Read Books Online and Download eBooks, EPub, PDF, Mobi, Kindle, Text Full Free.
Drainage Of Water Dissolved Organic Carbon And Ammonium Through Creekbank Salt Marsh Sediments
Download Drainage Of Water Dissolved Organic Carbon And Ammonium Through Creekbank Salt Marsh Sediments full books in PDF, epub, and Kindle. Read online Drainage Of Water Dissolved Organic Carbon And Ammonium Through Creekbank Salt Marsh Sediments ebook anywhere anytime directly on your device. Fast Download speed and no annoying ads. We cannot guarantee that every ebooks is available!
Book Synopsis Drainage of Water, Dissolved Organic Carbon and Ammonium Through Creekbank Salt Marsh Sediments by : Dale Dyer Goehringer
Download or read book Drainage of Water, Dissolved Organic Carbon and Ammonium Through Creekbank Salt Marsh Sediments written by Dale Dyer Goehringer and published by . This book was released on 1985 with total page 136 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Dissolved Organic Carbon Dynamics in a Salt Marsh Creek by : Christina Codden
Download or read book Dissolved Organic Carbon Dynamics in a Salt Marsh Creek written by Christina Codden and published by . This book was released on 2020 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Salt marshes are blue carbon systems that sequester carbon at higher rates than many terrestrial ecosystems due to a coupled relationship between high primary production and slow decomposition in anaerobic sediments. Annually, this coupled relationship allows for over 10 Tg of organic carbon to be sequestered in global salt marsh sediments alone, or a storage equivalent of over 55,000 Blue Whales per year. In turn, this storage ability enables salt marshes to help mitigate increasing atmospheric CO2. Despite high primary production in salt marshes and their ability to help mitigate increasing atmospheric CO2, a long-standing question remains in coastal carbon cycling and ecology which asks: Is a fraction of salt marsh produced carbon, prior to sequestration or mineralization, exported (i.e., outwelled) as dissolved organic carbon (DOC) to the coastal ocean? Answering this question of salt marsh DOC outwelling is critical for quantifying the significance of salt marsh carbon outwelling in comparison to total salt marsh carbon storage, total salt marsh primary production, and broader coastal carbon cycling. Because the question of DOC outwelling first arose on the Georgia coast and because the Georgia coast houses some of the most productive salt marshes in the world, this dissertation focuses on analyzing DOC outwelling in Groves Creek, a tidally-driven salt marsh creek on the Georgia coast. Groves Creek was additionally chosen as it lacks a freshwater head and has limited freshwater input, making the analysis of marsh-only DOC fluxes through the estuarine water possible without confounding results from terrestrial DOC input. In Groves Creek and other Georgia salt marsh creeks, DOC is a master variable that controls the light field, initiates photochemical reactions, and provides sustenance to microbes. The dynamics of DOC in these systems are complex as multiple DOC sources, sinks, and patterns of mixing occur. The complexity in salt marsh DOC dynamics plus the failure of past studies to capture export trends in marsh-derived DOC at both high-temporal resolution and across seasons may explain why it remains unclear whether salt marshes generally export DOC (i.e., outwell). Thus, at a Groves Creek study station, this dissertation sought to answer the question of salt marsh DOC outwelling over three research captures. At Groves Creek study station, Chapter 1 captured hydrology (water level, velocity, flow) at 10-minute resolution over 16-months using an in situ Acoustic Doppler Profiler (ADP) deployed in the creek bed over 7 deployments. After data collection, the hydrology record indicated that the ADP instrument was not deployed in precisely the same location of the creek bed for all deployments. Thus, to make hydrology comparable over the entire study, hydrology records required alignment using a novel alignment approach in which non-tidal signals from individual ADP deployments were added to an extrapolated tidal signal based upon three already aligned deployments. Chapter 2 went on to assess DOC concentration at Groves Creek study station at the same temporal resolution and study length as Chapter 1. As no in situ instrument exists that could directly measure DOC concentration, DOC was estimated in Chapter 2 through the use of site-specific machine learning and linear algorithms coupled with optical and other low-to-zero cost predictors (e.g., water level, salinity, local rainfall) collected at high-temporal resolution. Models were trained using 306 discrete lab-based DOC measurements collected as water samples from the study station. These discrete samples served as ground truth. Work from Chapter 2 included the first-ever incorporation of non-linear machine learning to estimate DOC concentration. By combining DOC concentration (Chapter 2) with water flux (Chapter 1), plus measured salinity (Chapter 3), Chapter 3 was able to calculate DOC fluxes at Groves Creek and ultimately assess the long-standing and inconclusive topic of DOC outwelling. Chapter 3 provided the first-ever estimation of both high-temporal (10-minute) and cross-seasonally (16-month) resolved DOC fluxes. Results show Groves Creek is hydrologically complex with ebb-dominated tidal asymmetry and often more water flowing into the main channel than out (Chapter 1). Since the marsh is hydrologically balanced overall, net imported water likely drained the marsh via unsampled flow paths (e.g., smaller channels, overmarsh flow at marsh edge). Concerning DOC estimation (Chapter 2), at seasonal timescales, machine learning (mean absolute error (MAE) 3.7%) modestly improved upon the accuracy of linear methods (MAE 6.5%) but offered substantial instrumentation cost reductions (~90%) by requiring only cost-free predictors (online data) or cost-free predictors in combination with low-cost in situ predictors (temperature, salinity, depth). At intratidal timescales, linear methods proved ill-equipped (median Pearson's correlation coefficient (R) 0.55) to predict DOC concentration compared to machine learning (median R 0.87-0.94), and again machine learning offered a substantial instrumentation cost reduction (~90%). Thus, one of the main advances set forth in this dissertation is a novel, improved accuracy, and lower-cost method to estimate DOC concentrations in complex aquatic ecosystems. The results of this portion of the dissertation, as presented in Chapter 2, are under a second round of review at Limnology and Oceanography: Methods. Chapter 3 marks the culmination of my PhD research by combining hydrologic fluxes (Chapter 1) and DOC estimates from the two top-performing machine learning algorithms (Chapter 2) to estimate net DOC fluxes through Groves Creek and test the hypothesis that salt marshes outwell DOC (Chapter 3). DOC flux results show that cumulative net DOC-flow and DOC-salt relationships were largely conservative, indicating DOC outwelling was not supported over most of the study period at the Groves Creek study station. However, during summer 2014, the conserved DOC-flow and DOC-salt relationships were disturbed with a loss of DOC from the marsh relative to salt and water fluxes. This discursion from conservative behavior marked a short-lived period of DOC outwelling from the marsh creek to the estuary in summer 2014 during which an estimated 5.7 to 42.1 tons of DOC were exported. Although this is a modest carbon flux, the outwelled DOC remains a significant net term in the marsh carbon budget (e.g., up to 12% of the annual organic carbon sequestration in Groves Creek salt marsh) and an important process to capture in mechanistic models of long-term carbon production, export, and storage for marshes and other blue carbon ecosystems. Results also indicate DOC outwelling from salt marshes may occur as a pulse during highly productive summer months. Resolving these hot moments of DOC export at high-temporal resolution across larger salt marsh ecosystems is required to assess the true extent and quantitative significance of DOC outwelling to coastal carbon cycles, coastal ecology, and the carbon budgets of salt marshes"--Author's abstract.
Book Synopsis Outwelling of Dissolved Organic Carbon from Salt Marshes by : Robert Francis Chen
Download or read book Outwelling of Dissolved Organic Carbon from Salt Marshes written by Robert Francis Chen and published by . This book was released on 2013 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: Salt marshes are among the most productive ecosystems on earth. Tidal inundation by seawater leads to outwelling of dissolved organic carbon (DOC) to the marsh creek, estuary, and ultimately the coastal ocean. Up to 90% of the exported DOC can come from fringing marsh areas. Marsh creek transects, continuous creek monitoring stations, continuous water velocity measurements, well transects established near the creek bank, modeling of marsh-creek exchange across the creek bank, incubations of sediment, water, and vegetation, chemical and isotopic compositional analysis of DOC, estimates of tidal water exchange volumes, and local meteorology all contribute to our overall understanding of salt marsh outwelling processes. We will present data from the Plum Island, MA, Neponset, MA, and Snipe Creek, FL salt marshes. In our estimation,a significant amount of DOC is exported from the marsh, but most of this labile DOC is rapidly remineralized in the creek and nearshore coastal waters. Precipitation, seasonal growth patterns, and wind events can significantly affect this carbon export and must be considered in large scale estimates of carbon outwelling from salt marshes
Book Synopsis Dissolved Organic Carbon Fluxes from a New England Salt Marsh by : Hayley Nicole Schiebel
Download or read book Dissolved Organic Carbon Fluxes from a New England Salt Marsh written by Hayley Nicole Schiebel and published by . This book was released on 2016 with total page 484 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Exchanges of Dissolved Inorganic Nitrogen and Dissolved Organic Carbon Between Salt Marsh Sediments and Overlying Tidal Water by : Betty Ellen Berry Neikirk
Download or read book Exchanges of Dissolved Inorganic Nitrogen and Dissolved Organic Carbon Between Salt Marsh Sediments and Overlying Tidal Water written by Betty Ellen Berry Neikirk and published by . This book was released on 1996 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Dynamics of Carbon and Nitrogen in a Southern California Salt Marsh by : Theodore Paul Winfield
Download or read book Dynamics of Carbon and Nitrogen in a Southern California Salt Marsh written by Theodore Paul Winfield and published by . This book was released on 1980 with total page 182 pages. Available in PDF, EPUB and Kindle. Book excerpt: This study explores three functional aspects of the salt marsh-estuarine ecosystem in the Tijuana Estuary (southern California): primary productivity of the salt marsh vascular plants, organic carbon cycle, and inorganic nitrogen cycle. The productivity study was designed to test the hypothesis that the salt marsh vascular plants in the Tijuana Estuary are not as productive as those in eastern coastal marshes. Spartina foliosa was found to be the most productive individual species in terms of dry weight and carbon, but succulent plant species as a group contributed more to the overall vascular plant productivity. On a dry weight basis net above-ground primary productivity (NAPP) averaged 0.8kg/m('2)/yr which was approximately 240g C/m('2)/yr. Carbon productivity of vascular plants was low in comparison to Atlantic and Gulf of Mexico marshes, and differences were attributed to the more saline soils of southern California. Standing dead biomass and litter averaged over the total marsh surface were constant throughout the study period. The decomposition rate of selected grass species was slower than that for succulent species and the decomposition rate for all plant material varied with elevation, being faster in the tidal creeks and slowest in the upper marsh. The organic carbon study was designed to provide data on the quality and quantity of the various forms of organic carbon being transported to and from the marsh surface in the tidal waters. The data were used in conjunction with those generated from the productivity study to evaluate the hypothesis that the Tijuana Estuary salt marsh exports a substantial amount (45-50%) of the organic carbon produced and that a major portion of the export is as particulate organic carbon (POC). The concentration of POC, dissolved organic carbon (DOC), ATP and chlorophyll a was measured in water samples collected periodically during a tidal cycle each month. Organic carbon was exported as DOC (40-110g C/m('2)/yr) and showed a slight import of POC (5-6g C/m('2)/yr). POC was mainly detrital carbon as opposed to biomass carbon. The Tijuana Estuary salt marsh exports substantially less than 50% of its NAPP, and export is in the dissolved form as opposed to particulate. Results of this and other recent studies suggest that a re-evaluation of salt marsh carbon flow models is needed. The purpose of the inorganic nitrogen study was to document the distribution of ammonium, nitrate and nitrite in the tidal waters draining the Tijuana Estuary salt marsh and to evaluate the tidal waters as a source of nitrogen for salt marsh vegetation. The inorganic nitrogen cycle was characterized by the annual import of ammonium and slight annual export of nitrate. Ammonium was found to be the dominant form of inorganic nitrogen except in the late spring when nitrate was dominant. Inorganic nitrogen import totalled 1.1 - 2.16g N/m('2)/yr. The import of inorganic nitrogen accounted for 28% of the nitrogen required by salt marsh vascular plants, but only 6% of the combined productivity of vascular plants and benthic algae. Nitrogen regeneration processes within the salt marsh are important in meeting the nitrogen needs of salt marsh vegetation.
Book Synopsis Studies of Microbial Production and Utilization of Dissolved Organic Carbon in a Georgia Salt Marsh-estuarine Ecosystem by : William Salvadore Sottile
Download or read book Studies of Microbial Production and Utilization of Dissolved Organic Carbon in a Georgia Salt Marsh-estuarine Ecosystem written by William Salvadore Sottile and published by . This book was released on 1973 with total page 306 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Nitrogen, Phosphorus, and Carbon Flux in Chesapeake Bay Marshes by : Donald M. Axelrad
Download or read book Nitrogen, Phosphorus, and Carbon Flux in Chesapeake Bay Marshes written by Donald M. Axelrad and published by . This book was released on 1976 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt: Annual nitrogen, phosphorus and carbon budgets for two Virginia salt marshes were determined by monthly measurements of water discharge and constituent concentrations over tidal cycles. Considering all three forms of phosphorus measured (total, dissolved organic and orthophosphate) there was a net loss from the estuary to the marches. The data reveal a loss of particulate phosphorus of estuarine origin to marsh sediments and mineralization of this phosphorus in the marshes with subsequent export of dissolved inorganic and organic phosphorus back to the estuary. Nitrogen flux data show a loss of nitrate and nitrite to the marshes. Particulate nitrogen is imported to the marshes where it is mineralized and returned to the estuary as ammonia and dissolved organic nitrogen. The magnitude of nitrogen export suggests significant fixation of atmospheric nitrogen by marsh flora with subsequent export as dissolved species. Carbon flux data show significant contributions of both particulate and dissolved organic carbon to the estuary from the marshes. Estimates of export, based on marsh grass productivity, suggest a loss of 36 and 49 percent of a year's primary production on the marshes as detritus for Ware and Carter Creeks respectively.
Book Synopsis Role of the Sediments for Dissolved Organic Carbon (DOC) in Drinking Water Reservoirs by : Tallent Dadi
Download or read book Role of the Sediments for Dissolved Organic Carbon (DOC) in Drinking Water Reservoirs written by Tallent Dadi and published by . This book was released on 2017* with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Benthic Flux; Dissolved Organic Carbon (DOC); Microbial Metabolic Potential; Resuspension; Sediment Core Incubation; Sediment-Water-Interface
Book Synopsis Dissolved Organic Carbon and Soil Solution PH as Affected by Drainage, Tillage, Depth and Season in an Agricultural Watershed by : Matthew Douglas Sullivan
Download or read book Dissolved Organic Carbon and Soil Solution PH as Affected by Drainage, Tillage, Depth and Season in an Agricultural Watershed written by Matthew Douglas Sullivan and published by . This book was released on 1997 with total page 242 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Flux of Dissolved Organic Carbon and Pore Water Through the Substrate of a Spartina Alterniflora Marsh in North Carolina by : G. Frank Yelverton
Download or read book Flux of Dissolved Organic Carbon and Pore Water Through the Substrate of a Spartina Alterniflora Marsh in North Carolina written by G. Frank Yelverton and published by . This book was released on 1984 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Seasonal Changes in Dissolved Organic Matter Outwelling in an Urban Salt Marsh System by : H. S. Cato
Download or read book Seasonal Changes in Dissolved Organic Matter Outwelling in an Urban Salt Marsh System written by H. S. Cato and published by . This book was released on 2013 with total page 2 pages. Available in PDF, EPUB and Kindle. Book excerpt: Macrophyte-dominated communities such as seagrass beds, mangroves and salt marshes have long been accepted as sources of large biodiversity, but are currently unaccounted for in global carbon budgets. Outwelling of dissolved organic carbon (DOC) from salt marshes has been hypothesized as highly productive marsh grasses are periodically inundated with seawater. Seasonal fluctuations of this vegetative flux have been observed, and this study investigates the variation of these fluxes from an urban salt marsh into the Neponset River Estuary through the "Fall Dump" period (August through December) as marsh grasses go senescent for the winter. Chromophoric dissolved organic matter (CDOM) and DOC were measured on monthly estuarine transects, continuously by mid-creek buoys, during week-long incubations of salt marsh below-ground and above-ground vegetatin, and in samples of seepage into secondary marsh creeks. CDOM and DOC outwelling reached a maximum in the late Fall, and was reduced to nearly zero in the winter months.
Book Synopsis Carbon Accumulation in Salt Marsh Soils by : Viktoria R. Unger
Download or read book Carbon Accumulation in Salt Marsh Soils written by Viktoria R. Unger and published by . This book was released on 2013 with total page 120 pages. Available in PDF, EPUB and Kindle. Book excerpt: Carbon accumulation in salt marsh soils is a beneficial ecosystem service that occurs as a result of in-situ macrophyte production, slow decomposition, and deposition of allochthonous sediments. Variation in rates of carbon accumulation within and among salt marshes may be influenced by factors including tidal flooding dynamics and sediment availability (Chmura et al. 2003, Mudd et al. 2009, DeLaune and White 2011). In this study, carbon accumulation and biomass dynamics were compared in two distinct estuary types with large differences in sediment availability and tide range. Nine soil cores approximately 60 cm long were collected in Spartina alterniflora-dominated marshes in a coastal plain estuary, Delaware Bay, and a coastal lagoon, Barnegat Bay. Accretion and mass-based accumulation of inorganic matter (sediment), and organic carbon were determined using 137Cs dating. Sediment accumulation rates were seven times greater whereas accretion, organic matter and organic carbon accumulation was two times greater in Delaware Bay than in Barnegat Bay. Accretion and accumulation processes were significantly different between the two estuaries. Inorganic sediment and organic matter in both estuaries contributed to vertical accretion and carbon accumulation. Our data suggest that the high sediment accumulation rates in Delaware Bay increase carbon accumulation rates to some degree, but that the degree to which it enhances carbon accumulation is influenced by some other factor(s). Coarse and fine root morphology in the soil cores was determined and related to sediment, organic matter and organic carbon content at analogous depth sections, as well as accretion and accumulation rates since 1963. Aboveground live and dead biomass was also measured at each core location. In Delaware Bay, the live:dead ratio of aboveground biomass was greater than that of Barnegat Bay. Live aboveground biomass was significantly greater in Delaware Bay, while dead aboveground biomass was slightly greater in Barnegat Bay. In Barnegat Bay there was little to no aboveground biomass at Island Beach and Reedy Creek, and little belowground biomass at Reedy Creek. Aboveground biomass dynamics such as stem density, stem height, and root:shoot ratios did not correlate with carbon accumulation processes at any sites. There were no significant differences in coarse, fine or total root material between the estuaries, however total belowground biomass contributed significantly to the soil carbon inventory in Barnegat Bay but not in Delaware Bay. Comparison of the biomass dynamics with soil characteristics and accretion and accumulation rates further emphasizes that factors other than sediment accumulation may be responsible for some of the differences in carbon accumulation within and among marshes in the two estuaries. The data suggest that belowground biomass may provide structural support to the soil column that is crucial for maintaining accretion and carbon accumulation processes, and more research should be conducted on the role of belowground biomass with respect to carbon accumulation.
Book Synopsis Degradation of Dissolved Organic Carbon in Permeable Coastal Sediments by : Lindsay Chipman
Download or read book Degradation of Dissolved Organic Carbon in Permeable Coastal Sediments written by Lindsay Chipman and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Approximately 70% of the shelf sediments are relict sands (Riggs et al., 1996), and in the shallow coastal zone a large fraction of these sands are highly permeable and permit circulation of water through the interstitial space (Marinelli et al., 1998; Huettel et al., 1996; Huettel and Gust, 1992). In this shallow environment, strong boundary currents caused by wind, waves, and tides force bottom water loaded with DOC through the sediment ripples and upper surface layers of the sand. Abundance and diversity of microbes in permeable sediments exceed that of the overlying water column (Hunter et al., 2006), and the question arises whether the filtration through the sediment affects the decomposition of DOC and water column DOC dynamics. I tested the working hypotheses that rapid DOC transport along relatively short pathways through the sand significantly enhances the degradation of the DOC and that the sedimentary flushing tightly links sedimentary and water column DOC concentrations.
Book Synopsis The Dynamics of Pore-water Dissolved Organic Carbon and the Fate of Organic Matter in Anoxic Marine Sediments by : Carol A. Seagle
Download or read book The Dynamics of Pore-water Dissolved Organic Carbon and the Fate of Organic Matter in Anoxic Marine Sediments written by Carol A. Seagle and published by . This book was released on 2002 with total page 246 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Role of Labile Dissolved Organic Carbon in Influencing Fluxes Across the Sediment-water Interface by : Deborah J. Read
Download or read book The Role of Labile Dissolved Organic Carbon in Influencing Fluxes Across the Sediment-water Interface written by Deborah J. Read and published by . This book was released on 2008 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt: Sediment diagenesis in aquatic systems is usually understood to be controlled by the concentrations of both organic carbon and the oxidant. However, the concept that sediment respiration may be limited by the supply of organic carbon, even in systems with moderate concentrations of organic carbon in the water column, has yet to be fully explored. Typically we assume that a direct coupling between water column and sediment diagenesis processes occurs and the chemical evolution of porewater and surface water are linked through fluxes of chemical species across the sediment-water interface. While the dynamics of supply of particulate organic carbon (POC) to the sediments via plankton deposition and resuspension, has previously been examined, the fate of dissolved organic carbon (DOC) once in the sediments, has rarely been investigated. A series of experiments comprising batch tests, microcosms and sediment cores were conducted on sediment and water from four diverse field sites in which sediment respiration was considered to be carbon limited. Three sites were oligotrophic, acidic lakes and the fourth an oligotrophic coastal embayment. During each experiment dissolved organic carbon was added and measurements were undertaken of solutes that were considered participants in diagenetic processes. While each system differed in its chemical, biological and geological makeup, a key commonality was the rapid onset of anoxic conditions in the sediments irrespective of the overlying water oxygen concentrations, indicating lack of direct coupling between biogeochemical processes in the water column and sediments. Also, similar apparent DOC remineralisation rates were observed, measured solute fluxes after the addition of DOC indicated adherence to the ecological redox sequence, and increased ammonium concentrations were measured in the overlying waters of the acidic microcosms. In marine system experiments it was noted that diagenetic respiration, as indicated by decreasing concentrations of oxygen in the overlying water, increased rapidly after labile DOC was added. To explore the influence of geochemical processes on sediment respiration, a diagenetic model was tested against the laboratory data. The model was able to capture the rapid changes observed in the microcosms after addition of DOC in both the marine and acidic systems experiments. The model has the potential to serve as an essential tool for quantifying sediment organic matter decomposition and dissolved chemical fluxes. This work has focussed our attention on the control of DOC availability on sediment respiration and thus its ultimate control on solute fluxes across the sediment water interface. The results highlight the need to understand and quantify the supply of DOC to the sediment (as POC or already as the dissolved form), its transport through the sediment and its eventual remineralisation. This understanding is critical for improved management of aquatic systems, possibly even in systems where water column organic carbon is plentiful but sediment respiration is constrained by high organic carbon turnover rates in the water column and a resulting low flux of organic carbon to the sediment.
Book Synopsis How Do Drying and Rewetting Events Affect Nutrient Fluxes and Bacteria Dynamics in Subtropical Estuarine Sediments? by : Jason D. Jenkins
Download or read book How Do Drying and Rewetting Events Affect Nutrient Fluxes and Bacteria Dynamics in Subtropical Estuarine Sediments? written by Jason D. Jenkins and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Drying and rewetting occur frequently in coastal marsh sediments due to oscillations of rising and falling tides, and episodic droughts and floods. Similarly, drying events also occur within freshwater systems due to changing precipitation patterns. However, little is known about how these events affect biogeochemical processes in sediments. In this study we examined the effects of drying on the release of nutrients from sediments to overlying waters, together with associated bacterial dynamics. We incubated dried and rewetted salt marsh sediments collected from the Nueces River mouth at the Nueces Salt Marsh (NSM) and from a freshwater section of the Mission River (MR) in South Texas. During the incubations, we quantified the nutrients released and changes of bacterial abundance and community structure in slurries of wet and dry sediments under anoxic conditions. Our results showed that ammonium concentrations increased steadily for both NSM and MR dry treatment incubations, reaching a maximum of 203 and 51 [mu] M respectively, as compared to only 124 and 2 [mu] M in the wet treatments. Phosphate concentrations steadily increased throughout the incubation in the NSM dry treatment, but not in the wet treatment where concentrations remained below 5 [mu] M. In contrast, we observed an opposite trend in the MR sediment with phosphate concentrations in the dry treatment remaining below those in the wet treatment throughout the incubation. The atomic C/N ratios for NSM and MR sediments ranged from 10 to 14 for both MR and NSM treatments, however they were significantly lower in the supernatants of the NSM dry treatment (5) than those in supernatants of the NSM wet treatment and in both MR wet and dry treatments (12). Although both NSM and MR had higher ammonium releases in the dry treatments than the wet ones, patterns in phosphate release and C/N ratios of dissolved organic matter differed in these two sediments, likely resulting from the differences in salinity and grain size distribution. Bacteria that developed in the slurry of NSM dried sediment included Bacillus, Anaerobacillus, Haloplasma, and Vibrio; these species were perhaps involved in decomposing sedimentary organic matter, including lysates from biota killed by the drying. The MR sediment slurry developed a different microbial community, where Gemmobacter, Rhodobacter, and Mycoplasma were most notable in the dried treatment. Overall, this study demonstrates that drying and rewetting events can increase nutrient fluxes out of marsh sediments and affect bacterial communities, important in estuarine biogeochemical processes. Information on this topic is important in the context of the increasing frequency of extreme droughts and floods and rising sea levels associated with global change.
