Wetland environments notes

1.1 Wetland Basics

Wetlands are ecosystems that have three basic characteristics: water, hydrophytes, and hydric soils.

Ex. Salt marshes, Freshwater tidal marshes, Freshwater swamps, Mangrove Swamps, Freshwater marshes, and Peatlands.

Wetlands have water, yet the depth and duration of flooding varies considerably from wetland to wetland. 

Because water levels in an individual wetland can fluctuate widely from season to season and year to year, defining the boundary of a wetland--called wetland delineation--can be very challenging.

Wetlands often support high biodiversity, and an individual wetland can support many species of plant life.

1.2 The Three-Component Basis

What are the three main components of a wetland?

1.    Hydrology

2.    Hydric soils

3.    Hydrophytes

What are the two external factors that influence wetlands?

Geomorphology and climate

Components and external factors interact with one another through…

Direct effects and biotic feedback

1.3Wetland Benefits

Why are they important?

Wetlands provide many important ecosystem services and other benefits to people.

Ecosystem services

Ecosystem services refer to any type of benefit to people that can be extracted from nature. 

-       Water quality improvement as they act as natural water purifiers.

-       Flood control as along coasts rivers and streams they collect rainfall and surface water flow which reduces flooding.

-       Coastal wetlands, such as mangrove forests, protect shorelines from erosion.

-       Streambank stabilization

-       Habitat for biodiversity

-       Carbon storage

-       Recreation

-       Food and water source

Wetlands have different properties than terrestrial and aquatic systems, in part because they are transitional ecosystems between them 

How productive are wetlands?  Estuaries (salt marsh), swamps, and marshes often outperform even tropical rainforests in terms of net primary productivity per unit area.

1.4   Wetland status and distribution

Currently, about 4-6% of the Earth's surface is covered by wetlands.  They are concentrated in five main areas: polar, boreal, temperate, and subtropical regions, plus rice paddies. Like the global distribution, about 5.5% of the contiguous U.S. is covered by wetlands.

 

Florida is about 31% wetland.  About 90% of those are freshwater wetlands, with the other 10% comprising saltwater marshes and mangrove forests.

An estimated 221 million acres of wetlands were originally found in the United States.  By the 1980s, only about 104 million remained, a loss of about 54%.  California and the Midwest experienced the greatest rates of loss, but Florida had the largest total area of loss (9.3 million acres or 46%).  The years from the 1950s to the 1990s were a time of major wetland loss across the nation, 87% due to agriculture, but since then rates have decreased.

 

Wetlands are lost primarily through drainage and subsequent conversion to upland.  Drainage is mostly for agriculture, but other reasons include controlling mosquitoes and extracting peat for fuel or as a soil amendment.

 

The 7 global drivers of wetland loss

The main causes of global wetland loss are conversion to croplands (61.7%), flooded rice (18.2%), urbanization (8.0%), forestry (4.7%), wetland cultivation (4.3%), pasture (2.0%), and peat extraction (0.9%).

 

Over 50% of wetlands were lost between 1700 and 2020, with the highest rates in the United States, Europe, Central Asia, India, China, Japan, and Southeast Asia.  

 

Wetland Degradation

refers to the reduction of quality of a wetland ecosystem.  Many remaining wetlands are degraded or at risk.

 

Causes

-       Dredging and stream channelization

-       Dikes, Dams, and Levees

-       Mining

-       Industry

-       Urbanization and Rural development

-       Agriculture

-       Grazing

-       Invasive species

-       Climate change

2.1 Wetland Hydrology and Water Budgets

What is Hydrology?

- Hydrology is the science that encompasses the occurrence, distribution, movement, and properties of water on the earth and its relationship with the environment within each phase of the hydrological, or water, cycle.

The hydrological cycle involves the continuous circulation of water in the Earth-Atmosphere system.  

Infiltration- the physical process involving movement of water through the boundary area where the atmosphere interfaces with the soil. The surface phenomenon is governed by soil surface conditions. Water transfer is related to the porosity of the soil and the permeability of the soil profile.

Evaporation- Water moves from the Earth's surface to the atmosphere via evaporation. Evaporation is the change of state in a substance from a liquid to a gas.  Evaporation occurs when energy (heat) forces the bonds that hold water molecules together to break.

Runoff- occurs when there is excessive precipitation, and the ground is saturated (cannot absorb any more water). Rivers and lakes are results of runoff. Some runoff evaporates into the atmosphere, but most water in rivers and lakes returns to the oceans.

Precipitation- results when tiny condensation particles, through collision and coalescence, grow too large for the rising air to support, and thus fall to the Earth. Precipitation can be in the form of rain, hail, snow, or sleet.

Condensation- the process whereby water vapor is changed into a liquid state. In the atmosphere, condensation may appear as clouds or dew.   Condensation is the opposite of evaporation.

Transpiration- the evaporation of water from plants through stomata. Stomata are small openings found on the underside of leaves that are connected to vascular plant tissues. In most plants, transpiration is a passive process largely controlled by the humidity of the atmosphere and the moisture content of the soil. Of the transpired water passing through a plant only 1% is used in the growth process of the plant. The remaining 99% is passed into the atmosphere. 

Transportation- the movement of water through the atmosphere, specifically from over the oceans to over land.

Sublimation- the direct conversion of snow and ice to atmospheric water vapor. Through this process, the water content within a snowpack may be reduced without melting. Sublimation causes significant cooling of the snowpack.

Deposition- when water vapor (gas) changes into ice (solid) without going through the liquid phase, such as when frost forms on the ground on clear, cold nights.

Groundwater- In addition to being important for water storage, groundwater is a major contributor to flow in many streams and rivers.

 

Hydrology of wetlands is the study of movement of water in and out of a wetland ecosystem. 

we are generally concerned with five simplified ones: precipitation, surface water flow, groundwater flow, evapotranspiration, and tides. 


Water Budgets

We use water budgets to quantify the inflows and outflows of water in a wetland.  Water budgets measure changes in water volume (v) in a wetland over time (t) based on: net precipitation (Pn), evapotranspiration (ET), surface water inflow (Si), surface water outflow (So), groundwater inflow (Gi), groundwater outflow (Go), and tides (T) .  

The formation, size, persistence, and function of a wetland are all directly controlled by hydrological processes.  Remember that the hydrology of a wetland determines if hydric soils will form and if hydrophytes will be present.

The formation, size, persistence, and function of a wetland are all directly controlled by hydrological processes.  Remember that the hydrology of a wetland determines if hydric soils will form and if hydrophytes will be present.

2.2 Hydrographs and Hydrological Regimes

Hydrographs are a diagram that displays changes in a water level (depth or volume) over time.  Water levels can be measured in the field using a depth gauge or an electronic data logger.  Water levels can be recorded every few seconds to every week or month.

Once we have collected our water level data, we simply plot it as an x-y chart, with date on the x-axis and depth (or volume) on the y-axis.

Note that a depth of zero represents the ground surface, where a value of 0 indicates water is exactly at the top of the substrate.  Positive values indicate the depth above water above the ground surface, while negative values indicate that the height of water occurs that distance below the surface.  

When we examine a hydrograph, there are three main ways we can describe patterns of flooding in a wetland: (1) depth of flooding and (2) duration of flooding, which is called the wetland's hydroperiod, and (3) the seasonal pattern of water levels in the wetland. Collectively, these descriptors define a wetland's hydrological signature.  

Hydrological signatures have a large influence on wetland properties and are used to classify wetlands by what we call hydrological regimes.  There are two main categories of hydrological regimes: (1) tidal and (2) non-tidal systems.


2.3 Field indicators of Wetland Hydrology

Field indicators are other clues that show the area is a wetland even without standing water

These include:

  • The presence of surface water, but flooding on its own can not be used to say it is definitively a wetland.

  • Soft, mushy, or waterlogged ground aka saturated soils.

  • Water marks on trees or other items indicate high water levels and previous flooding.

  • Sediment Deposits

  • Drift Lines which are small piles of debris lodged in tress or piled against other object this is caused but the direction of water movement.

  • Mud cracks as in low lying areas this can indicate soils had been previously saturated

  • Evidence of water drainage or flow