A5066176863- Soil and Water Nutrient Dynamics
- Fish Ecology and Management Studies
- Freshwater macroinvertebrate diversity and ecology
- Hydrology and Watershed Management Studies
- Neuroscience and Neuropharmacology Research
- Neurotransmitter Receptor Influence on Behavior
- Memory and Neural Mechanisms
- Peatlands and Wetlands Ecology
- Ion channel regulation and function
- Marine and coastal ecosystems
- Hydrology and Sediment Transport Processes
- Wastewater Treatment and Nitrogen Removal
- Water Quality and Pollution Assessment
- Atmospheric and Environmental Gas Dynamics
- Groundwater flow and contamination studies
- Soil erosion and sediment transport
- Aquatic Invertebrate Ecology and Behavior
- Nicotinic Acetylcholine Receptors Study
- Neuroinflammation and Neurodegeneration Mechanisms
- Adipose Tissue and Metabolism
- Stress Responses and Cortisol
- Isotope Analysis in Ecology
- Smart Materials for Construction
- Aquatic Ecosystems and Phytoplankton Dynamics
- Groundwater and Isotope Geochemistry
Medical University of South Carolina
2016-2025
Oregon Health & Science University
2023
Oregon National Primate Research Center
2023
Atrium Health Wake Forest Baptist
2023
Oak Ridge National Laboratory
2005-2021
Institute of Behavioral Sciences
2013-2017
University of Tennessee at Knoxville
2008-2013
University of Kentucky
2002-2009
University of Tennessee Health Science Center
2009
University of Massachusetts Chan Medical School
2009
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...
Lay Abstract The exchange of gasses between water and air is important to the budgets carbon, nutrients, pollutants. This driven, in part, by turbulent energy at air–water interface. Turbulent interface scales with gas transfer velocity ( k ), which can be measured streams through various methods. We performed a metadata analysis studies that have using direct tracer releases. evaluated models predict based on stream morphology. found use slope perform reasonably well are consistent general...
Nitrous oxide (N(2)O) is a potent greenhouse gas that contributes to climate change and stratospheric ozone destruction. Anthropogenic nitrogen (N) loading river networks potentially important source of N(2)O via microbial denitrification converts N dinitrogen (N(2)). The fraction denitrified escapes as rather than N(2) (i.e., the yield) an determinant how much produced by networks, but little known about yield in flowing waters. Here, we present results whole-stream (15)N-tracer additions...
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...
We conducted two experiments to determine the relative effects of herbivory and nutrients on an algal community in Walker Branch, a stream having effectively trophic levels: primary producers herbivorous snails. The first study (1989), performed streamside channels, tested three factors: (1) water nitrogen (N), (2) phosphorus (P), (3) snail grazing, periphyton biomass, productivity, composition. second (1990), situ, grazing (N + P). In 1989 study, had positive effects, herbivores negative...
Summary 1. Rates of whole‐system metabolism (production and respiration) are fundamental indicators ecosystem structure function. Although first‐order, proximal controls well understood, assessments the interactions between distal controls, such as land use geographic region, lacking. Thus, influence on stream across regions is unknown. Further, there limited understanding how may alter variability in regions. 2. Stream was measured nine streams each eight ( n = 72) United States Puerto...
Melanin concentrating hormone (MCH) is a cyclic neuropeptide present in the hypothalamus of all vertebrates. MCH implicated number behaviors but direct evidence lacking. To selectively stimulate neurons gene for light-sensitive cation channel, channelrhodopsin-2, was inserted into wild-type mice. Three weeks later were stimulated 1 min every 5 24 h. A 10 Hz stimulation at start night hastened sleep onset, reduced length wake bouts by 50%, increased total time non-REM and REM night, intensity...
In the present study, we used a mouse model of chronic intermittent ethanol (CIE) exposure to examine how CIE alters plasticity medial prefrontal cortex (mPFC). acute slices obtained either immediately or 1-week after last episode alcohol exposure, voltage-clamp recording excitatory post-synaptic currents (EPSCs) in mPFC layer V pyramidal neurons revealed that resulted an increase NMDA/AMPA current ratio. This appeared result from selective NMDA component EPSC. Consistent with this, Western...
We used nondisruptive, whole-stream methods to measure hydraulic characteristics, ecosystem metabolism, and phosphorus cycling in the west fork of Walker Branch (WB), Tennessee Hugh White Creek (HWC), North Carolina. Although similar many their hydrological chemical transient storage zone volume HWC was relatively large (∼1.5 times that flowing water zone), whereas WB small (∼0.1 zone). Both streams were highly heterotrophic (gross primary production: total respiration ratios <0.1), although...
ABSTRACT: We review published analyses of the effects climate change on goods and services provided by freshwater ecosystems in United States. Climate‐induced changes must be assessed context massive anthropogenic water quantity quality resulting from altered patterns land use, withdrawal, species invasions; these may dwarf or exacerbate climate‐induced changes. Water to meet instream needs is competing with other uses water, that competition likely increased change. recent predictions...
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...
Whole-stream metabolism in a first-order stream was measured using upstream–downstream changes dissolved oxygen (DO) concentration at 1-min intervals over 40-h period. The change DO corrected for reaeration flux coefficient determined from injections of conservative and volatile tracers. whole-stream measurement compared the spring with situ chamber measurements performed few days later same reach. Chamber community respiration extrapolated to 24-h period (CR 24 ) were about one third...
Distinct seasonal patterns in streamwater nutrient and dissolved organic carbon (DOC) concentrations are evident the data record from 7 years of weekly sampling West Fork Walker Branch (WB) 4 a nearby stream, upper White Oak Creek (WOC), both first‐order streams Ridge Valley Province eastern Tennessee. Concentrations NO 3 soluble reactive phosphorus (SRP) showed repeated pattern annual maxima summer biannual minima autumn spring. DOC WB exhibited distinct maxima. To determine whether...
The roles of terrestrial and instream processes in controlling stream‐water N P concentrations were studied over a 2‐yr period deciduous forest stream eastern Tennessee. Upper soil horizons highly effective sinks for inorganic throughfall, weathering the parent dolomite was dominant source to stream. riparian zone potential NH 4 + when dissolved oxygen groundwater low, but sink high. High rates immobilization observed from late autumn spring, primarily as result uptake by microbes on...
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...
Four radiotracer releases were performed over an annual period in 1981—1982 to determine seasonal variation indices and pathways of phosphorus spiralling Walker Branch, a small woodland stream eastern Tennessee, USA. Each release consisted addition °370 MBq each carrier—free 3 2 PO 4 H O 1—h during baseflow. Concentrations P dissolved water measured intensitively at several stations downstream for the input immediately following release. Activity coarse particulate organic matter (CPOM),...
Nitrogen uptake and cycling was examined using a six-week tracer addition of 15N-labeled ammonium in early spring Walker Branch, first-order deciduous forest stream eastern Tennessee. Prior to the 15N addition, standing stocks N were determined for major biomass compartments. During after measured water dominant compartments upstream at several locations downstream. Residence time (5–6 min) lengths (23–27 m) short relatively constant during addition. Uptake rates NH4 more variable, ranging...
The south-eastern United States and Gulf Coast of Mexico is physiographically diverse, although dominated by a broad coastal plain. Much the region has humid, warm temperate climate with little seasonality in precipitation but strong runoff owing to high rates summer evapotranspiration. southern Florida eastern subtropical distinct wet season winter dry season. Regional models suggest that change resulting from doubling pre-industrial levels atmospheric CO2 may increase annual air...
The importance of lotic systems as sinks for nitrogen inputs is well recognized. A fraction in streamflow removed to the atmosphere via denitrification with remainder exported loads. At watershed scale, there a keen interest understanding factors that control fate throughout stream channel network, particular attention processes deliver large loads sensitive coastal ecosystems. We use dynamic transport model assess biogeochemical (nitrate loadings, concentration, temperature) and...
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...