Abstract
Peri-urban aquacultures produce nutritious food in proximity to markets, but poor surface water quality in rapidly expanding megacities threatens their success in emerging economies. Our study compared, for a wide range of parameters, water quality downstream of Bangkok with aquaculture regulations and standards. For parameters not meeting those requirements, we sought to establish whether aquaculture practice or external factors were responsible. We applied conventional and advanced methods, including micropollutant analysis, genetic markers, and 16S rRNA amplicon sequencing, to investigate three family-owned aquacultures spanning extensive, semi-intensive and intensive practices. Canals draining the city of Bangkok did not meet quality standards for water to be used in aquaculture, and were sources for faecal coliforms, Bacteriodes, Prevotella, Human E. coli, tetracycline resistance genes, and nitrogen into the aquaculture ponds. Because of these inputs, aquacultures suffered algae blooms, with and without fertilizer and feed addition to the ponds. The aquacultures were sources of salinity and the herbicide diuron into the canals. Diuron was detectable in shrimp, but not at a level of concern to human health. Given the extent and nature of pollution, peri-urban water policy should prioritize charging for urban wastewater treatment over water fees for small-scale agricultural users. The extensive aquaculture attenuated per year an estimated twenty population equivalents of nitrogen pollution and trillions of faecal coliform bacteria inputs from the canal. Extensive aquacultures could thus contribute to peri-urban blue-green infrastructures providing ecosystem services to the urban population such as flood risk management, food production and water pollution attenuation.
Highlights
The urbanization of emerging economies brings dramatic social, economic and environmental change that becomes notable in the peri-urban regions around expanding megacities (Marshall and Dolley, 2019)
Insufficient understanding of water use and discharges by specific actors in the complex peri-urban environment are a major obstacle to sound planning and policy making (Vagneron, 2007). To address these knowledge gaps, we comprehensively assessed over a one year period water and sediment quality for three familyowned, peri-urban aquacultures which are situated along canals draining the city of Bangkok towards the Gulf of Thailand
In June 2018, duplicate water samples from each location were filtered at King Mongkut's University of Technology Thonburi (KMUTT), and DNA was extracted from the filters for molecular microbiology at Newcastle University (NU)
Summary
The urbanization of emerging economies brings dramatic social, economic and environmental change that becomes notable in the peri-urban regions around expanding megacities (Marshall and Dolley, 2019). Many stakeholders, including aquacultures, form a dense network of farming, industrial and housing activities in the peri-urban environment of Bangkok (Fig. 1) These activities depend on, and affect, local surface water quality. Insufficient understanding of water use and discharges by specific actors in the complex peri-urban environment are a major obstacle to sound planning and policy making (Vagneron, 2007). To address these knowledge gaps, we comprehensively assessed over a one year period water and sediment quality for three familyowned, peri-urban aquacultures which are situated along canals draining the city of Bangkok towards the Gulf of Thailand. The issues discussed in this paper are exemplary for other rapidly developing and urbanising regions in Southeast Asia and across the world (Brooks and Conkle, 2019)
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