Centennial to Decadal-Scale Changes in Algal Production and Community Composition in Santa Fe Lake, NM

As sentinel ecosystems, mountain environments serve as early warning signals for global change, including impacts of extreme weather conditions, climate change, and airborne pollutants. Fossil fuel combustion, anthropogenic nitrogen-fixation, industrial agriculture, human population growth, and land-use change have led to significant alterations in Earth systems. Imprints of these changes can be determined from sediments that accumulate sequentially over time in lakes. Here we analyzed stable isotopes, elemental composition (C, N), diatoms, and algal pigments in a 40-cm core from Santa Fe Lake, NM, to place anthropogenic activities into a multi-centennial context of environmental change. The core provided a ca. 500- 600-year record of change in phototrophic communities. Lake production (as total algal biomass, %C, %N) was elevated prior to the Little Ice Age (LIA), then increased again during the 20th century. Cryptophytes (as alloxanthin) and chlorophytes (pheophytin b / Lutein-Zeax) increased throughout most of the record. In contrast, cyanobacteria were more abundant early in the sediment record, declined during the Little Ice Age (LIA), and maintained a lower abundance for the remainder of the sediment record. Similar declines during the cool interval were recorded for diatoms (diatoxanthin); however, these taxa increased to a plateau during the mid-20th century, after which they declined. Preliminary diatom identification demonstrated the presence of planktonic diatoms throughout the core. Our preliminary findings suggest that trajectories of change within Santa Fe Lake during recent decades occurred in conjunction with accelerated human activities. Further analyses will focus on specific drivers and responses to environmental change within the Santa Fe Lake ecosystem.