Marsh Sediments Research Articles

The Difference of Litter Decay, Litter- and Sediment-Associated Hydrolytic Enzymes between Brackish and Freshwater Tidal Marshes

While an increase in saltwater intrusion into historically freshwater environments will undoubtedly affect ecosystem functioning, the resultant impacts on litter decay and hydrolytic enzyme activities remain poorly understood. Here, we examined the decay of shichito matgrass stem litter, the associated loss of total carbon (TC) and total nitrogen (TN), and the activity of litter- and sediment-associated hydrolytic enzymes in two subtropical tidal marshes (one brackish and one freshwater) in southeastern China. Results obtained after 202 days of incubation revealed that there was no significant difference in litter mass loss between the brackish and freshwater marshes during both the standing phase (aerially decomposing litter) and the late phase of sediment-surface decomposition (slow decomposition of relatively refractory materials) (p > 0.05). The loss of TC and TN from litter was most rapid during the first month of the sediment-surface phase, and the loss rates were significantly greater in the brackish marsh (mass loss 61.63%, TC released 50.55%, and TN released 36.40%) than in the freshwater marsh (mass loss 43.28%, TC released 46.31%, and TN released 41.31%). Moreover, we found significantly higher sediment-associated β-glucosidase activities in brackish marsh sediments during the sediment-surface phase, and it correlated significantly with litter mass loss. The enhanced β-glucosidase activities stimulated decomposition in the early sediment-surface phase in brackish marsh sediments; however, a decrease in decomposition caused by salinity and tidal SO42− levels at the last phase ultimately offset the previous difference. Our findings provide insight into the potential consequences of modest saltwater intrusion; these may not alter the rates of litter decomposition, but could change the dominant pathway.

Large ungulate mortality profiles and ambush hunting by Acheulean-age hominins at Elandsfontein, Western Cape Province, South Africa

At Elandsfontein, a Middle Pleistocene marsh deposit preserves an abundance of mammalian fossils, along with a partial cranium of Homo heidelbergensis and a significant number of Acheulean stone tools. Most of this material was collected from the surface of eroding deposits in the 20th century, and it seemed to derive from a combination of hominin foraging activities and other, natural processes. Prior archaeological research on the fossil collection has emphasized natural, carnivore-related mortality and accumulation of large ungulates and downplayed the potential role of hominin hunting or scavenging at the marsh and more broadly at this time period in human evolution (Klein et al., 2007).Here, reanalysis of the most abundant large bovid taxa yields new, comprehensive estimates of the minimum number of individual (MNI) bovids and their age at death. The MNI = 125 for six species of size group 3 bovids, and the MNI = 37 for one species of size group 4 bovid. Analysis of these mortality profiles on triangular graphs reveals a consistent living-structure (i.e., catastrophic) profile for the pooled size group 3 taxa but an attritional profile for the size group 4 taxon. These results are contrary to prior reports for the collection, and they may indicate a larger role for hunting by H. heidelbergensis than heretofore reconstructed. The Elandsfontein mortality profiles, when compared to older and younger profiles from Stone Age and modern contexts in Africa and Europe, indicate more broadly that capable ambush hunting of large ungulate prey occurred throughout the past two million years of evolution of the genus Homo.

Short-term effect of simulated salt marsh restoration by sand-amendment on sediment bacterial communities.

Coastal climate adaptation strategies are needed to build salt marsh resiliency and maintain critical ecosystem services in response to impacts caused by climate change. Although resident microbial communities perform crucial biogeochemical cycles for salt marsh functioning, their response to restoration practices is still understudied. One promising restoration strategy is the placement of sand or sediment onto the marsh platform to increase marsh resiliency. A previous study examined the above- and below-ground structure, soil carbon dioxide emissions, and pore water constituents in Spartina alterniflora-vegetated natural marsh sediments and sand-amended sediments at varying inundation regimes. Here, we analyzed samples from the same experiment to test the effect of sand-amendments on the microbial communities after 5 months. Along with the previously observed changes in biogeochemistry, sand amendments drastically modified the bacterial communities, decreasing richness and diversity. The dominant sulfur-cycling bacterial community found in natural sediments was replaced by one dominated by iron oxidizers and aerobic heterotrophs, the abundance of which correlated with higher CO2-flux. In particular, the relative abundance of iron-oxidizing Zetaproteobacteria increased in the sand-amended sediments, possibly contributing to acidification by the formation of iron oxyhydroxides. Our data suggest that the bacterial community structure can equilibrate if the inundation regime is maintained within the optimal range for S. alterniflora. While long-term effects of changes in bacterial community on the growth of S. alterniflora are not clear, our results suggest that analyzing the microbial community composition could be a useful tool to monitor climate adaptation and restoration efforts.

Using mineral compositions to indicate the origin of sediments in a tidal flat of an estuarine marsh

ABSTRACTGiven the importance of tidal flats as habitats for a wide range of organisms, a considerable amount of related research has accumulated. However, in Japan, as elsewhere in the world, tidal flats are disappearing because of increasing seaside population, urbanization, and development of coastal industries. We investigated the sediment characteristics of Tsuyabaru Marsh in Japan, using X-ray fluorescence and X-ray diffraction (XRD) analyses to trace their sources. The estuarine Tsuyabaru Marsh comprises a tidal flat, the peripheral basin, the Ooyodo River, and the Yae River. The mineral components of the tidal flat sediment were quartz, mica minerals, kaolinite, plagioclase, and dolomite. To trace the sediment source and characterize the sediment in the Tsuyabaru Marsh, cluster analysis was applied to the peak XRD intensity ratios. A strong similarity was demonstrated between the sediments collected from the tidal flat and the Ooyodo River. A comparably strong similarity was found between sediments from the bottom of Tsuyabaru Marsh and the upstream Yae River section. Our analysis helps understand the sources and distribution of sediments in estuarine marshes.

Significant Techno-stratigraphic development of the Caroni Basin, recorded in outcrops of the late Neogene Manzanilla and Springvale Formations, NE Trinidad

The Manzanilla and Springvale Formations outcrop along a 1.9 km stretch on the eastern coast of Trinidad, and provide vital information about the development of the Caroni Basin and north-central Trinidad. The Manzanilla Formation contains deposits that range from deepwater to delta plain facies. Sandstone turbidites are the oldest deposits and these transition upward into muddy slope deposits then shelf mudstones, siltstones and sandstones. The occurrence of sporadic conglomerate beds suggests debris flows or other coarse-grained sediment gravity flows additionally entering the basin at this time. The upper parts of the Manzanilla succession reflect marginal marine environments with delta front (including mouth-bar), crevasse splay, bay fill and marsh deposits. Most of these deposits originated as the northernmost part of the east to northeast flowing paleo-Orinoco Delta. The anomalous interfingering of coarse-grained lithic-rich debris flow deposits with the delta-derived deposits, strongly suggests a derivation directly from the steep-sloped alluvial-fan and fan-delta deposits eroding off of the Northern Range orogenic belt, some 10 km to the north. The facies associations of the Springvale Formation reflect channelized estuarine environments strongly influenced by tidal processes. Subtidal channels associate with and are succeeded by wave and tidal influenced intertidal facies and their overlying supratidal mudstones, paleo-sols and lignite beds.Examination of these two formations reveals that the Neogene Caroni Basin developed quite differently from the coeval Southern and Columbus basins to the south. The Southern and Columbus Basins are true foreland basins with growing accommodation space and expanded shelf section due to the movement of huge listric faults. When compared to similar aged formations in the Southern Basin, the Caroni Basin succession is relatively thin, starved of sediment, contains internal discontinuities and tectonically derived coarse-grained conglomerates. This contrast is due to the fact that the Caroni Basin is sited immediately adjacent to the northern Trinidad zone of Caribbean and South American plate-margin convergence. The compressional forces acting on the basin produced alternating periods of uplift/erosion and subsidence which inhibited continuous deposition. The outcrops examined herein present new detail of the tectonic impact on the evolving Caroni foreland basin within northern Trinidad, where compression-driven base level changes left their signals in the foreland succession.

Development of a two‐layer transport model in layered muddy–permeable marsh sediments using224Ra–228Th disequilibria

AbstractUnderground seepage and the sediment–water interface are important pathways for transporting concentrated pore water solutes through permeable sediments. In this study, we utilized radium‐224/thorium‐228 disequilibria to examine solute transport throughout shallow sediments (depth < 30 cm) of a tidal marshland, North Inlet, South Carolina, over a seasonal cycle. Distinct224Ra–228Th disequilibria patterns indicate that significant pore water exchange occurred both directly across the sediment–water interface and at depth as underground seepage. Temporal variations in phosphorus (P), iron (Fe), and manganese (Mn) pore water concentrations also support this two‐layer transport model. Solute transport across the interface was influenced by seasonal bioirrigation, with highest exchange rates occurring in the late spring. Interfacial flux of dissolved Fe ranged over two orders of magnitude, from 0.5 mmol m−2d−1to 134 mmol m−2d−1, and fluxes of soluble reactive phosphate (SRP) and dissolved Mn varied from 0.01 mmol m−2d−1to 0.72 mmol m−2d−1and from 0.04 mmol m−2d−1to 2.7 mmol m−2d−1, respectively. Seepage occurs year‐round, with fluid exchange rates related to the distance from the tidal creek. SRP transport via seepage ranged from 0.98 mmol m−2d−1to 5.0 mmol m−2d−1, one order of magnitude higher than across the sediment–water interface. Reduction/oxidation reactions at depth diminished trace metal concentrations in deep pore water, and lowered the transport efficiency of Fe and Mn along seepage paths. Although an appreciable fraction of exported solutes likely returns to marsh sediments during tidal circulation, our results indicate that organic‐rich sediments provide a potentially large source of nutrients and trace elements to the coastal ecosystem.

Hydrological and biogeochemical controls on Fe cycling at the Krabbenkreek supratidal/intertidal zone, the Netherlands: Why does the Fe pump sputter?

Frequent and unexplained iron enrichments have been localized in buried, Holocene, marine sediments in coastal areas. These buried sediments are nowadays often part of groundwater systems in densely populated deltas. Here, the Krabbenkreek intertidal/supratidal area in the Netherlands is considered as a present analogue for diagenetic processes in these near-shore sediments. We evaluate the role of tidally driven groundwater flow alternations on the transport and speciation of Fe in deep tidal sediments. This was achieved by examining geochemical sediment and porewater data in the context of 3-D geohydrological modelling results of the groundwater system. The Krabbenkreek area presents clear hydrologic and geochemical zonations across the supratidal/intertidal area. Due to the low hydraulic conductivity, groundwater flow and infiltration of rain water is limited in the mud-rich upper sediments of the supratidal flat. Despite tidal fluctuations of the hydraulic heads up to 1.5 m, the corresponding alternating groundwater flow is relatively minor in comparison to the net groundwater flow. Tidal variations in the groundwater force field alone did not lead to pronounced local enrichments in reactive Fe. Differences in reactive Fe contents in deep sediments can be related to textural differences, implying that no indications for local, diagenetic Fe enrichments were found in the sediments down to 5 m depth. Contents of FeS and amorphous Fe(III) are remarkably low indicating little current dynamics in Fe redox cycling in these deep sediments, while the porewater chemistry indicates that pyrite oxidation prevails. Long-term oxidation of pyrite is reflected by the presence of Fe(III) oxides in the high marsh sediments while pyrite still dominates in the middle marsh and the intertidal sediments. Absence of active Fe redox cycling can be attributed to low respiratory activity in the sediments. Previous studies reported that sedimentary organic matter in the vicinity of the investigated area can be predominately refractory, which can probably explain the low respiratory activity in the Krabbenkreek sediments.

Water salinity and inundation control soil carbon decomposition during salt marsh restoration: An incubation experiment.

Coastal wetlands are a significant carbon (C) sink since they store carbon in anoxic soils. This ecosystem service is impacted by hydrologic alteration and management of these coastal habitats. Efforts to restore tidal flow to former salt marshes have increased in recent decades and are generally associated with alteration of water inundation levels and salinity. This study examined the effect of water level and salinity changes on soil organic matter decomposition during a 60‐day incubation period. Intact soil cores from impounded fresh water marsh and salt marsh were incubated after addition of either sea water or fresh water under flooded and drained water levels. Elevating fresh water marsh salinity to 6 to 9 ppt enhanced CO2 emission by 50%−80% and most typically decreased CH4 emissions, whereas, decreasing the salinity from 26 ppt to 19 ppt in salt marsh soils had no effect on CO2 or CH4 fluxes. The effect from altering water levels was more pronounced with drained soil cores emitting ~10‐fold more CO2 than the flooded treatment in both marsh sediments. Draining soil cores also increased dissolved organic carbon (DOC) concentrations. Stable carbon isotope analysis of CO2 generated during the incubations of fresh water marsh cores in drained soils demonstrates that relict peat OC that accumulated when the marsh was saline was preferentially oxidized when sea water was introduced. This study suggests that restoration of tidal flow that raises the water level from drained conditions would decrease aerobic decomposition and enhance C sequestration. It is also possible that the restoration would increase soil C decomposition of deeper deposits by anaerobic oxidation, however this impact would be minimal compared to lower emissions expected due to the return of flooding conditions.

Assessing arsenic sources in landfill areas: a case study in Sardinia

Concentrations of dissolved As can be related either to natural processes or anthropogenic activities. The aim of this study was to distinguish natural processes from potential anthropogenic effects on As occurrence in landfill areas. The study area is located in Central Sardinia and is characterized by Upper Pleistocene and Holocene sediments (sand and gravel with silt-clay matrix and local occurrence of thin ochreous colour levels; marsh deposits rich in organic matter and vegetal residues). The study area hosts an exhausted landfill where construction and demolition debris were disposed.The mineralogical composition of solid materials was characterized by quartz, feldspars and clay minerals. Concentrations of As were within the ranges reported in sediments and soils, except one sample that showed 46 mg/kg As.The waters showed near-neutral pH, variable electric conductivity (

Инженерно-геологическая характеристика долины реки Припять в пределах Республики Беларусь

Рассмотрены особенности формирования и пространственной дифференциации инженерногеологических условий, выделены генетические типы грунтовых толщ: аллювиальные, озерные и болотные, водно-ледниковые, моренные. Проанализированы физико-механические свойства грунтов и дана оценка их использования как оснований инженерных сооружений. Определено, что в пределах речной долины Припяти целесообразно в качестве естественных оснований зданий и сооружений использовать суглинистые, супесчаные и песчаные отложения различного генезиса, а широко распространенные на изучаемой территории болотные отложения использовать в качестве естественных оснований крайне нежелательно.

IMPROVING PREDICTIVE MODELLING OF COASTAL PROTECTION BY SALT MARSHES

Salt marshes are vegetated tidal wetlands, which can typically be found at sheltered coastal areas in moderate climate zones. Their potential as natural coastal protection by wave attenuation (Möller et al, 2014), reduction of flood-surge propagation (Stark et al., 2016) and shoreline stabilization (Bouma et al, 2014) has been increasingly recognized among scientists and engineers, but it comes with risks. Our understanding of the biogeomorphological dynamics between salt marsh vegetation, hydrodynamics and sediment is limited, while these are essential to identify the protective value of marshes to coastal protection (Wu et al., 2017). In this study, we present a predictive process-based model with a newly validated vegetation module to study the potential of salt marshes to contribute to coastal protection for a case study site in West Wales, United Kingdom.

Long-term effect of crude oil and dispersant on denitrification and organic matter mineralization in a salt marsh sediment

The 2010 BP oil spill has an unprecedented impact on coastal wetland ecosystem along the northern Gulf of Mexico. A two-dimensional analysis (dispersant concentration and duration of exposure) was conducted by pre-incubation of a salt marsh sediment under an open or closed condition. Denitrification activity was characterized by N2O production using an acetylene (C2H2) blockage technique, and organic matter (OM) mineralization by CO2 production. The results show that even trace amount of the dispersant could significantly inhibit the denitrification activity by 20% (p < 0.05). However, the sediment was resilient to the oil/dispersant contamination, likely due to shift of its microbial communities, by recovering the denitrification activity within 46 days in the open incubation. Inhibitory effect of the oil/dispersant on denitrification persisted beyond 46 days in the closed incubation, and the recovery could take up to 137 days depending on the dispersant concentration. The dispersant continuously stimulated OM mineralization that lowered the sediment redox status. Mobilization of N in the sediment from the OM mineralization forms a positive feedback loop, leading to deterioration of the coastal ecosystem. The study concludes that minimum dispersant should be applied for oil spill remediation, and oil cleanup operations should avoid moving the oil/dispersant from surface into deeper layers of the sediment. Synergistic interactions between the crude oil and dispersant and their biodegradation products deserves future examinations.

The effect of a small vegetation dieback event on salt marsh sediment transport

AbstractVegetation is a critical component of the ecogeomorphic feedbacks that allow a salt marsh to build soil and accrete vertically. Vegetation dieback can therefore have detrimental effects on marsh stability, especially under conditions of rising sea levels. Here, we report a variety of sediment transport measurements associated with an unexpected, natural dieback in a rapidly prograding marsh in the Altamaha River Estuary, Georgia. We find that vegetation mortality led to a significant loss in elevation at the dieback site as evidenced by measurements of vertical accretion, erosion, and surface topography compared to vegetated reference areas. Below‐ground vegetation mortality led to reduced soil shear strength. The dieback site displayed an erosional, concave‐up topographic profile, in contrast to the reference sites. At the location directly impacted by the dieback, there was a reduction in flood dominance of suspended sediment concentration. Our work illustrates how a vegetation disturbance can at least temporarily reverse the local trajectory of a prograding marsh and produce complex patterns of sediment transport. © 2018 John Wiley &amp; Sons, Ltd.

Soil organic carbon stocks in a tidal marsh landscape are dominated by human marsh embankment and subsequent marsh progradation

SummaryTidal marshes are coastal and estuarine ecosystems that store large amounts of sedimentary organic carbon (OC). Despite the valuable ecosystem services they deliver, tidal marshes have been converted to other land‐use types over the past centuries. Although previous studies have reported large decreases in soil organic carbon (SOC) stocks after tidal marsh embankment, knowledge on the magnitude and rate of OC losses is still limited. Here, we studied the effect of stepwise embankments of brackish and salt marshes and subsequent marsh progradation on SOC stocks in the Scheldt estuary (the Netherlands). We collected samples from soil profiles along tidal marsh–reclaimed tidal marsh chronosequences and determined total OC stocks and the stable carbon signature of the OC. Our results showed that large losses of previously sequestered SOC occur on a decadal timescale with the embankment of brackish (−8.7 ± 0.7 kg OC m−2) and salt marshes (−6.7 ± 0.8 kg OC m−2). The (incomplete) replacement of tidal marsh OC by agricultural OC is substantially faster in topsoils (ca. a century) compared with subsoils (multiple centuries). Simulations with a coupled land use–SOC model showed that large rates of marsh progradation following embankment construction resulted in a substantial increase in landscape‐scale SOC storage, whereas large SOC losses occurred in landscapes dominated by embanked tidal marshes. The findings of our study might help to assess how these management practices affect regional SOC stocks.Highlights We studied how OC stocks in tidal marsh sediments are affected by embankment construction OC stocks of both brackish and salt marsh sediments were reduced by ca. 60% with embankment Gains in landscape‐scale SOC storage occurred with marsh progradation after embankment If no marsh progradation occurs, embankments always lead to SOC loss at the landscape scale

Water Chemistry of Managed Freshwater Wetlands on Marine-Derived Soils in Coastal Bay of Fundy, Canada

Waterfowl and migratory birds rely on wetland habitat in coastal temperate regions for breeding and feeding. Over the past few decades, freshwater impoundments have been created in the Cumberland Marsh Region of Canada to compensate for regional loss of ecosystem services and habitat. The objective of our study was to determine whether freshwater impoundments underlain by tidal marsh sediments, and located where marine influences exist, are predisposed to higher nutrient levels and more conducive to productive habitat than waterfowl habitat elsewhere in Canada and the northeastern United States. We found that impoundment subsurface waters were generally circumneutral with moderate concentrations of dissolved organic carbon ranging between 6.30 and 13.90 mg/L. Furthermore, these impoundments generally had higher concentrations of cations (Ca, K, Mg, Na), anions (Cl−, SO42−), and nutrients (phosphorus, nitrogen, dissolved organic carbon) than other freshwater waterbodies studied for waterfowl in central Ontario, Maine and Nova Scotia, but lower concentrations than found in Prairie potholes. Our data indicate that a lack of hydrological connectivity and nutrient pathways may be limiting impoundments from reaching their full potential for supporting wildlife. We recognize that additional research on fostering ecosystem services from wetland restoration and creation projects is necessary on former tidal marshland.

Bioaccumulation of heavy metals by Cyperus malaccensis and Spartina alterniflora in a typical subtropical estuary (Min River) of Southeast China

To understand the bioaccumulation of heavy metals by Cyperus malaccensis (CM) and Spartina alterniflora (SA) in a typical subtropical estuary (Min River) of Southeast China, the concentrations of five metals (Pb, Cr, Cu, Zn, and Ni) in plants and sediments of CM and SA marshes were determined. Two experimental plots (no flooding plot and flooding plot) were established in the intertidal zone of the Min River estuary in July 2015, and, in each plot, in situ sampling was conducted in CM and SA marshes, respectively. The concentrations of heavy metals in all samples were determined by inductively coupled plasma mass spectrometry (ICP-MS) analysis. Vertical variations of the five metals differed between marshes or plots, and, in most cases, there was no evidence of grain-size composition (particularly for clay) and sediment organic matter (SOM) contributing to the sorption of significant amounts of metals in sediments of different marshes. Flooding regime was an important factor inducing the difference of metals in sediments of the two experimental plots. Heavy metal levels in different tissues of CM and SA differed within species or plots. For the five metals, the root was generally the main stock, and, as water condition changed from non-flooding to flooding, allocations of Pb, Cu, and Zn in CM and SA decreased while those of Cr increased. The accumulation factors [AFs] of heavy metals in different tissues of CM and SA also differed between species or plots. In most cases, the [AF]plant of different metals were less than 1, implying that the metal accumulations in CM and SA of the two plots were uncommon. This study found that Cu and Zn pollution in non-flooding conditions and Pb and Cu pollution in flooding conditions might be more serious, indicating that intertidal sediments might be severely contaminated by the three metals if effective measures are not taken to control the pollutant loadings of the Min River estuary in the future. Moreover, CM generally accumulated more Pb, Cu, and Zn while SA absorbed more Cr and Ni (particularly in flooding conditions), implying that, when determining environmental pressures, the two plants could be used as specified biological indicators.

Controls on Sediment Suspension, Flux, and Marsh Deposition near a Bay-Marsh Boundary

The sustainability of marshes adjacent to coastal bays is driven by the exchange of sediment across the marsh-bay boundary, where edge erosion commonly leads to lateral marsh loss and enhanced vertical accretion. The timing and patterns of sediment deposition on salt marshes adjacent to larger bodies of water such as coastal bays, however, differ from those on better-studied tidal creek marshes primarily owing to the importance of wind-waves. We combined field measurements and modeling to examine controls on suspended sediment concentrations and fluxes on a tidal flat (tidal range of 1.2 m) and rates of sediment deposition on the adjacent marsh at a site on the Eastern Shore of Virginia. Suspended sediment concentrations over tidal flats were strongly controlled by waves. Yet, storm winds sufficient to drive large resuspension events often coincided with peak tidal elevations that were too low to flood the marsh, which was oriented away from the wind directions most favorable for storm surge, thereby restricting storm-driven, episodic sediment delivery to the marsh. Winds also drove wide variability in the direction of surface currents near the marsh edge when water depths were high enough to flood the marsh. Nevertheless, our results show that sediment in the upper water column over the tidal flat was effectively transported across the marsh edge during flooding tides. A sediment deposition model developed to investigate the combined effects of vegetation and wave action on depositional patterns predicted that waves displace maximum deposition inland from the marsh edge, consistent with measured deposition at the study site. Marsh deposition was sensitive to inundation frequency as well as the concentration of sediment in water flooding the marsh, underscoring the importance of nontidal controls on water surface elevation, such as meteorological effects (e.g., storm surge) and sea level rise. Whereas short-term increases in marsh inundation enhance deposition, sea level rise that results in deeper average water depths over the tidal flats decreases deposition if marsh elevation is rising in step with sea level.

Quantification of organic carbon concentrations and stocks of tidal marsh sediments via mid-infrared spectroscopy

Tidal marshes are coastal ecosystems that store large amounts of sedimentary organic carbon (OC). Reducing the current uncertainty on the amount of OC stored these sediments requires the analysis of a large number of sediment samples. Soil sensing techniques, using mid infrared (MIR) spectroscopy combined with partial least squares regression (PLSR), have been proven to be a valid alternative for standard OC measurements in a wide range of terrestrial ecosystems. However, the application of these techniques to tidal marsh sediments has been very limited and the error associated with calculated sedimentary OC stocks using MIR spectroscopy/PLSR data has up till now not been evaluated. Therefore, we assessed the potential of MIR spectroscopy/PLSR to predict the OC concentration and OC stock of tidal marsh sediments in a temperate estuary (Scheldt estuary, Belgium and The Netherlands). Based on a cross-validation procedure, the results show that MIR spectroscopy/PLSR predicts the OC concentration of tidal marsh sediments along the entire estuary with a high accuracy (R2 = 0.94, RMSE = 0.56% OC). Similar accuracies were obtained for the prediction of sedimentary OC concentrations from independent tidal marshes. Organic carbon concentrations from tidal marshes in the salt portion of the estuary were, however, predicted more accurately using a PLSR model trained exclusively with sediment samples from this salinity zone. Combining depth profiles of predicted OC concentrations with measured bulk densities resulted in predictions of total OC stocks with a relative error < 4% for freshwater and brackish marshes, while errors for salt marshes were up to 30%. As MIR spectroscopy/PLSR is not able to accurately predict bulk density or OC density, standard field measurements of bulk density remain necessary to reliably predict sedimentary OC stocks in tidal marshes.

200-year industrial archaeological record preserved in an Isle of Man saltmarsh sediment sequence: Geochemical and radiochronological evidence

The Isle of Man, situated in the central Irish Sea, was a significant centre for Pb and Zn mineral extraction during the Industrial Revolution. Comminuted mining debris from the East Snaefell and North Laxey mining areas was transported, through hydrological action, from upland catchments to the coast. This study focuses on an eastern coastal sediment sink and a salt marsh sediment sequence from Port Cornaa. A sediment monolith was excavated, sub-sampled and geochemically investigated using Itrax scanning, WD-XRF analysis and radionuclide methods. Since the island is only 55 km from one of the world's major nuclear reprocessing sites (Sellafield), it was anticipated that a record of these radionuclide discharges (1951-present) would be identifiable and contribute clear chronological markers. The 137Cs profile shows a Sellafield discharge component and also a larger component that is attributed to the 1986 Chernobyl airborne plume. This contribution in the salt-marsh sediment would be derived from the erosion and transport of Chernobyl-labelled upland soils into the marsh. Sediment depth was converted to age using natural (210Pb) and anthropogenic radionuclides (137Cs and 239, 240Pu) and a compelling age vs depth relationship was obtained. The ability to reliably date the overall sediment section shows that sediment accumulation is uniform for the top 25 cm (5 mm/y) and from −25 to −70 cm (3.2 mm/y). The robust age-depth model allows features in the geochemical profiles for S, As, Pb, Zn and Cu to be dated and used to infer events at the East Snaefell and North Laxey mines. These include start-up of mining, introduction of more-efficient mining practises (i.e. water-wheel technology), change in the intensity of mining and final mine closure. The study provides a 200-year industrial archaeological record for the east coast of the Isle of Man. It demonstrates the benefits offered by a combined study involving non-destructive, high resolution Itrax scanning, conventional WDXRF and radionuclide dating.

Applicability of Horton model and recharge evaluation in irrigated arid Mesopotamian soils of Hashimiya, Iraq

The drawbacks of Horton model for infiltration potential estimate in arid regions are a serious problem the hydrologists are facing. Horton model is inapplicable in regions of initial rainfall intensities less than initial infiltration capacity of soils as basically outlined by Horton. Four infiltration models including Horton are adopted to evaluate their validity for infiltration potential estimate namely as Horton, power, polynomial, and mixed fitting models. Infiltration field measurements by double ring infiltrometer, and geotechnical investigations for soils to estimating infiltration rate, specific gravity, and bulk density were conducted at Hashimiya area of 110 km2. The entire area was divided into nine administrative sectors namely as Jerboeyia, Hashyimia, Niwedra, Tebra, Sada, Zineyia, H3, Fayadhiya, and Bazul due to spatial hydrology. Geologically, the area consists of Mesopotamian plain which comprises the recent river sediments of Tigris and Euphrates, which consists of silts and clays and stacked river channel sands with occasional marsh deposits. The power model offers best fit to the measured infiltration with correlation coefficient of 0.996, whereas polynomial, mixed fitting, and Horton models offer 0.947, 0.958, and 0.84 respectively. Moreover, Horton model offers less infiltration potentials for both dry and wet seasons of 3 and 1 mm/day causing a rise in the average groundwater levels equal to 8.4 and 2.8 mm/day respectively. Similarly, the average infiltration potentials estimated by power model for both dry and wet seasons were 3.55 and 1.19 mm/day to rise in the average groundwater levels 9.88 and 3.31 mm/day respectively. These models create a paradigm for hydrology and environmental sustainability.