一项研究发现，周期性的洪水把汞污染的沉积物从19世纪中期在加州内华达山脉山麓丘陵的采金活动放置的大型矿床带到了低地中央谷，而且将很可能这样持续数千年。
自从淘金热以来，与沉积物结合的汞已经污染了旧金山湾-三角洲的食物网，但是汞输送的主要地理来源和机制仍不清楚。
Michael Bliss Singer及其同事分析了来自一个名为Yuba Fan的大规模采矿矿床和下游地区的沉积物样本。这组作者发现来自采矿之后时代的沉积物中的汞的水平至多达到了采矿前沉积物的数百倍。对地形和河流流量数据的进一步分析以及沉积物输送建模揭示出了Yuba Fan的侵蚀模式已经在过去一个世纪中发生了变化，让大量被汞污染的沉积物在一次次大规模洪水中运动到了下游。
这组作者估计，储存在Yuba Fan的这些采矿沉积物每10年会被这类事件释放大约0.1%。这组作者说，从Yuba Fan输出的这些被污染的沉积物的大部分留在了旧金山湾-三角洲的上游的低地泛滥平原和分洪河道里，但是它代表了旧金山湾-三角洲水生食物网的一个持续而不断增加的污染来源。（生物谷Bioon.com）
生物谷推荐的英文摘要
Proceedings of the National Academy of the Sciences of the United States of America doi: 10.1073/pnas.1302295110
Enduring legacy of a toxic fan via episodic redistribution of California gold mining debris
Michael Bliss Singera，b，1， Rolf Aaltoc， L. Allan Jamesd， Nina E. Kilhame， John L. Higsona， and Ghoshalf
The interrelationships between hydrologically driven evolution of legacy landscapes downstream of major mining districts and the contamination of lowland ecosystems are poorly understood over centennial time scales. Here， we demonstrate within piedmont valleys of California’s Sierra Nevada， through new and historical data supported by modeling， that anthropogenic fans produced by 19th century gold mining comprise an episodically persistent source of sediment-adsorbed Hg to lowlands. Within the enormous， iconic Yuba Fan， we highlight (i) an apparent shift in the relative processes of fan evolution from gradual vertical channel entrenchment to punctuated lateral erosion of fan terraces， thus enabling entrainment of large volumes of Hg-laden sediment during individual floods， and (ii) systematic intrafan redistribution and downstream progradation of fan sediment into the Central Valley， triggered by terrace erosion during increasingly long， 10-y flood events. Each major flood apparently erodes stored sediment and delivers to sensitive lowlands the equivalent of ～10–30% of the entire postmining Sierran Hg mass so far conveyed to the San Francisco Bay-Delta (SFBD). This process of protracted but episodic erosion of legacy sediment and associated Hg is likely to persist for >104 y. It creates， within an immense swath of river corridor well upstream of the SFBD， new contaminated floodplain surfaces primed for Hg methylation and augments/replenishes potential Hg sources to the SFBD. Anticipation， prediction， and management of toxic sediment delivery， and corresponding risks to lowland ecology and human society globally， depend on the morphodynamic stage of anthropogenic fan evolution， synergistically coupled to changing frequency of and duration extreme floods.
