Dipak Sarkar

Spatiotemporal variation in benthic polychaetes (Annelida) and relationships with environmental variables in a tropical estuary

Annelida constitute a dominant functional component in soft-bottom macrobenthic communities and reveal a wide range of adaptability to different marine and coastal habitats. Analyses in different polychaete assemblages and their responses to habitat conditions reflect the biological effects of marine pollution and habitat disturbance. The present study is designed to study colonization and community structure of polychaetes in two ecologically distinct locations of the Sundarban Biosphere Reserve on the northeast coast of India. Polychaete assemblages are characteristically different at the two sites in the extreme northern (Ghusighata) and southern (Gangasagar) portions of the Biosphere Reserve. Levels of heavy metals in polychaete body tissues also reveal interspecific and regional variations. The predominant polychaete fauna exhibited a distinct and unique assemblage of two types: (i) Mastobranchus indicus – Dendronereides heteropoda in the sewage-fed substratum at Ghusighata and (ii) Lumbrinereis notocirrata – Ganganereis sootai – Glycera tesselata at Gangasagar at the mouth of the Hugli estuary where chronic anthropogenic stress and contamination with agricultural and industrial effluents occur. The faunistic composition of polychaetes and their potential for the accumulation of heavy metals from the ambient medium are distinctly different. The study demonstrates that textural composition of the sediments, together with hydrodynamic and geotechnical properties, seem to have the greatest control to quantify the differences of the polychaete community in the two study stations. An in-depth comparative study of polychaete community structure at multiple spatial scales is strongly recommended for future environmental impact assessment in this fragile environment.

Site-Specific Nutrient Management (SSNM): A Unique Approach Towards Maintaining Soil Health

Agricultural production in India has increased from ~50 Mt in 1950 to ~251 Mt in 2011–2012 by the intensive use of external inputs. The negative nutrient balance due to the imbalanced fertilization to the tune of ~8–10 Mt is reported, resulting in nutrient mining, stagnation and/or deceleration in productivity and soil health decline. The indispensable role of geo-informatics (RS, GPS and GIS) aided site-specific nutrient management (SSNM) for efficient use of resources and nutrients is suggested for achieving the projected food production target ~300 Mt by 2025. Towards the better response of SSNM over blanket fertilizer recommendation in terms of nutrient use efficiency (NUE), productivity and profitability is reported and discussed under Indian context. Long-term pooled data across several locations in India revealed an increase in yield of rice and wheat crops by ~12 and 17% and profitability by ~14 and 13%, respectively as an outcome of SSNM. Web based farmers’ advisory launched recently in the state of West Bengal is reported. The development of such dissemination mechanisms that consolidates the complex and knowledge-intensive SSNM information into simple delivery system is suggested for rapid implementation by the farmers towards maintaining soil health and ensuring future generation food security.

Soil resource appraisal towards land use planning using satellite remote sensing and gis a case study in patloinala micro-watershed, district puruliya, west bengal

Visual interpretation of IRS ID LISS-III fused with PAN data (1:12,500 scale) ofPatloinala micro-watershed of Puruliya district, West Bengal was carried out for delineating the physiographic units based on the variations in image characteristics. The major physiographic units identified were upland(Tanr), medium land(Baid), and low land(Bahal andKanali). The satellite remote sensing data coupled with ground truth were translated in terms of soils using composite interpretation map as base. The abstraction level attained was phases of soil series based on Soil Taxonomy. On the basis of physiographic variation and soil or soil site characteristics such as texture, depth, slope, erosion etc. the problem areas were identified and land use plan has been suggested for the overall development of the micro-watershed.

Assessment of a sequential extraction procedure for fractionation of soil arsenic in contaminated soils

A sequential fractionation scheme, based on a soil phosphorous fractionation, was developed to assess the chemical nature, and thus the potential bioavailability and mobility of As, at the sites. Soil As was separated into five fractions with (i) anion exchange resin, (ii) NaHCO3, (iii) NaOH, (iv) HCl, (v) residual. Most sites contained relatively low concentrations of As in the two most labile fractions. The bulk of the contaminant As at the sites seemed to be associated with soil amorphous Fe and Al minerals and the dominant clay minerals which help in As sorption are montmorillonite and mica. Resin-extractable As in particular might provide a good index of potential As bioavailability and mobility.

Hazard assessment of heavy metal contamination by the paper industry, north-eastern India

The spatial distribution and hazard assessment of heavy metals in the paper mill contaminated area of Jagiroad, Assam, India were investigated using statistics, geostatistics and geographic information system techniques. The amounts of Cr, Cd, Ni and Pb were determined from 188 samples collected within the contaminated area. Log-transformation was applied in order to achieve normality in the data-set. The ordinary kriging estimates of Cr, Cd, Ni and Pb maps showed that high concentrations of heavy metals were located in the low-lying areas like bils (lakes). Indicator kriged probability maps of soil Cr, Cd, Ni and Pb were prepared based on the concentrations to exceed the respective Food and Agriculture Organization maximum permissible limit (MPL) value of 100, 3, 30 and 50 mg/kg, respectively. It was seen that more than 80% of the studied area has a higher than 50% probability to exceed the MPL value of Ni. Smaller areas in the north and west side of the study area displayed a higher concentration than the MPL value of Pb. For Cr, only a small portion at the centre of the study area had a higher concentration than the MPL value. In an attempt to identify the source of heavy metals through multivariate analysis, it was concluded that Cr, Ni and Pb mainly originated from paper mill effluent and soil Cd was associated with natural concentration.

Differences in Soil Properties Between Irrigation and Cropping Sequences in the Thar Desert of India

Watering is known to convert deserts into oases. However, information on how irrigation brings changes in physical and chemical properties of soils in a desert biome is not yet known, though pertinent to land use planning. This study reports influence of irrigation and cropping sequence on physico-chemical properties of soils in the Thar Desert, Rajasthan, India. Treatments included three irrigation conditions (not irrigated, low-irrigated, and high-irrigated) and eleven cropping sequences, cotton-gram (C-G), mung bean-mustard (M-Mu), moth bean-wheat (Mo-W), moth bean-mustard (Mo-Mu), cotton-fallow (C-F), cotton-wheat (C-W), cotton-mustard (C-Mu), mung bean-wheat (M-W), moth bean-fallow (Mo-F), mung bean-fallow (M-F), and pearl millet-fallow (P-F). The irrigation reduced soil temperature (9.7 to 12.2%) and bulk density (5.3 to 6.6%), but increased silt (5.1 to 7.2%) and clay (3.8 to 5.4%) content, water holding capacity (50 to 58.3%), moisture content at field capacity (100 to 133.3%), concentration (2.3 to 3.1 times), and stock (2.2 to 3.0 times) of soil organic carbon (SOC), microbial biomass carbon (4 to 8 times), available phosphorus (1.82 to 2.1 times), and potassium (25.9 to 67.1%). These changes were higher in the high-irrigated than the low-irrigated conditions. Cropping sequences C-W, C-Mu, and C-G sequestered more SOC and retained higher microbial biomass carbon, whereas M-Mu, Mo-W, Mo-Mu and M-W maintained the highest level of phosphorus and potassium. These observations suggest that irrigation and cropping sequence are promising management options for enhancing carbon sequestration in soils, which may reduce desertification in the Thar Desert and other similar deserts in the hot tropics.

Spatial variability and concentration of arsenic in the groundwater of a region in Nadia district, West Bengal, India

Arsenic pollution in ground water in India and Bangladesh is considered to be the largest contamination problem in the world. About 15 – 18% of the area of West Bengal, India comes under the threat of arsenic (As) contamination and around 5.36 million people are exposed to this hazard. A detailed isoline map corresponding to variations in arsenic concentration and their spatial distribution was prepared for the study area, which comprised two villages Ghentugachi and Gotera in Nadia district, West Bengal and the total area covered was 808 hectares. The pattern of arsenic contamination was highly irregular and diverse. About 11.2% of the study area was affected most ( > 0.50 mg As l−1) with sample As values reaching 0.71 and 0.80 mg l−1. About 22.5% of the area had As content between 0.20 and 0.50 mg l−1 and 33.9% of study area had As content below the WHO guideline of 0.01 mg As/l. Thus the local population living around these areas is vulnerable and exposed to arsenic contamination. None of the water samples exceeded the allowable limit (1.0 mg As l−1) of As for water used in irrigation purposes. The spatial distribution map helped to determine zones with different As concentrations, making it possible to identify high-risk zones.

Distribution of forms of potassium in relation to different agroecological regions of North-Eastern India

Distribution of potassium (K) in soils is governed by the agroecological region (AERs), as the operational intensity of factors and processes of soil formation vary with AER. Therefore, we aimed at finding out the relationship between the forms of K(K forms) with AER and the association of K forms with soil properties in the North-Eastern region of India. For this, horizon-wise soil samples were collected from pedons, three each from three AERs (15 (hot sub-humid to humid), 16 (warm per-humid) and 17 (warm per-humid with less cool winter)) in the North-Eastern India. The water balance diagram for AER shows that precipitation (P) exceeds the potential evapo-transpiration (PET) from June to October, AER 16 shows almost no period when the PET is more than the P and AER 17 shows that the region experiences only a short water deficit of 100–150 mm during post-monsoon period. Soil samples were analysed for physical and chemical properties and K forms. The soils were acidic to neutral with low cation exchange capacity (CEC). The water-soluble K ranged between 0.006 and 0.144 cmol kg−1, exchangeable K between 0.07 and 0.54 cmol kg−1, fixed K from 16.7 to 61.3 cmol kg−1 and total K from 17.4 to 63.6 cmol kg−1 in soils of different horizons. Further, the results revealed that all the K forms followed the trend of AER 16 > AER 17 >AER 15. Exchangeable K showed higher correlation with clay (r = 0.519**), while fixed K with organic carbon (r = 0.390*).

Assessment of Land Degradation and Its Impacts on Land Resources of Sivagangai Block, Tamil Nadu, India

A detailed cadastral level survey of land resources occurring in Sivagangai block of Tamil Nadu state, India, covering an area of about 44,600 ha, was carried out during the period 2006−2007. Based on this, 18 soil series were identified and 103 phases mapped at 1:12,500 scale. The study revealed severe sheet erosion on the uplands, heavy siltation of tanks and development of salinity/sodicity at the lowlands as major causes for the drastic decline in productivity. The study warrants systematic and timely efforts to arrest soil erosion on the uplands, proper maintenance of tanks to increase the storage capacity and recharge of the aquifers and providing drainage facilities to reclaim the lowlands and prevent the development of salinity/sodicity in the study area.

Water-Retention Characteristics and Available Water Capacity in Three Cropping Systems of Lower Indo-Gangetic Alluvial Plain

This study was conducted in Chinchura-Mogra and Polba-Dapur Blocks of Hugli District, West Bengal to determine the changes in cropping systems on water-retention characteristics (WRC) and available water capacity (AWC) and their relations with other soil properties. In the present study, three sites contained adjacent cropping systems of banana and mango orchard, paddy–paddy, and paddy–potato–vegetables were selected. Soil samples were collected from depths of 0–30 and 30–60 cm in three representative sites of each cropping system with three replications guided by land use and soil map of study area. Analysis of variance was performed to compare the impact of cropping systems on available water content and water-retention characteristics. The mean clay content was greater both on the surface (61.70%) and in the subsurface (55.06%) in the soils under the paddy–paddy cropping system than banana and mango orchard and paddy–potato–vegetable cropping systems. Paddy–potato–vegetables cropping system (0.55%) has lower soil organic carbon compared to the banana and mango orchard (0.63 %) and paddy–paddy cropping system (0.65%) at 0–30 cm deep, whereas no significant difference in soil organic carbon was recorded in 30–60 cm deep. The results of available water capacity indicated that paddy–paddy cropping system recorded lower available water capacity at both ranges of depth. Available water capacity is significantly positively correlated with silt and organic carbon. The results of water-retention studies indicated that 75 and 85% of available water was removed from the soil of paddy–potato–vegetable cropping system by 0.5 M Pa at 0–30 and 30–60 cm deep, respectively, whereas only 56–62% of available water was removed by 0.5 M Pa in the other two systems. The results show that the paddy–potato–vegetable cropping system is more vulnerable to moisture stress during drought periods.