Phytoplankton production and nutrient transformations in shallow water wetland habitats

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The objectives of this study are to quantify and characterize (1) phytoplankton production on Liberty Island, (2) utilization and transformation of nutrients, and (3) attenuation/loss of phytoplankton as the material is transported from Liberty Iisland into Cache Slough.

Map showing the Liberty Island study site

Map showing the Liberty Island study site. Inset shows the location of Liberty Island in the San Francisco Estuary Delta. Locations and directions of two types of transects are indicated by yellow arrows. See text for explanation of transects. Red circle marks location of USGS gage station continuously recording stage, velocity, discharge, turbidity, nutrients and other water quality parameters.

(Public domain.)

Map showing the Liberty Island study site. Inset shows the location of Liberty Island in the San Francisco Estuary Delta. Locations and directions of two types of transects are indicated by yellow arrows. See text for explanation of transects. Red circle marks location of USGS gage station continuously recording stage, velocity, discharge, turbidity, nutrients and other water quality parameters.

Under the Bay Delta Conservation Plan (BDCP), up to 100,000 acres of wetland restoration is proposed for the San Francisco Estuary Delta to improve habitat conditions and protect endangered species, with about 50% of this wetland area slated for the Cache Slough region. Two of the primary objectives of these wetland restoration efforts are (1) increased production and export of particulate organic carbon (POC) in the form of phytoplankton, and (2) mitigation of wastewater-derived nutrients. However, the production and export of phytoplankton and consumption of nutrients within Delta wetlands has not been explicitly verified or quantified.

One of the essential elements defining success of restoration is export of phytoplankton that supply energy to the pelagic foodwebs supporting threatened and endangered fish species. But the conditions that result in this outcome are not clear. Phytoplankton production results from a complex interaction between the presence of appropriate seed populations, nutrients, and light (Cloern, 2007; Dugdale et al., 2007; Glibert, 2010; Parker et al., 2012). Absolute nutrient concentrations, their chemical forms and concentration balance, all likely influence phytoplankton species composition, which in turn may limit the overall effectiveness of the restoration activity. This study will examine these processes in the Liberty Island wetland, an established freshwater tidal wetland located in the north Delta Cache Slough complex.

The wetland at Liberty Island is often highlighted as meeting the functional requirements of a successful wetland restoration project (Delta Science Program, 2010). Generally, it is thought that nutrients from the Sacramento River are tidally transported into shallow areas of the wetland, whereupon the water becomes clearer, phytoplankton assimilate the nutrients as they grow, and then this new phytoplankton is transported by the tides back into the deeper channels where it is available to support the pelagic foodweb. However, one recent study has suggested that Liberty Island is a net sink for POC, suggesting phytoplankton biomass may not be exported outside of the wetland site (Lehman et al. 2010). To achieve the goals of pelagic fish habitat restoration identified in BDCP, it is critical to resolve the functional properties of wetlands that export bioavailable POC to pelagic habitats (Müller-Solger et al., 2002; Sobczak et al., 2005). Studying wetland processes on Liberty Island in detail will help better guide future restoration efforts and better predict the outcome of large-scale restoration in the Delta.

The objectives of this study are to quantify and characterize (1) phytoplankton production on Liberty Island, (2) utilization and transformation of nutrients, and (3) attenuation/loss of phytoplankton as the material is transported from Liberty Iisland into Cache Slough.

This project relates explicitly to the US Geological Survey's mission to provide scientific information that will be utilized by decision-makers to effectively manage the landscape and water resources for water-related natural hazards, recreational and ecological use, aquatic health, and environmental quality. This project will consider several water-resource issues identified in the US Geological Survey Circular 1309 (USGS, 2007), including water quality, environmental health, contaminant control, land use change, and securing freshwater for our future. The study fits into the framework of "water-quality information and research (local- to regional-scale water contamination issues)" and "earth-science information and research (locations and characteristics of …geologic terrains naturally enriched in potentially toxic substances, and contaminated water, sediment, and soil)..." . This project will also "strengthen partnerships and enhance collaboration with others" through collaboration with State and Federal Contractors Water Association (SFCWA). This research will work towards the goal of formulating "effective methods of monitoring, remediating, and restoring contaminated ecosystems". This project also addresses priority issues of the USGS Cooperative Water Program Ecosystem Change; specifically the sections covering "water quality" and "estuaries, wetlands, lakes and reservoirs".

Literature Cited:

Bergamaschi, B., Fleck, J., Downing, B., Boss, E., Pellerin, B., Ganju, N., Schoellhamer, D., Byington, A., Heim, W., Stephenson, M., and Fujii, R., 2012, Mercury Dynamics in a San Francisco Estuary Tidal Wetland: Assessing Dynamics Using In Situ Measurements: Estuaries and Coasts, p. 1-13.

Cloern, J. E., 2007, Habitat connectivity and ecosystem productivity: implications from a simple model: The American naturalist, v. 169, no. 1, p. E21-33.

Delta Science Program, 2010, "Liberty Island Provides Insights Into Delta Ecosystem Restoration," Science News—a publication of the Delta Stewardship Council, April 2010, accessed at http://www.science.calwater.ca.gov/publications/sci_news_0410_liberty.html.

Downing, B. D., Boss, E., Bergamaschi, B. A., Fleck, J. A., Lionberger, M. A., Ganju, N. K., Schoellhamer, D. H., and Fujii, R., 2009, Quantifying fluxes and characterizing compositional changes of dissolved organic matter in aquatic systems in situ using combined acoustic and optical measurements: Limnology and Oceanography: Methods, v. 7, p. 119-131.

Dugdale, R. C., Wilkerson, F. P., Hogue, V. E., and Marchi, A., 2007, The role of ammonium and nitrate in spring bloom development in San Francisco Bay: Estuarine, Coastal and Shelf Science, v. 73, no. 1-2, p. 17-29.

Glibert, P. M., 2010, Long-Term Changes in Nutrient Loading and Stoichiometry and Their Relationships with Changes in the Food Web and Dominant Pelagic Fish Species in the San Francisco Estuary, California: Reviews in Fisheries Science, v. 18, no. 2, p. 211-232.

Müller-Solger, A. B., Jassby, A. D., and Müller-Navarra, D. C., 2002, Nutritional quality of food resources for zooplankton (Daphnia) in a tidal freshwater system (Sacramento-San Joaquin River Delta): Limnology and Oceanography, v. 47, no. 5, p. 1468-1476.

Parker, A. E., Dugdale, R. C., and Wilkerson, F. P., 2012, Elevated ammonium concentrations from wastewater discharge depress primary productivity in the Sacramento River and the Northern San Francisco Estuary: Marine Pollution Bulletin.

Sobczak, W. V., Cloern, J. E., Jassby, A. D., Cole, B. E., Schraga, T. S., and Arnsberg, A., 2005, Detritus fuels ecosystem metabolism but not metazoan food webs in San Francisco estuary's freshwater delta: Estuaries, v. 28, no. 1, p. 124-137.