Pond Boss Forums MANAGING AN EXISTING POND Fertilization Zooplankton Growth?

Need some help understanding what's happening with my pond. I've read some threads on phyto- and zooplankton and have been monitoring my pond more closely this year. The pond is in central Illinois and is ~1 1/4 ac in size and averages ~10' deep. The pond is a former limestone quarry and the total alkalinity is ~180 mg/l (pm). No need to add lime, ever!

The good news is all the large common carp (not sure if little ones remain) have been fished out. With the carp gone, the water clarity improved greatly as I can now easily see ~4' deep rather than ~1.5' from all the carp-generated suspended solids. The bad news is the aquatic weed growth is on steroids. Early in the spring there was a good phytoplankton bloom light green in color. As the water temperatures increased, the light green color began to decrease as the weed growth began to increase. The water became increasingly clear with the exception of when algae attached to the bottom of the pond began rising and introduced some turbidity. Surface algae remains on the perimeter of the pond in most area and does not look like cyano-bacteria. The water is now once again very clear.

My question is how to stimulate zooplankton growth rather than weed growth? My phosphate level in March was ~0.5 mg/l and has decreased to ~0.25 mg/l. I attribute the decrease in the P concentration to the weed growth uptake. I do not want to add more P since it may result in more weeds instead of more zooplankton. Any recommendations? I feel like I'm missing something fundamental here. Thank you!

Some of the quarry ponds in my area have very little aquatic plant growth around the shoreline - which is atypical compared to the more conventional ponds frequently discussed on the forum.

Is your shore mostly steep rock sides dropping nearly vertically into deep water?

If so, then nearly all of the "fertility" of your pond is available ONLY to suspended organisms.

Do you have a shallow end with some decent substrate? One option would be to plant some desired aquatic plants. Hopefully, that would take up some of the fertility available to the photosynthesizing algae, yet not impede the food chain for the zooplankton. If the rest of the pond is a relatively hostile environment to rooted aquatic plants, then you could even plant some of the slightly more aggressive "spreading" species.

Another option is some floating islands of plants. I have seen quarries with visibility down to 30'. Maybe some floating islands would take up some plant nutrients and provide a little shade or hiding places for your fish. (You should be able to find some old threads using the search function.)

Finally, dyeing your pond water is a common option on Pond Boss as a means to suppress the growth of filamentous algae. Especially, when the water is so clear that the algae is capable of starting its growth on the bottom in "deep" water. I do not know how much effect dyeing the water will have on your zooplankton food chain. Perhaps you could start a new thread on that specific option if you want further info, and some of the experts might chime into your thread.

A 1.25 acre quarry pond sounds like a beaut' to me. Good luck with your pond improvements!

Good point on the limited shallow zones with the pond. This pond has <10% of the shoreline with a relatively shallow slope before dropping into deeper water. Most of the limestone quarry ponds in the area lack shoreline vegetation with the exception of those surrounded by a tall water reed type of invasive plant (I don't know the name but I don't want them around my pond and actively work to keep them in check). The floating island concept is a good one to try. Dying the water is not an option for a number of reasons.

Was hoping to find a way to stimulate zooplankton growth with the existing phosphorous concentration. Perhaps aquatic plants harvest P at a lower concentration than zooplankton?

3Ponds, the problem you now face is the direct result of removing so many carp. To be sure, carp can be a problem that causes harm when their standing weight is excessive. But carp do something few other fish can do. They aerate the benthic sediments and mobilize nutrients increasing the production of phytoplankton and increasing the carrying capacity of fish that directly or indirectly depend on the food chain that arises from the phytoplankton. A good phytoplankton bloom and even a reasonable amount of turbidity will greatly reduce the plant problem you are mentioning. IOWs a sufficient standing weight of carp will probably put you in better place than you are now while not getting you into the situation you were before.

I'll probably take some heat for this but this is what I would do were it my water. I would hope that a few carp remain. I would take the pressure off of them and allow what is there to grow until there begins to be a turbidity problem again and then I would harvest the carp more sparingly on an annual basis. I've read somewhere that around 180 lbs/acre (200 kg/ha) of common carp begin to be problematic but that this can vary being a higher number when the water is more fertile. Did you weigh what you removed or can you provide an estimate of the total weight of carp removed? Not knowing anything and assuming a problem at 180 lbs/acre .... a harvest of 50 lbs each time turbidity becomes a problem might give you the best of both worlds. If they spawn well. The YOY are incredibly good food for predators. Just consider them a prey fish that you have to manage. Just like TP are prey fish you have to manage. Except with TP you will have to buy them and put them in every year. With Carp you might have to remove a few every year or two. Given you would need to remove carp, I would only fish for them when you intend to remove them. Don't make them more difficult to catch.

I found the article to which I referred to above. Read this if you are interested.

jpsdad, thank you for the article, it was a good read. Here's some detail on the pond's carp population. Since acquired ~4.5 yrs ago, 13 carp have been removed with an average weight of ~15 lbs/carp, a total of ~195 lbs of carp. The ponds surface are is 1.06 acres (Google Maps), This puts the original carp loading of the pond at 184 lbs./acre, which is near the concentration target you mentioned. At this carp loading the pond was very turbid and the fishery was fair at best. This may also be a function of the previous owners management practices or lack thereof. Moreover, if the ponds fish carrying capacity (pre-pellet feeding) was ~500 lbs. fish/acre, 40% of the biomass was carp. The reason I started removing carp count was my belief that 1) lowering the turbidity would help the LMB and BG and 2) the carp were probably eating A LOT of bottom dwelling bugs that would now be available to the BG.

Now getting more into the details, the 13 carp were primarily removed in two fishing seasons, 2019 (8) and 2022 (5). The pond turbidity before 2022 was improved, but still cloudy with suspended solids (could see down ~2-3 feet on GOOD day, usually <2'. The fish population was greatly improved through a combination of pellet feeding, selective culling, and re-stocking. I'm unable to quantitatively relate the removal of the 8 carp to the improvement in the fish population given all the changes being made at the same time (the pond as purchased was a train wreck in need of dramatic changes). The remaining 5 carp were removed between July - October last year. Every time a carp was removed, the water clarity improved.

It wasn't until this year that the weeds exploded with the clear water and my new learning that the available phosphorous would be used by the aquatic vegetation and not necessarily by phytoplankton (other than early spring) to produce more zooplankton. I cannot tell any difference in the fish population from last fall, when all the carp were finally removed, until now.

This begs the question of what to do next. I'm not yet sold on releasing common carp or a grass carp or two back into the pond given the effort required to fish them out. Plus, even a few of them may comprise 10-20% of the fish biomass. In addition, the article noted that in large lakes, common carp biomass is often negatively related to the abundance of other fish, especially BG and LMB. The most important reason may be habitat degradation by common carp, which increases the turbidity of the water in the lake through its benthic foraging behavior, switching lakes from the clear- to the turbid-water state (Stewart & Downing Citation2008). I recognize that my pond isn't a large lake, but the principle is the same. Using the carp to add turbidity will decrease light penetration and weeds. They may also improve the zooplankton population, but I don't know by how much and to what degree this would help LMB/BG fry grow bigger faster.

Not sure this info helps, as I'm still undecided on the path forward. Just wanted to share the background detail and current conundrum.

3Ponds,

Common Carp are under fished and definitely under harvested just about everywhere. There are lots of examples of detriment caused by standing weights that are too high. On the other hand, I have also seen data that suggested the other side where, for example, there was positive correlation between Common Carp and LMB standing weights. To be sure, I agree you had too much standing weight. But you have them and it may be very difficult to get rid of all of them.

I wouldn't be to concerned about the standing weight taking up niche for BG and LMB provided you keep them below your BOWs critical threshold. I think probably a good litmus test for that is the level of turbidity. They use a niche that the BG and LMB cannot access and in doing so they free nutrients that would otherwise not be available to the food chain for the BG and the LMB. So below that critical threshold they are probably increasing the carrying capacity for BG and LMB. Much like TP do but with regard to the sediments the Carp go much deeper to forage and have a more profound impact.

Finally, don't add any and don't release any you catch. I would have done the same as you ... that is ... I would have fished for them and took them out just like you did. I am just saying that especially after seeing the water's reaction to the removal ... that I would seek to harvest more when the turbidity becomes a problem again ... but probably not until then. A kind of don't fix what isn't now broke approach. If you still have carp, they are going to grow into the vacuum the removal created. If you caught them out, they will no longer be a management issue for you.

It is possible that you only just now broke below the threshold and that now the standing weight of carp is around 105 to 180 lbs/acre (assuming that 180 lbs/acre is the threshold). What I find interesting is how each one harvested increased clarity. So maybe now something along the line of 30 lbs each year may be sufficient. If your water is very clear, then there isn't much of bloom going on in the water column. Keep in mind, even slightly turbid water with more nutrients may produce more lettuce for the food chain than strictly clear water or water that grows macrophytes instead. You just don't want the turbidity to offset the benefit of additional nutrient cycling.

Plants are a challenge. There is benefit to having the right amount but too many and they have their own set of problems. There are some members who have extensive knowledge about chemical control and hopefully they'll drop in. If you inhibit the macrophytes and FA then phytoplankton will grow in their place.

Just a question. Could something like Gypsum or Alum work to inhibit the suspension of sediment from the carp foraging activities?

jpsdad, I'm coming around to the logic of managing the pond biological productivity indirectly by managing the turbidity, which in turn means managing the common carp population given the positive correlation between Common Carp and LMB standing weights. It may only take a few fish to achieve the right balance. As of now, I'm 90% confident I have them all out, at least the large ones. I could start by adding one big one from an adjacent pond that has some monsters in it. The other concept is to add more than one of the same sex carp if there's a way to determine male vs. female (probably is, I just haven't looked into this). Thanks for your guidance. Radically changed my thinking on managing the situation.