Bioswales and Constructed Wetlands

Early this AM, I was looking for some information on native willows. There are a lot of them on the river banks behind my place, and they provide forage for Black-tailed Deer, and nesting sites for Yellow Warblers and several other bird species, including cavity nesters such as Black-capped Chickadee, Tree Swallow, and various woodpeckers.

Searching for "Scouler's willow oregon bird usage" I found a link to an Oregon Department of Environmental Quality PDF titled BIOFILTERS (Bioswales, Vegetative Buffers, & Constructed Wetlands) For Storm Water Discharge Pollution Removal . I glanced through it, and while it wasn't what I was looking for, I noticed the following on page 25.

Obtainable reductions of pollutants in bioswales are:Total Suspended Solids – 83 to 92%Turbidity (with 9 minutes of residence) – 65%Lead – 67%Copper – 46%Total Phosphorus – 29 to 80%Aluminum – 63%Total Zinc - 63%Dissolved Zinc – 30%Oil/Grease – 75%Nitrate-N – 39 to 89%
These results can be obtained for a bioswale at least 200 feet in length with a maximum runoff velocity of 1.5 ft./sec., a water depth of from one to four inches, a grass height of at least 6 inches, and a minimum contact (residence) time of 2.5 minutes. 

It turns out that some random roadside ditch might be an engineered bioswale. Their generic usage is pretty much anywhere there is a need to remove pollutants from storm runoff. While I might care more than some because of where I live, anyone who uses rivers or lakes for recreation, or simply likes the notion of a healthy environment, should care to some degree.

The benefits of wetlands have been written about extensively, but nearly all of what I have seen has been about natural wetlands. What might be regarded as unnatural (though native plants are used) wetlands provide a lot of benefits as well. Also, they aren't subject to the same regulatory regime as natural wetlands. It's not as if, once built, they have to be protected for all time. Hopefully that will tend to increase their usage. We are all downstream of someone.