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1. Tectonic controls on Quaternary landscape evolution in the Ventura basin, southern California, USA, quantified using cosmogenic isotopes and topographic analyses

   https://doi.org/10.1130/B36076.1  

   Hughes, A. ; Rood, D.H. ; DeVecchio, D.E. ; Whittaker, A.C. ; Bell, R.E. ; Wilcken, K.M. ; Corbett, L.B. ; Bierman, P.R. ; Swanson, B.J. ; Rockwell, T.K. ( January 2022 , GSA Bulletin)

   Abstract The quantification of rates for the competing forces of tectonic uplift and erosion has important implications for understanding topographic evolution. Here, we quantify the complex interplay between tectonic uplift, topographic development, and erosion recorded in the hanging walls of several active reverse faults in the Ventura basin, southern California, USA. We use cosmogenic 26Al/10Be isochron burial dating and 10Be surface exposure dating to construct a basin-wide geochronology, which includes burial dating of the Saugus Formation: an important, but poorly dated, regional Quaternary strain marker. Our ages for the top of the exposed Saugus Formation range from 0.36 +0.18/-0.22 Ma to 1.06 +0.23/-0.26 Ma, and our burial ages near the base of shallow marine deposits, which underlie the Saugus Formation, increase eastward from 0.60 +0.05/-0.06 Ma to 3.30 +0.30/-0.41 Ma. Our geochronology is used to calculate rapid long-term reverse fault slip rates of 8.6–12.6 mm yr–1 since ca. 1.0 Ma for the San Cayetano fault and 1.3–3.0 mm yr–1 since ca. 1.0 Ma for the Oak Ridge fault, which are both broadly consistent with contemporary reverse slip rates derived from mechanical models driven by global positioning system (GPS) data. We also calculate terrestrial cosmogenic nuclide (TCN)-derived, catchment-averaged erosion rates thatmore »range from 0.05–1.14 mm yr–1 and discuss the applicability of TCN-derived, catchment-averaged erosion rates in rapidly uplifting, landslide-prone landscapes. We compare patterns in erosion rates and tectonic rates to fluvial response times and geomorphic landscape parameters to show that in young, rapidly uplifting mountain belts, catchments may attain a quasi-steady-state on timescales of <105 years even if catchment-averaged erosion rates are still adjusting to tectonic forcing.« less
2. Quantifying the effects of land use and model scale on water partitioning and water ages using tracer-aided ecohydrological models

   https://doi.org/10.5194/hess-25-2239-2021  

   Smith, Aaron ; Tetzlaff, Doerthe ; Kleine, Lukas ; Maneta, Marco ; Soulsby, Chris ( January 2021 , Hydrology and Earth System Sciences)

   Abstract. Quantifying how vegetation mediates water partitioning at different spatialand temporal scales in complex, managed catchments is fundamental forlong-term sustainable land and water management. Estimations fromecohydrological models conceptualising how vegetation regulates theinterrelationships between evapotranspiration losses, catchment water storage dynamics, and recharge and runoff fluxes are needed to assess water availability for a range of ecosystem services and evaluate how these might change under increasing extreme events, such as droughts. Currently, the feedback mechanisms between water and mosaics of different vegetation and land cover are not well understood across spatial scales, and the effects of different scaleson the skill of ecohydrological models needs to be clarified. We used thetracer-aided ecohydrological model EcH2O-iso in an intensively monitored 66 km2 mixed land use catchment in northeastern Germany to quantify water flux–storage–age interactions at four model grid resolutions (250, 500, 750, and 1000 m). This used a fusion of field (including precipitation, soil water, groundwater, and stream isotopes) and remote sensing data in the calibration. Multicriteria calibration across the catchment at each resolution revealed some differences in the estimation of fluxes, storages, and water ages. In general, model sensitivity decreased and uncertainty increased with coarser model resolutions. Larger grids were unable to replicate observed streamflow andmore »distributed isotope dynamics in the way smaller pixels could. However, using isotope data in the calibration still helped constrain the estimation of fluxes, storage, and water ages at coarserresolutions. Despite using the same data and parameterisation for calibration at different grid resolutions, the modelled proportion of fluxes differed slightly at each resolution, with coarse models simulating higher evapotranspiration, lower relative transpiration, increased overland flow, and slower groundwater movement. Although the coarser resolutions also revealed higher uncertainty and lower overall model performance, the overall results were broadly similar. The study shows that tracers provide effective calibration constraints on larger resolution ecohydrological modelling and help us understand the influence of grid resolution on the simulation of vegetation–soil interactions. This is essential in interpreting associated uncertainty in estimating land use influence on large-scale “blue” (ground and surface water) and “green” (vegetation and evaporated water) fluxes, particularly for future environmental change.« less
3. HyLands 1.0: a hybrid landscape evolution model to simulate the impact of landslides and landslide-derived sediment on landscape evolution

   https://doi.org/10.5194/gmd-13-3863-2020  

   Campforts, Benjamin ; Shobe, Charles M. ; Steer, Philippe ; Vanmaercke, Matthias ; Lague, Dimitri ; Braun, Jean ( January 2020 , Geoscientific Model Development)

   Abstract. Landslides are the main source of sediment in most mountain ranges. Rivers then act as conveyor belts, evacuating landslide-derived sediment. Sediment dynamics are known to influence landscape evolution through interactions among landslide sediment delivery, fluvial transport and river incision into bedrock. Sediment delivery and its interaction with river incision therefore control the pace of landscape evolution and mediate relationships among tectonics, climate and erosion. Numerical landscape evolution models (LEMs) are well suited to study the interactions among these surface processes. They enable evaluation of a range of hypotheses at varying temporal and spatial scales. While many models have been used to study the dynamic interplay between tectonics, erosion and climate, the role of interactions between landslide-derived sediment and river incision has received much less attention. Here, we present HyLands, a hybrid landscape evolution model integrated within the TopoToolbox Landscape Evolution Model (TTLEM) framework. The hybrid nature of the model lies in its capacity to simulate both erosion and deposition at any place in the landscape due to fluvial bedrock incision, sediment transport, and rapid, stochastic mass wasting through landsliding. Fluvial sediment transport and bedrock incision are calculated using the recently developed Stream Power with Alluvium Conservation and Entrainment (SPACE)more »model. Therefore, rivers can dynamically transition from detachment-limited to transport-limited and from bedrock to bedrock–alluvial to fully alluviated states. Erosion and sediment production by landsliding are calculated using a Mohr–Coulomb stability analysis, while landslide-derived sediment is routed and deposited using a multiple-flow-direction, nonlinear deposition method. We describe and evaluate the HyLands 1.0 model using analytical solutions and observations. We first illustrate the functionality of HyLands to capture river dynamics ranging from detachment-limited to transport-limited conditions. Second, we apply the model to a portion of the Namche Barwa massif in eastern Tibet and compare simulated and observed landslide magnitude–frequency and area–volume scaling relationships. Finally, we illustrate the relevance of explicitly simulating landsliding and sediment dynamics over longer timescales for landscape evolution in general and river dynamics in particular. With HyLands we provide a new tool to understand both the long- and short-term coupling between stochastic hillslope processes, river incision and source-to-sink sediment dynamics.« less
4. Topographical shifts in fine root lifespan in a mixed, mesic temperate forest

   https://doi.org/10.1371/journal.pone.0254672  

   Primka, Edward J. ; Adams, Thomas S. ; Buck, Alexandra ; Eissenstat, David M. ( July 2021 , PLOS ONE)

   Zang, RunGuo (Ed.)

   Root lifespan, often is estimated in landscape- and ecosystem-level carbon models using linear approximations. In water manipulation experiments, fine root lifespan can vary with soil water content. Soil water content is generally structured by complex topography, which is largely unaccounted for in landscape- and ecosystem-scale carbon models. Topography governs the range of soil water content experienced by roots which may impact their lifespan. We hypothesized that root lifespan varied nonlinearly across a temperate, mesic, forested catchment due to differences in soil water content associated with topographic position. We expected regions of the landscape that were too wet or too dry would have soils that were not optimal for roots and thus result in shorter root lifespans. Specifically, we hypothesized that root lifespan would be longest in areas that consistently had soil water content in the middle of the soil water content spectrum, while in soils at either very low or very high soil water content, root lifespan would be relatively short. We tested this hypothesis by collecting and analyzing two years of minirhizotron and soil moisture data in plots widely distributed in the Shale Hills catchment of the Susquehanna-Shale Hills Critical Zone Observatory in Pennsylvania. We found that fine rootmore »lifespans were longer in traditionally wetter topographic regions, but detected no short term (biweekly) effect of soil moisture on root lifespan. Additionally, depth in soil, soil series, slope face orientation, and season of birth strongly affected root lifespans across the catchment. In contrast, lifespan was unaffected by root diameter or mycorrhizal association. Failure to account for these variables could result in erroneous estimates of fine root lifespan and, consequentially, carbon flux in temperate forested regions.« less
5. Geotechnical Engineering in the Face of Climate Change: Role of Multi-Physics Processes in Partially Saturated Soils

   https://doi.org/10.1061/9780784481585.035  

   Vahedifard, Farshid ; Williams, James M. ; AghaKouchak, Amir ( June 2018 , Proc. 2018 International Foundations Congress and Equipment Exposition, IFCEE 2018: Advances in Geomaterial Modeling and Site Characterization, Geotechnical Special Publication No. 295)

   Climate change is expected to alter the statistics of extreme events including rainfall storms, floods, droughts, and heatwaves. Climate-adaptive geotechnical structures warrant a quantitative assessment of the impacts of emerging and projected extreme patterns on the short and long-term behaviors of earthen structures. Furthermore, long-term changes to soil carbon and moisture due to non-extreme climate events should also be considered. While several large-scale studies have been conducted to evaluate various aspects of climate change, there is a clear gap in the state of knowledge in terms of assessing the resilience of geotechnical structures to changes in climatic trends (e.g., warmer climate, protracted droughts, intensified extreme precipitations, and sea level rise). The majority of the aforementioned climatic trends pose multi-physics problems involving thermo-hydro-mechanical (THM) processes in partially saturated soils and earthen structures. This review paper discusses how soil-atmospheric interactions and extreme event patterns in a changing climate can alter soil properties and loading conditions, affecting the performance of partially saturated geotechnical structures. We speculate how changes in climatic trends may weaken partially saturated earthen structures through strength reduction, drying, soil desiccation cracking, shrinkage, microbial oxidation of soil organic matter, fluctuation in the ground water table, land and surface erosion, and highlymore »dynamic pore pressure changes. Each of these weakening processes is primarily induced by variations in the soil moisture and temperature. Finally, we discuss potential modes of failure imposed on partially saturated earthen structures by climatic trends.« less