The Importance of Tidal Circulation in the Restored Bolsa Chica
By Kim DiPasquale

The Bolsa Chica Ecological Reserve represents decades of challenges, legal battles, hard work, dedication, public education and multiple restorative efforts but it wasn’t until August 24, 2006 that the 367-acre full tidal basin was opened to the flow of ocean water near Seapoint Street. This part of the restoration brought marine life and salt marsh habitat back to an area that had been separated from the ocean for over 100 years.

The Bolsa Chica is best described as a tidal salt marsh: a coastal ecosystem within the intertidal zone that is regularly flooded by the tides. Its multiple services include the mixing and distribution of nutrients, oxygen production, natural flood and erosion control, a nursery for fish, a habitat and food source for migratory birds, and a repository for native and endangered plants and animals. The marsh also functions as a carbon sink and helps remove carbon dioxide from the atmosphere.

There are many interacting factors that affect the structure and ecological function of a salt marsh such as climate, salinity, nutrient supply, and substrate but the frequency and duration of tidal flooding is the dominating factor. The importance of hydrology (the movement of water across the land) cannot be minimized because even small changes in hydrology can result in significant biotic changes and decreased support for the food web in general.

An ecosystem is defined as a biological community of interacting organisms and their environment. In a wetland, the starting point is the climate and the structure of the basin. These two factors will influence the speed and frequency of water that enters the system and the water level. The hydrology will then have an effect on the physical and chemical properties of the marsh sediment accumulation and oxygen and nutrient availability. These factors then influence the health, abundance and diversity of the vegetation, animals, and microbes. Since part of an ecosystem’s function involves feedback loop mechanisms, the biota will then have an influence on both the physiochemical environment and the hydrology. To say that these mechanisms are complex is almost an understatement, but that is the reality of nature.

In Southern California, tidal circulation is especially important to coastal marshes because of our minimal rainfall, low runoff, and general drought conditions. Therefore, sea water provides most of the soil moisture for inter-tidal wetlands. There is also a tendency for our wetlands to become closed to tidal flow through the formation of sandbars across the ocean connection. One reason for this is that longshore currents move sand along the coast making the entrance to marshes unstable and if the tidal flow and circulation are blocked, the water becomes stagnant, the salinity increases in the tidal basin, the water temperature increases, and oxygen levels drop. This clearly has a detrimental impact on all plant and animal life and on the overall health of the ecosystem. If the lack of tidal circulation is left unattended long enough, death of the ecosystem will result not to mention the unaesthetic conditions, the offensive odors, and the increased pest densities which would include disease carrying mosquitoes.

In order to protect the Bolsa Chica inlet at Seapoint Street, annual dredging services are required so that the vital ebb and flow of seawater into the full tidal basin can be maintained.This is an expensive undertaking costing roughly one million dollars annually and funding is likely to run out by 2020 so new sources of funding will most likely be necessary. The Bolsa Chica is a precious resource that was saved from the development of a marina and large neighborhoods and t hen restored and protected as an ecological reserve. It behooves us to continue to nurture and protect it for the treasure that it so rightfully is.

References:
Mitsch, Gosselink. Wetlands, 2007.
Roman, Burdick. Tidal Marsh Restoration, 2012. Zedler, The Ecology of Southern California Salt Marshes, 1982