The Upper Aire catchment encompasses the watershed for the River Aire from its source by Malham Tarn to the Middle Aire at Keighley. The source of the River Aire is in The Yorkshire Dales National Park, Airehead Spring, North of Malham. This is a landscape characterised by iconic karst limestone, moorland and farmland, heather topped hills and green valleys of livestock divided by traditional dry-stone walls and hedgerows.
The fundamental importance of sites within the Upper Aire Catchment as nature and cultural conservation areas have been widely recognised and are reflected in multiple designations. These include: Ramsar sites (Malham Tarn), Special Areas of Conservation (Malham Tarn), National Nature Reserves (Malham, Malham Tarn), as well as multiple Sites of Special Scientific Interest within the Aire catchment.
The Upper Aire catchment bridges two counties, predominantly residing in Yorkshire with a small proportion sitting within Lancashire. Beyond the Yorkshire Dales and downstream from Skipton, the landscape of the catchment continues to impress with a mix of agriculture, moorland, and woodlands, however, the valley becomes increasingly urban. Industry and settlements have grown along the river, showcasing how the River Aire has influenced the development in this area.
Soils and Geology
The Upper Aire falls predominantly within the Yorkshire Dales National Park, synonymous for its limestone formations such as Malham Cove limestone pavement. Correspondingly, the underlying geology and bedrock of much of the catchment is Carboniferous Limestone strata, along with mudstone, siltstone and sandstone, overlain by varying depths of non-calcareous glacial drift. The superficial geology of the area includes alluvium (clay, silt and sand) and till (diamicton). Moreover, the Upper Aire is characterised by numerous highly productive aquifers. This means that water is stored in cracks and fissures in the rock.
A range of soil types and varying horizon depths can be found in the Upper Aire catchment. Principally, Upper Aire soils are characterised by either loamy and clayey floodplain soils, or acid loamy and clayey soils. However, spatial variations in soil type exist where localised areas of base rich soils, blanket bog peat soils, loamy and clayey soils with peaty surfaces and soils with impeded drainage also prevail. The differences between these soil types can influence local erosion rates, which in turn may affect water quality, flood regulation and carbon storage across the catchment when improperly managed.
Climate and Hydrology
Meteorological data is collected daily at the FSC Malham Tarn Field Centre. Whilst the FSC meteorological data site is ~25km from the lower reaches of the catchment, the data collected by the FSC may be used as a proxy for the climate in the Upper Aire Catchment. The climate is generally harsh with a mean of 220 days of rainfall per year and a mean annual precipitation of 1510mm. However, in the lower reaches of the catchment this value is modelled and predicted to be closer to 1000mm rainfall per year. As such, combined with its high altitude and northern latitude, the climate yields a relatively short growing season.
River levels in the Upper Aire rise and fall quickly dependent on intensity of rainfall events, topography and land use. Typically, in the upland areas characterised by steeper relief, rainfall runs straight off the hillsides as overland flow and causes flooding in towns and villages such as Skipton. Between Gargrave and upstream of Keighley, the Aire floodplain becomes wider and flatter and allows for frequent flooding. Unfortunately, there are no gauge stations situated in the upper reaches of the catchment. The station at the greatest upstream limit on the River Aire is situated at Gargrave.
The gauge at this site shows a typical river level range of 0.8m between 0.1m to 0.9m. Conversely, the river level station at the furthest downstream extent of the Upper Aire, in Kildwick, has a range twice as much as at Gargrave. The river level varies between 0.2 and 1.8m at this location. This highlights the spatial and temporal variability of hydrology along the River Aire. However, as there are few gauging stations situated on the tributaries to the Aire, little can be determined or assumed about the relative contribution and hydrological systems occurring across all waterbodies in the catchment.
Water Framework Directive Status
The EU Water Framework Directive (WFD) provides a strategy for water management, which aims to improve water quality and ensure waterbodies are kept clean. This is achieved through monitoring under two main classifications, ecological and chemical. Ecological classifications compare the biological community of the waterbody to conditions that would be expected in the absence of anthropogenic interference, rated on a five-part scale from 'bad' to 'high'. Similarly, chemical classifications of water quality are either 'fail' or 'good', based on whether pollutants are detected in the waterbody. A deadline of 2027 has been set for all waterbodies across the EU to reach 'high' and/or 'good' status.
Within the Upper Aire there are nineteen waterbodies (17 rivers and 2 lakes), and in most recent monitoring (2019) only four achieved a 'good' status for their ecological classifications and all nineteen 'fail' on chemical status. The dominant reason, as documented by the Environment Agency, for not achieving good status and reason for any deterioration is attributed to agriculture and rural land management, typically characterised by pollution from rural areas and physical modifications.
Land Use and Habitats
Land Use and Habitats
A myriad of habitats exist within the Upper Aire catchment, with many supporting a rich and diverse array of flora and fauna. For more information and to view the exciting developments due to change the landscape across the Yorkshire Dales National Park (including in the Upper Aire) please visit: Re:Cover Yorkshire Dales National Park
Upland acid grassland
Land cover in the Upper Aire catchment is predominantly improved grassland, notably used for grazing stock. This habitat is one of cultural importance and can be valued as an expression of the influence humanity has on the landscape over centuries of management. Environmental value can be found during autumn where waxcaps (Hygrocybe sp.) can be spotted in areas of shorter sward.
Purple grass and rush pasture
Areas of purple grass and rush pasture are often found amongst acid grassland habitats. Boggy, acid hillside can support tussocky purple moor-grass, which is less palatable for the livestock that graze much of the Upper Aire catchment. Rush pasture can be found on the lower fringes of upland acid grassland; these damp areas can provide valuable habitat for wading birds.
Blanket bog is found in the upper reaches of the Aire catchment. This habitat is created in areas of heavy rainfall where peat forms from organic vegetation matter under water-saturated, acidic conditions. Blanket bog favours specialist pant communities and has also been recognised as an important carbon store; restoration work is currently underway to undo damage caused by upland drainage.
Calaminarian grassland forms on land that has previously been used for mining, historically dating back to Roman mines in areas with limestone geology. The remnants of mining present in the soil with high levels of heavy metals including zinc, led, chromium and copper. This habitat can also form along rivers where these heavy metals have leeched from mines into watercourses and then deposited. The vegetation community is dominated only by those plants that can tolerate the metal-heavy soil, and a wider lack of nutrients and humus maintains this as a specialist environment.
Upland calcareous grassland forms in shallow soils on limestone and sandstone and is limited spatially by bedrock which contains high levels of calcium and magnesium. The habitat formed in the Upper Aire as a result of historic woodland clearance, and has since been maintained through livestock grazing. Calcareous grassland is relatively rare and supports a range of uncommon species.
Natural limestone features and anthropogenic activity have formed a range of different habitats including limestone pavement, caves, rocky crops and screes, quarries, and dry-stone walls. This variety has created a range of niches to suit plants, mosses and lichens that are specially adapted to thrive in these conditions.
Meadows and species rich grasslands
Species rich grasslands differ from much of livestock grazed grasslands that are found in the Upper Aire catchment. Much grassland is unimproved, indicating there has been no additional nutrients added to the soil, and less intensively grazed by livestock. They are found on lower, flatter slopes and are typically managed as hay meadows which are only grazed during winter and cut once annually. Meadows and species rich grasslands provide important habitat for a rich mix of grasses and flower species, which provides a nectar source for invertebrates and pollinator species, as well nesting habitat for bird species.
In the Upper Aire moorland and heathland can be found across the upper reaches of the catchment. This habitat is characterised by the dwarf-shrub vegetation community, constituting more than 25% land cover. It is a semi-natural habitat, as human intervention is required to maintain the characteristic vegetation assemblages.
Wetland habitat in the Upper Aire catchment predominantly includes areas of upland fen. Pooling of mineral-rich water, and surface runoff leads to the formation of these valuable habitats which can be incredibly species rich if not grazed intensively.
Within the River Aire catchment there are a range of woodlands, including areas of plantation, native woodland, wet woodlands and hedgerows. Woodland habitats deliver a range of ecosystem services, act as habitat corridors and can be some of the most species rich habitats.
Salmo trutta are typically found along the tributaries and main channel in the Upper Aire as they require fast-flowing, stony, and gravel sections of river for spawning. Sediment introduction to the river can reduce the number of hydrological features such as riffles and pools, thereby reducing the amount of appropriate habitat for trout; therefore presence of the species are indicative of good water health. S. trutta remain widespread along the Aire; however as they are a priority species, targeted work is carried out across the Yorkshire Dales to improve habitat availability.
Historically, Austropotamobius pallipes have been recorded across the River Aire catchment, and pockets still prevail today. They are the UK’s only native freshwater crayfish species and favour hard-water streams and rivers of less than 1m depth. The introduction of invasive American Signal crayfish (Pacifastacus leniusculus) to waterways has led to a dramatic decrease in the number of white-clawed in recent years due to crayfish plague, predation from P. leniusculus and interspecific competition between species. Unfortunately, A. pallipes have no natural resistance to crayfish plague, which spreads through direct contact with infected species and individuals as well as indirectly via fish and equipment that has been in contact with the invasive species. Biosecurity is therefore fundamental for controlling the spread of invasive species; more information can be found on the Yorkshire Invasive Species Forum.
Along the River Aire Vanellus vanellus can be seen in areas of farmland, moorland and wetland. V.vanellus nest on scrapes, mud or sand and defend their nests from threat by ‘attacking’ or ‘mobbing’ the potential predators. Unfortunately, populations of V.vanellus have declined across the UK and they have been added to priority species lists and biodiversity action plans within Yorkshire, to help protect and encourage development of current populations.
The flight of the male Allauda arvensis is unmistakable as they rise almost vertically while producing a long and complicated song-flight effortlessly. A. arvensis can be seen in the Upper Aire on farmland, grassland, and moorland. There is a stable population in the Yorkshire Dales National Park, however in the UK they are a red listed species of conservation concern. This indicates there is a threat of extinction of the species owing to reduced availability of appropriate breeding habitat. In the Upper Aire, lack of breeding habitat may be attributed to intensification of management in grassland habitats and high livestock densities.
From February until July the evocative call of Numenius arquata can be heard across the Upper Aire catchment where the wet grassland and moorland habitat provide breeding grounds. A notable decline in the numbers of N. arquata across the UK has been documented, and as such they have been added to priority species lists and biodiversity actions plans within Yorkshire.
Lepus europaeus can be seen across the Upper Aire catchment, on grasslands where there is a mosaic of habitats including arable fields, meadows, and hedgerows. They are a naturalised species, which means that they were introduced into the UK by humans and became established during Roman times. However, since then numbers of L. europaeus have declined and as a result have been listed as a priority species under the UK Post-2010 Biodiversity framework.
Lutra lutra may be spotted along reaches of the Upper Aire, where there are thought to be stable populations. However, more widely they have become an increasingly rare site and are listed on the IUCN Red list. L. lutra are an important environmental indicator due to their position in the food chain as a top predator; their presence indicates appropriate provision of habitat, resource and food for species lower down the food chain and therefore provide evidence of a healthy, functioning ecosystem.
Arvicola amphibius have been recorded along the Upper Aire; however, their population and abundance are in serious decline due to reduction in habitat availability and predation from the invasive non-native American mink (Neovison vison). As a result, A. amphibius are designated a priority species and across the UK projects have been carried out to improve the availability of habitat. Similarly, there have been multiple reintroduction projects carried out in the upper reaches of the catchment at Malham Tarn to help establish populations of A. amphibius.
References & further reading
Soils and Geology
- Vercruysse, K., Grabowski, R.C., Hess, T. and Lexartza-Artza, I. (2020). Linking temporal scales of suspended sediment transport in rivers: towards improving transferability of prediction. Journal of Soils and Sediments, 20, pp.4144-4159.
Land Use and Habitats
Upland acid grassland:
Purple grass and rush pasture:
- https://www.wildlifetrusts.org (purple-moor-grass-and-rush-pasture)
- https://www.wildlifetrusts.or (upland-acid-grassland-and-rush-pasture)
Meadows and species rich grassland:
- Natural England: Climate Change Adaptation Manual. Upland hay meadow.
- Kevin Sunderland (2013) ‘River Aire Fish Populations 2012’
White clawed crayfish:
- Howes, C.A. (2005). A historical gazetteer of the white-clawed crayfish
- Yorkshire Dales National Park Bird Species Action Plans