Freshwater Ecology Exam 2

Biogeochemistry

Study of chemical, physical, geological, and biological processes governing the natural environment.

Pool

A place or reservoir where a substance is stored.

Flux

Movement of a substance between pools per unit time.

Residence time

The average time a substance remains in a pool.

Weathering

Physical or chemical breakdown of material that moves dissolved substances and particles into water.

Biosphere

The sphere containing living organisms.

Cryosphere

The frozen-water component of Earth.

Hydrosphere

All water on Earth.

Atmosphere

The layer of gases surrounding Earth.

Lithosphere

The solid land and rock component of Earth.

Pedosphere

The soil layer that interfaces with other environmental spheres.

Dissolved material

Material that passes through a 0.45 µm filter under the lecture’s classification.

Particulate material

Material retained by a 0.45 µm filter under the lecture’s classification.

Gravitoidal particles

Particles that settle under gravity.

Colloids

Small particles that do not readily settle under gravity.

pH

A measure related to hydrogen-ion activity; pH = −log₁₀[H⁺]. Lower pH is more acidic.

Alkalinity

Water’s capacity to neutralize added acid; commonly influenced by bicarbonate, carbonate, and hydroxide.

Hardness

A water property associated primarily with calcium (Ca²⁺) and magnesium (Mg²⁺).

Oxidation

Loss of electrons.

Reduction

Gain of electrons.

OIL RIG

Memory aid: Oxidation Is Losing; Reduction Is Gaining electrons.

ORP

Oxidation-reduction potential, measured in millivolts, indicating tendency for electron-transfer reactions.

Oxic environment

An environment containing oxygen.

Anoxic environment

An environment lacking oxygen.

Negative ORP

The lecture’s guideline associates negative ORP with reducing conditions.

Positive ORP

The lecture’s guideline associates positive ORP with oxidizing conditions.

ORP-to-Eh conversion

Eh (V) = [ORP (mV) + 200] / 1000.

Eh-to-ORP conversion

ORP (mV) = 1000 × Eh (V) − 200.

Total dissolved solids (TDS)

Mass of dissolved material, including organic substances; the slides also mention a 1 µm classification context.

Conductivity

Water’s ability to conduct electrical current; it primarily reflects dissolved ions.

Salinity

Concentration of dissolved salts; conductivity can be used as a proxy.

Atmospheric diffusion

Transfer of oxygen from the air into water.

Photosynthesis

CO₂ + H₂O + light → CH₂O + O₂; uses light energy to form organic matter and release oxygen.

Respiration

CH₂O + O₂ → CO₂ + H₂O + energy; breaks down organic matter and consumes oxygen.

Oxygen saturation

The equilibrium concentration of dissolved oxygen under given conditions.

Temperature and oxygen saturation

Colder water generally holds more dissolved oxygen at saturation than warmer water.

Elevation and oxygen saturation

Higher elevation generally lowers atmospheric pressure and oxygen saturation.

Supersaturation

Dissolved oxygen above 100% saturation, which can occur during high photosynthesis.

Relative gas solubility in the lecture

CO₂ > O₂ > N₂.

GPP

Gross primary production: total production attributed to photosynthesis.

NPP

Net primary production: GPP minus producer respiration; NPP = GPP − R.

GEP

Gross ecosystem production.

ER

Ecosystem respiration.

NEP

Net ecosystem production: GEP minus ecosystem respiration; NEP = GEP − ER.

Compensation point

Light level at which photosynthesis equals respiration, so net production is zero.

Pmax

Maximum photosynthetic rate.

Photoinhibition

Reduced photosynthetic performance caused by excessively high light intensity.

Boundary layer

A thin layer of water near a surface where diffusion can constrain gas exchange.

Water velocity and oxygen diffusion

Higher velocity can thin the boundary layer and improve diffusion, but excessive velocity may disturb or dislodge organisms.

Respiration controls

Temperature, organic-carbon quality, diffusion, organism activity, toxins, and pollutants can affect respiration.

Fermentation

ATP-producing metabolism that does not require oxygen.

Alternative electron acceptors

Substances such as nitrate that microbes can use when oxygen is limited.

Light-and-dark bottle experiments

Method for estimating photosynthesis and respiration using changes in oxygen in light and dark bottles.

Stream metabolism

Can be estimated from chambers and diel dissolved-oxygen patterns; account for oxygen outgassing.

Piezometer

Instrument used to sample or measure groundwater conditions; also used in wetland studies.

Carbon cycle

Movement of carbon among atmosphere, lithosphere, hydrosphere, and biosphere via photosynthesis, respiration, diffusion, weathering, burial, and outgassing.

Dissolved inorganic carbon (DIC)

The combined dissolved inorganic carbon forms, also called ΣCO₂ in the slides.

Carbon dioxide (CO₂)

Dissolved inorganic carbon form that reacts with water to form carbonic acid.

Carbonic acid (H₂CO₃)

Forms when CO₂ reacts with water: CO₂ + H₂O ⇌ H₂CO₃.

Bicarbonate (HCO₃⁻)

DIC form produced when carbonic acid dissociates; often important in freshwater buffering.

Carbonate (CO₃²⁻)

DIC form produced by further dissociation of bicarbonate.

CO₂ and pH

Increasing CO₂ can increase carbonic acid and hydrogen ions, lowering pH.

Calcium carbonate precipitation

Ca²⁺ + CO₃²⁻ ⇌ CaCO₃; carbonate availability affects precipitation.

Limestone influence

Limestone can contribute bicarbonate and affect water buffering.

DOC

Dissolved organic carbon; classified in the guide as <0.45 µm.

POC

Particulate organic carbon; classified in the guide as >0.45 µm.

FPOM

Fine particulate organic matter; <1 mm.

CPOM

Coarse particulate organic matter; >1 mm.

Non-humic substances

Organic compounds such as sugars, carbohydrates, amino acids, proteins, lipids, urea, and pigments.

Humic substances

Products of breakdown of larger organic materials such as tannins, cellulose, and lignin.

Humic acids

Humic substances that precipitate in acids.

Fulvic acids

Humic substances that do not precipitate in acids.

Humin

Humic fraction that is not extractable under the lecture’s classification.

Humic-substance effects

Can color water, bind metals and organic pollutants, form colloids, and resist degradation.

Leaf decomposition equation

Mₜ = M₀e⁻ᵏᵗ; mass remaining depends on initial mass, decomposition constant, and time.

Decomposition rate constant (k)

A higher k means faster decomposition, all else equal.

Carbon decomposition and redox

Microbes use different electron acceptors depending on conditions; oxygen-based pathways generally yield more energy than alternatives discussed.

Wetland carbon accumulation

Wetlands can accumulate carbon when environmental conditions slow decomposition.

Nitrogen gas (N₂)

Makes up about 78% of the atmosphere; its triple bond makes biological use difficult.

Nitrogen fixation

Converts N₂ into biologically usable nitrogen; requires substantial energy and is performed by certain bacteria and archaea.

Molybdenum in nitrogen fixation

An important element for the nitrogen-fixation process.

Nitrification

Two-step oxidation: NH₄⁺ → NO₂⁻ → NO₃⁻; associated with oxidizing conditions and releases energy.

Denitrification

Reduction sequence NO₃⁻ → NO₂⁻ → NO → N₂O → N₂, commonly under low-oxygen conditions.

Assimilation

Conversion of inorganic nitrogen into organic nitrogen in organisms.

Ammonification / remineralization

Conversion of organic nitrogen back into inorganic nitrogen, commonly ammonium.

Ammonia (NH₃)

Un-ionized ammonia that can volatilize; its fraction increases with higher pH and temperature.

Ammonium (NH₄⁺)

A common nitrogen form in neutral-pH waters and often readily used by plants.

Nitrite (NO₂⁻)

An intermediate in the nitrogen cycle that can be toxic.

Nitrate (NO₃⁻)

The most oxidized inorganic nitrogen form; widely used by plants and algae.

DON

Dissolved organic nitrogen; <0.45 µm in the guide’s classification.

PON

Particulate organic nitrogen; >0.45 µm in the guide’s classification.

Ammonia pH example

The lecture’s example gives about 10% ammonia at pH 8 and 50% at pH 9.

Nitrogen assimilation energy ranking

N₂ > NO₃⁻ > NO₂⁻ > NH₄⁺; ammonium generally requires the least processing.

Nitrogenase

Enzyme involved in nitrogen fixation that is sensitive to oxygen.

Heterocyst

Specialized cyanobacterial cell that can protect nitrogen fixation from oxygen.

Methemoglobinemia

A health concern associated in the lecture with nitrate/nitrite exposure; also called “blue baby syndrome.”

Nitrosamines

Compounds discussed in the lecture as a nitrogen-related health concern.

Phosphate (PO₄³⁻)

The main inorganic phosphorus form emphasized for aquatic systems.

Organic phosphorus

Phosphorus in biological molecules such as nucleic acids, lipids, and proteins.

Bioavailable phosphorus (BAP)

Phosphorus accessible for biological use in the lecture’s context.