Occurrence, distribution and possible sources of organochlorine pesticide residues in tropical coastal environment of India: an overview

Organochlorine pesticides (OCPs) are an important potential component of chemical pollutants used extensively for agriculture and sanitation purposes in India as these are comparatively cheap and effective. These persistent organic compounds such as HCH isomers, DDT and its metabolites are the predominant chemical contaminants found along the Indian coast and thus constitute both alluring and grave areas of scientific research. Our objective in the paper is to provide a comprehensive account of the distribution of organochlorine pesticides in biotic and abiotic compartments of the Indian coastal environment, make some comments on their environmental sources, their movement through the food chain and possible ecotoxicological risk of health in biota including humans. The prevalent HCH, DDT and HCB concentrations differ markedly in eastern and western coast of India reflecting differing agricultural and other usage and their ultimate input into the coastal environment by several rivers and the bioturbation activities of macrozoobenthos (bivalve mollusks, polychaetous annelids, etc.). In several cases, the DDT levels exceeded the effects range-low (ER-L) and could thus cause acute biological impairments, in comparison with the sediment quality guidelines. Contributions of DDT metabolites (DDT, DDD and DDE residues) vary in different Indian coastal regions predominated by pp'-DDT and pp'-DDD. Measured concentrations of HCHs were lower than DDTs that might be due to higher water solubility, vapor pressure and biodegradability of the latter. HCH and DDT residues in fish in India were lower than those in the temperate countries indicating a lower accumulation in tropical fish, which might be related to rapid volatilization of this insecticide in the tropical environment. The concentrations of other chlorinated pesticides (aldrin, dieldrin, eldrin, methoxychlor, endosulfan sulphate) were lower and not generally of great concern.     

Land-based carbon storage and the European union emissions trading scheme: the science underlying the policy

Climate change is occurring with greater speed and intensity that previously anticipated. All effective environmentally and socially sound mitigation efforts need to be employed to effectively address this global crisis. Land Use, Land Use Change and Forestry (LULUCF) projects can provide significant climate change mitigation benefits as well as poverty alleviation and biodiversity conservation benefits. The policies of the European Union Emissions Trading Scheme (EU-ETS), the world’s largest carbon market exclude LULUCF. Scientific support for this exclusion was presented in a briefing paper published by the Climate Action Network—Europe (CAN) that puts forward the proposition that land based storage of carbon is ineffective. A careful review of the scientific papers cited in support of CAN’s position indicates that, while the papers themselves are scientifically sound, they do not support the continued exclusion of LULUCF projects from the EU-ETS. At the same time some important recent research papers that describe the carbon storage and social benefit potential of such projects are not included in the analysis. An in-depth consideration of the scientific evidence is necessary in evaluating this policy option. Based on this evidence a case can be made for the inclusion of LULUCF projects in the EU-ETS.     

Soil characteristics under cash crop farming in upland areas of Sarawak,Malaysia

This study discusses soil fertility under perennial cash crop farming (para rubber, Hevea brasiliensis; black pepper, Piper nigrum; oil palm, Elaeis guineensis) conducted by local farmers and an oil palm estate in an upland area of Sarawak, Malaysia, in comparison with the surrounding secondary forests. In the farmlands of the local farmers, rubber farming was conducted without fertilizer application, while 2–5 t ha^?1 of NPK compounds were applied annually on pepper farms. Soils under rubber farming were acidic with poor nutrient contents, resembling soils in secondary forests. In pepper farms, soils were less acidic and showed high nutrient contents, especially with respect to available P and exchangeable Ca. This trend became stronger with increasing farming duration. Fertilizers applied around pepper vines appeared to migrate and spread across the fields. Bulk density and hardness of surface soils were higher in pepper farms than in secondary forests, indicating soil compaction due to field works. In the oil palm estate, annual fertilizer application rates were moderate at 0.4–0.8 t ha^?1 of NPK compound fertilizers. However, the soil properties in the oil palm estate were similar to those of the small-scale pepper farms. Close to the bases of the palms where fertilizers usually are applied, the contents of exchangeable Ca and available P were high. Nutrient uptake by the dense root systems of the palms seemed to prevent excessive loss of nutrients through leaching. Loss of soil organic matter and deterioration of soil physical properties were brought about by terrace bench construction, but the soils seemed to recover to some extent over time. In conclusion, technologies such as intercropping and the appropriate allocation of different crops to specific locations as well as the proper selection and dosage of fertilizers should be developed and adopted to improve fertilizer efficiency and prevent water pollution due to fertilizer wash-off from farmlands.     

Trophic levels and trophic tangles: the prevalence of omnivory in real food webs

The concept of trophic levels is one of the oldest in ecology and informs our understanding of energy flow and top-down control within food webs, but it has been criticized for ignoring omnivory. We tested whether trophic levels were apparent in 58 real food webs in four habitat types by examining patterns of trophic position. A large proportion of taxa (64.4%) occupied integer trophic positions, suggesting that discrete trophic levels do exist. Importantly however, the majority of those trophic positions were aggregated around integer values of 0 and 1, representing plants and herbivores. For the majority of the real food webs considered here, secondary consumers were no more likely to occupy an integer trophic position than in randomized food webs. This means that, above the herbivore trophic level, food webs are better characterized as a tangled web of omnivores. Omnivory was most common in marine systems, rarest in streams, and intermediate in lakes and terrestrial food webs. Trophic-level-based concepts such as trophic cascades may apply to systems with short food chains, but they become less valid as food chains lengthen.     

Independent gradients of producer, consumer, and microbial diversity in lake plankton

Interactions between trophic levels during food web assembly can drive positive correlations in diversity between producers, consumers, and decomposers. However, the contribution of trophic interactions relative to local environmental factors in promoting species diversity is poorly understood, with many studies only considering two trophic levels. Here we examine correlations in diversity among zooplankton, phytoplankton, and bacteria in the pelagic zone of 31 lakes in British Columbia, Canada. We sampled species diversity of zooplankton and phytoplankton through morphological identification, and bacterial genetic diversity was estimated by denaturing gradient gel electrophoresis (DGGE) of 16S rDNA polymorphisms. We looked for correlations in diversity that were independent of the abiotic environment by statistically controlling for 18 limnological variables. No significant correlations were found between the diversity of zooplankton, phytoplankton, and bacteria. In addition, the physical factors that were associated with species composition in one trophic level were independent of those that were important for another. Our results provide no support for the importance of direct feedbacks between producers, consumers, and decomposers in maintaining diversity. Zooplankton, phytoplankton, and bacterial diversity and composition are regulated independently from one another and respond to different environmental variables. These results suggest that species of lake plankton show loose trophic associations with one another due to broad diets in consumers and decomposers.     

Predator and prey space use: dragonflies and tadpoles in an interactive game

Predator and prey spatial distributions have important population and community level consequences. However, little is known either theoretically or empirically about behavioral mechanisms that underlie the spatial patterns that emerge when predators and prey freely interact. We examined the joint space use and behavioral rules governing movement of freely interacting groups of odonate (dragonfly) predators and two size classes of anuran (tadpole) prey in arenas containing two patches with different levels of the prey's resource. Predator and prey movement and space use was quantified both when they were apart and together. When apart from predators, large tadpoles strongly preferred the high resource patch. When apart from prey, dragonflies weakly preferred the high resource patch. When together, large prey shifted to a uniform distribution, while predators strongly preferred the high resource patch. These patterns qualitatively fit the predictions of several three trophic level, ideal free distribution models. In contrast, the space use of small prey and predators did not deviate from uniform. Three measures of joint space use (spatial correlations, overlap, and co-occurrence) concurred in suggesting that prey avoidance of predators was more important than predator attraction to prey in determining overall spatial patterns. To gain additional insight into behavioral mechanisms, we used a model selection approach to identify behavioral movement rules that can potentially explain the observed, emergent patterns of space use. Prey were more likely to leave patches with more predators and more conspecific competitors; resources had relatively weak effects on prey movements. In contrast, predators were more likely to leave patches with low resources (that they do not consume) and more competing predators; prey had relatively little effect on predator movements. These results highlight the importance of investigating freely interacting predators and prey, the potential for simple game theory models to predict joint spatial distributions, and the utility of using model choice methods to identify potential key factors that govern movement.     

Widespread contribution of methane-cycle bacteria to the diets of lake profundal chironomid larvae

Reports of unexpectedly 13C-depleted chironomid larvae in lakes have led to an hypothesis that significant transfer of detrital organic matter to chironomid larvae may occur via methane-cycle bacteria. However, to date little is known of how such transfer might vary across species and lakes. We gathered data from 87 lakes to determine how widespread this phenomenon might be and to define boundaries for its likely magnitude. Carbon stable isotope values of chironomid larvae varied greatly between taxa. Very marked 13C-depletion was evident only in certain taxa, especially Chironomus plumosus, C. anthracinus, and C. tenuistylus, all characteristic of eutrophic or dystrophic lakes and known to be tolerant of low oxygen conditions. Furthermore, marked 13C-depletion was only found in larvae from lakes in which late-summer hypolimnetic oxygen depletion near the sediment surface was below an apparent threshold concentration of 2-4 mg O2/L. Similarly, application of a two-source mixing model suggested that methanotrophic bacteria made the greatest contribution to profundal chironomid growth (0-70% of larval carbon) when the late-summer oxygen concentration dropped below approximately 2 mg O2/L. Our study demonstrates that methane-derived carbon is an important, but often neglected, contribution to the flux of carbon through the food webs of many productive or dystrophic lakes.     

Revisiting the classics: considering nonconsumptive effects in textbook examples of predator-prey interactions

Predator effects on prey dynamics are conventionally studied by measuring changes in prey abundance attributed to consumption by predators. We revisit four classic examples of predator-prey systems often cited in textbooks and incorporate subsequent studies of nonconsumptive effects of predators (NCE), defined as changes in prey traits (e.g., behavior, growth, development) measured on an ecological time scale. Our review revealed that NCE were integral to explaining lynx-hare population dynamics in boreal forests, cascading effects of top predators in Wisconsin lakes, and cascading effects of killer whales and sea otters on kelp forests in nearshore marine habitats. The relative roles of consumption and NCE of wolves on moose and consequent indirect effects on plant communities of Isle Royale depended on climate oscillations. Nonconsumptive effects have not been explicitly tested to explain the link between planktonic alewives and the size structure of the zooplankton, nor have they been invoked to attribute keystone predator status in intertidal communities or elsewhere. We argue that both consumption and intimidation contribute to the total effects of keystone predators, and that characteristics of keystone consumers may differ from those of predators having predominantly NCE. Nonconsumptive effects are often considered as an afterthought to explain observations inconsistent with consumption-based theory. Consequently, NCE with the same sign as consumptive effects may be overlooked, even though they can affect the magnitude, rate, or scale of a prey response to predation and can have important management or conservation implications. Nonconsumptive effects may underlie other classic paradigms in ecology, such as delayed density dependence and predator-mediated prey coexistence. Revisiting classic studies enriches our understanding of predator-prey dynamics and provides compelling rationale for ramping up efforts to consider how NCE affect traditional predator-prey models based on consumption, and to compare the relative magnitude of consumptive and NCE of predators.     

Application of tree-ring isotopic analyses to reconstruct historical water use of riparian trees.

Historical patterns of water source use by trees inferred from long-term records of tree-ring stable isotopic content could assist in evaluating the impact of human alterations to natural stream flow regimes (e.g., water impoundments, stream flow diversions, and groundwater extraction). Our objective was to assess the utility of the hydrogen stable isotopic composition (SD) of tree rings as an index of historical water source use by riparian trees. We investigated the influence of site conditions that varied in climate and hydrology on the relationship between deltaD of Populus xylem water (deltaD(xyl)) and tree-ring cellulose (deltaD(cell)). deltaD(xyl) and deltaD(cell) were strongly correlated across sites (r2 = 0.89). However, the slope of this relationship was less than 1, indicating that factors other than deltaD(xyl) influenced deltaD(cell). Inverse modeling with an isotopic fractionation model for tree-ring cellulose suggested that the lack of one-to-one correspondence between deltaD(xyl) and deltaD(cell) was due to the influence of the hydrogen isotopic content of the atmospheric water vapor (deltaD(atm)). Empirically measured values of deltaD(cell) were typically within the seasonal range of deltaD(cell) predicted from the fractionation model. Sensitivity analyses showed that changes in deltaD(xyl) generally had a greater influence at high-elevation montane sites, whereas deltaD(xyl) and deltaD(atm) had about equal influence on deltaD(cell) at low-elevation desert sites. The intrasite relationship between deltaD(cell) and deltaD(xyl) among individual trees was poor, perhaps because of the within-site spatial variation in hydrologic conditions and associated tree physiological responses. Our study suggests that historical variation in deltaD(cell) of Populus provides information on historical variation in both time-integrated water source use and atmospheric conditions; and that the influence of atmospheric conditions is not consistent over sites with large differences in temperature and humidity. Reconstruction of xylem water sources of Populus in riparian ecosystems from deltaD(cell) will be more direct at higher elevation mountain sites than at low-elevation desert sites.     

Debunking myths about sustainable remediation

Sustainable remediation concepts have evolved during the decade 2007–2017. From the establishment of the first Sustainable Remediation forum (SURF) in 2007, to publication of ASTM and ISO standards by 2017. Guidance has been developed around the world to reflect local regulatory systems, and much has been learned in applying sustainability assessment to contaminated site management projects. In the best examples, significant improvements in project sustainability have been delivered, including concurrent reduction of the environmental footprint of the remediation program, improved social performance, and cost savings and/or value creation. The initial advocates for the concept of sustainable remediation were quickly supported by early adopters who saw its potential to improve the remediation industry's performance, but they also had to overcome some inertia and scepticism from other parties. During the debates and discussions that occurred at numerous international conferences and SURF workshops around the world, various opinions were formed and positions stated. Some proved to be correct, others not so. With the recent publication of ISO Standard 18504 and the benefit of a decade's‐worth of hindsight on sustainable remediation programs implementation and project delivery, this paper summarizes a number of myths and misunderstandings that have been stated regarding sustainable remediation and seeks to debunk them. Sustainable remediation assessment shows us how to manage unacceptable risks to human health and the environment in the best, that is to say the most sustainable, way. It provides the contaminated land management industry a framework to incorporate sustainable development principles into remediation projects and deliver significant value for affected parties and society more broadly. In dispelling some myths about sustainable remediation set out in this paper, it is hoped that consistent application of ISO18504/SuRF‐UK (or equivalently robust guidance) will facilitate even wider use of sustainable remediation around the world.