294 THE ESSEX NATURALIST
and further work, completed over a number of years would be
necessary if these conclusions were to be confirmed.
METHODS
Specimen Sampling—In two areas, B and G, transect sampling
was used. All other samples taken were random samples. Each
sample covered an area of 100 sq. cms. to a depth of 15 cms. The
figures in Table IV are obtained from two such samples at each
station.
Water Content—A core sample of the substratum at each
station was obtained by using a glass tube 5/8th of an inch in
diameter and 10 inches long. This was screwed into the sub-
stratum and a rubber bung inserted in the top of the tube. The
tube was then screwed out again and another bung inserted in
the other end, Fraser (1932), Stopford (1951), Southward (1953).
The water content of one inch of the core from half inch below
the surface was estimated in the normal way.
Soil Analysis—Core samples were obtained in the same way
as above, air dried and analysed later in the laboratory. The
method described by Rees (1940) was found to be unsatisfactory
and a more refined method, in which subsamples are taken from
a soil suspension by pipette, was therefore used. This method
will be described in detail in another paper.
Salinity—The amount of sodium chloride was estimated by
the usual method of titrating N/10 silver nitrate against 10 mls.
of seawater to which a few drops of potassium chromate had been
added. Total salt content was obtained by consulting Hydro-
graphical tables—Knudsen (1901—reprint 1953).
Salinity
PHYSICAL AND CHEMICAL DATA
TABLE I
The above table shows that there is little variation in the
salinity of the water with distance up the Creek, just over 1‰,
at low water and just less than 1‰ at high water.
Benfleet Creek is therefore not a true estuary in that there
is no real gradation in salinity between source and mouth. All
the salinities, however, are below the full North Sea salinity of
33‰ (Westcliff Sea Front being the nearest to this) as a result
of the infiltration of fresh water from the Thames Estuary.