Pond Boss Forums INTRO Questions & Observations sechi disc

Where can I find a sechi disc to check the visibility of my ponds?
https://www.noble.org/ag/wildlife/secchidisk/
Thanks for the help

I've never heard of anyone buying one. They're too easy to make. Get a white disc like the top of a 5 gallon plastic bucket. Almost anything will do. Bore or poke a hole through the middle and run a piece of cord through the hole. Tie a weight of some kind to which ever side will be the underside. You have a sechi disk. Lower it into the water until it disappears and measure the amount of wet string.

You have now.

Bruce did you miss the tornados and get some rain ?

I made mine also with the top of a 2 gal. white container screwed into the end of a 5 ft. broom stick with large washers on each side. The stick is marked every 6in. with depths for easy reading.

Tornadoes died out about 45 miles south. Only got .3 inch rain, but I'll take it. North Central Nebraska is going to be a lake.

Wildco (Wildlife Supply Company) sells them. Here is their main web page. Just search for secchi.

http://www.wildco.com/

No disrespect to anybody who makes their own disk, but I think the point is to give a reliable reference point from pond to pond, anywhere in the world. If you make your own, it would have value for your own personal use to compare water clarity from one point in time to another, but would have reduced value when speaking to a biologist who uses a standard Secchi. For example, if you were to want to make a decision on liming, or alum application, and was giving information on your pond to a specialist, the home made secchi wouldn't give as reliable information as the standard. Just being picky, I guess. Sort of like telling Lusk that your bluegill are as big as your hand. It would give him a general idea, but everybody's hand is a little different size.

So if you are a cheapskate who is going to make your own secchi disk (like moi ), I suggest you try to replicate the standard configuration (based on the Vatican City Navy original specifications) as much as possible. IIRC this is an 8" disk with alternating black and white quadrants. This could be done by adding black electrical tape to two opposite quadrants on an 8" circle cut from the above mentioned white lid. I made mine using white electrical tape on a black semi-truck mud flap remnant. The e-tape on plastic will stay together good in the water over repeated usage.

Bruce, would you care to clarify any wrt offical secchi disk size and weight requirements? I believe hanging it on a string may be the official suspension method, although mine is screwed to an old broomstick. How about usage method? You can get a big difference in reading depending upon whether the pond has direct sunlight or if it's cloudy.

Bruce and/or Doc Willis, can you elaborate on this? I find that you guys generally have a good reason for pickiness and I just might learn something here about the tools Biologists use or their methodology. Doc, neat website full of great toys for a guy like me. Thanks.

Quoting from Lusk's book "Raising Trophy Bass":

"Make a white disc, put it on a cord, lower it slowly into the water. If it disappears before 18 inches, do not fertilize. If visibility is between 18 and 24 inches, it's just right."

"If the disc disappears beyond 24 inches, consider fertilizing."

"Many pond pros tell their customers to stick their arm in the water, to the elbow, and look for fingertips. If the water is so cloudy or rich that you cannot see the fingertips, the water needs no additional nutrients. Do not fertilize. If you can see two feet beyond your fingertips, it's time to consider adding fertilizer."

OK, not everybodys span from elbow to fingertips is the same length. Nor are skins all the same color. I don't see how to really figure out whether I can see 2 ft. beyond my fingertips without making or buying a sechi.

Do Biologists use a professionally made tool to eliminate the questions of whether the string was accurately measured or whether the disc is of a real shade of white? It appears that it makes sure you guys are all on the same page.

Don't forget the wind Theo. LOL! Just when Bruce was about to start the Theo fan club yesterday, you rain on his parade today!

DaveD -- yes, Wildco has lots of good stuff, but all for TOP prices. I guess we're a low quantity profession, eh?

I'll let Bruce tackle the pickiness question a little more. Honestly, I've worked with both home-made and commercial Secchi disks all my life. My favorite was when one of my technicians cut one out of plywood, perfectly to Theo's specifications. He painted it black and white, dried it, painted it again, etc. Unfortunately, when he first tried it without a weight, the readings were always zero.

Yes, Secchi readings vary a lot with wind, waves, time of day, etc. However, it still remains a simple, highly useful tool despite that variability.

Zero, huh? Did you send him back to pick up a few prerequisites? Haven't had a laugh that good in a while.

What is the official shade of black to use?

The Secchi disk originated with Fr. Pietro Angelo Secchi, an astrophysicist, who was requested to measure transparency in the Mediterranean Sea by Commander Cialdi, head of the Papal Navy. Secchi was the scientific advisor to the Pope. Secchi used some white disks to measure the clarity of water in the Mediterranean in April of l865. Various sizes of disks have been used since that time, but the most frequently used disk is an 8 inch diameter metal disk painted in alternate black and white quadrants.

The Secchi disk is used to measure how deep a person can see into the water. It is lowered into the lake by unwinding the waterproof tape to which it is attached and until the observer loses sight of it. The disk is then raised until it reappears. The depth of the water where the disk vanishes and reappears is the Secchi disk reading. The depth level reading on the tape at the surface level of the lake is recorded to the nearest foot.

According to Dr. Lowell Keup, Physical Science Administrator Criteria and Standards, U.S. Environmental Protection Agency, Michigan State University in 1980," ...it is probably the most frequently abused and violated measurement undertaken by limnologists".

SECCHI DISK READINGS -- HOW VALUABLE ARE THEY ?
The greatest value of the Secchi disc measurements occurs when each lake compares its own readings from week to week, month to month and season to season. No comparisons between lakes should be made unless similarities in measurements are followed vigorously. Several factors are involved, such as the eyesight of the viewer, the time of day the readings are taken (midday- between 10 and 2 is preferred), the reflectance of the disc, the color of the water, clay particles or other materials suspended in the water, etc.

Some of the reports for any one season may show an increased water transparency depth after the first week of spring. This may be due to:

Reduced nutrient input from the watershed.
Increased grazing of algae by zooplankton.
Reduced soil erosion into the lake.
Seasonal algae succession.
If the Secchi Disk transparency depths are getting shallower during the summer season, it may be due to one or more of the following:

Increased abundance of free floating algae.
Erosion of the shoreline or erosion from site development near the lake.
Recirculation of bottom sediment from motorboat activity.
Discoloration of the water from wetland runoff and/or plant decomposition.
Increased turbidity.
Reduced zooplankton populations.

Significant storm events within the watershed with the resultant stormwater runoff could cause lower Secchi disk readings. Comparing Secchi disc readings immediately after a storm with readings between storms may suggest that runoff is increasing turbidity and, therefore, shallower transparency readings.

If the zooplankton populations have dropped off reducing the grazing of algae, the increase of algae will result in reduced Secchi disk readings. Dr. Robert Carlson, writing in News CLIPs, published by The Citizen Lake Improvement Program of Ohio, "If you find a sharp increase in transparency in May or June, it might be that tiny grazing animals, called zooplankton ('animal drifters') are eating the algae. When zooplankton are abundant, they can actually be seen as tiny black dots swimming over the Secchi disk.

SECCHI DATA CONTRIBUTES TO LAKE MANAGEMENT

Oligotrophic -- Greater than 16 feet.
Mesotrophic -- 6.5 to 16 feet.
Eutrophic -- Less than 6.5 feet.
One of the major reasons why Secchi disc measurements decrease from spring to fall, is due to the increase of plankton-- both phytoplankton and zooplankton. Since zooplankton graze on phytoplankton, (algae i.e.), the Secchi disc readings may increase during the summer by the reduction of algae in the water. Algae blooms may occur when the amount of available nutrients increases faster than the macrophytes (plants rooted in the bottom of a lake) can absorb them.

SECCHI DISK DATA
Water clarity should be measured with the Secchi Disk once a week from May 1 to September . In order that the Secchi Disk measurement be done to provide the greatest accuracy, the following conditions should be met:

The same person should be taking all readings since sharpness of vision varies from person to person.
The reading should be taken on the same day of the week, or at least not more than one day before or after the same day of the week.
It is preferable that the measurement be taken between 10:00 a.m. and 4:00 p.m. so that the light rays from the sky are at a similar angle each time the reading is taken.
Avoid taking the measurement when the lake is choppy or rough.
The Secchi disk measurement should be taken at the deepest part of the lake. This may be determined by viewing a bathymetric map or using a depth gage.
After anchoring the boat at the predetermined site, take the reading on the shady side of the boat.
The reading should be taken at the same location each week. In order to guarantee a sampling at the same location in the lake, a buoy may be permanently set at the site. If it is not possible to place a buoy at the site, line up two objects on the shore some distance apart (one at the shoreline) and line up two other objects on the shore and at right angles to the plane of the first two, anchor your boat and take the reading. Mark the shoreline objects and the intersect points on your map of the lake so that you will be able to find the same site the following week. If it is necessary that a substitute take the reading later in the season, they will be able to find the same location.
Some lake associations may want to take Secchi measurements at various parts of the lake for clarity comparisons. This may be done, but the measurements should not be part of the monthly report sent into the laboratory.

A Secchi Disk measures water clarity. Water clarity may be affected by three different factors -- algae, sediment and / or water color.

Algae may be free floating or rooted on the bottom of lakes. Chara is an example of algae that is rooted on the bottom of lakes and often forms dense beds that rarely reach the surface. Chara may actually out compete other kinds of plants for nutrients, thereby limiting the growth of less desirable aquatic plants.

Free floating algae may be threadlike or ball like and may consist of a single cell or clumped together and visible to the naked eye. The majority, however are microscopic and only visible under a microscope. EPA posters of algae picture many kinds and examples of algae found throughout Michigan. Biology textbooks divide algae into the more common groups of Blue-Green, Green, Golden, Brown and Red.

Algae are very important to a lake ecosystem. Dr. Richard Pippen writes about the value of algae in an article which he wrote for the Michigan Riparian magazine and appeared in the April l978 issue. He states,

"Algae are the most important element and first stage in the so-called food chain. Algae contain the green pigments, chlorophyll, and thus like grasses, garden flowers, and trees, are able to take energy from the sun and make food out of carbon dioxide and water. Small microscopic animals eat algae and in turn are eaten by larger animals which are eaten by still larger animals until they reach the stomachs of fish. Some fish, such as minnows, feed directly upon the algae, thus directly or indirectly the algae serve as a food source for fishes and eventually us."
Secchi disk readings which show a significant decrease during the summer season and often accompanied by a distinct green, brown or red color are probably due to the proliferation of free floating algae. Only when the populations become exceedingly high or are due to a preponderance of Blue-Green algae should the condition cause alarm. When this happens, the property owners around a lake should determine the sources of nutrient input and take ameliorative action.

Water color data should be recorded at the time the Secchi disk reading is taken. It will help to determine the kind of algae which predominate in the lake at that time.

The most valuable information from Secchi disk data is the graph which shows the weekly changes. Averaging the Secchi disk data for a summer season has very little immediate value. The greatest value of averaging will come when after a period of years the averages will show if the lake's water quality is remaining constant, improving or degrading.

Definition by the Michigan Lake & Stream Association.

I bet Offical or home made reading are skewed by how good of eye site you have. ( My water is clearer without my shades on.)

Polarized Shades work great! Of course those were not available in 1865. I think they just used broken wine bottles for sun glasses.

Thanks Cary. I've never seen anything quite this extensive. Every word of it makes sense. I've printed this one out. It's a keeper.

Thanks, Cary. I had just composed a post that was word for word the same as yours! :rolleyes:

Actually I'll just summarize my feelings on the subject.

1. If you just want to have a general idea as to your water clarity, go ahead and make a homemade disk. You can however, make a small effort to get the size and pattern down, so that if you're providing information to a biologist, the reading will be as accurate as possible. I'm one of those freaks who measures and speaks in metric, so I actually have to convert a lot of my posts to non-metric so you guys don't think I'm a nut.

2. I've found that the secchi disk is ideal for making measurements because the pattern makes it easier to see when the disk is very slowly spinning. It's easier to tell when it has officially disappeared from site because of the gentle rotation.

3. I'm weird.

Here's a quote from my favorite book in the whole world entitled "Fisheries Techniques".

...water transparency is commonly measured with a simple device called a Secchi disk. The disk consists of a circular plate (20 cm in diameter), painted black in two opposite quarters and white in the other two. To determine Secchi disk transparency, lower the disk into the water in the shade until it disappears and record the depth. Lower the disk a few feet and then slowly raise it until it reappears, and record this depth. The average of the two readings is the Secchi disk transparency. Make measurements at midday. Secchi disk measurements have been used in empirical estimation of the euphotic depth, the depth at which 99% of the surface radiation has been dissipated.

Bruce and Dave,

That was just some information I kept around. Again, I can not take full credit for that.

Bruce, Rotating Secchi Disk...hmmmm I see a new invention. Maybe I can get on that TV show "American Inventor".

Plus, Bruce uses the rotating disk to hypnotize the fish and plant suggestions: "You are getting very hungry. You are not interested in spawning this year." Dr. Frankenbruce, fish hypnotist! :p

Actually, I find that a slow rotation makes seeing the disk disappear/reappear easier also.

Bruce is that Fisheries Techniques 2nd by Murphy and Willis pg. 112 ?

Bruce, rotating the Secchi disc instead of keeping it motionless seems to contradict your suggestion about standardizing the sizes, etc,(i.e. home made variety) of Secchi discs so that ones data has meaning when compared to other peoples data.

LRunkle,

I don't intentionally rotate the disk. It does it on it's own. It's actually the combination of the standard pattern and that movement that helps you to be able to tell if you're really seeing the disk, or just imagining that you're seeing it. In reality, the disk only rotates a few degrees, clockwise, then counter-clockwise, etc. I suspect that all Secchi users are experiencing this phenomenon to a certain extent.

...but I do see your point.

Bruce, do you take your sechi disk measurments with your polarized sunglass on? I took a few sechi disk measurement Saturday in the shade of my jon boat, with my sunglasses on. I was actually suprised how far down it took to disappear considering the cold water algea bloom that is still going on and since it muddied up a little bit with all this rain, one measurement was 68", the other was 73".

Should I be doing this with out my polarized sunglasses on?

I always use polarized sunglasses when I'm at the pond anyway. So yes. It seems intuitive to me that you want to eliminate surface reflections so they don't skew your results. I think that may be why the readings are supposed to be taken midday, because if you're looking straight down you don't get a light bounce from angled, unpolarized light. When are we fishing?