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As human-caused climate changes accelerate, California will experience hydrologic and temperature conditions different than any encountered in recorded history. How will these changes affect the state's freshwater ecosystems? Rivers, lakes, and wetlands are managed as a water resource, but they also support a complex web of life, ranging from bacteria, fungi, and algae to macrophytes, woody plants, invertebrates, fish, amphibians, reptiles, birds, and mammals. In much of the state, native freshwater organisms already struggle to survive massive water diversions and dams, deteriorating water quality, extensive land cover modification for agriculture and urban development, and invasions of exotic species. In the face of climate change, we need to expand efforts to recover degraded ecosystems and to protect the resilience, health, and viability of existing ecosystems. For this, more process-based understanding of river, lake, and wetlands ecosystems is needed to forecast how systems will respond to future climate change and to our interventions. This will require 1) expanding our ability to model mechanistically how freshwater biota and ecosystems respond to environmental change; 2) hypothesis-driven monitoring and field studies; 3) education and training to build research, practitioner, stewardship, and policy capabilities; and 4) developing tools and policies for building resilient ecosystems. A goals-driven, hypothesis-informed collaboration among tribes, state (and federal) agencies, nongovernmental organizations, academicians, and consultants is needed to accomplish these goals and to advance the skills and knowledge of the future workforce of practitioners, regulators, and researchers who must live with the climate changes that are already upon us and will intensify. [ABSTRACT FROM AUTHOR]

Temporal fluctuations of wind strength and direction can influence aeolian bedform morphology and orientation, which can be encoded into the architecture of aeolian deposits. These strata represent a direct record of atmospheric processes and can be used to understand ancient Martian atmospheric processes as well as those on Earth. The strata can: give insight to ancient atmospheric circulation, how the atmosphere evolved in response to global changes in habitability, and how ancient processes differ from modern processes. The Stimson formation at the Greenheugh pediment (Gale crater) records evidence of fluctuating wind across multiple temporal scales. The strata can be subdivided into three intervals–Gleann Beag, Ladder, and Edinburgh intervals. Internally, the intervals record changes of dune morphology and orientation, correlatable to wind fluctuations at multiple temporal scales. The basal Gleann Beag interval comprises compound cross‐strata, deposited by oblique compound dunes. These dunes record a bimodal wind regime, resulting in net sediment transport toward the north. The Ladder interval records a reversal of sediment transport to the south, where straight‐crested simple‐dunes shaped by a seasonally variable winds formed. Finally, the Edinburgh interval records sediment transport to the west, where a unimodal wind formed sinuous‐crested simple dunes. These observations demonstrate active and variable atmospheric circulation in Gale crater during the accumulation of the Stimson dune field, at multiple temporal scales from seasonally driven winds to much longer time‐frames, during the Hesperian. These observations can be used to further understand ancient atmospheric conditions and processes, at a high temporal resolution on Mars. Plain Language Summary: The direction and strength of the wind varies, but typically follows predictable patterns over a variety of time‐scales ranging from the course of a day or a year through to decades or millennia. Within a dune field, these patterns of air flow control the shape, size and orientation of aeolian landforms‐such as dunes and ripples–and in‐turn be recorded in the rock record, where sediment accumulates over time. These deposits form a record of ancient atmospheric processes, and can be found on Mars, as well as Earth. On Mars, within the Stimson sandstone, evidence for short‐ and long‐term wind trends are identified in these strata deposited by ancient dunes. This partial record–resulting from episodic erosion and deposition characteristic of dune migration–indicates dunes were shaped by seasonal and longer‐term sediment transport processes, and that the shape of dunes, and their orientation changed in response long‐term changes in wind direction. These changing winds give us insight to the prevailing climate controlling the wind within Gale crater during the Hesperian period and can be used to constrain climate models and gain insight to habitability at that time. Key Points: The Greenheugh pediment capping unit is part of the Stimson formation, containing architectural elements consistent with aeolian processesHere, the formation is subdivided into three intervals based on sedimentary architecture: Gleann Beag, Ladder and Edinburgh intervalsThe preserved architecture is a product of fluctuating wind at multiple temporal scales, recording seasonal through to millennial cycles [ABSTRACT FROM AUTHOR]

One of the most striking examples of self-organization in landscapes is the emergence of evenly spaced ridges and valleys (1-6). Despite the prevalence of uniform valley spacing, no theory has been shown to predict this fundamental topographic wavelength. Models of long-term landscape evolution can produce landforms that look realistic (7-9), but few metrics exist to assess the similarity between models and natural landscapes. Here we show that the ridge-valley wavelength can be predicted from erosional mechanics. From equations of mass conservation and sediment transport, we derive a characteristic length scale at which the time-scales for erosion by diffusive soil creep and advective stream incision are equal. This length scale is directly proportional to the valley spacing that emerges in a numerical model of landform evolution, and to the measured valley spacing at five field sites. Our results provide a quantitative explanation for one of the most widely observed characteristics of landscapes. The findings also imply that valley spacing is a fundamental topographic signature that records how material properties and climate regulate erosional processes., The spacing between adjacent ridges and valleys is a fundamental dimension of hilly topography (1-6). Even a casual observer can see from an aeroplane window that ridges and valleys in [...]

Although the upstream translation of waterfalls is often thought to occur by undercutting of resistant strata, collapse, and headwall retreat (e.g., Niagara Falls), many propagating waterfalls maintain a vertical face in the absence of undercutting. To explain this observation, we propose that bedrock-fracture geometry exerts a fundamental control on knickpoint morphology and evolution such that vertical waterfalls can persist during retreat due to toppling in bedrock with near horizontal and vertical sets of joints (e.g., columnar basalt). At a waterfall, rock columns are affected by shear and drag from the overflowing water, buoyancy from the plunge pool at the foot of the waterfall, and gravity. We used a torque balance to determine the stability of a rock column and any individual blocks that comprise the column. Results indicate that rotational failure should occur about the base of a headwall (and therefore preserve its form during upstream propagation) where columns are tilted in the downstream direction or slightly tilted in the upstream direction, depending on the plunge-pool depth. Flume experiments were performed to test the model, and the model provides a good prediction of the flow necessary to induce toppling and the morphology of the headwall. Waterfall-induced toppling explains the morphology of canyon headwalls in the volcanic terrain of the northwestern United States, where catastrophic paleofloods (e.g., Bonneville Flood) have carved steep amphitheater-headed canyons in columnar basalt. This model may also explain similar landforms elsewhere on Earth and Mars, and it can be used to predict the minimum flow discharge needed to create these features. Keywords: knickpoint, amphitheater, plucking, toppling, bedrock erosion, Mars.

Gale crater, the field site for NASA's Mars Science Laboratory Curiosity rover, contains a diverse and extensive record of aeolian deposition and erosion. This study focuses on a series of regularly spaced, curvilinear, and sometimes branching bedrock ridges that occur within the Glen Torridon region on the lower northwest flank of Aeolis Mons, the central mound within Gale crater. During Curiosity's exploration of Glen Torridon between sols ∼2300–3080, the rover drove through this field of ridges, providing the opportunity for in situ observation of these features. This study uses orbiter and rover data to characterize ridge morphology, spatial distribution, compositional and material properties, and association with other aeolian features in the area. Based on these observations, we find that the Glen Torridon ridges are consistent with an origin as wind‐eroded bedrock ridges, carved during the exhumation of Mount Sharp. Erosional features like the Glen Torridon ridges observed elsewhere on Mars, termed periodic bedrock ridges (PBRs), have been interpreted to form transverse to the dominant wind direction. The size and morphology of the Glen Torridon PBRs are consistent with transverse formative winds, but the orientation of nearby aeolian bedforms and bedrock erosional features raise the possibility of PBR formation by a net northeasterly wind regime. Although several formation models for the Glen Torridon PBRs are still under consideration, and questions persist about the nature of PBR‐forming paleowinds, the presence of PBRs at this site provides important constraints on the depositional and erosional history of Gale crater. Plain Language Summary: Wind has played a major role in sculpting the surface of Mars. Gale crater, the field site for NASA's Mars Science Laboratory Curiosity rover since it landed there in 2012, contains a vast and varied record of deposition and erosion by the wind. This study focuses on a series of regularly spaced, generally straight bedrock ridges that occur within the clay‐bearing Glen Torridon region of Aeolis Mons (informally named Mount Sharp) in Gale crater. During Curiosity's exploration of the Glen Torridon region between sols ∼2300–3080 of the mission, the rover drove through this field of ridges, acquiring images and compositional observations along the way. This study characterizes the Glen Torridon ridges using orbiter and rover data to determine their shape, size, occurrence, and relationship to other wind‐formed features in the area. We find that the Glen Torridon ridges were carved by wind into the bedrock of Mount Sharp. Questions remain about the winds that formed these ridges, but this study provides important information about the history and environment of Gale crater and reports the first rover observations of this type of erosional feature on Mars. Key Points: Decameter‐long, regularly spaced bedrock ridges oriented northeast‐southwest occur throughout the Glen Torridon region of Aeolis MonsGlen Torridon ridges cross‐cut elevation contours and bedding, exhibit bifurcations, and are disrupted by small impact cratersGlen Torridon ridges are erosional periodic bedrock ridges whose formation places erosional and depositional constraints on Aeolis Mons [ABSTRACT FROM AUTHOR]

A theoretical model is developed to describe the process of fine sediment infiltration into immobile coarse sediment deposits. The governing equations are derived from mass conservation and the assumption that the amount of fine sediment deposition per unit vertical travel distance into the deposit is either constant or increases with increasing fine sediment fraction. Model results demonstrate that fine sediment accumulation decreases rapidly with depth into coarse substrate initially void of fine sediment, which is consistent with experimental observations that significant fine sediment infiltration occurs to only a shallow depth. Comparisons of the theory with flume data indicate that the model adequately reproduced the weighted-averaged fine sediment fraction values from experiments. An early model developed by Sakthivadivel and Einstein for fine sediment infiltration is in part based on the generally incorrect assumption that intragravel flow remains constant following fine sediment infiltration. Applying a correction to the Sakthivadivel and Einstein model based on alternate hypothesis that introgravel flow is driven by a constant head gives similar results as the proposed model. CE Database subject headings: Sediment; Infiltration; Filters; Theories; Hydraulic models; Sediment; Gravel.

One-dimensional numerical sediment transport models (DREAM-1 and DREAM-2) are used to simulate seven experimental runs designed to examine sediment pulse dynamics in a physical model of forced pool-riffle morphology. Comparisons with measured data indicate that DREAM-1 and -2 closely reproduce the sediment transport flux and channel bed adjustments following the introduction of fine and coarse sediment pulses, respectively. The cumulative sediment transport at the flume exit in a DREAM-1 simulation is within 10% of the measured values, and cumulative sediment transport at flume exit in a DREAM-2 simulation is within a factor of 2 of the measured values. Comparison of simulated and measured reach-averaged aggradation and degradation indicates that 84% of DREAM-1 simulation results have errors less than 3.3 mm, which is approximately 77% of the bed material geometric mean grain size or 3.7% of the average water depth. A similar reach-averaged comparison indicates that 84% of DREAM-2 simulation results have errors less than 7.0 mm, which is approximately 1.7 times the bed material geometric mean grain size or 11% of the average water depth. Simulations using measured thalweg profiles as the input for the initial model profile produced results with larger errors and unrealistic aggradation and degradation patterns, demonstrating that one-dimensional numerical sediment transport models need to be applied on a reach-averaged basis. CE Database subject headings: Sediment transport; Numerical models; Movable bed models; Channel morphology; Simulation.

Amphitheater-headed valleys are common on the surfaces of Earth and Mars. The abrupt terminations of these valleys at their headwalls have been used extensively to argue for valley erosion from springs (i.e., seepage erosion or groundwater sapping) rather than surface runoff. This interpretation has significant implications for Martian hydrology and the associated prospects for life. A connection between channel form and the erosion processes induced by groundwater, however, has not been demonstrated in resistant rock. Perhaps the most widely cited terrestrial analogs for Martian amphitheater-headed valleys in basalt are the spectacular canyons of Kohala, Hawai'i. Here we present new field observations and topographic analyses of the amphitheater-headed Kohala valleys. We found no evidence for intensively weathered rocks or alcoves around springs at valley headwalls. Instead, valley-head erosion appears to be dominated by waterfall plunge pools. Stream flow from peak annual precipitation events exceeds spring discharge by more than an order of magnitude, and such flow is responsible for evacuation of the coarse sediment that lines the streams. Bathymetric surveys along the Kohala coast have revealed a large submarine landslide, the Pololu Slump, directly offshore of the Kohala valleys. We propose that the headscarp of this massive landslide is expressed as the present-day ~400 m Kohala sea cliffs. As dominant streams poured over this headscarp as waterfalls, vertical plunge pool erosion and undercutting caused upstream propagation of knickpoints, eventually producing amphitheater-headed valleys. Island subsidence rates and the ages of volcanic eruptions and submarine terraces indicate that the average rate of valley headwall advance is as high as 60 mm/yr. We propose a simple expression for upslope headwall propagation by vertical waterfall erosion based on abrasion by impacting sediment particles in plunge pools. This model indicates that headwall propagation depends nonlinearly on the sediment flux passing over the waterfall and linearly on the ratio of kinetic versus potential energy of sediment impacts. After the Pololu Slump, many streams did not form upslopepropagating waterfalls because they had smaller discharges due to a radial drainage pattern and fault-bounded drainage divides, which prevented runoff from the wetter summit of the volcano. A threshold for headwall propagation due to sediment supply or sediment-transport capacity is consistent with the model. Island subsidence following valley formation has resulted in alluviation of the valley floors, which has created the observed U-shaped valley cross sections. Our interpretation implies that surface runoff can carve amphitheater-headed valleys and that seepage erosion cannot be inferred based solely on valley form on Earth, Mars, or other planets. Keywords: amphitheater, sapping, seepage, Hawai'i, knickpoint, plunge pool, waterfall.

Episodic debris flows scour the rock beds of many steepland valleys. Along recent debris-flow runont paths in the western United States, we have observed evidence for bedrock lowering, primarily by the impact of large particles entrained in debris flows. This evidence may persist to the point at which debris-flow deposition occurs, commonly at slopes of less than ~0.03-0.10. We find that debris-flow-scoured valleys have a topographic signature that is fundamentally different from that predicted by bedrock river-incision models. Much of this difference results from the fact that local valley slope shows a tendency to decrease abruptly downstream of tributaries that contribute throughgoing debris flows. The degree of weathering of valley floor bedrock may also decrease abruptly downstream of such junctions. On the basis of these observations, we hypothesize that valley slope is adjusted to the long-term frequency of debris flows, and that valleys scoured by debris flows should not be modeled using conventional bedrock river-incision laws. We use field observations to justify one possible debris-flow incision model, whose lowering rate is proportional to the integral of solid inertial normal stresses from particle impacts along the flow and the number of upvalley debris-flow sources. The model predicts that increases in incision rate caused by increases in flow event frequency and length (as flows gain material) downvalley are balanced by rate reductions from reduced inertial normal stress at lower slopes, and stronger, less weathered bedrock. These adjustments lead to a spatially uniform lowering rate. Although the proposed expression leads to equilibrium long-profiles with the correct topographic signature, the crudeness with which the debris-flow dynamics are parameterized reveals that we are far from a validated debris-flow incision law. However, the vast extent of steepland valley networks above slopes of ~0.03-0.10 illustrates the need to understand debris-flow incision if we hope to understand the evolution of steep topography around the world. Keywords: geomorphology, erosion, debris flows, river incision, landscape evolution.

Author(s): William E. Dietrich (corresponding author) [1]; J. Taylor Perron [1] Do biota affect landscape form and evolution? One way to think about this question is to imagine a very [...]

Soil-covered upland landscapes are common in much of the habitable world, and our understanding of their evolution as a function of different climatic, tectonic, and geologic regimes is important across a wide range of disciplines. Erosion laws direct quantitative study of the processes shaping Earth's surface and form the basis of landscape evolution modeling, but are based on limited field data. Here we use in situ-produced cosmogenic [sup.10Be] and [sup.26Al] concentrations from granitic saprolite to quantify an exponential decline in soil production with increasing soil thickness for a new field site in Point Reyes, California. Results are similar to soil production functions from two different, previously studied field sites, and are used with extensive measurements of soil thickness to quantify depth-integrated sediment transport flux. Plots of calculated sediment fluxes against the product of soil depth and hillslope gradient provide the first field-based evidence that soil transport is a nonlinear, depth-dependent function. Data from all sites suggest that the widely used linear diffusion equation is only appropriate for shallow gradient, convex-up regions, while the depth-dependent transport law is more broadly applicable. Quantifying both the mobile soil thickness and landscape morphology is therefore critical to understanding how landscapes evolve. Keywords: erosion, geomorphology, cosmogenic nuclides, landscape evolution, soil transport.

Burrowing organisms assist in shaping earth surfaces and are simultaneously affected by the environment they inhabit; however, a conceptual framework is not yet available to describe this feedback. We introduce a model that connects the population density of soil-burrowing animals to sediment transport via energy. The model, combined with available data from California hillslopes where soil erosion is driven by pocket gophers (Thomomys bottae), suggests that a gopher annually expends ~9 kJ of energy, or ~1% of reported burrowing energy expenditure, in generating sediment transport. The model is used to evaluate the case that gophers prefer to populate thicker soils. The results suggest that this behavior may drastically dampen the spatial and temporal variations of soil thickness and gopher populations, implying that burrowing organisms may create landscapes distinct from those affected by abiotic processes. Keywords: sediment transport, bioturbation, pocket gopher, soil thickness, hillslope.

In mountainous areas, landslides regulate temporal variations in sediment production and may suppress simple linkages between topographic development and tectonic forcing. Rates and mechanisms of mass wasting depend on lithology, bedrock structure, and climatic and tectonic setting. These factors tend to vary significantly in active tectonic regions, thus clouding our ability, to predict how landsliding modulates topographic development over human and geological time scales. Here, we use a novel DEM-based technique to document the distribution of large landslides in the Oregon Coast Range (OCR) and quantify how they affect topographic relief. We developed an automated algorithm that exploits the distinctive topographic signature (specifically the relationship between curvature and gradient) of large landslides to map their distribution within the gently folded Tyee Formation (Eocene deltaic-submarine ramp sediments). In contrast to steep and highly dissected terrain frequently identified as characteristic of the OCR (which exhibits steep, planar side slopes and highly curved, low-gradient ridge tops and valleys), terrain prone to large landslides tends to have low values of both drainage density and curvature and gradient values that cluster between 0.16 and 0.44. The distribution of failure-dominated terrain in our 10,000 [km.sup.2] study area is influenced by systematic variations in sedimentary facies and bedrock structure. The fraction of terrain altered by large landslides (>0.1 [km.sup.2]) varies from 5% in the sand-rich (delta-slope and proximal ramp facies) southern section of our study area to ~25% in the north (distal ramp facies), coincident with an increase in the thickness of siltstone beds and a decrease in the sandstone:siltstone ratio. Local relief declines progressively northward, suggesting that deep-seated landsliding is sensitive to the thickness and frequency of low-shear-strength siltstone beds and may serve to limit topographic development in the OCR. Structural controls are superimposed on facies-related variations as deep-seated landslides are frequently found on slopes whose downslope aspect corresponds to the bedrock dip direction. For 1516 strike and dip measurements in our study area, we calculated the fraction of proximal terrain ( Our technique for mapping large landslides has utility for hazard analysis and land management. Over million-year time scales, the progradational character of the Tyee Formation suggests that continued uplift and exhumation of the OCR should result in a southward propagation of slide-prone, silt-rich distal facies. As a result, deep-seated landsliding will become increasingly prominent, and topographic relief in the central and southern OCR will progressively decline. Whereas spatial variability in climatic or tectonic forcing is often invoked to explain systematic variations in topographic development, our results emphasize the importance of structural and intraformation lithologic controls on landsliding. As such, analyses linking surface processes, climate, tectonics, and landscapes should be couched in the context of diverse geologic and topographic data. Keywords: deep-seated landslides, landscape evolution, Oregon Coast Range, slope stability, Tyee Formation, relief.

Until recently, published rates of incision of bedrock valleys came from indirect dating of incised surfaces. A small but growing literature based on direct measurement reports short-term bedrock lowering at geologically unsustainable rates. We report observations of bedrock lowering from erosion pins monitored over 1-7 yr in 10 valleys that cut indurated volcanic and sedimentary rocks in Washington, Oregon, Calilornia, and Taiwan. Most of these channels have historically been stripped of sediment. Their bedrock is exposed to bed-load abrasion, plucking, and seasonal wetting and drying that comminutes hard, intact rock into plates or equant fragments that are removed by higher flows. Consequent incision rates are proportional to the square of rock tensile strength, in agreement with experimental results of others. Measured rates up to centimeters per year far exceed regional long-term erosion-rate estimates, even for apparently minor sediment-transport rates. Cultural artifacts on adjoining strath terraces in Washington and Taiwan indicate at least several decades of lowering at these extreme rates. Lacking sediment cover, lithologies at these sites lower at rates that far exceed long-term rock-uplift rates. This rate disparity makes it unlikely that the long profiles of these rivers are directly adjusted to either bedrock hardness or rock-uplift rate in the manner predicted by the stream power law, despite the observation that their profiles are well fit by power-law plots of drainage area vs. slope. We hypothesize that the threshold of motion of a thin sediment mantle, rather than bed-rock hardness or rock-uplift rate, controls channel slope in weak bedrock lithologies with tensile strengths below ~3-5 MPa. To illustrate this hypothesis and to provide an alternative interpretation for power-law plots of area vs. slope, we combine Shields' threshold transport concept with measured hydraulic relationships and downstream fining rates. In contrast to fluvial reaches, none of the hundreds of erosion pins we installed in steep valleys recently scoured to bedrock by debris flows indicate any postevent fluvial lowering. These results are consistent with episodic debris flows as the primary agent of bedrock lowering in the steepest parts of the channel network above ~0.03-0.10 slope. Keywords: geomorphology, erosion, neotectonics, rivers, weathering.

Water age and flow pathways should be related; however, it is still generally unclear how integrated catchment runoff generation mechanisms result in streamflow age distributions at the outlet. Here, we combine field observations of runoff generation at the Dry Creek catchment with StorAge Selection (SAS) age models to explore the relationship between stream water age and runoff pathways. Dry Creek is a 3.5 km2 catchment in the Northern California Coast Ranges with a Mediterranean climate, and, despite an average rainfall of ≈1,800 mm/yr, is an oak savannah due to the limited hillslope water storage capacity. Runoff lag to peak—after initial seasonal wet‐up—is rapid (∼1–2 hr), and total annual streamflow consists predominantly of saturation overland flow, based on field mapping of saturated extents and an inferred runoff threshold for the expansion of saturation extent beyond the geomorphic channel. SAS modeling based on daily isotope sampling reveals that streamflow is typically older than 1 day. Since streamflow primarily consists of overland flow, a significant portion of overland flow must not be event‐rain but instead derive from older, nonevent groundwater returning to the surface, consistent with field observations of exfiltrating head gradients, return flow through macropores, and extensive saturation days after storm events. We conclude that even in a watershed fed primarily by overland flow, runoff is primarily not composed of event water. Our findings have implications for the interpretation of stream chemistry and the assumptions built into widely used hydrograph separation inferences, namely, the assumption that overland flow consists of new (event) water. Plain Language Summary: Streams that respond most rapidly to rainfall tend to be fed by a process called overland flow. This study uses high‐frequency water tracking measurements to show that even in a watershed fed by overland flow, the water entering the stream during storm events tends to be older than the storm event causing the stream response. Hydrologic observations made during storm events reveal that water travels through the subsurface before reemerging as surface flow. The interaction between storm event water and subsurface soils and weathered bedrock likely lead to mixing such that the water entering the stream contains a substantial fraction of water from previous storm events. Key Points: Field observations of surface runoff, groundwater levels, and saturated extents indicate that saturation overland flow dominates streamflowStable isotope tracers show that stream water age decreases as streamflow increasesStreamflow is nevertheless mainly water greater than 1 day old, meaning that even overland flow is mostly not event water [ABSTRACT FROM AUTHOR]

Although shallow (<1.5 m) soil water storage has been extensively studied, the significance of deeper unsaturated zone water storage to flow generation is poorly documented. However, a limited but growing body of empirical work shows that the weathered bedrock vadose zone, not soil, stores the majority of plant available water in many seasonally dry and semi‐arid landscapes. Moreover, this storage dynamic mediates recharge to hillslope groundwater systems that generate stream discharge and support ecologically significant baseflows. Explicit representations of bedrock vadose zone processes are rarely incorporated into runoff models, due in part to a paucity of observations that can constrain simulations. Here, we develop a simple representation of the weathered bedrock vadose zone that is guided by in situ field observations. We incorporate this representation into a rainfall‐runoff model, and calibrate it on streamflow alone, on rock moisture (i.e., weathered bedrock vadose zone moisture) alone, and on both using the concept of Pareto optimality. We find that the model is capable of accurately simultaneously simulating dynamics in rock moisture and streamflow, in terms of Kling‐Gupta Efficiency, when using Pareto optimal parameter sets. Calibration on streamflow alone, however, is insufficient to accurately simulate rock moisture dynamics. We further find that the posterior distributions of some model parameters are sensitive to choice of calibration scenario. The posterior distribution of high‐performing model parameters resulting from the streamflow only calibration scenario include physically unrealistic values that are not yielded by the rock moisture only or Pareto calibration strategies. These results suggest that the accuracy of some model results can be increased and parameter uncertainty decreased via incorporation of rock moisture data in calibration, without sacrificing streamflow simulation quality. Emerging recognition of the global significance of weathered bedrock water storage in seasonally dry and semi‐arid regions motivates more observations of weathered bedrock moisture and integration of this variable into earth system models. [ABSTRACT FROM AUTHOR]

In a headwater catchment in the Oregon Coast Range, we find that solid-phase mass losses due to chemical weathering are equivalent in the bedrock and the soil. However, the long-term rate of mass loss per unit volume of parent rock is greater in the soil than in the rock. We attribute this finding to the effects of biotic processes in the soil and to hydrologic conditions that maximize contact time and water flux through the mineral matrix in the soil. This result stems both from earlier work in which we demonstrated that rock and soil contribute equally to the solute flux and from arguments presented here that the basin is in dynamic equilibrium with respect to erosion and uplift. The silica flux of 10.7 [+ or -] 7.1 t.[km.sup.-2]x[yr.sup.-1] from the basin is several times larger than the flux from older soils elsewhere, but comparable to the flux from sites with similar physical erosion rates. This result argues that physical denudation or uplift rates play an important role in setting the chemical denudation rate. Physical processes appear to influence chemical-weathering rates in several ways. First, they limit chemical evolution by removing material, thus setting the residence time within the weathered rock and the soil. Second, bioturbation mixes rock fragments into the more reactive soil and maintains high soil porosity, allowing free circulation of water. Because the weathering in the soil is more intense than in the rock, we argue that the chemical denudation rate will diminish where uplift rates--and, hence, physical-denudation rates--are great enough to lead to a bedrock-dominated landscape. Chemical denudation rates will increase with physical-denudation rates, but only as long as the landscape remains mantled by soil. Keywords: chemical erosion, denudation, physical weathering, soil dynamics, uplift, weathering.