Mod4Lab - Stream Ecology - TSS & Turbidity

Module 4 Stream Ecology Laboratory

SolidsTSS and Turbidity

Presentation NameUpdated March 16, 2003 – Author

Slide ID NumberPage 2

Total Suspended Solids

•Sediment plume off the south shore of Lake Superior



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





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




- 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

Figure 1








Drying oven

Analytical balance

Filter and petri dish



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)



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



May have stopper and valveMay have stopper and valve

•(for streams, ponds, wetlands, some coastal zones)

•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/

•Turbidity-Transparency Tube



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



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

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.



Turbidimeters -Nephelometric optics

http://www.bradwoods.org/eagles/turbidity.htm

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)



Bench vs Submersible TurbidimetersDiscrete depth - collect water sample and analyze water in Lab

vs

Continuous profile using submersible sensor

1. Portable

YSI wiping turbidity

YSI 6820 with unwiped turbidity

Hydrolab



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.



Field profiles-turbidity - calibration standards prep

Prepare daily2 to 20 NTUHach Company

Prepare weeklyAll dilutionsEPA Region 5

Prepare dailyAll dilutionsStandard Methods

Prepare monthly20 to 40 NTU

Suggested holding timesConcentrationsSource



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.

Documents

Mod4Lab - Stream Ecology - TSS & Turbidity