Limnology: food web

Course Logistics and Administrative Reminders

• Upcoming Deadlines: Boards and papers are due today for all students who have not yet submitted them.

• Monday Reading Assignment: The class will discuss a paper by Mike Bogan. He is associated with the University of Arizona in Tucson (correcting the initial mention of Arizona State).

• Paper Subject Matter: The research investigates how invertebrates recover following restoration projects and in streams that undergo drying. This topic is noted for its high applicability to the Rio Grande system.

• Course Evaluations: Feedback is highly prioritized by the instructor. The deadline for completion is Friday, the $8\text{th}$.

• Incentive Structure:     * Current participation as of the lecture is $4$ out of $30$ students, representing a $13\%$ response rate.     * If the response rate reaches $75\%$ by next Friday, the instructor will provide donuts or bagels for the class.

Definition and Goals of Bioassessment

• Core Definition: Bioassessment is a methodology used to determine water quality and ecosystem health. This is achieved by monitoring three key categories of data:     * Indicator Organisms: Monitoring the presence, absence, and health of specific biological taxa.     * Freshwater Chemical Properties: Identifying chemical concentrations and imbalances.     * Environmental Physical Properties: Assessing the structural habitat of the stream.

• Primary Purpose: By synthesizing data from these three groups, researchers determine if a stream is impaired and identify the specific stressors causing the impairment.

• Regulatory Context: Bioassessment was developed as a tool in the $1970\text{s}$ to assist regulators in determining if water bodies were compliant with the Clean Water Act.

• Key Questions Answered by Bioassessment:     * Is the water body in the desired biological condition? (Conditions that support the maximum possible aquatic life).     * Does the water quality meet established Clean Water Act standards?     * If the stream is impaired, how severe is the degradation?     * What specific stressors are resulting in the observed biological impairment?

The Role of Reference Conditions and Comparisons

• Comparative Process: Bioassessment relies on comparing the current biological state of a stream to a "reference condition."

• Reference Condition Definition: An aggregate of conditions found in unimpaired streams within a specific geographic region.

• Establishment of Reference States: Scientists identify reference conditions by sampling numerous streams in a region to define the "optimal biological potential." This includes establishing specific thresholds for chemical, physical, and biological integrity.

• Detection of Alteration: If a stream's biological condition differs from the reference condition, it is considered altered. Observations of surrounding habitat and chemical data then help determine whether chemical contamination or physical degradation is the root cause.

Stressors and Stressor Sources in Aquatic Systems

• Stressor Definition: Any human-induced or natural agent that limits the biological capacity for survival and reproduction in a system.

• Stressor Source Definition: The specific human activity or the result of human activity that creates or releases a stressor.

• Stressor-Source Relationships:     * Agriculture: Acts as a source for stressors such as pesticides, nutrients, or pathogens derived from manure.     * Municipalities/Towns: Act as a source for nutrient stressors typically found in wastewater.

• Leading Stressors in US Rivers (based on $2004$ data):     * Pathogens (identified as the leading stressor).     * Metals.     * Sediments.     * Nutrients.     * Low dissolved oxygen.     * Temperature extremes.     * Presence of non-native species.     * Flow alterations (e.g., controlled flows from dams vs. natural flows).     * Degraded physical habitat.

• Leading Stressor Sources (based on $2004$ data):     * Agriculture: Impaired approximately $37\%$ of US rivers.     * Hydromodifications: Includes dams and other water containers.     * Other sources include riparian degradation, watershed degradation, grazing, mining, municipal waste, and industrial contamination.

Biological Indicator Patterns and Responses

• Diagnostic Patterns: Observing shifts in biology can point researchers toward specific chemical or physical causes.

• Shredder Populations: A decrease in shredders suggests a change in habitat structure, such as a reduction in coarse particulate organic matter ($CPOM$) entering the stream (e.g., due to fire).

• Lake Lines/Mayflies: A decrease in these organisms suggests a change in water quality or toxicity, such as an influx of nutrients or toxins.

• Native Species Loss: A loss of native species combined with the entry of invasive species may signal biotic interaction stressors, often triggered by changes in water temperature or available food sources.

Classification of Bioassessment Approaches

• Organism Approach: Focuses on the presence or absence of specific individuals to signal water quality.

• Population Approach: Examines changes in the total count of organisms following a disturbance (population increases or decreases).

• Community Approach: Analyzes changes in community composition. A common metric is the dominance of $EPT$ taxa versus high-tolerance taxa.

• Ecosystem Approach: Measures changes in ecosystem processes and functions, such as nutrient cycles, after a disturbance.

Characteristics of Indicator Organisms and Communities

• Qualities of a Good Indicator: An organism whose unique characteristics correlate strongly with a degree of pollution or a specific point on an environmental gradient.

• Environmental Gradients and Diversity:     * $pH$ and Dissolved Oxygen: Bio-diversity of macroinvertebrates is highest at the mid-ranges of these gradients.     * Chloride and Turbidity: Diversity is highest at the low ranges of these gradients.

Methodologies for Monitoring Specific Biological Groups

• Algae Collection Methods:     * Phytoplankton: Collected using a net in the water column (as demonstrated at the duck path). Biomass is measured over a volume of water.     * Benthic Algae/Biofilm: Collected using a "turkey baster" suction tool (cost: $\$2.49$). Algae are sucked from a known sediment area and analyzed for biomass per unit area using "ash-free dryness."

• Algae Metrics:     * Chlorophyll a: Used to measure total algal biomass.     * Composition Metrics: Identifying orders, genera, and species.     * Growth Forms: Identifying if algae are colonial, filamentous, floating, or attached.     * Bio-volume: Measuring the physical volume occupied by specific algal types.     * Diversity/Similarity: Analyzing community similarity metrics.

• Macroinvertebrate Collection Methods:     * Kick Net: Used on cobble-bottom stream beds.     * Sieving: Required in sediment-bottom streams to separate organisms from the substrate.     * Throw Trap: A mesh-sided square with no top or bottom. It is placed on the substrate to prevent organisms from escaping during collection.

Macroinvertebrate Metrics and Disturbance Levels

• Key Metrics:     * Taxonomic Richness: The total number of different taxa in a sample.     * Taxonomic Composition: Measuring the dominance of $EPT$ taxa ($Ephemeroptera, Plecoptera, Trichoptera$). High proportions of $EPT$ indicate good water quality as these taxa typically have low tolerance for contaminants.     * Functional Feeding Groups: Categorizing based on roles (e.g., shredders, filtering collectors).     * Habit: Categorizing behavior (e.g., sprawlers, clingers, swimmers).     * Tolerance: Assessing the proportion of highly tolerant, intermediate, or low-tolerance taxa.

• Response to Disturbance Levels:     * Minimally Disturbed (e.g., Forested Watershed): Dominance of $EPT$ taxa; some intermediate and high-tolerance taxa may be present as they can survive nearly anywhere.     * Moderately Disturbed (e.g., Downstream of a Fish Hatchery): Increased proportions of intermediate and high-tolerance taxa. In some cases, $EPT$ numbers may actually increase if the disturbance (stressor) increases available food, but overall diversity shifts.     * Heavily Disturbed (e.g., Cow Pasture): Very low or zero $EPT$ richness. High dominance of intermediate and highly tolerant taxa such as snails, leeches, or midges.

Fish Bioassessment and Abundance Metrics

• Indicator Strengths: Fish respond well to nutrient contamination, toxins, organic pollutants, and habitat alterations affecting temperature.

• Collection Methods: Seining (large nets pulled through water) and electroshocking.

• Key Metrics:     * Taxa Richness/Composition: Presence of cold water vs. warm water taxa; native vs. invasive/introduced species.     * Trophic Composition: Ratios of omnivores, predators, and herbivores.     * Abundance (Catch Per Unit Effort - $CPUE$): Measured as fish caught per visit or per hour.     * Measurement Rational: Fish abundance is not measured by area (individuals per unit area) because fish are highly mobile; time-based metrics are more accurate for density assessments.     * Condition Metrics: Physical assessment of health, including counts of tumors, lesions, anomalies, and diseases.

Comparative Efficacy of Bioassessment Groups

• Multi-Taxa Recommendation: The EPA recommends using multiple groups (e.g., fish and algae) rather than a single indicator.

• Practical Constraints:     * Cost: Fish assessments are expensive due to the need for specialists (e.g., professional snorkelers or electroshocking teams).     * Expertise: Identification of species and physical health markers (like tumors) requires specialized training.     * Metric Availability: Some regions lack specific indices. For example, New Mexico currently only has an Index of Biotic Integrity for macroinvertebrates, lacking one for zooplankton.     * Case Specificity: Certain indicators are better for specific stressors; diatoms (algae) are particularly responsive to contaminants in fracking areas.

Functional Bioassessment at the Ecosystem Level

• Defining Function: Monitoring the processes that transfer energy, carbon, and light through the system.

• Key Functional Metrics:     * Nutrient cycling changes.     * Decomposition rates.     * Ecosystem metabolism.     * Primary and secondary productivity.

Indices of Biotic Integrity (IBI)

• Definition: A tool designed for the scientific evaluation of water quality that incorporates multiple metrics to calculate a single index number.

• Reference Comparison: The index score is compared against the optimal score of a regional reference site. Results are often expressed as a percentage of the reference condition.

• Regional Specificity: There is no universal IBI. Indices must be developed using local regional reference conditions.

• Example Fish IBI Scores:     * $49+$: Exceptional aquatic life.     * $41 \text{ to } 48$: High levels of aquatic life (e.g., site score of $45$).