Globally, there is a vast diversity of different temporary pond types and a wide range of geomorphological processes can contribute to their formation. Below we present an overview of a range of different temporary pond types that can be distinguished based on how they are formed.
Anthropogenic temporary ponds
Many temporary ponds are created by humans and they can become habitats for fauna and flora that can be as valuable as natural habitats. Often it cannot be inferred whether a pond is of natural or anthropogenic origin or whether it represents an anthropogenic modification of an existing pond.
Unpaved roads can become important habitats for temporary pond biota. Road traffic by cars and other vehicles generates hollows and result in erosion that prevents them from silting up with sediment. Many temporary pond inhabitants seem to be remarkably tolerant to passing of vehicles and the high turbidity this can generate. Wheel tracks on unpaved roads hold the last populations of fairy shrimp in Belgium and similar systems exist in many locations elsewhere in the world. It has been shown that vehicles can be important dispersal vectors of the resistant life stages produced by temporary pond organisms such as crustaceans and plants.
Wheel tracks in Beklemoto, Bulgaria (B. Goldyn)
Wheel tracks created by tanks and other armoured vehicles in Lommel, Belgium (B. Vanschoenwinkel), a stronghold of the tadpole shrimp Triops cancriformis
In forestry systems in moist temperate regions of Europe ditches ar often constructed between lines of trees. These can become temporary pond systems rich in leaf litter. In the Netherlands they provide an important habitat of rare large branchiopod crustaceans such as Lepidurus apus.
Anthropogenic forest pools in the form of drainage ditches (NL: rabatten) in Voorst, The Netherlands (E. Wannee)
Explosions can create depressions that become important habitats for aquatic biodiversity. There are few studies of the biodiversity of bomb craters but the habitat may be more common than generally assumed. In Belgium, a region which was quite heavily bombed during the second world war, there are several bomb crater sites of conservation importance. The more permanent craters can be important habitats for the great crested newt (Triturus cristatus) and those that dry out more frequently can have a substantial diversity of aquatic insects.
Bomb crater in Dunbergbroek, Holsbeek, Belgium (B. Vanschoenwinkel)
A variety of pond-creation processes are driven by the dynamics of ice and glaciers, in particular. For instance, ponds can be found in the debris of moraines left by retreating glaciers. Ice lenses that form in the permafrost through cycles of freezing and thawing can also result in ponds when they eventually thaw and disappear. In NE Germany and Poland, kettle holes are a very common pond type. They are defined as glacially created, small, shallow, depressional wetlands collecting their water from internal or closed catchments in young moraine landscapes.
Kettle hole in a forest setting in Poland (B. Goldyn)
Natural temporary ponds
Pans are systems that are typically shallow and ellipsoid in shape and wind can be an important factor during their initial development. They can be common in dryland areas and (semi) arid regions in general. Pans can also be found in dunes when the groundwater table surfaces between dunes. Dune pans are important for pioneer amphibians species such as the natterjack toad (Epidalea calamita) and specific flora.
A dune pan in Westhoek nature reserve, Belgium (B. Vanschoenwinkel)
Pans are particularly common in (semi) arid regions. They can have impermeable bedrock underneath or they can be lined with fine sediment and retain water in a clay lense. They can be very turbid and the muddy water may hide a rich invertebrate fauna from visual predators.
A temporary clay pan in Western Australia (above) and the results of a collection made in such a pan: various large branchiopod crustaceans including the large predatory fairy shrimp Branchinella orientalis
Tree fall ponds
A common natural mode of formation for temporary ponds are holes that appear when trees get toppled during storms. However, currently little work has been done to reconstruct the biota of these systems.
A tree fall pond in Dunbergbroek, Belgium (B. Vanschoenwinkel)
Dissolution of carbonate rocks and limestone in particular can lead to the formation of shallow or deeper depressions. Different types are locally known by different names such as turloughs (Ireland), poljes (Slovenia) and dayas (North Africa). Turloughs tend to be much larger than poljes and typically have a river temporary going through them. Smaller karstic depressions can also form on marl (a mixture of clay and carbonates), as is the case in the Gaume regon of Belgium where they are locally known as ‘mardelles’.
A karstic temporary pond in Morocco (L. Rhazi)
Animal created ponds
In Europe, wild boars are known to use shallow depressions known as wallows to cool down or roll in the mud to get rid of parasites. Elsewhere in the world, other swine species, but also larger mammals such as buffalo, elephant and rhinoceros indulge in the same behavior. These actions can make the water turbid and enrich it with nutrients, but it can also lead to the creation of new ponds and deepen existing basins. More work is needed to confirm the value of such animal made systems for aquatic biodiversity. In Belgium, wild boar wallows can be important (albeit atypical) breeding habitats of the fire salamander (Salamandra salamandra). In Poland bison watering holes are present which may – at least partly – result from the actions of the bisons themselves. It remains to be seen whether ongoing introductions of bison to other parts of Europe will result in pond creation. Without doubt some of the extinct megafauna will have been involved in (temporary) pond creation. Even elephant footprints can house a remarkable aquatic diversity. It is tempting to imagine a Mesozoic landscape with thriving freshwater communities in the footprints of sauropods or the wallows of Triceratops.
A bison watering hole in Bialowieza, Poland (B. Goldyn).
Dissolution and subsequent erosion of weathered material can result in the formation of depressions in bedrock where water can accumulate after rains. Such freshwater rock pools can be found in different areas where outcropping rock slabs can be found. Sometimes this is in coastal areas such as in Brittany (France) or in the supralittoral zone of rocky coastal areas in Scandinavia. Freshwater rock pools can also be found in inland areas such as on limestone cliffs in Malta and granite outcrops in Norway. Rock pools exist in different shapes and sizes but most will have surface areas <4m² and particularly in drier parts of the world, they do not hold water for a long time. Inundations can be just a few days or weeks and rarely exceed several months unless they are found in regions with a very moist climate such as Scandinavia where evaporation is compensated by precipitation.
A small rock pool on a limestone rock slab in Malta (B. Vanschoenwinkel).