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Through its Science Focus Area (SFA) projects the Subsurface and Biogeochemical Research program within the U.S. Department of Energy is tightly integrating observations, experiments, and modeling to advance a systems-level understanding of how watersheds function, and to translate that understanding into advanced science-based models of watershed systems. To broaden the impact of the existing SFAs, the IDEAS-Watersheds project builds on the success of a synergistic family of IDEAS projects initated in 2014. Specifically, it strives to improve wathershed modeling capacity by increasing software development productivity through an agile approach to creating a sustainable, reliable, parallel, software ecosystem with interoperable components.In this talk we highlight the unique structure of the IDEAS-Watersheds project and describe how it addresses many challenges of software development with interdisciplinary teams. Specifically, it is organized around six Research Activities that develop concrete use cases to drive advances in our software ecosystem. These use cases are designed to balance advancing software design and development practices for parallel architectures with the model and algorithmic development needed to address scientific challenges. In addition, we use a co-funding model to create a team of early career researchers that will be trained in modern software engineering, while acting as liaisons that contribute to shared deliverables.Presented at SIAM PP20 Minisymposium: Improving Productivity and Sustainability for Parallel Computing Software.

Soil organic carbon turnover to CO2 and CH4 is sensitive to soil redox potential and pH conditions. However, land surface models do not consider redox and pH in the aqueous phase explicitly, thereby limiting their use for making predictions in anoxic environments. Using recent data from incubations of Arctic soils, we extend the Community Land Model with coupled carbon and nitrogen (CLM-CN) decomposition cascade to include simple organic substrate turnover, fermentation, Fe(III) reduction, and methanogenesis reactions, and assess the efficacy of various temperature and pH response functions. Incorporating the Windermere Humic Aqueous Model (WHAM) enables us to approximately describe the observed pH evolution without additional parameterization. Although Fe(III) reduction is normally assumed to compete with methanogenesis, the model predicts that Fe(III) reduction raises the pH from acidic to neutral, thereby reducing environmental stress to methanogens and accelerating methane production when substrates are not limiting. The equilibrium speciation predicts a substantial increase in CO2 solubility as pH increases, and taking into account CO2 adsorption to surface sites of metal oxides further decreases the predicted headspace gas-phase fraction at low pH. Without adequate representation of these speciation reactions, as well as the impacts of pH, temperature, and pressure, the CO2 production from closed microcosms can be substantially underestimated based on headspace CO2 measurements only. Our results demonstrate the efficacy of geochemical models for simulating soil biogeochemistry and provide predictive understanding and mechanistic representations that can be incorporated into land surface models to improve climate predictions.

The International Soil Modeling Consortium (ISMC) was established in 2016 with the aim to integrate andadvance soil systems modeling, data collection, and observational capabilities. ISMC is a community effort. Itfollows a bottom-up approach, is based on scientific principles, voluntary contributions, and open to anybodywho wants to become a member of the consortium (https://soil-modeling.org/). Its activities are organized intothree science panels, organized around a broad workflow from data collection and observation (DO-LINK)to model development and intercomparison (Soil-MIP) to engagement with different scientific communities(CROSS-Connect). ISMC has an executive board and a scientific advisory board that guides ISMC in pursuing itsobjectives.The mission of the Soil-MIP science panel is to foster the further development of soil models that can predictsoil functions and their changes due to soil use and land management, as well as climate change and pollution.A number of model intercomparison studies were recently initiated, focusing on specific processes like soilhydraulic properties, soil thermal properties and related soil heat fluxes, root growth and root water uptake,soil evaporation, soil freezing, infiltration and runoff processes, and coupling between preferential flow in soilsand groundwater. From these comparisons, lessons can be learned about how process controls at small scalespropagate to larger scales and how this leads to effective process representations at larger scales. The missionof DO-Link is to assist with the development of a global soil data meta-repository that is openly availablefor soil system research. Data and data requirements are as diverse as the various disciplines developing andapplying soil models. The soil data meta-repository will be a resource to analyze past and recent model- anddata requirements for continuous standardization and harmonization of soil data. The CROSS-connect sciencepanel identifies soil related knowledge gaps between science communities, and shares this knowledge with otherISMC science panels to push forward development of new tools to better translate soil processes into functionsfor assessing sustainability and ecosystem services. CROSS-connect develops an exchange platform with otherinternational partners like AgMip/MACSUR, GEWEX, ISCN (International Soil Carbon Network), GSBI (GlobalSoil Biodiversity initiative) and CSDMS (Community Surface Dynamics Modeling System). In this presentation,we will highlight the most recent developments and activities that are currently underway as well as future projectsthat are under preparation.