Methods in Limnology P

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Methods in Limnology (P)
Lesson 8-P
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Contents

• Hydrographical profile (h.pr.)
• Physicochemical parameters
• Water sampling
• Plankton sampling
• Sediment Sampling (s.s.)
• Surface material (grab sampler)
• Sediment cores (gravity corer)
• Pore water
• Physical basin characterization (p.b.c.)
• Shoreline mapping
• Depth profiles
• In- and outflow determination
• Water balance

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I. Hydrographical profile (h.pr.)

• Options and objectives
• To obtain a momentary or (if regularly repeated)
  more or less continuous understanding of a lake
  water profile in respect to TC, O2 (mg L-1 and
  rel. saturation in ), k (µS cm-1), pH-value, and
  sometimes more behavior with water depth. The
  respective data allow for the characterization of
  a lakes stratification and for trophic state
  assessment.
• This profile may be further enhanced using
  chlorophyll characterization by fluorometry to
  determine phytoplankton densities with depth.
• Finally, the h.pr. may be used to selectively and
  efficiently take depth-oriented water, particle,
  and plankton samples.

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I. Hydrographical profile

• Equipment (1)
• General remark. In principle, an HP may be
  obtained with very simple methods (albeit time
  consuming and compromising in respect to accuracy
  and precision). Think, e.g., of repeatedly
  lowering a water sampler (Ruttner sampler or
  derivatives) and to sequentially measure the
  required parameters onboard. This presentation is
  focused on the availability of state-of-the-art
  multi-parameter probes.
• Boat and anchoring option. If no buoy is
  available, the boat(s) have to be anchored or
  held in position in another appropriate manner
  that does not interfere with the intended
  measurements. It goes without saying that the
  boat used needs to be safe for the intended use
  and the number of people on board. All safety
  gear must be familiar to you.

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I. Hydrographical profile

• Equipment (2)
• Multi-parameter probe. Probes are available from
  several companies, the most common being YSI and
  Horiba from Japan. Independent from the number of
  parameters that the probe may deliver, the user
  will have to verify well before the field
  measurements that the batteries are charged, that
  all sensors are properly calibrated and that they
  are working well. See manual for precise
  instructions and ask experienced personnel, e.g.,
  Kurt Herklotz, Jörg Matschullat, Alexander
  Pleßow.
• Mind the mechanical vulnerability of the
  individual sensors and the interface cable
  between the probe and the hand-held deck unit.
  Both are rather sensitive to mechanical damage
  and repair or replacement is rather expensive.

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I. Hydrographical profile

• Taking a hydrographical profile (1)
• Control and verify the depth of the water column
  before starting to work on the HP.
• After having made yourself familiar with the
  instrument and after having checked its
  functionality (see equipment), take a first
  reading from the lake water surface. Make sure
  that all sensors are fully submersed. Start
  taking the readings and wait until each parameter
  is equilibrated and delivers steady signals.
  Question the data and make control measurements
  if doubts arise.
• Keep repeating all measurements at each
  subsequent depth meter down to the thermocline.
  Try to describe the metalimnion as precise as
  possible (max. resolution 10 cm).

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I. Hydrographical profile

• Taking a hydrographical profile (2)
• Proceed with the measurements to the lake bottom,
  but do not allow the sensor head to touch the
  sediments. You neither want to mechanically
  damage the sensors, nor stir up sediments that
  might interfere with these and following
  measurements.
• Verify (control) your obtained data by taking
  selected readings on the way up.
• ! In the hypolimnion, you might decide to work
  with wider gaps between individual readings if
  your lake water column is high enough.

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I. Hydrographical profile

• Evaluation of the hydrographical profile (1)
• Download the data from the hand-held deck unit to
  another computer or manually transfer the data
  into a spreadsheet, e.g., MS-Excel.
• Plot the data and include the location onto each
  page (name of lake, sampling position GPS, date
  and time). Use an appropriate scale.
• Now define the upper and lower boundary of the
  metalimnion using TC as the master variable.
• Check all data for consistency
• Interpret the individual parameter profiles by
  putting them into perspective
• What is the absolute level in comparison to other
  systems that you know (e.g., local tap water,
  specific stream or river water, norms or
  regulatory values)
• How do the variables behave over the depth
  profile? Is this behavior consistent with your
  expectations?
• Can you explain the profile in respect to
  underlying processes? Use your knowledge from
  previous lectures.

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Experimental design
Which question do I want to answer? write it
down as specific as possible
How likely am I to answer my question?
Which field/laboratory methods do I intend to
use? pros and cons, how do they influence
results?
Which statistical tests, evaluation and
presentation methods models, scenarios etc. can
I use?

• How will I present final results?

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Field Sampling

• Depth-oriented with Go-Flow, Ruttner, Van Dorn
  etc. samplers (watch out for appropriate
  materials)
• Preparation filtration (dissolved/particulate)
  acidification (trace metals) cooling or freezing
• Plankton sampling nets of different mesh size
• Drift and emergence nets/traps
• Dredge, grab sampler and sediment corer
• Pore water sampling

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Selected physico-chemical methods

• irradiation (down- and upwelling light)
• flow velocity (tracer etc., see Hydrology)
• grain size distribution (set of sieves)
• electrodes temperature, conductivity, pH, O2, pe
• buffering capacity (titration with acid/base to
  given pH)
• colorimetric tests N, P, Si, Fe, Mn
• Biological and chemical oxygen demand (BOD/COD)
• total organic carbon (TOC)

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Selected biological methods

• Binoculars and microscope
• Sedimentation chamber and inverted microscope
• Species identification
• Species quantification distribution analysis
• Aufwuchs experiments (slide exposition)
• Biomass determination (e.g., by chlorophyll)
• Primary production by O2-measurements, 14C
• Water quality determination with indicator
  species

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Summary

• Experimental design
• Field Sampling
• selected physico-chemical measurements
• selected biological measurements

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Questions

• Limnology requires a whole set of unique methods.
  a) List as many as you can and b) Give some
  examples for their application
• Prior to doing any field or laboratory work, you
  need to think about an experimental design. a)
  Which questions do you have to answer, and b)
  What are the hierarchical steps to success?
• How do you access lake sediments at greater
  depth? B) how can you obtain undisturbed sediment
  material?
• How can you date sedimentary strata? List and
  briefly explain the methods.
• How do you describe the physical properties of
  lake/river sediments? Which methods do you use?
• How do you determine light penetration in a lake?
  And b) how do you determine visibility? C) what
  is the difference?

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Table of Contents
Lecture
Contents, Syllabus, Scope, Field training,
References
Lesson 1
Introduction
Lesson 2
Physical processes I
Lesson 3
Physical processes II and chemical processes I
Lesson 4
Chemical processes II
Lesson 5
Major groups of organisms
Lesson 6
Habitats and communities
Lesson 7
Energy fluxes
Lesson 8
Reservoirs
Lesson 9
Selected limnological methods
Lesson 10
Extraction and mining lakes
Lesson 11
Degradation and rehabilitation of streams and
rivers