Water
Nitrogen
Introduction

 Unlike energy, elements are NOT lost and
REPLACED as they pass through ecosystems
 Elements are RECYCLED REPEATEDLY
 All chemical elements that are needed by living
things are recycled in ecosystems
 Water, Carbon, Nitrogen and even hydrogen, oxygen,
phosphorus and sulfur.
Biogeochemical Cycles

 Def. – A closed loop through which a chemical
element or water moves through ecosystems
 Elements and water may be held for various lengths
of time (days to centuries)
 EXCHANGE POOLS = Components that hold
elements or water for a relatively SHORT PERIOD of
time (think the ATMOSPHERE - days)
 RESERVIORS = Components that hold elements or
water for a relatively LONG PERIOD of time. (think
the DEEP OCEAN – thousands of years)
Water Cycle

 Earth’s water is constantly moving
 No beginning or end to the water cycle (Keeps
repeating)
 During the water cycle, water can exist in 3 different
states of matter
 Solid (as ice or snow)
 Liquid (as liquid water)
 Gas (as water vapor, “humidity”)
 The SUN drives the water cycle

Main Processes in Water Cycle

 Evaporation (liquid water converted to water vapor)
 Sublimation (solid water directly converted to a gas) Sun
sublimates snow into water vapor
 Transpiration (plant process of converting ground water
into water vapor)
 Condensation (water vapor converting to liquid water)
 leads to Precipitation
 Infiltration (liquid water soaking into the ground;
aquifer) instead of Running-off
Water Cycle: Exchange
pools vs Reservoirs

Exchange Pools
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Atmosphere
Streams & Rivers
Shallow Ponds
Ocean Surface
Recent Snow
Reservoirs
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Seas & Oceans (deep)
Aquifers
Lakes & Deep Ponds
Ice Caps
Glaciers
Nitrogen Cycle

 Atmosphere = largest reservoir for nitrogen on Earth
(78% nitrogen gas [N2])
 Moves thru both biotic and abiotic components
 Moves thru both terrestrial (land) and aquatic
ecosystems
 Nitrogen is used by organisms to make compounds
such as, chlorophyll, proteins and nucleic acids
Nitrogen cycle Processes
 Nitrogen fixation: conversion of N2 into nitrate (NO3-) ions
that plants (producers) can absorb

 Done mainly by nitrogen-fixing bacteria (found in soil)
 Also done by certain human activities (fertilizers)
 Ammonification: conversion of dead organic compounds
(dead plants & animals) into ammonia (NH4) – ammonia
can be toxic to life forms
 Done by decomposers (fungus & bacteria)
 Nitrification: conversion of ammonia into nitrites (NO2-)
or nitrates which plants can use
 Done by nitrifying bacteria
 Denitrification: conversion of nitrates back into N2
(Opposite of Nitrification)
 Done by denitrifying bacteria in soil
Nitrogen Cycle
involving the Ocean

 Similar processes with terrestrial ecosystems except use
different species of bacteria that do the same processes.
 EXTRA process – ANAMMOX REACTION
 Converts ammonia and nitrites into nitrogen gas and
water (NH4+ + NO2-  N2 + 2H2O)
 Done by certain bacteria in water
 May contribute up to ½ of the N2 released into the
atmosphere from the ocean
 May also limit production in ocean ecosystems by
removing nitrites
Nitrogen Cycle: Exchange
Pools and Reservoirs

• Exchange Pools
– Soil (near
surface)
– Animals (urine
& feces)
 Reservoirs
 Atmosphere
 Plants & Animals
tissues
 Soil (mainly deep)
 Undecomposed
waste
 Deep Ocean