Rivers and streams

Overall vulnerability

Features assessed:

• Rivers and streams

Special qualities:

• Internationally important and locally distinctive wildlife and habitats
• Vital benefits for millions of people that flow beyond the landscape boundary

Feature description:

The PDNP is covered by six different catchments: the Dove, Derbyshire Derwent, Don and Rother, and Aire and Calder, which flow into the Humber; and the Upper Mersey and Weaver Gowy, which flow into the Mersey.

These rivers and streams provide habitat for many species, hydrological function to agricultural land, a supply of fresh drinking water, and recreational opportunities to residents and visitors. 757.2 km of rivers and 3,361.5 km of streams are thought to run through the PDNP, though the exact length is difficult to calculate. Most PDNP rivers rise in the Dark and South West Peak moorlands, either as natural drainage from the blanket bog covered tops or as upwelling springs from the shale-gritstone margin. Some rivers rise from cave system catchments, such as the river Lathkill, which rises from Lathkill Head Cave. Most PDNP rivers change their character over their length. Rising as fast-flowing streams on upland slopes, Dark and South West Peak rivers are broad, slow-flowing and nutrient poor, while White Peak rivers generally have a higher nutrient status despite similar beginnings. Rivers often flow from one character area to another, with the normal progression being from upland streams to lowland gritstone river to limestone dale. Some limestone rivers may be dry for parts of the year and these are assessed in Vanishing Rivers.

How vulnerable are rivers and streams?

Rivers and streams in the PDNP have been rated ‘high’ on our vulnerability scale. This score is due to high sensitivity and exposure to climate change variables, with a reasonable current condition, and a moderate adaptive capacity.

Most major rivers and streams are in a relatively good condition, with localised contamination and invasive species issues. The greatest effects on watercourses are likely to be from changes in precipitation cycles. Watercourses will become more variable, with higher flow in winter and lower flow in summer. Freshwater plant and animal communities are likely to be altered by these changes. Higher temperatures are also likely to affect freshwater communities, with suitable climate space moving northwards and upstream, and warmer conditions causing changes in water chemistry. Rivers and streams are relatively adaptable, with freshwater species having developed dispersal techniques and the watercourses having diverse forms. Much legislation exists to protect and improve rivers and streams, and some funding is available for water quality and flood management works, which will improve river and stream resilience.

Current condition:

The condition of rivers is assessed under the Water Framework Directive (WFD) by the Environment Agency. In the PDNP, approximately 400 km of surface water systems qualify for assessment. Of the water bodies included in WFD assessment, approximately 40% are good quality, 60% moderate and 2% poor. This data implies that water quality in the PDNP is generally reasonable; however, the majority of watercourses are too small for inclusion and so have not been assessed.

Invasive species are more prevalent in rivers and streams than other PDNP habitats, having a greater effect on ecosystem function. Invasive American mink and signal crayfish in the watercourses predate or outcompete native species with knock-on effects on water quality. Some fish have been introduced to the PDNP for angling, such as the non-native rainbow trout. Invasive plant species such as Himalayan balsam and Japanese knotweed dominate riverbanks at the expense of native species, destabilising banks and increasing erosion during winter dieback. This erosion causes sediment input to watercourses, decreasing water quality. Transfer of water between water bodies by water companies has the potential to increase the spread of these invasive species, as does the use of water bodies for recreation.

Environmental contamination is a problem in many areas. At the headwaters of many streams contaminated peat is deposited into the watercourse, introducing heavy metal pollutants that wash downstream. Peat input also increases acidity and dissolved organic carbon concentration in moorland streams. Some areas of the White Peak are still affected by mine efflux, introducing zinc and other heavy metals to the watercourse through soughs and mine workings. Pesticides and phosphates from agricultural runoff continue to affect some rivers and streams, being of high concern in parts of the South West Peak. Agricultural land use has also increased sediment deposition in adjacent watercourses. Accidental inputs to river systems also pose a threat to water quality. These may be long-term inputs such as microplastics and pharmaceuticals, or larger single events such as the 2018 detergent spill in Buxton. These chemical pollutants damage the freshwater community, reducing their abundance and function.

River systems in the PDNP have been drastically altered by human constructions in many areas. Despite having no natural lakes, the PDNP now has many large water bodies in the form of reservoirs. Habitat conditions are altered by reservoirs, with more open water and minimal flow. Weirs and dams are also a barrier to species migration and dispersal, although in some cases they may be preventing the spread of invasive species. Reservoirs also control the flow of the rivers downstream, altering natural flow conditions. Channels have been deepened and straightened in some areas near towns, and streams altered for irrigation and historical mill function. The flow conditions of these areas will have been changed, altering the hydrology and community composition of the watercourse.

What are the potential impacts of climate change?

Overall potential impact rating

Direct impacts of climate change

Increased average annual temperatures will cause a concurrent increase in water temperatures. As many PDNP freshwater species are cool-adapted, this is likely to have negative effects on river and stream communities. Invertebrate community composition will change, as well as their phenology; mayfly are sensitive to temperature changes, and their life cycles in the PDNP are known to be climate dependent. Salmonids are also at risk as cool water conditions are required for successful breeding. Some species may be able to move upstream to find cooler conditions at higher altitude, but species already at headwaters will be unable to move upstream and may be lost. Data Certainty: High

An increase in atmospheric carbon dioxide levels may have negative effects on watercourses. Higher carbon dioxide levels may cause increased dissolution in watercourses, raising the acidity and thereby changing the species composition of aquatic habitats. More carbon availability may also increase plant growth rates, with greater nitrogen deposition during more intense rainfall events exacerbating this effect. Eutrophication could therefore become more frequent and less easy to reverse, reducing abundance of freshwater species and changing water chemistry, increasing the cost of water treatment for drinking water. Data Certainty: Moderate

Changes in annual precipitation cycles will affect the flow regime of rivers and streams. Wetter winters will cause increased flow and drier summers with more frequent drought will cause lower flows. As invertebrate communities are sensitive to flow rates, this could change the species composition at different times of year. Specialist species may be lost in favour of generalists that can tolerate a wider range of flow conditions. Prolonged low flow periods may be the most damaging. Less water would mean a reduction in habitat space, increasing competition and predation. Species such as water vole are sensitive to water depth and may be lost from very shallow areas. Shallow waters are also at greater risk of excess heating, causing thermal stress in freshwater species. Sections of river may seasonally dry out, especially at moorland headwaters. The top sections of many streams are currently seasonal, but these sections may expand and reduce habitat space. This could also limit the opportunity for species to adapt to warmer waters by moving upstream. Data Certainty: Moderate

Nutrient changes or environmental contamination

Higher water temperatures may lead to changes in water chemistry. Warmer waters may have increased biological respiration rates leading to lower dissolved oxygen levels, particularly at night when photosynthesis is not active. Combined with higher nitrogen inputs due to increased nitrogen flux in soil decomposition and increased fertiliser input from agricultural practices and organic input from livestock, some areas of watercourses may be susceptible to eutrophication during dry summers. As river flow promotes recovery from eutrophication via flushing, only drier areas of watercourses could be affected. River sections downstream of reservoirs could also be affected by algal blooms upstream. Low dissolved oxygen levels and areas of anoxia due to eutrophication will disadvantage species with high oxygen requirements such as fish. Community composition would therefore be altered, favouring species with lower oxygen requirements. Data Certainty: High

Greater extremes in flow condition will be likely to have negative effects on water quality of watercourses. Low flows during summer may decrease the dilution of contaminants from sewage works outflow and agriculture, leading to increased concentrations of phosphorous for example. During high winter flows, increased runoff in the uplands will lead to acidic water, high dissolved organic carbon concentrations, and heavy metal pollutants being washed downstream. As a result, water quality and ecological condition may be decreased year-round. Data Certainty: Moderate

An increased frequency and severity of storm events may increase runoff, especially in areas with less vegetation cover. Runoff from agricultural land would increase siltation of watercourses and increase nutrient contamination and pesticide concentration. Runoff from degraded moorland would increase heavy metal pollution and peat particulate concentration. Reduction in water quality would likely lead to lower biodiversity and biomass in freshwater systems. Data Certainty: Moderate

Human behaviour change

Greater variability in river flows could lead to an increase in water infrastructure in the PDNP. Drier summers are likely to increase demand for water from already slow-flowing rivers. Increased abstraction could exacerbate the effect of drought, disadvantaging those species adapted to faster flows and removing some habitat spaces as smaller rivers run dry. Less water in the river systems will also increase the relative concentration of sewage outflows, decreasing water quality. Water being moved between catchments may also increase the spread of invasive species. Hard flood defences, dredging, and channel modification occurring as a result of wetter winters are likely to favour fast flowing species and create barriers to dispersal. Species composition may be altered, and freshwater habitat fragmented. Data Certainty: High

As climate change advances, renewable energy sources may become more desirable. Many of the smaller watercourses in the PDNP have the potential to house small hydroelectric generators. The channel modification and water diversion associated with these developments, as well as the physical barrier of the generator, would have a negative impact on freshwater communities. Watercourses would then be unable to be classified as in good condition by the WFD unless re-categorised as heavily modified water bodies. Data Certainty: Moderate

Hotter drier summer conditions may lead to increased visitor numbers in the PDNP. This would lead to an increase in recreational use of water bodies. Greater disturbance of wildlife and bank erosion could increase, as well as pollution in the form of litter, boat fuel on reservoirs, and skin care products from swimmers. Popular sites such as Padley Gorge may decline in ecological condition. Data Certainty: Low

Greater extremes of precipitation will have an effect on land use surrounding rivers. More frequent and severe incidences of drought and flooding will cause the wetness of land around rivers to be less reliable. It may therefore be abandoned for parts of the year, leaving pastureland to become floodplain meadow or scrub. Watercourse ecological condition could potentially benefit from such changes. Alternatively, less stable conditions in riverside areas may lead to higher agricultural inputs to counter decreased productivity, damaging the ecological condition of watercourses. A move from pastureland to arable would increase runoff and therefore siltation of river systems. Data Certainty: Low

Other indirect climate change impacts

Warmer water temperatures may have a negative effect on ecosystem health due to reduced oxygen availability. Warmer waters hold less dissolved oxygen, meaning water chemistry is likely to change as temperatures rise. Some invertebrate species are more sensitive to oxygen availability than others are, so community composition is likely to change. Salmonid fish and other larger animals with high oxygen requirements are also likely to be affected. Data Certainty: High

Sedimentation or erosion

An increase in intense storm events could lead to more sediment entering watercourses. Both runoff and flash flooding rise during storm events, both increasing the amount of sediment entering the water and spreading it further downstream. Fine sediment can fill up gravel banks, removing fish egg laying substrate and invertebrate habitat, as well as having direct effects on aquatic animals through blocking gills and other effects. Dissolved organic carbon and particulate carbon in the form of peat would be increased, changing the water chemistry and therefore the community composition. Water would also require increased treatment for consumption due to reduced water quality. Data Certainty: Moderate An increase in wildfire during hotter, drier summers could add to this effect due to opening up of bare ground and creation of fine sediment and ash. Data Certainty: Moderate Low flows in summer would reduce the ability of rivers to flush this sediment, making recovery more difficult Data Certainty: High

Invasive or other species interactions

Increased average annual temperatures may lead to a longer growing season and increased winter survival for some plants. This may benefit faster growing and less cold-adapted invasive species more than native plants. Riparian invasives may become frequently dominant on riverbanks, while aquatic invasive species may also benefit from increased water temperatures. Data Certainty: Low Invasive species may also take advantage of the increased disturbance and erosion associated with a greater frequency and intensity of storm and flood events. Many invasive species die back in winter, further increasing erosion. Invasive species may then not only disrupt the riparian ecosystem, but also be damaging to the watercourse itself. Data Certainty: Low

What is the adaptive capacity of rivers and streams?

Overall adaptive capacity rating

Some aspects of rivers and streams have low capacity to recover from damage. Species without an aerial life stage such as fish and crustaceans are unable to move beyond their catchment, and so could be lost from entire river systems. Even for those with high dispersal, structures such as weirs and dams may prevent them moving along watercourses. Some species may therefore be unable to move upstream into more suitable climate space as temperatures warm. The rivers themselves have low capacity for regeneration to their natural course, as human interventions will last a long time. However, increased winter flooding could enable rivers to reshape themselves to a more natural course. Data Certainty: Very High

Watercourses in the PDNP are relatively diverse. Small springs and streams emerge across the gritstone and shale moorland, with some others emerging from limestone cave systems. Larger watercourses flow as fast-flowing upland streams, slow and broad gritstone rivers, and limestone dales. Many rivers change character across their length, and join with other rivers as they flow through the PDNP. This diversity of form and bedrock increases the adaptive capacity of the overall system. Data Certainty: High

Rivers and streams in the PDNP are relatively fragmented. Many rivers have been dammed to form reservoirs in their upper reaches, creating barriers to species movement and meaning that flow is controlled. Rivers are usually limited to connection within their own catchment only, with very limited connectivity with other systems. However, some rivers have been artificially connected, and water is occasionally moved between systems during drought. There is therefore some degree of connectivity between naturally separate systems. Watercourses have also been heavily modified in some areas, either for historical industry or for flood management in their lower reaches. Where channels have been widened and deepened or given an artificial bank these will likely pose some barriers to recovery or adaptation. Data Certainty: Moderate

Some funding is present to improve watercourse condition in the PDNP, including for catchment level habitat works. The Severn Trent Boost for Biodiversity Fund is one such scheme working on PDNP catchments. However, insufficient incentives currently exist for private landowners to take part on a large scale. The UK’s exit from the European Union will also likely mean the end of the Common Agricultural Policy in the UK and presents potential to introduce payment for ecosystem services. Data Certainty: Moderate

Institutional support is available for rivers and streams in the PDNP. Legislation in the form of the WFD protects many rivers with the Environment Agency being the statutory body responsible for water quality. However, most watercourses in the PDNP are too small to be covered by the WFD, and these streams are likely to be the first affected by climate change. Many rivers and streams are also part of the Special Areas of Conservation (SACs) and Special Sites of Scientific Interest (SSSIs). The water companies in the PDNP are well-placed to conserve rivers, often owning many of the watercourses around reservoirs. Much research is funded by water companies, and drought and flood plans can provide guidance for future management. Data Certainty: Moderate

Management interventions that are beneficial for rivers and stream adaptation are relatively well-known. Practices such as restoring natural courses and reducing pollutant inputs are known to be beneficial to water quality, flood management, and ecosystem health. Lack of knowledge of effective interventions is not usually the factor preventing better management. Practical considerations such as insufficient funding and conflicting land use are more likely to be the reason for poor watercourse condition. Data Certainty: Moderate

Key adaptation recommendations for rivers and streams:

##Improve current condition to increase resilience The current condition of a feature is an important factor alongside its sensitivity and exposure, in determining its vulnerability to climate change. These recommendations are aimed at improving the condition of the feature at present, therefore making it better able to withstand future changes to climate.

• Restoration of natural processes across the catchment will improve watercourse health and therefore resilience to change.
• Consider removal of impoundments and weirs to restore natural river flow and improve species dispersal.
• Minimise agricultural inputs, especially fertilisers and pesticides. Give consideration to good management of waste to improve catchment quality, including effective slurry store management.
• Restoration of healthy soils in river catchments will increase infiltration of water and reduce runoff, thereby reducing sedimentation. Tree establishment is a known method to improve infiltration and reduce pollutant spread from runoff.
• Restoration of semi-natural vegetation on critical runoff pathways will slow the flow and reduce erosion.
• New hydroelectric power developments should not be allowed to prevent restoration of natural processes in river systems.
• Use of low nutrient livestock feeds will reduce contamination of the watercourse.
• Block artificial drainage where possible.
• Manage invasive species, including botanical species and signal crayfish.
• Evaluate whether the introduction of beavers would be a feasible and appropriate method of delivering ecosystem service benefits such as flood mitigation, water quality and wet woodland creation.

Adaptations that could aid other features

These recommendations are changes that could be made to this feature, which will have a positive impact on the ability of other vulnerable features to withstand future climate change.

• Creation of riparian shade through tree and scrub establishment will be beneficial to freshwater habitats, and may offset some of the effects of temperature rises.