Water Journal : Water Journal November 2013
WATER NOVEMBER 2013 6My Point of View circulation changes, and increased extreme events, will potentially interact synergistically, additively or antagonistically with chemical stressors to cause both acute and chronic effects on aquatic and terrestrial biota. For example, increased temperature could cause thermal stress and in uence food availability and, hence, growth, while salinity changes could exacerbate contaminant effects on biota, leading to reductions in larval survival and development. These stressors can interact in two ways: indirect stressors, e.g. climate change, can increase or decrease the toxicity of contaminants to biota, or the contaminants themselves can alter the ability of organisms to respond to climate change stressors. This can ultimately lead to ecological thresholds or tipping points, i.e. abrupt changes in community structure or function in response to relatively small perturbations. Populations living at the edge of their physiological tolerance range may be more vulnerable to the effects of these indirect stressors, particularly if the timing of the exposure to a contaminant coincides with a sensitive life stage, such as spawning. Historically, ecological risk assessment (ERA) frameworks were developed to examine risks from particular stressors (usually chemical), acting on particular receptors within small geographic boundaries and largely ignored other non-contaminant stressors (physical and biological). Traditionally, ERAs evaluated whether there was a change in ecosystem services (bene ts of nature to households, communities, and economies) relative to a reference site or condition. However, under a variable climate, baseline conditions will change over time making it dif cult to establish reference conditions that are also changing over time. Endpoints for assessing some components of ecosystem services and models at the regional scale have only recently been developed and have not been examined under conditions of multiple stressors -- e.g. the cumulative effects of climate change-induced wetland degradation on water quality. National management frameworks for environmental regulation of contaminants are now incorporating global climate change into the conceptual models that underpin their assessment framework. DEVELOPING A PREDICTIVE APPROACH Because ecological conditions will change unpredictably with global climate change, simplistic assumptions of static conditions and unidirectional change will no longer apply. Global climate change brings with it the need to consider both contaminant and non-contaminant stressors, which may lead to either negative or positive impacts. Since it is impractical to collect empirical data for all potential interactions between environmental variables affected by climate change and contaminants of concern, it will be necessary to develop predictive approaches, incorporating mechanistic data into the risk assessment process. Because there is considerable uncertainty associated with predicting these risks and with identifying appropriate management actions, an adaptive management approach will be essential. The complex interactions between potential climate change stressors and contaminants make the prediction of impacts on aquatic and terrestrial ecosystems problematic. While some species may be especially vulnerable to climate change per se, impacts will be exacerbated by other ecosystem stressors, notably chemical contaminants, pathogens, invasive species, over-harvesting and habitat destruction. More data at multiple levels of organisation are required to understand and predict the effects of climate change: at the organism level on physiology, toxicity and genetics; at the population level on reproduction, dispersal and recruitment; at the community level on species interactions and habitat; and at the ecosystem level on global processes, e.g. biogeochemical cycles. Both modelling and monitoring approaches will be required to address this knowledge gap. Contaminant effects could be of greater consequence under climate change in the case of synergistic interactions, and this will require more stringent environmental quality standards for chemical contaminants in that particular environment. From an ecological restoration perspective, removing one stressor may result in greater bene t than expected in the case of a synergistic interaction, or less than expected in the case of antagonistic interactions. It has been suggested that one immediate management action should be to monitor baseline contaminant concentrations in soils, water and sediments, and to reduce local exposure to contaminants (one stressor) where possible, as this may be more easily tackled initially than removing indirect stressors due to climate change. However, in cases where there are antagonistic interactions between stressors, local interventions may lead to ineffective, costly management actions and wasted management effort. Careful assessment is required on a case-by-case basis. The water industry has a role to support this science and to in uence policy development. Clearly, greater effort is required to understand multiple stressors and how to manage them in the broader context of earth systems science as we move forward into a period of likely change.
Water Journal September 2013
Water Journal December 2013