#6 Playas and Pocosins + Major wetlands review

Playa lakes

• shallow, depressional wetlands formed by accumulated precipitation and runoff

• They are highly ephemeral, filling after rain and drying seasonally, similar to vernal pools

What proportion of the High Plains region do playas cover, and what is their average size?

• cover about 2% of the High Plains region

• individual playas average around 15 acres

How does salinity vary in playa lakes?

Most playas are freshwater

• but some can become highly saline due to repeated filling and evaporation

  • concentrates salts and minerals

What are the dominant hypotheses for playa lake formation?

Wind erosion and Ground subsidence

Other causes:

• anthropogenic influences such as highway construction

Different playas may form through different mechanisms

What drives the hydrology of playa lakes?

entirely dependent on precipitation and surface runoff

• little contribution from snowpack

Why are playa lakes considered critical “recharge wetlands”?

• Their clay basins crack during dry periods

• When heavy rains occur, water infiltrates through these cracks and percolates into underlying aquifers

notably contributing to recharge of the Ogallala Aquifer

Why are some regional wetlands not considered recharge wetlands?

some have poor hydrological connectivity with the aquifer and limited capacity for water infiltration

How do saline lakes form within playa systems?

When wetlands have poor recharge capacity and undergo repeated evaporation

• salts accumulate over time

• creates saline or even hypersaline lakes that support specialized organisms

How does vegetation differ between dry and wet playas?

• Dry playas: summer cypress, ragweed, prairie grasses.

• Wet playas: barnyard grasses, cattails, typical wetland plants.

Why do playas exhibit little vegetation zonation compared to other wetlands?

shallow/ephemeral nature provides limited niche variation for different hydrologic tolerance zones to form (“bath-tub rings”)

Why are playa vegetation communities dominated by annuals?

• Annuals can rapidly germinate/grow/seed during brief wet periods

• they persist in the seed bank during long dry phases

What is the ecological importance of invertebrates in playa lakes?

they serve as an essential food source

• not well studied

Why are playa lakes especially important for birds?

can quickly locate and exploit ephemeral habitats due to their mobility

• currently support 90% of mid-continent Sandhill Cranes

• can host over two million waterfowl in good years

What mammals inhabit playa systems?

While large ungulates are mostly extirpated, deer, pronghorn, rabbits, rodents, and predators such as coyotes, badgers, raccoons, and striped skunks remain

Why are fish generally absent from playa lakes?

The high ephemerality prevents most fish species from persisting

• however, some more permanent human-made or stocked ponds may contain non-native fish

What is one of the main threats to playa lakes?

Agriculture (>90% of playa lakes occur on private land)

• Playa pitting/ditching

• Sedimentation

Playa pitting

involves digging holes to retain water longer for cattle or irrigation

• short term→ water persists longer

• long-term → hydrology is degraded, and recharge capacity can decline

How does sedimentation threaten playa function?

• Poor farming practices lead to soil erosion

  • Top-soil loss

• Free-flying sediments accumulate in playas

  • affecting permeability and fills them in

Make playas more shallow, more loss to ET, alter hydrology

How are playas typically managed?

Most receive little active management

• when managed→ they are treated similarly to moist-soil wetlands

  • objective → producing waterfowl habitat

What is a drawback of managing playas like moist-soil wetlands for ducks?

Stabilizing water regimes for waterfowl can decrease natural hydrologic variability

• reduces ecological diversity

• compromises recharge functions

Why are playas vital for human water supply?

major recharge source for the Ogallala Aquifer

• the largest aquifer in the U.S. and essential to Midwestern and Southwestern water security

Pocosins

acidic, peat-forming, shrub-dominated wetlands located on elevated land

• Typical synonyms for pocosins→

  • Shrub bogs

  • Raised bogs

How do pocosins form hydrologically?

largely groundwater-fed initially

• As peat accumulates, it forms a mound that holds water like a sponge

• The upper portions eventually become isolated from groundwater and are fed primarily by precipitation

Why are pocosins considered discharge wetlands?

they release water from their peat layer back into surrounding groundwater rather than receiving water from surface flow

Why do pocosins have little surface water?

• Their water is largely stored within peat

• hydrology is dominated by slow seepage rather than open flooding

What plants dominate pocosin vegetation?

Pond pines

• sphagnum moss

• shrubs, vines, ferns, and carnivorous plants

• Loblolly and longleaf pine may also occur

What notable endangered species relies on pocosins?

red wolf

• the only wild population exists in North Carolina pocosins

Why are pocosins not major waterfowl habitats?

They lack open water and shallow foraging habitat typical of waterfowl ecosystems

Why is fire a major concern in pocosin ecosystems?

• Peat becomes highly flammable when water tables drop

• Drought or hydrological alteration allows peat fires that can burn for months

  • release significant carbon

How do healthy pocosins resist fire?

High water tables keep peat saturated and unable to ignite

What is the primary goal of pocosin restoration today?

Re-wetting and raising water tables

• prevent peat loss, reduce fire risk, restore hydrology

• enhance carbon storage

What tools are used to restore pocosin hydrology?

Water control structures and other hydrological modifications to maintain high water tables around peat mounds

Review: What distinguishes moist-soil marshes from other wetland types?

They feature active management of flood-ups and draw-downs to promote seed production and wildlife habitat, especially for waterfowl

Review: What defines hardwood bottomlands/GTRs?

Flood-tolerant forests, typically maintained with winter flooding to maximize mast production and minimize tree stress

Review: What makes prairie potholes ecologically important?

• heterogeneous hydrology

• role in supporting waterfowl breeding

• location within endangered tallgrass prairie ecosystems

Review: What are some defining characteristics of playa lakes compared with other wetlands?

• extremely shallow

• highly ephemeral

• function as key groundwater recharge features

Review: How do pocosins differ from other wetland types in formation?

They form through peat accumulation on elevated land, eventually becoming rain-fed bogs with limited surface water.