Thornhill, I., Ledger, M., Batty, L., Friberg, N. The determinants of biodiversity and the effect of land use in urban ponds. The European Pond Conservation Network 4th Conference ‘The eyes of the landscape’, Leibniz Centre for Agricultural Landscape Research (ZALF), Germany, June 2010
Research on the biodiversity of small water bodies is increasing but few studies consider ponds within urban areas, despite their susceptibility to urban pollution and significant amenity value. Urban ponds are exposed to pollution from a number of sources, notable impermeable surface run off, which often degrades water quality, with consequences for biota. Out study assessed the conservation and functional value of ponds across the patchy environment of the West Midlands conurbation, UK. A key objective was to characterise spatial and temporal variation in physicochemical quality across a series of urban ponds and relate this to macroinvertebrate biodiversity.
A field survey of 30 ponds spanning a gradient of urbanisation from suburban to densley urbanised was undertaken seasonally in 2008-2009. The pond sites were located within approximately 240 square km. At each site, samples were collected to determine water quality (18 determinands) and habitat heterogeneity. Macroinvertebrates were also collected using a modification of the National Pond Survey methodology. Preliminary data reveal that water quality varied markedly across the sites. Oxygen availability ranged from < 10% saturation to super saturated > 150% whereas pH ranged from pH 6.2 to 8.8. Conductivity varied across the sites from 191 to 1,525 μS cm<sup>-1</sup>. Nitrate concentrations ranged from 0.1 to 117 mg<sup>-l</sup>, indicating nitrate limitation in some locations , and hypereutrophic conditions in others. Elevated chloride and sodium concentrations (up to 378 mg<sup>-l</sup> and 243 mg<sup>-l</sup> respectively) were recorded following prolonged salting of frozen surfaces in winter 2009.
For urban ponds to provide ecosystem services and support diverse macroinvertebrate communities, careful management is necessary on local and regional scales. Data collected suggests they are highly variable and often degraded. This may compromise the ability of ponds to support a diverse biota and their role as stepping stones across the urban landscape. Analysis of the macroinvertebrate data will enable us to determine the extent to which this applies.