By Mike Rigdon - July 2020
Much has been written over the last year or so about the appearance of blue-green algae in the waters of Lake Anna. What it all boils down to in the eyes of this author is the presence of nutrients in the water that the algae feed on: specifically phosphorous and nitrogen. The same stuff you put on your yard to make the green grass grow. What other sources other than rain water runoff from your yard are there? Failed/overloaded septic systems and agricultural operations round out the list.
Of these two nutrients, one is more of a problem than the other. Nitrogen is eventually converted to a gas by biological processes and is released into the atmosphere. Phosphorous on the other hand is persistent. Soluble phosphorous compounds are carried into the lake by flowing water along with nitrates and sediment. Once in the lake, phosphorous feeds aquatic life, including algae, before it is released to settle on the lake bottom. Thus, there are two sources of phosphorous available to feed algae: that which comes in constantly with flowing water and that resident in the lake bottom sediment.
The focus of this article is on the phosphorous that arrives in Lake Anna via the tributaries that supply runoff water from the land at the upper reaches of the lake. The Soil and Water Control Districts (SWCDs) have programs to do things like fence livestock out of the streams and plant vegetative buffers along the stream banks. Such efforts are effective but they are voluntary. Consequently not all land owners choose to participate and there are many miles of stream banks that are not in the SWCD program. The establishment of wetlands is another mechanism to reduce the flow of nutrients that doesn’t rely on the cooperation of a host of landowners.
Luck Stone Constructed Wetland in New Kent County, Virginia Soon After It was Established.
A well designed wetland disperses the flow of incoming water over a large enough area to slow the flow rate and let entrained sediment settle out. The plants and trees in the wetland then serve to take up the nitrogen and phosphorous as they grow thus keeping much of it from reaching the lake.
With that in mind, LACA has submitted a request to the National Fish and Wildlife Foundation for a Planning &Technical Assessment grant to study the feasibility of creating and/or restoring wetlands on the tributaries that bring water and nutrients to the upper end of Lake Anna. Our proposal was submitted on April 27 and we should learn the results sometime in August if they aren’t delayed by Covid-19. The end goal is to eventually have wetlands in places like those created by Luck Stone in New Kent County and pictured above and below.
The catch is it will take time measured in years and they will be expensive. But once in place, they are low maintenance, effective and long lasting.
Luck Stone New Kent County Constructed Wetland September, 2019. (Photographs courtesy of Mark Williams, Luck Companies)