The benthic ecology and community structure in Lyttelton Harbour ...

23.
visible particles to col16idal micelles that are
usually associated with the finest sedi~ent,
The quantities of orga~ic
the clays.
matter absorbed onto solid
surfaces as pelogloea may exceed the amounts suspended
in the water by 10 times in. coarser beach sand where
the~e
is commonly up to one percent organic matter.
But adsorbed'quantitiei may exceed ~uspended
organic
matter by 100,000 times in fine silt and bottom muds
such as those in Lyttelton Harbour where the organic
matter reaches 10 percent (~ig.12).
The amount capable of being adsorbed is a
function of the grain size, the surface area of which
increases rapidly as the diameter decreases.
FigG12
shows the change in the percentage of organic material
.as determined by the Walkley and Black wet combustion
method, (see appendix 2). This is graphically related
to the modal grain size. The sediments for this analy~is
were selected for their good sorting to minimize disturbance
from the va!iation in grain sizes. A regression line
was calculated using a computer program.
equation:
Y = -1.42 + 1.29 x
This had the
and ·a correlation coefficient of OG92 showing fai~l~, ,
low scatter. Grain sizes larger than phi 1 had extremely
small amounts of organic material but this rose in a
linear fashion to reach about ten percent at phi 5.
2.11 Sediment types at selected sites
Forty sites among the 74 sampled over the
investigation period were selected as being representative
of all of the areas under investigation. The results