Pickleweed productivity influenced by within-marsh location rather than regional salinity gradient

Results

We conducted an investigation into the effects of in-situ inundation and salinity on the annual net primary productivity (ANPP) of Sarcocornia pacifica (Figure 1; pickleweed, formerly known as Salicornia virginica) in three tidal marshes in San Pablo Bay throughout one growing season.

In the context of predicted climate change in the San Francisco Bay-Delta region, sea-level rise will result in increased duration of inundation in all tidal wetlands. As Sierran snow pack diminishes, late summer water salinity levels in the Bay will rise due to reduced river flows, potentially increasing wetland soil salinity. The combined effects of increasing inundation and salinity on wetland vegetation, specifically on plant productivity, are not well understood in this Mediterranean-climate system. We tested the effects of these two factors using a regional salinity gradient and within-marsh sampling to assess how predicted sea-level rise and increased salinity may alter tidal wetland plant communities.

Salinity: Since we were unable to differentiate well from poorly-drained plots at Pond 2a, the data were analyzed separately from the other sites. Pore water salinity levels increased more rapidly throughout the growing season at China Camp than Coon Island (Figures 4a and 4b; P < 0.001), at all soil depths (P < 0.001), and increased more rapidly in well-drained plots than poorly-drained plots (P < 0.001). There was no time*site*drainage or time*depth* drainage interaction (P > 0.40 for both). At Pond 2a, pore-water salinity increased over time at all depths (data not shown; P < 0.001) but it did not differ in magnitude among depths (P = 0.26). There was a significant positive relationship between average pore water salinity and distance to channel at Pond 2a (R2 = 0.68; P < 0.001).

Biomass: Biomass increased later in the season at all sites (Figure 5) (China Camp and Coon Island shown). Biomass appears to peak earlier at China Camp when salinity at all soil depths exceeds 40 ppt, while peaking later at Coon Island which has lower soil pore salinity concentrations.

ANPP: Average plant height and ANPP were significantly correlated across all sites (Figure 6; R2 = 0.30; P < 0.001). Irrespective of drainage, average plant height decreased with salinity at all sites (data not shown; R2 = 0.40; P < 0.001), although the relationship was stronger in poorly-drained sites (data not shown).

Across all sites, no significant relationship existed between salinity and ANPP (Figure 7; R2 = 0.06; P = 0.06). At Pond 2a, there was no significant relationship between distance from channel and ANPP (data not shown; P = 0.53) or between salinity and ANPP (data not shown; P = 76).

When inundation and drainage is considered, ANPP decreased with salinity in poorly-drained plots (Figures 8, 9; R2 = 0.39; P = 0.002) but not in well-drained plots (P = 0.96).

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Figure 4. Pore water salinity at depths of 5, 10, and 20 cm increases over time in a) poorly drained plots and b) well drained plots at China Camp and Coon island (error bars = ±1 SE).

Figure 8. Separating well- from poorly-drained plots yield 2 patterns: no ANPP vs salinity relationship in well-drained plots, significant negative relationship between ANPP and salinity in poorly-drained plots.

Figure 6. Across all sites, average S. pacifica height increases as ANPP increases.

DiscussionThe SF Bay-Delta tidal wetlands exist in a Mediterranean-climate with no summer rainfall. Salinity increases through the summer, especially above the low marsh. Because S. pacifica is physiologically adapted to saline conditions, productivity seems little affects by salinity alone.

Our data suggests that the combined effects of prolonged inundation and salinity have a negative effect on productivity. Salinity also has a negative effect on the average height of pickleweed and the effect is stronger under conditions of prolonged inundation. Since Pond 2a is still a relatively new marsh, the differences that we saw at China Camp and Coon Island were not detected; however, the increase in salinity with greater distances from channels would suggest that, over time, the effects of inundation and salinity become more profound.

In light of predicted climate change for the San Francisco Bay-Delta, increased inundation due to sea-level rise combined with less dilution of bay water by reduced river flows will result in a decrease of S. pacifica productivity, ultimately cascading into impacts on regional food web dynamics.

AcknowledgementsThis research was conducted as part of the Integrated Regional Wetland Monitoring Pilot Project (IRWM), an interdisciplinary research effort examining restoration in the North Bay and Delta regions of the San Francisco Estuary. Funding was provided by the California Bay-Delta Authority through the CalFed Science Program. Please visit our website at www.irwm.org. We would also like to thank the National Estuarine Research Reserve (NERR) for permitting us to conduct research in China Camp State Park and California Fish & Game for Coon Island and Pond 2a.

MethodsTotal standing biomass of S. pacifica was monitored for one growing season at three tidal marshes located along a salinity gradient in northern San Francisco Bay: China Camp State Park, Pond 2a, and Coon Island (Figure 2). China Camp is a natural salt marsh located along San Pablo Bay and is one of two sites in the San Francisco Bay National Estuarine Research Reserve (NERR). Located off the Napa River, Pond 2a is a former salt pond that was restored to tidal action in 1997. Coon Island is natural brackish marsh on the Napa River.Biomass SamplingIn February and March 2005, we established 20 1.5m by 1.5m plots at each site in monospecific S. pacifica stands of roughly uniform height and density. In China Camp and Coon Island, half of the plots were randomly located in areas of frequent tidal flushing and the other half were located in areas of poor drainage. Due to the patchy distribution of S. pacifica at Pond 2a, plots were established across the entire site and could not be classified as being well or poorly drained. The spatial coordinates were recorded for each plot, the corners were staked, and the plot was divided into nine 0.25m2 subplots (Figure 3). We collected S. pacifica biomass four times throughout the growing season. At each collection event, we recorded the plant species present in the subplot, relative percent cover of each species, and average plant height. Soil salinity was measured at depths of 5, 10, and 20 cm using a refractometer and water extracted by squeezing 2-cm long soil cores in a 20 CC syringe with filter paper at the tip. All above-ground biomass within the plot was removed and placed in plastic bags for sorting in the lab. All plant material was rinsed with fresh water, sorted by species, and bagged. All bags were dried to a constant weight in a drying oven for 2 days, after which they were weighed and the total biomass was adjusted for bag weight and converted to values on a meter-squared basis. ANPP was calculated by subtracting the smallest biomass from the largest biomass at each plot, irrespective of time.

Since we were unable to differentiate well from poorly-drained plots at Pond 2a, we used distance to nearest channel as a proxy for inundation duration. We created a channel network layer using ArcMap 9.0 and calculated the distance between each productivity point and the nearest channel to determine if there were any relationships between ANPP, salinity, and distance to channel.

All data were analyzed using either simple or multiple regressions using SAS version 9.0

V. Thomas Parker1, Lisa Schile1, John Callaway2, and Michael Vasey1

1 Department of Biology, San Francisco State University, San Francisco, CA 94132 2 Department of Environmental Science, University of San Francisco, San Francisco, CA 94117

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Introduction

Figure 1. Sarcocornia pacifica

Figure 2. Map of study sites.

Figure 3. Example of productivityplot, subdivided into 9 subplots

Poorly-drained plots

Well-drained plots

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For more information visit: www.irwm.org

Figure 5. Average biomass across the season in well-drained vs poorly-drained sites. The top graph (5a) shows the pattern for the salt marsh at China Camp, while the bottom (5b) shows results for the brackish marsh at Coon Island (error bars = ±1 SE).

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Figure 7. Across all sites and including all plots, no relationship occurs between ANPP and salinity.

Figure 9. Comparing averages of all well-drained vs poorly-drained plots for China Camp and Coon Island indicates the magnitude of ANPP differences within these marshes. Only the total average is shown for Pond 2a.

Well-drained plots

Poorly-drained plots