Press Release: Elkhorn Slough Researchers Link Salt Marsh Dieback to Algal Blooms Generated by Increased Nutrients

In Press, Research, Salt Marsh by Administrator

For immediate release: June 5, 2017

For more information:
Lorili Toth, Director of Development & Communications
Elkhorn Slough Foundation
Email:   phone: 831.728.5939

Kerstin Wasson, Ph.D, Research Coordinator
Elkhorn Slough National Estuarine Research Reserve
Email:  phone: 831.728.2822 ext 310

Download the PDFMEDIA_ADVISORY-Algal_Mats_Harm_Marsh_fin.pdf


Elkhorn Slough Researchers Link Salt Marsh Dieback to Algal Blooms Generated by Increased Nutrients

Moss Landing — Salt marsh habitat is threatened by massive algal blooms, according to a new study conducted by scientists at the Elkhorn Slough National Estuarine Research Reserve (ESNERR), published in the scientific journal, Biological Conservation.  The study reveals that piles of green algae form mats along bank edges that leads to dieback of the salt marsh below. When the marsh plants die, the roots no longer help to hold the bank together causing large pieces of the bank to fall into the channel in response to strong tidal currents or wind-driven waves in the slough. The result: marshes convert to mudflats at the edges, and, in the face of sea level rise and low sediment volumes, the conversion is permanent.

Citizen scientist, Elkhorn Slough Reserve volunteer, and avid kayaker Ron Eby, sparked the study with an observation of the algal mats and eroding bank chunks. “It just seemed there was a connection between the algal mats on the marsh edges and mud chucks calving off the banks,” Eby states. He brought his wonderings on whether the mats caused the erosion to ESNERR Research Coordinator Kerstin Wasson, Ph.D, who oversees the diverse research projects occurring at Elkhorn Slough.

“It’s heartening to see the curiosity and observational skills of our volunteer Ron Eby lead to significant discoveries about the challenges we face in the Elkhorn Slough,” said Reserve Manager Dave Feliz. With the question raised, ESNERR researchers led a collaborative investigation including Reserve staff, academics, summer research interns, and Eby himself. The team monitored 15 sites along the main channel of Elkhorn Slough where the edges had varying amounts of algal mats. The year-long surveying found that plant health decreased and bank erosion increased the more extensive the algal mats were.

To complement this observational study, an experiment involving 30 test plots was conducted. Interns lugged buckets of algae onto a marsh to cover marsh plants for either 0, 8 or 12 weeks. The plots showed the same results as the observational monitor — impaired marsh growth and retreat of the marsh edge —indicating the more often or the more algae the worse the impact on the marsh.

Green algae are natural parts of the estuary community, but their abundance can be tremendously increased by nutrients in the water. To determine whether algal blooms at Elkhorn Slough were natural or the result of human activities, the research team did some historical detective work. They examined aerial photographs dating from the 1930s to the present and found that algal mats on the marsh have increased dramatically during the 85 year period. Data on nitrate concentrations in the water and on fertilizer sales in the county were also compiled. The findings showed exactly the same pattern of exponential increase of nitrate concentration, fertilizer sales, and algal blooms over the same period.  The study thus concludes that agricultural fertilizer is not only fertilizing crops in the region, but also, through run-off, algal blooms in the estuary. These fertilizer inputs are responsible for marsh dieback along the channel edges of Elkhorn Slough, as well as for increased erosion rates of the banks.

A related study by Reserve scientists published late last year similarly concluded that nutrient-enrichment of Elkhorn Slough waters is harming biodiversity there. Sites with poor water quality had low oxygen conditions that killed fish and stopped oyster growth. Both of these investigations illustrate the importance of decreasing polluted run-off to the estuary and improving water quality.  “Salt marshes, fish and oysters will be healthier at Elkhorn Slough if fertilizer inputs are decreased,” says Dr. Kerstin Wasson, Research Coordinator of the Elkhorn Slough Reserve and author on both papers.  “The loss of marsh will reverberate into the future,” Wasson explains “we are learning that marsh is excellent at taking up carbon dioxide from the air and storing it deep in marsh soils, which can help to slow climate change.”

Restoration work by the Elkhorn Slough Foundation has improved water quality in wetlands in the estuary. On lands the Foundation owns, sustainable organic agriculture continues in appropriate areas, while very steep slopes prone to the most erosion and polluted run-off are taken out of production and restored to natural habitat, as are formerly farmed areas immediately adjacent to wetlands. These changes have translated into decreased nutrient inputs to adjacent wetlands. “The collaborative work of scientists, farmers, managers and local citizens has started to move the needle on water quality concerns at the slough,” states Mark Silberstein Executive Director of the Elkhorn Slough Foundation.  Silberstein concludes, “These new results motivate us to expand the work of runoff management and restoration and keep our eye on the prize of a healthy coastline.

The Elkhorn Slough National Estuarine Research Reserve (ESNERR) is managed by the California Department of Fish and Wildlife (CDFW) with funding support from the National Oceanic and Atmospheric Administration (NOAA). Established in 1972, the National Estuarine Research Reserve System is a national network of 29 sites along our nation’s coasts. Reserve-based monitoring, research, education, outreach, stewardship, and decision-maker training programs provide much needed information and services to coastal communities. The 1,700-acre Reserve provides 5 miles of public trails, education, research, and volunteer programs.

The Elkhorn Slough Foundation (ESF) is a community-supported non-profit land trust whose mission is to conserve and restore the Elkhorn Slough and its watershed. ESF protects nearly 4,000 acres of rare habitat including oak woodlands, maritime chaparral, and wetlands. Since 1982, ESF has been the non-profit partner of the Elkhorn Slough National Estuarine Research Reserve (ESNERR). For more information on Elkhorn Slough Foundation and the Reserve visit

Elkhorn Slough, located in the central Monterey Bay area encompasses a wide variety of habitats — from oak woodlands, maritime chaparral and coastal prairie the largest tract of tidal salt marsh in California south of San Francisco Bay — that support an incredible diversity of life. Elkhorn Slough hosts 550 species of marine invertebrates, and 100 species of fish, as well as resident sea lions, harbor seals and the highest concentration of endangered Southern sea otters on the west coast. As part of the Pacific flyway, Elkhorn Slough bird numbers can soar during migration seasons, nearly doubling the resident bird counts. The slough is designated a Globally Important Bird Area, with more than 340 species identified in and around the slough.




Please contact ESF for high resolution digital photos.  Photos included on PDF.

All photos credit: Elkhorn Slough National Estuarine Research Reserve (ESNERR)