Impacts of sediment mining on the hydrochemistry and macrozoobenthos community in a coastal lagoon, Lagos, Nigeria

The water chemistry and macrozoobenthos assemblage of ten study stations in the Lagos lagoon were studied from December 2016 to May 2017 to assess the impacts of sediment mining on the water quality and the biological indices of the macrozoobenthos. Water and composite benthic samples were collected monthly at each study station and analysed in the laboratory following standard procedures. Except temperature, pH, TSS, salinity and conductivity showed no significant (P>0.05) difference, while the other parameters were not significantly (P<0.05) different among the stations. The sediment grain size analysis of the study area indicated the dominance of sand in sediment. This could be as a result of the dredging of the study area as Lagos lagoon is originally known to have muddy substratum. A total of 1,237 organisms belonging to 3 phyla, 4 classes, 10 families and 10 Species were recorded during the study period. Analysis of benthic community structure of the study area reveals a community dominated by mollusks, with the Bivalve, Aloides trigona contributing 54% and the gastropod, Pachymelania aurita contributing 33% of the total benthic fauna assemblage during the period of study. The fluctuations in the physicochemical parameters, sediments, and the composition, abundance and diversity of the macrobenthic fauna of the study area were largely influenced by the anthropogenic activities. In particular, stations with pronounced sediment mining activities recorded highly turbid water, changed substratum type and defaunisation

Wet season spatial occurrence of phytoplankton and zooplankton in Lagos Lagoon, Nigeria.

Investigation into the spatial occurrence of wet season phytoplankton and zooplankton in Lagos lagoon, Nigeria was carried out in October, 2008 in 12 stations. A total of 36 species of phytoplankton from 21 genera, 20 zooplankton species from 17 genera and 10 juvenile forms were recorded for the study. The results showed that freshwater conditions within the lagoon were due to high freshwater inflow from adjoining waterways and reduced tidal incursion from the sea. The wet season spectrum of the lagoon was dominated by diatoms for the phytoplankton and copepods for the zooplankton. The presence and array of juvenile forms in the wet season suggest that the lagoon remain a sanctuary, nursery and breeding grounds for aquatic species Crustaceans dominated the spectrum of the juvenile forms. Keywords: Plankton, Physico-chemical characteristics, lagoon, juvenile forms, Lagos

Impacts of Anthropogenic Stressors on Hydrochemistry, Benthic Macroinvertebrates and Sediment Characteristics of the Lagos Lagoon, Nigeria

The anthropogenic impact on the water, benthic macroinvertebrates and sediment grain size of Lagos lagoon was investigated between July and October, 2019. Ten sampling stations were selected based on their importance as likely sources of different forms of anthropogenic stressor to the lagoon. Water temperatures, pH and salinity were measured in situ. Water and benthic samples were collected monthly and analysed using standard methods. Nutrient levels were determined using a spectrophotometer. The hydrochemistry of the stations differed significantly (p<0.05) with the exception of temperature and pH. The sediment grains across the study stations consists basically of sand and mud, with sand dominating the grain type. A total of 502 individuals comprising 3 phyla, 4 classes, 10 families and 11 species was recorded. The phylum mollusca which contributed 92% to the total number of individuals was represented by two Classes; Gastropoda and Bivalvia, with the gastropod Tympanotonus fuscatus having the highest number of individuals (321). Thephylum Annelida represented by one Class, Polychaeta and two Species Nereis sp. and Capitella capitata contributed 6% to the total number of individuals. The class Crustacea, representing the Phylum Arthropoda was the least sampled (7 individuals) constituting about 1.4% of the total population Result showed that different pollution sources have negatively impacted the water chemistry of the lagoon and reduced the diversity and abundance of its benthic macroinvertebrates community. The sedentary nature of this group of benthic fauna could be the major reason why they are most impacted

Seasonal Variations in the Composition and Distribution of Planktonic Fauna in the Eastern Lagos Lagoon, Nigeria

The composition and distribution of planktonic fauna (adult form of zooplankton and planktonic juvenile forms of higher animals) within the eastern part of the Lagos Lagoon were investigated in July, 2008 and March, 2009 representing rainy and dry season respectively. Samples of water and planktonic fauna were collected from twelve stations within the eastern axis of the Lagoon and analyzed using standard methods. The study area had brackish water characteristics with fresh water condition (0\u2030 salinity across the 12 stations) in the rainy season whereas the salinity ranged from 11.4\u2030 to 30.5\u2030 in the dry season. The adult forms zooplankton recorded in the rainy season were mainly Crustaceans, Chaetognathans and Rotifers while those collected during dry season belonged to Crustacean, Cnidaria and Chordata. Crustaceans dominate both adult zooplankton and planktonic juvenile fauna in the two seasons. The rainy season adult zooplankton count (515) was lower than that of dry season (580) but the reverse was the case for the juvenile stages count (520 and 325 in rainy and dry season respectively). Higher species abundance was recorded for both adult zooplankton (20) and juvenile stages (10) in rainy than dry season when 14 and 8 were recorded for the two groups respectively. Higher values were also of community structure indices (Margalef species richness and Shannon-Wiener species diversity) were recorded in the rainy than dry season for the two groups of planktonic fauna. The findings show the influence of salinity gradients on distribution of planktonic fauna of the Lagos Lagoon

Seasonal Variations in the Composition and Distribution of Planktonic Fauna in the Eastern Lagos Lagoon, Nigeria

The composition and distribution of planktonic fauna (adult form of zooplankton and planktonic juvenile forms of higher animals) within the eastern part of the Lagos Lagoon were investigated in July, 2008 and March, 2009 representing rainy and dry season respectively. Samples of water and planktonic fauna were collected from twelve stations within the eastern axis of the Lagoon and analyzed using standard methods. The study area had brackish water characteristics with fresh water condition (0‰ salinity across the 12 stations) in the rainy season whereas the salinity ranged from 11.4‰ to 30.5‰ in the dry season. The adult forms zooplankton recorded in the rainy season were mainly Crustaceans, Chaetognathans and Rotifers while those collected during dry season belonged to Crustacean, Cnidaria and Chordata. Crustaceans dominate both adult zooplankton and planktonic juvenile fauna in the two seasons. The rainy season adult zooplankton count (515) was lower than that of dry season (580) but the reverse was the case for the juvenile stages count (520 and 325 in rainy and dry season respectively). Higher species abundance was recorded for both adult zooplankton (20) and juvenile stages (10) in rainy than dry season when 14 and 8 were recorded for the two groups respectively. Higher values were also of community structure indices (Margalef species richness and Shannon-Wiener species diversity) were recorded in the rainy than dry season for the two groups of planktonic fauna. The findings show the influence of salinity gradients on distribution of planktonic fauna of the Lagos Lagoon