A recent review by Dr. Chris Hassall from Leeds University marks an important step in a more strategic understanding of the importance of pond environments in an urban setting.
The phenomenal pace of urbanisation including the large scale movement of people from rural areas towards towns and cities and the consequent expansion of such areas is one of the defining traits of recent decades and this is set to continue sharply in the near future. However, urbanisation also marks a progressive loss of biodiversity in those areas, with particular focus on freshwater habitats such as ponds, due to causes including invasive species, habitat degradation and water pollution. This 2014 paper presents a simple categorisation of urban pond types as well as an interesting review of studies that have investigated the biodiversity value of such habitats from across the world. Amphibians are one of the better studied groups in this category compared to other taxa and there are several listed studies that show the importance of urban ponds as habitat for amphibians, with the distance towards the centre of the urban area, lack of habitat connectivity and presence of fish all contributing to a decrease in amphibian species richness.
The numerous and diverse roles of urban ponds include their ecological function, with good quality ponds acting as stepping-stones and refuges for wildlife species within a matrix of inhospitable built-up habitat, for water management and treatment, including SUD systems (sustainable urban drainage) and potential for bioremediation of pollutants using designed wetland systems for chemical filtering and equally, their social function as areas of traditional community interest, health and well-being and where conservation activities can become an integral part of the management (Hassall, 2014).
Meanwhile, the challenges for biodiversity in urban ponds remain both obvious and very significant, with salt and heavy metal pollution, in particular related to water run-off from road surfaces, as an important factor influencing the quality of the habitat for amphibian species. Invasive species are an ever increasing negative factor, with urban ponds often acting as gateways due to the proximity of humans including centres for plant and animal importation and garden centres which results in both deliberate and accidental introductions of exotic and sometimes invasive species of a very wide range, from bacteria and fungi to species of plants and vertebrates such as terrapins. The establishment of such species in favoured in urban freshwater systems by the high diversity of microhabitats as well as the artificial and often highly modified and simplified aspect of such area. Finally, pond loss at a regional and landscape scale, although it has slowed down and even has been reversed in parts of Europe including the UK compared to the 19th and early 20th century, continues to dramatically influence the value of such habitats in many parts of the world.
This review highlights the complex and diverse opportunities presented by urban ponds as areas of biodiversity importance, of numerous societal benefits, including water management, community health and appreciation as well as amazing educational facilities but also as the fact that overall they remain poorly studied and quantified. However, the proximity and accessibility of urban ponds to large numbers of people, as well as their replicated aspect across sometimes very large spatial scales, offers huge potential for citizen science projects where valuable datasets could be collected by members of the public in association with environmental NGOs and universities.
Hassall, C. (2014) The ecology and biodiversity of urban ponds, WIREs Water, 1: 187–206. You can find a full version of the paper here: http://figshare.com/articles/The_ecology_and_biodiversity_of_urban_ponds/971394