GRAZING MARSH DITCHES - Sheet 3
Management for invertebrates
Management of grazing marsh ditches is essential in order to maintain a diversity of wildlife including invertebrates and plants. The following management recommendations are drawn from experience gained through the grazing marsh ditch survey carried out by Buglife (see Further information). Ditch management © Martin Willing
Managing pollution
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ditch margins
Pollution of ditch water should be prevented wherever possible. Contamination from fertiliser run-off or sewage
Leave at least some ditches unfenced to give cattle access to
effluent encourages the growth of algae and duckweeds, and
Salt levels
can result in reduced oxygen levels. Many invertebrates are
Some invertebrates are confined to freshwater, others are
sensitive to these types of changes and they can cause a
salt-tolerant, so distinct invertebrate assemblages and individual
reduction in invertebrate numbers. The effects of pollution are
rare species are dependent on particular levels of salinity.
often greatest in small watercourses. Pollution control can be
On marshes where there is a long history of stable, mildly saline
achieved by following the Defra Codes of Good Agricultural
conditions, this state should be maintained. However, the
Practice and by:
occasional influx of strongly saline water into freshwater ditches,
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Low or no inputs of fertilisers or manure on fields adjacent to
as has happened in the Norfolk Broadland, often leads to low
ditches, to reduce run-off
biodiversity and so is undesirable.
Use of grass buffers alongside ditches in areas where
Vegetation management
there is a high risk of pollution from fertiliser or pesticide application ●
Use of constructed wetlands (e.g. reedbeds) to improve water quality from defined pollution problems
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Raising water levels in minor ditches to reduce inflow from polluted main ditches. This is only of benefit if the source of water used to raise the levels is low in pollutants
The positive effects of cattle The Buglife survey project showed that grazing with cattle is of more benefit to aquatic invertebrate populations than grazing with sheep or no grazing. This is because poaching creates shallow water in which many invertebrate species thrive. Cattle grazing also helps to maintain a varied vegetation structure and
Cut ditch vegetation during the period from autumn to early spring. Dredgings should be moved as far away as possible from the ditch as run-off from rotting vegetation can cause water quality problems. Distinct invertebrate assemblages and individual rare species are dependent on different stages of vegetation development. As different types of ditch vegetation mature at different rates, the ditch cleaning cycle should be tailored to individual marshes, to encourage a balance of vegetation stages, with plenty of open water but also some dense areas. Management approaches that can be used to maintain a variety of vegetation stages are: ●
Stagger clearance: a clear alternate 10-15m stretches,
minimises shading. Recommended management measures
leaving 10-15m uncleared lengths between. This creates
are to:
refuge areas from which invertebrates can migrate back into
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the newly cleared stretches
Stock fields adjacent to ditches with low to moderate numbers of cattle to allow some poaching of margins and to create unevenly grazed marginal vegetation
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Clearance of one side only as this allows the uncut side to act as refuge
Management of ditch structure The dimensions and profile of a ditch influence the aquatic flora and fauna that it supports. For more information see Sheet 2 below. Management should aim to provide both deep and shallow water. Shallow areas are important for invertebrates as they provide warm ‘microhabitats’. Beneficial management practices include the following: ●
Reduce the steepness of ditch banks to 30-45° allowing grazing and poaching of ditch margins and to encourage a wide band of emergent vegetation to develop. But note that gentle gradients are unfavourable for water voles. If you are in an area where water voles occur, aim to have one ditch bank with a steep and the other with a gentle gradient
Common water measurer (Hydrometra stagnorum) © Entomart ●
Provide an underwater ledge or berm of 30cm or less to create water about 30cm deep, at the base of one bank
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Leaving at least some ditches, or sections of ditches,
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unfenced to allow cattle to soften the margins and graze
re-profile to create a gentle gradient with the centre-channel
them, so that a fringe of dense low vegetation is encouraged ●
Constructing cattle drinking bays with a shallow
at least 1m deep ●
slope along steep-sided ditches, to enable emergent and mat-forming aquatic plants to provide small refuges for invertebrates along otherwise sparsely vegetated margins ●
shading out water plants
Maintain high water levels so that the sloping upper bank is submerged, giving plenty of shallow water
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Provide a variety of profiles for any new ditches that are dug, from relatively deep with sloping sides to shallow
Maintaining shading at a minimum level. Most trees and bushes beside ditches should be cut back, to prevent them
Avoid over-deepening ditches during ditch clearance, but
and saucer-shaped ●
Areas of bare sediment should be left during management, but not total clearance of ditch, as these areas are favourable
Managing invasive plant species The presence of invasive plant species can have an impact on ditch vegetation and also affect the diversity of invertebrates present. Invasive plants such as Floating pennywort (Hydrocotyle ranunculoides), Nuttall’s waterweed (Elodea nuttallii), Parrot’s feather (Myriophyllum aquaticum) and Australian swamp stonecrop (Crassula helmsii) all compete with existing vegetation, reducing plant diversity. For information on the control of invasive plant species see Centre for Hydrology and Ecology reference at the end of this sheet.
Buglife has developed a series of advice sheets on the creation, conservation and management of grazing marsh ditches. These are available at www.buglife.org.uk ●
Sheet 1 - An important habitat for invertebrates
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Sheet 2 - Creation and restoration for invertebrates
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Sheet 4 - Agri-environment schemes in England
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Sheet 5 - Coastal realignment for invertebrates
to some animals and plants such as stoneworts
Agri-environment options For more information see Grazing marsh ditches - Sheet 4. Further information For more advice on grazing marsh ditches see the other Buglife information sheets and the references below: Buisson R.S., Wade P.M., Cathcart R.L., Hemmings S.M., Manning C.J., & Mayer L. (2008) The Drainage Channel Biodiversity Manual: Integrating Wildlife and Flood Risk Management. Association of Drainage Authorities and Natural England, Peterborough RSPB, English Nature and Institute of Terrestrial Ecology (1997) The Wet Grassland Guide: Managing Floodplain and Coastal Wet Grasslands for Wildlife For invasive plant species identification see the GB non-native species secretariat: https://secure.fera.defra.gov.uk/nonnativespecies/index.cfm?sectionid=47 For information on invasive plant species control see the Centre for Hydrology and Ecology website http://www.ceh.ac.uk/sci_programmes/AquaticPlantManagement.html DEFRA Codes of Good Agricultural Practice http://archive.defra.gov.uk/foodfarm/landmanage/cogap/documents/ cogap090202.pdf
Buglife – The Invertebrate Conservation Trust
www.buglife.org.uk
First Floor, 90 Bridge Street, Peterborough, PE1 1DY
Registered in England at First Floor, 90 Bridge Street, Peterborough, PE1 1DY. Company no. 4132695. Registered charity no. 1092293. Scottish charity no. SC040004.
Telephone: 01733 201210
Email: info@buglife.org.uk
This leafl et has been sponsored by the Esmée Fairbairn Foundation
08/2011