processes governing marsh formation in a rapidly subsiding coastal environment abstract processes governing the stability of marshes in louisiana s mississippi river delta plain were examined an accretionary budget was developed for barataria basin fresh brackish intermediate and salt marshes located along a salinity gradient extending inland from the coast the marshes represent a thin veneer overlying sediment stratum deposited by the mississippi river and it s ancestors at many locations rates of vertical marsh accretion were not sufficiently rapid to keep pace with increased water depth accompanying rapid subsidence due to compaction the life span of salt marshes of the mississippi river deltaic plain are estimated to be approximately 100 years the mineral sediment and organic carbon requirement of individual marsh units in response to water level increase is presented organic matter is an important component of accretionary processes and helps the marsh surface to keep pace with water level increase we estimated that at least 600 700 g of c m 2 yr 1 must be supplied to maintain marsh accretion to balance soil oxidation decomposition losses and organic carbon accretion peat formation even though subsidence is the primary factor in marsh deterioration accompanying factors salt water intrusion excess waterlogging stress vegetation and thus reduce the organic carbon source below minimum aggradation requirements inorganic sediment input is also necessary for maintenance of viable marshes many of the marshes within the basin are not receiving sufficient nutrients from sediment source to maintain significant plant growth necessary for organic matter production barataria basin marsh will likely continue disappearing unless means are implemented for reintroducing sediment from the mississippi river

methane production in mississippi river deltaic plain peat abstract seasonal methane production in a coastal peat deposit was studied dissolved methane content in interstitial water increased with increasing depth methane production rate was related to temperature in the 0 40 cm depth but was relatively constant at depths below 40 cm maximal methane content was found in spring and lowest content in november to january production rates were ph dependent with an optimum rate of methanogenesis at ph 7 7 the accumulation of metabolic end products produced within the peat water matrix appear to be important in limiting methanogenesis in wetland ecosystems the reserve of methane in the interstitial water of the brackish marsh was estimated to be 15 8 g ch 4 m 2 or 221 ch 4 per m 2 results suggest that the vast peat deposits in the mississippi deltaic plain could possibly be a potential source of renewable energy if in situ method for removal of the produced methane could be developed

rejuvenated marsh and bay bottom accretion on the rapidly subsiding coastal plain of u s gulf coast a second order effect of the emerging atchafalaya delta abstract sedimentation processes in marshes and bays under the influence of the emerging atchafalaya delta are described the atchafalaya delta is a major geological event in the holocene history of the mississippi river delta system because it represents the initial stages of a new delta cycle the delta has resulted from the capture of the mississippi river flow by the hydraulically more efficient atchafalaya river using 137 cs and 210 pb dating techniques maximum sedimentation of delta flanking environments was found to occur in the bay bottoms and marshes closest to the emerging delta marshes directly under the influence of the emerging delta were accreting at rates as great as 1 4 cm y 1 with appreciable mineral sediment inputs in addition to increasing shoreline progradation the added sediment is providing nutrients for increased net plant productivity which provides the organic source needed for vertical marsh accretion results show that the major area of coastal progradation will be in the immediate vicinity of the delta and along down drift coasts updrift marshes east terrebonne marshes away from the delta are accreting at a slower rate with smaller mineral sediment input and a larger percentage of organic material these marshes are likely to continue experiencing rapid rates of deterioration

significance of active growth faulting on marsh accretion processes in the lower pearl river louisiana abstract neotectonic processes influence marsh accretion in the lower pearl river valley active growth faults are suggested by groupings of ponded river channel sections transverse and linear river channel sections and down and across valley contrasts in channel sinuosity seismic profiles identified several likely fault induced structural anomalies two of which parallel the axes of surface distributary networks lithostratigraphy and biostratigraphy of six cores from across a suspected fault in the west middle river combined with 14 c based age control yielded evidence of vertical offsets indicating that this river section is on the plane of a growth fault these data were used to estimate fault slip rates over two time intervals 1 2 mm y over the last 1300 yr and 0 2 mm yr 1 over the last 3700 yr and delineated a sinusoidal pattern of deformation moving distally from the fault which we interpret as resulting from fault propagation folding higher rates of sediment accumulation of the order of cm yr 1 from 210 pb xs and 137 cs activity data on the down thrown side are consistent with sedimentary response to increased accommodation space and mass based sediment accumulation rates g cm 2 yr 1 exhibit a pattern inverse of that shown by fault driven sinusoidal deformation we contend that near surface growth faults are critically important to driving accretion rates and marsh response to sea level rise

marsh aggradation and sediment distribution along rapidly submerging louisiana gulf coast a coastwide study of the relationship between marsh aggradation and water level changes along the rapidly deteriorating louisiana gulf coast was conducted rate of vertical marsh accretion determined from137cs dating was compared to water level changes or submergence results identified marsh locations that are not keeping pace with submergence coastwide vertical accretion rates on the order of 0 7 0 8 cm yr are not sufficient to keep pace with water level increases occurring at rates in most locations of over 1 0 cm yr submergence rates were four to five times greater than eustatic sea level change for the gulf of mexico louisiana gulf coast marshes are likely to continue deteriorating unless means are implemented for distributing mississippi river sediment to the marsh it is estimated that sediment equivalent to less than 10 percent of the present annual suspended load of the mississippi would provide enough sediment for marsh accretionary processes to compensate for submergence or water level increase

234u 238u and δ87sr in peat as tracers of paleosalinity in the sacramento san joaquin delta of california usa abstract the purpose of this study was to determine the history of paleosalinity over the past 6000 years in the sacramento san joaquin delta the delta which is the innermost part of the san francisco estuary we used a combination of sr and u concentrations 87sr values and 234u 238u activity ratios ar in peat as proxies for tracking paleosalinity peat cores were collected in marshes on browns island franks wetland and bacon channel island in the delta cores were dated using 137cs the onset of pb and hg contamination from hydraulic gold mining and 14c a proof of concept study showed that the dominant emergent macrophyte and major component of peat in the delta schoenoplectus spp incorporates sr and u and that the isotopic composition of these elements tracks the ambient water salinity across the estuary concentrations and isotopic compositions of sr and u in the three main water sources contributing to the delta seawater sacramento river water and san joaquin river water were used to construct a three end member mixing model delta paleosalinity was determined by examining variations in the distribution of peat samples through time within the area delineated by the mixing model the delta has long been considered a tidal freshwater marsh region but only peat samples from franks wetland and bacon channel island have shown a consistently fresh signal

tracing the intrusion of fossil carbon into coastal louisiana macrofauna using natural 14 c and 13 c abundances the deepwater horizon oil spill released a large volume of 13c and radiocarbon depleted organic matter to the northern gulf of mexico evidence of petroleum derived carbon entering the offshore planktonic foodweb as well as widespread oiling of coastal areas documented in previous studies suggests that hydrocarbons could have entered the near shore foodweb to test this hypothesis we measured radiocarbon 14c and stable carbon isotopes 13c in an assortment of fish tissue invertebrate tissue and shell samples collected within a year of the spill at seven sites from louisiana to florida usa across the northern gulf of mexico we observed a west east gradient with the most depleted radiocarbon values found in terrebonne bay louisana and increasingly enriched radiocarbon values in organisms collected at sites to the east depleted radiocarbon values as low as 10 in invertebrate soft tissue from terrebonne suggest assimilation of fossil carbon 2 8 1 2 consistent with the hypothesis that organic matter from petrochemical reservoirs released during the deepwater horizon spill entered the coastal food web to a limited extent further there was a significant correlation between radiocarbon and 13c values in invertebrate tissue consistent with this hypothesis both oyster tissue and hard head catfish tissue collected in impacted areas of coastal louisiana were significantly depleted in 14c and 13c relative to organisms collected in the unaffected apalachicola bay florida p 0 014 alternative explanations for these results include the influence of chronic hydrocarbon pollution along the western gulf coast or that the organisms ingest carbon derived from 14c depleted organic matter mobilized during the erosion of coastal marshes in southern louisiana

an equilibrium profile model for retreating marsh shorelines in southeast louisiana abstract louisiana s coastal marshes are experiencing the highest wetland loss rates in the u s in part due to subsidence driven relative sea level rise these marshes are also vulnerable to the erosive power of wave attack 1 on the marsh edge adjacent to open water bodies and 2 after the marsh platform is submerged marsh shorelines in barataria bay breton sound and the active balize delta of southeastern louisiana were examined in areas where the subaerial marsh platform had disappeared since 1932 vibracore transects of marsh and adjacent bay surface sediments to 2 m depth were analyzed using geotechnical stratigraphic and radiochemical 137 cs and 210 pb methods and the subaerial to subaqueous transition of the marsh was mapped for elevation using standard stadia rod transit and fathometer measurements results indicate that marsh edge erosion of the platform takes place subaqueously until water depths of 1 5 m are reached this is observed even in interior pond regions but the shoreface elevation profiles are a function of fetch exposed open bay sites display greater incision depth and rate of the marsh platform than protected interior bay or pond sites core stratigraphy reveals that the outer part of the subaqueous platform switches from erosional to depositional as retreat proceeds covering the incised marsh deposits unconformably with estuarine shelly muds 137 cs and excess 210 pb activity indicates that these muds are deposited within a few decades of subaerial marsh loss the consistency of the cross shore profile results suggests that a single profile of equilibrium can approximate the morphology of eroding marsh edges in southeast louisiana platform stratigraphy and resistance to erosion have a limited effect on profile shape this equilibrium profile and remote sensing images of shoreline change are used to estimate the sediment yield to adjacent estuarine areas by this process on average 1 5 m3 of sediment are yielded per m shoreline length annually from both barataria bay and breton sound due to the highly organic nature of the eroded sediment 30 this supply of organic rich material could significantly impact estuarine productivity and hypoxia on the louisiana continental shelf

a comparison of factors controlling sedimentation rates and wetland loss in fluvial deltaic systems texas gulf coast abstract submergence of coastal marshes in areas where rates of relative sea level rise exceed rates of marsh sedimentation or vertical accretion is a global problem that requires detailed examination of the principal processes that establish maintain and degrade these biologically productive environments using a simple 210 pb dating model we measured sedimentation rates in cores from the trinity lavaca navidad and nueces bayhead fluvial deltaic systems in texas where more than 2000 ha of wetlands have been lost since the 1950s long term average rates of fluvial deltaic aggradation decrease southwestward from 0 514 0 008 cm year 1 in the trinity 0 328 0 022 cm year 1 in the lavaca navidad to 0 262 0 034 cm year 1 in the nueces the relative magnitudes of sedimentation and wetland loss correlate with several parameters that define the differing fluvial deltaic settings including size of coastal drainage basin average annual rainfall suspended sediment load thickness of holocene mud in the valley fill and rates of relative sea level rise there is some evidence that upstream reservoirs have reduced wetland sedimentation rates which are now about one half the local rates of relative sea level rise the extant conditions indicate that fluvial deltaic marshes in these valleys will continue to be lost as a result of submergence and erosion

historical rates of salt marsh accretion on the outer bay of fundy we examine rates of salt marsh accumulation in three marshes of the outer bay of fundy at each marsh we selected a site in the high marsh with similar vegetation and thus similar elevation accretion rates were estimated by 137 cs 210 pb and pollen stratigraphy to estimate rates of change over periods of 30 100 and 170 years respectively these rates are compared with records from the two closest tide gauges saint john new brunswick and eastport maine to assess the balance of recent marsh accretion and sea level change averaged marsh accretion rates have ranged from 1 3 0 4 to 4 4 1 6 mm year 1 over the last two centuries recent rates are similar to the rate of sea level change recorded at eastport maine suggesting that they are in step with recent sea level change but very sensi tive to short term variation in relative sea level based on the pollen stratigraphy in the marsh sediments the marsh ac cretion rate was higher during the late 18th to early 19th century higher rates probably were due to local increases in relative sea level as a result of neotectonic activity and may have been enhanced by increased sediment deposition through ice rafting

mangrove bank sedimentation in a mesotidal environment with large sediment supply gulf of papua the most extensive mangrove forests on earth are associated with major river systems the indo pacific region has numerous large rivers that discharge onto broad continental shelves and mangroves occur widely along these coastlines in the gulf of papua gop alone there are 3350 km2 of mangrove forests the majority of which 2900 km2 are associated with the fly kikori and purari river deltas this study examines data from 28 vibracores to describe preserved sedimentary strata and to determine rates of sediment accumulation in this dynamic coastal environment the observations suggest a common stratigraphy is contained in prograding mangrove banks of the mesotidal western gop and that it is similar to mud dominated and physically stratified stratigraphy recorded by other intertidal areas with and without mangroves experiencing large tidal range 2 m and sediment supply e g ganges brahmaputra and yangtze river deltas grain size sedimentary structure radionuclide and remotely sensed data are analyzed and four stratigraphic facies are identified 1 supratidal to high tidal muds 2 mid tidal sandy muds 3 low tidal sand and mud and 4 subtidal channel sands supratidal and high tidal sediments of gop mangrove forests are typically muddy but can have high sand contents 30 in areas exposed regularly to ocean waves these muds can be homogenous but commonly have physical structures laminations and bedding probably reflecting high rates of sediment accumulation relative to bioturbation mangrove muds may have low water contents due to infrequent inundation and because of their cohesive nature and abundant roots can form steep intertidal banks and erosional scarps mid tidal and low tidal sediments are thinly laminated 2 mm laminations likely deposited from fluid mud transport channel sediments have thin and thick mud and sand laminations but are identified by thick 5 cm sand beds a conceptual model of mangrove bank progradation is created using sedimentological and radionuclide data maximum sediment accumulation rates were determined using steady state 210pb profiles and greatest mean rates are found in mid tidal areas 4 4 cm year 3 9 g cm2 year slower accumulation occurs in high tidal and low tidal areas 1 8 and 1 5 cm year respectively 1 2 and 1 0 g cm2 year respectively remotely sensed data indicate that areas of erosion and accretion co exist in the kikori purari region very large 210pb accumulation rates were measured in areas of significant accretion supporting the validity of the calculated rates in areas of rapid accretion cores can have non steady state or event related 210pb profiles reflecting episodic sedimentation or complex radionuclide scavenging dynamics most cores from the fly river delta are of this type sediment trapping in western gop mangroves is estimated to account for 2 14 of the total gop sediment load

freshwater diversions as an ecosystem management tool for maintaining soil organic matter accretion in coastal marshes abstract marsh soil accretion processes were examined at 12 locations in fresh and brackish marshes in louisiana s northern barataria basin estuary soil accretion rate determined from 137 cs ranged from 0 59 to 1 03 cm yr 1 soil structure and accretion were controlled primarily by organic matter accumulation rather than mineral sediment deposition with water and entrapped gases occupying the majority of the soil volume ranging from 92 to 95 organic matter accumulation ranged from 328 to 580 g m 2 yr 1 while mineral accumulation ranged from 78 to 380 g m 2 yr 1 such organic based fresh and brackish marsh soil are more fragile than mineral based marsh soils and are subject to impact by salt water intrusion and hurricane storm surge forces the davis pond diversion is a conduit between the mississippi river and the coastal marshes of barataria basin currently reintroducing river water into the basin leading to lower basin salinities this hydrologic management measure should benefit and extend the stability of the studied marsh sites encouraging continued vegetation growth and soil organic matter accumulation accrual of organic matter is necessary to prevent drowning of the marsh which is subject to both the global eustatic sea level rise 1 2 mm yr 1 and significant local subsidence 10 mm yr 1 this high rate of relative sea level rise can lead to open water ponding and subsequent erosion of the surrounding marsh due to flooding and salinity stress

geological impacts on coastal wetland landscapes some general effects of sediment autocompaction in the holocene of northwest europe a simulation model is described providing general insights into autocompaction effects in stratigraphic sequences formed on coastal mudflats and marshes over uneven basements lithological units and buried landscapes are progressively displaced and distorted the synthetic sequences resembling bedding geometries described from the northwest european holocene autocompaction also promotes local deposition rates that may greatly exceed the rates at which accommodation space is created transgressive silts are associated with especially large deposition rates because of the high compressibility of underlying peats the experimental relationships between apparent rates of sea level rise and bed thickness resemble empirical trends for the holocene the latter are however reinforced by an intrinsic lithology related effect not included in the model

on autochthonous organic production and its implication for the consolidation of temperate salt marshes abstract the organic production related to minerogene salt marsh deposits represents a challenge to all attempts to model the development of these areas and evaluate their chances of survival under different sea level scenarios salt marsh deposits on a typical temperate backbarrier saltmarsh area at the skallingen barrierspit denmark were investigated for autochthonous or below ground organic production which was found to have a mean value of 0 14 kg m 2 y 1 or about 0 1 mm y 1 this production is concentrated in the upper approximately 5 cm of the salt marsh below this level the organic material decomposes with a decreasing organic content until about 15 cm below the surface hereunder the decomposition of organic material seems to stabilize at a very low level the constant rate of the below ground organic production results in a larger concentration of this type of organic matter in the slowest accreting salt marsh deposits the root activity is the primary reason for differences in the bulk dry density of salt marsh surface layers therefore the surface layers of slowly accreting salt marshes have the lowest bulk dry density during autocompaction the bulk dry density increases down core this process is only to a small degree

estimation of seasonal topographic variation in tidal flats using waterline method a case study in gomso and hampyeong bay south korea abstract morphologic and topographic changes of tidal flats can be key indicators for monitoring environmental changes and sea level rise recently a number of studies have been performed to estimate temporal topographic changes in tidal flats based on the waterline method using a number of remote sensing data that were acquired at different tidal heights however the effect of seasonal variation has not been taken into consideration nor been understood so far in this study 18 scenes of landsat tm and etm data covering the period 2003 2004 and corresponding tidal gauge observation data were used to estimate seasonal topographic variations in two major tidal flats in gomso and hampyeong bay in the southern part of the west sea of south korea using the waterline method our results showed that the summer deposition was dominant in gomso bay with overall average seasonal topographic increase of approximately 18 6 cm in contrast hampyeong bay showed more dominant summer erosion with overall average seasonal topographic subsidence of about 5 0 cm in addition the net overall sedimentation budget was estimated as 6 308 047 m 3 and 2 210 986 m 3 in gomso and hampyeong bay respectively the results also indicates that although both bays of gomso and hampyeong are classified as semi enclosed tidal flat the sedimentary facies caused by formation geometry and sediment type led to different topographic changes the results demonstrate that the amount of seasonal topographic variations is not negligible and are expected to improve the accuracy of topographic change derived by the waterline method

relationships among vertical accretion coastal submergence and erosion in a louisiana gulf coast marsh abstract vertical accretion in a southwest louisiana spartina patens brackish marsh has not kept pace with coastal submergence during the past three decades the rate of accretion determined from 137cs dating and the use of artificial marker horizons averaged 0 8 cm yr 1 whereas coastal submergence obtained from tide gauge data averaged 1 2 cm yr 1 conversion from marsh to open water bodies closely paralleled the increase in coastal submergence if the resulting aggradation deficit continues the marsh will likely complete its transformation to an open bay in less than 40 years in view of recent projections of increasing sea level rise the results presented may foreshadow a more widespread phenomenon

vertical salt marsh accretion since the roman period in the severn estuary southwest britain abstract using three methods of measurement and averaging over the whole estuary the vertical sediment accretion on mature clastic salt marshes amounts to 1 22 m since the roman period ca a d 150 1 05 m since the medieval period ca a d 1250 0 54 m since ca a d 1845 and 0 21 m since ca a d 1945 these data are cautiously interpreted to mean that the trend of relative sea level in the severn estuary is continuing upward shorter term negative tendencies are not excluded and that the current rate of rise could be a few millimetres per year the measured sediment thicknesses cannot be equated directly with relative movements of sea level however because of effects related mainly to 1 changes in the tidal range with general deepening 2 the possible transgression up the severn vale of the estuary as a whole and 3 the possible raising of tidal levels due to wetland reclamation after estimating for all these factors the true relative rise since the roman period could have amounted to 1 6 1 7 m

on the feasibility of magma fracture within volcanic conduits constraints from earthquake data and empirical modelling of magma viscosity 1 in the last decade several studies have indicated that magma within volcanic conduits can undergo repeated failure and healing thus providing a realistic source mechanism for the peculiar sequences of low frequency earthquakes that often announce eruptions although geological observations laboratory experiments and numerical modelling support such a hypothesis the links between geophysical observations and the proposed models remain qualitative this study focuses on providing constraints to the relationship between the occurrence of repeating earthquakes and magma fracture at andesite volcanoes empirical modelling of viscosity is incorporated into the fundamental physics of magma fracture in order to assess whether and where the conditions for brittle failure are met within volcanic conduits a case study from the 1995 ongoing eruption of soufriere hills volcano montserrat is presented the locations of earthquakes from a pre eruptive low frequency seismic swarm illuminate a relatively compact source volume at depths of 100 300 meters below sea level viscosity modelling confirms that the soufriere hills magma could rupture at those depths

impact of mississippi river freshwater reintroduction on enhancing marsh accretionary processes in a louisiana estuary abstract to counteract extensive wetland loss a series of diversion projects have been implemented to introduce freshwater and sediment from the mississippi river into louisiana coastal wetlands to keep pace with increases in water level due to subsidence louisiana coastal marshes must vertically accrete through the accumulation of both organic matter and mineral sediment the impact of mississippi river freshwater diversion on enhancing vertical marsh accretion mineral and organic matter accumulation was examined in breton sound estuary a coastal wetland experiencing marsh deterioration as result of subsidence and salt water intrusion using 137 cs dating and artificial marker horizons increases in the rate of vertical marsh accretion were measured at marsh sites along a spatial gradient which has been receiving diverted water from the mississippi river caernarvon diversion since 1991 vertical accretion and accumulation of mineral sediment organic matter and nutrients in the marsh soil profile increased at marsh sites receiving freshwater and sediment input iron and manganese content of the marsh surface sediment were shown to be an excellent signature of riverine sediment deposition soil extractable phosphorus was higher and extractable sodium was lower at sites nearest freshwater and sediment input results demonstrated that freshwater diversion through sediment input and lowering of salinity will enhance marsh accretion and stability slowing or reversing the rate of wetland loss