Lecture 5 - Hydrology and Physiography of Wetland Habitats

Lecture Title

• Hydrology and Physiography of Wetland Habitats

Introduction to Wetland Habitats

Lots of diversity

• Wetlands are difficult to define and delineate.

• Often serve as transitional habitats between terrestrial and aquatic ecosystems.

• Delineation based on:

  • Hydrophytes: Water-loving plants.

  • Hydric Soils: Soils rich in organic matter overlying gray, anaerobic mineral layers.

Wetland Functions

• Serve as critical and unique habitats for various plants and animal species.

• Help to dampen flood events and process/purify runoff.

• Act as hotspots for many biogeochemical cycles, including:

  • Carbon storage and processing.

Just because there is or isn’t water doesn’t identify it it’s a wetland

• Wetlands can have dry spells with no water

• If lots of rain, a place can look like a “wetland” but it’s not

Draining of Wetlands

• The draining and filling of wetlands is common in many parts of the world.

• In Canada it’s more recent, since the 1800s

• Primarily done for agricultural purposes.(lots of nutrients)

In Canada, southern ontario had a lot of wetlands. (mostly in high agricultural hotspots) and the prairies

Types of Wetlands

Low evaporation & relatively high precipitation leads to more wetlands in the higher northern hemisphere. Would be the same in the south but not enough land mass to see that

Types of Wetlands

• Wetlands present a diverse array of types distributed worldwide.

• Largest complexes linked with large rivers or high-latitude glacially influenced areas.

• Broadly classified based on:

  • Geomorphology

  • Hydrology

  • Climate

  • Nutrient input

  • Vegetation

• Two main categories:

  • Inland Wetlands

  • Coastal Wetlands

• Four broad geomorphic classes:

  • Riverine

  • Depressional

  • Coastal

  • Peatlands

Coastal (Fringe) Wetlands

• Include both fresh and saline water environments.

• can occur in the oceans and large lakes

  have/had wetlands in the great lakes (esp. lake erie)

• Act as important buffers against storms.

• Types include:

  • Tidal Salt Marshes

  • Mangrove Swamps

  • Floating Marshes

Tidal Salt Marsh

• Comprise brackish waters influenced by ocean tides.

• Dominated by grasses and rushes.

• Characterized by:

  • Wet-dry cycles

  • Large temperature fluctuations

  • Abundant, but limited biota diversity

• Further inland may transition to freshwater areas with higher diversity.

Mangrove Swamps

• Coastal wetlands dominated by halophytic (salt-tolerant) trees.

• Found in areas with:

  • Minimal wave action

  • Sediment accumulation

  • Anoxic sediments

• Trees possess structures called pneumatophores (aid in gas exchange, emerge above the water and soil/ roots submerged in water) and show distinct zonation.

important for storm surges

Floating Marshes

• Composed of thick mats of roots that float on water.

• Commonly found in river deltas and non-flooding areas.

Inland Wetlands

• Include both depressional and fringe formations such as marshes, swamps, riverine, and peatlands.

• Depressional wetlands form similarly to lakes.

• Marshes and swamps are the most abundant wetland types.

• Timing, frequency, and magnitude of inundation are highly variable.

More common

Most swamps don’t have standing water all the time- esp. the ones here

Usually dry in the summer (soil still wet but no water)

Swamp vs. Marsh

• Swamps are dominated by trees, which often evolve specific growth forms to adapt to inundation.

• Marshes are dominated by herbaceous (non-woody) plants.

Swamps has herbaceous plants but the same can’t be said for marsh for trees

Riparian Wetlands

• Wetlands typically adjacent to rivers and can be forested.

• Exhibit permanent to ephemeral inundation (wet all the time vs. wet depending on the season) flooding is essential for nutrient and energy exchange.

• Important for spawning of certain fish species, yet heavily impacted by human activities.

gets flooded on a regular basis

near rivers AND lakes

Moving nutrients out of the lakes and into the land for the plants

moving the leaves and stuff from the land into water for nutrients (exchange)

long periods of overbank flooding (defining feature)

Some fish will lay eggs here bc it has less predators and more food

Development in these areas - one of the most effected areas

Pothole Wetlands

• Marsh ecosystems formed in depressions created by retreating glaciers.

• Commonly found in the Prairies and vary greatly in size and water permanency.

• Can become highly saline due to evaporation and are crucial for various waterfowl species.

Prairies potholes - Wetlands are wet for very short amount of time - getting wetter and for longer as you get more northern

Peatlands

• Depressional wetlands that gain organic matter through accumulation over time.

• Characterized by production exceeding decomposition due to:

  • Low temperatures (often in arctic regions)

  • High acidity or alkalinity (in Bogs and Fens)

• Act as critical global carbon sinks and are often mined for peat.

Bogs vs. Fens

• Bogs:

  • Lack significant water inflow,

  • Nutrient-poor, acidic, with lower biodiversity.

• Fens:

  • Receive runoff or groundwater inputs,

  • Neutral to alkaline, generally nutrient-rich with higher biodiversity.

Smaller Wetlands

• Small depressions can act as highly ephemeral wetlands, such as vernal pools.

• Mostly fed by precipitation and can be seasonal hotspots for biodiversity.

• Some smaller wetlands can be created by animal activity.

Wetland Hydrology

• Hydrologic regimes can vary significantly among different wetlands.

• Key characteristics include:

  • Permanence: Influences predator presence and lower trophic level dynamics.

  • Predictability

  • Seasonality

  • Regional variability in permanence can enhance overall diversity.

  • More permanent wetlands can be sources of colonizers for less permanent wetlands.

Sources of Water

• Wetlands can derive water from:

  • Precipitation: Often leads to highly ephemeral wetlands.

  • Surface Water: Can provide constant or ephemeral water supply, typically directional downslope.

  • Groundwater: Offers a more constant supply, though can vary with water table changes.

  • Evapotranspiration: Very important in wetlands lacking inflows; tides also affect coastal wetland hydrology.

Subhabitats in Wetlands

• Many subhabitats can exist within a single wetland, leading to different chemical and hydrological characteristics:

  • Littoral: Near shore areas.

  • Limnetic: Open water areas.

  • Emergent Wetlands: Areas with plants growing above water level.

Wetlands and Global Change

• Wetlands face significant risk from:

  • Warming temperatures leading to increased evaporation.

  • Changing precipitation patterns.

  • Increased decomposition rates (especially in peatlands).

  • Effects on plants and animals will vary based on wetland type.

Summary of Key Points

1. Wetlands are defined by hydrophytic vegetation and hydric soils.

2. Classified by location, hydrology, geomorphology, and vegetation.

3. Perform diverse ecosystem services.

4. Distinction between coastal and inland wetlands.

5. Water sources include precipitation, runoff, groundwater, and tides in some cases.

6. Subhabitats can arise from variations in water permanence.