Sorption isotherm studies of Cd(II) ions using living cells of the marine microalga Tetraselmis suecica (Kylin) Butch

The present work reports the use of living cells of the marine microalga Tetraselmis suecica for the biosorption of cadmium ions. For a better understanding of the biosorption characteristics, three fractions of removed cadmium (total, bioadsorbed and intracellular) were measured in the cells after 24 and 72 h of exposure to different initial cadmium concentrations (0.6–45 mg L^?1). Both the Langmuir and Freundlich models were suitable for describing the sorption of cadmium ions by this microalga. The maximum sorption capacity was estimated to be 40.22 mg Cd g^?1 after 72 h using the Langmuir sorption model. In the lower cadmium concentrations, metal removed intracellularly was higher than that removed on the microalgal cell surface. Therefore, the intracellular fraction contributed more to the total removed cadmium than the fraction bioadsorbed to the cellular surface. The results showed that the cadmium removal capacity using living biomass could be much more effective than with non-living biomass due to the intracellular bioaccumulation. According to the microorganism selected and its tolerance to the toxic effect of the metal, the cadmium content in the intracellular fraction can become very significant, just like it happened with Tetraselmis.     

BIOGEOCIIEMISTRY OF AN OLD-GROWTH FORESTED WATERSHED,OLYMPIC NATIONAL PARK,WASHINGTON1

ABSTRACT: The biogeochemistry of a coastal old-growth forested watershed in Olympic National Park, Washington, was examined. Objectives were to determine: (1) concentrations of major cations and anions and dissolved organic C (DOC) in precipitation, throughfall, stemflow, soil solution and the stream; (2) nutrient input/output budgets; and (3) nutrient retention mechanisms in the watershed. Stemilow was more acidic (pH 4.0–4.5) than throughfall (pH 5.1) and precipitation (pH 5.3). Organic acids were important contributors to acidity in throughfall and stemflow and tree species influenced pH. Soil solution pH averaged 6.2 at 40 cm depth. Stream pH was higher (7.6). Sodium (54.0 μeq L-¹) and Cl (57.6 μeq L^?1) were the dominant ions in precipitation, reflecting the close proximity to the ocean. Throughfall and stemflow were generally enriched in cations, especially K. Cation concentrations in soil solutions were generally less than those in stemilow. Ion concentrations increased in the stream. Dominant ions were Ca (759.7 μeq L^?1), Na (174.4 μeq L^?1), HCO₃ (592.0 μeq L^?1), and SO₄ (331.5 μeq L^?1) with seasonal peaks in the fall. Bedrock weathering strongly influenced stream chemistry. Highest average NO₃ concentrations were in the stream (5.2 μeq L^?1) with seasonal peaks in the fall and lowest concentrations in the growing season. Nitrogen losses were similar to inputs; annual inputs were 4.8 kg/ha (not including fixation) and stream losses were 7.1 kg/ha. Despite the age and successional status of the forest, plant uptake is an important N retention mechanism in this watershed.     

Bioaccumulation of Selenium by the Bryophyte Hygrohypnum ochraceum in the Fountain Creek Watershed, Colorado

Aquatic bryophytes, Hygrohypnum ochraceum, were deployed “in situ” at 14 sites in the Fountain Creek Watershed, spring and fall, 2007 to study selenium (Se) accumulation. Dissolved, total, and pore (sediment derived) water samples were collected and water quality parameters determined while plants were exposed to the water for 10?days. There was a trend showing plant tissue-Se uptake with distance downstream and we found a strong correlation between Se in the water with total hardness in both seasons. There was a modest association between Se-uptake in plants with hardness in the spring of 2007 but not the fall. Plants bioconcentrated Se from the water by a factor of 5.8?×?10³ at Green Mountain Falls and 1.5?×?10⁴ at Manitou Springs in the fall of 2007. Both are examples of the bioconcentration abilities of the plants, primarily in the upper reaches of the watershed where bioconcentration factors were highest. However, the mean minima and maxima of Se in the plants in each of the three watershed segments appeared similar during both seasons. We found direct relationships between the pore and dissolved Se in water in the spring (R ²?=?0.84) and fall (R ²?=?0.95) and dissolved Se and total hardness in the spring and fall (R ²?=?0.92). The data indicate that H. ochraceum was a suitable indicator of Se bioavailability and Se uptake in other trophic levels in the Fountain Creek Watershed based on a subsequent study of Se accumulation in fish tissues at all 14 sites.     

HYDROLOGIC EFFECTS OF TWO METHODS OF HARVESTING MATURE SOUTHERN PINE1

ABSTRACT: Hydrologic responses to logging with skidders and responses to logging with a cable yarder are compared. After a 23-year calibration with an undisturbed control catchment, mixed stands of shortleaf pine (Pinus echinata Mill.) and hardwoods were clearfelled on two small catchments in the hilly Coastal Plain of north Mississippi and observed for five years. Runoff increased 370 mm (skidded) and 116 mm (yarded) during the first year with 1876 mm of rainfall, and 234 mm (skidded) and 228 mm (yarded) during the second year when 1388 mm of precipitation equaled the calibration mean. Sediment concentrations for the yarded catchment during the first two years averaged 641 and 1,629 mg L^?1, respectively, and yields were 6,502 and 12,086 kg ha^?1. Compared to calibration means of 74 mg L^?1 and 142 kg ha^?1, these extreme values can be attributed largely to transport of sediment stored in the channel and to erosion of subsurface flow paths, which was exacerbated by high flow volumes. During the first year, the concentration (231 mg L^?1) and yield (2,827 kg ha^?1) for the control catchment also exceeded the calibration means. However, concentrations (134 mg L^?1) and yields (1,806 kg ha^?1) for the skidded catchment were about 40 percent lower than for the control catchment during the first year, and were higher than those for the control only during the second year. Because deep percolation was limited and because rainfall was unusually high, increases in flows and sediment concentrations and yields probably approximate maximum responses to clearcut harvesting in the uplands of the southern Coastal Plain.     

Effect of salinity on metal-complex dye biosorption by Rhizopus arrhizus

In this study the biosorption of Yellow RL, a metal-complex anionic dye, by dried Rhizopus arrhizus, a filamentous fungus, was investigated as a function of initial solution pH, initial dye concentration and initial salt (sodium chloride) concentration. The fungus exhibited the maximal dye uptake at pH 2 in the absence and in the presence of salt. Dye uptake increased with the dye concentration up to 1000 mg l^?1 and diminished considerably in the presence of increasing concentrations of salt up to 50 g l^?1. The fungus biosorbed 85.4 mg dye g^?1of dried biomass at 100 mg l^?1 initial dye concentration in the absence of salt. When 50 g l^?1 salt was added to the biosorption medium, this value dropped to 60.8 mg g^?1 resulting in 28.8% reduction in biosorption capacity. The Redlich–Peterson and Langmuir–Freundlich were the most suitable adsorption models for describing the biosorption equilibrium data of the dye both individually and in salt containing medium. The pseudo-second-order and saturation type kinetic models depicted the biosorption kinetics accurately for all cases studied. Equilibrium and kinetic constants varied with the level of salt were expressed as a function of salt concentration.     

Nitrate transport in shallow groundwater at the stream–riparian interface in an urbanizing catchment

Drive point peizometers were installed at the stream–riparian interface in a small urbanizing southern Ontario catchment to measure the effect of buffers (presence/ absence) and land use (urban/agricultural) on the movement of NO^? ₃-N in shallow groundwater from the riparian area to the stream. Mean NO^? ₃-N concentrations ranged from 1.0 to 1.3 mg L^?1 with maximum values of 9.4 mg L^?1. Holding land use constant, there was no significant difference (p>0.05) in NO^? ₃3-N concentration between buffered and unbuffered sites. Nitrate-N levels were not significantly different (p>0.05) as a function of land use. The lack of difference between sites as a function of buffer absence/presence and land use is probably due to the placement of some peizometers in low conductivity materials that limited groundwater flow from the riparian zone to the stream. Subsurface factors controlling the hydraulic gradient are important in defining buffer effectiveness and buffer zones should not be used indiscrim inately as a management tool in urban and agricultural landscapes to control nitrate-N loading in shallow groundwater to streams without detailed knowledge of the hydrogeo logic environment.     

Leaching composted lignocellulosic wastes to prepare container media: Feasibility and environmental concerns

The leaching of salt and mineral elements from three composts prepared with residual vegetable crop biomass (melon, pepper or zucchini) was studied using methacrylate columns and distilled water. The benefits of the leached composts to be used for ornamental potted plant production were also analysed. After leaching 5 container capacities of effluent, both the electrical conductivity and the concentration of soluble mineral elements in compost leachates decreased substantially and remained close to the target levels. Composts reacted differently to leaching due to differences in the raw waste sources and the composting process and hence, in their physical and chemical characteristics. At the end of the experiment, after pouring 8 container capacities of water, the leaching efficiency of the salts was 96%, 93% and 87% for melon, pepper and zucchini-based composts, respectively. Mineral elements differed in their ability to be removed from the composts; N (NH₄⁺ and NO₃^?), K⁺, Na⁺, Cl^?, and SO₄^2? were leached readily, whereas H₂PO₄^?, Ca²⁺, and Mg²⁺ were removed hardly. Leached composts showed a range of physico-chemical and chemical characteristics suitable for use as growing media constituents. Potted Calendula and Calceolaria plants grew in the substrates prepared with the leached composts better than in those made with the non-leached ones. Finally, special emphasis must be paid to the management of the effluents produced under commercial conditions to avoid environmental pollution.     

Surface water and wastewater treatment using a new tannin-based coagulant. Pilot plant trials

A new tannin-based coagulant-flocculant (Tanfloc) was tested for water treatment at a pilot plant level. Four types of water sample were treated: surface water (collected from a river), and municipal, textile industry (simulated by a 100 mg L^?1 aqueous solution of an acid dye), and laundry (simulated by a 50 mg L^?1 aqueous solution of an anionic surfactant) wastewaters. The pilot plant process consisted of coagulation, sedimentation, and filtration. The experiments were carried out with an average coagulant dosage of 92.2 mg L^?1 (except in the case of the surface water for which the dosage was 2 mg L^?1). The efficacy of the water purification was notable in every case: total turbidity removal in the surface water and municipal wastewater, about 95% dye removal in the case of the textile industry wastewater, and about 80% surfactant removal in the laundry wastewater. Filtration improved the removal of suspended solids, both flocs and turbidity, and slightly improved the process as a whole. The efficiency of Tanfloc in these pilot studies was similar to or even better than that obtained in batch trials.     

STREAM WATER CHEMISTRY IN WATERSHEDS RECEIVING DIFFERENT ATMOSPHERIC INPUTS OF H+, NH4, NO3−, AND SO42−1

ABSTRACT: Weekly precipitation and stream water samples were collected from small watersheds in Denali National Park, Alaska, the Fraser Experimental Forest, Colorado, Isle Royale National Park, Michigan, and the Calumet watershed on the south shore of Lake Superior, Michigan. The objective was to determine if stream water chemistry at the mouth and upstream stations reflected precipitation chemistry across a range of atmospheric inputs of H⁺, NH₄⁺, NO₃^?_?, and SO₄^2?. Volume-weighted precipitation H⁺, NH₄⁺, NO₃^?_?, and SO₄^2? concentrations varied 4 to 8 fold with concentrations highest at Calumet and lowest in Denali. Stream water chemistry varied among sites, but did not reflect precipitation chemistry. The Denali watershed, Rock Creek, had the lowest precipitation NO₃^?_? and SO₄^2? concentrations, but the highest stream water NO₃^?and SO₄^2? concentrations. Among sites, the ratio of mean monthly upstream NO₃^?_? concentration to precipitation NO₃^?_- concentration declined (p < 0.001, R²= 0.47) as precipitation NO₃^?_? concentration increased. The ratio of mean monthly upstream to precipitation SO₄^2? concentration showed no significant relationship to change in precipitation SO₄^2? concentration. Watersheds showed strong retention of inorganic N (> 90 percent inputs) across inputs ranging from 0.12 to > 6 kg N ha^?1 y^?1. Factors possibly accounting for the weak or non-existent signal between stream water and precipitation ion concentrations include rapid modification of meltwater and precipitation chemistry by soil processes, and the presence of unfrozen soils which permits winter mineralization and nitrification to occur.     

Can Land Managers Control Japanese Knotweed? Lessons from Control Tests in Belgium

Japanese knotweed Fallopia japonica is an extremely abundant invasive plant in Belgium and surrounding countries. To date, no eradication method is available for land managers facing the invasion of this rhizomatous plant. We tested different chemical herbicides with two application methods (spraying and stem injection), as well as mechanical treatments, on knotweed clones throughout southern Belgium. The tested control methods were selected to be potentially usable by managers, e.g., using legally accepted rates for herbicides. Stem volume, height and density reduction were assessed after one or two years, depending on the control method. Labor estimations were made for each control method. No tested control method completely eradicated the clones. Stem injection with glyphosate-based herbicide (3.6?kg?ha^?1 of acid equivalent glyphosate) caused the most damage, i.e., no sprouting shoots were observed the year following the injection. The following year, though, stunted shoots appeared. Among the mechanical control methods, repeated cuts combined with native tree transplanting most appreciably reduced knotweed development. The most efficient methods we tested could curb knotweed invasion, but are not likely to be effective in eradicating the species. As such, they should be included in a more integrated restoration strategy, together with prevention and public awareness campaigns.     

Tolerance and phytoremediation potential of Calopogonium mucunoides to boron

Soil contamination by trace elements (TEs) is a problem of great concern since the industrial revolution. However, not all TEs are essentially toxic, and several micronutrients such as boron (B) play essential roles during plant development and, in this case, B acts in plants as a structural element. Soil B levels above 3.0 mg dm^–3 may be toxic to many plants and the greatest input of B to the environment occurs through the anthropic way. An environmentally promising alternative is phytoremediation, in which contaminant‐tolerant plants are used to remove or stabilize TEs in soils. Therefore, this work has been carried out to aim C. mucunoides’ tolerance to increasing B concentrations and its potential as a phytoremediator. We found out that C. mucunoides tolerates B doses up to 480 mg dm^?3, the B uptaken is transported at a 1:1 ratio between root and shoot, suggesting that C. mucunoides can be used as a phytostabilizer and phytoextractor due to its potential to be used in phytoremediation techniques because it can tolerate toxic concentrations of B.     

Resource utilization of wasted black pulping liquor for biodiesel production by Scenedesmus obliquus

The possibility of application of black liquor for oil-riched algae cultivation is inspected. The results show that after ligin removal and enzymatic hydrolysis, the hydrolysate of black liquor contained 9.18 g L^?1 of reducing sugar. When the hydrolysate was used for Scenedesmus obliquus (S. obliquus) cultivation, a 1.23 g L^?1, 24.52%, and 23.20 mg L^?1d^?1 was obtained for growth yield, oil content, and the lipid productivity, seperately. The hemicellulose was extracted from black liquor and hydrolyzed. With addition of 3 g L^?1 yeast extract, the growth yield of S. obliquus in hemicellulose hydrolysate increased to 2.7 g L^?1, an increase of 26.8% than that of in glucose medium, oil content was 25.7% and the final lipid productivity reached 53.37 mg L^?1d^?1. The results indicate that black liquor can not be directly used by microalgae, but with approprate treatment, the carbohydrate of it could be recovered and uitilized for the oil production from microalgae.     

Decontamination of water polluted by heavy metals with Taro (Colocasia esculenta) cultured in a hydroponic NFT system

The toxicity and bioaccumulation of two heavy metals—lead (Pb) and cadmium (Cd)—in a semi-aquatic plant, Colocasia esculenta (L. Schott), from a synthetic heavy metal solution were studied. Young plants of equal size were grown hydroponically in shallow raceways containing Hoagland medium amended with 20, 40, and 60 mg l^?1 of Pb and 2, 4, and 6 mg l^?1 of Cd. The medium containing heavy metals was allowed to flow through the raceways with a change in influent heavy metal solution on every 5th day. The experiment was continued for 20 days. A set of control raceways—one comprised of nutrient medium with heavy metal supplements, devoid of plants, and another with the plants and nutrient medium having no metal supplement—was also simultaneously run. Chlorosis in the leaves was the prominent toxicity symptom observed due to Pb and Cd on the test plants. A significant decrease in the relative growth, biomass productivity, and total chlorophyll content were noticed in the plants with an increase in concentration of metal supplement in the solution and exposure time. Both metals accumulated to higher concentrations in the roots than in shoots, suggesting that the metals were bound to the root cells and their translocation to the leaves was limited. The results of the 20-day-long experiments indicate that from a phytoremediation perspective, C. esculenta is a promising plant species for remediation of wastewater polluted with lower concentrations of Pb and Cd.     

Treatment and toxicity evaluation of methylene blue using electrochemical oxidation,fly ash adsorption and combined electrochemical oxidation-fly ash adsorption

Treatment of a basic dye, methylene blue, by electrochemical oxidation, fly ash adsorption, and combined electrochemical oxidation-fly ash adsorption was compared. Methylene blue at 100 mg L^?1 was used in this study. The toxicity was also monitored by the Vibrio fischeri light inhibition test.When electrochemical oxidation was used, 99% color and 84% COD were removed from the methylene blue solution in 20 min at a current density of 428 A m^?2, NaCl of 1000 mg L^?1, and pH₀ of 7. However, the decolorized solution showed high toxicity (100% light inhibition).For fly ash adsorption, a high dose of fly ash (>20,000 mg L^?1) was needed to remove methylene blue, and the Freundlich isotherm described the adsorption behavior well.In the combined electrochemical oxidation-fly ash adsorption treatment, the addition of 4000 mg L^?1 fly ash effectively reduced intermediate toxicity and decreased the COD of the electrochemical oxidation-treated methylene blue solution. The results indicated that the combined process effectively removed color, COD, and intermediate toxicity of the methylene blue solution.     

Environmental implications of Biological spectrum vis-à-vis tree species diversity in two protected forests (PFs) of Gandhamardan hill ranges, Eastern Ghats, India

Environmental implications of Biological spectrum vis-à-vis tree species diversity in two protected forests of Gandhamardan hill ranges of Eastern Ghats, India, are of great ecological significance in the perspective of climatic change. Biological spectrum includes phanerophytes (38.4?%), nanophanerophytes (11.4?%), chamaephytes (5.5?%), hemicryptophytes (2.4?%), geophytes (4.1?%), hydrophytes (0.7?%), therophytes (27.3?%), and lianas (10?%). The comparison with Raunkiaer??s normal spectrum depicts ??Phanero-Therophytic Phytoclimate??. The present study enlisted of a total of 10,775 trees belonging to 90 tree species within a 17.6?ha sampled area (441 plots). The Shannon?CWeiner index (H??) is 3.92 (Site-I) and 3.31 (Site-II) with Simpson??s value 1.0. This value indicates that the tropical moist deciduous forests are also species diverse systems. Mean stand density was 671?ha^?1 in Site-I and 565?ha^?1 in Site-II. Ascertaining the phytoclimate of Gandhamardan hill ranges vis-à-vis tree species diversity and comparing the area on a geographical scale would be helpful for conservation and management of the study area.     

A study on evaluation of probable sources of heavy metal pollution in groundwater of Kalpakkam region, South India

This study investigates the heavy metal pollution vulnerability of the groundwater in the coastal aquifers of Kalpakkam region in the state of Tamilnadu, India. Integrated-approach includes pollution evaluation indices, principal component analysis (PCA), and correlation matrix (CM) to evaluate the intensity and source of pollution in groundwater. The data have been used for the calculation of heavy metal pollution index (HPI) and degree of contamination (C _d). The mean metal levels in groundwater followed a descending order as: Zn?>?Ba?>?Fe?>?Al?>?Se?>?Mn?>?Cu?>?Ni?>?Pb?>?Cr?>?Mo?>?As?>?Cd?>?Sb?>?Be. The concentrations of Fe, Cd, Zn, Se, Ba, Mn, Ni, Pb, and Al in some of the groundwater samples exceed the maximum admissible concentration (MAC). The HPI and C _d yield different results despite significant correlations between them. The following elemental associations were obtained from PCA and CM: Fe?CMn?CNi?CCr?CPb?CCd?CZn?CBe?CAl, Cu?CAs, Sb?CAs, Al?CBa and Se?CMo, which could be linked to anthropogenic sources (i.e., processes of tannery and dying industries with some contribution from the landfill leachate and municipal sewage). GIS-based factor score maps suggest that the activities of tannery industries and landfill leachate are pervasive processes in the area. This study has provided the evidence that effluents discharged from the tannery and auxiliary industries and landfill leachate are the main sources of heavy metal pollution in the groundwater. The high metal concentrations observed in the groundwater may have serious public health and potential environmental hazard implications.     

Assessment of the Hydrogeochemistry and Groundwater Quality of the Tarim River Basin in an Extreme Arid Region, NW China

The concentrations of the major and trace elements in the groundwater of the Tarim River Basin (TRB), the largest inland river basin of China, were analyzed before and during rainy seasons to determine the hydrogeochemistry and to assess the groundwater quality for irrigation and drinking purposes. The groundwater within the TRB was slightly alkaline and characterized by high ionic concentrations. The groundwater in the northern sub-basin was fresh water with a Ca²⁺–HCO₃ ^? water type, whereas the groundwater in the southern and central sub-basins was brackish with a Na⁺–Cl^? water type. Evaporite dissolution and carbonate weathering were the primary and secondary sources of solutes in the groundwater within the basin, whereas silicate weathering played a minor role. The sodium adsorption ratio (SAR), water quality index (WQI), and sodium percentage (%Na) indicated that the groundwater in the northern sub-basin was suitable for irrigation and drinking, but that in the southern and central sub-basins was not suitable. The groundwater quality was slightly better in the wet season than in the dry season. The groundwater could be used for drinking after treatment for B³⁺, F^?, and SO₄ ^2? and for irrigation after control of the sodium and salinity hazards. Considering the high corrosivity ratio of the groundwater in this area, noncorrosive pipes should be used for the groundwater supply. For sustainable development, integrated management of the surface water and the groundwater is needed in the future.     

Light Availability Prevails Over Soil Fertility and Structure in the Performance of Asian Knotweeds on Riverbanks: New Management Perspectives

Asian knotweeds (Fallopia spp.) are considered one of the world’s most invasive species. Restoring habitats dominated by these exotic species requires a better understanding of the importance of abiotic factors controlling the invasive knotweeds performance. We used observational data obtained on the embankment of the Isère River (France) to study the performance of Fallopia spp. under different soil, light, and disturbance conditions. On the Isère riverbanks, light intensity assessed by light quantity transmitted through canopy was the most important factor explaining the variability observed on knotweed performance expressed as above-ground biomass per square meter. Asian knotweeds were more productive under intensive light conditions. Alternatively other factors such as mowing (twice a year), soil fertility, soil texture, position on the bank or exposure to the sun had no significant effect on knotweed biomass production. We conclude that decreasing light resources, for example, by increasing competitive pressure on sites dominated by Asian knotweeds could be included in management plans to control the populations of this invasive taxon.     

SPATIAL DELINEATION OF BIOTIC AND ABIOTIC GRADIENTS IN A RURAL NEW YORK RESERVOIR1

ABSTRACT: The spatial changes in abiotic and biotic variables from riverine to lacustrine areas characterized by the river-lake concept of reservoir function was applied to the Tomhannock Reservoir, Rensselaer County, New York. To identify these longitudinal gradients, a two-year investigation (May 1991 to October 1992) was conducted to measure primary productivity, nutrient concentrations, chlorophyll α and phytoplankton biomass at three locations in the 705-ha water supply reservoir. Emphasis was placed on the measurement of primary production using the carbon-14 artificial incubator (photosynthetron) technique. The average annual production in 1992 was 247.3 gm^?2 245 d^?1, ranging from 52 to 2677 mg C m^?2. Mean alpha^B (assimilation efficiency), P^Bm (assimilation number), and I_k (saturation irradiance) were 4.40 mg C mgChl^?1 E^?1 m^?2, 3.82 mg C mgChl^?1 h^?1, and 236.5 μE m^?2 s^?1, respectively. Neither seasonal nor spatial variability of these photosynethetic parameters were observed. Except for Secchi depth, distinct longitudinal zones from river inflow to darn were not statistically demonstrated in the Tomhannock Reservoir. Mean extinction coefficient, chlorophyll α and total phosphorus concentrations decreased; Secchi transparency and phytoplankton biomass increased; while primary productivity and dissolved inorganic nitrogen concentration remained the same from headwater to darn. These baseline data will be used to assess the future effectiveness of best management practices (BMPs) recently instituted on selected watershed farmland in an attempt to reduce the detrimental impact of agricultural activities on drinking water quality.     

Seasonal dynamics in earthworm density, casting activity and soil nutrient cycling under Bermuda grass (Cynodon dactylon) in semiarid tropics, India

This work illustrates the result of a study on earthworm abundance, seasonal population dynamics and casting activities under Bermuda grass cover in a semiarid tropical part of Rajasthan, India. The earthworm abundance and their casting activities showed the drastic variation during different seasons. The maximum density (individual m^?2) of earthworms was recorded in autumn (87.0?±?7.2) and minimum in winter (5.3?±?3.2) season in grassland. There was also variation in temperature and moisture of canopy soil in different seasons of the experimental year. The casting activities of earthworm also showed variations among different seasons. The maximum cast production rate was recorded during autumn (690.0?±?78.0?g?m^?2) while in winter (17.3?±?5.1?g?m^?2), earthworms showed the lowest cast production rate. The chemical composition of worm casts and parental soil layers (topsoil: 0?C10?cm depth and subsoil: 10?C25?cm depth) in grassland ecosystem was also monitored. The earthworm casts collected during winter showed the maximum level of total N (0.890?g?kg^?1), available P (0.373?g?kg^?1), exchangeable K (0.835?g?kg^?1), exchangeable Ca (7.10?g?kg^?1) and exchangeable Mg level (5.93?g?kg^?1) while the maximum organic C content (5.27?g?kg^?1) was recorded in surface casts deposited in rainy season. The level of major soil nutrients was also high in worm casts than parental soil and indicates the earthworm-mediated nutrient mineralization and organic matter transformation. Results thus clearly suggest the major role of earthworm in soil nutrient transformation in semiarid ecosystem.