WP5 - variables for fieldwork
The following is a list of the variables you are requested to measure in the WP5
fieldwork to be carried out at each study site. Please carefully read through this and
get back to Dror as soon as possible, a) to verify that you can determine all of the
variables, and b) if you have any comments.
Hydrography
a) Need hydrographic data for dispersion models such as Depomod that require a
local current record with the appropriate vertical and temporal resolution. For
non-tidal sites (e.g. Mediterranean) the longer the better – 15 day minimum, but
we would prefer months of data. For tidal sites, 15 days may be sufficient to
capture the tidal cycle.
b) We can estimate residence time for open sites by simply looking at the current
record and making some estimates (this would apply for Siteia and Sounion sites,
for the Bisceglie (and possibly Chioggia) sites, and also for the Spanish sites). For
enclosed sites we need to look at topography (bathymetry), volume, tidal prism,
or some tracer like salinity to estimate residence time. Thom Nickell adds: Strictly
speaking, flushing time does not depend on current meter measurements, but can
be calculated from
T = water body volume / tidal flow rate
(Edwards & Edelstein 1976), which involves determining the low water volume,
high water area, low water area and tidal range.
Sediment sampling
Where
Station positions should reflect gradients of impact. The principle is that some rationale
must be used to maximise the chance that one of the stations is selected in the area of
maximum impact. This can be done by modelling (using an appropriate current record)
or by a pre-survey which could be by sediment sampling for e.g. redox, by acoustic
methods or by video etc.
We want to maximise the chance of detecting a gradient and we also would like to
consider the distance from the farm that effects of the farm can be detected. This will
probably take a minimum of 5 stations per site but could require several more.
A reference station should be at a similar depth and sediment type but not be influenced
by the farm. If this is not possible, an additional station added to the transect may reveal
background conditions by comparing the trend away from the farm i.e. if stations become
more similar with distance.
Thom adds: Selecting sample station sites on the basis of contours derived from presurvey modelling will yield the most effective locations; if orders of magnitude of
deposition are selected as the basis for station selection, this will facilitate the testing of
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indices. Sample station location then becomes critical, with differential GPS or other
accurate position fixing needed to remain within contours.
How
Samples will be taken, in general, by van Veen grab with a sampling area of 0.1 m2.
A box corer may also be used (but since we are developing practical/affordable protocols,
it is less desirable since most farmers/regulators will not have access to box corers), as
long as this does not conflict with the optimal location of the sampling stations.
Diver-sampled sediment cores may be used where this is more practical – core diameters
should be 5cm for sediment chemistry and 10cm for macrofauna. Core depth should be at
least 12cm for sediment chemistry and at least 6cm for macrofauna. If possible, samples
should be taken with a Craib corer as this provides undisturbed sediment profiles.
It is crucial to point out that for macrofauna, grabs are a good way to sample, but
for sediment meiofauna and chemistry, we need undisturbed sediment cores. Gravity
corers and grabs tend to fluidize the samples and destroy the vertical stratification of the
sediments, thereby making the data extracted from them meaningless.
In order to clarify the effect of sampling method on the data, we would like the partners
to carry out the following comparison. Sediments should be sampled (several replicates)
at same site by both van Veen grab and by Craib corer or by SCUBA diver sampled
corers. Redox profiles should be run directly on the sediments in the grab and
subsequently, subsamples should be taken from the grab for redox profiles and these
should be compared to redox profiles performed on cores taken either by SCUBA divers
or by Craib corer.
How many
At each station, at least 4 grab replicates should be taken for macrofauna, and triplicate
cores for sediment chemistry. If an analysis is very expensive or complicated to perform,
duplicates may be sufficient.
When
Sampling should be done when impact is likely to be high.
What
Video or still photography of the seafloor, along a transect (from the fish/shellfish farm
toward the reference station) is extremely desireable as it will provide information on
macrophytobenthos, epibenthic macrofauna, seafloor status, etc. which core or grab
sampling cannot do.
Benthos samples will consist of the entire grab (i.e. no a priori subsampling) or the entire
core. Macrofauna samples must be sieved sequentially at 1mm and 0.5mm and
macrofauna will be identified to lowest practical taxon.
Meiofauna will be taken from all possible sites by cores, where possible. If necessary,
meiofauna may be subsampled from van Veen grab, by using sampling cores. Sample
collection and handling must be discussed with Katarina. Where possible, meiofauna
should be taken from cores collected by a Craib corer.
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Sediment chemistry will be measured from sub-cores taken from grab samples (and from
proper cores when possible). As mentioned above, it is essential that grabs are of good
quality with as little disturbance as possible. If the samples have been disturbed, best
thing to do is toss the sample and sample again to obtain a good, undisturbed sediment
sample. But if this is not possible, should analyze only the top 2cm layer and avoid the
vertical profile slicing described below.
Redox potential will be measured by profiling an electrode down a sediment core to as
deep as is necessary to detect the redox discontinuity layer (normally 10cm or 15cm).
Redox potential will be measured in duplicates at each station.
Sediment cores (or sub-cores) will be sliced at 1 cm intervals from sediment surface to
12cm depth. If redox discontinuity layer is deeper than 12 cm, should take slices down to
that depth.
The sediment slices will be taken for granulometry, TOC, TN, TP and LOI (sequential
combustion at 2 temperatures (250 and 500 C) determination.
Optional: hydrogen sulphide, fatty acids, phytobenthos, pore water nutrients, antibiotics,
sediment oxygen demand may be taken for specific research purposes, but are not
required by all partners.
Water column (water quality) sampling
Where
Vertical profiles at stations, e.g. 0, 25, 50, 100, 200m and 1000m (or other, better
reference station) from farm, along the axis of predominant current. However, in highly
dispersive areas with fast currents, we may limit water column sampling to 2 stations –
one in the vicinity in the farm and one at reference site, outside zone B.
When
Sampling dates should correspond to peak production and warmest water conditions to
capture maximal impact conditions. Samples should be taken along diel or tidal cycle
(minimally at low water and high water in tidal regimes) to include extreme conditions,
e.g. DO sag at end of the night.
How
Water column should be sampled by CTD, and by bottle sampler sampling at surface,
mid-depth and near bottom.
How often
Optimally, should establish diel measurement of all variables at a minimum of 2 stations
(e.g. one at farm site and second at anticipated intermediate effect station) within the area
of anticipated (from hydrographical data) effect and at a distant reference station.
What
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CTD vertical profiles at each station of: salinity, temperature, sigma-t, dissolved oxygen,
chlorophyll, PAR, light transmission, turbidity (nephelometer).
Water samples, to be collected using Niskin bottles, for nutrients: ammonia, nitrate,
nitrite, phosphate (SRP), silica, total N, total P, suspended particulate matter: total
suspended solids (including POC, PON, POP) and chlorophyll (for CTD fluorescence
ground-truthing). For shellfish farm sites, phytoplankton community composition is
extremely important.
Secchi disk depth and/or water transparency, using light meter should be measured at all
stations.
Bioassay (temporal/spatial integration of water quality features) is recommended at all
possible sites.
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