Tuesday, November 19, 2024

Introduction

• Video lecture replacement for missed session on Gaucho Space.

• Brief review of previous material on lake systems.

Lake Systems

• Transition from river systems to lake systems known as Atlantic River systems.

• Low tech: running water, while land tech refers to still water (though it has vertical movement).

Characteristics of Lakes

1. Distinct edges.

2. Homogeneous bottoms.

   • Consistent bottom types: sand, silt, rock, or gravel.

3. Well mixed during specific times of the year.

Freshwater Sources

• Majority of freshwater found in glaciers.

• Limited freshwater in lakes and rivers; scarcity increases value.

Types of Lakes

• Tectonic Lakes:

  • Formed by geological faulting.

  • Drop-out fall (e.g., Caribbean lakes, rift lakes) and uplift creating depressions.

• Volcanic Lakes:

  • Formed in calderas and blocked rivers due to lava flows.

  • Commonly seen in places like Hawaii.

• Glacial Lakes:

  • Most common in temperate zones; shaped by glaciers as they advance and retreat.

  • Three basic types:

    1. Cirque Lakes: Formed in depressions carved by glaciers.

    2. Valley Lakes: Created when glaciers scoop out the bottom of valleys.

    3. Kettle Lakes: Formed in depressions left by retreating glaciers.

• Artificial Lakes:

  • Created through river damming, reservoir carving, sinkholes, oxbow lakes, and floodplain lakes.

Lake Zones

Bathymetric Maps

• Bathymetric maps depict lake depth and shape, affecting function.

Distinct Lake Zones

1. Photic Zone:

   • Where light penetrates, driving photosynthesis.

2. Benthic Zone:

   • Bottom sediments too deep for light-dependent photosynthesis.

3. Aphotic Zone:

   • Water that cannot support photosynthesis due to lack of light.

4. Thermocline:

   • Layer of temperature change due to density differences.

   • Warm, oxygenated water above cold, nutrient-rich, oxygen-poor water.

Additional Layers

• Epilimnion:

  • Warm, well-mixed, oxygenated top layer.

• Hypolimnion:

  • Cold, dense, poorly mixed, and nutrient-rich lower layer.

• Metalimnion:

  • Transitional layer containing the thermocline.

Light and Water Motion

• Light diminishes with depth; absorption, reflection, and scattering happen based on water clarity.

• Wind drives water motion; induces vertical mixing.

• Stratification occurs if wind energy isn't sufficient to mix layers.

Substratum and Lake Effects

• Substratum types affect environmental conditions; similar structures may exist in lakes and rivers.

• Catchment areas (regions draining into a lake) mirror rivers' drainage basins.

Dissolved Oxygen Profiles

• Clean (Great) Profile:

  • High oxygen at the surface; steep transition marks the thermocline; lower oxygen in hypolimnion due to low mixing.

• Gradient Profile:

  • Uniform oxygen levels indicating well-mixed conditions across layers.

Factors Influencing Organisms

• Salinity impacts species diversity; freshwater fish struggle in saline environments.

• Acidity affects organisms and bioavailability of nutrients; low/high pH can be harmful—decreases ability to osmoregulate.

Oligotrophic vs. Eutrophic Lakes

• Oligotrophic Lakes:

  • Low nutrient, high oxygen; clear water; deep and round shape.

• Eutrophic Lakes:

  • High nutrient levels; turbid water; shallow and dendritic shape; supports more life due to excess nutrients.

Biota of Lake Zones

• Pelagic Zone:

  • Contains four trophic levels: phytoplankton, zooplankton, small fish, and larger predatory fish.

• Profundal Zone:

  • Simplified energy flow from detritus to primary consumers and then to fish.

• Littoral Zone:

  • Complex interactions; energy flow from plants to consumers; diverse structure of aquatic plants (submerged, floating, emergent).

Conclusion and Exam Preparation

• Expect fill-in-the-blank, matching questions.

• Light penetration and temperature-impacting mixing are crucial concepts.

• Understand the interaction within food webs rather than simple food chains.

• Algal succession in temperate zones shows seasonal patterns influenced by temperature and nutrient availability.

Final Notes

• Upcoming synchronous lecture via Zoom; no in-person session next week.