Ecology and Geomorphology of Streams
Spring, 2003
Lab 4 – Water Quality and Sediment Analyses
Description
The goal of this lab is to introduce you to common water quality measures and teach you how to measure
discharge and determine channel substrate composition. Water quality and discharge data are recorded on
side two of the Reach characterization form, and the sediment data is recorded on the sediment
characterization form.
The most common water quality parameters collected in a general stream assessment include temperature,
pH, specific conductance (or electrical conductance, EC), turbidity and dissolved oxygen (DO). Some
protocols require only water temperature and turbidity (USGS NAQWA physical stream assessment) and
some require bulk samples be collected for lab analyses of major cations and anions, nutrients and heavy
metals (EPA Environmental Monitoring and Assessment Program). For this class, our focus is on evaluating
stream habitat for native salmonids, so we’ll be following the EPA Rapid Bioassessment Protocol (RBP) in
collecting temperature, pH, EC, and turbidity (visual) using simple hand-held meters. These parameters have
critical importance throughout the salmonid lifecycle, and can often be limiting in habitat suitability. In
some cases, we’ll also collect DO and Total Dissolved Solids (TDS) when the equipment is available.
Characterization of the channel bed substrate not only provides a general description of the type of substrate
habitat available for macroinvertebrates and other aquatic organisms, but also indicates the degree of
sediment impacts from various land uses. Similar to the USFS and EPA RBP protocols, we’ll use pebble
counts to quantify the distribution of grain sizes present in the channel surface, complete a general
assessment of the quality of the substrate and document the abundance of organic materials.
For this lab, we’re going to review the exact protocols for taking water quality measurements, discuss the
velocity-area and float methods for measuring discharge and discuss how to complete the sediment
characterization datasheets. We’ll also complete a Wolman pebble count and review how to analyze the
sediment count data to determine median grain size from the cumulative distribution curve.
Readings
 Chapters 10 - 11 in ‘Stream Channel Reference Sites: An Illustrated Guide to Field Technique’.
Tips to Remember
Water Quality MeasurementsWe’ll be using simple hand-held meters to measure temperature, pH, and EC. The data is recorded on side 2
of the reach characterization form. Some tips:
 Check that each meter is properly calibrated BEFORE heading to the field site. The hand-helds are
convenient and portable, but they can quickly get uncalibrated.
 Take measurements in a gently flowing section of the reach at least 0.5 meters from the water’s edge.
Readings can vary between pools and riffles, so it’s important to be consistent in your sampling
location. If you’re unsure of your location, take several readings in different locations and pick the
most representative spot.
 Leave the instrument in the water as long as it takes for the readings to be stabilized – this can be up
to a minute or more.
 Always record the time you took the measurements – water temp especially can vary significantly
throughout the day.
Ecology and Geomorphology of Streams
Spring, 2003
Discharge Measurements See the USFS field guide for details on the methods. The data is recorded on side 2 of the reach
characterization form. Ideally if time allows, BOTH the velocity-area and float methods should be used to
estimate discharge. This will allow for comparison between reaches where only one method was used.
Other tips:
 Be sure to get the velocity meter as close to 0.4 of the total depth as possible. Velocities vary greatly
in the vertical direction, so consistency is key.
 Always do a common sense check of the readings you get from the velocity meter – does the
measurement make sense? Often small protrusions from the channel bed (small cobbles, etc) can
have large impacts on the velocities in the water column above. Try to avoid these areas if possible.
 Avoid standing too close to the location of the velocity reading – always stand well
DOWNSTREAM. You can have a large impact on the local water velocity if you’re not careful.
Sediment Analyses See the USFS field guide for how to complete a Wolman pebble count. The data is recorded on the sediment
characterization form. Some tips:
 If you have the man-power, 3 people can complete a count in about half the time as 2 people – have
two people select particles and call out the size to the data recorder.
 Be sure to select the particle at RANDOM. Be sure to not look at where you place your finger in
front of your toe. The count will be biased if you look before you select.
 Remember to categorize particles as LESS THAN the grain size of each bin category. This makes it
much easier to determine the cumulative percent less than for each size category. Ex: a 41mm
particle should be counted in the 45mm size bin – it’s less than 45mm, but not less than 32mm.