Variations in physico-chemical parameters and Chl-a concentration in Setiu Wetlands lagoon during the northeast and inter-monsoon seasons 2018

Abstract This study presents the seasonal changes of physico-chemical parameters and chlorophyll-a (Chl-a) concentration in Setiu Wetlands lagoon during the NEM (February 2018) and inter-monsoon (April 2018) seasons. The Chl-a and physico-chemical parameters of water temperature, dissolved oxygen (DO), pH and salinity were investigated for both surface and bottom waters at 3 sampling sites that are located in the upstream and downstream of the lagoon. The was a strong seasonal signal and spatial gradient in physico-chemical parameters within the Setiu lagoon. In February, when the strong northeast monsoon (NEM) prevailed, the surface and bottom waters of the lagoon were dominated by high pH and low water temperature, DO and salinity. As the weaker inter-monsoon dominated in April, the study area was characterized by low pH and high water temperature, DO and salinity. While the seasonal variation in physico-chemical properties of Setiu lagoon is well described, Chl-a concentrations varied between seasons and sampling locations. Chl-a showed an increased or only a slight change in the downstream stations but recorded a significant decreased in concentrations in the upstream station from the NEM to inter-monsoon season. Analysis of seasonal relationships clearly indicated the interchangeable negative and positive correlations of Chl, DO and salinity. These results suggest the influence of other environmental factors of the lagoon (e.g., nutrient enrichment, tidal and freshwater influx) that vary with seasons which require more detailed investigation.