Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations Winterkill

I put this here rather than in the aeration section because I think that aeration is only part of the solution.

Here's the scenario:

Northern Pond. Windmill aeration system, no supplemental feeding going on. No underwater plants to speak of in the pond.

A fellow PB'er had a 1 ac groundwater pond dug in 2008. The pond was dug in a wet spot in a mature woods, with trees 40'-60' tall surrounding the pond on all sides. There is a 75'-100' perimeter grassy area around the pond before the trees start.

It's water level has flowed and ebbed with the groundwater level, due to the sandy soil - no clay available to line the pond. The pond was spec'd. out at 12' deep in the deepest area, and the contractor made the sides roughly 2:1. Right now the pond is sitting at .72 ac, measured with handheld GPS with area calculation turned on. Currently, with this water level, the pond has the deepest part at 8'. If asked what the water depth was right now, I'd say 50% of the pond is 0-4' deep, 30% 4'-7' and the last 20% between 7'-8'. I don't know if the pond was ever full other than one time for a few months. If I were to guess, the pond will stay at roughly this level, maybe a foot deeper, but up to 2', maybe 3' shallower during dry periods like late 2010 to early 2011.

The pond was stocked light. First with FHM/GSH then later on with 125 RES that are now 5"-6" and a couple hundred YP that are now 4"-7". This pond stocking plan was to have SMB/RES/YP along with FHM/GSH for forage when stocking was completed. Fyke net survey last year showed no recruitment from either the RES, YP, GSH or FHM, but there was GSF recruitment. GSF weren't known to be in the pond until the Spring of 2011, but in retrospect they most likely were there when the pond was dug in the first place. (seasonal wet area in the woods)

Last winter, the O2 levels were monitored, and it showed a low of 5.9 mg/L with the windmill diffusers turned off. Last winter saw more ice and snow cover than this winter by far.

This winter the O2 levels were not monitored, but the windmill diffuser was turned on. The RES/YP/GSF and forage fish were in the pond last winter.

This October, 100 10" HSB and 20 2# RBT were stocked. The HSB to reduce the GSF population, the trout for the table. The plan was to remove the majority of HSB before stocking SMB.

The ice has been very thin, and virtually no snow cover. All was good until yesterday when a bunch of HSB were found dead. We have had a relatively calm, overcast period the past few weeks. The pond is ice free right now for about 20%-30% of the surface area, and has had a minimum of 10% of the surface area ice free all winter. No fish were noticed piping at the surface, but the pond owner does not live on site.

I counted 49 dead HSB and 1 dead RBT (laying on the bottom) today. I saw FHM and at least one large fish chasing them in the open water today.

The current plan is to drop the water level when temps rise, remove any good fish and relocate them to another pond on the property, then kill the remaining fish with Rotenone, drain it even further and hit it again with Hydrated Lime to ensure all the GSF are eradicated.

There is electric near the pond, and there are plans for a Koender EL2 compressor with a membrane type diffuser to be used in conjunction with the windmill.

What should be done to ensure that this doesn't happen in the future when the SMB/RES/YP/GSH are restocked?

What stocking rates for those fish should be used in this pond?

I think the biomass is pretty light for this sized pond. Going by what was caught in 3 or 4 different weekends of sampling with a fyke net, each 24 hr period showed 40-60 GSF caught, mostly 2"-4" in length. I'm estimating on there being less than 300# (probably closer to 200#) of fish biomass in the pond at the time of the Winterkill.

I think it happened due to (1) warmer temperatures - warmer water holds less oxygen and oxygen is consumed at a higher rate by organisms, (2)several days of cloudy weather - no sunlight, no photosynthesis, no oxygen production, and (3)no wind - no windmill aeration and no surface disturbance or diffusion of oxygen at the surface. The only thing that could prevent this from happening again is a reliable electric air compressor.

Would you mind take the last reading of O2 concentration in the water before the transfer and eradication process? O2 may not the primary suspect.

HSB have high DO needs, especially when larger. Sorry to hear they died on you. I suspect your other fish besides the trout are probably fine.

Leo, that shouldn't be a problem. Sue, I doubt water temp came into play, there is still ice on the pond. Temp shouldn't have changed even one degree. Cj, I don't think all the HSB bit the dust. I saw a swirl in the pond that could only be made by a fish around 10"-12" long. I doubt any of the HSB that kicked the bucket are larger than that. They were stocked the first week of November as 10" fish.

Scott

Why does client want to rotenone the lake? GSF will not likely pose a long term problem with YP, SMB, and HSB hammering them...just wondering why he's so set and starting all over? Not like he has a BH or White Perch infestation....then again, since you are applying the rotenone service maybe I have my answer already! The client is always right!

Is there a chance that groundwater flow through the pond brought on low O2 from the ground water? Since it is capped with ice, perhaps this flow-through removed a good chunk of the O2 and it couldn't be replenished.

Just a guess.

Scott,

Let me know if you want to use my D.O. meter although I'm not sure how you'd be able to get a safe reading with the half arse ice conditions we are having.

Have you had the water tested ? My guess is its not primarily an O2 problem. Did only HSB and a few trout die?

HSB are not particularly susceptible to having O2 problems in cool water.

One thing to note ,which may not be applicable in this case due to aeration, are the studies that indicate that waters which winter kill tend to be repeat offenders over time.

What changes occured over the last mth ? Aeration started , large run off , land fertilized , anything put in the pond , plants die , for example ? Did you look at the dead fish closely? Has /was there a plankton bloom in the past ?

liquidsquid, that is a very good possibility due to the porosity of the soil and the way that the pond is constructed. The pond is built so that ir receives absolutely no runoff from the surrounding land. All water that enters the pond has to come from underground or direct precipitation. The level of the pond has increased about 18" to 24" from October.

Thanks Cecil. I can drop my boat in the open area, or take a sample while in chest waders.

Eric, the HSB and RBT are the largest fish in the pond, and the only predators besides GSF. I'm assuming all the trout died, but I cannot be sure how many of them died unless they float. Only HSB and RBT were observed dead.

Changes in the last month was a warming trend that melted any snowpack that there was, and a melting of the ice. Last week there were a couple of days where the heavy fog didn't burn off until 1:00 p.m. and little to no wind. It's been overcast for a considerable amount of the time during the past few weeks with little wind. Aeration starts/stops with the wind. Diffuser is in 3' to 4' of water, and gets turned off for the summer. Diffusers are placed both deep and shallow in the pond and are switched for summer/winter use. Two of the dead HSB had 1" or so "hairs" growing all over them, but all the rest of the fish that I could closely examine were fresh dead - still had the stripes and their colors. Visibility in the pond has stayed around 36" or so from looking into the water from the bank and is a brownish, not greenish tint. There are oak leaves that blow into the pond during the Fall due to the pond location, but that cannot be changed. In the Fall, when the grass is cut, all the leaves are blown into the woods.

No, the water has not been tested. Would shipping a sample to TAMU frum South Bend, Indina make it in time for the test results to be valid?

There are 2 other ponds in close proximity to this one, within 300 or so yards. Pond #2 is stocked with the the same fish, minus the GSF, HSB and RBT. Pond #3 has BG, PS, FHM, GSH. All stocked lightly, and none of those shows any signs of winterkill. Those ponds are constructed exactly the same as this one and are groundwater ponds as well, but those ponds have electric compressors running the diffusers along with windmill diffusers in pond #2.

Were all the dead fish species sourced from the same place ?

I would suggest you get a water test like those done for a water well. I bet you have a local/state level test source like TAMU also.

Scott,


O.K. here are all the even remotely possibly causes and my comments. Sometimes mortality is caused by a combination of factors but typically hypoxia is the highest probability.

1.) Ground water influx zip in D.O. and the already low water volume (4 feet?) caused a hypoxic condition due to the shear volume of the ground water influx.

Comment: It would have to be a significant influx of low D.O. water this time of year as this cold of water typically has lots of D.O.

2) A lot of snow blew and drifted over the ice you didn't see and had melted by the time you came out? That combined with low water levels could have been a factor.

3.) The fish were caught and released in cold water prior to ice cover by your client or someone trespassed and did so. Having recently been stocked the fish perhaps were already in a stressed condition. Some fish have problems with catch and release in cold water and develop water fungus problems.

4.) The fish went into the pond in less them optimum condition. Or the water chemistry is so different from what they are used to this along with other factors put them over the edge.

5.) The low volume water was subjected to a rapid temp change (dropped in temp quickly) along with a heavy snow fall in open water. We did have sudden cold event this fall although it obviously moderated later.

6.) A sudden influx of ground water or precip caused acid shock. (doubtful in our high alkalinity waters but it's not uncommon out east.)

7.) The ground water in his area is contaminated with something. I'm doubtful of this as you would have seen this earlier.


Did the dead fish show the classic appearance of environmental hypoxia? That is, the opercula flared and mouths agape in a desperate attempt to get oxygen?

It may have been one of these factors or a combination of them. You may never know.

eric, no they weren't, and they were stocked about 3 weeks apart back in Oct/Nov.

I asked the county health department a year ago where I could send water to be tested and they looked at me like I was asking for a 2 headed snake. They had no idea. "Why would you want to do that?"

I think you had a DO sag low enough to kill just the HSB and trout in probably the deepest water or a section of the pond. Ponds typically lose the DO in the deepest water first. Those species not 'trapped' in the low DO or those that ventured out of the stressful water survived. Trout and HSB require higher DO compared to other species in the pond. Vulnerable fish in the stressed area were 'trapped' and killed. I say the deepest water because the diffuser is 3-4 ft deep during winter operation and IMO mixing primarily the upper 4 ft of water of the water column. IMO Shallow water diffusers with gentle, intermittent aeration (windmill sheltered by trees) will result in stratified (chemical &/or temperature) layers. Post kill DO tests in the surface waters (0-4ft) will likely show DO is just fine, esp. true if sunny days have followed the kill. The DO was probably 'okay' in the upper 4 ft during the presumed winterkill.

This system is a low air flow unit. I strongly advise against using this air producer in this application due to: 1. pond receives lots or organic inputs creating a unusually high BOD. High BOD requires the strongest aeration possible. Sewage plants are examples. 2. pond is only 7-8 ft deep and has a low DO reserve. A shallow placed intermitent weak diffuser (windmill) in 0.7 ac increases the chances of stratifiation events. 3. this EL2 unit is a low air volume unit compared to the hp involved. The best choice for this application is a unit that has high airflow per hp such as a rocking piston or rotary vane. A pond this size needs a strong or high volume diffuser and several diffusers. IMO essentially the current aerator is undersized. Ideally I would consider a 3/4 hp RV unit with at least 3 diffusers for this specific application. Considering the history, I would operate at least 1 diffuser in the deep section (20% bottom area) all winter.

Cecil, you are freaking amazing in the deduction. Are you sure you're not an environmental scientist, with a pH also in geotechnical?

Scott, the reason why I ask you to get the oxygen metered for your pond is the same reason that Cecil described.

1. Ground water has a high level of dissolved oxygen regardless of the temperature. Soil strata create an oxygen rich environment, and when the water flows through there, oxygen content get saturated. When you pump it up, oxygen content get stirred, and oxygen remains or enriched, that is, if you're constantly introducing new ground water into the pond..or ponds. However, thermal exchange is my suspicion that shocked the crap out of the fish when new water is introduced if you're trying to fill the pond during winter. Other than that, possible pollutants, pathogens, or bacterial that targeted the fishes.

2. Little does people know, snow do bring in oxygen content due the crystallized structure creating aerated pockets. Snow falling on surface of water will mix oxygen to the surface. Ice will trap the oxygen, but as it melts, it dissolves the oxygen to the surface, thus, fish like to hang about 2 to 5 feet below the ice. Oxygen rich environment.

4. Fish tend to survive by readapting, but can only push for so long. Larger fishes have great affinity for adaptation, so, you don't normally see it until later..way later. If there are 5 conditions you must meet for them to be perfectly healthy, and fulfilled the 3, they will readjust until their bodies become exhausted. Small species will last 2 days observed in the wild. Some will last a year or two based on conditions.

7. Looks like there are signs of something that leech the oxygen content from the water if the fishes show signs of hypoxia. We need that oxygen metered from the pond. Could be a sudden CO2 shift and/or in combination to a nitrate affixiation from the primary pond that get the first wave of ground water.

One thing to consider is the amount of ground water and its temp entering the low cold water pond. If its low O2 and warmer you could get some strange mixing events not to mention the shock/stress effect on the fish. If so then that problem is going to happen again unless avoided by some means.

That's the reason we don't like Cecil taking long "vacations" from the forum...

Hey Leo,

1. Ground water has a high level of dissolved oxygen regardless of the temperature.

Teach and instruct us properly on this statement you made.

Thanks.

JKB, quite simple actually. Imagine the soil strata (soil layers) have various soil type as water go from top to bottom as it percolates from an above ground water source, say a lake, pond, forest ground, or even from rain. As the water moves from the upper layers to the storage area below, like an underground reservoir or aquifer, impurities within the water get pulled from the water molecules, creating a higher ionic charge within the water structure, as the water percolates deeper and deeper into the ground. Pure water, or water molecular structure, is not H20. Rather, it's H2O2. There are still active sites for the oxygen to grab onto other molecules that around the soil. In the deep soil, what molecules are available, beside carbon, silica, oxygen (exist between gaps of soil structures), nitrogen, stabilized metals, and various other inert compounds under extreme pressure? The only thing that being exchanged under high pressure, possibly high heat would be hydrogen and oxygen.

Constant battle to occupy the missing bonds between oxygen, hydrogen, and various other molecules, oxygen is one of the stubborn molecule that will not give itself up. It rather bind to other oxygen, nitrogen, or carbon molecules to find a way to stabilize itself out rather than giving itself up. It will attempt to rip the hydrogen from other compounds aggressive if needed. So, in an underground reservoir, without pollutants within the strata, what can water adhere to but more oxygen and hydrogen molecules? Ground water is loaded with dissolved oxygen.

Just take this scenario. How can underwater creature found in caverns deep in the earth survive with lack of oxygen if the water source don't contain enough dissolved oxygen to survive on? How can cave explorer manage to go so deep into caverns without having continually air supplies given to them? Oxygen get continually renewed as water pull oxygen content from the upper strata to the lower bedrocks and reservoirs.

Hope I don't overstep my explanation somehow..geotechs and geologists? Mind adding more?

Cecil Peed in his tank That's why we Love Him

Amongst other reasons

The shape of a H20 bond allows it to become H2O2 or something else. The bond looks like Mickey Mouse's head with the "ears" being hydrogen atoms and the face being an oxygen atom. The ear want to bond with something negative, another oxygen atom would suffice. While the face wants to bond with something positive such as more hydrogen.

Chemistry, Physics, and Geology are all great!

Can you show us some peer reviewed studies with final conclusions? Just on the one statement!

Reason being, is that a new PB Subscriber might read this stuff and think the planets aligned!

Please back it up!

We are not talking about caves either.

jludwig, love the Mickey Mouse's head analogy. True that oxygen would love to bond with something else positive, but when you're in an compressed environment that search for affinity to stability, which of the element is willing to give itself up more to become stabilized? If there is free floating carbon radicals, yes, carbon will give itself up. If there is nitrogen radicals, yes, it will go to the one that demands it. Oxygen will be aggressive, so, yes, it will pull others to itself. Metals, crystals, they've reached their inert states. Good luck with oxygen in ripping anything out from those other heavier elements.

This is why I'm concern about Scott's pond groundwater issue. It may not be the oxygen. More of the pollutants that exist in the groundwater, and possible thermal shock. Could also be high load of nitrogen/carbon content that cause affixiation, which displayed as hypoxia in the fish. Don't know until the metered oxygen come back.

LOL Planets are aligning aren't they in 2012? Understand completely about the proof required. I will search through my studies and notes again. The similar argument was made by the debate groups in the geology field study I was with brought the same counter argument, "Where's the proof?" over a decade ago. We did a massive collaboration with the geology, environmental, and microbiology department to find all the documented studies as far back as the local libraries allowed. A fun project that lasted nearly a year.