Water Chemistry Field Sampling
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sample the outlet stream, if one is present, close to the lake. Outlet stream
chemistry should closely approximate average lake chemistry unless there
are major perturbations in the vicinity of the outlet stream. Note that even
though this sample is actually collected from the outlet stream, it is intended
to represent the chemistry of the lake. Thus, the sample should be labeled and
documented as a lake sample rather than a stream sample. In general, we do
not recommend collection of lake samples from the shoreline for the purpose
of characterizing overall lake chemistry as the chemistry of this water may
be different from the outlet or lake average, partly because of differences in
temperature and biological productivity. Nevertheless, if there is not an outlet
present, or if the outlet is not flowing at the time of sample collection, an alternative, less-desirable approach is to collect the sample from the shoreline. For
this approach, a shoreline sample collection location should be selected that
satisfies as many of the following criteria as possible:
• as close to the outlet as possible
• near the lowest point of land around the perimeter of the lake
• from a bedrock outcropping or otherwise-rocky area
• from the deepest accessible point
Water must be deep enough so that surface scum and sediments are not
collected into the bottle, preferably in a wind-exposed area so that the water is
relatively well mixed. Avoid sampling in locations having emergent vegetation
or downed logs or other woody debris.
Lake samples collected from the deepest lake location are normally collected using a Van Dorn sampler at a prespecified depth. The Van Dorn sampler
(and any associated tubing) should be rinsed three times with lake water and
then lowered to the specified sampling depth for sample collection. The sampler should be held at the sampling depth for approximately 1 min to allow
equilibration with the water at that depth. A weighted messenger is used to
trigger closure of the sampler doors prior to retrieval of the sample. Water
from the Van Dorn sampler is then used to rinse the sample bottle and lid (and
syringes if applicable) three times prior to filling.
Sample depth for lakes should be standardized, to the extent possible, across
lakes included within a particular program. For lakes deeper than 2 m, a sample
depth of 1.0 or 1.5 m is commonly specified. For lakes less than 2 m deep and
for lakeshore sampling (where required), the single-depth sample should be collected at 0.5-m depth. An alternate approach (not recommended as necessary
for the purposes described here) is to collect a depth-integrated sample using a
2-m long tube. The EPA’s NLA in 2007 collected depth-integrated samples of the
euphotic zone, estimated as two times the Secchi depth, to a maximum of 2 m.
Normally, a surface sample (i.e., 1.5-m depth) from the deepest part of the lake,
with or without replicates, is used to characterize lake chemistry at the time
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sample the outlet stream, if one is present, close to the lake. Outlet stream
chemistry should closely approximate average lake chemistry unless there
are major perturbations in the vicinity of the outlet stream. Note that even
though this sample is actually collected from the outlet stream, it is intended
to represent the chemistry of the lake. Thus, the sample should be labeled and
documented as a lake sample rather than a stream sample. In general, we do
not recommend collection of lake samples from the shoreline for the purpose
of characterizing overall lake chemistry as the chemistry of this water may
be different from the outlet or lake average, partly because of differences in
temperature and biological productivity. Nevertheless, if there is not an outlet
present, or if the outlet is not flowing at the time of sample collection, an alternative, less-desirable approach is to collect the sample from the shoreline. For
this approach, a shoreline sample collection location should be selected that
satisfies as many of the following criteria as possible:
• as close to the outlet as possible
• near the lowest point of land around the perimeter of the lake
• from a bedrock outcropping or otherwise-rocky area
• from the deepest accessible point
Water must be deep enough so that surface scum and sediments are not
collected into the bottle, preferably in a wind-exposed area so that the water is
relatively well mixed. Avoid sampling in locations having emergent vegetation
or downed logs or other woody debris.
Lake samples collected from the deepest lake location are normally collected using a Van Dorn sampler at a prespecified depth. The Van Dorn sampler
(and any associated tubing) should be rinsed three times with lake water and
then lowered to the specified sampling depth for sample collection. The sampler should be held at the sampling depth for approximately 1 min to allow
equilibration with the water at that depth. A weighted messenger is used to
trigger closure of the sampler doors prior to retrieval of the sample. Water
from the Van Dorn sampler is then used to rinse the sample bottle and lid (and
syringes if applicable) three times prior to filling.
Sample depth for lakes should be standardized, to the extent possible, across
lakes included within a particular program. For lakes deeper than 2 m, a sample
depth of 1.0 or 1.5 m is commonly specified. For lakes less than 2 m deep and
for lakeshore sampling (where required), the single-depth sample should be collected at 0.5-m depth. An alternate approach (not recommended as necessary
for the purposes described here) is to collect a depth-integrated sample using a
2-m long tube. The EPA’s NLA in 2007 collected depth-integrated samples of the
euphotic zone, estimated as two times the Secchi depth, to a maximum of 2 m.
Normally, a surface sample (i.e., 1.5-m depth) from the deepest part of the lake,
with or without replicates, is used to characterize lake chemistry at the time