While deforestation linked to palm oil has already been linked to a number of global concerns - including climate change and the destruction of wildlife habitats - there may be further, and as yet unexpected consequences from the expansion of plantations, warn scientists.
Writing in the Journal of Geophysical Research: Biogeosciences researchers from Stanford University and the University of Minnesota warned that 'significantly eroded' water quality as a result oof palm plantation expansion poses threats to freshwater streams that millions of people depend on for drinking water, food and livelihoods.
The US-based team noted that their findings contain surprising findings about the intensity and persistence of these impacts, even in areas fully forested with mature oil palm trees.
"Although we previously documented carbon emissions from land use conversion to oil palm, we were stunned by how these oil palm plantations profoundly alter freshwater ecosystems for decades," said study co-author and team leader Professor Lisa Curran, of Stanford.
The team warned that land clearing, plantation management (including the use of fertiliser and pesticides) and the processing of oil palm fruits to make crude palm oil can all send sediment, nutrients and other harmful substances into streams that run through plantations.
"Our study assessed five streams draining watersheds representing typical Kalimantan land uses. Compared to the stream draining an intact forest watershed, two catchments dominated by oil palm plantation agriculture had warmer stream temperatures, increased suspended sediment concentration and yield, and reduced oxygen saturation," reported the team.
In addition, vegetation removal along stream banks destroys plant life that stream organisms depend on for sustenance and shade, they warned.
Curran and her colleagues focused on small streams flowing through oil palm plantations, smallholder agriculture and forests in and around Gunung Palung National Park, Indonesia. They found that water temperatures in streams draining recently cleared plantations were almost 4 degrees Celsius (more than 7 degrees Fahrenheit) warmer than forest streams. Sediment concentrations were up to 550 times greater.
The team also recorded a spike in stream metabolism – the rate at which a stream consumes oxygen and an important measure of a stream's health – during a drought.
The impact of these land use changes on fisheries, coastal zones and coral reefs – potentially many miles downstream – remains unclear, noted the team - who added that this is one of the first studies examine the oil palm's effects on freshwater ecosystems.
"Local communities are deeply concerned about their freshwater sources," said Curran. "Yet the long-term impact of oil palm plantations on freshwater streams has been completely overlooked until now."
"We hope this work will highlight these issues and bring a voice to rural communities' concerns that directly affect their livelihoods."
Finding a solution
According to Curran and her team, potential management solutions include maintaining natural vegetative cover next to streams and designing oil palm plantations so that dense road networks do not intersect directly with waterways.
These kinds of improved practices are being pioneered by the Roundtable on Sustainable Palm Oil (RSPO) and other organisations that certify palm oil production as sustainable.
"Our findings suggest that converting logged forests and diverse smallholder agricultural lands to oil palm plantations may be almost as harmful to stream ecosystems as clearing intact forests," warned Curran - who added that there is very little protection for such non-intact forest ecosystems exist.
The US-based researcher warned that extensive land conversion to oil palm plantations could lead to a 'perfect storm' combining the crop's environmental effects with those from a massive El Niño-associated drought.
"This could cause collapse of freshwater ecosystems and significant social and economic hardships in a region."
Source: Journal of Geophysical Research: Biogeosciences
Published online ahead of print, doi: 10.1002/2013JG002516
"Authors: Influence of watershed-climate interactions on stream temperature, sediment yield, and metabolism along a land use intensity gradient in Indonesian Borneo"
Authors: Kimberly M. Carlson, Lisa M. Curran, et al