Estuaries are bodies of water which are semi-enclosed. Fresh water, which comes from river or streams, mixes together with salt water from the ocean. These bodies of water trap nutrients and sediments which travel in the rivers and oceans, they then mix the nutrients constantly with the rising and the falling of the tides.
Estuaries can prove to be hostile environments for most plant communities, due to their high salt content. According to “The Encyclopedia of New Zealand,” plants in this environment generally have to be able to deal with a variety of salinity levels, storm waves and intense currents, different levels of sunlight and wind and the low levels of oxygen found in the muddy soils. However, the plants that are found in these waterways, are some of the most productive of any found in other ecosystems.
According to the Marine Resources Research Institute, there are different areas or “zones” in an estuarine ecosystem.
The low marsh zone is the area of an estuary that is subjected to flooding daily by the changes in tide. These areas seem to consist of few plant species, the smooth cordgrass, or Spartina alterniflora, is one. In this part of the estuary can grow up to six feet in height and are usually found along creek banks. Inland and on natural levees can be found a variety which grows up to ten feet tall. This grass can stand submergence, and low-oxygen levels. In New Zealand, Seagrass, or Zostera capricorni, handles the difficulties of growing in this environment.
The high marsh zone has several species that are able to grow. These include glasswort (Salicornia spp.), salt grass (Distichlis spicata) and groundsel tree (Baccharis halimifolia) Several of these, such as glasswort, grow adjacent to the low marsh zone and dominate this higher zone. Further inland are the salt flats which are home to plant life such as saltgrass (Batis maritima), and sea lavender (Limonium carolinianum).
Next is a zone that is covered by a canopy of shrubs. This is generally upland from the marsh. The plants that can be seen here include sea myrtle (Baccharis angustifolia) and marsh elder (Iva frutescens). Most of the plants in this area grow between four and one-half to six feet tall. The water that these plant grow in is brackish water so its salt content is still high. Many of the plants that grow in the high marsh zone thrive in this area also. Others include marshhay cordgrass (Spartina patens), panic grass (Panicum virgatum) and fimbristylis (Fimbristylis spp.).
Trees can be seen growing in areas where there are large amounts of sediments and the land is not completely covered by water. The amount of salt in the water is diminished here but not eliminated entirely. Trees have to be able to withstand possible flooding and some saltwater. The trees that are found in this area are the live oak (Quercus virginiana), red oak (Quercus rubra), and the red maple (Acer rubrum ). The loblolly pine (Pinus taeda) and mangrove tree also do well in this environment in the Southern United States. Along with these trees, cattails and bulrushes are plentiful in this area, also.
The plants that grow along estuaries provide habitats and food sources for the wildlife that live in these environments. They provide shade as well as protection also. Estuaries, and the life around them, are a well-needed part of the world’s environment.