Nature today | The depth of garden ponds is important for the diversity of aquatic animals

In 2021, about six hundred citizens set out to map surface water quality using Waterdiertjes.nl. Together, these volunteers collected more than seven hundred samples from different types of water, but mainly from ditches, ponds, ponds, and city waters. The water quality was good at fifteen percent. The same class scores are inadequate to very poor. Thus the overall picture of quality is comparable to the picture it was in in previous years.

top ten

The speed skater will lead the top 10 species in most places in 2021. This is an animal that lives on the surface of the water and moves over the water like a skater. They rely on the surface tension of water for this. If it is too low, for example due to the presence of soap, it sinks to the surface of the water. The most commonly hunted species is the parasitic water mite. This is a spider that looks like a tick. Remarkably, the post-pod snail has disappeared from both the top ten lists, and the pond snail has also faltered. This is partly because different types of snails can be recognized and introduced into the current version of the web application. If we add these species together, pool snails will be high in the top ten, and post-pod snails again in the top ten.

An overview of the ten species found in most places (frequency) and the first ten species with the greatest number of individuals (numbers), excluding water fleas.  The ranking number is shown in 2021 (top left) and 2020 (top right) for each species.  The number in the lower left indicates the number of sites where the species was observed (frequency) or the total number of individuals (numbers)

Garden ponds in 2021

In 2021, garden ponds are central to Waterdiertjes.nl. Water board professionals do not have access to this private water. As a result, little is known about the quality of this water. From ecological research into biodiversity in other waters, we know that aquatic flora and fauna have a positive effect on the richness of aquatic fauna. This effect depends in part on the size of the water system. This positive effect is due to the fact that water and coastal vegetation provide structure in the water and provide shelter and food. Fish can have a detrimental effect on aquatic organisms because some types of fish eat them. But in many natural pools and small pools, this effect is minimal, because the fish cannot get there or survive.

But what about garden ponds exactly? In addition to conducting an inventory of aquatic animals, information was requested about the size and depth of the pond studied and whether it contained plants and fish. A total of 60 ponds for aquatic animals were examined. About half of those also have this additional information available.

An overview of the abstract characteristics of garden ponds.  The distribution over the categories is shown in a pie chart for each variable.  Most ponds are one to five meters wide, but smaller and larger ponds have also been studied.  The distribution over the three classes of depth is approximately equal.  About a third of the ponds are free of fish.  Most aquariums containing fish contain large fish (greater than five centimeters) and small fish.  Both submerged aquatic plants and floating leaf plants are well developed in most ponds, covering 25 to 75 percent of the surface.

pool of life

The animals that are hunted most often and in great numbers in garden ponds are surface-dwelling insects such as surfers and clerks, as well as mobile animals such as back-swimmers. The pool snail is often seen.

Main species found in garden ponds in 2021

Analyzes show that pond depth plays an important role in species richness and water quality. For example, most species are found in ponds between half a meter and a full meter deep. Surprisingly, there is no clear relationship between species richness or water quality in garden ponds and the presence or absence of aquatic plants or fish.

The number of aquatic animals found in garden ponds is the highest in the medium depths category.  The horizontal line in the box shows the value of the middle note, the value of the bottom of the box for one-fourth of observations and the top of the three-quarters of observations.  The lines outside the box give the impression of contrast

golden meaning

So fewer species of aquatic animals are found in deep and shallow waters. The fact that the richness is less in deep water may be due to the presence of large fish more often in deep ponds. These fish depend on these small aquatic animals for their food. It is not yet clear why diversity is low in shallow waters. This may also have something to do with how the animals were collected. For example, one volunteer noted that he digs more carefully in his private garden than in public ponds, so as not to disturb the pond too much. Dredging aquatic animals, especially in small and shallow ponds, can cause even greater disruption.

Join us in 2022!

For 2022, Waterdiertjes.nl will focus on urban ponds. They come in many shapes and sizes, for example the elongated ones in residential areas, the largest with ducks and geese and the smaller ones with lots of plants. Water quality in urban ponds can be very different. Many species do not live in polluted water, but they do live in clean water. What ponds are in your area, what lives there and what is the quality of the water? Waterdiertjes.nl would like to find better and worse city ponds in different cities and villages by 2022!

With WebApp Waterdiertjes.nl, water quality can be easily assessed based on the invertebrates that live in the water. The animals on the IVN search map form the basis of the web application. Pass through the water with a landing net, see the animals in it, pass the caught numbers and get the water quality score. Go to waterdiertjes.nl for more instructions and information.

Waterdiertjes.nl is an initiative of GLOBE Netherlands, Wageningen University & Research, the Netherlands Institute of Ecology (NIOO-KNAW), IVN Nature Education, TAUW, STOWA, Water Board Brabantse Delta, the Ministry of Infrastructure & Water Management, EIS Knowledge Center for Insects and notes.

Text: Edwin Peters, Wageningen University and Research, Michael Wilhelm, TAUW, Anton Giritzen, GLOBE The Netherlands, Froukje Rienks, Netherlands Institute for the Environment, Laura Seelen, Water Board Brabantse Delta and Jorrit Venema, Vaart Software
Photo: Michael Wilhelm
Formats: Waterdiertjes.nl

Leave a Comment