JAWRA - Ag Conservation

• Project Type: General OWC
• Title: Designing Impact Assessments for Evaluating Ecological Effects of Agricultural Conservation Practices on Streams
• Date: 12/15/2009
• Water Conservation - Doc Type: Reports

SMILEY, SHIELDS, AND KNIGHT
management. We concluded that developing a stan-
dardized protocol that designated the use of specific
techniques was not appropriate given the diversity of
potential environmental conditions and the variety of
conservation practices being evaluated. Instead, we
focused our efforts on developing a set of guiding
principles suitable for designing ecological assess-
ments and selecting response variables and methods.
FIVE GUIDING PRINCIPLES
We developed five guiding principles that provide a
framework for developing ecological assessments. The
principles were developed based on our past experi-
ences conducting ecological research in agricultural
watersheds and guidance provided by Green (1979),
Cooper and Barmuta (1993), and Downes et al.
(2002). Our intention was to highlight aspects of
experimental design that when used together would
result in robust ecological assessments. Although lab-
oratory and mesocosm experiments are feasible, we
focus on issues related to designing impact assess-
ments. One example of an impact assessment to eval-
uate conservation practices would involve an
investigator sampling habitat and biota from streams
with and without conservation practices before and
after the implementation of the conservation prac-
tices. An investigator's level of control of experimen-
tal treatments within impact assessments may range
from field experiments that involve pre - planned
implementation of conservation practices within
selected streams to those where the investigator lacks
manipulative control and exercises control by select-
ing and comparing sites that differ in the presence
and absence of a conservation practice.
Impact assessments are known by other names
such as impact studies (Green, 1979), natural experi-
ments (Diamond, 1983), comparative mensurative
experiments (Hulbert, 1984), impact assessments
(Stewart -Oaten et al., 1986), intervention analyses
(Eberhardt and Thomas, 1991), and impact monitor-
ing (Downes et al., 2002). Impact assessments are
extremely valuable because it is difficult to reproduce
the essential character of aquatic and terrestrial eco-
systems in the laboratory, in mesocosms, or through
numerical simulations. We feel impact assessments
will yield the most realistic information regarding the
ecological effects of conservation practices because
these studies are conducted at spatio - temporal scales
similar to that of the experimental treatment (i.e.,
conservation practices). We did not attempt to pro-
vide guidance relating to technical options such as
selection of taxonomic group(s) to evaluate, which
biotic sampling methods to use in specific ecoregions,
and data analyses. Specific decisions regarding these
issues are dependent on the hypothesis, experimental
design, site specific factors, and/or available funds.
Develop the Hypothesis First
Our first recommendation is to develop a hypothe-
sis first, and then select the response variables and
sampling methods based on the hypothesis. We feel
this is the most important recommendation because
many past field studies evaluating the influence of
anthropogenic habitat alterations did not develop
hypotheses (Cooper and Barmuta, 1993; Bennett and
Adams, 2004). Hypothesis development is a funda-
mental component of the scientific method that is
applicable to all forms of environmental research.
The hypothesis needs to be specific enough that it
can provide a basis for selection of response variables
and sampling methods (Kondolf, 1995). Those hypoth-
eses that provide an explanation for the expected
effect (observed pattern) will be the most useful and
will result in studies that are capable of providing an
explicit explanation for the impact (Jansson et al.,
2005). However, it is not always possible to identify
causal mechanisms that regulate the influence of a
conservation practice on the aquatic biota before
beginning an evaluation. In these cases simple
hypotheses can be developed based on the expecta-
tions as to which abiotic and biotic factors will be
altered by the implementation of a conservation prac-
tice. The use of a priori hypotheses to select response
variables and methods requires investigators to con-
sider what variables need to be evaluated before
beginning the field research. This should lead to cost -
effective studies as it will prevent the measurement
of response variables that are not relevant to the
hypothesis.
Use Replicated Experimental Designs With Appropriate
Controls and Treatments
We view the implementation of a conservation
practice within a stream or its watershed as an
experiment in which the conservation practice serves
as the experimental treatment having the potential
to alter dependent variables (i.e., habitat or biota)
(Underwood, 1990). Additionally, in the context of
impact assessments, streams without the conserva-
tion practice of interest serve as the control sites, and
streams that contain or will contain the conservation
practice serve as the treatment sites. Unfortunately,
many assessments of agricultural conservation prac-
tices have failed to include a control stream into the
JAWRA 870 JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION