Can plants indicate the health of ponds?
Dr Alan Law, lecturer in ecology, University of Stirling
“Are you here to improve the pond?” was the question I was asked by a member of the public when checking the water chemistry of Queen’s Park Pond in Glasgow in the summer of 2017. The short answer was no. The long answer was I was surveying the water quality and freshwater life of 30 ponds in the Glasgow area to get an idea of their quality, and did not intend to improve any ponds. This is part of a Natural Environmental Research Council funded project called Hydroscape, led by the University of Stirling, that looks at connectivity and stressors in freshwaters. However, knowing that folks can be incredibly passionate, intrigued and concerned about their local wildlife patches, yet the work I was doing couldn’t immediately help, I felt pretty guilty as I finished the survey.
To get an idea of the quality of any habitat you often have to choose between; surveying the same site at several different time periods, or, by comparing several sites of variable quality over a short time period (a few days). In this project, I chose the latter as I wanted to survey > 100 ponds around Britain to get a wide range of surrounding landuses and water qualities to observe the effects on the plants and animals we found… and I did not have the resources to repeat this.
Freshwaters and their biodiversity are a fascinating subject in which to study as they are very responsive to human influences, are found all over the globe and we seem to have a draw towards them (from feeding the ducks to boating). But freshwaters globally are in a bad way; there are now fewer of them, their quality is declining and their biodiversity is suffering as a result. Knowing about a problem is one matter, but understanding and doing something about this is more difficult. In an attempt to slow the decline of freshwater habitats, there are several approaches to conserve, restore or enhance waterbodies, e.g. constructing new ponds, removing some of the scrub surrounding overgrown ponds (particularly in agricultural areas), or naturalising hard edged ponds using soft techniques such as establishing shelves of wetland plants. But evaluating the effectiveness of any intervention is time-consuming and expensive. In an ideal world, land managers could assess the success of conservation interventions via straightforward monitoring, but first you have to identify a suitable indictor or surrogate of the wider pond quality.
As our research surveyed ponds over a huge range of ecological conditions and geographic range, this was an opportunity to search for a surrogate of biodiversity (and was hoping this could alleviate my guilt). Aquatic plants (macrophytes) immediately sprung to mind as they are present in both good and bad water qualities and are relatively easy to identify. Also, when I survey ponds for invertebrates the majority are mostly be found within the vegetated areas as these areas offer protection from fish, birds or larger invertebrates, food sources and a variety of microhabitats.
Having a number of different aquatic plants species can create complexity where there was none before. The differences in leaf and stem architecture of submerged, floating-leaved and emergent plants creates habitat diversity that was ideal for other life within the pond. For example, grazing and rasping molluscs may benefit due to increased food resources, reduced predation and increased microhabitat diversity. Beetles may benefit from the plant diversity for egg‐laying, refugia, and through increased prey availability. Furthermore, adult dragonflies use emergent macrophytes for perching, egg‐laying, and emergence, whereas their larvae use submerged plants for shelter and foraging. Moreover, generally having a range of plant types and growth forms indicates a good water quality as submerged plants require clean, clear water which can only occur when nutrient inputs are lower and grazing by waterfowl isn’t too destructive.
When looking for indicators of biodiversity quality you often also find what constrains biodiversity, e.g. having high amounts of agricultural or urbanised land surrounding the pond, or being located a high altitudes. These are interesting to observe, but it would be difficult to change the surrounding landuse in order to improve your pond, particularly in urban settings. However, you can influence the structural complexity of the pond by having a range of aquatic plants, and this will have wider benefits to the overall biodiversity, particularly invertebrates, that are food for amphibians, fish and birds, but potentially also act as important pollinators. This could be achieved through protecting areas of a pond from trampling, high disturbance and overgrazing, or softening the margins (particularly in Victorian boating ponds that are typical in many urban areas). Many of these techniques have been applied across Britain, e.g. new ponds built by the Freshwater Habitats Trust, ponds restored by the Norfolk Ponds Project, or soft engineering in several ponds in Glasgow by Froglife and Glasgow City Council. This research provides further supporting evidence that these interventions were successful, but will also help future projects in providing a rapid assessment tool. And personally, I hope this research leads to more pond improvements in Glasgow.
For access to the full article here
Project website: https://hydroscapeblog.wordpress.com/
The Hydroscape project was financially supported by the Natural Environmental Research Council Highlight Topics grant NE/ N006437/1.