Nutrient dynamics in the Sundarbans mangrove estuarine system of Bangladesh under different weather and tidal cycles

摘要

Introduction Seasonal and tidal variations in nutrient concentration and water quality were investigated in the western Sundarbans of Bangladesh during the post-monsoon, winter and monsoon seasons during 2010–2011. Methods Water collected from the surface, middle and bottom layers at six locations of the Kholpetua-Arpangashia river system during high and low tides was analyzed for temperature, salinity, pH, dissolved oxygen (DO), total dissolved solids (TDS), electrical conductivity (EC) and dissolved nutrients (NO₃–N, PO₄–P, SO₄ and NH₃–N). Results The study revealed that nutrient concentrations were influenced by seasonal changes. Mean nutrient levels during post-monsoon, winter and monsoon seasons, respectively, were in the following ranges: nitrate (0.06–0.40, 0.06–0.46 and 0.08–0.46 mg/L); phosphate (0.09–0.18, 0.05–0.42 and 0.10–0.16 mg/L); sulphate (58.71–86.14, 68.68–119.01 and 78.15–136.47 mg/L) and ammonia (0.02–0.08, 0.02–0.04 and 0.26–0.38 mg/L). Increased levels of PO₄–P, SO₄ and NH₃–N and lower DO and salinity were recorded during the monsoon period. Most of the experimental sites showed higher NO₃–N content during monsoon, whereas few elevated concentrations were observed during post-monsoon and winter periods. High and low tidal waters contained mean nutrient levels in the following ranges: nitrate (0.05–0.46 and 0.04–0.40 mg/L); phosphate (0.05–0.42 and 0.07–0.18 mg/L); sulphate (63.63–125.36 and 58.71–136.47 mg/L) and ammonia (0.02–0.38 and 0.02–0.37 mg/L) without following any distinct fluctuation patterns. The western part of the Sundarbans receives less freshwater input during the monsoon season than other areas of the ecosystem, which reduces the variability of nutrient levels and water quality components. Conclusions This study provides considerable advances in understanding the seasonality of nutrient distribution with possible tidal influence. The data generated from this study will guide continuing efforts to support a sound management for coastal mangrove ecosystems.