Watershed is just a body of land that all drains into a central body of water. That body of water could be a river, a lake, or a stream. And watersheds are going to be determined by slope.
And so what do I mean by that? You can think of a watershed as almost like a giant funnel of land that's all going to drain downward due to the force of gravity pulling runoff towards the central body of water. So if we take a look at this diagram, if water were to fall just on the right side of this ridge, it's going to trickle down and due to gravity run off into this river.
Now if it falls to the left of this dotted line here, it's going to follow the slope and go into a different watershed. And so watershed boundaries are basically determined by slope. You can think of it as if a drop of water lands on this piece of land, which body of water will it run off into?
There's some other factors that are important to consider when we think about watersheds, and those would be soil composition, vegetation, and slope. So the more vegetation that a watershed has, basically the more infiltration we're going to have. And so rainwater will be slowed.
It will be taken into the ground. The roots will absorb some, but the plants will also make the ground a little bit more permeable, make it easier for that groundwater to infiltrate rather than to run off. Then we have slope.
So the greater the slope, the faster the velocity of the runoff. And so it has a little bit more inertia or a little bit more steam. You could think it's got a head of steam to pick up, you know, soil or debris or any sort of... you know sediments that are on the ground and carry them into this body of water. Then finally we have soil permeability and so how permeable the soil is impacts whether or not water is running off or whether or not it is infiltrating and recharging groundwater.
So that would affect the rate at which water runs off of the watershed and into the central body of water and it may also impact the sorts of pollutants that it's gathering or the sediments that it's washing in. And the final thing we have to consider here is that human activities in a watershed directly determine the quality of water in that watershed. And that's because actions like mining or agriculture or clear cutting can produce pollutants or can loosen soil.
And that means that the runoff entering the body of water will carry those pollutants or carry those sediments into the body of water. Next, we'll take a look at one of the largest watersheds in America. And that is the Chesapeake Bay Watershed. So this is a six-state region where all of the bodies of water the rivers, the streams, all eventually collect and empty into the Chesapeake Bay. Why does this matter?
Why do we care about the Chesapeake Bay watershed? Well, it's a great way to study the ecosystem services and the value that these habitats can provide. And so a reminder that an estuary such as the Chesapeake Bay is a mixture of salt and fresh water.
So a lot of nutrients and a lot of sediments from all of these tributaries are collecting and emptying into estuary habitats here in the Bay. such as a salt marsh. And so here's a picture of a salt marsh.
You can see the grasses and kind of the low meandering water line. It's a really productive habitat. And because it's so productive, it offers a lot of ecosystem services. Remember, ecosystem services are things that have monetary benefit to humans.
And so tourism is one. People are going to come and stay in hotels and pay to go on tours here and just spend their time hiking and enjoying the natural beauty. There's a lot of water filtration too, though. So we don't have to filter as many pollutants out of our water. because estuary habitats and wetlands are really effective at trapping pollutants in their roots and recharging groundwater with more clean water than if they weren't there.
We also have habitats. So there are all sorts of animals here, such as crabs and other shellfish that can be harvested from these habitats, and they are the breeding ground for them. So without them, we wouldn't enjoy nearly as much seafood. A lot of people would not have jobs, and restaurants would lose revenue.
And then finally, we have stormwater protection as well. And so... it can basically act as kind of an overflow or a surge protection in the event of a large storm. Then we have a nice picture here of some kayakers.
I'm a big fan of canoeing and kayaking, so you can remember that, you know, people like to canoe and like to kayak in these bodies of water, and so that's a great way for tourism revenue to flow into an area. Now we'll take a look at some of the human impacts on the Chesapeake Bay ecosystem. So the first one is nutrient pollution.
Now nutrient pollution refers to excess nitrogen and phosphorus entering a body of water. leading to something called eutrophication. So eutrophication is when we have an algae bloom due to all of these excess nutrients entering the body of water.
Remember that nitrogen and phosphorus are often limiting nutrients, and so when we add an excess of them, it leads to this explosion of algae growth. We can see here in the picture we have this algae blooming because of all of these nutrient inputs. The problem is that this will block the sun.
so that plants underneath the surface are not getting the sunlight they need to photosynthesize, they will die and then bacteria in the water will start to break them down. Now because that's an aerobic process, it uses up oxygen, those bacteria will take up a lot of the oxygen that other organisms in the water need to survive. That leads to those organisms dying.
Then we basically have a positive feedback loop where more and more oxygen is consumed, so more and more organisms die and we call this again a positive feedback loop. It can lead to something called Hout. hypoxia, which is really low oxygen levels, and they can get so low that it's effectively a dead zone, meaning that we really don't have much life able to be supported by this body of water anymore.
So what are the sources of these nutrient inputs into bodies of water? Well, one would be the discharge of water from sewage treatment plants. So we can see here in a picture that all of our wastewater, so water that we flush down the toilet, is going to end up at this water treatment plant. Now there are... several steps in these water treatment plants designed to remove all the nutrients from our wastewater, but it's impossible to always get that down to zero.
And so there's going to be some inputs of nutrients, especially if these plants overflow. Now that's not ideal, but sometimes in really heavy rain situations, these facilities do flood and they do release raw sewage directly into a body of water. And so then you have, of course, really, really elevated nutrient levels entering the body of water. Agriculture is going to be another source here. So we can see that the runoff from CAFOs, so all of the manure lagoons that contain the waste of animals, those are going to of course have a lot of nutrients in them, both nitrogen and phosphorus.
And then we can also just get the synthetic nitrate fertilizers running off of agricultural fields. And so between wastewater treatment and agriculture, those are going to be two of the main drivers of nutrients entering bodies of water. There are some other pollutants we should consider and those would be endocrine disruptors. So remember from our previous video, the endocrine disruptors can be medications that just pass through the bodies of people and go to the wastewater treatment plant and aren't quite fully removed.
We could also have sediment pollution and so you know things such as clear cutting or urbanization or farming those are all going to lead to sediments being more loose and being more easily carried into the river. Here's a picture that can demonstrate how dramatic this effect can be so you can see from an aerial image just how different the water's color is and so that's going to decrease rates of photosynthesis. It's going to make the water warmer because it has a lower albedo and it's going to absorb more sunlight. But what we can also see here is that it's going to potentially cover up the rocky stream bottom that many organisms need in order to survive. So this is a great example of a stream bottom here that is not impacted by sediment pollution.
You can see how there's all of these little crevices underneath these rocks where tiny crustaceans or other macroinvertebrates will live. But when we get a lot of sediment pollution, those habitats can basically be covered over by all of these sediments coming in. Now we'll take a look at some solutions to these pollutants entering bodies of water.
And so if we take a look at C and at A in this diagram, these are two methods that could be used to reduce nutrient inputs from agriculture. So cover crops are a great strategy that you hopefully remember from our sustainable farming unit or our sustainable farming topic back in Unit 5. But a cover crop is going to be basically using some plant. in between the main crops that you're harvesting just to kind of hold the soil in place, anchor it, and keep those sediments and the fertilizer in your field from running off into bodies of water.
So you can see if you're continually planting a cover crop each season, it's just going to do a phenomenal job of preventing runoff from entering these bodies of water. It traps the runoff, it lets it infiltrate back into the soil, it uses up some of those excess nitrates, and so a really effective solution. You can also try to adopt better animal manure.
management practices. So this could involve a manure lagoon that's lined better, that has higher banks or berms to kind of contain that manure. Could be a system that even drains it more frequently and turns it into fertilizer pellets. And then if we look at B, another really good generalized strategy is riparian buffers. Riparian habitats or riparian areas refer to the areas alongside a body of water, such as a river.
And so when you plant vegetation in riparian... habitats, what you're doing is adding in basically a giant sponge or a giant filter so that the runoff entering that body of water has gone through all of this vegetation first. The roots are going to absorb a lot of the water. Depending on what kind of plants you use, the roots may be really effective at even trapping pollutants in their root structures and then metabolizing them or just preventing them from making it into that body of water.
And so riparian buffers are a really valuable strategy for kind of reducing these pollutants entering bodies of water. If we look at letter D and at letter F, these are both going to target human sewage. And so we can have septic tank upgrades. A septic tank is where you just have a tank in your backyard that collects your waste. And depending on how we optimize the drain field to more slowly, you know, drain the sewage out, it can just allow that to be filtered more naturally by the ground and prevent it from overflowing and contaminating nearby surface waters.
And then we can also have biological waste removal. So that's where there are microbes. that are going to be eating a lot of the waste and trying to utilize a lot of those nutrients to prevent those from being released into the river. And so just a ton of different options for trying to reduce nutrient and sediment inputs into bodies of water.