The Potomac Highlands Watershed School 

A Virtual Stream Sampler: About Accokeek Creek and Your Score

Accokeek Creek is a tidal tributary of Potomac Creek, which runs into the Potomac River within sight of Washington DC.  The site Cacapon Institute sampled for this activity is on The Alice Ferguson Foundation's Hard Bargain Farm. According to Maryland DNR, the watershed area of Accokeek Creek at this site is about 3.3 square miles, with 7.6% of the watershed urban, 5.7% farm, and 86.6% is forested. 

Courses at AFF Hard Bargain Farm immerse students in various field studies involving fun and innovative hands-on activities and field investigations designed to engage all learning styles.  Their programs for elementary to middle school students are designed to promote understanding and stewardship of the natural resources in the Potomac River watershed and the legacy of farming in America. Many students, teachers and environmental education practitioners from Maryland and Washington DC have sampled the same area of Accokeek Creek you just sampled virtually. 

If you used the other activities in the Benthic Macroinvertebrate Portal prior to using this activity, you should have a good understanding of everything you did in A Virtual Stream Sampler.  If you haven't used those activities, we suggest you run through the Introduction to Stream Sampling to get the basics.  Click here to see a summary of the BMIs you picked in Accokeek Creek and to see a picture of the BMI "take" that was collected in Accokeek Creek by CI staff.

Accokeek Creek on June 29, 2011, the day benthic samples were collected by CI staff.   CI also helped train teachers on that day. 

Your Score

The benthic macroinvertebrate section is worth 50% of the total score, the other two sections are each worth 25% of final score. 

  • In the benthic macroinvertebrate section, if there are 15 organisms, then finding everything in the net is worth 15 points, and correctly identifying everything is worth 15 points, for a total of 30 points (100%).  You are penalized heavily if you guess at answers on the list and get them wrong.  Every wrong guess is a point off.  Since you have three chances to guess at the answer for each organism before you are forced to use the dichotomous key, with 15 organisms that would be 45 points off.  Yes, you can get a very negative score.  So, if you don't know what something is, don't guess - use the key.  Guessing in the key is not penalized.
  • The habitat section has a maximum score of 5.  Each wrong answer counts off one.  Each question you don't try to answer counts off two.  So you are better off guessing and being wrong than not answering at all.  If you don't guess on anything you can get a negative 100% score in this section.  Ouch!

  • The water quality section has a maximum score of 6.  Each wrong answer counts one off.  Each question you don't try to answer counts 2 off.  So you are better off guessing and being wrong than not answering at all.   If you don't guess on anything you can get a negative 100% score in this section.  Ouch!

  • Even though you can get negative scores in each section, the worst total score you can get is zero. 

The Stream Score

Aquatic organisms can be used as indicators of water quality. The advantage of using aquatic organisms over chemical indicators - such as the amount of a certain chemical in a water sample - is that animals are constantly "sampling" their environment.  The communities of organisms found in benthic samples are indicative of water quality conditions over time. Chemical measures, in contrast, provide a momentary snapshot of conditions in a constantly changing environment. 

Many years ago, the focus was on "indicator species."  An indicator species is one that, by its presence, absence, or abundance relative to other organisms, indicates environmental conditions. For example, the presence of numerous  non-biting midge (Chironomidae) larvae in a stream may indicate severe organic pollution.

Over the years, researchers generally moved away from the use of individual indicator species and toward "metrics" that look at groups of species. A typical metric might look at the total number of different species or the relative abundance of different species. For instance, if a researcher finds that species tolerant of degraded water quality outnumber kinds that are intolerant of pollution, it is more likely that degraded conditions exist  But the mere presence of pollution-tolerant organisms does not necessarily equate to water quality problems, because these organisms are often widely distributed.

A Virtual Stream Sampler scores the stream using two popular methods in use by volunteers in the Chesapeake Bay Watershed, the West Virginia Save Our Streams Stream Score Index, and Virginia Save Our Streams Stream Score.  Both of these scores are based on a suite (a group) of "metrics" that, when averaged together, are an effective way to tell a stream's story.  Two metrics are used by both West Virginia and Virginia:

  • percent tolerant organisms tells you what percentage of the organism in the sample are tolerant of pollution, and

  • Virginia's percent Mayflies, Stoneflies, and most Caddisflies is similar to West Virginia's % EPT score.  This score looks at what percentage of the sample consist of theswe three groups of insects that are mostly sensitive to pollution.  Virginia's score breaks out the pollution tolerant "common netspinner caddisfly."

The two tables below provide details on each system, and links for more information. 

Virginia SOS Stream Score

Metric

Your Metric Score

Good (2)

OK (1)

Poor (0)

% Mayflies, Stoneflies, and Most Caddisflies

X%

> 32.2

16.1 to 32.2

< 16.1

% Common Netspinner

X%

< 19.7

19.7 to 34.5

> 34.5

% Lunged Snail

X%

< 0.3

0.3 to 1.5

> 1.5

% Beetle

X%

> 6.4

3.2 to 6.4

< 3.2

% Tolerant Organisms

X%

< 46.7

46.7 to 61.5

> 61.5

% Non-Insect Organisms

X%

< 5.4

5.4 to 20.8

> 20.8

Get details on how the Virginia Save Our Streams Score is calculated and learn much more about the Virginia program.   

Total # of 2s:

Total # of 1s:

Total # of 0s:

N2

N1

N0

Multiply by 2:

Multiply by 1:

Multiply by 0:

N2 x 2 = S2

N1 x 1 =S1

N0 x 0 = S0

Now add the 3 subtotals (S2 + S1 +  S0) to get the Save Our Streams Multimetric Index Score

_____ Acceptable Conditions (9 to 12)              

_____ Conditions cannot be Determined - Gray Area (8)               

_____ Unacceptable Conditions (0 to 7)                       

 

West Virginia SOS Stream Score

Metrics

What Values Mean

Best Standard Value (BSV)

Scores

1.  Total Taxa

Higher is better

22

Your Value/BSV x 100

2.  EPT Taxa

Higher is better

13

Your Value/BSV x 100

3.  Biotic Index

Lower is better

3

(10-Your Value)/7*100

4.  % EPT Abundance

Higher is better

90

Your Value/BSV x 100

5. % Tolerant

Lower is better

2

(100-Your Value)/(100-BSV)*100

6.  %Dominance

Lower is better

20

(100-Your Value)/(100-BSV)*100

Stream Score Index (SSI)

Average of the above scores

Reading the WV SOS Stream Score table: 

 > 85 = Optimal, 85-70 = Suboptimal, 69-50 =  Marginal, < 50 = Poor

 

The West Virginia Save Our Streams Program has three levels of stream sampling methods for volunteers to choose from.  All of them require training and volunteer certification by the state volunteer coordinator for their data to be accepted.  Level I requires the least technical expertise, Level III the most.   The Stream Score above is a hybrid of the Level II and Level III scoring (we wanted to add in percent Dominance), and similar to the professional level West Virginia Stream Condition Index.

  • "Total Taxa" = how many kinds of BMIs were found.  Higher values are better, 22 would be a very good stream.

  • "EPT Taxa" = how many kinds of Mayflies (Ephemeroptera), Stoneflies (Plecoptera), and Caddisflies (Trichoptera) were found.   Higher values are better, 13 would be a very good stream.

  • "Biotic Index" = the Hilsenhoff Biotic Index, that multiplies abundance of each organism by its sensitivity to pollution (ranked from 1-most sensitive  to 10 - least sensitive), and divides the sum by the total number of organisms caught.   Lower values are better, 3 would be a very good stream.

  • "% EPT Abundance" = how many Mayflies (Ephemeroptera), Stoneflies (Plecoptera), and Caddisflies (Trichoptera) were found.   Higher values are better, 90 (out of a total of 200 organisms) would be a very good stream.

  • "% Tolerant" = the percentage of the total number of organisms that were caught that are tolerant of pollution.   Lower values are better, 2 would be a very good stream.

  • "%Dominance" =  the percentage of the most abundant organism in the sample out of the total number of organisms caught.   Lower values are better, 20 would be a very good stream.

You can learn much more about the West Virginia SOS program, and even download spreadsheets for calculating your own stream scores.  

 

The BMIs of Accokeek Creek

Collected June 29, 2011 by N Gillies (Cacapon Institute)

Sorted and identified 1/8 of total sample

Caddisflies

 

Common Netspinner

143

Fingernet

1

Humpless Casebuilder

1

Stoneflies

 

Common 

11

Mayflies

 

Small Minnow

3

Beetles

 

Riffle, larva

10

Riffle, Adult

2

Dragonfly

3

Crane Fly

8

Chironomidae

300

Watersnipe Fly

4

Amphipods

3

Crayfish

2

Lepidoptera Larva change to alderfly

1

Roundworm

1

 

You might like to try entering the above BMI data into the Virginia or West Virginia spreadsheets to calculate the BMI Index Score for yourself, or try it using other state's volunteer and professional scoring methods.  Do they all give the same answer?  If not, how do they differ?  

 

The Potomac Highlands Watershed School 

A Virtual Stream Sampler

This web page is an informational component of the "A Virtual Stream Sampler" activity that simulates a volunteer stream assessment.  It is just one component of the Potomac Highlands Watershed School's watershed science and society curriculum, and is best used when accessed from within an eSchool classroom.  If you reached this page via a direct web-link, you might consider going to the Potomac Highlands Watershed School and visiting an eSchool classroom to use the Virtual Stream Sampler and other activities, review the literature in the bookshelf or, if you are a teacher, visit the "Teacher's" room and check out the lesson plans.