(Spoiler: no, they didn’t. In all honesty, I don’t think anyone has ever considered the use of filters to resolve sedimentation issues caused by agriculture, so that’s probably the wrong question to ask.)
(Also, I would like to apologise for not being able to update this blog for the past two weeks. I have been struggling with some mental health issues, but hopefully, things will continue to improve in the future.)
Agriculture is said to be one of the leading causes of erosion and sedimentation we find near water sources. According to Ongley (1996, p. 19), this form of pollution has two major dimensions – physical and chemical. The improper management of agricultural fields which are located near water sources can easily result in the aforementioned nonpoint source pollution, as sediments are dislodged from the soil, enter the water and get transported downstream. This may occur frequently during heavy rainfall, extreme weather events, or even while crops are being irrigated (assuming that the soil is extremely unstable).
A prominent short-term impact of anthropogenic sedimentation is the threat it poses to aquatic life. As commercial farming generally involves the use of synthetic fertilisers which contain nitrogen, phosphorus, or heavy metals, these elements may bind to to the soil particles and enter the water sources during erosion. As we already know from the previous posts, excess amounts of phosphorus can result in the eutrophication of water and generate toxic algal and cyanobacterial blooms which impede algae growth and fish survival. Meanwhile, the contamination of water with heavy metals can be even more deadly, as some of them tend to be persistent, bioaccumalative and toxic (PBT) in the environment. Even if humans do not drink directly from these water sources, the pollutants are able to travel great distances to affect other forms of marine life which may eventually end up on our plates.
Meanwhile, high levels of sedimentation also result in physical disruptions of the hydraulic characteristics of the channel, in terms of narrowing the channel and reducing its depth, as the sediments settle on river beds (Ongley, 1996, p. 20). Although it may seem harmless in the short run, the reduction of channel width and depth actually translates to higher flood risks for the surrounding areas in the long term. Coupled with the fact that even minor floods are capable of destroying or inhibiting the healthy growth of agricultural crops, the issue of sedimentation can actually be linked to a decline in food security in areas which depend on the harvests from the affected region. This is a point that may sometimes be overlooked by those who are unfamiliar with hydrology.
In addition, the Department of Water and Environmental Regulation, Government of West Australia (2017) notes that once sedimentation occurs in waterways, the sediments become extremely difficult and expensive to remove, as these procedures often involve heavy machinery and other engineering solutions. Perhaps it would be wise for humans to avoid clearing vegetated land for agriculture as much as we can, or these “hidden costs” may pile up over the next decades. (Or maybe, someone could invent a magical filter that can stop this from happening…but we can keep dreaming, I guess.)
Have a good weekend,
Jialing
Reference List
Department of Water and Environmental Regulation, Government of West Australia (2017) Erosion and sedimentation. Available at: https://www.water.wa.gov.au/water-topics/waterways/threats-to-our-waterways/erosion-and-sedimentation (Accessed: 19 September 2020).
Ongley, E. D. (1996) Control of Water Pollution from Agriculture – FAO Irrigation and Drainage Paper 55. Rome: Food and Agriculture Organization of the United Nations.