University Place

Groundwater, Wetlands, and Geology

I’m Tom Zinnen, I work here at the UW-Madison Biotechnology Center. I also work for UW-Extension, Cooperative Extension. And on behalf of those folks and our other co-organizers, Wisconsin Public Television, the Wisconsin Alumni Association, and the UW-Madison Science Alliance, thanks again for coming to Wednesday Nite @ the Lab. We do this every Wednesday night, 50 times a year. Tonight, it’s my pleasure to welcome back to Wednesday Nite @ the Lab, Ken Bradbury. He’s with the Wisconsin Geological and Natural History Survey. He was born in Richmond, Indiana, and graduated from Richmond Senior High School. And then he went to Ohio Wesleyan University and majored in geology. Got a master’s degree at Indiana University in geology. And he came here to UW-Madison to get his PhD and he went way, way out there and got a PhD in hydrogeology. (audience chuckling) Then he went directly to the Wisconsin Geological and Natural History Survey, that was in 1982. He’s been there 36 years. And since 2015, he has been the director there. And in that role, he also serves as Wisconsin State Geologist, which is a role that Thomas Chamberlin and Charles Van Hise I believe also held. And they became presidents of the university. (audience laughing) Tonight, Ken gets to talk with us about groundwater, wetlands, and geology, the invisible links. And now while he’s saying they’re invisible, I think we’re starting to see more and more that they’re pretty visible. And the question is what do we get to do about that? So please join me in welcoming Ken back to Wednesday Nite @ the Lab.
– Thank you, Ken.

– Thank you, Tom. (audience applauding) Well, thank you, Tom, and thanks, everybody, for coming tonight. So this is a reprise of a talk that I put together for the Wisconsin Wetlands Association for their conference about a year ago. The point I wanna make is that we all like wetlands and wetlands are pretty prolific in Wisconsin and the Upper Midwest. But groundwater, which as a hydrogeologist is my specialty, is pretty important for wetlands, and many people don’t understand all the links. And the more we think about wetlands, we really have to understand the groundwater system around them. So this talks a bit about wetlands and a bit about groundwater and how they act together. There’s a lot of wetlands in the Upper Midwest, lot of wetlands in the United States. On this map, all the green areas are wetlands. And you can see that in the Upper Midwest, we have our share of wetlands, more than many other places in the country. This hashed area are the pothole prairies of Minnesota and North Dakota, where there are many, many, many small wetlands.

And so we have a lot of wetlands in the Upper Midwest. And these are all connected to groundwater in one way or another. Why? Why do we have all these wetlands? And I think it’s interesting to think about why we have them. First of all, where do wetlands occur? They occur in– The main areas in the United states are glaciated terrain where we are now, also in coastal terrain like the coastal plain here and in Florida and the Southeast, and then along rivers like the Mississippi or the Wisconsin, so those are places wetlands occur. But it’s interesting to me that if you look at the pattern of wetlands in the Upper Midwest, kind of draw a line like this, you realize that they really follow our glaciated areas. So here’s a map of the glaciated region of the Upper Midwest. So this is the area covered by glaciers during the Pleistocene. And you can see that that fairly well matches the extent of major wetlands in the Upper Midwest. Why is that? Well, for one thing it’s a fairly leveled or lower leaf topography. We don’t have a lot of mountain ranges unfortunately. And it’s a fairly young landscape and it’s often kind of hummocky and pitted so there are a lot of places for water to collect. And in general, we have a humid climate and it’s not too far to groundwater in most of these places, so all these things work together to give us a lot of wetlands here.

I mentioned that wetlands are dependent on groundwater. So most people look at a wetland and they see a surface water feature and they don’t often think of the subsurface. So this is a cross-section across a stream with the wetlands along the shore and we’ve got some arrows here. The importance of this is just to think about the impact of groundwater in feeding the wetland. The wetlands are not always, to some extent, they’re based on surface water and runoff and rainfall, but groundwater is an important component of the wetland water budget. So in this talk, some takeaway messages for you is that the groundwater, wetlands, and surface water are often connected and we need to think of them as linked environmental systems. They’re linked in terms of water, chemistry, water quality. And what we do to one part of the system affects another part. Understanding the geologic setting, where they occur in the landscape, what kind of rocks are around, what the history of that landscape is, what the topography is helps us identify the wetland and helps us understand why the wetlands are there. And then water systems are transient. It means they change with time. They change with climate, with weather, with short- and long-term climate change or climate cycles.

They can change due to what we do on the landscape like changing land use or changing groundwater pumping. And I’ll talk a little bit about that too. If you’re interested in reading more about this, this is a free publication you can get from the U. S. Geological Survey, a really, really good publication about groundwater and surface water. And the subtitle here is “a single resource,” and that’s what we like to think about in the Midwest, particularly in the humid Midwest here. Groundwater and surface water are not separate things. They’re really one. They’re two parts of a single system. They need to be thought of and managed together. So that’s kind of our mantra as modern hydrogeologists that groundwater and surface water really represent a single water resource. I know some of you probably know a lot about groundwater, others, maybe not so much. So I’m gonna spend a little time bringing everybody up to speed on what is groundwater. Groundwater is the water that fills the cracks, pores, interstices, voids and fractures in the rocks and soil beneath our feet here.

So groundwater is water in the ground that’s filling these voids. And what do the voids look like? Well, this is a classic view of the different sorts of porosity that you see in geologic materials. Porosity refers to the open space between the sand grains or rocks or whatever is making up the subsurface. So we can see that these can be what are called primary openings, which are the spaces between, say, sand grains. If you thought of beach sand, there are spaces between those grains. Those are the pores. And depending on how well sorted it is, whether all the grains are the same size like here or a mixture of size, you could have either more or less porosity. So that’s called primary porosity because that exists from the time the rock was deposited. Secondary openings are things that occur later like fractures or dissolution or solution features or caverns in a karst environment or a cave environment where openings come later than the rock was originally deposited. We have both sorts of porosity in Wisconsin. What does that look like in the real world? Well, on the upper right, you see a optical microscope picture of some sandstone right here from under Madison, some Cambrian sandstone. And you can see the beautiful rounding and sorting of these sand grains. That’s a wonderful aquifer. That’s where all of you are getting your water. If you’re drinking any water in Madison, it’s coming out of an aquifer like that. And here is how it looks in the field on the lower left.

Cambrian sandstone, you can see some cross-bedding in there. Typically, rocks like this have a porosity of about 15%, 10% to 15%, meaning 10% to 15% of that material is just open space and that’s where the water can be stored and transmitted. Now if we go to other kinds of rocks like limestone or dolomite, which are not really made of grains, but instead are. . . more of a. . . formed from layers and layers of tiny sea creatures that have deposited over the years and then recrystallized, this rock is not very porous naturally, but it has lots of cracks and fractures in it and the water comes from cracks and fractures. So you can see this would be a outcrop that you’d see up in Door County, Wisconsin, or other places where we have a lot of limestone or dolostone, dolomite. I’ll talk about the water table and what the water table is and what the groundwater system looks like. So this is a cross-section of a typical cartoonish landscape. This is the land’s surface. And anywhere here in Wisconsin, if we dig a hole or we drill a well, sooner or later, we’re gonna hit water. And that water, where that sits is called the water table. The water table is a surface. And below that surface, it’s called the saturated zone, and all the pores and those cracks are full of water at that point, so they’re saturated. Above that water table, the pores are not full of water. They’re full of air or carbon dioxide or something besides water, probably a mixture of air, carbon dioxide, and maybe some other gases sometimes. Often right over the water table, there’s a thin zone called the capillary fringe where water gets pulled up into the pores by capillary action, just like you’d have water moving up in a soda straw, but that’s a fairly, fairly thin zone, only a few inches thick or less, usually. But it’s important to remember that the water table is the top of the saturated zone ’cause you’re gonna see some other diagrams that have water tables in them.

And then it’s always important to think about the water cycle. And I’m sure most of you, if not all of you, understand this, but water falls in a cycle starting as precipitation, rain and snow on the landscape, and then moving in to partitioning itself as it hits the landscape, and much of it runs off the landscape. Some of it evaporates and a bit of recharges or percolates down and becomes groundwater, and then it becomes part of the groundwater system. And so these rocks and soil down here are what we would call aquifers because they can transmit groundwater along these flow lines that might go to a well if there’s a well there or they might go a long way to discharge to a lake or a river, a discharge point, or they might discharge to our wetland here. So here comes a wetland. And then we have other process like evapotranspiration that’s gonna take that water back out and it’s gonna become part of the cycle again. So remember, it’s a closed cycle. So understanding how all these things fit together is part of our understanding here. Groundwater moves in three dimensions. Groundwater is not static. It’s not just sitting in one spot down there. It’s moving.

And in a humid climate like Wisconsin, it’s usually moving from higher parts of the landscape to lower parts of the landscape. But it’s not just moving horizontally, it’s moving vertically as well. So if we take this cartoon apart, we can see that groundwater is– it’s moving laterally, but it’s also moving in these curving flow paths that go moving down under the higher parts of the landscape and then actually moving upward under the lower parts of the landscape to discharge to a surface water feature. This happens to be a stream, but it could be a lake or a wetland as well. And so it’s quite common to see upward groundwater flow under these low parts of the landscape. And so, any of you have ever seen a spring or a flowing well, an artesian well? You’re getting water that’s coming up with pressure from somewhere deep below the surface, but that pressure is related to the altitude at which that water first entered the groundwater flow system. And then the other interesting feature here is that groundwater is moving two different directions from say the top of this hill. That’s called the groundwater divide. And that divides groundwater into flow systems so that on one side of a hill, groundwater’s going one way, the other side, it’s going the other way just as you would have topographic divides in the landscape.

The only difference here is that we can move this divide by doing things like pumping water or doing a change in land use. We can actually move that divide sometimes. Groundwater moves slowly. Generally, in a place like Wisconsin, we’re only talking about inches or a few feet per year. There are exceptions to that. In limestone or dolomite where those fractures are, like I showed you, you could get much more rapid movement, tens to hundreds to even thousands of feet per day sometimes. But in general, think of tens of feet per year, which is not very fast. Groundwater is moving fairly slowly. And if we get into something like a clay, we’re talking inches or millimeters per year sometimes. Sometimes very, very slow. I already mentioned groundwater flow systems, but to put it in another context, we need to think about the whole system as a place that starts with groundwater recharge or groundwater as entering the landscape and then it’s moving to groundwater discharge at a surface water feature or sometimes to a well, and then those flow paths, again, don’t just go laterally, they go vertically downward and then back up. And depending on the local geology, they could go very deep, and that water could be in the ground for maybe thousands of years or they can go very shallow and just be in the ground for a few days.

And of course, the length of the flow path has an influence on the chemistry of the water because the water is dissolving things along the way and then the water may also be picking up things that are spilled on the surface or things that are coming down from the soil. So understanding the flow path is also important. And again, I’m telling you all these things because when we get to think about wetlands, all these things become important in understanding wetlands. I mentioned groundwater recharge. And here we can think about wetlands a little bit. Are wetlands places that groundwater is discharging or groundwater is recharging? And so this might be a typical cross-section of a place in Wisconsin. We have clay moraine. A moraine is a glacial deposit. And often in Wisconsin, those are gray clayey and they create a hummocky upland.

And because it’s clay, we may say, well, there’s not much recharge going on there because it’s clay. Over here is more of a sandy place and there’s maybe more recharge there. And sometimes people want to protect recharge areas and so they may say, “Well, we better protect this recharge area.” But we don’t often think of what’s going on up here on the clay moraine. And in fact, there may be some wetlands up there we want to protect, and those wetlands are getting recharge that’s locally up here. These might be kind of high elevation wetlands. And so to protect those wetlands, we need to understand not only the area to protect down here with the high recharge area, but we need to protect the upland recharge areas too. And so wetlands can be either discharge or recharge areas depending on where they fall in the landscape. So let’s look again at our wetlands. We take our wetland here and we blow it up, where does the water come from? The groundwater component of this wetland, where is this wetland getting its water? Well, it’s getting rainwater and it’s getting some runoff, but it’s also getting groundwater from some sort of zone that’s hydraulically upgradient that we would call the capture zone or the contributing area for that wetland.

And so that means that this is the area of the landscape which is usually– Whoops, let me go back here- usually in map view kind of an oval-shaped zone where groundwater is coming from recharge, rainfall is landing on the soil, on the ground, becoming groundwater, and then that groundwater flow system is discharging to that wetland. So this is the area where groundwater is actually feeding that wetland. And that’s one of the things we do as hydrogeologists, is try to figure out where those areas are. So, many of you are probably familiar. . . with the springs over in Middleton, Pheasant Branch Springs, so this Pheasant Branch, one branch of Pheasant Branch Creek. This is looking sort of south, and Lake Mendota would be off here. If you ever go out to the Pheasant Branch Conservancy, there’s a wonderful big spring, one of the biggest springs in Dane County, by the way, that’s right here, that’s the start of this creek. And it’s nice that it’s protected in this conservancy. My colleague, Randy Hunt at the USGS a few years ago did some computer simulations looking at the capture area or the contributing area of groundwater for that spring.

And so if you keep that spring in mind and look at this map, he figured out that the groundwater coming out of that spring and feeding this wetland around it comes from a mile or so away in this oblong area. So that’s the contributing area for that spring. And the reason it’s important to know that is that some of this is an agricultural area, there are highways here, there are potential contamination sources, there are potential land use changes that if they occur up here can affect that wetland. And so this is why we try to understand these things. But this is also a good example of a capture area or a contributing area for a particular wetland. So when we think about groundwater and wetlands, what are the questions we wanna answer? How much groundwater is coming into a wetland, the water budget of the wetland? How fast is that groundwater coming in? And that has to do with hydraulic gradients, hydraulic conductivity, which is the ability of that rock and soil to transfer water, and its porosity, which I talked about. How far away this had come from? That has to do with the groundwater flow path. How dynamic is this system? How much does it change seasonally or with time or with climate change or even daily in some cases? What are the characteristics, the chemical characteristics of the water?

Here we can think about water quality, mixing of different waters from different places, even contamination sources on the surface. And finally, what’s the conceptual model of the system? So what is a conceptual model? Conceptual model is a pictorial representation of the groundwater flow system that’s basically a picture. We do a lot of modeling in science. And people often think of models as something we do with computers, and we often do. But before we start, the best practice is to make a cartoon or a picture or a small diagram of really what you’re talking about. And that’s what we call a conceptual model. What are the sources and sinks and boundary conditions on a model? Just what’s the concept of your wetland here? And so for wetlands, there are at least four conceptual models. And I’m gonna talk about these and show you examples of them. And these diagrams are a little small to see, so I’m just gonna move ahead and you’ll see these again. But they all have to do with different landscape settings in which wetlands occur. So let’s start in Wisconsin and go to some places here. I don’t know how many of you have been to the Mink River, the Mink River Estuary up at the tip of Door County. Really lovely, lovely place to go. But there are springs there.

And the springs there can be characterized by a conceptual model like this which is what we would call a complex flow field model. Now I’ll simplify this for you. You see two kinds of lines on here. You see light, your kind of narrow, dark lines. Those are lines of equal hydraulic head or hydraulic pressure. And then you see these thick or blue lines with little arrows on ’em. Those are lines of groundwater flow. And so groundwater is going to move from higher to lower hydraulic head, and it’s going to move generally sort of perpendicular to these equal potential lines or these lines of hydraulic head. And so when you see a– This is called a flow net, and one of the things hydrogeologists try to do is to delineate what these things look like and then try to understand how the groundwater flow lines go. So you see here, when you see groundwater coming to the surface, this is an area where we’d expect wetlands to occur. If you see the flow lines going downward, you think no, they’re not going to occur there because that’s a place where more recharge is happening. So if we look at the Mink River, why are we interested in it? Well, it’s a really cool place. It’s a natural area, a very pristine freshwater estuary going into Lake Michigan. And it’s really a fairly unsullied place. It’s also the home of the Hine’s emerald dragonfly, which is an endangered species that were asked to look at.

One reason we got involved up there is the Hine’s emerald dragonfly takes– It has to reproduce in small carbonate springs. . . in this wetland, and the nature conservancy and others wanted to know where the water was coming from for these springs, so we did some studies up there at these sites in Door County to try to understand where the water was coming from for this Hine’s emerald dragonfly habitat. Interesting enough, the immature Hine’s emerald dragonfly is just this little beetle thing here that doesn’t look very attractive, but that’s what people are worried about saving. So the conceptual model though is that we have this carbonate aquifer, fractured rock, we have a flow system or we have the water table that’s indicated by this dashed line, and it’s sloping down toward the wetland and toward Lake Michigan here.

We have recharge that’s occurring somewhere up to the left here and then these groundwater flow paths are going down and they’re coming back up to the wetland where there’s general seepage in the wetland and there are also springs. And the Hine’s emerald dragonfly needs carbonate groundwater, and so this is a carbonate rock, and so water that’s going through there is rich in carbonate minerals. And so that’s good habitat for reproduction. And so when we looked at that, here’s an air photo of the Mink River Estuary. This is Green Bay up here, Lake Michigan out here. And this is the Mink River right here. And the Hine’s emerald dragonfly habitat and the springs are right in here. If we zoom in, look at a different photo, you can see the spring channels here, and these are springs. And this is all a huge wetland complex, all being really sustained by groundwater. It’s interesting though, there are some little point discharges that cause these little springs to come out. The other interesting thing is this photo was taken a few years ago when Lake Michigan was low. If we took a picture like this now, it would look a lot different ’cause the lake is higher and most of this is underwater right now because Lake Michigan has come up. I also just like to show this because it’s so cool. This is lidar imagery of the same place. . . really high-tech topography measured with lasers. And you can really see the glacial topography and the way the landscape has gotten sculpted as the glaciers went over here. But this is the kind of information we use now in our mapping. But anyway, the springs and wetlands we’re interested in here are right in here. What we did, we built a computer model based on our conceptual model.

And so this is actually an aerial view. The blue lines here are lines of equal hydraulic head, or think of it as a map where the water table is. And then we can do these flow lines that are perpendicular to those. And that outlines the capture area for this, the springs and wetlands here. So this would be the area where groundwater comes from that actually ends up here. And we call that the contributing area for these wetlands. And so the hashed area are the actual habitat for the Hine’s emerald dragonfly, and the outlined area is the region where the water is actually coming from, the groundwater that’s sustaining these springs and this wetland here. So that’s one type of wetland and that’s the kind of thing that we study when we’re trying to understand the groundwater, where the groundwater’s coming from. And while we do this, we can figure out the water budget, how much groundwater is actually coming in, what percentage of the overall wetland water budget that is and so forth. Let’s move a little farther down Door County. We were up here, let’s move down to Peninsula State Park and the Niagara Escarpment which is this big dolomite cliff here. We can look at a different setting for springs here, springs that occur along a break in slope.

And so if you think of that escarpment, here’s that done in a conceptual model. We have the land surface, a big escarpment down to the lake. And we have a water table in there that intersects the land surface right at this nick point or this break in slope. And so we would expect springs and wetlands to occur at a place like this, along this break in slope. And if you go to Door County, along the Green Bay shoreline, it’s actually what you see. Here’s a conceptual pictorial diagram of that area done by my friends, Stan Collins, Nancy Alton, who are landscape architects, just to show you some of the features of Door County. But the important thing for the talk tonight is that there are springs and seeps and wetlands, perennial wetlands right along the base of this escarpment, and that’s what we see here. And so again, the reason that these springs are here is that the water table is sloping downward, hitting in a lake, but it’s very near the surface of the land, right at this nick point right here. And that’s why we see these perennial wetlands in this place.

And again, we can look at the contributing area for that. This is a map view of the same area. This is called the Bayshore Blufflands Reserve. It’s along the Green Bay side of Door County. And we again did some computer modeling to figure out the contributing area for the springs and wetlands right along the shoreline. And again, the groundwater is coming from even a couple of miles away to discharge there. So we can understand where the groundwater came from there. Now let’s look at a different sort of spring, and we’ll move down here to Walworth County and the village of Eagle in the Kettle Moraine area. So here, we’re looking at a different geologic and hydrogeologic setting. And I showed you this picture before where we have a stream or a river environment with contiguous wetlands along its shore and groundwater coming in from the sides. And this is the kind of environment you get along the Mukwonago River Watershed, which is a really high quality wetland-rich watershed there. I wanted to point out the importance of riverine environments in groundwater, is that there’s a lot of geochemistry and geochemical, biogeochemical changes that go on right under a stream, right under a wetland in zone called the hyporheic zone where there’s a lot of– this is only a few, maybe a few centimeters or a few inches thick sometimes, but it’s zone where there’s a lot of biological activity, geochemical activity, and you get a lot of chemical transformations that are occurring that can change water quality right under the stream or the wetland here.

So here again, you see a stream and you see groundwater converging to put water into that stream and into that wetland. If we go to the village of Eagle and the Mukwonago River, here’s the little village of Eagle is up here and the Mukwonago River goes through here and it goes through some really high-quality places that you’ve probably heard of like Lulu Lake, Eagle Spring Lake, and there’s a couple of state natural areas here. A really pristine environment. Reason we got involved with this study was that the village of Eagle had two new groundwater wells here that were drilled to serve the village. And this is about a mile– They’re about a mile south of the village, and they’re about a mile or two miles north of the Mukwonago River. And the question was were these wells, the pumping of these wells, was this gonna impact the river and the wetlands around it? So we developed a groundwater model for this area. And as part of that model, again, we were able to figure out the capture area or the contributing area for the Mukwonago River and these wetlands here. And that’s what’s shown on this diagram. This shaded area and all these dark lines are computer-generated flow lines going to the river and the wetlands around it.

So this is where the groundwater is coming from. Now you see this funny pattern right here. This is the contributing area for those two wells. So even though those two wells are right here, they are not pulling any water out of the wetland. They are just pulling water from this local area right here. And we can conclude that those wells really had very little impact on the overall system. Had they been located in a different place, they might have had more impact. They were actually located in a fairly good place to prevent any impact to the river there. This also shows you the importance of a groundwater divide because there was a groundwater divide here between this watershed and the Scuppernong Watershed which is up here. And you can see that this groundwater doesn’t cross that divide unless maybe the pumping can change it a little bit. But groundwater is coming to the Mukwonago just from this area, but not from up here. So it’s a real boundary there. Now let’s move to yet a different sort of wetland, and we’ll go way up to Northern Wisconsin to Bayfield County and the upland sand barrens there to show you a kind of wetland that’s precipitation dominated, which doesn’t mean it’s not connected to groundwater at all, but it’s a place where there’s groundwater– It’s recharging groundwater rather than the other way around. So here we see that the water table is actually sloping away from the wetland. Groundwater is tending to move downward. And the wetland is not getting any water from groundwater, but it’s getting water from precipitation. We see this sort of upland wetland in places like in Chequamegon-Nicolet National Forest. And a good place is what are called the sand barrens in Bayfield County, sometimes called the blueberry barrens because it’s ripe with blueberries certain times of the year. These are old sand dunes. And the water table can be a couple of 100 feet down sometimes, but there are small wetlands up here that are maintained mostly by rainfall because this is such a sandy environment. There’s very little runoff.

And that water is then, after it sits in the wetland for a while, it gradually soaks in and moves down to recharge the groundwater system below that. So these are important areas for groundwater recharge and the wetland function there is pretty important for maintaining groundwater recharge in this sandy place. Now sometimes, I mentioned things can change with time, and sometimes things, surface water and groundwater can become connected or disconnected different times of the year or different years depending on what the weather and the climate are doing. So here’s an example of a place where there’s maybe a stream that was flowing with water. And it may have been a place where it was somewhat disconnected from the water table here, but water was still coming out of the stream and moving into the water table, and that’s why you see a little mound in the water table here. But if that stream dries up in a very dry summer, it’s gone and the water table becomes completely flat. So, here’s a complete disconnection of the groundwater and surface water.

Another example of a wetland like that is something that I had the pleasure of observing when I spent some time in Zimbabwe about 10 years ago. I worked with some people there on wetlands in one of the conservancies they had in Zimbabwe. And in Zimbabwe and Africa, they call these wetlands pans. And these are the sort of watering holes that you think of the animals coming and getting a drink in the dry times and so forth. But in the dry time of year, this is really the same place. And you can see that this wetland is completely dried up in their dry season, which is November. And then it’s full of water and it’s got flowers and plants and it’s a pretty nice-looking place in February. And we were doing some research there with South Africans and some of the scientists from Zimbabwe about trying to understand where the water came from for this wetland. Was this groundwater that was rising up or was this entirely surface-water-dominated? And so we did some coring by hand because this was out in a place where we couldn’t get any motorized equipment out. So we did a lot of hand augering out there. And what we discovered was that this pan, this is a cross-section, was several meters above the regional water table and in fact never intersected the water table. So this is a wetland that’s completely, always above the water table, which doesn’t mean it doesn’t have anything to do with groundwater, because when the water soaks in, it gets down and recharges the groundwater table down here. But there’s a lot of unsaturated zone in between the two. So this was the profile of the landscape that we developed there based on these core holes that we drilled that went from this pan over to the Save River here.

And so that was really interesting work, but just another kind of wetland to see. Now we have a lot of lakes in Wisconsin. And lakes are sort of similar to wetland. Of course, they represent outcrops of the water table. And we do a lot of conceptual modeling of lakes too. Lakes can be places where they’re receiving groundwater from around their perimeter, or they’re seepage lakes, they’re losing groundwater everywhere, or they’re flow-through lakes where groundwater is flowing in one side and out the other. And they’re very analogous to wetlands because basically a wetland in a way is just a lake that’s very shallow, but has sort of the same features. We spend a lot of time trying to understand how lakes fit into groundwater flow systems for all the same reasons: understanding the lake water budget. And related to that, of course, are springs. And groundwater is sustaining springs and springs are usually located in places again where there are wetlands. Wetlands and springs often go together. In the last few years, we’ve done a lot of work at the Geological and Natural History Survey, mapping and compiling records of springs in Wisconsin. There have been over 10,000 springs identified in Wisconsin. There’s probably more than that. Those are the ones we have records for.

As far as big springs, which are over one cubic foot per second, which is a pretty darn big spring, there are fewer of those, there are a couple of 100 or more of big springs that people really would note, although they haven’t all been mapped. And we’ve just finished up a new mapping of the big springs in Wisconsin. But these are all related to where wetlands are as well. To show you how springs are important, I love this picture because this, if you know where Donald Park is out near Mount Vernon, this is a picture of people from the town, the village of Mount Vernon out around a place called Big Spring in Donald Park 100 years ago or so. And you can see there’s a brass band, there’s people in their Sunday best. Shows you that springs were a pretty important place.

And here’s the whole town having their pictures taken. That spring is still there and you can go there, and this is what it looks like now without a brass band. It’s a pretty neat place and if you go there, there’s boiling sand meaning the hydraulic gradients are making that sand churn and sort of boil down there from the hydraulic gradients coming up. So I recommend a visit to that place. And just to show you what that’s like, here’s another spring from our statewide spring inventory, some underwater photography just showing how the groundwater coming in is causing the sediment there to be roiled up. So springs are pretty neat places, but they’re always often related to wetlands, of course. Finally, let’s finish up with talking about high capacity wells and things that might affect wetlands that people do. Basically, high capacity wells are what we use for water supply. All the water in Madison is coming out of high capacity wells. Probably heard of high capacity wells being used for irrigation of crops. They’re a pretty important feature of our landscape and our society now. High capacity wells pull water out of the ground and they do two things that are just inevitable. They lower groundwater levels around the well and they reduce groundwater flow to nearby surface water features like wetlands.

And so understanding how those things are related is important for understanding how to protect wetlands. And the way that works, here’s again some conceptual models or cartoons. If we have a groundwater flow system and this here, it’s shown as a river, but it could be a wetland or a lake or whatever, we have again this recharge area up here, we have flow lines that are going down and then they’re discharging here. If we put a well here, near the stream in this case, and we pump that well, the well causes a corner depression. That’s the drawdown of the water table above the well here, making that cone. And that water’s getting pumped out. And because that water is getting pumped out, that water has to come from somewhere. And so it’s produced by, first of all, dewatering part of the aquifer here, but also diminishing the amount of water that’s hitting that stream.

Water is still coming into the stream. You can see the arrows are still going there, but there’s maybe not as many of them and there’s a little less water for the stream ’cause that water’s coming out of the well now. And here we’ve increased the pumping of that well even more. And so now we’ve actually reversed the flow and we’re pulling water out of the stream to feed the well. You don’t get something for nothing. If you’re gonna take water of the well, it always comes from somewhere and something else gets depleted. So you’ve probably heard of the Little Plover River. It’s an area of the state we’ve done a lot of research on in the last few years. It’s in the middle of our potato-growing area in Wisconsin. It’s a very important vegetable industry, potatoes and corn and so forth. But it’s also very dependent on irrigation. And so there’s been some controversy over irrigation wells. So we did a project there a couple of years ago looking at how irrigation wells in that area were affecting or interacting with the Little Plover River and the wetlands around it. Little Plover River was historically a trout stream. It’s now a state fishery area. But it’s right in the middle of a number of potato fields. It has a lot of nice looking wetlands associated with it. Here’s the Little Plover River. It’s just a couple miles south of the village of Plover and then Stevens Point. Here’s its watershed, its surface watershed. And here’s the river itself.

And all these little dots are irrigation wells, high capacity irrigation wells that are used mostly for potato growing, some for corn, and some for beans. And the question we had was how are these wells affecting the flow in the Little Plover River, because there was a perception that over time, the flow had been diminished. And there were questions about was that related to, say, climate change? Was it related to something else or could it be traced to just these wells themselves? And frankly, the records weren’t always all that clear. So here again, this is the results from a model. You have these lines. These are these groundwater water table contours going from higher to lower. And so we expect groundwater to be flowing perpendicular to those lines. So if we take all the wells away and we do a model without any wells in it and we look at the contributing area or the capture area for the river and the wetlands around it, it looks like this. This is called the no pumping simulation. And you can see how– Just take a look at the size of that. And so that means that any water, groundwater that gets into this area eventually ends up somewhere in this river.

And so there’s a balance between how much water is discharged by the river and the size of this area. And then we look at it today with the wells. And you can see it looks a lot different. It’s kind of jaggedy-looking and that’s because these wells, many of them are intercepting water that previously went to the river. And you can see overall the capture zone is smaller. And so if you overlay the two, you can see that it is significantly smaller than it used to be. And we can trace that directly to the number of wells that are pumping, are causing this to be smaller. Because it’s smaller, there’s less groundwater captured by the stream. There’s less water going into the river and so we would expect the flow to be less. And having a model like this, we can then do experiments and see which of these wells we would have to take out or move around to different places to improve or to restore flow in the river and flow to wetlands around it.

And actually, there are some groups that are using the model just for that purpose now. So to finish up today, some of the take-home messages are that wetlands and groundwater and surface water are all part of the same system. They should be thought of as one single resource, managed together. You can’t manage one without managing the others. And you can’t affect one really without affecting the others. All water comes from somewhere. And sometimes in my career. . . I know people understand this at some point, but they think you can pump water out of the ground and it has no effect on anything ’cause it’s a limitless supply. It’s not a limitless supply. Everything’s connected. So if you take water out of one place, it always affects something else. And so understanding the water balance is critical for management decisions. Wetlands are connected to local groundwater systems, and they are largely controlled by geologic and topographic settings. And pumping from high capacity wells near streams and wetlands can reduce stream flow or reduce water levels in wetlands. But these impacts, they depend on things like the amount of pumping, the distance between the wetland and the well or the stream and the well, how long the well was on and a lot of other things. So all those are parameters that we have to think about, but these are some of the main takeaways for here. I’ll stop there and answer any questions you might have. (audience applauding)