USA: California: Restoration of Batiquitos Lagoon (Carlsbad)

Overview

Batiquitos Lagoon is a coastal lagoon located in the southern part of California just 35 miles (56.3 km) north of San Diego city. During the 20th century many transportation routes had been built across the mouth of the Batiquitos Lagoon, cutting the lagoon off from the ocean. This included three transportation corridors (a railroad bridge, the Pacific Coast Highway, and Interstate 5) that were constructed across the lagoon. These corridors constricted the tidal flow of water in and out of the lagoon. Additionally, agriculture and urban development in the watershed area caused a significant influx of fine sediment into the lagoon. Heavy agricultural and residential land uses in the 30-square-mile (77.6 kmÁ‚²) watershed were the source of significant nutrient loading from fertilizers and runoff. All these factors contributed to the degraded state of the lagoon and the closure of the tidal inlet.
With the connection to the ocean lost, the lagoon’s water became less saline and sediment began to accumulate, reducing the lagoon’s habitat value for plant and wildlife species. The interface between salt and fresh water creates an ecosystem unique to lagoons because they are both nutrient rich and sheltered from wave action. In addition, due the change in elevation from the lagoon’s water surface to the top of the lagoon’s banks there are three general habitat types; 1) upland habitat, 2) intertidal habitat, and 3) open water (listed from highest to lowest in elevation). Each habitat houses its own plant, fowl and/or fish wildlife.
The ဘupland’ plant habitat consists of; scrub, grassland, willow, riparian, un-vegetated sand flat, and saline meadow. The birds in the upland area are bullock’s oriole (Icterus bullockii), western kingbird (Tyrannus verticalis), warblers, and black-headed grosbeak (Pheucticus melanocephalus) and other large birds such as raptors. In the intertidal environment the plant life includes; salt marsh, brackish marsh, freshwater marsh, algal beds, mudflats, and salt panne. The birdlife entails both wading and shore birds, and water fowl, such as mallard ducks (Anas platyrhynchos). ဘOpen water’ habitat type is characterized more by its physical characteristics than by the plants and birds that live in it. Based on these physical characteristics, this habitat can be subdivided into three areas: 1) salt water lagoon, 2) near shore, and 3) fresh water. Some fish species that are commonly found in open water habitat are the ဘaerial fish foragers’, for whom catch fish by flying low over the water to locate their food and then diving into the water to capture it. These aerial fish foragers include; pelicans, terns, and kingfishers. The lagoon fish community supports three guilds of fish: 1) Pelagic fish (fish that live and feed primarily in the water column, such as smelts), 2) Demersal fish (fish that live and feed primarily along the bottom, such as rays) and, 3) Structured-habitat fish (fish that use underwater structures, such as rock pilings and eelgrass).
Although once a ဘtidal system’, Batiquitos Lagoon has remained largely un-tidal for the last 90 years. By the early 1980’s, the lagoon had achieved an advanced state of sediment infilling and eutrophication resulting in serious natural habitat declines. In 1997, the Port of Los Angeles et al. began the environmental restoration of Batiquitos Lagoon. Since the end of construction, the ecosystem of the lagoon has gradually changed from a confined non-tidal system with limited habitat value to fully tidal, salt water system with greater habitat value.
The major construction process involved:
– dredging sand from the central basin for use in beach replenishment and creation of tern colonies (1994-1995)
– placement of fine sediment materials dredged from the eastern basin into the central basin borrow pit and construction of the lagoon mouth jetties (1995-1996)
– capping the central basin borrow pit, containing fine sediments, with sand dredged from the western basin.
The minor construction process involved:
– remove and re-contour an access ramp in the eastern basin
– plant pickleweed (Salicornia europeae) along parts of the northern shore of the eastern basin
– remove an undesirable underwater ridge in the entrance channel of the lagoon
– weed and repair erosion damage on tern colonies and prepare colonies for the 1997 nesting season
– enhance the facing of the railroad bridge abutments