Amending irrigation channels with jute-mesh structures to decrease arsenic loading to rice fields in Bangladesh

doi:10.1016/j.ecoleng.2014.10.030

Ecological Engineering

Volume 74, January 2015, Pages 101-106

https://doi.org/10.1016/j.ecoleng.2014.10.030 Get rights and content

Highlights

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Arsenic from irrigation water threatens rice production and human health in Asia.
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Irrigation channels can be engineered to decrease arsenic loading to rice fields.
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Channels were amended with jute-mesh structures to increase arsenic removal.
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Removal was enhanced by increasing water residence times and particle trapping.
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In-channel structures may be a useful tool for irrigation-water arsenic mitigation.

Abstract

Extensive use of arsenic-contaminated well water for irrigation of rice fields in Bangladesh has led to elevated arsenic concentrations in rice plants, decreased rice yields, and increased human exposure to arsenic. The goal of this study was to investigate whether arsenic removal from irrigation water could be improved within distribution channels by amending them with physical structures that both induce water treatment and maintain water-conveyance capacities. Chemical and hydraulic effects of amending channels with jute-mesh structures were characterized within 27 m-long experimental channels at a Bangladesh field site. Removal of total arsenic, iron and phosphorus from solution was enhanced within amended channels over unamended channels, with 7% of total As removed in amended channels vs. 3% in unamended channels. Increased elemental removal in amended channels was largely due to increases in residence time and particle-trapping efficiency, but removal via oxidative particle formation did not appear to be substantially enhanced. Results suggest that in-channel structures could be a useful tool for decreasing arsenic loading to rice fields, particularly where constrained channel spatial geometries limit the ability to overcome hydrogeochemical thresholds for enhanced arsenic removal. To improve the practical utility of structure-amended channels, future work could optimize structure designs and establish the season-long sustainability of enhanced arsenic-removal strategies.

Introduction

Around the globe, millions of people are exposed to dangerous levels of arsenic (As) through rice consumption, potentially leading to a myriad of health problems (Brammer, 2009, Consumer Reports, 2012, Duxbury et al., 2003, Meharg et al., 2009, Smedley and Kinniburgh, 2002, Stone, 2008). This issue is of particular concern in Southern Asia, where naturally As-contaminated well water has been used for irrigation of dry-season rice for the past 40 years (Brammer, 2009, Brammer and Ravenscroft, 2009, Hossain et al., 2003). Arsenic loading to fields has led to reductions in rice yields and elevated concentrations within rice grains, creating a pathway for As exposure through the staple food crop (Abedin et al., 2002, Liao et al., 2010, Meharg and Rahman, 2003, Meharg et al., 2009, Stroud et al., 2011, Williams et al., 2006). Practical, low-cost methods for large-scale mitigation of As are limited by the volumes of irrigation water required for rice production (i.e., ∼1 m/y of water) and the lack of alternate dry-season water sources (Brammer, 2009, Brammer and Ravenscroft, 2009).

In Southern Asia, As-laden irrigation water is generally pumped from wells, conveyed through soil-based distribution channels, and applied to fields. Dissolved As concentrations have been observed to decrease along the lengths of the channels (Hossain et al., 2008, Lineberger et al., 2013, Roberts et al., 2007), suggesting that despite short residence times (>10 min), high As-removal kinetics enable channels to be a potential location for As mitigation (Brammer, 2009). High As removal (>75%) from surface water has been previously reported in constructed wetlands, but such treatments have relied on hour-to-day residence times (Schwindaman et al., 2014).

The efficiency of contaminant removal from flowing-water systems can be related to a number of major factors, including: (1) kinetics of relevant biogeochemical reactions; (2) contact between water-column contaminants and a reactive soil substrate; (3) trapping of contaminant-bearing particles; (4) water residence times; and (5) hydraulic loads (Birgand et al., 2007). In Southern Asian irrigation water, specific flow properties may cause these factors to oppose one another, limiting As-removal efficiencies within channels. Increased flow velocities and induced turbulence may promote reaeration of water and soil-water contact, thereby favoring oxidative removal of dissolved Fe and As from solution and As sorption to channel soils–the two processes thought to govern in-channel As removal (Lineberger et al., 2013, Nemade et al., 2009). In contrast, increased velocities and hydraulic loads may also decrease As-bearing-particle settling capacities and water residence times, allowing for As transport through the channels.

We hypothesized that in-channel physical structures, preferably constructed from local materials, could be utilized to improve As removal from flowing irrigation water by (1) increasing As contact with soil and structure substrates; (2) increasing in-channel water paths, local flow velocities around the structures, and reaeration processes to enhance oxidative (co-) precipitation of As and Fe; (3) decreasing local flow velocities within structures to induce settling/trapping of suspended As-bearing particles; and (4) increasing water residence times and dispersion to enhance reaction time. Accordingly, the primary goal of this study was to investigate whether As removal from irrigation water would increase in structure-amended distribution channels. Here, we compare flow dynamics and transport of As (plus Fe and P, elements known to influence As) in irrigation water within unamended and jute-mesh-structure-amended channels in Bangladesh. Results suggest that in-channel structures could be useful tools for helping to decrease As loading to rice fields, but future work should first optimize removal rates and determine the season-long sustainability of such engineered systems.

Section snippets

Experimental design

Our well-characterized field site is located ∼30 km south of Dhaka in Bangladesh (Supplementary Fig. S1). Experimental irrigation channels were constructed within a bareground field in December 2012, using techniques described previously (Lineberger et al., 2013). Channels were located ∼73 m downstream of the irrigation well, were 27 m in length, and were ∼1.35 m in width, roughly 3× the width of local channels (Supplementary Fig. S2). Once constructed, one set of channels was left unaltered

Flow conditions in base and jute-amended channels

Amending the channels with jute structures led to an overall increase in channel residence time, with faster channel flow around the structures and slower flow within and through the structures (Supplementary Fig. S3). Jute increased the theoretical flow path around the structures from 27 to 66 m, a 2.44-fold increase. With the same overall channel slope, the increased flow path induced higher stage at the upstream end of the jute channel from 6 to 16 cm, a 2.67-fold increase. The jute structures

Acknowledgements

We thank Mehedi Hasan Tarek, Anisur Rahman, Sojib Chowdhury, Ethan Lineberger and residents of Bashailbhog village for field assistance, Kim Hutchison for analytical support, and Dean Hesterberg for helpful discussions. This work was supported by North Carolina State University and facilitated by the Bangladesh University of Engineering and Technology.

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Citation Excerpt :
Various options have been considered to reduce the uptake of soil As by rice and the impacts of soil As on rice yield. These include providing cleaner irrigation water, growing As-resistant rice varieties, growing rice under conditions that are less conducive to As uptake, and removing the upper layer of As-contaminated soil (Heikens, 2006; Brammer, 2009; Polizzotto et al., 2015). Farmers have also recently begun to dig up and exchange the upper layer of paddy soil with deeper soil from the same location, placing the deeper, lower-As soil in contact with the rice roots and improving rice yield (Huhmann et al., 2019).
Rice is the primary crop in Bangladesh and rice yield is diminished due to the buildup of arsenic (As) in soil from irrigation with high-As groundwater. Soil testing with an inexpensive kit could help farmers target high-As soil for mitigation or decide to switch to a different crop that is less sensitive to As in soil. A total of 3240 field kit measurements of As in 0.5 g of fresh soil added to 50 mL of water were compared with total soil As concentrations measured on oven-dried homogenized soil by X-ray fluorescence (XRF). For sets of 12 soil samples collected within a series of rice fields, the average of kit As measurements was a linear function of the average of XRF measurements (r² = 0.69). Taking into account that the kit overestimates water As concentrations by about a factor of two, the relationship suggests that about a quarter of the As in paddy soil is released in the kit’s reaction vessel. Using the relationship and considering XRF measurements as the reference, the 12-sample average determined correctly whether soil As was above or below a 30 mg/kg threshold in 86% of cases where soil As was above the threshold and in 79% of cases where soil As was below the threshold. We also used a Bayesian approach using 12 kit measurements to estimate the probability that soil As was above a given threshold indicated by XRF measurements. The Bayesian approach is theoretically optimal but was only slightly more accurate than the linear regression. These results show that rice farmers can identify high-As portions of their fields for mitigation using a dozen field kit measurements on fresh soil and base their decisions on this information.
Arsenic in Rice Soils and Potential Agronomic Mitigation Strategies to Reduce Arsenic Bioavailability: A Review
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Soils used for rice (Oryza sativa L.) cultivation in some areas contain high concentrations of arsenic (As) due to irrigation with groundwater containing As and intensive use of agrochemicals or industrial residues containing As. To restrict rice uptake of As in these soils, approaches to reduce As input and bioavailability must be considered. One approach to reduce As input into rice soils or uptake by rice is cultivating rice under aerobic, intermittent flooding, or alternate wetting and drying (AWD) conditions, rather than in submerged soils, or use of irrigation water low in As. For reducing As bioavailability in soil, aerobic or AWD rice culture and application of biochar, sulfur (S), and/or rice polish to soil are promising. Moreover, use of As-hyperaccumulating plant species (e.g., Pteris vittata L.) in rotation or combinations with favourable plant species (e.g., Azolla, Chlorella, or Nannochloropsis species) can also be promoted, in addition to using rice cultivars that are tolerant to As. Though applications of high doses of phosphorus (P), iron (Fe), and silicon (Si) fertilizers have shown promise in many instances, these methods have to be practiced carefully, because negative effects have also been reported, although such incidents are rare. Major factors affecting As speciation and bioavailability in soil are chemical properties such as redox status, pH, and Fe, P, Si, and S concentrations, physical properties such as texture and organic matter, and biological properties such as methylation activity by soil microorganisms. However, as many of these factors interact, long-term examination under field conditions is needed before measures are recommended for and implemented in farmers' fields.
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The As content in vegetable crops depends on the crop type and is also influenced by the soil environment in which the crop is cultivated (Imamul Huq et al., 2006; Kurosawa et al., 2008). As-contaminated wells in Bangladesh supply irrigation water, offering another pathway for addition of As to the soil and hence its subsequent availability for plant uptake (Alam and Sattar, 2000; Meharg and Rahman, 2003; Polizzotto et al., 2015). In the Bengal basin, As levels as high as 83 mg/kg have been reported for soils irrigated with As-contaminated water (Roychowdhury et al., 2005).
Groundwater, the most important source of water for drinking, cooking, and irrigation in Bangladesh, is a significant contributor to the daily human intake of arsenic. Other arsenic intake pathways, established as relevant for Bangladeshi adults through this review, include consumption of contaminated edible plant parts and animal-origin food, inhalation of contaminated air, soil ingestion, betel quid chewing, and tobacco smoking. This review qualifies and quantifies these arsenic intake pathways through analysis of the range of arsenic levels observed in different food types, water, soil, and air in Bangladesh, and highlights the contributions of dietary intake variation and cooking method in influencing arsenic exposures. This study also highlights the potential of desirable dietary patterns and intakes in increasing arsenic exposure which is relevant to Bangladesh where nutritional deficiencies and lower-than-desirable dietary intakes continue to be a major concern.
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Present status and mitigation approaches of arsenic in the environment of Bangladesh: A critical review
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Short communicationAmending irrigation channels with jute-mesh structures to decrease arsenic loading to rice fields in Bangladesh

Highlights

Abstract

Introduction

Section snippets

Experimental design

Flow conditions in base and jute-amended channels

Acknowledgements

Environ. Int.

Environ. Int.

Geochim. Cosmochim. Acta

Ecol. Eng.

Environ. Pollut.

J. Hazard. Mater.

Ecol. Eng.

Environ. Pollut.

Ecol. Eng.

Ecol. Eng.

Appl. Geochem.

Environ. Pollut.

Short communication
Amending irrigation channels with jute-mesh structures to decrease arsenic loading to rice fields in Bangladesh