We Need to Know if Stormwater Runoff in Near-Urban Agricultural Areas Impacts Soil or Plant Health

By Jordan Jobe, Master of Environmental Management,  Washington State University-Puyallup

view of field by a road, with houses and buildings in the far background
The Puyallup Watershed in Washington State has dozens of family farms pinned between townhomes, traffic-dense roads, commuter train tracks, and industrial sites. Photo: Jordan Jobe.

As farmland in the Puyallup Watershed increasingly finds itself pinned between townhomes, traffic-dense roads, commuter train tracks, and industrial sites, it seems important to be aware of unintended impacts on agricultural viability. Today, the Puyallup River floodplain is used in a variety of ways, including residential housing, commercial and industrial uses, salmon habitat (including restoration and mitigation sites), and agricultural production. The floodplain has fertile, rich soil and is home to dozens of farms growing mixed vegetable row crops.

The Puyallup Watershed has around 14,000 acres of active agricultural production, including dozens of family farms in these fertile floodplain areas. However, as land prices skyrocket and development occurs, farmers often have to face difficult decisions about what to do with their land. Keeping agriculture viable allows farming to continue in floodplains—a far more compatible, productive, and safe use of floodplains than warehouses, parking lots, or housing. As dozens of partners in the Watershed accelerate efforts and investments towards flood risk reduction and habitat restoration, support for agricultural viability is a critical part of integrated floodplain management. These partners recognize that not only is agriculture critical for local food supply, but it is also critical in maintaining floodplain health.

In recent decades, development and precipitation have increased sedimentation, interrupting natural agricultural drainage patterns (Mauger et. al 2015). Rising groundwater levels (whether from increased impervious surface, subsidence or other causes), inadequately maintained agricultural drainage infrastructure and growth of invasive plants like reed canary grass have led to significant problems for agricultural production. What’s more, these challenges are likely exacerbating flooding by slowing the flow of water off land into ditches, streams, and finally, the Puyallup River.

We’ve talked about challenges with the quantity of water in the area in an earlier article, but there’s something we aren’t talking about yet! While increasing quantities of water combined with inadequate drainage infrastructure have led to documented agricultural drainage problems in the Puyallup Watershed, we aren’t talking about the quality of this stormwater runoff. Stormwater runoff comes from several sources, including impervious surfaces on developed hills and plateaus adjacent to agricultural areas, industrial sites near agricultural areas, a two-rail train track that runs through a swath of the floodplain, and many roads, including the five lane River Road Levee (Highway 167), higher capacity arterials, and numerous residential roads.

However, we don’t know whether the quality of that water is affecting agricultural viability. If chemicals in stormwater impact soil health, or contaminate crops, yields may be affected, or lower quality crops may be produced; this will have an economic impact on the farmer, and impact overall agricultural viability in urbanizing areas. More broadly, there doesn’t appear to be significant published research on the impacts of stormwater on near-urban agricultural viability. You can find research that documents the impacts of agricultural runoff on water quality. But, not work that answers the question: how does poor water quality from stormwater impact agricultural viability? There are many research questions that could help us get at the answer (see Box 1, below, to get a sense for some of them).

List of research questions
Box 1. Some research questions that can help answer the question: how does poor water quality from stormwater impact agricultural viability?

Given the large body of research documenting the impact of stormwater runoff on salmon (and orca) health (McIntyre et al 2018), on the hydrology of the Puyallup Floodplain (NHC 2018), and the impact of some stormwater chemicals on soils or individual plants (Maliszewska-Kordybach 1996, 2003), the groundwork has been laid to investigate the impacts of this stormwater on agricultural viability. The situation in the Puyallup watershed is not unique; increasing urbanization around the country is likely leading to similar scenarios in other watersheds.

A great place to start is understanding whether stormwater contaminants from nearby roads are found in our soils. If so, we’ll want to understand if it is impacting soil or plant health. Understanding the potential effects of stormwater runoff on agricultural viability will help us work together with stormwater managers, transportation engineers, and producers to better protect our agricultural lands.

References:

Mauger, G.S., J.H. Casola, H.A. Morgan, R.L. Strauch, B. Jones, B. Curry, T.M. Busch Isaksen, L. Whitely Binder, M.B. Krosby, and A.K. Snover. 2015. State of Knowledge: Climate Change in Puget Sound. Section 8: How will Climate Change Impact Agriculture? Report prepared for the Puget Sound Partnership and the National Oceanic and Atmospheric Administration. Climate Impacts Group, University of Washington, Seattle. doi:10.7915/CIG93777D

 McIntyre, J. K., Lundin, J. I., Cameron, J. R., Chow, M. I., Davis, J. W., Incardona, J. P., & Scholz, N. L. (2018). Interspecies variation in the susceptibility of adult Pacific salmon to toxic urban stormwater runoff. Environmental Pollution, 238, 196-203.

 Maliszewska-Kordybach, B., & Smreczak, B. (2003). Habitat function of agricultural soils as affected by heavy metals and polycyclic aromatic hydrocarbons contamination. Environment International, 28(8), 719-728.

 Maliszewska-Kordybach, B. (1996). Polycyclic aromatic hydrocarbons in agricultural soils in Poland: preliminary proposals for criteria to evaluate the level of soil contamination. Applied Geochemistry, 11(1-2), 121-127.

Northwest Hydraulic Consultants, Inc. 2018. Clear Creek Floodplain Reconnection Hydrologic and Hydraulic Modeling, Revised & Expanded Final Report. Report prepared for Pierce County’s Surface Water Management. Available online at Farming in the Floodplain