Sampling diatoms from running waters 1: Introduction

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Sampling diatoms from running waters 1
Introduction

• Martyn Kelly and Marian Yallop

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DARES is a project funded by the Environment
Agency and SNIFFER to develop a diatom-based
method for monitoring ecological status, as
required for the WFD.These presentations are
designed to show biologists how to collect diatom
samples during routine GQA surveys. These
samples will then be processed by the DARES team.
Methods are very similar to those described in
the TDI manual, which is itself based on a
European standard method. However, there are a
few important differences between the DARES
method and the TDI manual which need to be
understood. This first presentation explains
the principles of sample collection for DARES.
Introduction
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When we sample diatoms for water quality
monitoring we assume that the distribution of
taxa is influenced primarily by water quality
variables
In this graph, we see Staurosirella (Fragilaria)
pinnata with a relatively low P optimum and
Achnanthes conspicua with a much higher optimum.
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However, as the following presentation will show,
other factors can influence the composition of
the diatom assemblage.For this reason it is
important that we adhere to strict sampling
protocols in order to minimise the impact that
these have.
The DARES protocols are based on those in the TDI
Manual which are compliant with EN 13946 the
European Guidance Standard for diatom sampling.
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Diatoms live in a thin, brown biofilm which can
be found on almost all surfaces in rivers
This video clip shows a biofilm that has
developed on a bottle found submerged in the
River Avon in Hampshire.
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It might not look very exciting, but it is
actually a complex 3-dimensional community of
which diatoms are typically the most abundant
group of photosynthetic organisms exhibiting a
range of ecological strategies.
Plankton in transit
Polysaccharide matrix
20 ?m
Motile taxa, e.g. Nitzschia
Stalked taxa, e.g. Synedra
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This biofilm can be found growing on many
surfaces in running waters .
Rocks plus filamentous algae
Man-made surfaces
rocks
Fine sediments
Submerged macrophytes
Emergent macrophytes
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and contains diatoms with a range of different
growth forms .
Resistance to scour
Competition for light
Resistance to grazing
Prostrate, e.g. Cocconeis
Stalked, e.g. Achnanthidium
Arborescent, e.g. Gomphonema
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Differences in growth forms can lead to different
assemblages depending upon the type of
substratum.
current
For example, stable rock surfaces favour attached
species such as Achnanthidium and Gomphonema
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Whilst less stable surfaces lead to different
assemblages.
Fine sediments favour motile species such as
Nitzschia .
whilst sand grains bear a distinctive flora of
attached diatoms such as Staurosira.
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Macrophytes and macroalgae also have distinctive
diatom assemblages associated with them.
Cladophora filaments, for example, often have
distinctive epiphytes such as Rhoicosphenia
(shown here) and Cocconeis.
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As a result, the diatom assemblage found in this
biofilm varies in both space
Areas with relatively low shear stress
Areas with low stability
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Pioneer species (r-strategists) colonise bare
surfaces and, over time, increase in quantity.
These pioneers are subject to competition from
other species until a scouring spate removes most
of these, allowing pioneer species to
re-establish.
... and time.
High Low
Increasing competition
Resource supply
r-strategists
c-strategists
spate
Low High
Disturbance frequency
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This can, in turn, influence the value of
diatom-based water quality indices.
Data from the River Wear, NE England. Note the
scale of within-site variation in indices.
Despite this, longitudinal trends in the TDI are
still apparent.
From Kelly (2002) J. appl. Phycol. 14 9-18.
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From theory to practice
Now that we have some idea of the structure and
composition of the biofilm, we need to think
about how best to collect samples for monitoring
ecological status.
The second part of this presentation will deal
with this.
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The TDI method diatoms for tactical monitoring

• The TDI was developed in response to the Urban
  Wastewater Treatment Directive.
• This required an assessment of point sources of
  nutrients on a case-by-case basis.
• We asked the question does this sewage works
  have a significant effect on this river?
• Methods needed to be robust but .
• . allow flexibility so that biologists can
  fine-tune sampling to suit local conditions

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UK strategy UWWTD

• The same substrate has to be sampled at all sites
  in a river system.
• Cobbles and boulders are the preferred substrates
• Artificial substrate (polypropylene rope) is also
  widely used.

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Water Framework Directive

• For this new Directive we need to compare the
  biota at a site with that expected in the absence
  of significant human impact.
• This means that we need to use substrates that
  are typical of the river type under
  investigation.
• Cobbles and boulders are not characteristic of
  all river types, so we need to include other
  natural substrates.
• Assemblages found on an artificial substrata do
  not fulfil this criterion.

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Sampling protocol

• The sampling strategy outlined in the TDI manual
  has had to be modified for DARES in order to take
  account of the requirements of the WFD.
• Cobbles and boulders are still the preferred
  substrate
• However, if these are not found, then emergent
  macrophytes should be sampled.
• If these are not found, then submerged
  macrophytes can be used.

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Selection of sampling sites.

• For DARES, samples will be collected from sites
  already used for GQA surveys.
• Issues that were considered when selecting these
  sites include
• Location with respect to discharges / confluences
  etc.
• Access from road
• Location with respect to other monitoring records
  (chemical / macrophyte / invertebrate)
• Glides, runs and riffles are all suitable for
  collecting diatom samples but most pools will be
  too slow-flowing.

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However, once you have arrived at the site, you
need to decide where in the survey reach to
collect your samples.

• Aspects to consider include
• Current speed
• Shade
• Water depth
• Selection of substrate

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Factors to consider when selecting a sample site
1. current speed

• Sample from main flow of river
• Not sidearms or backwaters
• Avoid areas of very high current velocity for
  safety reasons
• Areas of very slow flow (lt 0.1 m s-1) permit
  accumulation of loosely-attached species

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Factors to consider when selecting a sample site
2. depth

• Two rules to follow
• If you can see the substrate, it is in the
  euphotic zone
• If you can wade to it, then the water is not too
  deep
• In addition, ensure that surfaces are permanently
  submerged
• This will depend, to some extent, on local
  knowledge.
• As a rule of thumb ensure that the water depth
  is at least 10 cm.

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Factors to consider when selecting a sample site
3. light

• Avoid heavy shade, unless this is characteristic
  of the system under study
• Try to sample from sites with similar light
  regimes

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Selection of substrate There are three options

• Either cobbles

... or macrophytes
Emergentor submerged