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Streams and riparian zones are highly heterogeneous ecosystems. Their high biodiversity is promoted by variable flow velocities and water depths, strong hydrological gradients and disturbance regimes. However, human interventions like damming and channelization have degraded these ecosystems world-wide. And, although restoration efforts have increased in the past decades, ecological improvement is lagging. We assessed vegetation development in channelized lowland stream valleys in the Netherlands, combining innovative restoration measures to the stream and stream valleys. This “stream valley restoration” entailed construction of narrower and shallower channels to increase flow velocities during base discharges, meandering of the watercourse to increase flow and depth heterogeneity and excavation of banks to create wide v-shaped stream valleys. We evaluated the effects on functional aspects of the developing in-stream and riparian vegetation by comparing restored stream reaches to nearby unrestored reaches. The reduced channel dimensions led to higher flow velocities, which, through interaction with meandering, triggered a higher variability in flow and depth. Combined with enlargement of the floodplain, this promoted flooding in stream valleys and created wider environmental gradients. Plant diversity strongly increased in the floodplain area, the land–water interface and the shallow water habitat at the channel margins, but decreased in the central parts of stream channels. There, higher flow velocities led to more typically lotic (running water) in-stream plant communities, indicated by a sharp decrease in floating-leaved species and an increase in trailing species. Riparian vegetation showed a higher beta-diversity across the wider valley slopes of restored reaches, with more wetland species in areas with water-tables between 0.0 and −0.6 m, and more upland species as well. Synthesis and applications. This study demonstrates that the combination of strongly reduced channel dimensions, remeandering and widening of riparian zones, is effective in restoring in-stream and riparian habitat heterogeneity. The restoration efforts lead to distinct immediate increases in total and beta-diversity of many typical stream and riparian plant species. Overall, this stresses the importance of applying restoration measures to both streams and stream valleys simultaneously, considering them as a single landscape unit.

Peat-forming wetlands, and particularly floating fens forming the initial stages of these ecosystems, are globally declining due to excavation, dehydration and eutrophication. Restoration of these valuable ecosystems typically involves re-establishment of early-successional open-water stages with oligotrophic conditions that are characteristic for these systems. However, restoration success is notoriously limited and a potential solution may be to initiate succession by re-introduction of target plant species. Knowledge is needed on (a) which plant functional groups should be re-introduced to stimulate fen formation; and (b) how to manage nutrient levels during restoration, considering that plant growth may be slow in oligotrophic conditions. 2. We hypothesized that (1) increasing functional diversity of introduced species would stimulate the formation of peat-forming target communities, their biomass accumulation and expansion onto open water; and that (2) nutrient availability would mediate the relative contribution of specific functional groups to these effects. We experimentally investigated this in 36 artificial outdoor ponds by manipulating plant functional diversity (clonal dominants, clonal stress-tolerators and interstitials) on constructed rafts with fen-forming communities and subjected these to a range of nutrient loadings over two years. 3. Increasing functional diversity as well as increasing nutrient loadings had stimulating effects on plant biomass accumulation, cover formation and rhizome growth onto open water. Both complementarity (due to niche partitioning or facilitation) and selection effects were mechanisms underlying the diversity effect, with a constant relative importance over the entire range of nutrient availabilities. Different functional groups were important for biomass production at different nutrient availabilities. Rhizome formation by clonal stress-tolerators contributed disproportionately to open water colonisation, identifying this functional group as key across all nutrient levels. 4. Synthesis and applications Restoration of floating fen communities (1) can be stimulated during the first two years by introducing a high functional diversity of plant species, including fast-growing clonal species, clonal stress-tolerators and interstitials, which facilitate each other, (2) is dependent on the presence of clonal stress-tolerators such as Calla palustris, Comarum palustre and Menyanthes trifoliata for expansion onto the open water, (3) can start under a wide range of water nutrient levels, including eutrophic conditions.11-Jul-2018

Nitrous oxide (N2O) is a powerful greenhouse gas and the main driver of stratospheric ozone depletion. Since soils are the largest source of N2O, predicting soil response to changes in climate or land use is central to understanding and managing N2O. Here we find that N2O flux can be predicted by models incorporating soil nitrate concentration (NO3−), water content and temperature using a global field survey of N2O emissions and potential driving factors across a wide range of organic soils. N2O emissions increase with NO3− and follow a bell-shaped distribution with water content. Combining the two functions explains 72% of N2O emission from all organic soils. Above 5 mg NO3−-N kg−1, either draining wet soils or irrigating well-drained soils increases N2O emission by orders of magnitude. As soil temperature together with NO3− explains 69% of N2O emission, tropical wetlands should be a priority for N2O management.

Background and aims: Due to the production of large amounts of tannins and phenolics by Rhizophora mangle, it was hypothesized that the invasion of this mangrove species in salt marshes due to global warming will result in changes in the cycling of carbon and nitrogen. Methods: Leaf litter and/or seedlings of R. mangle were placed into 1-m2 experimental plots in a Distichlis spicata-dominated salt marsh on the Atlantic Coast of central Florida (USA). An additional litter decomposition experiment was conducted in all plots by adding litter bags containing 10 g of dried D. spicata shoot litter. Seedling growth was measured yearly. One and four years after the start of the experiment, soil samples were collected to determine physical and chemical soil conditions, potential nitrification and denitrification activities and abundances of genes that are related to microbial processes in the nitrogen cycle. Results: Growth of R. mangle seedlings was stimulated in the presence of R. mangle litter, while decomposition rates of D. spicata litter were lower in plots with R. mangle litter and seedlings. The presence of R. mangle litter and/or seedlings had no significant effect on potential nitrification and denitrification activities and on the abundances of genes. Conclusion: The colonization of R. mangle into D. spicata-dominated salt marshes will affect the carbon cycle, but not necessarily the nitrogen cycle, which is likely due to the pre-existing nitrogen-limited conditions in the salt marsh.

Restoration and conservation of species-rich nature reserves requires inclusion of landscape-scale connections and transport processes such as hydrologic flows and species dispersal. These are important because they provide suitable habitat conditions and an adequate species pool. This study aimed at identifying the key hydrologic flows and plant dispersal processes affecting a landscape with species-rich fen reserves where restoration measures are carried out to set back succession. It also intended to use this information for delineating the area relevant for conservation planning on an Operational Landscape Unit map. The study was carried out for complexes of fen ponds in former turbaries in the Vechtplassen area, The Netherlands. A number of recent insights on plant dispersal were integrated with knowledge on hydrologic flows in the present approach. The results showed that groundwater discharge to ensure mesotrophic, base-rich conditions, should be enhanced by restoring the groundwater recharge areas NE of the reserves. A nearby lake with suitable water chemistry was also identified as a key source of surface water to feed the fens in dry periods. Water dispersal was identified as important within the fen reserves, whereas dispersal by daily migrating dabbling ducks, typically occurring over 2–3 km, was the most important route connecting the reserves with the surrounding landscape. The delineation of the Operational Landscape Unit for this region provides a basis for conservation and restoration that take fundamental landscape connections and transport processes into account. This unique approach simultaneously considers hydrological transport processes as well as species dispersal in the larger landscape beyond the reserves themselves and therefore leads to greater success of restoration and conservation.