In the majority of existing studies, streams are conceived as static objects that occupy predefined regions of the landscape. However, empirical observations suggest that stream networks are systematically and ubiquitously featured by significant expansion/retraction dynamics produced by hydrologic and climatic variability. This contribution presents novel empirical data about the active drainage network dynamics of a 5 km² headwater catchment in the Italian Alps. The stream network has been extensively monitored with a biweekly temporal resolution during a field campaign conducted from July to November 2018. Our results reveal that, in spite of the wet climate typical of the study area, more than 70% of the observed river network is temporary, with a significant presence of disconnected reaches during wet periods. Available observations have been used to develop a set of simple statistical models that were able to properly reconstruct the dynamics of the active stream length as a function of antecedent precipitation. The models suggest that rainfall timing and intensity represent major controls on the stream network length, while evapotranspiration has a minor effect on the observed intraseasonal changes of drainage density. Our results also indicate the presence of multiple network expansion and retraction cycles that simultaneously operate at different time scales, in response to distinct hydrological processes. Furthermore, we found that observed spatial patterns of network dynamics and unchanneled lengths are related to the underlying heterogeneity of geological attributes. The study offers novel insights on the physical mechanisms driving stream network dynamics in low‐order alpine catchments.

In Europe, excessive inputs of nitrogen threaten ecosystems and public health. Wetlands act as natural filters, removing excess nutrients and protecting downstream waters. Using high-resolution data on nitrogen surplus and wetland distribution, we estimate that existing European wetlands remove 1,092 ± 95 kt of nitrogen per year. Restoring 27% of wetlands historically drained for agriculture (3% of land area), targeted in high nitrogen input areas, could reduce current nitrogen loads to the sea by 36%, but with potential costs to agricultural productivity. A more efficient strategy targets wetland restoration on farmlands projected to be abandoned by 2040, yielding a 22% load reduction and enabling major rivers such as the Rhine, Elbe and Vistula to meet water quality targets with minimal agricultural impact. Our findings highlight wetland restoration as a cost-effective, policy-relevant solution that, if spatially targeted, can deliver major water quality improvements while supporting the European Union’s broader goals on climate, biodiversity and agricultural sustainability.

A variety of interdisciplinary fields have provided distinct and complementary perspectives on human-water systems over the past few decades. In that context, an important distinctive feature of sociohydrology is its historical and methodological link to ecohydrology. This linkage implies a compatibility between the two fields that can be leveraged to address important modeling challenges in both fields. Sociohydrology has thus far focused on temporal dynamics and can benefit from recent advances in ecohydrology to represent spatial dynamics in coupled human-water systems. Conversely, as it increasingly focuses on human-altered catchments, ecohydrology can benefit from sociohydrology in terms of developing models of human behavior that are compatible with (eco)hydrological models, while being consistent with prevailing social science theories. We review recent work in ecohydrology and sociohydrology that substantiates these two arguments, and discuss the modeling of water-borne diseases as an example of a promising avenue of research that connects the two fields.

Natural wetlands are ecological, biogeochemical, and hydrological hot spots yet continue to disappear under human pressure. Their shapes and sizes control their hydroecological functions. We propose that elevation data can be used to delineate potential wetlands and that the (statistical) distributions of potential wetlands should be identical to the distributions of actual wetlands. We compare the shape and size distributions of wetlands reported in the National Wetland Inventory with those of potential wetlands identified using a topographic depression identification model. We estimated area and perimeter distributions as well as shoreline fractal dimension in six contrasting locations in the United States. Pareto distributions described the tails of these distributions, with similar slopes for both model and data. The shape of shorelines was also similar, and their fractal dimension clustered aroundD = 4/3, a pervasive value in nature. We also analyzed the entire wetland inventory data set for the conterminous United States (~20 million wetlands) for reference and found the statistics to be invariant across scales. Our results demonstrate that a simple topographic model can identify most reported wetlands as well as potential wetlands missing from the inventory. These findings could inform strategic surveys and the conservation of wetlandscapes.