W9 - Measurement and monitoring

Question 1

Why monitor river systems?

Answer 1

Evaluate the impacts of policy
Develop knowledge and understanding (…process)
Testing models
Measure, anticipate, and prevent the deterioration of environmental integrity

Question 2

What is a sample?

Answer 2

Just one measurement of an environmental variable at one point in time and one point in space

Question 3

Difference between monitoring and a survey

Answer 3

Monitoring is taking measurements over time all at the same place
A survey refers to measurements spread over space taken at the same time

Question 4

What is the larger group that a sample is collected from called?

Answer 4

Population

Question 5

Which variables would you use areal measurements?

Answer 5

Vegetation
Land use
Stream network density
Gully erosion

Question 6

Which variables would you use point measurements?

Answer 6

Discharge
Water quality
Biological factors
Water table measurements
Soil characteristics
Stream velocity
Acidity (pH)

Question 7

Types of primary data collection (spatial sampling techniques)

Answer 7

Random
Systematic
Stratified
Non-random

Question 8

What is random sampling + pros/cons?

Answer 8

Every part of the study area has an equal and independent chance of receiving a sampling point
Gives uneven areal coverage which is a disadvantage if spatial variations are of interest

Question 9

What is systematic sampling + pros/cons?

Answer 9

Initial point located randomly; all others determined by a fixed interval
Gives even areal coverage
If there is a spatial pattern in the data, the regularly spaced sample points could correspond with some parts of the pattern, giving a biased impression

Question 10

What is stratified sampling + pros/cons?

Answer 10

Area is divided into sub-areas within which sample points are chosen randomly.

If a regular grid is superimposed, points may be located randomly within each grid square to ensure good areal coverage while preserving the advantages of randomness.

Even coverage of different categories i.e. soil type

Can also tailor sampling points to capture variability

More points in area of higher variability

Question 11

What is non-random sampling + pros/cons?

Answer 11

Aka purposive or subjective sampling
Sample subjectively chosen by the investigator
* i.e. convenient sampling locations
Likely to be unusual or biased

Question 12

What is the best size and shape of sampling units?

Answer 12

Regular - grid-like quadrats
Irregular - catchment-shaped quadrats

Question 13

Spatial sampling of river networks: systematic or Stratified

Answer 13

Systematic would give an even spread over the system
Stratified might be better when trying to capture variability that depends on a specific variable

Question 14

How frequently should you take measurements

Answer 14

You need to match the frequency with the variability – pilot study?
Collect high frequency data and degrade > data handling issues

Question 15

Why are there problems with how frequently you need to take measurements?

Answer 15

Many environmental phenomena display regular temporal variation (cycles)
Measurements at fixed time intervals may record the same part of whatever cycles are present, missing the data’s variation

Question 16

How long should you sample for?

Answer 16

The length of the established cycle when it is possible

Question 17

What does scale mean?

Answer 17

Cartographic map scale - ratio of map distance to ground distance

Geographic scale - the size or spacial extent of the study, e.g. the watershed vs plot scale

Operational scale - a.k.a. the process scale or characteristic scale. Scale at which a process operates in the environment. Associated with the processes spatial extent and temporal duration (lifetime and scale)

Measurement scale - The space/time between samples (resolution) and the integration of time of a sample
Smallest discernible spacial unit (e.g. pixel) and event.
Fine vs. coarse resolution (space) low vs high resolution (time).

Question 18

Extensive vs intensive studies

Answer 18

Extensive = large area in little detail
Intensive = small area in a lot of detail

Question 19

Physical river catchment variables

Answer 19

o Land use
o Topography
o Precipitation
o Water quantity
o Sediment concentration/flux
o Soil properties
o Fluvial geomorphology

Question 20

Chemical river catchment variables

Answer 20

o pH
o conductivity
o DO
o BOD
o Nutrients
o Metals
o Pesticides

Question 21

Biological river catchment variables

Answer 21

o Macrophytes
o Invertebrates
o Diatoms

Question 22

Why should we measure precipitation?

Answer 22

o Need total daily or monthly measurements for water resources
o Need continuous monitoring to assess rainfall intensity for flood warning

Question 23

How do we measure precipitation?

Answer 23

o Rain gauges and snow gauges
o Suffer from air turbulence, evaporation losses, and wetting losses.
o Point measurements that must be interpolated
o Radar can provide an aerial measure

Question 24

How do we measure velocity?

Answer 24

Floats
Current Metering
o Need to work out where the average velocity of the stream is – 0.4 Depth (or 0.2 and 0.8)
o propeller or electromagnetic – don’t want these in the stream for long periods of time

Question 25

How do we measure stage?

Answer 25

Pressure transducer and data logger
* Continuous measurement of stage from a stilling well – a tube with lots of holes cut into it
* Stage related to known discharge data via a rating curve

Question 26

How do we measure water table?

Answer 26

Dip wells

Question 27

How do we measure sediment

Answer 27

• Grab sampling and then subsequent lab analysis
• Can use claw samplers

Question 28

How do we measure suspended sediment

Answer 28

• Collect water samples
• Spatial variation across the channel
• Depth integrated samples account for vertical variation – take water all the way from the top to the bottom then back to the top
• Automated samplers allow remote sampling and storm triggering

Question 29

How do we measure sediment concentration

Answer 29

• Filtration of water samples of known volume
• Expressed as dry weight of sediment per volume of water (mg l-1 )

Question 30

What is Turbidity

Answer 30

Cloudiness of water

Question 31

Secondary data websites

Answer 31

NRFA
Environment Agency

Question 32

Sampling in space:

Answer 32

Distribution of sampling locations
* Many environmental phenomena are continuous over space
o Precipitation, air temperature etc. changes constantly
o Need to split a continuum into discreet measurement units
* Measurements taken at particular points, along lines (traverses or transects), or in small areas (quadrats)

Question 33

When do you sample/take measurements for river system dynamics?

Answer 33

Discharges can be highly variable from year to year
You want to measure before the storm, the rising limb, falling limb, and after
Preferably you would measure under different antecedent conditions

Question 34

What do you have to consider when planning a project?

Answer 34

Include what you’re going to measure
Where you will measure it
When you will measure it
How you will measure it
Why you want to measure it

Question 35

What else can you use to measure discharge?

Answer 35

Natural Rated Sections
* Cheap and simple to install
* Ideally requires bedrock section
* Problems with overbank flow and gauging of high discharges

Question 36

What are suspended sediment rating curves?

Answer 36

• Usually collected randomly so don’t have continuous measurements
• Relationship between SSC and Q
• Simple to construct - log-log scale
• Applicable to long runs of pre-existing data – danger of extrapolation – if something in the catchment changes, you would have to alter the curve
• Not a particularly strong line – systems can be prone to sediment exhaustion
• Can be improved by dividing:
  o seasonally
  o by rising/falling limb

Question 37

How to measure turbidity and why is it useful?

Answer 37

Turbidity probes
Can help understand sediment conc. and grain size distribution

Question 38

What chemical things should be measures?

Answer 38

Routine
o pH
o Conductivity
o Dissolved oxygen
o Biochemical Oxygen Demand

Other methods
o Buffering capacity (alkalinity)
o Hardness
o Dissolved organics (carbon)
o Metals and salts (ICP-OES)
o Anions incl. nutrients (IC or spectrophotometer)

Question 39

spot vs continuous sampling

Answer 39

• Batch aka grab sampling – collected at a specific time and place
• Continuous sampling – uses data loggers over longer time periods

Question 40

In situ vs lab methods

Answer 40

In situ:
Portable probes
o pH
o Conductivity
o Dissolved oxygen
e.g. Sonde sensor
measures:
o pH
o DO
o Turbidity
o ORP
o Specific ions (e.g. NO3)
* Estimation of Solute Flux
* Can be left out for a long period of time

-ves
– less accurate than the lab ones
- Calibration

Lab methods
-ves = sample degradation

Question 41

Biological Indicators of Water Quality

Answer 41

• Water quality concerns
  o Longer term perspective
• Representivity of spot water samples
  o Water chemistry is dynamic
  o Longer life cycles of biological indicators
• Useful biological groups
  o Macrophytes (plants)
  o Macro-invertebrates
  o Algae (microscopic – e.g. diatoms)

Question 42

What is kick net sampling

Answer 42

Stand in the river and kick the bed sediment so anything that is disturbed will flow downstream into the next