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The effects of land use practices on water quality and quantity in the Hope River watershed, Jamaica Hayman, Alicia Antoinette

Abstract

The Hope River watershed in Jamaica supports over one-thirds of the population of Jamaica. The Hope River and its tributaries supply water for a variety of purposes to the capital city of Kingston, via the Mona Reservoir. Since the 1980's, water supply to the Mona Reservoir has had to be supplemented by the Yallahs River in an adjacent watershed as the Hope River's ability to supply the needs of the city has been weakening. The Hope River watershed is extremely fragile in that years of misuse of steep slopes, rapid population growth and agricultural expansion (mainly coffee) have been contributing to reduced availability of water, deteriorating conditions due to erosion, deforestation and degrading water quality. The study was conducted to develop a framework by which problems, initiatives and interactions between land use, water quantity and quality and management issues may be assessed in terms of historic development and current trends by employing Geographical Information Systems (GIS) and statistical techniques. The study aimed to determine the current hydrological and water quality conditions and evaluate the changes over the past ten years as well as to identify the land uses that impact the water resources. This was accomplished using historic climate data, determining water balances for the watershed and the reservoir, examining the land use dynamics with GIS, and by linking land use to water quality and quantity using statistical techniques. A n evaluation of the people's practices and perceptions was carried out using the Participatory Rural Appraisal (PRA) method. The water quantity study revealed that there is high spatial and temporal variability in rainfall, which has decreased significantly from a mean monthly rainfall of over 250 mm in 1933 to under 150 mm in the 1990's. Subsequently, the available water from runoff as well as peak flows have also decreased. There has been an increase of over 2° in temperature in the watershed over the study period. The water balance for the Hope River upper watershed area shows that the hydrologic cycle is dominated by evapotranspiration, which is greater than rainfall for 75% of the year. In a typical year, there is a deficit in the overall balance of 310 mm. In a dry year, the deficit is 696 mm and in a wet year there is an overall surplus of 270 mm. In the Mona Reservoir, there was a negative balance in storage for at least 1/3 of the decade. During the rainy months, there is an abundance of water available for storage but inadequate storage capacity. Also, when there is heavy rainfall, excess water runs out to the Caribbean Sea, as there is a high amount of sediments being transported along with it. Evapotranspiration is highest at the reservoir during July and August. Even though inflows to the reservoir and rainfall in the watershed have both been variable, outflows have been increasing significantly. This is related to the increase in population in the city, placing a greater demand on the system. The water quality study showed that the Hope River and its tributaries are deteriorating in both spatial and temporal dimensions. Not only have nutrient levels increased but conductivity, TDS, and conform levels have also risen over the decade 1989-1998. Fecal coliform levels have exceeded the maximum allowable limits for health and recreational use over 90% of the time. Though the nutrient levels have not exceeded the criteria they have been increasing and are a cause for concern. Nitrate, phosphate and fecal coliform levels tend to increase downstream. A GIS based evaluation of land-use dynamics in the Hope River upper watershed area showed that agriculture increased by 55%, from 737 to 1144 hectares; settlements by 23.6% from 55 to 68 hectares and forests decreased by 18.2% between 1989 and 1998. The increases are mainly attributed to conversion of land into coffee (163 ha) as there is a demand for Blue Mountain coffee on the international market. Population growth is a cause for concern, as 85% of the land in the upper watershed area is on steep slopes over 25°. There are many squatters living on the marginal lands in the area, many of whom practice some type of farming. Relationships between land use and water shows that between 1989 and 1998 streamflow has increased as a result of a decline in forest due to agricultural expansion. O f the nutrients studied, the variations in nitrate-N concentrations in streams and coliform levels were related to land use activities, especially agriculture and settlements respectively. High levels of conductivity were recorded in some tributaries but this was attributed to natural conditions, that is the geology of the area. Water in the Hope River and its tributaries can be categorized as hard and this is due to the geology of the area. A study of the perceptions of 107 persons living in the upper watershed communities revealed that most problems stemmed from the current economic situation. However, in terms of environmental issues, stream pollution was considered the most problematic. The people's perceptions were quite different from those of the Government's but sometimes showed similarities with the scientific data. The people did not consider deforestation a problem; however, the land use evaluation showed that deforestation was significant. An integrated management framework is needed which involves all stakeholders with specific focus on pollution prevention, maximizing storage and improving the efficiency of water use.

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