Browsing by Author "Mahu, E."
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Item The bulk fluorescein diacetate assay (FDA) as a technique for evaluating biotic impacts of crude oil to coastal sediments(Environmental Earth Sciences, 2018-11) Mahu, E.; Moore-Hanaway, J.; Maurer, B.; Welschmeyer, N.; Coale, K.H.This study adapted the bulk fluorescein diacetate (FDA) assay to evaluate the impact of crude oil on biological activity levels in marine sediments. Sediment cores from the Elkhorn Slough, California were incubated with different levels of sweet crude oil (Deepwater Horizon, Macondo Prospect) in the Moss landing Marine Laboratories aquarium facility over a 30-day period. During this period, the amount of fluorescein released, concentration of oxygen in overlying waters, and flux of oxygen into the sediments were monitored. For all treatments a strong negative correlation between added oil and FDA production was observed (p < 0.05). The concentration of oxygen in the first 2 mm of sediment cores decreased linearly with the addition of crude oil and correlated positively with fluorescein released (p < 0.05). A linear increase in sediment oxygen flux was also observed upon crude oil addition. The miniaturized bulk FDA assay could be powerful in evaluating oil spill impacts in coastal systems. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.Item Correction to: Probabilistic risk assessment and risk mapping of metals in tropical estuarine sediments using the Aquarisk model(Environmental Monitoring and Assessment, 2018-10) Mahu, E.; Nyarko, E.; Asiedu, D.; Laryea, W.S.; Szymczak, R.; Twining, J.Item Distribution and enrichment of trace metals in marine sediments from the Eastern Equatorial Atlantic, off the Coast of Ghana in the Gulf of Guinea(Marine Pollution Bulletin, 2015-06) Mahu, E.; Nyarko, E.; Hulme, S.; Coale, K.H.We present results of a preliminary geochemical assessment of Cd, Pb, V, As, Ni, Cu, Zn, Mg, Al, K, Ca, and Fe in marine sediments from the Eastern Equatorial Atlantic, off the Coast of Ghana. Samples were taken along 4 regions G1, G2, G3 and G4 at approximately 25 m, 100 m, and 250 m, 500 m and 1000 m depths. Elemental compositions were assessed through the estimation of Al-normalized enrichment factors and geochemical accumulation indices, and the concentrations determined to produce any potential toxic effects to biota. Significant enrichment of the bottom sediments with Cd, Ni and As were observed at some locations with sediments showing signs of heavy pollution with As at region G4. Apart from Ni, V and As which were beyond threshold effects levels at most regions, all other metals were below probable effect levels. Both natural and anthropogenic processes controlled trace metal accumulation and distribution in the Ghanaian coastal environment.Item Enhancing Satellite Oceanography-Driven Research in West Africa: a Case Study of Capacity Development in an Underserved Region(Remote Sensing in Earth Systems Sciences, 2021) Nyadjro, E.S.; Mahu, E.; Addo, K.A.; et al.Marine business and resources play a major role in the economics and way of life in coastal West African countries. Such countries see great profitability from their marine resources while also facing challenges that come with a bordering sea. Despite Due to this fact, there has been limited research into the optimal way for West African Coastal States to coexist with and sustainably use their marine resources, a research deficit that is mainly due to a lack of infrastructure for in-situ work, lack of capacity development, and comprehensive datasets to undertake oceanographic research. The Coastal Ocean Environment Summer School in Ghana (COESSING; www.coessing.org) was developed to help meet some of these challenges. Each summer since 2015, ocean scientists (e.g., biologists, chemists, physicists, hydrologists) from the USA and Europe have collaborated with West African colleagues to lead a week-long intensive summer school in Accra, Ghana, alternating in location between the Regional Maritime University and the University of Ghana. The school receives in excess of 100 participants drawn from universities, government agencies, and private sector organizations, mainly from Ghana and neighboring Liberia, Nigeria, Togo, and Benin, among others. The format of the school includes morning lectures, afternoon field trips, hands-on laboratory exercises and one-on-one coaching of students. Important to the COESSING program is the satellite oceanography component, which introduces participants to the extensive and often free, remotely sensed oceanographic datasets. Participants develop skills that allow them to access, process, and analyze these datasets in order to better understand regional oceanographic phenomena, such as upwelling, pollution, habitat characterization, sea level rise, and coastal erosion. Following school, facilitators keep in touch with program participants, helping them acquire and analyze data for their studies, dissertations, and often graduate school applications, etc. In summary, schools such as COESSING are critical not only for science in the region but for the global ocean community as such training develops eager, bright minds while leading to improved regional observation and modeling strategies in severely under-sampled seas. Here, we describe a unique case in which satellite oceanography has led to such outcomes for countries bordering the Gulf of Guinea, West AfricaItem Geochemistry of Estuarine Sediments of Ghana: Provenance, Tracemetal Accumulation Trends and Ecotoxicological Risks(University Of Ghana, 2014-07) Mahu, E.The sedimentary record, as revealed in sediment cores, can be used to reconstruct the past history of contaminant input into the aquatic environment. This is because contaminant inputs equilibrate rapidly with sediment supply, and the sediment column represents a continuous sequence of sediments that are associated with contaminant accumulation. With radiometric techniques, it is possible to date recent sediments over a period corresponding to about five half-lives (approximately 100-200 years using 210Pb). To understand the geochemistry of estuarine sediments in relation to their provenance, trace metal accumulation trends and potential ecotoxicological risks, this study investigated sediment cores and surficial sediments from the Ankobra, Pra, Amisa, Densu, Sakumo II and Volta estuaries of Ghana. Geochemical and petrographical techniques were used to reveal the source of sediment supply into the estuarine environments. In addition, Gamma Spectroscopy and Inductively Coupled Plasma Mass Spectrometric (ICP-MS) techniques were used for deriving geochronologies, sedimentation rates, spatial and temporal accumulation of Mo, Cd, Pb, V, Cr, Cu, Zn, As and Hg in the study sites. The pollution status of the estuarine sediments was investigated using Aluminum-normalized enrichment factors (EFs). Cluster and correlation analysis differentiated natural from anthropogenic sources of trace metal in the estuaries. The excess fluxes of trace metals, estimated using sedimentation rates helped in quantifying the extent of anthropogenic contamination of metals in each estuary. AQUARISK software was used to assess any potential ecotoxicological risks associated with trace metal enrichments. Results showed that sediments from the Ankobra, Pra, Densu and Volta estuaries comprised quartzose sedimentary provenance while those of Amisa and Sakumo II estuaries comprised mafic igneous provenance. The sedimentation rates estimated from the constant rate of supply model were 0.24±0.10 gcm-2y-1, 0.47±0.20 gcm-2y-1, 0.43±0.02 gcm-2y-1, 0.31±0.13 gcm-2y-1, 0.20±0.01gcm-2y-1 and 0.54±03 gcm-2y-1 for the Ankobra, Pra, Amisa, Densu, Sakumo II and Volta estuaries respectively. The sediment core from the Ankobra estuary was significantly enriched with Hg (5.0Item Impact of agricultural practices on ecosystem health of lagoons: a case study of the Keta Lagoon Complex in Ghana, West Africa.(Environmental Monitoring and Assessment, 2023) Mahu, E.; Danso, P.; Edusei, M.O.; deGraft-Johnson, K.A.A.The paper reports on the current ecological health of the Keta Lagoon Complex by analyzing a suite of physical, chemical, and biological environmental conditions prevailing within it. Results are discussed in relation to the main human activity (i.e., agriculture) prevailing in its catchment. The current water quality of the lagoon has declined compared to data collected 20 years ago with elevated levels in parameters such as nitrate, phosphate, turbidity, and temperature. Secchi disk depth, salinity, and dissolved oxygen levels in the lagoon have decreased. More than 60% of the total area of the lagoon is predicted to be currently unsuitable to support aquatic life. The Carlson’s TSI estimated for the various zones of the lagoon ranged between 72.40 and 80.61 depicting a highly eutrophic lagoon, with about 90% of the total area studied confirmed to be experiencing some degree of eutrophication. The plankton index of biotic integrity also yielded high values of between 3 and 6 in most areas of the lagoon, thereby affirming the poor health of the lagoon. The diversity of phytoplankton and benthic macroinvertebrate species in the lagoon has reduced significantly in the last two decades with about 11 genera of phytoplankton missing in the present study. Benthic macroinvertebrate assemblage richness, evenness, and diversity have decreased from 3.6, 2.0, and 5.8 in 2008 to 1.2, 0.8, and 1.7 respectively, in the present study. Overall, the health of the Keta Lagoon remains poorer and continues to decline with no signs of recoverItem Impact of the citizen science project Collect on ocean literacy and well-being within a north/west African and south-east Asian context(Frontiers in Psychology, 2023) Severin, M.I.; Mahu, E.; Akpetou, L.K.; et al.Plastic pollution is both a societal and environmental problem and citizen science has proven to be a useful tool to engage both the public and professionals in addressing it. However, knowledge on the educational and behavioral impacts of citizen science projects focusing on marine litter remains limited. Our preregistered study investigates the impact of the citizen science project Citizen Observation of Local Litter in coastal ECosysTems (COLLECT) on the participants’ ocean literacy, pro-environmental intentions and attitudes, well-being, and nature connectedness, using a pretest-posttest design. A total of 410 secondary school students from seven countries in Africa (Benin, Cabo Verde, Côte d’Ivoire, Ghana, Morocco, Nigeria, and Asia (Malaysia) were trained to sample plastics on sandy beaches and to analyze their collection in the classroom. Non-parametric statistical tests (n = 239 matched participants) demonstrate that the COLLECT project positively impacted ocean literacy (i.e., awareness and knowledge of marine litter, self-reported litter-reducing behaviors, attitudes towards beach litter removal). The COLLECT project also led to higher pro-environmental behavioral intentions for students in Benin and Ghana (implying a positive spillover effect) and higher well-being and nature connectedness for students in Benin. Results are interpreted in consideration of a high baseline in awareness and attitudes towards marine litter, a low internal consistency of pro-environmental attitudes, the cultural context of the participating countries, and the unique settings of the project’s implementation. Our study highlights the benefits and challenges of understanding how citizen science impacts perceptions and behaviors towards marine litter in youth from the respective regions.Item Lophelia reefs of North and West Africa–Comparing environment and health(Marine Biology, 2023) Buhl‑Mortensen, L.; Houssa, R.; Mahu, E.The health status of cold-water coral reefs on the West African coast was investigated with the main objective of obtain ing knowledge of the adaptive capacity of Lophelia pertusa to environmental stressors. Three coral sites were studied, in Northern Morocco, in the Morocco/Mauritania region (both in 2020) and, in the Ghana and Ivory coast region (visited in 2012, 2017, and 2019). Area cover of live colonies, explored through underwater videos, was used as an indicator of reef health and compared with the environmental variables: reef position, depth, water mass, temperature, dissolved oxygen con centration (DO), carbonate chemistry (pH, aragonite saturation (ΩAr), macronutrients and particles (visual). For a broader picture of the adaptations presented by Lophelia our results were compared with reefs in contrasting environments. Of Ghana and Mauritania healthy reefs (i.e., having areas with more than 20 % cover of live colonies) were found to reside at DO concentrations between 1.1 and 1.6 ml L−1, in corrosive waters (pH 7.7 and ΩAr 1.0) with high nutrient concentrations. By contrast, the reefs of the North of Morocco, sitting in well-oxygenated waters with oversaturated ΩAr, had no or few live colonies. Our fndings together with data from other studies show that Lophelia has a wide tolerance to hypoxia and acidifcation, and that in relation to climate change increased temperature and silting could pose more serious threats. These fndings highlight the importance of continued studies of Lophelia reefs in contrasting environmental conditions to better understand their adaptation potential to climate change-related stressorsItem Microplastic ingestion by pelagic and demersal fish species from the Eastern Central Atlantic Ocean, off the Coast of Ghana(Marine Pollution Bulletin, 2020-02-22) Adika, S.A.; Mahu, E.; Crane, R.; Marchant, R.; Montford, J.; Folorunsho, R.; Gordon, C.We present data on the occurrence of microplastics in fish from the Guinea current region off Ghana's Coast. Frequency of occurrence of microplastics in the fish species followed the order: Sardinella maderensis (41%) > Dentex angolensis > (33%) > Sardinella aurita (26%). Mean numbers of microplastics ingested were 40.0 ± 3.8, 32.0 ± 2.7 and 25.7 ± 1.6 for S. maderensis, D. angolensis and S. aurita respectively. Industrially produced pellets were the most dominant (31%) microplastic type followed by microbeads (29%), burnt film plastics (22%) and unidentified fragments (9%). Microfibers (2%), threads (2%) and foams (< 0.1%) were the least occurring microplastics in the fish species. Condition factors estimated for D. angolensis and S. aurita were>1 and below 1 for S. maderensis. The findings of the study show the common occurrence of microplastics in fish stocks and pave the way for future studies on microplastics in this RegionItem Petrography of detrital zircons from sandstones of the LowerDevonian Accraian Formation, SE Ghana: Implications onproven ance(Geological Journal, 2019-08-22) Anani, C.Y.; Anim, R.O.; Armah, B.N.; Atichogbe, J.F.; Sakyi, P.A.; Mahu, E.; Asiedu, D.K.Integrated petrographic studies entailing quartz‐type analysis and zircon typologic studies were carried out on sandstones of the Lower Devonian Accraian Formation of southern Ghana to constrain their provenance and tectonic setting. The stratigraphic succession of the Devonian Accraian Group consists mainly of sandstones in the Lower Accraian Formation, shales in the Middle Accraian Formation, and sandstone–shale intercalations in the Upper Accraian Formation. Systematic sampling of sandstones was conducted in the Lower Devonian Accraian Formation. Modal petrographic analysis indicates that the sandstones are quartz arenites with their framework grains consisting on average of, 99.8% quartz, 0.14% lithics with little or no feldspars. They are subangular to subrounded in shape. Modal mineralogy of the sandstones suggests that they are of craton interior origin with an affinity to recycled orogenic provenance. Quartz‐type analysis was used to unravel distinct characteristic features of the quartz grain, namely its polycrystallinity, nonundulose, and undulose nature to constrain the source rock. This pointed to multiple sediment supply from both a plutonic origin and a medium‐ to high‐grade metamorphic terrain. Furthermore, a comprehensive zircon typology study on 298 zircon grains indicate multiple provenances of calc‐alkaline affinity. This study revealed that the Lower Accraian Formation sandstones probably received sediment input from the Paleoproterozoic Birimian Basin granitoids and their associated metasedimentary rocks and some additional supply from the Neoproterozoic sedimentary rocks from the Volta Basin which are inclusive of sediments derived from the Dahomeyide Belt of the Pan‐African Orogeny.Item Provenance, paleo-weathering and -redox signatures of estuarine sediments from Ghana, Gulf of Guinea(Quaternary International, 2018-11) Mahu, E.; Asiedu, D.K.; Nyarko, E.; Hulme, S.; Coale, K.H.; Anani, C.Y.This paper discriminates the source of sediment supply (provenance), degree of chemical weathering, and redox conditions of Holocene sediments cored from the Ankobra and Pra estuaries of Ghana in the Gulf of Guinea using their geochemical characteristics. Considerable stratigraphical variations were observed in major element compositions in the sediments from both the Ankobra (Al2O3: 5.3–14.2%, SiO2: 75.9–88.2%, CaO: 0.3–1.2%, K2O: 0.5–1.2%) and the Pra (Al2O3: 7.8–16.9%, SiO2: 72.8–86.5%, CaO: 0.3–0.4%, K2O: 0.7–1.2%) estuaries. Elemental compositions were similar in both estuaries depicting similarities in their source rock characteristics. Some of the major and trace elements correlated significantly (r2 > 0.8) with Al2O3 in the Pra estuary confirming their possible hydraulic fractionation. Geochemical classification showed the sediments from both estuaries were predominantly composed of sub-arkoses with only a few litharenites. The chemical index of alteration (CIA*), Chemical index of weathering (CIW*), plagioclase index of alteration (PIA*), the Index of compositional variability (ICV), the SiO2/Al2O3 ratios and SiO2 vs. (Al2O3+K2O + NaO), suggest high degrees of chemical weathering coinciding with warm climatic conditions in the source regions as well as sub-matured to mature estuarine sediments deposited under semi-arid to semi-humid conditions. The sediment geochemistry and discrimination diagrams denote similar continental signature derivatives of the sediments from both estuaries. Both sediments are likely derived from intermediate to felsic granitoid source rocks as well as from a quartzose sedimentary provenance formed in a passive continental margin. The Ni/Co and V/Cr ratios depict sediment deposition under oxic conditions through time in both estuaries.