Action: Create scrapes and pools
- Three studies from Sweden and the UK (including two site comparisons one of which was replicated) found that the creation of scrapes and pools provided habitat for a range of plant, invertebrate or bird species and resulted in increased aquatic macroinvertebrate diversity. One of these studies found constructed pools supported locally or nationally scarce species of plant and water beetle.
- A study in Sweden found that a combination of large surface area, high shoreline complexity and shallow depth resulted in increased bird, bottom-dwelling invertebrate and aquatic plant diversity. However there were fewer fish species than in natural wetlands. Two replicated studies from Ireland and the UK (one controlled paired study and a site comparison) found that bird visit rates were higher but invertebrate numbers varied in ditch-fed paired ponds compared with dry controls and total macroinvertebrate and beetle richness did not differ between artificial and natural ponds, although communities did differ.
Creating scrapes and pools in wetlands and wet grasslands can help create a heterogenous habitat, with varying vegetation types and water levels. Scrapes consist of pools or strips of shallow water which dry during the summer. The muddy margins may provide suitable feeding conditions for invertebrates and wading birds (Natural England 2010).
Natural England (2010) Illustrated guide to ponds and scrapes. Natural England Technical Information Note TIN079.
Supporting evidence from individual studies
A study of 32 recently (1-7 years) constructed wetlands in an intensive agricultural area in southern Sweden (Hansson et al. 2005) found that a combination of large surface area, high shoreline complexity and shallow depth increased bird, aquatic plant and bottom-dwelling invertebrate diversity. Fish species richness was lower than in natural wetlands. There were 15-54 species of bottom-dwelling invertebrates per wetland, increasing with wetland age up to approximately five years, when numbers levelled off. Wetland bird species richness increased with wetland area up to about 4 ha (12 species). There were 0-2 species of amphibian and 18-51 aquatic plant species per wetland. Wetland plant species richness increased with shoreline complexity, but aquatic plant richness decreased with increasing depth. Fish species richness was lower in constructed wetlands (0-5 species) than natural wetlands (more than 100 years old) in the same region (0-9 species). Sampling was undertaken in 2000 (aquatic plants in 2001). Aquatic plant cover was visually estimated (July and November), vegetation was sampled 0-5 m above shore (September) and submersed vegetation was sampled by throwing an anchor 15 m out into the water (5-15 times). Birds were sampled by walking around each wetland twice during the breeding season (mid-May to early-June) and invertebrates at the bottom of the wetland were surveyed by kick-sampling along four 1 m lengths/wetland. Electro-fishing was undertaken in a 50 m stretch and amphibian larvae sampling in a 100 m length of the shallow, littoral zone.
A replicated, controlled paired study of eight created ditch-fed paired ponds in field corners and ten surface scrapes in arable field margins in Leicestershire, UK (Defra 2007) found that bird visit rates were significantly higher in ditch-fed paired ponds (1 visit/month) than dry controls (0.5 visits/month), particularly in the summer months; sample sizes were too small to analyse visits to scrapes. Paired ponds in field corners are fed with water from a nearby ditch. Surface-active adult flies (Diptera) were more abundant and fly larvae and butterfly/moth (Lepidoptera) larvae (in 2005) less abundant in the scrapes than the controls. Numbers of invertebrates active in the grass layer were lower in scrapes than nearby unmanipulated plots. Vegetation was more heterogenous (diversity and height), grass cover lower and bare ground more extensive in the scrapes than the control areas. Sampling involved bird observations (45 minutes, 1-2/month), pitfall traps and sweep-netting for terrestrial invertebrates (scrapes) and botanical quadrat (0.25-0.5m²) survey (scrapes). Data was obtained between April 2005-March 2007; birds all year, other groups spring-summer.
A single-site study from 2004 to 2006 in Leicestershire, UK (Stoate et al. 2007) found that a sequence of seven constructed pools within a riparian buffer strip provided habitat for a range of plant and invertebrate species. Pools each supported 9-18 species of aquatic plant (macrophytes) (30 overall) and 24-52 species of aquatic invertebrates (84 overall), these included the locally scarce marsh dock Rumex palustris and six Nationally Scarce and four locally uncommon water beetles (Coleoptera). The field drain fed wetland was constructed in 1998. The pool sequence was a maximum of 20 m wide, within a riparian buffer strip approximately 70 m wide by 100 m long. Aquatic plants were listed and aquatic macroinvertebrates sampled (3 minutes/pool, June 2004-2005) in six of seven pools.
A site comparison study of 36 newly created dual-purpose wetlands on agricultural land in Sweden (Thiere et al. 2009) found that wetland creation increased aquatic macroinvertebrate diversity in agricultural landscapes. Wetlands had between 6-51 aquatic macroinvertebrates (total 176). Flight-dispersed insects dominated macroinvertebrate species richness: beetles (Coleoptera): 6, dragonflies and damselflies (Odonata): 4, caddisflies (Trichoptera): 5, true bugs (Heteroptera): 5, flies (Diptera): 4, mayflies (Ephemeroptera): 3, slugs and snails (Gastropoda): 2, butterflies and moths (Lepidoptera): 1, leeches (Hirudinea): 1, others: 3. The estimated gain per created wetland ranged from 1 to 33 species. Sub-regions with high wetland density had higher species diversity and accumulation, but not different macroinvertebrate assemblage composition compared to sub-regions with low or moderate wetland densities. Species richness increased with wetland age and assemblage similarity increased with plant cover. Species richness in existing mature ponds (more than 50 years old) was approximately 10% higher than created wetlands. Composition showed overall similarity, diversity was similar, but the rate of species accumulation differed between new and mature water bodies. The 300 ha area of wetlands was created from 1996 to 2004 in natural depressions of former pasture, crop or fallow land by soil excavations and damming existing waterways or drainage systems. Wetlands were largely permanent, flow-through water bodies (<2 ha). Fifteen percent of wetlands in sub-regions with low, moderate, and high densities of created wetlands (i.e. 13, 8, and 15) were sampled. A D-shaped hand-net was swept twice at 15 points along each wetland margin in May 2004. Twenty-five mature ponds in the region had been sampled in April of 1996-2003.
A replicated site comparison study in March-July 2005 to 2007 within nine grazed wet grassland sites in Broadland, eastern England (Eglington et al. 2010) found that installation of shallow wet features provided valuable foraging areas for northern lapwing Vanellus vanellus chicks. The wet features also supported more than twice the biomass of surface-active invertebrates and a greater abundance of aerial invertebrates than the grazing marsh. Chick foraging rates and estimated biomass intake (monitored May-July 2006) were 2-3 times higher in wet features. Later in the breeding season when water levels were low, chick body condition was significantly higher in fields with footdrain densities of more than 150 m/ha. Invertebrate abundance was estimated in wet footdrain, dry footdrain, wet pool, dry pool and vegetated grazing marsh habitats. Each year, chicks (<100 g) were weighed and bill length measured to determine growth rates.
A replicated site comparison study in 2006 of five recently developed Integrated Constructed Wetlands in a catchment in Ireland (Jurado et al. 2010) found that the total number of macroinvertebrate taxa and beetle (Coleoptera) taxa did not differ between Integrated Constructed Wetlands and natural ponds, although communities did differ. A total of 134 taxa were found in Integrated Constructed Wetland ponds, 116 of which were in the last pond, compared to 129 taxa in natural ponds. Although taxon richness and beetle richness did not differ between natural and Integrated Constructed Wetland ponds, overall communities and beetle communities differed significantly. There were 151 taxa with the two pond types, of which 92 taxa (61%) were common to both types of ponds, 35 (23%) were found only in natural ponds and 24 (16%) only in Integrated Constructed Wetland ponds. There was no significant difference between the numbers of taxa in Integrated Constructed Wetlands and the river sites. Of 169 total taxa, 53 (31%) were found in both sites, 64 (38%) in only Integrated Constructed Wetlands and 52 (31%) only at river sites. Five Integrated Constructed Wetlands (consisting of interconnected ponds) and five natural ponds within pasture were sampled in March-April and July-August 2006. Sampling involved three, 3-minute multi-habitat net samples (mesh: 1 mm) and 10 horizontal activity traps in each of the different pond habitats (ponds >10 cm deep). Nine sites on Annestown River, upstream and/or downstream of discharges from the final Integrated Constructed Wetlands were also sampled. Two, 3-minute multi-habitat kick samples were collected (mesh: 0.5 mm) in each of the different river habitats (mesohabitats).
- Hansson L.-A., Brönmark C., Nilsson P.A. & Åbjörnsson K. (2005) Conflicting demands on wetland ecosystem services: nutrient retention, biodiversity or both? Freshwater Biology, 50, 705-714
- Defra (2007) Wetting up farmland for birds and other biodiversity. Defra BD1323 report. Defra.
- Stoate C., Whitfield M., Williams P., Szczur J. & Driver K. (2007) Multifunctional benefits of an agri-environment scheme option: riparian buffer strip pools within 'Arable Reversion'. Aspects of Applied Biology, 81, 221-226
- Thiere G., Milenkowski S., Lindgren P.E., Sahlen G., Berglund O. & Weisner S.E.B. (2009) Wetland creation in agricultural landscapes: Biodiversity benefits on local and regional scales. Biological Conservation, 142, 964-973
- Eglington S.M., Bolton M., Smart M.A., Sutherland W.J., Watkinson A.R. & Gill J.A. (2010) Managing water levels on wet grasslands to improve foraging conditions for breeding northern lapwing Vanellus vanellus. Journal of Applied Ecology, 47, 451-458
- Jurado G.B., Johnson J., Feeley H., Harrington R. & Kelly-Quinn M. (2010) The potential of Integrated Constructed Wetlands (ICWs) to enhance macroinvertebrate diversity in agricultural landscapes. Wetlands, 30, 393-404