RIVER-BED SEDIMENTATION CAUSED BY OFF-ROAD VEHICLES AT RIVER FORDS IN THE VICTORIAN HIGHLANDS,AUSTRALIA1

ABSTRACT: This study investigates some of the effects occurring at recreational off-road vehicle (ORV) crossings on two rivers in eastern Victoria, where many road crossings occur at low-level fords. Further, it provides a method whereby the amount of sediment redeposited downstream of a ford can be measured. Attention is drawn to the fact that sediment is contributed to the river by five major processes: the creation of wheel ruts and concentration of surface runoff, the existence of tracks and exposed surfaces, the compaction and subsequent reduction in the infiltration rate of soils leading to increased surface runoff, backwash from the vehicle, and undercutting of banks by bow wave action. The last two of these processes have not been reported previously. Sediment collection experiments in two Victorian upland rivers indicate a mean deposition rate at the stream bed of approximately 1000 g m^?2 over a period of 30 days.     

Allocation of nuptial gifts in tree crickets changes with both male and female diet

Male tree crickets, Oecanthus nigricornis, offer a nuptial gift to females during mating in the form of a secretion from a dorsal metanotal gland. I examined the effects of male and female nutrient limitation on allocation of the gift. Males were fed ¹⁴C radiolabeled amino acids, placed onto high- or low-quality diets and then mated with females also maintained on high- or low-quality diets. Female acquisition of radiolabel increased, and residual radiolabel within the metanotal gland decreased, over time verifying that gift size correlates with duration of courtship feeding. High-diet females produced greater egg numbers and allocated proportionally more of the male-derived amino acids to their ovaries. As predicted, duration of courtship feeding was greater for males on high-quality diets and females on low-quality diets. Amino acid transfer, measured as the proportion of total radiolabel transferred to the female, showed a significant interaction between male and female diet. High-diet females acquired available radiolabel more rapidly from high-diet males, but low-diet females acquired available radiolabel more rapidly from low-diet males. The causes of these differences between feeding duration and nutrient allocation are discussed.     

Chihuahuan Desert kangaroo rats: nonlinear effects of population dynamics, competition, and rainfall

Using long-term data on two kangaroo rats in the Chihuahuan Desert of North America, we fitted logistic models including the exogenous effects of seasonal rainfall patterns. Our aim was to test the effects of intraspecific interactions and seasonal rainfall in explaining and predicting the numerical fluctuations of these two kangaroo rats. We found that logistic models fit both data sets quite well; Dipodomys merriami showed lower maximum per capita growth rates than Dipodomys ordii, and in both cases logistic models were nonlinear. Summer rainfall appears to be the most important exogenous effect for both rodent populations; models including this variable were able to predict independent data better than models including winter rainfall. D. merriami was also negatively affected by another kangaroo rat (Dipodomys spectabilis), consistent with previous experimental evidence. We hypothesized that summer rainfall influences the carrying capacity of the environment by affecting seed availability and the intensity of intraspecific competition.     

Evaluation of nitrogen dioxide photolysis rates in an urban area using data from the 1997 Southern California Ozone Study

The photolysis of nitrogen dioxide and formaldehyde are two of the most influential reactions in the formation of photochemical air pollution, and their rates are computed using actinic flux determined from a radiative transfer model. In this study, we compare predicted and measured nitrogen dioxide photolysis rate coefficients (j_NO2). We used the Tropospheric Ultraviolet-Visible (TUV) radiation transfer model to predict j_NO2 values corresponding to measurements performed in Riverside, California as part of the 1997 Southern California Ozone Study (SCOS’97). Spectrally resolved irradiance measured at the same site allowed us to determine atmospheric optical properties, such as aerosol optical depth and total ozone column, that are needed as inputs for the radiative transfer model. Matching measurements of aerosol optical depth, ozone column, and j_NO2 were obtained for 14 days during SCOS’97. By using collocated measurements of the light extinction caused by aerosols and ozone over the full height of the atmosphere as model input, it was possible to predict sudden changes in j_NO2 resulting from atmospheric variability. While the diurnal profile of the rate coefficient was readily reproduced, j_NO2 model predicted values were found to be consistently higher than measured values. The bias between measured and predicted values was 17–36%, depending on the assumed single scattering albedo. By statistical analysis, we restricted the most likely values of the single scattering albedo to a range that produced bias on the order of 20–25%. It is likely that measurement error is responsible for a significant part of the bias. The aerosol single scattering albedo was found to be a major source of uncertainty in radiative transfer model predictions. Our best estimate indicates its average value at UV-wavelengths for the period of interest is between 0.77 and 0.85.     

DETERMINING THE SOURCE OF STREAM CONTAMINATION IN A KARST‐WATER SYSTEM,SOUTHWEST VIRGINIA,USA1

ABSTRACT: Karst terrane provides a linkage between surface water and ground water regimes by means of caves, sinkholes and swallets, and sinking streams, and facilitates the inter‐watershed transfer of water and contaminants through these subsurface systems. The goal of this study was to develop procedures to identify the sources of degradation of a creek situated in a complex karst‐water system. The study approach consisted of using dye tracing technique to determine subsurface flow paths through the karst system, a water‐sampling network to identify and characterize pollution sources within the surface watershed and subsurface flow regime, and evaluation of analytical data for several water quality parameters. The results of this study provide an interesting perspective of water and contaminant movement in karst‐water systems and pinpoint the sources of stream contamination for a case study site in southwest Virginia where two springs supply water to a contaminated freshwater stream.     

The potential for citizen science to produce reliable and useful information in ecology

We examined features of citizen science that influence data quality, inferential power, and usefulness in ecology. As background context for our examination, we considered topics such as ecological sampling (probability based, purposive, opportunistic), linkage between sampling technique and statistical inference (design based, model based), and scientific paradigms (confirmatory, exploratory). We distinguished several types of citizen science investigations, from intensive research with rigorous protocols targeting clearly articulated questions to mass-participation internet-based projects with opportunistic data collection lacking sampling design, and examined overarching objectives, design, analysis, volunteer training, and performance. We identified key features that influence data quality: project objectives, design and analysis, and volunteer training and performance. Projects with good designs, trained volunteers, and professional oversight can meet statistical criteria to produce high-quality data with strong inferential power and therefore are well suited for ecological research objectives. Projects with opportunistic data collection, little or no sampling design, and minimal volunteer training are better suited for general objectives related to public education or data exploration because reliable statistical estimation can be difficult or impossible. In some cases, statistically robust analytical methods, external data, or both may increase the inferential power of certain opportunistically collected data. Ecological management, especially by government agencies, frequently requires data suitable for reliable inference. With standardized protocols, state-of-the-art analytical methods, and well-supervised programs, citizen science can make valuable contributions to conservation by increasing the scope of species monitoring efforts. Data quality can be improved by adhering to basic principles of data collection and analysis, designing studies to provide the data quality required, and including suitable statistical expertise, thereby strengthening the science aspect of citizen science and enhancing acceptance by the scientific community and decision makers.