CWD Hydrology & Soils 3 — Questions and Answers
Question 1: Which soil texture class retains the most water and is most likely to develop hydric characteristics in a flat landscape?
- Sandy loam
- Loamy sand
- Silty clay (Correct answer)
- Gravelly sand
Correct answer: Silty clay
Silty clay has very fine particles with high surface area and low permeability, retaining water longest and promoting anaerobic conditions.
Question 2: What is 'episaturation' as defined in wetland hydrology?
- Saturation from below by a rising water table
- Saturation from above due to perched water on a restrictive layer (Correct answer)
- Saturation caused by artesian pressure
- Saturation due to tidal flooding
Correct answer: Saturation from above due to perched water on a restrictive layer
Episaturation occurs when water perches above a restricting layer in the soil profile, saturating the zone above while unsaturated conditions exist below.
Question 3: A soil has a matrix chroma of 1 with 20% distinct mottles of chroma 4. What does this pattern indicate?
- The soil is well-drained with occasional flooding
- The soil experiences alternating wet and dry conditions with redox cycling (Correct answer)
- The soil is permanently dry with oxidized iron coatings
- The soil has high organic matter masking true matrix color
Correct answer: The soil experiences alternating wet and dry conditions with redox cycling
Low-chroma matrix with higher-chroma mottles indicates redoximorphic features from cyclic wetting and drying with iron oxidation-reduction.
Question 4: Which USDA soil order is most commonly associated with hydric soils in freshwater wetlands of the eastern United States?
- Mollisols
- Histosols (Correct answer)
- Aridisols
- Ultisols
Correct answer: Histosols
Histosols are organic soils formed under prolonged saturation and are the most commonly designated hydric soils in eastern freshwater wetlands.
Question 5: What is the significance of a 'drift line' as a wetland hydrology indicator?
- It marks the ordinary high-water line on stream banks
- It shows debris deposited by receding floodwaters, indicating past inundation (Correct answer)
- It indicates the boundary between hydric and non-hydric soils
- It marks the transition from obligate to facultative wetland plants
Correct answer: It shows debris deposited by receding floodwaters, indicating past inundation
Drift lines are accumulations of water-transported debris (leaves, sticks, sediment) left behind as floodwaters recede, indicating the extent of recent inundation.
Question 6: Under the USACE Wetland Delineation Manual, what is the 'growing season' based on?
- Calendar dates from April 1 to October 31 nationwide
- The period when mean daily air temperature exceeds 5°C, region-specific
- Soil temperature at 50 cm depth exceeding 5°C for a defined period (Correct answer)
- The frost-free period between last spring and first fall freeze
Correct answer: Soil temperature at 50 cm depth exceeding 5°C for a defined period
The growing season is defined by soil temperature at 50 cm depth exceeding the biologic zero threshold (5°C), using region-specific methods from NRCS data.
Question 7: What does 'endosaturation' mean in the context of wetland hydrology?
- Saturation perched above a restricting layer
- Saturation of the entire profile from the seasonal high water table rising from below (Correct answer)
- Saturation caused by lateral flow from adjacent uplands
- Saturation limited to the surface O horizon only
Correct answer: Saturation of the entire profile from the seasonal high water table rising from below
Endosaturation refers to a condition where the entire soil profile is saturated from below by a rising water table with no unsaturated zone beneath.
CWD Hydrology & Soils 3
Which soil texture class retains the most water and is most likely to develop hydric characteristics in a flat landscape?