August Dissolved Oxygen Survey

NBEP, Brown University and Save the Bay conducted a water quality survey on Thursday, August 19th, and results were much better than expected! The west passage (from the Warwick Neck south to the tip of Jamestown) was well mixed throughout the water column.  The only area our boat saw dissolved oxygen levels below 3.0mg/L (milligrams per liter) was in Greenwich Bay, and even then, only at six of the 14 stations.


NBEP surveys all stations in Greenwich Bay, West Passage and meets up with the Brown boat at the southern station in Upper Bay.

NBEP surveys all stations in Greenwich Bay, West Passage and meets up with the Brown boat at the southern station in Upper Bay.

We not longer survey the Mount Hope Bay or most of the East Passage because low dissolved oxygen levels are rarely found and it is logistically very difficult to cover that area with our three boats. At the end of the summer all data will be posted to the Brown University's Insomniacs website.

Again we found Greenwich Bay to have patches of reddish colored water, and the Sea-bird was giving fairly high flourometry readings (Chlorophyll levels in the water measured in (μg/l, or micrograms per liter) , so we took some water samples with our fine mesh net to analyze back in the lab. Professor David Borkman was kind enough to come help identify the species, which he determined to be Procrocentrum micans, Dinophysis accuminata (not pictured below), and Sanguinium akashiwo.

Lesley and Chris collecting a water sample in Greenwich Cove.

Microscopic view of Sanguinium species.

Microscopic view of Prorocentrum species

Most folks know about eelgrass (Zostera marina), and it's benefits to estuarine critters, however, there is another species of seagrass living in Narragansett Bay. While surveying Apponoug Cove in Greenwich Bay, we came across large, floating patches of widgeon grass (Ruppia maritima). There are several species of seagrass found along the Atlantic Coast, however, many species such as turtle grass (Thalassia testudenum), and manatee grass (Syringodium filiforme) are found only in the warmer waters, south of the Chesapeake Bay.

Underwater Video image of a healthy bed of Ruppia maratima at the mouth of Apponaug Cove.

Patch of R. maratima floating with seaweeds Polysiphonia and Ceramium in Apponaug Cove.

Seagrass is an important estuarine habitat for many reasons. Seagrass beds provide shelter, and feeding grounds for juvenile fish, crabs, shellfish, and birds, and act as a biological filters and erosion control by trapping sediments in its interconnected root structure known as rhizomes. Historically, the southwestern part of Greenwich Bay (Greenwich Cove) was known as Scallop Town because of its healthy beds of shellfish living in and among the seagrass. Unfortunately, seagrass beds have been in decline over the years and efforts to re-vegetate affected areas has had mixed results. Much research has gone into understanding the decline of seagrass beds throughout the Atlantic Coast and globally. Some of the major factors in the decline of seagrass has been attributed to the "wasting disease" of the 1930s, dredging, oil leakage from outboard motorboats, hurricanes, and increased macroalgae due to eutrophication (excessive nutrients in waterways). Boat props can also damage seagrass beds, so it is important to be aware of the area you are boating in, and avoid traveling through an area when you see plant life in your wake.

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.

M² = 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

M² = total area of shoreline(meters squared) x average weight (grams)
÷ area of quadrat (meters squared)

August Video Survey

We had another great video survey this week! However, the currents were strong which made getting sediment samples difficult because the sediment grab kept on getting swept on its side, causing it to drag sideways along the seafloor, collecting sediment on the top, rather than closing around a proper sample. For many of the stations four times was the charm!

Dropping the sediment grab.

Collecting a sediment sample.

An improper sediment grab
(notice the mud sitting on top of the grab).

While Shelley, from URI was gathering sediment samples with her crew, Chris and Lesley were collecting water samples, measuring water quality with a YSI at both surface and bottom depths, and dropping the underwater video camera to get a look at the seafloor.

Setting up the underwater video camera.

Collecting a water sample.

Dropping the YSI for a water quality reading.

Our survey finished up with a family of swans crossing our path in the Greenwich Bay Marina. Although not as majestic looking, baby swans are hardly ugly ducklings!

Family of Swans crossing the shipping channel in Greenwich Cove.