Transcript Mod4Lab - Stream Ecology

Module 4
Stream Ecology Laboratory
Solids
TSS and Turbidity
Total Suspended Solids
•Sediment plume off the south shore of Lake Superior
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Total Suspended Solids
SAMPLING CONCERNS:
• collect from undisturbed water
• when standing in a stream,
reach upstream into the current
for the sample
•In lakes, boat propeller action
also may disrupt sediments in
shallow areas
• avoid sampling from
temporarily disrupted area
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Total Suspended Solids
TSS, as well as turbidity and
any other parameter
dominated by the particulate
fraction, can be very patchy it may be wise to composite
from a number of spots within
the site’s area
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Total Suspended Solids
Figure 1
- filter a known amount of water through a pre-washed, pre-dried at
103-105 oC, pre-weighed (~ + 0.5 mg) filter
- rinse, dry and reweigh to calculate TSS in mg/L
- possibly save the filters for other analyses such as volatile
suspended solids (VSS) that estimates organic matter
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Total Suspended Solids
Analytical balance
Drying oven
Filter and petri dish
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TSS – Methodology
Calculate TSS by using the equation below
TSS (mg/L) = ([A-B]*1000)/C
where
A = final dried weight of the filter (in milligrams = mg)
B = Initial weight of the filter (in milligrams = mg)
C = Volume of water filtered (in Liters)
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How does Turbidity relate to TSS ?
A general rule of thumb:
1 mgTSS/L ~ 1.0 - 1.5 NTU’s of turbidity
BUT – Turbidity scattering depends on
particle size so this is only a rough
approximation
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•Turbidity-Transparency Tube
•(for streams, ponds, wetlands, some coastal zones)
May have stopper and valve
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•Turbidity-Transparency Tube
 Analogous to secchi depth in lakes: a measure of
the dissolved and particulate material in the water
 Useful for shallow water bodies where a secchi
would still be visible on the bottom or fast moving
streams
 Best for clearwater bodies of water (not stained
with dissolved organic compounds from bogs) but
not too clear water
• It is a good measure of turbidity and suspended
sediment (TSS)
• Used in many volunteer stream monitoring
programs
Image: http://www.watermonitoringequip.com/
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How does Turbidity relate to TSS ?
A general rule of thumb:
1 mgTSS/L ~ 1.0 - 1.5 NTU’s of turbidity
BUT – Turbidity scattering depends on
particle size so this is only a rough
approximation
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Field Profiles-Turbidity
 Turbidity measures the scattering effect
suspended particles have on light
 inorganics like clay and silt
 organic material, both fine and colored
 plankton and other microscopic
organisms
 Field turbidity measurements are made with
 turbidimeters (bench meter for discrete
samples)
 Submersible turbidity sensors (Note USGS currently considers this a
qualitative method)
 Transparency or turbidity tubes
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Even small amounts of wave action can
erode exposed lakeshore sediments, in
this case a minepit lake from northeastern
Minnesota. Guess the mineral mined here.
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Turbidimeters -Nephelometric optics
Principle:
• nephelometric turbidity estimated by the
scattering effect suspended particles
have on light
• detector is at 90o from the light source
Units:
• Nephelometric Turbidity Units (NTU)
• standards are formazin or other certified
material
• JTU’s are from an “older” technology in
which a candle flame was viewed through
a tube of water
• 1 NTU = 1 JTU (Jackson Turbidity Unit)
http://www.bradwoods.org/eagles/turbidity.htm
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Bench vs Submersible Turbidimeters
Discrete depth - collect water sample and analyze water in Lab
1. Portable
vs
Continuous profile using submersible sensor
YSI wiping
turbidity
YSI 6820
with unwiped
turbidity
Hydrolab
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Field profiles-turbidity
Sensor calibration
 Turbidity free water = zero (0 NTU) standard
 USGS recommends filtering either sample water or deionized water
through a 0.2 um or smaller filter to remove particles
 WOW uses deionized water that is degassed by sparging
(bubbling) with helium to minimize air bubbles that give false
turbidity readings
 Standards range depends on anticipated sample values
 lakes - typically 0-20 NTU
 streams and wetlands - 0-20, 0-50 or 0-100 NTU
 2 non-zero standards typically adequate (response is linear)
 formazin particles (either from a “recipe” or purchase a certified,
concentrated stock solution (usually 4000 NTU)
 other commercially available materials - polystyrene
 need to worry about storage limits - Primary stock of 400 NTU’s
lasts < 1 month when refrigerated. Dilute working standards from
intermediate stock solution daily.
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Field profiles-turbidity - calibration standards prep
Source
Hach Company
Concentrations
Suggested holding times
2 to 20 NTU
Prepare daily
20 to 40 NTU
Prepare monthly
Standard Methods
All dilutions
Prepare daily
EPA Region 5
All dilutions
Prepare weekly
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Field Probes-turbidity
 Comparability of different methods:
 With the proliferation of automated in situ turbidity sensors
there is concern about the comparability of measurements taken
using very different optical geometries, light sources and light
sensors.
 The US Geological Survey and US Environmental Protection
Agency are currently (August 2002) developing testing
procedures for a field comparison of a number of instruments
produced by different manufacturers. We will include these
results when they become available.
 Standard Methods refers to :
APHA.1998. Standard methods for the examination of water and
wastewater. American Public Health Association, Washington,
D.C.
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