Nutrient Cycles in

choppedspleenMechanics

Feb 21, 2014 (3 years and 3 months ago)

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Nutrient Cycles in
Ecosystems

Biogeochemical Cycle


The flow of a nutrient from the
environment to living organisms and
back to the environment


Main reservoir for the nutrient is in the
environment

geochemical cycle

Main nutrient
reservoirs in the
environment

fraction of
nutrient
available to
ecosystem

primary
producers

herbivores,
carnivores,
parasites

detritivores,
decomposers

Fig. 47
-
14, p.852

Three Categories


Hydrologic cycle


Water


Atmospheric cycles


Nitrogen and carbon


Sedimentary cycles


Phosphorus and sulfur

Hydrologic Cycle

Atmosphere

Ocean

Land

evaporation
from ocean

425,000

precipitation
into ocean
385,000

evaporation from land
plants (evapotranspiration)
71,000

precipitation
onto land
111,000

wind
-
driven water vapor

40,000

surface and
groundwater
flow 40,000

Figure 47
-
15

Page 853

EVAPORATION

PRECIPITATION

TRANSPIRATION

dripping, trickling

down along stems

falling through

to ground

interception by plants

surface pooling, etc.

infiltration of soil

moisture in soil

seepage, percolation

groundwater storage

DEEP OUTFLOW

overland flow

lateral flow

base flow

STREAM OUTFLOW

Fig. 47
-
16, p.853

Water Use and Scarcity


Most of Earth’s water is too salty for
human consumption


Desalinization is expensive and
requires large energy inputs


Irrigation of crops is the main use of
freshwater

Fig. 47
-
18, p.855

Negative Effects of Irrigation


Salinization, mineral buildup in soil


Elevation of the water table and
waterlogging


Depletion of aquifers

Aquifer Problems

Figure 47
-
19


Page 855

Carbon Cycle


Carbon moves through the atmosphere
and food webs on its way to and from
the ocean, sediments, and rocks


Sediments and rocks are the main
reservoir

Figure 47
-
20


Page 856

diffusion between
atmosphere and ocean

bicarbonate and
carbonate in
ocean water

marine food
webs



marine sediments

combustion of fossil fuels

incorporation
into sediments

death,
sedimentation

uplifting

sedimentation

photosynthesis

aerobic
respiration

Carbon Cycle
-

Marine

Carbon Cycle
-

Land

photosynthesis

aerobic
respiration

terrestrial
rocks

soil water

land food

webs

atmosphere



peat,

fossil

fuels

combustion
of wood

sedimentation

volcanic action

death, burial,
compaction over
geologic time

leaching,
runoff

weathering

combustion of
fossil fuels

Figure 47
-
20


Page 856

Carbon in the Oceans


Most carbon in the ocean is dissolved
carbonate and bicarbonate


Ocean currents carry dissolved carbon

Carbon in Atmosphere


Atmospheric carbon is mainly carbon
dioxide


Carbon dioxide is added to atmosphere


Aerobic respiration, volcanic action, burning
fossil fuels


Removed by photosynthesis

Nitrogen Cycle


Nitrogen is used in amino acids and
nucleic acids


Main reservoir is nitrogen gas in the
atmosphere


Nitrogen Cycle

gaseous nitrogen (N
2
)

in atmosphere

NO
3
-


in soil

nitrogen fixation

by industry

fertilizers

NH
3
-
,NH
4
+

in soil

1. Nitrification

leaching

uptake by
autotrophs

excretion, death,
decomposition

uptake by
autotrophs

nitrogen

fixation

leaching

ammonification

2. Nitrification

dentrification

nitrogenous
wastes, remains

NO
2
-


in soil

food webs

on land

Figure 47
-
25

Page 860

Nitrogen Fixation


Plants cannot use nitrogen gas


Nitrogen
-
fixing bacteria convert
nitrogen gas into ammonia (NH
3
)


Ammonia and ammonium can be
taken up by plants

Ammonification & Nitrification


Bacteria and fungi carry out
ammonification


conversion of nitrogenous wastes to ammonia


Nitrifying bacteria convert ammonium to
nitrites and nitrates

Nitrogen Loss


Nitrogen is often a limiting factor in
ecosystems


Nitrogen is lost from soils via leaching and
runoff


Denitrifying bacteria convert nitrates and
nitrites to nitrogen gas

Human Effects


Humans increase rate of nitrogen loss by
clearing forests and grasslands


Humans increase nitrogen in water and air
by using fertilizers and by burning fossil
fuels


Too much or too little nitrogen can
compromise plant health

guano

fertilizer

terrestrial rocks

land food
webs

dissolved
in seawater

marine

food webs

marine sediments

excretion

weathering

mining

agriculture

uptake by
producers

death,
decomposition

sedimentation

settling out

leaching, runoff

weathering

uplifting over
geologic time

dissolved in
soil water,
lakes, rivers

uptake by
autotrophs

death,
decomposition

Phosphorus cycle

Fig. 47
-
27, p.862

Phosphorus Cycle


Phosphorus is part of phospholipids and
all nucleotides


It is the most prevalent limiting factor in
ecosystems


Main reservoir is Earth’s crust; no
gaseous phase

Phosphorus Cycle

GUANO

FERTILIZER

TERRESTRIAL ROCKS

LAND
FOOD
WEBS

DISSOLVED
IN OCEAN
WATER

MARINE
FOOD
WEBS

MARINE SEDIMENTS

excretion

weathering

mining

agriculture

uptake


by
autotrophs

death,
decomposition

sedimentation

settling
out

leaching, runoff

weathering

uplifting


over geologic time

DISSOLVED IN
SOILWATER,
LAKES, RIVERS

uptake

by
autotrophs

death,
decomposition

Figure 47
-
27, Page 862

Human Effects


In tropical countries, clearing lands for
agriculture may deplete phosphorus
-
poor soils


In developed countries, phosphorus
runoff is causing eutrophication of
waterways