Anatomy of an urban waterbody: a case study of Boston's Muddy River

The objective of this study was to characterize and understand the water quality of Boston's Muddy River prior to restoration, to help guide those activities and evaluate their success. We use a combination of monitoring, data analysis and mathematical modeling. The seasonal pattern of temperature, pollutant signatures (identified using a principal component analysis), correlations with precipitation and spatial patterns all point to a significant wastewater input at one of the outfalls and suggest significant receiving water impact. However, a quantitative analysis using a mathematical model (QUAL2K) suggests this source is not significant. Rather, internal loading from algae, sediment bed and waterfowl dominate the spatial pattern of water quality. These results suggest significant improvement can be expected from planned sediment dredging. The paper provides a case study of water quality assessment in the context of urban river restoration, and it illustrates the utility of combining monitoring and data analysis with modeling.     

Differential predation by males on moulted females may explain the competitive displacement of Gammarus duebeni by G. pulex (Amphipoda)

Summary Several studies have reported the ability of Gammarus pulex to successfully compete with and ultimately displace G. duebeni in freshwater. These studies have been unable, however, to provide adequate explanations for this displacement based on mechanisms of exploitative competition and/or differences in the environmental tolerances of the species. The present study investigates the role of predation as an extreme form of interference competition between G. pulex and G. duebeni. The data presented show that: (1) given the opportunity, males of both species prey on females of the other species, but only on females that have recently moulted; (2) mate guarding in both species significantly reduces the incidence of predation on moulted females; (3) mate guarding by male G. pulex is more successful in reducing predation on moulted females than is guarding by male G. duebeni. We propose that differential predation rate on moulted females may constitute the primary mechanism by which G. pulex displaces G. duebeni. Offprint requests to: J.T.A. Dick     

Lake of flies, or lake of fish? A trophic model of Lake Malawi

Ecosystem-focused models have, for the first time, become available for the combined demersal and pelagic components of a large tropical lake ecosystem, Lake Malawi. These provide the opportunity to explore continuing controversies over the production efficiencies and ecological functioning of large tropical lakes. In Lake Malawi these models can provide important insight to the effect of fishing on fish composition, and the potential competition that the lakefly Chaoborus edulis may have with fisheries production. A mass-balanced trophic model developed for the demersal fish community of the southern and western areas of Lake Malawi was integrated with an existing trophic model developed for the open-water pelagic. Input parameters for the demersal model were obtained from a survey of fish distributions, fish food consumption studies, and from additional published quantitative and qualitative information on the various biotic components of the community. The model was constructed using the Ecopath approach and software. The graphically presented demersal food web spanned four trophic levels and was based primarily on consumption of detritus, zooplankton and sedimented diatoms. Zooplankton was imported into the system at trophic levels three and four through fish predation on carnivorous and herbivorous copepods and Chaoborus larvae. It is proposed that the primary consumption of copepods was by fish migrating into the pelagic zone. Chaoborus larvae in the demersal were probably consumed near the lakebed as they conducted a daily migration from the pelagic to seek refuge in the sediments. This evidence for strong benthic-pelagic coupling provided the opportunity for linking the demersal model to the existing model for the pelagic community so producing the first model for the complete ecosystem. Energy fluxes through the resulting combined model demonstrated that the primary import of biomass to the demersal system was detritus of pelagic origin (72.1%) and pelagic zooplankton (10.6%). Only 15.8% of the biomass consumed within the demersal system was of demersal origin. Lakefly production is efficiently utilised by the lake fish community, and any attempt to improve fishery production through introduction of a non-native plantivorous fish species would have a negative impact on the stability and productivity of the lake ecosystem.     

Potential Applications for Pyrolysis-GC/MS in Bioremediation

Preliminary data are presented from a set of experiments designed to promote the use of pyrolysis-GC/MS in bioremediation. Studies were designed to aid researchers in developing a pyrolysis-GC/MS method and identifying how the method could help characterize bioremediation, particularly in organic soils. Since sample size affects the results of pyrolytic analyses, the first experiment demonstrated how an appropriate sample size might be selected for pyrolysis-GC/MS testing. In order to show how quantitative results can be obtained from pyrolysis-GC/MS, a second experiment determined the 'goodness of fit' for a standard curve relating the chromatographic area under a pyrogram to actual mass units. The third experiment investigated ways in which pyrolysis-GC/MS analyses could improve our understanding of bioremediation in organic soils contaminated with crude oil. Experimental results confirmed that differences in analyte mass affect the extent of pyrolytic cracking. In pyrograms of the test soil, the ratio of toluene to total product showed that for a sample mass between 1.8 and 2.0 mg, variability in the cracking pattern was minimized. Unlike deviations outside this range, small deviations within the range did not appreciably effect the toluene ratio. A standard curve was prepared for pyrolytic analyses by plotting the total chromatographic area of all pyrolysis products versus the mass of organic material pyrolyzed. These data were fit with a straight line having an 'R²' of 0.73. Based on a bench scale bioremediation experiment, preliminary pyrolysis-GC/MS results were used to predict that compounds derived from lignin and carbohydrates would be degraded faster in uncontaminated than contaminated soils. Appreciable degradation of both compounds, however, occurred in contaminated soils. In addition, results suggested that using pyrolysis-GC/MS to quantify the sum of all n-alkanes and the ratio of odd to even chain n-alkanes could help researchers distinguish between the degradation of petroleum and non-petroleum hydrocarbons in contaminated and uncontaminated soils.     

Evaluation of a combined macrophyte–epiphyte bioassay for assessing nutrient enrichment in the Portneuf River,Idaho, USA

We describe and evaluate a laboratory bioassay that uses Lemna minor L. and attached epiphytes to characterize the status of ambient and nutrient-enriched water from the Portneuf River, Idaho. Specifically, we measured morphological (number of fronds, longest surface axis, and root length) and population-level (number of plants and dry mass) responses of L. minor and community-level (ash-free dry mass [AFDM] and chlorophyll a [Chl a]) responses of epiphytes to nutrient enrichment. Overall, measures of macrophyte biomass and abundance increased with increasing concentrations of dissolved phosphorus (P) and responded more predictably to nutrient enrichment than morphological measures. Epiphyte AFDM and Chl a were also greatest in P-enriched water; enrichments of N alone produced no measurable epiphytic response. The epiphyte biomass response did not directly mirror macrophyte biomass responses, illustrating the value of a combined macrophyte–epiphyte assay to more fully evaluate nutrient management strategies. Finally, the most P-enriched waters not only supported greater standing stocks of macrophyte and epiphytes but also had significantly higher water column dissolved oxygen and dissolved organic carbon concentrations and a lower pH. Advantages of this macrophyte–epiphyte bioassay over more traditional single-species assays include the use of a more realistic level of biological organization, a relatively short assay schedule (~10 days), and the inclusion of multiple biological response and water-quality measures.     

Carcass Provisioning to Support Scavengers: Evaluating a Controversial Nature Conservation Practice

A number of scavenger species have suffered population declines across Europe. In attempts to reverse their decline, some land and wildlife managers have adopted the practice of leaving or placing out carcasses of wild or domestic herbivores to provide a source of carrion. However, this can be a controversial practice, with as yet unclear outcomes for many target species and the ecosystems they are part of. Here we bring out the key aspects of this increasingly common conservation practice illustrated using three contrasting cases studies. We show that the provision of carcasses is often motivated by a desire to benefit charismatic species or to facilitate nutrient cycling throughout an ecosystem. Evidence for the effectiveness of this practice in achieving these objectives, however, is mostly lacking, with ecologists studying “easier” species groups such as beetles and therefore not providing relevant insights. Moreover, conflicts between environmental policies that carcass provisioning is aimed at and other social and economic objectives do occur but these projects are often designed without taking into account this broader context. We conclude that expecting carcasses to simply be “good for biodiversity” may be too naïve a view. A greater knowledge of the impact of carcass provisioning and placement on ecosystems and society at large is required before it can become a more effective conservation tool at a wider scale.     

Wildlife contact analysis: emerging methods, questions, and challenges

Recent technological advances, such as proximity loggers, allow researchers to collect complete interaction histories, day and night, among sampled individuals over several months to years. Social network analyses are an obvious approach to analyzing interaction data because of their flexibility for fitting many different social structures as well as the ability to assess both direct contacts and indirect associations via intermediaries. For many network properties, however, it is not clear whether estimates based upon a sample of the network are reflective of the entire network. In wildlife applications, networks may be poorly sampled and boundary effects will be common. We present an alternative approach that utilizes a hierarchical modeling framework to assess the individual, dyadic, and environmental factors contributing to variation in the interaction rates and allows us to estimate the underlying process variation in each. In a disease control context, this approach will allow managers to focus efforts on those types of individuals and environments that contribute the most toward super-spreading events. We account for the sampling distribution of proximity loggers and the non-independence of contacts among groups by only using contact data within a group during days when the group membership of proximity loggers was known. This allows us to separate the two mechanisms responsible for a pair not contacting one another: they were not in the same group or they were in the same group but did not come within the specified contact distance. We illustrate our approach with an example dataset of female elk from northwestern Wyoming and conclude with a number of important future research directions.