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Conservation Issues
The RGCG have identified the top ten issues, which need to be addressed on the river system. These are placed in an order of priority that may change with time, are dependent on several factors.
These issues are highlighted below;
These issues are highlighted below;
Water quantity and flow
Anecdotal evidence over decades registers a fall in the quantity and flow of water in the river. In the late 1980s and the early 1990s, aggravated by drought, there was a poor flow, which was particularly noticeable over the summer months and in the autumn.
The per capita consumption of water has doubled over the past 30 years, and we continue to see an increase in population in North Norfolk, which is also swollen by visitors. The demands for water use by agricultural spray irrigation have also increased. The impact of climate change is in the longer term very likely to exacerbate these factors. The continuation of good flow of water in the river, is dependant on the levels in the underground chalk strata (the aquifer) of water, is fundamental to the wildlife of the river and associated wetland areas.
The per capita consumption of water has doubled over the past 30 years, and we continue to see an increase in population in North Norfolk, which is also swollen by visitors. The demands for water use by agricultural spray irrigation have also increased. The impact of climate change is in the longer term very likely to exacerbate these factors. The continuation of good flow of water in the river, is dependant on the levels in the underground chalk strata (the aquifer) of water, is fundamental to the wildlife of the river and associated wetland areas.
Water borne soil erosion
The nature of the soil and the valley slopes makes the Glaven vulnerable to water borne soil erosion from arable land. A heavy fall of rain, especially if prolonged for some time, can lead to rapid surface ‘run-off’ of the rainwater, carrying suspended soil particles in the flow.
This water finds entry points into the river, particularly from road surfaces and tracks, sometimes from a good distance away. The silt deposited in the river channel has several negative impacts including clogging of gravels and consequent destruction of spawning habitat for brown trout.
Water quality and the impact of ‘point’ and ‘diffuse’ sources of pollution
Pollution can come in several forms. The most common is from the plant nutrients nitrate and phosphate. These are applied to arable land as fertilisers and inevitably some washes into the river or percolates through the soil and into the aquifer. This will at a later date enrich the river, ponds and wetlands. A heavy rain and flooding will see this type of diffuse pollution occur alongside siltation.
‘Point’ sources of nutrients, particularly of phosphate are associated with the effluent from a sewage treatment works (STW) or from an accident involving livestock slurry.
The impact of nutrient enrichment, especially in slow moving water, is to promote the rapid growth of algae which both strips out oxygen and blocks out sunlight. Shallow lakes and ponds are particularly vulnerable to nutrient enrichment and in extreme cases water plants may be lost due to a lack of light.
‘Point’ sources of nutrients, particularly of phosphate are associated with the effluent from a sewage treatment works (STW) or from an accident involving livestock slurry.
The impact of nutrient enrichment, especially in slow moving water, is to promote the rapid growth of algae which both strips out oxygen and blocks out sunlight. Shallow lakes and ponds are particularly vulnerable to nutrient enrichment and in extreme cases water plants may be lost due to a lack of light.
River habitat degradation
Over centuries the Glaven has been modified through a combination of; (i) channelisation [widening, deepening, straightening and embanking]; (ii) drainage and clearance of the floodplain, and; (iii) regulation of flows by mills and weirs. These factors have significantly impacted upon the ecological value of the river by reducing the diversity of habitats and hence plants and animals that are present.
Recent surveys have identified several sections in the middle and lower reaches which have been significantly overwidened/deepened to improve land drainage. These works have led to loss of riffle/pool habitat, loss of bankside wetland habitat and importantly increased siltation. Straightening and embankment construction have also decreased the connection between river and floodplain, thus reducing the ecological quality of adjacent wetlands. The RGCG is keen to promote habitat restoration on the Glaven.
Recent surveys have identified several sections in the middle and lower reaches which have been significantly overwidened/deepened to improve land drainage. These works have led to loss of riffle/pool habitat, loss of bankside wetland habitat and importantly increased siltation. Straightening and embankment construction have also decreased the connection between river and floodplain, thus reducing the ecological quality of adjacent wetlands. The RGCG is keen to promote habitat restoration on the Glaven.
Loss or change of use of river meadow and grassland habitat
Historically we have seen some changes of use of river meadow habitat, for example the replacement of livestock grazing by poplar planting for the match making industry and the ploughing of grassland for arable crops such as beans; such changes can have major indirect affects on the river system.
River meadows and wet grassland are a Biodiversity Action Plan (BAP) habitat valuable for a range of wildlife and can be home to a number of protected species.
River meadows and wet grassland are a Biodiversity Action Plan (BAP) habitat valuable for a range of wildlife and can be home to a number of protected species.
Lack of grazing on river meadows
The aftermath of BSE, and now reduced financial support for cattle, make extensive grazing in dispersed locations unprofitable in the global market place. This leads to major imports from the USA, Argentina and Botswana. Supermarket pressures on the price received for milk is also a consideration. The result is that it is currently very difficult to attract grazing to some river meadows where the wildlife interest depends on regular grazing for the maintenance of a diverse flora. Some County Wildlife Sites, supported by Countryside Stewardship funding, are now suffering from this lack of essential management and one site has remained ungrazed for four years.
Cutting once a year provides some mitigation but is not a longer-term solution. It does not prevent the incursion of solid areas of rush, which results in loss of grass and associated wildflower interest. Furthermore long grass in the summer is a handicap to hunting barn owls..
The difficult economics of grazing cattle reinforce the pressures for a land-use change of the types mentioned above.
Cutting once a year provides some mitigation but is not a longer-
Invasive alien species
There is a long history of alien species introductions into Britain many of which can cause considerable harm to the aquatic environment and to native species. Examples include mink, signal crayfish, common carp and plants such a himalayan balsam , New Zealand pigmy weed and parrots feather. In the River Glaven mink have been seen close to the coast and pose a threat to water voles, a favourite prey. Himalayan balsam, a garden escapee has been found at a number of sites along the river. The RGCG are attempting to clear it before it can establish large stands, eliminating native vegetation. Furthermore New Zealand pigmy weed has been recorded at some Glaven ponds, having been brought in with imported plants originally sold from garden centres. Carp have escaped from Bayfield Lake and are a particular problem in the lower river where they reopen bed sediments and uproot aquatic vegetation. The RGCG is keen to educate people within the catchment about the problems of alien species introductions in an attempt to reduce the problem for the future.
Inadequate management in parts of the river, lakes and ditches
River systems can suffer both from insensitive management e.g. some flood protection measures; inadequate treatment of rush and or reed control; removal of fallen trees.
Silt removal from the river is an expensive process, which removes some gravel from the bed at the same time. This can also cause thistle and nettle growth on the banks. Silt removal is necessary to rehabilitate a river, but is a clear case of prevention being better than cure. Drainage ditches need cleaning out from time to time. The change from a hand process to heavy machinery is less sympathetic to the ditch and banks and cuts up the wet meadow in the process.
Silt removal from the river is an expensive process, which removes some gravel from the bed at the same time. This can also cause thistle and nettle growth on the banks. Silt removal is necessary to rehabilitate a river, but is a clear case of prevention being better than cure. Drainage ditches need cleaning out from time to time. The change from a hand process to heavy machinery is less sympathetic to the ditch and banks and cuts up the wet meadow in the process.
Inappropriate development
There are examples of inappropriate development that can affect wildlife and/or landscape of the river and its valley. Such applications need to be opposed with the aim of modification or rejection. Not all will be rejected by the planning system and they can represent an individual and cumulative problem.
Disruption of a normal flow regime
The major example if the tidal sluice at Cley next the Sea. This can increase ponding, causes sharp changes in the inflow and outflow and is a physical barrier for example to sea trout. Ponding may also increase siltation and the marked changes in water level generate can unstable habitat
