B51F-01 INVITED 08:00h
Remote Sensing of Subsurface Microbial Transformations
Understanding how microorganisms influence the physical and chemical properties of the subsurface is hindered by our inability to detect microbial dynamics in real time with high spatial resolution. Here we have used non-invasive geophysical methods to monitor biomineralization and related processes during biostimulation at both laboratory and field scales. Alterations in saturated sediment characteristics resulting from microbe-mediated transformations were concomitant with changes in complex resistivity, spontaneous potential, and acoustic wave signatures. Variability in complex resistivity and acoustic wave amplitudes appears tied to the nucleation, growth, and development of nanoparticulate precipitates along grain surfaces and within the pore space. In contrast, time-varying spontaneous potentials appear primarily sensitive to the electrochemical gradients resulting from metabolic pathways, such as iron- and sulfate-reduction. Furthermore, they enable us to track mobile fronts of active respiration that arise due to microbial chemotaxis. In this way, geophysical data may be used to image the distribution of mineral precipitates, biomass, and biogeochemical fronts evolving over time and suggest the ability to remotely monitor contaminated aquifers undergoing bioremediation.
B51F-02 INVITED 08:15h
Geoelectrical Effects Associated With the Presence of Bacteria in Contaminated Groundwater
Strong electrical potential anomalies (up to several hundreds of mV) have been evidenced at the ground surface above contaminant plumes rich in organic matter. These electrical disturbances, recordable with non-polarizable electrodes as "self-potential signals", allow to delineate the shape of these plumes and their dynamics. We have investigated the physics behind this geobattery process. Our conclusions are that biofilms, mainly located at the boundaries of the plume where both nutrients and oxygen are available (Monod kinetics), allow the transfer of electrons between the reduced and the oxidized parts of the system. The resulting current density produces electromagnetic disturbances in the Maxwell equations. We show from models, field and sandbox experiments that the electrical potential can be used to determine the redox potential at depth with a minimum of calibration with in situ measurements. Therefore, this method can be used as a redox non-intrusive sensor. The model implies that the areas rich in bacteria are also associated with anomalous high electrical conductivity and induced polarization anomalies as suggested from experiments by E. Atekwana, L. Slater, and co-workers.
http://www.cerege.fr/hydropor/index_hydropor.htm
B51F-03 08:30h
Experimental investigation of the link between geophysical signatures and biogeochemical properties and processes: experimental design, data collection and interpretation
Recent research indicates a correlation between geophysical data from a number of electrical methods (resistivity, induced polarization and self potential) and subsurface biogeochemical properties and processes. Thus, the hope is that electrical measurements will provide proxy indicators of the macroscopic changes in hydraulic and biogeochemical subsurface properties resulting from microbial activity at contaminated sites. A significant problem in making the link is the limited availability of well controlled three dimensional datasets: while field data is three dimensional, it provides little control, whereas most laboratory results are obtained from column experiments. We will report on out approach to highly controlled and automated experiments. In these experiments electrical geophysical data (SP and IP data) is being collected simultaneously and automatically with point measurement of aqueous geochemistry for both 2D and 3D environments. Integrated experimental control and data management for such experiment is critical as it allows transparent and reproducible acquisition and analysis, both of which are essential to build up baseline data for quantitative and qualitative correlation of geophysical data to biogeochemical properties and processes.
B51F-04 08:45h
Selective Characterization of Phosphorus Oxyanions in Synthetic Geothermal Water Using IC/MS Methods
Recent studies show microorganisms contain enzymes used to metabolize reduced trivalent (III) phosphite and univalent (I) hypophosphite, suggesting that microorganisms can utilize phosphorus oyxanions in oxidation states other than pentavalent (V) phosphate, the most common form of bioavailable phosphorus. Moreover, highly reduced forms of phosphorus, namely phophine (-III) have been detected in nature in reducing environments such as sewage, marine sediments, and in industrial and agricultural processes. The combination of these studies has made it increasingly important to develop sensitive and selective biogeochemical methods that distinguish between the different oxidation states of filterable inorganic phosphorus oxyanions in natural water. Our laboratory has developed ion chromatography methods that use conductivity detection to separate hypophosphite, phosphite and phosphate in a synthetic geothermal water matrix, however, resolution challenges limit the sensitivity of this technique. This paper will discuss a new 2-D technique that couples ion chromatography with electrospray mass spectrometry (IC/MS) with limits of detection up to 45 times lower than those reported in previous studies. The technique was optimized for the detection hypophosphite, phosphite, and phosphate in a synthetic geothermal water matrix consisting of fluoride, chloride, bromide, nitrate, bicarbonate, and sulfate. Samples were pretreated with Dionex OnGuard II silver and hydrogen cartridges to remove excess chloride, bromide and bicarbonate anions that reduced the instrument sensitivity for the phosphorus oxyanions. Injection loop sizes as large as 900 $\mu$L were employed to further improve instrument sensitivity. The estimated 3$\sigma$ limits of detection are 0.047 $\mu$M, 0.0086 $\mu$M, and 0.12 $\mu$M for hypophosphite, phosphite, and phosphate, respectively. The implications of these results to the biogeochemistry community will be discussed.
B51F-05 09:00h
Smart Sensor Arrays for Environmental and Atmospheric Research
This paper provides an examination of how smart sensory arrays can be used to study complex, interwoven environmental and meteorological processes. We begin with a summary of challenges researchers confront as they attempt to combine various measurements and modeling approaches into integrated land-atmosphere views. We describe land-atmosphere process models in general. We propose an architecture of sensors arrays that will incorporate land-atmosphere processes, their interactions and scale. A set of system design requirements are developed that convert the hardware design of the sensor nodes, the design of the sensor network and the capabilities for remote data access and management into a configuration suitable for land-atmosphere research. We present a specific instance of the architecture for monitoring carbon sequestration in subalpine forests. The proposed deployed network will consist of 320 microscale nodes, 9 mesoscale nodes and 2 network nodes. The application driven design exercise serves to identify important areas of further work in data sampling, communications, network retasking and health monitoring. Key Works : Array - collection of sensors in a network; Cluster - a dynamic connection of higher-level nodes with local lower-level nodes; Event - Internally generated or externally received diagnostic (including network), sensed or derived signal requiring response evaluation; Microscale -spatial scales 10 meters or less; Mesoscale - spatial scales 10 meters to 10 kilometers; Node - physical and conceptual model of a sensor in a network; Sensor - combination of one or more transducers, a data input/output(I/O) component, a power component, and a transmitter component; Transducer - sensor component that converts state property (temperature, humidity) to electronic signal. Examples: thermister, capacitive moisture transducer, etc.
http://www.colorado.edu/eeb/
B51F-06 09:15h
Understanding disturbance impacts on the ecosystem respiration with a continuous monitoring system
Respiration is a critical part of ecosystem carbon balance, yet we don't have sufficient ways of directly assessing respiration over large areas for a long time. This study is designed to assess ecosystem respiration rates at a large scale through modeling driven primarily by remotely sensed signals and ecosystem physical properties. The study was conducted at the Sky Oaks Field Station in Northeast San Diego County. This site was unique because it had experienced many disturbances, including extremely drought, wildfire, and ENSO oscillations. This provided a rich set of opportunities for studying perturbing respiratory processes. We have deployed an automated, dual-channel spectrometer mounted on a mobile "Tram system" that provided repeated sampling of the same 100m transect We used optical and thermal measurement to link the different components of the net ecosystem exchange measurement from the adjacent eddy tower. An automatic soil chamber system has been set up to monitor soil CO$_{2}$ fluxes to separate the net ecosystem exchange from the belowground contribution. Along the tram system, a series of soil temperature and soil moisture sensors have been set up to monitor the continuous spatial patterns of soil properties for the soil respiration model. From short-temporal scale measurement, soil temperature alone explained 76% of the variation in soil respiration rate, and soil moisture alone explained 63%, while both variables combined explained 81% of the variation. There was a strong link between normalized difference vegetation index (NDVI) and ecosystem respiration. However, this relationship changes under severe disturbance (e.g. drought and fire). Our goal is to extend the respiration model to larger scales through satellite (e.g. MODIS) remotely sensed signals.
B51F-07 09:30h
The Use of Wireless Sensor Networks in Soil Ecology
The availability of inexpensive, low power wireless sensors is changing the way we can acquire environmental information. This type of monitoring is especially necessary in systems, where conditions vary at different spatial and temporal scales. The most spatially complex stratum of a terrestrial ecosystem is its soil. Soil harbors an enormous variety of plants, microorganisms, invertebrates and vertebrates which provide numerous ecosystem services, such as decomposition of organic matter, soil aeration, modification of pore and aggregate size. We still poorly understand how biodiversity, abundance and functioning of the soil system are linked together. Our understanding of soil organism dynamics and, more importantly the role these organisms play in important ecosystem processes is limited due to the complexity of this environments and lack of continuously collected abiotic data. In particular, spatial and temporal variations in the environmental factors over mezoscopic (1-10m) distances is important to the distribution and behavior of soil invertebrates, to their role in litter and nutrient dynamics, and to soil nutrient processing. This presentation focuses on how low-cost wireless networks can be assembled and customized to augment several ongoing soil ecological studies in the Baltimore Ecosystem Study, and urban LTER site. A relatively modest configuration of a few hundred sensors will collect close to 100 million data points over a year. The projects range from neighborhood scale assessment of soil communities to reproductive biology of invasive soil invertebrates and to a detailed study of the enormous spatial and temporal heterogeneity of the soil substrate.
B51F-08 09:45h
Scaleable Nitrate Microsensors in the Form of a Plant Root
This work describes the development of flexible, miniature and inexpensive nitrate sensors by electropolymerizing pyrrole onto carbon fiber substrates, using nitrate as a dopant. Carbon microfibers were found to be an excellent substitute to expensive conductive materials, such as glassy carbon or platinum. The electrodes with a 3-5 micron layer of NO3 -doped polypyrrole (PPy) exhibited a promising lifetime (at least 2 month without changes in sensitivity and linear response), fast response times (seconds), and sensitivity competitive to commercial nitrate ISE. Nernstian sensor response slopes of 54 to 58 mV/(decade concentration) for single filament have been observed, with a linear response to nitrate concentrations spanning three orders of magnitude (0.1 - 10-4 M or 6200 - 6.2 ppm of NO3-), and a detection limit of (3  1) x 10-5 M (1.25-2.5 ppm). An advantage of using the carbon fibers as a substrate for pyrrole polymerization process is that these fibers are relatively easy to manipulate, lending themselves to root-like electrode designs which may be ideal for observing the water chemistry of soil moisture. Using prototypical PPy-coated microfibers, we have been able to directly measure nitrate concentrations in residual soil water contents as low as 8 percent by weight for a medium sand. Results for model soils and field samples are presented in which direct measurements with the microsensors compare reasonably well with a more conventional analytical method entailing soil extraction and analysis by the Griess-Romijn method.