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
agricultural streams throughout the United States
(U.S.) since the 1970s without pre- or postevaluations
of the resulting impacts (Bernhardt et al., 2005;
Alexander and Allan, 2006). Evaluations of the physi-
cal and biological responses of agricultural streams to
conservation practices are needed to document the
impacts of these practices and their effectiveness in
providing environmental benefits (Moore and Palmer,
2005; Vondracek et al., 2005). Documentation of the
ecological effects of conservation practices will pro-
vide guidance for developing management plans
intended to reduce the impacts of agriculture on
streams.
Introductory compilations of specific techniques for
assessing habitat and aquatic biota within streams
are available (Merritt and Cummins, 1996; Murphy
and Willis, 1996; Bain and Stevenson, 1999; Hauer
and Lamberti, 2006). Recommendations on technique
selection and descriptions of their use are provided
within the numerous sampling protocols that have
been developed for rapid bioassessment and other
types of monitoring (see Johnson et al., 2001; MRCS,
2001; USEPA, 2002; Somerville and Pruitt, 2004;
Stolnack et al., 2005 for descriptions of >400 sam-
pling protocols). Habitat assessment sampling proto-
cols focus on the measurement of hydrology,
geomorphology, or riparian habitat variables, while
biological assessment sampling protocols concentrate
on methods for sampling aquatic macroinvertebrates
or fishes (Table 1). Various rapid bioassessment pro-
tocols are widely used by regulatory agencies, con-
sulting firms, and private organizations within the
U.S. (Rabeni et al., 1999). These protocols are
designed to produce a spatially extensive dataset
capable of detecting impairments in streams using
cost and time - saving techniques (Rabeni et al., 1999),
but this dataset will not be effective in identifying
environmental factors responsible for the impairment
(Maddock, 1999; Winger et al., 2005). Thus, the use
of these protocols within studies intended to evaluate
the effects of specific management practices results in
sacrificing inferential power to gain rapid applicabil-
ity (Downes et al., 2002). Additionally, these sampling
protocols may not be suitable for evaluating the
effects of specific conservation practices because of
differences in the objectives between monitoring stud-
ies and impact assessments (Downes et al., 2002).
Monitoring studies are often conducted to evaluate
the status or condition of streams and rivers (Downes
et al., 2002). Monitoring studies are designed without
a priori knowledge of the stressor or the source of
impact and are intended to address the question:
"What is the status of the target populations1commu
nities and habitat conditions, and how does the sta-
tus change through time ?" Conversely, impact
assessments are conducted to evaluate the influence
TABLE 1. Percentage of Different Types of Sampling Protocols
Summarized Within Selected Reviews of Sampling Protocols for
Monitoring Biological and Habitat Characteristics of Streams.
Type of Somerville
Sampling and Pruitt NRCS Johnson USEPA
Protocol (2004) (2001) et al. (2001) (2002)
Biological
0
2
0
Bacteria
0
2
3
7
31
Algae
Aquatic or terrestrial
0
3
5
15
macrophyte
0
0
15
Phytoplankton
0
or zooplankton
12
22
29
86
Aquatic
macroinvertebrate
Fish
6
19
31
63
Amphibian
4
0
2
5
3
Waterfowl
0
0
0
Wildlife and other
0
8
5
5
vertebrates
Habitat
Chemical
20
11
51
2
Hydrology and
55
28
57
32
instream
habitat features
Geomorphology
73
44
42
23
Riparian
55
61
36
23
Watershed
20
17
14
0
Total reports
51
36
96
65
summarized
Note: Column totals may exceed 100% because they were calcu-
lated based on the number of reports listed within a review and
reports often contained descriptions of multiple sampling proto-
cols.
of specific disturbances or management practices
(Downes et al., 2002) and are designed with a priori
knowledge of the expected source of impact (i.e., the
disturbance or conservation practice). Impact assess-
ments are designed to answer the question: "How
does implementation of conservation practices influ-
ence the habitat and target populations1communi
ties?" An impact assessment would also attempt to
determine the environmental factors and causal rela-
tionships responsible for the observed impact of con-
servation practices on the aquatic biota. It is possible
that monitoring studies may fortuitously obtain data
that enables the evaluation of the impacts of a con-
servation practice. However, in this case the evalua-
tion of the effects of a conservation practice with a
monitoring study is a matter of chance, whereas the
evaluation with an impact assessment is a directed
and proactive effort specifically designed to document
the impacts.
The spatial and temporal scale of monitoring stud-
ies can differ from impact assessments. Monitoring
studies are analogous to weather stations and often
involve repeated measurements through time over
JAW RA
868 JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION