- Open Access
Tidal day organic and inorganic material flux of ponds in the Liberty Island freshwater tidal wetland
© Lehman et al. 2015
- Received: 13 November 2014
- Accepted: 28 May 2015
- Published: 17 June 2015
The loss of inorganic and organic material export and habitat produced by freshwater tidal wetlands is hypothesized to be an important contributing factor to the long-term decline in fishery production in San Francisco Estuary. However, due to the absence of freshwater tidal wetlands in the estuary, there is little information on the export of inorganic and organic carbon, nutrient or phytoplankton community biomass and the associated mechanisms. A single-day study was conducted to assess the potential contribution of two small vegetated ponds and one large open-water pond to the inorganic and organic material flux within the freshwater tidal wetland Liberty Island in San Francisco Estuary. The study consisted of an intensive tidal day (25.5 h) sampling program that measured the flux of inorganic and organic material at three ponds using continuous monitoring of flow, chlorophyll a, turbidity and salt combined with discrete measurements of phytoplankton community carbon, total and dissolved organic carbon and nutrient concentration at 1.5 h intervals. Vegetated ponds had greater material concentrations than the open water pond and, despite their small area, contributed up to 81% of the organic and 61% of the inorganic material flux of the wetland. Exchange between ponds was important to wetland flux. The small vegetated pond in the interior of the wetland contributed as much as 72–87% of the total organic carbon and chlorophyll a and 10% of the diatom flux of the wetland. Export of inorganic and organic material from the small vegetated ponds was facilitated by small-scale topography and tidal asymmetry that produced a 40% greater material export on ebb tide. The small vegetated ponds contrasted with the large open water pond, which imported 29–96% of the inorganic and 4–81% of the organic material into the wetland from the adjacent river. This study identified small vegetated ponds as an important source of inorganic and organic material to the wetland and the importance of small scale physical processes within ponds to material flux of the wetland.
- Freshwater tidal wetland
- Wetland material flux
- Vegetated ponds
- Carbon flux
Freshwater wetlands are generally thought to be a sink for nutrients and a source of particulate and dissolved organic carbon to adjacent rivers and lakes (Junk et al. 1989; Bouchard 2007). Total nitrogen and phosphorus were reduced by 79 and 88% after passing through the Amelia wetland in Louisiana (Day et al. 2006). In the Patuxent River Estuary, freshwater tidal wetlands removed 46–76% of the nitrogen and phosphorus load (Boynton et al. 2008). The Vaccarés lagoon wetlands in the Rhone River watershed removed over 95% of the nitrogen and phosphorus imported and exported 5–6 times more organic carbon than the wetlands imported (Chauvelon 1998). Organic carbon production in wetlands is facilitated by elevated net primary productivity of phytoplankton in shallow waters, where the euphotic zone to mixed depth ratio is high (Heip et al. 1995) and phytoplankton cells accumulate due to long residence time (Hein et al. 1999). Inorganic and organic material flux is highly variable among wetlands. Both the magnitude and direction of material flux can vary by many fold, even in adjacent wetlands (Arrigoni et al. 2008).
The quantity and quality of material exported from wetlands is influenced by internal and external physical, chemical and biological processes. External factors such as climate affect the magnitude of water flow and physical factors like water temperature and depth (Childers et al. 2000). Internal factors such as primary productivity, benthic recycling and denitrification affect the quantity and quality of nutrients and organic material available for export (Childers et al. 2000; Childers 2006). Sedimentation can also remove nutrients or organic matter from the water column (Moustafa 1999). The amount of inorganic and organic material exported from the wetland is further affected by wetland morphology, velocity heterogeneity and vegetation type that control the speed and direction of material movement in the wetland (McKellar et al. 2007; Lightbody et al. 2008).
Tide is also a major factor affecting material transport in freshwater tidal wetlands. For the Liberty Island freshwater tidal wetland in San Francisco Estuary (SFE), California, over 90% of the inorganic and organic material flux of open water habitat was tidal (Lehman et al. 2010). Inorganic and organic material flux in the summer was similarly influenced by tidal asymmetry in Mildred Island a flooded island in the delta region of SFE (Ganju et al. 2005; Lopez et al. 2006). Tidal impacts can be subtle in SFE wetlands. Carbon production increased on a fortnightly basis with the number of daylight hours that overlapped ebb tide (Lucas et al. 2006).
It is hypothesized that the long-term loss of over 90% of the wetland habitat in SFE reduced food resources and habitat needed to support estuarine fish production (Brown 2003). Estuarine production is a concern in SFE where there has been a decline in biomass and shift in species composition at all levels of the aquatic food web over time, including a downward shift in the production of phytoplankton, zooplankton and fish, particularly since 2000 (Lehman 2000, 2004; Kimmerer 2004; Sommer et al. 2007). The importance of freshwater tidal wetlands to fishery production in SFE is suggested by the abundance of native fish species in areas with adjoining freshwater tidal wetland habitat in northern SFE near the freshwater tidal wetland, Liberty Island (Sommer et al. 2001; Nobriga et al. 2008). Similarly, fishery production in the Everglades and Chesapeake Bay was also affected by the quantity and quality of nutrients and organic matter produced in adjoining wetlands (Childers et al. 2000; Childers 2006).
For SFE, modeling studies suggested that wetland and floodplain habitats with a high euphotic zone depth to mixed depth ratio could be a source of organic carbon (Jassby and Cloern 2000). Modeling studies also suggested high residence time and warmer water temperature enhanced chlorophyll a production in Yolo Bypass, a large floodplain in SFE (Sommer et al. 2004). Field studies further confirmed that 14–37% of the total chlorophyll a or diatom plus green algal carbon exported to SFE from the Sacramento River and Yolo Bypass floodplain was produced in the floodplain (Lehman et al. 2008). Wetlands in flooded islands within the delta region of SFE are also a source of chlorophyll a and suspended sediment during the spring and summer (Lopez et al. 2006). Much less is known about freshwater tidal wetlands in SFE. Recent research demonstrated that both inorganic and organic materials as well as phytoplankton and zooplankton carbon were periodically exported to river channels in SFE from the Liberty Island freshwater tidal wetland (Lehman et al. 2010). However, the factors within the wetland that influence the magnitude and direction of material flux are unknown. The lack of information is partially due to the difficulty of sampling in shallow freshwater tidal wetlands, where conditions change rapidly with the tide and environmental conditions and shallow water, thick mud, dewatering, remote access and human and animal disturbance impede sampling.
Water quality conditions
Mean and standard deviation water quality conditions measured at 1.5 h intervals over 25.5 h for each pond in Liberty Island wetland between 12 July and 13 July 2006
Water temperature (°C)
Specific conductance (µS cm−1)
Dissolved oxygen (mg l−1)
23 ± 1 a
389 ± 12 c
7.0 ± 0.7 a
7.7 ± 0.1 a
84 ± 18 a
23 ± 4 a
356 ± 65 c
9.4 ± 1.6 b
7.8 ± 0.4 a
126 ± 44 a
23 ± 4 a
254 ± 41 b
9.0 ± 1.3 b
8.2 ± 0.2 b
95 ± 38 a
21 ± 1 b
187 ± 8 b
8.9 ± 0.6 b
8.1 ± 0.1 b
39 ± 5 b
Phytoplankton carbon differed among ponds and with tide (not shown). Average green (525 ± 1,222 pg C ml−1) and miscellaneous flagellate (3,686 ± 9,198 pg C ml−1) carbon were greater (p < 0.01) at MAIN than other stations. However, there was no statistical difference among stations for diatom or cyanobacterial carbon (1,893 ± 2,345 and 328 ± 576 pg C ml−1). More diatom carbon (p < 0.05) on ebb tide at SSB (1,393 ± 3,768 pg C ml−1) and on flood tide at LIBN (16,276 ± 17,321 pg C ml−1), suggested diatoms were produced in the vegetated ponds. Maximum cyanobacteria carbon was detected in the interior of wetland on flood tide in Lower Beaver Pond at LIBN (12,050 ± 742 pg C ml−1) and LIBS (4,366 ± 8,515 pg C ml−1). In contrast, maximum (p < 0.05) miscellaneous flagellate carbon occurred on ebb tide at LIBN (1,577 ± 3,706 pg C ml−1).
The vegetated ponds were the primary source of total organic carbon and chlorophyll a within the wetland and to the adjacent rivers. The total organic carbon and chlorophyll a flux at SSB, LIBN and LIBS combined was greater than the flux of total organic carbon and chlorophyll a at MAIN (Figure 6). Most of the total organic carbon (4,624 kg day−1) and chlorophyll a (10 kg day−1) flux occurred at LIBS, which was also the major source of total organic carbon and chlorophyll a to Main Pond. The significantly (p < 0.05) lower and negative chlorophyll a flux at LIBN compared with the large positive chlorophyll a flux at LIBS indicated that the total organic carbon and chlorophyll a exported from Lower Beaver Pond at LIBS was produced within the pond and not imported from Upper Beaver Pond at LIBN. The relative health of the phytoplankton could not account for the greater chlorophyll a flux into Main Pond from Lower Beaver Pond. Both average chlorophyll a concentration and the percent chlorophyll a to total pigment (chlorophyll a plus phaeophytin) ratio was similar for Main Pond and Lower Beaver Pond (chlorophyll a 4.4 ± 1.0 and 4.4 ± 1.5 µg l−1 and percent chlorophyll a to total pigment 68 ± 9 and 58 ± 12%, respectively; Figure 4).
The river was the primary source of ammonium to the wetland. Ammonium entered the wetland at SSB from Shag Slough and at MAIN from the Sacramento River (Figure 6). The positive flux at SSB and negative flux at LIBN, combined with the relatively small difference between the nitrate flux at SSB and LIBN, suggested 97% of the ammonium imported at SSB was retained in Upper Beaver Pond, and not exported as either ammonium or nitrate. The greater negative ammonium flux at MAIN than the positive ammonium flux at LIBS, indicated that most of the ammonium in Main Pond was imported from the Sacramento River. The greater import of nitrate than ammonium at MAIN also suggested most of the nitrate in Main Pond was imported from the Sacramento River and not produced by the oxidation of ammonium within the pond.
Daily sum and standard deviation (parenthesis) of the hourly material flux and the percent of the total daily flux contributed by each pond, plus the total wetland material flux for inorganic and organic materials in Liberty Island wetland measured on July 12–13, 2006
Upper Beaver Pond (kg day−1)
Lower Beaver Pond (kg day−1)
Main Pond (kg day−1)
Wetland (kg day−1)
Total suspended solids
Volatile suspended solids
Total organic carbon
Dissolved organic carbon
Dissolved organic nitrogen
The net movement of organic material differed somewhat from the net movement of inorganic material in the wetland. High values characterized the volatile suspended solids and dissolved organic nitrogen flux in Main Pond and accounted for 67 and 81%, respectively, of the wetland flux for these materials (Table 2). Main Pond also accounted for 21–35% of the total and dissolved organic carbon flux of the wetland. Similar to the inorganic materials, the flux of total and dissolved organic carbon, volatile suspended solids and dissolved organic nitrogen was northward into the wetland from the Sacramento River. In contrast, the small and positive chlorophyll a flux of Main Pond accounted for only 4% of the chlorophyll flux (0.4 kg day−1) in the wetland. Greater and more positive chlorophyll a flux for Lower Beaver Pond than Main Pond indicated Main Pond received its chlorophyll a from Lower Beaver Pond. The greater negative phaeophytin flux than chlorophyll a flux for Main Pond and the reverse for Lower Beaver Pond also supported the contribution of live chlorophyll a from Lower Beaver Pond to Main Pond. Over all, Lower Beaver Pond accounted for 87% (9.1 kg day−1) of the chlorophyll a flux among the wetland ponds. Lower Beaver Pond also produced the majority of total organic carbon (72%) in the wetland, which again was exported southward into Main Pond. By contrast, Upper Beaver Pond accounted for only 2–11% of the organic material flux, with the largest flux associated with volatile suspended solids (−6,949 kg day−1). Like Lower Beaver Pond, the organic material flux in Upper Beaver Pond was characterized by negative values and indicated Lower Beaver Pond was a source of organic material to the river.
Lower Beaver Pond, a small vegetated pond in the interior of the wetland, was an important source of carbon and accounted for a large percentage of the total organic carbon and chlorophyll a flux within the wetland. Lower Beaver Pond contributed 87% of the chlorophyll a, 72% of the total organic carbon and 10% of the diatom flux among wetland ponds. The lack of water exchange between Lower Beaver Pond and the river may have been a critical factor contributing to the high export of carbon from Lower Beaver Pond to the other ponds, because it prevented export of carbon out of the wetland. Most of the organic matter in the freshwater tidal Shark River Slough in the Florida Coastal Everglades was produced in isolated bays (Xu et al. 2006). Algal biomass was also greater in pools with long residence time in 33 temporary freshwater pools in Hungary (Boven et al. 2008).
Both vegetated ponds combined exported 5–70% of the inorganic material exported by the wetland either to interior ponds or exterior river channels. Upper and Lower Beaver Ponds exported 31–60% of the total suspended solids, chloride and bromide and 5–70% of the major nutrients nitrate, ammonium, soluble phosphorus, total phosphorus and silica. Nitrogen, phosphorus, chloride and silica are often released from sediments in wetlands through plant uptake or leaching and decomposition of organic matter (Noe and Childers 2007; de Bettencourt et al. 2007). Main Pond also exported suspended sediment, soluble and total phosphorus in most seasons between 2004 and 2005 (Lehman et al. 2010). The amount of material exported by wetlands is partially dependent on the sedimentary source. Wetlands with terrigenous sediment sources like Liberty Island are characterized by greater material export than those with carbonate sediments like the Everglades (Sutula et al. 2003).
Increased tidal asymmetry coupled with wetland topography facilitated the inorganic and organic material export from Lower Beaver Pond in the interior of the wetland. During flood tide, high flows pushed water up and into the elevated region in the northern quadrat of Lower Beaver Pond. As the flood water receded, it left a pool of water that was isolated from the rest of Lower Beaver Pond by a sill, which prevented the pooled flood water from fully draining during ebb tide. The pooled flood water facilitated accumulation of inorganic material and the growth and accumulation of organic material. The pooled flood water and its accumulated inorganic and organic material was released back into the wetland during the next flood tide, when water was again pushed into the northern end of the pond and partially drained back into the wetland during ebb. The release of this pooled flood water back into the wetland produced a 40% increase in the organic and inorganic material export from Lower Beaver Pond on ebb tide. Most of the material flux also occurred on ebb tide for freshwater tidal bayous in the Atchafalaya River in Louisiana and freshwater tidal wetlands off the Hudson River (Stern et al. 1991; Arrigoni et al. 2008).
Vegetated ponds in freshwater tidal wetlands may function like floodplains along rivers that produce and store phytoplankton carbon until it is returned to the river with flood water (Junk et al. 1989; Tockner et al. 1999). Such processes commonly occur in floodplain habitat near Liberty Island. Long residence time during the drain phase of the flood-pulse cycle facilitated accumulation of more chlorophyll a concentration in the Yolo Bypass floodplain than the main Sacramento River channel (Lehman et al. 2008; Sommer et al. 2004). Carbon production in Yolo Bypass floodplain was also facilitated by an elevated growth efficiency and production to respiration ratio (Lehman et al. 2008). Elevated growth rate in the vegetated ponds was suggested by the net production of chlorophyll a concentration. Elevated nitrogen to phosphorus ratios may further enhance carbon production in vegetated ponds (Huang and Morris 2003). However, this was not the case for phytoplankton in Upper and Lower Beaver Ponds, where the nitrogen to phosphorus molar ratios were three times lower than the optimal Redfield N:P ratio of 16 and accompanied by relatively low chlorophyll a concentration. Higher vegetation may facilitate phytoplankton production in wetland ponds because of their influence on local physical conditions. Significantly greater water temperature, salinity and suspended sediment occurred in vegetated than open water ponds in Liberty Island. Local physical conditions were also affected by emergent vegetation in California and Georgia wetlands (Lightbody et al. 2008; Miller and Fujii 2010).
The daily tidal pulse of material created by the export of carbon from the vegetative ponds during the ebb tide and addition of nutrients needed to support future carbon production on flood tide may be a key element needed for the maintenance of tidal wetland production (Odum et al. 1995). Tidal pulse was determined to be essential for organic carbon production in a series of wetlands in the Hudson River, Florida Everglades and Cooper River Estuary (Romigh et al. 2006; McKellar et al. 2007; Arrigoni et al. 2008). Even though the retention time associated with this daily tidal pulse seems short, it could be essential to freshwater tidal wetlands which function at high frequency time scales due to the influence of daily tide. A few hours difference in the overlap of ebb tide with daylight hours was sufficient to significantly affect chlorophyll a flux in the Mildred Island wetland in SFE (Lucas et al. 2006). Small differences in light availability and water temperature were also important for diatom production in Yolo Bypass floodplain in SFE (Lehman et al. 2008).
The vegetated ponds were a relatively large source of material to the freshwater tidal wetland in this study, despite their small size, but information from a much longer time interval is needed to gain a full understanding of the potential magnitude of that contribution due to the high spatial and temporal variability. High spatial variability in water quality conditions characterize freshwater tidal wetlands due to differences in plant associations, elevation and hydrology (Pasternack and Brush 1998; Hein et al. 2004; McKellar et al. 2007) and influence material flux through small scale velocity gradients (Lightbody et al. 2008). In the Cosumnes River and Yolo Bypass floodplains, chlorophyll a concentration varied by a factor of 17 over 0.36 km2 and water quality conditions varied at the 0.5–1.3 km scale (Ahearn et al. 2006; Sommer et al. 2008). Material flux also varied by a factor of 5 within 1.5 km, a factor of 2–3 daily and by orders of magnitude seasonally in Main Pond between 2004 and 2005 (Lehman et al. 2010). Even greater variation would occur over time due to physical changes in wetland morphometry, tidal hydrography, vegetation type, spring-neap tidal variation and climate change (Pasternack and Brush 1998; Ganju et al. 2005; California Department of Water Resources 2006; Ross et al. 2006; McKellar et al. 2007).
This study demonstrated the dynamic variation of material flux among vegetated and open water wetland ponds over the tidal day due to material concentration, flow and tide. The study also demonstrated the importance of small vegetated ponds to the organic matter flux of a large wetland. The high variability of inorganic and organic material flux caused by physical factors such as geography, tide and flow lead to the conclusion that understanding material flux in a complex freshwater tidal wetland, such as Liberty Island, requires high frequency spatial and temporal sampling of both large and small pond habitats.
Liberty Island is a 21 km2 freshwater perennial tidal wetland that was created by a levee failure in 1998. A system of levees separates this wetland from the Yolo Bypass floodplain on the north, the Sacramento River on the south, Shag Slough on the west and the Sacramento deep water ship channel on the east (Figure 1). The wetland is called a flooded island because agricultural practices have stripped off the top soil within the levied region so that the surface of the sediment is below sea level. The upper third of the wetland consists of the two shallow ponds, Upper Beaver Pond (1.4 km2) and Lower Beaver Pond (5.6 km2). These vegetated ponds primarily contain emergent vegetation consisting of tule rush and cattail. Upper Beaver Pond exchanges water with Shag Slough at SSB and Lower Beaver Pond at LIBN (Figure 1). Lower Beaver pond is located in the interior of the wetland and is not directly connected to a river channel, but water exchange occurs with Upper Beaver Pond at LIBN and the open water pond, Main Pond, at LIBS. Main Pond is a large 14 km2 open water pond, which comprises two-thirds of the wetland. The southern end of Main Pond at MAIN exchanges water with the Sacramento River. Water is exchanged between all of the ponds, except at low water on ebb tide, when Upper and Lower Beaver Ponds become disconnected due to an elevated portion of land in the middle of Lower Beaver Pond. Water depth in Upper and Lower Beaver Ponds reaches 2 m at high tide. In Main Pond, water depth is less than 1 m at low tide in the north and gradually increases toward the south, where it is 20 m deep. The depth of Main Pond also decreases from 1.5 to 3 m in the west to 0.3 to 2 m in the east.
The flow of water in the wetland is controlled by exchange with the adjacent river channels and a semi-diurnal tide. Average daily discharge in the Sacramento River was 286 ± 3 m3 s−1 during the 12–13 July 2006 tidal day of this study and was representative of flow during the month, which ranged from 579 to 637 m3 s−1. Average daily discharge of Shag Slough during the study was 0.0016 ± 0.0003 m3 s−1 and was orders of magnitude lower than the flow in the Sacramento River.
Discrete samples were collected at SSB, LIBN, LIBS and MAIN every 1.5 h between 0600 hours on 12 July to 0730 hours on 13 July; 16–18 discrete water quality measurements per station (Figure 1). Water samples were collected using a van Dorn water sampler, immediately cooled to 4°C and processed within 2 h of collection. Processing times strictly followed Standard Methods (APHA et al. 1998). For chlorophyll a and phaeophytin pigment concentration measurements, 250–500 ml of raw water was filtered through a GF/F glass fiber filter to which 1 ml of saturated magnesium carbonate solution was added as a preservative, and filters were frozen until spectrophotometric analysis (APHA et al. 1998). The volume of water filtered was decreased to 250 ml, when elevated suspended sediment clogged the filter. A 40 ml water sample was also filtered through a pre-combusted GF/F glass fiber filter for dissolved organic carbon analysis (APHA et al. 1998).
Water samples (250–500 ml) for dissolved inorganic material analysis including soluble reactive phosphorus, nitrate, ammonia, silica, chloride and bromide were filtered through HA nucleopore filters with a 0.45 µm pore size and the filtrate was either frozen or kept at 4°C until analysis (US EPA 1983; USGS 1985). Unfiltered water for measurement of total and volatile suspended solids (1,000 ml), total organic carbon (40 ml) and total phosphorus analysis (250 ml) was kept at 4°C until processing (APHA et al. 1998). Error is based on 10% replication, which produced an average error of 2% for inorganic and 5% for organic variables.
Water for phytoplankton identification and enumeration was placed in a 50 ml amber glass bottle with 1 ml of Lugol’s solution added as a preservative. Phytoplankton cells were identified, sized and enumerated at 700× using the inverted microscope technique (Utermöhl 1958). Phytoplankton were divided into four groups, which comprised the majority of the cells, diatoms, green algae, cyanobacteria and miscellaneous flagellates. Miscellaneous flagellates included cryptophytes and chrysophytes. The biomass of the phytoplankton cells was computed from cell volume based on cell dimensions applied to simple geometric shapes (Menden-Deuer and Lessard 2000).
Continuous water temperature, specific conductance, dissolved oxygen concentration, pH, nephelometric turbidity units (NTU) and chlorophyll a fluorescence were measured with YSI 6600 sondes at each station. Chlorophyll a fluorescence and NTU were converted to chlorophyll a and total suspended solids concentration using linear regression analysis with discrete sample values.
Due to differences in terrain, flow was measured differently for each station. At SSB, the flow was computed as the sum of the change in water volume of Upper Beaver Pond measured by pressure sensors in Yellow Springs Harbor 6600 water quality sondes (YSI 6600 sondes) and the flow at LIBN. At LIBN, flow was computed using the index velocity method where water velocity, direction and depth were measured with a sideward looking acoustic Doppler continuous profile flow system (ADCP) deployed from a boat. The water flow was calculated as the mean velocity multiplied by the area of the pond. Hourly changes in water volume of Upper Beaver Pond were calculated as the change in water depth divided by the change in time multiplied by the area. The area of Upper Beaver Pond was variable and adjusted based on the effect of tide on water depth. It was estimated that high tide covered 82.5% of the pond area, while low tide covered approximately 40%. At LIBS, the flow was determined from the empirical relationship between the velocity measured by a fixed depth upward looking shallow water ADCP (SonTek Argonaut) and the total flow.
The Main Pond is virtually a lake with many small breeches in the surrounding levee and is connected to the Sacramento River at MAIN, in the southern portion of the pond. There was no practical way to calculate the flows at each levee breech, therefore the total flow at MAIN was calculated from changes in water volume of Main Pond estimated by the total area and change in depth measured using three pressure gauges in YSI 6600 sondes placed across the middle of the pond. It was estimated that 90% of the land in Main Pond was flooded during high tide and 85% was flooded during low tide. For LIBN, LIBS and MAIN positive water flow values indicated water movement in the wetland from north to south and negative water flow values indicated water movement from south to north. For SSB, positive water flow values indicated water movement from west to east, while negative flow values indicated water movement from east to west.
Material flux was measured at four stations located at water exchange points between Shag Slough and Upper Beaver Pond (SSB), Upper Beaver Pond and Lower Beaver Pond (LIBN), Lower Beaver Pond and Main Pond (LIBS) and Main Pond and the Sacramento River (MAIN; Figure 1). Lidar analysis of the wetland geography indicated these stations were the major water exchange points. Material exchange was estimated from continuous flow measurements and discrete water sample values averaged over 15 min intervals. The daily net change (flux) of each material at each station was computed as the product of the mean flow and the material concentration computed for 15 min intervals summed over the 25.5 h tidal day (n = 102). Negative material flux described the net movement of material northward at LIBN, LIBS and MAIN and westward at SSB. Positive material flux described the net movement of material southward at LIBN, LIBS and MAIN and eastward at SSB. The percentage contribution of each pond to the total flux of each inorganic or organic material within the wetland was computed as the absolute value of the material flux at each pond divided by the sum of the absolute value of the material flux of all ponds.
Due to the lack of normality, associations among data values were determined using nonparametric statistical techniques for single (Wilcoxon) and multiple (Kruskal–Wallis) comparisons (SAS Inc. 2013). Individual data values in the text were expressed as the mean and standard deviation.
PWL and SM designed the research; PWL, SM, LL and AT conducted the field research; PWL, SM, LL and AT analyzed the data; PWL wrote the manuscript. All authors read and approved the final manuscript.
This study was funded by a California Bay-Delta Authority (CALFED) Restoration Grant #2000-F06 to PWL. Significant assistance with the funding and field sampling was also contributed by the Division of Environmental Services and Northern California District Office within the California Department of Water Resources, as well as the California State Water Resources Control Board. M. Dempsey, S. Flory, C. Foe, J. Ho, K. Hochgraf, D. Huston, S. Louie, R. Mager, R. Mora, D. Pendleton, E. Santos, R. Schaap and R. Talley assisted with field sampling.
Compliance with ethical guidelines
Competing interests The authors declare that they have no competing interests.
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- Ahearn DS, Viers JH, Mount JF, Dahlgren RA (2006) Priming the productivity pump: flood pulse driven trends in suspended algal biomass distribution across a restored floodplain. Freshw Biol 51:1417–1433View ArticleGoogle Scholar
- American Public Health Association (APHA), American Water Works Association, Water Environment Association (1998) Standard methods for the examination of water and wastewater, 20th edn. American Public Health Association, Washington, D.C.Google Scholar
- Arrigoni A, Findlay S, Fischer D, Tockner K (2008) Predicting carbon and nutrient transformations in tidal freshwater wetlands of the Hudson River. Ecosystems 11:790–802View ArticleGoogle Scholar
- Bouchard V (2007) Export of organic matter from a coastal freshwater wetland to Lake Erie: an extension of the outwelling hypothesis. Aquat Ecol 41:1–7View ArticleGoogle Scholar
- Boven L, Stoks R, Forró L, Brendonck L (2008) Seasonal dynamics in water quality and vegetation cover in temporary pools with variable hydroperiods in Kiskunság (Hungary). Wetlands 28:401–410View ArticleGoogle Scholar
- Boynton WR, Hagy JD, Cornwell JC, Kemp WM, Greene SM, Owens MS et al (2008) Nutrient budgets and management actions in the Patuxent River Estuary, Maryland. Estuaries Coasts 31:623–651View ArticleGoogle Scholar
- Brown LR (2003) Will tidal wetland restoration enhance populations of native fishes? San Franc Estuary Watershed Sci 1(1):2Google Scholar
- California Department of Water Resources (2006) Progress on Incorporating Climate Change into Planning and Management of California Water Resources. California Department of Water Resources, Sacramento 94236 Google Scholar
- Chauvelon P (1998) Wetland managed for agriculture as an interface between the Rhone River and the Vaccares Lagoon (Camargue, France): transfers of water and nutrients. Hydrobiologia 373–374:181–191View ArticleGoogle Scholar
- Childers DL (2006) A synthesis of long-term research by the Florida Coastal Everglades LTER program. Hydrobiol 569:531–544View ArticleGoogle Scholar
- Childers DL, Day JW Jr, McKellar HN Jr (2000) Twenty more years of marsh and estuarine flux studies: revisiting Nixon (1980). In: Weinstein MP, Kreeger DA (eds) Concepts and controversies in tidal marsh ecology. Kluwer Academic Publishers, Dordrecht, pp 391–424Google Scholar
- Day JW Jr, Westphal A, Pratt R, Hyfield E, Rybczyk J, Kemp GP et al (2006) Effects of long-term municipal effluent discharge on the nutrient dynamics, productivity, and benthic community structure of a tidal freshwater forested wetland in Louisiana. Ecol Eng 27:242–257View ArticleGoogle Scholar
- de Bettencourt AM, Quaresma LS, Lanc MJ (2007) The issue of outwelling in the Guadiana River estuary (Portugal): some findings and research suggestions in the context of recent evidence. Hydrobiologia 587:157–168View ArticleGoogle Scholar
- Ganju NK, Schoellhamer DH, Bergamaschi BA (2005) Suspended sediment fluxes in a tidal wetland: measurement, controlling factors and error analysis. Estuaries 28:812–822View ArticleGoogle Scholar
- Hein T, Heiler G, Pennetzdorfer D, Riedler P, Schagerl M, Schiemer F (1999) The Danube Restoration Project: functional aspects and planktonic productivity in the floodplain system. Regul Rivers Res Manag 15:259–270View ArticleGoogle Scholar
- Hein T, Baranyi C, Reckendorfer W, Schiemer F (2004) The impact of surface water exchange on the nutrient and particle dynamics in side-arms along the River Danube, Austria. Sci Total Environ 328:207–218View ArticleGoogle Scholar
- Heip CHR, Goosen NK, Herman PMJ, Kromkamp J, Middelburg JJ, Soetaert K (1995) Production and consumption of biological particles in temperate tidal estuaries. Oceanogr Mar Biol Annu Rev 33:1–149Google Scholar
- Huang X, Morris JT (2003) Trends in phosphatase activity along a successional gradient of tidal freshwater marshes on the Cooper River, South Carolina. Estuaries 26:1281–1290View ArticleGoogle Scholar
- SAS Institute Inc (2013) SAS/STAT 12.3 user’s guide. SAS Institute Inc, CaryGoogle Scholar
- Jassby AD, Cloern JE (2000) Organic matter sources and rehabilitation of the Sacramento-San Joaquin Delta (California, USA). Aquat Conserv Mar Fresh Ecosyst 10:323–352View ArticleGoogle Scholar
- Junk WJ, Bayley PB, Sparks RE (1989) The flood-pulse concept in river-floodplain systems. In: Dodge DP (ed) Proceedings of the International Large River Symposium, vol 106. Can Spec Pub Fish Aquat Sci, pp 110–127Google Scholar
- Kimmerer WJ (2004) Open water processes of San Francisco Estuary: from physical forcing to biological responses. San Franc Estuar Watershed Sci 2(1):1Google Scholar
- Lehman PW (2000) The influence of climate on phytoplankton community biomass in San Francisco Bay Estuary. Limnol Oceanogr 45:580–590View ArticleGoogle Scholar
- Lehman PW (2004) The influence of climate on mechanistic pathways that affect lower food web production in northern San Francisco Bay estuary. Estuaries 27:312–325Google Scholar
- Lehman PW, Sommer T, Rivard L (2008) Phytoplankton primary productivity, respiration, chlorophyll a and species composition in the Yolo Bypass floodplain, California. Aquat Ecol 42:363–378View ArticleGoogle Scholar
- Lehman PW, Mayr S, Mecum L, Enright C (2010) The freshwater tidal wetland Liberty Island, CA was both a source and sink of inorganic and organic material to the San Francisco Estuary. Aquat Ecol 44:359–372View ArticleGoogle Scholar
- Lightbody AF, Avener ME, Nepf HM (2008) Observations of short-circuiting flow paths within a free-surface wetland in Augusta, Georgia, USA. Limnol Oceanogr 53:1040–1053View ArticleGoogle Scholar
- Lopez CB, Cloern JE, Schraga TS, Little AJ, Lucas LV, Thompson JK et al (2006) Ecological values of shallow-water habitats: implications for the restoration of disturbed ecosystems. Ecosystems 9:422–440View ArticleGoogle Scholar
- Lucas LV, Sereno DM, Burau JR, Schraga TS, Lopez CB, Stacey MT et al (2006) Intradaily variability of water quality in a shallow tidal lagoon: mechanisms and implications. Estuaries Coasts 29:711–730View ArticleGoogle Scholar
- McKellar HN, Tufford DL, Alford MC, Saroprayogi P, Kelley BJ, Morris JT (2007) Tidal nitrogen exchanges across a freshwater wetland succession gradient in the upper Cooper River, South Carolina. Estuaries Coasts 30:989–1006View ArticleGoogle Scholar
- Menden-Deuer S, Lessard EJ (2000) Carbon to volume relationships for dinoflagellates, diatoms and other protest plankton. Limnol Oceanogr 45:569–579View ArticleGoogle Scholar
- Miller R, Fujii R (2010) Plant community, primary productivity, and environmental conditions following wetland re-establishment in the Sacramento-San Joaquin Delta, California. Wetl Ecol Manag 18:1–16View ArticleGoogle Scholar
- Moustafa MZ (1999) Nutrient retention dynamics of the Everglades Nutrient Removal Project. Wetlands 19:689–704View ArticleGoogle Scholar
- Nobriga ML, Sommer TR, Feyrer F, Fleming K (2008) Long-term trends in summertime habitat suitability for Delta smelt (Hypomesus transpacificus). San Franc Estuar Watershed Sci 6(1):1Google Scholar
- Noe GB, Childers DL (2007) Phosphorus budgets in Everglades wetland ecosystems: the effects of hydrology and nutrient enrichment. Wetl Ecol Manag 15:189–205View ArticleGoogle Scholar
- Odum WE, Odum EP, Odum HT (1995) Nature’s pulsing paradigm. Estuaries 18:547–555View ArticleGoogle Scholar
- Pasternack GB, Brush GS (1998) Sedimentation cycles in a river-mouth tidal freshwater marsh. Estuaries 21:407–415View ArticleGoogle Scholar
- Romigh MM, Davis SE, Rivera-Monroy VH, Twilley RR (2006) Flux of organic carbon in a riverine mangrove wetland in the Florida Coastal Everglades. Hydrobiologia 569:505–516View ArticleGoogle Scholar
- Ross MS, Mitchell-Bruker S, Sah JP, Stothoff S, Ruiz PL, Reed DL et al (2006) Interaction of hydrology and nutrient limitation in the Ridge and Slough landscape of the southern Everglades. Hydrobiologia 569:37–59View ArticleGoogle Scholar
- Saunders DL, Kalff J (2001) Nitrogen retention in wetlands, lakes and rivers. Hydrobiologia 443:205–212View ArticleGoogle Scholar
- Sommer TR, Nobriga ML, Harrell WC, Batham W, Kimmerer WJ (2001) Floodplain rearing of juvenile Chinook salmon: evidence of enhanced growth and survival. Can J Fish Aquat Sci 58:325–333View ArticleGoogle Scholar
- Sommer TR, Harrell WC, Mueller Solger AB, Tom B, Kimmerer W (2004) Effects of flow variation on channel and floodplain biota and habitats of the Sacramento River, California, USA. Aquat Conserv Mar Freshw Ecol 14:247–261View ArticleGoogle Scholar
- Sommer TR, Armor C, Baxter R, Breuer R, Brown L, Chotkowski M et al (2007) The collapse of pelagic fishes in the upper San Francisco Estuary. Fisheries 32:270–277View ArticleGoogle Scholar
- Sommer TR, Harrell WC, Swift TJ (2008) Extreme hydrologic banding in a large-river Floodplain, California, USA. Hydrobiologia 598:409–415View ArticleGoogle Scholar
- Stern MK, Jay JW, Teague KG (1991) Nutrient transport in a river-influenced, tidal freshwater bayou in Louisiana. Estuaries 14:382–394View ArticleGoogle Scholar
- Sutula MA, Perez BC, Reyes E, Childers DL, Davis S, Day JW Jr et al (2003) Factors affecting spatial and temporal variability in material exchange between the Southern Everglades wetlands and Florida Bay (USA). Estuar Coast Shelf Sci 57:757–781View ArticleGoogle Scholar
- Tockner K, Pennetzdorfer D, Reiner N, Schiemer F, Ward JV (1999) Hydrological connectivity, and the exchange of organic matter and nutrients in a dynamic river-floodplain system (Danube, Austria). Freshw Biol 41:521–535View ArticleGoogle Scholar
- United States Environmental Protection Agency (US EPA) (1983) Methods for chemical analysis of water and wastes. Technical Report EPA-600/4-79-020. United States Environmental Protection Agency, Washington, D.C., USAGoogle Scholar
- United States Geological Survey (USGS) (1985) Methods for determination of inorganic substances in water and fluvial sediments. Open file report 85-495Google Scholar
- Utermöhl H (1958) Zur Vervollkommung der quantitativen Phytoplankton-methodik. Mitteilumgen Internationale Verejunigung fur Theoretische und Angewandtet Limnologie 9:1–38Google Scholar
- Xu Y, Mead RN, Rudolf J (2006) A molecular marker-based assessment of sedimentary organic matter sources and distributions in Florida Bay. Hydrobiologia 569:179–192View ArticleGoogle Scholar