National Institute for Water Resources, Water Resources Research Institute Program
3/1/2015 - 2/28/2017
The overarching goal of this work is to understand how microbial community structure and function in tropical coastal estuaries drive geochemical processes in response to climate forcing. Conditions in the Equatorial Pacific signify a developing El Niño but its current impact on environmental conditions in the Hawaiian Islands due to atmospheric teleconnections is not well defined. For Hawai‘i, El Niño events typically displace the subtropical jet stream, leading to decreased precipitation in boreal winter and slightly enhanced rainfall in summer as well as decreased trade winds. The investigator will sample weekly for 18 months to analyze changes in microbial diversity and metabolic potential within the He‘eia Coastal Ocean Observing System (Hawai‘i, USA), a network of sites within a coastal embayment across a salinity gradient. Over the past eight years, the on-going time series has conducted monthly (or more frequent) sampling and maintained in situ instruments, to record physical and biogeochemical variability in this estuarine system and the adjacent coastal ocean. In addition to providing a data-rich physical and biogeochemical baseline for interpreting the proposed microbial work, this accessible field site enables repeat sampling and more robust analyses that will inform us about seasonal variation in microbial community diversity and function. To help interpret patterns from field samples, enrichment experiments manipulating concentrations of nutrients will be incubated in situ as well as in vitro simulations of water column temperature gradients will be conducted jointly. These analyses test two hypotheses about the environmental factors driving microbial community structure: 1) increased sea surface temperatures will alter the frequency of extreme events such as flooding and tropical cyclone/hurricane activity, leading to increased mixing of estuarine environments as well as increased inputs of terrestrially-derived nutrients to the coastal ocean from surface runoff and groundwater input, and 2) El Niño conditions promote temperature stratification of the water column, which will decrease oxygen availability and drive a shift in benthic biogeochemistry to more reducing conditions.