Wednesday, September 8, 2010

Pond to Bog Conversion, Phase I

Neglected 300 gallon pond
I've taken on a new type of project at home - something I've never done before, but it's popular, so what could go wrong? God, I am going to be a great parent. In 2005, I dug out and lined a roughly 300 gallon pond in our backyard - fed through a dry creek bed, from a piped gutter, and also by direct rain (obviously). I dug it deep enough (>24") to allow fish to overwinter, put mounds of sandy soil around the edge to allow frogs to hibernate, and ran electrical (above ground - I know - stupid) to pump (250 gph) and aerate. I envisioned a tiny urban aquatic habitat. Hmmm. Dreams.
How can I quickly list the biggest problems of such a small urban pond? First, the black liner would heat the water, causing awful algae blooms in the spring and a resulting fish kill in the early summer. I stopped replacing big fish in the pond in 2005, only adding guppies, suckers, catfish and frogs after that. In 2008, it became evident that rats were using the pond as a water source and pooping all over the edge of the pond. In addition, they were living in the flexible ribbed pipe that ran from the gutter downspout to the dry creekbed, which routinely then needed to be flushed of rat feces, rat skeletons, half eaten trash/rat food, etc. I pulled the pipe in 2009, robbing the pond of about 50% of its hydrology and probably 80% of its flushing. I got sick of constantly flushing the pump and filter apparatus in 2008, and at that time, the pond was mainly inhabited by guppies (who ate mosquito larvae...very handy!) and green frogs. I kept the pond aerated, which worked great until fall 2009, when rats/raccoons/opossums chewed through the 100' supply wire. As a result, no fish survived the winter.
With Henry being my #1 personal time activity in 2010, the pond just did not get managed. The frogs (I guess) did not survive the winter and I only noticed 1 shell from a dragonfly nymph on a pickerelweed stem, causing a horrible mosquito problem. Embarassing. Well, Henry started walking 2 weeks ago (at 11 months old!) and suddenly, the pond is an enormous liability. These days, I do a lot of work with urban wetlands, rain gardens, and bog "creations" and I thought, "What if I empty the pond and keep the liner in place?" I called a colleague who has designed many created bogs over the years (a wetland restoration/creation specialty I do not have) and he gave me some basic tips.

I drained the pond.
It's bigger than it looks, and I originally built it to have "benches" at several depths, which will not serve any purpose once the site becomes a bog. I also slipped on the liner several times and got covered in mosquito-y nasty goo while completing this process.

Adding Sand
The value of bog wetlands is in the fact that unlike most wetlands, they occur in organic sandy soils that allow groundwater to move around slowly but constantly within the bog area. Pollutants can be processed by bacteria this way, and these bacteria form the basis of a very unique food chain. Since my pond is a little shady and I won't be planting shrubs or trees in it, I filled the deepest part of the pond with 200lbs of sand.

50/50 organic / sand mixing
For the "shallow" parts of the pond, I mixed (per my colleague's advice) 50/50 sand and peat moss. If you look around on the internet (which I did), you'll see recommendations from 70/30 to 30/70. This took a half-yard of compressed peat moss and another 100lbs of sand.

Starting to look like a real bog!
Since it's September, and on the heels of the hottest Maryland summer in recorded history, I think that I'll let nature adjust the bog over the winter before I plant anything. Right now, the soil elevation is a little below the pond's outfall, which means that ponding will eventually occur - something I do not want (at least for now). Once the winter rains set in, I plan to continue to add more sand (my mix in the top 12" is somewhere around 60/40 organic/sand, instead of the prescribed 50/50). That way, the top of the soil is just barely above the pond's outfall. This should created saturated conditions throughout all of the soil, and should keep the wetland plants happy.
Tune back in around February for Phase II of this tiny habitat project!


Leigh, Andrea Leigh Gil said...

You gave me a few ideas... I cant wait to see the progress. Looking forward to Feb.

Unknown said...

Thanks for sharing this. I now know that I will not be building a little pond for the yard anytime soon!

Kirk Mantay said...

Trey - if you can do a pond that's say, 25' x 25' instead of 10' x 8' like mine, then it might be a little more sustainable (and full of bugs that eat mosquitos). Mine was a giant pain in the rear, but I'm glad I tried it.

Kind of relieved that it's empty now - kind of like an old boat you just had somebody haul away for $25.

Leigh - let's see how it goes! Who knows what will happen. Failure is always an option!

Mike said...

is this going to be and Underwood special? With Atlantic white cedar and pitcher plants? That's what a real bog looks like!

Kirk Mantay said...

Ha ha, Mike. I just saw your message. Now that the dog is no longer roaming the landscape, I might be tempted to do pitcher plants if we had more sunlight.

I'm figuring out the planting plan right now.

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