River networks modify material transfer from land to ocean. Understanding the factors regulating this function for different gaseous, dissolved, and particulate constituents is critical to quantify the local and global effects of climate and land use change. We propose the River Network Saturation (RNS) concept as a generalization of how river network regulation of material fluxes declines with increasing flows due to imbalances between supply and demand at network scales. River networks have a tendency to become saturated (supply) demand) under higher flow conditions because supplies increase faster than sink processes. However, the flow thresholds under which saturation occurs depends on a variety of factors, including the inherent process rate for a given constituent and the abundance of lentic waters such as lakes, ponds, reservoirs, and fluvial wetlands within the river network. As supply increases, saturation at network scales is initially limited by previously unmet demand in downstream aquatic ecosystems. The RNS concept describes a general tendency of river network function that can be

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Wetlands are often vital physical and social components of a country’s natural capital, as well as providers of ecosystem services to local and national communities. We performed a network analysis to prioritize Sustainable Development Goal (SDG) targets for sustainable development in iconic wetlands and wetlandscapes around the world. The analysis was based on the information and perceptions on 45 wetlandscapes worldwide by 49 wetland researchers of the Global Wetland Ecohydrological Network (GWEN). We identified three 2030 Agenda targets of high priority across the wetlandscapes needed to achieve sustainable development: Target 6.3—“Improve water quality”; 2.4—“Sustainable food production”; and 12.2—“Sustainable management of resources”. Moreover, we found specific feedback mechanisms and synergies between SDG targets in the context of wetlands. The most consistent reinforcing interactions were the influence of Target 12.2 on 8.4—“Efficient resource consumption”; and that of Target 6.3 on 12.2. The wetlandscapes could be differentiated in four bundles of distinctive priority SDG-targets: “Basic human needs”, “Sustainable tourism”, “Environmental impact in urban wetlands”, and “Improving and conserving environment”. In general, we find that the SDG groups, targets, and interactions stress that maintaining good water quality and a “wise use” of wetlandscapes are vital to attaining sustainable development within these sensitive ecosystems.

Abstract. Wetlands are known to be effective sinks for nitrate. Wetland restoration and construction have gained traction as viable conservation measures to improve water quality in intensively managed agricultural landscapes. In addition to reducing nitrate in situ, wetlands may have impacts on water chemistry and temperature dynamics that extend beyond the confines of the wetlands themselves. Nonsaturating nitrate concentrations (NO 3 − ), enhanced organic carbon effluxes, and altered temperature dynamics in streams downstream of wetlands could all affect denitrification rates within a stream network, potentially extending water quality benefits beyond wetland boundaries. We investigated the effect of wetlands on water chemistry, water temperature, and benthic denitrification rates in downstream agricultural ditches through a field measurement campaign over the open water season. We found that although ditches located downstream of wetlands had lower NO 3 − and higher DOC, ditch denitrification rate was not significantly altered by the presence of upstream wetlands. Rather, wetlands indirectly affected denitrification within ditches by strongly influencing the stoichiometry of the two limiting resources, NO 3 − and organic carbon. Peak denitrification rates in ditches were observed when DOC and NO 3 − supplies were approximately balanced, that is, at DOC: NO 3 − ratios that were near the microbial requirement for denitrification. NO 3 − limitation occurred primarily at sites with >3% wetland cover, and in the fall season at all sites, and DOC limitation occurred primarily at sites with <1% wetland cover. Temperature was found to be a secondary control that was important only when NO 3 − and DOC availabilities were balanced. Our results suggest that wetland restoration and construction targeting nitrate reduction within intensively agriculturally managed basins should be implemented in a way that promotes balanced resource availability throughout fluvial networks. Wetlands are an important regulator of resource availability and thus could be used to create conditions that maximize denitrification in NO 3 − -enriched watersheds.