Harmful algae blooms (HABs) involve proliferation of nuisance photosynthetic organisms (cyanobacteria [blue-greens], dinoflagellates [red tides], and diatoms) in fresh and salt waters. Such blooms negatively impact humans and other organisms. They may reduce light penetration in the water column, cause hypoxic or anoxic conditions when blooms die and decompose, and produce toxins. Factors that promote HABs include excessive nutrient loading (nitrogen and phosphorus) to waterbodies, higher water temperatures from climate warming or industrial discharges, and longer water residence times. Harmful algae blooms appear to be increasing in intensity and frequency world-wide and pose threats to wildlife, livestock, and humans. This theme solicits presentations that explore causes and consequences of HABs, as well as strategies to reduce the probability of their future occurrence.

Water resources are impacted by many contaminants, including nutrients, pharmaceuticals, agricultural pesticides, poly- and perfluorinated substances (PFAS), microorganisms, and metals. The impacts and sources of these contaminants in waters vary depending on location, surrounding land use and development practices and can have profound effects on water quality, water use, economy, and quality of life. Such contamination may, in turn, impact the economy and development patterns of the watershed. Addressing the sources of these contaminants, their environmental and economic impacts, and how to control the spread of contamination in our environment is a high priority. This theme solicits presentations that examine the contaminants that affect water quality and explore ways to reduce contamination in the environment.

Water scarcity, which occurs when the demand for water by all sectors, including the environment, cannot be satisfied due to constraints on water quantity or quality, is one of the greatest challenges facing humanity. Water is not only the lifeblood of natural ecosystems, but it is essential for agriculture, human consumption, industry, and energy generation. Water scarcity will become more pressing as the world’s human population continues to grow, living standards increase, diets change, water needs for ecosystems change, and the effects of climate change intensify. This theme solicits contributions that present current research related to drivers and impacts of water scarcity, and the opportunities to implement new practices, ground-breaking technologies, and innovative policies that can mitigate the impacts of water scarcity on the ecological and economic health of a region. Contributions from all fields of research are welcome on topics ranging from supply, recycling technologies, water management and demand reduction.

Global atmospheric, climatic and oceanic cycles, including the El Niño Southern Oscillation, North Atlantic Oscillation, and Atlantic Multi-decadal Oscillation, are important drivers of variations in rainfall patterns, changes in drought and flood cycles, and changes in terrestrial freshwater availability. Over longer time scales, climate change is likely to alter freshwater availability as a consequence of changes in precipitation, temperature, and sea level rise. Water management and decision-making in this changing regime require new scientific information that is regionally specific, evidence-based, and policy-relevant. This theme solicits presentations that include innovative methods for evaluating potential impacts of climate change, climate variability, and sea level rise on human and natural water-dependent systems, as well as policy, management, community engagement, and regulatory programs that may promote the resilience of these systems in a changing environment.