Lecture 28 HUMAN ALTERATIONS OF INTERSYSTEM CYCLES
How are humans altering water cycle? 23.4
 Depletion from overuse

Fossilized vs. re-chargeable aquifers

Overpopulation

Used to produce crops to produce meat
Irrigation  salt buildup in soil 578-9; 27.10, 27.11
 Land-use changes lower local cycling 514; 24.13
50% of water in the Amazon Basin is internally recycled. Predict how
deforestation there might be affecting the hydrological cycle and the tropical forest.
 Links to other cycles:

Water carries solutes (e.g. N, P, K, H+)

C cycle – link to global warming 

precipitation changes worldwide

glacial melt – loss of water source
What are consequences of human changes in C cycle? 23.6; 23.6; 583-5
Human production of CO2 by burning of fossil fuels has increased greatly. 27.16
Greenhouse gases and other human inputs add to the heat budget of the atmosphere =
(radiative forcing) 27.17
Global warming
Lower snowpack  colder soil temp  kill roots  greater leaching
More drought  wildfires more frequent/severe  alter several cycles
positive feedback  fires generate more CO2 570-1; 27.1
Accelerate decomposition, especially in N biomes (boreal; tundra) 515-16; 24.14, 24.15
positive feedback  faster decomposition generates more CO2
How are humans altering the N cycle? 23.11
Humans fix as much nitrogen industrially as occurs naturally.
Through what processes are we altering the N-cycle?
 Nitrogen-fixing crops
 Fossil fuel burning
 Nitrogen fertilizer
 Animal feed lots + manure
 Invasive species fix N
 What are some major consequences of our alterations of the N cycle?
Nitrous oxide, a greenhouse gas, is produced.
N-run-off from excess fertilizer and feedlots gives excess N to aquatic systems change
algae relative abundances + lower water quality; causes eutrophication (see below)
Saturate soils with N in forests  initially increasing leaf N and NPP; but then
altering soil chemistry, eventually causing heavy leaching of nitrates.
Biodiversity and species mix are altered
What is the major way in which humans are altering the P cycle? 23.14
Mining for P to add to fertilizer for crops -->
run-off into aquatic communities --> 24.20
increases algal abundance-->
eutrophication (see below); lower water quality.
Moves P to geologic time scale if sedimentation occurs
How do human activities affect input from land to water?
 runoff/seepage

agriculture land, especially NPK

animal feedlots, especially N
 sewage input, C, N
  into ground water/aquifers/streams/oceans
Human eutrophication (overproduction of organic matter in aquatic systems) is harmful.
 Added nutrients stimulate algal GPP, BUT
 Too much overwhelms intrasystem regeneration
 Increase in dead organic matter
 Energy flows to bacteria, not higher trophic level
 Increase in decomposition + respiration

 depletes oxygen (hypoxia + anoxia)

 kills aerobes, including fish
 lower quality of drinking water
 change freshwater aquatic communities
 create ‘dead zones’ in oceans 522; 24.23
What are consequences of human activities on sulfur cycle? 23.17
Burning of fossil fuels containing H2S puts SO4 into air
SO4 reacts with H20 to form sulfuric acid  acid rain 505-6; 579-80; 24.1
Of what consequence is S presence in coal?
Strip-mine - sulfuric acid directly into streams-->
lowers pH and disrupts aquatic community 23.18
Acid rain
Lowers Ca in soils-->lowers forest productivity.
Lowers pH in lakes disrupts aquatic community.
Ozone (O3) + UV radiation 582-3; 27.15
1. at surface
 O2 with NO2 with light  O3
 NO2 from burning gas in cars
 Ozone = oxidant of organic molecules
 SOYFACE: elevated O3 lowers crop productivity
2. CFCs destroy ozone in upper atmosphere and creates ‘black hole’
increase damage from UV radiation