Category: Earth Sciences

Cameroon’s Wouri Estuary

Eliot Atekwana talks about his work in Cameroon’s Wouri Estuary

July 06, 2021 Written by Adam Thomas | Photo by Eliot Atekwana

In 2019, Eliot Atekwana took four students—one from the University of Delaware, two from Fort Hays State in Kansas and one from Compton College in California—to Cameroon to look at the effects of pollution from agriculture, urbanization and industry on carbon cycling in the Wouri Estuary. The project was funded by the National Science Foundation to train U.S. undergraduate and graduate students in research, education and cultural activities in a foreign country.

Findings from that trip were recently published in Eos, a source for news and perspectives about Earth and space science. With continued research on the Wouri Estuary in Douala, Cameroon planned for the future, Atekwana, professor in the Department of Earth Sciences, took time to speak about the effect plastic is having on mangrove forests in the country as well as future research steps.

 

How did this paper come about?

When we went to Cameroon, we stayed in a hotel right next to the estuary. The hotel had a wooden platform that was built as part of the restaurant overlooking the estuary. We would go out there for breakfast and stand and watch the water. All you would see around the hotel and at the edges of the water was plastic strewn all over the place.

We took some walks around and saw there was plastic everywhere. We also noted that during the high tides, the plastic would be pushed into a boat dock and then at low tide, the plastic would be trapped on the dock and that one of the works in the hotel would come and pick up all the plastic and put it in this large container, scheduled for disposal. That piqued our interest, and we thought, ‘Oh, the plastic is there but there are people who are trying to mitigate the effect of the plastic by physically removing it.’

 

How do these large amounts of plastic accumulate?

One reason is that there is a lot of plastic being produced and it exceeds the capacity for people to mitigate the plastic in the environment. We noticed the behavior of the plastic during high tides. We’d come and watch and during high tides, the plastic would move away towards the mangroves and the tidal creek. Then, during low tides, the plastic would start moving back towards the estuary. It was interesting because between low and high tide, you get this debris of plastic spinning inside the creek.

When we would go out to do our normal sampling in the estuary and it seemed like there was plastic everywhere, on tree roots and tree branches. We would stop by fishing villages and would see used nets thrown along the shoreline. I think we began to realize that, maybe the people just didn’t know what to do with the plastic waste.

Flooding during the rainy season can also bring plastic debris from the City of Douala into the estuary. That material gets washed off the surface into the stream channels where it’s directed into the estuary. That is a common way for the plastic to get in because it’s unlikely that people actually are physically going out there to the estuary with trash. There are some communities, that have large, communal trash containers. The trash is supposed to be put inside that container, but it doesn’t get emptied regularly. And that has to do with the resources to physically remove the trash from the community, especially for communities that live right along the coastline.

 

What ecosystem services do mangroves provide and what is the importance of mangrove forests?

Mangroves provide filtering and [carbon] sequestration, and they help natural substances to degrade. They are unique because they thrive at the interface between freshwater and saltwater, and they can survive in both. They are trees that are able to breathe by extending their roots up into the air, but they can also be flooded and they will still be fine. By adapting that strategy, they are able to survive at this saltwater/freshwater interface.

Because of the way their roots are designed, they also trap a lot of sediment. When you trap a lot of sediment, you trap a lot of the things that come off the continent. In that way, they build land towards the ocean. Because of the way they have evolved, they can actually trap debris. Naturally, it would be just wooden debris and natural or organic material that would eventually degrade and be part of the forest. The problem with plastic is, they do the same thing for plastic, but the plastic does not degrade. It just sits there.

They also serve as a filter. They filter the water, trap it, use up the nutrients, the nitrates and all of the phosphates. The mangroves can use those nutrients if they’re not in excess.

 

How does plastic negatively impact the mangroves?

The obvious one is aesthetically: it’s just ugly. That’s why you notice it because it’s not supposed to be there. If you boat around, it becomes obvious. In the absence of the plastic, it looks majestic and beautiful. The things that we can see come in all shapes and sizes and consist of every kind of material you can imagine. From plastic bags to handbags to shoes to tires.

 

You went to Cameroon in 2019—what are your plans for future research?

I was supposed to go back in 2020 and then COVID-19 hit. Hopefully, with COVID-19 vaccinations, we’ll be able to go back. We plan on conducting two experiments. One would be to estimate how much plastic has been transported in that little creek next to the hotel. For several hours during a tide out cycle, we would go out and physically work with the people who are collecting the trash, weigh it and see how much is being collected and then get an estimate on how much is being brought in. We will probably try to do a survey and look at the amount we can see physically around that creek. The other thing that we will do is try to document the variety of items that exist in the plastic litter and take some samples.

The next study would be to look at the sediment and the water column and filter out the plastic and then study the plastic, similarly to what Jonathan Cohen [associate professor in the School of Marine Science and Policy] is doing in the Delaware Bay. We are trying to see whether the material we see on the shores is the same material that we find in the water column and in the sediment column. It would be like conducting a parallel study of what is happening in the Delaware Bay estuary to what is happening in the Wouri Estuary. It allows us to connect these two estuaries. One in a developed country and one in a developing country.

There are not many documentations of plastic research in tropical West Africa and in Africa as a whole so these kinds of studies can help show the extent to which this is a growing problem. There are hundreds of kilometers of tidal creeks through the Wouri Estuary, which is evidence that there is still plenty of trash trapped in there. We physically attempted to remove some of the trash and it’s tough. It will take quite a bit to clean up the estuary, and it’s something that will have to happen in order for the estuary and the ecosystem to be restored and to restore the aesthetics of the estuary.

It will take an effort beyond the local community to do this because of the resources and logistics that will be required. The person-hours it will take to go through all the tidal creeks and physically remove the plastic will cost money. Then there is the question of what do you do when you actually remove it? And then, what do you do to prevent further release of plastic? It’s a daunting task that requires cooperation between the government, the local citizens and maybe even support from the plastic manufacturers because they seem to be in part responsible for that problem.


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