Tidal day organic and inorganic material flux of ponds in the Liberty Island freshwater tidal wetland.

Peggy W Lehman,Alison Tang,Shawn Mayr,Leji Liu

doi:10.1186/s40064-015-1068-6

Abstract

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.

Highlights

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)
Hydrodynamics The magnitude and timing of water flow within the wetland was strongly influenced by water exchange with the river channels
Average water flow was over an order of magnitude greater at Main Pond and the Sacramento River (MAIN), which was connected to the large Sacramento River, than at Shag Slough and Upper Beaver Pond (SSB), which was connected to the small Shag Slough

Summary

Introduction

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). 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). 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)

Methods

Results

Discussion

Conclusion