Key morphological changes and their linkages with stream power and land-use changes in the Upper Tapi River basin,India

Knowledge on spatio-temporal variations in planform, hydraulic geometry, and bed-level variations of alluvial streams is required for planning and development of hydraulic structures and bank protection works. In the current study, a Geographic Information System (GIS) has been used to analyze topographical maps, multi-temporal remotely sensed imagery, and hydrologic and hydraulic data to extract the morphological parameters of the Upper Tapi River, India. The river has been found to have consistent migration towards the northern direction, with erosion/deposition on right/left banks. The river has not experienced any major meander except in the lower reaches of the Upper Tapi Gorge and minor braiding conditions at the location where the river emerges from mountainous topography to the plain region. The analyzed river cross sections were found to be depth dominated, and contain large flows within the channel banks. The cross-sections exhibited moderate channel bed adjustments in 1994, 2006, and 2007 wherein excessive sediment flux and stream power were capable of causing morphological changes in the river. High intensity rainfall in the subcatchment resulted in high sediment flux into the river during 1994, which was reported to cause significant aggradation at the downgauging station. The analysis of sediment flux into the river in conjunction with decadal land use land cover, revealed that sediment yield from the catchment was reduced during 2000–2010 due to an increase in water bodies in the form of minor hydraulic structures. The entry of comparatively less sediment laden water into the river, resulted in moderate bed degradation especially in 2006 and 2007 as observed at the downstream station. The methodology applied in the current study is generic in nature and can be applied to other rivers to identify their morphological issues.     

Crusting effects on erosion processes under simulated rainfall on a tropical Alfisol

Sealing and crusting of soil surfaces have dramatic effects on water infiltration into and runoff from soils, thereby greatly influencing erosion processes. This study focused on the effect of the initial stage of crusting on inter-rill erosion processes for a crust-prone Alfisol sampled from south-central India. Soil aggregates ranging from 2·4 to 8 mm collected from ploughed (PL) and naturally vegetated (NV) treatments were subjected to rainfall simulation under laboratory conditions. Runoff from PL soil aggregates was 2–2·5 times higher, while percolation was 20–100% lower, than for NV aggregates. Soil wash and splash losses were 0·5–3 times greater for PL than for NV soil. Runoff and inter-rill erosion were significantly higher during the wet simulation run compared with the dry run. The results indicated that NV soil aggregates were more resistant to breakdown from raindrop impact and slaking, and subject to less rapid sealing, than PL soil. Total soil loss was influenced most by initial aggregate stability and the extent of seal development. Splash and wash losses of soil both increased as a result of surface sealing regardless of soil condition for short (30–60 min) rainfall durations. High drying rates resulted in the highest crust bulk densities. Increased crust strength for PL soil compared with NV soil reflected the greater susceptibility of cultivated soil to surface sealing and crusting. © 1998 John Wiley & Sons, Ltd.     

Study of Ozone and NO2 over Gadanki – a rural site in South India

We have studied long-term changes in tropospheric NO₂ over South India using ground-based observations, and GOME and OMI satellite data. We have found that unlike urban regions, the region between Eastern and Western Ghat mountain ranges experiences statistically significant decreasing trend. There are few ground-based observatories to verify satellite based trends for rural regions. However, using a past study and recent measurements we show a statistically significant decrease in NO_X and O₃ mixing ratio over a rural location (Gadanki; 13.48° N, 79.18° E) in South India. In the ground-based records of surface NO_X, the concentration during 2010–11 is found to be lower by 0.9 ppbv which is nearly 60 % of the values observed during 1994–95. Small but statistically significant decrease in noon-time peak ozone concentration is also observed. Noon-time peak ozone concentration has decreased from 34?±?13 ppbv during 1993–96 to 30?±?15 ppbv during 2010–11. NO_X mixing ratios are very low over Gadanki. In spite of low NO_X values (0.5 to 2 ppbv during 2010–11), ozone mixing ratios are not significantly low compared to many cities with high NO_X. The monthly mean ozone mixing ratio varies from 9 ppbv to 37 ppbv with high values during Spring and low values during late Summer. Using a box-model, we show that presence of VOCs is also very important in addition to NO_X in determining ozone levels in rural environment and to explain its seasonal cycle.     

Influence of aerosol on clouds over the Indo-Gangetic Plain, India

Using Total Ozone Mapping Spectrometer Aerosol Index (AI) and NCEP/NCAR reanalysis clouds data for the period 1979–1992, the influence of aerosol on the clouds (low and high cloud cover) over the Indo-Gangetic Plain (IGP) in India has been brought out for the first time in the present study. AI shows increasing tendency over the IGP suggesting that aerosol loading over this region increased significantly during the study period. In our analysis, High Cloud Cover (HCC) shows increasing trend and Low Cloud Cover (LCC) shows decreasing trend over the IGP during the same period. During pre-monsoon season when aerosol loading is more, HCC increases in positive correlation with AI. On the other hand, LCC show decreasing trend and is anti-correlated with AI. During summer monsoon, aerosol shows increasing trend but their effect on HCC and LCC is not seen to be significant. Similarly, the role of humidity on aerosol induced changes in HCC and LCC over the IGP region was also analyzed. In the low to moderate humid areas of IGP region (western and middle IGP), increasing AI leads to increase in HCC and decrease in LCC. On the other hand, in high humid areas (eastern IGP), increase in AI does not show any significant effect on HCC, but LCC shows positive trend. Therefore, we strongly argue that increasing aerosol loading enhances Cloud Condensation Nuclei over the region which in turn, alters the microphysical properties of clouds by reducing the size of cloud droplets, and atmospheric humidity controls the aerosol effect on clouds. During the recent period (2005–2010), similar features have also been observed over the IGP region.     

Relationship between rainfall and lightning over central Indian region in monsoon and premonsoon seasons

Lightning activity and rainfall over the central Indian region (lat, 15.5° N to 25.5° N and lon, 75° E to 85° E) from the TRMM satellite have been analyzed. Ten years' data of monthly lightning and hourly averaged monthly rainfall from 1998 to 2007 have been used for analysis, which shows quite different relationships between lightning and rainfall in monsoon and premonsoon seasons in this region. Very good positive correlation is observed between rainfall and lightning during the premonsoon period, however, in the monsoon period a correlation between them is not so good. The different relationship between lightning and rainfall in the monsoon and premonsoon has been attributed to the low updraft during the monsoon period due to low cloud base height and low aerosol concentration during this period. This analysis shows that deep electrified convective systems do form over the central Indian region during active monsoon periods; however the relationship between convective rainfall and lightning frequency during this period is not as consistent as during the premonsoon period.     

The assessment of aerosol optical properties over Mohal in the northwestern Indian Himalayas using satellite and ground-based measurements and an influence of aerosol transport on aerosol radiative forcing

The present study deals with the aerosol optical properties which are assessed during the period 2007 to 2009 over Mohal (31.9oN, 77.12oE) in the northwestern Indian Himalaya, using ground-based measurements and multi-satellite data. The daily average value of aerosol optical depth (AOD) at 500?nm, ?ngstr?m exponent and turbidity coefficient are 0.24?±?0.08, 1.02?±?0.34 and 0.13?±?0.05, respectively. The comparative study of satellite and ground-based measurements reveals that the percentage retrieval for daily AOD at 550?nm over Mohal within the expected accuracy (???? _p?? ?=?±0.05?±?0.15?? _p?? ) is around 87%, with a significant correlation coefficient of 0.76. The present study suggests that the retrieval of AOD through satellite data is able to characterise the distribution of AOD over Mohal. However, further efforts are needed in order to eliminate systematic errors in the existing Moderate Resolution Imaging Spectroradiometer (MODIS) algorithm. The transport of desert dust and anthropogenic aerosol during high aerosol loading days caused a significant reduction in surface-reaching solar radiation by 149 and 117%, respectively. This large reduction in surface-reaching solar radiation increased the atmospheric heating rate by 0.93 and 0.72?K?day^?1, respectively. This study indicates significant climatic implications due to the transport of aerosols in the northwestern Indian Himalaya.     

Submicron aerosols over Indian Ocean: some meteorological characteristics

The concentrations of submicron aerosols in the size range 10⁻⁷ to 10⁻⁵ cm, also called Aitken nuclei (AN) were measured over the Indian Ocean enroute India-Antarctica-India within the 10°E–70°E longitude zone from about 10°N to 70°S latitude on board MV Thuleland during the period from November 26, 1986 to March 18, 1987 as part of the scientific activities on the Sixth Indian Antarctic Expedition. Our analyses showed that only in about 25% of the cases, AN count fell below 1000 cm⁻³. Throughout the tropical trade wind region, the concentrations of AN were relatively stable with an average of about 3000 cm⁻³ (medians of 2600 and 1700 cm⁻³ in Northern and Southern Hemispheres, respectively). Large AN concentrations were found to be associated with higher sea surface temperatures and stronger surface winds in this region. In contrast, the scatter of single observations was found to be remarkable over South Indian Ocean and in Antarctic waters. The average AN concentration over the Indian Ocean to the south of 30°S was of the order of 1500 cm⁻³. No definite correlation could be established between large AN concentration and sea surface temperature, wind speed or wave height. Period with very low concentrations were, however, associated with clear sky conditions and calm winds or light breeze. Many events of sudden short-lived but large increase in AN concentrations were observed over the south Indian Ocean and in Antarctic waters and these were always associated with the approach of frontal systems. It is likely that particle production by bursting bubbles and sea spray as well as photochemical reactions and gas-to-particle conversions play important role in the observed high concentration of AN over South Indian Ocean.     

Deglacial Control on Sedimentation and Basin Evolution of Permo-Carboniferous Talchir Formation, Talchir Gondwana Basin, Orissa, India

The Permo-Carboniferous Talchir Formation in the southeastern part of the Talchir basin is represented by about 260 m thick clastic succession resting on the Precambrian basement rocks of the Eastern Ghats Group. The succession is tentatively subdivided into four lithostratigraphic units, namely A-I, A-II, B and C from base to top. Unit A-I comprises mud-matrixed, very poorly sorted diamictites and interbedded thin sandstone and mudstone yielding dropstones. They reveal deposition in a proglacial lake environment in which ice rafting and suspension sedimentation, as well as meltwater-underflow processes, produced variety of facies. The succession of unit A-II is dominated by pebble to boulder conglomerates and sandstones. They were deposited mostly from various kinds of high-energy sediment gravity flows, both subaerial and subaqueous, and formed steep-faced fan-delta on the margin of the basin. Unit B demonstrates turbidite sedimentation in lake-margin slope and base-of-slope environments, in which a sublacustrine channel-fan system developed. The lake-margin slope was dissected by channels which were accompanied by overbank and levee deposits. Sediments delivered from the mouth of a channel were deposited at the base-of-slope, forming a fan lobe which prograded onto the lake basin floor. Unit C dominantly consists of mudstone with intercalations of siltstone and sandstone and forms a large-scale coarsening-upward deltaic sequence eventually covered by the fluvial deposits of the Karharbari Formation.Following the glacially influenced sedimentation, the Talchir succession shows a vertical facies progression suggesting gradual deepening of the lake basin and eventual filling up of it due to rapid delta progradation. Such a succession represents deglacial control on basin evolution during the Talchir time. In the initial stage of glacial recession, collapse of a glacier and failure of montane glacial lakes frequently occurred and gave rise to generation of a highly sediment-laden debris flow and a catastrophic flood, which brought abundant coarse clastics into the lake and built a fan-delta on the basin margin. The continued recession and disappearance of glacier resulted in abundant supply of ice-melt water into the graben as well as eustatic sea-level rise, being the cause of the rise in lake-level. Subsequent rapid delta progradation and eventual filling-up of the lake basin suggest rapid lake-level fall after deepening of lake basin. It was possibly caused by the regional uplift due to post-glacial isostatic rebound. Rapid draining of lake water through the graben gave rise to the establishment of an axial drainage system which rapidly filled the lake basin in form of an axially fed delta.     

Water retention characteristics of swelling clays in different compaction states

The soil–water retention (SWR) characteristics of the clays play an important role in controlling their engineering behaviour, particularly, in the unsaturated state. Although, researchers have attempted to understand the water retention characteristics of the clays in their reconstituted or remoulded state, such studies are rare for the clays in their intact state. In this context, it becomes important to understand the influence of initial state of compaction, which would create different pore and fabric structure (viz., microstructure), on the water retention characteristics of the clays. With this in view, SWR behaviour was experimentally determined for the swelling clays (dried from different compaction states, viz., intact, reconstituted and remoulded) by employing Dewpoint PotentiaMeter (WP4C®). The changes in the pore size distribution of the clays at different stages of drying cycle were also studied by employing the Mercury Intrusion Porosimetry. The study reveals that the SWR curves for the intact and reconstituted specimens of the clays converge beyond a certain stage of drying. Also, a critical analysis of changes in the pore structure of the swelling clay specimens, during drying, indicates that the progressively deforming pore structure plays an important role in controlling its water retention characteristics to a great extent.     

Soil quality evaluation under different land management practices

Sustainable agricultural production requires prudent management backed by reliable information that accurately elucidates the complex relationships between land management practices and soil quality trends. Therefore, this study investigates the influence of management on soil properties acquired at different depths, and yields, at five different field sites within Ohio, USA. The principal management systems considered were no till with or without manure and cover crops, natural vegetation (NV) or forest, and conventional tillage (CT) defined as farms with surface residue cover (<30 %). Analyses of variance (ANOVA), correlation analyses, stepwise regression, and the principal component analyses (PCA) were used to elucidate and model the link between four different management practices and the soil physical and chemical properties. The ANOVA results indicate that the available water capacity and electrical conductivity (EC) were the major variables affected by management. In contrast, soil pH, bulk density (ρ _b), porosity, soil organic carbon (SOC), and total nitrogen (TN), were invariable with management, yet only pH and EC did not significantly vary with the interaction of soil type and management effects. In comparison, the PCA results suggest that SOC, TN, porosity, ρ _b, and EC were the major determining factors controlling yield variability. Interestingly, the derived models revealed that the highest yields, notably 10 and 2.7 Mg ha^?1 for corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) occurred in soils under CT management. Quantifying the nexus between soil properties and management choices as demonstrated in this study, can provide critical insight for sustainable agricultural production.