Friday, August 13, 2010

Biomass Survey

Unfortunately, our aerial survey was canceled this week due to unforeseen circumstances. This however, gave us time to do some biomass estimates. Because we analyze our aerial photography for percent cover of macroalgae, it is important to have a strong understanding of the density, or total biomass for each percent cover classification. Our analysis is based on five density classes (0=no cover, 1= 1-10%, 2=11-40%, 3=41-70%, 4=71-100%). Below you will find an image that helps us identify the density class for each picture.

Each block represents a percent cover which helps us determine the density of algae seen in each aerial photograph.
Everything you will need to do your own biomass estimates!

To measure biomass you will need:
  • 1 quadrat (1/2 meter squared is ideal, but any size will do);
  • Measuring tape;
  • 1 scale (one with a hanging clip that can weigh at up to 500 grams is ideal);
  • Box cutter or razor blade to cut macroalgae overhanging quadrant sample area;
  • Salad spinner to remove excess water from the macroalgae;
  • A zip-lock bag to hold and weigh the sample;
  • paper and pencil to record your readings, and;
  • A camera to capture images of your findings!

Step by step instructions on measuring biomass:
Kids, be sure to have an adult help you out!

We sampled Sandy Point on Tuesday, and the Wilson Park Fishing Area (pictured here) and Bissel Cove on Wednesday.
First, you will need to select the area you wish to measure. Find a shoreline and define the area by starting at one end, along the water's edge and walking to the opposite end, counting each step (you will need to measure your steps to get exact length). Do the same thing perpendicular to the water's edge and multiply both sides to get the area of your shoreline.

Take your quadrat and drop it at random within your sample area.

Quadrat laid along shore at random.

Using your box cutter or razor blade, cut along the edge of your quadrat to trim away pieces of macroalgae that are not in your selected area. If a piece is only half in your selected area you will need to carefully cut away the section that is not in your area.
Using a razor blade, carefully cut away excess macroalgae from your sample.
Note: Be sure to have an adult help you with the sharp blade!

A salad spinner is the quickest and easiest way to get rid of excess water.
Next, you will need to clean and dry your sample. We use a salad spinner to get rid of excess water, but sometimes we need to clean the sample of sand, snails and shells first. Be sure to remove everything from your sample that is not macroalgae or your readings will be off!

Once you have cleaned and dried your sample you will need to separate it into the different types of macroalgae. Make a pile for each of the classes (green, red and brown)
Our sample has been separated. Notice we did not find any brown algae so only green and red are shown.
Note: distinguishing color can be trickier than you think! A good rule of thumb; dying algae can lose its color, but greens and browns will never look red. Also, there are few browns you will see in the waters of Narragansett Bay and are most often found attached to rocks; if there are bubbles or air pockets on it, it is a brown algae.

Once you have your sample separated, you will need to weigh each sample. First weigh the bag so you can subtract that weight from your total. Weigh each color separately and record your measurements on a piece of paper. Once you have measured all three individually, put all three in the bag and measure the total. This will help verify your measurement and account for any evaporation.
Note: some samples may be too large to measure all in one, so you will need to break it into two part measurements.
Weigh the algae using a hanging scale and plastic bag.

Repeat these steps four more times to get a total of five samples. Using these numbers you will be able to calculate the total biomass of your shoreline. You will need to calculate the area of your shoreline and your quadrat as well as the percent of the total for each color and sample. Below are some equations you will need for your calculations.

Area = length multiplied by height. (Be sure to use consistent measurements, for example meters (m) and centimeters (cm) OR foot (ft) and inches (in) for all calculations.
= length(meters) x height (meters)

Average weight = sum of all samples divided by total number of samples
Grams (g) = {[sample 1(g)] + [sample 2(g)] + [sample 3(g)]} ÷ 3 (samples)

Percent = individual sample weight divided by total sample, multiplied by 100%

% = Green sample (g) ÷ total sample weight (g) x 100 percent

Total cover = total area multiplied by average weight, divided by sample area

= total area of shoreline(meters squared) x average weight (grams)
÷ area of quadrat (meters squared)

1 comment:

Will said...

Great article! I'm doing a lot of research into biomass and it's benefits so I've found your article really helpful! Thank you.