Methods
of Ecosystem Analysis - Water
Methodology
for Chemical Analysis of
Precipitation
and Stream Water
Study Objectives
As part of the Methods of Ecosystem Analysis
project near Lake Gaillard, the water chemistry group took on a study of
rainfall/snowfall and the chemistry of two feeder streams to Crooked Brook,
a major feeder of the Lake Gaillard reservoir. Click on the thumbnail at right to see a full-size image of our site location. Our objectives were
to obtain data on incoming amounts of calcium (Ca), magnesium (Mg), and
sodium (Na) in rain and snow to compare with amounts of Ca and Mg in the
two tributaries to Crooked Brook. The results can complement studies
of Ca, Mg, and Na concentrations in plants from this watershed and can
ultimately be compared to similar studies done in other locations.
Study Methodology
Precipitation in southern New England in
winter occurs as rain and snow events. We used two types of colletctors
to be sure of measuring both types of precipitation. Click on the thumbnail image at right to see a larger picture of the collectors. We used a funnel
collector to ensure minimal evaporation.
We used open buckets to ensure collection of snow;
unfortunately, these provided a significant open surface for evaporation.
Since evaporation in winter in New England is minimal, we have not included
estimates of it in our calculations.
In a forested setting, precipitation reaching
the ground must pass through the forest canopy. In winter, this consists
of twigs and branches, while in the summertime this also includes leaves.
In order to examine the impact of the winter canopy on the measurement
of precipitation chemistry, we set up funnel and bucket collectors in both
forested and open settings.
Four funnel and four bucket collectors
were set up - three sets in a wooded area near Crooked Brook and one set
in an open area near to Lake Gaillard. Each funnel collector included
a 500 mL plastic bottles attached below the funnel. The collectors
were mounted on poles approximately 1.8 meters high.
The bottles and buckets were capped, collected,
and weighed each week for 8 weeks. After collection, samples from
the rain bottles and snow buckets were put into 120 mL plastic bottles
and refrigerated for no more than 14 days before calcium, magnesium, and
sodium concentrations were measured on the Inductively
Coupled Plasma Spectrometer (ICP). Click on the thumbnail at left to see a larger image of an ICP. The ICP performs
elemental analysis by using a plasma as the ionization source and
a spectrometer analyzer to detect the ions produced. The machine
is highly sensitive, giving very accurate data on elemental concentrations
in water samples.
Stream Water Analysis
Water samples were collected weekly from
a wetland in the Crooked Brook watershed and from two streams that run
from the wetland to Crooked Brook (eight sampling sites in total - please
see site map for sampling locations).
120 mL plastic bottles were filled at each sampling site after being rinsed
with water from the site three times. Following collection, the samples
were refrigerated and analyzed on an ICP within 14 days.
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