Friday Fun Fact!
Native freshwater mussels play a variety of important roles in any ecosystem, but perhaps the most important is water filtration. Mussels are filter feeders, that is, they get all of their food and oxygen from the flow over water over their internal gills, much like a fish. And they are REALLY REALLY GOOD AT IT - they can filter, on average, a gallon of water every hour. Observe a simple demonstration set up streamside:
Two small tanks filled with water from the stream in the background. Sediment has been stirred up, as would occur with stormwater flow or someone walking or driving across a stream. The tank on the right has about a dozen native mussels, the one on the left has nothing but water and substrate.
Elapsed time: 10 minutes
20 minutes
30 minutes
35 minutes
The difference is pretty dramatic. These animals are helping to keep your water clean by feeding on algae and bacteria that I'd prefer NOT to be in my glass of water! How effective are they in a large body of water? Take Chesapeake Bay for example: before we buggered it up, that particular gigantic estuary was FULL of oysters, a mussel relative, also a filter feeder. Those oysters kept that water crystal clear, filtering every single drop about every 2 days. In the whole estuary. Just to give you an idea, that's about 19 trillion gallons of water in that particular bay. 19,000,000,000,000 gallons. More than we can comprehend. In two days.
However, there is limit to their "mad filtering skillz." If the water has any toxic chemicals in it (for example, mussels are VERY sensitive to chlorine and ammonia, both commonly found in wastewater outfalls draining into streams and rivers), they cannot survive and typically, fatal levels of these chemicals are far lower than water quality standards set by states. Also, sediment can quickly smother a mussel if the source is ongoing. Think of it this way: if you make a cup of coffee and it has a few grounds in it, you will probably still drink it. However, if it's chockablock full of grounds, you will clam up (haha) and abstain. Same thing for mussels: they can filter out small amounts of sediment but if there is too much, they will be unable to breathe and they will die. Yet another reason to control sediment input into water, which I discussed
here.
So who knows what the #1 pollutant in the US is?
I'll give you a hint:
Figured it out yet?
Yep, it's sediment. Dirt. Earth. Soil. Mud. Whatever you want to call it, it is carried by runoff and pulled from banks by erosion and our streams are FULL of it.
But, you say, dirt is part of nature, that's no pollutant! Well, you know the saying, "all things in moderation?" Well, that applies to ecology too.
Because of a variety of factors that have to do with channel shape, current speed, and stream path, a running body of water has a limit to the amount of sediment it can carry and move without becoming overloaded. Each stream, therefore, does have the ability to clear sediment out by carrying it and depositing it either along the bottom, on a bank or bar, or at its mouth. Likewise, the animals that live in the stream, mussels, fish, bugs, etc, each have their own tolerance to limited amounts of sediment for short periods of time.
It's when those tolerances are exceeded that this sediment becomes, in fact, a pollutant. When streams are frequently running muddy, when the bottom is nothing more than shifting mud or unconsolidated sand, when the banks are cut by erosion, dumping their clay into the water itself, problems abound.
Sediment smothers mussels so they cannot feed or breathe. Fish gills get clogged so the fish can no longer absorb oxygen. Many fish also rely on their excellent eyesight to find food; in muddy water, they are hungry and helpless. By blocking light, sediment also suffocates plant life beneath the surface that may be vital to fish and insect life. When all of this happens, it is an ecosystem in chaos and it also means the water supply is in trouble.
I mentioned that this sediment can come from bank erosion -- this erosion is often caused by a stream trying to channel more water than it is built for. This is usually due to our compulsion to pave and cover everything we can. Every square inch of ground we pave or harden with a rooftop is one less square inch that can absorb water. Thus, every drop of water that hits there will become runoff and we all have seen what a powerful force runoff can be.
In developed areas, most of the time, runoff is channeled into storm drains. Which usually then lead directly to a stream or other body of water, they ARE NOT filtered or cleaned in any way. This water also usually enters the stream at a single point -- it's like turning a fire hose on and blasting sediment right off of the banks, that's what kind of power this water has, especially during rain events. I remind you again, streams are your water supply, so anything you dump down that storm drain, you are effectively pouring into your glass of water. Sediment often enters the water supply here, running off from construction sites and yards. Most counties do have regulations about sediment control on construction sites, but the problem is that, even if these regulations are enforced (the enforcers are often far too few), the conventional technologies they require (silt fences, stormwater ponds) are very ineffective.
If you see a stream choked with sediment, especially if it is not raining, you can and should notify your county and notify your state water quality agency. A simple Google search can direct you right to them. Notice silt fences around a construction site are collapsed or leaking mud everywhere? Call and report it to your county, contractors and developers ARE required by law to maintain those. You have a right to clean water, wanderers, and it is up to each of us to stand up for that!
