1

Nutrient Cycling and Retention

Chapter 19

www.sws.uiuc.edu/ nitro/biggraph.asp

2

Focus Areas• Nutrient Cycles

Phosphorus Nitrogen Carbon

• Rates of Decomposition Terrestrial Aquatic

• Organisms and Nutrients• Disturbance and Nutrients

3

Phosphorus Cycle

• Global phosphorus cycle does not include substantial atmospheric pool. Largest quantities found in mineral

deposits and marine sediments. Much of this in forms not directly

available to plants. Slowly released in terrestrial and aquatic

ecosystems via weathering of rocks.

4

Phosphorus Cycle

http://arnica.csustan.edu/carosella/Biol4050W03/figures/phosphorus_cycle.htm

5

Nitrogen Cycle

• Includes major atmospheric pool - N2. Nitrogen fixers can use atmospheric supply

directly (only prokaryotes). Energy-demanding process; reduces to N2 to

ammonia (NH3). Industrial N2- fixation for fertilizers equals the

biological process annually. Denitrifying bacteria release N2 in anaerobic

respiration (they “breath” on nitrate). Decomposer and consumers release waste N in

form of urea or ammonia. Ammonia is nitrified by bacteria to nitrate.

6

7

Nitrogen Cycle

http://muextension.missouri.edu/xplor/envqual/wq0252.htm

8

Carbon Cycle

• Moves between organisms and atmosphere as a consequence of photosynthesis and respiration. In aquatic ecosystems, CO2 must first

dissolve into water before being used by primary producers.

Although some C cycles rapidly, some remains sequestered in unavailable forms for long periods of time.

9

Carbon Cycle

http://www.ucar.edu/learn/images/carboncy.gif

10

Rates of Decomposition

• Rate at which nutrients are made available to primary producers is determined largely by rate of mineralization. Occurs primarily during decomposition.

Rate in terrestrial systems is significantly influenced by temperature, moisture, and organic chemical compositions (labile versus refractory).

11

Decomposition in Temperate Woodland Ecosystems

• Gallardo and Merino found differences in mass loss by the target species reflected differences in the physical and chemical characteristics of their leaves.

12

Decomposition in Temperate Forest Ecosystems

• Melillo et.al. used litter bags to study decomposition in temperate forests. Found leaves with higher lignin:nitrogen

ratios lost less mass. Suggested higher N availability in soil

might have contributed to higher decomposition rates.

Higher environmental temperatures may have also played a role.

13

Decomposition in Aquatic Ecosystems

• Gessner and Chauvet found leaves with a higher lignin content decomposed at a slower rate. Higher lignin inhibits fungi colonization of

leaves.• Suberkropp and Chauvet found leaves

degraded faster in streams with higher nitrate concentrations.

14

Decomposition in Aquatic Ecosystems

15

Nutrient Cycling in Streams

• Webster pointed out nutrients in streams are subject to downstream transport. Little nutrient cycling in one place.

Nutrient Spiraling Spiraling Length is the length of a stream

required for a nutrient atom to complete a cycle.

Related to rate of nutrient cycling and velocity of downstream nutrient movement.

16

Nutrient Spiraling in Streams

17

Stream Invertebrates and Spiraling Length

• Grimm showed aquatic invertebrates significantly increase rate of N cycling. Suggested rapid recycling of N by

macroinvertebrates may increase primary production.

Excreted and recycled 15-70% of nitrogen pool as ammonia.

18

Stream Invertebrates and Spiraling Length

19

19_16.jpg

20

Animals and Nutrient Cycling in Terrestrial Ecosystems

• MacNaughton found a positive relationship between grazing intensity and rate of turnover in plant biomass in Serengeti Plain. Without grazing, nutrient cycling occurs

more slowly through decomposition and feeding of small herbivores.

• Huntley and Inouye found pocket gophers altered N cycle by bringing N-poor subsoil to the surface.

21

Animals and Nutrient Cycling in Terrestrial Ecosystems

22

Disturbance and Nutrient Loss From the Hubbard Brook Forest

Likens and Bormann

23

Disturbance and Nutrient Lossfrom Diverse Forest Types

• Vitousek studied effects of disturbance and environmental conditions on N loss. Trenching increased concentrations of

nitrate in soil water up to 1,000 x. Nitrate losses are generally greatest at

sites with rapid decomposition. Uptake by vegetation is most

important in ecosystems with fertile soils and warm, moist conditions.

24

Flooding and Nutrient Export by Streams

• Meyer and Likens found P exports were highly episodic and associated with periods of high flow. Annual peak in P input associated with

spring snowmelt. Most export was irregular because it

was driven by flooding caused by intense periodic storms.

• Inter-annual variation in balance of inputs and exports indicate tha low flow years are storage years.

25

Flooding and Nutrient Export by Streams

26

Human influences on nutrient cycling

• Loss of nutrients via deforestation• Addition of nutrients

Fertilizers Nitrogen in atmosphere from coal burning

Consequences Reduced biodiversity Reduction of mycorrhizal fungi Eutrophication of lakes http://www.epa.gov/maia/html/eutroph.html

27

(Peierls et al., 1991)