A Rock Glacier's Response to Climate and Influence on Water Quality in the Colorado Front Range

Little research has been conducted on the chemical content of ice and runoff from rock glaciers. However, recent work has refocused efforts on the potential of rock glaciers to indicate past climate signals and reflect current changes in climate. Furthermore, rock glaciers have the potential to affect biogeochemical processes, water quality, and buffering capacity in alpine systems. In this study, we examine water quality from the Green Lake 5 Rock Glacier outlet stream in the Green Lakes Valley, Colorado Front Range. We compare the stream water quality with that of precipitation and outlet streams from the nearby Arikaree Glacier and Martinelli Snowpatch. Precipitation samples were collected year round, and stream water samples were collected roughly between May and October in the years 1998 to 2001. Water samples were analyzed for ANC, NH₄, Ca, Mg, Na, K, Cl, NO₃, SO₄, Si and δO¹⁸. The water quality from all three land types was strongly controlled by chemical weathering and hydrologic flow paths, among other variables. In contrast with the other land types, solute concentrations in the rock glacier were lowest at snowmelt and then increased through summer and into early fall. Solute concentrations in snowpatch and glacial runoff were highest during snowmelt. On average, the solutes from chemical weathering products were often an order of magnitude higher in the rock glacier runoff. For example, mean Ca was 447 μeq/L at the rock glacier compared with 17 μeq/L at the Arikeree glacier and 66 μeq/L at the Martinelli snowpatch. Mean NO₃ concentrations were also higher at the rock glacier at 50 μeq/L compared with 8-12 μeq/L in the glacial and snowpatch runoff. The exception is that Na and Cl concentrations were not significantly different between the rock glacier and snowpatch (95 % confidence level). The high concentrations of solutes in the rock glacier, especially in late summer and early fall, suggest the melting of old ice and change of climatic conditions. The increased yield of chemical weathering products indicates that rock glaciers have the potential to alter water quality and buffering capacity locally, and this land type should be considered when modeling water quality at fine spatial scales.