A reaction-based paradigm to model reactive chemical transport in groundwater with general kinetic and equilibrium reactions

This paper presents a reaction-based water quality transport model in subsurface flow systems. Transport of chemical species with a variety of chemical and physical processes is mathematically described by M partial differential equations (PDEs). Decomposition via Gauss-Jordan column reduction of the reaction network transforms M species reactive transport equations into two sets of equations: a set of thermodynamic equilibrium equations representing N(E) equilibrium reactions and a set of reactive transport equations of M-N(E) kinetic-variables involving no equilibrium reactions (a kinetic-variable is a linear combination of species). The elimination of equilibrium reactions from reactive transport equations allows robust and efficient numerical integration. The model solves the PDEs of kinetic-variables rather than individual chemical species, which reduces the number of reactive transport equations and simplifies the reaction terms in the equations. A variety of numerical methods are investigated for solving the coupled transport and reaction equations. Simulation comparisons with exact solutions were performed to verify numerical accuracy and assess the effectiveness of various numerical strategies to deal with different application circumstances. Two validation examples involving simulations of uranium transport in soil columns are presented to evaluate the ability of the model to simulate reactive transport with complex reaction networks involving both kinetic and equilibrium reactions.     

A GIS tool to estimate West Nile virus risk based on a degree-day model

West Nile virus (Flaviviridae: Flavivirus) is a serious infectious disease that recently spread across the North America continent. A spatial analysis tool was developed on the ArcMap 9.x platform to estimate potential West Nile virus activity using a spatially explicit degree-day model. The model identifies when the virus Extrinsic Incubation Period (EIP) is completed within the vector longevity during mid-summer months. The EIP is treated as a threshold indicator of the potential for virus emergence and activity. Comparing the number of West Nile virus cases in Wyoming reported from 2003 to 2005 with model results, actual cases and predicted events of West Nile virus activity match relatively well. The model represents a useful method for estimating potential West Nile virus activity in a large spatial scale.     

Radio-acoustic positioning as a tool for studying site-specific behavior of the white shark and other large marine species

We describe a method, radio-acoustic-positioning (RAP), for continuously monitoring the movements and behavior of large marine animals. An ultrasonic transmitter on the animal can be localized with high spatial accuracy (2 to 10?m) within an area of 1?km², based on when the same pulse arrives at three hydrophones on sonobuoys aligned in a triangular array. Radio transceivers communicate with the base station, where the x and y coordinates of the subject are calculated using hyperbolic equations. The base station plots the individual's position and displays information from the tag's sensors in real time on a computer monitor before saving the data on a disk. The base station must be situated either on land or on a vessel within the reception range of the three buoys. We used a RAP system to monitor the movements and behavior of white sharks (Carcharodon carcharias) near the elephant seal rookery at Año Nuevo Island in central California. This type of system is an ideal tool to study the predatory behavior of the white shark because individuals patrol for seal prey within a zone <1300?m from shore. We describe the operation of the system, including acoustic triangulation, range of detection and positioning, data acquisition and analysis, and positional accuracy. We illustrate the implementation of the method and its advantages and disadvantages by describing an ongoing study of white shark hunting-behavior. Sample data from this study are presented to illustrate specific points. We describe the movements of five sharks within the receiving range and their behavior relative to each other. The RAP system is compared to other complementary tracking methods. We conclude that this system has great potential for monitoring the movements and behavior of large marine animals within a relatively small zone, where feeding or reproduction takes place.     

The hunting strategy of white sharks (Carcharodon carcharias) near a seal colony

The degree to which white sharks, Carcharodon carcharias, are social while hunting is unclear. Our aim was to describe the behavior and interactions among white sharks hunting seals near a seal colony. We attached ultrasonic beacons to five adult white sharks, 4.5–5.2?m long, and recorded their movements and behavior toward each other over a 15-day period in October 1997 at Año Nuevo Island, California. This site is home to colonies of four species of seals and sea lions. Two additional sharks, females 5.5 and 4.7?m in length, were later tracked intensively during periods of 12 and 3?days during October 1998 and November 1999, respectively. We recorded stomach temperature (indicative of feeding on warm-bodied seals) and swimming depths from the 5.5-m female, swimming speed and depth from the 4.7-m female. We monitored the movements and behavior of these sharks using an array of sonobuoys moored near the island; the receptive field measured 1?km². Our principal findings were: (1) the sharks spent a mean time of 39.5% of each day patrolling within the receptive field; (2) no shark ever moved far out of it; (3) the sharks spent an equal amount of time and activity in the receptive field at all times of the day, daytime, twilight, and nighttime; (4) movements with respect to the island rookery were most often back and forth parallel to the shoreline, (5) tracks of three sharks, tagged at the same time and place, overlapped more often than those of the other two sharks; and (6) some sharks patrolled certain areas in the field preferentially, but there was no conclusive evidence that they defended these areas as territories. Feeding appeared to be infrequent: only two likely feeding bouts occurred during a cumulative 78-day/shark period that individuals were monitored at Año Nuevo Island. The behavior and movements of the sharks were consistent with a hunting strategy, in which individuals search for prey independently but, at the same time, remain close enough to each other to “sense” and exploit a kill by any one of them by joining in on the kill to feed.     

Design and Testing of a Turbulence Probe for Harsh Flows

The force of wind on the ground created by turbulent eddies is commonly used to describe the horizontal flux of material during wind erosion. Here we present the Murdoch Turbulence Probe, an instrument for use in both clean and eroding flows which uses pressure differences to measure the three components of wind velocity. Correlation techniques calculate the forces near the ground and turbulence statistics in nearly real time, including turbulent velocity fluctuations from less than 0.1 Hz to 200 Hz, mean flow velocities, Reynolds stresses as well as the integral length and time scales. In the portable wind-tunnel used by Agriculture Western Australia, turbulence statistics were recorded over stable surfaces and in blowing sand from the initiation of erosion up to the time the sand supply was exhausted. Estimates of the friction velocity derived from the turbulence probe were compared with estimates obtained from the wind speed profile measured with a rake of pitot and static tubes. The Murdoch Turbulence Probe appears to work well in sandblasting conditions. Relative turbulence intensities ranged from 0.11 to 0.2 and are in close agreement with values in the literature. The ratio of the turbulence to the friction velocity (3 to 3.2) is at the high end of the reported range. The Reynolds stress measurements agree closely with predictions of the threshold friction velocities of the sand and estimates from the wind speed profile with a von Kármán constant of about 0.3, lower than the commonly accepted value of 0.4. We suggest that the wind-tunnel profile represents the `outer layer' of the boundary-layer that may best be described by a `Wake Law' or `Defect Law'. At about 54 mm above the surface, the friction velocity decreases from 0.64 m/s to 0.39 m/s and the mean velocity increases from 9.6 m/s to 11.6 m/s as the supply of sand is depleted. In addition to the friction velocity, other scales may be necessary to characterise the overriding effect of the wind and in extending wind-tunnel results to the field.     

Inventory methods for trees in nonforest areas in the great plains states

The US Forest Service’s Forest Inventory and Analysis (FIA) program collects information on trees in areas that meet its definition of forest. However, the inventory excludes trees in areas that do not meet this definition, such as those found in urban areas, in isolated patches, in areas with sparse or predominantly herbaceous vegetation, in narrow strips (e.g., shelterbelts), or in riparian areas. In the Great Plains States, little is known about the tree resource in these noninventoried, nonforest areas, and there is a great deal of concern about the potential impact of invasive pests, such as the emerald ash borer. To address this knowledge gap, FIA’s National Inventory and Monitoring Applications Center has partnered with state cooperators and others in a project called the Great Plains Initiative to design and implement an inventory of trees in nonforest areas. The goal of the inventory is to characterize the nonforest tree resource using methods compatible with those of FIA so a holistic understanding of the resource can be obtained by integrating the two surveys. The goal of this paper is to describe the process of designing and implementing the survey, including plot and sample design, and to present some example results from a reporting tool we developed.     

Rangeland and pasture monitoring: an approach to interpretation of high-resolution imagery focused on observer calibration for repeatability

Collection of standardized assessment and monitoring data is critically important for supporting policy and management at local to continental scales. Remote sensing techniques, including image interpretation, have shown promise for collecting plant community composition and ground cover data efficiently. More work needs to be done, however, evaluating whether these techniques are sufficiently feasible, cost-effective, and repeatable to be applied in large programs. The goal of this study was to design and test an image-interpretation approach for collecting plant community composition and ground cover data appropriate for local and continental-scale assessment and monitoring of grassland, shrubland, savanna, and pasture ecosystems. We developed a geographic information system image-interpretation tool that uses points classified by experts to calibrate observers, including point-by-point training and quantitative quality control limits. To test this approach, field data and high-resolution imagery (∼3 cm ground sampling distance) were collected concurrently at 54 plots located around the USA. Seven observers with little prior experience used the system to classify 300 points in each plot into ten cover types (grass, shrub, soil, etc.). Good agreement among observers was achieved, with little detectable bias and low variability among observers (coefficient of variation in most plots <0.5). There was a predictable relationship between field and image-interpreter data (R ² > 0.9), suggesting regression-based adjustments can be used to relate image and field data. This approach could extend the utility of expensive-to-collect field data by allowing it to serve as a validation data source for data collected via image interpretation.     

Can juvenile corals be surveyed effectively using digital photography?: implications for rapid assessment techniques

Seasonal variations in the concentrations of groundwater with respect to arsenic, lead, cadmium and aluminium has been studied in Dhemaji district of Assam, India. The water samples were collected from 20 different sites in both dry and wet seasons. The metals were analysed by using atomic absorption spectrometer, Perkin Elmer AAnalyst 200 model. The concentrations of aluminium, lead and cadmium in groundwater were found to be significantly elevated. High concentrations of all the metals were recorded in the dry season than in the wet season. Univariate statistics along with skewness, kurtosis and confidence limit have been calculated for both the seasons to test the distribution normality for each metal. Statistical analyses of the data reveal non-uniform distribution of the metals in the area. The metal contamination of groundwater in the district follows the trend Al > Pb > Cd > As in both the seasons.     

Use of space-filling curves to select sample locations in natural resource monitoring studies

The establishment of several large area monitoring networks over the past few decades has led to increased research into ways to spatially balance sample locations across the landscape. Many of these methods are well documented and have been used in the past with great success. In this paper, we present a method using geographic information systems (GIS) and fractals to create a sampling frame, superimpose a tessellation and draw a sample. We present a case study that illustrates the technique and compares results to those from other methods using data from Voyageurs National Park in Minnesota. Our method compares favorably with results from a popular plot selection method, Generalized Random Tessellation Stratified Design, and offers several additional advantages, including ease of implementation, intuitive appeal, and the ability to maintain spatial balance by adding new plots in the event of an inaccessible plot encountered in the field.     

Relative Phytoplankton growth responses to physically and chemically dispersed South Louisiana sweet crude oil

We conducted controlled laboratory exposure experiments to assess the toxic effects of water-accommodated fractions (WAFs) of South Louisiana sweet crude oil on five phytoplankton species isolated from the Gulf of Mexico. Experiments were conducted with individual and combinations of the five phytoplankton species to determine growth inhibitions to eight total petroleum hydrocarbon (TPH) equivalent concentrations ranging from 461 to 7,205 ppb. The composition and concentration of crude oil were altered by physical and chemical processes and used to help evaluate crude oil toxicity. The impact of crude oil exposure on phytoplankton growth varied with the concentration of crude oil, species of microalgae, and their community composition. At a concentration of TPH <?1,200 ppb, dinoflagellate species showed significantly better tolerance, while diatom species showed a higher tolerance to crude oil at higher concentrations of TPH. For both groups, the larger species were more tolerant to crude oil than smaller ones. The toxicity potential of crude oil seems to be strongly influenced by the concentration of polycyclic aromatic hydrocarbons (PAHs). The addition of the dispersant, Corexit® EC9500A, increased the amount of crude oil up to 50-fold in the water column, while the physical enhancement (vigorous mixing of water column) did not significantly increase the amount of TPH concentration in the water column. The species response to crude oil was also examined in the five-species community. Each phytoplankton species showed considerably less tolerance to crude oil in the five-species community compared to their individual responses. This study provides baseline information about individual phytoplankton responses to crude oil and dispersed crude oil for subsequent research efforts seeking to understand the impacts of oil on the phytoplankton in the bigger picture.