Pond Boss Forums INTRO Questions & Observations Secchi Disk

I built myself a new Secchi disk.

I have been fearful of posting about it because it is only 6” (15 centimeters) in diameter rather than 12” (30 centimeters).

How wrong am I?

I don't think it makes that much of a difference. I made mine out of the bottom of a 5 gallon bucket.

A frisbee works great.

Chris, The bottom of a 5G bucket is around 12" in diameter so you are pretty much in line with specs. Do you use a rope labeled every inch on your disk or a stainless steel rod marked in hundredths of an inch?

Not quite.

I used a 4 ft. wooden dowel and marked it every 6 inches.

I use an 8" circle of black plastic mud flap with alternate quadrants covered with white electrical tape. It is mounted on an old broom stick with tape marking off every 3".

Since most of us use different techniques and eyes to measure secchi depths I think internal consistency wrt what you use and how you do it are more important than worrying about what exact object you submerge.

My Secchi reading this afternoon was 50 inches, that is why I use a small rope with labels to drop it down.

In case anyone is interested:
The secchi disk was invented by the Italian Astronomer Pietro Angelo Secchi circa 1860. In 1865, Pietro Secchi was asked to assist the commander of the papal ship S.S. I'Immacolata Concezione in measuring the transparency of the coastal waters of the Mediterranean Sea. Secchi experimented with two types of disks, a 43 cm disk of white clay and a 60 cm diameter disk of sailcloth painted white and stretched over an iron ring. Secchi lowered the disks until they became invisible; this depth was thereafter known as the secchi depth. Secchi tested brown and yellow disks; occasionally he would shade them from the sun with umbrellas or hats. He also tested variations in the secchi depth in calm and stormy waters.

Sounds like a Jeoparody question. He invented the Secchi Disk.

Alex, who is Astronomer Pietro Angelo Secchi?

6 inches ought to work OK.

I work in the water quality field and have taken a few thousand secchi readings. More important than size of your disk is consistency in how you take your reading. Always take it in the shade of the boat and never with sunglasses on. Ropes are also a bad thing if you are taking depths deeper than about 3-4 feet; most ropes stretch when wet and will give innacurate data. The disk should also be painted in non-reflective (flat) paint.

The only reason you should worry about the size of your disk is if you want to compare numbers with other people or reference info. A small disk will disappear slightly sooner and a larger than standard disk will stay visible for slightly longer.

Using a standard size disk is also helpful when you lose the first one and can't remember its dimesions. I've had two coworkers lose disks when they just simply dropped them.

Standard is 20 cm or 8 inches. Problem with some homemade is it will not sink thus the reason for mounting on a stick, etc. I have not noticed the line stretch on ours b/c it is always same amount of weight. I tired this it does not make diff. We mark it every 6 inches you can guess between these marks. You can make your own but we got tired of payiong $40 from other aqutic sources so had 100 made up. It is thick pvc with eye bolt. They are $20 and about $5 shipping if anyone if interested. Link is http://lakework.com/cart/index.php?p=product&id=30&parent=5
WOrks fine unless you have a loose knot, sorry bing. I sold out of these at last PB conference. I think they are one of the most improtant tools a pond manager can have.

A friend of mine told the story, of while in graduate school, witnessing a student painting a Secchi disk blaze orange. When asked why, the student responded that he couldn't see the disk while taking readings in his study lake with depths greater than 10 inches.

I've taken readings in some Iowa lakes where you could see the eyebolt, but not the disk. 1/2" visibility is probably not too good for the fish....

I've always wondered why the dark part.

For contrast, I think, DD.

Dwight, if you want to go bigger use the top of a 5 gallon bucket. Poke a hole in it and tie onto it. I use heavy nylon cord. I see no reason for you to try and over engineer, automate, electrify or build a remote sensor.

Dave - You are saying there is no need for a real time computer controlled video Secchi disk feed on the Internet? It would be an intriguing project funded by some stimulus grant money.

This is the Dwecchi disk, out of spec as it may be.

I was expecting calibrated magnetic depth markers on the rope and some waterproof read relays, at a minimum.

Mark Twain.
I use a white coffee cup with lil kids with black hair painted on it. It's all relative. When I lift it and the string measures 3 to 4 pier boards, I'm good to go. I know; not as accurate as the hand and elbow method.

Dwight, you better hang on real tight to that cute yaller rope.
Some whopper will hit that curly tailed grub and make you spill your Corona.

LakeChair GF ordered a secchi disk for me of my own! Will have to get the fav guy "Boy of Summer" to mark for me, will be easy we have no clarity, about 2 feet, maybe that will change with the fish kill, no phos. and drains cleaned, maybe some of our Chara Bombs worked?

Lynda,

"Chara bombs?" So you planted chara to take up some or most of the nutrients to starve the phytoplankton?

Hey Cecil:
We had lots of Chara in our lake before the bad guys nuked us with copper sulfate a couple of years in a row, they killed it all.
GF LakeChair and I harvested some from the best lake which has no zebra mussels - we tied it to rocks and dropped it everywhere. Bill Cody told us of a better way to try and get it going, we will try it this year.

I like meaningful, descriptive terminology like "Chara Bomb"! One of my all time favorties is "Gut Bomb", in no way related to Secchi or Chara.