The primary goal of the project is to determine how changes in hydrologic connections among landscape units affect the functional and compositional response of alpine aquatic bacteria. As alpine landscapes are transformed, e.g., glacier recession and changes in vegetation, terrestrial linkages and respective water sources feeding aquatic ecosystems will change (some flowing waters will even become temporary); thereby altering ecosystem functioning and potentially affecting downstream receiving waters intensely used by humans. Specific questions to be addressed include: 1) Does bacteria biodiversity differ among alpine waters in relation to the physical-chemical characteristics of the water source and season? Presently, there is a paucity of general knowledge on microbial assemblages in alpine waters. The ecology of other organisms, e.g., aquatic macroinvertebrates, differ distinctly from their lower elevation counterparts. Bacterial abundances will be quantified using SybrGreen counts and bacteria genetic structure will be characterized using DGGE; 16S rRNA sequence analysis and CARD-FISH. 2) Is there a relationship between bacterial function and differences in water source and season? Bacteria functioning will be measured using sediment respiration, functional gene markers and CARD-FISH, esterase activity, and specific enzyme assays. Using these same measures, we will test (3) whether bacteria diversity changes along hydrologic flow paths, both lateral subsurface flow paths and larger-scale longitudinal surface flow paths. Hydrologic properties, e.g. flow paths and exchange rates, will be evaluated using standard techniques with minipiezometers and conservative tracers. -and 4) How does nutrient and carbon enrichment affect bacteria biodiversity and functioning in alpine streams with different water source? Here, field experiments using replicated flow-through chambers (mesocosms) filled with natural sediments will be used to determine the effects of nutrient enrichment (C, N, P), i.e., a change in resource quality and quantity, on bacteria biodiversity and functioning using relevant measures mentioned above. Our earlier studies have shown that nutrient enrichment increased periphyton biomass and leaf decomposition rates, while also altering the response of invertebrates to disturbance. The overall study will involve both comparative analysis and field experiments to answer the proposed questions. The comparative assessment provides the context and justification for experiments intended to reveal mechanistic connections and underlying causes of patterns.