One of the conceptual riddles Bob Berrens and I are working through in the new book we’re pursuing on New Mexico’s Middle Rio Grande, and the work surrounding it, is the ecosystem goods and services across our valley floor provided by the Middle Rio Grande Conservancy District’s web of irrigation ditches.
Where once we had a river meandering across a broad flood plain, we now have a river tightly confined between levees, replaced by said web of irrigation ditches.
Anecdotally, I see a couple of things in my wanders of the valley floor.
The most obvious is the neighborhood amenity value. People love these ditches! During the pandemic’s peak, ditch walking exploded (says Mr. Anecdotal Evidence, whose ditch bike riding similarly exploded).
My basic conception of what I mean by the “river” long tended toward the main channel itself – the relatively narrow strip that includes the flow of water between the levees. But in recent years I’ve become increasingly convinced that doesn’t fully capture the modern ecosystem.
The bits between the levees – a narrow channel of water dotted with sand bar islands that are increasingly covered by vegetation, accompanied by a lovely strip of our “bosque” forest of cottonwoods and the like – is a novel ecosystem, bearing only scant resemblance to the natural ecosystem before humans built dams and levees and diversions.
So also is the ditch network – a novel ecosystem, a tree-studded ribbon of green that spreads across much of the valley floor. Yes, a bit of cropland in there, but most of the green and the ecosystem is not that.
This is a far longer introduction than I had intended to a blog post pointing out a neat new piece of research by Frida Cital and colleagues at the Universidad Autónoma de Baja California in Mexicali. They looked at irrigation systems in the Mexicali Valley of the Colorado River Delta and found interesting ecosystem benefits (sorry, seems to be behind a paywall, but the abstract provides the gist):