Today, May 22, is the International Day of Biodiversity, which this year, coincides with the 2013 Year of Water Cooperation. It’s the ideal day to spend the coffee break mulling over the relationship between water, biodiversity, and agriculture in some of the world’s most critical life raft ecosystems - regions where poverty is high, populations are dense and highly dependent upon nature (agriculture, fisheries, logging) for livelihoods, and where ecosystem services are severely degraded.
Life Raft Ecosystems
The notion of Life Raft Ecosystems was put forth by The Nature Conservancy’s controversial Chief Scientist, Peter Kareiva, as a call to ecologists and conservation biologists to shift their focus from conserving pristine wilderness areas to critical regions where both nature and human populations are threatened. The CGIAR research programs on Aquatic Agricultural System (AAS), and Water Land and Ecosystems (WLE) are taking up this call by redefining agricultural research with a greater focus on the contribution of ecosystem service based approaches that integrate aquatic systems, irrigated production systems, and interactions from field to basin scales. Cambodia’s Tonle Sap provides a critical example of one of our major challenges.
The lake’s unique ecosystem has been likened to the heart of the Mekong due to its annual flood pulses. During half the year (November to May) the lake drains into the Mekong, shrinking to 2500 km2, whereas during the monsoon, the flood waters from the Mekong backup in the river’s delta reversing the flow of the Tonle Sap river into the lake, which expands up to 15,800 km2 in size absorbing the excess water from the monsoon and slowly releasing it as flood waters recede. Some would liken this ecosystem function to the role of a bladder rather than a heart, a more functional definition, but granted less romantic.
Livelihood strategies on the Tonle Sap
The nearly 1.7 million inhabitants, amongst the poorest in Cambodia, have adopted unique livelihood strategies to make the most of this annual pulse. Whereas the majority of the inhabitants live on the edges of the high water line (including the famed Angkor Wat), others live in stilted houses located at water level half the year, or invariably at 2-10m above ground during the other half. Others still, have adopted a more mobile strategy, building entire villages of floating houses that follow the lake’s edge.
A natural livelihood gradient occurs between these three community types, with the edge dwellers primarily depending on up to three rice harvests a year by following the receding floodwaters. The flood plain dwellers divide their time between fishing the lake’s waters and rice cultivation. Finally, the mobile floating villages, comprised of dedicated fishermen, fish mongers and associated small-scale merchants follow the lake’s shoreline during its annual pulses to ensure easy access to the road where fish can be transported to markets in Phnom Penh, Thailand and Vietnam.
Water in the "hands of the sky"
In a recent AAS scoping study of the lake, meeting with farming families and community groups quickly made it clear how central water and biodiversity are to these farming families. Village after village the chorus from most groups we spoke with on “water”, either too much or too little being the primary concern of the rice farmers. Better irrigation systems, deeper ponds or canals to store water in the dry season, and better information systems to provide advanced warning of flood timing and heights, were among the list of things that farmers felt were needed. While the flood pulse provides a natural “pump” for irrigating rice fields, the pump remains in the “hands of the sky” in the words of one farmer.
The fishermen also recognize the impact of the floods on their livelihoods. High flood years are correlated with high fish years – the more surface area covered in water, the greater the resource available to 296 species of fish that inhabit the lake, and the greater the harvestable fish population. The lake’s fisheries are some of the most productive in the world accounting for 60% of the national fish catch serving the livelihoods and food security of the people of Cambodia and neighboring countries.
In addition to providing key livelihood resources to the communities in and around the lake, the Tonle Sap is an internationally recognized biosphere reserve comprised of critical wetland habitat, with rather unique though highly threatened “flooded forests” that provide critical habitat to both avian and aquatic biodiversity. These include six IUCN Red Listed mammals species including the Long-tailed Macaque, Germain’s Silver Leaf Monkey, Smooth and Hairy-nosed Otters; 210 bird species, 17 of which are IUCN Red listed; and at least five globally threatened fish species including the Mekong Giant Catfish.
The future of the pulse
What does the future of the lake hold? Conversations with stakeholders around the lake highlight both the contributions that Tonle Sap’s annual pulse makes to providing for human livelihoods – water for agriculture, water for fish, and water for a unique biodiversity. More than the lake ecosystem itself however, is the ecosystem process, the annual rise and fall of the waters, the annual pulse of nutrients, and the shifting of habitat types that is the really unique feature of this landscape – and also its most threatened feature.
It is tempting to think that development solutions in this basin would involve increasing irrigation infrastructure, giving farmers more control over when and how much water is available. Intensifying agricultural development by increasing farm size, and diversifying income strategies presents an important solution for many families with the growth of the garment industry in Phnom Penh and neighboring countries. The rapid development of hydroelectric projects on the Mekong River promises to provide electricity for the growing electricity demand of the region. Elements of these approaches, while providing important opportunities, may have hidden consequences however. Unsustainable agricultural development within the larger basin threatens to increase sedimentation and siltation within the shallow lake reducing its capacity to store monsoon waters and threatening the lake’s fisheries.
Arias and colleagues argue that water infrastructure development could increase the area of open water (+18 to +21%) and the area of rainfed habitats (+10 to +14%), while reducing the area covered with seasonally flooded habitats (-13 to -22%) and flooded forest (-75 to -83%) – each habitat type effectively becoming more stable and thus increasing the predictability of flow. Some research suggests that the combined impact of these schemes would effectively put the Tonle Sap into cardiac arrest.
The question we should be asking ourselves, however, is what is the cost of putting the Tonle Sap into cardiac arrest for agricultural and energy production? This situation is likely to pit fishers against farmers; and conservationists against hydropower. Do alternative options exist that would allow us to maintain the flood pulses of the Tonle Sap? What kinds of structures, both physical and institutional would be needed to ensure equal access to water and fisheries by these groups?
Can we envision a space that keeps multiple interests at heart? Where development is managed within ecosystem boundaries by harnessing and shoring up ecosystem processes while providing farming families with opportunities for growth, and preserving a safe space for wild biodiversity? Promoting cooperation between the different people of the Tonle Sap is critical in finding locally driven solutions for livelihoods through the protection and management of agricultural and ecological systems. No more so than this year, where cooperation around water resources and biodiversity is highlighted as a global priority concern.
 Kareiva and Marvier. (2005). Conservation for the People. Scientific American
 M. E. Arias, T. A. Cochrane, T. Piman, M. Kummu, B. S. Caruso and T. J. Killeen. 2012. Quantifying changes in flooding and habitats in the Tonle Sap Lake (Cambodia) caused by water infrastructure development and climate change in the Mekong Basin; Journal: Journal of Environmental Management. 112:53-66.