Beavers and BMI – Worth A Dam

Last night I was watching a Colbert report rerun that idly mentioned that the EPA had released a report saying that more than half the nations river’s and streams couldn’t support life. What? More than HALF? How did this story slip by me? Of course I immediately thought of beavers and the idea that if half our streams can’t sustain them, and we kill them off wherever they appear, we might not have to worry about climate change or colony collapse disorder because we’ll all be dead from the water toxins before it really gets intolerable.

More than half of the country’s rivers and streams are in poor biological health, unable to support healthy populations of aquatic insects and other creatures, according to a new nationwide survey released Tuesday.

The Environmental Protection Agency sampled nearly 2,000 locations in 2008 and 2009 — from rivers as large as the Mississippi River to streams small enough for wading. The study found more than 55 percent of them in poor condition, 23 percent in fair shape, and 21 percent in good biological health.

Of course I rushed to the EPA website this morning to try and understand more. The report crashed my computer four times and the fact sheet is so badly designed as to be illegible, but I was able to glean this:

Biological communities are at increased risk for poor condition when phosphorus and nitrogen pollution levels are high
Phosphorus and nitrogen pollution comes from excess fertilizers, wastewater and other sources, and can cause algae blooms, low oxygen levels, and more.
Poor vegetative cover and high levels of human disturbance near river and stream banks are also widespread, reported in 24% and 20% of the nation’s river and stream miles respectively.
These habitat conditions make rivers and streams more vulnerable to flooding, contribute to erosion and allow more pollutants to enter waterways.
Excess levels of streambed sediments, which can smother the habitat where many aquatic organisms live or breed, are reported in 15% of river and stream miles. Excess sediments are found to have a significant impact on biological condition

What does this mean for fish and heron and otters? What does it mean for pond turtles and kingfishers or dragonflies? Forget about them, what does it mean for US? It means we’re in deep, deep trouble. How do the different parts of the country compare?

Okay, so we in the west aren’t a lot better but we’re slightly less awful. I’m curious, how do beaver dams affect the BMI life they were measuring in this study?

Generally found to improve diversity and density of BMI. Contradictory data explained by water health baseline. The effects of beaver-induced changes on water chemistry to fish will vary depending upon the original (pre-beaver) water chemistry. For example, if nutrients were limiting, then an increase in nitrates and phosphates from beaver activity would have a positive effect on salmonid production, while in a rich eutrophic site effects might be negligible or negative.

Reviews in Fish Biology and Fisheries 10: 439–461, 2001.

In other words, beavers and their dams could make conditions for aquatic life (and ultimately everything that eats it, or eats something that eats it) BETTER in 93% of the rivers and streams in entire United States, trapping sediment, filtering toxins, and cooling temperatures through hyporheic exchange. Admittedly, for the lucky 7 percent that are already in excellent biologic condition, the contribution of beavers will be minimal.

Well, okay then.