BIOL305: Aquatic Biology Exam 1 (Summers)

What is limnology?

The scientific study of inland aquatic ecosystems, including lakes, ponds, streams, and rivers.

What is a lotic system?

A flowing-water ecosystem, such as a stream or river.

What is a lentic system?

A relatively standing or still-water ecosystem, such as a lake or pond.

What is the difference between lotic and lentic systems?

Lotic systems have directional flowing water; lentic systems have relatively standing water.

What is the pelagic zone?

The open-water portion of a lake, away from the shoreline and bottom.

What is the littoral zone?

The shallow nearshore region where light commonly reaches the bottom and aquatic plants may grow.

What is the benthic zone?

The bottom region of an aquatic ecosystem, including its sediments and associated organisms.

What is density?

Mass per unit volume; density = mass/volume.

What is unusual about the density of freshwater?

Freshwater reaches its maximum density at approximately 4°C.

Why is 4°C important in freshwater lakes?

Water is densest at 4°C, so 4°C water sinks while water colder than 4°C remains above it.

Why can lakes freeze at the surface without freezing completely?

Water colder than 4°C becomes less dense and remains near the surface, where it can reach 0°C and freeze, while denser ~4°C water remains below.

What is viscosity?

A fluid's resistance to flow.

How does temperature affect water viscosity?

Colder water has higher viscosity; warmer water has lower viscosity.

What is dissolved oxygen (DO)?

Oxygen gas dissolved in water that is available for aquatic organisms.

What happens to oxygen solubility as water temperature increases?

Oxygen solubility decreases.

Why can cold water contain more dissolved oxygen than warm water?

Gases are generally more soluble in colder water, allowing cold water to hold more O₂.

What biological processes add oxygen to water?

photosynthesis and atmospheric gas exchange.

What biological processes remove oxygen from water?

Respiration and decomposition.

What is hypoxia?

A condition in which dissolved oxygen is unusually low.

What is anoxia?

A condition in which dissolved oxygen is essentially absent.

What is the difference between hypoxia and anoxia?

Hypoxia means low oxygen; anoxia means essentially no oxygen.

What is Henry's Law?

At equilibrium, the concentration of a dissolved gas in a liquid is related to the gas's partial pressure above the liquid and its solubility.

How does Henry's Law relate to oxygen in lakes?

Atmospheric oxygen can dissolve into water, with equilibrium concentration influenced by oxygen's partial pressure and its solubility.

What is pH?

A logarithmic measure of hydrogen-ion concentration; pH = -log[H+].

What does low pH indicate?

Greater acidity and higher hydrogen-ion concentration.

What does high pH indicate?

More basic or alkaline conditions and lower hydrogen-ion concentration.

What is buffering capacity?

The ability of a system to resist changes in pH when acid or base is added.

Is buffering capacity the same as pH?

No. pH describes current acidity/basicity, while buffering capacity describes resistance to changes in pH.

What is morphometry?

The measurement and description of the physical dimensions and shape of a lake.

What are examples of lake morphometric characteristics?

Surface area, depth, volume, shoreline length, and basin shape.

What is a bathymetric map?

A map showing underwater depth and topography.

What do bathymetric contour lines represent?

Lines connecting locations of equal water depth or elevation.

What is a drainage basin?

An area of land in which water drains toward a common outlet.

What is a watershed?

A drainage divide or boundary separating one drainage basin from another.

What is a stream?

A channel of flowing water.

What is a river?

A larger flowing-water system or channel, generally receiving water from tributaries and/or smaller streams.

What is a tributary?

A smaller stream or river that flows into a larger stream or river.

What is a distributary?

A channel that branches away from the main channel and carries water away from it.

What is stream order?

A hierarchical classification describing the position and branching structure of streams within a drainage network.

What is a first-order stream?

A stream with no other ordered tributaries flowing into it.

What happens when two first-order streams join?

They form a second-order stream.

What happens when two second-order streams join?

They form a third-order stream.

What happens when two third-order streams join?

They form a fourth-order stream.

What happens when a first-order stream joins a second-order stream?

The resulting stream remains second order.

What happens when a second-order stream joins a third-order stream?

The resulting stream remains third order.

What is the key rule for stream order?

Stream order increases only when two streams of the same order join.

What is discharge?

The volume of water passing a particular point per unit time.

What is the equation for discharge?

Q = WDV

What does Q represent in the discharge equation?

Discharge.

What does W represent in the discharge equation?

Channel width.

What does D represent in the discharge equation?

Channel depth.

What does U represent in the discharge equation?

Water velocity.

What are common units for discharge?

Cubic meters per second (m³/s).

What is the discharge of a stream 4 m wide, 1.5 m deep, with a velocity of 2 m/s?

12 m³/s.

If velocity doubles while width and depth remain constant, what happens to discharge?

Discharge doubles.

If channel width doubles while depth and velocity remain constant, what happens to discharge?

Discharge doubles.

If channel depth doubles while width and velocity remain constant, what happens to discharge?

Discharge doubles.

What is drainage density?

The amount of stream-channel length relative to the area of a drainage basin.

What does high drainage density mean?

A relatively large amount of stream channel occurs within a given drainage-basin area.

What is erosion?

The removal of soil, rock, or sediment by processes such as flowing water.

What is transportation?

The movement of sediment from one location to another.

What is deposition?

The settling or accumulation of transported sediment.

What is the sequence of sediment movement?

Erosion → Transportation → Deposition.

Where does erosion commonly occur around a meander?

On the outside of the bend, where flow is generally faster.

Where does deposition commonly occur around a meander?

On the inside of the bend.

What is a point bar?

A depositional feature formed on the inside of a meander bend.

What is a riffle?

A relatively shallow, fast-flowing, turbulent section of a stream.

What is a pool?

A relatively deep, slower-flowing section of a stream.

How do riffles and pools differ?

Riffles are shallow, fast, and turbulent; pools are deeper, slower, and relatively calm.

What is a dendritic drainage pattern?

A branching, tree-like drainage pattern.

What is a parallel drainage pattern?

A pattern in which streams flow generally parallel to one another.

What is a radial drainage pattern?

Streams flow outward from a central high point.

What is a centripetal drainage pattern?

Streams flow inward toward a central low point.

What is a pinnate drainage pattern?

A feather-like drainage pattern with many relatively short tributaries entering a main channel.

What is a rectangular drainage pattern?

A drainage pattern characterized by streams with frequent right-angle bends, often controlled by fractures or faults.

What is a distributary drainage pattern?

A pattern in which channels branch outward from a main channel, commonly associated with deltas.

What is the difference between radial and centripetal drainage?

Radial flows outward from a center; centripetal flows inward toward a center.

What drainage pattern resembles a tree?

Dendritic.

What drainage pattern resembles spokes extending from a center?

Radial.

What drainage pattern flows toward a central depression?

Centripetal.

What is thermal stratification?

The formation of relatively distinct temperature and density layers within a lake.

What are the three major thermal layers of a stratified lake?

Epilimnion, metalimnion, and hypolimnion.

What is the epilimnion?

The warm, upper layer of a stratified lake most directly influenced by sunlight and wind.

What is the metalimnion?

The middle transition layer between the epilimnion and hypolimnion where temperature changes substantially with depth.

What is the hypolimnion?

The deeper, colder layer below the metalimnion.

What is the thermocline?

The zone of rapid temperature change with depth.

Where is the thermocline generally located?

Within the metalimnion.

Which layer is warmest during summer stratification?

Epilimnion.

Which layer is coldest during summer stratification?

Hypolimnion.

Which layer receives the most direct influence from wind?

Epilimnion.

Why can the hypolimnion become oxygen depleted?

Stratification limits exchange with oxygen-rich surface water while respiration and decomposition continue consuming oxygen.

What is stratification?

The development of distinct layers within a lake that resist complete mixing.

What is mixing?

Movement of water that redistributes temperature, oxygen, nutrients, and other dissolved substances.

What is turnover?

Whole-lake mixing that occurs when density differences become small enough for wind and convection to mix the water column.

What are convective currents?

Water movements caused by differences in density, often resulting from temperature differences.

What role does wind play in lake mixing?

Wind transfers energy to the surface and can mix surface water and, during turnover, contribute to mixing the entire water column.

What does isothermal mean?

Having approximately the same temperature throughout the water column.

What is a dimictic lake?

A lake that undergoes whole-lake mixing twice each year, typically during spring and fall.

What happens during spring turnover?

The lake becomes relatively uniform in temperature and density, allowing wind to mix the water column.

What happens during summer stratification?

Warm, less-dense surface water separates from colder, denser deep water.