About this Research Topic
Urbanization, industrialization, and agriculture have fundamentally altered lateral fluxes of carbon and nutrients in the last 150 years, causing eutrophication, toxic cyanobacteria blooms, and expansive hypoxic dead zones that erode the capacity of ecosystems to feed and water human societies. Over the past 50 years, global fertilizer application has increased 5-fold, and anthropogenic pressures on aquatic ecosystems are expected to further intensify through the middle of the century due to population growth and increasing meat consumption. Therefore, understanding how water and solutes enter and propagate through freshwater landscapes in the Anthropocene is critical to protecting and restoring aquatic ecosystems and ensuring human water security.
Substantial investment has been made to reduce carbon and nutrient pollution at local, national, and international levels, but results remain mixed in part because of difficulty monitoring and predicting water quality in dynamic freshwater landscapes. Indeed, current water quality monitoring schemes are a consequence of historical priorities and choices, and most regulatory frameworks impose limits on annual fluxes or mean concentrations in medium to large rivers. This is an appealing strategy because water quality in larger rivers integrates many small catchments, and from an estuarine or oceanic perspective, total nutrient flux is the main metric of concern. Yet, monitoring large rivers may not provide information either on how to reduce these nutrients loads from source areas (most of which are low-order headwater catchments), nor on whether current regulations are being met. Indeed, there is growing evidence that to reduce downstream nutrient fluxes, we need to consider conditions far upstream in headwater catchments, which represent the vast majority of stream length and basin area. Many monitoring designs are not able to provide information on relationships between landscape structure, land use, and water quality, nor on the time lags in the response of water quality after land use change. Therefore, they are unlikely to usefully inform management efforts to improve water quality.
Because headwater catchments are extremely numerous and highly variable, both spatially distributed and temporally intensive monitoring and simulation are needed to understand the production, processing, and propagation of water, solutes, and particulates through freshwater landscapes.
This Research Topic brings together applied and fundamental research addressing this headwater conundrum. It invites interdisciplinary observations and analyses that address the following question: given the high cost of high-frequency water quality monitoring, how can we meaningfully quantify ecohydrological heterogeneity in freshwater networks to generate new ecological understanding and improve monitoring and management? Contributions are particularly welcome that explicitly address scaling predictions and implementing effective interventions in dynamic ecological mosaics.
Keywords: Headwater catchment, water quality, landscape, hydrology, stream
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