Deep Water Sources Research Articles

Macrobenthic red algae and their hydrocarbon generation in the Paleogene deep-water source rocks, Qiongdongnan Basin

To solve the contradiction between the discovery of natural gas field in the deep water area of Qiongdongnan Basin under the background of low organic matter abundance of Paleogene (Oligocene) source rocks and the current recognition of higher plants as the main source material, selects four exploration wells in the study area for the first time with the help of “mild” maceration kerogen identification technology and scanning electron microscopy observation, and finds that the source materials are mainly marine macrobenthic red algae with high abundance rather than the before thought higher plants. The marine macrobenthic red algae have the characteristics of early oil generation and late gas generation, especially in the high to over mature stage, which has a good gas prospect. It is the first time to find the source rocks with carpospores and the disk-shaped hard pads as the main source materials in China and abroad, which indicates that macrobenthic red algae are a kind of source materials that should not be ignored, which provides a possible explanation for the formation of large gas fields in the deep water area of Qiongdongnan Basin under the background of low organic matter abundance of source rocks.

Impact of Deep-Rooted Vegetation on Deep Soil Water Recharge in the Gully Region of the Loess Plateau

To investigate the impacts of vegetation change on deep soil water recharge, it is essential to identify the sources of deep soil water and deep drainage. The combination of stable and radioactive water isotopes is an effective method for studying deep vadose zones, though it has been rarely applied in complex gully areas. In this study, we measured δ2H, δ18O, and 3H in soil water under long-term natural grassland and C. korshinskii on the same slope. Both natural grassland and C. korshinskii plots received deep soil water from rainfall during the rainy season; however, the replenishment thresholds for soil water at depths of 2–10.4 m differed between the two vegetation types, corresponding to rainfall intensities of ≥20 mm and ≥50 mm, respectively. Following the conversion of natural grassland to C. korshinskii vegetation, the rate of soil water storage deficit increased by 46.4 mm yr−1, and deep drainage shifted from 39.6 mm yr−1 to 0 mm yr−1. Deep-rooted vegetation significantly depletes soil water to meet transpiration demands, thus hindering rainfall recharge. These findings have important implications for water and land resource management, especially in areas undergoing significant vegetation changes.

Influences of conifer encroachment and removal on oak woodland ecophysiology and biodiversity—a case study from northern California, U.S.A.

Oregon white oak (Quercus garryana) woodlands are threatened by conifer encroachment established during decades of fire exclusion. Widespread restoration efforts are underway to remove conifers from many oak woodlands in California, Oregon, and Washington. Using water potential, stomatal conductance, stable isotopes, and three metrics of biodiversity, we investigated the effects of Douglas‐fir (Pseudotsuga menziesii) encroachment and removal at the ecosystem scale across 3 years in a northern California woodland. We found that heavily encroached stands had the highest water potential and often the lowest stomatal conductance, compared to moderately encroached and open stands. Xylem water stable isotopes indicated that oaks and Douglas‐firs were likely not directly competing for water, as oaks appeared to use a relatively deeper water source. Under certain climatic conditions, heavily encroached oaks were more vulnerable to water stress than oaks in open or moderately encroached stands. Following low‐intensity conifer removal, thinned stands had slightly lower predawn water potential and higher gas exchange compared to unthinned stands, particularly under dry conditions. For ecosystem biodiversity, understory plant and bird diversity did not meaningfully vary with encroachment or thinning, but mammal diversity was greater in encroached stands compared to open stands. Findings from this work demonstrate that negative impacts of conifer encroachment on oaks are not due to increased competition for water, conifer removal is physiologically beneficial for shaded oaks, and that heavier thinning treatments are likely needed to yield long‐term responses and influence biodiversity.

Seasonal shifts in depth-to-water uptake by young thinned and overstocked lodgepole pine (Pinus contorta) forests under drought conditions in the Okanagan Valley, British Columbia, Canada

Abstract. As drought and prolonged water stress become more prevalent in dry regions under climate change, preserving water resources becomes a focal point for maintaining forest health. Forest regeneration after forest loss or disturbance can lead to overstocked juvenile stands with high water demands and low water-use efficiency. Forest thinning is a common practice with the goal of improving tree health, carbon storage, and water use while decreasing stand demands in arid and semi-arid regions. However, little is known about the impacts of stand density on seasonal variation in depth-to-water uptake or the magnitude of the effect of growing season drought conditions on water availability. Existing reports are highly variable by climatic region, species, and thinning intensity. In this study, stable isotope ratios of deuterium (δ2H) and oxygen (δ18O) in water collected from various soil depths and from branches of lodgepole pine (Pinus contorta) under different degrees of thinning (control: 27 000 stems per hectare; moderately thinned: 4500 stems per hectare; heavily thinned: 1100 stems per hectare) over the growing season were analyzed using the MixSIAR Bayesian mixing model to calculate the relative contributions of different water sources in the Okanagan Valley in the interior of British Columbia, Canada. We found that under drought conditions the lodgepole pine trees shifted their depth-to-water uptake through the growing season (June to October) to rely more heavily on older precipitation events that percolated through the soil profile when shallow soil water became less accessible. Decreased forest density subsequent to forest thinning did not cause a significant difference in the isotopic composition of branch water but did cause changes in the timing and relative proportion of water utilized from different depths. Thinned lodgepole pine stands were able to maintain water uptake from 35 cm below the soil profile, whereas the overstocked stands relied on a larger proportion of deep soil water and groundwater towards the end of the growing season. Our results support other findings by indicating that, although lodgepole pines are drought-tolerant and have dimorphic root systems, they do not shift back from deep water sources to shallow soil water when soil water availability increases following precipitation events at the end of the growing season.

Soil moisture and water redistribution patterns in white oak (Quercus alba) saplings and trees in fragmented urban woodlands

In the midwestern United States, models predict extended summer heatwaves and increasingly frequent and prolonged drought conditions. In the Chicago region, the potential for large-scale mortality of white oak trees (Quercus alba) coupled with the ongoing decline of white oak sapling recruitment are major concerns for researchers and practitioners. In this study, we determined the sources of water used by mature white oak trees and saplings in three qualitatively different sites within a remnant oak forest in Chicago during the 2021 drought. We investigated soil moisture dynamics (volumetric water content, VWC) and water isotope composition of leaf tissues (δD, δ18O), rainwater, and groundwater. These data were linked to sapling height (proxy for biomass) and ectomycorrhizal (ECM) functional types. We predicted that: (i) mature oak trees use deeper water sources and conducted hydraulic redistribution (HR), and (ii) mature trees shared water with saplings during dry periods via long-distance ECM functional types. Soil moisture decreased progressively from June to October (spring to fall), with August and September having the lowest moisture (<20 % VWC). Following rainfall recharge, temporal patterns of soil moisture showed gravity drainage and then ongoing stair-stepwise drawdown consistent with plant evapotranspiration. Leaf δD and δ18O values in mature trees and saplings were consistent with water uptake from rainfall and subsequent enrichment via evapotranspiration. In two sites, mature trees and saplings demonstrated distinct δD: δ18O slopes, with mature trees more enriched than saplings. In the third site, mature trees and saplings δD: δ18O slopes overlapped but here, the ECM community was dominated by contact-type ECM and sapling height increased with distance from the mature oak. Our findings indicate that HR was not a component of site ecohydrology, and future climate conditions may present increasing challenges for white oak recruitment as both mature trees and saplings compete for limited rainfall-derived soil moisture.

Distributions of nutrients, trace metals, phytoplankton composition, and elemental consumption in the Ross and Amundsen Seas

The Southern Ocean (SO) not only functions as an important carbon sink but also serves as a crucial source of intermediate and deep waters to lower latitudes. The Ross Sea and Amundsen Sea in the West Antarctic are highly productive regions of the Southern Ocean, critically vulnerable to climate change. Hence, comprehending the source-sink patterns of nutrients, particularly trace metals, in these regions is of paramount significance for understanding their ecological effect and the effect on elemental distribution in global ocean. Here, we reported the surface and vertical distributions of phytoplankton composition, Chlorophyll-a (Chl-a), particulate organic carbon (POC), macronutrients, and trace metals (TMs) in the Ross and Amundsen Seas. Deplete dissolved iron concentrations were observed in surface waters averaging 0.17 ± 0.09 nM. High POC and Chl-a were observed that corresponded to elevated Fe in shallow subsurface water (100–300 m), while low POC and Chl-a were found to associate with depleted iron (∼0.1 nM) throughout the upper water column down to 300 m. Sea-ice melting and islands were found to be possible external TMs sources in the Amundsen Sea offshore. Phytoplankton act as a sink for trace metals and regulate the elemental concentration and composition of water bodies, while also being influenced by environmental conditions such as temperature, salinity, and the mixing layer depth. Elemental consumptions in surface water were associated with diatom abundance in both Ross and Amundsen Seas. Based on elemental drawndown ratios in the surface mixed layer, the stoichiometries of the two major phytoplankton functional groups, diatoms and haptophytes, were estimated. Our observations offered insights into the relationships among iron supply, nutrients distribution patterns, and phytoplankton composition in the Southern Ocean.

Growth, earlywood anatomy and wood nutrients respond to precipitation and flow in semi-arid riparian tamarisk forests

Riparian forests from semi-arid regions with saline soils are dominated by facultative phreatophytes such as tamarisks (Tamarix spp.). Tamarisks tolerate drought and salt stress by using shallow and deep soil water sources depending on precipitation and flow variability in ephemeral or permanent streams. Therefore, their radial growth and wood anatomy would differently respond to precipitation and drought severity depending on stream ephemerality. To assess these responses, tree-ring-width, earlywood anatomy and sapwood nutrient concentrations were measured in five riparian tamarisk stands located in semi-arid north-eastern Spain. These sites experienced different aridity degrees and were located near ephemeral (e.g., Lanaja-dry site) or permanent streams in intensively irrigated agricultural areas (e.g., Valcuerna). Tree rings were widest in Peñaflor (2.94 mm) and narrowest in the driest Lanaja-dry site (1.11 mm), where tree-to-tree growth coherence was higher than in the other sites. Wet conditions during the water year enhanced growth, particularly in the most responsive Lanaja-dry site and in Lopín, whereas elevated flow increased the earlywood hydraulic diameter in Valcuerna. In the Lanaja-dry site, Ca, Cu, K and Mn wood concentrations were higher than in Valcuerna, but C and N concentrations were lower. Elevated Ca wood concentrations correspond to higher drought stress in the Lanaja-dry site, whereas higher N concentrations reflect eutrophication due to extensive use of agricultural fertilizers in Valcuerna. In sites near permanent streams such as Valcuerna, depth to groundwater may be a more robust proxy of growth than in drier sites located near more ephemeral streams such as Lanaja-dry site where tamarisk growth is constrained by 12-month long spring droughts.

Influence of HEM Drilling Fluid on Organic Geochemical Characteristics of Deep-Water Source Rocks in the Qiongdongnan Basin.

The influence of oil-based drilling fluid on the geochemical characteristics of source rocks has been widely reported in the northern South China Sea. However, contamination from water-based HEM drilling fluid has long been neglected in previous deep-water petroleum exploration. To further understand the impacts of HEM drilling fluid on deep-water source rocks, the organic matter abundance and type, kerogen maceral composition, and saturated biomarkers of the deep-water source rocks in the Qiongdongnan Basin were investigated. The influence of HEM drilling fluid on the organic geochemistry data of cuttings is significant but minor for sidecores. It is evident that the organic drilling additives in HEM drilling fluid can increase the organic matter abundance and optimize the organic matter types of shale cuttings. Specifically, the total organic carbon, S1, S2, and hydrogen index are increased by 28.5 ± 6.1, 90.8 ± 2.0, 34.2 ± 2.0, and 51.9 ± 4.0%, respectively. Furthermore, the organic drilling additives will greatly enhance the levels of C29 regular steranes, especially for C29-ααα-20R sterane, with the influence still persisting even when conducting GC-MS-MS analysis. The highly abundant 17α (H) -22, 29, 30-trisnorhopane, 17β (H)-22, 29, 30-trisnorhopane, C29-3117α (H), 21β (H) hopanes, and C29-31 17β (H), 21α (H) hopanes may directly originate from the organic drilling additives. It is dangerous to directly use organic geochemical data from deep-water source rock cuttings contaminated by HEM drilling fluid as it may lead to conclusions that are entirely inconsistent with the basin's geological background.

Save or spend? Diverging water‐use strategies of grasses and encroaching clonal shrubs

Abstract Shrub encroachment is one of the primary threats to mesic grasslands around the world. This dramatic shift in plant cover has the potential to alter ecosystem‐scale water budgets and responses to novel rainfall regimes. Understanding divergent water‐use strategies among encroaching shrubs and the grasses they replace is critical for predicting shifts in ecosystem‐scale water dynamics as a result of shrub encroachment, particularly if drought events become more frequent and/or severe in the future. In this study, we assessed how water‐use traits of a rapidly encroaching clonal shrub (Cornus drummondii) and a dominant C4 grass (Andropogon gerardii) impact responses to changes in water availability in tallgrass prairie. We assessed intra‐annual change in depth of water uptake, turgor loss point and stomatal regulation in each species. Sampling took place at Konza Prairie Biological Station (northeastern KS, USA) during the 2021 and 2022 growing seasons. Cornus drummondii shifted from shallow to deep soil water sources across the 2021 and 2022 growing seasons. This plasticity in depth of water uptake facilitated a ‘wasteful’ water‐use strategy in C. drummondii, where stomatal conductance and transpiration rates continued to increase even when no further gain in photosynthetic rate occurred. A. gerardii photosynthetic rates and stomatal conductance were more variable through time and were more responsive to changes in leaf water potential than C. drummondii. However, intra‐annual adjustment of turgor loss point was more pronounced in C. drummondii (ΔπTLP = −0.48 MPa ± 0.15 SD) than in A. gerardii (ΔπTLP = −0.29 MPa ± 0.19 SD). Synthesis. These results suggest that C. drummondii is highly resilient to changes in water availability in surface soils and will likely remain unaffected by future droughts unless they are severe enough to reduce the availability of deep soil water. Given that clonal shrubs are key invaders of grasslands world‐wide, increased leaf‐level water loss is expected to accelerate ecosystem‐level drying as clonal shrub encroachment proceeds in mesic grasslands.

Larger water use efficiency associated with greater dependence on deep water sources in hot-dry valleys with reservoirs

Identifying the carbon–water relationship of plants helps to understand their adaptive water use strategies. The relationship between WUE and the water source remains uncertain in the hot-dry valleys with reservoirs. The leaf δ13C and soil and xylem water isotopes (δ2H and δ18O) were determined to identify the WUE and water source contributions, respectively, in Leucaena leucocephala (Lam.) de Wit communities. We propose a source contributing score (SCS), calculated as a value for the contribution of water from different soil layers (a higher SCS value indicates plants use deeper water sources). The positive relationship between leaf δ13C and SCS (R2 = 0.16, P = 0.022) and the negative relationship between leaf δ13C and topsoil contribution (R2 = 0.21, P = 0.009) confirmed the close association of larger WUE with less reliance on shallow soil water. The redundancy analysis suggested a stronger connection between leaf δ13C and d-excess than leaf δ13C and topsoil moisture content, which emphasized the key role of soil moisture d-excess. Variation partitioning analysis (VPA) suggested soil properties and microclimate explain more than 89.8 % of the variations in tree water use. VPA also suggested different roles of microclimate and soil properties in explaining tree water use strategies. Findings broadened the understanding of the relationship between WUE and water sources and emphasized the key role of soil moisture d-excess in hot-dry valleys with reservoirs.

The waveguide invariant close to the deep-water bottom

Waveguide invariant, denoted by β, describes the dispersive nature of the underwater acoustic waveguide. In most range-independent shallow-water waveguides β≈1, whereas β is no longer constant in deep water and is more appropriately described by a distribution. This paper investigates the characteristic of β close to the deep-water bottom. The adiabatic normal mode theory is used to analyze β resulting from the bottom-bounce dominated acoustic field qualitatively. Then, the Wentzel–Kramers–Brillouin approximation with bottom reflection phase shift and the dominance of the acoustic field by groups of modes are employed to amend the original waveguide invariant theory. The interference between the phase-compensated dominant modal groups is calculated to obtain the value of β and analyze the distribution in the two-dimensional spectrum of the interference pattern. For a typical deep-water waveguide, both qualitative and quantitative analyses indicate that β≈1 when close to the bottom instead of a distribution. Simulation and experiment data demonstrate that the interference between phase-compensated dominant modal groups produces particular structure in the two-dimensional spectrum resulting from β being approximately equal to 1. The characteristic of β proposed in this paper has potential application in remote ranging the underwater acoustic source in deep water, which is verified using experimental data.

Shallow and deep geothermal water sources identification in Unai geothermal field, Gujarat, India with applications of Magnetotelluric (MT)

The aim of this study is to conduct and examine the results of a Magnetotelluric (MT) survey in Unai, Gujarat, India for geothermal prospect identification. At Unai, the data was acquired, processed, and interpreted in the form of 2D and 3D MT surveys. Data were acquired at 56 stations in uniformly spaced profiles along the ENE-WSE direction (geological strike direction) with a station spacing of 2 km. Qualitative and quantitative data understanding has been done for geothermal prospect identification. Deep and shallow 1D and 2D models of electrical resistivity were made, which suggests the presence of a geothermal aquifer. This is corroborated by polar and skew tipper diagrams. The one-dimensional Occam models and two-dimensional conjugate gradient models confirm the presence of a low resistivity anomaly near the surface ranging from the depth of 100–700 m. This suggests the presence of a shallow geothermal zone. Apart from the shallow geothermal prospect, this study also delineates a deep conductive body which may be attributed to a matured geothermal reservoir. For a better understanding of the prospect geoelectrical cross sections are analysed from a depth of 10 m to 15 km. The MT cross-sections show the presence of geological features such as a series of faults. These faults form horst and graben in nature and may act as a good trap for the shallow reservoirs.

Groundwater Circulation in the Shallow Crystalline Aquifer of Tharisa Mine, South Africa: Evidence from Environmental Isotopes and Near-Surface Geophysics

For underground mining, efficient groundwater management is one of the critical mining economics components. The region of interest, known as Tharisa Mine, is situated on the western limb of the Bushveld Igneous Complex, which is home to South Africa’s premier platinum-group metal resources. This work aimed to provide the findings from the investigation and imaging of the near-subsurface hydrogeological architecture in a shallow profile using stable isotopes of water (18O and 2H) and radioactive water isotopes (3H). Regarding isotope data, 18O varied from −3.5 to 1.5‰; 2H from −24 to 4.7‰; and 3H from 2.0 to 3.4 T.U. Utilizing combined geophysical techniques, the results were verified. Additionally, the geophysical methods, including seismic refraction tomography, multichannel analysis of surface waves, electrical resistivity tomography, and magnetics, helped identify the fluid’s pathways and lineaments during migration to verify the isotope results. The groundwater inflow volumes into the open pit were initially determined by integrating the following findings: the delineation of fracture systems/zones and fluid migration pathways; mining activities enhance the storage and transmission ability of the aquifer; and the main sources of water in the mine include mixing of surface and deep water sources, recycling of water possibly via lineaments, and tailings dam seepages.

Wave-driven sediment transport potential on a tropical coast: Implications for the northeastern Australian sediment budget

Coastal dynamics are governed by the interface of complex, multidimensional processes that result from the interaction between offshore wave climate and local geomorphology. Nearshore waves are usually the primary driver of sediment transport in the coastal zone. However, nearshore wave processes in sub-tropical to tropical regions are often poorly understood, since deep-water waves are often substantially transformed, via interaction with coral reefs, as they propagate towards the nearshore zone. Here, we produce a suite of nearshore wave conditions using a discrete set of representative deep-water wave parameters to determine the potential for large-scale, wave-driven longshore sediment transport along the sub-tropical to coral reef mediated tropical northeastern coast of Australia (15-28oS). Representative conditions at deep-water source points, determined using a Maximum Dissimilarity Algorithm (MDA), were used as boundary conditions for a coastal wave model. Potential longshore sediment transport is largely dependent on offshore wave direction and the presence (or lack thereof) of the Great Barrier Reef (GBR). There is a decrease in mean, wave-driven transport potential from >500,000 m3/year in southern Queensland to <50,000 m3/year north of Fraser Island and along the section of the coast regulated by wave transformation through the GBR. Seasonal changes in the deep-water wave regime control patterns of sediment transport along the entire coast, even in the low wave energy regions. We also show that there are complex sediment transport pathways on this tropical coast with large variability in both direction (up-coast vs. down-coast transport) and magnitude in the nearshore. Our results provide insights into the potential volumes, pathways, and complexity of sediment transport on tropical and sub-tropical coasts and a methodological approach that can be applied globally to efficiently construct wave-driven sediment flux estimates on tropical coastlines where coral reefs influence nearshore wave processes.

Seasonal water source patterns in a northern Arizona pine forest

The relationships among stand density and seasonal plant water source patterns in ponderosa pine (Pinus ponderosa) forests are important for informed management decisions in a bimodal climate with increasing variability in winter and monsoon precipitation inputs. Winter precipitation recharges soil moisture, yet it has declined over the past 20 years in the southwestern United States, and monsoon precipitation is becoming more variable in both magnitude and timing. Near Flagstaff, Arizona in August 2013 (monsoon), October 2013 (post-monsoon), and May 2014 (post winter snow melt), we measured soil moisture, soil water δD at five depths, and xylem water δD in Muhlenbergia montana (a perennial C4 grass), Festuca arizonica (a perennial C3 grass), and P. ponderosa seedlings (&amp;lt; 2 years old), saplings (2–5 cm basal diameter), and mature trees (&amp;gt; 60 cm diameter at breast height) in treated (thinned and burned) and untreated (no thinning, no burning) stands. We found that soil moisture was higher at all soil depths in treated stands in May, after snow melt, and this pattern persisted through August in the deepest soil (60 cm). We also found that, in all sampling months, δD in xylem water of grasses and pine seedlings indicated use of shallower soil water than for pine saplings and mature trees, presumably due to differences in rooting depths. Additionally, in August, δD in xylem water of pine saplings and mature trees indicated greater reliance on a deeper water source in untreated stands than in treated stands, likely due to greater competition for shallow water in untreated stands. Our isotopic data indicate that grasses and seedlings used predominantly monsoon water in August and October, while pine saplings and mature trees used predominantly winter water during all sampling months. Importantly, our data indicate that regenerating trees (seedlings and saplings) used both winter and monsoon seasonal water sources, suggesting an increasingly important role for monsoon precipitation if winter precipitation inputs continue to decline. Collectively, these findings demonstrate that management actions can benefit forests via increased soil moisture, that overstory trees rely predominantly on winter precipitation, and that monsoon precipitation is important for herbaceous species and younger, regenerating overstory trees.

Deep-water circulation in the northeast Atlantic during the mid- and Late Cretaceous

Abstract The Cretaceous ocean was significantly different from its modern counterpart due to its ice-free condition. Deep waters were primarily sourced by evaporation at the ocean surface, although their circulation pattern and bottom-current dynamics have been largely unknown. Here we present a study of deeply buried contourite drifts in the southern proto–Bay of Biscay to unravel the circulation pattern of the mid- and Late Cretaceous deep waters across the northeast Atlantic. The generation of plastered drifts (120 Ma to 100–90 Ma) and a mounded drift (100–90 Ma to 65 Ma) suggests that a significant change in deep-water source regions from the Tethys to the high-latitude region occurred at ca. 100–90 Ma. These contourite drifts were buried after ca. 65 Ma when the Cretaceous ocean circulation transitioned to the Cenozoic style in the northeast Atlantic. Tectonic configurations of the Pyrenean and the Equatorial Atlantic gateways were moreover tied to significant changes in northeast Atlantic deep-water circulation at ca. 100–90 and ca. 65 Ma. Northeastern Spain and France might be potential sites for the detection of Late Cretaceous contourite outcrops. These outcrops could have fundamental implications for the sedimentary facies and sequence model of contourites as well as shed light on the paleoceanography and paleoclimate of Cretaceous Earth.

Structure and Seasonal Variability of Groundwater Microbial Communities in the City of Moscow

Abstract—Groundwater, which appears on the surface in the form of springs, is an important ecologically significant component of the aquatic ecosystem, sensitive to changes in environmental conditions. The anthropogenic impact associated with urbanization leads to a change in the characteristics of groundwater, which in turn affects the composition of microbial communities in spring waters. Using high-throughput sequencing of the 16S ribosomal RNA gene fragments, we characterized the composition of microbial communities in five natural springs in the city of Moscow in the spring, summer, and winter seasons. The microbial communities of each spring in different seasons were similar to each other and clearly differed from the microbiomes of other springs. Among the Archaea, which averaged about 20% of microbial communities, ammonium-oxidizing Crenarchaeota predominated, as well as Nanoarchaeota. Most of the Bacteria belonged to the phyla Proteobacteria, Patescibacteria, Verrucomicrobiota, Chloroflexi, and Bacteroidota. Autotrophic bacteria, including iron-oxidizing bacteria of the family Gallionellaceae and nitrifiers, as well as methanotrophs, accounted for significant proportions in microbial communities in the springs with a presumably deeper water source. Chemical and molecular analyzes did not reveal contamination of spring waters with toxic substances and oil-derived products, as well as the presence of pathogenic microorganisms and indicators of fecal pollution. However, during the spring season, the proportions of halophilic and hydrocarbon-oxidizing bacteria increased in water microbiomes, which may reflect entry into groundwater after snow thawing of deicin reagents and hydrocarbons, which are successfully biodegraded in the soil.

Study on the Performance of a Newly Designed Cooling System Utilizing Dam Water for Internet Data Centers

A novel energy-saving hybrid cooling system that combines a forced-cooling cycle and a free-cooling cycle was developed to increase the energy efficiency of cooling systems in year-round operation of an internet data center with high heat loads. This system effectively utilizes a dam deep water source to reduce energy consumption in internet data centers. The hybrid cooling system operates in forced-cooling mode when the entering water temperature exceeds the mode change temperature of 9 °C, but switches to free-cooling mode when the ambient temperature falls below the mode change temperature. In this paper, the cooling performance of the hybrid system was assessed under various operating conditions based on entering water temperature fluctuation. Because the cooling effectiveness of this type of system is highly dependent on the outside climate, its usefulness and suitability for different periods and zones must be investigated. The annual energy saving performance of the new system was estimated and compared to a conventional cooling system in terms of the integrated coefficient of performance, based on the hourly weather air temperature and water temperature bin data collected from 16 cities of different climate zones in South Korea. The experimental findings revealed that the novel hybrid internet data center cooling system showed a 67% annual operating performance over a conventional air source internet data center cooling system due to the adoption of a dam deep water source.

Nutrient composition (Si:N) as driver of plankton communities during artificial upwelling

Artificial upwelling brings nutrient-rich deep water to the sun-lit surface to boost fisheries or carbon sequestration. Deep water sources under consideration range widely in inorganic silicon (Si) relative to nitrogen (N). Yet, little is known about how such differences in nutrient composition may influence the effectiveness of the fertilization. Si is essential primarily for diatoms that may increase food web and export efficiency via their large size and ballasting mineral shells, respectively. With a month-long mesocosm study in the subtropical North Atlantic, we tested the biological response to artificial upwelling with varying Si:N ratios (0.07-1.33). Community biomass increased 10-fold across all mesocosms, indicating that basic bloom dynamics were upheld despite the wide range in nutrient composition. Key properties of these blooms, however, were influenced by Si. Photosynthetic capacity and nutrient-use efficiency doubled from Si-poor to Si-rich upwelling, leading to C:N ratios as high as 17, well beyond Redfield. Si-rich upwelling also resulted in 6-fold higher diatom abundance and mineralized Si and a corresponding shift from smaller towards larger phytoplankton. The pronounced change in both plankton quantity (biomass) and quality (C:N ratio, size and mineral ballast) for trophic transfer and export underlines the pivotal role of Si in shaping the response of oligotrophic regions to upwelled nutrients. Our findings indicate a benefit of active Si management during artificial upwelling with the potential to optimize fisheries production and CO2 removal.

Variation in Water Uptake Dynamics of Dominant Wood Plants of Pinus taiwanensis Hayata Communities Based on Stable Isotopes

Plant community formation is determined by plant competition, while the water uptake depth of vegetation is regarded as a critical factor in maintaining species coexistence under competition. However, the source variation of montane plant water uptake remains poorly understood, especially under the condition of climate change. We introduced stable hydrogen and oxygen isotopes to investigate the water uptake pattern of the trees and shrubs in a Pinus taiwanensis Hayata community in subtropical mountains. The results showed that the main sources of water uptake in plants varied with soil water content, due to variations in annual precipitation distribution. In July and September, under extremely wet conditions, the evergreen conifer species P. taiwanensis and the shrub Eurya muricata mainly absorbed water from the deep soil layer (40–80 cm, more than 70%). By contrast, the deciduous shrub Rhododendron dilatatum largely relied on upper soil water (0–40 cm, 75.4%) in July but the same deep water source in September. In August and the non-growing season (January), when soil moisture content was low, plants preferred surface layer soil water (0–20 cm, above 50%). In October, the soil water in the middle (20–40 cm) and deep layers (40–80 cm) were the main water source of the three plants. However, the plant water sources showed great difference between P. taiwanensis and shrubs in November: P. taiwanensis absorbed more water from the soil surface layers (89.5%), while R. dilatatum mainly took up surface soil water (54.2%) and E. muricata predominantly obtained water from surface soil water (49.6%) and the deep soil layer (39.3%). These findings suggest that the water uptake of dominant woody plants in a P. taiwanensis community has great plasticity, and its water uptake depth varies with soil water content. In addition, these co-existing species generally absorbed water from similar soil layers in the P. taiwanensis community and exhibited a hydrological niche overlap, indicating a very possible competition between species in future water-limited conditions caused by climate change.