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һ퓣
INTRODUCTION
Water quality management has been considered one of themost important aspects of pond aquaculture for many years,but less attention has been given to the management of pondbottom soil quality. There is increasing evidence that thecondition of pond bottoms and the exchange of substances between soil and water strongly influence water quality(Boyd, 1995). More attention is being devoted to the study of pond soils, and practical aquaculturists are beginning to seek information on pond bottom management.
The purpose of this small manual is to provide a practicalguide to the management of aquaculture pond soils.
POND SOILS
Development
During pond construction, surface soil in the area to become the pond bottom usually is scraped off and used as earth fill for embankments. The newly finished pond bottom normally is subsoil low in concentrations of organic matter and nutrients. In tropical and subtropical areas with highly leached soils, pond bottoms often are high in clay content and of low pH.After filling with water, various processes begin to transform the bottom of a new pond into a pond soil. Erosion of the watershed results in suspended particles of mineral soil and organic matter entering a pond in runoff. Wave action, rainfall, and water currents from mechanical aeration erode embankments and shallow edges to suspend soil particles. In addition,nutrients added to ponds in fertilizers, manures, and feeds cause phytoplankton blooms that increase the concentration of suspended organic particles. Suspended particles settle in ponds with large sand particles settling first, followed by
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