In search of sediments: probing the past in Bangladeshi waters to help solve the problems of the here and now
By Dr Richard E. Walton
Introduction
Deltas are landscapes rich in water (rivers, lakes, wetlands) and sediments. Lake sediments from these regions can contain information on flooding frequency, ecological change, as well as other impacts on the environment and their accumulation over time can help us make sense of the past to inform the future about arising challenges. Reconstructing the past through lake sediments is a process called paleolimnology and it is a key part of Work Package 3 in the Living Deltas Hub. Bangladesh has been the first country in the Hub we have been able to visit to obtain sediment cores, putting the work the Hub is doing into greater context.
Bangladesh SES and palaeolimnology
It’s no secret that Bangladesh is a land of water. With abundant river channels, lakes and wetlands, this nation is built around the food systems all this water supports. However, it is also particularly vulnerable to flooding from the annual monsoon and sea-level rise which disrupts livelihoods. Community resilience is needed to live in this environmentally-dynamic region. Furthermore, human influences on the aquatic landscape have led to ecosystem degradation that threatens the important ecosystem services the waterways provide.
A beautiful day on Goalanda Baor
Photo credit: Richard Walton, Research Assistant, Living Deltas Hub
Bangladesh is a prime example of a socio-ecological system (SES), where human communities and the surrounding environment are intricately linked together. As the issues facing the Bangladeshi SES grow ever more precarious due to climate change and population growth, it is necessary to obtain data that allows us to identify risks to livelihoods and the state of aquatic ecosystems supporting these villages and cities. A lot of data over a long period of time is needed for identification of trends and impacts. With contemporaneous data often in short supply, one way the Living Deltas Hub is overcoming this problem is by using palaeolimnology. In short, palaeolimnology involves studying sediments from the bottom of lakes and wetlands to understand the environmental and ecological conditions of the past. These can then be used to make management decisions here in the present day and play a role in predicting how certain changes in the future will affect these systems.
Focus of palaeolimnology in the Hub
My main work within the Hub is as a palaeolimnologist to reconstruct flood histories of each delta region in our project. Flooding, while often devastating to human lives, is also an important part of deltaic life and environmental dynamics. Each flood can bring with it nutrients and sediments that can benefit surrounding agricultural lands. By analysing the size of sediment grains accumulating through time, we can understand the frequency and intensity of floods in the past to create a baseline of these events over that last ~100 years. Resource managers and climate modellers can then use this baseline to understand how changes to monsoonal rains and cyclone intensity due to climate change may impact these flooding patterns. Furthermore, we can use these sediments to also look at recent ecological impacts to the baors (lakes) and beels (wetlands) in Bangladesh to provide informed advice for water managers and policymakers on how to protect or improve these important aquatic systems.
Palaeolimnological fieldwork in Bangladesh
After 2 years of disruption to Hub plans due to Covid-19, I have finally been able to get out to the deltas to obtain lake sediments, with Bangladesh as my first destination (late February-early March 2022). Andy Large, Andrew Henderson, and I were guided by our wonderful BUET colleagues, Anisur Majumdar, Sumon Rabby, and Feisal Rahman through the Khulna, Jashore, and Dhaka districts to visit the many baors and beels that make up the southwestern region of Bangladesh. With their help and connections to local leaders, especially the Department of Social Services, we were able to successfully obtain 23 sediment cores on this first visit. These sediments will be taken back to Newcastle University for laboratory analysis over the coming months to determine the flood history of the region as well as other ecological changes.
Pulling a sediment core from the bottom of Khajura Baor
Photo credit: Andy Large, Principal Investigator, Living Deltas Hub
Expanded understanding of the deltas while in the field
Being a physical geographer by training, my focus during the fieldwork was naturally turned toward the physical and ecological environments the baors and beels were located. Yet, what struck me most during this time were the interactions we had with local communities that use these waterways. Their daily reliance on these waterbodies for food, transport, and other daily activities such as bathing was very apparent. They were able to provide us with valuable knowledge about how the lakes are used and when the last major floods occurred. My interactions with them over our two-week excursion really helped me grasp the concept of what an SES is – truly the welfare of the people and of the waterways are inescapably linked. To think in terms of the physical/natural environment alone is not enough, because people’s livelihoods are at stake here. With that strongly imprinted in my mind, I look forward to getting into the lab to analyse these sediments so we can provide crucial guidance to the Bangladeshi people that will allow them to be prepared for future changes and to work with their natural resources in more sustainable ways.
Fishermen using traditional techniques at Hariharanagar Baor
Photo credit: Richard Walton, Research Assistant, Living Deltas Hub
Conclusion
The last two years have been challenging for many members of the Hub who have been waiting to visit each delta region to obtain the data needed to produce meaningful guidance and knowledge to all stakeholders involved. Carefully, each region is starting to re-open and Bangladesh has provided the first opportunity for us to get the sediments we need to analyse flooding histories and ecological change in the region. The sediments obtained will form a crucial part in assessing the coping and adaptive capacity, within the delta environment and its communities, to future impacts to currently existing conditions that may occur as climate change and further development progresses. More broadly, fieldwork allows us as researchers to really grasp the concept of deltas as socio-ecological systems as countries like Bangladesh have such an intricate link between the environment and communities that they are inseparable. The delta environment is the perfect place to find lessons from the past and to help us broaden our own horizons.