On the role of Remote Sensing in environmental impact analysis of shrimp farming
Tripathi. N. K
Space Technology Application and Research
Program, School of Advanced Technology,
Asian Institute of Technology
Bangkok, P.O. Box. 4,
Klong Luang, Pathumthani 12120, THAILAND
Tel:
66-2-524-6392, Fax: 66-2-524-5597 nitinkt@ait.ac.th
Annachchatre, A
and ., Patil, A. A.
Environmental Engineering, School of Environment of
Resource Development,
Asian Institute of Technology Bangkok, P.O. Box. 4,
Klong Luang,
Pathumthani 12120, THAILAND
Abstract
Intensive shrimp farming has developed
rapidly in response to dramatic increase in Seafood demand. It has become a
thriving business in many developing countries including Thailand. Shrimp
farming and aquacultural activities are mostly carried out in mangroves and
coastal regions as they provide a nice habitat. But intensive shrimp farming has
adverse impact on mangroves and marine environment. An attempt has been made to
find the effect of effluent from shrimp ponds on neighboring surface water
bodies in terms of suspended solids and organic matter. The residual salts from
the dried shrimp ponds are generally thrown on nearby land. This is causing
serious salinity of the soil thus making the arable land infertile and turning
them into wasteland. As a case study, a coastal province of Thailand has been
undertaken. This paper investigates the environmental impact of shrimp farming
on landuse pattern, surface water bodies, marine water, mangrove forests and
agricultural land using satellite data.
Introduction
Thailand has experienced rapid growth in shrimp farming in
response to dramatic increase in seafood demand and decline in natural fisheries
due to pollution and over exploitation. It has developed rapidly into a thriving
business in many countries and has provided more than 25% of world's annual
shrimp market since 1990. In 1994, 733,000 metric tons of shrimp from 1,144,000
ha of ponds were produced in which tiger shrimp (Penaeas monodon) was most
dominant species comprising about 61% of total shrimp production (Rosenberry
1994) and it is still increasing.
Despite the apparent economic success
of intensive shrimp farming, its sustainability has been a major concern of the
industry. The externalities associated with modern production have become
increasingly evident and now confront difficult problems related to effluent
discharge (Landesman 1994). The effluent laden discharge form shrimp pond can be
a potential for nutrient enrichment and eutrophication of natural water bodies
and its impact on coastal environment has caused greater concern (Phillips et.
al. 1993). Increasing, eutrophication in natural water can lead to ecologically
undesirable consequences. Shrimp farming, while generating important benefits
has also contributed to degradation of coastal environment and this threatens
sustainability of the production. The risk of failure increases with greater
stocking density, which requires extra intensive management, meaning more food
input, more water exchange. It relates directly to greater amount of waste being
produced in the ponds, which may eventually reach the flash point of pond
carrying capacity by poisoning with excessive waste.
Shrimp farming and
Aquacultural activities are mostly carried out in mangroves and coastal regions
all over the world. The intensive shrimp farming has significant impact on
mangroves and marine environment as well. It has been realized that the polluted
water discharge from shrimp farms causes deterioration of water quality of
adjacent water bodies like mangroves and coastal zone. Coastal zones are places
of ending changes. Effective inventorying and monitoring of these changes are
required for the understanding and managing these environments (Pundharikanthan,
1997).
There are many conventional methods to find out the impact of all
concentrations on the ecosystem. These conventional methods only give us the
concentration of pollutant at a particular point or so but can not show the
dispersion pattern or extent of pollution at the same time. Much harder to
detect is pollution that has had great length of time to disperse and hence
cover large area, or pollution that does not emanate from a point source (Clark,
1993).
Remote sensing provides better tool to serve all these purposes
to give synoptic coverage of water bodies. The greatest advantage of remote
sensing technology is that it provides augmented view of spatial and temporal
variability of water quality and land use status which can not be obtained by
any conventional measuring techniques. Several workers have utilized the
satellite remote sensing and GIS for detecting and analysing water qualities
like ch-a, SSC, Chemical composition etc. (Alfoldi (1982), Lathrop and Lillesand
(1991), Clark (1993)).
In the present study an attempt is made to
determine the environmental changes that has occurred due to shrimp farming in
Ranong, Thailand. The interpretation from satellite data has been compared with
past records to estimate the changes. The focus in present work being discussed
in this paper is effect on water quality and degradation in forest and mangrove
area.
Study Area
The study area is located at western coast of Thailand. It has
extensive mangrove forests and dense tropical vegetation. The vegetation
predominantly comprises of evergreen forests, coconut, rubber and palm
plantations. The shrimp farms are frequently seen inside the mangroves or
adjacent to it. The physical location of the study area can be given as 9o 50¢
00¢¢ N to 10o 00¢ 00¢¢N and 98o 30¢ 00¢¢ E to 98o 40¢ 00¢¢ E. The study area is
shown in figure 1. The study area has high hill ranges that are covered with
tropical rain forests. There are numerous streams flowing down these hills
carrying silt and organic wastes in the marine regions.
Landsat TM
digital image in all the bands has been acquired for the study region falling
under scene path no. 130 and row no. 053. Topographic map nos. NC 47-6 and NC
47-10 were used for generating the base map and geo-referencing the satellite
data.