Widewater:   SALINITY PAGE
Widewater is a landlocked brackish lagoon approximately 1066 metres long and 90 metres at its widest point when the lagoon is in flood. It was created by Man from the original Adur estuary after been landlocked by longshore drift and violent storms. The waters are replenished by the sea, which filters up through the basin of the lagoon on very high tides, and also by rain water. There is a dramatic rise in the level after heavy rainfall, more than can be explained by the rain landing directly on the lagoon flood plain. Man has built up banks on the perimeter of the lagoon to prevent flooding to this nearby reclaimed land, now turned to residential use. The quantity of water contained within the lagoon and salinity are liable to fluctuate wildly. The flood plain covers an area of 18.5 acres.

At its maximum flooding with a measurement on the gauge by the bridge giving a depth of 1.60 metres, the lagoon will cover an area of 4.6 hectares (=11.4 acres) with a perimeter of 2282 metres.

by Steve Barker and Andy Horton


 
17 December 2012
The gauge registered 1.76 metres after persistent rain.

18 October 2012
The gauge registered 1.76 metres, the highest I have ever recorded by 10 cm, after the high tides and storm surge.

7 October 2010
The gauge registered 1.65 metres, the highest I have ever recorded,
19 February 2007
The flooded Widewater Lagoon registered 1.64 metres on the gauge by the bridge, as high as the lagoon gets after the spring tides and recent rain, with the pipeline fully open. 

12 September 2006
The flooded lagoon registered 1.64 metres on the gauge by the bridge, as high as the lagoon gets after the spring tides of the last few days.


11 November 2005
The level is 1.62 metres and the salinity was measured by John Knight (WSCC) at 27. The salinity reduction was expected after the rain in the last few days.
Adur Weather Page

7 November 2005
There were at least eleven Cormorants and two Little Egrets on a flooded (1.64 metres) Widewater.

20 June 2005
Shore Crabs, Carcinus maenas, were observed dying in isolated pools in Widewater Lagoon. (These were probably moulted shells.)

Report by Derek Neate (FOWL)


With the low level (0.27 metres) of the lagoon, the patch of water by the inlet pipe became isolated from the main body of water. In this puddle the salinity was recorded at a hypersaline 42.8 after two weeks of warm weather (air temperatures over 24° C and over 27° C) and a water temperature of 30.2° C. The main body of the lagoon registered a salinity of 37. (The conditions were favourable for evaporation.)

Readings by John Knight (WSCC)


These two events are probably connected. In June (in Sussex) the Shore Crab moves in estuaries and into lower salinity water than the sea. In water temperatures of over 28° C or with a salinity over and above natural seawater at about 34.5 this crab has been known to leave the water and perish if it is unable to find a favourable niche. (The conditions are outside its natural amplitude for survival.)

12 April 2005
Five Little Egrets fished in the flooded lagoon (1.59 metres). One Little Egret caught and swallowed  what, because of the flash of silver, looked like a small fish. The salinity near the bridge was 33.1.

8 February 2005
The lagoon level had dropped to one of the lowest since the pipeline was installed. The gauge read 1.35 metres (above Chart Datum or Ordnance Datum?). The explanation was a lack of rain in January.
 
Cllick on the image for a detail of the gauge The electronic meter for measuring salinity and water temperature Eastern end showing the extended bar and the island

Salinity is now measured by John Knight of West Sussex County Council using an electronic meter that recorded 26.
WSCC Environmental Monitoring at Widewater Lagoon 2004 & 2005 (Link)

12 October 2004
The salinity readings taken by West Sussex County Council Rural Strategy Unit with the electronic meter measured 34.7 which is full strength seawater. This matched my hydrometer readings from previous years since the pipeline has been installed.

The Strong Breeze (Force 6) and showers were from the south and south-east.

3 September 2004

The gauge by the bridge read 1 m 55 cm.

28 May 2004
Despite the pipeline still being open the level is down to 35 mm leaving muddy margins and the bar near the island exposed. A black and white dog disturbed a pair of Ringed Plovers which may be nesting on the Thrift covered flood plain. It had been a generally sunny and dry month with very little rain.

6 May 2004
High spring tides had raised the water level in Widewater Lagoon to 65 mm.

10 March 2004
Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.025 at 15° C. This gives a salinity of about 34 (ppt). However, after deducting the hydrometer correction figure we arrive a salinity of 29 (ppt). However, I am not sure the calibration is correct as the more accurate hydrometer shows full strength seawater at 35 (ppt). The water seems clearer (like tap water now) than the normal orangey colour when viewed in a white bucket.

6 January 2004
After missing taking the salinity reading in December 2003 because of influenza, I passed the travellers camped in the car park to collect the water sample.
Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.020 at 15° C. This gives a salinity of about 28 (ppt).
However, after deducting the hydrometer correction figure we arrive a salinity of 23 (ppt).
This compares to a figure of 15 (ppt) in January 2003.

28 December 2003
After over 40 mm of rain the previous day and over night, the water level of Widewater Lagoon on the gauge by the bridge is 1 m 66 cm, the highest level recorded in 2003. A water sample was not taken because of illness.

28 November 2003
The water level of Widewater Lagoon on the gauge by the bridge is 163 cm. At the high spring tide a Little Egret was stationed by the inlet where the water was flooding in.

24 November 2003
Despite the steady rain in the last two days and some high spring tides, the level of Widewater Lagoon has only risen to 1 m 58 cm.
Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.022 at 17° C. This gives a salinity of about 30 (ppt).
However, after deducting the hydrometer correction figure we arrive a salinity of 25 (ppt).

23 November 2003
A considerable amount of heavy rain fell continuously throughout the day, stopping as darkness fell. By midnight the total was 27.69 mm (just over an inch). This was the greatest amount of rainfall in a single day this year and the heaviest since 10 August 2002. On 22 November 2003 the rainfall total was 14.93 mm.

5 November 2003
The water level gauge read 1 m 52 cm, a fall of 13 cm in six days.

3 November 2003
After a couple of days of rainfall, I expected the lagoon to be more dilute. Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.022 at 16° C. This gives a salinity of about 30 (ppt).
However, after deducting the hydrometer correction figure we arrive a salinity of 25 (ppt).
(I am not happen about the accuracy of these hydrometer readings, so they should be just a general guide.)

31 October 2003
 

Estimated 1 m 50 cm level
1 m 65 cm (31 October 2003)
1 m 52 cm (5 November 2003)

After nearly 25 mm of rain in the last three days and the high tides, Widewater was in flood and the spit at the east end near the island was completely under water. The height reading was 1 m 65 cm. This level was higher than at any time this year. West Way, Lancing (at a lower level) was not flooded, the rain water quickly drained away.

Gauge on 5 October 20035 October 2003
It seems hardly worth taking the specific gravity (to calculate salinity) readings as I expect again that the readings will be identical to natural seawater.
The water sample seemed clearer than previous ones (the water looks very orange in the small bucket, but always looks clear in the glass.measuring chamber).
Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.029 at 13° C. Using the method before correction this would give a salinity of 39. However, after deducting the hydrometer correction figure we arrive a salinity of 34 (ppt). The more reliable narrow spectrum hydrometer gave a reading of 1.026 which actually would mean a saline figure of 35.
It is fairly clear that Widewater (at least in summer) is now a fully saline lagoon.

2 October 2003
Despite a small rain shower of just 3.54 mm, the lower high tides means the water level of the lagoon has fallen fractionally, by 2.5 cm, since 30 September 2003. The has been a report of small flood in West Way, Lancing, an event that is associated with high spring tides.

30 September 2003
It is surprising how full Widewater Lagoon can look after just a small rise because of the percolation and sea rushing through the inlet. The water spreads out over the flat flood plain, submerging most of the Glasswort.
 

Gauge on 30 September 2003

26-27 September 2003
The inlet pipe to Widewater Lagoon has not been detrimental to the autumn Glasswort, Salicornia,as if anything the splendid and unusual scarlet fringe to the lagoon is even more dramatic than usual. A large Little Egret was feeding to the west of the bridge. The amount of water coming in was at a greater volume than I had seen before, but this may be because it was at the peak of a high 6.5 metre equinoctial spring tide. The lagoon water level is as high as I ever seen after a slight fall of a few centimetres during the neap tides last week.
 

 Inlet Pipe
Red Glasswort  by the Inlet Pipe

8 September 2003
Despite the huge influx of seawater through the pipeline, the water lagoon is still orangey, which may (guessing) reflect a large amount of dissolved organic carbon (DOC). The local residents are happy with the flooded lagoon and as the smells (hydrogen sulphide) are gone and it looks more attractive (arguable). The level of the lagoon is as high as I have ever seen it, and as high as after exceptionally heavy rainfall in October 2000. The dissolved oxygen level was almost certainly low in the summer so the lagoon does not mimic estuarine conditions (e.g. if the Adur estuary was flooded their would be a dissolved oxygen shortfall below limits which could support large or even small fish).

Comment:
Nobody has written down the hydrology of Widewater Lagoon and the nearby water table, at least not in the public domain. I am not sure if the amount of water coming in and the salinity is being monitored by the authorities, at least not publicly. The long term ecological and hydrological consequences is their responsibility. The best the public can ask for is to make the information public and pray that the Environmental Agency (in charge of the pipeline) know what they are doing.
 

Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.028 at 22° C. Using the method before correction this would give a salinity of 40. However, after deducting the hydrometer correction figure we arrive a salinity of 35 (ppt), which is full strength seawater. The other hydrometer (calibrated at 15° C and verified accuracy with fresh seawater) gave a SG reading of 1.027, which would give a salinity of 37. Unfortunately, hydrometer readings are not really accurate enough for more than a general guide.

4 August 2003
The level of Widewater Lagoon exceeded any observed level during the summer and the lagoon was as high as it is at peak levels in February of each year. This can be judged most clearly by the water coming over the wooden slats near the bridge. This will extra water coming in through the pipe and some much seawater has been allowed in, I would feel fairly confident to predict that the salinity will match that of the open sea, i.e. 35 or thereabouts. There seemed to be excessive sediment as well and broken off bits of weed or plankton in the collection bucket.
 

Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.026 at 24° C. Using the method before correction this would give a salinity of 38. However, after deducting the hydrometer correction figure we arrive a salinity of 33 (ppt). The more reliable narrow spectrum hydrometer gave a reading of 1.026 which actually could mean a hypersaline figure of 38. Unfortunately, hydrometer readings are not really accurate enough for more than a general guide. (The explanation in this case, is maybe the correction figure is wrong to adjust for the different calibration? I expect the calibration scale on the wide spectrum Taiwanese hydrometer is just wrong.)

18 July 2003

The combination of the high tides and the new inlet pipe have resulted in Widewater Lagoon being in flood comparable to winter. The flood plain wild flowers (weeds) are under threat from the saline conditions, possibly including the Sea Heath, Frankenia laevis.

16 July 2003
The pipeline is still open and the lagoon level has risen considerably after the recent high spring tides (in excess of six metres). With evaporation in the recent excessively hot weather, I would anticipate that the salinity can only have risen above that of in the sea. However, as I have never recorded salinities in excess of sea water in Widewater Lagoon, there may be a reservoir of water under the lagoon which maintains a maximum level of 35 or thereabouts even when the lagoon dries out, i.e. it does not necessarily go hypersaline.

Pupils from St. Andrew's School, Worthing, were collecting lagoon critters in the rain.

High tide occurred about 2:00 pm and I have never seen so many bubbles going up through the bottom of the lagoon for almost its whole length. Furthermore, the sea was gushing in through the pipeline. According to Derek Neate (FOWL), four slats have been lifted off the inlet pipe.

Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.026 at 22° C. Using the method before correction this would give a salinity of 37.5. However, after deducting the hydrometer correction figure we arrive a salinity of 32.5 (ppt).  The narrow spectrum hydrometer (calibrated at 15° C) recorded 1.025 (a small fall) which translates to 35 (ppt).

As I was beginning to suspect, the salinity in the lagoon does not actually rise above that of fresh seawater, as none of my readings in the past have exceeded 35 (ppt).

Where does the water go when it leaves through the lagoon floor? Does it go back out to sea? It would be ironic if it actually builds up the water table in the Hasler Estate (to the north and below sea level) as the whole sea defence plan was to prevent winter floods.

There is also the impact of the high lagoon levels on the wild flowers of the lagoon flood plain to consider.
 

10 July 2003

The mud was very soft in a metre band on the lagoon's southern edge.

4 July 2003
 
I would say that a Management Plan should be drawn up, although my initial summary as as follows:

1)  I would say that Widewater was too small and isolated to maintain as a brackish water lagoon with precise control. Always there will be a once in a decade extreme conditions. (With the best will in the world, extreme conditions leading to species loss would be inevitable and new recruitment would not be certain. These occurrences could be minimised.)
2)  I do NOT think Edwardsia ivelli (sea anemone) was a good species in the first place.
3)  It might be a good idea if it did not become excessively salty though, for bird food: sticklebacks and prawns
4)  It might be a good idea if it didn't become too salty for the Lagoon Cockles, Cerastoderma glaucum, and if it did not dry out completely either. Some cockles are lost through desiccation.
5)  I might be inclined to restrict the seawater intake in May and June as their is excessive plankton, Phaeocystis, in the seawater. It might end up looking grotty with excessive nutrients and a possible mass kill of the exceptionally hardy lagoon life through a dissolved oxygen shortfall. (The cockles may be tolerant of low oxygen concentrations in sometimes hypoxic mud.)
6)  I have know idea of how the saline concentration affects Salicornia sp. (Glasswort). It is probably counterproductive to Ruppia (an unattractive looking flowering plant of brackish conditions), but I am not sure that Ruppia is an asset, or that it is naturally occurring as almost every other species is of marine origin.
7)  The current sea anemone found, Haliplanella lineata, is an alien, as is (probably) the missing hydroid, Thieliana navis (=Clavopsella navis).
8) The water must run out of the bottom in hot weather through the cracks? (The hydrology of the lagoon must be the most important management concern.)
9)  In very hot summers, the amenity value of the lagoon diminishes with the lack of water and the hydrogen sulphide smell (probably occurs to some extent every year) is an unpleasant pong. (This occurs on the Adur estuary as well at low tide.)
10) It might be an idea to include suspended particles in seawater in any ecological equation. 
11) The level of the lagoon can effect the distribution of wild plants on the flood plain as some will not tolerate an increased immersion in salty water. 

In short, although Widewater is unique, its main wildlife amenity interest is botanical (plants on the shingle) and ornithological (birds will not be attracted to a dead salt pan lagoon though).

 


Popular activities at or around Widewater (excluding beach):

Birdwatching in all months of the year
Dog exercise area, with faeces remaining
Cycling: important route from Shoreham to Worthing (marked on OS map)

Minority interests:

Botanical interest in shingle and some unusual and rare plants


4 July 2003
Afternoon
It looks like that far more sea water is being allowed in through the pipe than was ever percolated through the shingle, and the salinity figures seem to indicate this.
 

Water intake on a 5.7 metre high tide
Despite the regular updates with fresh sea water, on a humid 70% and overcast day, temp. 21° C, wind force 4, the photograph shows an area of wet mud. This is not  evaporation. There is there a leak in the bottom of the lagoon where the water runs out through the cracked alluvium/clay after a dry spell. 

Surprisingly a fall in salinity was detected today. Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.026 at 22° C. Using the method before correction this would give a salinity of 37.5. However, after deducting the hydrometer correction figure we arrive a salinity of 32.5 (ppt).  The narrow spectrum hydrometer (calibrated at 15° C) recorded 1.025 (a small fall) which translates to 35 (ppt).
 
 

A very cleverly designed inlet pipe that would foil anything but the most adventurous Shore Crab

The lagoon may not be going hypersaline. There may be a reservoir underneath the lagoon? (This will contain seawater at 35 in low rainfall times, and it is leakage rather than evaporation that is causing the fall in water during the summer. In the past, in five years measurements during the 1980s, I never recorded any salinity readings in excess of full strength seawater and virtually all summer salinities were in the brackish range, i.e. under 30.)

Morning
Another appreciable rise has been caused by the pipeline being left open on the medium spring tides, which will cause the water in Widewater Lagoon becoming too saline to support aquatic life if it continues at this rate of increase.

The water level rise can be compared in the photographs below. This is caused by the input of seawater, not by rainfall.

2 July 2003
I got caught in a rainfall deluge and there was intermittent showers and early morning rain since the photograph yesterday. By midday the rain had caused the level of the lagoon to rise as shown in the following photograph:

 
The level was still not as high as on 11 June 2003. The rainfall according to the for the period both between the two photographs and the two specific gravity readings was 12.19 mm (precise figures available). I would estimate that the lagoon level has risen by about this amount which is rather convenient (but, perhaps, not surprising) and expected.
Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.028 at 22° C. Using the method before correction this would give a salinity of 40. However, after deducting the hydrometer correction figure we arrive a salinity of 35 (ppt), which is full strength seawater. This is the same as yesterday. The other hydrometer (calibrated at 15° C and verified accuracy with fresh seawater) gave a SG reading of 1.026, which would give a salinity of 36.
The Environmental Agency should be monitoring the salinity levels if they are the agency responsible. They have the more accurate equipment capable of measuring the small changes, which is not practical using a hydrometer. The hydrometer calibration scale is only 1 mm for 0.001 which could represent a salinity change of 1 to 3. I think there was a very small fall in salinity, but I was unable to measure it.
 
If you study the chart and correlate the falls in salinity with exceptionally heavy rainfall and rises with the high spring tides (even before the pipeline was installed). However, it should be possible to maintain salinity levels at a maximum of just under 35, which is the maximum long term figure to support a biodiverse aquatic fauna. In the short term the salinity should not exceed 38 for a few days at the most to minimise the extinction of species in a harsh environment that is used to population crashes. It is still unclear if the all the water is lost by evaporation or if some drains away. 
Comment by Andy Horton


1 July 2003
The Environmental Agency opened up the four inch slats and three workers (in two vehicles) supervised the the input of seawater into Widewater Lagoon on the high spring tide. Despite this topping up the lagoon (are the figures available for the amount of water?), the water level was still fractionally down compared to 11 June 2003. The two photographs can be compared:
 

 Pipeline sea inlet at High Tide
One hundred cuttlebones decorated the strandline
Looking down on to the internal weir in the pipeline
Outlet into the lagoon, in operation with a slow flow of water

Small prawns, Palaemon elegans, were being swept over the weir into the lagoon, but there were not other visible animals introduced.

Although it was nearly two weeks ahead of schedule, I collected an extra water sample from the usual place by the bridge.
Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.028 at 22° C. Using the method before correction this would give a salinity of 40. However, after deducting the hydrometer correction figure we arrive a salinity of 35 (ppt), which is full strength seawater. This was such an alarming rise that I checked it with my other narrow range hydrometer which gave a reading of 1.026, and this hydrometer was calibrated at 15° C, which would give a salinity of 36 (ppt). The lagoon is going hypersaline.
The Project Manager at the Environmental Agency is Stuart Meakins. (Tel: 01903 832000)

At the meeting with Peter Midgely and the Environment Agency and Tim Loughton MP it was agreed that the pipeline would only be put into operation when the tide levels exceeded six metres which would thought to mimic natural conditions.

Anyrate, the Widewater Management Group have now had an Extraordinary General Meeting to get the levels reduced to a lesser figure, at least 5.7 metres which is thousands, probably millions of gallons of extra salty water, which has already turned the lagoon as salty as the English Channel. The grounds for this is that the lagoon levels were getting too low.

14 June 2003
Stuart Meakins (Environmental Agency) advises me that this was the date the pipeline was first put into operation (by telephone conversation of 3 July 2003). This is a Saturday with a high spring tide of 6.4 metres (WXTides).
The pipeline was actually opened on 13 June 2003 at 8:00 pm by the FOWL Pipeline Management Team. However, as this was only at half spring tide of 3 metres at this hour, I assume that the water would not come through until 10:30 pm when the tide reached 6 metres in height.

11 June 2003
Despite the recent rain, the level of the lagoon was about 50 mm lower than May and this leaves bare patches of mud.

Widewater Isle
Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.025 at 22° C. Using the method before correction this would give a salinity of 35. However, after deducting the hydrometer correction figure we arrive a salinity of 30 (ppt).
 


Despite the fall in water, the salinity remains the same comparatively high figure.

11 May 2003
April and early may were exceptionally dry with hardly any rain. It is inconceivable that the salinity should fall although the water level remained constant, so I would expect little change from last month.
Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.026 at 16° C. Using the method before correction this would give a salinity of 35. However, after deducting the hydrometer correction figure we arrive a salinity of 30 (ppt).
 


This is the highest recorded salinity in the last year. Is fresh seawater being allowed through the pipeline into the lagoon to maintain a high level?

8 April 2003
There has been hardly any rainfall in the last month and the pipeline is now installed (although I do not know if it has been letting any sea water in) so it is not expected that the reading will show a dilution of the lagoon water. There has been a negligible fall in the water level since last month.
 

Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.023 at 12° C. Using the method before correction this would give a salinity of 30.5. However, after deducting the hydrometer correction figure we arrive a salinity of 25.5 (ppt). This reading is almost up to the maximum figure recorded last year.
 


6 March 2003
After a month of very little rainfall, I would guess that the salinity fall would not be maintained, and perhaps a rise from the minimum figure. The lagoon is heavily in flood and this is usually associated with heavy rainfall. Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.020 at 11° C. Using the method before correction this would give a salinity of 27. However, after deducting the hydrometer correction figure we arrive a salinity of 22 (ppt). This reading represents the largest monthly rise in salinity for a whole year. I have now (3 July 2003) been advised that the pipeline was not in operation at this date. In the middle of February, there were certainly some very large spring tides.
The only conclusion to draw is that there must have been a massive (unprecedented) amount of seawater percolating through the shingle.

10 February 2003
It is in this month I would forecast the minimum salinity.
Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.012 at 10° C. Using the method before correction this would give a salinity of 16.  However, after deducting the hydrometer correction figure we arrive a salinity of 11 (ppt).

4 January 2003
After a period of rainfall up to a maximum of 13 mm a day, not that much, but enough to cause a few minor floods, Widewater Lagoon has risen a few centimetres and the whole lagoon flood plain is flooded at the east end. I would estimate fall in salinity of about 5 and 8.
Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.016 at 7° C. Using the method before correction this would give a salinity of 20.  However, after deducting the hydrometer correction figure we arrive a salinity of 15 (ppt). This is a fall of 7 from 15 days ago.

20 December 2002
The lagoon water had risen at most an inch since last month. Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.020 at 8° C. Using the method before correction this would give a salinity of 27. This is the same as last month. However, after deducting the hydrometer correction figure we arrive a salinity of 22 (ppt).

17 November 2002
There has been a considerable amount of rain and Widewater Lagoon was flooded but not all that much more, but enough for me to estimate a salinity of 21 (ppt). Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.020 at 10° C. Using the method before correction this would give a salinity of 27. However, after deducting the hydrometer correction figure we arrive a salinity of 22 (ppt).

3 November 2002
After a couple of days of rainfall, I expected the lagoon to be more dilute. Using the same wide spectrum hydrometer used for the other readings, the specific gravity at the meniscus read 1.022 at 15° C. This gives a salinity of about 30 (ppt).
Alas, I suddenly had doubts about the accuracy of the calibration in this Taiwan made instrument. I decided to take the measurement using the old smaller spectrum tropical aquarium hydrometer and this gave a reading of 1.018, which would gave a salinity of about 25 (ppt) (which really is a large difference). I will check the readings with real seawater. (The tropical aquarium hydrometer has a lowest reading of 1.018, which is why it was not used before.)
The small pawns were absent on the edge of the lagoon.
Salinity corrected to 25 (ppt)

NOTE: the manufacturers have probably calibrated the hydrometer at about 23° C  to 28° C and I will have to adjust all the salinity readings.

7 October 2002
After a month of minimal rain and with an Indian Summer summer preceding some of the highest and lowest equinoctial spring tides for over 20 years, I visited Widewater Lagoon, 1½ hours after the midday high spring tide of 6.8 metres. The bubbles of percolating seawater had ceased by then and the only water commotion was caused by a small flock of Ringed Plover. There was a band of about 40 cm of wet mud (west of the bridge) where it looked as though the water had recently receded. The lagoon level was higher than that of a month ago, as the separate westerly lagoon was a continuous sheet of water, but still scarcely more than a large puddle. The air temperature was recorded at 21° C and water temperature in the lagoon at 16.5° C. The specific gravity reading in the main channel was about 1.018 at 20° C (accurate home laboratory testing) which gives a salinity of about 26 (ppt) which is into the brackish range that could support cockles and other marine organisms. There were thousands of small prawns in the lagoon.
Salinity corrected to 21 (ppt)

4 September 2002
After a dry spell, Widewater Lagoon had receded/dried/leaked out and the small separate lagoon west of the western causeway was reduced to a few puddles since 14 August 2002. A live Lagoon Cockle was found on the surface.
The specific gravity reading in the main channel was about 1.022 at 21° C which gives a salinity of about 31 (ppt) which is above brackish water into the seawater range. Full strength seawater is 34 (ppt).
Salinity corrected to 26 (ppt).

14 August 2002
Widewater Lagoon was very full of water for August which could be explained by the heavy rainfall of the last few days which caused flooding in some places. The high tide of 6.1 metres (WXTide Table) occurred at 4.27 pm BST and the air bubbles shooting up through the cracks in the alluvium floor of the lagoon began one hour before the high tide. They occurred as a steady stream of small bubbles and sometimes as large less frequent bubbles and these bubble points occurred more often in the shallow water but also could be seen at the surface in water that was two metres deep. The conjecture is that this is seawater being forced into the lagoon through the shingle bank and the bubbling only occurs on tides of over 6 metres in height.

Supplementary Report

At 3.10 pm I saw some air bubbles in the area approx. 200 metres west of main ridge and spreading a further 100 metres west. There must have been at least 100 sets of bubbles! At least six had water rising at least 25 mm over the level of the Widewater. At this time there were no other areas showing this effect.
At 5.00 pm I then witnessed the same again this time some 200 metres east of the bridge and extending another 50 metres east. The bubble form was less pronounced than the previous lot.

Supplementary Report by Trevor Nicholson

The specific gravity reading in the main channel was about 1.014 at 24° C which gives a salinity of about 23 (ppt) which is into the medium brackish range that could support cockles and other marine organisms. This represents a fall of 6 (ppt) from the previous reading which made me have reservations about the earlier reading taken in far from ideal conditions. On this clear day I brought a large bucket, and I took several samples and even in the areas of bubbles the hydrometer readings were all the same. A small area to the west of the main lagoon, a dry causeway cuts off a small separate lagoon (see map) which can dry up in summer. This area was over a boot deep and the hydrometer reading in this area was 1.016, which gives a salinity of about 25 (ppt) (corrected to 20). (The error range using this method is +/- 2 (ppt) because of the small scale on the hydrometer.)
Salinity corrected to 18 (ppt).

10 August 2002
The rainfall for the day totalled 34.6 mm.
Recent Historical Records

7 July 2002
The trip in the unseasonal drizzle to Widewater Lagoon, ostensibly in the search for the sea anemone Edwardsia ivelli, but actually the collection of anaerobic mud and hundreds of dead shells of the Lagoon Cockle, Cerastoderma glaucum, with just the remotest long shot that something interesting would creep out.The specific gravity reading in the main channel was about 1.021 at 16° C which gives a salinity of about 29 (ppt) which is into the high brackish range that could support cockles and other marine organisms.
Salinity corrected to 24 (ppt).

Notes:  Salinity readings for Widewater using a hydrometer where measured each year during the summer, usually July,  in 1981, 1982, and in 1986, 1987, 1988, and all these readings were below full strength sea water. Readings were taken in the main body of the lagoon and all the readings on the same day were exactly the same, at different locations in the lagoon water.



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Brackish water Lagoons habitats for Cerastoderma glaucum, Dorset to Sussex.
 
 
The Fleet: Gore Cove  SY 615 807
Studland (Purbeck): Little Sea  SZ 030 843
Gillkicker Point  SZ 608 977
Cockle Ponds, Gosport  SZ 618 996
Moat, Gosport  SZ 618 996
Hilsea Lines: West Moat  SU 668 041
Hilsea Lines: East Moat  SU 653 045
Mill Pond: Emsworth  SU 748 053
Slipper Pond:  Emsworth  SU 753 056
Birdham Lake  SU 826 008
Pagham Harbour
Littlehampton (Pond)  SZ 028 015
Widewater
Cuckmere River Estuary  TY 518 993
Report by Terry Wimbleton (Havant) of the Conchological Society
UK Conchology


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