Abstract
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.
Highlights
Lagoons serve as ecotones between freshwater, marine and terrestrial biotopes (Saki-Yao et al, 2017) and are heavily impacted (Kennish, 2002)
There was no significant difference in the water temperature (p0.05) across the study stations in consonance with previous works which confirms that temperature is a conservative factor in most tropical waters
This observation is in harmony with earlier works on the Lagos lagoon (Okoye et al 2010; Nkwoji and Edokpayi, 2013)
Summary
Lagoons serve as ecotones between freshwater, marine and terrestrial biotopes (Saki-Yao et al, 2017) and are heavily impacted (Kennish, 2002). Macroinvertebrates are impacted by pollutants primarily as a result of changes in primary production and in the chemistry of water column and sediment. These changes potentially lead to reduced diversity and abundance, shifts in community composition, physiological changes and mass mortality. Ajao and Fagade, (1991) studied of the sediments and communities in Lagos Lagoon. The study focused more on the role of sediment composition and type in the structure of the benthic communities. Nkwoji et al (2010) worked on the benthic macroinvertebrates Bioindicators at the Lagos lagoon and emphasized on the importance of The study focused more on the role of sediment composition and type in the structure of the benthic communities. Nkwoji et al (2010) worked on the benthic macroinvertebrates Bioindicators at the Lagos lagoon and emphasized on the importance of
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