Picture if you will, a river flowing through the countryside with farms and forests alongside its banks. Imagine you are on a boat floating down that river. Look as you pass the tributaries coming into the river. See cows and barns in the distance. Notice the erosion along the banks of the river. See shallow waters lapping along sandbars and mudflats which sometimes trail along the sides of the banks. Pass a tangle of forest with bushes and vines and trees overhanging the river. Notice the banks tapering away and a marsh with reeds appearing. Watch as another forest comes into view, this time with trees standing in shallow water then gradually transitioning into trees standing in mud left behind from when the river was higher, maybe back in the spring when there was a flood. Pass back into the sunlight as the bank rises again and more farmland appears.

Then imagine what the same landscape looks like from overhead as if you were floating by in a hot air balloon. Acres and acres of land are set out below you, with a long and wide sinuous river wandering through it. You see the square plots of farmland and the little dots of farm buildings. You can’t see the cows from up here. Look at all the forests and swamps along the banks of the river stretching far into the farmland. You can see all the vast network of tributaries entering the river. You can see some of them entering directly into the river. Others go into and wind through the marsh before flowing into the river. Sail over state forest land running for miles along and away from the river, disappearing into the horizon. What you are looking at from up here in the hot air balloon is the watershed of the river. You may not see all of it, because it is a big river with no other large water body in sight. But up here, you can see the tributaries all branching off of the river which means all the water in the area is going into the river. That is a simple way hydrologist often define watershed: it is an area where all the surface water is flowing into the same place; in our case here – a river. Water washes off the forest land, it washes off the farm, it enters a tributary, and it goes out into the river. Watersheds can be large or small. In fact, the U.S. Geological Survey has coded them by size in their system of Hydrologic Units that covers the United States. Marshes and forested wetlands are an integral part of the watershed.

The Environmental Protection Agency’s (EPA) January 2015 report “Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific Evidence” looks closely at wetland features adjacent to rivers in order to determine if they have a  “significant nexus”  to the chemical, physical or biological integrity of downstream waters of the United States. “Significant nexus” are the words the Supreme Court used to tell EPA a connection must be established between wetlands and a river if wetlands are to be regulated as waters of the United States under the Clean Water Act. The Supreme Court has taken up a number of cases over the last fifteen years where plaintiffs have sued the United States because of federal Clean Water Act violations they received for filling in wetlands. Dredge and fill regulations under the Clean Water Act are actually handled by the Army Corps of Engineers not the EPA. But EPA is largely responsible for writing the rules and regulations under the Clean Water Act. So the EPA took on the challenge that the Supreme Court gave them and issued what the EPA calls the Clean Water Rule. The Rule seeks to define the waters of the United States. In order to write the Rule, EPA prepared a scientific report containing the summation of their review of thousands of research papers by scientists in many different fields of study from hydrology to biology who have examined and researched watersheds all over the world.

Today’s post reviews the section of EPA’s report examining wetlands adjacent to a river; the ones we have seen in our boat trip and our cruise in the hot air balloon. These adjacent floodplains can be permanent low lying wetlands or temporary wetlands during a flood. Wetlands, which we often refer to as marshes or swamps, and found in the floodplain of a river or stream, are called riverine wetlands. Some people call them riparian wetlands. And although they can be reed filled or filled with scrub and shrub, they are mostly known for supporting forested wetlands (often called forested swamps). These types of wetlands have been studied endlessly for a long time. There is a huge body of scientific work that documents them. There is even a classification system for them. What EPA was looking for, in this large body of research dating back to the 1960’s, was data that shows the connection of riverine wetlands to their rivers. You would think, just by them being called riverine wetlands, they would have a connection to the river, wouldn’t you? But EPA needed to document the physical, chemical and biological connection in order to write their Clean Water Rule.

One of the chief things that EPA set out to document was the hydrologic connection between the wetlands and the river. Many of these wetlands are inundated during flooding. As you can imagine, a scientist could probably find a lot of grant money for this type of research. People are interested in floods; generally because they don’t want them. The slowing of flood waters downstream by riverine wetlands is well documented in the scientific literature. Water during a flood goes over the river bank into the floodplain wetlands. The wetland hangs on to that water and keeps areas downstream from flooding worse than if the wetland didn’t exist. In fact, that was the big talk after Hurricane Katrina. Scientists determined that floodplain wetlands had been reduced so much in Louisiana that they no longer had the ability to moderate flooding. One of the big projects going on right now in Louisiana is the attempt to restore the floodplain wetlands. Scientists can approximately calculate the floodwater that can be stored in a riverine wetland based on the number of acres and so forth. Once the flood stops, water in the wetlands can flow back through the soils and through channels into the river. It is kind of a two way street. Water goes in and water comes out.

Water in watersheds doesn’t move just through channelized bodies, there is a lot of overland flow moving into the whole watershed system. Some of this flow can come off of farmland in the case of our watershed, or in a less attractive and more urban environment it can come off of city streets and other paved surfaces. The great thing about floodplain wetlands is that they serve as a kind of buffer for the deposit of sediments from agricultural lands. EPA cites one study that showed wetlands were removing greater than 80 percent of sediments leaving agricultural fields in North Carolina. That kind of removal really helps streams from being overwhelmed with sediment. Of course we know that rivers overtopping their banks can bring a lot of sediment out of the river during a flood and deposit it in the wetlands and other areas adjacent to the river. I think we’ve all studied, at some point in our elementary school education, the River Nile and how thousands of years ago flooding which deposited sediments in the land adjacent to the river made the Nile valley a hugely fertile agricultural area and gave birth to a major civilization. Or maybe people don’t study that in school anymore.

A major connection EPA documents in their report is the influence floodplain wetlands have on nutrients entering a watershed. The big three nutrients in water are nitrogen, carbon and phosphorous. All three are needed for a healthy biologic community, but when they get out of whack in a river system, it can create problems with oxygen levels and result in fish kills and unhealthy streams. EPA cites recent studies looking at how riverine wetlands adsorb these nutrients in organic matter and sediments, how they are taken up by the living vegetation and animals in the wetland, and how they are transformed into other compounds by microbes that live in the wetlands.  All of these processes reduce the amount of nutrients entering a river system. So wetlands provide a useful service to improve water quality. EPA’s report cited a recent study in which scientists calculated that three fourths of the nitrates in runoff from Maryland agricultural fields are removed by forested wetlands. Another study was cited that showed forested wetlands in Georgia removed 65 percent of nitrogen and 30 percent of phosphorous from nearby agricultural fields. These wetlands are providing a significant service in the health of our river systems.

Another service riverine wetlands are providing to the river system is the input of carbon to the food chain for the vast amount of biological life living in the watershed. You know carbon. We are carbon based life forms on this planet, including the plants and the trees. Carbon is a major nutrient. Lots of carbon forms in floodplain areas where algae and microorganisms enjoy the huge supply and multiply unchecked. They in turn are a great source of food for wetland biologic communities like insects, who are then eaten by fish, frogs and the like. These wetland sources of carbon also flow from the wetland into a river and are a source of nutrition for downstream bugs.

EPA also looked at biological connections in their scientific assessment. What and who lives in floodplain wetlands and what connection do they have to the adjacent rivers and streams. One thing that we noted on our earlier tour of the riverine environment is the diverse aquatic vegetation. There are also microscopic plants living in the wetlands too – all sorts of phytoplankton. Both types of plants move from wetland to river system and beyond. Seeds are transported out of wetlands and move downstream to seed other areas. Phytoplankton move easily with the water into and out of the floodplain areas.

Insects, crayfish and mollusks are all living in the wetlands too as well as microscopic invertebrates – zooplankton like copepods. EPA looked at studies during their assessment which showed that the greater the connection between a river and a floodplain wetland, the greater the abundance of invertebrates. You might not care, but the fish and the frogs sure do. Even just periodic flooding allows dormant eggs of some invertebrates laid in floodplain areas to hatch, providing ongoing populations of those invertebrates. Flying insects such as katydids and their fellow fish snacks are more prevalent in a watershed when there are floodplain wetlands. You probably don’t care to know the scientific research, since you have probably experienced the increased numbers of flying insects yourself whenever you have been near a wetland. But just to let you know, there are people who set out sample trays in wetlands to count the vast hordes of the bugs living and breeding there.

All these great sources of food for fish and animals are just one way the floodplain wetlands benefit river systems. Fish and mammals regularly commute between rivers and wetlands. EPA cites numerous studies of fish movement between both environments in their hunt for food, their need for breeding and rearing habitat, or just to take refuge when they are having a bad day. And mammals, well they get out of the river and use wetlands too. One study referenced by EPA said otters poop in the wetlands. Really I am not making this up.

EPA says the scientific evidence is strong that there is a physical, chemical and biological connection of rivers to floodplain wetlands even when the wetland is infrequently inundated by water. I think we clearly can see the connection in how a floodplain can store water and reduce flooding, how they can store sediment and nutrients, and how back and forth flow can affect both the river and the wetland and all the critters therein. I think EPA can declare victory on establishing the connection between rivers and riverine wetlands through their assessment of the scientific literature.

My next post on the science report behind the Clean Water Rule will be EPA’s greatest challenge yet: the assessment of the connection between river systems and non-floodplain wetlands.