I have three small ponds in the backyard of my suburban double lot. Two goldfish ponds bristle with rushes, cattails, lilies and irises, and the occasional bullfrog. I’ve devoted the third pond to a fishless preserve where Pacific Tree Frog tadpoles have better odds of growing up, without fleeing from ravenous, larger goldfish.
I manage that pond as the Frog Mitigation Area (FMA), pursuant to the Frog Environmental Regulatory Commission’s (FERC) Record of Decision, issued in 2014. The ROD contains 763 conditions of operation. Condition 1538.5 states, “The FMA operator shall spend a lttle too much money every year on cool scientific stuff if it can be rationalized that it will help the tadpoles.”
The Backyard Science group features The Daily Bucket. Here we—and you—can record our observations of the world around us. Insects, pretty places, fossils, climate, birds, flowers and more are all worthy additions to a Bucket. Please let us know what goes on around you in a comment. Include, as close as is comfortable, where you are located. Each note records a reference for the future, as we try to understand the glorious life cycles unwinding around us.
Unfortunately the FERC inspectors arrived unannounced at the FMA last week to verify my ongoing permit compliance, even though I was previously assured those conditions were “just a formality.”
They cited me for non-compliance with condition 1538.5, claiming I failed to make adequate purchases of scientific tools, even though I had purchased a pH meter.
So, to abate that violation, I purchased a Milwaukee Model MW600 handheld meter with a digital display, for measuring Dissolved Oxygen (DO) in the Ponds’ waters.
Aquatic life needs oxygen. Oxygen enters water by dissolving from the air, and water plants discharge oxygen during photosynthesis. Turbulent water dissolves more oxygen from the air than does water in a quiet pond. Cool water holds more oxygen than warm water.
Decaying organic matter in the water, on the other hand, consumes oxygen. Hot water can’t contain as much oxygen as cool water. These factors reduce DO concentrrations.
Critters with gills don’t have to work so hard in water with high DO levels. All aquatic critters and plants need oxygen for respiration .
DO levels are so important that regulating agencies usually require industrial water pollution discharges to not degrade DO levels. (cough)
Typical DO levels in surface waters run about 4 to 10 milligrams per cubic liter (mg/l, which is virtually the same as parts per million ppm.)
However, my new meter can only test in moving water. The how-to handbook suggests “manually agitating” the meter in the water. In my tepid ponds, I was churning the water until my arm got tired but the meter wouldn’t calm down on a number.
Finally I just turned on the pumps and tested in the flowing water right below the pump nozzles. The FMA’s pear pond DO level ran a little low at 6 ppm. A nearby larger pond was about the same. But my largest pond had a very low water level due to the recent hot weather. It tested at only 1 ppm of DO.
I was aghast. I don’t know how the gold fish (and bullfrogs) were staying alive in there. The pond is full of plants so there’s a ton of photosynthesis going on that should be returning DO into the water, but no.
I promptly stuck the garden hose in and filled that pond back up, and ran the pumps for all the ponds for several hours.
Today all the ponds are over 7 ppm. Recent studies have documented amphibian survival in backyard ponds with DO as low as 2.6 ppm.
I became concerned about the DO levels because I was reluctant to run the pumps in Pear Pond while the tadpoles were so tiny during the spring. Tadples are weak swimmers and the pump could draw them in and produce tadpole sushi. Without water movement, the DO levels would fall.
I screened the pump intakes but I fear my effforts didn’t meet the requirements of Section 316(b) of the Clean Water Act. Freshly born tree frog tadpoles are very small; Here’s an photo of young tadpoles next to a hairclip.
Next, for comparison, is a pic of the hair clip next to the pump filter mesh. There’s a hairclip next to the mature tadpoles in the first picture of the Bucket also.
As an interim measure, I ran some hose water into the pond every day. I noticed how the tadpoles became very lively after a few minutes of added, cooler water.
Now It's Your Turn
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