aqatic exam.docx

Bio 370 – Practice questions – Exam 2

Think of these questions as the large topics that we have gone over in class. I will ask much more specific questions on the test. Many of the questions will come from these topics. Realize this is meant to help you study. Not as a complete preparation for the test. Just answering the questions won’t completely prepare you for the test. Look at the question, determine the greater context of what is being asked, answer the question, then look at what was left out. This should help you prepare.

What are the problems with Strahler stream ordering?

because the Strahler stream order is roughly correlated with stream discharge which is the amount of water flowing down a river. but the problem with this is that some rivers may be classed incorrectly because if may have a very high discharge but is not really that big of a river. it also has nothing to do with river size which can mean a short river is classed higher than a longer river

With what does stream discharge vary?

Precipitation: More rain or snow increases discharge, while dry conditions lower it.

Season: Discharge often peaks during rainy seasons or spring snowmelt and drops during dry periods.

Watershed Size and Shape: Larger or more efficiently shaped watersheds can collect and deliver more water to streams.

Topography: Steeper terrain causes faster runoff, increasing discharge quickly after precipitation events.

Soil and Rock Permeability: If the ground absorbs water easily (permeable), less runoff reaches the stream, lowering discharge.

Vegetation: Plants absorb water, so heavily vegetated areas may reduce discharge, while deforested areas can increase it.

Human Activities: Urbanization (more pavement = more runoff), dam construction, irrigation, and water withdrawals can all affect stream discharge.

Temperature: Warmer temperatures can melt snow and ice, increasing discharge, or cause more evaporation, reducing it.

What are the major characteristics of the different river channel patterns?

• Comparison across river sites
• Ecology more similar in same pattern type vs. proximity

Substrate

• Bedrock
• Colluvial 
• Alluvial

Determinants of channel pattern

• Slope
• Discharge
• Sediment load

Meandering river 

• Single channel 
• Fine sediments
• Large alluvial plains
• Low slope 
• River course changes on decadal scales

Anastomosing river

• Multiple semi-permanent channels 
• Lower discharge and slope and finer sediments than meandering
• Channels change on century/multidecadal scale

Constrained/constricted river 

• bedrock/valley rivers 
• Naturally constrained 
• little/no floodplain
  • Floods dangerous/scouring
• Leveed rivers

Braided river

• Many temporary channels 
• Change course daily
• Steep, high discharge
• Large sediment load 
  • gravel/sand
• Harsh environment 
• Little habitat predictability

Straight river

• Very difficult to find 
• May not actually be a river type 
• Meandering river at a given time

What does a hydrograph tell us about a river? How are they constructed?

A hydrograph is a graph that shows how a river's discharge changes over time—usually in response to a rainfall event. It tells us a lot about how a river and its surrounding landscape respond to precipitation.

What a Hydrograph Tells Us:

1. Peak Discharge: The highest flow after a rainfall event—helps predict flood risk.
2. Lag Time: Time between peak rainfall and peak discharge—short lag = flashier flooding.
3. Rising Limb: How quickly the river level rises after rain starts.
4. Falling Limb: How slowly or quickly the river returns to normal flow.
5. Base Flow: The normal day-to-day discharge of the river from groundwater or previous rainfall.

Hydrographs help us understand:

• Flood potential and timing
• Watershed characteristics (urban vs. rural, forested vs. deforested)
• Impact of land use or climate change

How Hydrographs Are Constructed:

1. Rainfall Data Collection: Using rain gauges spread across a watershed.
2. Streamflow Monitoring: Gauging stations measure river discharge over time.
3. Time-Series Graphing:
   • X-axis: Time (hours or days)
   • Y-axis: Discharge (cubic meters per second, cfs, etc.)
   • Optionally, rainfall can be shown as a bar chart overlay to relate rain to discharge.

What is a flow duration curve? How can they be used for management purposes?

What Is a Flow Duration Curve?

• It's a graph that plots discharge (flow rate) on the Y-axis against the percent of time that flow is equaled or exceeded on the X-axis.
• The left side of the curve shows high flows (e.g., flood events, exceeded only a small % of time).
• The right side represents low flows (base flows, exceeded most of the time).

Example:
A value at 10% on the curve means that flow was equaled or exceeded 10% of the time (i.e., high flow), while a value at 90% represents low flow, exceeded most of the time.

How Are Flow Duration Curves Made?

1. Gather streamflow data over a long time (daily, monthly, etc.).
2. Rank the flows from highest to lowest.
3. Calculate the exceedance probability for each flow:

P=mn+1P = \frac{m}{n + 1}P=n+1m​

where:

• • PPP = exceedance probability
  • mmm = rank of the flow
  • nnn = total number of observations

1. Plot the flow values against their exceedance probabilities.

Uses for Management:

1. Hydropower Planning: Helps estimate reliable water supply for energy generation.
2. Water Supply Design: Determines how much flow is available for domestic, industrial, or irrigation use over time.
3. Environmental Flow Assessment: Ensures enough water remains in rivers for ecosystems during low-flow periods.
4. Flood Management: Understands frequency and magnitude of high flows.
5. Reservoir Operations: Guides when to store or release water.
6. Drought Planning: Identifies typical low-flow conditions and water scarcity risks.

What alters flow regimes? What are the consequences?

A flow regime is the pattern of streamflow variation over time—daily, seasonally, and yearly. It’s like the river’s natural rhythm. Several factors can alter this rhythm, and those changes can have big consequences for ecosystems, people, and water infrastructure.

What Alters Flow Regimes?

1. Climate Change
   • Alters precipitation patterns and snowmelt timing
   • Increases evaporation due to higher temps
2. Dams and Reservoirs
   • Store water and release it unnaturally (often for power, irrigation, flood control)
   • Flatten seasonal peaks and create sudden surges
3. Urbanization
   • Impervious surfaces (like pavement) increase runoff
   • Flashier flow: more frequent floods, less infiltration = lower base flows
4. Deforestation or Land-Use Change
   • Less vegetation = more runoff, less water stored in soil
   • Can increase erosion and reduce water quality
5. Water Withdrawals (Irrigation, Industry, etc.)
   • Reduce downstream flows, especially during dry periods
6. Channel Modification (e.g., straightening, dredging)
   • Speeds up flow, changes sediment transport, affects timing
7. Mining or Extractive Industries
   • Can contaminate water and physically disrupt natural flow

Consequences of Altered Flow Regimes:

1. Ecological Impacts
   • Fish and aquatic species rely on seasonal flows for spawning, feeding, and migration
   • Disruption can lead to loss of biodiversity
   • Wetlands may dry out or flood too often
2. Water Quality Problems
   • Lower flows = less dilution of pollutants
   • Faster runoff can carry more sediments and toxins
3. Increased Flood Risk
   • Urbanization and deforestation can lead to flash floods
4. Drought Stress
   • Artificial withdrawals or climate shifts can lower base flow, stressing human and ecological systems
5. Changes to Sediment Transport
   • Dams trap sediment → downstream erosion
   • Altered flows can cause either sediment starvation or overload
6. Conflict Over Water Use
   • Especially where demand is high and supply becomes less predictable (e.g., agriculture vs. ecosystems vs. cities)

Discuss the consequences of dynamic equilibrium in the context of fluvial geomorphology.

dynamic equilibrium is at the heart of fluvial geomorphology, which is all about how rivers shape and are shaped by the landscape.

What Is Dynamic Equilibrium in Rivers?

In fluvial geomorphology, dynamic equilibrium refers to a state where a river system balances the inputs (like water and sediment) with the outputs, maintaining a relatively stable shape and flow over time—despite constant change.

The river is always adjusting but stays within a certain range of form and behavior. It’s like walking on a tightrope—you’re constantly making micro-adjustments to stay balanced.

What Happens When This Balance Is Disrupted?

When the equilibrium is thrown off—by natural or human causes—the river responds. That response is where the consequences come in:

Consequences of Disrupted Dynamic Equilibrium

1. Channel Incision (Downcutting)

• Cause: Reduced sediment supply (e.g. due to a dam) or increased flow velocity
• Effect: River cuts deeper into its bed, lowering the water table and disconnecting from its floodplain
• Consequence: Loss of wetlands, groundwater recharge, and floodplain habitat

2. Aggradation (Sediment Build-up)

• Cause: Increased sediment input (e.g. from deforestation, landslides, mining)
• Effect: Riverbed rises, making flooding more likely
• Consequence: Risk to infrastructure, farmland, and human settlements

3. Bank Erosion & Lateral Migration

• Cause: Changes in flow of energy or sediment transport
• Effect: River starts meandering more or eroding banks rapidly
• Consequence: Land loss, damaged property, and infrastructure

4. Channel Instability

• Cause: Over-widening, straightening, or other modifications
• Effect: The river may braid, avulse (change course suddenly), or become unstable
• Consequence: Harder to manage or predict; ecological degradation

5. Loss of Habitat Complexity

• Cause: Loss of equilibrium flattens flow regimes and channel forms
• Effect: Homogeneous habitat conditions (e.g., no pools or riffles)
• Consequence: Decline in aquatic biodiversity

Human Context—Why It Matters:

• Engineers and planners must understand dynamic equilibrium to design sustainable river interventions (e.g., bridges, levees, restoration projects).
• Restoring equilibrium is often a goal in river restoration, aiming to reconnect the river with its floodplain, restore sediment balance, and support natural processes.

How does water flow down the course of a river?

Water flows down the course of a river in a dynamic and evolving way, shaped by gravity, landscape, geology, and the river’s own energy. As a river moves from its source to its mouth, the flow characteristics—speed, volume, shape, and erosive power—change noticeably.

Upper Course (Source Area)

• Steep gradient
• Low discharge (not much water yet)
• Turbulent, fast-flowing water over rocks and boulders
• Vertical erosion dominates (deepening the channel)
• Create features like:
  • V-shaped valleys
  • Waterfalls
  • Rapids
  • Interlocking spurs

Water flows in a rough, energetic way here, carving down into the landscape.

Middle Course

• Gradient decreases, but still sloping
• Increased discharge as tributaries join
• Lateral erosion increases (widening the channel)
• Flow becomes smoother and more efficient
• Create features like:
  • Meanders
  • Wider floodplains
  • River cliffs and slip-off slopes

Water starts to “wander” more, carving side-to-side as energy is split between erosion and transport.

Lower Course (Near the Mouth)

• Very gentle gradient
• High discharge due to many tributaries
• Slow, smooth flow in a wide, deep channel
• Deposition dominates as energy decreases
• Creates features like:
  • Oxbow lakes
  • Levees
  • Deltas
  • Floodplains

The river becomes lazy and loaded with sediment, dropping much of it as it nears the sea or a lake.

Along the Way:

• Erosion (wearing away rock/soil)
• Transportation (carrying sediment: solution, suspension, saltation, traction)
• Deposition (dropping sediment when energy is lost)

Which types of sediments get eroded and transported when/how?

the core of how rivers shape landscapes and move materials from mountains to the sea. Sediment transport depends on the energy of the water, particle size, and flow velocity. Different types of sediments are eroded and transported in different ways.

How Sediment Is Eroded

Rivers erode sediment through several key processes:

1. Hydraulic Action:
   • The force of water hitting riverbanks and beds loosens material (especially in fast-flowing water).
2. Abrasion (Corrasion):
   • Sediment already in the water scrapes and wears away the channel, like sandpaper.
3. Attrition:
   • Rocks and sediment knock into each other, breaking into smaller, rounder pieces.
4. Solution (Corrosion):
   • Minerals in the rock (e.g. limestone) dissolve in slightly acidic river water.

How Sediment Is Transported

Rivers move sediment in four main ways, depending on particle size and river energy:

Which Sediments Move When?

River Energy Matters:

• High energy = more erosion and transport of larger particles
• Low energy = deposition of heavier materials
• When energy drops (e.g., when slope flattens or river enters a lake/sea), the river starts depositing from largest to smallest particles.

How does stream water chemistry differ from lakes?

stream water and lake water may both be “freshwater,” but they differ significantly in chemistry due to their movement, sources, residence time, and interaction with the landscape.

Here’s a breakdown of how and why they differ:

Key Differences in Stream water vs. Lake water Chemistry

Why These Differences Matter

1. Residence Time:
   • Streams: Days to weeks → less time for chemical reactions or nutrient buildup.
   • Lakes: Weeks to years → more time for biological processes and chemical changes.
2. Oxygen:
   • Streams: More oxygen from turbulence.
   • Lakes: Stratification can lead to anoxic (no oxygen) conditions at the bottom, affecting nutrient cycling and fish habitat.
3. Nutrient Cycling:
   • Streams: Nutrients often flushed downstream.
   • Lakes: Nutrients can settle, recycle from sediments (especially phosphorus), and trigger eutrophication.
4. Stratification & Mixing:
   • Streams: Constant mixing = uniform chemistry.
   • Lakes: Layers develop, especially in summer, leading to very different chemical conditions at the surface vs. bottom.
5. Sensitivity to Pollution:
   • Streams: More “self-cleansing” due to flow, but vulnerable to pulse pollution (e.g., after storms).
   • Lakes: Can trap and accumulate pollutants, making recovery slower.

Real-World Implications

• Stream management focuses on erosion control, stormwater runoff, and rapid pollution events.
• Lake management often deals with long-term nutrient loading, algal blooms, and internal cycling of nutrients from sediments.

What does water extraction do to the flow/chemistry of a river?

Water extraction, whether for agriculture, industry, or domestic use—can significantly alter both the flow and chemistry of a river. The effects depend on how much water is taken, when it's taken, and what other environmental factors are at play (like climate or land use).

Effects on River Flow (Hydrology)

1. Reduced Discharge
   • Less water in the river = lower flow rates
   • Can change the river from a perennial to an intermittent or even dry stream in extreme cases
2. Altered Flow Regimes
   • Changes the natural variability of high and low flows
   • Can flatten seasonal peaks, harming species adapted to flow pulses (like spawning fish)
3. Increased Flow Variability
   • Some systems experience irregular surges when water is suddenly released from upstream reservoirs or returned from irrigation
4. Reduced Connectivity
   • Lower flows can disconnect tributaries, floodplains, and wetlands, which are vital for biodiversity and natural flood management

Effects on River Chemistry

1. Concentration of Pollutants
   • Less water = less dilution of nutrients, heavy metals, and other pollutants
   • Higher concentrations can lead to toxic conditions, especially in warm weather
2. Temperature Increase
   • Shallower water heats up faster → lower oxygen levels
   • Warmer water can change species composition and boost algal blooms
3. Changes in Nutrient Cycling
   • Slower flow means more time for nutrients like nitrogen and phosphorus to accumulate, sometimes leading to eutrophication
4. Salinization
   • In arid regions or where groundwater is over-pumped, rivers can become salty due to poor flushing or return flows from irrigation
5. Altered pH and Mineral Balance
   • If extraction affects groundwater inflow, it can change the carbonate buffering system, affecting pH and overall chemical balance

Consequences for Ecosystems and People

• Fish and aquatic life: Many species depend on specific flow levels or timing for spawning/migration
• Riparian vegetation: Reduced flows can dry out floodplain ecosystems
• Water quality: Less flow = greater vulnerability to pollution spikes
• Downstream users: Communities or ecosystems downstream may face water shortages or degraded quality

Example: The Colorado River

Due to heavy extraction for agriculture and urban use, the Colorado River now often fails to reach the sea, its flow is heavily regulated, and salinity is a major issue in the lower basin.

How do organisms of differing sizes deal with the water flow in streams and rivers?

Water flow is a powerful force, and organisms in streams and rivers have evolved all kinds of clever ways to cope with it, depending on their size, mobility, and body structure. Let’s break it down by organism size and type:

Small Organisms (Micro- and Macroinvertebrates)

These include things like insects (mayflies, caddisflies), worms, small crustaceans, and larvae.

How they deal with flow:

• Flattened Bodies: Reduces drag (e.g., stoneflies).
• Clinging Structures: Hooks, suction cups, silk threads (e.g., blackfly larvae stick with silk pads).
• Live Under Rocks or in Sediment: To avoid strong currents.
• Build Shelters: Caddisflies build cases from pebbles, wood, or sand to anchor themselves.
• Drift During High Flow: Some let go and ride the current when flow is too strong, then resettle downstream.

Medium-Sized Organisms (Fish)

Different species use different flow zones (riffles, pools, etc.) depending on their strength and needs.

How they deal with flow:

• Streamlined Bodies: Reduces resistance (e.g., trout, salmon).
• Strong Musculature: For active swimming and holding position in current.
• Use of Shelter: Hide behind rocks, logs, or undercut banks to rest.
• Specialized Fins: Pectoral fins help stabilize and “grip” the streambed in some benthic fish.
• Behavioral Adaptations: May feed in low-flow zones or during lower-flow times of day.

Large Organisms (Amphibians, Reptiles, Birds, Mammals)

Less directly affected by the velocity of small-scale flows, but still adapt in broader ways.

How they deal with flow:

• Use of Slower Waters: Frogs, turtles, and waterfowl tend to stay in pools, eddies, or river margins.
• Nest or Den Site Selection: Away from flood-prone areas (e.g., otters, beavers).
• Behavioral Timing: Some species only enter the water during calm conditions or seasons.

Sessile Organisms (e.g., Algae, Mosses, Freshwater Sponges)

They can't move—so they evolve structural or anchoring solutions.

How they deal with flow:

• Strong Attachment Structures: Algae may grow close to the substrate or produce mucilage.
• Flexible Structures: Bendy stems or filaments that move with the flow.
• Microhabitats: Grow in crevices, behind rocks, or in low-flow areas.

General Patterns:

Flow Matters Because:

• It determines who lives where (riffle vs. pool habitats)
• It affects oxygen, temperature, and nutrient delivery
• It controls how organisms feed, reproduce, and move

What are the main determinants of riverine ecology in the context of flow/flood pulse predictability?

The predictability of flow and flood pulses plays a critical role in shaping riverine ecology. River ecosystems have evolved in response to the timing, frequency, and magnitude of flow fluctuations. These flow patterns influence everything from species distribution to food availability and reproductive strategies.

1. Flow Variability and Timing

• Seasonal Flow Variability:
  Many species rely on predictable seasonal changes in river flow for reproduction, migration, and feeding. For example:
  • Fish species like salmon time their spawning to coincide with higher flows, ensuring their eggs are deposited in well-oxygenated gravel beds.
  • Floodplain ecosystems depend on flood events to provide nutrients and moisture, especially in seasonal wetlands.
• High-Flow vs. Low-Flow Periods:
  Species are adapted to different phases of the flow cycle:
  • High flows can lead to increased habitat availability by inundating floodplains and creating new aquatic habitats.
  • Low flows typically lead to more stable, predictable conditions in river channels, allowing organisms to establish more permanent habitats.

2. Flood Pulse and Habitat Creation

• Flood Pulse:
  The flood pulse concept (introduced by Junk et al.) explains how floods not only shape river morphology but also drive ecological processes in riverine systems. Floods bring:
  • Nutrient enrichment to floodplains and wetlands, supporting high biodiversity.
  • Disturbance events, which reset ecosystems and maintain diversity by preventing the dominance of any single species.

These flood pulses are especially crucial for:

• • Migratory fish that use floodplain habitats during high flows.
  • Floodplain plants, which need to be inundated for growth or seed dispersal.
• Floodplain Connectivity:
  Flood pulses create a connection between the river and its floodplain, allowing organisms to move between the river, floodplain, and back. This supports species diversity, increases food availability, and provides breeding grounds.

3. Species Adaptations to Flow and Flood Predictability

• Timing of Reproduction:
  Organisms like fish, amphibians, and insects have evolved reproductive strategies that align with predictable flow and flood patterns. For example:
  • Fish may spawn just before or during peak flow to maximize the chance of offspring survival, as higher water velocities can flush larvae into less hazardous habitats.
  • Floodplain plants time their germination to coincide with the wet season or a specific flood event.
• Life Cycle and Migration Patterns:
  Some species, such as migratory fish (e.g., salmon, eels), depend on the predictability of flow for migration. They time their journeys based on flood or low-flow periods to ensure proper conditions for breeding, food, and shelter.

4. Water Quality and Sediment Transport

• Sediment Transport:
  The flood pulse influences sediment dynamics in rivers. Regular floods can help:
  • Create new habitats by depositing fresh sediment on the floodplain.
  • Shape river channels, providing new microhabitats for species.
• Water Quality:
  High flow events can reduce the concentration of pollutants by diluting contaminants, whereas low flow periods can lead to increased concentration of pollutants due to reduced water volume. Predictable flow patterns allow organisms to adapt to these water quality changes, but unpredictable flow can cause stress on ecosystems, especially when pollution spikes.

5. Resilience and Ecological Stability

• Predictable Flow Cycles and Ecosystem Resilience:
  Riverine ecosystems that experience predictable flow and flood pulses are typically more resilient. Regular flooding can prevent the establishment of invasive species, reset ecological processes, and create stable, dynamic habitats. On the other hand, unpredictable or reduced flooding can cause:
  • Habitat loss or fragmentation.
  • Loss of species adapted to regular flow pulses.
• Disruption of Flow Cycles:
  Human activities, such as dam construction, water extraction, and land-use change, can disrupt natural flow regimes. This unpredictability can destabilize ecosystems by altering the timing, magnitude, and frequency of floods. For example:
  • Dams may prevent seasonal floods from reaching floodplains, reducing nutrient flow and disrupting breeding cycles for fish.
  • Flow regulation for irrigation may lead to unseasonal water flow, impacting species dependent on specific conditions.

Summary: Key Determinants of Riverine Ecology in Relation to Flow/Flood Predictability

Implications of Flow/Flood Unpredictability:

• Reduced biodiversity: Many species thrive only in predictable flood cycles.
• Loss of habitat: Floodplains and wetlands may become disconnected from rivers.
• Changes in species composition: Some species may benefit, while others struggle to adapt.

When do invertebrates drift? Why? Consequences?

Invertebrate drifting refers to the passive movement of small organisms (like insects, crustaceans, and larvae) downstream with the current, which can be triggered by various factors. Drifting is a common behavior in many riverine species, and it’s often influenced by environmental conditions, life cycle stages, and behavioral triggers.

When Do Invertebrates Drift?

1. Life Cycle Stages
   • Larvae and Juveniles: Many aquatic insects (such as mayflies, caddisflies, and stoneflies) drift as part of their larval or juvenile stage. This can be part of their developmental process when they are moving to new habitats or settling in areas that are better suited for their growth.
   • Adults: In some species, adult emergence (such as when caddisflies or mayflies leave the water to mate) can cause drifting as they are swept downstream before they can fly.
2. Environmental Triggers
   • High Flow or Flood Events: During high water events (such as heavy rainfall or spring floods), invertebrates are more likely to be dislodged and carried downstream. The increased velocity and turbulence of the water makes it harder for these organisms to maintain their position.
   • Predation or Disturbance: Some invertebrates may drift to escape predation or avoid other disturbances like habitat changes (e.g., pollution or changes in substrate).
   • Temperature and Oxygen Changes: If a river experiences dramatic changes in temperature or oxygen levels (for example, during droughts or during the night when oxygen levels can drop), organisms may drift in search of more favorable conditions.
3. Resource Availability
   • Food Shortages: Invertebrates may drift to find more abundant food sources if their current environment becomes depleted or overgrazed.
   • Reproductive Timing: Certain species might drift during peak reproductive periods, either to spread their offspring to new areas or to find mates.

Why Do Invertebrates Drift?

1. Dispersal
   • Drifting helps invertebrates colonize new areas of the river or floodplain. By dispersing downstream, species can expand their range and find suitable environments for feeding and reproduction.
2. Escape from Unfavorable Conditions
   • Drifting can be a strategy to escape unfavorable water quality conditions, such as low oxygen levels, pollution, or extreme temperatures. By drifting to a different part of the river, they may find more favorable conditions.
3. Life Cycle Requirements
   • In some species, drifting is a key part of their life cycle, helping to move through different developmental stages. For example, larvae may drift to settle in areas with suitable substrates for pupal development.
4. Predator Avoidance
   • Some species drift as a defense mechanism to avoid predators. Being swept downstream can move them out of the predatory zone or into areas with lower predation risk.

Consequences of Invertebrate Drifting

1. Ecological Disruption
   • Dispersal to New Areas: Drifting can help colonize new habitats, but it can also spread invasive species. For example, non-native species can use drifting to reach new ecosystems, potentially outcompeting native species.
2. Impacts on Food Webs
   • Loss of Biomass: If invertebrates drift away from an area where they are a key food source for higher organisms, predators (like fish and birds) may suffer due to a reduction in available prey.
   • Changes in Community Structure: High rates of drifting may alter the species composition in particular river segments, leading to an imbalance in the ecosystem.
3. Pollution and Habitat Loss
   • Accidental Dispersal of Pollutants: If invertebrates drift through contaminated areas, they can carry pollutants (like toxins or nutrients) downstream, potentially affecting ecosystems in new areas.
4. Energy and Resources
   • Energy Expenditure: Drifting downstream requires energy expenditure for organisms to maintain position, even if it’s passive movement. If they’re moved too far downstream, it can become difficult for them to find food or suitable habitats, especially if they end up in areas with low food availability.
5. Species Reproduction and Survival
   • If drifting disrupts the timing or location of species' reproductive cycles, it could affect their success in breeding or finding suitable sites for offspring development (e.g., for species like mayflies or caddisflies).

In Summary: When and Why Invertebrates Drift, and the Consequences

What limits/allows periphyton to grow in a fluvial system?

Periphyton (the complex community of microalgae, bacteria, fungi, and other microorganisms) that grows on submerged surfaces in aquatic environments plays a vital role in riverine ecosystems. Its growth, distribution, and health are influenced by a variety of environmental and ecological factors. Let's explore the limits and allowances of periphyton growth in fluvial (river) systems.

Factors That Allow Periphyton to Grow

1. Light Availability
   • Key Factor: Periphyton relies on photosynthesis, so light availability is crucial. This is especially important in shallow rivers or areas with clear water that allow light to penetrate to the substrate.
   • Optimal Conditions: Shallow waters, low turbidity, and clear skies create ideal conditions for periphyton growth. Riparian vegetation or overhanging trees can provide shade, which may limit growth in certain areas.
2. Nutrient Availability (Nitrogen and Phosphorus)
   • Key Factor: Like all plants, periphyton requires essential nutrients, particularly nitrogen (N) and phosphorus (P), for growth. These nutrients are often absorbed from the water or from sediments.
   • Optimal Conditions: High nutrient levels—often from natural sources (e.g., upstream runoff, groundwater) or anthropogenic sources (e.g., agricultural runoff)—can promote periphyton blooms. However, excessive nutrients can lead to eutrophication, causing nutrient imbalances that may negatively affect species diversity and ecosystem health.
3. Substrate Type and Stability
   • Key Factor: Periphyton requires a stable substrate to attach to, such as rocks, logs, aquatic plants, or artificial surfaces. Substrate texture also plays a role: rougher surfaces like cobbles provide more surface area for colonization than smooth surfaces like boulders.
   • Optimal Conditions: Stable substrates in low-flow or moderate-flow zones are ideal for periphyton growth. Areas with constant or slow-moving currents allow organisms to colonize and build dense layers without being washed away.
4. Water Flow and Turbulence
   • Key Factor: Water movement can both help and hinder periphyton growth. Moderate flow is beneficial because it prevents the buildup of sediment or dead organic material that can smother the periphyton. However, strong flow or turbulence can dislodge periphyton from surfaces.
   • Optimal Conditions: Moderate flow or low turbulence allows periphyton to grow and stay attached to surfaces. In fast-moving water, periphyton will struggle to establish a stable hold.
5. Temperature
   • Key Factor: Temperature influences the metabolic rates of periphyton, affecting its growth rates. Warm temperatures generally promote faster growth rates for many species, especially in temperate or tropical regions.
   • Optimal Conditions: Seasonal variability in temperature can drive growth, especially in spring and summer months when conditions are warmer. In colder conditions, periphyton growth is slower, but it may still occur in temperature-regulated systems.

Factors That Limit Periphyton Growth

1. Excessive Flow or Turbulence
   • Dislodgement: In high-flow systems or during flood events, strong water movement can dislodge periphyton from surfaces, preventing stable colonization. This can lead to reduced biomass and hinder growth.
   • Smothering by Sediment: High sediment loads in rivers, often associated with floods or human activity (like construction or agriculture), can bury periphyton or cause abrasion, killing attached organisms.
2. Light Limitations
   • Shading: Excessive shading from overhanging vegetation, turbid water, or high algae biomass can reduce the amount of light available for photosynthesis.
   • Turbidity: Suspended particles (from soil erosion or urban runoff) can reduce light penetration, limiting periphyton's ability to photosynthesize and grow effectively.
3. Nutrient Limitation
   • Low Nutrient Availability: In environments where nutrient concentrations (especially nitrogen and phosphorus) are low, periphyton growth can be limited. In many rivers, nutrients are often a limiting factor during certain seasons or drought periods.
   • Nutrient Imbalance: While periphyton needs nutrients to grow, an excessive supply of nutrients, particularly phosphorus, can lead to eutrophication, causing an overgrowth of algae and a decrease in biodiversity. This creates an unstable environment for periphyton and can lead to oxygen depletion.
4. Toxic Pollutants and Contaminants
   • Pollution: Chemical pollutants, such as heavy metals, pesticides, and herbicides, can be toxic to periphyton. These pollutants can disrupt cellular functions, impair growth, or kill periphyton communities.
   • Polluted Water: Urban runoff or industrial discharge that carries contaminants into rivers can damage periphyton and the broader food web.
5. Competition and Grazing Pressure
   • Herbivory: Grazing by invertebrates (e.g., snails, certain fly larvae) or fish can limit the growth of periphyton, especially in areas with high herbivore densities. Grazers often feed on the periphyton, reducing their biomass.
   • Competition with Other Algae: In rivers, periphyton competes with planktonic algae and other aquatic plants for nutrients and light. If planktonic algae bloom due to excess nutrients, they can outcompete periphyton for resources.

Summary: Key Determinants of Periphyton Growth in Fluvial Systems

Be familiar with each functional feeding group. What are their characteristics? What do they eat? What would you expect to affect them?

In riverine and freshwater ecosystems, functional feeding groups (FFGs) are categories used to classify organisms based on their feeding behavior and resource use. These groups are particularly important for understanding how different organisms interact with their environment and contribute to ecosystem processes like nutrient cycling and energy flow.

There are five main functional feeding groups commonly used to classify aquatic invertebrates (such as insects, crustaceans, and mollusks), each of which plays a unique role in processing organic matter within the system. Here's a detailed look at each group:

1. Shredders

Characteristics:

• Physical traits: Shredders often have strong mandibles or other specialized mouthparts that allow them to break down large pieces of organic material, such as leaves and detritus.
• Feeding behavior: They feed on coarse particulate organic matter (CPOM), particularly detritus and leaf litter that falls into streams from terrestrial plants.
• Habitats: Common in areas with leafy vegetation, especially riparian zones (along the riverbank) where there’s a high input of plant material.

What They Eat:

• Leaves, woody debris, and decaying plant material. Some may also feed on dead animal matter or algal material if available.

What Would Affect Them:

• Reduction in leaf litter: Deforestation or changes in riparian vegetation can decrease food supply for shredders.
• Water quality: Pollution, such as toxic chemicals or low oxygen, can negatively impact their survival and feeding ability.
• Flow regime: High flow velocities may wash away available substrate or reduce habitat stability, which affects shredders' ability to access food.

2. Collectors (Filterers and Gatherers)

Characteristics:

• Physical traits: Collectors have specialized adaptations for gathering or filtering small particles from the water. They typically have brushes, setae, or nets to trap fine organic matter.
• Feeding behavior: They feed on fine particulate organic matter (FPOM), which includes smaller particles like detritus, bacteria, phytoplankton, and other microscopic organisms suspended in the water.
• Habitats: Collectors are found in areas with moderate to slow flow where sediment accumulation is higher, such as in pools or backwaters.

What They Eat:

• Fine particulate organic matter (FPOM), which includes small pieces of decaying plant material, detritus, microalgae, and bacteria.
• Filterers (like caddisfly larvae) remove particles from the water column, while gatherers (like mayfly larvae) collect FPOM from the riverbed.

What Would Affect Them:

• Turbidity: High sediment loads or turbid water can block feeding structures and reduce food availability.
• Flow rates: Strong currents may dislodge or wash away fine particles, making it harder for collectors to gather food.
• Nutrient levels: Excessive nutrients can lead to algal blooms, which may clog filter-feeding structures and decrease food availability.

3. Scrapers (Grazers)

Characteristics:

• Physical traits: Scrapers have mouthparts (often shaped like scrapers or brushes) that help them scrape biofilm or algae from hard surfaces, such as rocks and submerged vegetation.
• Feeding behavior: They primarily feed on periphyton, which includes microalgae, diatoms, and other biofilm organisms that grow on submerged surfaces.
• Habitats: Common in areas with stable rocks or plants where algal growth is abundant.

What They Eat:

• Periphyton (attached algae and biofilms), including green algae, diatoms, and bacteria.

What Would Affect Them:

• Light availability: Reduced light due to turbidity or shading from vegetation can limit algal growth, thus reducing food availability.
• Pollution: Eutrophication from excess nutrients can lead to algal blooms, which may alter the composition of periphyton and make it less suitable for grazing.
• Substrate availability: Changes in riverbed structure (e.g., scouring or sediment deposition) can affect available surfaces for periphyton growth.

4. Predators

Characteristics:

• Physical traits: Predators generally have powerful mandibles, piercing mouthparts, or venom to capture, kill, and consume prey.
• Feeding behavior: They prey on other aquatic organisms, including smaller invertebrates, larvae, and even smaller fish. Some are active hunters, while others might be ambush predators or scavengers.
• Habitats: Found in areas with a diverse range of prey, including riffles, runs, and pools. Predators are often more mobile and can move through different habitats.

What They Eat:

• Other invertebrates (such as shredders, collectors, or scrapers), small fish, amphibians, and even other predators (in some cases).

What Would Affect Them:

• Prey availability: Reductions in prey species due to pollution, habitat destruction, or changes in the food web can decrease predator populations.
• Water quality: Pollution or toxins can impair predator health and reduce hunting efficiency.
• Competition: In some systems, predators may face competition from other species for food, which can limit their abundance.

5. Detritivores (Decomposers)

Characteristics:

• Physical traits: Detritivores often have small, specialized mouthparts that allow them to consume decomposing organic material (dead plants, animals, and feces). They often work at a microbial level, breaking down organic matter into smaller particles.
• Feeding behavior: They feed on detritus (decaying organic matter) and break it down into fine particulate organic matter (FPOM), recycling nutrients in the ecosystem.
• Habitats: Common in areas where organic matter accumulates, such as sediments or the streambed, where decaying matter is readily available.

What They Eat:

• Detritus, including decaying leaves, dead animals, and feces, as well as bacteria and fungi that colonize decaying organic material.

What Would Affect Them:

• Organic matter input: A reduction in organic matter (e.g., due to vegetation loss or deforestation) limits the food supply for detritivores.
• Pollution: Pollutants can disrupt the decomposition process and kill detritivores. Excess nutrients can change the composition of decomposing material, making it harder for them to feed.
• Temperature: Extremely cold or warm temperatures can alter the rate of decomposition and the availability of food for detritivores.

Summary of Functional Feeding Groups:

Detail the main points of each ecological model. (ie. What is the take home message of each riverine ecological model?)

1. River Continuum Concept (RCC)

Vannote et al., 1980

Main Idea:

• Rivers are longitudinal gradients—ecological communities and processes change predictably from headwaters to mouth.
• Organism types, energy sources, and functional feeding groups shift as the river widens and physical conditions change.

Take-Home Message:

“The structure and function of river ecosystems change predictably from upstream (headwaters) to downstream (lowland rivers).”

Key Points:

• Headwaters (1st–3rd order): Shaded, cold → energy input mainly leaf litter → shredders dominate.
• Mid-reaches (4th–6th): More light, more algae and macrophytes → grazers and collectors increase.
• Large rivers (>6th): Turbid, deep, less light → fine organic matter dominates → collectors prevail.

2. Flood Pulse Concept (FPC)

Junk et al., 1989

Main Idea:

• In floodplain rivers, seasonal flooding is the primary driver of productivity and ecological dynamics.
• Flood pulses connect rivers to their floodplains, enhancing nutrient exchange, productivity, and biodiversity.

Take-Home Message:

“The floodplain is not marginal—it’s essential to river function, and floods are beneficial.”

Key Points:

• Floods bring nutrients and organic matter onto the floodplain.
• Many fish and invertebrates time their reproduction or migrations with flood pulses.
• Disconnection from the floodplain (e.g., via dams or levees) leads to loss of productivity and biodiversity.

3. Serial Discontinuity Concept (SDC)

Ward and Stanford, 1983

Main Idea:

• Dams and other interruptions break the natural longitudinal connectivity of rivers.
• These “discontinuities” cause upstream and downstream ecological shifts, disrupting RCC patterns.

Take-Home Message:

“Dams and flow alterations disrupt the natural gradient of a river—changing temperature, flow, sediment, and biota.”

Key Points:

• Below dams: colder water, reduced sediment, altered invertebrate and fish communities.
• The farther downstream you go, the more natural conditions may re-establish (depending on river size and flow).

4. The Riverine Productivity Model (RPM)

Thorp and Delong, 2002

Main Idea:

• Contrary to RCC, in large rivers, autochthonous production (in-channel algae and macrophytes) can be more important than upstream inputs.
• Productivity can be locally driven by in-stream processes and light availability, especially in wider, clearer rivers.

Take-Home Message:

“In big rivers, what grows inside the river can matter more than what floats in from upstream.”

Key Points:

• Emphasizes primary production within the river channel.
• Highlights local heterogeneity, like side channels and backwaters.
• Important for understanding food web dynamics in non-turbid, lowland rivers.

5. The Riverine Ecosystem Synthesis (RES)

Thorp, Thoms, and Delong, 2006

Main Idea:

• River ecosystems are made up of Functional Process Zones (FPZs)—distinct segments shaped by geomorphology, hydrology, and ecological processes.
• Encourages a patch-based or mosaic view of rivers rather than simple longitudinal or lateral gradients.

Take-Home Message:

“Rivers are mosaics of functional zones, and each zone operates under different physical and biological conditions.”

Key Points:

• Emphasizes spatial complexity at multiple scales.
• Good for management and conservation planning, especially in fragmented rivers.
• Integrates RCC, FPC, and other concepts into a broader, more flexible framework.

6. Network Dynamics Hypothesis (NDH)

Grant et al., 2007

Main Idea:

• Rivers are not linear—they are branched networks.
• The confluence points, tributaries, and network structure strongly influence habitat complexity and species distributions.

Take-Home Message:

“The branching structure of rivers creates hotspots of ecological interaction and diversity.”

Key Points:

• Network structure affects dispersal, species connectivity, and disturbance spread.
• Tributaries can act as refugia or sources after disturbances.
• Supports metacommunity and meta-ecosystem perspectives in river science.

Bonus: Patch Dynamics Concept (PDC)

Townsend, 1989

Main Idea:

• Rivers are dynamic systems made up of patches that change over time due to disturbance, succession, and recolonization.

Take-Home Message:

“Disturbance is normal in rivers. Life adapts to change through patchy recovery and renewal.”

Key Points:

• Focus on resilience and adaptation after floods, droughts, etc.
• Emphasizes temporal change and spatial heterogeneity.
• Supports concepts of disturbance regimes and ecological memory in rivers.

Summary Table of Riverine Ecological Models

Discuss the pros and cons of damming a river. Levees?

Damming a River

Pros (Advantages of Dams):

1. Hydroelectric Power
   • Dams generate renewable electricity with relatively low greenhouse gas emissions (compared to fossil fuels).
   • Provides reliable energy and can help reduce reliance on coal or gas.
2. Water Storage and Supply
   • Reservoirs store water for drinking, irrigation, and industrial use, especially in arid regions.
   • Supports agriculture and urban development during dry seasons or droughts.
3. Flood Control
   • Dams regulate flow and reduce flood risk downstream by capturing high flows and releasing them gradually.
4. Recreation and Tourism
   • Reservoirs often become sites for boating, fishing, and other recreational activities, boosting local economies.
5. Navigation
   • In some cases, dams help maintain navigable waterways by regulating water depth and flow.

Cons (Disadvantages of Dams):

1. Disruption of Natural Flow Regimes
   • Dams alter the timing, magnitude, and frequency of flows, disrupting the life cycles of aquatic organisms (e.g., fish spawning tied to seasonal flow pulses).
2. Fragmentation of River Systems
   • Dams block fish migration (e.g., salmon, sturgeon), reduce biodiversity, and isolate populations.
   • Impacts riverine species that rely on longitudinal connectivity.
3. Sediment Trapping
   • Dams trap sediment that would normally replenish downstream habitats and floodplains.
   • Can lead to erosion below the dam and reduce delta formation at river mouths (e.g., Mississippi Delta shrinkage).
4. Loss of Floodplain Connectivity
   • Reduced overbank flooding disconnects floodplains, limiting nutrient exchange and reducing habitat quality for fish and birds.
5. Greenhouse Gas Emissions
   • Especially in tropical areas, decomposing organic matter in reservoirs can produce methane, a potent greenhouse gas.
6. Social and Cultural Impacts
   • Damming often leads to displacement of local communities and loss of culturally significant lands.
   • Altered flow regimes can affect traditional fisheries, agriculture, and livelihoods.

Levees (Embankments Along Riverbanks)

Pros (Advantages of Levees):

1. Flood Protection
   • Levees confine floodwaters to the river channel, protecting farmland, infrastructure, and urban areas from inundation.
2. Land Development
   • Once protected, land behind levees becomes available for agriculture, housing, or industry—especially in flood-prone areas.
3. Infrastructure Stability
   • Levees help protect critical infrastructure like roads, railways, and bridges in floodplain regions.

Cons (Disadvantages of Levees):

1. False Sense of Security
   • People may develop or farm in areas behind levees, believing they're fully protected—when extreme floods can overtop or breach levees, causing catastrophic damage (e.g., Hurricane Katrina).
2. Loss of Floodplain Function
   • Levees prevent floodplain inundation, reducing nutrient cycling, groundwater recharge, and habitat for aquatic and terrestrial species.
3. Increased Flood Risk Elsewhere
   • Levees can shift floodwaters downstream, worsening floods in unprotected areas.
   • Can narrow the channel, increasing flow velocity, and potentially damaging levees or structures.
4. Maintenance and Failure Risk
   • Levees require constant maintenance; if they fail, damage can be worse than if no levee existed at all.
   • Aging infrastructure and climate change increase the risk of catastrophic failure.
5. Ecosystem Fragmentation
   • Like dams, levees can fragment habitats, prevent animal movement, and degrade riparian ecosystems.

Dams vs. Levees: Summary Table