一項(xiàng)研究發(fā)現(xiàn),，周期性的洪水把汞污染的沉積物從19世紀(jì)中期在加州內(nèi)華達(dá)山脈山麓丘陵的采金活動(dòng)放置的大型礦床帶到了低地中央谷,，而且將很可能這樣持續(xù)數(shù)千年。
自從淘金熱以來,，與沉積物結(jié)合的汞已經(jīng)污染了舊金山灣-三角洲的食物網(wǎng),，但是汞輸送的主要地理來源和機(jī)制仍不清楚,。
Michael Bliss Singer及其同事分析了來自一個(gè)名為Yuba Fan的大規(guī)模采礦礦床和下游地區(qū)的沉積物樣本,。這組作者發(fā)現(xiàn)來自采礦之后時(shí)代的沉積物中的汞的水平至多達(dá)到了采礦前沉積物的數(shù)百倍,。對(duì)地形和河流流量數(shù)據(jù)的進(jìn)一步分析以及沉積物輸送建模揭示出了Yuba Fan的侵蝕模式已經(jīng)在過去一個(gè)世紀(jì)中發(fā)生了變化，讓大量被汞污染的沉積物在一次次大規(guī)模洪水中運(yùn)動(dòng)到了下游,。
這組作者估計(jì),，儲(chǔ)存在Yuba Fan的這些采礦沉積物每10年會(huì)被這類事件釋放大約0.1%。這組作者說,，從Yuba Fan輸出的這些被污染的沉積物的大部分留在了舊金山灣-三角洲的上游的低地泛濫平原和分洪河道里,，但是它代表了舊金山灣-三角洲水生食物網(wǎng)的一個(gè)持續(xù)而不斷增加的污染來源。（生物谷Bioon.com）
生物谷推薦的英文摘要
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.
