Pond ecology – managing a ‘natural’ pond

The Freshwater Habitats Trust (formerly known as Pond Conservation), the national charity dedicated to protecting the wildlife of our freshwaters including ponds, rivers, streams and lakes, has kindly given us permission to reproduce the information below on the ecology of ponds and the “natural” way of managing a pond.

This sets a context for our own situation here in Biddenham.  Our village pond is fed largely by direct precipitation, with local surface run off from its immediate surrounds (fields, both pasture and cultivated, with consequent impact on water quality) and water piped from the nearby Manor Hospital roof. The pond has been topped up with mains water in the past, but most recently nature has been allowed to take its course to the extent that in 2011 the pond dried out completely for the first time in living memory. We removed a small amount of accumulated silt by hand when the pond was dry but did not attempt large scale mechanical extraction.

By the end of 2012, after the more substantial than usual rainfall during that year, the pond was as full as anyone can remember! There were very few fish, if any, left before the pond dried out and we decided not to restock the pond with fish. Nor did we replace the former duck house on the pond when it came to the end of its life. We regularly mow a grassed area to one side of the pond, tend the rest of the surrounds in a more “natural” way, contain reed growth in the pond to avoid it taking over completely, and remove azolla which periodically appears and spreads over the pond.

Before its restoration in 1986 the pond had become overgrown and fallen into disuse – an old (late succession) pond in the terms described below by the Freshwater Habitats Trust. We regard our pond now as a mid-succession pond, and essentially we are trying to manage it as a “natural pond”. We are currently undertaking a species survey with expert help to identify the flora and fauna currently in and around the pond and in the light of the results, and in the context too of our pond being a breeding pond for the great crested newt, will be considering what action may be necessary to help conserve better what we have and whether we could beneficially encourage a greater diversity.

General pond ecology
Despite a commonly held traditional vision of what is a good pond, research by the Freshwater Habitats Trust has shown that all ponds can be ecologically valuable for wildlife. The four most important controlling factors for ponds are:

  • clean water (the amount is less important);
  • the variety of habitats or physical structure within the pond;
  • how wildlife friendly the surrounding area is; and
  • fourth (to a lesser extent) being close to other freshwater habitats including other ponds.

Other factors eg the actual type(s) of habitat in which the pond is located, the amount of shade, depth and permanence of water, etc, are only variables that control the type of life that can live in a pond. The Freshwater Habitats Trust uses a broad definition of what a pond is ie a more or less still water body up to two hectares (five acres) in area, which normally holds water for four months of the year or more. This definition thus includes many small and temporary water bodies most people would not even think of as ponds.

The classic “good” pond is often seen as one with some aquatic and marginal vegetation, but also lots of open water, perhaps light shade from scattered trees around the margin and sometimes a greater or lesser numbers of water birds and/or fish. This vision of a standard or good pond has probably been derived from, and maintained by, the type of pond found in the traditionally managed (agricultural) landscape – a pond type whose form has been created and controlled by its social and economic function(s) more than its ecology. In a technical sense this type of pond would be described as a mid-succession pond – that is neither a brand new (early succession) pond, nor a very old (late succession) pond – which is full of plants or other debris – these often being described as “overgrown”, “choked” or “drying out”. Good mid-succession ponds can indeed support a large number of species. They would often have been maintained it in this state by regular use and/or specific management.

However, each phase of the life of a pond will be suitable for and used by a suite of different organisms, some being specialists of one particular phase. A brand new pond with no plants and little or no below or above water structure will be suitable for open water specialists – some of which are only or usually found in the first few months of its existence. Similarly an old pond, for example a woodland pond entirely surrounded by and filled with living and dead trees, will have lost most of the species from its early and middle incarnations. But under the right conditions a suite of specialist species only capable of living in shady ponds full of natural woodland debris will have colonised. None of these ponds are ecologically better or worse, they are just different!

Even ponds that dry out every year, or every few years are good – with most aquatic organisms having mechanisms to cope with regular (eg seasonal) or occasional drying. Some specialist species actually need regular dry conditions as part of their life cycle. There is no part of a pond that is not used by plants or animals. Having said this open water is generally a poor habitat for most species – as it is often barren and dangerous – it is the plants and other accumulated debris (silt, large and small) which provides the structure for organisms to shelter, lay in ambush, hide, lay eggs, sources of food, sources of material to build larval cases (caddis flies), etc.

Thus a whole range of ponds can be good for wildlife, including:

  • large/small;
  • deep/shallow;
  • sunny/shady;
  • permanent/semi-permanent /temporary water;
  • long lived/short lived; and
  • calcareous/acid.

Where one or more of the four controlling factors are not as good as they could be a pond may still be ecologically useful, but it will not fulfil its maximum potential. When managing ponds it is important to understand their whole ecology, including their biological and hydrological conditions. Where problems exist these either need to be solved or work plans devised such that the problems are negated as far as possible if it can’t be fixed. Water quality is the single most important factor controlling the ecological quality of a pond, and poor water quality is one of the most common and difficult overriding issues, which often cannot be solved. Common factors, which cause poor water quality include contaminated run off from agricultural land or roads and overstocking with fish and/or ducks. Water may appear clean but in reality be enriched – for example mains (tap) water has relatively high levels of nitrates and phosphates and can contribute to algal blooms and other water quality related problems. Particular management actions may improve water quality – but often it is a fact of life, which has to be accepted and worked with. It is very normal for pond water levels to fluctuate on an annual or seasonal basis and over a period of years. Species that live in ponds have adaptations to cope with this and some actually require drying out as part of their lifecycles.

Silt removal on a large scale can be very expensive. Pond silts would need to be tested as part of any planned removal and if heavily contaminated or enriched cannot be dumped just anywhere. If badly contaminated they could be classed as hazardous or toxic waste which is potentially even more expensive to remove as it has to be taken away to a secure landfill site.

If possible larger scale silt removal is to be avoided for other reasons as well. For example, larger scale physical disturbance can lead to even worse temporary water quality problems than existed prior to its removal. Many animals live in or use the silt and thus species could be lost.

Silt in ponds is natural and a valuable habitat and resource for animals and plants. In duck ponds or other polluted ponds silts can become very rich and along with closely related issues of poor water quality cause major problems for life in ponds. Perversely however, ducks seem to live very happily in large numbers on the most polluted urban park ponds – which are otherwise almost lifeless.

Ponds are wetland habitats and water is the key component of the system – thus a complete understanding of where it is from, what it is like and when it gets to the pond is essential.

Pond ecology or “How ponds work”
Generally there is little widespread understanding of how ponds actually work as natural environments. Thus the relationship between factors such as ducks, duck feeding, fluctuating water levels, water quality and the best way to improve its nature conservation value and/or aesthetic appeal (eg nobody likes green smelly ponds) is poorly understood.

Managing as a “natural pond”
The aim is to manage a pond in a “natural” way for the maximum benefit of wildlife, eg allowing water levels to fluctuate over the whole of the pond. This would impact on some of its uses, for example, as a duck pond and potentially its aesthetic appeal. In this form of management the pond would not always be full of water and at least some of the surrounds would be managed less frequently and in a less regimented way.

Work tasks could include the following:

  • if required, partially or completely drain the pond and/or allow its level to drop naturally over the course of one or two years. Dig out more recent (top) layer of heavily enriched silt and dispose of as required in legal manner;
  • remove all fish (if any still alive) from the pond, and do not return when work is finished. Fish removal would be easier when the water level is lower;
  • adopt a policy of not artificially topping up the pond during low periods. Fluctuating water levels are an important component of the ponds ecology. Remove the feed pipe from the pond and/or the adjacent land;
  • stop or ameliorate the effects of any road run off. Methods to do this could include one or more of the following: routeing run off away from pond altogether, allowing it to enter only part of the pond (ie sealed off from the main bulk of the pond) which soaks away to ground and not the main pond, install an external silt trap, install internal “reedbed” to filter and clean water either as part of main pond or a stand-alone small internal pond;
  • limit, and control, if required the number of resident domestic water birds. The best option would be to have no resident domestic birds at all. Ban additional feeding of any sort to discourage birds to move onto and/or stay on the pond. Truly wild birds that come and go are an accepted and welcome part of the ponds wildlife. Ducks can have major negative effects on water quality, which is the most important factor for a good wildlife pond;
  • allow pond level to fluctuate naturally to encourage typical species associated with seasonally dry areas and shallow waters; and
  • record/monitor pond water levels (probably monthly) and other ecological features as required (eg extent and type of plant cover, etc.) These features could include water depths, silt depths, width of draw down zone, aquatic plants, amphibians, dragonflies, etc.