(SGER) Collaborative Research: Transport and Fate of Mercury Within the Carson River Valley During the January 1997 Flood

9714150 1860年至1890年期间，康斯托克洛德的米勒采矿导致估计有7 500吨汞释放到卡森河水系，包括拉洪坦水库。许多受污染的沉积物与被填塞的古河道有关，人们认为这些河道是由以前切断主河道的废弃弯道被填满而产生的。鉴于目前卡森河中的汞负荷大部分来自河岸侵蚀，因此在洪水期间，大部分被侵蚀的沉积物通过沉积在被遗弃的弯道中的沉积物而恢复储存。因此，在淹没谷底的洪水事件期间，受污染的碎屑可能会在河道和山谷填充物之间循环。1997年1月初，洪水淹没了卡森河流域的大片地区，洪水的规模在过去57年中只有一次超过一次。在事件发生期间和之后进行的现场观察显示，沿航道的许多河段遭受了广泛的侵蚀，而谷底的其他地区则沉积了厚厚的沉积层序。根据这些现场观测，我们认为这一低频率、高震级的事件对卡森河流域汞污染颗粒的运输和储存产生了重大影响。这项调查的主要目的是(1)记录1997年1月洪水期间卡森河流域从卡森市到拉洪坦水库发生的侵蚀和沉积模式，(2)确定新形成的洪水沉积物中汞浓度的空间变化，以及(3)评估对受污染沉积物的沉积和汞在这些沉积物中的分布的主要控制措施。通过将这次调查得出的结论与以前对卡森河的研究相结合，我们将能够评估从个别洪水事件到数十年的时间段内物理过程中汞的迁移和命运。此外，对风暴前后测量的地理趋势进行比较，将有助于深入了解罕见的高强度洪水对冲积沉积物中重金属扩散的重要性。

9714150 Miller Mining of the Comstock Lode (1860-1890) resulted in the release of an estimated 7,500 tons of mercury to the Carson River system including Lahontan Reservoir. Much of the polluted sediment is associated with filled paleochannels which are thought to have been produced by the filling of abandoned meanders previously cutoff from the main channel. Given that a majority of the present day mercury load in the Carson River is derived from bank erosion, it follows that during floods, much of the eroded sediment is returned to storage by the deposition of sediment within the channels of the abandoned meanders. Thus, there may be a cycling of contaminated debris between the channel and the valley fill during flood events which inundated the valley floor. In early January, 1997 flood flows, with a magnitude which has only been exceeded once in the past 57 years of record, inundated large regions of the Carson River valley. Field observations made during and following the event revealed that numerous reaches along the channel suffered extensive erosion, while thick sedimentary sequences were deposited over other regions of the valley floor. Based on these field observations, we believe that this low frequency, high magnitude event had a significant affect on the transport and storage of mercury contaminated particles along the Carson River valley. The primary objectives of this investigation are to (1) document the patterns of erosion and deposition that occurred along the Carson River valley from Carson City to Lahontan Reservoir during the January, 1997 flood, (2)determine the spatial variations in mercury concentration that occur within the newly formed flood deposits, and (3) assess the primary controls on both the deposition of contaminated sediments and the distribution of mercury within those deposits. By combining the conclusions reached in this investigation with previous studies of the Carson River, we will be able to assess the transport and fate of mercury by phys ical processes over time periods ranging from individual flood events to decades. In addition, a comparison of the geographic trends measured prior to and following the storm will lead to significant insights into the importance of rare, high magnitude floods on the dispersal of heavy metals in alluvial deposits.