In a 1994 paper, Jeremy Biggs and colleagues listed 9 major misconceptions about ponds and these are still very relevant today.
1. Drying-out is disastrous for pond communities
2. Ponds should be deep (at least 2m)
3. All pond zones, from deep open water to shallow margins, should be created and maintained
4. The bigger the pond, the better
5. Ponds should not be shaded by trees
6. Ponds should be dredged to prevent them from being ‘choked’ with vegetation
7. Pond water-level fluctuations should be minimised
8. Livestock should be prevented from having access to ponds
9. Ponds are entirely self-contained systems, isolated ‘islands’ in a sea of dry land
These misconceptions can be eaily falsified. Drying may be a problem for some species such as (most) fish. However, many temporary pond species benefit from pond drying and refilling for different reasons. They can benefit from the pioneer conditions, low predation predator and rich resources that are available early during inundations. The (near) absence of fish in temporary ponds is a blessing for many invertebrate taxa that are sensitive to fish predation and many of these are therefore restricted in their distribution to temporary ponds.
Fish are typically absent from temporary ponds. Yet this juvenile pike (Esox lucius) was found in a temporary meadow pond in Belgium which had been inundated for about 6 months. It grew fast on a rich invertebrate diet which it did not have to share with any other fish. It is not clear how it got there as the overland distance to a nearest fish habitat was about 400m and no river flooding occured in that year. Perhaps it arrived as an egg or larva attached to a vertebrate e.g. a heron. We can only speculate.
Ponds need not be deep. Shallow zones are important for the growth and development of aquatic vegetation and the warmer water benefits the growth of amphibian larvae. Water can fluctuate and the dynamics of flooding and drying can promote the development of specific flora. Tree shade and leaf litter input may alter the food web of temporary ponds and the water chemistry and, in turn promote different communities.
As also argued by Biggs and colleagues, there is no such thing as a perfect pond. Instead, many organisms have very different requirements and hence it is recommended to maintain heterogeneous landscapes with different types of ponds: shallow and deep ones, vegetated and non-vegetated ponds and ponds with leaf litter in shaded conditions as well as sunlit ponds. Ponds will silt up over time and this process should not necessarily be reversed. It may be more beneficial to regularly create new ponds to ensure that different stages of pond succession can be maintained in our landscapes that are preferred by different sets of species. Although frequent visits by large numbers of visiting cows can degrade ponds, access to livestock and wild terrestrial herbivores should not always be prevented. They can help to create habitat heterogeneity within pools e.g. by removing aquatic and terrestrial vegetation in the parts of the pond they can access and may transport seeds of water plants and dormant eggs of freshwater crustaceans such as water fleas and fairy shrimp.
Biggs lists four main rules of thumb:
- Make the most of existing habitats
- Avoid that all ponds look the same
- Do not suddenly change the management regime
- Create or maintain buffer zones where possible