My pond is in urgent need of help!

[JohanJ]

Originally Posted by JohanJ

King Edward, I think we'll just have to agree to disagree I'm afraid. Fact is shallow ponds can and do freeze over killing things - see this link - update on frozen frogs. Totally agree with you though that the marginals are where a lot of the action happens. But no I wouldn't ever make a pond a 100% marginal 1 foot deep saucer shape - I'd hate to end up like some of the people in the link above with dead fish corpses, rotting frogs etc.

How odd. The link on my post above seems to be different to the one I actually posted and doesn't even work anymore. This is the link:

http://xexexexexexexexexexexexexexex...-frozen-frogs/

http://xexexexexexexexexexexexexexex...-frozen-frogs/

[JohanJ]

Ok. There's some weird filter going on. Let's try this another way

Update on frozen frogs The Garden Pond Blog

I wonder why this site thinks it's neccessary to filter out a garden pond blog?!?!

[nightshade]

After netting out as much as he could my UN-wildlifefriendly workmate used one of these Clarke HSEC650A 2 inch Industrial Submersible Water Pump - Machine Mart it pumped almost every thing out!

[King Edward]

Originally Posted by JohanJ

King Edward, I think we'll just have to agree to disagree I'm afraid. Fact is shallow ponds can and do freeze over killing things - see this link. Totally agree with you though that the marginals are where a lot of the action happens. But no I wouldn't ever make a pond a 100% marginal 1 foot deep saucer shape - I'd hate to end up like some of the people in the link above with dead fish corpses, rotting frogs etc.

I don't really see how the comments on the link support your view - I don't think any of the ponds were described as being at the very shallow end of the scale (apart from one 8"-18"). Many seemed to be fairly typical goldfish ponds of unspecified depth. In the Pond Thaw survey I mentioned before, there was actually a positive correlation between depth and dead frog numbers (although this isn't very informative, given that larger/deeper ponds may attract more hibernating frogs and we don't know the percentage of the total that died). This is obviously an area that needs more research.

The ironic thing is also that, whatever their hibernation requirements, frogs much prefer shallow water for breeding (whether as wholly shallow ponds or in the margins of larger ones) - this is exactly the kind of area that gets lost when someone digs their small garden pond down to some great depth. And if a very shallow pond is unsuitable for hibernation, chances are the frogs will overwinter elsewhere anyway (perhaps terrestrially) and so avoid being ice-bound.

And another thing - being inherently less suitable for fish (as you point out), chances are that these ponds are going to be more suitable for fish-intolerant wildlife on that basis alone. In general, garden ponds also tend to be on the deep side for their size (only 7% in the survey were under 1' deep, compared to 42% over 2' deep, which is probably not atypical) so wholly shallow ponds are definitely underrepresented in gardens.

Originally Posted by JohanJ

Ponds that have some 'spare depth' for to pander to human idleness - ie a 6 inches of gunk - probably do a better job for wildlife than ponds that have no 'spare depth' and cannot accommodate 6 inches of gunk.

This does sound like a good point, although those species that prefer the shallow edges are hardly going to appreciate the margin for error. I don't see why a transient, high quality habitat (i.e. a shallow pond that silts up quickly) shouldn't be as valuable as a longer lived but lower quality habitat (e.g. a standard goldfish pond, even without the goldfish).

It is, though, something I have been thinking about in relation to my own recently constructed shallow pond (max 14"), which since being constructed earlier this year has acquired quite a decent range of wildlife. It will be interesting to see how it fares over winter, and also how quickly it accumulates autumn leaf debris.

PS I've had the same link trouble with the forum software before - I normally check it in the preview before posting, then use TinyURL if it's broken.

[Liz Howlett]

I am beginning to like the idea of supermarket cress more and more! What depth should I throw it in to (obviously, I assume, without it's little green Tesco's tray)? Would it be OK at about 2 feet? The truth about the ideal design of ponds (I believe) is this: There should be various levels for different wildlife and plants to live at, access for birds/hedgehogs to drink (but also with safe escape route if they fall in), and as deep a depth as possible in the middle for wildlife to safely overwinter. I understand that this is simply for frogs to stay warm and to trap enough oxygen under the ice for them to breath. This all becomes irrelevant if the sludge is so deep and toxic that toxins become trapped under the ice - which is my problem. Also, I have to disagree that ponds in this country don't generally ice over - ARE YOU KIDDING? I live at the highest point on the Cotswolds (about 900') and the pond freezes over every year, sometimes to 4" - 6" thick, for weeks at a time. That is why I wanted an ice-proof pond. As regards the stickleback, although they are obviously fish, they don't interfere much with the other wildlife. I did occasionally have to rescue a tadpole from the gullet of stickleback by pulling the two apart - quite a fiddly operation, I can tell you - but their entertainment value (like choosing a spot to rear their young and fighting all intruders - even big water beetles) is worth any trouble they might cause. Warning though, they do need well oxygenated water, so running a pump for a few hours a day and keeping water pretty clean is vital. If anyone has any tips about how to reliably keep one area of the pond unfrozen in winter, I would love to hear them. What I need is a kind of solar-powered element (like in a kettle) which would heat the water around it just enough to keep a hole open - has anyone ever seen or tried to build something like that? Otherwise a mains-powered something could also be useful. The same kind of thing would also be invaluable in my birdbath - I have to go to a lot of trouble to keep this free of ice in winter - quite time-consuming.

[Liz Howlett]

I do agree with the quote below, though, a pond should certainly not be like a water tank which just becomes a death trap to anything that falls in, and it shouldn't have any steep sides. Mine has a bog area along one edge into which excess water can drain off and in which bog plants can grow - also a lovely safe haven for newly legged tadpoles. It is surrounded on all sides by old tree-trunks and branches laid into a kind of "woodery" (as opposed to "rockery") and planted up with native wildplants to provide safe overwintering for newts etc. Inside the pond, it has levels at 1', 2', 4' and then the central area (equivalent to about 1/10 of surface area) is at about 6'. I think the shallow areas are generally the most useful and more interesting in a pond - I just tried to construct mine to cover every possible contingency.

Originally Posted by King Edward

The most damaging thing about the excessive depth recommendation, though, is that especially for small garden ponds it encourages people to construct over-deep, steep sided ponds with limited scope for shallower areas.

[King Edward]

Originally Posted by Liz Howlett

Also, I have to disagree that ponds in this country don't generally ice over - ARE YOU KIDDING?

Whoever said they didn't? They don't freeze solid though, unless they're extremely shallow. The whole idea that a 'wildlife pond' needs to be several feet deep is, quite frankly, ridiculous. Large numbers of pond species are adapted to living in shallow ponds, and they are quite capable of dealing with ice in winter and (in many cases) drought in summer as well.

Rather than trying to keep the pond from freezing over winter, you could try some kind of air pump to oxygenate the water. Running this should be less expensive than running a heater, and it would probably be more effective.

[Tringa]

There is no need to do anything with the watercress other than open the bag and throw it in. It floats around the top for a bit then grows roots and the stems grow about 15 - 20 cm above the surface.

We we cleaned out and refilled our pond last year the only plants we had to begin with we an iris, a small water lily and a bag of watercress.

The watercress grew very quickly and fairly soon covered a lot of the surface but it is very easy to remove, just check for livestock in the roots.

I removed most of it earlier this year and other more traditional plants are growing well.

Dave

[nightshade]

I was not to certain what to do with the cress after it cleaned up the nutrients so I used it as a green compost.

[wanlock dod]

I just thought I'd give my thoughts on the issues that resulted in the original question. Some of the issues have already been noted, but I think that some have not.

Excessive plant growth is probably caused by elevated nutrient levels. Phosphate is commonly reckoned to be the limiting nutrient in many aquatic systems, so there may have been a release of phosphate.

There are relatively few ways in which nutirents can be removed from the available pool in a lake or pond. Removal to sediments and removal via the outflow (if present) are probably the main ones. Removal as biomass by "cropping/harvesting" is another for a managed pond.

Phosphate can be bound to iron oxide particles and removed to the sediments. The same principle is sometimes used to remove phosphate from sewage effluents. This can maintain low levels of phosphate provided that the iron oxides remain stable.

Gas from the sediments is probably a mixture of carbon dipxide, methane and hydrogen sulphide. Hydrogen sulphide is toxic, but also odorous at levels well below those which will cause toxicity to humans. Those that have a sense of smell should be able to avoid any significant exposures that could cause problems.

The gases and black sludge are indicative of an anoxic sediment. The black is most likely due to reduced forms of iron. Iron oxides can be used as an "oxygen source" by some microorganisms. This reduction of the iron results in the release of the phosphate that was associated with it.

The release of phoshpate probably caused the increased plant growth. If the plant material is left to decay in the pond this will add to the organic loading of the sediments and recycle the nutrients.

I can't claim to have a practical solution, although oxygenation and sediment removal have been used in some lakes with some success.

I suspect that in this case all was fine until there was sufficient organic sediment matrial for the sediment to become anoxic, which released nutrients which caused more plant growth, and consequently more organic loading to the sediments. A sort of positive feedback mechanism perhaps?