Some ecological implications on clearing streams

In my blog entry of Aug, 22, More on debris in creeks, I reported on a recent conversation that I had on the issue with a friend of mine who is an environmental scientist. She read my blog and sent me a reply where she offered some further insights on the issue debris in streams including the effect clearing streams has on the larger ecosystem surrounding the stream. I learned a lot from her e-mail, which helped to fill some "holes" in my thinking. She gave me her permission to reproduce her response in my blog. I hope that the title of this entry, some ecological implications on clearing streams, correctly summarizes her response.

She says:

I took a look at your "ramblings" - interesting comments. I think I should clarify something we talked about that I didn't state well, about the debris that holds water. You have to think about the entire stream, even to what it flows into, when you think about debris. You also have to think about local conditions vs. what's happening farther away.

Let's start with local conditions. Say you have a stream in your backyard. Any rain that comes down too fast for the ground and vegetation and debris around the stream to absorb will run off into the stream. If you take out the "debris", it will run off faster. If there's enough water, it may even run off fast enough to remove vegetation. Certainly if you have bare soil, some of the bare soil will run off with the water. Vegetation and debris help hold the soil in place (vegetation is more effective at that), but some soil is likely to wash away in any case when there's a lot of water. If your house is right next to the stream, you may consider that faster runoff a good thing, but too much of it can take the soil away from your foundation. It's not considered very smart to build a house right next to a stream (in the stream's floodplain), and most places require buffer zones between construction and streams now. If your house is not right next to the stream, then, as the stream rises, the buffer zone with all the vegetation and debris will help hold the water away from your house. Debris also provides essential habitat for some wildlife: think of chipmunks living in fallen tree trunks near streams, and crayfish and other aquatic invertebrates (some that trout like to eat) finding shelter among debris in the streams.

OK, what about not-so-local conditions? Say you're pretty far upstream and you clear out your debris to get faster runoff or maybe just to make your lawn "prettier", and all your neighbors do the same. Then, when it rains more than the ground can absorb, all that water goes downstream, with its inevitable load of soil and whatever pollutants also ran off. So there is lots more water downstream, and those downstream neighbors get more flooded than they would have if you hadn't cleared out the upstream. (For example, Route 17 in Hackensack and Lyndhurst floods when it rains a lot in Mahwah in northern NJ.) In the meantime, because there's more water coming into the river, it's inevitably getting more soil, pollutants, and other stuff washing into the river. That means that the river in general is getting shallower and more prone to flooding. It's also getting more polluted (and so is the bay that the river goes into). Buffer zones of wetlands along a river provide conditions that break down pollutants and keep surface waters cleaner.

Debris is such a pejorative word. It sounds like "garbage" or "trash". Our society favors flat green monocultures, often of species that aren't native to the area. People remove trees and shrubs because of the "untidyness" of dropped leaves and limbs and seeds. We remove water and spray poisons to get rid of mosquitoes and other insects, even though those insects serves as food for other species. It's no wonder we're having a biodiversity crisis.