| Summary: | 碩士 === 國立中興大學 === 國際農學碩士學位學程 === 105 === Agriculture nonpoint source pollution is on the major sources of freshwater eutrophication. This research undergoes a water quality analysis of North Stann Creek Watershed (NSCW) and South Stann Creek Watershed (SSCW) in Belize. It Assessed and compare the temporal variation of total nitrogen (TN), total phosphorus (TP), dissolved oxygen (TB), turbidity, temperature (T), pH and fecal coliform bacteria in wet and dry period, identified if riparian buffer zone (RBZ) width, slope, vegetation type, agriculture fertilizer and human activities is important to nutrients in surface water, lastly determined if TN and TP in adjacent farms and affect TN and TP in water after rainfall. Six sites in both watersheds were selected include reference site, and six site adjacent water site were selected for farm and RBZ site. A multi-meter probe was used to measure physical parameters, a colorimeter was used to measure chemical parameters, and bacteria were cultured on petri film. RBZ width, slope, vegetation type and coverage was recorded. TN and TP increases significantly (P <0.05) from upstream to downstream. In both watershed TP and TN were higher in wet period than dry period and varied in levels at sites with wide-ranging RBZ characteristics and influence of villages, factory waste ponds and packaging facilities. DO was significantly higher in NSCW dry period and SSCW wet period. DO in NSCW comes from aquatic plant photosynthesis and DO in SSCW comes from mixing of water by rapids. DO did not decrease significantly with increased T because there is no major seasonal variation in T as research was done in the same season. TB is significantly higher in SSCW wet period indicating excessive nutrient loads via surface runoff. EAB is significantly higher in NSCW wet period and comes from village sewage via surface runoff or leaching into groundwater. RBZ vegetation type, width and slope, human activities and agriculture fertilizer was important to TP and TN in water. NSCW has patchier citrus farms, less concentration of trees and more natural drains. SSCW has concentrated citrus and banana farms, less natural drains. Point source pollution affected SSCW and is more polluted, agriculture nonpoint source pollution affected both watersheds. Water quality standard were within USEPA, 1988 criterion. RBZ should be improved by increasing width and vegetation type, application of fertilizer during rainy season should be adjusted and the washing of fertilizer bags as well as laundry in the rivers should be stopped. Concrete drains should be converted to natural drains in various areas of SSCW to ensure buffering of nutrients by RBZ.
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