APES Unit 1: Nitrogen, Phosphorus, Lakes, Eutrophication & Primary Productivity

Vocabulary terms and definitions extracted directly from lecture notes on AP Environmental Science Unit 1 covering nutrient cycles, lake zonation, eutrophication, and productivity.

Nitrogen Cycle

The movement of nitrogen between the atmosphere, soil, organisms, and water.

Atmospheric Nitrogen ($N_2$)

The main atmospheric reservoir of nitrogen, which exists as a gas that cannot be directly absorbed or utilized by most plants.

Nitrogen Fixation

The conversion of atmospheric $N_2$ gas into usable nitrogen compounds, carried out mainly by bacteria.

Nitrification

The process in which soil bacteria convert ammonia and ammonium ($NH_3$ / $NH_4^+$) into nitrites ($NO_2^-$) and then into nitrates ($NO_3^-$).

Assimilation (Nitrogen Cycle)

The process where plants absorb nitrogen forms such as $NO_3^-$ or $NH_4^+$ and incorporate them into their tissues, while animals acquire nitrogen by eating organisms.

Ammonification

The process by which decomposers break down dead organisms and organic waste, converting nitrogen into $NH_3$ or $NH_4^+$.

Denitrification

The conversion of nitrates ($NO_3^-$) by specialized bacteria into nitrogen gases that return to the atmosphere.

Nitrate Leaching

The movement of dissolved nitrate through soil into groundwater.

Ammonia Volatilization

The movement of ammonia gas from soil into the atmosphere.

Nitrous Oxide ($N_2O$)

A greenhouse gas released during nitrogen transformations that contributes to atmospheric warming and stratospheric ozone depletion.

Weathering

The physical and chemical breakdown of rocks that releases phosphate into soil and aquatic environments.

Phosphate ($PO_4^{3-}$)

The biologically accessible form of phosphorus that plants absorb from soil or water, essential for DNA, ATP, bones, and tooth enamel.

Geological Uplift

The movement of ocean sediments and deep rock layers containing phosphorus back up to the Earth's surface.

Eutrophication

A process where excess nutrient inputs cause rapid, excessive growth of plants and algae in an aquatic ecosystem.

Algal Bloom

A dense, rapid growth of algae on the surface of a body of water caused by high nutrient availability.

Cultural Eutrophication

Eutrophication caused or accelerated by human activities, such as fertilizer runoff, animal waste, and wastewater discharge.

Littoral Zone

The shallow lake zone near the shore where light reaches the bottom and emergent rooted plants grow.

Limnetic Zone

The open surface water zone of a lake where sunlight penetrates and photosynthesis occurs, inhabited mainly by plankton.

Profundal Zone

The deep water zone of a lake where sunlight does not reach and photosynthesis cannot take place.

Benthic Zone

The bottom sediment layer of a body of water containing nutrient-rich sediments and organisms such as invertebrates.

Oligotrophic Lake

A lake characterized by low nutrient concentration levels and low primary productivity.

Mesotrophic Lake

A lake characterized by moderate nutrient levels and an intermediate level of primary productivity.

Eutrophic Lake

A lake characterized by high nutrient levels and high primary productivity.

Hypereutrophic Lake

A lake with extremely high nutrient levels and very high primary productivity, often caused by human nutrient pollution.

Primary Productivity

The rate at which autotrophic producers convert environmental energy into organic matter or biomass.

Limiting Factor

A specific environmental resource or condition that restricts the growth, abundance, or productivity of an organism or ecosystem.

Photic Zone

The upper layer of water in an aquatic ecosystem that receives sufficient sunlight for photosynthesis.

Aphotic Zone

The deeper layer of water in an aquatic ecosystem where sunlight is too scarce for photosynthesis to occur.

Estuary

A highly productive aquatic ecosystem where freshwater rivers flow into and mix with saltwater from the ocean.

10% Rule

The ecological concept stating that only approximately $10\times 10^{-1}$ or $10\text{--}10\text{\%}$ (about $10\text{\%}$) of energy/biomass is passed to the next trophic level, with about $90\text{\%}$ lost to metabolism, waste, and heat.