of the results requires very practical methods of field collection and data analysis, statistical and
18.104.22.168 The Methods of Assessment - Field Collections
Here the methods of lake assessment are restricted to those procedures likely to be performed
in the field. These include in situ measurements as well as collecting water or biological samples for
The number of lake characteristics that we can sample using in situ instrumentation is growing
rapidly. These characteristics include several parameters that are nearly always measured: temperature,
dissolved oxygen, pH, specific conductance, depth, location and time, and secchi transparency.
Sometimes included are also turbidity, light intensity, oxidation reduction potential, and a growing list of
specific ions. The technologies are mature for most of the basic parameters and instrumentation for
measuring them has become very refined. Most improvements in recent instrumentation are related to
ease of use or digital manipulation of the data. Occasionally, new technologies are added - optical or
solid state sensors, for example.
These instruments are great improvements over earlier ones because the assessment process
can begin in the field. Quick, accurate assessment of thermal or chemical trends is possible and field
decisions can be made or changed to optimize the return of useful data per unit effort. For example,
unexpected thermal trends can be more intensively studied at the time that they are observed or else
additional chemical observations can be added depending on decisions in the field.
This latitude of judgement contains risks. The first step toward all subsequent analyses is the
field collection step and if this is inaccurate or the result of poor judgement then all subsequent steps in
analysis or assessment are compromised. Field personnel must understand the measurement
technology and the limnological processes relevant to the parameters measured. In addition, the ease
of use allowed by modern instrumentation can convey false confidence in measurements - confidence
which did not exist for more <primitive' instrumentation. There is still much good work that can be done
with basic and technologically simple methods.
The two best references for field and laboratory analyses are Standard Methods (Greenberg
1995) and the EPA manual (EPA 1979). There are other sources of methods and these include
Strickland and Parsons (1972), Wetzel and Likens (1991) as well as manuals specific to instrument
manufacturers such as Hydrolab, Bran Luebbe, YSI/Endeco, Perkin Elmer, and others.
2.3.3 SAMPLING CONSIDERATIONS
Many issues to be considered prior to sampling have already been stated or discussed. After
the problem or question has been identified, the design of a sampling program to address the problem