Source Identification of Particulate Metals/Metalloids Deposited in the San Juan River Delta of Lake Powell, USA

Whereas mining and non-mining sourced particulate metal/metalloids (PM) (>0.45m) are present in the tributaries of the San Juan River, USA, the individual contributions of PM from the San Juan River tributaries to the sediment of the San Juan River Delta of Lake Powell were previously unknown. Suspended PM signatures, including enrichment factors (ratios of PM concentrations to ubiquitous metals such as aluminum), lead isotopes, color, and particle size, were used to tie layers in a San Juan River sediment core to upstream tributary sources. Tributary PM concentrations and loads were compared to Lower San Juan River suspended PM loads to estimate the relative contribution of tributary PM (both mining and non-mining sourced) directly upstream of Lake Powell. Results suggest elevated enrichment factors of lead, cadmium, copper, and zinc in deposited sediment were sourced from mined tributaries, whereas elevated manganese in deposited sediment was sourced from unmined tributaries. Sediment Pb isotope ratios reflected the depleted signature of the mineralized vein (present in the headwaters of mined tributaries), the enriched signature of the Chinle Sandstone (predominant underlying geology of unmined tributaries), or a mixture of these two endmembers. These independent lines of evidence were used to link probable tributary source and runoff category to sediment layers, where similar to 10% and 5% of the overall PM deposited in the sediment core was attributed to mining versus non-mining sources, respectively. Because traditional dating methods were not possible, runoff category signatures were used to estimate that the 3.37m San Juan River Delta core was deposited over similar to 1.3years.