Marshes, Playa Wetlands, Wet Meadows, and Fens - Mountains and Plains: The Ecology of Wyoming Landscapes - page 70

wetland plants develop a pressure gradient that acceler-
ates the transport of oxygen to the roots. 15 Plants with
aerenchyma include buckbean, common reed, horse-
tails, pond lily, sedges, and white marsh marigold.
Another problem for wetland plants is the toxicity
of reduced sulfur, iron, and manganese compounds
produced by the soil microbes. Adapting to this stress
involves the diffusion of oxygen from fine roots into the
millimeter-thick environment immediately adjacent to
roots, known as the rhizosphere. oxidation in the rhi-
zosphere essentially immobilizes the toxic compounds
and renders them virtually harmless. the oxidized iron
of the rhizosphere remains long after the roots have
died and decayed, appearing in the soil as red or orange
streaking—a diagnostic sign of hydric soils.
Vertebrates and terrestrial invertebrates avoid the
oxygen deficiency problem by living at the well-aerated
wetland surface. Aquatic invertebrates have the same
array of adaptations as aquatic organisms in lakes and
streams, such as gills capable of extracting oxygen from
the water.
As noted, two-thirds of Wyoming wetlands usually
dry out every year. in such wetlands, the microbes,
plants, and animals must be adapted for drought as
well as soil saturation. Perennial plants that survive as
roots or rhizomes actually may benefit from short dry
periods, because some of the soil organic matter decom-
poses when exposed to the air, increasing the supply of
nutrients during the next wet period. Another group of
plants persists as seeds that germinate when water again
floods the wetland. A third group consists of plants
that occupy the wetland during the dry period but are
absent during the wet period. these plants grow from
seeds that persist in the soil during the wet period or
that blow into the dry wetland from nearby shoreline
plants. considering that some organisms benefit from
dry or low water conditions, it is not surprising that
the diversity of plants and animals in wetlands can be
greater if water levels fluctuate.
invertebrates also have strategies for living in sea-
sonal wetlands. immobile or slow-moving species, such
as clams, survive dry periods buried in moist sediments,
either as adults or larvae, or they survive as eggs that
hatch during the next wet period. in contrast, aquatic
invertebrates that metamorphose into flying adults
leave the drying wetland and fly to nearby water bodies.

Among both plants and invertebrates, the mix of spe-
cies in a wetland at a given time depends on the length
and timing of the preceding wet and dry periods.
Similarly, wetland vertebrates have evolved to opti-
mize their chances of survival in seasonal wetlands.
Wetland birds, for example, fledge their young in the
spring while marshes are usually flooded and emergent
cattails and bulrushes provide nest sites and cover. Simi-
larly, tadpoles develop and metamorphose into adults
quickly, usually before the ponds dry out. Animals with
limited mobility, such as many amphibians, must be
adapted for dry periods and winter. Spadefoot toads
burrow into moist soil or occupy burrows dug by small
mammals on the nearby upland, where they hibernate
until the next favorable period. 16

Marshes

For many, the word “wetland” brings to mind blackbirds,
marsh wrens, muskrats, and a variety of emergent plants
that includes cattails—all characteristic of marshes.
of the various wetland types, marshes are flooded to
a greater depth and for longer periods. the substrate
of silt, clay, and organic matter is soft and, when wet,
is commonly referred to as mud or muck. Hard-bottom
marshes have more sand. the frequency, duration, and
depth of flooding exert strong influences on the kinds
of plants and animals that are present. Many lakes do
not have marshes, primarily because their banks often
slope quickly into deep water, and wave and ice action
prevent plant establishment, or because water levels fluc-
tuate excessively, such as on the shorelines of reservoirs. 17
in the mountains, marshes tend to occur in small
areas, such as closed depressions in glaciated terrain,
also known as potholes (fig. 5.5) . other mountain
marshes are often associated with old beaver ponds and
abandoned stream channels. 18 two common sedges—
northwest territory sedge and water sedge—are the
common dominants in shallow and moderately deep
standing waters in high-elevation marshes. Forbs occur
less frequently, but one can often find twinleaf bed-
straw, elephanthead lousewort, white marsh marigold,
and pond lily, among others (table 5.1). Willows along
the margin of some mountain wetlands are commonly
Booth's willow, diamondleaf willow, Drummond's wil-
low, Geyer's willow, and Wolf's willow.