How to Rewild

Standing Open Water and Canals

Habitat Management Plan

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Standing Open Water and Canals
Habitat Guide

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While most waterbodies in this category are ‘lentic’ (slow or non-moving) systems, canals are lotic (flowing). They may also sit above the water table, or be separated from drainage systems, making these artificial rivers less nutrient-polluted than our actual rivers, acting as refuges for some pollution-intolerant species. With a nationwide network carrying water across watersheds, canals may transport plants and other organisms from one region to another.

In contrast, lakes, ponds and ephemeral water bodies only affect the local area. Like streams and rivers, they may be polluted by nutrients, sediment, microplastics and other human activities. But these habitats can also be highly biodiverse, even if they were created artificially, which makes their loss from rural landscapes over the past few centuries even more significant. While some types of lake have high biodiversity potential at scale, ponds are typically undervalued, even by ecologists, as even newly-dug systems may support a substantial variety of terrestrial and aquatic species.

Sub Habitats

Water bodies with a high nutrient load due to natural or artificial inputs, creating a highly productive ecosystem which may be dominated by algal growth.

Water bodies with a moderate nutrient load, typically with low artificial inputs, creating a moderately productive ecosystem which is often dominated by plants.

Water bodies with a low nutrient load or high peat content, creating a low productivity ecosystem.

Smaller water bodies which are filled from a swallow hole in the bed. The water may completely dry out for several seasons or years at a time.

Artificial water bodies, constructed for shipping or crop irrigation – distinguished from ditches, which drain agricultural land. These systems often cross multiple watersheds, carrying plants and animals between separate rivers and ponds.

Puddles, scrapes and ponds which are typically dry for more than half of the year.

Puddles, scrapes and ponds which are typically wet for more than half of the year.

Value

Most larger water bodies in the UK are Eutrophic Standing Waters – this means they have higher levels of nutrient input, which typically leads to high productivity. But a highly-productive ecosystem is not necessarily healthy (e.g. a conifer plantation) – and these lakes are typically characterised by low water clarity, high algae concentrations and low levels of submerged vegetation. Many of these systems are in Poor condition, including most fishing and ornamental lakes, which are of low value to biodiversity, but this category also includes some water bodies in Good condition, which are extremely biodiverse.

Mesotrophic, Oligotrophic and Dystrophic Lakes are more rare, and the few examples which exist are often under threat from nutrient pollution. These systems are low in nutrients (Oligo), contain moderate (Meso) levels or are acidified and coloured by nutrient/sediment input (Dys). This results in lower productivity ecosystems than a Eutrophic lake, but with clearer waters that are more suitable for submerged plants. The specialist community of zooplankton, phytoplankton, plants, fish, amphibians and invertebrates which are at home here make these valuable for biodiversity despite the lower bioabundance.

Aquifer-fed Naturally Fluctuating Water Bodies and Temporary Water Bodies are both ephemeral in nature. They may be seasonal, or arise for longer periods and then disappear again, creating unique communities of organisms which thrive in temporary standing water. Amphibians are more likely to thrive in non-permanent ponds, as their young are less likely to be predated by fish, while predatory invertebrates benefit from the lack of competition. With a shifting waterline comes a specialist plant community which is adapted to the variable soil moisture levels and seasonal drying (though fewer aquatic plants are present than in a permanent pond). Meanwhile, waterbirds and mud-feeding species value these seasonal ponds as a rich source of invertebrates, while terrestrial animals use the habitat as a watering hole.

Canals vary significantly in their value for biodiversity depending on their traffic levels, nutrient load and presence of invasive species. A healthy canal can be a low nutrient refuge for threatened aquatic species which allows these organisms to disperse easily across a large region. Conversely, these are also systems where invasive species quickly spread from one place to another, carried along by boats and the current. Canals are a mixed deal for biodiversity, with both positive and negative impacts at the local and national level.

Other Standing Water is perhaps the most important ‘Other’ category in this system. Ponds have been rudely dumped into this catch-all term, which also includes drainage ditches and low value lake ecosystems. Yet ponds are one of the highest biodiversity systems in the British countryside, supporting not just aquatic life, but also terrestrial and airborne animals, which use this habitat as a watering hole and hunting site, especially in summer.

The edges of lakes are the richest zone in terms of biodiversity and bioabundance, and a pond is like a lake which only has edges. There is less open water in this system, so fewer fish, but the high levels of sunlight in the shallow water creates rich plant growth, which in turn fuels up to ⅔ of the UK’s freshwater invertebrate species. These are rich and abundant ecosystems, which restore the local aquifer while acting as an effective nutrient and pollutant treatment station. They are also a rapidly-maturing system, with benefits to local biodiversity from very early-on in their development. We have lost many ponds from our rural landscape, and the artificial creation of these ecosystems is both an affordable and effective method for biodiversity restoration.

Froglet in pond
Many organisms that are found in standing waters are able to migrate between systems at some stage during their life cycle, whether by flying, walking or sticking to other animals.

Protect

To make this section easier to follow, it’s important to understand the idea of eutrophic stable states. Waterbodies flip between two different states – eutrophic and mesotrophic/oligotrophic. A eutrophic state is dominated by algae and phytoplankton, with murky water. In contrast, mesotrophic/oligotrophic systems are dominated by submerged plants like waterlilies, with clear water. This is not a typical equation, though – waterbodies can become eutrophicated when nutrient levels are raised, fish stocking density is too high, plants are destroyed by wind, choked by algae or damaged by human activity – but it takes much less effort to push a system into eutrophication than it does to pull it out.

Alongside artificial dams/weirs and invasive species, eutrophication is perhaps the biggest threat to the health of aquatic habitats. While eutrophic lakes and ponds do occur naturally, these are far less common in the wild, as we now have many different factors which cause this kind of ecosystem to develop. Agricultural fertilisers and muck spreading, untreated sewage outflows, fishing bait, fish stocking and urban runoff can all shift a waterbody into a eutrophicated state by raising nutrient levels.

Submerged plants protect the sediment at the bottom of a waterbody from being stirred up into the water column. This stirred-up sediment releases nutrients, which lead to algal blooms, which kills off submerged plants (i.e. a vicious cycle). This means excess sediment in the water and damage to submerged plants are both issues that can shift a water body towards eutrophication. So herbicide contamination, bank erosion, sediment input, boating, predation of algae grazers (by fish), and intensive leisure activities can threaten the health of a clear water lake. In canals, the passage of more than 1000 boats each year will hamper the development of a diverse ecosystem.

Acidification of a water body can cause it to shift into a dystrophic state, with low productivity and stained water, characteristic of blanket bogs. But some acidity resists eutrophication, so that the reduction in British acid rain over the past few decades has led to more eutrophication, especially in upland areas and Northern/Eastern England. Additionally, fish are more successful at breeding in higher pH water, which exacerbates this effect by boosting fish populations. This compounding effect means nutrient inputs must not only be reduced down to, but significantly below 1980s levels to maintain the same level of eutrophication. 

Reducing nutrient inputs ideally means stepping human activities back from the waterline, with a buffer zone of wilder habitat. Rural car parks, arable land, urban development, ditches and paths can all leach nutrients or sediment into pond/lake water, so these are the highest priority. Any activity which directly introduces nutrients or pollutants into the water itself could be limited through signage or restrictions; fishing bait (especially ground baiting), duck feeding, spraying of herbicide and intensive grazing of livestock could all be mitigated by working with local stakeholders. Destruction of submerged plants is typically caused by boats and the smothering effect of periphyton – a sort of leaf surface algae which is usually grazed by snails (which are eaten by fish) – so, reducing boat activity or removing predatory fish can restore plant health.

To prevent the spread of invasive species into new ecosystems, biosecurity protocols must be followed when carrying out any maintenance work in the area. This includes detailed risk assessments, the mapping and marking out of any invasive species on site, and washing of all equipment before and after use. Invasive species include not just plants (of which there are many!), but also animals like the giant Signal Crayfish and the tiny Killer Shrimp. With so many species to cover, it is better to look at a dedicated guide.

As with any ecosystem, a high predator presence is likely to have negative impacts on biodiversity. Dogs are commonly found around ponds, lakes and canals, but they drive off waterborne species like ducks. Their disturbance also reduces the abundance of shoreline wildlife – they are even known to eat water voles. Flea collars create unsafe levels of pesticide contamination in ponds when the number of dogs using the water regularly rises above 1. Requiring dogs to be walked on a lead may help alleviate some of these issues, but many nature reserves and landowners have banned dogs entirely.

Contrary to popular belief, it is valuable to have some muddy areas around pond/lake edges, created by intensive animal activity. Whether it’s livestock movement, deer, fox or humans activity, some patches of ‘poached’ ground where plants are sparse and bare mud is visible in winter are valuable habitat for invertebrates, with variability in disturbance, encouraging the formation of a sloping vegetation profile. The mud itself can be used as nesting material by everything from birds to bees, while footprints in it can be a useful way of identifying which species are visiting your pond/lake.

Standing Water - pond
Most of the issues which Standing Waters face come from human disturbance or pollution - water bodies which are in high use are more likely to be affected.

Restore

The value of artificial lakes and ponds is similar to their wild equivalents, as both types of ecosystem typically end up with the same community of organisms. In fact, artificial ponds and lakes include some of the UK’s most valuable aquatic habitats, such as Hatchet Pond in the New Forest, which is one of the UK’s reference condition lakes, or Orton Pit in Cambridgeshire – reputed to be home to the highest concentration of Great Crested Newts in the UK. Creating an aquatic habitat from scratch has the potential to deliver enormous value for biodiversity, especially in an area with scarce Standing Water resources.

Digging a pond or creating a lake by flooding a low-lying area of land isn’t without its issues. The resulting habitat will create short term increases in atmospheric carbon, but in the longer term, by ‘rewetting’ the adjacent soils, local carbon sequestration may offset this impact. Flooding high value (Priority) habitat is to be discouraged, but certain areas may benefit from rising water levels; in scrub and woodland, this can create valuable riparian zones, Wet Woodland and carr habitat, while limiting encroachment across grassland. Flooding or digging up Modified Grassland and degraded Arable land can lead to high nutrient levels in the water, but may offer benefits to the landowner in the form of increased water availability during drought.

Making a large new water body typically requires planning permission, and may also require consent from the authority which manages drainage in the area. But creating these features isn’t just a case of digging a pit – the profile of the hole should encourage colonisation of marginal plants, with shelves or gentle sloping margins – the structural diversity in a pond will be reflected in its biodiversity. Seasonal (‘ephemeral’) ponds and scrapes are almost as valuable as permanent water bodies, and the difference between the two may be hard to determine until after the hole has been dug. However, a pilot hole can allow you to assess the depth of the water table at its lowest point during late summer/early autumn.

New ponds do not need to be planted out, and in fact, placing plants into the water risks spreading invasive species – birds will bring water plants in over time on their legs (but only if you tip them generously). However, if your local area is lacking certain species due to a scarcity of water bodies, then sourcing seed within the region is a good way of improving plant diversity (be sure to check the plants are native). Some species, like Common Reed and Bulrushes, will rapidly colonise a new pond, so caution is advised when taking this approach. Transplanting rushes from damp ground immediately adjacent to the pond/lake into the margins can help to kickstart a thriving new ecosystem, by creating a valuable refuge and perch for invertebrates, without the risk of invasive aquatic hangers-on.

When an invasive plant has taken over an existing pond, it may be next to impossible to remove it. The species could be washed into nooks and crannies in bank vegetation, sink into the substrate or be regularly transported-in on wellies or animal fur. The best course of action is usually mitigation, rather than eradication. This starts with reduction of nutrient inputs, as high levels of nutrients favour lush, dominant growth of invasive species. Regular removal of plant matter may be necessary to reduce dominance and comply with legislation which specifies that landowners must prevent invasive species spreading off their property. However, in smaller, degraded water bodies it may be worth considering the ongoing cost of control versus the cost of creating a replacement, healthy pond nearby.

Pigs and wild boar are valuable in restoring degraded grassland, but wild boar are restricted to limited parts of the UK, and pigs require huge areas of land. For smaller landowners, pond creation can provide some of the benefits of pig rooting, as this process involves scraping off topsoil from a large area and spreading it across the land in jumbled clumps of turf and earth. On the pond edges, by stripping off the topsoil, a nutrient-poor substrate is exposed, while in the jumbled clumps, wildflower seeds, long-buried below the grass, are exposed and germinate. What you’ll typically get is a flush of thistles, ragwort and other agricultural weeds, unless the land was in particularly good condition prior to digging the pond. But this flush of growth will create an abundant ecosystem, which supports large populations of butterflies and seed-feeding birds.

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