Coastal landscape dynamics in the Mouths of Cameroon and adjacent watersheds: morphological, environmental, and socio-ecological challenges

The coast is rarely a static line where the land simply ends and the sea begins. In many parts of the world, this boundary is a shifting zone of interaction, where rivers carry sand and silt from the mountains, and ocean waves push that material back toward the shore. This constant exchange creates landscapes like estuaries, where fresh water meets the sea, often forming rich wetlands and mangrove forests that protect the land from storms. However, these delicate systems are increasingly caught in a tug-of-war between natural forces and human activity. When people build cities, cut down forests, or dig up sand, they alter the flow of water and sediment, often tipping the balance toward erosion or flooding. Understanding how these changes happen requires looking beyond the water's edge to the entire drainage basin—the vast area of land where rain flows into a single river system. If the land upstream is stripped of its vegetation, the river carries more mud and less stability, changing the shape of the coast far downstream.

In the southern part of Cameroon, a team of researchers set out to understand exactly how these forces are reshaping the "Mouths of Cameroon," a complex estuarine system that serves as the country's primary economic gateway. This area is not just a natural wonder; it is home to Douala, the nation's largest city and main port, as well as vast mangrove forests and agricultural lands. The scientists wanted to see how the landscape has changed over recent decades and to determine whether the problems facing the coast are caused only by local actions or by changes happening far inland. By combining satellite images taken over forty years with field visits and geological maps, they traced the connections between the rivers, the forests, and the shoreline to reveal a story of rapid transformation.

The researchers found that the inner part of the estuary, particularly around Douala, is undergoing a dramatic physical reshaping driven by the city's relentless growth. Between 1975 and 2020, the urban area expanded significantly, swallowing up large sections of what was once dense forest and mangrove. In 1975, the area was dominated by relict forests, but by 2020, those forests had shrunk considerably, replaced by concrete, industrial zones, and port facilities. This expansion is not just a matter of buildings replacing trees; it has altered the very ground the city sits on. The port, which handles the majority of Cameroon's trade, requires deep channels for ships to enter. To keep these channels open, workers dredge millions of cubic meters of sediment every year, removing material that would otherwise help build up the coastline. This removal, combined with the extraction of sand for construction, has disrupted the natural supply of sediment that the coast needs to maintain its shape.

Beyond the city limits, the landscape tells a different but equally important story. The researchers looked at four major river basins that feed into the estuary: the Sanaga, the Wouri, the Dibamba, and the Moungo. They discovered that these basins are not uniform; each has a unique character and a different relationship with the coast. The Sanaga basin is enormous, covering more than 140,000 square kilometers, and while it carries a massive amount of water and sediment, its connection to the estuary is now mostly indirect, occurring only during rare, massive floods. In contrast, the Wouri and Dibamba basins are smaller but directly connected to the city and the inner estuary. These areas have seen intense degradation, with forests cleared for agriculture, timber, and fuelwood. The Moungo basin, which drains the slopes of Mount Cameroon, is heavily influenced by large-scale industrial plantations for oil palm and rubber. These plantations have replaced natural vegetation, altering how water and soil move through the landscape.

The most striking finding of the study is how unevenly the coastline is reacting to these pressures. When the scientists analyzed the shoreline between 2016 and 2020, they did not find a single trend of the coast either growing or shrinking. Instead, they found a patchwork of behaviors occurring side by side. In some places, such as near Cap Cameroun, the land is retreating rapidly, with the shoreline losing up to 25 meters of ground in a single year. In these eroding zones, the researchers found the remains of houses destroyed by the sea, a stark visual proof of the land's instability. Yet, just a short distance away, other sections of the coast are actually growing, with new land forming at rates of up to 42 meters per year. This happens because the natural flow of sand and the human removal of sediment create a complex balance where some areas lose ground while others gain it.

The study concludes that the health of the Mouths of Cameroon cannot be understood by looking at the coast alone. The degradation of mangroves, which act as natural barriers against waves and traps for sediment, is a critical factor. These forests are being cut down for firewood and to make way for farming, leaving the shoreline vulnerable. The pollution from the city and the industrial plantations further stresses the ecosystem. The researchers emphasize that the problems in the estuary are the downstream result of actions taken across the entire watershed. When forests are cleared in the highlands, when sand is dug out of riverbeds, and when wetlands are filled in, the consequences are felt at the water's edge. The coast is not a passive victim of the sea; it is a dynamic system responding to a combination of natural currents and human demands.

For the people living in this region, the implications are profound. The erosion threatens homes and infrastructure, while the loss of mangroves reduces the natural protection against storms and the ability of the land to recover. The researchers suggest that managing this area requires a new approach that looks at the entire system, from the mountains to the sea. Protecting the coast means protecting the forests upstream, regulating the extraction of sand, and finding ways to restore the mangroves that have been lost. It is a reminder that in a world where human activity and natural processes are deeply intertwined, the fate of the shoreline is written in the decisions made far inland. The Mouths of Cameroon stand as a vulnerable but vital example of how a coastal landscape is shaped by the continuous interaction of water, land, and people.