6.21.26

Superior watersheds: investigating stream health

Will sampling macroinvertebrates from a stream using a D net.

Fresh water is one of our most important natural resources and an essential daily need for all people. Ten percent of the world’s freshwater is in Lake Superior. It is the largest lake in the world by surface area. It is also one of the cleanest, clearest, and coldest lakes in the United States. 

Watersheds are the network of rivers and streams, called tributaries, that flow into a single point and empty into a larger body of water. The water at the end of a watershed therefore reflects all the changes that happened across a large area. Thousands of tributaries flow through forests, wetlands, and farmland before reaching Lake Superior. These tributaries carry soil, nutrients, and any pollution from the land into the lake.

For a long time, people living near Lake Superior assumed that the tributaries had good water quality, but they didn’t have data to support this. In 2002, some residents living along the lake’s southern shore in Wisconsin came together to monitor the health of local tributaries themselves. They were already hearing how climate change, pollution, and land use were affecting water systems around the world. They formed an organization, now called Superior Rivers Watershed Association (SRWA) to collect long-term data so they could track changes in local tributaries.

SRWA volunteer sorting through macroinvertebrates from a stream sample.

Today, over 20 years later, SRWA has an established monitoring program. Members train volunteers to visit streams and rivers to collect data. Through these volunteers, SRWA has data on over 50 tributaries in the Lake Superior watershed. They collect data on both the water chemistry of the tributaries, as well as the life they find there. This helps them understand how water conditions affect organisms. 

Every spring and fall, volunteers visit their sites and sample macroinvertebrates, or small organisms that spend most or all their lives living on the stream bottoms. Many are larvae for insects you might know, such as dragonflies. After collecting samples, the volunteers identify each type of macroinvertebrate.

Each species has a different tolerance for stress, such as pollution, changes in temperature, low oxygen, or flooding. So, along with their biological data SRWA also collects data such as temperature, the amount of oxygen available in the water, and turbidity, or the amount of sediment in the water. Some species are indicators of good water quality because they need very clear, cold water, with a lot of oxygen, while others can survive in dirtier or harsher conditions. By seeing which macroinvertebrates live in each stream, scientists can learn about the health of the water.

A macro invertebrate preserved for identification in the lab.

Two scientists, Will and Emma, are now analyzing over 20 years of volunteer data to identify trends and patterns. They want to see whether the water quality variables of temperature, dissolved oxygen, and turbidity affect the types of macroinvertebrates that can live in the tributaries. If there are a lot of sensitive indicator species in the sample, that is a good sign because it means the water quality is high. If they only find tolerant species, the water quality is likely poor, because indicator species were unable to survive in the environmental conditions at that site.

To do so, they use a tool called the Hilsenhoff Biotic Index. This index looks at which macroinvertebrates are present and how tolerant they are to pollution. HBI uses the living organisms that live at a site to provide an assessment of stream health over time, unlike chemical water tests which provide a snapshot of conditions at the time of testing. The index assigns a number from 1 to 10 based on the number and type of species in the sample. Lower numbers mean excellent water quality, and higher numbers mean poor water quality. 

Featured Scientists: Emma Holtan and Will Kendall with community volunteers from Superior Rivers Watershed Association. Written with: Andrea Pokrzywinski from Ashland High School.

Flesch–Kincaid Reading Grade Level = 10.8

Additional Teacher Resources:

2.24.21

Stop that oxidation! What fruit flies teach us about human health

Laboratory fruit flies in their natural habitat: a plastic vial. Photo credit: Conni Wetzker

The activities are as follows:

Have you ever eaten an apple and noticed that, after a while, the core turns brown? That’s because of oxidation – a chemical reaction between the oxygen in the air and the inside of the apple. The same thing is happening inside our own bodies all the time.

Each of our cells is home to mitochondria, tiny factories whose job is to turn the food we eat into the energy we need to live. But mitochondria also make molecules called reactive oxygen species, or ROS. As the name suggests, these molecules contain oxygen and tend to react with the things around them. Like the oxygen in the air reacting with the apple core and turning it brown, ROS react with different parts of the cell, causing oxidative damage. Everything in the cell, including our DNA, can be damaged by ROS molecules. Too much damage contributes to diseases including cancer, heart disease, diabetes, and Parkinson’s.

Bodies can prevent oxidative damage in two ways. First, they can use antioxidants. Antioxidants work by reacting with ROS to stop them from harming cells. Some antioxidants come from the food we eat, while others are made inside the body. If a body doesn’t have enough antioxidants, it can get sick. One example is a genetic mutation called DJ-1. It stops the body from producing antioxidant molecules. Many people with Parkinson’s disease, a neurological illness, have this DJ-1 mutation.

Some living things have evolved a second way to stop oxidative damage: their mitochondria actually make fewer ROS! These species have a special protein called alternative oxidase, or AOX. It works by shortening the pathway that mitochondria use to turn food into energy. A shorter pathway means fewer ROS are made. Scientists have been able to take the AOX gene and move it into other species.

Biz, a scientist studying oxidative damage, wanted to study the effects of the DJ-1 mutation and the AOX gene. To do their research, Biz uses fruit flies. Fruit flies are useful because they are easy to work with and scientists can control the types of mutations and genes they have in the lab. Some of these mutations are the same as those found in humans, so scientists can use them to study human disease. In one study, scientists were able to take the AOX gene and put it into the fruit fly. Fruit flies can also have the DJ-1 mutation that stops antioxidants from being made. Biz used these genetic tools to work with flies that have less oxidative damage (AOX mutants), more oxidative damage (DJ-1 mutants), or normal levels (controls).

Biz was interested in how AOX and DJ-1 affect reproductive cells – sperm and eggs. Oxidative damage is even more dangerous for reproductive cells than for other cells. Whereas most cells can just self-destruct or stop replicating when they build up too much damage, sperm and eggs have to stay healthy up until the moment of fertilization. This wait can last a long time. In many species, females store the male’s sperm inside their own bodies for days, months, or even years after mating! In addition to making their own ROS and antioxidants, sperm and egg cells stored inside the female can be damaged or protected by ROS and antioxidants made by the female’s reproductive tract. Either way, damage to reproductive cells is very important because it can be passed on to future generations or can cause the offspring to die.

Biz wanted to test whether the level of oxidative damage in eggs and stored sperm would influence how many offspring a female had. If cells with oxidative damage do not produce healthy offspring, then fruit flies with less damage should have more offspring.  Biz also expected that fruit flies with more damage should have fewer offspring. To test these ideas, Biz mated normal male fruit flies to three groups of females: females with the AOX gene, females with the DJ-1 mutation, and normal (“control”) females. Aside from having the AOX or DJ-1 gene, the females in all treatments were genetically the same. The males used in the experiment were also genetically identical. After the males and females mated, Biz counted the number of surviving offspring from each group.

Featured scientist: Biz Turnell from Cornell University and Technische Universität Dresden

Flesch–Kincaid Reading Grade Level = 9.0