Were Early Saltmarsh Surveys Wrong? – Jan 2014

DEFRA targetted EA with recreating 100 ha/year saltmarsh by flooding farmland following saltmarsh surveys. Were surveys wrong?

Around 1973 there was a plan to build an airport on Maplin Sands off south Essex.  The airport was never built but there was a lot of preparatory work, including aerial photographs of much of Essex coast and a report, the ecology of Maplin Sands.

In 1988 another aerial survey was conducted. Fiona Burd compared the 1973 and 1988 photographs and concluded saltmarsh there was 876.1ha in 1973 and 765.4ha in 1988 so saltmarsh was being lost at 7.4ha/year.

A further study was conducted by Nick Cooper in 1998 who found there was on 621.1 ha of saltmarsh so the rate of loss between 1988 and 1998 had doubled to 14.4ha/year.

Natural England conducted a saltmarsh survey   in conjunction with University of Hull from 1997 to 2008. EA also independently conducted a saltmarsh survey of UK between 2006 and 2009.  Both reports emerged in 2011.

EA seems to be more than a little embarased that for the England and Wales as a whole their survey finds MORE  saltmarsh than Fiona Burd did in 1988!  Pretty embarassing for an organisation trying to justify their actions on the basis there is a national emergency over the rate saltmarsh is being eroded.

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The following table sumarises the results of these surveys for Hamford Water.  In this post I will concentrate on Hamford Water as it’s near where I live.

survey date ha saltmarsh
maplin sands 1973 876.10
burd 1988 765.40
iecs start 1997 694.82
cooper 1998 621.10
iecs end 2008 698.13
ea 2006-2009 674.81

The next table sumarises rates of saltmarsh loss between different surveys ASSUMING saltmarsh was lost at a constant rate.

period start ha end ha gain/loss ha rate gain/loss ha/year
1973-1988 876.10 765.40 -110.70 -7.38
1988-1998 765.40 621.10 -255.00 -14.43
1997-2008 694.82 698.13 +3.31 +0.03

I have chosen these three sets of start and end dates as

  1. The first row caused everyone to panic and to start flooding farmland in an attempt to recreate saltmarsh.  DEFRA targetted EA with creating 100ha/year in UK,
    40 ha/year in East Anglia.
  2. The second row caused them to panic even more especial as by now UK had signed EU Habitats Directive which apparently meant we had to recreate saltmarsh by “EU Law”
  3. The final row made them realise there was no reason to panic but  DEFRA doesn’t seem to have gotten around to telling EA to stop flooding farmland yet.

Are The Numbers Right

There is a clear difference between the rates of loss/gain found by the different surveys.

This may be due to uncertainty in measurement.  No measurement is ever completely accurate and it is standard practice to quote a measurement along with and indication of uncertainty (commonly called error – though error in this context does not mean mistake).

For example  876 ± 20 ha.  Rather than just 876.01.

Another issue all undergraduate scientists are warned about is not to confuse accuracy with precision.  In other words if you can only measure to within ±20ha, which means your result may be anywhere within a 40ha range, there is no point in quoting your result to 1 decimal place, not least because it makes you look silly.

The assumption saltmarsh (which consists of plants) dies of at a constant  rate is almost certainly wrong.  Just about every gardener will be familiar with plants coming and going.  In particular plant growth is dependent on weather and seasons.

There is no indication of what time of year the saltmarsh surveys were conducted or even if they were conducted at the same time of year.

Apart from this I have a huge problem with the 255ha loss claimed by Cooper between 1973 and 1998.  It’s just to big.

Now lets go back to basics what’s a ha (hectare)?  It’s a square 100 metres by 100 metres.

Here I have superimposed a grid where the light black squares  are approximately 100 x 100 metre.  The larger dark black squares are  1 km x 1km.


Now can you pencil in 255 little squares to indicate which might have had saltmarsh eroded?

The squares have to be in places which are covered by the sea at high tide, well at least spring high tides.

I think the figure quoted is probably as much as 100 times to large.  Perhaps they counted in a few fields by mistake.

The snappily titled EnglishNature Report710 discusses some of the shortcomings in the earlier reports.

Natural England Survey

The report of Natural England survey included maps of different regions where

  • areas of saltmarsh loss were marked in red
  • areas of saltmarsh gain were marked in green

Here’s the map for area near Quay Lane.  I have a problem for the area on west side, opposite Quay Lane.


Here’s an aerial photograph of backwaters from later 1950s.  Whenever it was taken it’s clearly before the marina was built as the marina ain’t in the picture.

Aerial photo of Walton to Beaumont backwaters circa 1959

For comparison here’s something just taken from google maps


Here’s a close up of the area covered in NE survey from the 1950s photo


It doesn’t seem that different from NE picture, though the area marked in red to west does not exist here either.

Here are some images from Google Earth

31 December 2000


31 December 2005


6 November 2006


31 July 2007


31 December 2009


Here’s a current image from google maps


It seems to me the saltmarsh has not changed that much since 1950s.

Things seem a bit bleak in 2005 picture but light was not clear.  In any case things look at lot better on 6 November 2006, though light is a lot better and it’s nearly 2 months earlier in the year.

Overall the biggest mistake seems to be to assume that saltmarsh is eroding (or growing) at a constant rate.


Worse this assumption, that saltmarsh is all being eroded away, is part of the reason for DEFRA/EA obsession with knocking sea walls down.  They believe global warming is going to causing sea level rise which in turn causes saltmarsh erosion in a process they call coastal squeeze  and accelerating temperatures are going to cause accelerating loss of saltmarsh.

Bit embarrassing your surveys show saltmarsh growing back then chaps?

I wrote to Natural England to point out the influence of time of year on saltmarsh and got this reply

We note your photos of the same areas of salt marsh at different times of the year, and the suggestion that surveying these in different seasons may lead to different calculations of salt marsh extent. Our advisers and field staff are very mindful of the need, and are able to distinguish between salt marsh vegetation and its characteristics between winter and summer, and this would be taken into account in any survey, either desk or field based.

I also questioned the idea of coastal squeeze pointing out Rob Hughes idea of ragworms and Richard Steward idea of crabs (Video of Rob and Richard).  In the video Dr Rob Hughes states there isn’t a saltmarsh ecologist in the world that doesn’t believe saltmarsh accretes (rises) with rising sea level.  This is his polite way of saying coastal squeeze is rubbish. By the way what do think is Rob’s area of research?

This was the response

You asked about our response on the shore crab and ragworm erosion theory, and queried that we are not being aware of a large evidence base for the theories. This is true. To be exact, we are aware of Hughes and Paramour (2004), a response to it (Morris et al 2004), and Wolters et al (2005) all from the Journal of Applied Ecology. We have also said that we have an open mind on the issue, and are prepared to revisit it. Your photos may also be helpful in any fresh look at the issue.

 NE and EA are both organisations which serve DEFRA.  I am constantly amazed at the difference between them.

NE seems to be open to new ideas, doesn’t mean they will act on them, but they are at least open.

EA on the other hand seems to have a mind that is firmly and tightly closed.

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