abatement (pollution)abiogenesisabiotic
abiotic componentsablationaboringe
abrasionabscissionabsolute humidity
absolute instabilityabsorbed waterabsorbent
absorptionabsorption spectrumabundance
acaciaaccelerated erosionacceleration
acceptable daily intakeacceptable noise standardaccessory mineral
accidental speciesaccidental violationacclimation
acclimatisationaccounting for natureaccretion
accretion theoryaccumulationaccumulation zone
accumulator plantaccuracyachieving sustainability
acidacid (acidic) rockacid and base
acid depositionacid mine drainageacid rain
acid soilacid sootacidity
acidophilousacquired characteractinomycetales
action spectrumactivated carbonactivated charcoal  
activated sludgeactivated sludge processactivation
activation energyactivatoractive flood plain
active immunityactive transportactivism
acute effectsadaptationadaptive radiation
adaptive thresholdadaptive valueadaptive zone
adb (asian development bank)addictionadditive mortality
additivesadiabatic (change)adiabatic gradient
adiabatic lapse rateadiabatic processadirondack mountains
adsorbed wateradsorptionadulterants
adulterationadvanced waste treatmentadvection
adventitious rootadventive plantaeogenic
aeolian depositaerationaeration, soil
aerial reconnaissanceaerial rootaerial spraying
aerial surveyaeroallergenaerobic
aerobic / anaerobic systemaerobic bacteriaaerobic biological oxidation
aerobic compostingaerobic decomposeraerobic process
aerobic respirationaerobic sludge digestionaerobic waste treatment
aerologyaestivationaetiology
afforestationafricanized bees (apis mellifera scutellata)  afterburner
ageage classage distribution
age structureage structure pyramidageing
agent orangeagglomerationaggradation
aggregateaggressionagricultural chemicals
agricultural chemistryagricultural droughtagricultural economics
agricultural engineeringagricultural geologyagricultural investigation
agricultural landagricultural meteorologyagricultural pollution
agricultural regionagricultural revolutionagricultural revolution stages
agricultural scienceagricultural stabilization and conservation serviceagricultural waste
agrobiologyagroecologyagroforestry
agrologyagronomyagrophilous
agrostologyaids (aquired immune deficiency syndrome)air
air chemistryair environmentair pollutant
air pollutionair pollution - sourcesair pollution control
air pollution indexair pollution statusair quality
air quality standardsair sampler operationair stripping
air-pollutant transportairborne diseasesairmass
airshedaitken counteralar
alarm responsealaskan disasteralbedo
albinismalbuminalcoholic fermentation
aldrinalgaealgal bloom
algal genus indexalgal matalgicide
alien speciesalimentary canalalkali metals
alkaline soilalkalinityalkaloid
alkyl sulphonatesalleleallergen
alley croppingallogenic successionallometry
allopatric speciationalloyalluvial
alluvial landalluviumalmagorado cattle
alpha diversityalpha particlesalpine tundra
alpine zonealternate agriculturealternate bearing
alternate energy sourcesalternate hostalternate technology
alternation of generationsaltimeteraltitude
altitudinal biomealtruismalvarez hypothesis
amazonamberambient
ambient noiseambient pressureambient standards
amenityammonificationamnes test
amoco cadizamoebaamoebiasis
amorphousamphimixisamphiphyte
amphotericanabatic windanabolism
anaerobic conditionanaerobic decomposeranaerobic process
anamalous audibilityanatomyandroecium
androgenandrogenesisanemia
anemometeraneomophilous plantangiosperm
angle of indroughtanimal behaviouranimal glue
animal haulinganimal husbandryanimal rights
animal unitanimal wasteanimal welfare
anionannelidaannual plant
antagonismantarctic airantarctic icesheet
antarcticaantheranthracite
anthrafiltanthropo geomorphologyanthropocentric
anthropocentrismanthropogenic effectsanthropogeny
anthropological areaantibioticantibody
antichloronesteraseanticycloneantigen
antiknock additivesantimetaboliteantireflection coating
antiserumantitoxinaphotic zone
apomixisapomorphaposematic colouration
appetiteappletin layerapplication factor
applied ecologyaquacultureaquafalfa
aquatic chemistryaquatic ecosystemaquatic microbiology
aquatic toxicologyaquiferaquifer restoration
arablearachnidaral sea
arctic air/hazearctic zonearenaceous
argonaridarid landscaping
arid zonearidizationarsenic
artesian wellarthropodaartificial classification
artificial fertilizationartificial habitatartificial rain
artificial rechargeartificial reefartificial regeneration
artificial reproductionartificial selectionasbestos
asbestos removalasbestosisasexual reproduction
ashash pitaspection
asphyxiantassemblageassimilation
assimilative capacityassociationassortative mating
asthenosphereasthmaastroids
asulumatavismatmometer
atmosphereatmospheric dispersionatmospheric inversion
atmospheric pollutantsatmospheric pressureatmospheric stagnation
atmospheric structureatmospheric windowatom mass
atomicatomic bombatomic energy
atomic fissionatomic fusionatomic number
atomic structureatomizationatp
attainment areaattenuationattrial
augeraurora borealisaustralian realm
autapomorphautecology (ecv.)autoclave
autogamyautogenic successionautolysis
automatic weather station (aws)automobile emissionautomobile emission control
autotrophauxinauxotroph
available energyavailable nutrientavailable water
avalancheavesavoidance
avulsionaxilazonal soil