A5053742374- Climate change and permafrost
- Soil and Water Nutrient Dynamics
- Cryospheric studies and observations
- Hydrology and Watershed Management Studies
- Fish Ecology and Management Studies
- Arctic and Antarctic ice dynamics
- Peatlands and Wetlands Ecology
- Geological Studies and Exploration
- Methane Hydrates and Related Phenomena
- Freshwater macroinvertebrate diversity and ecology
- Environmental DNA in Biodiversity Studies
- Indigenous Studies and Ecology
- Marine and coastal ecosystems
- Coastal wetland ecosystem dynamics
- Smart Materials for Construction
- Soil erosion and sediment transport
- Landslides and related hazards
- Ancient Mediterranean Archaeology and History
- Groundwater flow and contamination studies
- Geology and Paleoclimatology Research
- Geophysical Methods and Applications
- Soil Carbon and Nitrogen Dynamics
- Hydrology and Sediment Transport Processes
- Microbial Community Ecology and Physiology
- Archaeology and Historical Studies
University of Vermont
2015-2025
Ecological Society of America
2017-2018
University of Nottingham
2012-2018
John Wiley & Sons (United States)
2017-2018
Carleton University
2014
University of New Hampshire
1992-2013
Providence College
2011
Hannover Re (Germany)
2011
Manaaki Whenua – Landcare Research
1998-2005
University of Wisconsin–Oshkosh
2005
A comparative 15 N-tracer study of nitrogen dynamics in headwater streams from biomes throughout North America demonstrates that exert control over nutrient exports to rivers, lakes, and estuaries. The most rapid uptake transformation inorganic occurred the smallest streams. Ammonium entering these was removed water within a few tens hundreds meters. Nitrate also stream but traveled distance 5 10 times as long, on average, ammonium. Despite low ammonium concentration water, nitrification...
Abstract. The Arctic is a water-rich region, with freshwater systems covering about 16 % of the northern permafrost landscape. Permafrost thaw creates new ecosystems, while at same time modifying existing lakes, streams, and rivers that are impacted by thaw. Here, we describe current state knowledge regarding how affects lentic (still) lotic (moving) systems, exploring effects both thermokarst (thawing collapse ice-rich permafrost) deepening active layer (the surface soil thaws refreezes...
1. We studied whole‐ecosystem metabolism in eight streams from several biomes North America to identify controls on the rate of stream over a large geographic range. The had climates ranging tropical cool‐temperate and humid arid were all relatively uninfluenced by human disturbances. 2. Rates gross primary production (GPP), ecosystem respiration (R) net (NEP) determined using open‐system, two‐station diurnal oxygen change method. 3. Three general patterns evident among streams: (1) high GPP...
Approximately 1700 Pg of soil carbon (C) are stored in the northern circumpolar permafrost zone, more than twice as much C atmosphere. The overall amount, rate, and form released to atmosphere a warmer world will influence strength feedback climate change. We used survey quantify variability perception vulnerability Experts were asked provide quantitative estimates change response four scenarios warming. For highest warming scenario (RCP 8.5), experts hypothesized that release from zone...
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...
Abstract As high latitudes warm, a portion of the large organic carbon pool stored in permafrost will become available for transport to aquatic ecosystems as dissolved (DOC). If DOC is biodegradable, much be mineralized atmosphere freshwater systems before reaching ocean, accelerating transfer from atmosphere, whereas if recalcitrant, it reach marine where may persist over long time periods. We measured biodegradable (BDOC) water flowing collapsing (thermokarst) on North Slope Alaska and...
Abstract Storm events dominate riverine loads of dissolved organic carbon (DOC) and nitrate are expected to increase in frequency intensity many regions due climate change. We deployed three high‐frequency (15 min) situ absorbance spectrophotometers monitor DOC concentration for 126 storms watersheds with agricultural, urban, forested land use/land cover. examined intrastorm hysteresis the influences seasonality, storm size, dominant cover on loads. was generally anticlockwise at all sites,...
Summary 1. The Lotic Intersite Nitrogen eXperiment (LINX) was a coordinated study of the relationships between North American biomes and factors governing ammonium uptake in streams. Our objective to relate inter‐biome variability physical, chemical biological processes. 2. Data were collected from 11 streams ranging arctic tropical desert rainforest. Measurements at each site included hydraulic characteristics, parameters, whole‐stream metabolism uptake. Ammonium measured by injection 15...
Detailed studies of stream N uptake were conducted in a prairie reach and gallery forest Kings Creek on the Konza Prairie Biological Station. Nutrient rates measured with multiple short-term enrichments NO3− NH4+ at constant addition spring summer 1998. was also 15N-NH4+ tracer additions unlabeled 12 sites across North America. Concurrent conservative used to account for dilution all experiments. rate per unit area (Ut) positively correlated nutrient concentration (r2 = 0.41, log–log...
Many methods developed for calibration and validation of physically based distributed hydrological models are time consuming computationally intensive. Only a small set input parameters can be optimized, the optimization often results in unrealistic values. In this study we adopted multi-variable multi-site approach to Soil Water Assessment Tool (SWAT) model Motueka catchment, making use extensive field measurements. Not only were number processes (model components) catchment evaluated, but...
Permafrost is a defining characteristic of the Arctic environment. However, climate warming thawing permafrost in many areas leading to failures soil structure called thermokarst. An extensive survey 600 km 2 area and around Toolik Lake Natural Research Area (TLNRA) revealed at least 34 thermokarst features, two thirds which were new since ∼1980 when high resolution aerial was done. Most these features associated with headwater streams or lakes. We have measured significantly increased...
A long-term stream fertilization experiment was performed to evaluate the potential eutrophication of an arctic ecosystem. During 16 years summer phosphorus (H3PO4) fertilization, we observed a dramatic change in community structure Kuparuk River on North Slope Alaska. positive response at all trophic levels with increases epilithic algal stocks, some insect densities, and fish growth rates. After approximately eight P bryophytes (mosses) replaced diatoms as dominant primary producers River....
Nutrient uptake length is an important parameter for quantifying nutrient cycling in streams. Although tracer additions are the preferred method measuring under ambient concentrations, short-term addition experiments have more frequently been used to estimate Theoretical analysis of relationship between determined by (SW′) and (SW) predicted that SW′ should be consistently longer than SW, overestimate related level above concentrations degree limitation. To test these predictions, we data...
There has been a long-term decline in nitrate (NO3−) concentration and export from several monitoring watersheds New England that cannot be explained by current terrestrial ecosystem models. A number of potential causes for this nitrogen (N) have suggested, including changes atmospheric chemistry, insect outbreaks, soil frost, interannual climate fluctuations. In-stream removal NO3− not included attempts to explain regional watershed export, yet streams may high rates NO3−. We make use 40...
Abstract. As high latitudes warm, vast stocks of carbon and nitrogen stored in permafrost will become available for transport to aquatic ecosystems. While there is a growing understanding the potential effects collapse (thermokarst) on biogeochemical cycles, neither spatial extent nor temporal duration these known. To test hypotheses concerning patterns persistence elemental export from upland thermokarst, we sampled hydrologic outflow 83 thermokarst features various stages development...
Abstract Hydrological scientists develop perceptual models of the catchments they study, using field measurements and observations to build an understanding dominant processes controlling hydrological response. However, conceptual numerical used simulate catchment behaviour often fail take advantage this knowledge. It is common instead use a pre‐defined model structure which can only be fitted via parameter calibration. In article, we suggest alternative approach where different sources data...
ABSTRACT Fisheries and Oceans Canada has collected a unique, long‐term data set on the social, biological, economic dynamics of Canada's recreational fisheries. Starting in 1975, these were through mail surveys to anglers at 5‐year intervals. A longitudinal analysis revealed that there was an average 4.5 million licensed catching annual 255 fish. Release rates relatively high (53% fish released average), with recent survey (2010) suggesting release had exceeded 60%. Recreational also...
Abstract Headwater streams remove, transform, and store inorganic nitrogen (N) delivered from surrounding watersheds, but excessive N inputs human activity can saturate removal capacity. Most research has focused on quantifying the water column over short periods in individual reaches, these ecosystem‐scale measurements suggest that assimilatory uptake accounts for most removal. However, cross‐system comparisons addressing relative role of particular biota responsible incorporating into...
We used 15 NH 4 tracer additions to determine travel distances of ammonium (NH4 ) and suspended particulate organic nitrogen (SPON) in six streams ranging from second fifth order located within a single watershed on the North Slope Alaska. Based distribution N stored stream bottom compartments (primary producers or grazers), we estimated lengths. two‐compartment model estimate length SPON based source SPO water column. Both lengths (S w S p , respectively) increased with discharge primarily...