Summer storms trigger soil N₂O efflux episodes in forested catchments

Climate change and climate-driven feedbacks on catchment hydrology and biogeochemistry have the potential to alter the aquatic versus atmospheric fate of nitrogen (N) in forests. This study investigated the hypothesis that during the forest growth season, topography redistributes water and water-soluble precursors (i.e., dissolved organic carbon and nitrate) for the formation of gaseous N species. Soil nitrous oxide (N₂O) and nitrogen (N₂) efflux and soil physical and chemical properties were measured in a temperate forest in Central Ontario, Canada from 2005 to 2010. Hotspots and hot moments of soil N₂O and N₂ efflux were observed in topographic positions that accumulate precipitation, which likely triggered the formation of redox conditions and in turn intercepted the conversion of nitrate N flowing to the stream by transforming it to N₂O and N₂. There was a strong relationship between precipitation and N₂O efflux (y = 0.44x1.22, r² = 0.618, p<0.001 in the inner wetland; y = 1.30x^{1.16} r² = 0.72, p<0.001 in the outer wetland) and significantly different N₂:N₂O ratios in different areas of the wetland (19.6 in the inner wetland and 10.1 in the outer wetland). Soil N₂O+N₂ efflux in response to precipitation events accounted for 16.1% of the annual N input. A consequence of the higher frequency of extreme precipitation events predicted under climate change scenarios is the shift from an aquatic to atmospheric fate for N, resulting in a significant forest N efflux. This in turn creates feedbacks for even warmer conditions due to increased effluxes of potent greenhouse gases."This research was funded by an NSERC Discovery grant to IFC (217053‐2009 RGPIN)."https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015JG00302

Peak grain forecasts for the US High Plains amid withering waters

ACKNOWLEDGMENTS. This paper stems from discussions during the Ettersburg Ecohydrology Workshop in Germany (October 2018), with the corresponding manuscript preparation ensuing in subsequent months. The workshop was funded by the UNIDEL Foundation, Inc. and the University of Delaware. Accordingly, partial support for this paper derived from funding for the workshop. A.M. was supported by the US NSF (Grants NSF-AGS-1644382 and NSF-IOS-175489).Peer reviewedPublisher PD

Snow covered soils produce N₂O that is lost from forested catchments prior to snowmelt

The magnitude of net soil nitrous oxide (N₂O) production from a snow‐covered catchment in a northern temperate forest was investigated. There was considerable net soil N₂O‐N production and consumption through the snowpack, ranging from −6.6 to 26.2 g‐N ha⁻¹ d⁻¹. There was no difference in net N₂O production among topographic positions despite significant variation in soil moisture, reduction‐oxidation conditions, and pore water dissolved organic carbon and nitrate. Soil temperatures did not vary among topographic positions, suggesting that temperatures at or above the freezing point allow N₂O production to proceed under the snowpack. Redox conditions were lower at wetland positions compared to lowlands and uplands, suggesting that the biogeochemical pathway of N₂O production varies with topography. Over the entire nongrowing season, 1.5 kg of N₂O‐N was exported to the atmosphere from the 6.33 ha catchment, representing 31% of the growing season N₂O‐N production. These results suggest that winter is an active time for gaseous N production in these forests and that N₂O production under the snowpack represents an often unmonitored flux of N from catchments."This research was funded by an NSERC Discovery grant to I.F. Creed (217053-2009 RGPIN)."https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016JG00341

Why monitor carbon in high‐alpine streams?

In this short communication, we report on dissolved organic and inorganic carbon concentrations from a summer stream monitoring campaign at the main hydrological catchment of the Tarfala Research Station in northern Sweden. Further, we place these unique high-alpine observations in the context of a relevant subset of Sweden's national monitoring programme. Our analysis shows that while the monitoring programme (at least for total organic carbon) may have relatively good representativeness across a range of forest coverages, alpine/tundra environments are potentially underrepresented. As for dissolved inorganic carbon, there is currently no national monitoring in Sweden. Since the selection of stream water monitoring locations and monitored constituents at the national scale can be motivated by any number of goals (or limitations), monitoring at the Tarfala Research Station along with other research catchment sites across Fennoscandia becomes increasingly important and can offer potential complementary data necessary for improving process understanding. Research catchment sites (typically not included in national monitoring programmes) can help cover small-scale landscape features and thus complement national monitoring thereby improving the ability to capture hot spots and hot moments of biogeochemical export. This provides a valuable baseline of current conditions in high-alpine environments against which to gauge future changes in response to potential climatic and land cover shifts

Forest-Water Interactions Under Global Change

This chapter reviews how global change affects forest-water interactions and water availability to ecosystems and people and synthesises current understanding of the implications of present and anticipated changes to forests and tree cover for local and global hydrology. Forest cover has declined in the past half-century, despite an increase in plantation forestry. Natural and human disturbances affect forest components (e.g. canopy and leaf area, litter and soil surface, rooting depth, and soil porosity) that in turn affect hydrological processes (e.g. interception, evapotranspiration, infiltration, soil moisture storage, and percolation). Many of these changes result from several influential natural disturbance processes including insects and pathogens, wildfire, ice storms, and windthrow, and human disturbances including establishment and harvest of forests, plantations, agroforestry areas, and urban/peri-urban forests. However, each disturbance process affects different components of the forest, producing distinctive hydrologic effects. Climate change will directly alter forest hydrological processes, and social and economic factors will directly alter forest management, via intensive plantations, deforestation, forest degradation, selective logging, loss of riparian forest, and loss of urban trees, and changes in disturbance regimes. Despite extensive knowledge of forest hydrology, forest changes and their effects on hydrology are poorly documented in many areas of the world, and novel combinations of processes and contexts may produce surprising outcomes. Thus, there is a clear need for more geographically extensive and long-term place-based studies of forest and water. In summary, future climate and social changes will alter forests and water, requiring continued research and collaboration with forest managers and forest owners both for improved resilience to such changes, and to better realize multiple benefits

Is There Synchronicity in Nitrogen Input and Output Fluxes at the Noland Divide Watershed, a Small N-Saturated Forested Catchment in the Great Smoky Mountains National Park?

High-elevation red spruce [Picea rubens Sarg.]-Fraser fir [Abies fraseri (Pursh.) Poir] forests in the Southern Appalachians currently receive large nitrogen (N) inputs via atmospheric deposition (30 kg N ha�1 year�1) but have limited N retention capacity due to a combination of stand age, heavy fir mortality caused by exotic insect infestations, and numerous gaps caused by windfalls and ice storms. This study examined the magnitude and timing of the N fluxes into, through, and out of a small, first-order catchment in the Great Smoky Mountains National Park. It also examined the role of climatic conditions in causing interannual variations in the N output signal. About half of the atmospheric N input was exported annually in the streamwater, primarily as nitrate (NO3-N). While most incoming ammonium (NH4-N) was retained in the canopy and the forest floor, the NO3-N fluxes were very dynamic in space as well as in time. There was a clear decoupling between NO3-N input and output fluxes. Atmospheric N input was greatest in the growing season while largest NO3-N losses typically occurred in the dormant season. Also, as water passed through the various catchment compartments, the NO3-N flux declined below the canopy, increased in the upper soil due to internal N mineralization and nitrification, and declined again deeper in the mineral soil due to plant uptake and microbial processing. Temperature control on N production and hydrologic control on NO3-N leaching during the growing season likely caused the observed inter-annual variation in fall peak NO3-N concentrations and N discharge rates in the stream

Emerging threats and persistent conservation challenges for freshwater biodiversity

In the 12 years since Dudgeon et al. (2006) reviewed major pressures on freshwater ecosystems, the biodiversity crisis in the world's lakes, reservoirs, rivers, streams and wetlands has deepened. While lakes, reservoirs and rivers cover only 2.3% of the Earth's surface, these ecosystems host at least 9.5% of the Earth's described animal species. Furthermore, using the World Wide Fund for Nature's Livin