rice fields, and fruit orchards; some are also used for aquaculture. To most inhabitants in mountainous areas in 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 surveys have been conducted in Thai Nguyen to evaluate biological, physical, social, and economic conditions for aquaculture development. However, most lack systematic spatial data. Planning activities to promote aquaculture in Thai Nguyen require spatial analysis because of geographical variation in biophysical features and socioeconomic 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, 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).
Therefore, the purposes of this study were to:
1) Conduct a survey on biophysical features, land and water uses, and socio-economical conditions of watershed areas in Dai Tu District of Thai Nguyen Province, Vietnam;
2) Develop a GIS database for planning of aquaculture development in the study area; and
3) Identify and estimate suitable watershed ponds for aquaculture.
Methods and Materials
This study was conducted in the 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 (Figure 1). This study consisted of two components. The first component included surveys and field measurements of soil and water quality in watershed ponds to assess the current state of these aquaculture systems, and the second was to develop a GIS database for identifying suitable watershed ponds for aquaculture using the collected data.
Surveys and Field Measurements
Surveys included the collection of secondary data and primary data. Secondary data about socioeconomic conditions and aquaculture practices in watershed ponds in the study areas were collected from the provincial Department of Statistics and at the district level. Primary data were collected using a structured checklist and open-ended type of questionnaires. The questionnaires focused on farmers' socioeconomic status and attitudes on aquaculture as well as potential and constraints for aquaculture development in watershed ponds. One-hundred farmers were randomly selected to be interviewed. Results are presented as means, with the Standard Error (SE) where possible.
Field measurements were conducted in four communes (Binh Thuan, Hung Son, Tan Thai, and Van Tho) of Dai Tu District from February 2002 through January 2003. Sixty watershed ponds (15 from each commune) were randomly selected for soil and water quality analyses. Soil samples were collected from the selected ponds for the determination of soil pH (Boyd and Tucker, 1992). Water samples were collected monthly from the ponds for analyses of total hardness, total alkalinity, total ammonia nitrogen (TAN), soluble reactive phosphorus (SRP), total suspended solids (TSS), total volatile solids (TVS), and conductivity (APHA, 1985; Egna et al., 1987). Water temperature and pH were measured in situ. The locations of the selected watershed
