) concentrations, varying widely in response to precipitation-driven inputs of soil-derived suspended sediments. Methylmercury (MeHg) concentrations in these waterways have not been studied, and little is known about mercury uptake mechanisms in resident fish populations. To begin to identify factors influencing MeHg concentrations and loadings in these streams, we measured THg and MeHg concentrations in unfiltered whole water samples from the Minnesota River and two of its major tributaries, the Blue Earth and Le Sueur Rivers. Land use in the watersheds of these rivers is over 90% row-crop agriculture, and extensive artificial drainage systems deliver runoff and associated solids quickly to local streams and rivers. THg concentrations were elevated (>10 ng/l) during much of Spring 2000 and part of the summer when runoff from precipitation events increased stream discharge and carried soil materials into the streams. Reduced precipitation resulted in low flow conditions from August through October, and THg concentrations decreased to <4.0 ng/l in all three rivers. MeHg concentrations in the Le Sueur River ranged from 0.07 to 0.42 ng/l between June and December. Higher MeHg concentrations (>0.2 ng/l) were measured during summer months when THg and TSS concentrations were high after precipitation events. Elevated MeHg concentrations were also observed in late October after leaf litter inputs. Conditions on the Blue Earth River were different, with elevated MeHg concentrations (>0.5 ng/l) observed during low flow in August and September. These higher concentrations coincided with a period of enhanced microbial growth stimulated by high late-summer temperatures. A late-October increase in MeHg concentration attributed to leaf litter inputs was also observed in this river. MeHg concentration trends in the Minnesota River were similar to those in the Blue Earth River. Indicators of biological productivity (chlorophyll a, volatile suspended solids, and total Kjeldahl nitrogen) were higher in the Blue Earth and Minnesota Rivers compared to the Le Sueur River, which may signal a connection between higher biological activity and increased MeHg concentrations.
美国明尼苏达州耕种流域内溪流中的总汞（THg）浓度与总悬浮沉积物（TSS）浓度密切相关，因降水驱动的土壤源悬浮沉积物输入量变化很大。这些水道中的甲基汞（MeHg）浓度尚未得到研究，对于当地鱼类种群中汞的吸收机制也知之甚少。为了开始确定影响这些溪流中甲基汞浓度和负荷的因素，我们测量了明尼苏达河及其两条主要支流蓝地球河和勒苏厄尔河中未过滤的全水样中的总汞和甲基汞浓度。这些河流流域的土地利用超过90%为行栽作物农业，广泛的人工排水系统将径流和相关固体迅速输送到当地溪流和河流。2000年春季大部分时间以及夏季部分时间，总汞浓度升高（>10纳克/升），此时降水事件产生的径流增加了溪流流量，并将土壤物质带入溪流。降水减少导致8月至10月流量较低，三条河流中的总汞浓度均降至<4.0纳克/升。勒苏厄尔河6月至12月间的甲基汞浓度在0.07至0.42纳克/升之间。夏季降水事件后总汞和总悬浮沉积物浓度较高时，测量到较高的甲基汞浓度（>0.2纳克/升）。10月下旬树叶凋落物输入后也观察到甲基汞浓度升高。蓝地球河的情况有所不同，8月和9月低流量期间观察到甲基汞浓度升高（>0.5纳克/升）。这些较高浓度与夏末高温刺激微生物生长增强的时期一致。该河10月下旬因树叶凋落物输入导致甲基汞浓度增加也被观察到。明尼苏达河中的甲基汞浓度趋势与蓝地球河相似。与勒苏厄尔河相比，蓝地球河和明尼苏达河中的生物生产力指标（叶绿素a、挥发性悬浮固体和凯氏总氮）更高，这可能表明较高的生物活性与甲基汞浓度增加之间存在联系。
