Martin has just completed a comprehensive assessment of the state of our ponds, using the grandly-titled “Predictive System for Multimetrics”, or PSYM for short. Developed by the Environment Agency and Pond Conservation (now the Freshwater Habitats Trust , this methodology is based on six measurements of ecological quality, such as the diversity of wetland plants and the number of dragonfly families found in each pond.
Eleven of the Flood Basin ponds were surveyed: four were rated as being of Good ecological quality with three more on the borderline between Good and Moderate quality. Two were of Moderate quality and two were Poor. The larger pond at the southern end of the Meadows was also categorised as being of Good quality. Good quality ponds represent the best 20% for wildlife in England and Wales.
The main negative finding is that the pond vegetation indicates higher nutrient levels than we would expect in clean-water habitats. This is probably the result of polluted flood water from Blue Beck, which is fed by urban run-off from Clifton Moor and Rawcliffe. Throughout the Vale of York, air pollution from vehicle and power station emissions also contributes to excessive nutrient levels.
At the same time, the survey showed that many of our ponds support diverse communities of plants and invertebrates. These include uncommon species such as Stonewort, Tubular Water-dropwort, Bladder Sedge, the Flecked General soldierfly and the Pink Water-speedwell Weevil.
This data provides us with a scientific basis to monitor the quality of our ponds, but what does it tell us about how we should manage them? Research over many years by the Freshwater Habitats Trust has shown that we should be cautious about “cleaning out” ponds: often this has more to do with people’s perceptions about what ‘looks nice’ rather than what’s best for wildlife.
There are lots of seasonal pools (ones which dry-up in summer) in the Basin, and these provide valuable habitats in their own right. However, the two poorest ponds switch between lengthy ‘dry’ and ‘wet’ periods. When dry, they become thickly overgrown with grass; when they fill-up again, this dies and rots, leaving a stinky, de-oxygenated soup. These pools would provide better habitats for wildlife if they held water more predictably, though not necessarily all the time. So, we plan to dig-out the sediment, deepen them slightly and thoroughly ‘puddle’ the natural clay bed to improve water retention. We’ll be starting work during the next few months, and can promise you a really mucky, smelly workout if you’d care to join us!
We’re also seeking out expert advice on whether to fence off the newest pond to expand Water Vole habitat. We know Water Voles are well-established in the ‘reedbed’ pond next door but unlikely to breed in the cattle-trampled edges of its newer neighbour. Fencing would improve Water Vole habitat by allowing them to excavate burrows and by enabling tall, reedy vegetation to take-over. This would benefit other species of conservation concern such as Reed Bunting but would entail a loss of open-water habitat. Ideally, we’d dig another new pond to ensure continuity of open water.
Pond life in a changing climate
As well as helping us monitor the ecological quality of our ponds, Martin’s survey provides evidence of ongoing changes in the wildlife of local wetlands in a shifting climate. The Vale of York is right on the divide between the warmer, drier climes of southern and eastern Britain and the cooler, wetter north and west. Since the mid-1990s, we have seen many warmth-loving southern species spreading northwards in a consistent pattern. A wide range of aquatic insects which were unknown in the Vale 20 or 30 years ago are now widespread and well-established: Emperor and Migrant Hawker dragonflies, Saucer Bug, Water Stick-insect and Screech Beetle to name but a few. Naturalists have been studying aquatic life in the York area for 200 years, with eminent figures such as Rev. W.C. Hey providing comprehensive records during the late 19th century – so we can be confident that this influx of new species is a real phenomenon and not simply the result of better recording.
Rawcliffe Meadows has the distinction of having provided ‘most northerly’ British records for several aquatic insects, although some of these have proved to be short-lived as species continue to expand. Many species once described as occurring “south of the Humber” now reach the Tees or, in some cases, southern Scotland.
This year notable new records have included the Slender Groundhopper, a semi-aquatic grasshopper which has colonised Yorkshire and continued to spread since the late ‘90s, and the weevil Gymnetron villosulum, whose larvae develop in the seedpods of Pink Water-speedwell.
So, our ponds provide a microcosm of changes in the wider environment. Warmth-loving species which have good powers of dispersal and aren’t too picky about their habitats will continue to spread northwards into the Vale of York; at the same time, cool-climate, northern species inhabiting the uplands of the Moors and Dales will increasingly struggle to maintain a foothold in North Yorkshire.