Rivers play a critical role in connecting terrestrial and aquatic ecosystems, and linking the continents and oceans. Increasing global pressure on water and energy resources has led to extensive modification of river systems for agriculture, water supply, and energy production. The effects of water withdrawals and land development propagate through rivers to downstream cities, ecosystems, and eventually the ocean. Rivers not only carry a wide range of dissolved and particulate constituents—organic matter, nutrients, eroded soil and sediments, toxic contaminants, pharmaceutical compounds, microorganisms, and mobile genetic elements such as antibiotic resistance genes—but also contain complex and diverse ecosystems that drive high rates of biogeochemical transformation.
Despite the recent focus on water resources sustainability and ecosystem resilience, the movement of water and what it carries down-valley in rivers remains difficult to predict because of their complex heterogeneous structure and pronounced temporal variability. It is now understood that rivers are directly connected to shallow groundwater in floodplains and the underlying groundwater aquifers through a wide range of surface–subsurface exchange processes. These connections are critical to the ecology, geomorphology, and biogeochemistry of river corridors; however, development of a deep understanding of rivers needed for resource management and ecosystem conservation remains elusive.
Crucial challenges that must be overcome to transform our understanding of river corridors from descriptive to predictive have been identified by Ward and Packman in WIREs Water. They focus on the key role of river corridor exchange as a regulator of both the propagation and transformation of river-borne material and interactions with the surrounding terrestrial landscape. Part of the challenge is that these connections are so fundamental to the functioning of river corridors, that research has been conducted from a wide variety of scientific perspectives with different questions and methods—most notably hydrology, ecology, geomorphology, and biogeochemistry.
Ward and Packman seek to unify river corridor science through systematic re-evaluation of methods in the context of broader conceptual models and quantitative theory. They identify two key barriers to synthesis of current data: 1) failure to account for multi-scale feedback; and 2) uncertainty in the information content of common measurement methods. They propose to re-conceptualize river corridors in terms of interacting multiscale spatial and temporal domains, and use this conceptual model to guide hypothesis-driven integration of quantitative theory, measurements, and models.
Ward and Packman recommend four tangible strategies for advancing prediction of river corridor exchange: 1) standardize multi-scale system characterization; 2) critically re-evaluate the information content of observation methods; 3) design research with iterative data collection and modeling; and 4) advance theory to integrate observations and models. Successful development of new integrated theory, predictive models, and multi-scale observations will enable improved assessment and management of critical outcomes for river systems, such as river ecosystem sustainability, fate and effects of emerging contaminants, and retention and export of carbon and nitrogen.
Kindly contributed by the authors.