Survival in an Estuary | Teacher Guide

Life Science Module—Activity 1

Activity Summary

In this activity, students investigate the range of

conditions that selected animal and plant species need to

survive in an estuary. They examine data for abiotic

factors that affect life in estuaries—salinity, dissolved

oxygen, temperature, and pH. Students use archived da-

ta (trend analysis graphs) and real-time conditions at the

Elkhorn Slough National Estuarine Research

Reserve (NERR) to predict whether a particular animal

or plant species could survive in an estuary.

Learning Objectives

Students will be able to:

1. Describe three types of estuarine environments.

2. Describe the particular environmental conditions

necessary for organisms to survive in an estuary.

3. List four principal abiotic factors that influence the

survival of aquatic life in estuaries.

4. Determine the range of pH, temperature, salinity,

and dissolved oxygen tolerated by some common

estuarine species.

Grade Levels

9-12

Teaching Time

3 (55 minute) class sessions + homework

Organization of the Activity

This activity consists of 4 parts which help deepen

understanding of estuarine systems:

The Estuarine Environment

Surviving Changes: Abiotic Factors that Affect Life

Surviving in an Estuary: Extreme Conditions

Optional: Investigating Other NERRS sites

Featured NERRS Estuary:

Elkhorn Slough National Estuarine

Research Reserve, CA

http://nerrs.noaa.gov/Reserve.aspx?ResID=ELK

Teacher Guide—Life Science Module

Activity 1: Survival in an Estuary

Background

This activity introduces students to the

nature of estuaries, estuarine environmental

factors, and four important abiotic

factors—pH, temperature, dissolved

oxygen, and salinity—and how they vary in

estuaries. The study centers on Elkhorn

Slough National Estuarine Research

Life Science Module—Activity 1

When algae naturally begin to increase in estuaries as

they may do when days lengthen and the water

temperature rises in spring, pH levels tend to rise.

Respiration, on the other hand, releases CO

into the

water, thus resulting in a lower pH, so pH levels may

drop during the summer nights.

All aquatic organisms have a pH range to which they are

adapted. Outside of this range, critical biological

processes may be disrupted, leading to stress and death.

Most organisms cannot live below a pH of 5 or above a

pH of 9. Additionally, pH is used to monitor safe water

conditions. Once the background range of pH has been

established, a rise or fall in pH may indicate the release

of a chemical pollutant, or an increase in acid rain.

Additionally, pH affects the solubility, biological

availability, and toxicity of many substances. For

example, most metals are more soluble, and often more

toxic, at lower pH values.

Temperature

Just knowing the temperature of the water in an estuary

can give us a pretty good idea of how healthy it is. One

important thing we can tell from water temperature is

how much oxygen can be dissolved into the water.

Dissolved oxygen is critical for the survival of animals

and plants that live in the water. As the water

temperature increases, the amount of oxygen that can

dissolve in the water decreases. For example, 100 % sat-

urated fresh water at 0°C contains 14.6 mg of oxygen

per liter of water, but at 20°C, it can only hold 9.2 mg of

oxygen per liter. Because dissolved oxygen is critical for

survival, seasonal water temperature (and dissolved

oxygen) is an important indicator of habitat quality for

many estuarine species.

The temperature of the water also tells us what types of

plants and animals are able to live in the estuary. All

plants and animals have a range of temperatures in

which they thrive and reproduce. For instance, salmon

will only breed at temperatures below 18°F. If the water

in the estuary is outside the normal seasonal temperature

range in which most estuarine organisms can

comfortably live, it is probably an indication that

something is adversely affecting the health of the

estuary.

Reserve (NERR) in California. Elkhorn Slough is one of

the relatively few coastal wetlands remaining in Califor-

nia. The main channel of the slough, which winds inland

nearly seven miles, is flanked by a broad salt marsh

second in size in California only to San Francisco Bay.

The reserve lands also include oak woodlands,

grasslands and freshwater ponds that provide essential

coastal habitats that support a great diversity of native

organisms and migratory animals.

Review of Abiotic Factors

What follows is some basic information about four abi-

otic factors.

pH is a measure of how acidic or basic a solution is. The

pH scale ranges from 0 to 14. Solutions with a pH of

less than 7 are acidic, and those with a pH greater than 7

are basic (or alkaline).

Knowledge of pH is important because most aquatic

organisms are adapted to live in solutions with a pH

between 5.0 and 9.0. The pH in an estuary tends to

remain relatively constant because the chemical

components in seawater resist large changes to pH.

Biological activity, however, may significantly alter pH in

the freshwater portions of the estuary.

pH is actually a measure of the amount of hydrogen ions

in a solution. In fact, some people think of pH as being

the “power of hydrogen.” A lower pH indicates that

there are more free hydrogen ions in the water, which

creates acidic conditions, and a higher pH indicates there

are less free hydrogen ions, which creates basic

conditions. pH is equal to the negative logarithm of the

hydrogen ion activity, meaning that the hydrogen ion

concentration changes tenfold for each number change

in pH unit. Water on the surface of Earth is usually a

little acidic or basic due to both geological and biological

influences.

Through a process called photosynthesis, plants remove

carbon dioxide (CO

) from the water and emit oxygen

). Since CO

becomes carbonic acid when it

dissolves in water, the removal of CO

results in a higher

pH, and the water becomes more alkaline, or basic.

Life Science Module—Activity 1

Differences in water temperature cause the formation of

distinct, non-mixing layers in water, otherwise known as

stratification, because the density of water changes with

temperature. This stratification leads to chemically and

biologically different regions in water.

Dissolved Oxygen

To survive, fish, crabs, oysters and other aquatic animals

must have sufficient levels of dissolved oxygen (DO) in

the water. The amount of dissolved oxygen in an

estuary’s water is the major factor that determines the

type and abundance of organisms that can live there.

Oxygen enters the water through two natural processes:

(1) diffusion from the atmosphere and (2)

photosynthesis by aquatic plants. The mixing of surface

waters by wind and waves increases the rate at which

oxygen from the air can be dissolved or absorbed into

the water.

DO levels are influenced by temperature and salinity.

The solubility of oxygen, or its ability to dissolve in

water, decreases as the water’s temperature and salinity

increase. Therefore, DO levels in an estuary can also

vary seasonally, with the lowest levels occurring during

the late summer months when temperatures are highest.

Bacteria, fungi, and other decomposer organisms can

reduce DO levels in estuaries because they consume ox-

ygen while breaking down organic matter. Oxygen de-

pletion may occur in estuaries when many plants die and

decompose, or when wastewater with large amounts of

organic material enters the estuary. In some estuaries,

large nutrient inputs, typically from wastewater,

stimulate algal blooms. When the algae die, they begin to

decompose. The process of decomposition depletes the

surrounding water of oxygen and, in severe cases, leads

to hypoxic (very low oxygen) conditions that can kill

aquatic animals. Shallow, well-mixed estuaries are less

susceptible to this phenomenon because wave action

and circulation patterns supply the waters with plentiful

oxygen.

Salinity and Conductivity

Under laboratory conditions, pure water contains only

oxygen and hydrogen atoms, but in the real world, many

substances, like salt, are dissolved in water. Salinity is the

concentration of salt in water, usually measured in parts

per thousand (ppt). The salinity of seawater in the open

ocean is remarkably constant between 30 and 35 ppt.

Salinity in an estuary varies according to one’s location

in the estuary, daily and storm-driven tides, and the vol-

ume of fresh water flowing into the estuary.

Salinity and conductivity are closely related. Both

measure the water’s ability to conduct electricity, which

is a surrogate measure estimating the quantity of salts

dissolved in the water. Conductivity is a more sensitive

measure (parts per million or less) than salinity (parts per

thousand or greater). Pure water is a very poor

conductor of electrical current, but salts such as sodium,

calcium, magnesium, and chloride, dissolved in the water

are in ionic (charged) form and conduct electrical

current. Conductivity, which is the opposite of

resistance, measures the ability of water to conduct

current. A higher conductivity indicates less resistance,

and means that electrical current can flow more easily

through the solution.

In saltwater estuaries, salinity and conductivity levels are

generally highest near the mouth of a river where ocean

water enters, and lowest upstream where freshwater

flows in. Actual salinities vary throughout the tidal cycle,

however, because as the tide rises more ocean water

enters the estuary. In saltwater estuaries, salinity and

conductivity typically decline in the spring when

snowmelt and rain increase the freshwater flow from

streams and groundwater. In freshwater estuaries,

salinity or conductivity is normally the reverse. The

waters of the Great Lakes have a lower salinity that the

streams and rivers flowing into them. Lake water

intrusion due to storm surges or seiches results in lower

salinity near the mouth of the estuary. During storms

and the resulting runoff, both salinity and conductivity

levels usually decrease, as rainwater and the resulting

surface runoff are very low in salts. Although this

decrease is measurable in freshwater estuaries, it does

not have the same ecological impact that it would in a

marine estuary. Salinity and conductivity are frequently

higher during the summer when higher temperatures

increase levels of evaporation in the estuary.

Conductivity and salinity are dependent on many

factors, including geology, precipitation, surface runoff,

and evaporation. Conductivity, because it is a much

Life Science Module—Activity 1

more sensitive measurement, is also very temperature

dependent. It increases as water temperature increases

because water becomes less viscous and ions can move

more easily at higher temperatures. Because of this, most

reports of conductivity reference specific conductivity.

Specific conductivity adjusts the conductivity reading to

what it would be if the water were 25°C. This is

important for comparing conductivities from waters

with different temperatures.

Environmental factors that increase conductivity and

salinity include: increased temperature, fertilizers from

agriculture, sewage, road runoff containing automobile

fluids and de-icing salts, and a local geology high in

soluble minerals, such as carbonates. Conductivity and

salinity also increase due to evaporation. The Great Salt

Lake in Utah is an extreme example of how evaporation

can increase salinity. On warm days, the evaporation of

water concentrates the ions that remain behind, resulting

in water with higher conductivity and salinity. Often,

small diurnal fluctuations in conductivity and salinity are

seen as a result of evaporation during the day and

condensation and groundwater recharge at night. In

saltwater estuaries, the influx of ocean water due to

rising tides increases salinity and conductivity within the

estuary.

Estuarine organisms have different tolerances and

responses to salinity changes. Many bottom-dwelling

animals, like oysters and crabs, can tolerate some change

in salinity, but salinities outside an acceptable range will

negatively affect their growth and reproduction, and

ultimately, their survival.

Salinity also affects chemical conditions within the

estuary, particularly levels of dissolved oxygen in the wa-

ter. The amount of oxygen that can dissolve in water, or

solubility, decreases as salinity increases. The solubility

of oxygen in seawater is about 20 percent less than it is

in fresh water at the same temperature.

- Adapted from the NOAA/NOS Estuary Discovery Kit..

URL:http://oceanservice.noaa.gov/education/kits/estuaries/

estuaries10_monitoring.html. Accessed: 2008-07-20.

(Archived by WebCite

at http://www.webcitation.org/5ZSbp3Ivp)

Students

 Need to work in a computer lab or with a

computer and projector

 Copy of the Student Reading 1

Introduction to South Marsh

 Copy of the Student Reading 2

Survival in an Estuary

 Copy of Student Worksheet

Survival in an Estuary

 Copy of Data Sheet

South Marsh at Elkhorn Slough 2004-05

 View the SWMP tutorial http://coast.noaa.gov/

swmp/tutorial/tutorial.html

Teachers

 Download the PowerPoint presentation entitled

Survival in an Estuary. (To find the presentation

go to the Estuaries.noaa.gov website, choose

the Curriculum tab, search for this lesson by

name and then select the file from the

downloads in the box on the right.)



To find more about these abiotic factors go to

the Estuaries.noaa.gov Web site, choose the

Science and Data tab, click on Data Parameters.



Bookmark the site:

https://coast.noaa.gov/swmp/#/index

Equipment:

 Computer lab or

 Computer and Projector

Materials

Life Science Module—Activity 1

Preparation

 Download the PowerPoint presentation entitled

Survival in an Estuary, and prepare to project it in

front of the class.

 To find more about these abiotic factors go to the

Estuaries.noaa.gov Web site, choose the Science

and Data tab, click on Data Parameters. Students

will be able select various factors to visually explain

abiotic parameters to them.

 If possible, arrange for students to have access to

online data either by obtaining a computer projector

to present the data in front of the whole class or by

arranging for student groups to view the data on

individual computers. On the computer(s),

bookmark the site: <https://coast.noaa.gov/swmp/

#/index>. Static data are also provided in this guide

if arranging computer access is difficult.

 Make copies of the Student Reading, Student Worksheet,

and Student Data Sheet. The graphs on the Student

Data Sheet can alternatively be projected in front of

the class.

National Science Education Standards

Content Standard A: Science as Inquiry

A3. Use technology and mathematics to improve

investigations and communications.

A4. Formulate and revise scientific explanations

using logic and evidence.

A6. Communicate and defend a scientific argument.

Content Standard C: Life Science

C4. The interdependence of organisms

C5. Matter, energy, and organization in living sys-

tems

C6. The behavior of organisms

Content Standard E: Science and Technology

E2. Apply and adapt a variety of appropriate

strategies to solve problems

Procedure

Part 1 — The Estuarine Environment

1a. Ask the students what resources and conditions they

need to survive in their environment. They will

probably mention food, water, warm clothes, etc.

They may forget things like oxygen to breathe, and

the right array of vitamins and minerals, amino acids,

and other chemical compounds needed to maintain

good health. Choose an estuarine animal or plant

and ask students to suggest factors such as

temperature that affect conditions in its habitat. List

them on the board. Bring up the water quality

factors used in this activity if students do not include

them:

• temperature

• pH

• salinity

• dissolved oxygen.

For your information, the student worksheet

contains a list of specific conditions necessary for

survival for selected species.

1b. Show students the Data Parameters

sections that deal with SWMP data and water

quality factors.

2. Show the PowerPoint Survival in an Estuary and ask

students to describe the environment they see. Ask

some probing questions as they view the slides:

• What are the water conditions like—deep or

shallow, wide or narrow, salty or fresh?

• What is the biological community like—rich and

abundant, sparse, or in between?

• Have students read the introductory section of

their handout.

3. Have students complete Part 1 of the Student

Worksheet—Survival in an Estuary.

Life Science Module—Activity 1

Check for Understanding

1. Direct your students to the Data Graphing Tool on

estuaries.noaa.gov: <https://coast.noaa.gov/swmp/#/

index>. Help students navigate through the site until

they can successfully download trend analysis data for

2005 from one monitoring sta-tion at four other NERR

sites. Encourage them to choose sites both in your

region and in other parts of U.S. coastal areas. OR,

download sample data from four sites and hand them

out to students.

2. Direct students to fill out an Extreme Conditions table

for each site.

3. Have students create graphs comparing parameter

ranges and time between extremes for new sites with

South Marsh data.

4. Discuss with students the patterns they see and ask

them to explain why the ranges and rates of change for

each factor vary at different estuary sites. Or ask them

to write their answers down and collect student work to

serve as a summative evaluation for this activity.

Optional Extension Inquiries

 Locate a local water source (pond, river, stream, or

lake) close to your school.

 Have students monitor water temperature, pH, salinity,

and DO (if possible) daily or weekly over an extended

period of time.

 Direct students to graph their summary data and then

compare their data to the variation of parameters in the

NERR sites featured in this activity.

 Discuss with students the differences in water quality

between your local site and that of the NERR sites. Is

your local water source habitable for all animal species

featured in this activity? What could be done to improve

the water quality in your local water source?

4. Have students read the Student Reading—Survival in an

Estuary and Student Reading—Introduction to South

Marsh.

Part 2 — Survival Changes: Abiotic Factors that

Affect Life

5. Go over the graphs on the Student Data Sheet—South

Marsh at Elkhorn Slough 2004-5, discussing the units

on the axes: the y-axis of each graph is different; the

x-axis of each graph represents one year of time at

South Marsh in the Elkhorn Slough.

6. Have students complete Part 2 of the Student

Worksheet—Survival in an Estuary.

7. Review and discuss the Part 2 tasks and questions.

Part 3 — Surviving in an Estuary: Extreme

Conditions

8. Use the following procedure to have students access

or display in front of the class the graphs that show

the actual values, measured by buoy, of the four

factors: water temperature, pH, salinity, and

dissolved oxygen.

 Go to <https://coast.noaa.gov/swmp/#/

index> to find the graphing tool and click on

the tutorial to learn how to generate a graph.

 Choose the type of data: water for water quality

parameters and then click on “CA, Elkhorn

Slough, South Marsh”

 Project the buoy data on the screen and assist

students in interpreting the readings.

9. Have students complete Part 3 of the Student

Worksheet—Survival in an Estuary.

Teacher Notes:

 To find whether a station will have today’s data we recommend

checking this link first: https://coast.noaa.gov/swmp/#/index

and select the station you want to see data for.

 If you cannot access today’s gauge data, use data for 10/4/07. You

will need to choose, at minimum, one day’s worth of data. You may

want to increase the amount of data that students analyze and

compare by adding several more days, months or years’ worth of

data.

Timestamp: 10/04/2007 06:15

Water Temp: 17.1 C

Percent Saturation: 66.8 %

Turbidity: 5 NTU

Specific Conductivity: 47.98

Salinity: 31.3 ppt

Dissolved Oxygen: 5.3 mg/l

Depth: 1.72 meters

pH: 8.2 units the student

handouts section.

Life Science Module—Activity 1

1a. Why is it important to monitor abiotic factors in estuarine environments?

Answer: It is important to monitor parameters such as pH, temperature, salinity, and DO because each of these factors must re-

main within a certain range to ensure the survival of species living in the estuary. Each of these parameters can exceed their normal

range when either natural (storms, floods) or human-caused events (runoff from farms, factories, power plants, sewage treatment facil-

ities) occur.

1b. Based on your observations of the images, describe the environment of species living in an estuary. Consider

factors such as temperature, water flow, salinity, and weather to name a few.

Answer: Estuaries are complex environments in which diverse species exist or vanish depending on physical and chemical factors.

The environment of South Marsh is governed by large swings of temperature and other factors due to seasonal changes. Student an-

swers about their organism will vary.

1c. How is surviving in an estuary different than surviving in a forest, a desert, or in the open ocean?

Answer: Surviving in an estuary is difficult. In an estuary, environmental factors can change rapidly. Conditions in estuaries vary

more than in many other types of habitats. Dramatic changes in pH, salinity, and temperature occur frequently and regularly in

estuaries. In deserts or the open ocean, conditions are more stable and changes usually take place more slowly.

2. Choose one animal that was highlighted in the images of Part 1. What strategies and adaptations do you think

your chosen aquatic species uses to cope with changing abiotic conditions in South Marsh?

Answer: Answers will vary. Hibernation might be mentioned as a strategy to cope with cold, wintry conditions. Some plants such as

cordgrass have special filters in their root system that removes salt from the water it absorbs in from the saltmarsh. Bivalves like

mussels, clams, and oysters close their shells during low tide and stop feeding and change their method of respiration until they are

again covered with seawater. Some aquatic species can migrate to areas with more favorable conditions and move up river or down

depending on the salinity at a particular time.

3a. After examining the range of tolerance information for five estuarine species, which of the five organisms do

you think would thrive in the abiotic conditions of South Marsh today? Which could survive over the course of

a year?

Answer: Answers will vary depending on the current abiotic data.

3b. Review the two-year data set for each abiotic factor in this activity. Choose whether each of the

five species on your list is:

i) likely to survive and live in South Marsh

ii) might do fairly well

iii) doubtful to survive given the long-term environmental conditions of South Marsh.

Teacher Worksheet with Answers

Activity 1: Survival in an Estuary

Life Science Module—Activity 1

Explain your reasoning for each species.

Answer:

oysters = Salinity of the water is uniformly too high for oysters.

clams = Water temperatures are too cold for clams to spawn.

alewife = DO levels are on the low side.

blue crab = Yes, all factors are within the survival limits of a blue crab.

cohoe salmon = DO somewhat low for salmon, average temperature is too high even though the salinity is good.

Life Science Module—Activity 1

South Marsh is part of the Elkhorn Slough National

Estuarine Research Reserve in California. The South

Marsh Complex is located on the southeastern side of

Elkhorn Slough. The entire complex is approximately

415 acres in size. Mudflat areas with some subtidal

creeks, fringing tidal marsh, and created tidal marsh

islands dominate the main areas.

Elkhorn Slough is one of the relatively few coastal

wetlands remaining in California. The main channel of

the slough, which winds inland nearly seven miles, is

flanked by a broad salt marsh second in size in

California only to San Francisco Bay.

The reserve lands also include oak woodlands,

grasslands and freshwater ponds that provide essential

coastal habitats that support a great diversity of native

organisms and migratory animals.

Student Reading—1

Activity 1: Introduction to South Marsh

Figure 1. Satellite view of Elkhorn Slough NERR

Life Science Module—Activity 1

More than 400 species of invertebrates, 80 species of

fish, and 200 species of birds have been identified in

Elkhorn Slough. The channels and tidal creeks of the

slough are nurseries for many species of fish.

At least six threatened or endangered species utilize the

slough or its surrounding uplands, including peregrine

falcons, Santa Cruz long-toed salamanders, California

red-legged frogs, brown pelicans, least terns, and sea

otters.

Additionally, the slough is on the Pacific Flyway,

providing an important feeding and resting ground for

many types of migrating waterfowl and shorebirds. The

slough and surrounding habitat are renowned for their

outstanding birding opportunities.

Many habitat types are located within a short distance

from the slough. Upland hills with oak, pine, eucalyp-

tus, grassland and maritime chaparral surround the

slough. Several thousand acres of salt marsh, tidal flats

and open water comprise the main channel of the

slough. Beach and sand dunes separate the estuary from

Monterey bay. Riparian habitat is also found on the re-

serve. Agricultural lands and residential areas border the

reserve. The close proximity of these varied habitats

supports a remarkable diversity of plant and animal spe-

cies in a relatively small area.

— Adapted from http://nerrs.noaa.gov/ElkhornSlough/welcome.html

Figure 2. South Marsh is in the foreground of this image.

Figure 3. The Elkhorn Slough National Estuarine Research Reserve encom-

passes only 1400 acres of marsh and upland habitat in the top right corner of

this image. The rest of Elkhorn Slough and the surrounding lands are owned

and managed by a variety of other individuals and entities including the

California Department of Fish and Game, The Nature Conservancy, the Elkhorn

Slough Foundation, the Moss Landing Harbor District, and the

Monterey Bay National Marine Sanctuary

Life Science Module—Activity 1

Figure 4. Vegetation map of the Elkhorn Slough watershed courtesy

of the Elkhorn Slough Foundation.

Life Science Module—Activity 1

An estuary is a partially enclosed body of water where

two different bodies of water meet and mix such as

fresh water from rivers or streams and salt water from

the ocean, or fresh water from rivers or streams and

chemically distinct water of the Great Lakes. In estuar-

ies, water levels are affected by lunar or storm driven

tides. In fresh water, the concentration of salts, or sa-

linity, is nearly zero. The salinity of water in the ocean

averages about 35 parts per thousand (ppt). The mix-

ture of sea water and fresh water in estuaries is called

brackish water.

Estuaries are transitional areas that connect the land

and the sea, as well as freshwater and saltwater habitats.

The daily tides (the regular rise and fall of the sea’s sur-

face) are a major influence on many of these dynamic

environments. Most areas of the Earth experience two

high and two low tides each day. Some areas, like the

Gulf of Mexico, have only one high and one low tide

each day. The tidal pattern in an estuary depends on its

geographic location, the shape of the coastline and

ocean floor, the depth of the water, local winds, and

any restrictions to water flow. For example, tides at the

end of a long, narrow inlet might be heightened be-

cause a large volume of water is being forced into a

very small space. However, the tidal change in wetlands

composed of broad mud flats might appear to be ra-

ther small.

While strongly affected by tides and tidal cycles, many

estuaries are protected from the full force of ocean

waves, winds, and storms by reefs, barrier islands, or

fingers of land, mud, or sand that surround them. The

characteristics of each estuary depend upon the local

climate, freshwater input, tidal patterns, and currents.

Truly, no two estuaries are the same.

Survival for any species, regardless of its environment,

depends on the ability to adapt to changing conditions.

Humans can go inside to get warm on a freezing cold

day or put on a heavy coat and gloves. Or if the water

main breaks or if the well runs dry, we can hop in our

cars and obtain water from another source like a neigh-

bor or local store. For plants and animals that live in an

aquatic environment, adaptation is sometimes much

more difficult. And for every species that spends most

of its time in water, sudden changes in the environ-

ment, whether caused by natural agents (storms) or hu-

man intervention (pollutants), can spell disaster and

lead to the death of many members of the aquatic com-

munity.

In estuaries, all plant and animal species live in a transi-

tion zone where fresh and salt water meet. Factors that

cause change in estuarine environment fall into two

categories: abiotic and biotic. Abiotic factors are those

that occur in physical environment such as amount of

sunlight, climate, and the geology of the area. Biotic

factors are those that deal with the organism and other

organisms they share their environment with, including

their interaction, wastes, disease and predation.

To measure changes in the physical environment, biol-

ogists use factors that relate to natural processes or hu-

man actions. These include:

Scientists use pH as an indicator of whether water is

acidic or basic. pH is measured on a scale of 1 to 14,

where numbers less than 7 are increasingly acidic and

numbers greater than 7 are increasingly basic. Distilled

water has a pH of 7 and is said to be neutral. Water on

the surface of Earth is usually a little

acidic or basic due to both geological

and biological influences.

pH is actually a measure of the amount of

hydrogen ions in solution. In fact, some

people think of pH as being the “power

Student Reading—2

Activity 1: Survival in an Estuary

Life Science Module—Activity 1

Figure 5. Barrier beach closed Figure 6. Barrier beach open

of hydrogen.” A lower pH indicates that there are more

free hydrogen ions in the water, which creates acidic

conditions, and a higher pH indicates there are less free

hydrogen ions, which creates basic conditions. pH is

equal to the negative logarithm of the hydrogen ion

activity, meaning that the hydrogen ion concentration

changes tenfold for each number change in pH unit.

Water on the surface of Earth is usually a little acidic or

basic due to both geological and biological influences.

All aquatic organisms have a pH range to which they

are adapted. Outside of this range, critical biological

processes may be disrupted, leading to stress and death.

Most organisms cannot live below a pH of 5 or above a

pH of 9. Additionally, pH is used to monitor safe water

conditions. Once the background range of pH has

been established, a rise or fall in pH may indicate the

release of a chemical pollutant or an increase in acid

rain. Additionally, pH affects the solubility, biological

availability, and toxicity of many substances. For exam-

ple, most metals are more soluble, and often more tox-

ic, at lower pH values.

Temperature

Temperature is a measure of kinetic energy, or energy

of motion. Increasing water temperature indicates in-

creasing energy, or motion of water molecules and sub-

stances dissolved in the water. Temperature is a critical

factor for survival in any environment. Organisms that

live in water are particularly sensitive to sudden chang-

es in temperature.

The Celsius temperature scale is used worldwide to

measure temperature. Temperature has a significant

impact on water density. Water density is greatest at 4

degrees Celsius, meaning that water at higher or lower

temperatures will float on top of water at or near 4º C.

This is why ice floats on water, and warm water floats

over cooler water. Differences in water temperature

cause the formation of distinct, non-mixing layers in

water, otherwise known as stratification. This stratifica-

tion leads to chemically and biologically different re-

gions in water.

Salinity and Conductivity

Salinity and conductivity are measures of the dissolved

salts in water. Salinity is usually described using units of

parts per thousand or ppt. A salinity of 20 ppt means

that there are 20 grams of salt in each 1000 grams of

water. Because it is impractical to routinely determine

the total amount of salts dissolved in water, a surrogate

measure—the ability of the water to conduct electrici-

ty—is made for determining both conductivity and sa-

linity. All aquatic life in an estuary must be able to sur-

vive changes in salinity. All plants and animals have a

range of salinity to which they are adapted. Outside of

this range, they will be unable to function and may die.

Salinity and conductivity are closely related. Conductiv-

ity and salinity are measures of what is dissolved in the

water. Pure water is a very poor conductor of electrical

Life Science Module—Activity 1

current, but salts dissolved in the water are in ionic

(charged form) and conduct electrical current. Conduc-

tivity, which is the opposite of resistance, measures the

ability of water to conduct current. A higher conductiv-

ity indicates less resistance, and means that electrical

current can flow more easily through the solution. Be-

cause dissolved salts conduct current, conductivity in-

creases as salinity increases. Common salts in water

that conduct electrical current include sodium, chloride,

calcium, and magnesium.

Salinity affects the ability of water to hold oxygen, and

seawater holds approximately 20% less oxygen than

freshwater. Many chemical reactions that determine the

concentration of nutrients and metals in the water are

influenced by salinity. The conductivity and salinity of

seawater is very high while these parameters are com-

paratively low in tributaries and rivers. Freshwater lakes

typically have conductivities and salinities even lower

than those of inland streams. This is because inland

streams pick up salts from rocks, soils, and roads as

they flow over the landscape.

Many chemical reactions that determine the concentra-

tion of nutrients and metals in the water are influenced

by salinity. For instance, salinity and conductivity affect

the ability of particles to flocculate, or stick together,

which is important in determining turbidity levels and

sedimentation rates. Salinity also increases the density

of water, with seawater being heavier than freshwater.

This density difference inhibits mixing. In fact, conduc-

tivity and salinity serve as excellent indicators of mixing

between inland water and sea or lake water, and they

are particularly useful in indicating pollution events or

trends in freshwater. For example, an overdose of ferti-

lizers or the application of road salt will cause spikes in

conductivity and salinity.

Conductivity and salinity are dependent on many fac-

tors, including geology, precipitation, surface runoff,

and evaporation. Since conductivity is a much more

sensitive measurement than salinity, it is more impacted

by changes in temperature. Conductivity increases as

water temperature increases because water becomes

less viscous and ions can move more easily at higher

temperatures. Because of this, most reports of conduc-

tivity reference specific conductivity. Specific conduc-

tivity adjusts the conductivity reading to what it would

be if the water was 25°C. This is important for compar-

ing conductivities from waters with different tempera-

tures.

Dissolved Oxygen

Dissolved oxygen (DO) is the amount of oxygen gas

that is dissolved in a sample of water. DO is usually

measured in units of milligrams per liter (mg/L). Just as

we need air to breathe, aquatic plants and animals need

dissolved oxygen to live. Dissolved oxygen is used for

respiration, which is the process by which organisms

gain energy by breaking down carbon compounds,

such as sugars. Dissolved oxygen is also essential for

decomposition, which is a type of respiration in which

bacteria break down organic materials for energy. De-

composition is an important process that recycles nu-

trients and removes organic materials such as dead veg-

etation from our waterways. Because dissolved oxygen

is required for aquatic life, balancing the sources and

sinks of dissolved oxygen is essential in maintaining a

healthy ecosystem.

The concentration of dissolved oxygen in water is de-

pendent on a number of interrelated factors, including

biological factors, such as the rates of photosynthesis

and respiration, and physical and chemical factors, such

as temperature, salinity, and air pressure.

Dissolved oxygen enters the water by diffusion from

the air and as a byproduct of photosynthesis. Diffusion

from the air occurs very quickly in turbulent, shallow

water or under windy conditions. The amount of oxy-

gen that can dissolve in water is dependent on water

temperature, salinity, and air pressure. As temperature

and salinity increase, and pressure decreases, the

amount of oxygen that can be dissolved in water de-

creases. Cold water holds more dissolved oxygen than

warm water, and water at sea level holds more dis-

solved oxygen than water at high altitudes. Seawater

holds approximately 20% less oxygen than freshwater

at the same temperature and altitude.

— Adapted from NOAA’s National Ocean Service Estuaries Discovery Kit

Life Science Module—Activity 1

Student Worksheet

Activity 1: Survival in an Estuary

Student Name:

Procedure

Part 1 — The Estuarine Environment

You will be shown a number of images of estuaries. If you were a (specific) animal or plant living in an (specific loca-

tion) estuary, what factors seen in these images might influence whether you survive or not? Take notes as the images

are shown and then answer the following questions.

1a. Why is it important to monitor abiotic factors in estuarine environments?

1b. Based on your observations of the images, describe the environment of species living in an estuary. Consider fac-

tors such as temperature, water flow, salinity, and weather to name a few.

1c. How is surviving in an estuary different than surviving in a forest, a desert, or in the open ocean?

Life Science Module—Activity 1

Part 2 — Surviving Changes: Abiotic Factors that Affect Life

You will investigate two years’ worth of graphical data that describe four abiotic factors affecting the survival of

aquatic species at South Marsh in the Elkhorn Slough.

For each graph on the Student Data Sheet—South Marsh at Elkhorn Slough 2004-5, determine the lowest and highest val-

ue of each abiotic factor. Then determine the approximate time (in days) that elapsed between these two measure-

ments.

Extreme Conditions at South Marsh Table

2004 2005

Factor High Low Time Between High Low Time Between

temperature ___________________________________________________________________

pH __________________________________________________________________________

salinity _______________________________________________________________________

dissolved oxygen _______________________________________________________________

Next, find the range for each factor (high value - low value) for 2004 and 2005.

2. Choose one animal that was highlighted in the images in Part 1. What strategies and adaptations do you think

your chosen aquatic species uses to cope with changing abiotic conditions in South Marsh?

Life Science Module—Activity 1

Part 3 — Surviving in an Estuary: Extreme Conditions

You will explore the actual values for each abiotic factor on a specific day. Your teacher will project the buoy readings

for today's date or supply a hardcopy sheet with data for another day.

Record the date your data was gathered.

date ______________________________________________________________________

Record the values for temperature, salinity, dissolved oxygen, and pH.

temperature ________________________________________________________________

pH _______________________________________________________________________

salinity ____________________________________________________________________

dissolved oxygen ____________________________________________________________

Consult the list of Limits of Tolerance to Environmental Factors for Selected Organisms for the animals, and answer the follow-

ing questions.

3a. After examining the range of tolerance information for five estuarine species, which of the five organisms do

you think would thrive in the abiotic conditions of South Marsh today?

Life Science Module—Activity 1

3b. Review the two-year data set for each abiotic factor in this activity. Choose whether each of the five species on

your list is:

i) likely to survive and live in South Marsh

ii) might do fairly well

iii) doubtful to survive given the long term environmental conditions of South Marsh.

Explain your reasoning for each species.

Limits of Tolerance to Environmental Factors for Selected Organisms

Oysters

 Grow best in water with a salinity of 12 ppt and

above, perish if salinity is below 5 ppt or above 25 ppt

 Spawn only when the water temperature hits 18°C for

four hours

 Spawn much more prevalent when salinity is over 20

ppt

 Need a DO level of around 4 mg/l

 Best growth when pH is between 7.5 and 8.5

Clams

 Grow best when the water salinity is above 15 ppt

 Spawn only when the water temperature hits 24°C for

four hours

 Clam eggs die when the salinity is below 20 ppt

 Need a DO level of around 4 mg/l

 Optimal growth occurs between 10 and 25°C

Alewife

 Adult and juvenile fish need a DO level of at least 3.6

mg/l

 Alewife eggs and larvae need a DO level of 5 mg/l or

 Must have a pH higher than 5 but less than 9

Blue Crab

 Needs a DO level of 3 mg/l or more for survival, opti-

mal at 5 mg/l

 Thrives if pH is between 6.8 and 8.2

Coho Salmon

 Like a DO level of 6 mg/l or higher

 Require a salinity of greater than 15 ppt

 Prefer temperatures between 4° and 20°C, do best at

13°C

 Spawn only when temperature is 18°C or higher

 Newly hatched salmon need a DO level of at least 5

mg/l to survive

 pH of 4.0 or lower or higher than 9 is lethal for salmon

Life Science Module—Activity 1

Student Data Sheet

Activity 1: South Marsh at Elkhorn Slough 2004

Salinity

Dissolved Oxygen

Figure 8.

DO: South Marsh

Figure 7.

Salinity: South Marsh

Life Science Module—Activity 1

Figure 9.

Water temperature:

South Marsh

Water Temperature

Figure 10.

pH: South Marsh