Precipitation Type Research Articles

Catalytic transfer hydrogenation of furfural to furfuryl alcohol over Al-containing ferrihydrite

Al-containing ferrihydrite (Fh-Al) was prepared by co-precipitation method using ferric nitrate nonahydrate and aluminum nitrate nonahydrate as precursors. The prepared Fh-Al was systematicallycharacterized and then employed for the catalytic transfer hydrogenation (CTH) of furfural (FUR) to furfuryl alcohol (FOL). The influence of precipitant type, hydrogen donor, the molar ratio of Fe to Al, catalyst amount, reaction time and reaction temperature were investigated. It was found that Fh-Al with 1:2 molar ratio of Fe to Al was amorphous with acidic and basic sites, and the largest specific surface area of 303 m2/g was obtained using NaOH and Na2CO3 as the co-precipitator. Fh-Al with 1:2 molar ratio of Fe to Al possessed excellent catalytic performance and stability. The conversion of FUR, the yield and the selectivity of FOL reached 100 % at 150 °C for 5 h using isopropanol as the hydrogen donor. Moreover, only slight decrease in the catalytic performance was observed during the recycle. After 4 cycles, the conversion of FUR, the selectivity and the yield of FOL still reached 99.1 %, 99.7 % and 98.8 %, respectively. A plausible reaction mechanism for the CTH of FUR to FOL was also proposed, in which both acidic and basic sites play roles.

Exploration and Optimisation of High-Salt Wastewater Defluorination Process

The typical lime precipitation method is used to treat high-concentration fluorine-containing wastewater. In this way, the fluorine in the wastewater can be removed in the form of CaF2. Thus, this method has a good fluoride removal effect. In this study, calcium hydroxide was used to adjust the pH and achieve a significant fluoride removal effect at the same time. The removal rate of fluoride ion decreases gradually with the increase in the concentration of sulphate in the raw water. When the synergistic defluorination cannot meet the requirements of water production, adding a step of aluminium salt flocculation and precipitation can further reduce the fluoride ion concentration. According to the feasibility of the actual project, this study improves the lime coagulation precipitation defluorination process on this basis, and the combined process is synchronised. In the process optimisation, barium chloride is added to remove the influence of sulphate radicals in the water, and then, the pH is adjusted to 5–6. The fluoride ion concentration in high-salt wastewater can be reduced from 446.6 mg/L to 35.4 mg/L by defluorination after pre-treatment whose removal rate was 92.1%. The combined process synchronously removes fluorine and purifies the water quality to a certain extent. Indicators such as COD, total phosphorus, ammonia nitrogen, and chloride ions in wastewater are reduced, and the removal rate is increased by 35.5% under the same conditions. This scheme improves the wastewater treatment effect without increasing the existing treatment equipment. Thus, it achieves a better defluorination effect and reduces the dosage of chemicals as much as possible, which is conducive to lowering the discharge of sludge after treatment.

Localized urban canopy model and improved anthropogenic heat parameters in the weather research and forecasting model: Simulation of a warm-sector heavy rainfall event over the pearl river delta urban agglomeration

Warm-sector heavy rainfall in South China is a frequent type of precipitation in summer in the Pearl River Delta region. The complexity of the mechanisms involved in the triggering of convection, especially the effects of urbanization, has greatly increased the uncertainty of numerical simulations of warm-sector heavy rainfall. In this study, five new surface parameters with five new anthropogenic heat (AH) parameters were constructed and coupled with the urban canopy model (UCM) of the Weather Research and Forecasting model, version 4.1, based on the local climate zone system over the Pearl River Delta Urban Agglomeration (PRDUA). Taking a typical warm-sector heavy rainfall process that occurred in the PRDUA on 20 April 2019 as an example, five groups of experiments involving different schemes were compared and analyzed, revealing that the precipitation simulated using the localized UCM with the new AH parameters was the best (closest to observations). The localized UCM successfully simulated the increase in 2 m temperature and sensible heat flux and the resultant thermal forcing in urban areas, which promoted the convergence of low-level southerly winds with water vapor and the lifting of the lower-layer warm and humid water vapor to the upper layers in the urban center, leading to a significant increase of precipitation. The improved AH parameters enhanced the anthropogenic heat and its vertical conduction in urban areas, but contributed only marginally to the convergence of 10 m winds. Compared with observations from wind profile radar, it was found that the localized UCM enhanced the accuracy of the simulated horizontal wind field convergence at upper and lower levels, while the improved AH parameters enhanced the accuracy of the simulated low-level jet intensity and vertical movement, which are important drivers for the spatial variation in warm-sector heavy rainfall over the PRDUA. The current findings will be helpful for improving the model skill in simulating warm-sector heavy rainfall over high-density urban areas, as well as enhancing understanding of the impact mechanism of urbanization on the occurrence and development of warm-sector heavy rainfall.

Sulfonic acid-functionalized covalent organic frameworks as the coating for stir bar sorptive extraction of fluoroquinolones in milk samples.

Sulfonic acid-functionalized covalent organic frameworks (COF-SO3) as a coating of stir bar sorptive extraction (SBSE) for capturing three fluoroquinolones from milk have been developed. The COF-SO3 material was characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and infrared spectroscopy. Milk without any typical treatments like protein precipitation and defatting was only diluted five times with water for test. Combined with high-performance liquid chromatography (HPLC), a SBSE-HPLC method was established for detecting fluoroquinolones in milk samples. The corresponding wide linear ranges (4.00-500.0µg L-1), low detection limits (1.20-2.62µg L-1), good test repeatability (RSD < 5.2%), and acceptable enrichment factors (56.2-61.5) were implemented for three fluoroquinolones. The analytical method was applied to determine trace targets and provided satisfactory results. Furthermore, the research displayed satisfied reproducibility for bar-to-bar (RSD < 6.5%) and batch-to-batch (RSD < 8.6%) tests.

Ecological determinants and risk areas of Striga hermonthica infestation in western Kenya under changing climate

AbstractStriga hermonthica (Del.) Benth is a parasitic weed that is damaging major cereal crops in sub‐Saharan Africa (SSA). Although Striga is recognised as an agricultural scourge, there is limited information available indicating the extent of its growth and spread as impacted by the changing climate in Kenya. This study investigated the impact of current climate conditions and projected future (2050) climate change on the infestation of Striga hermonthica in the western Kenya region. Specifically, the study aimed to predict Striga hermonthica habitat suitability in five counties in the western Kenya region through using the maximum entropy (MaxEnt) model and bioclimatic, soil, topographic and land use, and land cover (LULC) variables. Striga hermonthica geolocations were collected and collated and ecological niche models were developed to determine the habitat suitability. The results showed that approximately 1767 km2 (10% of the total study area) is currently highly suitable for Striga hermonthica occurrence. The future projections showed a range between 2106 km2 (19% of the total study area) and 2712 km2 (53% of the total study area) at the minimum carbon (RCP 2.6) and the maximum carbon emission scenarios (RCP 8.5) respectively. Elevation, annual precipitation, LULC, temperature seasonality and soil type were determined to be the most influential ecological predictor variables for Striga hermonthica establishment. The study revealed the importance of using climate, soil, topographic and LULC variables when evaluating agricultural production constraints such as Striga's prevalence. The methodology used in this study should be tested in other Striga affected areas.

Effective Path Length for Estimating Rain Attenuation Over an Earth‐Space Path Using Features of Stratiform and Convective Precipitation at a Tropical Location

AbstractThe effective path length (LE) for the rain attenuation estimation over the Earth‐space path depends on rain cell size, rain rate, and rain height which in turn are determined by the types of rain. The present study examines the variation of LE based on the experimental measurements of Ku‐band attenuation and rain rate at a tropical location Kolkata (22°34′N, 88°22′E) in comparison with the ITU‐R. The study also utilizes measurements from a 24‐GHz micro rain Doppler radar to differentiate the precipitation types as stratiform and convective rain on the basis of the presence and absence of a melting layer. Power‐law models of LE in terms of rain rate are proposed for convective and stratiform types of rain. The investigation reveals the physical phenomena behind the variability of LE at low and high rain rates which are associated with stratiform and convective rain respectively. The proposed models provide a significantly better agreement with the experimental data compared to the ITU‐R model and also account for distinguishing features of two types of rain, thus giving a physical basis of the proposed model which is not reflected in the ITU‐R formulations.

Enhanced tensile strength in an Al–Zn–Mg–Cu alloy via engineering the precipitates along the grain boundaries

An investigation was conducted to study the influence of peak-ageing and double ageing treatments in the precipitation along the different grain boundary orientations of an extruded Al–Zn–Mg–Cu alloy. The results display that the peak-aged grain boundary precipitates along the Low Angle Grain Boundaries (LAGBs) are mainly of θ'' with the existence of few η′ precipitates, while the η′ and θ'' precipitates are along the High Angle Grain Boundaries (HAGBs). The major grain boundary precipitates are mainly of θ'' precipitates along LAGBs and θ′, η′, and η along the HAGBs after the double ageing treatment. The variation in the precipitate types along different grain boundary orientations was attributed to the different diffusion rates of solutes along the grain boundaries. In addition, it is observed that the yield strength (YS) (∼ 690 MPa) of peak-aged Al–Zn–Mg–Cu alloy increased by ∼ 73% and ∼ 18% by comparison with the extruded and double-aged alloys, respectively. The double-aged alloy displays good elongation to fracture (∼16%) compared to the peak-aged alloy. Precipitation hardening contributes to the tensile strength of the alloy, and the improvement of the elongation owed to the growth of the grain boundaries precipitates and the corresponding absence of the precipitate-free zone area. The current study provides new insights in engineering the grain boundary precipitates to the required precipitate type and the corresponding mechanical properties.

Selective Separation Recovery of Copper and Arsenic from the Leaching Solution of Copper Soot

Through the main chemical reaction of metal ions and S2−, a new type of sulfide precipitant was first prepared and used to realize the selective separation recovery of copper and arsenic from the leaching solution of copper soot. It is proven by experimental results that the prepared sulfide precipitant could realize the efficient separation recovery of copper and arsenic. Indeed, the copper sulfide slag with Cu grade of about 47% and arsenic trisulfide slag with As operation recovery of about 98% could be obtained. The results of chemical reaction energy calculation analysis and SEM images analysis illustrate that the selective separation recovery of copper and arsenic mainly depended on the chemical reactions of sulfide precipitation. The ions of S2− and HS− produced by the prepared sulfide precipitant could react with Cu2+ and arsenic components to form CuS and As2S, respectively, in the copper and arsenic recovery procedure. In addition, the smaller solubility of CuS and the lower rate of S2− engendered by the sulfide precipitant were key to achieving the efficient separation and recovery of copper and arsenic.

Impacts of tropical cyclones on summertime short-duration precipitation extremes over the middle-lower reaches of the Yangtze River valley

This study investigated variations in summertime short-duration precipitation extremes over the middle-lower reaches of the Yangtze River valley (MLYRV) and the possible impacts of tropical cyclones (TC) on these changes over the 1961–2016 period. Three short-duration precipitation types, including all events and the events in the 75th and 95th percentiles, are defined. At the 75th percentile, both the amount and number of TC-induced extreme short-duration rainfall events exhibit slightly declining trends, and the trends are not pronounced for the 95th-percentile cases. The number and amount of TC-induced 95th-percentile events are approximately one order of magnitude larger than those of the 75th-percentile cases, indicating that TCs play a more significant role on the upper tail of the rainfall distribution over the MLYRV in summer than on the rest of the precipitation distribution. A large number of the defined non-TC precipitation events are mainly distributed over the central-south MLYRV and southeastern regions. The spatial patterns of TC-induced rainfall resemble the contributions of TC-induced precipitation events to the total summer rainfall, with large values located in southeastern regions of the MLYRV. The spatial distribution of 95th-percentile events is principally attributed to the frequency of TC activities and to the TC tracks. Most of the TCs that trigger 95th-percentile events make landfall over the southeast MLYRV, and the corresponding large frequency of TC tracks is mainly situated over the ocean to the east of Taiwan. Both environmental factors and atmospheric circulations modulate the variations in extreme short-duration rainfall events. In particular, equatorward displacement of the western Pacific subtropical high impacts TC track density, resulting in more occurrences of precipitation extremes in 95th-percentile events over the MLYRV.

Enhanced Role of Convection in Future Hourly Rainfall Extremes Over South Korea

AbstractA convection‐permitting regional climate model (CPRCM) with 2.5 km resolution has been simulated over South Korea for current and future conditions, and the role of convection in the scaling of hourly extreme precipitation (EP) with temperature is examined. It is found that the CPRCM can reproduce the observed super Clausius‐Clapeyron (C‐C) scaling for hourly EP. Precipitation type estimated based on the convective available potential energy reveals the important role of convection in the super C‐C scaling. Fraction of convective rainfall events increases rapidly with temperature, and the contribution of convection becomes dominant in future simulations under high‐emission scenarios. In the late 21st century, as temperature ranges shift to warmer conditions, unprecedented hourly extreme rainfall events are projected to occur particularly during the late summer season. Future changes in hourly extreme events are found to be affected much by boundary conditions from different global climate models.

Predictive model of spatial scale of forest fire driving factors: a case study of Yunnan Province, China

Forest fires are among the major natural disasters that destroy the balance of forest ecosystems. The construction of a forest fire prediction model to investigate the driving mechanism of fire drivers on forest fires can help reveal the mechanism of forest fire occurrence and its risk, and thus contribute to the prevention and control of forest fires. However, previous studies on the mechanisms of forest fire drivers have not considered the effect of differences in spatial scale of action of forest fire drivers on the predicted effect. Therefore, the present study proposes a spatial prediction model of forest fires that considers the spatial scale effect of forest fire drivers to predict forest fire risk. First, based on historical forest fire data and geographic environmental data in the Yunnan Province, geographically weighted logistic regression (GWLR) was used to determine the forest fire drivers and to estimate the probability of forest fire occurrence at locations where fire observations are absent. Then, multi-scale geographically weighted regression (MGWR) was used to explore the spatial scales of action of different drivers on forest fires. The results show that meteorological factors such as relative humidity, air temperature, air pressure, sunshine hours, daily precipitation, wind speed, topographic factors such as elevation, slope, and aspect, anthropogenic factors such as population density and road network, as well as vegetation type, were significantly correlated with forest fires; thus, they are identified as important factors influencing occurrence of forest fires in the Yunnan Province. The MGWR model regression results show that the role of different forest fire drivers on forest fire occurrence has spatial scale differences. The spatial scale of drivers such as altitude, aspect, wind speed, temperature, slope, and distance from the road to the fire point was larger and their spatial influence was relatively stable, with spatial heterogeneity having less influence on the model evaluation results. The spatial scale of drivers such as relative humidity, sunshine, air pressure, precipitation, population density, and vegetation type were smaller, and spatial heterogeneity had a more obvious influence on the model evaluation results. This study provides a reference for selecting drivers and evaluating their spatial scale effects to construct predictive regional forest fire models.

Effect of over-aging on the microstructure, mechanical properties and crashing performance of thin-walled Al–Mg–Si–Cu alloy profiles

The thin-walled Al–Mg–Si–Cu alloy (AA6008) crash-box profiles were treated by over-aging at 215 °C for 60 min, 120 min and 300 min, and then their corresponding microstructure, mechanical properties, and crashing performance were investigated. The results show that with the increase of aging time, the number density of precipitation is decreased significantly, the size of precipitate is coarsened, and the precipitate type is transformed from β″ to β′, resulting in a reduction of microhardness and strength. The crashed morphology of the profile is improved showing a more regular folding deformation and less crack, but the corresponding values of energy absorption and mean crash force are decreased owing to the decrease of the strength. The medium overaged treatment, i.e., AA 215 °C-120 min sample, can obtain a balanced combination of excellent mechanical properties (yield strength > 280 MPa) and crashing performance. The influence of precipitation on the mechanical properties and crash deformation is also discussed based on experimental results.

Climatological characteristics of nocturnal eastward‐propagating diurnal precipitation peak over South India during summer monsoon: Role of monsoon low‐level circulation and gravity waves

AbstractThis study explores the climatological diurnal cycle of precipitation during the summer monsoon season over southeast India using the Tropical Rainfall Measuring Mission (TRMM) 3G68 precipitation product from 2000 to 2014. The primary area of focus is the leeward side of the Western Ghats. We found that the climatological diurnal cycle over this area exhibits a bimodal peak with an afternoon/evening peak near the eastern slopes of the Western Ghats and a nocturnal peak near the southeast coast. This nocturnal peak near the southeast coast propagated offshore in the eastward direction with a phase speed of 18–20 m s−1 and attained an offshore peak in the late night/early morning. The afternoon diurnal peak is associated with daytime convection and propagates eastward over southeast India. The nocturnal peak is due to the convergence of intensified monsoon low‐level westerly winds along the land–sea boundary over the leeward side and supports the nocturnal diurnal peak to cross the coast at late night. The eastward‐propagating gravity waves support further eastward offshore propagation of nocturnal diurnal precipitation patterns. Altogether, the leeward‐side climatological diurnal peaks and diurnal variability in southeast India are controlled by complex precipitation types and their formation mechanisms due to monsoon low‐level westerly winds and gravity waves.

Trends and spatial variations of rain-on-snow events over the High Mountain Asia

Rain-on-snow (ROS) events can greatly affect the snow process and cause severe snowmelt-related hazards. It is important to monitor the spatiotemporal distribution of ROS events over the ungauged High Mountain Asia (HMA). This study investigated the spatiotemporal variability of ROS events over the HMA and its potential influencing factors from 1981 to 2020 based on stand-alone Noah-MP land surface model simulations forced by hourly HARv2 reanalysis dataset. The results demonstrated that ROS activity occurred more frequently in the higher-elevation (2500–4000 m and 5500–6000 m a.s.l) regions of the Tianshan Mountains, Pamir, eastern Hindu Kush, Himalayas, and the western Hengduan Shan, with an annual maximum ROS frequency exceeding 15 days and a maximum intensity reaching 40 mm concentrated in spring and summer. ROS frequency experienced a significant decrease in the high-elevation (3000–4500 m a.s.l) regions of the eastern Hindu Kush, West Himalaya, and western Hengduan Shan with a rate exceeding −1.5 days/decade. The decrease in ROS frequency could be explained by a shifting of precipitation type from snowfall to rain driven by dramatic warming and resulting in a decline in snowfall and shortened snow cover persistence, particularly in spring and summer. On the contrary, significantly increasing trend mainly prevailed in the high-elevation (5000–6000 m a.s.l) regions of Transhimalaya and East Himalaya, exceeding 0.9 days/decade. The attribution of the increased ROS frequency was related to the significant increase in summer precipitation over the Inner Tibetan Plateau, along with an absolute increase in snowfall, which was beneficial to snow accumulation with frequent transition of the precipitation phase. The above outcomes improve our understanding of ROS events and highlight the importance of ROS in extreme snowmelt events and water resources management under a warming climate.

Effects of Co/Si Atomic Ratio on Hardness and Electrical Conductivity of Cu–Co–Si Alloys

Cu–Co–Si alloys are being intensively studied as alternative candidates for Cu–Ni–Si alloys for integrated circuit lead frames. However, the effects of different precipitate types on the comprehensive properties of Cu–Co–Si alloys are not clear. Herein, several Cu–Co–Si alloys with various precipitates (CoSi, Co2Si, and Co) are designed based on phase diagrams calculation. The designed alloys are melted, cold‐rolled, and aged to test the corresponding hardness and electrical conductivity (EC). X‐ray diffraction and transmission electron microscopy are utilized to analyze the precipitates generated in those alloys. In the alloys with Co/Si ≤ 1, the excess Si atoms are not easy to precipitate from the copper lattice after CoSi precipitation, which seriously damages the EC. Co‐precipitation in alloys with Co/Si &gt; 2 is beneficial to improve EC without sacrificing hardness. According to thermodynamic calculation, precipitates in Cu‐1.62Co‐0.35Si (wt%) alloy with total elements between 1.5 and 2.0 wt% are all Co2Si and have the highest mass fraction in the equilibrium state. The different precipitates are highly dependent on the Co/Si atomic ratio and essential to Cu–Co–Si alloys’ mechanical and electrical performances.

Radial Growth Responses of Four Southeastern USA Pine Species to Summertime Precipitation Event Types and Intense Rainfall Events

Previous dendroclimatic studies have examined the relationship between total precipitation amounts and tree radial growth in the southeastern USA, yet recent studies indicate that specific precipitation event types and rainfall intensities influence longleaf pine (Pinus palustris Mill.) radial growth unequally. It remains unknown if other pine species respond similarly regarding specific precipitation types and intensities as most dendroclimatic studies have focused on precipitation amounts on monthly-to-annual scales without examining either the event type or intensity nor focusing on daily data. Here, we examine summertime climate–radial growth relationships in the southeastern USA for four native pine species (longleaf, shortleaf, Virginia, pitch) during 1940–2020. We examine and compare each species’ response to precipitation event types and intense rainfall events (IREs) and address if the temporal sensitivity to these events is species specific. Distinct temporal sensitivities exist among species, and there is a consistent association between convective, stationary front, and quasi-stationary precipitation and radial growth. All species except Virginia pine have significant (p &lt; 0.001) associations between IREs and radial growth, even though IREs account for ~49% of summertime rainfall. These results suggest precipitation-type sensitivity to radial growth may have dendroclimatic implications.

Homogenization of a mineral dissolution and precipitation model involving free boundaries at the micro scale

In this work we present the homogenization of a reaction-diffusion model that includes an evolving microstructure. Such type of problems model, for example, mineral dissolution and precipitation in a porous medium. In the initial state, the microscopic geometry is a periodically perforated domain, each perforation being a spherical solid grains. A small parameter ϵ is characterizing both the distance between two neighboring grains, and the radii of the grains. For each grain, the radius depends on the unknown (the solute concentration) at its surface. Therefore, the radii of the grains change in time and are model unknowns, so the model involves free boundaries at the micro scale. In a first step, we transform the evolving micro domain to a fixed, periodically domain. Using the Rothe-method, we prove the existence of a weak solution and obtain a priori estimates that are uniform with respect to ϵ. Finally, letting ϵ→0, we derive a macroscopic model, the solution of which approximates the micro-scale solution. For this, we use the method of two-scale convergence, and obtain strong compactness results enabling to pass to the limit in the nonlinear terms.

Identifying the spatiotemporal pattern and driving factors of vegetation dynamics in Shaanxi Province, China

Exploring the long-term spatiotemporal pattern of vegetation changes and its response to natural factors and human activities is vital for making informed decisions regarding ecosystem protection. The spatial–temporal distribution characteristics of vegetation dynamics and its driving factors in Shaanxi Province from 2000 to 2019 were analysed using the normalized difference vegetation index (NDVI). The explanatory power of solar radiation was the highest (63.45%), followed by relative humidity (59.07%), land use (56.73%), precipitation (52.17%), temperature (51.28%), and vegetation type (50.95%). In terms of climatic factors, the influences of solar radiation and relative humidity on vegetation changes were stronger than those of precipitation and temperature. The comprehensive impact of the pairwise factors was higher than those of the independent factors. Our results contribute to a better understanding of the complex mechanisms of vegetation changes and provide scientific recommendations for the prevention remediation of vegetation degradation in fragile ecosystems.

Sources, spectral characteristics, and fluxes of dissolved organic matter in coastal groundwater and river water in western Guangdong, China

Groundwater discharge and river runoff are two important ways for allochthonous dissolved organic matter (DOM) to enter the ocean, but they vary spatially. Currently, the source, composition, and efflux of groundwater and riverine dissolved organic matter to the tropical northern South China Sea remain poorly understood, preventing an accurate estimate of coastal carbon budgets. In July 2021, nine groundwater and six river water samples were collected along the coast of western Guangdong and were characterized using dissolved organic carbon (DOC) analysis, UV-visible, and fluorescence spectroscopy techniques. Atypical absorption spectra were strongly observed in groundwaters, which were mainly attributed to the high-level nitrates. An exponential-Gaussian equation showed that the average contribution of nitrate to total groundwater absorbances was up to 36% at ∼ 300 nm. Groundwater showed lower levels of DOC, colored dissolved organic matter (CDOM), and fluorescent dissolved organic matter (FDOM) as compared to river water, whereas the humic-like components dominated both groundwater and river water FDOM pools. Higher values of spectral slope S350–400, fluorescence index, biological index, and the ratio of two humic-like fluorescence jointly reveal that groundwater DOM mainly originated from microbial activities, whereas the river water DOM had considerable contribution from terrestrial soil. High precipitation, natural or agricultural land types, and a lack of seawater intrusion are expected to cause low levels of groundwater DOM in western Guangdong. Among 52 rivers from across the globe, high watershed productivity and precipitation may lead to high–moderate DOM levels in river water in western Guangdong. The DOM fluxes via fresh groundwater discharge in western Guangdong are comparable in magnitude to those by river runoff, accounting for 16%–18% of the Pearl River DOM fluxes. Based on the slopes of linear correlations between CDOM and DOC obtained in groundwater samples and 52 rivers, as well as the data on water fluxes and DOC levels, the global CDOM fluxes via groundwater discharge and river runoff are estimated to be 3.5–12.2 × 1012 m2 yr−1 and 4.3 ± 0.3 × 1014 m2 yr−1, respectively, highlighting the importance of considering groundwater discharge and river runoff in coastal carbon budgets.

Investigating a microbial approach to water conservation: Effects of Bacillus subtilis and Surfactin on evaporation dynamics in loam and sandy loam soils

Semi-arid regions faced with increasingly scarce freshwater resources must manage competing demands in the food-energy-water nexus. A possible solution modifies soil hydrologic properties using biosurfactants to reduce evaporation and improve water retention. In this study, two different soil textures representative of agricultural soils in Kansas were treated with a direct application of the biosurfactant, Surfactin, and an indirect application via inoculation of Bacillus subtilis. Evaporation rates of the wetted soils were measured when exposed to artificial sunlight (1000 W/m2) and compared to non-treated control soils. Experimental results indicate that both treatments alter soil moisture dynamics by increasing evaporation rates by when soil moisture is plentiful (i.e., constant rate period) and decreasing evaporation rates by when moisture is scarce (i.e., slower rate period). Furthermore, both treatments significantly reduced the soil moisture content at which the soil transitioned from constant rate to slower rate evaporation. Out of the two treatments, inoculation with B. subtilis generally produced greater changes in evaporation dynamics; for example, the treatment with B. subtilis in sandy loam soils increased constant rate periods of evaporation by 43% and decreased slower rate evaporation by 49%. In comparing the two soil textures, the sandy loam soil exhibited a larger treatment effect than the loam soil. To evaluate the potential significance of the treatment effects, a System Dynamics Model operationalized the evaporation rate results and simulated soil moisture dynamics under typical daily precipitation conditions. The results from this model indicate both treatment methods significantly altered soil moisture dynamics in the sandy loam soils and increased the probability of the soil exhibiting constant rate evaporation relative to the control soils. Overall, these findings suggest that the decrease in soil moisture threshold observed in the experimental setting could increase soil moisture availability by prolonging the constant rate stage of evaporation. As inoculation with B. subtilis in the sandy loam soil had the most pronounced effects in both the experimental and simulated contexts, future work should focus on testing this treatment in field trials with similar soil textures.