The Watershed Vol. 4, no. 2, pg. 3
Pond Samplings
In addition to rather warm temperatures, there was a drought this summer
that lasted from mid-May
through most of August. This created perfect stress conditions for our pond: no rain to
dilute the nutrient-laden water inflow into the pond; essentially no flushing with seawater
from Vineyard Sound due to the high silt ledge in Trunk River, and temperatures that were
ideal for rapid growth of algae and pond weeds. Would the pond pull through, or
would the algae take over and lead to anoxic conditions? There were times in early summer
when parts of the pond were dotted with small islands of thick mats of yellow-green algae,
when the fish traps came up enveloped by slimy long strings of algae, and the water then
had a faint foul reek to it. Yet, there were lots of fish and insect larvae, the algae
receded, the pond water became clearer again and no longer smelled foul. The pond did
pull through.
Pond level:
Although the level in other Falmouth ponds
and water reservoirs fell considerably due to the drought, the level of Oyster Pond
continued to be 6 inches above "design" level all summer, and up to 10 inches
higher in the fall, because of the silt ledge in Trunk River. Few of even the highest
tides reached the pond.
Salinity and Dissolved Oxygen:
Salinity has become rather
low 1.3 ppt -- and uniform down to 5m. This lack of stratification allowed the bottom
waters to mix with the upper layers during stronger winds so that oxygen was found even at
the notoriously anoxic 4 and 6 m deep basins during one summer sampling a most unusual
condition.
Frogs:
Salinity was so low that frogs (bull frogs?) mated
in the pond this year, keeping up a bellowing ruckus (quite a contrast to the sweet chiming
of the peepers) from spring through at least half the summer. Their tadpoles were numerous
and grew big and fat and presumably turned into an army of frogs.
Turtles:
Sadly, two painted turtles (about 6 inches each)
were found dead on the road (one on a Ransom Rd driveway, the other on Oyster Pond Rd),
but a live one was also encountered, on Surf Dr by the weir, and duly helped across the
traffic-busy road. It is nice to know that there still are some painted turtles left in
the Oyster Pond watershed. Snapping turtles on the other hand are quite numerous and reach
respectable size in the pond. They apparently are cannibalistic: While inspecting a freshly
killed 15 inch turtle on a dock ramp and wondering who the assassin might be, I saw a huge
snapping turtle make its escape from underneath the ramp. Presumably, it was the killer who
fled the scene of murder.
Fish:
In the spring, marsh killifish showed up in traps
but they vanished later in the summer, at which time rain killifish made their appearance.
The most abundant species was the banded killifish. There were plenty of big (1 year and
older) but few young (this year's spawn) white perch this year perhaps the tadpoles got
the better of them or the early algae bloom did them in, or has the pond become too fresh
for their successful breeding? Alewife, hatched in the pond, schooled at the weir in the
fall, gathering courage for the dash through the dark and dangerous culvert into Trunk
River Lagoon and from there into Vineyard Sound. Eels thrive in the pond and frequented
the minnow traps. Sticklebacks were numerous, silver sides rare.
Birds:
The birds wintering on the pond were described in the summer edition of the Watershed. The summer’s news were the many swans. Up to 40 (yes, forty) of them called Oyster Pond home and grazing ground. Who knows: the pond might have turned into a meadow had they not been around to pull and consume those abundant pond weeds. The ospreys were there again, but not so frequently as last summer, perhaps a sign that fewer herring came to spawn.
Mammals:
Although I suspect they were around every now and then, I did not see any otters during the summer. However, muskrats were busy, including one that has its burrow right by the culvert. Quite active were Homo sapiens: lots of boating and swimming activity went on. Rowboats, sculls, sailing dinghies, sunfish, kayaks, sail boards, they were all out there as well as the swimmers for fun and for exercise.
Oyster Pond Reflections, Photo by B. Rose
More Pond Studies
SEA Students Look at Nitrogen and Phospate
The most recent class (W-166) of students from the Sea Education Association (SEA)
studied the nitrogen and phosphate dependence of the growth of algae in water samples
from three different locations: Spohr Gardens dock, weir, and north end of Trunk River
Lagoon. Rule of thumb is that algae growth requires nitrogen concentration at least 15
times that of phosphate (N:P ratio = 15). Trunk River Lagoon samples were found lowest
in nitrogen and phosphate, with an N:P ratio of 4.2, and addition of nitrogen or phosphate
or both showed that growth was stimulated by nitrogen and not by phosphate. At the weir,
the ratio was 16, and growth required addition of phosphate. The Spohr dock data were
inconclusive other than that there, too, the N:P ratio (12) was higher than in the lagoon.
What does it mean? The pond has a higher nitrogen load than the lagoon -- which had a few
rinses by high tides -- and algae growth in the pond at this time may be limited more by
phosphates (watch those fertilizers!) than nitrogen.
Botanist at Work
To learn how the freshening of Oyster Pond affects its aquatic
plant community, Board member Bob Livingstone recruited OPET member Dick
Backus to "inventory" the pond's vegetation. Bob and Dick could be seen out on the
pond in OPET's research vessel -- a sturdy metal row boat donated by the
Hockers, former residents of Ransom Rd -- collecting aquatic plant species for
identification. The Backus method for underwater plant sampling is to drag a rake that
lacks its handle but has a rope instead, along the pond bottom and then haul it up.
Samples have contained a variety of Potamogeton crispus pond
weed which occurs "In hard or brackish water, often where polluted; naturalized from
Europe" (Fassett, 1940 Manual of Aquatic plants, p. 57). The study will continue next
spring and summer when plants bear flowers and fruit -- a necessity for accurate species
identification.
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This page updated July 2, 2002