Groundwater Flow And Flushing Of Animal Burrows In Tropical Mangrove Swamps
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Tidal groundwater in a mangrove swamp can return to the mangrove creek by one of two mechanisms: (a) flowing through the swamp soil due to water table difference between the creek and the groundwater in the swamp; or (b) flowing via tidal flushing of animal burrows. This paper compares the magnitude of these two mechanisms for different regions of a mangrove swamp. Direct groundwater flow rates resulted from water stored in the sediment as a consequence of infiltration, especially during and after tidal inundation, were calculated for every square meter in the surface of a mangrove forest from piezometer data. Flow rates of water due to burrow flushing were determined based on published surveys, by estimating the burrow volume and the percentage of the burrow water that was flushed at each tidal inundation. Although direct groundwater flux was found to decrease further away from the creek compared to that close to the creek, it has similar range to burrow flushing flow. The direct groundwater flow ranged from 0.004 to 0.04 m 3 /m 2 /day, whilst burrow flushing flux ranged from 0.01 to 0.04 m 3 /m 2 /day. Considering the errors involved in the experiments and calculations, these ranges can be considered as being the same and neither of the two processes can be considered as superior to the other. As a consequence, surveys of groundwater processes in mangrove areas, and more generally in swamp and tidal areas where animal burrows are present, will need to consider both mechanisms. Investigations of the influence over flushing mechanisms of different residence times of the water in burrows and in the sediment body would also be recommended in order to establish salt and nutrient budget in mangrove swamps. Keywords: burrow flushing, groundwater flow, mangrove swamp, piezometer.
burrow flushing, groundwater flow, mangrove swamp, piezometer.