THE ENVIRONMENTAL IMPACTS OF MINING IN THE EAST MANCOS RIVER BASIN AS REVEALED BY DENDROCHEMICAL SIGNATURES FROM TREE-RING ANALYSES
Multiple tree-cores from Douglas Firs and Blue Spruces were sampled at three different locations along the East Mancos River. Standard dendrochronological techniques were used to determine accurate time records preserved in the samples. ICP-MS analyses on core samples constrained the dendrochemical signatures of specified tree-rings.
There were no significant time increments where polluting events related directly to mining activities. Prior to 2000 there were only minor increases in some chemical signatures above background levels, with a few periods marked by 14.78 to 49.60 parts per million (ppm) increases from previous time increments. Dendrochemical data displayed a significant increase ranging from 76.79 to 282.98 ppm in metal concentrations during the increment from 2000-2019 for each site location.
The lack of direct correlation between the period of most active mining from 1890-1920, and the dendrochemical data, reveal that mining did not have an immediate impact on the system or the effects were not detected in the tree-rings. Other possibilities to explain the observed patterns include factors related to trees-growth and chemical uptake, climatic effects, timing of decomposition of minerals and rocks, and the effect of sealing the mines. A combination of all four factors is likely.