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Student Data Sheet 1

Name __________________________________________________ 

Date ______________________________

Latitude (e.g. 75o N)______________________ Longitude (e.g.18oW) ________________

Recent weather conditions:

Current weather (circle one) Clear Partly Cloudy Fog Overcast Rain Snow

Air Temperature ______________________°C or °F 

Wind Speed _______________________mph_

Water Sample: (circle one from each category) 

Type of water: Freshwater ------Brackish------Seawater

Clarity of water: Clear------Cloudy------Muddy

Odor of Water: Fishy ------Rotten Egg------Gas------No Smell

Surface conditions: Calm------Light chop------Heavy chop with white caps-----Ice

Condition of the water (check one box for each category)

Many Few None

Suspended particles/debris 

in the water?

Plants or algae in the 

water?

Any visible living species?
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WATER 

INDICATOR Local Site Local CBIBS Compare/Contrast

Dissolved 

Oxygen

(ppm)

Salinity

(ppt)

Water 

Temperature

°C/°F

Turbidity

(cm/m)

pH

Water Depth

(cm/m)

NA

Surrounding Area

Landmarks and description of the site:

Which of these are nearby? Land use descriptions and wildlife observation (check all that 

apply):

______FARMS ______LIVESTOCK FARMING ______POULTRY 

______HOUSES ______FACTORIES ______STORES

______PARKING LOT ______WALKWAYS ______EMPTY LOT 

______CARS ______TRUCKS ______BOATS 

______ QUARRY ______LOGGING ______CONSTRUCTION
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______ WOODS ______TREES ______PLANTS 

______LIVESTOCK ______DOGS/Pets

Others (Please specify): 

___________________________________________________________

Describe the soil in detail, sketch and /or take some photographs of the surrounding area. This 

will enable you to note any changes in the area later, such as erosion caused by a major storm 

or new development on the shoreline. 

Can you say that the area is covered with porous (water moves through easily) or impervious

(water cannot move through easily) material? (Circle one)

MOSTLY POROUS IN THE MIDDLE MOSTLY IMPERVIOUS

Is there any evidence of water runoff and/or erosion? (Circle one) YES NO

If yes, what do you think is/are the possible cause(s)?
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Student Data Sheet 2

Scientists measure Bay water temperatures, turbidity (clearness of the water) and other 

indicators to monitor the health of the Chesapeake Bay. We will take a look at some archived 

data from the Chesapeake Bay Buoy system data to help answer some questions about the 

relationships between water quality indicators. 

The air and water temperature graph below is from the Susquehanna Buoy between June 1 and 

August 30, 2015. (Temperatures are degrees Celsius)

1. What is the air highest temperature?

2. What do you notice in the changes in air temperature compared to the water 

temperatures?

3. Why do you think that the water temperatures have a smoother plot than the air 

temperatures?

4. What weather events might cause the dramatic changes in the air temperatures?

Dissolved oxygen 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. 
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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 the Bay’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 also increases the rate at 

which oxygen from the air can be dissolved or absorbed into the water.

The graph below compares water temperature and the amount of dissolved oxygen from July 1 

to December 31, 2015. (Note that mg/L is used here instead of ppm for dissolved oxygen)

5. What do you notice about the pattern of water temperature over the 6 months 

compared to the dissolved oxygen?

6. What kind of relationship would we say exists between temperature and dissolved 

oxygen?

Proportional - when one goes up, the other goes up

Inverse proportional – when one goes up, the other goes down.

7. Less oxygen dissolved in the water is often referred to as a “dead zone” because most 

marine life either dies, or, if they are mobile, such as fish, leave the area. Habitats that 

would normally be teeming with life become, essentially, biological deserts. Go to this 

site. http://oceanservice.noaa.gov/facts/deadzone.html. What is the primary cause of 

these zones? 
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Turbidity in water is caused by suspended 

matter, such as clay, silt, and organic matter and 

by plankton and other microscopic organisms 

that interfere with the passage of light through 

the water. Turbidity also includes plankton and 

other organisms, and the cloudier the water, the 

greater the turbidity. The effects of large 

amounts of rainfall around the Bay’s watershed 

make the turbidity change. Turbidity of natural 

waters tends to increase during runoff

events because of increased overland flow, 

stream flow, and erosion.

In this image, a “plume” of water carrying 

sediment and debris is entering the Bay from the 

Susquehanna River (on the top of the image) can 

even be seen by satellites.

The turbidity of the Bay’s water affects life above 

and below the surface. Water clarity is 

influenced by weather events such as droughts 

and rain storms. When rains fall in the watershed, it carries sediments that eventually lead to 

the Bay. This combines with decaying plant and animal matter, sewage, and industrial wastes 

to form suspended particles in the water, causing it to be more turbid because the particles 

scatter light. Clear waters are healthier waters. Turbidity affects organisms that are directly 

dependent on light, like aquatic plants, because it limits their ability to carry out 

photosynthesis. This, in turn, affects other organisms that depend on these plants for food 

and oxygen. The graph below compares turbidity and dissolved oxygen from September 1 to 

September 30, 2015. (Note that mg/L is used here instead of ppm for dissolved oxygen)
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8. What kind of relationship would we say exists between turbidity and dissolved oxygen?

(Circle one)

Proportional - when one goes up, the other goes up

Inverse proportional – when one goes up, the other goes down.

9. In mid-September, there is a spike in turbidity and a drop in dissolved oxygen. What 

weather event might have caused this?

10. Animals are dependent on the amount of dissolved oxygen that is available in the water 

for respiration. Compare the graph with the fish listed below and determine if any of 

these fish species were at risk during September. (Numbers are the Lowest DO at which 

fish survived for 24 hours in summer)

• Black Bass - 5.5 ppm

• Common Sunfish - 4.2 ppm

• Yellow Perch - 4.2 ppm

• Black Bullhead - 3.3 ppm

Plants only produce oxygen when light is available for photosynthesis, and turbidity reduces the 

amount of light in the water. The chart below is from data at the Potomac CBIBS buoy from 

July 1 to December 31, 2015 comparing turbidity and chlorophyll produced from 

phytoplankton. 
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11. The turbidity and chlorophyll patterns are very similar. Why do these seem to be 

connected?

12. There is a delay between the rises and drops of turbidity and corresponding chlorophyll

levels. Why?

13. On October 5, a spike of turbidity resulted in a quick drop in Chlorophyll. What weather 

event might have caused this disturbance?

14. The oyster population in the Bay is less than 1% of what it once was. It has been 

estimated that oysters were once able to filter all the water in the Bay in about a week. 

The sharp decrease in the number of oysters means that it now takes the current oyster 

population about a year to filter the same amount of water. Degrading water quality is 

both a cause and an effect of the oyster decline, because fewer oysters mean less 

filtration capacity. But oysters, as hardy as they are, can be killed by prolonged periods 

of low dissolved oxygen at the Bay's bottom. From your investigation into water 

quality, what water parameters do you think are most important to the Bay’s health?

In what ways can repopulating the Bay with oysters contribute to the overall quality of 

the Bay’s water?
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Student Data Sheet 3

Water Quality Parameters and Effect on aquatic organisms

Let’s look at several water quality parameters and their influence on oyster populations. 

Dissolved oxygen plays a role in oyster survival and growth. Low dissolved oxygen can result in 

oyster mortality. In shallow waters where nutrient pollution runs high, oxygen levels can 

plummet to nearly zero at night. Oysters living in these zones are far more likely to pick up the 

lethal Dermo disease. Researchers at the Smithsonian Environmental Research Center exposed 

oysters to low-oxygen cycles similar to those in the Bay. Some had constant levels of normal 

dissolved oxygen concentrations (about 7 milligrams dissolved oxygen/liter), some dropped to 

1.5 mg/L for a few hours each day, and some dropped to 0.5 mg/L.

1. What was the dissolved oxygen at your test site? 

2. What time of day was the test done? 

3. Is your reading in the normal range? 

pH is measured on a scale of 1 – 14 with 7

being neutral. The lower the number the 

more acidic a solution is; the higher the 

number the more basic it is. Acidity is 

increasing in some regions of the 

Chesapeake Bay even faster than is occurring 

in the open ocean. These more acidic 

conditions in key parts of Chesapeake Bay 

reduce rates of juvenile oyster shell 

formation and growth. Inputs of nutrients 

from sewage systems and agriculture 

promote increased phytoplankton 

populations in the upper Bay. As these plants 

grow, they absorb large amounts of carbon 

dioxide from the water column, thereby 

making waters in that region less acidic.

When the algae decompose, the pH becomes 

more acidic because the algae respiration 

and decomposition. This results in the 

release of carbon dioxide making it significantly more acidic. 
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The eastern oyster can spawn in water with pH between 7.8 and 8.2, and has difficulties in pH 

that is lower than 6 or higher than 10. Larvae mortality rates increase rapidly when the pH is in 

the 9.00 to 9.50 range. The pH also affects the respiration rate, and the pumping rate of water

over the gills. 

4. Would oysters be able to live and reproduce with the pH of your local stream?

Measuring pH in the Bay is a challenge. Levels can vary widely over time and at different 

locations. 

The graph on the right shows the 

variation of pH over 14 days in July 

2010 at Fort Howard.

Source: Maryland Department of Natural 

Resources, Eyes on the Bay.

5. What might have caused the 

decrease in pH between July 10 and 

11?

6. Would oysters be able to spawn 

in this area?

The graph on the left shows the 

ranges of monthly pH at one station 

in the Bay, Cedar Point, from 1985 

to 2010. The wide plot shows many 

years of data. 

Source: Maryland Department of Natural 

Resources, Eyes on the Bay.

7. In general, at what time of year 

is the pH the highest? 

8. What might account for this 

increase of pH (less acidic)?
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Salinity

Oyster reefs can be found in a wide salinity range (12 ppt to 28 ppt). Extreme salinity 

fluctuations affect the survival, growth, and distribution of oysters that form reefs. During 

severe storms, salinity changes occur in estuaries which may promote oyster diseases. 

The ideal salinity range for growth and development is 10 to 22 ppt. Salinity below 10 ppt 

inhibits spat set. Seed oyster production does well within a salinity range from 10 to 15 ppt. 

9. What was the salinity at your site? 

Is it within the salinity range for oyster grown and development?

Is it within the salinity range for oyster reproduction?

Nitrates are essential nutrients used by plants and animals for maintenance and growth 

(building protein), but too much can be toxic. Oysters are tolerant of high nitrates compared to 

other marine species and can remove excess nitrogen from the water. Some of it is absorbed in 

the shell and flesh where it is stored. It is thought that the oyster also takes nitrogen (N) from 

the water and converts it into harmless nitrogen gas. Oysters are powerful filters. (We will learn 

more about this in the next activity). The U.S. Public Health Service has established 10 mg/L of 

nitrate-nitrogen as the maximum contamination level allowed in public drinking water.

10. Compare the nitrate-nitrogen level of your site to the maximum allowed in drinking water. 

Turbidity

Although oysters filter water and improve its quality, a big increase in turbidity can influence 

oyster reef growth and survival. Too much from storms or tides can smother oyster larvae, and 

disturb the filter feeding process of oysters, affecting their growth and development. High 

levels of sediment can cause permanent changes in the oyster reef community. Oysters can be 

overwhelmed and buried by heavy sedimentation. Waters with low concentrations of total 

suspended solids (TSS) are clearer and less turbid than those with high TSS concentrations.

11. What was the Secchi or turbidity reading at your site?

Was there a recent weather event that might have affected the level of turbidity at your site?

Temperature

Oysters spawn at temperatures greater than 60.0F. Adult oysters grow well at 500 to 800F or 

higher, but the most favorable temperatures are 770 to 790F.

12. Were the water temperatures at your site within the range for adult oysters?

Were the water temperatures high enough for oysters to spawn?