John F. Dowd

Assemblage stability in stream fishes: a review

We quantified the stability of nine stream fish assemblages by calculating coefficients of variation of population size for assemblage members. Coefficients of variation were high and averaged over 96%; indicating that most assemblages were quite variable. Coefficient of variation (CV) estimates were not significantly affected by: (1) years of study, (2) mean abundance, (3) familial classification, or (4) mean interval between collections. We also detected minor regional differences in CVs. The high variability exhibited by many stream fish assemblages suggests that it may be difficult to detect the effects of anthropogenic disturbances using population data alone. Consequently, we urge managers to exercise caution in the evaluation of the effects of these disturbances. More long-term studies of the ecological characteristics of undisturbed stream fish assemblages are needed to provide a benchmark against which disturbed systems can be compared.We suggest that CVs are a better estimator of population/assemblage stability, than either Kendalls W or the standard deviation of the logarithms of numerical censuses. This conclusion is based on the following reasons. First, CVs scale population variation by the mean and, hence, more accurately measure population variability. Second, this scaling permits the comparison of populations with different mean abundances. Finally, the interpretation of CV values is less ambiguous than either of the aforementioned metrics.

Maximum vehicle cabin temperatures under different meteorological conditions

A variety of studies have documented the dangerously high temperatures that may occur within the passenger compartment (cabin) of cars under clear sky conditions, even at relatively low ambient air temperatures. Our study, however, is the first to examine cabin temperatures under variable weather conditions. It uses a unique maximum vehicle cabin temperature dataset in conjunction with directly comparable ambient air temperature, solar radiation, and cloud cover data collected from April through August 2007 in Athens, GA. Maximum cabin temperatures, ranging from 41–76°C, varied considerably depending on the weather conditions and the time of year. Clear days had the highest cabin temperatures, with average values of 68°C in the summer and 61°C in the spring. Cloudy days in both the spring and summer were on average approximately 10°C cooler. Our findings indicate that even on cloudy days with lower ambient air temperatures, vehicle cabin temperatures may reach deadly levels. Additionally, two predictive models of maximum daily vehicle cabin temperatures were developed using commonly available meteorological data. One model uses maximum ambient air temperature and average daily solar radiation while the other uses cloud cover percentage as a surrogate for solar radiation. From these models, two maximum vehicle cabin temperature indices were developed to assess the level of danger. The models and indices may be useful for forecasting hazardous conditions, promoting public awareness, and to estimate past cabin temperatures for use in forensic analyses.

Quantification of pore size distribution and the movement of solutes through isolated soil blocks

Techniques to provide a quantitative description of soil structure in a reasonable time scale using equipment that is widely available are examined. Three complementary techniques for quantifying soil structure within the pore size range from 136 to 4000 μm (equivalent diameter) are evaluated for two isolated, unsaturated soil blocks (0.85 m3). Profile tracing and binary transect methods were used to examine the pore sizes >1000 μm. Pore sizes <1000 μm were quantified using 2-dimensional image analysis of resinated core samples. Prior to collection of the blocks, the technique of mole ploughing was used to generate a range of pore sizes in the heavy clay soil (Hallsworth series) by shattering. Pore size distribution was related to observed changes in solute concentration following a miscible displacement of a 250 mg l−1 Cl− solution applied at an irrigation rate of 3 mm h−1. Analysis of soil matric potential data showed that solute movement was predominately limited to pores of between 136 and 1000 μm equivalent diameter. Using a combination of Poiseuilles law and pore-size distribution data, it was inferred that the observed rate of flow in the soil could have been achieved through a range of pore-size distributions, between 300 and 1000 μm as a sufficient quantity of pore space within the range of 136 to 1000 μm (diameter) was recorded. It is concluded that the rapid movement of tracer to depth can occur within an unsaturated soil in which active porosity is limited to mesopores and this rapid movement can be described as preferential flow.

QUAntIfyInG thE hEAt-RELAtED hAzARD fOR ChILDREn In MOtOR VEhICLES

Thirty-seven children on average die each year in the United States from vehicle-related hyperthermia. In many cases, the parent or caregiver intentionally left the child unattended in the car, unaware of how quickly temperatures may reach deadly levels. To better quantify how quickly temperatures may increase within a car, maximum rates of temperature change were computed from data collected on 14 clear days in Athens, Georgia. Also, a human thermal exchange model was used in a case study to investigate the influence of different meteorological factors on the heat stress of a child in a hot vehicle. Results indicate that a car may heat up by approximately 4°C in 5 min, 7°C in 10 min, 16°C in 30 min, and 26°C in 60 min. Within the vehicle, the dominant energy transfers toward the child are via longwave radiation and conduction from the hot interior surfaces of the car. Modeling simulations show that sun exposure and high-humidity conditions further increase the heat stress on the child but that a negative...

Trends in Extreme Apparent Temperatures over the United States, 1949–2010

AbstractBiometeorological indices, such as the apparent temperature, are widely used in studies of heat-related mortality to quantify the human sensation to the environmental conditions. Increases in the frequency of environmentally stressful days as indicated by biometeorological indices may augment the risk for heat-related morbidity and mortality. This study examines trends in the frequency of days with extreme maximum and minimum apparent temperatures across the United States for 1949–2010. An increase in occurrence of 1-day extreme minimum apparent temperatures is particularly notable, especially in the eastern and western United States, with 44% of stations exhibiting positive trends. About 20% of stations have positive trends in 1-day extreme maximum apparent temperature, mostly in the western United States. The median trend for both 1-day extreme maximum and minimum apparent temperature is approximately 2 days per 10 yr, indicating that by 2010 there were 12 more days with extreme apparent tempera...

Use of inexpensive pressure transducers for measuring water levels in wells

Frequent measurement of below ground water levels at multiple locations is an important component of many wetland ecosystem studies. These measurements, however, are usually time consuming, labor intensive, and expensive. This paper describes a water-level sensor that is inexpensive and easy to construct. The sensor is placed below the expected low water level in a shallow well and, when connected to a datalogger, uses a pressure transducer to detect groundwater or surface water elevations. Details of pressure transducer theory, sensor construction, calibration, and examples of field installations are presented. Although the transducers must be individually calibrated, the sensors have a linear response to changing water levels (r2 ≈ .999). Measurement errors resulting from temperature fluctuations are shown to be about 4 cm over a 35°C temperature range, but are minimal when the sensors are installed in groundwater wells where temperatures are less variable. Greater accuracy may be obtained by incorporating water temperature data into the initial calibration (0.14 cm error over a 35C temperature range). Examples of the utility of these sensors in studies of groundwater/surface water interactions and the effects of water level fluctuations on tree growth are provided.

Using 18O/16O data to examine the mixing of water masses in floodplain wetlands

Oxygen isotopic data were used to assess how far waters from the Savannah River, a major river in the Southeastern United States, backed up and inundated the wetlands along a small Coastal Plain tributary during a flood. This approach worked because the water of this tributary, Unper Three Runs, had an oxygen isotopic composition (δ18O = −4.9 ‰) distinct from Savannah River water (δ18O = −3.2 ‰).Two sample surveys were taken from the mouth of Upper Three Runs to 2 km upstream. Waters were isotopically uniform along the length of the sample transect when both river and tributary water levels were below bankfull. Visual estimates of turbidity taken when both the river and tributary overflowed their channels and inundated adjacent wetlands indicated that Savannah River water extended about 300 meters up the tributary channel. In contrast, the isotopic data indicated that a mixing zone of river and tributary waters extended about 1100 meters upstream. Although this mixing zone was documented only in the channel of Upper Three Runs, it probably extended into adjacent parts of the riparian wetland, potentially affecting ecological processes due to the differing water quality. This study was conducted in a single river-tributary system and the approach is probably applicable in other large rivers.Corresponding Editor: R. Sharitz

Computer control for investigating water and chemical transport in a large isolated soil block

Abstract This paper describes the computer controlled data acquisition systems designed to obtain fine spatial and temporal resolution data of tracer in soil water within a large undisturbed soil block. Such information is desirable to help understand and model transport mechanisms in light of increasingly strict environmental pollution limits. The soil block was 5.4 × 3.4 × 1.2 m, instrumented in nine layers with time domain reflectometry (TDR) waveguides multiplexed using a PC; pressure transducer equipped tensiometers multiplexed using a datalogger and suction samplers connected to in situ flow-injection analysis systems controlled by a PC. A rainfall simulator capable of applying tracer to the block without altering the surface flux (which could range from 1 to 30 mm h −1 ) was controlled by a datalogger. Initial conditions when the soil block was subjected to a surface flux of 10 mm h −1 are presented along with an example of a chloride breakthrough curve to illustrate the nature of the data obtained from the soil block system. It is concluded that the integrated system described is a significant advance in working technology for field and plot scale tracer experiments because the spatial and temporal resolutions achieved are possible with a single person maintaining the system.

A field-based spectrophotometric flow-injection system for automatic determination of chloride in soil water

The use of chloride as a tracer for soil water investigations is discussed. Limitations with laboratory based soil core and field based sampling are considered with respect to the poor suitability of the data for rigorous assessment of mechanistic models. Investigation of water movement in soil has been restricted by limitations in spatial and temporal sampling. Fine resolution sampling generates large numbers of samples which cause problems with post sampling laboratory analysis. This paper describes a field-based system for the analysis of chloride in soil water. There are three component parts to the system, (i) a custom sampling sub-system comprising of ceramic cup suction samplers and sample traps, (ii) a sample routing sub-system to channel sample to (iii) a sample analysis sub-system utilizing a flow injection method for sample analysis using a custom built photo-diode detector. The three sub-systems were controlled by a suitably equipped personal computer. A calibration procedure is described with a third order polynomial equation derived to convert millivolt response from the detector into chloride concentration. Field and laboratory data from a tracer experiment are presented and discussed, and it is concluded that the system is well suited to field-based applications. Finally it is noted that the photo-detector is suitable for colourimetric analysis of any tracer with suitable chemical determination.

Near Real-Time Determination of Nitrate Leaching as an Integrated Component of a Large Soil Block Experiment for Fine Resolution Investigation of Preferential Flow

A large soil block was isolated in situ at North Wyke, Devon, UK. It was designed as the basis for fine spatial and temporal resolution investigations of water and chemical movement by preferential flow through a well structured soil. Three simultaneous tracer experiments were conducted within the block using a chloride/nitrate/deuterium cocktail. This paper consideres the nitrate experiment. The block was densely instrumented with time domain reflectometry waveguides (to measure volumetric water content), tensiometers (to measure matric potential) and suction samplers (to extract soil water and tracer). All instrumentation was automated using computers, and chloride concentration was determined using in situ flow-injection systems. To determine nitrate concentrations, samples were obtained from the samplers (54) once an hour. In the day-time some samples were analysed using test-strip technology and some stored for analysis the next day. In a 24 hour period a total of 1296 samples were available for analysis. The temporal resolution obtained, while not as fine as that for chloride, was greatly in excess of anything previously attempted in the field. The fine resolution was possible, partially because a single operator could perform analysis as sample became available without total reliance on a busy laboratory facility.