Marine and Freshwater Research Marine and Freshwater Research Society
Advances in the aquatic sciences
RESEARCH ARTICLE

The salinity responses of tropical estuaries to changes in freshwater discharge, tidal mixing and geomorphology: case study of the man-affected Senegal River Estuary (West Africa)

C. Chevalier A C , M. Pagano A , D. Corbin A and R. Arfi A B

A Aix-Marseille University, Mediterranean Institute of Oceanography (M I O), 13288, Marseille, Cedex 9, France; Université du Sud Toulon-Var, 83957, La Garde Cedex, CNRS–INSU/IRD UM 110, France.

B Institut de Recherche pour le Développement (IRD) 44, Boulevard de Dunkerque Immeuble ‘Le Sextant’ 13002 Marseille, France.

C Corresponding author. Email: cristele.chevalier@univ-amu.fr

Marine and Freshwater Research 65(11) 987-1002 http://dx.doi.org/10.1071/MF13169
Submitted: 27 June 2013  Accepted: 10 February 2014   Published: 1 October 2014

Abstract

Salinity in estuaries is influenced by a variety of processes including tidal advection and diffusion and river discharge. The effect of hydrodynamic features on salinity was studied in the Senegal River Estuary (SRE). This estuary is of strategic importance for large populations, but it has been greatly affected by human action (regulation of the freshwater inflow, change in the location of the river mouth ...), which has caused major changes in salinity and ecological functioning. To analyse the impacts of these changes and to determine the spatial and temporal variations in salinity in the SRE, we used a combination of three-dimensional modelling and field measurements. The overall salinity depends on freshwater inflow and tidal fluctuations. Salinity variation is mainly driven by ebb and flood near the mouth and by fortnightly cycles upstream. The enlargement of the mouth increases salinity, whereas its shifting location changes the location of the salinity front and creates a slack water zone downstream. Connection and disconnection of the tributaries also affects the salinity. The present study explains how the recent modifications have increased spatial variation and reduced seasonal differences of salinity and provides a tool for managing the water in the estuary.

Additional keywords: hydrodynamic estuarine model, salinity variability, tidal and freshwater inflow effects.


References

Abood, K. A. (1974) Circulation in the Hudson River Estuary. In ‘Hudson River Colloquium. Vol. 250’. (Ed. O. A. Roels.) pp. 38–111. (New York Academy of Sciences: New York)

An, Q., Wu, Y., Taylor, S., and Zhao, B. (2009). Influence of the Three Gorges project on saltwater intrusion in the Yangtze River Estuary. Environmental Geology 56, 1679–1686.
Influence of the Three Gorges project on saltwater intrusion in the Yangtze River Estuary.CrossRef | 1:CAS:528:DC%2BD1MXhtlKrs7k%3D&md5=736ca1a13989e6456550af3b05634664CAS | open url image1

Baklouti, M., Chevalier, C., Bouvy, M., Corbin, D., Pagano, M., Troussellier, M., and Arfi, R. (2011). A study of plankton dynamics under osmotic stress in the Senegal River Estuary, West Africa, using a 3D mechanistic model. Ecological Modelling 222, 2704–2721.
A study of plankton dynamics under osmotic stress in the Senegal River Estuary, West Africa, using a 3D mechanistic model.CrossRef | 1:CAS:528:DC%2BC3MXotl2ntbk%3D&md5=358f83d55f42b8ab50d7e6f2b83bbda8CAS | open url image1

Bao Y.Liu J. (2008) The study of salt intrusion limit in Modaomen Estuary during dry season (in Chinese). Shipbuilding 49, 441–445.

Becker, A., Cowley, P. D., and Whitfield, A. K. (2010). Use of remote underwater video to record littoral habitat use by fish within a temporarily closed South African estuary. Journal of Experimental Marine Biology and Ecology 391, 161–168.
Use of remote underwater video to record littoral habitat use by fish within a temporarily closed South African estuary.CrossRef | open url image1

Blaber, J. M. (1997) ‘Fish and Fisheries of Tropical Estuaries.’ (Chapman & Hall: London)

Bourret, A., Devenon, J.-L., and Chevalier, C. (2005). Investigation on passive open boundary conditions adapted to the conjonction of strong currents, standing tidal wave and high stratification: application to the French Guiana continental shelf. Continental Shelf Research 25, 1353–1373.
Investigation on passive open boundary conditions adapted to the conjonction of strong currents, standing tidal wave and high stratification: application to the French Guiana continental shelf.CrossRef | open url image1

Bouvy, M., Arfi, R., Bernard, C., Carré, C., Got, P., Pagano, M., and Troussellier, M. (2010). Estuarine microbial community characteristics as indicator of human-induced changes (Senegal River, West Africa). Estuarine, Coastal and Shelf Science 87, 573–582.
Estuarine microbial community characteristics as indicator of human-induced changes (Senegal River, West Africa).CrossRef | 1:CAS:528:DC%2BC3cXlt1Ontrc%3D&md5=d57d4f230e884e4c02673b1cba831037CAS | open url image1

Bowen, M. M., and Geyer, W. (2003). Salt transport and the time-dependent salt balance of a partially stratified estuary. Journal of Geophysical Research – Oceans 108, . open url image1

Brenon, I. (1997). Modélisation de la dynamique des sédiment fins dans l’estuaire de la Seine (France). Ph.D. Thesis, Université de Bretagne Occidentale, Brest, France.

Brenon, I., and Le Hir, P. (1999). Modelling the turbidity maximum in the Seine Estuary (France): identification of formation processes. Estuarine, Coastal and Shelf Science 49, 525–544.
Modelling the turbidity maximum in the Seine Estuary (France): identification of formation processes.CrossRef | 1:CAS:528:DyaK1MXntVOrtr4%3D&md5=e5cf86010bf83f278ede816fdcff2eb8CAS | open url image1

Cecchi, P. (1992) Phytoplancton et conditions de milieu dans l’estuaire du fleuve Sénégal: effets du barrage de Diama. Ph.D. Thesis, Université de Montpellier 2, Montpellier, France.

Champalbert, G., Pagano, M., Sene, P., and Corbin, D. (2007). Relationships between meso- and macro-zooplankton communities and hydrology in the Senegal River Estuary. Estuarine, Coastal and Shelf Science 74, 381–394.
Relationships between meso- and macro-zooplankton communities and hydrology in the Senegal River Estuary.CrossRef | open url image1

Champalbert, G., Pagano, M., Arfi, R., and Chevalier, C. (). Effects of breaching the sandbar on hydrobiological parameters and zooplankton communities in the Senegal River Estuary (West Africa). Marine Pollution Bulletin , . open url image1

Chen, X. (2004). Modeling hydrodynamics and salt transport in the Alafia River Estuary, Florida during May 1999–December 2001. Estuarine, Coastal and Shelf Science 61, 477–490.
Modeling hydrodynamics and salt transport in the Alafia River Estuary, Florida during May 1999–December 2001.CrossRef | 1:CAS:528:DC%2BD2cXos1yrsbY%3D&md5=3fd27018bca0a39ecae3982d4d1e6768CAS | open url image1

Chevalier, C., Baklouti, M., and Ramamonjarisoa, A. (2004). Modeling the influence of wind and rivers on current, salinity and temperature over the French Guiana continental shelf during the rain season. Journal of Coastal Research 204, 1183–1197.
Modeling the influence of wind and rivers on current, salinity and temperature over the French Guiana continental shelf during the rain season.CrossRef | open url image1

Crousse, B., Mathieu, P., and Seck, S. M. (Eds) (1992) ‘La Vallée du Fleuve Sénégal: Evaluations et Perspectives d’une Décennie: d’Aménagement (1980–1990).’ (Ed. Karthala, Coll, Economie et Développement’

Cugier, P., (1999) Modélisation du devenir à moyen terme dans l’eau et le sédiment des éléments majeurs (C, N, P, Si, O) rejetés par la Seine en Baie de Seine. Ph.D. Thesis, Université de Caen, Caen, France.

Day, J. W. J., Hall, C. A. S., Kemp, W. M., and Yáñez-Arancibia, A. (1989) ‘Estuarine Ecology.’ (John Wiley & Sons: New York.)

Duvail, S. (2001) Scénarios hydrologiques et modèles de développement en aval d’un grand barrage. Les usages de l’eau et le partage des ressources dans le delta mauritanien du fleuve Sénégal. Ph.D. Thesis, Université Louis Pasteur, Strasbourg, France.

Flather R. A. (1976) A tidal model of the northwest European continental shelf. Mémoires de la Société Royale des Sciences de Liège Ser. 10, 141–164.

Gac, J. Y., Kane, A., and Monteillet, J. (1981–82). Migrations de l'embouchure du fleuve Sénégal depuis 1850. Cahiers – ORSTOM. Série Géologie 12, 73–76. open url image1

Gac, J.-Y., Carn, M., and Saos, J. L. (1986). L’invasion marine dans la basse vallée du fleuve Sénégal. I. Période1093–1980. Revue d'Hydrobiologie Tropicale 19, 3–17. open url image1

Gong, W., and Shen, J. (2011). The response of salt intrusion to changes in river discharge and tidal mixing during the dry season in the Modaomen Estuary, China Continental Shelf Research 31, 769–788.
The response of salt intrusion to changes in river discharge and tidal mixing during the dry season in the Modaomen Estuary, ChinaCrossRef | open url image1

Hess, K.W. (1989) ‘Mecca Program Documentation.’ NOAA Technical Report NESDIS 46.

Hetland, R. D., and Geyer, W. R. (2004). An idealized study of the structure of long, partially mixed estuaries. Journal of Physical Oceanography 34, 2677–2691.
An idealized study of the structure of long, partially mixed estuaries.CrossRef | open url image1

Huang, H., Justic, D., Lane, R. R., Day, J. W., and Jaye, E. (2011). Hydrodynamic response of the Breton Sound estuary to pulsed Mississippi River inputs Cable. Estuarine, Coastal and Shelf Science 95, 216–231.
Hydrodynamic response of the Breton Sound estuary to pulsed Mississippi River inputs Cable.CrossRef | open url image1

Knowles, N. (2002). Natural and human influences on freshwater inflows and salinity in the San Francisco Estuary at monthly to interannual scales. Water Resources Research 38, 25–1-25–11. open url image1

L’Hôte, Y., Mahé, G., Somé, B., and Triboulet, J. P. (2002). Analysis of a Sahelian annual rainfall index from 1896 to 2000; the drought continues. Hydrological Sciences 47, 563–572.
Analysis of a Sahelian annual rainfall index from 1896 to 2000; the drought continues.CrossRef | open url image1

Lee, S. B., and Birch, G. F. (2012). Utilising monitoring and modelling of estuarine environments to investigate catchment conditions responsible for stratification events in a typically well-mixed urbanised estuary. Estuarine, Coastal and Shelf Science 111, 1–16.
Utilising monitoring and modelling of estuarine environments to investigate catchment conditions responsible for stratification events in a typically well-mixed urbanised estuary.CrossRef | open url image1

Lerczak, J. A., Geyer, W. R., and Chant, R. J. (2006). Mechanisms driving the time-dependent salt flux in a partially stratified estuary. Journal of Physical Oceanography 36, 2296–2311.
Mechanisms driving the time-dependent salt flux in a partially stratified estuary.CrossRef | open url image1

MacCready, P. (2007). Estuarine adjustment. Journal of Physical Oceanography 37, 2133–2145. open url image1

Mahé, G., and Olivry, J. C. (1999). Assessment of freshwater yields to the ocean along the intertropical Atlantic coast to Africa (1951–1989). Sciences de la Terre et des Planètes 328, 621–626. open url image1

Mellor, G. L. (1996) ‘User’s Guide for a Three-dimensional, Primitive Equation, Numerical Ocean Model.’ Atmospheric and oceanic sciences program in Atmospheric and Oceanic Sciences, Princeton University, NJ, USA.

Monismith, S. G., Kimmerer, W., Burau, J. R., and Stacey, M. T. (2002). Structure and flow-induced variability of the subtidal salinity field in northern San Francisco Bay. Journal of Physical Oceanography 32, 3003–3019.
Structure and flow-induced variability of the subtidal salinity field in northern San Francisco Bay.CrossRef | open url image1

Nixon, S. W., Olsen, S. B., Buckley, E., and Fulweiler, R. (2004) ‘Lost to the Tide. The Importance of Freshwater Flow to Estuaries.’ (University of Rhode Island, Graduate School of Oceanography: Narragansett, RI)

Nunes, R. A., and Lennon, G. W. (2012). Episodic stratification and gravity currents in a marine environment of modulated turbulence. Journal of Geophysical Research-Oceans 92, 5465–5480. open url image1

Nunes-Vaz, R. A. (2012). The salinity response of an inverse estuary to climate change & desalination. Estuarine, Coastal and Shelf Science 98, 49–59.
The salinity response of an inverse estuary to climate change & desalination.CrossRef | 1:CAS:528:DC%2BC38XhtVKrs7Y%3D&md5=b53507ef9f964be94d755456b760b182CAS | open url image1

Pagès, J., Debenay, J. P., and Lerrusq, J. Y. (1987). L’environnement estuarien de la Casamance. Revue d’Hydrobiologie Tropicale 20, 191–202. open url image1

Postel, S. (1992) ‘Last Oasis: Facing Water Scarcity.’ World Watch Environmental Alert Series. (Norton: New York)

Prandel, D. (1992) ‘Dynamics and Exchanges in Estuaries and the Coastal Zone.’ (American Geophysical Union: Washington, DC.)

Ralston, D. K., Geyer, W. R., and Lerczak, J. A. (2010). Structure, variability, and salt flux in a strongly forced salt wedge estuary. Journal of Geophysical Research 115, C06005.
Structure, variability, and salt flux in a strongly forced salt wedge estuary.CrossRef | open url image1

Rochette, C. (1974) ‘Le Bassin du Fleuve Sénégal.’ Monographies hydrologiques Rapport ORSTOM. (Editions de l’ORSTOM: Paris.)

Roddie, B. D., Leakey, R. J. G., and Berry, A. J. (1984). Salinity–temperature tolerance and osmoregulation in Eurytemora affinis (Poppe) (Crustacea: Calanoida) in relation to its distribution in the zooplankton of the upper reaches of the Forth Estuary. Journal of Experimental Marine Biology and Ecology 79, 191–211.
Salinity–temperature tolerance and osmoregulation in Eurytemora affinis (Poppe) (Crustacea: Calanoida) in relation to its distribution in the zooplankton of the upper reaches of the Forth Estuary.CrossRef | open url image1

Schlacher, T. A., and Wooldridge, T. H. (1996). Ecological responses to reductions in freshwater supply and quality in South Africa’s estuaries: lessons for management and conservation. Journal of Coastal Conservation 2, 115–130.
Ecological responses to reductions in freshwater supply and quality in South Africa’s estuaries: lessons for management and conservation.CrossRef | open url image1

Simmons H.B. (1955) Some effects of upland discharge on estuarine hydraulics. Proceedings of the American Societyof Civil Engineers 81, 1–20.

Sobey, R. J. (1970) Finite-difference schemes compared for wave-deformation characteristics in mathematical modeling of two dimensional long-wave propagation. Techical Report 32. US Army Corps of Engineers, Coastal Engineering Research Center.

Telesh, I. V., and Khlebovich, V. V. (2010). Principal processes within the estuarine salinity gradient: a review. Marine Pollution Bulletin 61, 149–155.
Principal processes within the estuarine salinity gradient: a review.CrossRef | 1:CAS:528:DC%2BC3cXksFOmu7g%3D&md5=9f84265478493dcfec4e837da2a800bbCAS | 20304437PubMed | open url image1

Thain, R. H., Priestleya, A. D., and Davidson, M. A. (2004). The formation of a tidal intrusion front at the mouth of a macrotidal, partially mixed estuary: a field study of the Dart Estuary, UK Estuarine, Coastal and Shelf Science 61, 161–172.
The formation of a tidal intrusion front at the mouth of a macrotidal, partially mixed estuary: a field study of the Dart Estuary, UKCrossRef | open url image1

Troussellier, M., Got, P., Mboup, M., Corbin, D., Giuliano, L., Cappello, S., and Bouvy, M. (2005). Daily bacterioplankton dynamics in a sub-Saharan estuary (Senegal River, West-Africa): a mesocosm study. Aquatic Microbial Ecology 40, 13–24.
Daily bacterioplankton dynamics in a sub-Saharan estuary (Senegal River, West-Africa): a mesocosm study.CrossRef | open url image1

Vijith, V., and Shetye, S. R. A. (2012). stratification prediction diagram from characteristics of geometry, tides and runoff for estuaries with a prominent channel. Estuarine, Coastal and Shelf Science 98, 101–107.
stratification prediction diagram from characteristics of geometry, tides and runoff for estuaries with a prominent channel.CrossRef | open url image1

Waeles, B., Le Hir, P., and Lesueur, P. (2008). A 3D morphodynamic process-based modelling of a mixed sand/mud coastal environment: the Seine Estuary, France. In ‘Sediment and Ecohydraulics: INTERCOH 2005. Proceedings in Marine Science 9, 477–498.

Wen, P., Chen, X.-H., Liu, B., and Yang, X.-L. (2007). Analysis of tidal saltwater intrusion and its variation in Modaomen Estuary. Journal of China Hydrology 27, 65–67. open url image1

Whitfield, A. K., Elliott, M., Basset, A., Blaber, S. J. M., and West, R. J. (2012). Paradigms in estuarine ecology. A review of the Remane diagram with a suggested revised model for estuaries. Estuarine, Coastal and Shelf Science 97, 78–90.
Paradigms in estuarine ecology. A review of the Remane diagram with a suggested revised model for estuaries.CrossRef | open url image1

Wong, K. C. (1996). The effect of tidal motion on the salinity distribution in lower Delaware bay. In ‘Buoyancy Effects on Coastal and Estuarine Dynamics’. (Eds D. Aubrey and C. Friedrichs.), Buoyancy Effects on Coastal and Estuarine Dynamics. AGU, pp. 373–394.

Xing, Y., Ai, C., and Jin, S. (2013). A three-dimensional hydrodynamic and salinity transport model of estuarine circulation with an application to a macrotidal estuary. Applied Ocean Research 39, 53–71.
A three-dimensional hydrodynamic and salinity transport model of estuarine circulation with an application to a macrotidal estuary.CrossRef | open url image1

Yang, Z. Q., and Khangaonkar, T. (2009). Modeling tidal circulation and stratification in Skagit River estuary using an unstructured grid ocean model. Ocean Modelling 28, 34–49.
Modeling tidal circulation and stratification in Skagit River estuary using an unstructured grid ocean model.CrossRef | open url image1



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