Explore the vast range of titles available.

The Lower Critical (LCZ)–Upper Critical Zone (UCZ) boundary of the Rustenburg Layered Suite is an intrusion-wide, major stratigraphic transition from intercumulus plagioclase in the LCZ to cumulus plagioclase in the UCZ. No consensus exists regarding the nature of this boundary, with some regarding the attainment of cumulus status by plagioclase at this level of the intrusion due to continued fractionation of the resident magma, whilst others argue for the addition of compositionally distinct magma(s) at this level of the intrusion. Here we report in-situ Sr-isotopic compositions for plagioclase along with whole-rock major- and trace element geochemical and mineral chemical data across the LCZ–UCZ boundary as intersected by borehole BH6958 on the farm Forest Hill in the eastern Bushveld Complex. Major and trace element data across the LCZ–UCZ boundary (e.g. the Cr content of orthopyroxene) support the notion that no compositionally distinct magma was added at this level of the intrusion. Sr- and Nd-isotopic data, however, point to open-system behaviour. The isotopic excursion cannot be explained through mixing between resident (B1) magma and other proposed parental magmas (e.g. B2 or B3 magmas). Modelling suggests that the observed isotopic excursion may be explained through mixing of resident (B1) magma with small amounts of lower crustal melts. Whether such mixing would have resulted in plagioclase stabilisation remains unclear. The observed isotopic excursion can also be explained through mixing of resident (B1) magma with small amounts of crustal fluids. In this case, the introduction of these fluids appears to have happened gradually, with 87 Sr/ 86 Sr i in plagioclase being higher in LCZ rims than cores, and higher yet in the lower UCZ. We argue on the basis of thermodynamic modelling that when plagioclase joined the crystallising assemblage, the system contracted at a rate higher than that preceding plagioclase stabilisation, with fluids from the surrounding hydrothermal system entering the magma chamber to counter the volume loss experienced by the cooling system.

The study of the critical zones (CZs) of the Earth link the composition and function of aboveground vegetation with the characteristics of the rock layers, providing a new way to study how the unique rock and soil conditions in karst regions affect the aboveground vegetation. Based on survey results of the rocks, soils and vegetation in the dolomite and limestone distribution areas in the karst area of central Guizhou, it was found that woody plant cover increases linearly with the number of cracks with a width of more than 1 mm, while the cover of herbaceous plants shows the opposite trend (p<0.01). The dolomite distribution area is characterized by undeveloped crevices, and the thickness of the soil layer is generally less than 20 cm, which is suitable for the distribution of herbaceous plants with shallow roots. Due to the development of crevices in the limestone distribution area, the soil is deeply distributed through the crevices for the deep roots of trees, which leads to a diversified species composition and a complicated structure in the aboveground vegetation. Based on moderate resolution imaging spectroradiometer (MODIS) remote sensing data from 2001 to 2010, the normalized differentiated vegetation index (NDVI) and annual net primary productivity (NPP) results for each phase of a 16-day interval further indicate that the NDVI of the limestone distribution area is significantly higher than that in the dolomite distribution area, but the average annual NPP is the opposite. The results of this paper indicate that in karst CZs, the lithology determines the structure and distribution of the soil, which further determines the cover of woody and herbaceous plants in the aboveground vegetation. Although the amount of soil in the limestone area may be less than that in the dolomite area, the developed crevice structure is more suitable for the growth of trees with deep roots, and the vegetation activity is strong. At present, the treatment of rocky desertification in karst regions needs to fully consider the rock-soilvegetation- air interactions in karst CZs and propose vegetation restoration measures suitable for different lithologies.

In drylands worldwide, biological soil crusts (BSC) form a thin photosynthetic cover across landscapes, and provide vital benefits in terms of stabilizing soil and fixing nitrogen (N) and carbon (C). Numerous studies have examined the effects of climate and disturbance on BSC functions; however, few have characterized these responses in rolling BSCs typical of northern ecosystems in the Intermountain West, US. With temperature increases and shifts in precipitation projected, it is unclear how BSCs in this region will respond to climate change, and how the response could affect their capacity to perform key ecosystem functions, such as providing ‘new’ N through biological N₂ fixation. To address this important knowledge gap, we examined nitrogenase activity (NA) associated with rolling BSCs along a climatic gradient in southwestern Idaho, US, and quantified how acetylene reduction rates changed as a function of climate, grazing (using exclosures), and shrub-canopy association. Results show that warmer, drier climates at lower elevations hosted greater cover of late successional BSC communities (e.g., mosses and lichens), and higher NA compared with colder, wetter climates at higher elevations. Highest NA (0.5–29.3 lmol C₂H₄ m⁻² h⁻¹) occurred during the early summer/spring, when water was more available than in late summer/autumn. Activity was strongly associated with soil characteristics including pH and ammonium concentrations suggesting these characteristics as potentially strong controls on NA in BSCs. The relationship between grazing and NA varied with elevation. Specifically, lower elevation sites had lower NA at grazed locations, whereas higher elevation sites had higher NA with grazing. At both low and high ends of the elevation gradient, shrub-canopy associated BSCs maintained two to three times higher NA compared to BSCs in the interspace among shrubs. Taken together, our findings indicate that the controls and rates of NA in BSCs vary seasonally and strongly with climate in the Intermountain West, and that drier springs are likely to influence rates of NA more than warmer summers.

In dryland soils, spatiotemporal variation in surface soils (0–10 cm) plays an important role in the function of the “critical zone” that extends from canopy to groundwater. Understanding connections between soil microbes and biogeochemical cycling in surface soils requires repeated multivariate measurements of nutrients, microbial abundance, and microbial function. We examined these processes in resource islands and interspaces over a two‐month period at a Chihuahuan Desert bajada shrubland site. We collected soil in Prosopis glandulosa (honey mesquite), Larrea tridentata (creosote bush), and unvegetated (interspace) areas to measure soil nutrient concentrations, microbial biomass, and potential soil enzyme activity. We monitored the dynamics of these belowground processes as soil conditions dried and then rewetted due to rainfall. Most measured variables, including inorganic nutrients, microbial biomass, and soil enzyme activities, were greater under shrubs during both wet and dry periods, with the highest magnitudes under mesquite followed by creosote bush and then interspace. One exception was nitrate, which was highly variable and did not show resource island patterns. Temporally, rainfall pulses were associated with substantial changes in soil nutrient concentrations, though resource island patterns remained consistent during all phases of the soil moisture pulse. Microbial biomass was more consistent than nutrients, decreasing only when soils were driest. Potential enzyme activities were even more consistent and did not decline in dry periods, potentially helping to stimulate observed pulses in CO2 efflux following rain events observed at a co‐located eddy flux tower. These results indicate a critical zone with organic matter cycling patterns consistently elevated in shrub resource islands (which varied by shrub species), high decomposition potential that limits soil organic matter accumulation across the landscape, and nitrate fluxes that are decoupled from the organic matter pathways.

We present an integrated petrological, petrophysical, and hydrogeological study of the critical zone (CZ) developed in the Hercynian granitic basement of the Strengbach watershed (Vosges Massif, France) to characterize its deep architecture and water circulation levels. For this purpose, six boreholes (50–120 m depth), from which three are cored, and three piezometers (10–15 m depth) were drilled to define the vertical extension and lateral variability of the main CZ horizons. The Strengbach watershed is composed of a topsoil horizon of limited vertical extension (0.8–1.2 m), a mobile saprolite level, and an in-place fractured bedrock. The latter is subdivided into a few meters thick saprock horizon, defined by open sub-horizontal fractures and a deeper fractured bedrock horizon with steeply dipping fractures ( > 50°). In the north-facing slope, the vertical extension of the mobile saprolite horizon increases from ≈ 1–2 m at the top of the slope to ≈ 9 m downstream, close to the valley bottom. In contrast, the south-facing and more easterly slope shows a mobile saprolite horizon with limited vertical extension ( ≈ 2–3 m thick). Such a difference is associated with the existence of a knickpoint in the river bed, separating a downstream zone marked by currently active erosion from an upstream one, less prone to erosion, with preserved reliefs formed around 20 ka ago. The water circulation scheme within the Strengbach watershed involves two different systems: a subsurface circulation within the shallow aquifer, corresponding to the mobile saprolite horizon and the saprock, and a deeper circulation in the fractured bedrock. The water circulation in the fractured bedrock is controlled by fractures of regional orientations, linked to the Vosges massif and the Rhine Graben Tertiary tectonics, and partly to reactivated Hercynian fracture zones. The unaltered bedrock was not reached by any of the three cores. These results from the Strengbach CZ demonstrate the importance of integrating geological history of the watershed, either the long-term geological bedrock evolution or the Quaternary erosion patterns, to better understand and model the CZ hydrological functioning at the watershed scale.

Critical Zone Science (CZS) explores the deep evolution of landscapes from the base of the groundwater or the saprolite‐rock interface to the top of vegetation, the zone that supports all terrestrial life. Here we propose a framework for CZS to evolve further as a discipline, building on 1st generation CZOs in natural systems and 2nd generation CZOs in human‐modified systems, to incorporate human behaviour for more holistic understanding in a 3rd generation of CZOs. This concept was tested in the China‐UK CZO programme (2016–2020) that established four CZOs across China on different lithologies. Beyond conventional CZO insights into soil resources, biogeochemical cycling and hydrology across scales, surveys of farmers and local government officials led to insights into human‐environment interactions and key pressures affecting the socio‐economic livelihoods of local farmers. These learnings combined with the CZS data identified knowledge exchange (KE) opportunities to unravel diverse factors within the Land‐Water‐Food Nexus, that could directly improve local livelihoods and environmental conditions, such as reduction in fertilizer use, contributing toward Sustainable Development Goals (SDGs) and environmental policies. Through two‐way local KE, the local cultural context and socio‐economic considerations were more readily apparent alongside the environmental rationale for policy and local action to improve the sustainability of farming practices. Seeking solutions to understand and remediate CZ degradation caused by human‐decision making requires the co‐design of CZS that foregrounds human behavior and the opinions of those living in human modified CZOs. We show how a new transdisciplinary CZO approach for sustainable Earth futures can improve alignment of research with the practical needs of communities in stressed environments and their governments, supporting social‐ecological and planetary health research agendas and improving capacity to achieve SDGs. Plain Language Summary Critical Zone Science (CZS) explores how landscapes evolve from below the Earth’s surface to the top of trees, supporting life on Earth. CZS was established by studying pristine landscapes, with little or no human modification of the land, water and soil. These pristine natural systems are rare in our modern world. In this paper, we have proposed a new approach to CZS for studying the human‐modified landscapes that dominate our world. To help explain why this is needed, we have re‐drawn a diagram explaining how the critical zone works to show the role of humans. We also give examples of research in three regions of China where we learned from local farmers living in our study areas, to improve our scientific understanding and to try to align our research process to address the biggest pressures affecting their lives. This new approach to CZS can help focus research to directly support local people and improve our ability to achieve the United Nations Sustainable Development Goals. Key Points Integrating local knowledge with critical zone science can improve interpretation of scientific findings and delivery of Sustainable Development Goals Third generation science can improve alignment of research with the practical needs of communities and governments A new conceptual diagram for human‐modified critical zones is produced to illustrate transdisciplinary Critical Zone Observatories for sustainable Earth futures

The Earth’s Critical Zone (CZ) is a dynamic and essential layer extending from the canopy top to the unweathered bedrock, where interactions among the atmosphere, lithosphere, hydrosphere, and biosphere sustain ecosystems. This study focuses on mapping the critical zone thickness in northeastern India. To achieve this, the CZ was delineated into two key components: canopy height and depth to bedrock. Canopy height was estimated using the ALT08 data product of the ICESat-2 satellite using the laser altimetry principle, while depth-to-bedrock modelling incorporated environmental factors such as temperature, precipitation, humidity, canopy height, groundwater levels, rock type and soil type. An artificial neural network (ANN) was employed to predict the spatial variation of bedrock depth using publicly available soil profiles, borehole data, and remote sensing-derived environmental covariates. The estimated depth to bedrock (DTB) varies from 12.75 to 460.12 m across Northeast India. CZ thickness (CZT) was determined as the sum of canopy height and bedrock depth, ranging from 20.08 to 485.78 m with an increase northward from the Bramhaputra River and decreases southward, indicating a general trend of increase in DTB from south to north direction across the Kamrup district. The findings of this research provide an assessment of how human activities, land use changes, and climate shifts impact the CZ and the ecosystems it sustains. This knowledge can be instrumental in improving CZ management and contributing to the sustainability of ecosystems in a rapidly changing world.

Grasslands are one of the most common land‐cover types, providing important ecosystem services globally, yet few studies have examined grassland critical‐zone functioning throughout hillslopes. This study characterised a coastal grassland over a small hillslope at Point Reyes National Seashore, California, using multidisciplinary techniques, combining remotely‐sensed, geophysical, plant, and soil measurements. Clustering techniques delineated the study area into four landscape zones, up‐, mid‐, and down‐slope, and a bordering riparian ecotone, which had distinct environmental properties that varied spatially across the site, with depth, and time. Soil moisture increased with depth and down slope towards a bordering riparian zone, and co‐varied with soil CO2 flux rates both spatially and temporally. This highlighted three distinct controls of soil moisture on soil respiration: CO2 fluxes were inhibited by high moisture content in the down‐slope during the wet winter months, and converged across landscape positions in the dry summer months, while also displaying post‐rain pulses. The normalised difference vegetation index (NDVI) ranged from 0.32 (September)–0.80 (April) and correlated positively with soil moisture and aboveground biomass, moving down slope. Yet, NDVI, aboveground biomass, and soil moisture were not correlated to soil organic carbon (SOC) content (0.4%–4.5%), which was highest in the mid‐slope. The SOC content may instead be linked to shifts in dominant grassland species and their rhizosphere properties with landscape position. This multidisciplinary characterisation highlighted significant heterogeneity in grassland properties with landscape position, and demonstrated an approach that could be used to characterise other critical‐zone environments on hillslopes. Plain Language Summary Globally, grasslands are both common and important landscapes, but less studies have investigated the influence of hillslope processes on these environments and their properties. This study investigated a coastal grassland on a hillslope at Point Reyes National Seashore, California, by combining data sets from different disciplines, covering satellite, field, and laboratory measurements. The site could be grouped into four environmental zones with different properties along the hillslope. Satellite measurements revealed that plants were more active in the wetter, down‐slope throughout the dry summer months. Soil carbon content was not linked directly to soil moisture. Yet, soil carbon dioxide emissions were related to soil moisture, displaying three different behaviors depending on the moisture level. First, soil carbon dioxide emission was lower in the down‐slope during the wet months (negative relationship), but then behaved similarly at all slope locations during the summer and early fall, and increased when it rained (positive relationship). The clustering analysis showed that our site varied significantly over a small distance (<8 m elevation and 150 m distance) and time (1 yr). Beyond the investigation of this specific site, this study highlights an approach for combining data sets to study ecosystems along hillslopes. Key Points The study used a critical‐zone approach to combine multidisciplinary data sets and characterise a California coastal grassland Heterogeneity was large over a short distance (<150 m) and time (1 yr) and could be clustered by landscape position into four distinct zones Soil CO2 fluxes exhibited contrasting responses to soil moisture, which differed with slope and season at the grassland

The Critical Zone (CZ) includes the biophysical processes occurring from the top of the vegetation canopy to the weathering zone below the groundwater table. CZ services provide a measure for the goods and benefits derived from CZ processes. In intensively managed landscapes, cropland is altered through anthropogenic energy inputs to derive more productivity, as agricultural products, than would be possible under natural conditions. However, the actual costs of alterations to CZ functions within landscape profiles are unknown. Through comparisons of corn feed and corn‐based ethanol, we show that valuation of these CZ services in monetary terms provides a more concrete tool for characterizing seemingly environmental damages from agricultural production systems. Multiple models are combined to simulate the movement of nutrients throughout the soil system, enabling the measurement of agricultural anthropogenic impacts to the CZ's regulating services. Results indicate water quality and atmospheric stabilizing services, measured by soil carbon storage, carbon respiration, and nitrate leaching, among others, can cost more than double that of emissions estimated in previous studies. Energy efficiency in addition to environmental impact is assessed to demonstrate how the inclusion of CZ services is necessary in accounting for the entire life cycle of agricultural production systems. These results conclude that feed production systems are more energy efficient and less environmentally costly than corn‐based ethanol. Key Points Critical Zone services are useful in quantifying and comparing various environmental and economic factors on the same currency Corn cultivated for bioenergy is less energy efficient and results in larger adverse environmental impacts than corn grown for feed/food Soil nutrient fluxes are essential in quantifying total environmental impacts of agricultural systems

Recent theory and field observations suggest that a systematically varying weathering zone, that can be tens of meters thick, commonly develops in the bedrock underlying hillslopes. Weathering turns otherwise poorly conductive bedrock into a dynamic water storage reservoir. Infiltrating precipitation typically will pass through unsaturated weathered bedrock before reaching groundwater and running off to streams. This invisible and difficult to access unsaturated zone is virtually unexplored compared with the surface soil mantle. We have proposed the term “rock moisture” to describe the exchangeable water stored in the unsaturated zone in weathered bedrock, purposely choosing a term parallel to, but distinct from, soil moisture, because weathered bedrock is a distinctly different material that is distributed across landscapes independently of soil thickness. Here, we report a multiyear intensive campaign of quantifying rock moisture across a hillslope underlain by a thick weathered bedrock zone using repeat neutron probe measurements in a suite of boreholes. Rock moisture storage accumulates in the wet season, reaches a characteristic upper value, and rapidly passes any additional rainfall downward to groundwater. Hence, rock moisture storage mediates the initiation and magnitude of recharge and runoff. In the dry season, rock moisture storage is gradually depleted by trees for transpiration, leading to a common lower value at the end of the dry season. Up to 27% of the annual rainfall is seasonally stored as rock moisture. Significant rock moisture storage is likely common, and yet it is missing from hydrologic and land-surface models used to predict regional and global climate.