All posts by bobgomes

Pond Scum

Floating mats of pond scum are an annual feature in Stonebridge Pond and on the allotment watercourses, where they tend to accumulate upstream of the two sluice outfalls. I thought I would take a closer look to see what the scum consists of. The samples which I took showed that the majority of the scum consists of two species of green filamentous algae, Spirogyra species and Vaucheria sp that form threads or mesh like filaments, with lesser amounts of other algae and diatoms. What we see with the naked eye as one strand are several microscopic strands lying adjacent. The strands shown below are 77 -90 microns in width. 1micron (µm) is 1/1000 of a millimetre.

Spirogyra low magnification. Vaucheria and Spirogyra high magnification

The algae are important because they produce oxygen and food for animals that live in the pond. These primitive plants grow under water lying on or loosely attached to the silt, especially in shallow water where the light penetration is high; but they can break free and form the floating mats of algae. The algae photosynthesise, producing oxygen and bubbles get trapped in the mats, causing them to float to the surface. This is when they can also cause problems such as clogs and stagnancy and create a sometimes unpleasant stench as the clumps decay.

Are clumps of filamentous algae unhealthy?

Most filamentous algae do not produce toxins that are harmful to humans and wildlife, but some of the bacteria and other pathogens living on the algal mats and assisting with the breakdown the algae may do so. Filamentous algae do not have roots. They get their nutrients directly from the water, meaning that their growth and reproduction are entirely dependent on the nutrients in the water. Accumulations of filamentous algae are caused by an overload of nutrients in the pond or water channels, especially nitrogen or phosphorus. Excess nutrients can unintentionally enter the water bodies as run off from fertilised crops, wildlife waste from ducks and gulls, storm water inflows and road run off. There are many sources of nutrients in residential areas. Disturbance of the silt may also contribute to the nutrient load because it may release chemicals bound to the silt.

Is the scum a problem?

1. Apart from large concentrations of scum that cause an unpleasant smell when it decays, the mats of scum are not hazardous to people or wildlife per se.

2 . If there was a toxicity issue we would quickly see multiple fish kills and sick and dying waterfowl.

3. If the source of nutrients is animal waste – and we don’t know that it is – it is likely that bacteria and other pathogens are living on the algae mats. Plot holders who come into contact with the scum, should wash their hands thoroughly or use sanitiser, as a precaution.

4. Physical removal of mats near to the sluices is undertaken and helps break up the mats clogging the outfall.

5. A reconfiguration of the outfall on the North Stream by the construction of a weir, as on the main outfall, would allow the algae to flow over the weir and into the creek.

6. Aquatic vegetation should be encouraged along the margins of the watercourses because the plants help the uptake of excess nutrients such as phosphates and nitrates and oxygenate the water. Much of the food for waterfowl, ducklings especially and other wildlife is in this marginal habitat..

There are other types of bacteria, known as cyanobacteria, formally known as blue-green algae, which can produce toxic chemicals that are very harmful to the health of people and animals. Cyanobacteria are particularly a health risk during hot summers. They also form scums on the surface and often accumulate along shorelines. They look like green or turquoise, wispy paint and leave smear trails across the water surface, when for example a stick is dragged across the surface. We have, to date, not suffered from this bloom in the allotments. The photographs below show cyanobacteria, Microcystis on a lake near to Faversham.

Algal growth is a natural occurrence and Nature’s way of capturing nutrients. The algae play an important role in the pond and allotments water and support a whole ecosystem, teeming with life, producing oxygen and food for animals that live in the water body. Much of the life is microscopic and invisible to the eye and is in turn a food source for larger animals. I have attempted to show some of it in the photos and videos below taken through the microscope. There is a large fauna of unicellular protozoans and other organisms, many of which feed on the algae and bacteria and help break down the scum. These are just a few microns in length, but even though single celled, some have very intricate organelles. All the organisms depicted were in one drop of water about 5mm in diameter! The grey background and halos around the organism are due to phase contrast illumination that is used to show otherwise transparent objects.

Click on the images to play videos.

Amoeba

Amoeba creep over surfaces using pseudopodia and change shape continuously by a process of cytoplasmic streaming as they wrap around prey and engulf it.

Paramecium
Stilonychia between decaying strands of algae.
Watch the middle one catch and engulf a free swimming algal cell. the small black dots are bacteria being wafted towards the animal by the beating cilia.

The above three are Ciliate protozoans. Ciliates have small hairs on their body to propel themselves through the water. Often there are specialised groups of cilia around the mouth opening which beat to draw in water and contents which are then ingested, as shown above. Others such as the species immediately above have cilia fused together into stiff bristles or cirri , mainly on the underside and the animals run about using the cirri as “legs”.

All photos and videos by Bob Gomes

A Minor Drama on the creek

Sunday 6th March

Emergency fire services vehicles and volunteers from British Divers Marine Life Rescue rushed to the top of Faversham Creek early on Sunday morning after being alerted to a Common Dolphin that had stranded in shallow water just below the outfall from the allotments.

Up to four fire service vehicles attended including the specialist animal rescue vehicle based in Faversham.

Thanks to a good team effort from the two services the animal was rescued successfully and taken to the Harty Ferry slipway at Oare Marshes where it was released into the Swale. Allotment Society members who were angling in the Swale on Saturday were treated to the sight of 4 – 5 dolphins east of Sheerness, so perhaps this unlucky youngster had become separated from the family pod.

Many thanks to the local Fire Service and BDMLR who responded so promptly and whose efforts resulted in a happy ending.

Road closure for Dolphin Rescue
Loading the Dolphin onto the rescue vehicle for transport to the Swale

New Gauge Board Installed

A water monitoring gauge board has been installed in the stream in Flood Lane. This, with two boards upstream in the Westbrook Stream and the water measurement levels taken on the allotment watercourses will contribute to a better understanding of how water levels fluctuate in the Westbrook catchment and inform management.

Thanks are due to the Friends of Westbrook and Stonebridge Pond who purchased the gauge boards and to Nigel of the Friends who calibrated the Flood Lane board to Ordnance data, Newlyn Cornwall.

An Exotic Visitor to the Pond

A drake Mandarin Duck has been on the Stonebridge Pond for the last few days.

The Mandarin Duck is a native of Eastern Asia where it is found mainly in China and Japan. It was introduced to Britain in the 1800s, with later introduction of free flying individuals at the beginning of the twentieth century and is now established as a breeding species in the wild. It nests in tree holes or nest boxes in woodland next to rivers and lakes. It first bred in Kent in 1935 and there are now 100 – 150 pairs nesting in the county.

It is perhaps the most beautiful duck species in the world. I photographed it today near to the duck feeding area.

Stream Clear

On Sunday 29th August four plotholders assisted the many volunteers from The Friends of Westbrook and Stonebridge clear encroaching vegetation from the channel between the allotments and Morrisons Green in Flood Lane. Sedges and Yellow Flag that had grown out from the allotment side and were partially blocking the stream were cut back to increase the width of clear water. A narrow fringe of vegetation was left to provide habitat for aquatic invertebrates, food for ducklings and other water birds and provide a refuge for young chicks. The Friends pulled out the cut vegetation for collection by SBC. Good work by all.

An unwanted Alien

Last year we discovered a few plants of the alien Indian or Himalayan Balsam, Impatiens glandulifera, also known as Policeman’s helmet after the shape of the flowers, growing in one of the water courses and on the adjacent allotment. The origin of these plants is not known.

Himalayan balsam is listed under schedule 9 of the Wildlife Act. Himalayan Balsam is regarded as an invasive weed by the Environment Agency of the UK Government. It is legislated under The Wildlife and Natural Environment (Scotland) Act 2012 under section 14 of the Wildlife and Countryside Act 1981nd Countryside Act 1981. It is an offence to plant this species or to cause it to grow in the wild. It was introduced to the UK in 1839 and is now a naturalised plant found mainly on riverbanks.

As an occupier of land –

We must not plant in the wild, or cause to grow in the wild, listed plants which are either non-native, or invasive non-native. This can include moving contaminated soil or plant cuttings. If we do, we can be fined or sent to prison for up to 2 years.

We must not do any of the following with them:

grow, cultivate or permit to reproduce.

The invasive weed can tolerate low light levels and can ‘shade out’ other plants so that it will gradually kill them off due to a lack of light.

Whilst Himalayan Balsam is an annual plant, its high level of seed production and vigorous seed dispersal means that it is highly invasive. Each plant produces at least 500 seeds, which can be propelled up to 7 metres from the parent plant by seed pods that are explosive to touch. Seeds remain viable in the soil for two to three years.

Hand pulling can be a very effective strategy where an infestation is relatively low. To attempt to fully eradicate Himalayan Balsam from a site, a key objective is to exhaust the plant’s seed bank. This is done by repeatedly removing adult plants before they set seed. Last year we managed to pull up and dispose of the plants before they set seed. So far, we have not recorded it again at the original location.

If you see this plant growing anywhere on the allotment, please pull it up and inform the committee of its presence. This should be done carefully to avoid stimulating the explosive release of any seed present. As a responsible Allotment Society, we have an obligation to control Himalayan Balsam populations on our land and help prevent the spread of the non-native invasive species. The photographs below by Bob Gomes illustrate the plant.

Recent cold weather arrivals

During the recent cold spell we were lucky enough to be visited by a Great White Egret. This large all white heron is about the size of the Grey Heron but more elegant with a longer neck and legs. It is almost twice the size of the more familiar Little Egret. In most years the Great White Egret has started to become a regular visitor to the UK. Its numbers have increased in the recent twenty years and it has now started to nest in a few sites in GB. The snow and freezing conditions appear to have forced the egrets off frozen inland wetlands or perhaps triggered an influx from the continent; up to 9 were seen on the coastal marshes in the Faversham area. One of these visited the allotments on Sun 14th Feb. when I was lucky to obtain some photographs. It was, however, seen off by our local Grey Heron that appeared not to want to share its favourite fishing spot!

Cormorants also moved onto Stonebridge Pond during the freeze. Normally we see just one or two occasionally, but there were up to 14 on the pond during the cold spell.

Great White Egret
Great White Egret and Grey Heron
Cormorants on platform
Cormorant