|Chad Wiseman labeling a sample bottle after processing samples.|
This page provides a quick overview on how we conduct our sampling. For more detailed information on our field procedures, please see Standard Operating Procedures for the Collection, Processing, and Analysis of Stream Samples. That document lists the laboratory methods we use as well. You may also want to refer to the Manchester Laboratory webpages for more information about lab analyses.
The majority of samples are collected as single surface grab samples from highway bridges. A few stations are sampled from the bank. We collect samples using a rope and weighted containers. Temperature is read in-stream using a long-line thermistor; other samples are carried back to the van and processed. Twelve water quality constituents are monitored monthly, shown below, though we sample additional constituents at some stations. (We sample metals at 12 stations each year; procedures for that monitoring are not included here.) In addition, we collect instantaneous flow at long-term and some basin stations.
|Monitored water quality constituents|
|ammonia, total||conductivity||fecal coliform bacteria||nitrate + nitrite, total|
|nitrogen, total||oxygen, dissolved||pH||phosphorus, soluble reactive|
|phosphorus, total||suspended solids, total||temperature||turbidity|
Consistency is particularly important in long-term monitoring programs. Normally, procedural or analytical changes will result in improved precision or reduced bias. Most changes will have only a minor affect on a synoptic analysis of the data but even improvements in procedures can mislead the unwary analyst of long-term trends. For this reason, we try to follow standardized procedures for equipment cleaning, maintenance, and calibration; sample collection, preparation, and shipping; and data management.*
* For more information on standard procedures, see SOPs for the Collection, Processing, and Analysis of Stream Samples.
(click to enlarge)
|At stations without continuous flow recording devices, we determine instantaneous flow from a measurement of stream height. Here, Chad is using a wire weight gage to determine the distance from the surface of the water to a known reference point on the bridge. Some stations have staff gages and at some we use a measuring tape.|
|The fecal sampler is lowered away from the bridge to keep material from falling off the bridge and into the sampler.|
|Chad has collected his water samples and is capping the fecal coliform bottle--being careful not to contaminate the cap.|
|To be suitable, a sampling location must not be too far from a safe parking area. The stainless steel bucket with its two 1-liter passenger bottles, plus all the other gear, is too heavy to carry far--though we do hike up to a half mile at rare locations. We avoid bridges with low railings, lots of traffic and no walkway, or other problems affecting safety.|
|Dissolved oxygen samples are fixed in the field but not titrated until we return to the office after the sampling trip. Experiments indicate that results remain accurate for a number of days.|
|The bacteria sampler has a fin on the back to orient it to the flow thus minimizing the possibility of contamination from the sampler itself. The foil on the cap reduces contamination entering between cap and bottle.|
|The design for the stainless steel bucket, which is modified from one in "Standard Methods", allows BOD bottles to overflow while filling. This keeps air bubbles from affecting the dissolved oxygen concentration. One of the one-liter passenger bottles is sent to the lab for TSS analysis; the other is acid-washed between samples and is used for nutrients.|
|Both meter and probe of the long-line thermometer are protected by home-made cases. The meter is calibrated against a thermometer before every trip.|
|The layout of the van's cargo area is shown here. Note the strobe light and orange vest in the box on the right. The use of these is required at most stations.|
|We record barometric pressure uncorrected for elevation (barometer at far right) to use in percent oxygen saturation calculations. Conductivity and pH meters are in the center; calibration solutions are visible on the shelf under the meters.|
|The "mini-lab" inside our vans is set up with cups, on the right, for pH and conductivity measurements, and a peristaltic pump on the left for filtering dissolved nutrient samples.|
|Samples are tagged and shipped on ice overnight to the laboratory. We either deliver the samples ourselves, or ship them by bus or by air. In the last case, "blue ice" must be used. Holding times are a concern, as is incubation time for bacteria samples. To be read by Friday, bacteria samples must be delivered to the lab no later than Thursday morning.|
Because our data are used to assess water bodies for trends, as well as possible 303(d) listing and subsequent TMDL investigations, we work hard to produce quality data. We follow strict protocols for sampling and processing. We spend a lot of time calibrating our meters. Conductivity meters are calibrated twice daily and pH meters three times. We also check the calibration whenever a pH reading exceeds state standards. We use modified Winkler titrations to measure dissolved oxygen, because they are more accurate than meters and because we often change elevation between sample stations.
To evaluate data quality, we collect a second set of samples at one randomly-chosen station during each sampling trip. This tests total variability, including short-term, instream variability. The second sample set is split in the field (to assess variability due to lab and field processing, plus analytical variability), and one of the splits is split again at the lab (to assess variability due to only lab processing plus analytical variability). Results are reported in our annual reports, and there is an interesting display of our precision on our home page.
Data quality requirements are documented in our "Quality Assurance Monitoring Plan" (Hallock and Ehinger, 2003) and in its addendum.
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