Monitoring Program Design
contributions from the two major sources, streambank erosion and irrigation
return flow, were similar in magnitude when the project began. In contrast, from
1987 to 1990, monitoring indicated that streambank erosion contributed two to
in the subbasins
over five times the amount of sediment added from
during the May through August irrigation season.
In the Illinois RCWP project, turbidity, siltation, and nutrients were thought to
threaten Silver Lake, the water supply for the city of Highland. Sediment survey
results showed that siltation was low, which meant there was little threat of rapid
loss of lake storage capacity. Analysis of lake turbidity indicated that alga1
production was limited more by light than by nutrients. It was found that turbidity,
which increased the cost of water treatment, was due mostly to suspended soil
particles. Monitoring demonstrated that loading of fine particle natric soils and
their resuspension from lake sediments was the primary factor causing lake
turbidity. To target pollutant sources, the project placed special emphasis on
keeping natric soils in place and reducing their delivery into the lake.
Nutrient sources can be the most widespread and the most difficult
sources to identify and quantify. Watershed sources include commercial fertilizer,
animal waste, soil reserves, and atmospheric deposition. Streambeds and lake
sediments can release stored nutrients into the water resource, as well.
For the Vermont RCWP project, significant phosphorus loading to St.
Bay
originated from a point source, bay sediment, and a wetland adjoining the bay.
Project area soils also contributed part of the total phosphorus load. A budget of
all major phosphorus sources was needed to determine the potential for reducing
lake or bay phosphorus levels.
The Minnesota RCWP project found high nitrate levels in project area domestic
wells. Sources of nutrients included animal operations and cropland. The topog-
raphy is karst limestone with extensive sinkhole formations. Sinkholes were
thought to be a primary source of conveyance to ground water until lysimeter
studies showed rapid leaching of nitrate from fertilized cropland. Further study
indicated that
should be targeted for treatment and sinkholes should be
given a lower priority.
Physical, chemical, and biological variables in the receiving water may undergo
Detecting Trends
extreme changes without the influence of human activity. Understanding and
monitoring the factors responsible for variability in a local system are essential for
detecting the improvements expected from management actions. Simple point
estimates taken before and after treatment will not confirm an effect if the natural
variability is typically greater than the changes due to treatment. Therefore,
knowledge of the variability and the distribution of the variable is important for
change in order to determine
statistical testing. Greater variability requires a
that an observed change is not due solely to random events (Spooner et al. 1987b).
Examination of historical data sets can help to identify the magnitude of natural
variability and possible sources.
Management actions may not be detectable as a change in a mean value but rather
as a change in variability. Platts and Nelson (1988) found that a carefully designed
study was required to isolate the large natural fluctuations in trout populations so
that the effects of land use management could be distinguished. They assumed
normal fluctuation patterns were similar between the control and the treatment
4.5
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