Potential watershed impacts on Elkhorn Slough

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A watershed-related issue examined by the ENVS 560/L Watershed Systems class at CSUMB.

Elkhorn Slough, located in the California central coast, is fed primarily by Carneros Creek. Settlement and development in and around the Carneros Creek Watershed, such as the cultivation of steep slopes for agriculture and the increase of residential structures and roads, has caused major changes in water flow and quality [1]. In addition, human activities allow for the distribution of pollution and pathogens. Several groups and organizations work in the area to address these concerns.

Aerial photo of Elkhorn Slough. The Carneros Creek Watershed is contained within the Elkhorn Watershed and includes all areas upstream from Elkhorn Slough. Copied from Elkhorn Slough Foundation.


Elkhorn Slough is located along the central California coast within the curve of the Monterey Bay, one hundred miles south of San Francisco. Its watershed stretches from the Parajo Valley south to Castroville, and from the headwaters in San Benito County west to Monterey Bay [2]. Its main fresh water tributary is Carneros Creek. (Arguably, during incoming tides at Moss Landing Harbor, the watershed of Elkhorn Slough also includes the watersheds of the Old Salinas River Channel, which also drains into Moss Landing Harbor. In turn, this incorporates the watersheds of Tembladero Slough, the Salinas Reclamation Canal, Gabilan Creek, etc.).

Resources at stake

The Elkhorn Slough is a biologically rich wetland system that provides habitat for migratory birds, rare plant species, and nursery grounds for fish [1]. Agricultural and residential development that occur throughout the Elkhorn Slough watershed have created sedimentation and pollution concerns [1]. The Elkhorn Slough Watershed Conservation Plan, created in 1999 to address these issues, identified the riparian forests in the lower Carneros Creek floodplain and the upland ridges with unfragmented maritime chaparral in the Elkhorn Highlands as areas in need of protection and restoration [1].

Resources present in Elkhorn Slough that are considered of high priority for conservation include [1]:

  • Coastal marsh: Anthropogenic modifications to the hydrology of the Elkhorn Slough have caused the loss of much of its historical marshland [3]. Migrant and resident birds such as the Great Blue Heron and the Snowy Egret use the marsh areas as feeding and roosting habitat. A small breeding population of the endangered Snowy Plover was found along the shores of the marsh, along with nesting pairs of Golden Eagles and White-Tailed Kites.
  • Freshwater wetlands and Riparian forests: The wetlands house numerous threatened and endangered species that depend on moist, cool habitats including the Santa Cruz Long-toed Salamander, California Tiger Salamander, California Red-legged frog. Functioning wetlands also provide important services to the ecosystem by acting as filters to trap sediment and contamination.
  • Maritime chaparral and Coast live oak woodlands: Maritime chaparral, a unique California plant community, contains endemic plants such as Hooker's manzanita, Pajaro manzanita, Monterey ceanothus, Eastwood's goldenbush. Coast live oak is a more common plant community, but those found in association with the rare chaparral plants are considered a priority for conservation. In addition, plant communities that are associated upland of riparian forests and wetland areas may have an important role in the life history of the threatened amphibian species[4].
  • Water quality: Increase of residential development and agricultural practices on steep slopes surrounding Elkhorn Slough have increased pathogens, chemicals, and nutrients in watershed waterways (citation needed).
  • Stream physical structure: Erosion caused by human activities has increased sedimentation and has altered or filled in natural waterways (citation needed).


Several groups, organizations, and government agencies with interests in Elkhorn Slough work to address the environmental threats to its watershed. These include:

  • Elkhorn Slough Foundation (ESF): a non profit organization concerned with the health, conservation, and management of Elkhorn Slough. ESF also provides educational opportunities (tours, interpretive literature, etc.) for the public [5].
  • Elkhorn Slough National Estuarine Research Reserve (ESNERR)
  • ALBA & Triple M Ranch: maintain sustainable farming practices on their lands and attempt to reduce erosion and pollution flow into downstream waters [6].
  • Family and corporate farms
  • Residents: Residents of Elkhorn Slough and residents of the surrounding watersheds
  • County regulators
  • US Fish and Wildlife Service (FWS): US FWS designated Elkhorn Slough as a Critical Habitat for the threatened California red-legged frog (Rana draytonii) [7] Accessed on Feb. 1, 2011.
  • California Department of Fish and Game
  • Audubon Society: Elkhorn Slough is listed by the National Audubon Society as a Globally Important Bird Area for migratory birds along the Pacific Flyway [8] Due to eutrophication of the Slough, bird food source supplies have decreased. This decrease may have a negative effect on Elkhorn bird populations.[9]
  • Local businesses:dependent on fisheries, recreation and tourism associated with the watershed Moss Landing Harbor at the mouth of the Slough
  • The Natural Resources Conservation Service(NRCS):NRCS created the Elkhorn Slough Watershed Project which aids farmers in soil conservation practices to reduce erosion and subsequent sedimentation of adjacent marshlands.

Laws, Policies, & Regulations

  • The Monterey North County Land Use Plan (LUP): Residential development is discouraged under the LUP, which designated much of the western portion of the watershed to be used for "Agricultural Preservation" or "Scenic and Natural Resource Recreation." In the Carneros Creek area and the Elkhorn Highlands, land use designation restrict residential development in wetlands, chaparral and ridge tops.
  • Ord. 2806, 198 1.: Monterey County has attempted to reduce watershed erosion by enacting ordinances that require permits to be obtained for land clearing, building, and grading. Development activities in areas of highly permeable soils must retain all sediments on site through tools such as, infiltration basins and percolation pits. In areas of impervious surfaces sediment from the development must be spread on a non-erodible vegetated area. Government agencies have the authority to charge landowners fines if runoff is detected from agricultural fields [10].


Scientific studies conducted on the watershed effects on Elkhorn Slough have considered runoff from human activities and other alterations of the upstream land and how it relates to the following:

  • California sea otter: Studies conducted at Elkhorn Slough describe sea otter distribution and factors effecting density [11]. Another study looks at the increase the parisite, Toxoplasma. gondii, occurrence in sea otters in Elkhorn Slough. T. gondii is a parasitic pathogen with two life stages, transferred from the first host (typically a domestic cat) through waterborne fecal matter that is carried downstream to Elkhorn Slough. T. gondii affects muscle and nerve tissue and has resulted in fatal brain infections of California sea otters [12].
  • Human health: Runoff from the watershed surrounding the slough can severely degrade the water quality and may even pose health risks to humans. E.Coli outbreaks between 2002 and 2006 in California were studied to better understand the sources and methods of transport of environmental contaminants[13].
  • Eutrophication: This study quantifies the eutrophication within the slough caused by nutrient loading[14].


A variety of tools and technology have been used to better understand the processes within Elkhorn Slough, these tools include:

  • Solarization has been studied as a possible tool to help control non-native plants from invading native plant communities. [17].
  • Vessel based LiDAR monitoring has been used as a method for determining areas of erosion and accretion in Elkhorn Slough[18].
  • Aerial LiDAR monitoring is the current method for detecting geomorphic changes within the slough[18].
  • Hyperspectral imaging has been used as a tool to assess the responses of eutrophocation and nutrient enrichment at Elkhorn Slough [19].

Future Research

A list of research topic, as well as, a list of student research ideas can be found on the Elkhorn Slough website.


  1. 1.0 1.1 1.2 1.3 1.4 Elkhorn Slough Watershed Conservation Plan http://www.elkhornslough.org/eswcp/ESWCP.pdf
  2. http://www.elkhornslough.org/watershed/index.htm
  3. http://www.elkhornslough.org/tidalwetland/downloads/VanDykeWasson2005.pdf Van Dyke et al 2005
  4. Olson DH, Anderson PD, Frissell CA, Welsh HH, Bradford DF.2007 .Biodiversity management approaches for stream-riparian areas: perspectives for Pacific Northwest headwater forests, microclimates, and amphibians. Forest Ecology and Management. 246:81-107
  5. About ESF http://www.elkhornslough.org/esf/index.htm
  6. ALBA wetland restoration http://www.elkhornsloughctp.org/reference/subissue_detail.php?SUBISSUE_ID=48&sort=MAIN_PUB&order=ASC Accessed on Feb. 2, 2011
  7. FWS http://www.fws.gov/pacific/news/2001/2001-43.htm
  8. Audubon Society http://www.elkhornslough.org/conservation/why.htm Accessed on Feb. 1, 2011
  9. Elkhorn Slough: Technical Report Series 2009:1 http://www.elkhornslough.org/conservation/why.htm
  10. Erosion Control http://www.co.monterey.ca.us/building/docs/ordinances/Erosion_Control.pdf
  11. Reference text http://library.elkhornslough.org/research/bibliography/McCarthy_otters_technicalreport_2010.pdf
  12. Miller et al. 2002. Coastal freshwater runoff is a risk factor for Toxoplasma gondii infection of southern sea otters (Enhydra lutris nereis). International Journal for Parasitology. 32(8)997-1006 http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T7F-45RFM7B-4&_user=521395&_coverDate=07%2F31%2F2002&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_searchStrId=1633461532&_rerunOrigin=scholar.google&_acct=C000059570&_version=1&_urlVersion=0&_userid=521395&md5=157ab5acb408c2f012bfbd4288ba6d90&searchtype=a
  13. Cooley M, et al. 2007. Incidence and tracking of Escherichia coli 0157:H7 in a major produce production region in California. PLoS ONE 2(11): e1159. doi:10.1371/journal.pone.0001159
  14. Huges, Haskins & Wasson. 2010. Assessment of the effects of nutrient loading in estuarine wetlands of the Elkhorn Slough watershed: a regional eutrophication report card.http://library.elkhornslough.org/research/bibliography/Elkhorn_Eutrophication_Report_Card_Tech_Report.pdf
  15. http://www.elkhornslough.org/research/waterquality_main.htm
  16. Modeling Nitrogen in Elkhorn Slough http://www.elkhornsloughctp.org/reference/subissue_detail.php?SUBISSUE_ID=8
  17. Lambrecht S, D'Amore A. 2010. Restoration note: Solarization as a technique for exotic plant control in a cool coastal region of California. Ecological Restoration (In Press)http://www.biology.sjsu.edu/facultystaff/lambrecht/Publications.aspx
  18. 18.0 18.1 http://adsabs.harvard.edu/abs/2010AGUFMOS31B1423M Accessed on Feb 3, 2011.
  19. Siciliano D, Wasson K, Potts DC, Olsen RC. 2008. Evaluating hyperspectral imaging of wetland vegetation as a tool for detecting estuarine nutrient enrichment. Remote Sensing of Environment 112:4020-4330 http://www.nps.edu/Academics/Centers/RemoteSensing/docs/hyperspectral_estuarine.pdf



This is a watershed-related issue examined by the ENVS 560/L Watershed Systems class at CSUMB.

This page may contain student work completed as part of assigned coursework. It may not be accurate. It does not necessary reflect the opinion or policy of CSUMB, its staff, or students.