PH ---- Other than dissolved oxygen, acid levels are likely to be my chief water chemistry concern.
Everything in my environment seems to be acidic ---- the rain, the soil, the water and even my own tongue.
---- Luckily, the remedy for this involves applying lime. Lime is cheap. If you overdo it, pump in some acidic water or just wait. The deepest part of ponds tend to be the most acidic, due to all the crap that accumulates. The depths also tend to be the most oxygen poor. Have I touched on what to do with bottom muck ?
Keeping the pond clean, also reduces acidity. I'll regularly check ph, and lime according to need. Most plants that I'm likely to irrigate, will prefer neutral water.
The internet has plenty of bad news for those with very alkaline water. It is more difficult and expensive to remedy.
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Parasites ---- The only parasite issue that affects swimmers around here is " swimmer's itch ". It is associated with a snail that fish eat. I always thought that ducks caused it because the cases I've seen, came from ponds that are filled with duck shit. It turns out that the ducks degrade the environment for the fish that eat the snails. And they eat any fish that strays into their sewage lagoon. The snails thrive in dirty water that has no fish to eat them, and the ducks create that environment. Did I mention anything about my distaste for swimming in duck poo ?
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I think we're done with water issues for now.
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Unwanted critters - MOSQUITOS, leeches, mink, weasels, herons, eagles, osprey, king fishers, raccoons, bears, tigers and other fish eaters.
--- Mosquitos are seldom a problem here. Lots of fish, frogs and dragonflies will eat most in the larval stage. I haven't seen 100 of them, so far this year.
Leeches --- are mostly a problem in stagnant water that lacks fish. If they ever become a problem, a predator will be introduced.
Raccoons, mink and weasels are likely to be my worst enemies. A dog will be trained to pursue them. Traps may be employed.
Fishing birds will be constantly chased off and their flight paths will be interrupted by fishing line strung over the water. A sling shot with clay balls will be employed. The dog will be sent after them.
A few resident swans, geese and Muscovy ducks may be allowed to use the ponds. Something needs to eat slugs and snails that attack emergent vegetation. I'll look for birds that are aggressive toward intruders, so that they can help keep wild ducks and geese away. The dog would need to be taught to leave resident birds alone. Labs are good at that. Many breeds are not bright enough.
Steps will be taken to ensure that the fish have hiding spots. By keeping the water clean and oxygenated, I'll provide suitable conditions for the fish to go into deep water to escape. In many ponds, only the surface water is livable. This puts surface dwelling fish at constant risk of predation.
Dealing with fish predation will be a learn as you go experience. It could go a hundred different ways.
Passive Aeration ---- There will be times when the oxygen can be added to by people and animals that play in the pond. A daily fluctuation usually occurs with the greatest oxygen saturation occurring in late afternoon for ponds with lots of algae and other plants. During the night, plants, fish and agents of decay all consume stored oxygen. In clean ponds, living things consume the bulk of it. In dirty ponds, decay processes can use over 90% of it.
Recreational activities will add oxygen, but not early in the morning when supplies are at their lowest. Certain water toys splash water everywhere.
Sometimes, hot tubs, wading pools etc. will be drained into a pond. This could happen before dawn, if the need ever arises. A series of little waterfalls would serve nicely.
For at least a year, I'll experiment with stocking rates and plant manipulation as my only means of controlling oxygen levels.
If well water is used to top up ponds, it could be pumped through a sprinkling system on a timer.
A windmill would work intermittently as wind is prone to do.