Measuring abiotic components Objectives To make an exhaustive list of abiotic
factors To discuss the ways they are measured To critically appraise the methods.
Abiotic components
Temperature pH Humidity Nutrient availability Oxygen concentration Soil depth Salinity disturbance Light exposure/turbidity pollution Wind exposure flow velocity Wave action slope gradient Sand blasting particle size drainage
Marine habitats
Very stable except for inter tidal Intertidal habitats often experience extremes
of change Key factors: Temp pH Dissolved oxygen Salinity Wave action Turbidity
Oceanic temperatures
Temp
Measured with a thermometer or temperature probe
Temperature falls with depth Influence of ocean currents greater than
that of surface heating Annual fluctuations greater in shallow seas Dramatic fluctuations in intertidal habitats
salinity
Salinity measured by conductivity meter pH very constant Salinity constant over huge areas Lower in polar areas due to melt waters Lower in coastal areas where river waters
empty into sea – freshwater may float on salt Estuaries have salt wedge Some seas have low salinity, e.g. Baltic Some more saline due to evaporation e.g.
Mediterranean.
Map of salinities
diagram of salt wedge
Dissolved oxygen
Measured oxygen sensitive electrodes or through Winkler titration
Highest near surface Higher in day than at night due to input
of photosynthesis Falls in deeper waters Cold currents from meltwater may be
richer in oxygen
pH and nutrient concentration pH measured by pH meter or data logging
probe. Nutrient concentration measured through
chemical analysis Varies Low in open ocean Higher in shallow seas, coastal areas and in
upwellings of cold water. Varies through year in temperate waters
due to algal blooms.
Wave action
Measured by dynamometer Result of prevailing winds Impact affected by coastal morphology Vary according to weather conditions Affected by size of water body Erosive powers amplified by material
that the waves can carry
Turbidity
Measured with a secchi disc High in nutrient rich coastal waters Low in nutrient poor oceanic waters Maximum depth of light penetration in
oceans may be 100m May be only a few cm in sandy shallow
coastal areas such as the Gulf Coast Varies in temperate regions due to algal
blooms.
Changes in depth
FRESHWATER HABITATS
Temperature pH Dissolved oxygen Turbidity Conductivity/nutrients Flow velocity
Temperature
Closely related to climate in rivers and lakes
Cooled by upstream waters More stable in ground water fed rivers Most lakes are stratified especially in
summer/warm conditions Impact of air temperature and sun
related to volume and flow Higher in slow rivers.
Lake stratification explained
pH
Dependent on underlying bedrock Affected by soil Varies daily and yearly due to impact of
photosynthesis Affects nutrient availability Affects decomposition of organic matter May be different at different levels in
lake waters when the lake is stratified.
Dissolved oxygen
Higher in fast flowing rivers Higher in colder water Lower in slow flowing rivers and warmer
waters Decreases from surface in lakes Stratified Varies seasonally and daily due to
impact of photosynthesis.
Turbidity
Poor in shallow disturbed waters Poor in waters rich in humic acid Better in nutrient poor lakes Affected by water chemistry Affected by mixing Affected by algal blooms Affected by animal action Affected by sediment load
Conductivity/nutrients
Affected by bed rock and drift Affected by depth of lake and
stratification Affected by plankton blooms Affected by sediment load
Flow velocity
Affected by gradient Affected by weather factors such as rainfall and
snow melt Varies dependent on position of channel Laminar flow – flow near surface of rocks and
river bed much less than in mid-water due to impact of friction.
Varies with season Variation less in groundwater fed rivers than
surface water fed Varies with bed morphology – riffle pool.
Flow types
Upland fast flowing
Lowland slow flowing
Riffle pool flows
Terrestrial factors
Temperature humidity Soil pH Light intensity Wind speed Particle size of soil Slope Soil moisture Mineral content of soil drainage
Temperature
Measured with a thermometer or a maximum minimum thermometer
Dependent on season, latitude, altitude Dependent on exposure/shelter Dependent on light intensity Reduces with increased altitude and
latitude Varies daily
Humidity
% humidity measured with humidity sensors Varies geographically. Low in deserts, higher in
forests and near coasts and lakes Varies with temperature – hot air can contain
more water vapour Varies daily, seasonally, with weather patterns Varies with exposure Is a very important factor limiting the
distribution of many flora and fauna.
Soil
pH, drainage, nutrient concentrations and particle size are all linked
Soil comprises the mineral abiotic and organic biotic matter.
Particle composition affects drainage which affects soil moisture which in turn interacts with soil mineral composition to determine pH which affect nutrient availability. Underlying bedrock may strongly influence all these factors.
Soil analysis can include particle analysis dry and wet weight calculations and burning of organic matter plus chemical analysis.
Exposure and shelter
These affect Light intensity and shade Humidity Wind speed and exposure to wind borne
particles Also affected by orientation. i.e. direction
of slope
Slope or gradient affects drainage and light intensity