Pages: (97-112 )
Abstract
Algal pigments are useful in the estimation of primary production and phytoplankton biomass. Chlorophyll a, chlorophyll b and phaeophytin a are notable algal pigments in this regard. Open lagoon are coastal environments known to exhibit continuous environmental gradients daily and seasonally. Algal pigments and environmental variables of the western parts of the Lagos Lagoon were investigated for six month at seven stations (November, 2015 – April, 2016). The environmental indices reflected seasonal changes related to rainfall distribution pattern and tidal sea water incursion. Air temperature (25 - 350C), water temperature (26 – 32.50C), total dissolved total (656 – 19611.31 mg/L), dissolved oxygen (4.15 - 6.83 mg/L), transparency (22.5 and 135cm), pH (6.73 - 7.59), salinity (23.24‰) and calcium (4.69 - 258.17mg/L) recorded increased values in the dry than wet season. On the other hand biological oxygen demand (1 - 4mg/L), chemical oxygen demand (4 – 18mg/L), total suspended solids (1 - 38mg/L), nitrate (0.19 - 12.85mg/L), copper (0.002- 0.004mg/L), zinc (0.01 and 0.057) and cadmium (0.0006 - 0.0018mg/L) recorded higher values in the wet season. Chlorophyll a, chlorophyll b and pheophytin a values were higher in the dry season. Notable correlation coefficient (r) was recorded between chlorophyll a and nitrate (r = 0.73, p< 0.05), phosphate (r = -0.82, p< 0.01), chemical oxygen demand (r = -0.35, p< 0.01), biochemical oxygen demand (r = 0.22, p<0.01) and copper (r = -.387, p<0.01). On another hand correlation between chlorophyll b and rainfall (r = 0.62, p< 0.01), pH (r = -0.31, p< 0.05), zinc (r = 0.44, p<0.05), manganese (r = 0.36, p< 0.05) and cadmium (r = 0.33, p< 0.05) were noteworthy. Furthermore phaeophytin a showed a correlated relationship with rainfall (r = 0.39, p<0.01), dissolved oxygen (r = 0.31, p<0.05) and cadmium (r = -0.36, p<0.05). Recorded chlorophyll a values place the western Lagos Lagoon between the mesotrophic and eutrophic status. Increasing nitrate (nutrient) levels coupled with the reduced rainfall events led to the development of more algal cells (phytoplankton) thus higher algal pigments level within the western Lagos lagoon ecosystem.
Keywords: Physico-chemical parameters; estuarine lagoon; Algal pigment; Lagos.,