ABSTRACT
The present study assessed the pollution fingerprints of two estuaries (Pra and Ankobra) in the Southwestern region of Ghana. Contaminations of sediments in the two estuaries were evaluated for particle size distribution, total organic matter, microplastics, nitrate-nitrogen, phosphorous, and metals. The results revealed the mean concentration of microplastics particles in Pra as follows: fibre (14.22 ± 4.99); sheet (24.44 ± 13.21); fragment (38.00 ± 25.47); bead (4.22 ± 4.84); and in Ankobra as follows: fibre (13.00 ± 7.56); sheet (20.60 ± 12.59); fragment (8.70 ± 11.22); bead (3.30 ± 4.14). Metal concentrations were in the order Fe > As > Zn > Cu > Pb; concentrations of Cd and Hg were below the detection limit. Pb, Cu, and Zn were within Interim Marine Sediment Quality Guidelines except for Fe and As. The respective order of contamination factor and geo-accumulation index of the metals were As > Fe > Zn > Pb > Cu and As > Fe > Pb > Cu. The pollution load index recorded for Pra and Ankobra estuaries were 1.94 and 2.71, respectively, suggesting deterioration of the estuaries due to metal pollution. The principal component analysis indicated that pollution fingerprinting is strongly influenced by Fe, Cu, As, Zn, silt, and sand associated with illegal artisanal gold mining activities. Thus, the findings from this study imply that the levels of pollution recorded could have deleterious impact on human health and the communities that depend on the services rendered by the estuaries. There is the need to adopt strategies for pollution control to protect these fragile ecosystems that support livelihoods.
ABSTRACT
Long-term depositions of animal manures affect P dynamics in soils and can pose environmental risks associated with P losses. Laboratory studies were done on P solubility characteristics in a manure-impacted Immokalee soil (sandy, siliceous, hyperthermic Arenic Alaquod) and the effectiveness of water treatment residual (WTR) in controlling P leaching. Soil samples with contrasting initial total P concentrations were prepared by mixing samples of a manure-impacted surface A horizon and a minimally P-impacted E horizon. Effects of mixing various ratios of A and E horizons, WTR rates (0, 25, 50, and 100 g kg(-1)), and depths of WTR incorporation (mixed throughout the soil column or partially incorporated) on P leaching were determined. Between 62 and 77% of total P was released from the soil mixes by successive water extractions, suggesting a considerable buffering capacity of this manure-impacted soil to resupply P into solution. Between 224 and 408 mg kg(-1) P were leached during the 36-wk leaching period in the absence of WTR. Mixing WTRs with soil reduced soluble P concentration in leachates by as much as 99.8% compared with samples without WTR. Thoroughly mixing WTR with the entire soil column (15 cm) was much more efficient than mixing WTR with only the top 7.5 cm of soil. Calcium- and Mg-P forms appear to control P release in soils without WTR, whereas sorption-desorption reactions probably determine P leaching in WTR-treated samples. Soil P distribution in various chemical forms was affected by WTR additions. Data suggest that WTR-immobilized P is stable in the long term.
