Journal of Environmental Biology

Assessment of groundwater arsenic vulnerable zones using Geographic Information System for employing bio-char as soil amendment in irrigated rice ecosystem - A case study from Central Assam

B.K. Medhi¹*, I.H. Hazarika², P.P. Hazarika¹, R.K. Thakuria³ and Sanjay-Swami⁴ 

¹Department of Soil Science, Assam Agricultural University, Jorhat-785 013, India

²Department of Agriculture, Government of Assam, Guwahati-781 022, India

³Department of Agronomy, Assam Agricultural University, Jorhat-785 013, India

⁴School of Natural Resource Management, College of Post Graduate Studies in Agricultural Sciences, Umiam-793 103, India

*Corresponding Author Email : binoykrmedhi@gmail.com

Received: 13.06.2020                                                                   Revised: 15.11.2020                                                    Accepted: 15.12.2020

Abstract

Aim: To delineate groundwater arsenic vulnerable zones using Geographic Information System and evaluating the feasibility of bio-char application for reduction of arsenic entry into rice irrigated with arsenic laden groundwater. 

Methodology: Grid (1.6 × 1.6 km) based water samples, totalling 893 numbers from the entire district (Nagaon of Central Assam) were collected following the standard protocol (WHO, 1996) and location of each sampling site required for preparation of GIS map was recorded using Global Positioning (GPS) system unit (GARMIN GPS 64). Inverse Distance Weighted (IDW) approach in GIS was used to delineate the arsenic vulnerable zones. Field experiment with three rice varieties grown with arsenic laden groundwater was conducted to study the feasibility of using bio-char prepared from rice straw and toria stover under slow pyrolysis for reduction of arsenic entry into rice plant.

Results: Groundwater arsenic content of the study area as depicted from GIS map varied from 2.40 to 127.58 µg l^-1. About 42% of the study area had arsenic contents above the bench mark level 50 µg l^-1 recommended by Bureau of Indian Standard. Application of graded doses of bio-char significantly reduced the grain arsenic content of rice to the tune of 0.135 mg kg^-1 (44%) at 1% and 0.118 mg kg^-1 (51%) at 2% with respect to no added bio-chars. Bio-char prepared from both rice straw and toria stover were found effective in reducing arsenic content in grain, straw and rice root irrespective of the varieties and levels of bio-char application.      

Interpretation: GIS guided map of groundwater depicted that 99.5% of the total water samples recorded arsenic concentration above the World Health Organization (WHO) recommended (10 µg l^-1) guidelines while, 40.4% samples showed above the permissible level (> 50 µg l^-1) of Bureau of Indian Standard (BIS). Bio-char prepared from rice straw and toria stover was found to be the best possible option to reduce arsenic content in rice plant.       

Key words: Arsenic, Bio-char, Groundwater, Rice

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