Tidal freshwater wetlands
01 Jan 2009-pp 619-640
TL;DR: Tidal freshwater wetlands link terrestrial and estuarine habitats as mentioned in this paper, where the amount of freshwater flow from upstream watersheds is of sufficient volume to create a dynamic tidal zone in which there are tides but the water is almost completely fresh.
Abstract: Tidal freshwater wetlands link terrestrial and estuarine habitats. They occur in coastal systems around the world, primarily rivers, where the amount of freshwater flow from upstream watersheds is of sufficient volume to create a dynamic tidal zone in which there are tides but the water is almost completely fresh. Tidal freshwater wetlands are characterized by high biodiversity, high productivity, and high rates of decomposition. The animal community is characterized by species that occur in freshwater and estuarine and marine species that spend important life history stage in freshwater environments. Given their location near urban areas in coastal rivers, many tidal freshwater wetlands have been destroyed and the wetlands that remain are threatened by sea level rise, salt water intrusion, and invasive species. Effective conservation, restoration, and management of tidal freshwater wetlands will require vigilance and commitment by governmental and nongovernmental organizations.
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TL;DR: The relationship between methane emissions and salinity is not well understood in tidal marshes, leading to uncertainty about the net effect of marsh conservation and restoration on greenhouse gas balance.
Abstract: The relationship between methane emissions and salinity is not well understood in tidal marshes, leading to uncertainty about the net effect of marsh conservation and restoration on greenhouse gas balance. We used published and unpublished field data to investigate the relationships between tidal marsh methane emissions, salinity, and porewater concentrations of methane and sulfate, then used these relationships to consider the balance between methane emissions and soil carbon sequestration. Polyhaline tidal marshes (salinity >18) had significantly lower methane emissions (mean ± sd = 1 ± 2 g m−2 yr−1) than other marshes, and can be expected to decrease radiative forcing when created or restored. There was no significant difference in methane emissions from fresh (salinity = 0–0.5) and mesohaline (5–18) marshes (42 ± 76 and 16 ± 11 g m−2 yr−1, respectively), while oligohaline (0.5–5) marshes had the highest and most variable methane emissions (150 ± 221 g m−2 yr−1). Annual methane emissions were modeled using a linear fit of salinity against log-transformed methane flux (
$$ \log ({\text{C}}{{\text{H}}_4}) = - 0.056 \times {\text{salinity }} + { 1}{.38} $$
; r2 = 0.52; p < 0.0001). Managers interested in using marshes as greenhouse gas sinks can assume negligible methane emissions in polyhaline systems, but need to estimate or monitor methane emissions in lower-salinity marshes.
450 citations
TL;DR: Results indicate that salinity increases microbial decomposition rates in low salinity wetlands, and suggests that these ecosystems may experience decreased soil OM accumulation, accretion, and carbon sequestration rates even with modest levels of saltwater intrusion.
Abstract: Climate change-associated sea level rise is expected to cause saltwater intrusion into many historically freshwater ecosystems. Of particular concern are tidal freshwater wetlands, which perform several important ecological functions including carbon sequestration. To predict the impact of saltwater intrusion in these environments, we must first gain a better understanding of how salinity regulates decomposition in natural systems. This study sampled eight tidal wetlands ranging from freshwater to oligohaline (0-2 ppt) in four rivers near the Chesapeake Bay (Virginia). To help isolate salinity effects, sites were selected to be highly similar in terms of plant community composition and tidal influence. Overall, salinity was found to be strongly negatively correlated with soil organic matter content (OM%) and C : N, but unrelated to the other studied environmental parameters (pH, redox, and above- and below-ground plant biomass). Partial correlation analysis, controlling for these environmental covariates, supported direct effects of salinity on the activity of carbon-degrading extracellular enzymes (β-1, 4-glucosidase, 1, 4-β-cellobiosidase, β-D-xylosidase, and phenol oxidase) as well as alkaline phosphatase, using a per unit OM basis. As enzyme activity is the putative rate-limiting step in decomposition, enhanced activity due to salinity increases could dramatically affect soil OM accumulation. Salinity was also found to be positively related to bacterial abundance (qPCR of the 16S rRNA gene) and tightly linked with community composition (T-RFLP). Furthermore, strong relationships were found between bacterial abundance and/or composition with the activity of specific enzymes (1, 4-β-cellobiosidase, arylsulfatase, alkaline phosphatase, and phenol oxidase) suggesting salinity's impact on decomposition could be due, at least in part, to its effect on the bacterial community. Together, these results indicate that salinity increases microbial decomposition rates in low salinity wetlands, and suggests that these ecosystems may experience decreased soil OM accumulation, accretion, and carbon sequestration rates even with modest levels of saltwater intrusion.
289 citations
TL;DR: The impact of saltwater intrusion on microbial organic carbon (C) mineralization in tidal freshwater marsh (TFM) soils was investigated in a year-long laboratory experiment in which intact soils were exposed to a simulated tidal cycle of freshwater or dilute saltwater as discussed by the authors.
Abstract: The impact of salt-water intrusion on microbial organic carbon (C) mineralization in tidal freshwater marsh (TFM) soils was investigated in a year-long laboratory experiment in which intact soils were exposed to a simulated tidal cycle of freshwater or dilute salt-water. Gas fluxes [carbon dioxide (CO2) and methane (CH4)], rates of microbial processes (sulfate reduction and methanogenesis), and porewater and solid phase biogeochemistry were measured throughout the experiment. Flux rates of CO2 and, surprisingly, CH4 increased significantly following salt-water intrusion, and remained elevated relative to freshwater cores for 6 and 5 months, respectively. Following salt-water intrusion, rates of sulfate reduction increased significantly and remained higher than rates in the freshwater controls throughout the experiment. Rates of acetoclastic methanogenesis were higher than rates of hydrogenotrophic methanogenesis, but the rates did not differ by salinity treatment. Soil organic C content decreased significantly in soils experiencing salt-water intrusion. Estimates of total organic C mineralized in freshwater and salt-water amended soils over the 1-year experiment using gas flux measurements (18.2 and 24.9 mol C m−2, respectively) were similar to estimates obtained from microbial rates (37.8 and 56.2 mol C m−2, respectively), and to losses in soil organic C content (0 and 44.1 mol C m−2, respectively). These findings indicate that salt-water intrusion stimulates microbial decomposition, accelerates the loss of organic C from TFM soils, and may put TFMs at risk of permanent inundation.
266 citations
TL;DR: In this article, in situ manipulations in a Zizaniopsis miliacea (giant cutgrass)-dominated tidal freshwater marsh in South Carolina have raised porewater salinities from freshwater to oligohaline levels and/or subtly increased the amount of water flowing through the system.
Abstract: Tidal freshwater marshes exist in a dynamic environment where plant productivity, subsurface biogeochemical processes, and soil elevation respond to hydrological fluctuations over tidal to multi-decadal time scales. The objective of this study was to determine ecosystem responses to elevated salinity and increased water inputs, which are likely as sea level rise accelerates and saltwater intrudes into freshwater habitats. Since June 2008, in situ manipulations in a Zizaniopsis miliacea (giant cutgrass)-dominated tidal freshwater marsh in South Carolina have raised porewater salinities from freshwater to oligohaline levels and/or subtly increased the amount of water flowing through the system. Ecosystem-level fluxes of CO2 and CH4 have been measured to quantify rates of production and respiration. During the first 20 months of the experiment, the major impact of elevated salinity was a depression of plant productivity, whereas increasing freshwater inputs had a greater effect on rates of ecosystem CO2 emissions, primarily due to changes in soil processes. Net ecosystem production, the balance between gross ecosystem production and ecosystem respiration, decreased by 55% due to elevated salinity, increased by 75% when freshwater inputs were increased, and did not change when salinity and hydrology were both manipulated. These changes in net ecosystem production may impact the ability of marshes to keep up with rising sea levels since the accumulation of organic matter is critical in allowing tidal freshwater marshes to build soil volume. Thus, it is necessary to have regional-scale predictions of saltwater intrusion and water level changes relative to the marsh surface in order to accurately forecast the long-term sustainability of tidal freshwater marshes to future environmental change.
193 citations
135 citations
References
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TL;DR: In this paper, the authors define definitions of diversity and apply them to the problem of measuring species diversity, choosing an index and interpreting diversity measures, and applying them to structural and structural diversity.
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TL;DR: In this paper, a global oxygen isotope record for ocean water has been calculated from the Barbados sea level curve, allowing separation of the ice volume component common to all isotope records measured in deep-sea cores.
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TL;DR: The authors showed that rivers with large sediment loads (annual discharges greater than about $15 \times 10^{6}$ tons) contribute about $7 −times 10 −9$ tons of suspended sediment to the ocean yearly.
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3,409 citations