Multiple Urban Wastewater Discharge Pathways as Drivers of Water Quality Degradation in the Cotonou Lagoon, Benin

Dogbè Clément Adjahouinou^1, , Mouhamadou Nourou Dine Liady², Chaim Vivien Doto³, Richard Adandé⁴, Elias Alexandre Sètondji Adanlokonon⁵, Yaovi Zounon^{2, 6}, Sètondé Baptiste Karen Dossoukpèvi^{2, 6}, Simon Ahouansou Montcho¹ and Zacharie Sohou^{2, 6}

¹Unité de Recherche en Aquaculture et Gestion des Pêches, Ecole d’Aquaculture, Université Nationale d’Agriculture, Porto-Novo, République du Bénin

²Laboratoire d’Hydrobiologie et de Recherche sur les Zones Humides, Faculté des Sciences et Techniques, Université d’Abomey-Calavi, République du Bénin

³Laboratoire de Génie Rural, Ecole de Génie Rural, Université Nationale d’Agriculture, Porto-Novo, République du Bénin

⁴Département de Gestion des Ressources Naturelles, Faculté des Sciences de l’Environnement, Université de N'Zérékoré, République de Guinée.

⁵Laboratoire de Recherche en Biochimie et de Toxicologie de l’Environnement, Université d’Abomey-Calavi, République du Bénin

⁶Institut de Recherches Halieutiques et Océanologiques du Bénin, République du Bénin

Cite this paper:
Dogbè Clément Adjahouinou, Mouhamadou Nourou Dine Liady, Chaim Vivien Doto, Richard Adandé, Elias Alexandre Sètondji Adanlokonon, Yaovi Zounon, Sètondé Baptiste Karen Dossoukpèvi, Simon Ahouansou Montcho and Zacharie Sohou. Multiple Urban Wastewater Discharge Pathways as Drivers of Water Quality Degradation in the Cotonou Lagoon, Benin. American Journal of Water Resources. 2026; 14(1):1-7. doi: 10.12691/ajwr-14-1-1

Abstract

This study aimed to evaluate the physicochemical pollution levels in the Cotonou Lagoon, focusing on the dry season, when it receives raw wastewater through various stormwater sewers and drains in the city. Six stations were identified and monthly sampled on the lagoon for this purpose, taking into account the discharge point of the sewers. Temperature, pH, electrical conductivity, dissolved oxygen content, and water transparency of the lagoon waters were measured in situ. Turbidity, suspended solids, and nutrient concentrations, including ammonium, nitrites, nitrates, orthophosphates, and sulfates, of the water samples, were determined using molecular spectrophotometry. Through the assessed physico-chemical, the lagoon waters were found to be nutrient-rich, particularly with ammonium and orthophosphates (up to 10 mg L^-1 and 0.5 mg L^-1, respectively), detected at levels toxic to aquatic life and indicating early risk of eutrophication, despite the high dissolved oxygen levels recorded. The organic pollution index calculated (varying from 2.67 to 4.33), revealed a heterogenous a moderate organic pollution in most of the lagoon sectors, but a strong and a weak pollution level noticed in other sectors. An effective management of wastewater should be undertaken to significantly reduce the pollution of the lagoon, thereby preventing ecological disasters that may result from eutrophication.

Keywords:
Aquatic ecosystem estuary pollution eutrophication aquatic biodiversity sanitation

This work is licensed under a Creative Commons Attribution 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

References:

[1]	Davies-Vollum, K.S., Koomson, D. and Raha, D., “Coastal lagoons of West Africa: a scoping study of environmental status and management challenges”, Anthropocene Coasts, 7(7). 1-16. 2024.
[2]	Newton, A., Icely, J., Cristina, S., Perillo, G.M.E., Turner, R.E., Ashan, D., Cragg, S., Luo, Y., Tu, C., Li, Y., Zhang, H., Ramesh, R., Forbes, D.L., Solidoro, C., Béjaoui, B., Gao, S., Pastres, R., Kelsey, H., Taillie, D., Nhan, N., Brito, A.C., de Lima, R. and Kuenzer, C., Anthropogenic, direct pressures on coastal wetlands, Frontiers in Ecology and Evolution, 8 (144). 2020.
[3]	Manzoni, S., Maneas, G., Scaini, A., Psiloglou, B.E., Destouni, G. and Lyon, S.W., “Understanding coastal wetland conditions and futures by closing their hydrologic balance: the case of the Gialova lagoon, Greece”, Hydrol. Earth Syst. Sci., 24. 3557-3571. 2020.
[4]	Vollenweider, R.A. and Kerekes, J., Eutrophication of Waters: Monitoring, Assessment and Control. Report of the Cooperative Program on Eutrophication. Organization for the Economic Co-operation Development (OECD), Paris; France, 1982, 158p
[5]	Atinkpahoun, C.N.H., Pons, M.-N., Louis, P., Leclerc, J.-P. and Soclo, H.H. “Rare earth elements (REE) in the urban wastewater of Cotonou (Benin, West Africa)”, Chemosphere, 251. 126398. 2020.
[6]	Ravina, M., Galletta, S., Dagbetin, A., Kamaleldin, O.A.H., Mng’ombe, M., Mnyenyembe, L., Shanko, A. and Zanetti, M. “Urban wastewater treatment in African countries: Evidence from the Hydroaid initiative”, Sustainability, 13(22). 12828. 2021.
[7]	Onu, M.A., Ayeleru, O.O., Oboirien, B. and Olubambi, P.A., “Challenges of wastewater generation and management in sub-Saharan Africa: A review”, Environmental Challenges, 11. 100686. 2023.
[8]	Abahi, K.S., Piscart, C. and Gnohossou, P.M., “Responses of the macroinvertebrate community to urban wastewater pollution in the upper Ouémé Basin in Benin”, International Journal of Limnology, 60(6). 2024.
[9]	Djihouessi, M.B., Tigo, B.A. and Aina, M.P., “The use of nutrient-budget approach for informing eutrophication management in urbanised shallow coastal lakes: A case study from Lake Nokoué in Benin”, Limnologica, 90. 125915. 2021.
[10]	Preisner, M. “Surface water pollution by untreated municipal wastewater discharge due to a sewer failure”, Environmental Processes, 7(3). 767-780. 2020.
[11]	Adjahouinou, D.C., Liady, N.D. and Fiogbé, E.D., “Diversité phytoplanctonique et niveau de pollution des eaux du collecteur de Dantokpa (Cotonou-Bénin), Int. J. Biol. Chem. Sci., 6(5). 1938-1949. 2012.
[12]	Hounkpè, S.P., Adjovi, E.C., Crapper, M. and Awuah, E., “Wastewater management in third world cities: case study of Cotonou, Benin”, Journal of Environmental Protection, 5(5). 387-399. 2014.
[13]	Adjahouinou, D.C., Doto, CV, Adanlokonon, E.A.S., Zouhir F. and Liady, M.N.D., “Pollution Levels of Urban Drainage, Stormwater and Wastewater Mixtures Released Into Coastal Waters in Cotonou City (Benin, West Africa)”, Journal of Environment Pollution and Human Health, 13(3). 37-45. (2025).
[14]	Roche International. “Etude du Projet d’aménagement des plans d’eau du Sud- Bénin : l’Environnement, les eaux et les forêts”, Vol 2, Tome 4.
[15]	Rodier, J., Legube, B. and Merlet, N., “L’Analyse de l’eau : contrôle et interprétation”, 10th ed., Dunod, Paris, 2016, 1190p.
[16]	APHA, AWWA and WEF, “Standard Methods for the Examination of Water and Wastewater”, 23th ed., APHA Press, Washington, DC, 2017, 1796 p.
[17]	Leclercq, L. “Intérêt et limites des méthodes d’estimation de la qualité de l’eau”, Station scientifique des Hautes Fagnes, Belgique, 2001, 75p.
[18]	Adam, K. S. and Boko, M., “Le Bénin”. Les Editions du Flamboyant, EDICEF, Vanves, Cedex, 1993.
[19]	Dovonou, F., Aina, M., Boukari, M. and Alassane, A., “Pollution physico-chimique et bactériologique d’un écosystème aquatique et ses risques écotoxicologiques : cas du Lac Nokoue au Sud Benin”, Int. J. Biol. Chem. Sci, 5(4). 1590-1602. 2011.
[20]	Capo-Chichi, H.B.P., Adandedjan, D., Agblonon Houelome, T.M. and Laleye P. “Physico-chimie et pollution organique du lac Nokoué au Sud du Bénin”, Journal of Applied Biosciences, 170. 17752-17774. 2020.
[21]	Dèdjiho, C.A., Mama, D., Tomètin, L., Nougbodé, I., Chouti, W., Sohounhloué, C.K.D. and Boukari M, “Évaluation de la qualité physico-chimique de certains tributaires d’eaux usées du lac Ahémé au Bénin”, Journal of Applied Biosciences, 70. 5608-5616. 2013.
[22]	Onuoha, P.C., Nwankwo, D.I., Chukwu, L.O., Wim, V., “Spatio-temporal Variations in Phytoplankton Biomass and diversity in a Tropical Eutrophic Lagoon, Nigeria”. Journal of American Science, 7(8). 33-46. 2011.
[23]	Kumolu-Johnson, C.A. and Ndimele, P.E. “Some aspects of the limnology and heavy metal content of water, sediment and Oreochromis niloticus (Linnaeus, 1758) from Ologe Lagoon, Lagos, Nigeria”, Research Journal of Environmental Toxicology, 6(5). 210-221. 2012.
[24]	Issola, Y., Kouassi, A.M., Dongui, B.K. and Biemi, J., “Caractéristiques physico-chimiques d’une lagune côtière tropicale: lagune de Fresco (Côte d’Ivoire)”, Afrique Science, 4(3). 368-393. 2008.
[25]	Seu-Anoï, N.M., Ouattara, A., Koné, Y.J.-M. and Gourène, G., “Seasonal distribution of phytoplankton in the Aby lagoon system (Ivory Coast, West Africa)”, African Journal of Aquatic Science, 36(3). 321-330. 2011.
[26]	Assemian-Niango, S., Konan, S.-E. and Konan Kouakou, J.-M., “Seasonal variations of physicochemical parameters and nutrients of a coastal tropical lagoon’s waters: Aby lagoon (Côte d’Ivoire)”. International Journal of Innovation and Applied Studies, 31(1). 14-20. 2020.
[27]	Muthucumaran, S., Pathmarajah, S. and Mowjood, M.I.M. (2015) “Vertical variation of salinity, electrical conductivity, temperature and pH of Batticaloa Lagoon”, International Journal of Applied and Physical Sciences, 1(2). 36-41. 2015.
[28]	Koledoye, T.Y., Akinsanya, B., Adekoya, K.O. and Isibor, P.O., Physicochemical parameters of the Lekki Lagoon in relation to abundance of Wenyonia sp. (Cestoda: Caryophyllidae) in Synodontis clarias (Linnaeus, 1758). Environmental Challenges, 7. 100453. 2022.
[29]	MELCCFP (Ministère de l’Environnement, de la Lutte contre les Changements Climatiques, de la Faune et des Parcs), “Critères de qualité de l'eau de surface”. 2025. https:// www.environnement. gouv.qc.ca/eau/criteres_eau/index.asp.
[30]	Okpeitcha, O.V., Chaigneau, A., Morel, Y., Duhaut, T., Marsaleix, P., Rétif, F., Honfo, J., Stieglitz, T., Sohou, Z., Sintondji, L.O. and Mama, D., “Modeling seasonal salinity variations in a large West African lagoon (Nokoué, Benin): major drivers and mechanisms”, Regional Studies in Marine Science, 69. 103330. 2024.
[31]	Adingra, A.A., Kouadio, A.N., Blé, M.C. and Kouassi, A.M., “Bacteriological analysis of surface water collected from the Grand-Lahou lagoon, Côte d’Ivoire”, African Journal of Microbiology Research, 6(13). 3097-3105. 2012.
[32]	Akpor, O.B. and Muchie, M., “Environmental and public health implications of wastewater quality”, African Journal of Biotechnology, 10 (13). 2379-2387. 2011.
[33]	Paerl, H.W., Gardner, W.S., Havens, K.E., Joyner, A.R., McCarthy, M.J., Newell, S.E., Qin, B. and Scott, J.T., “Mitigating cyanobacterial harmful algal blooms in aquatic ecosystems impacted by climate change and anthropogenic nutrients”, Harmful Algae, 54. 213-222. 2016.
[34]	Hammami, J., Brahim, M., Gueddari, M., “Essai d'evaluation de la qualite des eaux de ruissellement du bassin versant de la lagune de Bizerte”, Bull. Inst. Natn. Ccien. Mer de Salammbô, 32. 69-77. 2005.
[35]	Kpannieu, D.E., Kouadio, K.N., M’Bra, I.C., Hippolyte, C.N., Coulibaly, L. and Ouffouet, S., “Physico-Chemical Pollution and Trophic State of Biétry Bay (Ebrié Lagoon, Abidjan, Ivory Coast)”, Journal of Materials Science and Chemical Engineering, 10. 87-99. 2022.
[36]	Glibert, P.M. (2020) “Harmful algae at the complex nexus of eutrophication and climate change”, Harmful Algae, 91. 101583. 2020.
[37]	Oluwajoba, E.O., Ikewenwei, N.B., Abdul, W.O., Idowu, A.B. and Popoola, S.O., “Spatio-temporal trends in the physicochemical parameters of mid-Lagos Lagoon water, South-Western Nigeria”, Nigerian Journal of Fisheries, 19(1). 2381-2388. 2022.
[38]	Newton, A., Brito, A.C., Icely, J.D., Derolez, V., Clara, I., Angus, S., Schernewski, G., Inácio, M., Lillebø, A.I., Sousa, A.I., Béjaoui, B., Solidoro, C., Tosic, M., Cañedo-Argüelles, M., Yamamuro, M., Reizopoulou, S., Tseng, H.-C., Canu, D., Roselli, L., Maanan, M., Cristina, S., Ruiz-Fernández, A.C., de Lima, R.F., Kjerfve, B., Rubio-Cisneros, N., Pérez-Ruzafa, A., Marcos, C., Pastres, R., Pranovi, F., Snoussi, M., Turpie, J., Tuchkovenko, Y., Dyack, B., Brookes, J., Povilanskas, R. and Khokhlov, V., “Assessing, quantifying and valuing the ecosystem services of coastal lagoons”, Journal for Nature Conservation, 44. 50-65. 2018.
[39]	Griffith, A.W. and Gobler, C.J., Harmful algal blooms: a climate change co-stressor in marine and freshwater ecosystems, Harmful Algae, 91(101590): 1-12. 2020.
[40]	UNESCO WWAP. United Nations World Water Development Report 2023: Partnerships and Cooperation for Water. Paris: UNESCO. 2023. https:// www.unesco.org/ reports/ wwdr/ 2023/ en/download.