A5012594882- Climate change and permafrost
- Cryospheric studies and observations
- Methane Hydrates and Related Phenomena
- Marine and coastal ecosystems
- Atmospheric and Environmental Gas Dynamics
- Geology and Paleoclimatology Research
- Microbial Community Ecology and Physiology
- Arctic and Antarctic ice dynamics
- Aquatic Ecosystems and Phytoplankton Dynamics
- Peatlands and Wetlands Ecology
- Aquatic Ecosystems and Biodiversity
- Soil and Water Nutrient Dynamics
- Fish Ecology and Management Studies
- Isotope Analysis in Ecology
- Polar Research and Ecology
- Geological Studies and Exploration
- Indigenous Studies and Ecology
- Environmental DNA in Biodiversity Studies
- Ecology and biodiversity studies
- Groundwater and Isotope Geochemistry
- Water Quality and Pollution Assessment
- Soil Carbon and Nitrogen Dynamics
- Hydrology and Watershed Management Studies
- CO2 Sequestration and Geologic Interactions
- Oceanographic and Atmospheric Processes
University of Michigan
2015-2024
Michigan United
2020-2023
Ann Arbor Center for Independent Living
2020
University of Florida
2005
United States Geological Survey
2005
Tokyo Institute of Technology
2005
Marine Biological Laboratory
1989-1999
University of Applied Sciences Kaiserslautern
1999
University of Kansas
1999
Manaaki Whenua – Landcare Research
1999
Data on the partial pressure of carbon dioxide (CO(2)) in surface waters from a large number lakes (1835) with worldwide distribution show that only small proportion 4665 samples analyzed (less than 10 percent) were within +/-20 percent equilibrium atmosphere and most (87 supersaturated. The mean CO(2) averaged 1036 microatmospheres, about three times value overlying atmosphere, indicating are sources rather sinks atmospheric CO(2). On global scale, potential efflux (about 0.14 x 10(15)...
Arctic tundra has large amounts of stored carbon and is thought to be a sink for atmospheric dioxide (CO(2)) (0.1 0.3 petagram per year) (1 = 10(15) grams). But this estimate balance only terrestrial ecosystems. Measurements the partial pressure CO(2) in 29 aquatic ecosystems across arctic Alaska showed that most cases (27 29) was released atmosphere. This probably originates environments; erosion particulate plus ground-water transport dissolved from contribute flux surface waters If...
Carbon in thawing permafrost soils may have global impacts on climate change; however, the factors that control its processing and fate are poorly understood. The dominant of dissolved organic carbon (DOC) released from to inland waters is either complete oxidation CO2 or partial river export oceans. Although both processes most often attributed bacterial respiration, we found photochemical exceeds rates respiration accounts for 70 95% total DOC processed water column arctic lakes rivers. At...
Actual food—web structure or function is difficult to determine based on visual observation, gut analyses, the feeding interactions expected from a given list of species. We used C and N stable—isotope distributions define in arctic lakes, we compared that with results more traditional analyses. Although zooplankton species composition was similar across eight lakes studied, varied greatly. In some copepod predator Heterocope fed herbivorous Diaptomus as conventional food web. most however,...
Region 2 comprises arctic and subarctic North America is underlain by continuous or discontinuous permafrost. Its freshwater systems are dominated a low energy environment cold region processes. Central northern areas almost totally influenced air masses while Pacific becomes more prominent in the west, Atlantic east southern at lower latitudes. Air mass changes will play an important role precipitation associated with climate warming. The snow season prolonged resulting long-term storage of...
ABSTRACT Seasonal shifts in bacterioplankton community composition Toolik Lake, a tundra lake on the North Slope of Alaska, were related to source (terrestrial versus phytoplankton) and lability dissolved organic matter (DOM). A shift composition, measured by denaturing gradient gel electrophoresis (DGGE) 16S rRNA genes, occurred at 4°C near-surface waters beneath seasonal ice snow cover spring. This was associated with an annual peak bacterial productivity ([ 14 C]leucine incorporation)...
The sudden, catastrophic release of gas from Lake Nyos on 21 August 1986 caused the deaths at least 1700 people in northwest area Cameroon, West Africa. Chemical, isotopic, geologic, and medical evidence support hypotheses that (i) bulk released was carbon dioxide had been stored lake's hypolimnion, (ii) victims exposed to cloud died asphyxiation, (iii) derived magmatic sources, (iv) there no significant, direct volcanic activity involved. limnological nature suggests hazardous lakes may be...
An ongoing debate in ecology revolves around how species composition and ecosystem function are related. To address the mechanistic controls of this relationship, we manipulated dissolved organic matter (DOM) fed to aquatic bacteria determine effects on both bacterial activity community composition. Sites along terrestrial flow paths were chosen simulate movement DOM through catchments, was downslope control communities. Bacterial production measured, chemistry (using denaturing gradient gel...
Summary 1. Lake Victoria endured multiple stresses over the past century including population growth, increased cultivation of land, meteorological variability, resource extraction, intensive fishing, introduction exotic species and more recently climate warming. These stressors became manifest through a fundamental rapid change in fish community fishery early 1980s visible eutrophication. However, relation these two phenomena possible interaction have been difficult to establish because...
As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release offset by increased production Arctic boreal biomass; however, lack robust estimates net balance increases risk further overshooting international emissions targets. Precise empirical or model-based assessments critical factors driving are unlikely in near future, so address gap, we present from 98...
Hydroxyl radical (•OH) is a highly reactive and unselective oxidant in atmospheric aquatic systems. Current understanding limits the role of DOM-produced •OH as an carbon cycling mainly to sunlit environments where produced photochemically, but recent laboratory study proposed sunlight-independent pathway which forms during oxidation reduced dissolved organic matter (DOM) iron. Here we demonstrate this non-photochemical for formation natural environments. Across gradient from dry upland wet...
Abstract CO 2 emissions from inland surface waters to the atmosphere are almost as large net carbon transfer Earth's land surface. This flux is supported by dissolved organic matter (DOM) and its complete oxidation in freshwaters. A critical nexus global cycle fate of DOM, either or partial oxidation. Interactions between sunlight microbes control DOM degradation, but relative importance photodegradation vs. degradation poorly known. The knowledge gaps required advance understanding key...
Recent climate change has increased arctic soil temperatures and thawed large areas of permafrost, allowing for microbial respiration previously frozen C. Furthermore, destabilization from melting ice caused an increase in thermokarst failures that expose buried C release dissolved organic (DOC) to surface waters. Once exposed, the fate this is unknown but will depend on its reactivity sunlight attack, light available at surface. In study we manipulated water released activity show newly...
Human activities are causing a global proliferation of cyanobacterial harmful algal blooms (CHABs), yet we have limited understanding how these events affect freshwater bacterial communities. Using weekly data from western Lake Erie in 2014, investigated the community varied over space and time, whether bloom affected non-cyanobacterial (nc-bacterial) diversity composition. Cyanobacterial composition fluctuated dynamically during bloom, but was dominated by Microcystis Synechococcus OTUs....
In sunlit waters, photochemical alteration of dissolved organic carbon (DOC) impacts the microbial respiration DOC to CO2. This coupled and biological degradation is especially critical for budgets in Arctic, where thawing permafrost soils increase opportunities oxidation CO2 surface thereby reinforcing global warming. Here we show how why sunlight exposure draining soils. Sunlight significantly increases or decreases depending on whether photo-alteration produces removes molecules that...
Hydrologic processes control much of the export organic matter and nutrients from land surface. It is variability these hydrologic that produces variable patterns nutrient transport in both space time. In this paper, we explore how “connectivity” potentially affects transport. connectivity defined as condition by which disparate regions on hillslope are linked via subsurface water flow. We present simulations suggest for year, draining through a catchment spatially isolated. Only rarely,...
1. We studied the spatial and temporal patterns of change in a suite twenty‐one chemical biological variables lake district arctic Alaska, U.S.A. The study included fourteen stream sites ten sites, nine which were direct series surface drainage. All twenty‐four sampled between one five times year from 1991 to 1997. 2. Stream tended have higher values major anions cations than while had particulate carbon, nitrogen, phosphorous chlorophyll . There consistent statistically significant...
The colonization cycle hypothesis states that stream ecosystems would become depleted of insects if flying adults did not compensate for drifting immatures. Using long—term drift and benthic abundance data, we show a Baetis mayfly nymph population moves downstream during development in the Kuparuk River arctic Alaska. relative decreased from early to late season an upstream unfertilized river section, while simultaneously increasing fertilized section. nymphs drifted significantly more...
Vertical and horizontal exchanges in Pilkington Bay, a shallow (9 m) embayment of Lake Victoria, were determined from surface energy budget, time series measurements temperature, quasi synoptic transects conductivity, depth conducted over 2‐d period. The budget is the first tropical lake diurnal timescale. Strong stratification developed during morning early afternoon (>40 cycles h −1 ) but was eroded beginning by combination wind heat loss. Surface losses contributed >70% for layer...
Bacterioplankton community composition was compared across 10 lakes and 14 streams within the catchment of Toolik Lake, a tundra lake in Arctic Alaska, during seven surveys conducted over three years using denaturing gradient gel electrophoresis (DGGE) PCR-amplified rDNA. communities draining were very different than those lakes. Communities similar to In connected series streams, stream changed with distance from upstream changes water chemistry, suggesting inoculation dilution bacteria...
CO 2 exchange between lake water and the atmosphere was investigated at Toolik Lake (Alaska) Soppensee (Switzerland) employing eddy covariance (EC) method. The results obtained from three field campaigns two sites indicate importance of convection in driving gas flux across water‐air interface. Measurements were performed during short (1–3 day) periods with observed diurnal changes stratified convective conditions lakes. Over EC net efflux 114 ± 33 mg C m −2 d −1 , which compares well 131...