Ponds, Pools and Lochans

2.6 Threats to ponds


Pond loss

It is often assumed that pond loss is the main threat to ponds in Britain - but this is only partly true. Pollution and mismanagement are also important problems facing ponds.

During the 20th century, large numbers of ponds have been destroyed. However, data from the DETR Lowland Pond Survey suggests that net loss rates may now be slowing. Instead there is now a high turnover of ponds in lowland Britain with about 1% of the total number of ponds lost and replaced every year. This means that, although a lot of ponds are being filled in, similar numbers are being created. At first sight this might seem quite satisfactory - however, we do not know whether the new ponds being created are better or worse than the old ones being filled in. It is quite likely that some high quality ponds are being lost by this process; the DETR survey also showed that the majority of new ponds are being created for fishing, which means that these ponds will be unsuitable for the many plants and animals that prefer shallow fish-free water (Williams et al., 1998a).

Although nationally, pond numbers may be comparatively stable, there is probably marked regional variation in the rate of pond loss and gain. As noted in Section 2.2 above, numbers in some parts of Scotland may be stable and possibly increasing. In some English regions (e.g. Lancashire, Cheshire), there is evidence that pond loss continues at a high rate (around 1% per annum) with relatively little compensatory pond creation (Nicolet, 1998).

Pollution

Recent evidence from a range of pond surveys suggests that, in the modern landscape, pollution now has an even more pervasive and damaging influence on ponds than pond loss (Williams et al., 1998a, b).

The DETR Lowland Pond Survey provides evidence of extensive damage to pond quality in many countryside ponds, particularly those associated with intensive arable land use. This includes widespread evidence of eutrophication (Williams et al., 1998a). In areas of basepoor soils, acidification may also be a significant impact (Beebee et al. 1990).

Ponds are particularly vulnerable to pollution because of their small size and the small volumes of water available to dilute pollutants. Ponds which are connected to streams and ditches are at particular risk since, in many areas, these watercourses carry significant pollutant loads.

On the plus side, however, there is at least the potential for ponds to be better protected from pollutants than is often possible with larger waterbodies such as lochs and rivers. Many ponds have quite small surface water catchments. In these instances it is quite feasible for the whole of the pond catchment to be maintained in a seminatural land use (e.g. woodland, extensive grassland, moorland) to protect the pond from polluted surface water, a difficult thing to achieve with freshwater ecosystems that have large catchments, such as rivers and lochs.

Specially designed ponds can also be used to help control pollution. Section 7 describes designs for Sustainable Urban Drainage System ponds which are used to trap and improve the quality of the polluted water.

Mismanagement

A surprising threat to ponds comes from mismanagement. Until recently, there has been little information about the ecology of ponds and traditional management practices had developed in the absence of any real understanding of their effects. Techniques, such as cleaning-out ponds and rescuing ponds that dry out, can often be far more damaging than doing nothing and just leaving the pond alone. New guidance on pond management, in the light of more recent information, is given later in this handbook.

Table 5. Biodiversity Action Plan species associated with ponds in Scotland
  • Violet crystalwort
  • Sea bryum
  • Baltic bog-moss
  • Lesser bearded stonewort
  • Slender stonewort
  • Pilwort
  • Shetland pondweed
  • Slender naiad
  • Donacia aquatica (a reed beetle)
  • Hydroporus rufifrons (a diving beetle)
  • Medicinal leech
  • Natterjack toad
  • Great crested newt
  • Reed bunting
  • Water vole
  • Otter

 

Ponds_fig9.jpg (12700 bytes)

Figure 9. The great crested newt is a protected species in Britain; it is threatened by pond loss, fish stocking, mismanagement of ponds (including over-zealous vegetation removal) and fragmentation of terrestrial habitat.
Sue Scott
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