136
E. V. Djagoua et al.
d’Ivoire coastline, to better classify marine waters impacted by upwelling processes
or anthropogenic pollution due to river runoff.
7.1 Introduction
Environmental management, in the sustainable development framework, is an absolute necessity for our society. Historically, narrow and fragile coastal zones have
been strategically chosen by large resident populations to establish their economic
activities. Today, the safeguard of coastal, semi-enclosed and enclosed water bodies represent one of the major challenges for environmental mangers, due to the
combined impact of both anthropogenic and natural factors (Jaquet 1989).
In addition to human activities, river discharges constitute important sources of
nutrients, organic matter and inorganic particles to the coastal ocean (Dagg et al.
2004; Geyer et al. 2004). These materials have great influence on the bio-geochemistry and bio-optical characteristics of coastal waters (Froidefond et al. 2002;
Hu et al. 2004), as they can stimulate primary productivity, but also cause pollution
and/or oxygen depletion, thereby hampering the very survival of halieutic species.
As a consequence, careful monitoring of coastal zones by means of continuous and
long-term observations is required, in order to ensure that their ecological balance is
maintained and their natural resources preserved.
Given the optical impact of continental runoff onto marine waters, Remote Sensing (RS) from satellite sensors, operating in the visible part of the electromagnetic
spectrum, is well suited for monitoring basic ecosystem dynamics of coastal zones.
It is well known (see e.g. Robinson 2004) that the radiometric signatures of coastal
waters depend mainly on three types of optically-active water constituents, namely
phytoplankton and their derivative products; dissolved organic material, also known
as yellow substance, in the RS jargon; and suspended sediments, as well as other
particles of inorganic nature. All of these can occur in different proportions, highly
variable in both space and time (see e.g. Lahet et al. 2001 and references therein).
The assessment of such parameters by means of RS techniques allows deriving invaluable information for the sustainable management of coastal regions, in particular
when in situ data are lacking.
In the following, optical RS of water constituents will be used to monitor the
impact of the Sassandra River—one of the four major rivers of Côte d’Ivoire—onto
the coastal waters of the Gulf of Guinea, in which it flows directly without passing
through a lagoon system (see Fig. 7.1 for a geographical description of the area
of interest in the African continental context). The Sassandra River has its origin
in the high grounds of the north, where the Tiemba River joins the Férédougouba
River, flowing from the Guinea highlands. It is joined by the Bagbé, Bafing, Nzo,
Lobo, and Davo rivers and winds through shifting sandbars to form a narrow estuary
(which is navigable for about 80 km inland from the port of Sassandra). Like many
other rivers, the Sassandra River also serves as a receptacle for domestic sewage,
agricultural runoff (often carrying a sizeable load of fertilizers and pesticides), industrial production waste and other uncollected materials (CEDA 1997). In addition,
E. V. Djagoua et al.
d’Ivoire coastline, to better classify marine waters impacted by upwelling processes
or anthropogenic pollution due to river runoff.
7.1 Introduction
Environmental management, in the sustainable development framework, is an absolute necessity for our society. Historically, narrow and fragile coastal zones have
been strategically chosen by large resident populations to establish their economic
activities. Today, the safeguard of coastal, semi-enclosed and enclosed water bodies represent one of the major challenges for environmental mangers, due to the
combined impact of both anthropogenic and natural factors (Jaquet 1989).
In addition to human activities, river discharges constitute important sources of
nutrients, organic matter and inorganic particles to the coastal ocean (Dagg et al.
2004; Geyer et al. 2004). These materials have great influence on the bio-geochemistry and bio-optical characteristics of coastal waters (Froidefond et al. 2002;
Hu et al. 2004), as they can stimulate primary productivity, but also cause pollution
and/or oxygen depletion, thereby hampering the very survival of halieutic species.
As a consequence, careful monitoring of coastal zones by means of continuous and
long-term observations is required, in order to ensure that their ecological balance is
maintained and their natural resources preserved.
Given the optical impact of continental runoff onto marine waters, Remote Sensing (RS) from satellite sensors, operating in the visible part of the electromagnetic
spectrum, is well suited for monitoring basic ecosystem dynamics of coastal zones.
It is well known (see e.g. Robinson 2004) that the radiometric signatures of coastal
waters depend mainly on three types of optically-active water constituents, namely
phytoplankton and their derivative products; dissolved organic material, also known
as yellow substance, in the RS jargon; and suspended sediments, as well as other
particles of inorganic nature. All of these can occur in different proportions, highly
variable in both space and time (see e.g. Lahet et al. 2001 and references therein).
The assessment of such parameters by means of RS techniques allows deriving invaluable information for the sustainable management of coastal regions, in particular
when in situ data are lacking.
In the following, optical RS of water constituents will be used to monitor the
impact of the Sassandra River—one of the four major rivers of Côte d’Ivoire—onto
the coastal waters of the Gulf of Guinea, in which it flows directly without passing
through a lagoon system (see Fig. 7.1 for a geographical description of the area
of interest in the African continental context). The Sassandra River has its origin
in the high grounds of the north, where the Tiemba River joins the Férédougouba
River, flowing from the Guinea highlands. It is joined by the Bagbé, Bafing, Nzo,
Lobo, and Davo rivers and winds through shifting sandbars to form a narrow estuary
(which is navigable for about 80 km inland from the port of Sassandra). Like many
other rivers, the Sassandra River also serves as a receptacle for domestic sewage,
agricultural runoff (often carrying a sizeable load of fertilizers and pesticides), industrial production waste and other uncollected materials (CEDA 1997). In addition,