| Title | When Yesterday's Agriculture Feeds Today's Water Pollution | |
| Date | Monday October 15 2018, @07:54AM | |
| Author | takyon | |
| Topic | ||
| from the garbage-out-garbage-in dept. | ||
Submitted via IRC for chromas
When yesterday's agriculture feeds today's water pollution
A study led by researchers at Université de Montréal quantifies for the first time the maximum amount of nutrients – specifically, phosphorus – that can accumulate in a watershed before additional pollution is discharged into downriver ecosystems. That average threshold amount is 2.1 tonnes per square kilometre of land, the researchers estimate in their study published today in Nature Geoscience. "Beyond this, further phosphorus inputs to watersheds cause a significant acceleration of (phosphorus) loss in runoff."
[...] Focusing on 23 watersheds feeding the St. Lawrence River in Quebec, the researchers reconstructed historic land-use practices in order to calculate how much phosphorus has accumulated on the land over the past century. The two main sources of phosphorus to watersheds, the land adjacent to tributaries, come from agriculture (fertilizers and animal manure) and from the human population (through food needs and sewage).
Using Quebec government data, the researchers matched the estimated accumulation with phosphorus concentrations measured in the water for the last 26 years. Since the watersheds they studied had different histories – some had been used intensively for agriculture for decades whereas others were forested and pristine – this method allowed the researchers to establish a gradient of different phosphorus accumulations among sites. In so doing, they were able to see at what point the watershed "tipped" or reached a threshold and began to leak considerably more phosphorus into the water.
"Think of the land as a sponge," Maranger said. "After a while, sponges that absorb too much water will leak. In the case of phosphorus, the land absorbs it year after year after year, and after a while, its retention capacity is reduced. At that point historical phosphorus inputs contribute more to what reaches our water."
Low buffering capacity and slow recovery of anthropogenic phosphorus pollution in watersheds (DOI: 10.1038/s41561-018-0238-x) (DX)
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