BIODIVERSITY PACK HABITAT GUIDE HEADWATERS

Headwaters are the ephemeral and permanently-flowing tributaries feeding a river system. Various definitions exist, based on location (within 2.5 km of source), catchment area (<10 km2) or stream ‘order’, but however defined, headwaters make up the largest portion of river length across the country (estimated at around 70%) and so can be considered the essential ecological foundation for healthy functioning river systems. Varying greatly in character, they are vital both as habitat in their own right and as a support-system for the downstream rivers that they feed.

Freshwater and terrestrial wetland habitats wildlife, and work benefit a wide range are formed by the flow and retention of continues today, as a of species that are water in the landscape. Their nature is key part of the delivery Headwaters are a the focus of B2020 determined by landform and hydrological within Biodiversity Outcome 3. Whilst pathways, the characteristics of the water 2020 and the Water significant habitat many headwaters supply, and climatological and biological Framework Directive resource. They fall outside of influences which generate a mosaic of (WFD). are also crucial in the formal WFD rivers, lakes, wet grasslands, reedbeds monitoring network, and other habitats of various degrees of Across catchments, controlling water their protection wetness and types of hydrochemistry. action to enhance supply to rivers and enhancement our many freshwater downstream, and is integral to the The UK Biodiversity Action Plan (published habitats is intrinsically objectives of the in 1994), described the biological resources linked; with works to are particularly Directive and can of the UK which were identified as rivers able to benefit important in flood risk make a significant wetland habitats and being the most threatened and required management improvement to the conservation action – our priority species vice versa. Delivery on status of monitored and habitats. Detailed plans set out actions a catchment scale can water bodies to protect and restore our threatened take account of these downstream. synergies, and can look to secure opportunities to achieve © Linda Pitkin/2020VISION biodiversity benefits across the full range of HEADWATERS IN A habitats present within a catchment. CATCHMENT CONTEXT WFD AND B2020 Whilst estimates of the headwater stream resource vary with definition used, SYNERGIES: VERY their prevalence means that they are a ACHIEVABLE significant habitat resource. They are also crucial in controlling water supply (both As for rivers, targets for Good Ecological quality and quantity) to rivers downstream, Status under the Water Framework and are particularly important in flood risk Directive focus on the physico-chemistry management as the ‘gathering grounds’ for (pH, temperature, nutrients) and biology flood flows. (aquatic plants, invertebrates, fish) of headwaters. Status improvements under The condition and management of WFD can contribute to all targets under headwaters can therefore impact upon Outcome 1 of Biodiversity 2020 which calls the biodiversity and ecosystem services for Priority Habitats to be maintained in provided by associated river and wetland HEADWATERS PROVIDE IMPORTANT favourable condition, degraded ecosystems habitats, and vice versa, highlighting the HABITAT FOR JUVENILE FISH INCLUDING to be restored and areas of importance for need to consider the functional connectivity BROWN TROUT biodiversity and ecosystem services to be (existing and future) between habitats safeguarded. Such improvements can also when planning catchment restoration.

1 BIODIVERSITY PACK: HEADWATERS NATURAL ECOSYSTEM In the uplands, intact peat moorland NYMPHS OF THE SCARCE BLUE-TAILED supports a complex mosaic of wet and DAMSELFLY LIVE IN THE RUNNELS AND FUNCTION IN dry biotopes, including dystrophic (peat- FLUSHES THAT FEED INTO STREAM SYSTEMS stained) pools and headwater streams of HEADWATERS high biodiversity value. Historic gripping and burning of moorland has severely The habitat mosaics typical of naturally degraded this mosaic, causing degradation functioning larger rivers can be seen in of streams through excessive soil erosion miniature within headwater streams, and river bed siltation. Eroded peat and including both in-channel and riparian nutrients are also carried downstream, habitats. Habitat features and species impacting the freshwater communities assemblages change as environmental below. Water retention within the character changes moorland is downstream, just as impeded, they do in the larger exacerbating rivers into which they Natural headwater low flows and feed. Highly dynamic compounding and diverse, the streams are highly high flows in the character of headwaters connected to the downstream river also varies across the springs and flushes network. Grip- country, ranging from blocking is therefore high gradient, naturally that feed them, vital for restoring treeless cascades in providing a wetland upland moorland the uplands to chalk including the pools winterbournes in transition zone of and stream network lowland England. They high conservation © Chris Lawrence that form a key are strongly influenced importance part of the natural by their catchments habitat mosaic. and often, in contrast to AT A GLANCE GUIDE more heavily-modified In the lowlands, downstream reaches, have avoided intact valley mire systems support a wealth HEADWATERS extensive canalisation and erosion control of biodiversity in a patchwork of spring, measures, remaining hydrologically flush, runnel, fen, bog, swamp and wet Headwaters are estimated to connected to their adjacent floodplain woodland. Species supported by these habitats. systems include the southern damselfly make up 70% OF TOTAL and the scarce blue-tailed damselfly, whose Natural headwater streams are highly STREAM LENGTH IN nymphs exploit the shallow runnels running connected to the springs and flushes that off mires into the stream system. Flush and GREAT BRITAIN feed them, providing a wetland transition mire habitats gradually give way to stream zone of high conservation importance. habitat as water collects in surface and sub- Acid and calcareous springs each generate Headwaters are crucial in surface pathways and flows down the valley. their own distinctive flush communities, controlling water supply to with characteristic flora and specialist The permanence of flowing water has downstream rivers, acting as the invertebrate communities exploiting the a major bearing on the flora and fauna, ‘GATHERING GROUNDS’ flush and runnel habitat provided. with ephemeral sections favouring a range of species adapted to a seasonally dry FOR FLOOD FLOWS channel, such as certain stoneflies, scarce © Maggie Shelton/HIWWT mayflies and crane-flies. Natural headwater streams are The presence of riparian trees and woody highly connected to the springs material within the channel is a critical and flushes that feed them. component of the habitat mosaic, adding Acid or calcareous, these springs a high degree of characteristic habitat generate their own characteristic complexity through the creation of debris flora and fauna, including scarce dams, exposed tree root systems and channel sinuosity. This provides niches for a species like SOUTHERN wide range of species, particularly for lower and BLUE-TAILED plants and invertebrates. DAMSELFLIES In wooded headwater streams, leaf litter provides the main natural nutrient source Lowland headwater streams and generates a food web based on provide better habitat leaf-shredding, dominated by freshwater opportunities for higher plants, shrimps and stoneflies. In treeless upland streams, attached algae replace leaf such as BROOKLIME AND litter as the most important food source, and the supporting invertebrates with a scraping WATER-CRESS, RIPARIAN TREES ADD TO THE HABITAT COMPLEXITY OF HEADWATER SYSTEMS or grazing feeding habit. Such factors chalk-loving BROOK WATER- fundamentally affect the composition of the biological assemblage. CROWFOOT

2 BIODIVERSITY PACK: HEADWATERS © Ben Hall/2020VISION

LEAF LITTER IS A KEY NATURAL NUTRIENT SOURCE IN WOODED HEADWATER STREAMS

In open lowland headwater streams, better declines in reaches further downstream for water supply; the natural flow regime habitat opportunities are created for higher as a progressively greater area of the of a headwater is influenced by the effects plants, including the drained catchment of climate, geology and soil type, most chalk winterbourne contributes to the river’s noticeably giving rise to the intermittent specialist brook sediment load and as stream sections nearest the source. These water-crowfoot. Headwater streams substrate eroded by are termed ephemeral, or more specifically Headwater the river channel itself winterbourne in chalk landscapes. They streams provide a are a key habitat becomes increasingly flow only when winter groundwater levels disproportionate for the European important. This said, and rainfall combine, and recede in the amount of marginal even in the lowest river summer along a gradient of least inundated habitat for their protected species sections, many fish and (upstream) to most inundated (approaching length compared brook lamprey and invertebrate species are the perennial head). Downstream flows to larger rivers, and bullhead, for which reliant on the headwater are progressively added to as channels this is exploited processes that sustain combine, fed by an increasingly larger fully in open parts of the UK are supplies of coarse proportion of the catchment, and so lowland streams by major strongholds substrates in which are decreasingly influenced by the flow encroaching species they shelter or spawn. signatures of the individual headwaters. such as brooklime Similarly the relatively Plant and animal assemblages are and water-cress. low supply of fine distributed along this spectrum of wetness In turn this provides an additional habitat sediment generated by natural headwater according to their habitat preferences and niche for plant-dwelling invertebrates such stream/mire systems is critical to avoiding life cycle strategies, with some species as the nymphs of the southern iron blue excessive siltation in downstream river highly resistant to long periods of dryness mayfly. reaches. A classic example is chalk streams, and others not. where gravels with low silt levels provide Headwater streams are limited in the spawning opportunities for salmonids and Impacts upon the headwater channels diversity of their fish assemblages but are play host to a range of specialist chalk river can therefore be damaging to these a key habitat for the European protected plants and invertebrates associated with middle and lower river reaches, which are species brook lamprey and bullhead, gravel substrates. dependent upon the natural hydrological, for which parts of the UK are major hydrochemical and sedimentary processes strongholds. Headwaters also provide A similar longitudinal pattern is observed of the headwaters. critical spawning and juvenile habitat for other fish, including brown and sea trout and Atlantic salmon. © Ali Morse/HIWWT

Downstream river sections are inherently influenced by the supply of water, sediment and species from the headwater streams that feed them. Although a proportion of invertebrate taxa found in catchments are exclusive to headwaters, many other species are also found in downstream rivers, where populations are constantly topped with individuals drifting down from the headwaters above.

The geomorphological characteristics of a river’s middle reaches are in part THE VEGETATED MARGINS OF determined by the type and scale of HEADWATER STREAMS PROVIDE COVER sediment supply generated by the FOR A RANGE OF SPECIES upstream catchment. This influence

3 BIODIVERSITY PACK: HEADWATERS © Linda Pitkin/2020VISION downstream contraction of headwaters and can alter the position of the perennial head. The impacts upon the headwater’s specialist plants and animals, adapted to withstand seasonal drought, can be extreme.

Drainage can also have a severe effect on headwaters, typically associated with the loss of mire and flush habitats from which the streams arise. Channels are artificially extended into mire areas that are consequently drained and lost, and the channels created are of poor quality. Where the drained land is given over to intensive grazing or arable, the HEADWATERS CAN PROVIDE A REFUGE channels can quickly deliver resulting FOR THREATENED SPECIES LIKE THE sediment and pollutants to freshwater NATIVE WHITE-CLAWED CRAYFISH habitats downstream. The invertebrate communities of upland headwaters suffer from heavy organic siltation associated with drainage works, particularly the PRESSURES ON OUR can be more severe due to the lower water drainage (‘gripping’) and burning of peat volumes of headwaters which have a lesser moorlands. HEADWATERS dilution capacity than the lower river. As a result, both upland and lowland headwater Headwater streams are typically As for rivers more broadly, headwaters are streams are still slowly recovering from amongst the last places in a catchment never completely physically destroyed in the legacy of acidification from sulphur to be invaded by non-native species, the way that a wood or meadow can be, as deposition, while acidification stress from because of their remoteness and natural water falling on the catchment will always on-going nitrogen deposition remains. inaccessibility. They are therefore often require a route by which to drain away. critical refuges for native species that are However, habitat extent and quality can The more pronounced flow signatures of threatened by predation, competition and be significantly reduced by anthropogenic headwaters, and especially ephemeral disease from non-natives (e.g. the white- impacts. sections, can be significantly altered clawed crayfish, water vole). However, the by impoundments or abstractions, increasing spread of non-natives means Although broadly facing the same exacerbating or masking peak or low that the pressure of invasion is growing all pressures as the river resource as a whole, flows, altering temperature regimes, and the time. the impacts upon headwaters can be sometimes fundamentally altering the more pronounced. The effects of excessive nature of the river channel. For example, inputs of nutrients and other pollutants groundwater abstractions can lead to

KEY PRESSURES ON HEADWATERS

DRAINAGE: POLLUTION: IMPOUNDMENT: Drainage of mire and Excessive inputs of Impoundments, such flush habitats from nutrients and other as dams, alter natural which headwaters pollutants can severely flow and temperature arise can result in affect headwaters as regimes, and the heavy organic siltation they hold less water, nature of the river and the delivery of so have less dilution channel, impacting pollutants downstream capacity habitat niches

HABITAT LOSS: INVASIVE SPECIES: ABSTRACTION: Historic gripping and Non-native and Abstraction of water burning of moorland invasive species can for supply and has resulted in the loss impact characteristic consumption alters and degradation of biological communities natural flow regimes, peatland headwaters, through direct often exacerbating impacting habitats competition or the peak or low flows and downstream alteration of habitats affecting species

4 BIODIVERSITY PACK: HEADWATERS KEY MANAGEMENT MESSAGES

• RESTORATION OF parts of their English range. The value (trampling) caused by high intensity of riparian trees in mitigating against livestock grazing, the ruderal bankside NATURAL PROCESSES rising air temperatures can be more vegetation which results is of low Measures that restore natural processes prominent in the smaller headwater conservation value. In addition, close – natural flow, geomorphological channels, where increases above the bankside fencing can interfere with and water quality regimes – allow broad minimum target of 30% tree natural stream behaviour and encourage expression of a characteristic and self- cover (to promote climate change measures to be taken to stop lateral sustaining mosaic of river biotopes, resilience) are particularly consistent channel movement. Reducing grazing and provide the best opportunities for with restoring natural ecosystem pressure to a suitable level is often priority species to survive in a changing functioning. Trees also provide the preferable to bankside fencing. However, climate. A catchment-scale approach leaf litter and woody debris that some in the headwaters, flush and mire encourages practitioners to consider nutrient-poor headwater streams rely habitats are highly vulnerable to grazing how the river system would operate on for their productivity, supporting pressure and the impact of livestock under natural processes as a foundation characteristic biological communities needs to be carefully considered. Where for planning restoration. adapted to this condition. In addition, needed, fencing that is well set back the re-wooding of headwater valleys from the bankside and allows scope for • LARGE-SCALE can also help to regulate the delivery occasional access by livestock provides of water, nutrients and sediments to the greatest scope for characteristic PERSPECTIVE freshwater and wetland habitats further marginal and riparian habitats to develop. Running water ecosystems are complex, down the catchment. physically connected habitats, with • UNDERSTANDING THE conditions dependent on those • MANAGEMENT OF LOCATION OF EXISTING upstream and across the catchment. In LARGE WOODY MATERIAL FRESHWATER BIODIVERSITY the case of headwaters, restoring flow, sediment and water quality regimes is ‘Woody debris’, as a critical component To maximise the benefits of restoration therefore key, not only to the quality of of a naturally functioning stream work, and eliminate damage to priority the headwater habitat, but also to the ecosystem, can be more easily retained or endangered species, it is important to downstream river system into which the in headwater streams. Lower hydraulic obtain a clear picture of the distribution headwaters feed. energies mean material is at low risk of local freshwater biodiversity, (indeed, of becoming dislodged and causing this knowledge is legally necessary for • IN-CHANNEL damage or flood risk downstream. some species). Practitioners should STRUCTURES ‘Passive’ restoration of woody debris take account of standing water, running is the best means of providing woody water and wetland biodiversity. Weirs and dams have a range of material in headwater systems; Specialist advice can be valuable; for physical effects on river habitats, as well including tree-planting to generate example, work being undertaken by the as blocking the free movement of some native woody input over time, and Freshwater Habitats Trust to identify species. Their impact in headwaters leaving material in situ where it falls. ‘Important Freshwater Areas’ could can be great, not only because they Active introduction of woody material, inform local delivery. fundamentally alter characteristic flow in patterns consistent with natural river signatures but also because they can function, is a good interim measure interrupt the natural supply of water, whilst riparian trees (that will provide a sediment and even species to the river future natural supply) are maturing. downstream. Structure removal should REFERENCES AND be the aim wherever possible, with • ENSURE EPHEMERAL FURTHER READING modification to minimise all impacts HABITATS ARE CATERED FOR the next best option. • A narrative for conserving Seasonally variable habitats like freshwater and wetland habitats winterbournes can house much of the • RIPARIAN in England VEGETATION biodiversity of rivers. Natural seasonal flow and water level recession is essential • Climate Change Adaptation A patchy mosaic of riparian vegetation for their maintenance. This requires Manual – Rivers and Streams can incorporate long and short careful management of abstraction and swards, trees and shrubs, and bare the removal of impounding structures ground created by natural river wherever possible. CONTACT US processes. Tree cover won’t always be a natural component of bankside • AIM TO AVOID  catchmentbasedapproach.org vegetation (e.g. on peat), but where it BANKSIDE FENCING is appropriate, cover can have a major @CaBAforum effect on maintaining thermal regimes Whilst bankside fencing protects in headwater streams in the face of in-channel fauna from the sediment @ [email protected] climate change, which threatens to and nutrient inputs (poaching and eliminate many cold water species from bank erosion) or physical disturbance

Edited by The Wildlife Trusts on behalf of the CaBA Biodiversity Group 2018. Design: lonelycottage.co.uk. Header image P1: © Ben Hall/2020VISION.