Nitrous oxide emissions from drying streams and rivers

Peer reviewe

Inland Water Greenhouse Gas Budgets for RECCAP2: 1. State‐of‐the‐Art of Global Scale Assessments

Inland waters are important sources of the greenhouse gasses (GHGs) carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) to the atmosphere. In the framework of the 2nd phase of the REgional Carbon Cycle Assessment and Processes (RECCAP-2) initiative, we review the state of the art in estimating inland water GHG budgets at global scale, which has substantially advanced since the first phase of RECCAP nearly ten years ago. The development of increasingly sophisticated upscaling techniques, including statistical prediction and process based models, allows for spatially explicit estimates which are needed for regionalized assessments of continental GHG budgets such as those established for RECCAP. A few recent estimates also resolve the seasonal and/or interannual variability in inland water GHG emissions. Nonetheless, the global-scale assessment of inland water emissions remains challenging because of limited spatial and temporal coverage of observations and persisting uncertainties in the abundance and distribution of inland water surface areas. To decrease these uncertainties, more empirical work on the contributions of hot-spots and hot-moments to overall inland water GHG emissions is particularly needed

Inland water greenhouse gas budgets for RECCAP2: 2. Regionalization and homogenization of estimates

Inland waters are important sources of the greenhouse gasses (GHGs) carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) to the atmosphere. In the framework of the 2nd phase of the REgional Carbon Cycle Assessment and Processes (RECCAP-2) initiative, we synthesize existing estimates of GHG emissions from streams, rivers, lakes and reservoirs, and homogenize them with regard to underlying global maps of water surface area distribution and the effects of seasonal ice cover. We then produce regionalized estimates of GHG emissions over 10 extensive land regions. According to our synthesis, inland water GHG emissions have a global warming potential of an equivalent emission of 13.5 (9.9-20.1) and 8.3 (5.7-12.7) Pg CO₂-eq. yr⁻¹ at a 20 and 100 year horizon (GWP₂₀ and GWP₁₀₀), respectively. Contributions of CO₂ dominate GWP₁₀₀, with rivers being the largest emitter. For GWP₂₀, lakes and rivers are equally important emitters, and the warming potential of CH₄ is more important than that of CO₂. Contributions from N₂O are about two orders of magnitude lower. Normalized to the area of RECCAP-2 regions, S-America and SE-Asia show the highest emission rates, dominated by riverine CO₂ emissions

River network saturation concept: factors influencing the balance of biogeochemical supply and demand of river networks

Este artículo contiene 19 páginas, 3 tablas, 6 figuras.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 used to compare the fate of different constituents among river networks. New approaches using nested in situ high-frequency sensors and spatially extensive synoptic techniques offer the potential to test the RNS concept in different settings. Better understanding of when and where river networks saturate for different constituents will allow for the extrapolation of aquatic function to broader spatial scales and therefore provide information on the influence of river function on continental element cycles and help identify policy priorities.This paper is a product of the AGU Chapman Conference on Extreme Climate Events held in San Juan Puerto Rico in January 2017. We would like to thank the USDA (award # 2016-67019-25280), NSF-EPSCoR (#1641157), USGS, National CZO office, and the US Forest Service IITF for funding this AGU Chapman conference on Extreme Climate and providing travel funds to the attendees. This research was also supported by National Science Foundation (NSF) Macrosystem Biology (EF-1065286), NSF EPSCoR (EPS-1101245), and NSF LTER to Plum Island Ecosystem (OCE-1238212 and 1637630). Partial funding was provided by the New Hampshire Agricultural Experiment Station, USDA National Institute of Food and Agriculture Hatch Project NH00609, and is Scientific Contribution #2743.Peer reviewe

Biofilm-induced bioclogging produces sharp interfaces in hyporheic flow, redox conditions, and microbial community structure

Riverbed sediments host important biogeochemical processes that play a key role in nutrient dynamics. Sedimentary nutrient transformations are mediated by bacteria in the form of attached biofilms. The influence of microbial metabolic activity on the hydrochemical conditions within the hyporheic zone is poorly understood. We present a hydrobiogeochemical model to assess how the growth of heterotrophic and autotrophic biomass affects the transport and transformation of dissolved nitrogen compounds in bedform-induced hyporheic zones. Coupling between hyporheic exchange, nitrogen metabolism, and biomass growth leads to an equilibrium between permeability reduction and microbial metabolism that yields shallow hyporheic flows in a region with low permeability and high rates of microbial metabolism near the stream-sediment interface. The results show that the bioclogging caused by microbial growth can constrain rates and patterns of hyporheic fluxes and microbial transformation rate in many streams