Helping Ecosystems Recover

In 1977, a survey found only 33 pairs of bald eagles nesting in Virginia. In 2016, a larger search, which also used ground checks and volunteer reports, counted 1,070 pairs.

Something had gone wrong for eagles, and then people changed what they did. Can people help a damaged ecosystem come back?

Explore: bring the eagles back

The simulation shows a Bay shoreline, with a bar of eagle nests for each decade from the 1950s to the 2020s. You choose the year a harmful pesticide is banned, or never ban it. You set how much shoreline forest is protected for nests, and you can switch on a new pollution problem.

Start here: under “Pesticide banned in”, choose 1972 and watch the bars.

Pesticide banned in

1962 1972 1982 1992 Never

Protected shoreline forest for nests

Low Medium High

A new pollution problem

Pollution: off

Pin this run to compare Reset

• Top strip: pesticide in use
• Top strip: pesticide banned
• Lower strip: pollution problem on

In this sketch, the pesticide is never banned. Choose a ban year to compare.

Assumptions made up for this sketch: The pesticide is in use from 1950 (invented). Bar heights are relative units, not nest counts, and the starting height in the 1950s is invented. There is one cause of egg failure: while the pesticide is used, far fewer young are raised. Young eagles reach nesting age after a delay of 5 years. Food is the same every year, and no eagles arrive from other states. Forest only sets how many young find a safe nest place (the lesson does not say how much it helps). The pollution starts in 2000 and halves the young raised. All rates are invented. Each bar is a decade average.

Rule to keep: removing the harmful pesticide and protecting nesting places let eagles recover over decades, because young eagles take several years to grow old enough to breed.

Try this.

1. Predict how fast the nests come back if the pesticide is banned in 1972. Test it. Do the nests return right away?
2. Keep the same ban year. Predict what more protected forest will do. Compare low and high.
3. With a 1972 ban, after the nests recover, predict what a new pollution problem will do. Switch it on.

Explain: living and nonliving changes

A biotic factor is a living part of an ecosystem, such as eelgrass, oysters or eagles. An abiotic factor is a nonliving part, such as water, air, sunlight or temperature. A change in either one can change the whole ecosystem.

Natural changes count too. By 1933, a disease and a hurricane had wiped out the eelgrass in Virginia’s coastal bays. The disease was a biotic change. The storm was an abiotic one.

You met habitat loss and invasive species in People Change Habitats. Here are six more ways people change ecosystems.

Area	What people do	One effect
Climate	Burn coal, oil and gas	Carbon dioxide builds up in the air and warms Earth
Water supply	Pump water from streams and wells	Streams can carry less water
Air quality	Release exhaust from cars and factories	The gas ozone near the ground can slow photosynthesis in sensitive trees, such as black cherry and tulip poplar
Energy production	Run power plants	Some release carbon dioxide and gases that pollute the air; some return warmer water to rivers
Ocean acidification	Add carbon dioxide to the air	The ocean absorbs it and becomes more acidic
Waste management	Throw away, reuse or treat waste	Wastewater with extra nutrients can feed algae; reusing things saves energy

A fossil fuel is a fuel formed from the remains of ancient living things, such as coal, oil or natural gas. Deforestation is clearing forests for farms, roads or towns. Burning fossil fuels and clearing forests both add carbon dioxide to the air.

Air moves around the whole planet, so a smokestack in one place adds to climate change everywhere. Factories can also pollute air and water far away.

Ocean acidification is ocean water becoming more acidic as it absorbs carbon dioxide from the air. Seawater is still not an acid like vinegar. But the change leaves less of the material oysters and corals use to build their shells.

These changes touch the cycles of matter. Burning fossil fuels moves carbon from underground into the air (The Carbon and Water Cycles). Extra fertilizer adds nitrogen to rivers. Changes can help too: new meadows and forests take in carbon dioxide for photosynthesis.

Explain: why Virginia’s eagles came back

A pesticide is a chemical used to kill pests, such as insects. DDT was once a common one in the United States.

DDT breaks down into a related chemical called DDE. DDE can make bird eggshells thin. Very thin bald eagle eggshells often broke while the parents sat on them. Other eggs failed to hatch. So few young eagles were raised.

DDT was not the only problem. People also destroyed eagle habitat, and some shot eagles illegally.

Then people acted:

• In 1972, the United States banned most uses of DDT.
• Laws protected eagles and their nests.
• People protected the places where eagles nest.

Conservation is protecting living things and their habitats so they last into the future. Saving eagles was conservation.

Recovery took decades, because young eagles take several years to grow old enough to breed. The count also did not rise every single year.

Recovery is a bit like savings that earn interest: new pairs raise young that become pairs too. The comparison breaks because eagles also die and face new dangers.

Explain: helping damaged places heal

Restoration is helping a damaged ecosystem recover. Virginia scientists spread eelgrass seeds by hand in the coastal bays. The new plants made seeds that spread past the planted areas. A 2020 study reported 3,612 hectares of eelgrass.

Other Virginia projects build oyster reefs in rivers such as the Lafayette, keep strips of trees along streams and upgrade wastewater plants (Big Changes).

A sustainable practice is a way of using resources that meets people’s needs now and leaves enough for the future. Examples are using only the fertilizer crops need and reusing things.

Recovery has limits:

• It is often partial. A review of 400 studies found that damaged places often improve. Full recovery was less common while scientists watched.
• It can look different. The restored eelgrass held some small animals missing from nearby natural meadows.
• Protecting comes first. A 2017 study found that restoring cannot always replace protecting a healthy ecosystem.
• It depends on the damage. Recovery usually goes better when the cause is removed and the damage was not too severe or too long.

Elaborate: read 40 years of eagle counts

Breeding year	Eagle pairs (occupied nesting territories)	Chicks counted in spring
1977	33	not listed
2003	435	454
2004	428	612
2005	453	657
2007	560	737
2008	584	864
2010	684	883
2011	726	938
2016	1,070	not listed

Counts are from the Virginia bald eagle survey, flown each year from late winter into spring over the Bay’s tidal rivers and the lower Eastern Shore. Sources: a 2002 survey history by Watts and Byrd (1977), yearly reports of the Center for Conservation Biology at William and Mary and Virginia Commonwealth University (2003 to 2011), and the Center’s 2016 survey release. Each pair is two adults using and keeping up a nest. The survey does not count every eagle. The area searched grew over the years, and by 2016 the count also used ground checks and volunteer reports from inland counties.

1. How many more pairs were counted in 2011 than in 1977?
2. Find a year when the number of pairs went down. What happened the next year?
3. From 2003 to 2004, pairs fell. Did chicks rise or fall?

Design problem

Does a strip of plants along a stream keep soil from washing into the water? Plan a fair test with trays of soil.

One way to do it

• Question: Does a strip of grass at the low end of a soil tray reduce the soil that washes off?
• Independent variable: a strip of grass sod at the low end, or bare soil.
• Dependent variable: the mass of soil in the runoff, in grams. Weigh a dry coffee filter first. Pour the runoff through it, let the filter dry, weigh it again and subtract the filter’s mass.
• Control: trays of bare soil with no grass strip.
• Constants: the same soil, tray size, slope, amount of water (500 mL) and pouring speed.
• Repeated trials: three trays of each kind. Find the mean for each.
• Safety: wear goggles and gloves, wipe up spills so no one slips, and wash your hands.
• Meaning: less soil from grass trays supports the idea that the strip holds soil back. Trays are a model, not a stream.

Evaluate: check your thinking

Virginia’s eagles became rare because DDE from DDT thinned their eggshells and people harmed their habitat. After the DDT ban and laws protecting eagles and nests, pairs rose over decades. People can help damaged ecosystems come back, but recovery is often slow, may be partial, and can leave a place different from before.

Science practices you used: testing a model and naming its limits, reading a data table and finding a difference, planning a fair test, and making a claim from evidence.