Environmental Factors

Environmental Factors

Environmental Factors At Cabrillo National Monument

 Excerpt from The Cabrillo National Monument webpage: http://www.nps.gov/cabr/naturescience/environmentalfactors.htm

 An “Island” in the Big City

Cabrillo National Monument sits at the end of a naturally beautiful promontory affected by numerous environmental factors and influenced by a nearby city and port. The Point Loma Peninsula used to be an actual island but today the Point Loma Ecological Conservation Area (PLECA) stands out in aerial views as an isolated island of native vegetation in an urban landscape. One of the reasons it is now an ecological island is that historically there was a marsh at the base of it that isolated it in many ways. This is where the San Diego River used to switch back and forth between Mission Bay and San Diego Bay.

The monument contains 160 acres at the tip of the Point Loma peninsula, which reaches an elevation of 422 feet. It is bordered to the west by the Pacific Ocean, on the east and south by San Diego Bay, and on the north by an urban environment. The portion of the peninsula that is not owned by the National Park Service is divided among the U.S. Navy, U.S. Coast Guard, the City of San Diego, and the U.S. Department of Veterans Affairs. All of these landowners have collaborated and established the PLECA, which covers 662 acres, in order to enable management of the natural resources on the entire peninsula.

Weather data is recorded for San Diego at Lindbergh Field (the airport), which is directly across the bay from the monument. The average annual temperature is 64 degrees and the average annual rainfall is a scant 9.5 inches. Rainfall is concentrated in the winter, from November to April, but the amount can drastically change year to year, from 3.4 inches to 19.4 inches. This variability in rainfall causes certain types of plants to thrive one year and barely survive another. Nature makes up for this lack of rain when cold air from the ocean meets the balmy air on the land and dense fogs roll in. The fog adds moisture to allow species requiring more water to coexist with the desert plants and animals. The ocean also keeps air temperatures mild year-round, which allows heat-loving cactus to grow next to evergreen shrubs common in cooler climates, salamanders to walk past sunning desert snakes, and mosses to grow in the cool shade, a stone’s throw from where parched lichen cling to dry, hot boulders.

The peninsula is comparable to an island because of the aquatic borders and the urban landscape to its north. Sources of factors that continually influence the monument and the PLECA are the North Island Naval Air Station across the bay, the San Diego airport seven miles to the northeast, and the city of San Diego, an urban environment surrounding the park. Air quality issues include pollution from vehicles which compromise the views from the scenic overlook at the monument’s Visitor Center. An even greater issue is habitat fragmentation which results in animals being unable to interact with other animals to the east because of a large bay and city in the middle.

There are a number of influences on the soundscape, including military and commercial aircraft, the fog horn on the jetty, Coast Guard and Navy activity, vehicular traffic, and operation of the Point Loma Waste Water Treatment Plant. San Diego Bay is a major port of entry, especially for ships traveling north from Mexico. The Navy operates several bases with direct access to San Diego Bay including Naval Base Coronado, Naval Base San Diego, and Naval Base Point Loma (with associated submarine bases). The U.S. Coast Guard also actively uses the bay for daily operations and maneuvers.

Water quality is affected by the industries around the bay, and commercial, governmental, private, national, and international ships and boats. Personal watercraft are also used in the bay and are a source of pollution. The City of San Diego operates a Wastewater Treatment Plant north of the monument’s intertidal area. This plant treats 180 million gallons per day of sewage, and deposits the treated effluent four miles offshore at a depth of 400 feet. In 1992, an accidental leak released effluent along the rocky intertidal coast. While there have been several smaller sewage spills since then, there is no current direct discharge, but there is an on-going possibility of a leak.

Non-native species are one of the biggest threats to the park. These species are sometimes called “exotics.”  Exotics are plants and animals that are not from the monument’s coastal sage scrub and marine communities, but have somehow been introduced (either accidentally or intentionally) to the environment and have adapted to it. Exotic species can be detrimental to native species. One example of this is the non-native Argentine ant. These ants have displaced the native ants and have caused major problems for the coast horned lizard population. The coast horned lizard survives on native ants, and does not eat the Argentine ants. In those areas where Argentine ants have established colonies, the coast horned lizard has died off and no longer exists. This has occurred at the park where insufficient numbers of native ants and a lack of habitat no longer allow the coast horned lizard to exist.

Habitat fragmentation, climate change, and ocean acidification are also big threats to the health of our Point Loma “island”.

To learn more about the peninsula, a good book is Understanding the Life of Point Loma, available in the Visitors Center Bookstore.

Understanding the Life of Point Loma

Last revised 17-Aug-13