BI 423: Phosphorus and Nitrogen Aquatic Ecology Test 1

What is Required for autotrophic growth & reproduction

nutrients

Nutrient limitation/availability does what

sets upper limit to rate at which "algae" can photosynthesize

Diatoms are frequently limited by

silica

Flagellates limited by certain

vitamins

Different algal types may be limited by

varied factors

In general, ______ = most important nutrients

Nitrogen & Phosphorus

what are the most limiting nutrients in the environment

N and P

N is ______, but P is ______

occasionally limiting; nutrient limiting freshwater productivity

Atmosphere ~___% N2 gas

~78%

N2 not utilized by most

autotrophs

Only ____ can use free N2

nitrogen fixers

Aquatic systems: ___ most important

Cyanobacteria

Most important utilizable forms of N: Only forms available for photosynthetic algae & plants

NO3-N and NH4 -N

____ in large quantities in lakes as organic matter

N

N-fixation by ____ and by _____ in sediment

Cyanobacteria (blue-green algae), N-fixing bacteria

Denitrification by ____

anaerobic bacteria

Denitrification

NO3 → N2

Nitrogen cycle in order

Fixation, Nitrification, Assimilation, Denitrification

Humans influences on N-cycle

agriculture, fossil fuels, sewage

N-fixing crops (>/

N-fixing crops > wastewater

human influence Manifests in ___ in Gulf of Mexico and elsewhere

"Dead Zones"

CAFO

Concentrated Agriculture Feeding Operation

Summer Stratification and Nitrogen: _____ in the epilimnion

decreases

Summer Stratification and Nitrogen: decreases in the epilimnion due to

rising temperature

N-fixing lowest when (____) is high

NH4-N

N2 during summer stratification ___ in hypolimnion of eutrophic lakes due to _____

increases; denitrification

Little change from top to bottom in Oligotrophic lakes except for____

Epilimnetic temperature decrease

NH4-N Mainly from ___ due to _____

ammonification; heterotrophic bacteria (decomposers)

Where is ammonification usually low where?

epilimnion

Ammonification is lowered by ___

nitrification

Nitrifying bacteria lowers NH4-N when ____ is present

O2

Where are NH4-N levels low

Epilimnion

NH4-N In Eutrophic lakes, is high in the

anaerobic Hypolimnion

NH4-N high in anaerobic hypolimnion of eutrophic lakes due to

No nitrification due to no O

Most common form of utilizable Nitrogen in lake

NO3-N

This chemical is relatively high in Epilimnion because of algal/plant preference for NH4-N when available

NO3-N

NO 3-N • Low in ____ of Eutrophic lakes

anaerobic Hypolimnion

NO 3-N • Low in anaerobic Hypolimnion of Eutrophic lakes due to

denitrification

Readily assimilated by Autotrophs

NO3-N

N2 fixed by ____ along w/ NH4 and NO3 from lakes basin assimilated into living organic matter

cyanobacteria

DON

Dissolved Organic Nitrogen

PON

Particulate Organic N

As lakes become more eutrophic DON:PON

decreases

Organic matter decomposes in sediments releasing ____ in the nitrogen cycle

NH4

Nitrogen net result over time

overall accumulation of Nitrogen in lake water & sediment

Rarest of elements required by Autotrophs

phosphorus

Most P (>90%) cane be found in __

organic matter

Sources of P in lakes

Soil/rock formations containing P, mainly Apatite Ca(PO4), Anthropogenic/Cultural Eutrophication

Losses of P in lakes

Chelation, Adsorption, & Outflow

Oligotrophic lakes are ____ distributed

Low & uniformly

How does P behave in the epilimnion

Relatively Low amounts due to overall rarity; Adsorbs to particles (e.g., clays, silts, etc.) • Settles to bottom • Reacts readily w/ cations like Fe3+, Ca2+ under aerobic conditions • Form relatively insoluble compounds & precipitate, Some dead OM takes P to bottom

how does P behave in hypolimnion

All P reaching sediments will remain trapped in insoluble form Under later anaerobic conditions Complexes become soluble and P is released into overlying water

How does P behave during turnover

Some of released P is mixed back into H2O column, used by Autotrophs Most recombine w/ cations

Net result of phosphorus during turnover

An overall accumulation of P in lakes

Conductivity:

measures total ions in H2O

he more impurities in the water, the more ____

conductive

higher temp =

higher conductivity

Industrial wastewater and seawater ____ much better than fresh water

Industrial wastewater and seawater conduct much better

Thermocline separates Aerobic ((epi +) meta) from Anaerobic

aerobic from anaerobic