Pond Management Guide Ulster Wildlife Trust

Transcription

1 Ulster Wildlife Trust Guide to Managing a Wildlife Pond

2 Introduction This leaflet is designed to outline the main principles of good pond maintenance and to provide a step-by-step practical guide to tackling some common problems. However, there is no easy prescription for maintenance of a wildlife pond and the approach will vary depending on individual site conditions and the main objectives for management. These may include management for plant diversity, for waders and wildfowl, for conservation of a particular species or for general aesthetics. Ponds are dynamic habitats and change naturally over time in terms of the plant life and animal communities they support, as stated in the Ulster Wildlife Trust Guide to the Creation of New Wildlife Ponds. The process by which a pond infills with vegetation and silt to eventually form a marsh or wet grassland is called succession. The classic wildlife pond is generally a mid-succession pond and most text books gear management advice to maintaining ponds at this stage. However, temporary ponds that dry out annually in mid-late summer, early successional ponds and more mature, overgrown ponds are all important habitats in their own right. Careful consideration should always be given to the existing wildlife value of a pond before any restoration work is undertaken. There will be cases where some kind of intervention is beneficial, particularly when dealing with artificially created and/ or isolated ponds. Work may include repairing a leak to retain a pond s function, removal of fallen leaves and other debris to reduce shading and nutrient load, or careful management of pond plants to retain sunny, shallow areas of open water for breeding amphibians. The key point to bear in mind is that any active pond management should be carried out gradually and over a long period of time. Sudden and drastic changes to the pond or surrounding vegetation should be avoided at all cost. 1. Managing Plants Algae There are two basic forms of these simple plants: microscopic and filamentous algae, or blanket weed. The former are invisible to the naked eye but give the water a greenish tinge, while a filamentous alga will have the appearance of slimy cotton-like strands over the surface of the water. Although algae are natural components of water bodies on productive land, excessive growth or algal blooms can pose a threat to pond wildlife. As well as blocking out light, to the detriment of other pond plants, their decay leads to oxygen depletion. Even minor losses of available oxygen in a pond can kill fish and sensitive invertebrates like mayfly nymphs and freshwater mussels. The small size and static water of most garden ponds make them more vulnerable to algal pollution, and algal blooms are quite a common occurrence in a new pond. Blanket weed covers the surface of a recently restored pond

3 Method and timing of control The best way to control algal growth in the long term is to reduce the pond s nutrient input. In the garden, avoid the use of lawn feeds, compost, pesticides and fertilizers close to the pond. It is essential to maintain a broad buffer area of rough grass or other semi-natural vegetation around the entire pond to reduce nutrient seepage into the water. On a larger stream-fed pond, the problem may lie with nutrient enrichment further upstream and may be more difficult to tackle. Blanket weed can be easily removed by raking or winding it round a stick. All types of algal blooms can be treated using barley straw. This produces chemicals that limit algal growth, without affecting other pond plants or animals. The straw takes one or two weeks to become active in hot weather and longer in cold weather, but it remains effective until it has completely rotted. Using barley straw to control algae Three applications of barley straw are recommended to treat algal blooms. Initially you need approximately 50g straw/m 2 of surface water. The second application of 25g/m 2 is applied once the first straw has rotted, and the third application should be 10g/m 2. If the water is turbid or muddy, double the amount of straw used each time. In a small pond, where only a few grams are needed, the straw can be stuffed into a net bag or stocking, or simply tied neatly with a string. It s best not to pack the straw too tightly. Floating, submerged and marginal plants Ponds are a refuge for wetland plants, many of which are suffering local declines due to the impacts of drainage and land improvement. They provide sites for egg-laying and emergence of insects, materials for case building and a source of food for pond creatures. Marginal grasses, commonly regarded as weeds, can be extremely beneficial: creeping bent (Agrostis stolonifera) around the pond edge provides excellent habitat for water beetles, and in deeper water the floating sweet-grasses, Glyceria, are amongst the favourite egg-laying plants of the smooth newt. Invertebrates make use of all types of wetland plants, from those rooted in the shallow margins right through to the truly aquatic floating plants, and their needs often change at different stages of their life cycle. It is important therefore to have a good range of pond plants, but also to have variation in plant structure and density. There is no ideal plant cover, but certainly more is better than less. If the plants extend across the entire water surface, or if one or two species start to dominate, it may be time to consider their partial removal. In most circumstances it will be desirable to retain a fringe of marginal and emergent vegetation around at least half of a pond s edge. Marsh marigold (above) and ragged robin (above right) are pond edge plants whose populations in the wider countryside are in decline due to drainage and land improvement

4 A few pointers Don t remove more than a third of any species in one year. Remove a wedge from deeper water to shallow water, rather than, for example, removing all the vegetation in deep water. Gentle management of very large single species stands of plants may allow room for others to colonise, but take care not to completely destroy large stands they provide valuable cover for birds and other pond creatures. Method and timing of control In most cases, hand pulling and thinning of vegetation is the best option. A little bit of digging may be necessary in order to remove the roots and prevent rapid re-colonisation. On a larger pond, use of machinery to carry out this work may be more effective. Submerged aquatic plants can be removed by raking. Long handled nets can be used for removing duckweed. With the exception of duckweed (see inset box), clearance of pond plants should be carried out in September when semi-aquatic insects have emerged from the pond and frogs and newts have left in search of hibernation sites. Place cleared material at the pond edge for 24 hours to allow any trapped wildlife to escape back into the water. Duckweed Duckweeds, or Lemna species, are among the commonest floating plants on ponds and are especially abundant in nutrient-rich water. They are a favourite food source for ducks and many other water birds, hence the name. If duckweed becomes too abundant in a pond, it can be harmful to the creatures living below it as it cuts off the supply of air and light. Removal should be carried out in late spring, to prevent carpets of duckweed developing over the summer. It is not advisable to leave it by the pond edge, as when it rots toxins and nutrients are released back into the pond. Common duckweed, Lemna minor Managing trees and scrub Trees and shrubs provide sheltered environments in which adult dragonflies like to hawk, frogs and newts may hibernate and birds use for nesting and perching. Good bank side cover is also important so that animals can approach the pond in safety. However, excessive shading of a pond causes a reduction in the number of aquatic plant and invertebrate species that can be supported, and leaf fall from surrounding trees tends to exacerbate the problem. A compromise is to aim for tree and shrub cover on the north side of the pond, and keep vegetation on the south side low.

5 Before heading in with a chainsaw, its worth considering a few points: Naturally occurring ponds are often associated with scrub and woodland, for example standing water is a common feature in wet alder or willow woods. Some mature and shaded ponds are home to rare species that can t survive anywhere else. Invertebrates, in particular, benefit from the leaf litter and rotting wood that end up in the water. In an area with few examples of these overgrown, shady ponds, it may be better to create a new pond than to attempt restoration. Method and timing of control Never attempt to clear-fell a continuous belt around the pond to open it up or trim all over-hanging branches at once. It is much better to tackle a small section of the perimeter at a time. Coppicing and pollarding are good methods of managing vegetation height. Coppicing involves cutting the main stem right back to roughly 10cm above the ground, whilst pollarding a tree means cutting it to a height of 3-5m. By dividing the pond edge into sections, you can introduce a coppice rotation, working on one section each year in sequence right around the pond, perhaps keeping the south side free from any kind of scrubby growth at all times. This creates good structural diversity around the pond as the trees in each section will be at various stages of re-growth. Trees and shrubs which respond well to coppicing are willow, hazel, alder and ash, though most other native species can tolerate it also. Refuge areas for newts and small mammals can be created by stacking the piles of coppiced material. Winter is the best time for this kind of work, when trees and shrubs are dormant and less disruption is caused to bird nesting. This fen/ woodland complex developed over many years on the site of an old mill dam in Co. Antrim. Intervention by tree or scrub clearance would not be recommended here as the site already has a high wildlife value. Winter coppicing to control rapidly colonising willow around a small pond Alien invasions Ponds are susceptible to invasive non-native species that rapidly cover the water surface and prevent other plants from growing. Examples are parrot s feather, water fern, floating pennywort, curly waterweed and New Zealand stonecrop. Canadian pondweed, while a good oxygenator, can also reach pest proportions in a pond. Most alien pond plants were either planted in formal and garden ponds as

6 ornamentals, or transferred from their country of origin as a weed along with other ornamentals. Once these species become established in a pond, they can be extremely difficult to control. For this reason, transferral of plant material between ponds should be done with extreme caution, and pond plants should be purchased from reliable stockists only. Water fern, Azolla filiculoides, is clogging up our freshwater habitats and causing problems for our native plants In most instances the complete removal of these species is recommended. The 3 main approaches are: Physical control Cutting, pulling or raking are the most common methods used in garden ponds. Pulling works well for rooted plants as it removes the entire plant, whereas plants that grow from tiny fragments will merely be spread by this method. These include floating pennywort, New Zealand stonecrop and water fern. Environmental control Includes shading problem plants with taller plants, placing polythene over them or increasing water flow. Shading will only be effective if it can be done without killing native submerged plants, as these may die off more quickly than the aliens. Increasing the water flow may simply transfer the problem downstream. Chemical control As a last resort, judicious use of glyphosate pesticide may be an option. However, even this mild, biodegradable chemical can cause problems for amphibians, so it should not be used during spring. There are regulations relating to spraying of chemicals on or near waterways, and the relevant Codes of Practice regarding pesticide use must be adhered to. On farmland In Northern Ireland the Code of Practice for the Safe Use of Pesticides on Farms and Holdings (the Green Code) applies, and is available from the Department of Agriculture and Rural Development (DARD). More guidance on safe use of pesticides can be found in Section 6 of the DARD Water Code. If in doubt, employ a qualified specialist to spray the problem plants. 2. De-silting As already stated, silting up of a pond is part of its natural transition to marsh and wet grassland. To maintain the classic wildlife pond at its mid-succession stage, some removal of silt may be necessary. If the pond has already progressed beyond this stage to a late-succession marsh, fen or wet woodland, de-silting is inadvisable. It will likely eliminate the entire plant and animal community that may have developed over many years. As with heavily wooded and shaded ponds, the best management option would be to create new ponds nearby in appropriate sites. Method and timing The best time for de-silting is from autumn until December, when most plants are inactive. For a small pond, drain the water and carefully scoop the silt into a bucket. Store a few specimens of each plant temporarily in buckets or plastic bags. It is a good idea to retain the top layer of silt on a board, keep it wet and replace it once the de-silting is over. Take care not to remove more than half the silt in any one year, as

7 it will be full of eggs and larvae, and the silt remaining will allow the pond to restock itself next year. For a larger garden pond, one option is to partially drain it using a bucket, leaving some water as a refuge. Silt and excessive plant growth can then be cleared from one-quarter of the pond, and this operation repeated every other year. Mechanical removal of silt may be more practical for large farm ponds. If the ramp is still in existence from the original pond excavation, this is a convenient point from which to access the pond with machinery. Where the excavations were banked up around the pond, access may be a problem and manual silt removal may be more appropriate. Disturbance from the use of heavy excavation machinery and dumper trucks can be minimised by taping off a track. The timing of work will be determined by ground conditions. Dry summer spells are often exploited for pond restoration as pond silt dries out and is easier to excavate and spread. The main disadvantage with carrying out the operation in summer is damage to pond plants and disturbance to breeding amphibians, birds, emerging insects and other pond animals, although disturbance will be even greater in spring. Another consideration with large-scale removal of silt is its safe and legal disposal. On farmland, seek advice from your local DARD advisor prior to spreading silt. It is an offence to discharge suspended solids into a watercourse under the Water Act. Temporary ponds Naturally occurring temporary ponds support a unique range of plant and animal species, each one adapted to flooding in the winter and summer drying. The best known sites in Ireland are in the limestone area of the Burren, where small temporary ponds known as turloughs provide perfect conditions for many rare and interesting species. For example, the scarce emerald damselfly, Lestes dryas, is restricted in Ireland to turloughs, where fish cannot survive and the damselfly larvae escape predation. Contrary to popular belief, temporary ponds are one of the most stable of freshwater habitats, filling in much more slowly than larger and deeper ponds and lakes. Although temporary ponds can often look uninteresting during their dry summer phase, resist the temptation to improve them by de-silting or drainage, as both options will destroy the rich wildlife that they support. Scarce emerald damselfly (male)

8 3. Fallen leaves Dead leaves in the water provide food and habitat for pond invertebrates, most notably the detritivores, whose role it is to recycle nutrients from dead organic matter. A build-up of leaves may lead to nutrient enrichment and more rapid siltation, so clearing them out regularly is advisable. A slightly untidy approach to this will benefit the pond wildlife it s not necessary to remove all the leaves. Skim fallen leaves from the surface of the water with an ordinary garden rake or a long-handled net. As with most other cleared vegetation, leaves should be positioned by the pond edge for 24 hours, so that small creatures clinging to them can crawl back into the water. 4. Repairing leaks If you suspect a leak, the first thing to do is double-check, as it could simply be a natural drop in the water level. Fill the pond in the evening, and check the water level the next day. If it has fallen overnight, you have a leak. Ponds with a butyl or heavy duty plastic liner Allow the water level to drop, checking regularly above and below the water level until the puncture or tear is spotted. When this has been located, drain the pond further so the water level is a few cm below the leak and allow the area around it to dry off completely before attempting any repair. If it s necessary to actively drain the pond, many of the plants will survive temporarily in buckets and pots. Aquatic sealant can work well for repairing butyl lined ponds, but aquatic glues such as Aquasure are even better. Once dried off, roughen the damaged area with fine sandpaper and then apply the sealant. For a small hole, simply squeeze the glue all around the puncture. For a larger hole or tear, try gluing a patch over it. Allow the glue to set and dry properly before refilling the pond. If the liner has perished with age it may be time to replace it with a new one. Remove the old liner, check that the protective under layer is still in good condition, and then fit a new liner. Leave the water to settle for a few days before putting the plants and animals back in the pond. Ponds with a clay liner Clay is easy to repair by adding more clay and re-puddling (compacting the clay while it is moist). If the leak is caused through temporary drying and cracking, the clay may swell and re-seal the crack by itself. To prevent re-cracking try to keep the water levels a little bit higher, but see section below. Try to repair any leaks in your pond so that there is always standing water for amphibians like the common frog to breed in Other types of liner A brick or concrete pond is very difficult to repair. The cracked areas have to be chipped away and re-concreted, or filled with a chemical sealant. This is best done by professionals, as if not done properly it can make the cracks worse in the long term.

9 5. A drying pond The water level in any pond will fluctuate naturally with the seasons and with day to day conditions. Most plants and animals found in shallow ponds will be adapted to temporary drought, whilst additional species may exploit the new opportunities provided by temporary drying. The band of soil and sediment around the pond edge that becomes exposed during summer drying is called the draw-down zone. This zone is important in the life cycle of many pond creatures and over-management to prevent its natural occurrence can be extremely harmful. If you decide that the water levels need to be topped up, the best source of water is rainwater. It s a good idea to keep a water butt for this purpose. Allow the water to warm up in the sun before adding it to the pond, as cold water can be a shock to its inhabitants. 6. Winter freezing Long cold spells in winter may cause water to freeze, especially in shallow ponds. This freezing can threaten the survival of aquatic animals as it prevents oxygen diffusion from the air into the water. Holes should be opened in the ice to allow oxygen into the pond, and for toxic gases to escape. A good way to do this is to place a bucket of hot water onto the ice. Avoid banging holes in the ice because this sends shockwaves through the pond that can kill pond creatures and damage the liner. We hope that this guide answers some of your queries on pond management and helps you to maintain these important habitats for the benefit of wildlife. Should you require further information, please contact: Ulster Wildlife Trust, 3 New Line, Crossgar, Downpatrick, Co. Down, BT30 9EP, T: , info@ulsterwildlifetrust.org Recommended Further Reading: The Wildlife Pond Handbook Louise Bardsley, New Holland Publishers (UK) Ltd., 2003, ISBN Great Crested Newt Conservation Handbook Tom Langton, Catherine Beckett and Jim Foster, Froglife, 2001, ISBN Waterways and Wetlands a practical handbook Alan Brooks and Elizabeth Agate, BTCV Publications, revised 2004, ISBN The Ulster Wildlife Trust Guide to the Creation of New Wildlife Ponds Ulster Wildlife Trust leaflet 2003 (available on request) Farm Ponds 6: Management, Department of Agriculture Northern Ireland (DANI) leaflet series, 1994, ISBN New Approaches to the Management of Ponds Jeremy Biggs, Antony Corfield, Dave Walker, Mercia Whitfield and Penny Williams, a paper produced by Pond Action