Have you ever looked at a big river like the Mississippi or the Colorado and admired the beauty of the flowing water, the little eddies around sand banks, the floating logs and leafs, the sight of a fish jumping, the reeds along the banks, and wading birds foraging for frogs and other goodies in the shallow water? There is a certain calmness in looking at a river and all the water making its way to sea. Maybe that is why there are so many songs about rivers. My favorite is “Old Man River” from the musical Showboat. And maybe it is why artists so frequently paint rivers. I think my favorites are all those wonderful paintings of the Thames that Whistler did or maybe it is that beautiful painting by Van Gogh of the Rhone River at night. If you’ve thought these things, you are probably an artistic soul.

Have you ever looked at a big river and wondered where does all that water come from, why are there so many sand banks, how did all those logs make their way into the river and what in the world is going to happen to all those leafs, what kind of fish is that in the river and how did it get there, what kind of reeds are those, and what in the world is the bird eating that is wading around in the reeds? If you have wondered these things, you are probably a scientist and you would love reading the Environmental Protection Agency’s  (EPA) January 2015 report entitled: “Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific Evidence.”

The report synthesizes the work of thousands of scientific papers found in the peer reviewed journals where scientific research is published. The report provides a scientific basis for the definition of the “waters of the United States.”  The definition was issued as the Clean Water Rule in the summer of 2015. EPA and the Army Corps of Engineers have long been regulating upstream and adjacent waters to rivers as “waters of the United States.” This led to a number of court cases over the years which eventually wound up in the Supreme Court. The Supreme Court told EPA that they needed to find the physical, chemical, and biological connection upstream and adjacent waters had to downstream waters and define the connection clearly so that the Court didn’t have to be continually harassed by plaintiffs seeking relief from violations they’d received from the federal agencies. Well that’s not exactly what they said but it is the boiled down version.

Today’s post reviews the part of the report covering the connection of streams to rivers. Yes I know that sounds silly. We learned in elementary school that streams are connected to rivers or other water bodies like lakes (even in the desert, streams connect to playa lakes). Look at a map. All the little blue lines indicating water are connected to other larger blue lines. We know them from geography class as tributaries. Who hasn’t walked along a stream and found another little stream coming into it? Who hasn’t jumped the little incoming stream and walked further along the stream bank to find yet another little stream coming into the bigger stream? And if you turned up one of the little incoming stream, you might find the same thing – more tiny incoming streams- all forming a network of tributaries coming into a larger stream which eventually flows into a river.

The uppermost reaches of tributaries are called headwaters. You might call them the origin point of a river’s network of streams. Headwaters have been the source of many an adventurous real life epic. Take for example the great age of explorers back in the 19^th century and all those guys like John Speake, Samuel Baker and his wife Florence, and Richard Burton who risked malaria, nasty critters, and a lot of discomfort looking for the headwaters of the Nile River. But in the 21^st century we tend to like more facts and figures drawn from satellite imagery versus slogging around in the bush. We also like collecting data. So many rivers and streams have permanent hydrographs installed which collect flow data. EPA’s report shows in many parts of the country, headwater streams make up over 50 % of the total stream length in a river’s network of streams. Headwater streams are also called 1^st order streams. First order streams run into second order streams which then run into 3^rd order streams and so forth. Anyway these headwater streams are providing a lot of the water going into rivers. EPA cites one study done in the northeastern part of the United States which shows all the headwater streams in the river systems there are contributing 60 % of the flow to the downstream network of streams and rivers.

The water from those headwater streams comes not just from precipitation but also from groundwater. You may have heard someone say a creek is spring fed. That means groundwater is entering the stream. Groundwater can also feed a river directly. Probably the most striking example I have ever seen of groundwater entering a river is on the Snake River in Idaho where there are rivulets of water cascading from the high basalt banks into the river. Groundwater often provides what hydrologists call baseflow in a stream during dry periods.

So physically streams are connected to rivers by water flow. Even headwater streams that are dry most of the year are providing downstream flows. If you are an easterner, you may not realize in the western part of the United States that people need to be aware of storms going on upstream. Many a person has drowned on a sunny day in a slot canyon when a storm upstream produced a wall of water that swept down an ephemeral stream and filled up a slot canyon where hikers had no escape route.

All sorts of things can affect the physical flow of water in a stream. EPA’s report outlines many of the types of physical flow of water through a river network and how flow in headwater streams impacts the flow downstream through physical changes in the streambed, stream banks and the channel itself. Stream networks are messy natural systems. They are not smooth conduit like pipelines providing a nice unimpeded flow. Large amounts of sediment are being carried by headwaters downstream. Sediment can come from bank erosion and also from natural runoff. Strong storms and floods can move boulders and cobbles downstream. Trees fall into headwaters and are also carried downstream. I spend a lot of time looking at streams. Many of their flows are turbulent because of the amount of sandbars, the huge piles of boulders and cobbles, and the enormous log jams of trees. So obviously the flow of water downstream is being affected by what is being washed out of the headwaters.

EPA also cites temperature as another physical connection linking streams and rivers. This may surprise you, but not if you live on the water. Riparian trees are often protected all along a river network. Ask my ex-neighbor who got a big fine for cutting down trees along the creek bank so he could have a better view of the water. Trees and other vegetation provide shade and lower the water temperature. Solar heat, size of the tributary and entry of groundwater into surface water all control temperature. Temperature has all sorts of effects on downstream waters including eutrophication (low oxygen) which result in fish kills. EPA refers to a number of scientific studies which show upstream waters can impact downstream temperatures over long distances.

EPA has made a clear case for streams having a significant physical “nexus” to rivers. Now let’s look at their evidence for a chemical connection between streams and rivers. The strongest connection as you might well guess is that of nutrients. If you live anywhere near a river you are sensitive to how nutrients impact water. EPA primarily looked at nitrogen and phosphorus. I’m old enough to remember when they took phosphorous out of laundry detergent. Now they’ve taken it out of lawn fertilizer where I live. It’s that old eutrophication problem. The reason phosphorus is in lawn fertilizer is because it promotes plant growth. Put it in the water and it does the same thing. Algae just love it and you get algal blooms which deplete the water of oxygen, which fish need to live. Phosphorous runoff is natural of course, but these days a lot of it comes from agricultural practices. Nitrogen is also a natural occurring nutrient but agricultural development can be a large contributor in stream systems as well.

There have probably been more scientific studies looking at nutrients in river networks than any other kind of study and these studies have clearly documented nutrient connection between headwaters and downstream waters. EPA’s report cites a study which says 1^st order streams contribute 65 % of nitrogen to second order streams and approximately 40 % of the nitrogen in 4^th order and higher streams. EPA also cites studies on processes in headwater streams where nitrogen is sequestered thereby improving water quality downstream. EPA further cites studies where both dissolved nitrogen and phosphorous entering headwaters are taken up by algae and microbes which can be consumed by larger organisms, transported downstream as particulates, and returned to the water via death and decomposition. There are all sorts of complex interactions going on with nutrients in headwater streams that impact downstream water in rivers. EPA has made another clear cut case of connection within river networks.

For me a more interesting chemical connection point is the giant amount of organic detritus entering headwaters and being transported downstream. Not something I’ve thought about much, but all that dissolved and particulate organic matter entering the headwaters from leafs, eroded soil, wetlands and so forth is providing energy for the whole biologic community up stream and down. Downstream organisms such as microbes and algae are feasting on the organic carbon, larger organisms like invertebrates are feasting on the microbes and algae, and fish are feasting on the invertebrates. EPA estimates 31 % of total carbon in downstream waters comes from headwater streams.

This leads right into EPA’s assessment of the biological connection between headwaters and downstream rivers. Again the biological connections between the two are well documented in the scientific literature. All those invertebrates eating and breeding up there in the headwaters are a great source of floating food for downstream fish. I never knew all the functions that these little invertebrates performed nor that so many people spend their time studying what they are up to, but EPA cites a large number of studies that show how invertebrates are breaking down organic particulates into finer and more mobile dissolved forms, how they are promoting algal and microbial productivity, and temporarily storing and transferring sediments, nutrients and even contaminants by their actions. And the fish? Well of course we know that salmon, eels and so forth migrate from the ocean up whole river systems to spawn in headwaters. But did you know other fish spawn in one place then make a runner for it. EPA cites a study of cutthroat trout that spawn upstream than migrate up to 80 kilometers downstream after spawning. There’s even another study of a fish whose eggs float downstream up to 144 kilometers before hatching.  Fascinating. Anyway it is pretty clear fish don’t just stay in one place; they travel up and down river networks for breeding, spawning, feeding and other activities of the daily grind.

I think we can clearly put a mission accomplished banner up for EPA on proving through existing research that headwater streams are connected to downstream waters physically, chemically and biologically.

Today’s post is the second post in a series reviewing EPA’s report “Connectivity of Streams and Wetlands to Downstream Water.”  In my next post I’ll discuss EPA’s findings on connectivity of riparian and floodplain wetlands to downstream