Grassroots September 2016, Vol. 16, No. 3 | Page 21

Article diverse as the Great Lakes, the east coast's Chesapeake Bay and the Gulf of Mexico, the severity of summer hypoxia has been linked to the effects of weather on nutrient loading, watercolumn structure and water circulation. Although these examples all relate to harmful algal blooms and hypoxia, other types of water pollution are also affected by weather conditions, which are altered by climate change. The challenge Several factors explain the paucity of research. First, the role of climate is difficult to pinpoint, because changes in water quality result from a delicate and complex interplay of human activities across local, regional and global scales. Complex chains of causative steps must be understood. These start with how climate change affects factors such as precipitation, temperatures and wind patterns for given regions and watersheds. Next, we must understand how these conditions alter the flow of water, nutrients, contaminants and other constituents to water bodies. Finally, we need to assess how these inputs, combined with meteorological conditions that influence freshwater and coastal systems directly, will change water quality. We do not yet know how to put the pieces of this puzzle together. For example, the harmful algal blooms in Lake Erie are driven by excess phosphorus from changing farming and land-management practices in the region, but a summer 2011 bloom shattered previous records. A forensic analysis9 revealed that a series of intense rainstorms led to record springtime discharge from rivers, which flooded the lake with a record amount of nutrients flushed from fields. Warmer-than-average summer temperatures and low winds then accelerated the growth of buoyant Microcystis cyanobacteria. Unusually weak water circulation during the summer kept nutrients in the lake for longer, further feeding the bloom. How climate change influences the occurrence of all these factors, individually and together, needs to be elucidated to predict the likelihood of similar events happening more frequently in the future. “There is disagreement about which variables best capture water quality.” Second, water-quality and climate scientists work in disciplinary silos, and each tends to have a different scale of focus. Whereas much of climate science is global or concerned with large regions, most hydrologists and limnologists study processes in individual streams, lakes, watersheds or estuaries. Similarly, water-quality impacts have been treated mostly as local or regional issues, Grassroots resulting from human activities in a particular basin or watershed. Little attention has been given to the local impacts of human action at global scales. For example, strategies for preventing harmful blooms and hypoxia often rightly focus on limiting nutrient loads through land management, but should also consider how a shifting climate will alter local meteorology, and thus nutrient loads. A clear understanding of the interplay between climate and severe water-quality impairment events is predicated on tracking cause and effect across a cascading range of scales, from the globe to individual watersheds and from decades to days. Third, observational evidence to underpin a global view of this interplay is lacking. Unlike for weather variables such as temperature and precipitation, no global network tracks water quality. Existing monitoring of water quality is sparse in space and time, and site-specific. Satellite-based observations could expand coverage, but there are no widely accepted approaches for doing so. There is even disagreement about which variables best capture water quality. For example, is the severity of a harmful algal bloom best represented by its area, the total mass of phytoplankton it contains, the amount of toxins that it produces or the ecosystem and human impacts that it engenders? Each brings a different observational challenge. Next steps Researchers need to assess which meteorological conditions, in what combination, make extreme water-quality impairments most likely. In doing so, they must also consider land use, land management, population distributions and other regional factors that compound the effects of weather. An initiative such as Future Earth, which provides a research platform for global sustainability science, would be a good umbrella for developing and integrating such knowledge globally. The first step should be a retrospective analysis of past extreme events, to understand commonalities and differences across types of systems and impacts. The resulting conceptual model will differ depending on the type of problem — hypoxic dead zones and microbial outbreaks in recreational waters will not link to climate in the same ways. The water-quality and climate research communities will have to work together to identify key mechanisms and feedbacks. Understanding meteorological drivers would allow researchers to assess whether climate models can accurately represent the occurrence of key September 2016 Vol 16 No. 3