Research published in the journal One Earth reports that ecosystem services are responsible for up to 18% of sanitation in cities around the globe. The study explains that nature and the services that ecosystems provide, such as water filtration by way of soils and wetlands, play a crucial role in the sanitary health of 48 surveyed cities.
Given that in 2017, 25% of the world's population did not have access to basic sanitation facilities and an additional 14% of people used toilets in which waste was disposed of onsite, understanding the role that nature can play and does play in sanitation could be key to improving public health.
"Nature can, and does, take the role of sanitation infrastructure," said study author Alison Parker, a Senior Lecturer in International Water and Sanitation at Cranfield University in the United Kingdom. "While we are not marginalizing the vital role of engineered infrastructure, we believe a better understanding of how engineered and natural infrastructure interact may allow adaptive design and management, reducing costs, and improving effectiveness and sustainability, and safeguard the continued existence of these areas of land."
Parker is part of a team of collaborators from universities and institutions in the UK and India. Together with her colleagues from Bangor University, Cranfield University, Durham University, University of Gloucestershire, University of Hyderabad (India), and the Fresh Water Action Network, South Asia, she analyzed the flow of human waste through 48 cities totaling approximately 82 million people. The team was specifically interested in looking at data from sites labeled as sanitary systems with "fecal sludge contained not emptied" (FSCNE). These tagged sites refer to places where waste is contained in a pit latrine or septic tank underneath the ground but does not pose a risk to groundwater.
Using Excreta Flow Diagrams to track the movement of waste, the team relied on a variety of in-person interviews, informal and formal observations, and direct field measurements. "We realized that nature must be providing sanitation services because so many people in the world do not have access to engineered infrastructure like sewers," comments study author Simon Willcock, a Senior Lecturer in Environmental Geography in Bangor University. "But the role for nature was largely unrecognized."
The results from the team’s analysis estimate that nature processes 2.2 million cubic meters of human waste per year within the 48 cities that they surveyed and 41.7 million tons of human waste per year before the liquid enters the groundwater. While ecosystem services are notoriously difficult to quantify, the team reports that these sanitation services could be valued at a minimum of $4.4 billion annually. That’s something that worth thinking about.
Referring to what the investigators have in mind for their future work, Parker stated, "We would like to promote a better collaboration between ecologists, sanitation practitioners and city planners to help nature and infrastructure work better in harmony, and to protect nature where it is providing sanitation services.”