Stream Temperature

Introduction to Stream Temperature

  • Overview of relevance in stream ecology.

    • This lecture will not cover all aspects of temperature but will provide context.

    • There is additional reading (by Seth Menger) discussing the implications of temperature changes on fish distributions.

  • Objective:

    • Explain the importance of water temperature in stream ecology.

    • Recognize different ways stream temperature can be characterized and appropriate metrics for various contexts.

Why Temperature Matters

  • Temperature exerts a fundamental control over biological processes in stream ecosystems.

  • Historic Reference:

    • 1979 paper demonstrates fish growth response related to temperature.

    • Fish growth rate is graphed with species-specific optimal temperatures labeled as the "thermal niche."

    • Key Insight: Species grow at different optimal rates, each requiring varied thermal conditions.

Temperature and Fish Growth

  • The thermal niche determines where species can survive and thrive:

    • Growth rates vary with temperature.

    • Each species has a distinct curve for growth in response to temperature changes.

    • Example:

    • Species-specific growth responses range from optimal growth at around 15°C to declines observed at 20°C.

  • Fundamental Niche:

    • Temperature affects reproductive rates and planktonic development time.

    • Increased temperature significantly reduces developmental time for plankton, affecting algal blooms and other aquatic organisms.

  • Remarks on ectothermic organisms:

    • Many stream organisms rely on environmental temperatures, emphasizing stream temperature's role in regulating biological functions.

Specific Case Studies

  • Growth Rate Study: Sockeye Salmon

    • Investigation of growth rates related to temperature and food availability (ration size).

    • Display of different curves for fish growth at 5°C, 10°C, 20°C, and 24°C.

    • Observed trends indicate optimal growth at 15°C; growth rates decline beyond this.

  • Temperature Tolerance Study:

    • Fish were subjected to stable vs. fluctuating thermal regimes to understand thermal tolerance.

    • Result: Fluctuating temperatures allow for higher mean daily temperatures due to nocturnal recovery.

  • Life Stages and Their Thermal Requirements:

    • Different developmental stages of fish (e.g., brook trout) exhibit varied optimal temperatures.

    • Embryos prefer cooler temperatures than fry, which are warmer than juveniles and adults.

    • The spatial distribution and thermal needs evolve through an organism's life stages, affecting spawning and survival.

    • Raises awareness about context when assessing temperature effects on aquatic life.

Ecosystem Effects of Temperature

  • Temperature influences not only fish but also broader ecosystem processes:

    • Increased stream temperature correlates to enhanced Gross Primary Production (GPP), evident through oxygen production rates.

    • Nutrient uptake rates for phosphates and nitrates increase with temperature, driving nutrient demand in streams.

  • Importance:

    • Temperature drives pivotal biological and ecological processes, suggesting that any deviations from normative ranges may have severe implications across multiple species and ecosystem functions.

Influences of Stream Temperature

  • Key drivers affecting stream temperature include:

    • Shade vegetation: A dominant factor in moderating temperature.

    • Shortwave (solar) radiation increases temperature directly, while longwave radiation has variable effects.

    • Groundwater contributions can be dual-faceted, cooling streams in summer but warming them in winter.

  • Examination of heat gains and losses:

    • Essential to understand various thermal interactions through conceptual models relating to water heat budgets.

Aspects of Stream Temperature Measurement

  • Stream temperature is dynamic, making it complex to assess:

    • Various metrics can be captured based on research questions.

    • Examples include:

    • Maximum vs. minimum vs. mean temperatures

    • Duration and frequency of temperature events

    • Accumulated degree days (e.g., degree days above a certain threshold)

  • Various aspects to consider for temperature profiles:

    • Magnitude, variability, frequency, duration, and timing of temperature events.

  • Questions to ponder:

    • How would different metrics of temperature (max, mean, etc.) lead to varying ecological insights?

Implications of Stream Temperature on Fish Distributions

  • Reference to Wenger's paper on stream temperature and distributions of cutthroat trout in the Mountain West.

    • Predictions for future climate scenarios show potential habitat loss for cutthroat trout due to thermal sensitivity.

    • Observations on invasive species (brook and brown trout) and their variable responses to temperature changes.

    • Recognition of bull trout as particularly sensitive to climate shifts due to their specific thermal requirements.

Thermal Sensitivity Evaluation

  • Study on thermal sensitivity based on stream's base flow index illustrates the interaction between groundwater and thermal stability:

    • High base flow correlates with thermal stability, while a decrease leads to increased thermal sensitivity, especially in smaller streams.

    • Complexity noted in larger streams regarding their thermal response and groundwater interactions.

Conclusion

  • Key insights on stream temperature and its implications are essential for understanding aquatic ecosystems and managing them effectively under changing climate scenarios.