Behaviour and distribution of the sand-beach amphipod Orchestoidea corniculata

The field distribution of Orchestoidea corniculata Stont a talitrid amphipod inhabiting the upper intertidal zone of sandy beaches, was measured by pitfall trap and subsurface core transects. Variations in the distribution of juveniles and adults were recorded. At Coal Oil Point (Goleta, California, USA), the population was concentrated on the leeward side of the Point and, with increasing distance from the Point, both the number and size of beachhoppers decreased. The amphipods burrowed in a 5 to 7 m wide band during the day, and were active over a 15 to 25 m area at night. When they emerged from their burrows, a net seaward movement of 3 m was observed for the population. Behavioural tests suggested that sand penetrability is an important factor determining the location of burrow sites. Diurnal orientation was investigated, and it was found that the amphipods oriented in a landward direction despite overcast sky conditions, beach slope, moisture gradients, or displacement to a new beach.     

Siting a liquid hazardous waste incinerator: Experience with California's tanner act

The siting of hazardous waste facilities is complex, controversial, time-consuming, expensive, and sometimes impossible. Pressures for and against these facilities are immense. California is developing the “Tanner process,” a one-stop concept in which a single agency serves as the focal point (lead agency) for all the state institutions involved. In this paper I review the experience gained to date with the proposal for the largest liquid toxic waste incinerator proposed for California. I present positive and negative aspects of the process, and draw some policy conclusions. I explore a key policy goal: the search for win/win solutions such that both the community and industry come out ahead environmentally and economically. The experience, especially the approach to negotiation/discussion, is a model for possible use elsewhere in California and the nation.     

Reproductive biology and biochemical composition of the brooding echinoid <Emphasis Type="Italic">Amphipneustes lorioli</Emphasis> on the Antarctic continental shelf

The bathyal West Antarctic Peninsula (WAP) shelf experiences intense seasonal variability in primary production, with summer phytoplankton blooms yielding intense pulse of phytodetritus to shelf sediments. Echinoderms form a conspicuous proportion of the deposit-feeding megabenthos on the shelf and of these Amphipneustes lorioli was the most abundant irregular echinoid. To explore the reproductive response of A. lorioli to this seasonal production cycle, A. Lorioli was sampled at one location on the WAP shelf during four separate cruises between March 2000 and March 2001. Reproductive patterns were determined by histological analyses of gonad tissue, and elemental (CHN) analyses were used to estimate the nutritional and energetic status of the body tissues. Histological analysis of the brooding echinoid A. lorioli suggested a quasi-continuous gametogenic pattern in both the ovaries and the testes. Biochemical analysis of the gonads and the gut tissues were consistent with a continuous gametogenic cycle, showing no significant changes in the biochemical composition of the tissues among seasons. Size-frequency distributions of the embryo and juvenile echinoids within the adults’ brood pouches revealed a synchronous recruitment of embryos and juveniles in specific cohorts between different adult specimens. Whilst this occurrence of different cohorts of the developing brood may be an adaptation to limited brood space, there may also be an external factor influencing the synchrony between adult individuals. Nonetheless, a continuous gametogenic cycle and the lack of seasonal variation in the biochemical composition of gonad and gut tissues suggest that this deposit-feeding irregular urchin is exploiting a persistent sediment food bank in WAP shelf sediments throughout much of the year.     

Field water balance of landfill final covers

Landfill covers are critical to waste containment, yet field performance of specific cover designs has not been well documented and seldom been compared in side-by-side testing. A study was conducted to assess the ability of landfill final covers to control percolation into underlying waste. Conventional covers employing resistive barriers as well as alternative covers relying on water-storage principles were monitored in large (10 x 20 m), instrumented drainage lysimeters over a range of climates at 11 field sites in the United States. Surface runoff was a small fraction of the water balance (0-10%, 4% on average) and was nearly insensitive to the cover slope, cover design, or climate. Lateral drainage from internal drainage layers was also a small fraction of the water balance (0-5.0%, 2.0% on average). Average percolation rates for the conventional covers with composite barriers (geomembrane over fine soil) typically were less than 12 mm/yr (1.4% of precipitation) at humid locations and 1.5 mm/yr (0.4% of precipitation) at arid, semiarid, and subhumid locations. Average percolation rates for conventional covers with soil barriers in humid climates were between 52 and 195 mm/yr (6-17% of precipitation), probably due to preferential flow through defects in the soil barrier. Average percolation rates for alternative covers ranged between 33 and 160 mm/yr (6 and 18% of precipitation) in humid climates and generally less than 2.2 mm/yr (0.4% of precipitation) in arid, semiarid, and subhumid climates. One-half (five) of the alternative covers in arid, semiarid, and subhumid climates transmitted less than 0.1 mm of percolation, but two transmitted much more percolation (26.8 and 52 mm) than anticipated during design. The data collected support conclusions from other studies that detailed, site-specific design procedures are very important for successful performance of alternative landfill covers.     

Competitive Displacement of Trees in Response to Environmental Change or Introduction of Exotics

Various global change factors such as natural and anthropogenic climate change, tropospheric ozone, CO₂, SO₂, and nitrogen deposition affect forest growth, but in species-specific ways. Since even small differences in growth rates between competing species can lead to eventual competitive exclusion, it is important to know the rate at which displacement might occur. Similarly, invasive species may displace native species and cause their extinction. A simulation study of displacement velocity was conducted. Competitive displacement between pairs of similar tree species in which one species has a growth advantage produced trajectories that fit an exponential decay model, leading to the use of the half-life as a useful summary statistic. At any given level of growth differential, the half-life for shade-tolerant species was found to be much longer than for shade-intolerant species due to the ability of shade-tolerant species to survive even when their growth is very slow. Trees with longer life-spans also persisted longer, but this effect was weaker than the shade-tolerance effect. Disturbances speeded up displacement by increasing turnover. For short-lived, intolerant species with a 20% disturbance rate and 20% growth suppression, the estimate of an 100-year half-life could be considered a precipitous rate of decline, with a risk of extinction at about 500 years. In the absence of disturbance, and with a 20% growth reduction or differential between competing species, half-lives for species replacement ranged from 100+ to nearly 800 years. With lesser growth differentials, half-lives are much longer. Such gradual competitive displacement processes will be very difficult to detect in the field over periods of even decades. Results of this study have implications for exotic species invasions. It is predicted that intact forest is not truly resistant to invasion, but that invasion of shade-tolerant tree species should be very slow. Invasion of shade-intolerant species is predicted to be accelerated by disturbance, as has been frequently observed. Results of the simulations were supported by data compiled from several parts of the world.     

Effects of predator visibility on prey encounter: a case study on aerial web weaving spiders

Summary Perhaps the most important factor affecting predator-prey interactions is their encounter probability. Predators must either locate sites where prey are active or attract prey to them, and prey must be able to recognize potential predators and flee before capture. In this study we manipulate and describe three components of the foraging system of predatory, web-weaving spiders, the presence of viscid droplets, silk brightness (achromatic surface reflectance), and visibility of the orb pattern, to determine their effect on insect attraction, recognition, and web avoidance. We found that webs with viscid droplets were more visible to prey at close range, but at greater distances the sparkling droplets lured insects to the web area and hence increased insect capture probability. Although the size of viscid droplets and silk brightness are closely correlated (Table 2, Fig. 3), the relationships among droplet size, spider size, and the visual environments in which webs are found are more complicated (Fig. 2, Tables 2, 3). In environments with predictable light exposure, droplet size and hence silk visibility correlate with spider size, and spiders that forage at night produce relatively more visible silks then spiders that forage during the day (Table 3, Fig. 4). In habitats in which light levels are not predictable, silk surface reflectance and spider size are not closely correlated, suggesting that the complexity of the light environment, as well as the visual and foraging behaviors of insects found there, has played an important role in the evolution of spider-insect interactions.Offprint requests to: C.L. Craig     

Mixing Zone Characterization of Two Transition Terrain Streams With Tracers1

Abstract: For most wastewater discharges to streams, the effluent creates a plume that becomes less distinct as it mixes with the receiving water. Constant‐discharge tracer studies were used to characterize the plume or physical mixing zone (PMZ) at two similar transition terrain streams. At both sites, the laterally unmixed PMZs did not extend across the entire stream and mixing occurred relatively quickly. The observed plumes were significantly smaller than the regulatory mixing zone (RMZ) allowed by the State of Colorado. At Site 1 mixing occurred within a much shorter distance due to the presence of a riffle zone located a few meters downstream of the discharge point. Interpretation of field data with an analytical model suggests that the effective transverse dispersion coefficient (k_z) for the riffle zone at Site 1 (～1 m²/s) was significantly higher than the average value over the longer nonriffle section at Site 2 (～0.01 m²/s). These results imply that to achieve the fastest mixing in transition terrain streams, thereby minimizing the size of the PMZ, discharge outfalls should be located upstream and close to riffle zones.     

Approaches to Evaluate Water Quality Model Parameter Uncertainty for Adaptive TMDL Implementation1

Abstract: The National Research Council recommended Adaptive Total Maximum Daily Load implementation with the recognition that the predictive uncertainty of water quality models can be high. Quantifying predictive uncertainty provides important information for model selection and decision‐making. We review five methods that have been used with water quality models to evaluate model parameter and predictive uncertainty. These methods (1) Regionalized Sensitivity Analysis, (2) Generalized Likelihood Uncertainty Estimation, (3) Bayesian Monte Carlo, (4) Importance Sampling, and (5) Markov Chain Monte Carlo (MCMC) are based on similar concepts; their development over time was facilitated by the increasing availability of fast, cheap computers. Using a Streeter‐Phelps model as an example we show that, applied consistently, these methods give compatible results. Thus, all of these methods can, in principle, provide useful sets of parameter values that can be used to evaluate model predictive uncertainty, though, in practice, some are quickly limited by the “curse of dimensionality” or may have difficulty evaluating irregularly shaped parameter spaces. Adaptive implementation invites model updating, as new data become available reflecting water‐body responses to pollutant load reductions, and a Bayesian approach using MCMC is particularly handy for that task.     

Effect of Starch Granule Size on Viscosity of Starch-Filled Poly(hydroxy ester ether) Composites

The effect of starch granule size on the viscosity of starch-filled poly(hydroxy ester ether) (PHEE) composites was characterized using size-fractionated potato starch, as well as unfractionated starches (rice, corn, wheat, and potato). Potato starch was separated using an air classifier into four particle size fractions: <18 m, 18-24 m, 24-30 m, and >30 m. The starch was dried to a moisture content of 0.5% to minimize moisture effects on composite rheology. PHEE and potato starch were extruded with starch volume fractions of 0.46 and 0.66. Stress relaxation, frequency and strain sweep, and temperature-dependence measurements were carried out. Although small variations in viscosity were seen with the different potato starch fractions, differences were not significant at a volume fraction of 0.46. Viscosity differences between the different particle size fractions were more pronounced at a volume fraction of 0.66. The temperature dependence could be described by an Arrhenius relation, with an apparent activation energy of 84 kJ/mole. At a volume fraction of 0.46, the starch/PHEE viscosities increased in the order potato starch < wheat starch corn starch < rice starch.     

Unified methodology for site-characterization and sampling of highway runoff

Hydrology, roadway traffic conditions, and atmospheric deposition are three essential data categories for the planning and implementation of highway-runoff monitoring and characterization programs. Causal variables pertaining to each data category could be site specific but have been shown to correlate with runoff pollutant loads. These data categories were combined to derive statistical relationships for characterization and prioritization of the respective pollutant loads at highway runoff sites. Storm runoff data of total suspended solids (TSS), total dissolved solid (TDS), chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN) and total phosphorus (TP) collected from three highway sites in Charlotte, North Carolina, USA, were used to illustrate the development of site-specific highway-runoff pollutant loading models. This unified methodology provides a basis for initial assessment of the pollutant-constituent loads from highway runoff using hydrologic component variables. Improved reliability is achievable when additional traffic and/or atmospheric component variables are incorporated into the basic hydrologic regression model. In addition, operational guidance is suggested for implementing highway-runoff monitoring programs that are subject to sampling and resources constraints.