Risa ERF 2005

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Information about Risa ERF 2005
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Published on January 3, 2008

Author: Heng

Source: authorstream.com

Slide1:  How does nutrient availability relate to primary productivity in natural and restored wetlands in the San Francisco Estuary? INTEGRATED REGIONAL WETLANDS MONITORING PROJECT BACKGROUND Tidal wetlands in the San Francisco Estuary (SFE) have been greatly reduced in area, to where they now comprise only about 15% of their historical extent. This problem led to a growing interest in and commitment to conservation and restoration programs, most notably the CALFED Bay/Delta Program. What has been lacking is a comprehensive monitoring program to evaluate how (or if) restoration sites are changing over time, and which ecological functions are (or are not) returning to “normal”. However, CALFED recently established the Integrated Regional Wetlands Monitoring (IRWM) Program for the North Bay and Delta. Initial funding for 2 years of pilot monitoring was established. This poster describes the first year of monitoring data from the 2004 growing season and estimates of primary production by wetland autotrophs and the concentrations of inorganic nutrients in marsh waters, within both restored (Bull Island, Pond 2A) and natural/reference (Coon Island) tidal wetlands in the SFE. Little is known of the relative availability of nutrients in wetlands of the SFE. Changes due to restoration efforts may impact the different inorganic sources entering SFE, which in turn will influence the aquatic primary producers (both macro and micro) that grow and feed higher trophic levels. The balance of various constituents of the nitrogen cycle (e.g., NO3- vs. NH4+) may be important in determining the food web and plant species that result. Si(OH)4- is required for diatoms, the key primary producers in short energetically efficient pelagic food chains and in benthic sediment ecosystems. CONCEPTUAL MODEL OBJECTIVE To evaluate differences in nutrient availability and the contribution of different groups of autotrophs to primary production  METHODS • Water samples (n=3 for all sites) - collected and filtered monthly during the growing season and analyzed for NO3-, NH4+, PO4- and Si(OH4) - using autoanalyzer and colorimetric techniques. • Primary productivity of 4 groups of primary producers (phytoplankton, benthic diatoms, macroalgae and low marsh vegetation collected monthly at each site) was determined by: 1) Phytoplankton - C fixation rates measured following incubations with radioactive 14C. 2) Low marsh vegetation - measurement of direct CO2 uptake by the plants using an infrared gas analyzer (IRGA). 3) Benthic diatoms - surface cores (5mm depth, 25mm diameter) incubated with 14C. 4) Macroalgae - incubated in BOD bottles to determine O2 evolution to calculate productivity. All carbon rate measurements were calculated on a per chlorophyll basis. There was a general trend of increased phytoplankton productivity until late summer at all locations. High spring and summer productivity at all sites corresponds with the depletion of NO3-, NH4+, and Si(OH)4- in the water column (e.g. July data). The peak in productivity rates was highest at Pond 2A, the site closest to the mouth of the River, followed by Coon Island and Bull Island. Plant productivity generally increased through the spring months and started to decline in late summer. The highest productivity occurred earlier at Coon and Bull than at Pond 2A. The natural marsh, Coon, had higher productivity than either of the restored Napa River locations (Bull, Pond 2A) throughout the spring and summer months. Benthic diatom productivity generally peaked in the spring followed by an overall decrease with time. Peaks in productivity were similar at all three sites, but productivity remained higher at Pond 2A for a longer duration. The high spring productivity appears to correspond to high levels of water column nutrients available at that time. Risa Cohen, Frances Wilkerson, Edward Carpenter, Richard Dugdale - San Francisco State University incubation Location Location Location Location Location Location Location Phytoplankton Productivity mg C*mg Chlorophyll a-1*h-1 Benthic Diatom Productivity mg C*mg Chlorophyll a-1*h-1 Plant Productivity mg C*mg Chlorophyll a-1*h-1 Water column [NO3-] (mM) Water column [PO4-] (mM) Water column [Si(OH)4-] (mM) Water column [NH4+] (mM) CONCLUSIONS - The data from this study are the first detailed measurements of nutrients and the dominant sources of primary productivity in wetlands of the San Francisco Estuary. - There appeared to be no nutrient limitation at the start of the growing season with the exception of low NO3- at Pond 2A. - The relationship between nutrients and productivity is very complex, but the general trends were as follows: A. Nutrient concentrations decreased over the spring, and NO3- levels were low at all locations by May. B. Productivity generally increased through the spring months, corresponding to nutrient drawdown. C. Productivity by all autotrophs started to decrease in the late summer, coinciding with an increase in water column nutrient concentrations into the fall. - The order of autotroph productivity rates from greatest to least were: Low marsh plants>benthic diatoms>phytoplankton - Macroalgae were not common at Coon Island or Pond 2A, but at Bull Island macroalgal productivity rates were similar to those of benthic diatoms. - These data provide water quality and ecosystem productivity sampling and analytical strategies that may be implemented by resource managers. Nutrients NO3- NH4 + Si(OH)4 - PO4 - Plants Phytoplankton Benthic Diatoms Macroalgae Terrestrial Food Chain Benthic Grazers Zooplankton NO3- concentrations showed variability with location, likely related to distance down river. Values were greatest in March with maxima at Coon and Bull (>50µM) compared to the peak value for Pond 2A (<10µM). All sites showed reduction to almost limiting levels by May, and then concentrations increased slightly from late summer into fall. NH4+ concentrations tended to be high at the start of the growing season at Coon, Bull, and Pond 2A. As with NO3-, NH4+ was reduced until mid-summer, when concentrations began to increase at all three locations. The reduction in NO3- and NH4+ in the late spring and early summer corresponds to peaks in productivity of phytoplankton, low marsh vegetation and benthic diatoms. Si(OH)4- concentrations followed similar trends to NO3-, with highest values in March, decreasing through spring and early summer followed by a gradual increase in late summer. The highest concentrations (>400µM) were measured at Coon and Bull which are sites close together. Pond 2A (most recently restored) showed the lowest levels of Si(OH)4-, analogous to the low NO3- that occurred there also. PO4- concentrations were variable across sites and over the 8-month growing season. Concentrations generally increased over the course of the growing season at all sites, and did not appear to be limiting. Water collection for nutrient and chlorophyll analysis and phytoplankton productivity. Core collection for benthic diatom productivity and chlorophyll analysis. IRGA measurements and biomass estimates for vegetation productivity. Green macroalgae were present at Bull Island over most of the growing season, but were rarely found at Coon, and never observed at Pond 2A. Macroalgal productivity at Bull Island generally increased until June and then decreased with time, similar to the patterns observed for the other groups of primary producers at this site. Location Macroalgal Productivity mg C*mg Chlorophyll a-1*h-1 Coon Island Bull Island Pond 2A Natural Restored 1950 Restored 1995 ACKNOWLEDGEMENTS This Integrated Regional Wetland Monitoring project was funded by a grant from CALFED to the groups listed below. We would also like to extend special thanks to C. Little, D. Reineman, S. Govil, R. Foster, A. Lorenzi, and V. Hogue whose help in the field and in the lab made this portion of the project possible. nd nd nd * * *

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