Freshwater Ecology: Evolution, Biodiversity, Aquatic Chemistry, and Carbon Dynamics

Comprehensive practice flashcards covering freshwater evolution, species diversity measures, ecoregions, aquatic chemical parameters, oxidation-reduction thermodynamics, dissolved oxygen dynamics, photosynthesis-irradiance kinetics, and carbon biogeochemical cycles.

What is species richness?

The total number of species found in a specific area.

How is evenness defined in community ecology?

How equally represented the numbers of individuals of each species are in an assemblage.

What mathematical expression defines the Shannon index ($H'$) and what does it measure?

The Shannon index is calculated as $H' = -\sum_{j=1}^{S} p_j \ln(p_j)$, where $S$ is species richness and $p_j$ is the proportion of species $j$ relative to the total community. It measures diversity by integrating both richness and evenness.

How do $\alpha$-diversity and $\beta$-diversity differ in linking spatial scale to biodiversity?

$\alpha$-diversity refers to within-habitat diversity, whereas $\beta$-diversity refers to between-habitat diversity.

Based on the provided illustration of communities (A–D) versus (E–H), how do their $\alpha$-diversity and $\beta$-diversity compare?

Sets (A–D) and (E–H) have identical total diversity and evenness; however, (A–D) exhibits lower $\alpha$-diversity and higher $\beta$-diversity than (E–H).

What is the Ecoregion concept, and how many ecoregions exist across North America?

It is the classification of habitats based on $\beta$-diversity and abiotic conditions. In North America, there are $76$ ecoregions distributed across $8$ major freshwater habitat regions.

Which eight freshwater ecoregions are located in the state of Texas?

U.S. Southern Plains, Ouachita Highlands, Sabine-Galveston, East Texas Gulf, West Texas Gulf, Pecos, Upper Rio Grande, and Lower Rio Grande.

What two primary temporal and spatial factors influence the evolution of new freshwater species?

Time available for evolution and reproductive isolation.

What is an endemic species?

A species that is restricted in its geographical distribution to a specific area.

What equation defines the species-area relationship in ecological habitats?

$S = cA^z$ or $\log(S) = \log(c) + z \log(A)$, where $S$ is species richness, $A$ is the area of the habitat island, $c$ is a constant measuring species richness per unit area, and $z$ is the slope of the log-log line.

What three characteristics are typically shared by cosmopolitan freshwater species?

Life history stages capable of surviving transport, production of high numbers of individuals in that transportable stage, and the ability to survive, compete, and avoid predation in new habitats.

What is the Intermediate Disturbance Hypothesis?

A hypothesis stating that species diversity is maximized at intermediate levels (frequencies and intensities) of natural disturbance.

What is the difference between Minimum Viable Population and Effective Population Size?

Minimum Viable Population is the lowest number of individuals needed for a population to avoid extinction from stochastic environmental or demographic events, while Effective Population Size represents the subset of individuals actively contributing genetic material to succeeding generations.

In source-sink population dynamics, what distinguishes source populations from sink populations?

Source populations occupy prime habitats where individuals survive, multiply, and emigrate, while sink populations occur in marginal habitats where local mortality exceeds reproduction and populations would go extinct without immigration.

What proportion of introduced nonnative species typically succeeds in establishing populations?

Approximately $1$ in $10$ introduced invaders establishes, while the vast majority fail.

What is the distinction between extinction and extirpation?

Extinction occurs when no living individuals of a species exist anywhere on Earth, whereas extirpation occurs when a species is eliminated from the wild but living individuals still survive in captivity.

What is the estimated economic value provided by aquatic microbes solely for processing human wastes?

More than $\\$700\text{ billion}$$ per year.

How is the operational distinction between dissolved and particulate matter made in aquatic chemistry?

By filtration through a standardized membrane filter, typically with a pore size of $0.45\,\mu\text{m}$ or $1\,\mu\text{m}$.

How do dissolved, colloidal, and gravitoidal materials differ?

Dissolved materials are fully in solution; colloidal materials are not dissolved but remain suspended without settling due to gravity; gravitoidal materials are large undissolved particles that settle out under the influence of gravity.

What do the water quality metrics TDS, Salinity, and Conductivity measure?

TDS (Total Dissolved Solids) measures the total mass of dissolved material; Salinity measures the amount of dissolved inorganic salts; Conductivity measures the water's ability to conduct an electric current based on dissolved ion concentrations.

What is the difference between water hardness and alkalinity?

Hardness is the combined concentration of calcium ($\text{Ca}^{2+}$) and magnesium ($\text{Mg}^{2+}$) ions, whereas alkalinity is the acid-neutralizing capacity represented by the sum of titratable bases (primarily carbonate, bicarbonate, and hydroxide).

What is redox potential ($E_H$), and what do high versus low millivolt readings indicate?

Redox potential measures the relative concentration of electrons available for chemical reactions. A high reading indicates an oxidizing environment with few transferable electrons, whereas a low reading denotes a reducing environment rich in transferable electrons.

Why is dissolved oxygen ($\text{O}_2$) considered the master variable controlling redox potential in aquatic systems?

Due to its high affinity for electrons; when $\text{O}_2$ is abundant, redox potential remains high, limiting electron availability and preventing most reduction reactions from proceeding spontaneously.

How does redox state affect iron solubility in natural waters?

Under high $\text{O}_2$ and oxidizing conditions, iron is oxidized to ferric iron ($\text{Fe}^{3+}$), which precipitates out of solution; under low $\text{O}_2$ and reducing conditions, it is reduced to soluble ferrous iron ($\text{Fe}^{2+}$).

What physical factors determine the saturation concentration of dissolved oxygen in water?

Temperature (lower temperatures increase solubility), atmospheric pressure (higher pressure increases solubility), and dissolved solute content (higher solute concentrations decrease solubility).

How are Net Primary Production (NPP) and Gross Primary Production (GPP) related mathematically?

$\text{NPP} = \text{GPP} - \text{Respiration}$.

What do the compensation point and $P_{\max}$ represent on the provided Photosynthesis–Irradiance (P-I) curve?

The compensation point is the irradiance where gross photosynthetic rate equals the respiration rate (net photosynthesis is $0$), and $P_{\max}$ is the maximum attainable rate of photosynthesis before photoinhibition occurs.

Why does increased water velocity increase the rate of photosynthesis in aquatic primary producers?

Faster water movement thins the stagnant diffusion boundary layer adjacent to photosynthetic surfaces, accelerating the diffusion rate of $\text{CO}_2$ into the cells.

What equation models the relationship between environmental temperature and respiration rate?

The Van't Hoff-Arrhenius equation: $R = e^{-E/(kT)}$, where $R$ is the metabolic rate, $E$ is activation energy, $k$ is Boltzmann's constant, and $T$ is absolute temperature in Kelvin.

What was the atmospheric $\text{CO}_2$ concentration recorded in Hawaii in 2013?

$400\,\text{ppm}$.

What four chemical forms constitute total dissolved inorganic carbon ($\sum \text{CO}_2$)?

Dissolved carbon dioxide ($\text{CO}_2$), carbonic acid ($\text{H}_2\text{CO}_3$), bicarbonate ($\text{HCO}_3^-$), and carbonate ($\text{CO}_3^{2-}$).

According to the provided carbonate system graph, which dissolved inorganic carbon form dominates at neutral pH values between $7$ and $9$?

Bicarbonate ($\text{HCO}_3^-$).

How are fine particulate organic matter (FPOM) and coarse particulate organic matter (CPOM) categorized by size?

FPOM consists of particles between $0.45\,\mu\text{m}$ and $1.0\,\text{mm}$, whereas CPOM consists of particles greater than $1.0\,\text{mm}$.

What does Biochemical Oxygen Demand (BOD) measure?

The total amount of oxygen required by biological and chemical oxidative processes to break down organic matter in a water sample.

How do humic acids, fulvic acids, and humin differ in chemical solubility?

Humic acids dissolve in alkaline solutions and precipitate in acidic solutions; fulvic acids remain soluble across both acidic and basic solutions; humin is insoluble in both acids and bases.

In what order are terminal electron acceptors utilized for oxidizing organic carbon as redox potential drops?

Oxygen ($\text{O}_2$) is used first, followed by nitrate ($\text{NO}_3^-$), manganese(IV) oxide ($\text{Mn}^{4+}$), ferric iron ($\text{Fe}^{3+}$), sulfate ($\text{SO}_4^{2-}$), and finally carbon dioxide ($\text{CO}_2$) in methanogenesis.

Based on the provided Winogradsky column zonation diagram, which groups of anaerobic photosynthetic bacteria develop below heterotrophic and iron-oxidizing zones?

Purple non-sulfur bacteria, purple sulfur bacteria, and green sulfur bacteria.

Why does organic matter degradation eventually cease in anoxic fermentation environments like peat bogs?

Fermentation releases organic acids that progressively lower the pH; high acidity suppresses microbial activity until decomposition stops completely, causing organic peat to accumulate.

What is the ecological function of methanotrophic bacteria?

They oxidize and metabolize methane into $\text{CO}_2$, preventing excessive release and atmospheric buildup of methane.

What chemical transformation occurs during the disproportionation of acetate?

Acetate is cleaved under anoxic conditions into methane ($\text{CH}_4$) and carbon dioxide ($\text{CO}_2$) by acetoclastic methanogens.

What is the conceptual difference between nutrient assimilation and remineralization?

Assimilation is the biological incorporation of inorganic nutrients into organic molecules, whereas remineralization (regeneration) is the breakdown and release of organic compounds back into inorganic forms.