A Bayesian approach to evaluating site impairment

In the United States, each state is required to list water resources that are declared to be impaired under guidelines set by the Clean Water Act. Measurements are typically collected on a number of chemical constituents and compared with a standard. If there are too many measurements exceeding the standard, then the site is declared impaired. The approach is non-statistical but similar to a Binomial test. The Binomial approach would convert the measurements to binary data then test if the proportion exceeding the standard is excessive. Both methods convert measurements to binary values hence exclude potentially important information in the data. We present a statistical approach using a Bayesian model that uses the raw data instead of the binary transformed data. The population distribution of a family of location-scale parameter models is studied under the model. Posterior distributions from the Bayesian analysis are used in the decision-making process and error probabilities for the Bayesian and the Binomial approaches are compared for a normal population.     

Optimal patch time allocation for time-limited foragers

The Charnov Marginal Value Theorem (MVT) predicts the optimal foraging duration of animals exploiting patches of resources. The predictions of this model have been verified for various animal species. However, the model is based on several assumptions that are likely too simplistic. One of these assumptions is that animals are living forever (i.e., infinite horizon). Using a simple dynamic programming model, we tested the importance of this assumption by analysing the optimal strategy for time-limited foragers. We found that, for time-limited foragers, optimal patch residence times should be greater than those predicted from the classic, static MVT, and the deviation should increase when foragers are approaching the end of their life. These predictions were verified for females of the parasitoid Anaphes victus (Hymenoptera: Mymaridae) exploiting egg patches of its host, the carrot weevil Listronotus oregonensis (Coleoptera: Curculionidae). As predicted by the model, females indeed remained for a longer time on host patches when they approached the end of their life. Experimental results were finally analysed with a Cox regression model to identify the patch-leaving decision rules females used to behave according to the model’s predictions.     

The Residence Time of Settling Particles in the Surface Mixed Layer

The transport from the upper mixed layer into the pycnocline of particles with negative buoyancy is considered. Assuming the hydrodynamic parameters to be time- independent, an adjoint model is resorted to that provides a general expression of the residence time in the mixed layer of the constituent under study. It is seen that the residence time decreases as the settling velocity increases or the diffusivity decreases. Furthermore, it is demonstrated that the residence time must be larger than z/w and smaller than h/w, where z, h and w denote the distance to the pycnocline, the thickness of the mixed layer and the sinking velocity. In the vicinity of the pycnocline, the residence time is not necessarily zero; its behaviour critically depends on the eddy diffusivity profile in this region. Closed-form solutions are obtained for constant and quadratic diffusivity profiles, which allows for an analysis of the sensitivity of the residence time to the Peclet number. Finally, an approximate value is suggested of the depth-averaged value of the residence time.     

Importance of heterotrophic planktonic communities in a mussel culture environment: the Grande Entrée lagoon,Magdalen Islands (Québec,Canada)

Mussel culture in coastal environments relies on the availability of food of sufficient quality and quantity. Both to determine this availability and to examine impacts that this aquaculture practice may have on the environment, it is important to have good knowledge of the type of plankton communities present in aquaculture sites. It is usually thought that phytoplankton make up the bulk of mussel diet in many of these sites. Here we show that the Grande-Entrée lagoon [Magdalen Islands, Gulf of St Lawrence (GSL), Canada], where commercial mussel culture has been on-going since 1980, differs from this pattern. Heterotrophic protists dominate for most of the summer-early fall season (apart from short diatom bursts), with a high average biomass of 160 mg C m⁻³. The dominance of small-sized phytoplankton cells (notably green algae), low nutrient concentrations (e.g. 0.3 μM NO₃⁻ on average) and high biomass of heterotrophic protists (mostly naked ciliates and tintinnids) all point to the importance of the microbial food web in this shallow marine environment. Sustained cultivation of suspended mussels in the lagoon suggests that these heterotrophic protists could be an important source of food for the mussels, supplementing the small amount of phytoplankton present.     

Compensation and the stability of restored grassland communities.

The relationship between community diversity and the stability of summed community biomass has been an area of great theoretical and empirical interest in basic ecology. In general, it has been found that the complementary/compensatory dynamics among species that comprise a community can stabilize aggregate measures of community biomass. Although the potential importance of diversity-stability relationships to restoration ecology has been recognized, to date there has been no quantification of the role these relationships play in increasing the persistence of restored communities in the face of altered disturbance regimes, climatic variability, and over the course of succession. In a large-scale experimental restoration of a California grassland community, aggregated abundance of restored grasses was more stable than were the individual species in response to disturbance, drought, and succession. Compensatory dynamics among the restored grass flora increased aggregate stability in response to natural and anthropogenic disturbances. Successful restorations must persist in the face of altered management and disturbance regimes, climactic variability, and over the course of succession. Incorporation of diversity-stability relationships into restoration plans will likely increase restoration success. This case study further demonstrates the relevance of community ecology theory to restoration ecology.     

Beyond "Hotspots": How to Prioritize Investments to Conserve Biodiversity in the Indo-Pacific Region

We present a conservation index based upon the interaction of the size of terrestrial protected areas, remaining forest habitat, deforestation rates, and biological richness to identify conservation potentials, threats, and strategies for 23 Indo-Pacific countries. This conservation potential/threat index shows that four of the largest and most species-rich countries—China, Indonesia, India, and Thailand—contain 82% of the region's large reserves (more than 1000 km²) and 86% of the region's area designated for protection. The skewed regional distribution and small number of large reserves per country call for the expansion of existing protected areas and, where possible the establishment of new parks and transfrontier reserves. The index indicates high potential for conservation efforts in Papua New Guinea, Laos, Myanmar, New Caledonia, Vanuatu, and the Solomon Islands, which have a high percentage of remaining forested habitats. high species richness, or endemism, but which lack comprehensive protected area systems. The index also predicts that if current rates of deforestation continue, only Brunei, Bhutan, Indonesia, Taiwan, and Malaysia will have adequate proportions of their respective land areas under some form of protection while still maintaining a minimal percentage (20% or more) of forested habitat outside reserves. Based on the regional analysis, we identify priority countries for investment in biodiversity conservation, and we evaluate funding responses earmarked for those countries. We then show how the index can be adapted to different geographical scales using examples from Indonesia, Malaysia, and the Philippines.     

Persistent organic pollutants in Detroit River suspended sediments: polychlorinated dibenzo-p-dioxins and dibenzofurans,dioxin-like polychlorinated biphenyls and polychlorinated naphthalenes

Suspended sediments from the Detroit River were collected in 1999 and 2000 using sediment traps at sites ranging from western Lake Erie to southern Lake St. Clair and analyzed to determine the spatial distributions of contaminants including polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/PCDFs), dioxin-like PCBs (DLPCBs) and polychlorinated naphthalenes (PCNs). Concentrations of all three contaminant classes were clearly elevated at sites in the lower reaches of the river in the Trenton Channel. The potential influence of the Trenton Channel as a source of contamination to western Lake Erie was further evidenced by PCDD/PCDF homologue profiles, which indicated a contribution from chemical manufacturing in addition to the normal background combustion profile. Toxic equivalents (TEQs) for PCDDs/PCDFs generally exceeded those for DLPCBs; combined total TEQs in July 2000 for these two compound classes ranged from 2.30 pg/g in southern Lake St. Clair to 306 pg/g at a station just downstream of the outflow of Monguagon Creek in the Trenton Channel. The spatial distribution of PCN contamination was similar to that of PCDDs/PCDFs and DLPCBs, with the highest level of total PCNs (8200 ng/g) detected at a site in the Trenton Channel near Elizabeth Park; TEQs for PCNs in the Trenton Channel ranged from 73 to 3300 pg/g. The data indicate that PCNs represent a significant contribution to dioxin-like biological activity in Detroit River suspended sediments.     

Sustainable oil and grease removal from synthetic stormwater runoff using bench-scale bioretention studies.

One of the principal components of the contaminant load in urban stormwater runoff is oil and grease (O&G) pollution, resulting from vehicle emissions. A mulch layer was used as a contaminant trap to remove O&G (dissolved and particulate-associated naphthalene, dissolved toluene, and dissolved motor oil hydrocarbons) from a synthetic runoff during a bench-scale infiltration study. Approximately 80 to 95% removal of all contaminants from synthetic runoff was found via sorption and filtration. Subsequently, approximately 90% of the sorbed naphthalene, toluene, oil, and particulate-associated naphthalene was biodegraded within approximately 3, 4, 8, and 2 days after the event, respectively, based on decreases in contaminant concentrations coupled with increases of microbial populations. These results indicate the effectiveness and sustainability of placing a thin layer of mulch on the surface of a bioretention facility for reducing O&G pollution from urban stormwater runoff.     

Review of disposal technologies for chromated copper arsenate (CCA) treated wood waste, with detailed analyses of thermochemical conversion processes

Several alternative methods for the disposal of chromated copper arsenate (CCA) treated wood waste have been studied in the literature, and these methods are reviewed and compared in this paper. Alternative disposal methods include: recycling and recovery, chemical extraction, bioremediation, electrodialytic remediation and thermal destruction. Thermochemical conversion processes are evaluated in detail based on experiments with model compounds as well as experimental and modelling work with CCA treated wood. The latter category includes: determination of the percentage of arsenic volatilised during thermal conversion of CCA treated wood, identification of the mechanisms responsible for arsenic release, modelling of high temperature equilibrium chemistry involved when CCA treated wood is burned, overview of options available for arsenic capture, characterisation of ash resulting from (co-)combustion of CCA treated wood, concerns about polychlorinated dibenzo-p-dioxins/furans (PCDD/F) formation. Finally, the most appropriate thermochemical disposal technology is identified on short term (co-incineration) and on long term (low-temperature pyrolysis or high-temperature gasification).