Are there any studies on what percent of the snow cover needs to be removed over ice to prevent a fish kill? I know that every situation is different, but we will have over 6 inches of snow over ice for the foreseeable future and I am wondering if clearing a 10' x 10 area on a 1 acre pond will have any real effect? Guessing that a lot of ponds are in the same boat.
I was out shoveling today to rearrange some snow to create some snow free areas on the pond. Ice under the snow had primarily a clear top; very little cloudy ice developed this winter on my pond. Clear top ice is unusual for my winter iced pond conditions. Thus the sunlight can penetrate easily through the clear ice and easily stimulate DO production deep in the water by the phytoplankton: thus I did not clear the snow from shallow areas.
In the next few days I will collect a winter pond water sample and analyze it for phytoplankton. I will report back here the results to give readers an idea of what the phytoplankton is doing in my pond with 7 inches of snow cover on the ice. Stay tuned to this Pond Boss thread.
Bill, we finally had courage to put the snow removal machine (4 wheeler with plow) on the ice. We had heat trapped under heavy layer of snow since early December and edges stayed soft. Even the bitter cold wouldn't firm up the edges. Finally some of the snow melted and the cold won out. We have layers of ice, frozen snow and then ice on top. Got the ice cleared and pond flooded for skating finally in February!! Need a few more floodings to get to that super smooth ice. I'm happy last weekend that the sun had 2 days of direct access through clear ice to help whatever plants are in there to make some oxygen.
At a small pond down the road the nephews got to do some ice fishing and tied into a skinny NP. It is lots of fun for the kids to be able to walk where they want and see the fish through the hole in the ice.
RAH - I think you are very correct - ".... that every situation is different". Probably very different In my experienced opinion 1. The deeper the pond the larger the DO amount of consumable oxygen that will be present in the pond due to lower surface to volume ratio. The shaller the water the quicker the water layer above the bottom loses its DO. When the DO is below what it requires for that particular specie at that temperature to survive then they usually die. Different species of pond inhabitants have different tolerances to low DO or lack of it.
2. Water clarity often has a significant influence on how fast the DO is consumed during lack of sufficient sunlight for photosynthesis going on under the ice during snow covered ice conditions. The clearer the water the deeper sunlight can penetrate into more volume of the pond to stimulate the various forms of oxygen production by photosynthesis usually by most often by winter dwelling phytoplankton. Winter dwelling phytoplankton in relatively clear water can often be as many as 150,000 cells per ounce of water.
3. Most all ponds have a high amount of dead decomposing suspended detritus that creates turbidity in the water column. Thus the clearer the water has less dead suspended detritus that is present to be consuming DO. Suspended detritus enveloped by bacteria is constantly consuming DO. Amount of DO consumption is dependent on water temperature. The lower the water temperature the slower and less DO that is consumed. Thus suspended detritus and dead dying phytoplankton together due to lack of sunlight can consume measurable amounts of DO in the water column above the bottom even during winter conditions.
3. The amount of dead organic biomass in the pond has a big influence on the rate of DO consumption due to bacterial decomposition. Bacterial decomposition in the pond is by far the greatest DO consumer in the pond. Without sunlight all the photosynthetic activity ceases and then all the plant life as it dies, it decomposes and adds to the DO consumption on the bottom. The accumulated dead organic biomass on the pond bottom is the biggest consumer of pond DO, thus the loss of DO starts mostly on the bottom and advances upward. When DO is exhausted on the bottom anaerobic bacteria begin producing hydrogen sulfide (H2S). H2S is toxic to fish and almost all invertebrates.
4. Ice Conditions. Various winter conditions affect the clarity of ice and how far sunlight will penetrate through the ice for producing DO via photosynthesis. Many times during the top surface freezing conditions snow accumulates and with any melting snow and refreezing this creates a top cloudy layer. The thickness of this layer varies from ¼” to several inches thickness of cloudy milky ice. Obviously this top cloudy ice layer inhibits sunlight penetration. Here are some examples of light transmission through ice for sufficient photosynthesis of algae and plants (Mgmt of Lakes and Ponds G.W. Bennet 2nd edition). Some photosynthesis can occur when 10-12% of the light on the ice reaches the water below. 7.5” of clear ice permits 85% of the light to pass through 1” of snow over 3” of clear ice stops all but 10-17% of the light 5” of snow over 3” thick of clear ice allows only 2.5% light penetration. 15” of clear ice with a cloudy toping permits 11.5% of the light to pass through
Water under ice needs penetration of 10-12% of the light for some dissolved oxygen to occur from the plants. In one reference I found, if one can diligently keep about 1.1% of the pond area as snow removed from an ice covered pond it ‘should’ allow enough sunlight penetration for plant life to increase the oxygen concentration enough under the ice for fish to survive. One acre of water is 43560 sqft. And 1.1% is at least 400 to 480 sqft such as 20 ft x 25ft.
Note - Some have suggested if one can create 10% of the pond as ice free with shallow water aeration, this will allow DO by diffusion and photosynthesis to be high enough for fish survival. In one acre, this is a shoreline open water area of about a 70ft circle as ~3800 sqft. IMO more research needs to be done on this entire topic. I think the big variable in all this is - how fast does the pond lose its DO? Ponds are highly variable for this DO loss topic as noted in the first sentence of this post and by RAH. Literature showed in one ice/snow covered pond the DO decreased from 12.3 on Feb 12 to 2.4 on Feb 14 about 5ppm per day whereas on another pond with snow cleared ice the DO increased from 1.8 ppm of Feb 5 to 8.0ppm on Feb 8 as 2.7ppm increase per day.
Note - I try to make sure that some of that snow is removed from the shallow areas of the pond where algae & some plant-life are most likely to occur and create DO when those shallow are most likely to receive sufficient sunlight for photosynthesis.
Personally I don't mind non-grammatical titles that include keywords that would allow the most people to find the post.
For example: Snow removal over ice, oxygen, winter fish kill
I am sure the experts can come up with better thread titles. I just want to see people receiving maximum help for solving their problems - I hate reading the PB posts about people's fish kills.
I was seeing the same thing as Bill Cody and some of the above, any place where there was a protrusion thru the ice, that wound up letting water up thru the ice wound up in a huge, 50' plus diameter of water logged snow around the perimeter of whatever protrusion created the hole, the weird part was, even after some really cold weather for several nights, the slush only crusted over and there was still a wet, soft layer between the original ice and the surface which had obviously crusted over but to me should have been frozen solid after several single digit days.
This is a timely thread. I hosted an ice skating/bonfire/dog sledding event last weekend and cleared the pond of snow down to essentially glare ice (cloudy, not clear this year). Although my motivation to do this was for ice skating, it wasn't lost on me that the extra sunlight should give the DO a boost. I use a 40hp tractor with a front mounted snowblower, then drop the back blade to skim off the remainder.
In retrospect, I suppose I could have taken a sample and analyzed it for DO before and after. Unfortunately, the big snow storm that hit the Right Coast laid down another 15" of snow within 48 hours of clearing it so it's dark down there again. After reading this thread, I'll get back out there on the tractor this weekend to clear a path around the shore for skating, but I doubt I'll clear the whole pond again this year. A 12' wide path around the shore edge will hopefully be adequate to keep some O2 production during these cold months. If I remember to, I'll auger a hole to get a sample to test my DO currently.
For what it's worth, I added 750 pounds of ag salt to the pond about a month ago. I didn't do it quite as suggested by Rod, although that thought went through my mind. The pond already was pretty locked in ice for the season, but there is an inflow and outflow that are running. I've never tested the volume, but I suspect it is 25-50 GPM. It flows quickly enough that it didn't freeze even in our -10F temps. Anyways, I poured the ag salt in a small pool area at the inflow and allowed the current to dissolve it. I checked a week later and it was all gone.
My motivation to do so was a water test I had done by Texas A&M that showed my salinity was 0.031 ppt (optimal range 0.5-3ppt). They suggested "150-200 lbs of non-iodized stock salt per acre foot of water to get them into the optimal range for fish". That would be about 3,000 lbs of salt total. I bought all that the ag store had, figuring something was better than nothing. I'll send off another sample, however I wonder if it will all just wash out eventually given that I have a constant flow of water going through. I suppose the results of the next sample should help answer that.
RAH - Here is what I think caused some holes in the ice cover with unfrozen water away from the pond edges. My pond also had 7"-8" of snow cover on mainly 4" of ice. When I went out to collect my water sample by drilling a 6" hole in the ice, the weight of all the surrounding snow on the ice caused a lot of weight on top of the ice. All this snow on only 4" of ice put downward pressure on the iced snow area around the newly cut hole and water started noticably upwelling through the hole onto the ice until the down pressure was not strong enough to force anymore water onto the ice. After a short time while collecting the water sample, I was standing and slipping in at least 3/4" of water with water still upwelling out of the hole. The next morning I estimate at least a 50ft diameter of underlying snow of about 1" thick was water logged and then later refroze in the 0F-5F nightly temps. The next day there was still some unaffected clean snow topping the frozen snow layer below. I have seen this type of thing years previously. However in those years the nightly temps were not cold enough and the next day a slushy layer of wet snow remained under a thin layer of frozen ice.
With enough snow weight on 4" or less of ice this down pressure from snow weight I think will evenutally cause water to start seeping up through a crack or thin spot in the ice. As the water finds its way to the top of the ice, the moving water gradually melts some ice and enlarges the ice hole to allow more water to upwell through the ice hole or widen the crack. This keeps occuring until the down pressure of the weight of the snow equalizes to the strength of the ice thickness. When a pond freezes, I find that the increasing thickness of ice surface layer is not perfectly level and some pond iced areas are a little higher than other areas probably due to the expansion of the ice will heave or force some areas of the pond surface upward.
As a beer league hockey player, I am always interested in trying to get my pond ice in a good state for skating. This year has been troublesome! The first part of winter, we were low pool, but the ice surface was in decent shape, except for a very slow rise in water. This opened a gap in the ice around the perimeter of open water, while the center floated with nice 3-4” ice. Of course nobody wanted to play on that as the pucks would all be lost quickly. Plush it was sketchy near the edges.
Then we had a thaw, and the water level rose to full pool. It lifted my dock with it, and left that nice sheet of ice stranded 4’ out in the center. The ice melted enough that the 500lbs of concrete blocks pushed the dock back down at least.
Then it refroze to the edges, and was well ripened until we had a wind storm. That popped holes in the ice, and pumped water in and out of the holes with the wind. 5” of ice compromised by that wind storm! However, that resurfaced the ice into perfection when it finally refroze. Then we had 4” of fluffy snow, and the ice held up well. Nobody was able to come help shovel off a rink, but that appeared to be the one good day.
Then we got 18” of snow, and the weight pushed the ice downwards, and a lot of water flowed into the snow. The thin layer of snow left on top is excellent insulation, so it took a long time to refreeze. Now it is like frozen layer cake. Useless for skating, yet very thick, especially in the center. Last time I checked last weekend I stopped drilling a hole at 6” where previously there was no ice. It hasn’t gotten above 12 degrees since then.
It is the longest stretch of below 20F weather here since 1979 when Lake Ontario froze from shore to shore.
"how large an area is typically impacted by limited mixing and diffusion?" Or, "If the cold water in the open hole has a concentration of 13-14 mg/L of oxygen, at steady state, how far from the hole must you be before the oxygen level is lethal, assuming no additional sources of oxygen?"
My commentary - To my knowledge very little testing has been done for the amount of water current movement that occurs from a bottom diffuser aerator. Depth placement of the diffuser I think will have a significant influence on how far the diffuser currents spread. One has to keep in mind that water that is at a uniform 39F will move and spread a lot further distance compared to summer water temperatures. IMO the water will spread a lot further than one would expect.
Solar radiation through the iced shoreling areas causes water current movement.
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If you can only do "partial aeration" of a pond, and the pond is getting close to winterkill low oxygen conditions, are the fish capable of sensing the column of aerated water and congregating there until conditions improve?
After thinking about this especially during iced winter conditions, I believe that the sound of the rising bubble plume and is perceived a long distance by fish. I don't think we realize how sensitive fish are to their surroundings. Fish can readily feel water movement, current and underwater sounds. This is the habitat that they grow up in. This is their adapted world. For them, sensitivity is critical to survival. IMO bubbling action at one end of a 1 acre ice covered pond will be perceived at the opposite end of the pond. The bubbling sound in the middle of a 5 acre pond during calm winter ice cover may even be perceived throughout the entire pond.
Bill, you are correct about how sensitive the fish are. In the summer, I can walk to the feeder and the fish can "hear" me walking. They start swimming to the feeder because they know I will throw out a couple handfuls of food.
While I still have ice on the pond, I can do a test. There is open water to the shore in my pond from the winter diffuser. I have 7" ice on the pond away from that open hole. I can take a 10' piece of PVC pipe, hang my O2 meter sensor from it and take an O2 reading. Then I can take readings away from the open water all across the pond.
My question to you is at what water depth do you think I should test the O2 concentration in the open hole? I will have to take the sensor to the PVC pipe and hold it out from shore. I have depth markings on the sensor cable.
