The Limb Brook

South Leigh is very fortunate to have its own natural stream running through and either side of the village and potentially it provides a wonderful range of habitats for our local wildlife. A brief survey of historical flora and fauna observed in and around the Brook, (as reported to me by local residents in March 2021; thank you to all who contributed), reveals that indeed it was a lively and thriving environment not so many years ago, supporting water voles, an otter, kingfishers, little egrets, moorhens, mallard, sticklebacks, dace, gudgeon, small trout, small pike, newts, frogs, toads, native crayfish, water boatmen, dragon flies and common water snails. Sadly, it seems very devoid of any life in recent years, with only some submerged water weed and flag irises surviving.

We have a working party in the village whose aim is to re-establish biodiversity in and around the Brook.

We will endeavour over time to share our progress and plans with everyone in the village.

It is very much a collaborative effort and all residents in South Leigh are welcome to contribute to our goal. Initial suggestions of how this may be possible will be outlined below, but any input would be very welcome. If you feel you can contribute further suggestions, please do not hesitate to get involved. You can contact me on the email below.

Improving the health of the Limb Brook

I am sure many of you are well aware of what is necessary for a stream to be regarded as healthy but I thought it might be helpful to summarise here what constitutes a healthy stream, as achieving this is our ultimate goal.

Pools, Riffles and Runs

No, this is not a polite description of incontinence, but it describes the natural structure of a stream.

Pools: These are areas of the stream characterized by deep depths and slow current. Pools are typically created by the vertical force of water falling over logs and large stones. The movement of the water carves a deeper indentation in the stream bed. Pools are important because they can provide depth and still water.

The depths of pools provide refuge during dry conditions, protection from predators and shelter. The water flows a little slower which allows the organic debris to settle out and provides a food source. Another advantage is that species do not have to relocate to another area if the stream level starts to lower.

Riffles: These are areas of the stream characterized by shallow depths with fast, turbulent water. The riffles are short segments of the stream where water flow is agitated by rocks on the bed of the stream. The rocky bottom provides protection from predators, food deposition and shelter. Riffle depths vary depending upon stream size but can be as shallow as 2.5cm or as deep as 1m. The turbulence and stream flow results in high dissolved oxygen concentration.

Riffles are a food source, a shelter from predators, and a conveyor belt that brings food to the animals. Many species of invertebrates reproduce or grow to maturity in riffles. Riffles also hold larger prey and only animals that cling very well, such as midges, caddisflies, stoneflies, some mayflies and fish, can spend much time here, and plant life is restricted to diatoms and small algae. Riffles are a good place for mayflies, stoneflies, and caddisflies to live because they offer plenty of cobble gravel to hide in.

Runs: These are areas of the stream characterized by moderate current, continuous surface and depths greater than riffles. Runs are stretches of the stream downstream of pools and riffles where stream flow and current are moderate. The smooth surface allows for light to penetrate.

Runs are preferred by fish that are too small to compete in ponds, such as minnows.

Columnize Setting

A diagram to show pools, riffles and runs in a stream

These different areas in a stream create different conditions of stream flow, dissolved oxygen, turbidity, temperature and light and therefore create very different microhabitats for organisms.

Why are these conditions so important?

Stream Flow

Stream flow is greatest in riffles, moderate in runs and slowest in pools. If water flows too quickly some organisms cannot maintain their hold on rocks and vegetation. Current that is too slow results in stagnant water with low aeration and therefore low dissolved oxygen. The ideal flow rate is 0.3 – 0.69m / sec.

Dissolved oxygen

Dissolved oxygen is a source of oxygen for many living organisms and chemical processes. Dissolved oxygen is a measure of how much oxygen is mixed in with molecules of water. Wind, waves and bubbling of riffles can increase the amount of oxygen that enters the stream from surrounding air. Water with high and relatively stable levels of dissolved oxygen is typically considered to be a healthy ecosystem because it can support greater biodiversity.

0-2 ppm - not enough oxygen to support most animals
2-4 ppm - only a few kinds of fish and insects can survive Aquatic Earthworms, Leeches, Snails, True Flies
4-7 ppm - good for most kinds of pond animals Dragonflies and Damselflies, Craneflies, Alderflies, Crayfish, Clams and Mussels
7-11 ppm - very good for most stream fish Stoneflies, Mayflies, Water Beetles, Caddisflies

Turbidity

Clear water is ideal for wildlife.

Loss of clarity in water can be caused by algae and sediments.

Microscopic algae are present in most natural sources of fresh water and are an important food source for many small water organisms such as insect larvae. Their growth is dependent on good light and dissolved nutrients such as phosphates and nitrates.

Sediment is anything else the stream can carry, from stones down to tiny particles of soil. When there is heavy rainfall, sediment can wash into streams from surrounding fields and gardens, streams can run fast and banks can be eroded. Sediment can also be deposited into streams from sewage treatment plants and industry. Cloudy water can cause a number of problems for wildlife:-

  1. It absorbs more sunlight, raising the water temperature and reducing the amount of oxygen the water can carry.
  2. It creates shade and stops sunlight getting through to rooted aquatic plants; fewer plants means less photosynthesis and less released oxygen for aquatic fauna.
  3. The particles can clog fish gills, depriving them of oxygen and inhibiting normal growth.
  4. It hides predators from their prey.
  5. When the sediment settles out, it may smother fish and insect eggs and suffocate newly-hatched insect larvae. It eliminates living spaces for aquatic insect larvae and covers spawning beds for some fish species. It can also make the stream shallower.
  6. Sediment can carry pollutants which accumulate in the decomposing vegetation in the bed of the stream. Invertebrates which feed on this source of nutrients absorb the pollutants, which then accumulate over time in the bodies of their predators.

Temperature

Temperature varies depending upon climate, light penetration, surrounding vegetation and groundwater input sources. Stream temperature can affect species composition through biological processes (metabolic rates) and ecosystem processes (leaf breakdown, nutrient uptake). Warmer water holds less oxygen, which means a decrease in dissolved oxygen levels. Colder water temperatures are favoured by many fish and macroinvertebrates.

Temperatures of between 4ºC and 25ºC would support good plant growth and species diversity.

Light

A balance of light and shade in a stream is important to create conditions and habitats for a variety of flora and fauna.

Dissolved chemicals and assessing water quality

A stream requires some level of dissolved nutrients in its waters to nourish plants and to support their growth. If there is an excess of these nutrients however, a process called eutrophication can happen and ultimately lead to a lack of oxygen which then leads to the death of many organisms. In addition, the chemicals themselves can also be toxic and fatal to wildlife.

As a starting point to investigating the lack of life in the Limb Brook, I have been analysing and recording the ammonia, nitrites, nitrates, phosphates, pH and temperature of the water in the Brook from four sites around the village since February 2021, and I will continue to do so throughout the year, to provide a baseline of data on chemical composition to see if that is a contributary factor to the paucity of observable wildlife. The sites chosen are:-

Site 1: Just before Shuttles on the Witney side.
Site 2: The Mason Arms.
Site 3: Lymbrook Close.
Site 4: Barnard Gate Road first bridge before the confluence.

In summary, February and March samples have revealed the following:-

  • Ammonia levels are zero. That is excellent.
  • Nitrites have ranged from 0 to 0.5 ppm. This is an acceptable level.
  • Nitrates have ranged from <10 to 25ppm. This is a toxic level to wildlife, particularly invertebrates. The highest levels are recorded downstream from the sewage plant outlet in Lymbrook Close, but they are also fairly high in the water upstream from there.
  • Phosphates have ranged from 0 to 0.40 ppm, the highest levels again being downstream from the sewage outlet in Lymbrook Close. Moderate wildlife diversity will be seen when levels are around 0.10 ppm, and maximum diversity around 0.01ppm so the higher levels I am seeing are worrying.
  • The pH has ranged from 6.5 to 9; 6.5 – 7.5 is ideal; 9 is a bit high.

What wildlife should we expect to see in our stream?

Macroinvertebrates

Macroinvertebrates such as snails, worms, molluscs, leeches, crustaceans and insects are essential to the health of a stream. Not only do they serve as food for larger animals, but they also serve to recycle decomposing nutrients and help support the ecosystem of the stream. Macroinvertebrates are very sensitive to changes in the environment such as oxygen levels, pH changes and pollution.

The dominance of aquatic worms, leeches and midge larvae (pollutant tolerant) and the absence of mayflies, stoneflies and caddis flies (pollution sensitive) indicate an unhealthy stream.

The microhabitats of a stream provided by pools, riffles and runs can result in different communities of macroinvertebrates.

The table below may display better if viewed in a landscape position so, if you're reading this, turn your device 90º

Feeding group

Food source

Habitat found

Major group

Predators

Other animals

Pools, riffles & runs

Stoneflies, Dragonflies and Damselflies, Caddisflies, Crayfish, Leeches, Planaria

Scrapers

Algae, bacteria, anything they can scrape off.

Pools

Water beetles, Snails

Shredders

Bacteria and fungi on leaf surfaces. They tear up leaves into smaller pieces (detritus).

Riffles

Crane Flies, Caddisflies, Stoneflies

Collectors - Gathering

Small pieces of food and organic matter, like broken up leaves along the stream bed.

Pools & Riffles

True Flies, Mayflies, Sowbugs, Crayfish, Clams and Mussels, Aquatic Earthworms

Collectors - Filtering

Catch small pieces of food and organic matter, like broken up leaves floating in water.

Runs & Pools

Caddisflies, Blackflies

Plants

Plants growing near the bank of the stream provide important shade that shelters the wildlife and helps regulate the temperature of the water. Leaves falling into the stream also provide food for the invertebrates. Vegetation is essential for filtering runoff before it enters the stream.

A healthy stream will have native trees, shrubs and wetland vegetation growing on its banks.

Grass, weeds and short tussock plants do not provide the shelter and filtration that tall plants do and can lead to an unhealthy stream.

Too many floating plants will exclude light from plants rooted in the bed of the stream.

If the populations of macroinvertebrate and plant species can be increased, it would attract larger vertebrate species higher up in the food chain to frequent the stream.

So how can YOU contribute to creating a healthy Limb Brook in South Leigh?

Many of you are lucky enough to have the stream running through or by your gardens. I would like to invite you to help by taking some action where you think you can make a difference and by keeping records of what you have done alongside a record the species that you see. Small differences from the efforts of many people can add up to major improvements overall.

So here are my suggestions:-

  1. Keep a dated record of your section of the Limb Brook alongside your garden. Rough notes are fine as long as I can read them.

  2. a) Take photographs of the Brook and the banks surrounding it each week as you put into action some of the ideas previously summarised. Record what you have done. An ongoing record of the stream's condition is important. Label your photos clearly with location and date.

    b) Keep a diary alongside your photographic record of any wildlife you see in the water, flying above the water, living along the banks. This includes plant life, birds, mammals, amphibians, insects and other invertebrates. Alongside this, if possible…

    c) Record how turbid (cloudy) the water is on a scale of 0-5 (0 = not turbid to 5 = really turbid)

    d) Measure the speed of flow of the Brook when you take your photo and record your wildlife diary (ie find a buoyant, shallow object. Measure out a fixed distance of water. Put your object into the water at the start and time its flow to the end of the measured distance. Calculate the speed of flow in m/sec.)

    e) Record water temperature.

    f) Record whether or not it is raining.

  3. Capture and destroy any American Signal Crayfish. They are destructive to our native freshwater fauna. Apparently, they are good to eat!

  4. Check your own household drainage from your property. Check for cracks and leaks in sewage pipes which run over the Brook where you live. Check that your appliances, such as dishwashers and washing machines, are not draining straight into the freshwater drain, but into the treatment drain. Otherwise, their contents will go directly into the Brook and detergents are powerful pollutants. If you take a sample of the water on the downstream side of your pipe, I am happy to analyse it to check its chemical content.

  5. Consider creating pools, riffles and runs along your stretch of the Brook to increase potential habitats and improve the general condition of the Brook. If your stretch is dammed, consider allowing the natural flow to be re-established. This serves to keep any pollutants moving, to introduce good nutrients for wildlife and to improve oxygenation.

  6. Ensure that the brook gets a good balance of light and shade. Clear some of the overhanging plants / trees / dead vegetation where there is too much shade.

  7. Re-introduce native plant species and create specific habitats for specific fauna; this can only help to revitalise the Brook once the water is healthier.

Please share your records with me about once a month if you can on the email below, or drop them round to my house if they are hand-written. I will collate the data so that we have an ongoing record of the Brook’s condition and its inhabitants.

I appreciate that there are stretches of the Limb Brook which run through local landowner’s fields which need attention and in order to work on these areas we will have to negotiate with and work alongside the landowners.

Let us work as a community to revitalise this precious natural environment.

Many thanks for your help.
Rita E. Sawrey-Woodwards, limb-brook@southleigh.info


Flooding, Limb Brook Pollution and Water Voles

Three important environmental initiatives have started, and all hands and eyes are welcome!

They are Flooding, Water Pollution and the encouragement of Water Voles and other wildlife along the Limb Brook. We shall report on water voles (and Forest Restoration) in due course, but while work on the other two has just started, here is an update and a call for help from anyone who might like to be involved. Much more will follow in the months and years ahead.

Flooding

This is a recurring problem in South Leigh and it has multiple causes. These range from inadequate drainage to blocked drains and seriously overgrown and congested streams. While the problem goes far beyond our Parish, it certainly starts in it because so does the Limb Brook. There are steps that we can take locally to help, but first we need to understand the problem.

Parish Councillor, Lysette Nicholls, has taken this long-term project in hand and, with others, has been researching the Limb Brook and other areas where run off causes problems - most of which end up in the Limb Brook.

Lysette has been in contact with our County Councillor highlighting the flooding issues and has drafted an in depth email with photos which has been escalated to Oxfordshire County Council to get them to look at issues that are directly under their remit. The areas highlighted include High Cogges, the pipe inlets on Chapel Road near Shuttles Cottage, the pipe inlets by The Mason Arms and where the Limb Brook passes under the road on the Barnard Gate Road through to Station Road.

Thames Water is also going to be contacted in regards to the brook in Lymbrook Close once further investigations have been completed in regards to pollution.

Flooding, Limb Brook Pollution

Like flooding, water pollution is a serious and long-term problem that we believe has increased over the years and must now be assessed and addressed. Again, we must understand it, but what we already know is that it starts in our Parish. Why? Because, like noted above, the Limb Brook starts in our Parish. Also, as above, we need help!

The pollution in the Limb Brook is there for us all to see. Murky water, thick brownish foam, even a smell. With polluted water, the whole natural cycle suffers - plant life, water-borne life and other animals all of which live, or would like to live, along the banks or in the stream.

Here, Parish Councillor, Graham Soame, has been making vital early steps and has formed a close alliance with similarly concerned people in Eynsham and the Eynsham Nature Recovery Network.

The Preliminary Plan

Before we can do anything to fix the problem, we need to know what the problem is, and then the exact extent of it. In this, our neighbours in Eynsham have been very helpful through giving us some spare water testing kits.

Initial tests have been done and Lymbrook Close resident, Rita Sawrey-Woodwards, has brought her invaluable knowledge as a bio-chemist to the task to help us understand what the results mean and how to go forward. She has recommended a programme that is this, in brief:

  1. Map the course of the Limb Brook and its source. This has been done.
  2. Identify land use / industrial use / possible sewage sources along the brook.
  3. Start chemical water testing to identify the pollutant(s).
  4. Start regular fauna / flora observation.
  5. The above schedule of activity would be monthly for a year in order to cover the farming and climate cycle and to see 'patterns'. Then:
  6. Collate, quantify, analyse and understand the data.
  7. Understand what levels are acceptable/liaise with local and national bodies.
  8. Approach possible polluters to make changes of practice.
This process will continue until the pollution itself can be eliminated at which point the re-wilding can be started. As noted, this is a long-term initiative and supporters are most welcome to help build the data and clean up what was in living memory, a natural haven for wild life.

Martin Spurrier (February 2021)

Flood outside pub
You will remember this light-hearted picture from 2019. But flooding is serious.
Flooding
Flooding of the Limb Brook at the east of the village. (Photo © Martin Spurrier)
Brown scum
Thick brown scum on the Limb Brook along Chapel Road (Photo © J. Ashwell)

As part of the investigation into the paucity of life in our local stream, the Limb Brook, if you have any memories of any plants or animals that you have seen in and around the Limb Brook in the time you have lived in the village, can you please contact me and tell me about them.

Many thanks.

Rita E. Sawrey-Woodwards    limb-brook@southleigh.info