Blue-green algal bloom on the River Stort. May 2. 2020.

At the end of April, there was a report of a blue-green algal bloom on the River leading to the death of fish and other wildlife. The bloom had been recorded as being between Lower Sheering and Roydon Park. The river was seen to be a dark khaki colour.

A sample was taken using a very fine plankton net and the sample then centrifuged to concentrate and looked at under a microscope at x100, x400 and x1000 magnifications.

 Here are the trillions of microscopic cells at x100 making the water khaki coloured.

 There was also quite a variety of other different types of algae such as this green one which is very much related to the green mould you get on the North face of a tree.

 There were some diatoms, but not anywhere near as numerous as would be expected.

 This is almost certainly a colonial form called Synura with each cell having beating filaments.

 This is a desmid called Closteruim.

 The actual identification of the golden/yellow/brown cells has been found to be quite difficult. In some cases the cells are joined in chains.

 In the majority of cases the chains seem to have broken up into individual cells which are shown in different aspects. The oval structures inside the cells are chloroplasts which the alga will use for photosynthesis.

Further Investigation will be needed to prove that these are the cause of the algal bloom but what could be causing the bloom anyway?

The reports put it down to a 'natural phenomenon' but I would suggest it is a natural phenomenon aided by Man.

Natural causes:

One of the driest April is on record = low river flow rate.

Unusually high temperatures for the latter part of April.

Man made causes:

7 sewage treatment works discharging effluent into the River rich in phosphates.

Low flow rate from low rainfall made worse by abstraction from the chalk aquifer in the Bishops Stortford area.

 Numerous narrowboat passages continually stirring up organic silt rich in phosphates from the treatment works.

This organic silt is smothering of water weeds which should be growing in the river and thus reducing their ability to oxygenate the water.

Road and hard surface run-off in times of heavy rain bringing pollutants from road traffic.

Is this something which we must expect on a regular basis because it is causing an ecological disaster on the river?

One of the solutions would be to have phosphate stripping at the treatment works which would remove the fertilising effect of the phosphates, thus reducing the organic silt and nutrients which is what is promoting algal growth along with the higher temperatures.

Frog Blog.

Frogs spawned on Sawbridgeworth Marsh on the 9th March.

Pictures by DS. Sound recording RR.

The eggs in the spawn are surrounded by mucus which helps to protect the eggs from predators and changes in temperature.

The egg is dividing many times to form an early embryo called a blastula. This becomes a hollow ball of cells which then gets pushed inwards to form a cup shape which is called a gastrula. At this stage the fate of the cells becomes determined into which ones will become muscle, nerve and organ tissues.

Areas can now be determined which will become the head, body and tail. Small gill buds are appearing on the side of the head.

The gill buds have formed into feathery gills. The whole body is still contained within the egg membrane.

The developing tadpoles have now got some degree of muscular movement and start to break free from the egg membranes. They tend to collect together at the top of the spawn mass.

Where is Badgers Patch?

In his inaugural speech to the newly formed Bishops Stortford Natural History Society in 1935, PBM Allan, author and publisher described to the newly assembled members the wide scope of natural history available within a radius of the Corn Exchange which is the central point in Bishops Stortford, at the intersection of Wind Hill, Bridge Street, North Street and South Street. There is some uncertainty as to the actual size of the area and so I have chosen a 5 mile radius, which is the basis of Badgers Patch and is the study area for the Natural History Society today.

Although we have a lot of housing development taking place locally there is still a huge amount of varied countryside available for us to study and enjoy. To the North the area extends onto the Chalk with its characteristic fauna and flora. To the West we have typical Herts countryside with isolated woodlands in a rolling landscape. There is also here the River Ash which is a chalk river. To the South. We have the River Stort Valley with its backwater loops and mill streams set in a relatively un-drained alluvial floodplain. There are also a chain of nature reserves and SSS eyes. To the East we are onto the undulating Chalky Boulder Clay lands of Essex with Hazel and hornbeam woodland.
How fortunate we are to have all this relatively local to us. In the current crisis where travel is going to be limited and restricted we can still access these areas and in the coming weeks I hope to be able to illustrate some of these aspects but please do send me your own records and photographs to be added to the website and this blog.