What are Wetlands?
What are wetlands? In the simplest terms, wetlands are transitional zones between uplands and large bodies of water such as rivers, lakes, or oceans, where water tends to stand for prolonged periods of time. The main types of wetlands are swamps, marshes, and bogs which are best recognized by their dominant plants: trees and shrubs, grasses or sedges, and mosses, respectively.
The Petaluma area contains marshes, which are either freshwater or saltwater in character. We also have seasonal ponds, which contain rainwater in the wet season but tend to dry up during the summer. The central pond in Shollenberger Park is a seasonal pond while the side channels (where the cattails live) are a classic freshwater marsh. The main pond is somewhat brackish since it gets recharged with river water once every few years during the river dredging. The Petaluma River is actually a brackish tidal slough which connects to San Francisco Bay and supports along its edges brackish tidal marshes, or tidal wetlands.
Since all these wetlands are covered with water much or all of the year, the soil under them is saturated with water, lacking in oxygen, and as such supports a unique group of plants called hydrophytes, which can live happily with their roots submerged in water. Our freshwater marshes abound with cattails and bulrush, while our saltwater marshes contain cordgrass, pickleweed, and salt grass. Lesser-known hydrophytes are also present.
These wetlands are home to many species of invertebrates, fish, reptiles, amphibians, birds, and mammals that are adapted to live in wetland environments, some preferring the fresh and others the brackish waters. Some species live exclusively in wetlands while other species depend on wetlands for part of their life cycles. The biological productivity of Bay Area wetlands is among the highest of any ecosystem in the world.
Why are Wetlands important?
Since the 1970s we have learned that wetlands are NOT wastelands but perform several very important functions in our world. These functions are summarized as follows:
1) Wetlands detain water, which reduces flooding and erosion downstream during major storms. Think of a wetland as a giant sponge lying between our uplands or cities and the major waterways that drain them, or as a sponge lying between our uplands and our cities. Wetlands help to maintain shipping channels by reducing siltation.
2) Because wetlands detain water, there is time for the natural biological processes that occur in wetlands to purify the water. This is how all of mankind’s sewage was purified before people started to build wastewater treatment plants a century ago.
3) In some wetlands the detained water can recharge the groundwater, thus storing water for future needs.
4) Wetlands are among the world’s most productive ecosystems in the mass of plants and animals produced per acre per year!
5) Wetlands provide critical habitat for many plant and animal species. Many species of fish and seafood use wetlands as their nursery. Over half of the world’s migratory birds depend on wetlands to survive during their annual migrations north or south. Hundreds of species depend on wetlands for their existence. Of the nearly 400 species of birds found in California, nearly 75% are migratory and depend upon marshes and ponds for shelter and food during migration. In addition, Petaluma’s wetlands provide habitat for endangered and threatened species such as the Clapper Rail, Salt Marsh Harvest Mouse, Black Rail, and Western Pond Turtle.
6) Wetlands provide humans with many marketable crops, including seafood, fish, cranberries, wild rice, timber, etc.
7) Wetlands provide for human recreational activities, including hunting, fishing, birdwatching, boating, swimming, camping, and nature studies.
8) Marshes contribute to the stability of global levels of nitrogen, sulfur, carbon dioxide, and methane.
Wetlands are critical to our well-being as a modern urban species, and we need to understand, preserve, and maintain our remaining wetlands.
How do Wetlands Work?
Healthy wetlands are complete ecosystems, containing many species of microscopic organisms, invertebrates, plants, fish, birds, reptiles, amphibians, and mammals that form a complex food web, or series of food chains. Wetland plants get their energy from the sun but require other nutrients, which they get from the water or the detritus (dead plant and animal material that collect on the bottom of the wetland). Detritus also feeds many microorganisms, small invertebrates, baby insects, baby fish, etc, which in turn feed larger animals, which then provide food for larger animals, and, in turn, perhaps even larger animals such as wading birds, mink, and humans. Some wetland animals eat the wetland plants. When these plants and animals die, new detritus is formed. When humans use wetlands as the final step in their wastewater treatment process, they are pumping into the marsh a very dilute solution of the detritus from our human lifestyle. Our detritus is broken down and consumed by the same mechanisms as the natural detritus of the marsh. This complex food web recycles energy through both the plant and animal life of the wetland. Because of the rich nutrition of most wetlands, due to the quantity of detritus, the dissolved nutrients, and the abundance of plants and animals living there, wetlands compete with the richest farmlands in the world for the title of “Most Productive Ecosystems.”