BioGeo test 2

In what form is most nitrogen (95–98%) found in wetland soils?

Organic compounds

What happens to denitrification when temperature increases?

It increases (microbial activity speeds up)

What happens to denitrification when oxygen decreases?

It increases (denitrification is anaerobic)

Which process removes nitrogen from the biosphere to the atmosphere?

denitrification

What nitrogen process needs oxygen?

Nitrification NH4+ → NO3-

What nitrogen process happens in anerobic conditions?

denitrification

what is mineralization?

Break down of organic nitrogen to ammonium (ammonification)

What is immobilization?

The buildup of organic matter where inorganic Nitrogen converts to organic matter

What are forms of organic matter

Proteins (amino acids), Amino sugars, urea, and nucleic acids

What is biological N2 fixation?

When bacteria convert atm nitrogen into a usable form

Which process converts nitrogen to a gas and releases it to the atmosphere?

Ammonia volatilization

Does mineralization remove nitrogen from the system?

No (it converts organic → inorganic nitrogen)

Does plant uptake remove nitrogen from the system?

No (it stores it in biomass)

if C:N > ~25

immobilization dominates, C:N < ~25 → Ammonification dominates

Under anaerobic conditions, what process is generally favored?

Slower decomposition but still follows C:N rule (high C:N → immobilization)

What happens to nitrogen during denitrification?

NO₃⁻ → N₂ (reduction, nitrogen gas released)

What happens to nitrogen during dissimilatory nitrate reduction (DNRA)?

NO₃⁻ → NH₄⁺

Which process involves the MOST electron transfer?

Denitrification (NO₃⁻ → N₂)

Which nitrogen process dominates under highly reduced (low oxygen) conditions?

DNRA (NO₃⁻ → NH₄⁺)

What does alkaline phosphatase indicate?

Phosphorus limitation (low available P)

How does phosphatase activity change when phosphorus is limited?

It increases

Where is phosphatase activity typically highest?

Plant litter layer

How does phosphatase activity change with soil depth?

Decreases with depth

What is the largest global nitrogen pool?

Atmosphere

Which is larger: soil nitrogen or living organisms?

soil

What is porewater P?

Dissolved phosphorus in sediment water

Name an inorganic mechanism that retains phosphorus in soils

sorption

Name an organic mechanism that retains phosphorus

microbial uptake

what is EPC?

The concentration where no net P sorption or release occurs

what does low EPC mean?

System absorbs P (less impacted)

What does high EPC mean?

system releases P

what lake would be more impacted high ECP or low?

High ECP

What is eutrophication?

Excess nutrients → algal blooms → oxygen depletion

Why is nitrogen pollution harmful to humans?

Contaminates drinking water (e.g., nitrate toxicity)

How does nitrogen affect food production?

increases crop yields

Why are phosphorus fertilizers important?

increase crop productivity

What is a major concern with phosphorus use?

the depletion of phosphate rock bc it is non-renewable

How can we sustain phosphorus for future agriculture?

• Use fertilizers more efficiently

• Recycle phosphorus (waste/manure)

• Reduce runoff losses

• Manage soils for better retention

What happens to nitrogen cycling if denitrification is removed?

Nitrogen accumulates in the system (less loss to atmosphere)

What happens to available nitrogen over time without denitrification?

it increases

What happens to primary productivity when available nitrogen increases?

it increases

What environmental issue can result from excess nitrogen?

Eutrophication (algal blooms, hypoxia)

What is the main cause of harmful algal blooms in Lake Pontchartrain?

Nutrient input from the Mississippi River

Why is denitrification important for ecosystems?

It removes excess nitrogen and prevents buildup

What happens if nitrogen is not removed efficiently?

Nutrient pollution and ecosystem imbalance

Why do tropical soils require more phosphorus fertilizer?

High sorption capacity locks up phosphorus

What happens to added phosphorus in tropical soils?

it binds to minerals and becomes unavailable

What happens if nitrogen is abundant but phosphorus is limited?

Growth is still limited (P becomes the limiting nutrient)

Why does NH₄⁺ diffuse slower than PO₄³⁻?

NH₄⁺ is positively charged and binds to negatively charged soil particles

Where is ammonium (NH₄⁺) typically highest?

In deeper, anaerobic soils

Why does ammonium increase with depth?

Less oxygen → more mineralization + less nitrification

What direction does ammonium flux usually go?

Upward toward the water column

Which nitrogen forms act as electron acceptors?

NO₃⁻ (nitrate) and NO₂⁻ (nitrite)

If denitrifiers are removed, what nitrogen process dominates?

Nitrogen fixation + retention processes

What happens to N₂ gas cycling without denitrification?

Less N returns to atmosphere → buildup in system

What’s the key difference between nitrogen and phosphorus limitation?

• Nitrogen = often mobile and lost via gas

• Phosphorus = often stored and limited by soil binding

What’s the link between nitrogen buildup and eutrophication?

More N → more algal growth → oxygen depletion

What does the Carbon/Nitrogen (C/N) ratio tell you about decomposition?

• Microbes need C/N ≈ 10 to grow

• High C/N (too much carbon): not enough nitrogen → microbes take N → immobilization

• Low C/N (more nitrogen): extra N released → mineralization

• Aerobic systems need more N