Protecting the world’s precious wetlands

Professor Tooth is currently co-supervising Tasmin Griffiths, a PhD student at the University of Gibraltar,  who is studying soils in the wetlands of Doñana National Park in southwest Spain. Using a combination of field and laboratory work, Tasmin is investigating the amount of carbon stored within the wetland soils, and assessing their vulnerability to climate and land-use changes.

The park’s wetlands play a key role in maintaining the area’s biodiversity, and as long as the soils remain moist, the carbon is locked in. However, a combination of climate change and excessive groundwater abstraction for irrigation agriculture appears to be driving increasing desiccation of many of the large freshwater marshes and interdunal wetlands for which the park is famous, potentially with profound impacts on soil carbon stocks.

“Even though Doñana is a specific case with its own distinctive characteristics, in many ways it is a microcosm of what’s happening more generally across the southern Mediterranean, with many regions starting to see warmer, more variable climates,” says Professor Tooth.

“Doñana National Park is largely managed for its unique biodiversity and we want to assess how vulnerable it is to climate and land-use changes, including the extent to which the soil carbon stock is being impacted by surrounding land encroachment and, in some cases, illegal groundwater extraction.

“Parts of the park used to be subject to periods of flooding, which are now happening less often as a consequence of a much drier climate and human activity. This has potentially serious implications, not only for soil carbon stocks but also for the visible aspects of the park’s functioning, such as the birds, amphibians, fish and other life forms. Working with the park authorities, Tasmin’s project is helping to generate baseline data on soil carbon stocks in the wetlands as well as providing insights into the wider landscape and ecosystem changes that may be anticipated over coming decades. Our aim is that these insights can feed into park management plans.” 

Another region of interest is the Thar Desert in the Indian state of Rajasthan. Previous geomorphological, geological and archaeological studies have shown that many thousands of years ago the now-desert region was home to major river systems that supported sophisticated civilisations such as the Harappan. But as the climate became more arid, what had once been well-watered, fertile land became less suitable for sustaining large settlements, and the Harappan civilisation went into decline.

Professor Tooth says: “What we are seeing today is a different story, with attempts to water parts of the desert using a system of irrigation canals. Many floodplain wetlands and topographic depressions in and around the desert are subject to excess runoff from irrigated agricultural land, which is leading to rampant salinisation of surface waters and soils. Some natural saline depressions have been highly modified for purposes of salt production and aquatic bird populations are suffering.

“Other rivers and wetlands in the region are subjected to sewage disposal from nearby settlements, which is causing marked declines in water quality, with implications for human health. Even some protected wetland sites have been severely impacted.

As part of these investigations in 2024 and 2025, Professor Tooth is co-supervising Jayesh Mukherjee, an AberDoc-funded PhD student from India. Jayesh is investigating the history of the lower Luni River on the eastern desert margins.  Evidence for changes in the size and shape of the river over the last few thousand years can be used to anticipate future changes to the channels, floodplains and wetlands resulting from climate and land-use changes, and help assess how these changes may affect the local populations.

Working with Dr Manudeo Singh – a Royal Society Newton International Fellow based at Aberystwyth University - Professor Tooth is also interested in what’s happening to rivers and wetlands in other parts of India. Some rivers are huge – around 20 times the size of the Thames – and subject to large monsoon floods and a following long dry period.

Professor Tooth explains: “Using satellite images and other data, my colleague Manudeo Singh has developed algorithms to look at the hydrological behaviour of rivers and wetlands over recent decades. We are particularly interested in finding out whether the wetlands are being maintained in their current state, or whether they are getting drier or wetter.

“Preliminary results are remarkably consistent: in the lower lying parts of India, many wetlands are getting drier, in some cases dramatically, and this is because of climate change and human activities such as excessive groundwater extraction.  The exceptions include areas where excessive irrigation runoff or sewage disposal is leading to wetter conditions.” 

The extensive region of Argentine Patagonia is another focus of investigation. Professor Tooth worked initially with Dr Hywel Griffiths at Aberystwyth University on a project looking at the memories of floods and droughts among descendants of Welsh settlers in the area commonly referred to as ‘Welsh Patagonia’, which largely corresponds to parts of present-day Chubut Province.

Collaborations have expanded since to include Dr Singh and staff in universities and research organisations in Argentina. In 2018, a Memorandum of Understanding was signed between Aberystwyth University and La Universidad Nacional de La Patagonia San Juan Bosco (National University of Patagonia) to support research and teaching related to dryland rivers and wetlands.

Professor Tooth says: “The rivers and wetlands of Argentine Patagonia provide some fascinating comparisons and contrasts with those in other drylands. Some of the major rivers in Patagonia are fed by snowmelt from the Andes, and flow year round. For example, the Río Chubut starts in the Andes and in its long eastwards passage through the desert to the Atlantic Coast, the river and its floodplain wetlands provide a ‘green corridor’ of biodiversity.  The river water is also essential for sustaining extensive areas of irrigation agriculture in the lower Chubut valley. 

“Unfortunately, the health of the river and its wetlands are threatened by a toxic combination of factors.  Climate change is reducing the amount of snowfall each winter, with potential implications for the reliability of year-round river flows.  Invasive vegetation, such as introduced poplars and willows, is fundamentally altering river geomorphology and ecosystems.  Dams and reservoirs are changing river flows and sediment and nutrient transport, while agricultural pollution and sewage disposal are negatively impacting water quality.

‘Work with our Argentinian colleagues is looking at how we can combine different sources of information – memories of floods and droughts, the lived experiences of people, and state-of-the-art geomorphological and hydrological data – to improve water security in the region.  We have been involving local communities and other stakeholders in our work because this is essential for identifying key challenges and identifying practical solutions to those challenges.  Raising awareness of the multiple benefits of healthy rivers and wetlands is an essential part of our communication efforts.”