D.R. Barton and M.E. Farmer,
Department of Biology, University of Waterloo,
Waterloo, Ontario, Canada, N2L 3G1.
M.E. Dillon and D.R. Oliver,
Centre for Land and Biological Research Resources, Agriculture Canada,
Ottawa, Ontario, Canada K1A 0C6.
report (32 KB pdf)
1.0 RATIONALE / OBJECTIVE
The primary objective was to develop a set of techniques, a protocol,
for monitoring and assessment of surface water quality in agricultural regions
of southern Ontario based on benthic invertebrates.
This involved determining the best way to collect appropriate samples,
how closely the animals should be identified, and how the results can be
interpreted. The protocol will be used to assess the status of small streams
relative to other streams draining land under the same crop, or to monitor
changes in water quality due to changes in farming practices. The assessment
function is intended to identify sites which are better or worse than the
average for southern Ontario; monitoring will be valuable in evaluating
the results of mitigative measures such as leaving riparian buffer strips
or adopting conservation tillage. It was tested in a study of four pairs
of streams. One of each pair drained land primarily under conservation tillage
and the other under conventional tillage.
Agriculture has profound local and regional effects on both the quality
and quantity of surface waters. Removal of the forest which originally covered
most of southern Ontario led to higher summer and lower winter water temperatures,
as well as destabilization of hydrologic regimes, increased erosion and
siltation. Subsequent use of this cleared land for agriculture has additional
effects on the quality of surface waters, with the nature and magnitude
of the effects reflecting different farming practices.
In addition to each of the basic suites of stresses which are characteristic
of each major kind of crop, the relative impact of fields under the same
crop may differ substantially because of individual farming practices, variations
in soil conditions or chance events such as heavy rain just after application
of fertilizers. Such variation can make it very difficult, and expensive,
to monitor the effects of agricultural practices on surface water quality
through chemical assays. Pulsed inputs of chemicals resulting from spills
or heavy precipitation may easily be missed in routine surveys, but may
have severe biological impacts.
The problem of rapid fluctuations in the chemistry of running waters
has long been recognized with respect to discharges of wastes from industrial
and municipal sources, so the alternative approach of measuring biological
effects directly has been widely accepted (Rosenberg and Resh 1992). Benthic
invertebrate communities are nearly ideal for this purpose because they
are easily sampled and include large numbers of individuals belonging to
many species, each with its own response to any particular type of stress.
These animals live on the bottom of the stream or lake and have life-cycles
lasting months to years, so are exposed to the conditions in the stream
over fairly long periods of time. Schindler (1987) and Gray (1989) have
suggested that biological surveillance of communities, characterizing taxonomic
richness and composition, is a very sensitive tool for the detection of
alterations in aquatic ecosystems.
For point sources, the usual approach is to sample upstream and downstream
of the point of discharge and to express the differences in terms of changes
in total abundance, numbers of species, some expression of "diversity",
or a biotic index. In such situations, the benthic fauna reflects average
conditions as well as intermittent discharges, and biological monitoring
tends to be much cheaper and more sensitive than routine chemical analyses.
The potential utility of benthic invertebrates for monitoring and assessment
of the effects of agriculture on water quality should be equally great,
but the situation differs in one very fundamental way. With a few exceptions
such as runoff from feed lots or manure storage, agricultural effects do
not originate as point sources, thus upstream-downstream comparisons are
rarely practical. Furthermore, agricultural activities tend to inflict a
number of stresses simultaneously so it is not easy to ascribe the composition
of the fauna at any particular point to any single aspect of farming practice.
4.0 STUDY CONCLUSIONS
This study has demonstrated that the biodiversity of benthic invertebrates
in small streams in agricultural southern Ontario is very high. These diverse
communities respond in distinctive ways to inputs of eroded soil, pesticides,
fertilizers and other organic matter. There is a strong seasonality in the
composition of the benthic fauna, and those species which grow more actively
during the warmer months appear to be more sensitive to agricultural activities
than those which are most active in winter.
Percent Model Affinity proved to be the most versatile and sensitive
way to summarize invertebrate data for the purposes of water quality monitoring
and assessment. Samples from additional streams can be compared to the expected
community from forested reference streams to identify any which are significantly
impacted. Inspection of the detailed composition of the fauna usually gives
an indication of the nature of the problem and the kind of subsequent detailed
monitoring or analysis which might be warranted. Where remedial actions
or changes in farming practices have occurred, monitoring of the biological
effects would involve comparing benthic samples with the average communities
from both forested streams and streams draining the same crops. Changes
would be seen as decreasing PMA over time relative to the same crop; increasing
PMA relative to forested streams would indicate improving water quality.
5.0 NEW TECHNOLOGY AND BENEFITS
The most important result of this work is the Monitoring Protocol which
has been developed for invertebrate-based monitoring and assessment of surface
water quality in southern Ontario. The procedure for this protocol is as
1. Field Collecting.
Record location of stream (e.g. UTM), adjacent landuse and general
land use in area.
Take sample by disturbing portions of all microhabitats (mid-channel
riffles and pools, marginal vegetation, undercut banks, etc.) in the
stream with a booted foot.
Capture the dislodged substrate in a dip net with 300 m mesh bag.
Rinse the contents of the net to remove fine sediments, discarding
large pieces of vegetation, wood and stones.
Save 400 ml of contents in net in a jar and preserve with 10% formalin.
2. Laboratory analysis
Empty sample into a fine-meshed (100 m aperture) net; rinse to remove
the preservative and fine sediments not washed through in the field.
Examine sample under a dissecting microscope and remove, at least,
the first 200 animals encountered.
Briefly examine unsorted sample for large rare animals which may
not have been included in the first 200 individuals.
Preserve animals in 70% ethanol.
Identify and enumerate the animals to the lowest practical taxonomic
Convert the counts to percentages of the total number of animals
sorted from the sample.
Calculate the Percent Model Affinity (PMA) between the sample and
the appropriate expected reference community.
Values of PMA which are more than 2 standard deviations away from
the mean for the reference community are significantly different.
The cost of invertebrate biomonitoring can be estimated from the time
and skill of the personnel needed for each step. Collection of the sample
requires about 10-15 minutes at the site. Sorting the sample in the laboratory
takes 2-3 hours. Personnel performing each of these steps require, at most,
a few hours of training. The time and expertise required for the identification
stage vary with the taxonomic level. An experienced benthic taxonomist should
be able to identify the specimens to the family level in about half an hour,
to the lowest practical level in about 1-3 hours, depending on the number
of taxa present. Less experienced personnel will need more time and should
have their identifications confirmed by experts in the field.
6.0 IMPLICATIONS FOR THE GREAT LAKES BASIN
Agriculture is the predominant landuse in the lower Great Lakes basin,
so any inputs to surface waters enter the Lakes themselves, either directly
or indirectly. Our results suggest that about 80% of the small streams in
southern Ontario are negatively impacted by agriculture.
Substantial investments over the past 25 years have reduced the inputs
of nutrients and organic wastes from municipal sources, and these efforts
appear to be resulting in significant improvements in water quality. Some
progress has also been made with respect to industrial effluents. Such point
sources are easily identified so remedial efforts can be concentrated.
The Monitoring Protocol presented here can be used to identify streams
subjected to significant non-point source pollution, and to monitor improvements
which result from changes in landuse practices. Agricultural streams receive
inputs of eroded sediment, inorganic and organic nutrients, and a variety
of agro-chemicals. Broad chemically based surveys to locate problem sites
are prohibitively expensive; the invertebrate fauna can provide much more
information, at a much lower cost.
7.0 TECHNOLOGY TRANSFER POTENTIAL
The Monitoring Protocol is useful to any organization interested in the
effects of agriculture on the water quality of streams. User groups include
conservation authorities, provincial Ministries (Environment, Natural Resources,
Agriculture), federal Departments (Agriculture, Environment, Fisheries),
as well as private organizations (e.g. Ducks Unlimited, OFAH), and private
The taxonomic descriptions and keys will increase the capability of environmental
impact workers to distinguish and name Chironomidae living in small streams.
8.0 INFORMATION GAPS AND FUTURE RESEARCH
In order to increase the sensitivity of PMA for monitoring of agricultural
impacts, expected communities could be refined to reflect narrower spatial
and temporal scales. This can be accomplished through extension of the existing
database by sampling at different times at some of the sites already surveyed,
as well as new ones. Additional data from forested reference sites are especially
needed. Similarly, sensitivity will be enhanced with improvements in our
ability to identify invertebrates to the species level. This will require
continuing taxonomic studies.
The database should also be expanded to include larger streams. Concentration
on headwater streams during this phase, in order to isolate the effects
of individual crops, has left several questions to be answered:
Does the fauna of larger rivers integrate all landuses upstream?
Are certain agricultural inputs processed (i.e. removed from circulation)
within the stream?
Answers to these questions would allow more meaningful interpretations
of the effects of agriculture on the Great Lakes themselves, and could increase
the efficiency of biomonitoring programs by reducing the number of sites
needed for initial surveys.
Thursday, May 05, 2011 04:02:41 PM