Urbanization and Estuary Eutrophication

Charles Hopkinson out taking dissolved O2 measurements.

Charles Hopkinson out taking dissolved O2 measurements.Student activity, Graph Type A, Level 4

The activities are as follows:

An estuary is a habitat formed where a freshwater river or stream meets a saltwater ocean. Many estuaries can be found along the Atlantic coast of North America. Reeds and grasses are the dominant type of plant in estuaries because they are able to tolerate and grow in the salty water. Where these reeds and grasses grow they form a special habitat called a salt marsh. Salt marshes are important because they filter polluted water and buffer the land from storms. Salt marshes are the habitat for many different kinds of plants, fish, shellfish, and birds.

Hap Garritt removing an oxygen logger from Middle Road Bridge in winter.

Hap Garritt removing an oxygen logger from Middle Road Bridge in winter.

Scientists are worried because some salt marshes are in trouble! Runoff from rain washes nutrients, usually from lawn fertilizers and agriculture, from land and carries them to estuaries. When excess nutrients, such as nitrogen or phosphorus, enter an ecosystem the natural balance is disrupted. The ecosystem becomes more productive, called eutrophication. Eutrophication can cause major problems for estuaries and other habitats.

With more nutrients in the ecosystem, the growth of plants and algae explodes. During the day, algae photosynthesize and release O2 as a byproduct. However, excess nutrients cause these same algae grow densely near the surface of the water, decreasing the light available to plants growing below the water on the soil surface. Without light, the plants die and are broken down by decomposers. Decomposers, such as bacteria, use a lot of O2 because they respire as they break down plant material. Because there is so much dead plant material for decomposers, they use up most of the O2 dissolved in the water. Eventually there is not enough O2 for aquatic animals, such as fish and shellfish, and they begin to die-off as well.

Two features can be used to identify whether eutrophication is occurring. The first feature is low levels of dissolved O2 in the water. The second feature is when there are large changes in the amount of dissolved O2 from dawn to dusk. Remember, during the day when it’s sunny, photosynthesis converts CO2, water, and light into glucose and O2. Decomposition reverses the process, using glucose and O2 and producing CO2 and water. This means that when the sun is down at night, O2 is not being added to the water from photosynthesis. However, O2 is still being used for decomposition and respiration by animals and plants at night.

The scientists focused on two locations in the Plum Island Estuary and measured dissolved O2 levels, or the amount of O2 in the water. They looked at how the levels of O2 changed throughout the day and night. They predicted that the upper part of the estuary would show the two features of eutrophication because it is located near an urban area. They also predicted the lower part of the estuary would not be affected by eutrophication because it was farther from urban areas.

A view of the Plum Island estuary

A view of the Plum Island estuary

Featured scientists: Charles Hopkinson from University of Georgia and Hap Garritt from the Marine Biological Laboratory Ecosystems Center

Flesch–Kincaid Reading Grade Level = 9.6

The mystery of Plum Island Marsh

Scientist, Harriet Booth, counting and collecting mudsnails from a mudflat at low tide.

Scientist, Harriet Booth, counting and collecting mudsnails from a mudflat at low tide.

The activities are as follows:

Salt marshes are among the most productive coastal ecosystems. They support a diversity of plants and animals. Algae and marsh plants feed many invertebrates, like snails and crabs, which are then eaten by fish and birds. This flow of energy through the food web is important for the functioning of the marsh. Today, we are adding large amounts of fertilizers to our lawns and agricultural areas. When it rains these nutrients runoff into marshes. Marsh plants and algae can then use theses extra nutrients to grow and reproduce faster. Changes in any links in the food chain can have cascading effects throughout the ecosystem.

To understand how these nutrients will affect the marsh food web, scientists working at Plum Island Marsh experimentally fertilized several salt marsh creeks for many years. In 2009, they noticed that fish populations were declining in the fertilized creeks. Because fertilizer does not have any direct effect on fish, they wondered what could fertilizer be changing in the system that would affect fish? That same year they also noticed the mudflats in the fertilized creeks were covered in mudsnails, far more so than in previous years. These mudsnails eat the same algae that fish eat, and they compete for space on the mudflats with the small invertebrates that the fish also eat. The scientists thought that the large populations of mudsnails were causing the mysterious disappearance of fish in fertilized creeks by decreasing the number of algae and invertebrates in fertilized creeks.

View of a Plum Island salt marsh.

View of a Plum Island salt marsh.

A few years later, Harriet began working as one of the scientists at Plum Island Marsh. She was worried mudsnails were getting a bad reputation. There was no evidence to show they were causing the decline in fish populations. She decided to collect some data. If mudsnails were competing with the invertebrates that fish eat, she expected to find high densities of mudsnails and low densities of invertebrates in the fertilized creeks. In the summer of 2012, Harriet counted and collected mudsnails using a quadrat (shown in the photo), and took cores down into the mud to measure the other invertebrates in the mudflats of the creeks. She randomly sampled 20 locations along a 200-meter stretch of creek at low tide. The data she collected is found below and can help determine whether mudsnails are responsible for the disappearance of fish in fertilized creeks.

Mudsnails on a mudflat, and the quadrat used to study their population size.

Mudsnails on a mudflat, and the quadrat used to study their population size.

Featured scientist: Harriet Booth from Northeastern University

Flesch–Kincaid Reading Grade Level = 9.9

Click here for a great blog post by Harriet detailing her time spent in the salt marsh: Harriet Booth: Unraveling the mysteries of Plum Island’s marshes

Growing energy: comparing biofuel crop biomass

The activities are as follows:GLBRC1

Most of us use fossil fuels every day. Fossil fuels power our cars, heat and cool our homes, and are used to produce most of the things we buy. These energy sources are called “fossil” fuels because they are made from plants that grew hundreds of millions of years ago! After these plants died, their tissues were slowly converted into coal, oil, and natural gas. An important fact about fossil fuels is that they are limited and non-renewable. It takes a long time for dead plants to be converted into fossil fuels. Once we run out of the supply we have on Earth today, we are out! We need to think of new ways to power our world, now that we use more energy than ever.

Biofuels are a potential replacement for fossil fuels. Biofuels, like fossil fuels, are made from the tissues of plants. The big difference is they are made from plants that are alive and growing today. Biofuels are renewable, meaning we can produce them as quickly as we use them up. At the Great Lakes Bioenergy Research Center sites in Wisconsin and Michigan, scientists and engineers are attempting to figure out which plants make the best biofuels. Plants that grow bigger and faster make more tissues that can be used to produce more biofuel.


Gregg is a scientist who wants to find out how much plant tissue, called biomass, can be harvested from different crops like corn, grasses, weeds, and trees. Gregg is interested in maximizing how much biomass we can produce while also not harming the environment. Each plant species comes with a tradeoff – some may be good at growing big, but need lots of inputs like fertilizer and pesticide. Corn is an annual, meaning it only lives for one year. Corn is one of the best crops for producing a lot of biomass. However, farmers must add a lot of chemical fertilizers and pesticides to their fields to plant corn every year. These chemicals harm the environment and cost farmers money. Other plants harvested for biofuels, like switchgrass, prairie species, poplar trees, and Miscanthus grass are perennials. Perennials grow back year after year without replanting. Perennials require much less chemical fertilizers and pesticides to grow. If perennials can produce high levels of biomass with low levels of soil nutrients, perhaps a perennial crop could replace corn as the best biofuel crop.

Gregg out in the GLBRC

Gregg out in the WI experimental farm.

To test this hypothesis, scientists worked together to design a very large experiment. Gregg and his team grew multiple plots of six different biofuel crops on experimental farms in Wisconsin and Michigan. The soils at the Wisconsin site are more fertile and have more nutrients than the soils at the Michigan site. At each farm, they grew plots of corn to be compared to the growth of plants in five types of perennial plots. The types of perennial plots they planted were: switchgrass, Miscanthus grass, poplar saplings (trees), a mix of prairie species, and weedy fields. Every fall the scientists harvested, dried, and then weighed the biomass from each plot. They continued taking measurements for five years and then calculated the average biomass production in a year for each plot type at each site.

Featured scientist: Dr. Gregg Sanford from University of Wisconsin-Madison

Flesch–Kincaid Reading Grade Level = 8.5

This Data Nugget was adapted from a data analysis activity developed by the Great Lakes Bioenergy Research Center (GLBRC). For a more detailed version of this lesson plan, including a supplemental reading, biomass harvest video and extension activities, click here.

This lesson can be paired with The Science of Farming research story to learn a bit more about the process of designing large-scale agricultural experiments that need to account for lots of variables.

For a classroom reading, click here to download an article written for the public on these research findings. Click here for the scientific publication. For more bioenergy lesson plans by the GLBRC, check out their education page.

Aerial view of GLBRC KBS LTER cellulosic biofuels research experiment; Photo Credit: KBS LTER, Michigan State University

Aerial view of GLBRC KBS LTER cellulosic biofuels research experiment; Photo Credit: KBS LTER, Michigan State University

 For more photos of the GLBRC site in Michigan, click here.


Marvelous mud


You can tell that the mud in this picture is high in organic matter because it is dark brown and mucky (in real life you’d be able to smell it, too!)

The activities are as follows:

The goopy, mucky, (sometimes stinky!) mud at the bottom of a wetland or lake is a very important part of the ecosystem. Mud is basically wet soil, but because it has different properties than soil because it is wet most of the time. Mud is usually dark brown because it contains partially decomposed plants, called organic matter. Dead organic matter tends to build up in wetlands. Organic matter decomposes more slowly under water than on land. This is because underwater microbes do not have all the oxygen they need to break it down quickly.

A successful core! You can see that the tube has mud, as well as some of the water from the wetland that was on top of the mud.

A successful core! You can see that the tube has mud, as well as some of the water from the wetland that was on top of the mud.

Under the right conditions, mud can act like fertilizer for a wetland. Nutrients, such as phosphorus, tend to build up in mud. This makes mud an important source of the phosphorus that algae and other plants need to grow. As a graduate student at Michigan State University, scientist Lauren was interested in what helped phosphorus stick to mud. She also wanted to know why phosphorus builds up more in some wetlands than others.

Although most mud is high in organic matter and high in nutrients, all mud is not created equal! The amounts of organic matter and nutrients are different from one ecosystem to the next. How quickly these materials enter or leave the mud may also change across ecosystems. Even within the same ecosystem mud can be very different from place to place. The molecules in organic matter could be a major source of phosphorus in mud. This would mean that wetlands with more organic matter would have more phosphorus.

Scientist Lauren measured organic matter and phosphorus in mud from 16 ecosystems (four lakes, five ponds, and seven wetlands). She wanted to determine if there was a relationship between the amount of organic matter and the amount of phosphorus in mud.

Featured scientist: Lauren Kinsman-Costello from Kent State University

Flesch–Kincaid Reading Grade Level = 8.7

More photos associated with this research can be found here. There is one scientific paper associated with the data in this Data Nugget. The citation and PDF of the paper is below:

Kinsman-Costello LE, J O’Brien, SK Hamilton (2014) Re-flooding a Historically Drained Wetland Leads to Rapid Sediment Phosphorus Release. Ecosystems 17:641-656

Fertilizing biofuels may cause release of greenhouse gasses

An aerial view of the experiment at MSU where biofuels are grown

An aerial view of the experiment at MSU where biofuels are grown. Photo credit: K. Stepnitz, MSU

The activities are as follows:

Greenhouse gases in our atmosphere, like carbon dioxide (CO2) and nitrous oxide (N2O), trap heat from the sun and warm the earth. We need some greenhouse gases to keep the planet warm enough for life. But today, the majority (97%) of scientists agree that the levels of greenhouse gases are getting dangerously high and are causing changes in our climate that may be hard for us to adjust to.

Scientist Leilei collecting samples of gasses released by the growing of biofuels

Scientist Leilei collecting samples of gasses released by the growing of biofuels. Photo credit: K. Stepnitz, MSU

Greenhouse gases are released when we burn fuels to heat and cool our homes or power our cars. Most of the energy we use today comes from fossil fuels. These energy sources are called “fossil” fuels because they are made from plants that grew hundreds of millions of years ago! After these plants died, their tissues were slowly converted into coal, oil, and natural gas. An important fact about fossil fuels is that when we use them, they release CO2 that was stored millions of years ago into our atmosphere. The release of this stored carbon is adding more and more greenhouse gases to our atmosphere. In order to reduce the effects of climate change, we need to change the way we use energy and think of new ways to power our world.

One potential solution could be to grow our fuel instead of drilling for it. Biofuels are a potential substitute for fossil fuels. Biofuels, like fossil fuels, are made from the tissues of plants. The big difference is that they are made from plants that are alive and growing today. Unlike fossil fuels that emit CO2, biofuel crops first remove CO2 from the atmosphere as the plants grow and photosynthesize. When biofuels are burned for fuel, the CO2 is emitted back into the atmosphere, balancing the total amount that was removed and released.

Scientists are interested in figuring out if biofuels make a good replacement for fossil fuels. It is still not clear if the plants that are used to produce biofuels are able to absorb enough CO2 to offset all of the greenhouse gases that are emitted when biofuels are produced. Additional greenhouse gases are emitted when producing biofuels because it takes energy to plant, water, and harvest the crops, as well as to convert them into fuel. In order to maximize plant growth, many biofuel crops are fertilized by adding nitrogen (N) fertilizer to the soil. However, if there is too much nitrogen in the soil for the crops to take up, it may instead be released into the atmosphere as the gas nitrous oxide (N2O). N2O is a greenhouse gas with a global warming potential nearly 300 times higher than CO2! Global warming potential is a relative measure of how much heat a greenhouse gas traps in the atmosphere.

Leilei is a scientist who researches whether biofuels make a good alternative to fossil fuels. He wondered whether there were steps that farmers could take to reduce the amount of N2O released when growing biofuel crops. Leilei designed an experiment to determine how much N2O is emitted when different amounts of nitrogen fertilizer are added to the soil. In other words, he wanted to know whether the amount of N2O that is emitted into the atmosphere depends on how much fertilizer is added to the field. To test this idea, he looked at fields of switchgrass, a perennial grass native to North America, that is one of the most promising biofuel crops. These fields of switchgrass were first planted in 2008 as a part of a very large long-term study at the Kellogg Biological Station in southwest Michigan. The researchers set up eight fertilization treatments (0, 28, 56, 84, 112, 140, 168, and 196 kg N ha−1) in four replicate fields of switchgrass, for a total of 32 research plots. Leilei measured how much N2O was released by the soil in the 32 research plots for many years. Here we have two years of Leilei’s data.

Featured scientist: Leilei Ruan from Michigan State University

Flesch–Kincaid Reading Grade Level = 10.1

More information on LTER climate change research can be found hereInformation on the effects of climate change in Michigan can be found here.

Data associated with this Data Nugget can be found on the MSU LTER website data tables under GLBRC Biofuel Cropping System Experiment. Bioenergy research classroom materials can be found here. More images can be found on the LTER website.


Fair traders or freeloaders?

Measuring chlorophyll content in the greenhouse

Measuring chlorophyll content in the greenhouse

The activities are as follows:

When two species do better when they cooperate than they would on their own, the relationship is called a mutualism. One example of a mutualism is the relationship between a type of bacteria, rhizobia, and legume plants. Legumes include plants like peas, beans, soybeans, and clover. Rhizobia live in bumps on the legume roots, where they trade their nitrogen for sugar from the plants. Rhizobia fix nitrogen from the air into a form that plants can use. This means that legumes that have rhizobia living in their roots can get more nitrogen than those that don’t.

Under some conditions, this mutualism can break down. For example, if one of the traded resources is very abundant in the environment. When the plant doesn’t need the nitrogen traded by rhizobia, it doesn’t trade as many sugars to the rhizobia. This could cause the rhizobia to evolve to be less cooperative as well. Less-cooperative rhizobia may be found where the soil already has lots of nitrogen. These less-cooperative bacteria are freeloaders: they fix less nitrogen, but still get sugars from the plant and other benefits of living in nodules on their roots.

Photo by Tomomi Suwa, 2013

Rhizobia nodules on plant roots. In exchange for carbon and protection in the nodules from plants, rhizobia provide fixed nitrogen for plants.

One very important legume crop species is the soybean. Soybeans are used to produce vegetable oil, tofu, soymilk, and many other food products. Soybeans trade with rhizobia for nitrogen, but often farmers add more nitrogen into the field as fertilizer. Since farms use a lot of nitrogen fertilizer, researchers at KBS were interested in how different types of farming affected the plant-rhizobia mutualism.

They grew soybean plants in a greenhouse and added rhizobia from three different farms: a high N farm, low N farm, and organic farm that used no N fertilizer. After four weeks, the researchers measured chlorophyll content of the soybean plants. Healthy plants that have lots of nitrogen will have high chlorophyll content, and plants with not enough nitrogen will have low chlorophyll content. Because high nitrogen could lead to the evolution of less-cooperative rhizobia, they expected that rhizobia from organic plots would be most cooperative. They predicted rhizobia from high N plots would be the least cooperative, and rhizobia from low N plots would fall somewhere in the middle. More-cooperative rhizobia provide more nitrogen, so the researchers expected plants grown with cooperative rhizobia to have higher chlorophyll content than plants receiving less-cooperative rhizobia.

Featured scientist: REU Jennifer Schmidt from the Kellogg Biological Station

Flesch–Kincaid Reading Grade Level = 10.1

For more information on the evolution of cheating rhizobia, check out these popular science articles:

If you are interested in performing your own classroom experiment using the plant-rhizobium mutualism, check out this paper published in the American Biology Teacher describing methods and a proposed experimental design: Suwa and Williamson 2014