Seminar on Environment and Development in Vietnam

Friday and Saturday, December 6-7, 1996

Common Room, University House,
and J G Crawford Building, National Centre for Development Studies,
Australian National University

BACK TO INDEX

Will salt water intrusion floodgates on the lower Mekong have the same impacts on estuarine acidification as they do in eastern Australia?

Prof. Ian White,
Water Research Foundation of Australia, CRES, ANU

Abstract

Seawater intrusion and acid production from acid sulfate soils during dry seasons, and the export of acid through drainage systems during the wet season, are major constraints to agricultural and aquatic production in Vietnam's lower Mekong Delta and in coastal floodplains in eastern Australia as well. The massive freshwater flows which inundate much of the Mekong Delta during the wet season nourish the Delta's highly productive and essential rice crops. During the dry season, the Mekong River flows are so low that sea waters intrude into the lower reaches of the River, producing brackish water conditions that are unsuitable for rice growth. At present approximately 2 Mha of land are subject to dry season salinity with saline water extending 50 km inland. Increasing diversions of upstream Mekong flows for dry season irrigation, both in Vietnam and in countries upstream, threaten to exacerbate saltwater intrusion into productive lands.

To limit saltwater intrusion into agricultural areas, salinewater intrusion floodgates have been installed or are planned for much of the lower Mekong River. In eastern Australia, many floodplains have already been drained and floodgated. Floodgate design has been based on purely engineering criteria to reduce incursions of seawater. Impacts on soil acidification, the transport and storage of acid, and the impacts of stored acid on agricultural and aquatic productivity have been ignored.

As we shall show, research in eastern Australia has shown that floodgates on estuarine, acid sulfate floodplains, promote soil acidification, lower plant production, act as large acid reservoirs, form barriers to fish migration, decrease recruitment and feeding areas, diminish tidally-driven acid neutralisation and release hundreds of tonnes of acidity into estuarine reaches. The impacts on aquatic communities are massive.

Based on Australian experience, our hypotheses are that firstly, installation of floodgates in Vietnam will result in extremely poor upstream water quality during the dry season; and secondly, the resulting water quality will cause major decreases in upstream, dry-season, irrigated crop production and fish and aquatic production.

Professor Ian White
Water Research Foundation of Australia
Centre for Resource and Environmental Studies
Australian National University
Canberra, ACT 0200

Tel: +61 (6) 249-0660
Fax: +61 (6) 249-0757
Email: Ian.White@cres.anu.edu.au