You know what a natural stream looks like, right? The Yukon in northern Canada or the Onega in Russia come to mind. If you are like me, you are pondering images of a sinuous stream with meandering channels after meandering channels. Ever since scientists started studying fluvial geomorphology - the study of rivers - those meandering channels have become the backbone that defines a natural stream.
Turns out there were 16,000 milldams in Pennsylvania alone in the 1800s. Among other things, those damns substantially changed the way streams flowed. In in a nutshell, here are the roots of our "natural" east-coast streams: 1) people built thousands of small dams to power mills and other things, 2) those damns eventually filled up with sediment from the river upstream, and 3) those damns eventually broke which resulted in lots of water cutting deep streams with high banks, and the stream began meandering. So what?--you might be wondering. Well, the "natural" meandering river paradigm guides a multi-billion dollar stream restoration industry. This study is a classic example of how different environmental contexts and histories leave their mark on nature. It pays to know your ecological history. For rivers and for their restoration, it might behoove us to go beyond our normal baseline of 1492.
Dreams of streams or nightmares of milldams?
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Very interesting, Josh. I had caught some of that when it was first announced a while back but your perspective help to make it relevant in particular as it applies to our efforts to re-establish natural system now. Thanks. What do you think stream restoration projects should be shooting for? Are there any examples of stream systems such as would have been naturally evolving on the east coast of the US that are still in existence?
Posted by: Doug l | March 8, 2008 10:58 AM
PS...and I meant ask in additions; if we go back to the 1492 baseline have we gone back far enough? What about Native American activities in cultivating the landscape? Any thoughts on Charles C. Mann's book "1491"?
Posted by: doug l | March 8, 2008 11:12 AM
In many ways (in my view), settling on a baseline is a balance between knowing the ecological history of the environment your are dealing with and a value judgement by society (e.g., what kind of ecosystem/biodiversity does society want to co-exist with?). In some cases that might be 1492 in others it might be 10,000 years ago - these are issues that surprisingly have not been discussed or debated much.
I sorely need to read Mann's 1491. I had a copy last year, but it burned in a fire before I can tackle it. It has been on my list for a while now. You've motivated me to pick up a copy soon. Thanks.
Posted by: Josh Donlan | March 8, 2008 12:40 PM
Hang on one cotton-pickin' minute! What about meandering rivers in the Amazon jungle? Those display a lot of the same fluvial morphology, and I'm pretty sure mill-dams have never touched that floodplain.
Posted by: octopod | March 11, 2008 11:13 AM
When I look at the streams that I am familiar with in Western Canada, it seems to me that the meandering is more a consequence of how steep the terrain is, and how much water is flowing. Three years ago, we had an abundance of spring rains that had a dramatic effect on a stream that I spend a lot of time around. Fish Creek generally meanders through a shallow valley, but when the torrent of water came through, the stream cut through the "s" shaped banks and went straight downhill, changing the flow pattern once again. If you stand at the top of the valley and observe, you can see evidence of earlier meandering stream beds that have been abandoned by the current flow of Fish Creek.
Posted by: Holzfaller | March 11, 2008 2:45 PM
This is an important paper and shows the importance of recognizing baselines in highly dynamic systems, such as rivers. In terms of settling on a baseline, there are science-based data to consider in addition to value judgments. One of the most important points to consider about baselines and the conservation and restoration efforts to achieve them is how that baseline affects ecosystem structure and function. In the case of rivers and historic mill dams in the northeast, it may be that we have changed the shape of rivers in a way that has negatively affected nutrient retention, for example. There is great concern about nutrient inputs to downstream areas, particularly estuaries, and the role of rivers in retaining nutrients input from the uplands. Thus, a baseline that maximizes nutrient retention may not be consist with a value judgment baseline (based on human historical events), or a baseline that is best for biodiversity or migratory fishes. As Josh mentions, in addition to what baselines humans want, I think it is also important to discuss the associated trade offs with what baselines are needed to maintain ecosystem goods and services. Maybe there is a paper on this already, or maybe not? -Brad
Posted by: B. Taylor | March 29, 2008 8:17 AM