11
DEC
2017

Variation of Nutrients and Phytoplankton Abundances with Tides during Different Seasons in Setiu Wetland

Name: Nur Hafizah binti Merzuki
Course: Master of Science (Marine Sciences)

A study on variation of nutrients and phytoplankton abundances with tides during different seasons in Setiu Wetland was conducted during inter-monsoon (September and October 2012) and Northeast (NE) (February and December 2013) monsoon seasons. Three sampling stations were selected for this study. Station 1 and 2 were located at marine and brackish waters, respectively while station 3 was located at freshwater area. Salinity and temperature values were lowest during the spring tide on NE monsoon which due to the large freshwater inflow from heavy rainfall. In addition, massive clouds during NE monsoon period decreased the intensity of light from the sun. Higher concentrations of nutrients i.e. ammonia and nitrate were recorded during NE monsoon which might be due to runoff from land to the wetland area and this was more pronounced in spring tide. Phytoplankton density was recorded higher during neap tide on NE monsoon. In general, phylum Bacillariophyta was found to be most dominant group of phytoplankton despite of the tide and seasonal changes. The Canonical Correlation Analysis (CCA) showed positive correlation between environmental parameters and phytoplankton. Most of parameters showed positive correlation with marine phytoplankton at station 1 and 2. Station 3 showed strong negative correlation with salinity as the phytoplankton were from the freshwater genus. Variation of nutrients and phytoplankton community were probably due to the effect of tidal cycle during spring and neap tides. Nutrient is considered as one of the important parameters that influences growth of phytoplankton community. Hence, phytoplankton community structure in Setiu Wetland were found to be influenced according to the availability and concentration of nutrients which are affected by tidal cycle and season.

 

Figure 1

Figure 2
Figure 1: (a) CCA showing scatter plot for all seasons against environmental variables at all station during spring and neap tide cycle in Intermonsoon; (b) CCA showing scatter plot for phytoplankton species against environmental variables at all station during spring spring-neap tide cycle in Intermonsoon, (c) CCA showing scatter plot for all seasons against environmental variables at all station during spring and neap tide cycle in NE monsoon; (d) CCA showing scatter plot for phytoplankton species against environmental variables at all station during spring-neap tide cycle in NE monsoon season. Spring tide= (ST), neap tide = (NP);

 

Canonical correlation analysis (CCA) was applied to explore variables of physic-chemical parameter between phytoplankton genus groups throughout the study period. The results shows in Figure 1 (a, b, c and d) revealed that season and tidal cycle affected the environmental condition and changed the phytoplankton assemblages. Changes in genus composition and diversity may affect phytoplankton growth rate and those parameters regulating the photosynthetic response to irradiance or other limiting factors. The tidal cycle and seasonal changes directly affect the nutrients concentration in water of Setiu Wetland. This was indicated by the changes in physical water parameters, phytoplankton abundance and species composition of according to seasons.

 

The phytoplankton composition was found being effected by the seasonal changed. During intermonsoon, marine phytoplankton obviously dominating the area with Bacillariphyta as major represented. However, freshwater phytoplankton density surprisingly increases with the decreasing of salinity during NE monsoon. The environmental factors change will directly affect the composition of phytoplankton. It is because different genus phytoplankton favours different of factors for growth. Bacillariophyta maintain as a most dominating phylum for all the result presented, corresponding with high number of genus present throughout the study period even within the changes of abundance in each sampling time. Physico-chemical variables collectively varied across the four sampling periods although this was not necessarily evident when considering the variables independently. Density and diversity of phytoplankton also varied with the changing season.