Water Chemistry Field Sampling
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Any subsequent sampling of a given site should rely on global positioning system (GPS) coordinates, site photographs, detailed maps, and written
description of the site location to return to precisely the same location each
time that site is sampled. Where allowed, if a site is intended to be sampled
repeatedly, the placement and documentation of uniquely numbered metal
tags at the base of a tree or on a rock adjacent to the sampling site can provide
confirmation of site location.
The field crew should follow these guidelines in selecting new nonrandom
sites for repeated long-term sampling:
• The best point to sample a lake will be the deepest part of the lake. This
requires use of a boat, raft, or float tube. If it is not possible to collect such an
open-water sample, the next-best option is to sample the largest flowing
outlet from the lake; the outlet should be sampled, using stream-sampling
procedures, as close to the lake as is practical. The third, and leastdesirable option, is to sample the lake from the shoreline. Shoreline sampling should be conducted, if possible, from a large rock or by wading a
short distance from the shore. Care must be taken to avoid disturbing the
sediment in any way that could affect the quality of the sampled water.
Proximity to logs and aquatic vegetation should be avoided. If possible,
use wind currents to advantage by collecting the sample from an area
that receives wind-driven surface water movement from the larger lake.
• The best point to sample a stream will be where the water is flowing fast or falling, where there are no eddies, and where the depth
is at least 15 cm (6 in.). Ideally, the sampling point is one that can be
reached during most flow conditions while kneeling on the stream
bank or on stable rocks downstream from the sampling point. Where
possible, sites should be selected that allow the sampler to avoid standing or stepping in the water to reach the sampling point and to avoid
any disturbance of the streambed upstream from the sampling location. Ideally, sites should be selected that allow the sampler to reach
upstream to collect the sample, well upstream of his or her immediate
location and well upstream of any location that has been disturbed.
• Stream sample sites should be readily identifiable by reference to semipermanent landmarks, such as confluence points of major tributaries,
well-marked boundary lines, and stream crossings by permanent roads
or well-marked trails if they occur in proximity to the selected site.
• Stream sample sites should be selected to avoid direct runoff from
roads and trails, as well as unmixed flow from tributaries, unless the
goals of the sampling include those conditions. This will be achieved
for most small streams by selecting sampling sites at least 50 m above
road or trail crossings or 50 m above or below inflowing tributaries.
34
Any subsequent sampling of a given site should rely on global positioning system (GPS) coordinates, site photographs, detailed maps, and written
description of the site location to return to precisely the same location each
time that site is sampled. Where allowed, if a site is intended to be sampled
repeatedly, the placement and documentation of uniquely numbered metal
tags at the base of a tree or on a rock adjacent to the sampling site can provide
confirmation of site location.
The field crew should follow these guidelines in selecting new nonrandom
sites for repeated long-term sampling:
• The best point to sample a lake will be the deepest part of the lake. This
requires use of a boat, raft, or float tube. If it is not possible to collect such an
open-water sample, the next-best option is to sample the largest flowing
outlet from the lake; the outlet should be sampled, using stream-sampling
procedures, as close to the lake as is practical. The third, and leastdesirable option, is to sample the lake from the shoreline. Shoreline sampling should be conducted, if possible, from a large rock or by wading a
short distance from the shore. Care must be taken to avoid disturbing the
sediment in any way that could affect the quality of the sampled water.
Proximity to logs and aquatic vegetation should be avoided. If possible,
use wind currents to advantage by collecting the sample from an area
that receives wind-driven surface water movement from the larger lake.
• The best point to sample a stream will be where the water is flowing fast or falling, where there are no eddies, and where the depth
is at least 15 cm (6 in.). Ideally, the sampling point is one that can be
reached during most flow conditions while kneeling on the stream
bank or on stable rocks downstream from the sampling point. Where
possible, sites should be selected that allow the sampler to avoid standing or stepping in the water to reach the sampling point and to avoid
any disturbance of the streambed upstream from the sampling location. Ideally, sites should be selected that allow the sampler to reach
upstream to collect the sample, well upstream of his or her immediate
location and well upstream of any location that has been disturbed.
• Stream sample sites should be readily identifiable by reference to semipermanent landmarks, such as confluence points of major tributaries,
well-marked boundary lines, and stream crossings by permanent roads
or well-marked trails if they occur in proximity to the selected site.
• Stream sample sites should be selected to avoid direct runoff from
roads and trails, as well as unmixed flow from tributaries, unless the
goals of the sampling include those conditions. This will be achieved
for most small streams by selecting sampling sites at least 50 m above
road or trail crossings or 50 m above or below inflowing tributaries.