B53A-0975 1340h
The Development of an Aquatic Nutrient Sensor Network for Coastal Oceanography
The Land/Ocean Biogeochemical Observatory (LOBO) is an ongoing project designed to quantify the biogeochemical processes of a coastal ecosystem by the development and operation of an {\it in situ} sensor network in Elkhorn Slough, California. The primary goal is to design and operate autonomous moorings that measure ambient nutrient concentrations and standard water properties at appropriate spatial and temporal scales to investigate the biogeochemical processes of an estuarine environment. The embedded network relies on newly developed instruments that are capable of high resolution, long-term measurements of nitrate, ammonium, phosphate, and silicic acid. Sensor network design, calibration and operation of the instrumentation, and real-time data collection via a wireless network have been accomplished. A nearly continuous dataset from the first year of operation in Elkhorn Slough demonstrates many of the advantages of using {\it in situ} instruments to study biogeochemical cycles in aquatic systems. The sensor network can address the practical challenges of studying complicated nutrient cycles, tidal mixing, and small-scale physical variability that are faced in coastal biogeochemical research and monitoring.
http://www.mbari.org/lobo
B53A-0976 1340h
Application of wireless sensor networks to study flow over heterogeneous surfaces: flow over an isolated mountain in the marine atmosphere
A combination of standard meteorological equipment (3d sonic anemometer, energy balance sensors) and Crossbow MPR400 (Mica2) wireless motes and sensorboards were deployed along the slope of Pico mountain in the Azores, Portugal, between z = 1200 m and z = 2300 m MSL. The isolated location and uniform, conic shape make Pico mountain an ideal location to study orographic effects. This experiment focuses on upslope and downslope flow. Cost effective wireless sensor technology allows for high density of observations in time and space as necessary for characterization of flows over heterogeneous surfaces. Thus the features of upslope and downslope flows (speed, location and duration) and their effect on atmospheric physics and chemistry (temperature, relative humidity) can be studied in great detail. Synchronous measurements of O3, CO, NOx, NOy and NMHC at the PICO-NARE observatory (Honrath et al. 2004) situated at the mountaintop give further clues on airmass origin and dispersion. Findings regarding the occurrence and impacts of upslope and downslope flow and the advantages and disadvantages of wireless sensors relative to standard meteorological instruments will be presented. In particular, practical issues of wireless sensor deployment, such as durability in harsh conditions, power management, accuracy, and cost will be discussed.
B53A-0977 1340h
Establishing a Multi-spatial Wireless Sensor Network to Monitor Nitrate Concentrations in Soil Moisture
The use of reclaimed wastewater for irrigation in agriculture can be a significant source of nutrients, in particular nitrogen species, but its use raises concern for groundwater, riparian, and water quality. A 'smart' technology would have the ability to measure wastewater nutrients as they enter the irrigation system, monitor their transport in situ and optimally control inputs with little human intervention, all in real-time. Soil heterogeneity and economic issues require, however, a balance between cost and the spatial and temporal scales of the monitoring effort. Therefore, a wireless and embedded sensor network, deployed in the soil vertically across the horizon, is capable of collecting, processing, and transmitting sensor data. The network consists of several networked nodes or 'pylons', each outfitted with an array of sensors measuring humidity, temperature, precipitation, soil moisture, and aqueous nitrate concentrations. Individual sensor arrays are controlled by a MICA2 mote (Crossbow Technology Inc., San Jose, CA) programmed with TinyOS (University of California, Berkeley, CA) and a Stargate (Crossbow Technology Inc., San Jose, CA) base-station capable of GPRS for data transmission. Results are reported for the construction and testing of a prototypical pylon at the benchtop and in the field.
B53A-0978 1340h
Embedded Networked Sensing in Support of Managing Irrigation with Reclaimed Wastewater
An issue associated with agricultural irrigation using reclaimed wastewater is the potential threat to underlying groundwater quality. A prime example is nitrate, which serves as a fertilizing agent but has the potential to leach into groundwater. In order to balance water reuse and groundwater protection, intelligent irrigation management and monitoring systems are required for such water reuse systems. In this work, a nonlinear programming-based control algorithm is proposed to optimize irrigation scheduling subject to contaminant transport constraints. In support of the algorithmic developments, a networked sensor array is being designed for deployment at an agricultural research plot. This array will supply real-time field information about water infiltration and distribution, nitrate propagation, and heat transport, to the irrigation scheduling algorithm. The control scheme (measurement, decision, and action) will be continuously updated using on-line feedback from sensors. The simulator on which the management algorithm depends is a one-dimensional form of the Richards equation coupled to energy and solute transport mass balances. The simulator is used to (1) estimate key soil hydraulic and transport parameters in near real time, and (2) predict nitrate concentrations with respect to time and depth as input to the management algorithm. The quantity and timing of irrigation is determined based on an optimization algorithm which maximizes the reclaimed water usage while preventing nitrate propagation below a predetermined depth. Additional constraints are associated with plant water needs, and avoiding runoff and spray drift from the experimental plot. Results from a parameter sensitivity analysis are presented and preliminary management schemes are demonstrated for an on-going field experiment.
B53A-0979 1340h
SEAMONSTER: Applications and Challenges of Distributed Sensor Array to Southeast Alaska Science
SEAMONSTER, the SouthEast Alaska MOnitoring Network for Scientific TElecommunication and Research, is a network being developed to provide infrastructure to benefit research through Southeast Alaska. The array will be composed of 'bricks,' which are small Linux-based computers with digitizers and wireless network communication capabilities. The first use of this network is for bioacoustic monitoring of bats in Southeast Alaska for species identification and measurements for population dynamics. Addition projects during summer 2004 include experiments for range link budget estimation, measurements to study network requirement, and seismic and glaciology test-of-concept experiments. The presentation will highlight the results of development and testing during 2004 while emphasizing possible uses of the network which can enable and enhance current and future research projects in southeast Alaska. The capabilities and possibilities of the 'bricks' will be described.
B53A-0980 1340h
Electric Potential Variations on a Poplar: Beyond Electrokinetic Effects Associated With Sap Flow
Electric potential has been monitored since December 2003 in the roots and at two circumferences and one vertical profile in a standing poplar (Populus incognitus). Electric potential is sampled using 5 mm diameter stainless steel rods, inserted 5 mm deep in the cambium, and is referenced to an unpolarizable Petiau electrode installed 80 cm deep in the soil. Various types of signals are observed. Transient signals with long relaxation times affecting some electrodes simultaneously, may be contact potentials triggered by condensation and evaporation. Diurnal variations are observed which present a seasonal variation. During winter, diurnal variations depend on the measurement point, with variable amplitudes and sometimes anticorrelations between electrodes. By contrast, a stable and coherent organization is established in the spring, with larger amplitudes, and lasts during summer. Such signals have been reported previously (Koppan et al., 2000; Morat et al., 1994; Fensom, 1963), have been interpreted as electrokinetic effects associated with sap flow. However, a comparison of the electrical signals with a measurement of the sap flow by a heat flow method, shows that the electrical variation, although clearly correlated to sap flow, is not simply proportional to it. In a living system, electrokinetic effects, in addition to thermoelectrical effects, are probably modified significantly by additional electrochemical effects, such as membrane diffusion potentials, ion active transport by proteins, and action potentials. Such effects have been evidenced in laboratory experiments with plants (e.g., Fromm and Hei, 1998). Electric potential variations in trees may thus reveal mechanisms not accessible by other methods, and maybe reveal new aspects of the physics of living systems. A better understanding of the electrical response of trees to meteorological, chemical or biological forcing may improve the knowledge of transfer processes between the soil and the atmosphere. This is important for the modeling of water and carbon balance in relation to climate change, as well as of the contribution of trees to the migration, retention and dispersion of contaminants. Fensom, D. S., The bioelectric potentials of plants and their functional significance : V. Some daily and seasonal changes in the electrical potential and resistance of living trees, {\it Canadian J. Botany}, {\bf 41}, 831-851, 1963. Fromm, J., and H. Fei, Electrical signaling and gas exchange in maize plants of drying soil, {\it Plant Science}, {\bf 132}, 203-213, 1998. Koppan, A., L. Szarka, and V. Wesztergom, Annual fluctuation in amplitudes of daily variations of electrical signals measured in the trunk of a standing tree, {\it C. R. Acad. Sci. Paris}, {\bf 323}, 559-563, 2000. Morat, P., J.-L. Le Mou{\"e}l, and A. Granier, Electrical potential on a tree. A measurement of the sap flow ?, {\it C. R. Acad. Sci. Paris}, {\bf 317}, 98-101, 1994.
B53A-0981 1340h
Flow and Transport in Permeable Sediments Induced by Rising Gas Bubbles
The transport of methane from marine sediments into the seawater and then into the atmosphere is important in the context of its role as a greenhouse gas. The amount of methane that escapes from the sediments can be significantly reduced due to microbial processes like anaerobic oxidation of methane (AOM). The efficiency of these processes is dominated by the local hydrodynamics of the seep. In the present work, we use an artificial laboratory setup in order to investigate the mechanisms of flow and transport induced by rising gas in a permeable sediment. A combination of the experimental techniques Particle Image Velocimetry (PIV), 3D Planar Laser-induced Fluorescence (3D PLIF) and refractive-index matching is employed for the visualization and quantification of different aspects of this multiphase flow phenomenon. We find that the gas, which is injected continuously into the sediment, forms a cone-shaped, vertical structure of trapped gas and leads to a spatially and temporally fluctuating escape of bubbles at the upper interface. The temporal variability of the total volume of trapped gas results in fluctuations of liquid velocities in the sediment pores and therefore leads to an enhanced mixing of solutes in the sediment. The area surrounding the seep is characterized by a reverse, i.e.\ downward directed flow of liquid into the sediment induced by the rising gas. From the analysis of a series of experiments with different sediment types and gas flow rates, we provide a quantitative description of the downward velocity as a function of the distance from the seep, the gas flow rate and the permeability of the sediment.
B53A-0982 1340h
Spectral-IP Characteristics of Bacterial Activity on Sulfide Mineral Surfaces: Implications for Detection and Environmental Impact Assessment of Acid Mine Drainage.
Spectral induced polarization (IP) measurements were carried out, over a frequency range of 1.0-106 Hz, on pyrite crystal surfaces colonized by thiobacilli at different growth stages and in `sedimentary systems' with different pyrite-quartz ratios. The purpose was to determine if these varied pyrite-bacteria conditions are reflected in the spectral-IP responses and whether IP, as a geophysical tool, is able to detect and assess the potential for acid mine drainage due to bacterial activity. The study used an Acidithiobacillus ferrooxidans subspecies, isolated from the Kam Kotia mine tailings, Timmins, Ontario, using limiting dilutions in 9K buffer medium (pH 3; (NH4)2SO4, 0.4 g; K2HPO4, 0.1 g; MgSO4 7H2O, 0.1 g) supplemented with 3.3 g/L of filter sterilized FeSO4 7H2O as their energy source. Duplicate syringe columns experiments were prepared using varying concentrations of acid-washed silica and/or pyrite (simulating either disseminated or stratified pyritic ore) and colonized with thiobacilli. All columns were maintained under saturating conditions with circumneutral 9K buffer. Each column began with an acidic pH and became more alkaline over the 2-month experiment, typically ending close to the circumneutral pH of the media. The spectral-IP measurements responded directly to bacterial activity, i.e., changes in impedance were observed in all samples. Samples that contained bacteria were higher in impedance (with significant differences observed between frequencies of 10-100000Hz). Over time, scanning electron microscopy revealed increases in the bacterial corrosion surface area, bacterial ferric-sulfate encasement, the number of bacteria colonies and abundance of ferric precipitates. Bacterially induced mineralization was observed as patches in all systems. In the disseminated and stratified environments, the patches covered 8-10% of the grains, predominantly along the fractured mineral edges. In the `massive' 100% pyrite systems, bacteria-mineral patches covered up to 15% of grain surfaces and were not constrained to specific mineralogical features. Spectral-IP responses differed for each of these bacterial systems and can be modeled by equivalent circuits, implying that the application of these principles to field geophysics is possibile.
B53A-0983 1340h
Self-potential and Geochemical Measurements of Microbially Mediated Bacterial Sulfate Reduction in Saturated Sediments
In situ bioremediation is a non-invasive groundwater remediation technique that stimulates microorganisms to catalyze desirable redox reactions. Using a series of laboratory experiments, we explored the suitability of self-potential methods for monitoring bioremediation of metals contamination. Each experiment was designed to quantify the relationship between electrical potential and changing redox conditions and to determine factors influencing this relationship. In the first experiment, we introduced sulfate-reducting bacteria (SRB) into a Plexiglas tank containing autoclaved quartz sand saturated with an iron-rich Desulfovibrio (a sulfate-reducing bacteria) media. An array of non-polarizable electrodes positioned on the sediment surface was used to record electrical potentials both prior to and after inoculation for about 40 days. Changes in water chemistry were determined through a series of samples taken before, during and after the experiments. A significant decrease in total iron occurred after 3 days near the injection site; however, a clearly discernable decrease in electrical potential was not perceived until ~ day 10. Contoured SP data indicate that the redox front migrated away from the injection site over time. This change probably reflects the changing water chemistry as well as bacterial migration, as iron close to the injection site was consumed. The second experiment consisted of 4 glass columns, two of which were inoculated with SRB. The first pair contained sediment similar to the tank experiment saturated with an iron-rich media. The second pair contained the same sediment but was saturated with acid-mine drainage (AMD) collected from a contaminated field site. Each column was identically instrumented with a system of four electrodes. In the active columns, an increase in pH, a decrease in sulfate and a significant decrease in total iron in the media column accompany a decrease in electrical potential after about 10 days. Results of the study suggest that the redox reactions catalyzed by SRB are detectable using self-potential geophysical methods and that these methods may offer a low-cost supplement to more costly monitoring programs.
B53A-0984 1340h
Spatial Distribution of Sulfate and the Formation of Ettringite in Lime-Amended Soils of Central Texas
During road construction, the use of calcium-based stabilizers, such as calcium oxide (lime), in sulfate-bearing clay soils has historically lead to distress and heave due to the formation of ettringite and possibly thaumasite. Ettringite (Ca6(Al(OH)6)2(SO4)3*26H2O) is a hydrous calcium alumino-sulfate mineral that precipitates in environments with high pH and high sulfate activity. Field surveys of soil conductivity quantified using electromagnetics (EM31), geochemical characterization of soils, geochemical modeling of ettringite precipitation in lime-amended soils, and landscape characterization using existing geospatial databases were coupled to prediction the potential for ettringite formation along the SH 130 corridor, a new toll road being constructed in central Texas. Electromagnetic surveys of soil conductivities were conducted at two sites near HWY 290 and HWY 79, in the SH 130 corridor. Soil conductivities at the two sites were correlated extractable SO42- and other soil properties (extractable Al, Ca, and Mg) quantified by water extracts at two pHs (pH 8-9 and 12). At the HWY 290 site, the soil conductivity ranged from 111 to 184 ms/m, while the conductivity ranged from 34-48 ms/m at the HWY 79 site. The concentration of extractable SO42- in HWY 290 and HWY 79 sites are up to 7269 mg/kg and 406 mg/kg, respectively. Soils at these sites are dominated by smectitic clay with relatively high amounts of carbonate. Information from STATSGO, the USDA soil database, and the comparisons between the results of the field surveys and laboratory soil analyses show that variations in sulfate levels at the two sites are strongly influenced by topography. The HWY 79 site is fairly level and there are only very weak trends in the sulfate composition of the soils. The HWY 290 site, on the other hand, is fairly hilly, with a dry stream channel, whose soil and sediments exhibited very high sulfate concentrations. The strong topographic slope influences hydrologic flow, including both surface runoff and subsurface flow, which transports sulfate down slope. In addition, evapotranspiration during the dry season would also help accumulate sulfate in low-lying areas due to solute transport from near-surface ground waters. This study demonstrates that electromagnetics can be used for in-situ, field-scale survey of sulfates. Coupled with the application of geochemical speciation models, we assess the potential of ettringite formation in the SH 130 corridor.
B53A-0985 1340h
Poroelastic Parameters of Peru Margin Sediments: Implications for Flow and Transport at Multiple Scales in the Marine Biosphere
As part of a broader investigation of the deep marine subsurface environment, the first biosphere-focused drilling expedition, Leg 201, of the Ocean Drilling Program (ODP) occupied five unique sites in the Peru Margin (in a 1200 km$^2$ region centered at 10 S, 80E). These sites represent the entire range of shallow biogeological conditions associated with this convergent margin:deep-water, mixed clay-pelagic sediments ocean-ward of the trench; slope-apron and prism toe sediments at the deformation front; and several distinct lithostratigraphic sequences on the continental shelf. Microbial enumeration and pore-water geochemistry results show that each particular site is both consistent and unique--consistent in terms of general biotic quantity and activity as predicted by energy flux and redox potential given the depositional environment and sedimentary record, but unique at key biogeological boundaries such as lithologic and/or physical property interfaces. This research addresses questions related to our understanding of how and why these boundaries form by looking at poroelastic and hydrologic parameters measured at multiple scales, from sub-millimeter to several centimeters. The issue of measurement scale, especially in regard to permeability and diffusivity characterization, is vital to interpreting observations of biologically-mediated diagenetic fronts (e.g., dolomitic lenses, depth- or time-varying barite fronts). These parameters are derived from (i) hydrologic and wave propagation experiments, (ii) SEM images, and (iii) shipboard split-core measurements, and structured in a modified Biot poroelasticity framework. This approach also allows quantification of the local heterogeneity of these parameters at the scale applicable to (and controlled by) microbial life; these results can then be used to formulate predictive models of the impact of biogeochemical processes. Ultimately, these models could then be used in interpretation of new remote-sensed data (e.g., from borehole tools, high-frequency backscatter devices), a fundamental challenge for all types of biospheric imaging everywhere.