January 12, 2018
Water and sediment: news from the Mara Wetland, Tanzania
Posted by larryohanlon
By Francesco Bregoli
Where the Mara River leaves the Serengeti National Park, Tanzania, a meandering reach expands to form a delta and a wide wetland before flowing into Lake Victoria. The wilderness of Serengeti dissolves into rural areas that envelope the swamps (Fig 1), but still the riverine system provides unique water resources and essential ecosystem services that should be preserved.
Water and sediment are the raw materials necessary to build up the wetland habitat and are vectors of nutrients feeding the ecosystem. When their natural equilibrium is broken, the habitat morphology is altered and the ecosystem health is likely jeopardized. Previous studies report an increment of sediment supply to the wetland due to increasing deforestation, farming and grazing activities along the basin. New river structures are planned and the river management will become an important challenge for the area.
Motivated by the great opportunity to picture the current condition in a changing environment, I went for a three weeks mission on the Mara Wetland to gather data on morphology, water discharge and sediment transport. I built up the field data collection from two past missions of Paolo Paron and Ken Irvine, when they used drones to collect data on hydrology and ecosystems. The data are important to understand the current configuration and to model the future evolution of the wetland under different scenarios of climate, water use and land use changes along the river basin. The measurements will support an analysis of the water and sediment balance within the area of the Lower Mara floodplain. Furthermore the model will serve as a tool to improve the water resources and land use management in order to prevent the deterioration of the Mara wetland habitat and ecosystem.
During the mission I deployed UAV flights to observe areas otherwise unattainable from the ground and to represent the wetland morphology features at high resolution (Fig 2 and 3). I measured water discharges with an ADCP (Fig 4) in several key channels of the network, cruised the wetland to map the bed topography with a sonar and gathered suspended sediments samples.
I realised that even in remote areas you are never alone. Thanks to the support of BirdLife International I had the chance to talk with people of the local communities. In many cases I have noted the awareness that the organizations are creating among the communities: I have found them curious, participative and willing to preserve their territories. I have witnessed their perception of the importance of the ecosystem services the wetland provide them. Still, there is a number of ongoing human activities that might modify the environment and particularly the river network: riparian vegetation burning to create new croplands and to provide fisherman access to the river, livestock paths and wades as well as banks opening for land irrigation are among the reasons of natural levees destruction and therefore river bifurcation or deviation.
The knowledge to which extent the human actions change the natural water-sediment balance of this delicate ecosystems will be the object of further analysis of my research.
For your information, a follow up of this story is available at
a link to our article in Science of the Total Environment.
Bregoli, F., Crosato, A., Paron, P., & McClain, M. E. (2019). Humans reshape wetlands: Unveiling the last 100 years of morphological changes of the Mara Wetland, Tanzania. Science of The Total Environment, 691, 896-907.
[…] reported on his most recent trip to the wetlands in a blog on the website for earth and space scientists, hosted by the American Geophysical Union […]
Having grown up next to the Mara wetlands in the 1950 to 1970 period I have been very aware of it as a vital and very valuable ecological resource, and the habitat for a very diverse water based fauna and flora. It is also the home of the Sitatunga antelope and the Goliath heron. The wetlands are also a filter preventing the waters of Mara bay from turning muddy as well as being a nursery for fish.
It is facing many threats to its integrity, the main one being the water abstraction upstream in both Kenya and Tanzania.
It is also facing a threat to the water quality from the operations of the mega gold mining operations at the upstream end of the wetlands.
I am wondering if any environmental monitoring for mercury is being done downstream of the mine?