Appendix - Monitoring of environmental attributes
i. Intertidal sediments
For sediment analysis the size of the sample is not of great importance as long as
sufficient material is collected for analysis. A core of approximately 8cm diameter is
generally sufficient and at least the top 2 cm of sediment will be representative for
analysis of the physico-chemical characteristics. In sediments that are inhomogenous
sub-samples may be taken which can be pooled and thoroughly homogenised. Core samples
allow an undisturbed sample to be taken and this allows an inspection of the sediment
structure. This may be important if for example if the substratum is characterised by a
layer of silt overlying coarser sandy material. Information on other features such as the
depth of the anoxic layer should also be noted.
ii. Subtidal sandbanks
Subtidal monitoring of the substratum will require the use of large box corers if
possible, as they take an undisturbed sample of sediment from which cores can be taken in
a similar fashion to that used in intertidal areas. The other possibility is the use of
grabs e.g. Day or Van Veen grab (Rees et al, 1990). The grab should take a sample
such that disturbance to the sediment structure is minimised and samples which have low
quantities of sediment or have lost sediment in transit are rejected. The use of
Flow-through corers, e.g. the Craib corer, will prevent surface material being removed by
any bow-wave created by the largest sampling devices. A small corer can be used to take
the sediment sample and detailed methodologies for sampling subtidal areas are given in
Kramer et al (1994) and Holme and McIntyre (1984). Subtidal sandbanks can be
heterogeneous and remote operated video (ROV) equipment is useful to visually inspect the
nature of the substratum as described above. If sediment samples are collected during
biological sampling it is more reliable to take the samples from each biological sample
rather than from a separate grab. However, a strict methodology for subsampling the grab
must be employed to ensure that the biological sample is uniformly affected.
The use of grabs or corers to sample subtidal areas is somewhat limited and, as
mentioned, ROV equipment can greatly enhance the coverage and knowledge of areas where
turbidity is not a problem. Other tools include acoustic ground discrimination equipment
(Hiscock, 1998b) as described above e.g. RoxAnnTM or side scan sonar.
Ground-truthing should be carried out by grab sampling. This is probably the most
effective means at present to gain sufficient coverage of offshore areas and these methods
are extremely useful in initial site characterisation of the substratum and consequent
monitoring of change.
Particle analysis and distribution
Particle size analysis can be carried out by several methods. These are dry sieving
(Buchanan, 1984), pipette analysis, Coulter counter analysis, and laser granulometry
techniques. Laser and pipette/sieve techniques tend to be the most widely used; the former
are quick and accurate but costly. In addition, laser techniques cannot however analyse
coarser (>2mm) material so are limited to areas of fine sands and silts e.g. intertidal
mud and sand flats. Coarser sediments, as often found on more exposed beaches and on
offshore sandbanks in areas of higher currents, will require dry sieving which is a time
consuming process although it is possible to split samples and use laser techniques on the
Results of particle size analysis should be shown graphically as percentage per size
class and features such as bimodality of sediments noted. Summary statistics e.g.
Mean/median grain size, sorting coefficient, skewness and % silt, sand and gravel should
also be calculated. Sediment trigons may also be constructed based on the quantity of
silt, sand and gravel from which samples can be classified, for example,. sand, muddy sand
and muddy gravel. Details of the derivation of these and other parameters are given in
Dyer (1979) and Buchanan (1984). These summary statistics provide an easily interpretable
analysis of the nature of the substratum although it must be remembered that traditional
methods of sedimentary petrography do not take into account the structure of the sediment
and in fact tend to destroy aggregated material to allow total dispersion.
Other features which may be examined include porosity which will relate to the water
content of the sediment. This is a difficult property to measure with accuracy but is of
importance on intertidal mud and sand flats and will influence the abundance of meiofauna.
Porosity can be measured gravimetrically (Holme & McIntyre, 1984) and by sonograph
interpretation (Taylor et al, 1966). This feature will also be related to the other
characteristics of the sediment such as grain size and sorting and due to the difficulties
in obtaining an accurate value it is not often measured. Qualitative estimates of the
porosity or water content of the intertidal areas may be just as useful.
The organic content of the samples should be analysed. Several methods exist and these
are described by Dyer (1979), Holme & McIntyre (1984) and Kramer et al (1994).
The most common technique is by loss on ignition (LOI) at 600°C but other techniques e.g.
by CHN analyser can be used to determine levels of organic carbon and nitrogen and derive
C/N ratios. Chlorophyll levels (as an indicator of phytoplankton biomass) measured by
spectrophotometric or fluorimetric techniques and particulate organic phosphorous measured
by wet digestion and spectrophotometric analysis can also be measured. The quantity of
organic matter is particularly important in determining the food availability for benthic
communities and increased organic enrichment can lead to a deterioration in the health of
the benthic population (Pearson & Rosenburg, 1978). This parameter is particularly
important in intertidal mudflats. In areas of coarser material e.g. subtidal sandbanks,
levels of organic material may be of less importance where levels are very low.
Measurements of the redox potential of the sediment can be done using hand held redox
probes either directly into the sediment intertidally or into the contents of the grab
subtidally if the sediment is relatively undisturbed. Details of determining the redox
potential are given by Morris (1983), and Pearson & Stanley (1979). This parameter is
useful in identifying the electrochemical regime of the sediment, oxygenation of the
sediment and assessing levels of organic enrichment. High levels of microbial activity may
be expected in reducing sediments though this should if necessary be determined using more
specialised methods e.g. by C14 tracing (Strickland & Parsons, 1972; Dyer, 1979). The
redox potential is of more use in intertidal silts than in well oxygenated substrata such
as well sorted sands.
e. Trace metal and other persistent contaminants determination
An extensive literature exists on this topic and is considered outside the scope of
this review. For example, if it is suspected that the areas to be studied may be subject
to influxes of particulate trace metals particularly in finer substratum such as
intertidal mudflats. Sediment samples can be totally or partially digested with acid
followed by instrumental analysis, Kramer et al (1994) provides detailed
methodologies. It should be emphasised that contamination should be kept to a minimum with
no metal components used in sampling. If metallic equipment is used e.g. when grab
sampling then stainless steel grabs should be used and the sample taken from the centre of
the grab away from contact with the grab.
Other contaminants which can be measured from sediments include particulate polycyclic
aromatic hydrocarbons (PAHs) measured by fluorescence and UV absorption or gas
chromatography, particulate polychlorobiphenyls (PCBs) measured by gas chromatography with
mass-spectrometric detection. Precise details of the sampling and analysis are not given
in the present report but details are given in Kramer et al (1994) and it is of
paramount importance with these techniques that contamination is avoided.
If necessary measurements of current strength/direction, residual flow circulation
patterns etc. can be determined with simple drifters or drogues at surface and depth.
Eulerian techniques can also be employed using direct reading current meters or recording
current meters if long term measurements are necessary. If a SAC may be affected by a
potential discharge dye tracer techniques e.g. with Rhodamine B dye may also be utilised
to track the direction and extent of the dispersal of the effluent. These techniques
utilise fluorimeters e.g. the Chelsea systems Aquapack to measure the concentration of
dye. This equipment can be towed either at surface or as a series of transects at various
depths depending on the buoyancy of the effluent. A known quantity of the dye should be
mixed with saline or fresh water to obtain the correct density and deployed at the depth
at which the effluent will be released either directly from a boat or via the discharge
installation. Several deployments should be made so that dispersion can be monitored at
slack, ebb and flood conditions. Positional data from DGPS can also be linked to output
from the fluorimeter and the results logged onto a PC for further processing.
The results of current data profiles and dye tracking may be used with recent computer
software to describe circulation patterns, dispersion and to derive peak stress and
tidally averaged stress levels on the sea bed. Detailed methodologies for this type of
survey are given by Morris (1983) and Dyer (1979). Areas of subtidal sand banks are often
subject to considerable stress from tidal currents and this is one of the most important
factors controlling the sedimentary and biological environment (Warwick & Davies,
1977) and a detailed knowledge of natural patterns in tidal dynamics is essential in
differentiating between natural fluctuations and severe disturbance.
Salinity temperature depth probes can be employed where data are unavailable in order
to monitor long term changes in these variables. Turbidity levels should be monitored
preferably with transmitometers or nephelometers (McCave, 1979) to assess changes in
levels of suspended sediment. The equipment used to for dye tracing mentioned above can
often measure a whole suite of parameters simultaneously (for example, temperature,
salinity, depth, turbidity, chlorophyll, dissolved oxygen and pH) and can be towed to
provide a continuous set of data across an area or deployed throughout the water column at
specified sites. Many survey vessels e.g. those employed by the Environment Agency have
continuous recording equipment for these parameters. This equipment could be employed
whilst carrying out routine monitoring of the subtidal communities as required. Other
parameters e.g. dissolved metals, inorganic and organic nutrients etc should be measured
when necessary. This will normally involve the use of specialised water samplers which
allow water samples to be taken at specified depths without contamination from other parts
of the water column. The laboratory procedures required for the analysis of these
parameters are complex and details are given in Kramer et al (1994).