Poster Session Presentations

COMPARATIVE WATER AND PARTICLE RESIDENCE TIMES WITHIN REARING UNITS USED FOR INTENSIVE CULTURE OF STEELHEAD TROUT Oncorhynchus mykiss IN IDAHO

Tim Allan*, Christine Moffitt [1,2], Kelly Stockton [1], Barnaby Watten [2], and Brian Vinci [3]

[1] University of Idaho, [2] U.S. Geological Survey, [3] Freshwater Institute

Dworshak National Fish Hatchery (DNFH) is the world’s largest steelhead trout Oncorhynchus mykiss hatchery and is integral to conservation hatchery supplementation programs in the Snake-Columbia River systems of the Pacific Northwest. Concerns about settleable solids in rearing tanks due to low velocities and hydraulic dead zones led to the conversion of two rectangular circulating rearing ponds, Burrows ponds (BP), into experimental mixed-cell raceways (MCR) in 2008.

Hydraulic tests were conducted on a BP and MCR to determine velocity, hydraulic residence time (HRT) and particle removal efficiency. Velocities were measured in three dimensions at depths of 1 and 2 meters across the rearing tanks. A salt tracer and conductivity measurements were used to model HRT. Plastic beads were introduced into the BP and MCR to simulate the fate of feces and waste feed. The MCR exhibited fewer dead zones, more homogenous velocity distribution, and a higher average velocity than the BP (Table 1). Vectors revealed well-defined, counter-rotating cells in the MCR. The HRT turnover of the MCR was closer to ideal than was the BP (83.7% compared with 81.1%; Table 1).  Particle removal in the MCR was 99.8% after 50 minutes, while recovery in the BP over the same time frame was a mere 6.1%.

The larger, more homogeneous velocities observed in the MCR are desirable for uniform water quality and optimal fish growth. Although HRT tests did not reveal significant inter-tank differences, the bead tests validated staff observations of solids accumulation in BPs. The persistence of such solids facilitates bacteria growth and requires frequent cleaning. The results of this study suggest that the MCR design provides considerable advantages over the BP design, potentially enhancing downstream survival rates of steelhead smolt.

Keywords: salmonid production, hydraulics, water quality 


EVALUATING THE EFFECTS OF COMPLEX TERRAIN ON CARBON AND WATER CYLCING IN A FORESTED WATERSHED IN WEST VIRGINIA

Jeff Atkins*, Howard Epstein and Danny Welsch [1] 

[1] Canaan Valley Institute

Complex terrain spatially and temporally redistributes resources throughout a watershed resulting in profound effects on bio geochemistry and carbon and water cycling. To examine the influence of complex terrain in a forested, topographically heterogeneous watershed, we deployed  a plot-based study along an elevation gradient in (950—1150m) in the Weimer Run watershed located near Davis, West Virginia. At each of three different elevation levels (high, middle, low) are three sites. At each site are three 4 m2 plots, each underneath a different vegetation cover type (open, closed tree canopy, shrub canopy), for a total of 27 plots. At each plot, surface CO2 efflux, soil temperature, PAR, air temperature and volumetric soil water content at 0-12 cm are measured weekly during the growing season. Soil samples and measurements of Leaf Area Index (LAI) and soil nutrient concentrations (NH4+, NO3-) have also been taken for each plot. Each plot also has gas wells at both 5 and 20 cm to measure CO2 concentrations below the soil surface. Preliminary findings indicate that vegetation cover type exerts a profound influence upon soil respiration, nutrient availability, LAI, soil moisture and sub-surface soil CO2 concentrations at 20 cm;  elevation exerts a profound control on soil temperature, soil moisture, sub-surface soil CO2 concentrations at 5 and 20 cm and LAI.

Keywords: Soil respiration, soil efflux, carbon, water, complex terrain


EFFECT OF LAND-USE ON SEDIMENT FLUXES, DUNE MOBILIZATION, AND SOIL NUTRIENT LOSS IN THE SOUTHERN KALAHARI

Abinash Bhattachan*, Paolo D’Odorico, Greg Okin [1], Kebonye Dintwe [1]

[1] Department of Geography, University of California- Los Angeles, Los Angeles, CA 90095.

The Kalahari, one of the largest drylands in the Southern Hemisphere, is currently covered by savanna and rangeland vegetation. The most arid areas, however, exhibit signs of vegetation loss, which results in the mobilization of ancient dunes.

It has been suggested that aridification of the region, in concert with land use, will result in further dune remobilization, with important social and environmental consequences. The impact of vegetation loss on sediment transport and dust emissions in the Kalahari remains poorly quantified. It is unclear to what extent this enhanced aeolian activity may in the long run affect the soil properties and cause the loss of nutrient-rich soil particles. We report the results of field measurements with dust samplers installed on the crests of vegetated dunes in well-managed farms, and on bare dunes in overgrazed communal land. We then compare the mean horizontal sediment flux, calculate the vertical sediment flux, and determine the rate of  soil nutrient loss associated with dust emissions at sites with different  vegetation cover. 


ASSESSING THE IMPORTANCE OF SEAGRASS HABITAT RESTORATION TO CARBON SEQUESTRATION IN THE SHALLOW COASTAL ZONE 

Jill Greiner*, Karen McGlathery

Seagrass meadows are highly productive habitats and provide many important ecosystem services to the coastal zone, including carbon and nutrient sequestration.  Organic carbon accumulates in seagrass sediments from both in situ production and sedimentation of water column particles.  We evaluated the impact of seagrass restoration on carbon storage in sediments of shallow coastal ecosystems using the large-scale seagrass restoration (>4000 acres) in the Virginia coastal bays as a model system.  Carbon accumulation rates were determined in meadows 4 and 10 years of age (time since restoration was initiated by seeding) and were compared with nearby bare sediments.  Sediments of seagrass meadows and bare sites were sampled for organic matter content, percent carbon, and lead 210 for dating.  Seagrass shoot density, productivity, and above and below ground biomass were also determined in each seagrass meadow.  Initial results show that the older 10 year seagrass lagoons have higher levels of organic matter and percent carbon compared to the 4 year meadows and bare sediment.  The 4 year old meadows show higher levels of organic matter and percent carbon compared to surrounding bare sediment; however, only the percent carbon levels are significantly different from the corresponding bare sediment due to variable seagrass densities.  Carbon burial rates are related to seagrass meadow age and shoot density, and are also compared with published carbon accumulation rates from natural meadows in other locations.  This is one of the first studies to address the potential importance of seagrass habitat restoration in enhancing carbon sequestration in the coastal zone. 

Keywords: Carbon Sequestration, Seagrass, Restoration


GAP MODEL VALIDATION FOR A SUBTROPICAL DRY FOREST AND RESPONSE TO HURRICANE DISTURBANCE IN CLIMATE CHANGE SCENARIOS

Jenn Holm*Herman H Shugart, Skip Van Bloem [1] , Guy R. Larocque [2] 

[1] USDA Forest Service, International Institute of Tropical Forestry, San Jaun, Puerto Rico, United States. 
[2] Canadian Forest Service, Laurentian Forestry Centre, Quebec, QC, Canada.

Because of human pressures, the need to understand and predict the long-term dynamics and development of subtropical dry forests is urgent. Through modifications to the ZELIG simulation model, including the development of species- and site-specific parameters and internal modifications to the model, the capability to model and predict forest change within the 4500-ha Guanica State Forest in Puerto Rico can now be accomplished. Published datasets and additional data from the U.S. Forest Service Forest Inventory Analysis were used to parameterize the new gap model, ZELIG-TROP. We used data from a 1.44-ha permanent plot located inside the Guanica State Forest in Puerto Rico to test the model. 

Our first objective was to accurately re-create the observed forest succession for a Puerto Rican subtropical dry forest using ZELIG-TROP. For this objective, the model testing was successful. Simulated total basal area, species composition, total stem density, and biomass all closely resembled   the observed Puerto Rican forest. Leaf area index was the variable predicted least accurately. 

Our second objective was to test the capability of ZELIG-TROP to predict successional patterns of secondary forests across a gradient of abandoned fields currently being reclaimed as forests. Abandoned fields that are on degraded lands do recover and have the potential to reach a mature forest status, but there is a delayed time period of 50-100 years. Our third objective was to develop a new hurricane damage routine in ZELIG-TROP with a parameterization for site- and species-specific damage. With this model, we assessed the long-term forest dynamics in Puerto Rico in response to simulated hurricane disturbances using 800 year simulations. This objective reports the change aboveground forest biomass (Mg ha-1), and the net primary production (NPP) (Mg C m-2 yr-1). Increased hurricane frequency decreased the aboveground biomass by 5%-40% and increased the NPP by 32%-50%.

Keywords Puerto Rico, succession, secondary forest, carbon, biomass, net primary productivity.



HYDROGEN ISOTOPE FRACTIONATION IN AQUATIC PRIMARY PRODUCERS: IMPLICATIONS FOR FOOD WEB STUDIES

K.L. Hondula
*
, M.L. Pace, J.J. Cole [1], R.D. Batt [2]

[2] Cary Institute of Ecosystem Studies, Millbrook New York 12545
[3] Center for Limnology, University of Wisconsin, Madison Wisconsin 53706

Hydrogen in the organic matter of aquatic plants has a lower relative abundance of the deuterium isotope in comparison to the surrounding water due to a series of fractionation processes including photosynthesis and the biosynthesis of lipids. Expected differences between the deuterium values of different types of plant tissue have been used to observe terrestrial contributions to aquatic food webs and to discriminate organic matter sources in 3-isotope studies with more precision than in 2-isotope studies, however some values used in these studies are derived from an estimated fractionation value (e) between water and plant tissue. We found significant differences in fractionation values between different groups of aquatic plants sampled from three system types: lakes, river, and coastal lagoon. Fractionation values between water and plant tissue of macrophytes and marine macroalgae were more similar to those of terrestrial plants and distinctly different than those of benthic microalgae and phytoplankton. Incorporating the variability in fractionation values between plant types will improve models and experimental designs used in isotopic food web studies for aquatic systems.

Keywords: Isotope fractionation, deuterium, food web tracers, aquatic plants


SURVEY OF STREAMS OF THE EASTERN SHORE OF VIRGINIA: MAGNITUDE OF NITRATE REMOVAL IN STREAMBED SEDIMENTS AND THE EFFECT OF PORE-WATER VELOCITY

George McFadden*

Recent studies on the Virginia Eastern Shore (VAES) and on the coastal plain of North Carolina show that as groundwater travels through streambed sediments, denitrification can decrease nitrate concentration by approximately 50 to 80 %.  This large potential for nitrate removal is significant in the context of elevated nitrogen levels in the underlying aquifer from dense agricultural land use.   The streambed sediment area where denitrification can occur is called the biologically active zone.  This study examines the magnitude of nitrate removal in the biologically active zone of numerous low order streams on the VAES flowing to the Atlantic Ocean and whether the process is hydrologically controlled.  Preliminary results show instances of large potential for nitrate removal in the biologically active zone.  A sample location at Goose Creek showed a NO3- concentration decrease of 7 mg N L-1 at 60 cm depth below the streambed to < 1 mg N L-1 at 10 cm depth.  Eleven streams were sampled for a reconnaissance of stream conditions and four streams were selected for a more spatially intensive study.  A portable oil-water manometer drive-point was constructed modeling the design of Kennedy et al. (2007), in order to measure the relative hydraulic head gradient between surface water and groundwater, as well as to collect pore-water samples for analysis of dissolved oxygen, chloride, nitrate, and sulfate concentrations.  Streambed sediment temperature profiles were measured using a thermocouple to calculate pore-water velocity.  Sediment cores will be taken primarily for quantification of total organic matter content over discrete depth intervals.  This research quantifies nitrate removal in the biologically active zone of multiple streams on the VAES, as well as investigates the spatial layout of the biologically active zones.

Keywords: denitrification, velocity, streambed


SIMULATING THE FORMATION OF LARGE ALLUVIAL FANS ON MARS 

A.M. Morgan* [1,2,3], R.A. Beyer [2], A.D. Howard [3], J.M. Moore [2]

[1] Department of Earth and Planetary Sciences, University of California,Santa Cruz, CA 95060, [2] NASA Ames Research Center, MS-245-3, Moffett Field, CA 94035, [3] Department of Environmental Sciences, University of Virginia, Charlottesville, Va 22903

Numerous alluvial fans have been identified within large craters in the southern Martian highlands [1]. With our work we aim to answer several questions: (1) Why is the erosion of the deep crater-wall alcoves that source the alluvial fans restricted to one or a few locations around the crater circumference? (2) What were the characteristics of water discharges (flow magnitude and duration) and sediment supply (quantity and grain size range) during fan formation? (3) What are the implications of the fans with regard to the responsible climatic environment (e.g. amounts and frequency of precipitation as rain or snow)? 

The model used combines discharge and sediment transport with channel avulsion and abandonment [2,3]. This allows the model to simulate both the micro and macro scale processes responsible for fan formation. Eolian erosion of the Saheki Crater fans has revealed distributaries etched into positive relief, suggesting that deposition involved both in-channel aggradation of coarser bedload plus overbank sedimentation of wind-erodible suspended sediment. The model incorporates both processes and allows for basic stratigraphy to be recorded as the fan is simulated. 

Output from the model is being statistically compared with Digital Elevation Models (DEM) of the region using measures such as channel width, relative proportions of channel and overbank sediments, frequency of branching and recombination, and distributary lengths. In addition to current DEMs made from MOLA data, we have produced high resolution DEMs derived from HiRISE stereo pairs. Model output will also be compared with appropriate terrestrial examples (e.g. select alluvial fans in the Atacama Desert).

The model successfully creates fans. The simulated fan features similar distributary patterns to fans seen on Mars, including distributaries of different age and elevation that cross paths. The range of model assumptions that result in fans statistically similar to the Martian counterparts (based on our DEMs) will constrain the possible range of sediment properties and environmental conditions responsible for the Martian fans.

References: [1] Moore, J.M., and A.D. Howard (2005), JGR,110, E04005, doi:10.1029 / 2004JE002352. [2] Howard, A.D. (2007) Geomorphology, doi:10.1016 / geomorph.2007.04.017. [3] Sun, T., C. Paola, G. Parker, and P. Meakin (2002), Water Resour. Res., 38, no.8, 10.

Keywords: Mars, alluvial fan, fluvial geomorphology


MODELING TRANSPORT PROCESSES AND RESIDENCE TIMES IN THE SHALLOW COASTAL BAY COMPLEX OF THE VIRGINIA COAST RESERVE

 I. Safak*, P.L. Wiberg

Patterns of transport and particle residence times influence the morphology and ecology of shallow coastal bays in important ways.  The Virginia Coast Reserve (VCR), a barrier island-lagoon-marsh system on the Eastern Shore of Virginia, is typical of many shallow coastal bay complexes that lack a significant fluvial source of freshwater and sediment.  Sediment redistribution within the bays in response to storms and sea-level rise, together with the dynamics of marsh and lagoon-bottom plants, largely governs the morphological evolution of this system.  There are also important feedbacks between sediment and ecosystem dynamics.  This is particularly true in the VCR, which is relatively unaffected by human activities. 

As a step towards evaluating the impact of hydrodynamics on sediment and ecological processes in the VCR, we employ a single unified model that accounts for circulation, surface waves, wave-current interaction, and sediment processes. This three-dimensional unstructured grid finite-volume coastal ocean model (FVCOM) is validated with field observations of wind- and tide-induced water flow (water level and current velocities) in Hog Island Bay, centrally located within the VCR.  We present here the resulting patterns of transport and particle residence times over event and seasonal time scales. Water and particle exchange within the VCR and between the VCR and the ocean is examined with the Lagrangian particle-tracking module in FVCOM.  We focus on three bays with strongly varying bathymetry and coastline geometry, which are also located along a gradient of nitrogen input to the system. The results indicate that residence time of particles within the system vary greatly depending on the location of particle release, bay morphology, and wind conditions.  The implications for morphologic evolution and ecosystem response to climate and land-use changes are evaluated.

Keywords: Virginia Coast Reserve, particle residence time, exchange between bays, ocean circulation


VERTICAL DISTRIBUTION OF SAHARAN DUST AND RADIATIVE FORCING OVER THE NORTHERN TROPICAL ATLANTIC

Weijie Wang*

Dust storms from Africa are a persistent feature over the northern tropical Atlantic. Advection of desert boundary layer air over the moist marine layer, termed as the Saharan Air Layer (SAL), is characterized by a dry and dusty mid-level warm anomaly.  Although it is well established that dust aerosols have an important impact on the Earth’s radiation budget through absorbing and scattering visible and infrared radiation, modeling the radiative forcing remains a challenge due to the limited understanding of the vertical distribution of dust. Therefore, it is necessary to quantify the vertical distribution of dust in order to better understand surface to top of the atmosphere forcing. In this work we create a spatially explicit monthly Atlantic climatology of the vertical profile of dust aerosols using data from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) from June 2006 through February 2009. We also present a climatology of the regional radiative impact of dust based on these profiles and MODIS aerosol products using a radiative transfer model and examine the relative importance of dust variability to regional processes on long time scales.