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• Research on land-atmosphere interactions covers a large breadth of disciplines. • Silos between research areas are reinforced by increasingly complex approaches. • This issue integrates research across the soil-vegetation-atmosphere continuum. • New funding opportunities are needed to support this trans-disciplinary work. • Coordinated networks are expensive but will facilitate transformational knowledge. To help bridge science topics related to land-atmosphere interactions, we organized a virtual special issue in this journal (Agricultural and Forest Meteorology [AFM]) entitled, "Land-Atmosphere Interactions: Integrating Surface Flux with Boundary Layer Measurements." The motivation for the special issue was driven by existing disciplinary barriers between research areas that all address land-atmosphere interactions. In particular, it addressed research silos between those who study features of the land surface, surface fluxes (including water, energy, and trace gases), atmospheric boundary layer growth and thermodynamics, and atmospheric composition and aerosols. The special issue sought to bring these communities together to integrate multiple observations across the soil-vegetation-atmosphere continuum with the aim of 1) improving broader understanding of land-atmosphere interactions, feedbacks, and coupling, 2) fostering new collaborations between atmospheric and surface flux scientists, and 3) identifying new paths for integrative research. Here, we provide an overview and synthesis of the special issue. [ABSTRACT FROM AUTHOR]

• We investigated effects of tree species diversity on rainfall partitioning. • Rainfall partitioning was highly dependant on tree species identity. • Non-additive diversity effects were detected in mixed plots. • Tree species diversity did not affect rainfall partitioning directly. • Species richness affected rainfall partitioning indirectly by increased basal area. Rainfall partitioning is a key process in forest ecosystems, affecting evaporation, transpiration and water storage in the canopy, litter and soil. Although rainfall partitioning has been well studied in forest ecosystems, less is known about how rainfall partitioning is modified by tree species diversity. To disentangle the effects of tree species identity and diversity on rainfall partitioning, we installed 128 rain gauges in an experimental plantation, located in Zedelgem (Belgium), part of a large, multi-site forest diversity experiment in Belgium (FORBIO). With these rain gauges, we monitored throughfall for a full year, with a temporal resolution of two weeks. Based on these data, we analysed identity (i.e. whether throughfall is species-specific), non-additive (i.e. whether throughfall in mixtures is different from the expected amounts based on monocultures) and richness effects (i.e. how species richness affects throughfall). First of all, we found that rainfall partitioning highly differed between tree species, due to pronounced species identity effects. The presence of Pinus sylvestris [pine] was always associated with lower throughfall. Year-round throughfall was, for example, the lowest in mixtures of pine and Tilia cordata [lime] (43.8 ± 14.5% of the open-field rainfall) and monocultures of pine (48.6 ± 11.8%). Additionally, non-additive effects were significant, leading to a 10% decrease of rainfall reaching the forest floor in mixtures compared to the expected throughfall based on measurements in monocultures. Tree species richness effects on rainfall partitioning acted indirectly, mostly via an increased basal area in mixed stands. Our findings suggest that mixing tree species leads to a higher than expected reduction in throughfall, which lowered soil moisture in mixed plots. Whether this reduced throughfall and soil moisture affects ecosystem functioning remains to be quantified. [ABSTRACT FROM AUTHOR]

Quantitative prediction of environmental impacts of land-use and climate change scenarios in a watershed can serve as a basis for developing sound watershed management schemes. Water quantity and quality are key environmental indicators which are sensitive to various external perturbations. The aim of this study is to evaluate the impacts of land-use and climate changes on water quantity and quality at watershed scale and to understand relationships between hydrologic components and water quality at that scale under different climate and land-use scenarios. We developed an approach for modeling and examining impacts of land-use and climate change scenarios on the water and nutrient cycles. We used an empirical land-use change model (Conversion of Land Use and its Effects, CLUE) and a watershed hydrology and nutrient model (Soil and Water Assessment Tool, SWAT) for the Teshio River watershed in northern Hokkaido, Japan. Predicted future land-use change (from paddy field to farmland) under baseline climate conditions reduced loads of sediment, total nitrogen (N) and total phosphorous (P) from the watershed to the river. This was attributable to higher nutrient uptake by crops and less nutrient mineralization by microbes, reduced nutrient leaching from soil, and lower water yields on farmland. The climate changes (precipitation and temperature) were projected to have greater impact in increasing surface runoff, lateral flow, groundwater discharge and water yield than would land-use change. Surface runoff especially decreased in April and May and increased in March and September with rising temperature. Under the climate change scenarios, the sediment and nutrient loads increased during the snowmelt and rainy seasons, while N and P uptakes by crops increased during the period when fertilizer is normally applied (May through August). The sediment and nutrient loads also increased with increasing winter rainfall because of warming in that season. Organic nutrient mineralization and nutrient leaching increased as well under climate change scenarios. Therefore, we predicted annual water yield, sediment and nutrient loads to increase under climate change scenarios. The sediment and nutrient loads were mainly supplied from agricultural land under land use in each climate change scenario, suggesting that riparian zones and adequate fertilizer management would be a potential mitigation strategy for reducing these negative impacts of land-use and climate changes on water quality. The proposed approach provides a useful source of information for assessing the consequences of hydrology processes and water quality in future land-use and climate change scenarios. [ABSTRACT FROM AUTHOR]

Abstract: Hybrid rocks formed by fluid–rock interactions at high-pressure (HP) metamorphic conditions are active players in the recycling of volatiles in subduction zones. Such rocks include chlorite–talc–amphibole-rich (± carbonate) rocks formed by chemical and mechanical mixing of mafic, ultramafic and sedimentary protoliths. Recent discovery of widespread formation of lawsonite-rich hybrid rocks extends the composition range of these rocks and their significance for volatile transfer to the deep Earth. In this study we quantify the drastic water enrichment across a metasomatic aureole characterized by intense chemical resetting and massive lawsonite precipitation in Alpine Corsica (France). The chemical composition of the metasomatic product, which in many cases approaches the CASH system, favors (i) the precipitation of lawsonite and the unexpected reincorporation of free water at HP conditions, and (ii) the stability of lawsonite at higher temperature and at greater depth compared to the system. We conclude that these hybrid rocks may contribute to transfer water to great depth in subduction, with implications for water cycling to the mantle. [Copyright &y& Elsevier]

• Fresh Southwestern Indian Ridge basalt glasses are found to have high water contents and H 2 O/Ce ratios (>600). • High water contents and H 2 O/Ce ratios are not caused by assimilation or diffusion. • The water enrichment is associated with the recycling of arc-mantle residue. Trace amounts of water in the sub-oceanic mantle play crucial role in the vigor of mantle convection and the production of oceanic crust, and other many geodynamic processes. Consequently, the cycling of H 2 O between the mantle and the exosphere in the mantle is one of the critical processes governing Earth's geodynamical and geochemical evolution. While the deep cycling of altered oceanic lithosphere was considered as the main way to replenish the water in oceanic upper mantle, the significance of the arc mantle wedge after the genesis of arc magmatism dragged down by the subducting slab concomitantly has been not well constrained. Here, we report that fresh depleted basaltic glasses from the ultraslow-spreading Southwestern Indian Ridge (SWIR), located far from any recent subduction zones, show unusually high H 2 O/Ce ratios (>600), water contents and heavy hydrogen isotopic compositions. These results could be best explained by recycling of water through melting of a residual hydrous mantle wedge after early melt extraction. Considering that such mantle wedges residue dragged down to the deeper mantle could occupy a volume one order of magnitude larger than that of the subducted lithosphere in the earth history, we suggest that the potential role of such shallow recycling should be considered in studies of global water recycling and the origin of water in the upper asthenosphere. [ABSTRACT FROM AUTHOR]

• Iceland crust hydration was studied using δ D and H 2 O content of altered basalt. • oceanic crust hydration and associated δ D values were assessed by isotope modeling. • H 2 O uptake of oceanic crust upon seawater alteration was 1400–1650 Tg H 2 O/yr. • H 2 O flux from oceanic crust to subduction trenches was 610–1240 Tg H 2 O/yr. Oceanic crust is a major transport medium of water into the mantle wedge and the convecting mantle. Yet, the water content of the oceanic crust remains uncertain. Active geothermal systems situated at on-land spreading centers provide a unique opportunity to study the hydration of the oceanic crust, with well constrained systems and boreholes reaching depths of >4 km. Here, we present hydrogen isotope data of geothermal fluids and altered basalt for three Icelandic geothermal systems: the meteoric water fed system at Krafla and the seawater fed systems at Reykjanes and Surtsey. The bulk rock δ D values of altered and hydrated basalts from these localities, which exhibit significantly higher water contents (up to 8.9 wt.%) than magmatic (non-hydrated) basalts, vary greatly from −125 to −96‰ at Krafla, from −80 to −46‰ at Reykjanes and from −78 to −46‰ at Surtsey. The corresponding fluids have δ D values of −84.1 to −81.1‰ at Krafla, −23.1 to −14.9‰ at Reykjanes and +2.1 to +4.3‰ at Surtsey. Comparison of isotope modeling results to the natural data reveals that hydration of the Icelandic crust and corresponding hydrogen isotopic characteristics are controlled by (1) the isotope composition of the source fluid, (2) isotope fractionation between the aqueous geothermal fluids and the alteration minerals formed, and (3) the type and quantity of alteration minerals formed. These factors in turn depend on the extent of fluid-rock interaction and temperature. Using the same modeling approach and expanding it to datasets available for the oceanic crust, we assessed the hydration state and δ D values of the oceanic crust as a function of depth. We show that 1400 to 1650 Tg H 2 O/yr is added to the igneous oceanic crust upon alteration by seawater and that the upper part (<2 km) of oceanic crust hosts almost 50% of the added water. The corresponding hydrogen isotope composition of the hydrated crust was calculated to an average of − 55 ± 6 ‰. Upon subduction and subsequent dehydration, 80–90% of water with δ D values of −35 to −10‰ will be released to the crustal forearc and mantle wedge. The remaining dehydrated slab with δ D values of ∼−160 to −85‰ is expected to be transported to deeper levels modifying the mantle's water budget and isotopic composition. [ABSTRACT FROM AUTHOR]