Rainfall pH Research Articles

Leaching characteristics and environmental impact of heavy metals in tailings under rainfall conditions: A case study of an ion-adsorption rare earth mining area

Following ion-adsorption rare earth mining, the residual tailings experience considerable heavy metal contamination and gradually evolve into a pollution source. Therefore, the leaching characteristics and environmental impact of heavy metals in ion-adsorption rare earth tailings require immediate and thorough investigation. This study adopted batch and column experiments to investigate the leaching behaviour of heavy metals in tailings and assess the impact of tailings on paddy soil, thereby providing a scientific basis for environmental protection in mining areas. The results showed that Mn, Zn, and Pb contents were 431.67, 155.05, and 264.33 mg·kg−1, respectively, which were several times higher than their respective background values, thereby indicating significant heavy metal contamination in the tailings. The batch leaching experiment indicated that Mn and Pb were priority control heavy metals. Heavy metals were divided into fast and slow leaching stages. The Mn and Pb leaching concentrations far exceeded environmental limits. The DoseResp model perfectly fitted the leaching of all heavy metals from the tailings (R2 > 0.99). In conjunction with the findings of the column experiment and correlation analysis, the chemical form, rainfall pH, ammonia nitrogen, and mineral properties were identified as the primary factors controlling heavy metal release from tailings. Rainfall primarily caused heavy metal migration in the acid-extraction form from the tailings. The tailing leachate not only introduced heavy metals into the paddy soil but also caused the transformation of the chemical form of heavy metals in the paddy soil, further exacerbating the environmental risk posed by heavy metals. The study findings are significant for environmental conservation in mining areas and implementing environmentally friendly practices in rare earth mining.

The leaching behavior of heavy metal from contaminated mining soil: The effect of rainfall conditions and the impact on surrounding agricultural lands

Contaminated mining soils could lead to heavy metal pollution of surrounding farmlands under rainfall conditions. With the aids of sequential extraction, batch leaching, and dynamic leaching experiments, this study was carried out to investigate the characteristics of heavy metals in contaminated mining soils, understand their leaching behavior under different rainfall conditions, and evaluate the potential effects on surrounding farmlands. The results indicated that the concentrations of heavy metals (Cr, Ni, Cu, Zn, As, Cd, and Pb) in the contaminated mining soils were several or even twenty times higher than their corresponding background values, and Cd, Zn, Cu and Pb had considerable proportions (>50 %) in mobile forms. The leaching amounts of heavy metals from the contaminated mining soils had positive correlation with their contents in acid soluble form, and showed strong dependence on rainfall pH conditions. Acid rainfalls (pH = 4.32) can greatly increase the average annual release of Cd, Zn, Cu and Pb from mine soils in the study area, with increments ranging from 72.4 % (Pb) to 85.9 % (Cd) compared to those under alkaline conditions (pH = 7.42). The leaching of heavy metals was well fitted by two-constant, pseudo second-order and parabolic equations, indicating that their multi-layer sorption/desorption behavior on soil surface was dominated by chemical processes and their release was controlled by the diffusion within the soil pore channels. The two-column leaching experiment showed that the metal-rich leachate can lead to obvious increments of heavy metals in non-residual fractions (in particular Cd in acid soluble form) in surrounding farmlands, which would significantly raise the potential ecological risk associated with heavy metals. These findings indicate the importance of contaminated mining soils as a long-term source of heavy metals and the needs for mitigating the releases of toxic elements, especially in areas with heavy acid precipitation.

Acidity of Soil and Water Decreases in Acid-Sensitive Forests of Tropical China.

Acid deposition in China has been declining since the 2000s. While this may help mitigate acidification in forest soils and water, little is known about the recovery of soils and water from previous severe acidification in tropical China. Here, we assessed the chemistry of mineral soils, water, and acid gases (SO2 and NOx) from three successional forest types in tropical China from 2000 to 2022. Our results showed that soil pH increased synchronously from 3.9 (2000-2015) to 4.2 (2016-2022) across all three forest types, with exchangeable acid initially decreasing and thereafter stabilizing. Surface and ground water pH also gradually increased throughout the monitoring period. Soil pH recovery was stronger in the primary than in the planted forest. However, soil pH recovery lagged behind the increase in rainfall pH by approximately a decade. The recovery of soil pH was likely related to the positive effects of the dissolution of Al/Fe-hydroxysulfate mineral and subsequent sulfur desorption on soil acid-neutralizing capacity, increased soil organic matter, and climate warming, but was likely moderated by increased exchangeable aluminum and potentially proton-producing hydroxysulfate mineral dissolution that caused the lagged soil pH recovery. Surface and ground water pH recovery was attributed to increased water acid-neutralizing capacity. Our study reports the potential for the recovery of acidified soil and water following decreased acid deposition and provides new insights into the functional recovery of acid-sensitive forests.

Changes in rainfall pH after passing through the forest canopy: Increase in throughfall but decrease in stemflow

Acid rainfall has the potential to harm the structure and function of forest ecosystems. Forest canopy, which is the first surface of contact for rainfall entering the forest ecosystem, may play a role in filtering acid and increasing pH, acting as a natural protective layer for the understory communities in the forest. However, there is currently a lack of global quantitative assessments on the impacts of forest canopy on rainfall pH. To better understand and predict the relationship between forest canopy and rainfall pH that reaches the forest floor (i.e., throughfall and stemflow), we systematically combined data from 244 published articles, including 2563 paired observations for throughfall and 1431 for stemflow, to investigate whether forest canopy has a buffering effect on rainfall pH. We found that (1) throughfall pH significantly increased by an average of 0.14 after passing through forest canopy, while stemflow pH significantly decreased by 0.74; (2) understory rainfall (throughfall and stemflow) ΔpH was higher in broadleaved compared to needleleaf forests, while stemflow ΔpH was lower in evergreen forests and plantations than in deciduous, primary or secondary forests; (3) throughfall ΔpH was mainly influenced by tree height, rainfall K+ concentration and leaf type, while stemflow ΔpH was mainly affected by stemflow ΔMg2+, ΔNO3- and leaf phenology. Our results showed that forest canopy has a significant impact on the pH of rainfall entering forests, which can be influenced not only by rainfall partitioning, but also by vegetation type and rainfall characteristics. Our findings have important implications for predicting understory rainfall pH in the context of global climate change and will contribute to a better understanding of nutrient cycling associated with hydrological processes in forests.

Assessment of Wet Inorganic Nitrogen Deposition in an Oil Palm Plantation-Forest Matrix Environment in Borneo

Nitrogen (N) deposition significantly affects forest dynamics, carbon stocks and biodiversity, and numerous assessments of N fluxes and impacts exist in temperate latitudes. In tropical latitudes, however, there are few such assessments. In this study, we measured the inorganic N concentration (wet deposition) deposited in rainfall and rainfall pH throughout one year at the boundary of a forest reserve in Malaysian Borneo. We considered that the N deposition may be either from forest and agricultural fires or derived from agricultural fertiliser. Therefore, we determined the wind trajectories using the HYSPLIT model provided by NOAA, the location of fires throughout the landscape throughout one year using NASA’s FIRM system, and obtained the land use cover map of Malaysia and Indonesia. We then correlated our monthly cumulative wet N deposition with the cumulative number of fires and the cumulative area of oil palm plantation that wind trajectories arriving at our study site passed over before reaching the rainfall sampling site. At 7.45 kg N ha−1 year−1, our study site had the highest annual wet inorganic N deposition recorded for a Malaysian forest environment. The fire season and the cumulative agricultural area crossed by the winds had no significant effect on N deposition, rainfall N concentration, or rainfall pH. We suggest that future research should use 15N isotopes in rainfall to provide further information on the sources of N deposition in tropical forests such as this.

Evidence for entomophily in “Knothole Moss” (Anacamptodon splachnoides)

Anacamptodon splachnoides is an uncommon moss almost entirely restricted to water-filled treeholes in deciduous trees in eastern North America and Europe. There has been uncertainty regarding taxonomic placement of the genus because of conflicts between gametophytic characters, in which it resembles Amblystegiaceae, and sporophytic characters, which seem to ally it with Fabroniaceae, Campyliaceae, or other families. Recent evidence from DNA sequencing clearly places Anacamptodon in Amblystegiaceae despite features of the sporophyte such as an erect capsule, rostrate lid, reflexed peristome teeth, and low endostome membrane. All these unusual features, including sticky spores (which seem to have been overlooked), are characteristic of species of Splachnaceae, until now the only group of mosses whose spores are known to be dispersed by flies. Field observations of A. splachnoides over a period of 16 months revealed that the moss mat and sporophytes are regularly visited by many species of flies that are also treehole specialists. Of 12 species of flies captured, nine carried spores of the moss. Many of these are strong fliers with hairy legs and bodies that inadvertently pick up the sticky spores, dispersing them in a directed fashion to other treeholes, where the females lay eggs that develop into aquatic larvae that later emerge as adults. Though differing in some respects from the adaptations seen in Splachnaceae, the parallel evolution of sporophytic characters related to entomophily is remarkable. In addition, we consider other aspects of the ecology of this moss that may help explain its rarity, such as treehole location, pH of rainfall versus stemflow and treehole water, and a possible beneficial relationship with certain wood-rotting fungi.

Effect of rainfall pH value on fretting corrosion characteristics of 60Si2Mn steel for high-speed railway track fastener clips

Fretting corrosion degrades the materials of high-speed railway track fastener clips. It reduces their mechanical properties, affecting the service performance of the fastener and even threatens the safety of train operations. To explore the fretting corrosion characteristics of high-speed railway clips, the spatial coupling distribution diagram of the annual mean pH value of rainfall in China's high-speed railway network is proposed, the pH value parameter range of the fretting corrosion test was then determined. Fretting corrosion tests were carried out on 60Si2Mn steel of high-speed railway fastener clips. The fretting behavior and damage mechanism of the clips' materials under different rainfall pH values are discussed in detail. Faraday's law is then used to study the interaction between the wear and corrosion of the clips. The results show that there are different wear mechanisms at different pH values. The wear mechanisms in acidic conditions with a pH value of 4.5 and above are mainly abrasive and corrosive wear, accompanied by fatigue wear. In conditions with a pH value of 7.0, the wear mechanisms are mainly abrasive wear and oxidative wear. For alkaline conditions where the pH is 8.5 and below, these mechanisms are mainly abrasive and oxidative wear. The acidic and alkaline environments will strengthen the abrasive wear effect. The corrosive environment will strengthen the abrasive wear effect and increase the wear amount on the contact surface of the clips. The corresponding wear amount is the largest at a pH value of 4.5, followed by 5.5, 8.5, and the smallest at 7.0. Compared with the pH value of 7.0, wear and corrosion will promote each other under acidic and alkaline conditions, presenting a “positive interaction.”

Release behavior of uranium from a uranium tailing in Jiangxi Province

In this study, nine soils at different depths in a decommissioned uranium tailing pond in Jiangxi Province are selected as the research objects to study their mineralogical properties and reveal the leaching law of radioactive element uranium under natural rainfall conditions. The research results are as follows: 1) The distribution characteristics of uranium are affected by the mineral composition, microscopic morphology and physical and chemical properties of uranium tailings. 2) In static leaching experiments, acidic solutions, small particles, and high solid-to-liquid ratios all promote the release of uranium. 3) In the dynamic leaching experiment, the lower the pH of simulated rainfall, the more uranium is released. According to Fick theory, the migration mechanism of uranium is mainly surface dissolution, and the release of uranium is related to the content of migratory uranium.

Influence of acid rain on slope instability mechanism—a case study in Sichuan provincial highway, China

Acid rain has important influences on the physical and mechanical properties of rock as a result of mineral conversion and dissolution of cement. There are clear spatial correlations between the occurrence of slope failure and rainfall pH value in acid-rain areas. Although some fatal landslides have been ascribed to acid rain, those landslides all consisted of sedimentary rocks that generally contained carbonate minerals, which are particularly susceptible to dissolution in acidic conditions. This paper describes the mechanical deterioration of the structural plane based on acid-rain simulation experiments on a slope cut in hard rock along Sichuan provincial highway S211, China. In the experiments, the cohesion and internal friction angle of the structural plane fell to 35.4% and 6.8% of their original values, respectively, and the strength deterioration exhibited a power-law relationship with the exposed area of the rock bridges. Mineralogical and hydrochemical analyses including polarising microscopy, X-ray diffraction, scanning electron microscopy, and inductively coupled plasma optical emission spectrometry were employed to describe the micromechanisms of weakening. Mechanical weakening of the structural plane is attributed to deterioration of both the composition and the structure. Transformation from hard essential minerals to clay minerals through pyroxene chloritisation, plagioclase illitisation, illite smectitisation, and chlorite dissolution reduced the strength properties of rock bridges. In addition, abundant secondary micro-cracks were formed by propagation of worm-like dissolution pits, thus disintegrating rock bridges and further reducing the strength of the structural plane. This paper provides a better understanding of slope failure mechanisms in areas affected by acid rain.

Predicting Event-Based Sediment and Heavy Metal Loads in Untreated Urban Runoff from Impermeable Surfaces

Understanding the amount of pollutants contributed by impermeable urban surfaces during rain events is necessary for developing effective stormwater management. A process-based pollutant load model, named Modelled Estimates of Discharges for Urban Stormwater Assessments (MEDUSA), was further developed (MEDUSA2.0; Christchurch, New Zealand) to include simulations of dissolved metal loadings and improve total suspended solids (TSS) loading estimations. The model uses antecedent dry days, rainfall pH, average event intensity and duration to predict sediment and heavy metal loads generated by individual surfaces. The MEDUSA2.0 improvements provided a moderate to strong degree of fit to observed sediment, copper, and zinc loads for each modelled road and roof surface type. The individual surface-scale modelling performed by MEDUSA2.0 allows for identification of specific source areas of high pollution for targeted surface management within urban catchments.

Toward Modeling of Nitrous Oxide Emissions Following Precipitation, Urine, and Feces Deposition on Beef Cattle Feedyard Surfaces

HighlightsNitrous oxide is a greenhouse gas emitted from feedyard pen surfaces.Experiments were conducted to quantify nitrous oxide emissions from precipitation, urine, and feces.Nitrous oxide emissions from urine were about 30% of those from equal amounts of precipitation.Regression equations were developed for empirical modeling of emissions.Abstract. The amount of moisture deposited annually as urine (~320 mm) and feces (~95 mm) on typical semi-arid Texas beef cattle feedyard pens is considerable compared to the regional 470 mm mean annual precipitation. Precipitation is a primary factor affecting nitrous oxide (N2O) emissions from manure, but specific effects of urine and feces deposition are unknown. The objectives of this research were to (1) quantify N2O emissions following precipitation, urine, and feces deposition on a dry feedyard manure surface, and (2) develop equations for future empirical modeling of these emissions. Four experiments (Exp.) were conducted using recirculating flux chambers to quantify N2O emissions. Exp. 1 had treatments (TRT) of water (W), artificial urine (AU), and two urines collected from beef cattle fed high-quality forage (FU) or corn-based concentrate (CU). Exp. 2 had TRT of W, AU, and two feces levels (Fx1 and Fx2). In Exp. 3, N2O emissions were quantified from fresh feces pats. In Exp. 4, the effect of rainfall pH on N2O emissions was evaluated. Results from Exp. 1 showed that the W TRT had the highest mean cumulative N2O emission, while AU, FU, and CU ranged from 31.0% to 70.0% of W on an equal volume-applied basis. There was little correlation between N2O emissions and urine or water nitrogen (N) content. In Exp. 2, W again had the highest cumulative N2O. Cumulative N2O emissions expressed per unit of water added were 29.0, 3.8, 4.5, and 5.1 mg N kg-1 water added for W, AU, Fx1, and Fx2, respectively. In Exp. 3, fresh feces pats emitted no direct N2O, but N2O originated from the dry manure beneath the feces pat due to wetting. In Exp. 4, the highest N2O emissions occurred at pH 5 and pH 8, with lower emissions at pH 6 and pH 7. This research has shown that the addition of moisture to the pen surface from urine and feces contributes considerably to N2O emissions as compared to precipitation alone. The following recommendations were developed for future empirical modeling purposes: (1) N2O emissions from urine should be calculated as 32.7% of those emissions from the equivalent mass deposition of water, and (2) N2O emissions resulting from the mass of water in feces should be calculated as 15.6% of those emissions from the equivalent mass deposition of water. Keywords: Beef cattle, Greenhouse gas, Manure, Nitrous oxide, Urine, Precipitation.

Ammonia emission control in China would mitigate haze pollution and nitrogen deposition, but worsen acid rain

China has been experiencing fine particle (i.e., aerodynamic diameters ≤ 2.5 µm; PM2.5) pollution and acid rain in recent decades, which exert adverse impacts on human health and the ecosystem. Recently, ammonia (i.e., NH3) emission reduction has been proposed as a strategic option to mitigate haze pollution. However, atmospheric NH3 is also closely bound to nitrogen deposition and acid rain, and comprehensive impacts of NH3 emission control are still poorly understood in China. In this study, by integrating a chemical transport model with a high-resolution NH3 emission inventory, we find that NH3 emission abatement can mitigate PM2.5 pollution and nitrogen deposition but would worsen acid rain in China. Quantitatively, a 50% reduction in NH3 emissions achievable by improving agricultural management, along with a targeted emission reduction (15%) for sulfur dioxide and nitrogen oxides, can alleviate PM2.5 pollution by 11-17% primarily by suppressing ammonium nitrate formation. Meanwhile, nitrogen deposition is estimated to decrease by 34%, with the area exceeding the critical load shrinking from 17% to 9% of China's terrestrial land. Nevertheless, this NH3 reduction would significantly aggravate precipitation acidification, with a decrease of as much as 1.0 unit in rainfall pH and a corresponding substantial increase in areas with heavy acid rain. An economic evaluation demonstrates that the worsened acid rain would partly offset the total economic benefit from improved air quality and less nitrogen deposition. After considering the costs of abatement options, we propose a region-specific strategy for multipollutant controls that will benefit human and ecosystem health.

Experiment study on stability of heavy metals Cr and Pb in solidified body of river and lake sediment

The residual soil containing heavy metals after solidification/stabilization treatment (test residual soil), was selected as the study object of heavy metal release kinetics. Firstly, the properties of test residual soil were analyzed, and then the test residual soil was placed in the treatment tank and tested under different composite conditions. The test conditions include temperature, simulated rainfall, simulated rainfall pH and simulated light intensity. Different compound conditions were selected for testing, and each composite condition test was conducted in two groups. The experiment lasted 110 days. The simulated rainfall test was conducted every 10 days. The soil samples and leachate samples were sampled at each time. At the same time, the overflow and leachate samples were measured. The heavy metal content in each sample was analyzed and the release rule of heavy metals in the remaining soil was deduced.

Intra-event variability of bacterial composition in stormwater runoff from mixed land use and land cover catchment

Microbial community and composition in stormwater runoff from mixed land use land cover (LULC) catchment with ongoing land development was diverse across the hydrological stage due different environmental parameters (hydrometeorological and physicochemical) and source of runoff. However, limited studies have been made for bacterial composition in this catchment. Therefore, this study aims to: (1) quantify the concentration of fecal indicator bacteria (FIB), stormwater quality and bacterial composition and structure according to hydrological stage; and (2) determine their correlation to environmental parameters. The 454 pyrosequencing was used to determine the bacterial community and composition; while Pearson\'s correlation was used to determine the correlation among parameters—FIB, stormwater quality, bacterial composition and structure-to environmental parameters. Results demonstrated that the initial and peak runoff has the highest concentration of FIB, stormwater quality and bacterial composition and structure. Proteobacteria, Bacteroidetes, Actinobacteria and Firmicutes were dominant bacteria identified in this catchment. Furthermore, the 20 most abundant genera were correlated with runoff duration, average rainfall intensity, runoff volume, runoff flow, temperature, pH, organic matter, nutrients, TSS and turbidity. An increase of FIB and stormwater quality concentration, diversity and richness of bacterial composition and structure in this study was possibly due to leakage from septic tanks, cesspools and latrines; feces of domestic and wild animals; and runoff from forest, destroyed septic system in land development site and urban LULC. Overall, this study will provide an evidence of hydrological stage impacts on the runoff microbiome environment and public health perspective.

The surprising recovery of red spruce growth shows links to decreased acid deposition and elevated temperature

Following growth declines and increased mortality linked to acid deposition-induced calcium depletion, red spruce (Picea rubens Sarg.) in the northeastern United States are experiencing a recovery. We found that more than 75% of red spruce trees and 90% of the plots examined in this study exhibited increasing growth since 2001. To understand this change, we assessed the relationship between red spruce radial growth and factors that may influence growth: tree age and diameter, stand dynamics, plot characteristics (elevation, slope, aspect, geographical position), and a suite of environmental variables (temperature, precipitation, climate and precipitation indices (degree days, SPEI [standardized precipitation evapotranspiration index], and acid deposition [SO42−, NO3−, pH of rainfall, cation:anion ratio of rainfall]) for 52 plots (658 trees) from five states (spanning 2.5°N × 5°W). Examining the growth relationships from 1925 to 2012, we found that while there was variability in response to climate and acid deposition (limited to 1980–2012) by elevation and location, plot and tree factors did not adequately explain growth. Higher temperatures outside the traditional growing season (e.g., fall, winter, and spring) were related to increased growth. Nitrogen deposition (1980–2012) was associated with lower growth, but the strength of this relationship has lessened over time. Overall, we predict sustained favorable conditions for red spruce in the near term as acid deposition continues to decline and non-traditional growing season (fall through spring) temperatures moderate, provided that overall temperatures and precipitation remain adequate for growth.

Adsorption by and artificial release of zinc and lead from porous concrete for recycling of adsorbed zinc and lead and of porous concrete to reduce urban non-point heavy metal runoff

This report describes the use of porous concrete at the bottom of a sewage trap to prevent runoff of non-point heavy metals into receiving waters, and, secondarily, to reduce total runoff volume during heavy rains in urbanized areas while simultaneously increasing the recharge volume of heavy-metal-free water into underground aquifers. This idea has the advantage of preventing clogging, which is fundamentally very important when using pervious materials. During actual field experiments, two important parameters were identified: maximum adsorption weight of lead and zinc by the volume of porous concrete, and heavy metal recovery rate by artificial acidification after adsorption. To understand the effect of ambient heavy metal concentration, a simple mixing system was used to adjust the concentrations of lead and zinc solutions. The concrete blocks used had been prepared for a previous study by Harada & Komuro (2010). The results showed that maximum adsorption depended on the ambient concentration, expressed as the linear isothermal theory, and that recovery depended on the final pH value (0.5 or 0.0). The dependence on pH is very important for recycling the porous concrete. A pH of 0.5 is important for recycling both heavy metals, especially zinc, (8.0–22.1% of lead and 42–74% of zinc) and porous concrete because porous concrete has not been heavily damaged by acid. However, at a pH of 0.0, the heavy metals could be recovered: 30–60% of the lead and 75–125% of the zinc. At a higher pH, such as 2.0, no release of heavy metals occurred, indicating the safety to the environment of using porous concrete, because the lowest recorded pH of rainfall in Japan is. 4.0.

Dynamics of the Water Quality in a Broad-leaf Evergreen Forest at Different Spatial Levels on Jinyun Mountain

A typical forest stand on the subtropical Jinyun Mountain in China was selected to investigate water quality and interception characteristics for several important ions at different levels in the subtropical forest ecosystem. Based on field and laboratory experiments, the effect of precipitation, throughfall, litterfall, and soil percolation on water quality and ionic interception were investigated from September 2013 to August 2014. Results indicated that the rainfall on Jinyun Mountain was obviously acidic, with an average pH of 4.75. The soil and canopy can elevate the pH of rainfall, while the soil had a greater capability for adjusting pH than did the forest canopy. In addition, the concentrations of NH4+, SO42-, PO43-, Mg2+, Ca2+, and K+ in the litterfall increased with litterfall tissue disintegration, while the other ions decreased. Moreover, functional groups and colloids in the soil can bind or neutralize many ions, such as NO3-, SO42-, NH4+, PO43-, K+, and Mg2+. However, some ions were released from the soil by erosion from acid rain over a long time. Generally, the forest ecosystem is a sink for ions found in precipitation with diverse functions for different layers, and the forest canopy has the highest interception capacity for the ions found in precipitation.

Assessing acid rain and climate effects on the temporal variation of dissolved organic matter in the unsaturated zone of a karstic system from southern China

Acid rain has the potential to significantly impact the quantity and quality of dissolved organic matter (DOM) leached from soil to groundwater. Yet, to date, the effects of acid rain have not been investigated in karstic systems, which are expected to strongly buffer the pH of atmospheric rainfall. This study presents a nine-year DOM fluorescence dataset from a karst unsaturated zone collected from two drip sites (HS4, HS6) in Heshang Cave, southern China between 2005 and 2014. Cross-correlograms show that fluorescence intensity of both dripwaters lagged behind rainfall by ∼1 year (∼11 months lag for HS4, and ∼13 months for HS6), whereas drip rates responded quite quickly to rainfall (0 months lag for HS4, and ∼3 months for HS6), based on optimal correlation coefficients. The rapid response of drip rates to rainfall is related to the change of reservoir head pressure in summer, associated with higher rainfall. In winter, low rainfall has a limited effect on head pressure, and drip rates gradually slow to a constant value associated with base flow from the overlying reservoir- this effect being most evident on inter-annual timescales (R2 = 0.80 for HS4 and R2 = 0.86 for HS6, n = 9, p < 0.01). We ascribed the ∼1 year lag of fluorescence intensity to the effect of the soil moisture deficit and the karst process on delaying water and solute transport. After eliminating the one year lag, the congruent seasonal pacing and amplitude between fluorescence intensity and rainfall observed suggests that the seasonality of fluorescence intensity was mainly controlled by the monsoonal rains which can govern the output of DOM from the soil, as well as the residence time of water in the unsaturated zone. On inter-annual timescales, a robust linear relationship between fluorescence intensity and annual (effective) precipitation amount (R2 = 0.86 for HS4 and R2 = 0.77 for HS6, n = 9, p < 0.01) was identified, implying that annual (effective) precipitation is the main determinant of DOM concentration in the aquifer. Conversely, the insensitivity of fluorescence intensity and fluorescence wavelength maxima to variations in the pH of local rainfall suggests that acid rain over the study period (∼pH 5.6 to ∼ 4.5) had no discernable effect on the quantity and quality of DOM in karst soil and soil solution, likely being strongly buffered by soil carbonates. Therefore, despite large increases in anthropogenic acid rain in recent Chinese history, hydrologic forcing is the predominant factor driving variations in DOM in karst aquifers.

Major Factors Influencing the Cd Content and Seasonal Dynamics in Different Land Cover Soils in a Typical Acid Rain Region

Understanding the seasonal variations in active heavy metal components and sensitive impact factors is of importance for the ecological risk reduction during the agricultural production processes. Paddy fields, vegetable lands, and hilly forests were selected as three main land cover types to assess the seasonal characteristics of Cd bioavailability and reveal how or to what extent it was affected by the physiochemical parameters of soils, under different land-use types in a typical Cd-contaminated watershed in the middle and lower reaches of Xiangjiang River. One-year in situ monitoring results showed that natural rainfall pH in winter and spring was lower than in summer and autumn in the study region. The total Cd content of paddy soils was significantly higher than that of the vegetable soil, while the hilly forest soil showed the lowest total Cd value. Similar seasonal variations in total Cd content were found in three soil types with slightly lower summer and autumn concentrations than spring and winter values, but no obvious correlation was detected between the total and the available Cd components. The paddy soil available Cd concentration during the 5-9-month crop growth season was significantly lower than the other months of the year, while vegetable cultivation and hilly forest soils showed the opposite trend. Eh was the key factor that had a positive influence on the Cd activity in paddy soil. Soil TOC concentration was negatively correlated with soil activity in vegetable soil. TOC, water soluble organic carbon, showed a significant positive correlation with Cd effectiveness. The results provide scientific references for Cd contamination control and safe agricultural production.

The Effect of Rainwater Quality on The Methane Concentration

&lt;p&gt;Research on the effect of pH of rainfall on the emission of methane (CH&lt;sub&gt;4&lt;/sub&gt;) has been made. And what about the influence of the pH of rainfall at a concentration of CH&lt;sub&gt;4&lt;/sub&gt;? That question will be answered through this research. The problem in this research is not yet known and the effect of the interaction of water quality in these clouds pH (degree of acidity) of rain on the concentration of CH&lt;sub&gt;4&lt;/sub&gt;. The purpose of the study was the first object to determine acid rain in research location and to determine and analyze the influence of the pH of rainfall on the CH&lt;sub&gt;4&lt;/sub&gt; concentration. The research location is at Balai Pengamat Atmosfer dan Antariksa LAPAN in Kototabang hills, West Sumatra. The data used in this study is the pH of rainfall and CH&lt;sub&gt;4&lt;/sub&gt; concentrations. The analytical method used is the analysis of statistical and descriptive analysis. The results showed a correlation coefficient between the pH of rainfall with CH&lt;sub&gt;4&lt;/sub&gt; concentration of 0,87. The correlation coefficient indicates that the effect of the pH of rainfall is linearly proportional to the concentration of CH&lt;sub&gt;4&lt;/sub&gt;. This means that the pH of rainfall is higher, then the CH&lt;sub&gt;4&lt;/sub&gt; concentration will increase.&lt;/p&gt;&lt;p&gt; &lt;/p&gt;