October 25, 2013

Small Engineered Wetland & Climate Change

The Global Power of Wetlands: The Absorption of Carbon

Ecological designThere is a lot of data out there about how important wetlands are to the safety and future of the planet but there is little emphasis placed on the ability of wetlands to capture carbon. Wetlands absorb carbon at a higher rate than more dry land for a few reasons.

First, the plants that thrive in wetlands tend to grow at an amazing rate and their growth is carbon reliant. That is to say the structures that wetland plants create to help them grow fast are carbon heavy structures. Much like how skyscrapers are built of steel (a high carbon substance) wetland plants need to be able to be built tough to withstand the pressures of living in their chosen environment.

The second reason is that wetlands are almost always anaerobic environments. When those carbon rich plants die and begin to be broken down by the microbes the lack of oxygen prevents the microbes from creating gaseous CO2 so much of the carbon, (carbon that the plant pulled from the atmosphere), stays locked up in the soil.

In a report published in 1999 and available on the International Institute for Sustainable Development’s website (here) wetlands abilities to sequester carbon, specifically those on the prairie in Canada, are explained in the following excerpt.

.. wetlands are the largest terrestrial carbon reservoir in Canada, covering 14 per cent of the land surface but containing about 60 per cent of the carbon stock (approximately 150 Gt C).

Clearly wetlands are a powerful tool in the fight to reverse global warming.

The Local Power of Wetlands: Cleaning Water, Lowering Risks of Floods, Reducing Water Costs, & Tax Expenditures

Wetlands stack a lot of functions into small spaces. When properly employed both surface wetlands and sub-surface wetlands perform a myriad of tasks from cleaning water that’s been tainted from domestic and industrial chemicals to slowing stormwater and dealing with it where it falls which saves municipal water authorities money both in treatment costs and in infrastructure costs.

Wetlands can and should be included in all new developments and our legislatures should be looking at ways to incentivize the installation of new wetlands on existing properties in all areas from the country to the city. In the city where miles and miles of stormwater pipes need to be installed, monitored, cleaned, and eventually replaced strategic wetland construction can save billions of dollars. They can also save time, can further reduce a municipalities carbon footprint by reducing the use of concrete, and can increase land values by adding beautiful splashes of nature to the urban landscape. These splashes will also help cool and even clean the air while providing habitat for small animals creating an ever expanding chain reaction of positive results.

Automobiles create more than just air pollution they often leak oils and other fluids that wetland microbes can breakdown. Additionally many property owners spray a wide array of chemicals from chemical lawn treatments to pesticides and while a wetland may be damaged by large amounts of these chemicals they can and often do filter out and/or lock up these chemicals when exposed in small enough quantities. Stormwater that would otherwise run down a concrete pipe to be discharged into future drinking water sources can be first filtered by wetlands making the water that eventually finds its way into the drinking supply is cleaner having passed through these natural systems.

The Power of Balance That Wetlands Bring

As we’ve heated and continue to heat the planet we’re going to face less predictable weather, more storms, more droughts, more rapid changes of more extreme weather. Wetlands have a calming and balancing effect.

In both water rich and water poor areas wetlands can help to balance out seasonal changes by holding onto water through dryer times and catching water and keeping it from running off too quickly in wet times. Wetland plants protect that water and further increase the stability of the local water supply by reducing usage, by slowly sinking cleaned water into aquifers, and by providing a source of humidity via evaporation that can cause more frequent rain events.

Clearly wetlands are a good idea but what about for individual property owners? What is the motivation for a suburban family to give up part of their lawn and or garden to a wetland?

The Power of Food Producing Wetlands

If you’re interested in being part of the grow food not lawns movement you might shy away from including any wetland area on your property if you see it as unproductive. However wetlands can be extremely productive and beyond that they can be a huge help in your garden. Whereas typical garden plants might not grow in wetlands they present the opportunity to experiment with plants that like to have wet feet. Additionally as wetland areas fill up with organic material over time they may need to have some of their rich organic soil removed. This soil is often an excellent potting soil saving you the trouble of buying new potting soil that’s been trucked in from who knows how far.

If you’re not interested in growing food in a wetland you can still plant items that are useful for pollinators and other beneficial insects in your wetland. If your wetland is engineered properly you can use it to help keep the rest of your garden watered.

Our Wetland Plans

Our property is a sloping hillside but in the winter there is a steady flow of water running across the property near the top down to an area that has become quite eroded. We’ve got to properly plan out how to redirect this energy in a more positive way. Additionally we have neighbors that are at the bottom of the hill and if storms are going to be more powerful we don’t want to see our land beating down their front door.

We’ve thought about swales for some time but do to the slopes and terracing that we already have I’m leaning more towards keyline contour ditches that are at the back of the terraces so that the terrace in front of them can slowly absorb that water but wherein there may often be quite a lot of pooling. In these ditches and very small ponds we will plants clumping grasses, wild rice, reeds, and other water productive loving plants.

We’re planning a series of these along with a living roof and back yard space that can drain into a cistern and a larger pond or subsurface wetland on the lowest part of the property with a large basin that can catch and slow large amounts of water in a torrential situation without creating large problems for our neighbors in the valley.

I’ve got a design that I’ve worked up in Sketchup but it may not be true to the land so I’m hesitant to post it but when we do the actual work I’ll take loads of photos and will be sure to post about it. If you have any questions please contact me.

October 25, 2013 | W.D.Orkoskey
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