Can polluted stormwater affect soil health?
During a heavy rainstorm, that water you see washing across the road and flowing into drains is stormwater. It’s the most common way toxic chemicals enter Puget Sound. Whether or not we realize it, these toxic chemicals are often a result of normal life in Puget Sound — driving a car, or fertilizing a lawn. When rain hits hard surfaces like roads or roofs, it can collect toxic chemicals and other types of pollution. Stormwater runoff often goes untreated and enters Puget Sound waterways, where it damages wildlife and the environment.
Urban areas have a high amount of hard or impervious surfaces. There are also near-urban areas — the areas between urban and rural regions — with structures that contribute to a flow of stormwater runoff.
Jordan Jobe is a research associate faculty member at Washington State University — Puyallup Research and Extension Center (WSU Puyallup) and manager of the Farming in the Floodplain Project. She wrote an article about one of those near-urban areas, the Puyallup River watershed. Her article, “We Need to Know if Stormwater Runoff in Near-Urban Agricultural Areas Impacts Soil or Plant Health,” published by the Agricultural Climate Network, asks questions about whether stormwater runoff might affect soil health or crops. Soil and crop health are important factors for local food systems.
Jobe’s article arose from what she’s observed in the watershed and from talks with local farmers. She had seen that heavy rainfall made farming more difficult — because ponding water can prevent farmers from being able to get into their fields in time to plant crops — and she knew that stormwater runoff had harmful effects on salmon. As she put it, stormwater runoff is a problem for both fish folks and farm folks — and so the issue might be a good way to bring together two different groups of people.
There are methods to deal with stormwater runoff in urban or suburban areas — such as bioswales, rain gardens, permeable pavements, rain barrels, and green roofs. These methods are often referred to as green stormwater infrastructure. Jobe, along with her colleagues Ani Jayakaran, associate professor and green stormwater infrastructure specialist at WSU Puyallup, and Courtney Gardner, assistant professor of civil and environmental engineering at Washington State University, explained what the next steps would be to figure out the impact of stormwater runoff on farming areas like the Puyallup River watershed.
First, they would need to see how much stormwater pollution happens in farming areas that border highways or railroads, for example. Next, they’d need to show the impacts that pollution has on soil and plant health, maybe by showing how a chemical in the stormwater affects soil or crop health.
As for managing stormwater in near-urban areas, it turns out that the green stormwater infrastructure used in cities — like rain gardens and permeable pavement — might not be good for farmland. Jobe said that one option for managing stormwater on a farm would be to plant trees between roads or train tracks and cropland. However, she explained that it would be better to see what could be put in place at the source of the runoff, so that farmers aren’t asked to give up some of their own land in order to reduce pollution from stormwater.
Jayakaran said that we need to be careful about how we manage stormwater infrastructure in landscapes that are close to farmland. He explained that, in areas like the Puyallup River watershed, the proximity of stormwater to agricultural fields could lead to polluted stormwater impacting nearby soils and crops. If it does, and how much it does are of course unknown at this point but bear further research.
The effects of stormwater runoff on farmland is relevant to areas throughout the country. Jobe said that stormwater runoff could be a problem in urban and near-urban counties in wetter regions, and specifically within floodplains — areas of low-lying land near streams or rivers.
Research on the effects of stormwater runoff on farmland could be key for making plans to deal with climate change too. The recent “Shifting Snowlines and Shorelines” report from the University of Washington’s Climate Impacts Group states that, in the future, more of Washington’s winter precipitation will be rain instead of snow. More rain means that there will be more stormwater runoff that needs to be controlled, and springtime rainfall events might be more intense too. Jobe mentioned that more intense rainfall would overwhelm existing stormwater infrastructure, lead to worse local flooding problems, and put more untreated stormwater onto farmland.
