Bacterioplankton community dynamics in high elevation lakes of the Sierra Nevada
Collaborator: Steven Sadro @ UCD
Summary: Since 2004 our group has been studying the identity, abundance and dynamics of bacterioplankton in the high elevation rivers and lakes of the Sierra Nevada mountains of California. This work has taken place throughout the range, with focus on those areas above 2500 m where fish were historically not found. Our past findings have documented how landscape vegetation, snowmelt dynamics, watershed structure and biogeochemical properties of catchmants affect the abundance and types of bacterioplankton found in lakes, as well as shown how those communities vary over depth across seasons and space.
Collaborator: Roland Knapp @ UCSB
Student Trainee: Krissy Remple
Publications:
https://www.waterboards.ca.gov/lahontan/publications_forms/available_documents/microbial_report.pdf
Summary: One of the primary causes of water quality impairment is the presence of pathogens associated with human and animal feces. Such feces can originate from a wide variety of sources, including sewage treatment facilities, septic tanks, farms, rangeland livestock, pets, and wildlife. Fecal-associated pathogens in waters can cause illnesses in humans, including those associated with bacteria (e.g., Escherichia coli, Enterococcus, and Campylobacter), protozoans (e.g., Giardia and Cryptosporidium), and viruses (e.g., rotaviruses). Some of these microorganisms can be pathogenic even at very low concentrations, and these low concentrations can make their detection difficult. Therefore, water quality monitoring often relies on detecting bacteria that are common in vertebrate feces and that can provide useful indicators of the presence of fecal material and associated pathogens. The most commonly tested-for fecal indicator bacteria (FIB) include fecal coliforms, E. coli, and Enterococcus. The primary focus of the current contract was to assess FIB concentrations and sources in a subset of streams in the eastern Sierra Nevada in which FIB levels commonly exceed both the current fecal coliform standard and the EPA E. coli-based criteria. Our goal was to provide a detailed description of spatial and temporal patterns of FIB concentrations in impaired stream reaches in the eastern Sierra Nevada portion of the Lahontan Region (Mono and Inyo counties), with specific reference to recent EPA E.coli-based water quality criteria. We sought to develop microbial source tracking (MST) assays that are based on quantitative real-time polymerase chain reaction (qPCR) methods to identify the relative contribution of humans versus ruminant animals (including cattle) to FIB concentrations in impaired stream reaches in the eastern Sierra Nevada. Finally we seek to determine the generality of the finding that in the Mono-Inyo County study area cattle are a primary driver of FIB concentrations, analyze FIB and MST results from samples collected from a large portion of the Lahontan Region (by Lahontan personnel) to identify possible landscape-scale and site-specific drivers of FIB concentrations at this broader scale.
Dissolved organic matter in high elevation lakes of the Sierra Nevada
Collaborators: Lihini Aluwihare @ SIO, Steven Sadro @ UCD, Pieter Dorrestein @ UCSD, Linda Wegley Kelly @ SDSU
Summary: Terrestrial aquatic ecosystems are hotspots of biogeochemical processing of key elements such as C, N and P, accounting for a significant portion of the global flux of carbon dioxide to the atmosphere. Although climate change is altering the timing, magnitude and composition of organic matter delivered to aquatic habitats, our understanding of how organic matter is transformed by microbial communities in these systems remains limited. One critical shift occurring rapidly worldwide is an increase in the quantity of terrigenous dissolved organic matter (DOM) delivered to aquatic habitats. We have shown that pulses of this allochthonous DOM fundamentally alter biogeochemical processes and food web structure of aquatic ecosystems, shifting microbial community structure, increasing aquatic respiration with corresponding inorganic carbon efflux and increasing nutrient remineralization facilitating subsequent phytoplankton blooms. In contrast, our work has also demonstrated that autochthonous DOM (produced in situ) is a potential sink for nitrogen as recalcitrant proteinaceous compounds and is metabolized by bacteria with increased trophic transfer efficiency, illustrating the fundamental effects that shifting DOM sources may have on nutrient cycling in terrestrial systems. A crucial next step in understanding how climate change will impact biogeochemical fluxes in terrestrial aquatic ecosystems is characterizing the chemical composition and microbial processing of different sources of DOM. We propose to develop a comprehensive understanding of the molecular character and mechanistic microbial metabolism of allochthonous and autochthonous DOM. This work will form a foundation to facilitate predictions of how increasing terrestrial DOM inputs may alter terrestrial biogeochemical nutrient cycling. High elevation lake ecosystems provide contrasting habitats to examine how these two distinct sources of DOM are processed by microbial communities because they exhibit large interannual variability in snowmelt driven hydrological dynamics, which in part drives strong seasonal and spatial diversity in the absolute quantity and proportions of autochthonous to allochthonous DOM. Using these natural gradients, genome-enabled approaches will be used to define and contrast both 1) the molecular composition and microbial transformations of these two DOM sources using untargeted liquid chromatography tandem mass spectrometry, isotopic characterization and proton nuclear magnetic resonance and 2) the metabolic genes differentially expressed by microbes processing these two sources of DOM using comparative metagenomics and metatranscriptomics.
California Mountain Lake Observatory Network (CaMoLON)