Environmental pollution loads on surface water chemistry and potentially ecological risks of inland aquatic ecosystem in South-Eastern State, Nigeria

Abstract

The study assessed water chemistry of Nworie inland aquatic ecosystem in South eastern, Nigeria from January, 2020 to December 2022. Water samples were taken from the upper, middle, and lower river at 200 m interval. Data collected were subjected to multivariate analyses. Results of physicochemical tracers indicated mean CaCO3, Ca2+&Chemical Oxygen Demand (COD) to be 172.8 mg/l, 103.1 mg/l, 16.50 mg/l respectively above the World Health Organisation (WHO) critical limits, while turbidity (NTU), dissolved oxygen (DO) mgl−1, chloride (Cl−) mg/l, Magnesium (Mg) mg/l, Sodium (Na) mg/l, sulphate (SO42+) mg/l, nitrate (NO3−) mg/l, potassium (K) mg/l and phosphate (PO34) were below the limits. Heavy metals (mg/l) showed mean values viz: Cd 2+(0.053), Cr2+(0.049), Fe2+(0.443), Ni2+(0.024), and Pb (0.787) which were all above some critical global limits, except for Cu2+ and Zn2+ and in decreasing abundance: Pb2+ ≥ Fe2+ ≥ Cu2+ ≥ Zn2+ ≥ Cd2+ ≥ Cr2+ ≥ Ni2. Physicochemical tracers and elements in water correlated in both positive and negative directions. Principal component analysis (PCA) showed significant loads of PC3; CaCO3, NO3, COD, DO, Ca, PO4, Cu, Fe, Zn, PC2; moderate loads of SO4, Cl, & Na originating from complex human activities. Contamination factor (Cf), recorded high for cadmium while pollution load & ecological risk recorded low in decreasing order: Cr2+ ≥ Zn2+ ≥ Ni2+ ≥ Cd2+ ≥ Pb2+ ≥ Cu2+ ≥ Fe2+ with contamination degree in order of: Lower River (LR) ≥ Upper River(UR) ≥ Middle River(MR) and low risk index. Continuous monitoring of human activities along the whole River is important to mitigate any aquatic ecosystem damage for water quality sustainability.

Characterizing River Manafwa Floodplain and Adjacent Soils

“…Cultivated floodplains have more silt composition than upland and midstream areas. This is in agreement with Ubuoh (2016), during the studies on the effect of flooding on soil quality in Abakaliki-Nigeria, which concluded that such results are a clear sign of more soil fertility that favours crop production. Soils in floodplains have a higher composition of clay than sand and silt, making floodplains more fertile and favourable for crop production (Ogbodo, 2011) )…”

“…According to Montgomery (2017), this result implies that there is a significant difference between the upland and the floodplains fallowed for over a year for Nitrogen. This result supports findings by Ubuoh (2016), during the study of the effects of flooding on soil quality in Abakaliki agro-ecological zone, Nigeria that concluded that there were significant differences among treatments in total Nitrogen, a strong indication of rapid fruiting and ripening of fruits. Flooding lowlands fallowed for a year posted the highest percentage at 0.32%, followed by the floodplains fallowed for over a year at 0.20% as compared to the lowest posting of 0.09% from the upland.…”

“…Further studies have revealed that soil properties such as total porosity, moisture content, pH and organic carbon were higher after flooding than before, whereas others like bulk density, available P and total N were lower in the soil after flooding than before flooding (Rahman & Ranamukhaarachchi, 2003;Ubuoh, 2016;Njoku & Okoro, 2015). Flooding leads to both increases and decreases in soil nutrient content, with the former occurring by availing nutrients that are lacking in the soil (Ubuoh, 2016;Rodríguez et al, 2016). During flooding, floodwater dissolves and transports soil nutrients from flooding surfaces to adjacent rivers and vice versa through lateral flow (Ubuoh, 2016;Tsheboeng et al, 2014;Rahman & Ranamukhaarachchi, 2003).…”

“…Wetting of the floodplains and meadows by floods releases immediate nutrients that were left over from the last flood and those that result from the rapid decomposition of organic matter that has accumulated during the flood (Njoku et al, 2015;Kaur et al, 2020). Further studies have revealed that soil properties such as total porosity, moisture content, pH and organic carbon were higher after flooding than before, whereas others like bulk density, available P and total N were lower in the soil after flooding than before flooding (Rahman & Ranamukhaarachchi, 2003;Ubuoh, 2016;Njoku & Okoro, 2015). Flooding leads to both increases and decreases in soil nutrient content, with the former occurring by availing nutrients that are lacking in the soil (Ubuoh, 2016;Rodríguez et al, 2016).…”

“…Flooding leads to both increases and decreases in soil nutrient content, with the former occurring by availing nutrients that are lacking in the soil (Ubuoh, 2016;Rodríguez et al, 2016). During flooding, floodwater dissolves and transports soil nutrients from flooding surfaces to adjacent rivers and vice versa through lateral flow (Ubuoh, 2016;Tsheboeng et al, 2014;Rahman & Ranamukhaarachchi, 2003). During flooding, soil becomes highly reduced, resulting in a decrease in pH, which leads to an increase in the mobility of soil nutrients such as P, N, Mg, Ca, Na and K through leaching (Orimoloye et al, 2018;Wright et al, 2001).…”