Earth-Science Reviews最新文献

Solute transport in partially-saturated porous media plays a key role in multiple applications across scales, from the migration of nutrients and contaminants in soils to geological energy storage and recovery. Our understanding of transport in unsaturated porous media remains limited compared to the well-studied saturated case. The focus of this review is the non-reactive transport driven by the displacement of immiscible fluids, where the fluid-fluid interface acts as a barrier that limits the solute to a single fluid phase. State-of-the-art pore-scale models are described, with a critical analysis of the gaps and challenges. A numerical example is provided to demonstrate the acute sensitivity of solute transport prediction to minute, inevitable uncertainties in the spatial distribution of the fluids' velocities and interface configuration associated with the multiphase flow modeling.

Groundwater dynamics in the coastal unconfined aquifer is one of the most important physical factors in the coastal zone since it greatly influences the nearshore hydrodynamics and beach morphodynamics, as well as interactions between oceanic and inland water systems. A solid understanding of the groundwater behavior in the coastal area is necessary for maintaining efficient coastal water management and supporting sustainable social-ecological development. Coastal unconfined aquifers are complicated while active systems in response to multiple oceanic forces such as tides and waves in various spatiotemporal scales, which have been evaluated and investigated over the last few decades. The present paper provides a comprehensive review of current understandings and advances in groundwater dynamics in coastal unconfined aquifers with respect to water table fluctuations and groundwater flow patterns, with a particular focus on wave-induced groundwater hydrodynamics. Existing analytical approaches for predicting the groundwater response to oceanic forces are summarized and evaluated to reveal their pros and cons. Although great advances have been achieved, some knowledge gaps still remain. While the influences of tide forces on coastal groundwater dynamics are generally well understood and tide-induced groundwater dynamics could be appropriately reproduced by various existing analytical or numerical models, groundwater dynamics in response to wave forces are relatively poorly understood. Accordingly, research needs with respect to groundwater dynamics are discussed and identified in this review. Many studies evaluate the wave-induced groundwater hydrodynamics based on experimental or field observations, while sophisticated theoretical approaches are still lacking to quantify the influence of various complex physical factors during wave swash events, such as capillary truncations, seepage face dynamics, and wetting front evolutions. Such knowledge gaps need to be filled in order to further advance our understanding of the coastal groundwater dynamics and, furthermore, to conduct effective and sustainable coastal water management and protection.

Major sea-level cycles occurred in the Cenomanian-early Turonian greenhouse world and impacted depositional conditions and ecosystems across the paleo-shelf seas. These sea-level cycles have been interpreted from various paleogeographic settings around the globe, such as the Western Interior Seaway (North America), the Proto-North Atlantic, Western Europe, and eastern Tethys (SE India). However, their drivers remain poorly understood and may include glacio-, aquifer-, thermo-, and/or tectono-eustasy. Uncertainties also persist regarding the timing, synchronicity, and magnitude of Cenomanian-early Turonian eustatic cycles. By combining palynological data from northern Africa (Gindi Basin, Egypt) with data available in the literature, a detailed synthesis of Cenomanian palynostratigraphy and sea-level dynamics is presented. Age-diagnostic spores, pollen, and organic walled dinoflagellate cysts (dinocysts) are correlated to global marine biozonation schemes, which provide a comprehensive biostratigraphic framework for the Cenomanian-early Turonian. Additionally, palynological data enable the identification of an early late Cenomanian Dinopterygium bio-event marked by the highest abundances of dinocysts. This bio-event can be correlated to the Neolobites ammonite bio-event and the Jukes-Browne Carbon Isotope Event. The bio-events stratigraphically constrain with a major transgression, which occurred in the early late Cenomanian, slightly preceding Oceanic Anoxic Event 2 (OAE2). Another major transgression spans the late Cenomanian-early Turonian, referred to the Plenus transgression bio-event, and consistent with the onset of the OAE2. Regional to global correlations indicate that these transgressive events reflect eustatic sea-level rises that can be recognized throughout the Tethys, Proto-North Atlantic, Europe, Western Interior Seaway, and India. These transgressions occurred within <1.0 Myr with modest magnitudes of 10–60 m. Rates of sea-level change has commonly been attributed to glacio-eustasy, which is however difficult to reconcile with a probably ice-free Cenomanian-early Turonian greenhouse world. Both transgressions coincide with phases of rising temperatures, whereby warming was most pronounced during the early late Cenomanian transgression. However, we can only speculate whether rising temperatures indicate the demise of polar glaciations. Eustatic processes, including tectono-eustasy, and to some extent aquifer- and thermo-eustasy, likely played a role in the sea-level rise during the early late Cenomanian and early Turonian. Environmental changes associated with the early late Cenomanian transgression may have triggered the onset of OAE2 possibly exacerbated by sluggish ocean circulation in a warming greenhouse world where sea ice formation was limited.

Peatlands are potent landscape sinks of natural and industrial toxic metals and metalloids (TMMs) but the long-term sequestration of TMMs in peatlands is at increasing risk due to climate change enhanced peatland fires. The ability of peatlands to retain TMMs results from a host of interacting hydrological, biological, geomorphological, and chemical feedbacks, which underpin peatland functionality in general. Fire is a transformative force that often disrupts these interactions and feedbacks, leading to the potential release of TMMs to our air, land, and water. Given that wildfire burned area and severity are increasing there is a need for a conceptual understanding of these interactive processes. Prior to a fire, peatland TMM mobility is relatively low, controlled by a peatland's degree of minerotrophy, degradation status, hydrogeomorphic setting and hydroclimate. Incidentally, these peatland characteristics also control the likelihood of peat ignition, creating important feedbacks on the landscape. Following ignition, the temperature and duration of a peat fire plays a critical role in determining the potential TMM emissions to the atmosphere and the post-fire geochemical conditions. We elucidate the varied emission factors of different metals, where emission factors range from 0.2 (Co or Cd) to 300 (Al) mg of metal per kg of particulate matter emitted depending on the specific metal and likely the pre-fire peat metal concentration. Following a peat fire, the geochemical and hydrological changes become increasingly important. For example, post-fire increases in pH play the strongest chemical role in limiting TMM mobilization but concurrent increases in dissolved organic matter aromaticity complicate our understanding of these processes, leading to a critical knowledge gap. At larger spatial scales, peatland and watershed ecohydrological connectivity and peat erosion modulate the release of TMMs to aquatic systems. Yet, the evolution of the ecohydrological connectivity and peat erosion potential as the peatland vegetation and hydrology recover to pre-fire conditions over the course of several to tens of years is governed by the same controls that impact pre-fire TMM mobility. Critically, the uncertainty in evolution trajectories depends on changes in biological, hydrological, climatological, and chemical conditions, limiting our ability to accurately predict these changes under a rapidly changing climate. This extensive and interdisciplinary review guides the development of a conceptual framework and highlights future research needs to better respond to the emerging threat of legacy TMM release from peatland wildfires.

Microplastics (MPs), particles with a size <5 mm, are ubiquitous in water, soil, and atmosphere, and have become a highly discussed environmental issue. Although atmospheric MPs have received less attention than MPs in soil and water, their possible environmental consequences are being examined in more depth. This study systematically reviews the sources, transport, distribution, and variations of atmospheric MPs, their interactions with other pollutants in the environment and impact on human health based on the literature. The results show that MPs have been identified in diverse atmospheric settings such as urban, sub-urban, and remote areas as well as in indoor air. These airborne MPs can originate from terrestrial sources like landfills, synthetic clothing, and plastic manufacturing, use and recycling activities, as well as from aquatic sources like MPs resulting from bubble bursting. The outdoor MP abundance was detected in a range of 2 to 1159 MP/m²/day in depositions and 0 to 224 MP/m³ in suspended samples, while significantly higher abundance was observed indoors with depositions ranging from 22 to 760,000 MP/m²/day and suspended from 0.4 to 1583 MP/m³. The distribution characteristics of atmospheric MPs are affected by several factors such as urbanization, anthropogenic activities, indoor and outdoor environments and seasons. Atmospheric transport of MPs occurs through suspension, horizontal transport and deposition processes that are greatly influenced by the morphology of the MP, wind speed and direction, precipitation and other atmospheric factors. The transport path of MPs in the atmosphere is studied by Lagrangian atmospheric models by conducting backward trajectory simulations to estimate linear trajectories of MPs at sampling locations to discern their potential origin and travel distance. MPs can also interact with a variety of chemical pollutants and microorganisms in the environment and thus act as a vector for pollutant transport. The toxicity of MPs may be increased by the release of pathogens and chemical contaminants into the environment, thereby increasing the health risk to humans. Based on the study, it is suggested that further scientific research on atmospheric MPs should focus on the standardization of research methods, atmospheric transport mechanisms, interactions of MPs with atmospheric pollutants and ecological impacts. As MPs could enter the human body through various mechanisms, it is urgent to study their physiological effects on the human body when exposed to atmospheric MP pollution.