Dao Huy Giap Yang Yi
Aquaculture and Aquatic Resources Management
School of Environment, Resources and Development
Asian Institute of Technology
P.O. Box 4 Klong Luang,
Pathumthani 12120, Thailand
Tel. 66-2-5245454
Fax 66-2-5246200
Email:-[email protected]>
Nguyen Xuan Cuong and Le Thanh Luu
2. Research Institute for Aquaculture No.1
Tu Son, Bac Ninh
Vietnam
James S. Diana, C. Kwei Lin
School of Natural Resources and Environment
University of Michigan, Ann Arbor,
USA
Introduction
A large number of watershed ponds and reservoirs have been constructed mostly for household water supply and crop irrigation in mountainous areas of central and northern Vietnam. Occasionally, these ponds are also used for fish culture. Thai Nguyen district, situated approximately 100 km north of Hanoi, is a population center serving as a gateway to northern Vietnam. There are numerous small reservoirs and watershed ponds used for irrigation for tea plantations, rice fields and fruit orchards; some are also used for aquaculture. To most inhabitants in mountainous areas of northern Vietnam, supply of animal protein is relatively limited, with very small contributions from fish. Recently, the Vietnamese government has initiated aquaculture development in those areas as a means to increase protein availability. Therefore, the development of aquaculture in Thai Nguyen may also serve as a model for watersheds in other provinces.
In recent years, several surveys had been conducted in Thai Nguyen province to evaluate biological, physical, social and economic conditions for aquaculture development. However, most of the surveys lack systematic spatial data. Planning activities to promote aquaculture in Thai Nguyen province require spatial analysis because of geographical variation in biophysical features and socio-economic status (Kapetsky et al., 1987; Nath et al., 2000). This project proposes to develop a GIS database of watershed ponds, coupled with other physical, biological, and social attributes of northern Vietnam. Development of a GIS database is a first step in formally evaluating the effects of local geographic and social conditions on the production of fish in watershed ponds.
With an adequate database, Geographic Information Systems (GIS) can serve as a powerful analytic and decision-making tool for aquaculture development. Furthermore, it can also be used for management and to test consequences of development (Aguilar-Manjarrez and Ross, 1995). In this paper, we examine the potential of integrated social and environmental data with GIS and remote sensing as a tool for assessing watershed ponds for aquaculture development by integrating socio-economic and environment data with GIS, detect the land use change, and identify and estimate potential area for watershed pond development for aquaculture.
Methods and Materials
This study was conducted in Dai Tu district of Thai Nguyen province, Vietnam during November 2001 to January 2003. Dai Tu district, about 100 km north of Hanoi, is a mountainous area, covering 57,618 ha (Fig. 1). The primary data sources were social-economic survey, field measurement and three SPOT multi-spectral band satellite images for land use change detection. Land use types, roads, and hydrological systems were taken from topographic maps and updated with SPOT satellite images. Field survey, digital topographic, land use map and related information were used to identify suitable sites for watershed ponds to be used in aquaculture.
F 1.Location map of the study area.
GIS Software and Systems used
The GIS software used in this study was ArcView GIS for windows (version 3.2) developed by Environmental Systems Research Institute, Inc. The remote sensing image analysis used in this study was ENVI (version 3.4) developed by Research Systems and MLR XP24 GPS for field sample collection and verification.
Surveys and field measurements
The socio-economic and environment data were collected using pre-test questionnaires and field measurement from randomly selected sixty farmers and sixty watershed ponds respectively. Soil and water samples were collected from these ponds for the determination of soil pH, soil texture, water pH (Boyd and Tucker, 1992. The locations of the selected watershed ponds were recorded by a GPS navigator (MLR SP24).
Remotely sensed data and thematic maps
The primary data sources were three SPOT multi-spectral bands satellite images acquired for the dates of 22 October 1994, 10 November 1998, and 9 November 2002. Cloud-free images of the study area were taken from these three scenes and geo-registered with topographical maps (1:25,000) using reference points.
Fourteen base layers (thematic maps) were used in the study and grouped into 4 main land use requirements for aquaculture: (1) potential for pond construction (slope, land use types, soil thickness, and elevation); (2) soil quality (soil types, soil texture, and soil pH); (3) water availability (distance to water, water sources, and precipitation); and (4) geographical and social economic status (distance to roads, population density, distance to local markets, and distance to hatcheries) (Table 1). Slope, elevation, soil type, soil thickness, precipitation, and local market centers and hatchery locations data were extracted from the digital topographic map of Dai Tu (1:25,000) (Vietnam Cartographic Publishing House, 1999). Land use types, roads, and hydrological systems data were taken from the topographic map and updated with SPOT satellite imagery acquired for 9 November 2002. Soil pH and soil texture were collected during the survey and extracted from soil information in Vietnam (Agriculture Publishing House, 2000). Population density data were taken from Statistical Yearbook of Thai Nguyen (Thai Nguyen Statistics Department, 2002).
Table 1: Land characteristics and rating rules used for assessing watershed pond for aquaculture development
| Parameters | Suitability rating and score | ||||||
| Highly | suitable a Suitable b Marginally suitable c | Not suitable d | |||||
| (4) | (3) | (2) | (1) | ||||
| Potential for pond construction | |||||||
| Slope | < 5 | >5 – 15 | >15 – 25 | > 25 | |||
| Land use types | Paddy field | Resident land, Unused land, Water body | Agriculture land, Brushwood | Planted and natural forest, Tea plants | |||
| Soil thickness (cm) | >100 | 50-100 | 1000 | ||||
| Soil quality | |||||||
| Soil types (FAO systems) | Fluviols | Haplic acrisols | Haplic calcisols | Humic Ferralsols, Rhodic ferralsols | |||
| Soil pH | 6-7 | 5-6 | 4-5 or 7-8 | 8 | |||
| Soil texture (% clay) | >35 | 18-35 | 2000 | ||||
| Water sources | Irrigation | Rain-fed | —- | —- | |||
| Precipitation (mm/year) | 1500-2500 | >2500 | 600 | 300-600 | 200-300 |
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