1. ESS Topic 2.2 - Measuring Abiotic Components of the Ecosystem
2.2.1 List the significant abiotic (physical) factors of an ecosystem.
2.2.2 Describe and evaluate methods for measuring at least three
abiotic (physical) factors within an ecosystem.
Assignment: Measuring Abiotic Factors at IST - Practical Write-up assessed under DCP. Click
here for the complete description and instructions.
Read pp.306-309 in the IB ESS Course Companion before studying the notes below!
There's a wide variety of abiotic factors that influence what may live in an ecosystem, some
examples of which are listed below:
Marine ecosystems:
• salinity - many marine organisms tolerate a variety of salt concentration levels in the
water, which can be checked with a few tools:
◦ hydrometer measures specific gravity or density of a sample (relative weight of
1.0L salt water compared to 1.0L pure fresh water)
◦ refractometer measures differences in light refraction between the saltwater
sample and a freshwater control
◦ electrical conductivity can also indicate the amount of dissolved ions in solution
• pH - use a pH meter (available in the IST science building). The pH of saltwater is naturally
higher (i.e. more alkaline) than that of fresh water. According to several marine
aquarium websites, a pH of 8.2 is ideal for saltwater fish.
• temperature - every organism has an optimal temperature range in which it thrives. An
organism may be able to survive at warmer or cooler temperatures, but it will do so
under stress, which requires more energy (and therefore food), and decreases its' ability
to compete for other resources within the ecosystem. This is particularly important for
ectothermic (cold-blooded) organisms, which are a majority of marine animals. A
change in temperature can also influence the pH of water.
• dissolved oxygen (DO) - the amount of oxygen available for marine organisms, like
terrestrial organisms, determines which organisms can survive in a particular location.
DO levels fall with increased temperature and organic compounds from either sewage,
agriculture, or industry. DO can range from 0-18 ppm, but most healthy ecosystems
have a DO level of 5-6
ppm(http://www.ncsu.edu/sciencejunction/depot/experiments/water/lessons/do/). Measuring DO
can be tricky and labor-intensive, requiring either a complicated Winkler titration or
oxygen-selective electrodes.
• wave action - waves carry energy; thus, larger and prolonged waves can move larger
particles, thereby 'mixing' water, oxygen, and sediment more. Areas with a lot of wave
action tend to have higher DO levels. Waves can also increase the turbidity of the water
International School of Tanganyika 2010 - 2011 Mr Brad Kremer

2. ESS Topic 2.2 - Measuring Abiotic Components of the Ecosystem
and determine the nature of a coast line - i.e. sandy vs rocky.
(http://www.pals.iastate.edu/agron154/Agron_154/Unit_7/terms.htm)
Freshwater ecosystems:
• turbidity - "A cloudy condition in water due to suspended silt or organic
matter."(www.groundwater.org/gi/gwglossary.html) Cloudy = high turbidity and clear = low
turbidity. According to Wikipedia (I know, I know...)
◦ "Turbidity in lakes, reservoirs, channels, and the ocean can be measured using a
Secchi disk. This black and white disk is lowered into the water until it can no
longer be seen; the depth (Secchi depth) is then recorded as a measure of the
transparency of the water (inversely related to turbidity). The Secchi disk has the
advantages of integrating turbidity over depth (where variable turbidity layers
are present), being quick and easy to use, and inexpensive."
• flow velocity - the rate at which water moves through a specified area in a given amount
of time. Some aquatic organisms prefer high flow velocity (fast water) while others
thrive at lower flow velocities. The simplest way is to time how long a partially-
submerged object takes to travel a certain distance. For an explanation of how to more
precisely measure stream flow, visit this site from the USGS describing the method -
it's complicated!
• pH - normal readings for freshwater ecosystems range from about 6.5 (acidic) to 8.5
(basic) depending on the underlying rock substrata, surrounding vegetation, and human
activities within the watershed
• temperature - see notes above
• dissolved oxygen - see notes above
Terrestrial ecosystems
• temperature - depends on insolation (incoming sunlight), wind & ventilation, latitude,
color and texture of the surface. Measure temperature with liquid thermometers or
datalogging
• light intensity - influences photosynthesis rates as well as body temperature of
ectotherms (cold-blooded animals). Light intensity is highly variable with weather
conditions, season, time of day, and surrounding terrain & vegetation cover. It can be
measured with light meters available from photography stores or the IST science
department.
• wind speed - wind carries sediment and acts as a dessicating (drying) force in ecosystems,
increasing evaporation and transpiration rates. Wind speed is measured with a few
different tools:
◦ anemometer: spinning cups on a permanent or hand-held post. The number of
revolutions per time period can be converted to a wind velocity.
◦ Ventimeters use differences in air pressure to determine the velocity of wind
passing over the open end of a tube.
◦ Beaufort scale of wind speed from 0 to 12. The table below describes it better
than I can. Image source:
(http://media.graytvinc.com/images/beaufort_scale_tbp.gif)
International School of Tanganyika 2010 - 2011 Mr Brad Kremer

3. ESS Topic 2.2 - Measuring Abiotic Components of the Ecosystem
• particle size - influences how well a soil holds water as well as its cation exchange
capacity (CEC) - the mechanism by which nutrients are swapped between the physical
soil matrix and the organisms living in the soil. Soils with large average particle sizes
(such as boulders, pebbles, and sand) drain more quickly and hold fewer cations than
soils with small particles (silt and clay). Seiving through different size screens is the most
frequently used method to determine particle sizes.
• slope - steep slopes drain water rapidly and dry out quickly, have thinner soil layers, and
tend to have lower levels of organic matter (OM) than more gently-sloping areas. Steep
slopes also erode faster than gentle slopes. Slope can be measured with a clinometer, a
field level, or calculated as a % (rise/run).
• soil moisture - influenced by particle size and climatic factors. The easiest way to measure
soil moisture is to measure the mass of a sample, then dry it for several days until its
mass is constant. The difference in the two masses is the mass of the water evaporated
from the sample.
• drainage - influenced by slope and particle size
◦ internal drainage: how rapidly water percolates down through soil layers
◦ external drainage: how rapidly water moves across the landscape
• mineral content - Soils are a combination of minerals from eroded rock, organic matter in
the form of detritus, pore spaces (the gaps between particles) which hold air and/or
water, and living organisms. Mineral content is usually measured by burning off all the
living material in a sample at very high temperatures.
Questions to consider for the end-of-term exam OR the IB ESS exam in May 2011:
1. How might each of these factors vary in a given ecosystem with depth? At different times
of day? At different distances? During different seasons?
2. Outline and evaluate a method for measuring one of the abiotic factors listed above.
International School of Tanganyika 2010 - 2011 Mr Brad Kremer