BIOGEOCHEMISTRY AND SEDIMENT TRANSPORT THROUGH A TROPICAL ANDEAN PATERNOSTER LAKE SYSTEM

We sampled paternoster lakes and their connecting streams in the Queshque Valley on the west side of the Cordillera Blanca, Peru during June and July 2014. The objectives of this study are to understand modern biogeochemical and sedimentological dynamics though the paternoster lake system. These analyses will serve as a modern proxy calibration for limnologically-based paleoclimate reconstructions. Water samples were taken throughout the lake system and analyzed for temperature, pH, total alkalinity, total suspended material (TSM), dissolved inorganic carbon (DIC), dissolved oxygen (DO), pCO₂, specific conductivity, and turbidity. Water δ¹⁸O and δ¹³C DIC will be analyzed in addition to δ¹³C, percent carbon, and organic/inorganic content of the TSM. Sediment traps were placed in two lakes to determine sediment flux through the system, and surface sediments of these lakes were collected as a comparison tool against the recent past. In one stream, samples were taken at ~6 hour intervals over a 24 hour period to decipher any possible trends in a diurnal cycle of glacial erosion and biological activity. Comparisons will be made to both a glacially fed and non-glacially fed lake in the nearby Quilcayhuanca Valley to provide a regional scale perspective. Preliminary data show a decrease in specific conductivity with increasing distance from the glacier (from 0.088 to 0.062 mS/cm), indicating a glacial source of dissolved material. TSM values, however, are highly variable (average 1.102 ± 0.581 mg/L) with distance from the glacier, which suggests either an influx of organic material or a non-glacial inorganic sediment source. A possible source of TSM are the steep slopes in each lake’s drainage basin, all of which exhibited evidence of slope instability of underlying glacial till. Alkalinity values increase with distance from the glacier, possibly illustrating the consumption of alkalinity by the bogs present between most lakes, but overall were low (average 0.056 ±0.037 mmol/L). DO increases slightly with distance from the glacier, indicating higher primary productivity possibly due to lower light attenuation.