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

DESIGNING IMPACT ASSESSMENTS FOR EVALUATING ECOLOGICAL EFFECTS OF AGRICULTURAL CONSERVATION PRACTICES ON STREAMS
large geographic areas to provide a time series repre-
senting the status of the target/populations and habi-
tat conditions. Conversely, impact assessments are
conducted at a variety of spatial and temporal scales
depending on the research hypothesis and funding
base (Engel and Voshell, 2002). Impact assessments
with large spatial and temporal scales are considered
the most robust and necessary for evaluating the
impacts of conservation and restoration practices
(National Research Council, 1992; Kondolf, 1995), but
smaller scale studies can provide valuable informa-
tion as long as their limitations are recognized.
Differences between monitoring studies and impact
assessments highlight the need for guidance in
designing impact assessments. Our objective is to
provide five guiding principles that will assist others
in designing impact assessments of ecological
responses of agricultural streams to conservation
practices. We first provide background information
and describe the challenges faced in developing the
guiding principles. Second, we explain each principle
and defend their importance. We conclude with an
example of how the guiding principles were applied
in designing an evaluation of the influence of herba-
ceous riparian buffers on the habitat and aquatic
communities within channelized headwater streams
(i.e., drainage ditches).
TOWARDS THE DEVELOPMENT OF
GUIDING PRINCIPLES
The guiding principles below resulted from an
attempt to develop standardized sampling protocols
for the Agricultural Research Service (ARS) compo-
nent of the Conservation Effects Assessment Project
(CEAP). The ARS component of CEAP consists of the
Watershed Assessment Study that is intended to pro-
vide detailed findings on the influence of conservation
practices from 14 watersheds in the U.S. (Mausbach
and Dedrick, 2004) (Figure 1). The ARS research
effort focuses mostly on evaluating water chemistry
and hydrological responses to conservation practices.
Ecological responses are currently being evaluated in
only three watersheds (Figure 1) despite the critical
need for this information due to the elevated threat
level currently faced by stream ecosystems (Richter
et al., 1997; Karr et al., 2000). Additionally, the
national assessment of conservation practices as part
of CEAP plans to use watershed models (Mausbach
and Dedrick, 2004) to evaluate water chemistry and
selected hydrological responses to conservation prac-
tices (Shields et al., 2006a). These models are not
capable of evaluating physical habitat responses (i.e.,
FIGURE 1. Locations of Agricultural Research Service Conserva-
tion Effects Assessment Project Watershed Assessment Study
Watersheds Within the United States. Watersheds symbolized by a
black circle within a white circle are study sites where ecological
assessments are being conducted.
base -flow discharge, substrate types, large woody deb-
ris, water temperature) or biological responses (i.e.,
fish and macroinvertebrate community responses)
(Shields et al., 2006a). Ecological assessments (i.e.,
joint assessments of habitat and biological responses)
have the potential to provide information for novel
developments in these watershed models that would
allow the national assessment of conservation prac-
tices to conduct a cross - disciplinary assessment of
conservation practices through the evaluation of
water chemistry, hydrology, physical habitat, and
ecological responses. We initiated the development of
a standardized protocol to facilitate the: (1) initiation
of ecological research within ARS watersheds, (2) col-
laborative ecological research among watersheds, and
(3) cross - disciplinary assessments of conservation
practices.
Developing a standardized sampling protocol
immediately proved to be a challenge. Twelve of the
ARS watersheds are lotic ecosystems, while two of
the watersheds are lentic ecosystems. Watershed
sizes range from 850 to 827,000 ha. The watersheds
are located in 11 states within the Northeast, Mid-
west, Southeast, and Northwest U.S. and encompass
11 ecoregions ranging from the Middle Atlantic
Coastal Plain to the Northern Basin and Range Ecog-
regions (Omernik, 1987, 1995). The amount of crop-
land within each watershed ranges from 2 to 100%
and land use in seven watersheds is predominately
cropland ( >_60 %). Six of the ARS studies are evaluat-
ing the influence of nutrient management and/or
riparian buffers. However, research within 13 ARS
watersheds also includes assessments of one to three
other conservation practices from among 12 types
ranging from manure management to drainage
JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 869 JAWRA