Biogeochemical Cycles and Primary Productivity (Nitrogen, Phosphorus, Water, PP)

Flashcards covering key concepts from the nitrogen cycle, phosphorus cycle, the water cycle, and primary productivity as described in the lecture notes.

What is nitrogen fixation and what does it accomplish?

The conversion of atmospheric N2 into biologically usable forms such as NH3 (ammonia) or NO3− (nitrate), enabling uptake by plants and incorporation into tissue.

What are the two main nitrogen fixation pathways described in the notes?

Synthetic fixation (industrial conversion of N2 to nitrate) and bacterial fixation (soil bacteria and rhizobia in root nodules convert N2 to NH3).

What is the major reservoir of nitrogen in the cycle?

The atmosphere, primarily as N2 gas.

Which nitrogen forms can plants assimilate from the soil?

Nitrate (NO3−) and ammonia (NH3/NH4+).

What is nitrification and which organisms perform it?

The biological oxidation of NH4+ to NO2− and then NO3− by soil bacteria.

What is ammonification in the nitrogen cycle?

The microbial decomposition of organic N from waste and dead biomass to NH3, returning nitrogen to soil.

What is assimilation in the nitrogen cycle?

Plants and animals taking up inorganic N (NO3− or NH3) and incorporating it into tissues.

What is denitrification and what gas is produced?

The microbial reduction of NO3− to gaseous N2O (and often N2), returning nitrogen to the atmosphere.

Why is nitrogen essential for living organisms?

It is required for DNA, amino acids, and proteins.

Why is atmospheric N2 not directly usable by most organisms?

Because it is N2 gas, which is relatively inert and not readily taken up by plants or animals.

What is leaching in the nitrogen cycle?

Nitrates dissolved in water moving through soil and entering groundwater or surface waters.

What is eutrophication and how is it linked to N and P?

Excess nutrients (N and P) promoting algae blooms, oxygen depletion, and aquatic ecosystem harm.

What role do synthetic fertilizers play in the nitrogen cycle impacts?

They add nitrates to soils, increasing leaching and runoff, leading to algal blooms and nitrogen losses from soil; can volatilize as NH3.

What greenhouse gas is associated with the nitrogen cycle and how is it produced?

N2O (nitrous oxide), produced during denitrification in soils, contributing to climate warming.

What does the FixNAAD acronym stand for in the nitrogen cycle?

Fixation, Nitrification, Assimilation, Ammonification, Denitrification.

What are the major reservoirs of phosphorus in the phosphorus cycle?

Rocks and sediments containing phosphate minerals; oceans contain dissolved phosphate but the major reservoirs are rocks and sediments.

Is there an atmospheric component to the phosphorus cycle?

No. Phosphorus does not have a gaseous phase in its cycle.

Why is phosphorus naturally scarce in many ecosystems?

Weathering is slow, there is no atmospheric transport to replenish phosphate, making P a limiting nutrient.

What role does weathering play in the phosphorus cycle?

Weathering of phosphate-containing rocks releases phosphate (PO4^3−) into soil and water.

What human activities contribute to phosphorus input into ecosystems?

Phosphate mining, application of phosphate fertilizers, detergents/cleaners containing phosphates, and wastewater.

How do plants and animals assimilate phosphorus?

Plants take up phosphate; animals assimilate by eating plants or other animals; phosphate returns via excretion and decomposition.

What happens to dissolved phosphates in water that are not assimilated?

They may precipitate and form sediments, eventually becoming part of sedimentary rocks.

What is sedimentation in the phosphorus cycle?

Phosphates settle out of solution as sediments and contribute to ocean sediments and eventual phosphate rocks.

What is geological uplift and its role in phosphate cycling?

Tectonic forces push phosphate rocks from the ocean floor upward, restarting the cycle via weathering.

Why is phosphorus often a limiting nutrient in aquatic and terrestrial ecosystems?

Because weathering is slow and there is no atmospheric phase to replenish it quickly.

What is eutrophication and how is it driven by phosphorus?

Excess phosphate from runoff and wastewater stimulates algae growth; decomposition depletes oxygen, harming aquatic life.

What powers the hydrologic (water) cycle?

The sun.

What are the major reservoirs of Earth's surface water?

Oceans are the primary reservoir; ice caps and groundwater are smaller reservoirs.

What is evapotranspiration?

The combined process of evaporation from surfaces and transpiration from plants.

What is runoff in the water cycle?

Water moving across the land surface into streams and rivers, eventually reaching the ocean.

What is infiltration in the water cycle?

Water seeping through soil to recharge groundwater aquifers.

What is groundwater recharge and why is it important?

Infiltration recharges groundwater; groundwater and surface water are important freshwater reservoirs for humans and animals.

How does precipitation affect groundwater and surface water?

Precipitation can recharge groundwater via infiltration and recharges surface waters via runoff, while carrying pollutants.

What is primary productivity (PP)?

The rate at which solar energy is converted into organic compounds via photosynthesis per unit time.

What is Gross Primary Productivity (GPP)?

The total rate of photosynthesis in an area over a given period.

What is Net Primary Productivity (NPP)?

GPP minus the energy respired by producers.

In what units is productivity typically measured?

Energy per unit area per unit time (e.g., kcal/m^2/yr).

How does light penetration affect aquatic photosynthesis in clear water?

Most red light is absorbed in the upper 1 m; blue light penetrates deeper (over 100 m) in the clearest waters.

What does ecological efficiency say about the fraction of solar energy captured and stored as biomass?

About 1% of incoming solar energy is captured as GPP; about 0.4% becomes NPP.

What factors typically increase ecosystem productivity (NPP) and biodiversity?

Water availability, higher temperature, and nutrient availability; higher PP generally supports more biodiversity.

What is the relationship between productivity and biodiversity in biomes?

More productive biomes usually support greater biodiversity; productivity varies with environmental conditions.

What are example biomes cited as high- and low-productivity?

Desert (low water/nutrients), tundra (low temperature/air-filled water), open ocean (low nutrients).