July 17, 2019, by sustainablenottingham

A quick (pond) dip in the Djanogly pond

Guest blog by Dr. Tom Hartman, School of Life Sciences, on a brief survey of one of the ponds on University Park.

The pond by the Djanogly arts centre has been in existence for many decades until the tram line was installed in 2014 when it was completely destroyed. A smaller pond was then excavated and allowed to develop with minimal management from the University. The Pond relies on rainfall to fill it up as there is no inflow or outflow, but the water is kept moving by the inclusion of a fountain in the centre that adds to its attractiveness as a water feature that entices people to look at while having their lunch at Djanogly arts centre.

When you first approach the pond, you notice that the water is clear so you can see right to the bottom around the edge but you can also see the large amounts of blanket weed growing next to the shoreline. Blanket weed is a term used to describe hair like algae that grows in profusion even stagnant water but this one is a particularly attractive one when you look at it under the microscope known as spirogyra. On closer inspection there is also other pondweed in the water such as Canadian pondweed (which is a proper plant and not an alga). If you look at the bottom of the pond for only a few minutes you will certainly see a large number of pond snails [1] which can grow up to a relatively large size (maybe 4cm). The clarity of the water and the presence of pond snails in such quantity tells you to things about the quality of the water. First of all that it is well oxygenated and, second, that it is a hard water area. Clear water is normally the sign that the amount of nutrients is not overwhelming the plants are growing it and although, during the spring and summer, it will become cloudy due to the algae bloom the water is very healthy. A hard water area is one in which there is a lot of dissolved calcium carbonate and this promotes the growth of strong shells in pond snails.

If you go pond dipping, then the quality of the water and how much pollution is in it can be judged very quickly by the sort of invertebrates that you can catch. The Djanogly pond, after a very cursory sweep of the net, was found to be full of different species, and the species that indicate that there is a low pollution index were found in very first sweep of the net. Living on the weed and the bottom of the pond were damselfly larvae [2] which emerge and break out of their skin to form beautiful four- winged flying insects reminiscent of little dragonflies and they can be seen perching on the brick wall of the building. Mentioning dragonflies also brings us to point out that their larvae [3] were also present in abundance, but they were all very young and so this might be the first year the dragonflies have considered the Djanogly pond to be suitable for laying their eggs in.  Dragonflies may spend up to 5 years as a fierce underwater predator before climbing up a reed and metamorphosing into the flying adult which unlike damselfly cannot fold their wings when at rest.

Among the other insects that were present where the larval stages of alder flies [4], whirligig beetles [5], mayfly larvae [6], caddis fly larvae that make a shell out of materials like sand [7], and huge numbers of water boatmen [8]. These are insect that paddle underwater with enormously elongated legs that look like oars. The large water boatman swim upside down and are occasionally called back swimmers. They have along proboscis that pierces through the skin of other insects so they can suck their insides out. There are also crustaceans, shrimp [9] and, if you use a more powerful microscope, huge numbers of water fleas [10] and cyclops [11].

In the planted edges of the pond there are more insect larvae, non-biting midges [12], worms that look like tiny earthworms [13], black flatworms [14] and leeches [15], but don’t be worried, these are carnivorous leeches that eat insects and crustaceans. You can tell them apart by the arrangement of their eyes, they have eight [16].

With minimal management the pond has become attractive to many invertebrates who have made it their home. Their presence is a testimony to the resilience of wildlife to repopulate an area after disturbance and their presence will enrich the local wildlife and provide delight to those who want to watch dragonflies darting about the skies and to pond dippers who wish to see how the wildlife prospers in the future.

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