Geology and Soil of Agua Hedionda Lagoon

GEOLOGY AND SOIL OF AGUA HEDIONDA LAGOON

Overview of Geology and Soil Characteristics

  • Agua Hedionda Lagoon is characterized by a combination of sandy and silty soils, which illustrate its classification as a coastal lagoon.

    • The lagoon serves as a transition zone for freshwater mixing with seawater.

Substrate Composition

  • Near the ocean inlet and throughout the outer basin, the substrate predominantly consists of:

    • Coarse marine sand

    • This sand is primarily deposited by tidal actions and dredging activities.

    • Dredging helps maintain the inlet's openness.

  • Inland Areas:

    • As the location moves away from the inlet into the lagoon, water movement slows, leading to a gradual transition into:

    • Finer silts and muds

  • Formation of the Lagoon:

    • The lagoon is an estuarine lagoon, developed through natural processes that include:

    • Sea level rise

    • Formation of a sand barrier

    • Connection with Agua Hedionda Creek

    • This means the lagoon is fundamentally influenced by both freshwater input from the watershed and salty seawater from the ocean.

Human Modifications

  • The natural landscape of Agua Hedionda Lagoon has been significantly altered due to human activities which include:

    • Construction of causeways

    • Development of trails

    • Installation of rail lines

    • Periodic dredging of specific areas

Physical Description of the Lagoon

  • The lagoon itself is generally shallow.

    • Surrounding landscape features:

    • Coastal plain

    • Mudflats

    • Salt marshes

    • Upland scrub

    • Developed areas influenced by urbanization or infrastructure.

Soil Sampling Process

  • During a site visit, a soil sample was collected to analyze substrate conditions:

    • Sampling Method:

    • Sample was taken just off the edge of the designated trail.

    • A hole was dug to a depth of approximately 30 cm.

    • Soil filled a mason jar, which was then topped with water.

    • Observation of Soil Separations:

    • After resting for several hours, the contents of the jar separated into distinct layers:

      1. Coarse sand particles settled at the bottom (heaviest particles).

      2. Middle layer of silt.

      3. Top layer: A cloudy mixture consisting of clay and organic material.

Analysis of Soil Composition

  • Soil Texture Analysis:

    • The layered pattern indicates a texture mix, which can be classified as sandy to loamy in nature.

    • Findings align with earlier sediment reports indicating:

    • Sandy substrates near the lagoon's outer regions.

    • Muddier deposits found farther inland.

  • Influence of the Trail:

    • Given the transect is near a trail instead of deeper marsh areas, it is expected that the soil would demonstrate higher sand content.

    • Across various transects:

    • Soil texture remained generally consistent.

    • Patches that were wetter exhibited higher concentrations of fine particles and organic material.

  • Human Impact on Soil:

    • The top layers of soil near the trail appeared to be slightly disturbed due to:

    • Foot traffic

    • Trail maintenance efforts

    • Long-term usage by humans of the surrounding area.

    • Such disturbances generally lead to:

    • Soil compaction

    • Loss of organic litter

    • Blending of different surface layers.

  • Deeper Soil Observation:

    • Soil at a depth of around 30 cm displayed more natural stratification.

    • The upper layers revealed signs of disturbance affecting the overall soil quality and makeup.

Conclusion

  • The results from the soil sample analysis align well with prior expectations based on historical data but also highlight the impact of anthropogenic activities on the ecology and geology of Agua Hedionda Lagoon's substrate.