This post is an update on the recovery of wildlife in and around the pond in 2013, together with an account of the year’s maintenance issues.
To recap, it was striking how quickly the wildlife in the pond recovered in 2012, the first full year after the mud was removed. The two maintenance issues this year were stopping the blanket weed takeover and stabilising the pond level using the old farm well nearby.
Several enormous dragonflies around the pond in the warm spell of the first week of October – same species as the photo below in August. Pond exceptionally clear, with bottom visible even at the deep end. Very few ducks, often not around at all, so there is little to disturb the water. Too much blanket weed across much of the pond, though growth restrained (creatures eating it?) and only breaking surface in one place.
Pump off at the end of September. After a fortnight the water is down 9 cms, to a level about 25 cms below spring maximum. Weather very warm for time of year.
A water vole swimming across the pond. Exciting. After all we’ve heard about their diminishing numbers, we must research the best ways to protect and encourage them. The previous find was of a dead one, which did at least allow time to positively identify it. Doesn’t seem to have been discouraged by Georgia swimming in the pond in the 85 degree Fahrenheit mini-heatwave of early September.
Pond level on 12 September had fallen 16 cms from the spring peak, even with the pump from the well, but in the next three days it rose 5 cms – the weather has cooled dramatically, and it has been raining. I put a notch on a post to measure changes in the water level.
Water pumps, water voles and refugee fish
The pond water level is staying constant this month, held there by 2 to 3 cubic metres of water a day pumped in from our garden well from June onwards. The pump is automatic, operated by a float switch, and comes on for short bursts once the well water reaches a certain level.
The pump has a dual function: for much of the year it keeps the water table by the house down, because the well is by the back door and its water reaches near the level of the kitchen floor by mid-winter, which seems a bit of a risk. In June we dropped the automatic pump down a couple more metres than usual which much increases the flow rate. The result is that instead of a pond level fluctuating by a foot or more as evaporation increases in the summer (and willow roots draw more water) we have a near constant depth. Instead of a rapidly changing habitat from deep to shallow as the summer progresses, we have created different permanent habitats round the pond – there are two deep areas, two large shallow areas, and three boggy areas.This makes planting much easier.
Stabilisation of the water level is also much helped by the larger volume since we cleared the mud, which keeps the water cooler, thus reducing evaporation.
Found a dead water vole near the pond. That at least allowed us to identify it carefully from photographs. Great news in one way, in that they are back, but sad in another. Hope it was not the only one. There’s plenty of cover in the reeds now if others are around. Could that rat seen in the spring have been a water vole?
Lots of dragonflies around the pond this month, not quite so many damselflies. Getting to grips with identifying them now.
Pond has cleared and the blanket weed is mostly confined to a layer on the bottom, looking like underwater grass. Just the occasional cloud of harvest dust descending on the surface, soon to sink. Near the end of the month, some blanket weed breaking surface again in a shallow, warm area. How interventionist should we be? To think about in the next few months. Still thinking about doing an aggressive clean up of the blanket weed in the late autumn.
Ducks are relatively rare this year – only three or four compared with the peak of more than twenty last year. Only two seemed to survive from the brood, whereas last year there were two broods and more survivors. Moorhens are still busy.
Found another three fish escaped from next door, grey and about 15 – 20 cm long. (The smaller arm of the pond goes into next door’s garden through a reed bed). They have been identified as grass carp which, among other food, munch blanket weed. They can grow enormous – pictures on the web of 35 pounders – and eat three times their weight of vegetation daily when mature.
This is why they are used for weed control in rivers and lakes in Europe, including the UK, and the US. However, they are classified as invasive in the UK, and controlled. Licences are not needed to keep them as long as the pond is less than 1 acre, not connected to any other watercourse, entirely surrounded by a private garden, and not used for fishing.
It seems they can only breed in running water, but one website specialising in selling them says they can be very determined to find it if the pond has an outlet (which ours does, though only in winter and spring.) If they are stocked anywhere other than garden ponds, it seems only infertile triploid fish are allowed. Triploids are produced by treating the eggs and then testing the young to ensure the treatment has worked. Amazing what you can find out by typing ‘grass carp’ in a search engine.
I don’t buy the idea that they are good for blanket weed control, because the bulk of the nutrients in the weed will be excreted back into the pond by the fish, raising nutrient levels and encouraging more blanket weed – we’d be farming it. I think mechanical removal of excess blanket weed once a year is better, because the nutrients are taken out of the pond and disposed of away from it.
The neighbours will try to retrieve their fish soon, with our help. If they don’t catch them, and they grow too big, then we may have to start looking up carp recipes!
A grass snake swimming in the pond. At least four carp have escaped from the neighbour’s pond across the reed bed that separates the two. He has put out a fish trap to get them back! The neighbour did put up a small mesh wire net across the reed bed, but it seems it was after the fish had bolted.
Also found a couple of leeches in the blanket weed when that was being removed. No sign of the weed regrowing, but there is now some duckweed. Lots of bright blue damselflies and some brown dragonflies.
The blanket weed still spreading early June, and blocking light and clogging the pond. Decided on more vigorous action: have been clearing the pond about 30 or 40 sq metres at a time with a grass rake, partly from the edge and partly using waders. Six wheelbarrows heavily loaded after clearing about half of it. Even though this is a very active time of year for pond life, the thought is that each section will have time to recover and animals can also migrate from the disturbed area, when work is being done, into cleared areas.
Checked after clearing the first couple of areas and teeming again with underwater creatures. Have actually been raking the bottom to get up as much as possible, including last year’s dead leaves. It is clear that a large part of the rotting debris on the bottom is last year’s blanket weed.
In the autumn, I plan to rake out all the debris after leaf fall in the hope of reducing next year’s nutrient content, because it is high nutrients that encourage blanket weed. Not too worried about damaging wildlife given that the pond was full of it within months of digging it out and refilling in 2012. But best done thoroughly in the late autumn.
Where are the nutrients coming from? The likeliest source is the cleared pond mud. The banks are of pond mud held back by planks, so nutrients in the mud are likely to be leached into the pond through the gaps in the timbers, especially after the heavy rain of the autumn and winter. The more we can grow on the banks the better because plants will use up the nutrients.
Other possible sources are next door’s chicken run, from which runoff may reach the pond in heavy rain, and the well water which we are pumping in to the pond to maintain the level in dry periods. The well is shallow, only 20 feet deep, so it is possible it may be contaminated by fertiliser. We will buy a testing kit and see. But the volume is only a small proportion of what is in the pond so it does not seem the likeliest suspect.
There are also rotting leaves on the bottom but since there has only been one season since the pond was cleared this seems unlikely to be the cause of a large excess of nutrients.
Plants round the pond thriving.
April and May 2013
No shortage of frogspawn and tadpoles.
Newts not yet seen. Vast clouds of daphnaea on a sunny day.
Blanket weed is a much bigger problem than last year, in some areas blocking the sunlight very thoroughly, so we are gradually clearing it, a patch at a time. This risks some damage to pond life, because of the time of year, but on balance the blocking of sunlight and the effect of the dense mass of underwater vegetation could be more damaging if there is no control – that’s our theory, anyway.
Some sources say clearing releases spores and makes blanket weed grow faster, but it is hard to imagine it growing faster than it does already. The Royal Horticultural Society website does not in fact mention the release of spores as a threat and its first suggestion (in a long list which we may have to work through) is to twirl the weed filaments on a stick and pull out. A grass rake proved to be much more effective.
In late May, we saw a large brown rat : disappointing, because we were hoping for the return of the water vole. The rat jumped out of the pond at lightning speed when ducks landed nearby and ran straight across Peter’s foot in a panic. Later it was seen slinking into next door’s chicken run. The rat could explain the number of freshly eaten duck eggs in the grass.