Using our many measurements, we have made substantial process toward understanding rates and sources of atmospheric deposition, and how N and P in soils and sediments are mobilized and transformed, and affected by climate variability. However, our recent paleolimnological investigations have provided evidence that many Sierra Nevada lakes, including Emerald, may have been affected by human-caused acid rain, nutrient deposition and snowpack variability much earlier in the 20th Century (Bennett et al., in review; Sickman et al., in prep.). Recent work by our group has yielded diatom-inference models that allow for the reconstruction of past ANC and nitrate levels in Sierra Nevada lakes. This work has identified a strong correlation between snowpack variability and ANC in Emerald Lake, and we used this information to reconstruct a nearly 200-year record of snowpack based on diatom-reconstructed ANC which suggests a gradual decline and increased variability in SWE since the mid-19th Century (Fig. 9A). ANC reconstructions done by our group at other Sierra Nevada lakes and measurements of spheroidal carbonaceous particles show a pattern of acidification and recovery over the 20th Century largely driven by changing air quality (Fig. 9B). We are continuing paleo-investigations in Emerald Lake in order to extend the analyses back several hundred years into the Holocene. In 2013, we plan to collect the first full core of Emerald Lake sediments (estimated to be 2-3 meters in length) using a piston corer. Radiometric dating of the core will be accomplished with 210Pb in the upper ca. 25 cm and 14C in lower sections. Diatom species will be enumerated in all sections and used in our diatom inference models to reconstruct ANC and NO3. To gain information regarding past snowpack variability, we will use the relationship between ANC and SWE at Emerald Lake (Bennett et al. in review) to re-construct several hundred years of snowpack variability in the Emerald Lake watershed and validate the reconstruction through comparison to dendroclimatic reconstructions of Sierra Nevada climate (e.g., Meko 2002; Graumlich 1993).