Soil Sink Research Articles

A spatial source-oriented and probability-based risk-assessment framework for heavy metal and PAH contamination of urban soils in Guangzhou, China

The identification and quantification of high-risk hotspots for soils contaminated by heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) remains a challenge due to their various sources and heterogeneous sink properties in urban soil systems. In this study of 221 soil samples from Guangzhou, China, a novel framework combining Bivariate local Moran’s I (BLMI), positive matrix factorization (PMF), human health risk (HHR) assessment, Monte Carlo simulation (MCS), and a newly developed spatial risk model were proposed to conduct probabilistic source-oriented HHR assessment, high-risk hotspot quantification, and risk formation mechanism elaboration. Study results indicate that traffic emissions are the largest contributor of HMs (47.6 %) and PAHs (40.2 %), but not always the largest contributor of HHR. Agricultural or urban green-space management activities of HM, and mixed source of PAH, are the largest contributors of non-carcinogenic risk (NCR, 48.7 % and 51.1 %, respectively), while mixed source of HM and traffic emissions of PAH are the largest contributors of carcinogenic risk (CR, 53.9 % and 71.2 %, respectively). The probability of risk exceeding safe threshold levels is < 5.0 % for NCR and > 90.0 % for CR. High-risk hotspots were identified in the mid-west and south of the city, making up 15.0 % of the total Guangzhou area. Risk mechanisms were deduced from the spatial heterogeneity and inter-dependence of emission sources and soil sink, based on source–sink theory. Our findings provide a new framework for precisely identifying risk sources and target areas, thereby alleviating HHR associated with co-occurring HMs and PAHs in urban soil systems.

The increase of particle size shifts the biogeochemical cycle functions of mineral-associated microorganisms and weakens the mineral-associated organic carbon sink in mangrove soils.

Carbon with stable forms, such as mineral-associated organic carbon (MOC), is crucial for the sink capabilities in mangrove soils, and mineral-associated microorganisms (MMOs) are important players for the formation and metabolism of MOC. Therefore, the future successions of the MMO functions and MOC contents under the background of climate change are of value for a deeper understanding of mangrove ecology. The relative sea level rise caused by the global warming results in the increase of mangrove soil particle size (PS), which provides distinct microcosms for MMOs and MOC. However, the responses of MMO functions and MOC content to the PS increase of mangrove soils are unknown. The current study aims to reveal the succession regulations of MMO functions and their potential ecological impacts for the storages of MOC in different PS fractions, therefore widening our knowledge of future function migration and promoting the research development of mangrove.

Dry and wet periods determine stem and soil greenhouse gas fluxes in a northern drained peatland forest

Greenhouse gas (GHG) fluxes from peatland soils are relatively well studied, whereas tree stem fluxes have received far less attention. Simultaneous year-long measurements of soil and tree stem GHG fluxes in northern peatland forests are scarce, as previous studies have primarily focused on the growing season. We determined the seasonal dynamics of tree stem and soil CH4, N2O and CO2 fluxes in a hemiboreal drained peatland forest. Gas samples for flux calculations were manually collected from chambers at different heights on Downy Birch (Betula pubescens) and Norway Spruce (Picea abies) trees (November 2020–December 2021) and analysed using gas chromatography. Environmental parameters were measured simultaneously with fluxes and xylem sap flow was recorded during the growing season. Birch stems played a greater role in the annual GHG dynamics than spruce stems. Birch stems were net annual CH4, N2O and CO2 sources, while spruce stems constituted a CH4 and CO2 source but a N2O sink. Soil was a net CO2 and N2O source, but a sink of CH4. Temporal dynamics of stem CH4 and N2O fluxes were driven by isolated emissions' peaks that contributed significantly to net annual fluxes. Stem CO2 efflux followed a seasonal trend coinciding with tree growth phenology. Stem CH4 dynamics were significantly affected by the changes between wetter and drier periods, while N2O was more influenced by short-term changes in soil hydrologic conditions. We showed that CH4 emitted from tree stems during the wetter period can offset nearly half of the soil sink capacity. We presented for the first time the relationship between tree stem GHG fluxes and sap flow in a peatland forest. The net CH4 flux was likely an aggregate of soil-derived and stem-produced CH4. A dominating soil source was more evident for stem N2O fluxes.

Reanalysis of NOAA H2 observations: implications for the H2 budget

Abstract. Hydrogen (H2) is a promising low-carbon alternative to fossil fuels for many applications. However, significant gaps in our understanding of the atmospheric H2 budget limit our ability to predict the impacts of greater H2 usage. Here we use NOAA H2 dry air mole fraction observations from air samples collected from ground-based and ship platforms during 2010–2019 to evaluate the representation of H2 in the NOAA GFDL-AM4.1 atmospheric chemistry-climate model. We find that the base model configuration captures the observed interhemispheric gradient well but underestimates the surface concentration of H2 by about 10 ppb. Additionally, the model fails to reproduce the 1–2 ppb yr−1 mean increase in surface H2 observed at background stations. We show that the cause is most likely an underestimation of current anthropogenic emissions, including potential leakages from H2-producing facilities. We also show that changes in soil moisture, soil temperature, and snow cover have most likely caused an increase in the magnitude of the soil sink, the most important removal mechanism for atmospheric H2, especially in the Northern Hemisphere. However, there remains uncertainty due to fundamental gaps in our understanding of H2 soil removal, such as the minimum moisture required for H2 soil uptake, for which we performed extensive sensitivity analyses. Finally, we show that the observed meridional gradient of the H2 mixing ratio and its seasonality can provide important constraints to test and refine parameterizations of the H2 soil sink.

Investigating the Sorption/Desorption of the Cationic Herbicide Paraquat in Clay Minerals Using Batch and Electro–Ultrafiltration Techniques

The sorption/desorption processes of the cationic herbicide paraquat (PQ) onto various clays, namely, kaolinite (KLN), illite (ILT), and montmorillonite (MNT), were investigated. After the attainment of sorption equilibrium, PQ was extracted from the clays by a double-stage desorption process utilizing an electro–ultrafiltration (EUF) procedure. The Freundlich isotherm model and a pseudo-first kinetic release model were found to adequately fit the sorption and desorption data, respectively. The experimental maximum sorbable amounts of paraquat were 5.56, 31.88, and 91.63 mg g−1 for KLN, ILT, and MNT, respectively, consistently with the order of magnitude of the cation-exchange capacity (CEC) of the clay minerals. The desorption experiments revealed that the amounts of PQ retained by the MNT samples were significantly larger than the respective amounts retained by KLN or ILT. The EUF-PQ desorption patterns of differently cation-saturated MNT samples indicated that the presence of monovalent cations could further hamper PQ release, while the opposite seemed to be true for divalent cations. Our results clearly show that a substantial aliquot of PQ is strongly retained by montmorillonite, probably via interlayering, thus suggesting that smectitic clays could act as a stable soil sink for cationic herbicides such as paraquat, favoring soil long-term contamination.

Dispersal of microbes from grassland fire smoke to soils.

Wildland fire is increasingly recognized as a driver of bioaerosol emissions, but the effects that smoke-emitted microbes have on the diversity and community assembly patterns of the habitats where they are deposited remain unknown. In this study, we examined whether microbes aerosolized by biomass burning smoke detectably impact the composition and function of soil sinks using lab-based mesocosm experiments. Soils either containing the native microbial community or presterilized by γ-irradiation were inundated with various doses of smoke from native tallgrass prairie grasses. Smoke-inundated, γ-irradiated soils exhibited significantly higher respiration rates than both smoke-inundated, native soils and γ-irradiated soils exposed to ambient air only. Microbial communities in γ-irradiated soils were significantly different between smoke-treated and control soils, which supports the hypothesis that wildland fire smoke can act as a dispersal agent. Community compositions differed based on smoke dose, incubation time, and soil type. Concentrations of phosphate and microbial biomass carbon and nitrogen together with pH were significant predictors of community composition. Source tracking analysis attributed smoke as contributing nearly 30% of the taxa found in smoke-inundated, γ-irradiated soils, suggesting smoke may play a role in the recovery of microbial communities in similar damaged soils. Our findings demonstrate that short-distance microbial dispersal by biomass burning smoke can influence the assembly processes of microbial communities in soils and has implications for a broad range of subjects including agriculture, restoration, plant disease, and biodiversity.

Estimation of Carbon and Nitrogen Contents in Forest Ecosystems in the Background Areas of the Russian Arctic (Murmansk Region)

In this study, carbon and nitrogen contents in the undisturbed terrestrial ecosystems in the northern taiga zone of Russia’s Murmansk region were estimated. The goal of this study was to examine the carbon and nitrogen dynamics in atmospheric precipitation, assimilating organs of coniferous trees (Picea obovata and Pinus sylvestris), needle litter, soils, and soil water. The objects of our research were the most common dwarf shrub-green moss spruce forests and lichen-dwarf shrub pine forests of the boreal zone. The study was carried out on permanent plots between 1999 and 2020. The long-term dynamics of carbon concentrations in snow demonstrated a trend towards increasing carbon concentrations in forested and treeless areas of the Murmansk region. It was shown that in representative spruce and pine forests, the concentrations and atmospheric precipitation of carbon compounds and carbon leaching with soil water were higher below the tree crowns, compared to between the crowns. In soil water, a decrease was found in carbon concentration with the soil profile depth. For soils, the highest carbon concentrations were found in the organic and illuvial soil horizons. The main soil sinks of carbon and nitrogen in northern taiga forests were found to be located in the organic soil horizon below the crowns. In northern taiga forests, the carbon content of living Picea obovata and Pinus sylvestris needles and Pinus sylvestris needle litter had minor variability; no significant interbiogeocoenotic and age differences were found. We found that the nitrogen content in brown needles and needle litter was significantly lower compared to photosynthetically active needles, probably due to retranslocation processes (withdrawal before needle abscission), corroborating the literature in the results session. The largest stocks of carbon and nitrogen in northern taiga forests are concentrated in the soil organic horizon, and the removal of these elements with soil water is insignificant. Carbon and nitrogen stocks in living and fallen needles are lower than in soil. The least amount of carbon and nitrogen is contained in atmospheric precipitation.

Decoupling of nitrogen, phosphorus, and carbon release from fine and coarse roots during 7 years of decomposition

Abstract Below‐ground litter decomposition represents an important source of the limiting nutrients nitrogen (N) and phosphorus (P) to forest soils, but roots also immobilize these nutrients during the decomposition process. Despite clear implications for soil fertility, the rates and drivers of nutrient immobilization and release (as the percent of increase and decrease of the initial pool) from root litter remain poorly understood, especially in coarse roots (&gt;2 mm diameter). To address this gap, we conducted a 7‐year field decomposition experiment using roots from three species, across five diameter classes (&lt;1, 1–2, 2–5, 5–10 and 10–20 mm) in a temperate forest. Nitrogen dynamics were largely decoupled with P and carbon (C) over the course of the experiment, and both varied by species and root diameter. Roots released P to the surrounding soil within the first year of decomposition. In contrast, roots immobilized N for much longer, with the coarsest roots remaining a net N sink after 7 years. Long‐term N release was jointly controlled by initial nutrient and C quality, whereas P release and decomposition rate were better predicted by initial C quality. Initial root nutrients well predicted the difference between long‐term N versus P release. Synthesis. Our results highlight the fact that N and P dynamics should be considered separately when modelling nutrient release during root decomposition, and suggest that the functional diversity of below‐ground biomass may have considerable afterlife effects on the relative availability of N and P in soil. We conclude that root litter, especially coarse root litter, represents an underappreciated N sink in forest soils.

Temporal Variability in Soil Greenhouse Gas Fluxes and Influencing Factors of a Primary Forest on the Eastern Qinghai-Tibetan Plateau

Soil greenhouse gas (GHG) fluxes relate to soil carbon and nitrogen budgets and have a significant impact on climate change. Nevertheless, the temporal variation and magnitude of the fluxes of all three major GHGs (CO2, CH4 and N2O) and their influencing factors have not been elucidated clearly in primary forests on the eastern Qinghai-Tibetan Plateau. Herein, field chamber GHG fluxes from May to November, soil microbial community and enzyme activity were analyzed in a fir-dominated (Abies fargesii var. faxoniana) primary forest. The emission rates of CO2 and N2O ranged between 64.69–243.22 mg CO2 m−2 h−1 and 1.69–5.46 ug N2O m−2 h−1, exhibiting a temporally unimodal pattern with a peak in July. The soil acted as a CH4 sink, and the uptake rate varied between 52.96 and 84.67 μg CH4 m−2 h−1 with the higher uptake rates in June and November. The temporal variation in the CO2 flux was significantly correlated with the geometric mean of enzyme activities, suggesting that the soil CO2 flux was determined by microbial activity rather than soil microbial biomass. The soil N2O flux was positively related to nitrate concentration with marginal significance, probably because N2O was a byproduct of nitrification and denitrification processes. The soil CH4 uptake was closely associated with methanotrophic biomass (18:1ω7c). The results highlight divergent temporal dynamics of GHG fluxes owing to different driving mechanisms and an important CH4 sink in the primary forest soil, helping to evaluate the carbon and nitrogen budgets of primary forests on the eastern Qinghai-Tibetan Plateau.

Functional analysis of bacterial genes accidentally packaged in rhizospheric phageome of the wild plant species Abutilon fruticosum

The study aimed to reveal the structure and function of phageome existing in soil rhizobiome of Abutilon fruticosum in order to detect accidentally-packaged bacterial genes that encode Carbohydrate-Active enZymes (or CAZymes) and those that confer antibiotic resistance (e.g., antibiotic resistance genes or ARGs). Highly abundant genes were shown to mainly exist in members of the genera Pseudomonas, Streptomyces, Mycobacterium and Rhodococcus. Enriched CAZymes belong to glycoside hydrolase families GH4, GH6, GH12, GH15 and GH43 and mainly function in D-glucose biosynthesis via 10 biochemical passages. Another enriched CAZyme, e.g., alpha-galactosidase, of the GH4 family is responsible for the wealth of different carbohydrate forms in rhizospheric soil sink of A. fruticosum. ARGs of this phageome include the soxR and OleC genes that participate in the “antibiotic efflux pump” resistance mechanism, the parY mutant gene that participates in the “antibiotic target alteration” mechanism and the arr-1, iri, and AAC(3)-Ic genes that participate in the “antibiotic inactivation” mechanism. It is claimed that the genera Streptomyces, which harbors phages with oleC and parY mutant genes, and Pseudomonas, which harbors phages with soxR and AAC(3)-Ic genes, are approaching multidrug resistance via newly disseminating phages. These ARGs inhibit many antibiotics including oleandomycin, tetracycline, rifampin and aminoglycoside. The study highlights the possibility of accidental packaging of these ARGs in soil phageome and the risk of their horizontal transfer to human gut pathogens through the food chain as detrimental impacts of soil phageome of A. fruticosum. The study also emphasizes the beneficial impacts of phageome on soil microbiome and plant interacting in storing carbohydrates in the soil sink for use by the two entities upon carbohydrate deprivation.

Major carbon losses from degradation of Mauritia flexuosa peat swamp forests in western Amazonia

AbstractTropical peat swamp forests are major global carbon (C) stores highly vulnerable to human intervention. In Peruvian Amazonia, palm swamps, the prevalent peat ecosystem, have been severely degraded through recurrent cutting of Mauritia flexuosa palms for fruit harvesting. While this can transform these C sinks into significant sources, the magnitude of C fluxes in natural and disturbed conditions remains unknown. Here, we estimated emissions from degradation along a gradient comprising undegraded (Intact), moderately degraded (mDeg) and heavily degraded (hDeg) palm swamps. C stock changes above- and below-ground were calculated from biomass inventories and peat C budgets resulting from the balance of C outputs (heterotrophic soil respiration (Rh), dissolved C exports), C inputs (litterfall, root mortality) and soil CH4 emissions. Fluxes spatiotemporal dynamics were monitored (bi)monthly over 1–3 years. The peat budgets (Mg C ha−1 year−1) revealed that medium degradation reduced by 88% the soil sink capacity (from − 1.6 ± 1.3 to − 0.2 ± 0.8 at the Intact and mDeg sites) while high degradation turned the soil into a high source (6.2 ± 0.7 at the hDeg site). Differences stemmed from degradation-induced increased Rh (5.9 ± 0.3, 6.2 ± 0.3, and 9.0 ± 0.3 Mg C ha−1 year−1 at the Intact, mDeg, and hDeg sites) and decreased C inputs (8.3 ± 1.3, 7.1 ± 0.8, and 3.6 ± 0.7 Mg C ha−1 year−1 at the same sites). The large total loss rates (6.4 ± 3.8, 15.7 ± 3.8 Mg C ha−1 year−1 under medium and high degradation), originating predominantly from biomass changes call for sustainable management of these peatlands.

Silicon in Plants: Alleviation of Metal(loid) Toxicity and Consequential Perspectives for Phytoremediation.

For the majority of higher plants, silicon (Si) is considered a beneficial element because of the various favorable effects of Si accumulation in plants that have been revealed, including the alleviation of metal(loid) toxicity. The accumulation of non-degradable metal(loid)s in the environment strongly increased in the last decades by intensified industrial and agricultural production with negative consequences for the environment and human health. Phytoremediation, i.e., the use of plants to extract and remove elemental pollutants from contaminated soils, has been commonly used for the restoration of metal(loid)-contaminated sites. In our viewpoint article, we briefly summarize the current knowledge of Si-mediated alleviation of metal(loid) toxicity in plants and the potential role of Si in the phytoremediation of soils contaminated with metal(loid)s. In this context, a special focus is on metal(loid) accumulation in (soil) phytoliths, i.e., relatively stable silica structures formed in plants. The accumulation of metal(loid)s in phytoliths might offer a promising pathway for the long-term sequestration of metal(loid)s in soils. As specific phytoliths might also represent an important carbon sink in soils, phytoliths might be a silver bullet in the mitigation of global change. Thus, the time is now to combine Si/phytolith and phytoremediation research. This will help us to merge the positive effects of Si accumulation in plants with the advantages of phytoremediation, which represents an economically feasible and environmentally friendly way to restore metal(loid)-contaminated sites.

Soil organic carbon is a key determinant of CH4 sink in global forest soils

Soil organic carbon (SOC) is a primary regulator of the forest–climate feedback. However, its indicative capability for the soil CH4 sink is poorly understood due to the incomplete knowledge of the underlying mechanisms. Therefore, SOC is not explicitly included in the current model estimation of the global forest CH4 sink. Here, using in-situ observations, global meta-analysis, and process-based modeling, we provide evidence that SOC constitutes an important variable that governs the forest CH4 sink. We find that a CH4 sink is enhanced with increasing SOC content on regional and global scales. The revised model with SOC function better reproduces the field observation and estimates a 39% larger global forest CH4 sink (24.27 Tg CH4 yr−1) than the model without considering SOC effects (17.46 Tg CH4 yr−1). This study highlights the role of SOC in the forest CH4 sink, which shall be factored into future global CH4 budget quantification.

Enhanced soil methane oxidation in both organic layer and topsoil during the succession of subtropical forests

Although (sub)tropical forests account for 10–20% of the atmospheric methane (CH4) uptake by soils, the study of soil CH4 oxidation rates and the controlling factors during the chronosequences of forest succession remains poorly understood. The objectives of this study were to characterize the vertical distribution patterns and dynamics of CH4 oxidation among the early-, mid-, and late-successional stages of subtropical forests, and to investigate the main drivers of soil CH4 fluxes. Three successional forests soils were collected and the ambient and potential CH4 oxidation rates, the related enzymes as well as the key soil parameters were determined in the laboratory. The soils at mid- and late-successional stages functioned exclusively as a CH4 sink while the soil at early-succesional stage was either a CH4 source or sink. Soil CH4 oxidations showed significant vertical distributions along with the successional gradients. The highest rate of ambient CH4 oxidation was observed in the A-horizon of the mid-successional stage (forest age ∼ 100 years), increased by 26-fold compared to the early successional stage, while the highest rate of potential CH4 oxidation was detected in the O-horizon of the late-successional stages (forest age > 300 years), which increased the CH4 oxidation by 29% and 21% respectively compared to the early- and mid-successional stages. Soil CH4 oxidation enhanced with decreasing of soil nitrite and nitrate content but weakened with declining of soil moisture at the successional chronosequence. Collectively, subtropical forests have the potential to increase the soil sink capacity for CH4 oxidation along the successional gradient, and thereby providing the negative feedbacks to ecosystems under climate changing.

Effects of sewage sludge hydrochar on emissions of the climate-relevant trace gases N2O and CO2 from loamy sand soil

This work explores the effects of amending a loamy sand soil with hydrochars having different physicochemcial characteristics. The effects of different hydrochars on emissions of the greenhouse gases nitrous oxide (N2O) and carbon dioxide (CO2) were investigated together with the relationship between the hydrochar's mineral nitrogen content and the soil microbial biomass. Soil samples were amended with eleven different hydrochars and feedstocks having different carbon and nitrogen contents at application rates of 5 t ha−1 and 25 t ha−1. Microbial immobilization was the main mineral nitrogen sink in soil following hydrochar application. Moreover, the processing conditions applied during hydrochar production (i.e., the pyrolysis temperature and residence time) had significant effects on N2O and CO2 emissions: treatment with incubated hydrochars yielded significantly lower N2O emissions than treatment with non-carbonized feedstocks, particularly at the highest level of hydrochar application (25 t ha−1). Further analysis revealed that increasing the process temperature and residence time during hdyrochar production significantly increased the final product's total organic carbon content but reduced its content of hot water extractable carbon. Hydrochars produced with higher process temperatures and longer residence times therefore yielded lower CO2 emissions during a 44-day incubation experiment than raw feedstocks or hydrochars produced under less severe conditions. Hydrochars formed from sewage sludge at high process temperatures and with long residence times are thus promising soil additives for reducing GHG emissions.

Mapping Groundwater Potential Zone and Flood Risk Zone in the Visakhapatnam District, India.

Groundwater is a vital resource that significantly contributes to the annual supply. On the other hand, Overexploitation has resulted in a significant reduction in groundwater supplies and, in some cases, soil sinking. Therefore, it’s critical to assess the possible zone of groundwater rejuvenation to safeguard water quality and manage subsurface water systems. Potential groundwater zones are detected using RS and GIS technologies. GIS technologies were used to build the composite map. Accurate data is required to determine the criteria used to estimate the potential groundwater zone. DEM, soil, Rainfall, and LULC data are all generated by the satellites, and, at a scale of 1:50000, topo sheets are collected from the Survey of India (SOI). All the input data is combined with a weighted overlay in ArcGIS. Each of these criteria is given an appropriate ranking. The ability of various geomorphic units to store groundwater is assigned weight values. This procedure is repeated for each of the remaining layers, with the resulting layers being categorized. Extremely poor, poor, moderate, good, and exceptional are the five categories of potential groundwater zones. The method is used in a particular research area in the Visakhapatnam district. This data will help you figure out where you can get water, where water can be recharged, and where groundwater is limited.

Greenhouse-temperature induced manure driven low carbon footprint in aquaculture mesocosm

In an aquaculture system, estimates were made of soil organic carbon content, carbon burial rate, soil structure and algal productivity with the intention of examining the synergistic effects of both greenhouse gas (GHG) induced temperature and manure-driven carbon reduction potentials in sediments that depend on productivity as well as tilapia spawning responses under greenhouse mimicking conditions during winter. Different manure treatments such as cattle manure and saw dust (T1); poultry droppings and saw dust (T2); vermi-compost and saw dust (T3); mixture of cattle manure, poultry droppings, vermi-compost and saw dust (T4); iso-carbonic states maintained with vermi-compost (T5); and with poultry droppings (T6) were applied three times (frequency of application) in the tank during the course of investigation. Different parameters like soil organic carbon, carbon burial rate, algal productivity and water quality were examined in aquaculture system. GHG effect impacted on the enhanced carbon reduction potential (44.36-62.36%) which was directly related with soil organic carbon (38.16-56.40 mg C/g) dependent carbon burial rate (0.0033-0.0118 g/cm2 per 100 days). Average carbon burial rates for different manure treatments at GHG impacted temperature (0.0071 g/cm2 per 100 days) was as high as 27.90% than at ambient air temperature (0.0054 g/cm2 per 100 days). Residual carbon or sink in soils has been increased by 8.49 to 43.11% in different treatments or 23%, on an average attributed to almost 6 °C rise in GHG mediated atmospheric temperature. The low carbon footprint potential in different treatments was conspicuous inside the polyhouse (maximum 62.36%) due to greenhouse driven temperature compared. As a positive impact of the study, breeding of tilapia occurred where in T3 100% survival occurred in close polyhouse and also exhibited maximum carbon burial rate. In this study it has been observed that one degree rise in atmospheric temperature resulted in a ~ 4% rise in residual carbon in the experimental tank. However, future work can be conducted on other different treatments and large scale application.Graphical Graphical representation of greenhouse-temperature induced manure driven carbon accumulation in aquaculture mesocosm.

Soil Moisture Control of NO Turnover and N2O Release in Nitrogen-Saturated Subtropical Forest Soils

Acid forest soils in South China experience a chronically elevated input of atmospheric nitrogen (N), turning them into hot spots for gaseous N emissions. Soil moisture is known to be a major controller for the partitioning of gaseous N loss to nitric (NO) and nitrous oxide (N2O), which may be of particular relevance in the monsoonal climate of South China. To study this partitioning in more detail, we determined gas phase kinetics of NO and N2O release during laboratory dry-out of acidic surface soils from the headwater catchment TieShanPing (TSP), situated close to Chongqing, SW China. Soils were sampled from two hydrologically distinct environments, a well-drained hill slope (HS), and a periodically flooded groundwater discharge zone (GDZ). Production and consumption of NO were studied in an automated flow-through system purged with NO-free or NO-spiked air. Production rates peaked at 21% and 18% water filled pore space (WFPS) in HS and GDZ soils, respectively, suggesting nitrification as the dominant process of NO formation in both landscape units. In HS soils, maximum production and consumption occurred at the same WFPS, whereas GDZ soils displayed maximum NO consumption at higher WFPS than maximum production, suggesting that denitrification is an important NO sink in GDZ soils. Net N2O release was largest at 100% WFPS and declined steadily during drying. Integrated over the entire range of soil moisture, potential NO-N loss outweighed potential N2O-N loss, suggesting that N-saturated, acid forest soil is an important NO source.

Soil organic carbon estimation along an altitudinal gradient of chir pine forests in the Garhwal Himalaya, India: A field inventory to remote sensing approach

AbstractChir pine (Pinus roxburghii, Sarg.) forests are dominant in the Indian Himalayan region and act as a huge carbon (C) sink. However, measuring the C sink in soil is complex and time‐intensive, and therefore the present study attempts to estimate the soil organic carbon (SOC) through a remote sensing (RS) approach. We estimated SOC stock of chir pine forests along an altitudinal gradient at three soil depths (0–30, 30–60 and 60–100 cm) in the Garhwal Himalaya, Uttarakhand. Fourteen forest stands at four altitudes, viz., &lt;1000 m above sea level (m asl), 1001–1400 m asl, 1401–1800 m asl and &gt;1801 m asl were surveyed and served for data collection. A model for predicting SOC was developed through stepwise regression analysis based on vegetation information and altitude as independent variables with the field data on SOC. For vegetation information, we used the normalized difference vegetation index (NDVI) measured through remote sensing (RS). The mean SOC stock up to 100 cm depth was increased with increasing altitude and were in the order of 69.66 ± 19.86, 85.27 ± 17.53, 95.68 ± 7.90 and 148.41 ± 71.39 million g ha−1 (million gram per hectare) for &lt;1000, 1001–1400, 1401–1800 and &gt;1801 m_asl, respectively. The result showed that NDVI was a good predictor for SOC estimation. The model predicted SOC stock between 57 and 152 million g ha−1 with a mean of 93 million g ha−1, which was close to the SOCs from field inventory. Therefore, RS could be used to precisely map the SOC stock in the chir pine forests of the Himalayas through NDVI and provide information to policymakers for forest management.

Profiling ponded soil surface in saturated seepage into drain-line sink: Kalashnikov’s method of lateral leaching revisited

Two boundary value problems are solved for potential steady-state 2D Darcian seepage flows towards a line sink in a homogeneous isotropic soil from a ponded land surface, which is not flat but profiled. The aim of this shaping is ‘uniformisation’ of the velocity and travel time between this surface and a horizontal drain modelled by a line sink. The complex potential domain is a half-strip, which is mapped onto a reference plane. Either the velocity magnitude or a vertical coordinate along the land surface are control variables. Either a complexified velocity or complex physical coordinate is reconstructed by solving mixed boundary-value problems with the help of the Keldysh-Sedov formula via singular integrals, the kernel of which are the control functions. The flow nets, isotachs and breakthrough curves are found by computer algebra routines. A designed soil hump above the drain ameliorates an unwanted ‘preferential flow’ (shortcut) and improves leaching of salinised soil of a cropfield during a pre-cultivation season.