Printed in ISRS Symposium 2011
Database Creation and Modeling for Estimating Atmospheric/Soil CO2 Consumption in Chemical Weathering Process. Rishikesh Bharti†, S. K. Srivastava*, S. P. Aggarwal*, V K Dadhwal# †Department of Earth Sciences, Indian Institute of Technology, Mumbai, *Indian Institute of Remote Sensing, Dehradun # National Remote Sensing Centre, Hyderabad
EXTENDED ABSTRACT The earth crust comprises 95% igneous rocks and only 5% sedimentary and metamorphic rocks, but if the area of rock exposed at the surface is considered, then 75% of the earth’s surface underlain by sedimentary rocks (Edinburgh et al., 1969). Rocks formed at high temperature and pressure within the earth surface, are unstable when they exposed to atmosphere and water. Weathering is a general term for this kind of transformation (Saether, et al., 1997). The weathered materials are transported by different medium of nature. Rivers are an important medium to transport sediments from continents to the ocean. Geochemical weathering plays crucial role in affecting the global climate. On a major scale chemical weathering can affect the global climate (Krishnaswami and Singh, 2005). Understanding the processes of chemical weathering would help us to understand the role of the natural factors in climate change (Chakrapani, et al., 2005). In the chemical weathering process atmospheric CO2 gets converted to bicarbonate which is balanced by silicate and carbonate rocks. Silicate rocks weathering consume double CO2 from the atmosphere than the carbonate rocks weathering (Sarin, 2001). The flux of CO2 consumed by weathering processes is mainly produced by oxidation of soil organic matter. On a geological time scale, the flux of CO2 consumed by carbonate dissolution on the continents is balanced by the CO2 flux released to the atmosphere by carbonate precipitation in the oceans (Mortatti and Probst, 2003). The largest exchange of carbon occurs between surface water, atmosphere and terrestrial biota. Weathering processes influence more than others in carbon cycle. About 0.3 gigatons of carbon per year (Gtc/yr) are consumed in chemical weathering of rocks and transferred to the ocean as HCO3 (Suchet and Probst, 1995). Global cooling of 40 million years
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Printed in ISRS Symposium 2011 ago has been thought to have taken place because of Himalayan uplift because of increased rate of silicate weathering and CO2 drawdown (Chakrapani, et al., 2005). The present study aims at evaluating the spatial variability of CO2 consumption during the process of chemical weathering with three related sub objectives- estimation of spatial runoff, characterization of lithological distribution and estimation of spatial variability of CO2 consumption based on empirical models developed by Suchet and Probst (1995). The whole study was divided into three phases- data collection; database creation; and spatial modelling. Geological map, geomorphological map, daily rainfall data, soil texture map, soil depth map, HYDRO1km DEM and landcover map have been used to achieve the main objective. SCS curve number method of Soil Conservation Services is used to estimate the spatial runoff which requires the antecedent moisture condition, daily rainfall and curve numbers for hydrological soil cover complexes. The hydrological soil cover complexes are obtained by integrating the hydrologic soil group (derived from soil texture, soil depth and geomorphology). Slope derived from HYDRO1km data is used to adjust the curve numbers. The Indian Meteorological data (IMD) of ten years (1995 to 2004) and Climatic Prediction Centre (CPC) data of six years (2002 to 2007) are used to derive antecedent moisture condition. The lithological map with dominant lithological units prepared from published geological map (GSI, 1998). The maximum runoff value obtained with SCS curve number method is 3900 mm and 3000 mm from IMD and CPC daily rainfall data respectively. The maximum value for the CO2 consumption in chemical weathering process derived from IMD rainfall data is estimated about 3.1×103mol.km-2.yr-1 and from CPC rainfall data is about 2.1×103mol.km-2.yr-1. Coastal region of Maharashtra, upper northern part of West Bengal and foothills of Himalaya show very high CO2 consumption values. The runoff and flux of CO2 consumed in chemical weathering process has been estimated for major river basins of India, i.e. Ganga, Godawari, Brahamputra, Krishna, Narmada and Mahanadi river basins. There is a variation in the values of runoff and CO2 flux consumption estimated from IMD and CPC data. This variation is mainly because of the difference in spectral resolution of IMD and
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Printed in ISRS Symposium 2011 CPC rainfall datasets. The total consumption of CO2 is found maximum in Ganga basin, i.e. about 4.6×107 mol yr-1 from CPC data and 4.7×107 mol yr-1 from IMD data.
Figure1: Spatial Variability of CO2 consumption derived from IMD and CPC rainfall data
References: Chakrapani et al., 2005: Chemical Weathering by Rivers in India, Journal of Indian Water Resource Society, 25(2). Krishnaswami and Singh, 2005: Chemical Weathering in the River Basin of the Himalaya, India, Current Science, 89(5). M. M. Sarin, 2001: Biogeochemistry of Himalayan Rivers as an Agent of Climate Change, Current Science, 81(11). Mortatti and Probst, 2003: Silicate rock weathering and atmospheric/soil CO2 uptake in the Amazon basin estimated from river water geochemistry: seasonal and spatial variations, Chemical Geology, 197, 177– 196. Saether et al., 1997: Geochemical processes, weathering and groundwater recharge in catchments, Geological survey of Norway. Suchet And Probst, 1995, A Global 1 Degree Distribution of Atmospheric/Soil CO2 Consumption by Continental Weathering and of Riverine HCO3 Yield, A Report From Centre National De La Research Scientifique Center De Geochimie Cedex, France.
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