Development of generalizable theories and predictive models that describe the behavior of stream and river ecosystems is centrally important to advancing aquatic ecology. Fundamental aspects of stream ecosystem function such as controls on rates of primary production, the production and consumption of dissolved organic matter, and internal nutrient cycling are poorly known relative to their terrestrial and lacustrine counterparts. Several recent advances facilitate development of continental-scale understanding of these and other important processes in aquatic ecosystems. Robust real-time sensors for nitrate and organic matter, new global estimates describing stream and river networks, and new modeling approaches that capture river geometry can all be used to develop new insights into aquatic ecosystem function. Observatories such as NEON, CZO, and LTER will be central to successful application of these new technologies and approaches to understanding aquatic ecosystems, as they provide important ancillary data describing the terrestrial matrix within which these flowing waters are embedded.
Results/Conclusions
Earlier continental-scale assessments of streams include measurements of ecosystem metabolism, denitrification, and N2O flux. Sensors currently being deployed at many NEON, LTER, and CZO sites will greatly improve many of these earlier continental-scale assessments. Continuous measurement of metabolism, for example, will describe the “phenology” of aquatic primary productivity, and a test of the earlier conclusion that light rather than nutrients drives continental-scale variability in rates of GPP. Continuous nitrate sensors are providing new insights into the role of aquatic metabolism in regulating nutrient dynamics, with clear diel signals in NO3 occurring in a surprisingly wide range of streams and rivers. Fluorescent DOM is proving to be a useful proxy for dissolved organic matter concentrations, and should provide additional insights into the extent to which C and N dynamics are coupled in aquatic ecosystems. Although many ecological functions of streams and rivers can be described with the raster-based approach used by the sampling design of NEON, the geometry of channel networks means that a vector-based sampling scheme is also needed to scale up point results to the continent. This is a challenging area that will provide many opportunities in the coming decades for aquatic ecologists.