CBC Chat Forum Thread

AuthorTopic: The Death and Re-Birth of a Lake
Leonard Bentley The Death and Re-Birth of a Lakeposted at 30/09/2014 10:25:50


For most of December 2012 there wasn’t a lake at Bayfield, just a long tongue of mud.  There were a few muddy pools which were fished by 5 Herons and 2 Little Egrets, catching only small items.  When this food supply was exhausted the birds departed leaving only an apparently dead stretch of black mud.  How had this come about?

Silt and silting can change landscapes, Ephesus, in Turkey once a mighty Roman port is now 7 miles from the sea behind a plain of fertile alluvial (i.e. silt) soil.  On a very much smaller scale the southern end of the Bayfield lake silted up, dried out and a succession of plant life flourished.  (There is a plus side and this habitat holds Water Rail).  Silting occurs when a fast flowing river has its flow interrupted.  In the case of Ephesus the walls of the port and at Bayfield the construction of the dam around 1879 by Jodrell, the then owner, to form the lake.  While flowing naturally the velocity of the water holds the silt, washed off the land, in suspension.  When the flow is slowed the silt sinks to the bottom.  Silting of the lake began  the moment the dam was in place.

In May 2012 it became apparent that the lake would again need to be de-silted.  Mud pumping began in June and continued until the end of October.  It was only partially successful so the river was cut off by a sluice and lake was drained leaving things as already described.  However taking more silt out mechanically proved not  to be feasible.  Then something dramatic happened.  Around 26th, 27th December the lake re-filled to near capacity while still isolated from the river.  Ground water from the sloping grazing flanks was apparently the cause.  It seemed magical, but there were more surprised to come.  Within a day 5 Mallard appeared and by 31 December there were 28 Mallard and 14 Teal.  Both are dabbling duck and could feed on the marginal vegetation.  It was nice to see, but below the surface we knew that there was only seemingly lifeless mud.

With the encouragement of Robin Combe it was decided to form a team to study the progress of the lake’s recovery.

-   Carl Sayer (CS) Lecturer at University College, London, on shallow lakes etc

-  Lorraine Marks (LM) Environment Agency, water quality

-  Len Bentley (LB) Birds and other wildlife

This team was to have a series of lakeside visits, while LB would monitor the breeding success  of the returning birds.  Salient dates were as follows:-

31st Dec 2012   : 28 Mallard, 14 Teal.  About half the “normal” (i.e. pre 
                          silting) level

8th  Jan 2013     : Also present 12 Gadwall, 2 Shoveller, 6 Moorhen, 6   
                           Tufted.  The latter feed by diving and grazing the                
                           the submerged vegetation of which there was none.
                          so they presumably fed elsewhere.

2nd Feb             : Male and female Mute Swan, 10 Tufted, perhaps keeping
                          contact with their breeding site

22nd April       : Pair of Canada Geese and 3 Greylag Geese present but did
                         not breed.  Brood of  Mallard (6), Egyptian Goose (6).
                         Mute Swan building nest at traditional site (abandoned in                
                         2012) 
                
30th April        : First visit of the team.  CS had maintained that the mud                
                         bottom would hold a seed bank.  He was right.  Using a drag
                         rake samples of vegetation were hauled in and he identified              
                         5 species (Ridged hornwort, Curled pondweed, Least         
                         pondweed, Fennel leaved pondweed, Horned pondweed)
                         This vegetation was about 3cm high and contained a small
                        amount of snails’ eggs.  Also small patches of White water-
                         lily and Ringed water lily.  This result was hugely
                         encouraging.  Water green-brown with algae.  May clear                      
                          soon.

1st May           : Female Mute Swan incubating eggs.  Egyptian Goose
                        brood of 6 all eventually  predated.  Not by pike (as previously
                        thought) but probably by Carrion Crows (or otter or gulls)

18th June       :  Pair of Mute Swans with 4 cygnets, eventually 3 to fledging





27th June       :  A team visit yielded Amphibious Bistort and Blanket weed.  The
                       other aquatic vegetation  had grown considerably and held many
                        invertebrates we could not identify.  Thousands of froglets.

24th July         : A team visit yielded Canadian pondweed and Stonewort.
                        also the water was clear of algae. 2 pairs of  Moorhen
                        with chicks and 1 brood of Tufted.  Dragonflies: Emperor and
                        Migrant Hawker, Broadbodied Chaser, Common Darter.Banded    
                        Demoiselle.

27th August    : 1 Little Grebe.  This species relies heavily on invertebrates
                         which it reaches by diving to search the submerged 
                         vegetation.  Water still crystal clear.

25th Sept         :  5 Little Grebe indicating a good supply of invertebrates,
                         which will be good for fish when restocking takes place.

There was a spell of hot weather during July and August but the lake level did not fall significantly.

Mute Swan (3 cygnets to fledging), Egyptian Goose, Mallard, Tufted Duck and Moorhen all bred.  Present but not breeding were Canada and Greylag Geese and Gadwall. Curiously Coot did not re-colonise.

The lake was noticeably deteriorating in 2008 and Canada and Greylag geese did not breed in 2008-2011, indeed in 2012 there were very few broods of anything.  Prior to 2008 the breeding success was: Canada 1 brood, Greylag 1 brood,  Egyptian Goose 1 brood, Gadwall 2 broods (none in 2013), Tufted 4 broods (1 in 2013), Moorhen 4 broods (2 in 2013), Coot 2 broods (none in 2013).



…….
Thinking back to the black mud, the recovery of the lake has been more rapid than expected.  The hope is that a full recovery will be reached in 2014.  In the coming year we shall make every effort to reduce the level of phosphate, which is staying stubbornly too high.  Also, we shall widen our scrutiny of returning wildlife.







Carl Sayer
Lorraine Marks
Len Bentley


January 2014


                                        


 

Leonard Bentley 2014 Updateposted at 30/09/2014 10:35:02



The further recovery of the lake did not take place at the pace that had been expected.  Canada, Greylag and Egyptian geese did not breed, nor did Gadwall. Tufted duck did, but only 1 female with 1 duckling.  Previously 4 with some 8 – 14 ducklings.  Mallard broods were fewer.  The established pair of Mute Swans failed because the female was obviously a sick bird and for the first time another pair nested at the northern end but were only partially successful, raising 1 cygnet.  At different times a female Mandarin and a drake in eclipse  were present for a couple of weeks or so.  Mandarin did breed in 1998 but all ducklings were quickly predated. Coot did eventually return, but to the southern end not the usual northern end.  Moorhen had a satisfactory breeding season.  Many dragonflies and damselflies present.
There was, however, one important success: Little Grebe nested and raised two broods, one of 4 young to fledging and a late brood of just one young. This as the first time Little Grebe had nested since 1997.  To see 2 adults and 4 chicks all diving and catching very small fish was a clear indication of the health of the fish stocks and of the lake itself.
The second brood hatched after the excavation of the new channel for the river on 4 August .  The noise virtually emptied the lake of ducks, but the Little Grebe did not desert.

L G Bentley
September 2014

Kath & Mick Claydon Re: 2014 Updateposted at 03/10/2014 22:03:25

An interesting read - thank you for posting this article. 

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