Freshwater reports

Jul 20, 2023

Here I review some recent research and policy events that caught my eye and got me thinking, or suggested some practical actions we could take. In addition, the PONDERFUL consortium is now publishing a growing number of papers with results from the project. Keep an eye on the scientific publications page of our website for updates.

Ponds and other small habitats

There are a variety of activities that lead to increases in pond numbers. In the UK, Jeannie Beadle, Joseph Holden and Lee Brown report on one of these which is probably creating a lot of new ponds: re-wetting peatland. The authors suggest that “hundreds of thousands to millions of new peatland ponds” are being created in the UK as a side effect of this process.

For a sense of scale, in the UK it’s estimated that there about 0.5 million ponds in the countryside, with perhaps 2 million in gardens, so peatland restoration could be having a very big impact on pond numbers in the UK. This year, the state conservation regulator in England, Natural England, is starting a new national count of ponds, based on a national stratified random 1 km square survey. So, we should get a better idea of the effect of peatland restoration on total pond numbers fairly soon.

The Beadle et al. paper is mainly concerned with the biodiversity value of new peatland ponds and also reports interesting observations on this subject. They conclude that new ponds quite quickly (over 15 years) came to resemble naturally created peatland ponds. This ability of new ponds to take on the qualities of much older ponds, and of the quality of species rich regional freshwater biotas generally, is an important part of the argument about the value of ponds for protecting biodiversity. This new evidence from rewetted peatlands is, therefore, a useful addition to our understanding of the role of ponds in helping to protect freshwater biodiversity.

Yet again, recent new work by Lenore Fahrig and her colleagues (in this case, Federico Riva) has important implications for pond lovers, provide interesting ideas from terrestrial ecology that are relevant to pond conservation. In the paper Obstruction of biodiversity conservation by minimum patch size criteria they reflect on the conservation principle that a single large (SL) patch of habitat has higher biodiversity than several small (SS) patches of the same total area (SL>SS). Research has shown that this idea often turns out to be incorrect so that biodiversity conservation requires much more emphasis on the protection of large numbers of small patches (SS>SL). This is an almost exact statement of the paradox we see with freshwater, with more species collectively in the smaller area of habitat provided by ponds compared to other freshwaters. Riva and Fahrig used a global database reporting the abundances of species across hundreds of terrestrial patches to assess the SL>SS principle in systems where small patches are much smaller than the typical minimum patch size criteria applied for biodiversity conservation (i.e., ∼85% of patches were less than 100 ha in area). Consistent with previous syntheses, they found that species richness accumulated more rapidly when adding several small patches (45.2% SS>SL vs. 19.9% SL>SS) to reach the same cumulative area, even for the very small patches in their data set. They concluded that, when a given total area of habitat is to be protected, overall biodiversity conservation will be most effective if that habitat is composed of as many small patches as possible, plus a few large ones. This advice, which is about terrestrial habitats, could have been designed specifically for ponds, and perhaps for freshwater more generally.

We often say that ponds can be found on all continents and probably most of us don’t know much about how this happens in the Antarctic. The paper The need for increased protection of Antarctica’s inland waters is a useful introduction to the occurrence and ecology of ponds in Antarctica where they are a prominent part of the freshwater environment.

Recent studies on the condition of rivers in various parts of the world (UK: taxon richness, UK: taxon abundance, Switzerland, Ireland etc) have reported both ups and downs in river invertebrates, the most widely monitored group of freshwater organisms. To almost everyone reading this review it will be no surprise that much less is known about what’s happening to ponds or to freshwater biodiversity at whole landscape scale – to which ponds make such a big contribution. Although PONDERFUL demo sites are giving us some clues, and national studies, at least in the UK, provide some evidence of on-going decline generally, we have little idea of the condition of ponds across Europe. If only we had as much information to play with as we do for rivers! Surveys being undertaken in the UK by Natural England for the England Ecosystem Survey will hopefully help update understanding in one European state at least.

Finally, you may already have seen news of underwater sounds in ponds which was covered by the BBC. This is a quickly growing and interesting area of research which seems to have some promise for assessing pond condition. Jack Greenhalgh, Martin Genner and Gareth Jones collected 840 hr of underwater sound recordings from five large ponds – which varied in size from 0.2 ha to 1.9 ha – in the southwest of the UK and compared this with macroinvertebrate survey data. They found sounds peaked between 02:00 and 04:00 in the morning and around the solar noon. Surveys were undertaken in late spring and early summer, so the early morning peak was not long before dawn. Aquatic bugs, particularly corixids, and photsynthesising water plants seemed to dominate the soundscape, and Greenhalgh and his colleagues concluded that to get a good indication of the soundscape it was necessary to deploy microphones throughout the 24 hr light-dark cycle.

Other interesting papers

Many people reading this newsletter will probably already be aware of a recent important paper by PONDERFUL colleagues Tom Davidson and Carl Sayer, and their co-authors, on the subject of alternative stable state in shallow lakes, and patterns of chlorophyll a concentrations and nutrients. Their work adds further doubt to one of freshwater’s most enduring and influential theories and, at risk of summarising this interesting paper too pithily, it looks like the alternative stable states theory may now have had its day as simpler explanations can account for the patterns seen in the natural world. Although we’ll probably never know whether it also applies to ponds (I suspect not), the alternative stable states concept has had a big impact on the way lakes are managed. What is perhaps as interesting is what the theories demise might mean for observations on critical tipping points, which have had a considerable influence on the debate about safe planetary boundaries. However, even if alternative stable states hypothesis is en route to rejection, one thing hasn’t changed. As Tom and his colleagues note: the “pressing need to reduce nutrient inputs in shallow lakes to help maintain the resilience of their ecological processes and biodiversity in the face of rapid global change” still remains.

Practical actions

As everyone in PONDERFUL will know, the Ramsar Convention recently adopted a resolution on enhancing the conservation and management of small wetlands. An international group of freshwater scientists, co-ordinated by the PONDERFUL team, wrote to congratulate the Ramsar secretariat on the adoption of the small wetland resolution. This is an international signal of the importance of small freshwater habitats, including ponds. We are now in the process of drafting suggestions for PONDERFUL members and others to specifically promote the measures recommended by Ramsar in the small wetland resolution. We hope to meet with Ramsar later in the project as we finalise our policy advice. As important was the progress of the EU Nature Restoration Law which has several significant items for small waters, including ponds. The amendment to Article 7 requiring member states to consider small waters, as well as removing barriers in rivers, was unfortunately, rejected in a vote in the EU Parliament. It’s possible that there will be opportunities to recover this article but the chances don’t look good. Despite this, there are still several opportunities in the Nature Restoration Law to help further the protection, creation and management of ponds and other small waters. In brief these are:

  • Article 11. Perhaps the most important part of the Nature Restoration Law will be the National Restoration Plans. Inclusion of ponds in these plans is the key outcome that pond lovers should now aim for. Given the strength of scientific evidence, there seems every chance that plans on small waters and small wetlands could be included if they are lobbied for at national level.
  • Article 4: restoration targets and obligations offer potential to help ponds which support Annex I, II, IV and V habitat types and species. These are:
  1. Member States shall aim to put in place the restoration measures in Natura 2000 sites that are necessary to move towards reaching favourable conservation status of habitat types listed in Annex I which are not in good condition. Such measures shall be put in place on Natura 2000 network area of habitat types listed in Annex I that are not in good condition, as quantified in the national restoration plan referred to in Article 12. [Am. 21]
  2. Member States shall put in place the restoration measures that are necessary to re-establish the habitat types listed in Annex I in areas not covered by those habitat types with the aim to reach their favourable reference area. Such measures shall be in place in areas necessary to ensure fulfilment of the goals laid down in paragraph 1 of this Article. [Am. 99]
  3. Member States shall put in place the restoration measures for the terrestrial, coastal and freshwater habitats of the species listed in Annexes II, IV and V to Directive 92/43/EEC and of the terrestrial, coastal and freshwater habitats of wild birds covered by Directive 2009/147/EC that are, in addition to the restoration measures in accordance with paragraphs 1 and 2 of this Article, necessary to improve the quality and quantity of those habitats, including by re-establishing them, and to enhance connectivity, until sufficient quality and quantity of those habitats is achieved.
  • Article 6. There are also opportunities for pond conservation work in relation to Article 6 covering urban areas.
  • Article 7, although rejecting the small water regulation, does require that “Member States shall ensure that natural connectivity of rivers and natural functions of the related floodplains restored in accordance with paragraphs 2 and 3 are maintained.” As floodplains are naturally a hotspot for ponds, this offers good support for measures to restore ponds on the many thousands of square kilometres of floodplain land alongside the streams and rivers of the continent. PONDERFUL demo site Pinkhill Meadow is a classic example of the restoration of floodplains by pond creation.
  • Article 8. There are opportunities to make use of ponds for pollinator restoration, perhaps starting with research on the role of ponds for pollinators. This is a relatively little-known area but has been studied by PONDERFUL partners.
  • Small waters and wetlands, including ponds, are specifically identified in the NRL as: “High-diversity landscape features on agricultural land, including buffer strips, rotational or non-rotational fallow land, hedgerows, individual or groups of trees, tree rows, field margins, patches, ditches, streams, small wetlands, terraces, cairns, stonewalls, small ponds and cultural features, provide space for wild plants and animals…..”.

We will write more about this later in the year.

By Professor Jeremy Biggs, CEO, Freshwater Habitats Trust