The sulfur cycle

1. The Sulfur Cycle
BY SOPHIA VELIS & CHEN WU

2. Natural Process

3. The way it works
 Most sulfur is stored in ocean sediments and underground in
rocks and minerals in the form of sulfate (SO4
2-)
 It enters the atmosphere as hydrogen sulfide (H2S) through
highly active volcanoes and decomposing organic matter by
anaerobic decomposers normally found in flooded swamps,
bogs, and tidal flats. Sulfur dioxide (SO2) is also released from
volcanoes.
 Sea spray, dust storms, and forest fires release sulfate salts
into the atmosphere. Plants absorb the sulfates and
incorporate them as an essential component of many
proteins.

4. The way it works
 Certain kinds of marine algae produce large amounts of
volatile dimethyl sulfide or DMS (CH3SCH3). While in the
atmosphere DMS is turned into sulfur trioxide gas (SO3) and
to tiny droplets of sulfuric acid (H2SO4) which fall down to
earth as acid rain.
 In the oxygen-deficient environments like flooded soils,
freshwater wetlands, and tidal flats, specialized bacteria
convert sulfate ions to sulfide ions (S2-). The sulfide ions can
then react with metal ions to form insoluble metallic sulfides,
which are deposited as rock or metal ores, and the cycle
continues.

5. Natural
reservoirs
 The atmosphere
 In animals
 In plants
 Ocean sediments
 Soil
 Rock
 Fossils fuels

6. Why is it important?
The sulfur cycle is important
because it helps with
functioning of enzymes and
protein for plants and animals
that depend on plants.

7. Human Impact
 Humans impact this cycle by releasing to much sulfur into the
atmosphere. It interrupts the cycle. MDCs like the US and
Japan greatly impact it because of their large oil industries.
The burning of fossil fuels increases the rate at which sulfur is
entering the atmosphere greatly, and that prevents the sulfur
from going back into the soil and the biosphere and it also
results in acid rain. LDCs such as Venezuela or India also
contribute to the interruption of the sulfur cycle.

8. Human Impacts (continued)
 In India, because of their
worship of cows, they don't
kill them and therefore,
there is a surplus of cows.
Because cows are
herbivores, they eat lots of
grass, and that grass
contains sulfur. Which is
released in the form of
flatulence, which they do
very often.

9. Pathway affected by human activities
 The natural state of sulfur is normally found in rocks, ocean
sediments, and in metals. They can be released naturally into the
atmosphere through volcanoes and algae. But humans mine for
fossil fuels that contain sulfur in them. The extraction of sulfur in
the soil and rocks takes away from the plants that obtain sulfur
from the soil. Humans also burn the fossil fuels that contain
sulfur, and increase the rate in which sulfur enters the
atmosphere. In natural circumstances, sulfur returns to the
ground in the form acid rain that is basic enough to be safe to
organisms. But because of the increased amount of sulfur in the
atmosphere, the acid rain is too acidic and can damage the
biosphere.