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