Inundation Regimes Research Articles

Differential impacts of fire and inundation on a wetland plant community after wildfire

Context Understanding fire and inundation impacts on wetland vegetation communities is crucial for effective post-fire wetland management. Aims We aimed to determine the impact of post-fire inundation on plant community structure and seedling germination and establishment after a large wildfire. We asked two questions, namely (1) did fire, drought or inundation affect plant communities the most; and (2) did fire or inundation affect seedling germination and establishment? Methods Using a before–after–control–impact (BACI) design, we monitored vegetation changes in water-couch wetland communities before and after a wildfire. Also, soil samples were collected from burnt and unburnt sites and assessed for impacts of fire and post-fire inundation regimes on seed germination and seedling establishment. Key results Inundation variables had more pronounced and more consistent impacts on vegetation measures than did fire or drought variables. Fire impacts were mainly short-term, with impact thresholds at 72 and 143 days after fire. Low germination levels and zero seedling survival were observed without inundation. Conclusions Fire was a major but short-term contributor to wetland vegetation change, whereas drought had longer-term impacts, and inundation regimes had the greatest impacts. Implications Providing a range of inundation conditions post-fire may enhance wetland vegetation recovery and have modifying effects on invasive species.

Time to anoxia: Observations and predictions of oxygen drawdown following coastal flood events

The coastal terrestrial-aquatic interface (TAI) is a highly dynamic system characterized by strong physical, chemical, and biological gradients. In particular, shifting soil redox conditions and consumption of terminal electron acceptors, due in part to dynamic hydrologic conditions, is a strong driver of carbon availability and transformations across TAIs. However, while redox dynamics are well described, our ability to quantitatively forecast rates ofoxic to anoxic shifts in soils with different characteristics and inundation regimes is limited. We integrated field measurements, laboratory incubations, and model simulations to improve mechanistic understanding of oxygen consumption dynamics in coastal soils. Continuous in situ monitoring unexpectedly revealed that flooding caused temporary spikes in subsurface dissolved oxygen followed by rapid consumption in the wetlands. To further investigate these mechanisms in a controlled setting, we performed laboratory incubations using surface and subsurface soils from a TAI gradient (defined here as upland forest to transitional forest to wetland) in Western Lake Erie to measure oxygen consumption rates in TAI soils during flood events. In our experiments, wetland soils reached anoxia the fastest, in ∼ 9 h on average, whereas upland soils turned anoxic in ∼ 18 h. Subsurface upland soils did not turn anoxic even after two weeks of saturation in the lab, and their oxygen consumption patterns suggested carbon and/or nutrient limitation. These results are consistent with in-situ groundwater redox and oxygen measurements in the field, where wetland soils exhibited the highest rates of oxygen consumption along the TAI. Model simulations of oxygen consumption suggested that oxygen consumption had stronger abiotic controls in wetland soils but stronger biotic controls in upland soils, providing a useful framework for future incubation experiments. Microbial activity is a strong driver of oxygen consumption in TAI soils, although it is constrained by the availability of dissolved carbon in subsurface soils.

One sixth of Amazonian tree diversity is dependent on river floodplains.

Amazonia's floodplain system is the largest and most biodiverse on Earth. Although forests are crucial to the ecological integrity of floodplains, our understanding of their species composition and how this may differ from surrounding forest types is still far too limited, particularly as changing inundation regimes begin to reshape floodplain tree communities and the critical ecosystem functions they underpin. Here we address this gap by taking a spatially explicit look at Amazonia-wide patterns of tree-species turnover and ecological specialization of the region's floodplain forests. We show that the majority of Amazonian tree species can inhabit floodplains, and about a sixth of Amazonian tree diversity is ecologically specialized on floodplains. The degree of specialization in floodplain communities is driven by regional flood patterns, with the most compositionally differentiated floodplain forests located centrally within the fluvial network and contingent on the most extraordinary flood magnitudes regionally. Our results provide a spatially explicit view of ecological specialization of floodplain forest communities and expose the need for whole-basin hydrological integrity to protect the Amazon's tree diversity and its function.

Coastal inundation regime moderates the short-term effects of sediment and soil additions on seawater oxygen and greenhouse gas dynamics: a microcosm experiment

The frequency and persistence of tidal inundation varies along the coastal terrestrial-aquatic interface, from frequently inundated wetlands to rarely inundated upland forests. This inundation gradient controls soil and sediment biogeochemistry and influence the exchange of soils and sediments from terrestrial to aquatic domains. Although a rich literature exist on studies of the influence of tidal waters on the biogeochemistry of coastal ecosystem soils, few studies have experimentally addressed the reverse question: How do soils (or sediments) from different coastal ecosystems influence the biogeochemistry of the tidal waters that inundate them? To better understand initial responses of coastal waters that flood coastal wetlands and uplands, we conducted short-term laboratory experiments where seawater was amended with sediments and soils collected across regional gradients of inundation exposure (i.e., frequently to rarely inundated) for 14 sites across the Mid-Atlantic, USA. Measured changes in dissolved oxygen and greenhouse gas concentrations were used to calculate gas consumption or production rates occurring during seawater exposure to terrestrial materials. We also measured soil and water physical and chemical properties to explore potential drivers. We observed higher oxygen consumption rates for seawater incubated with soils/sediments from frequently inundated locations and higher carbon dioxide production for seawater incubated with soils from rarely inundated transect locations. Incubations with soil from rarely inundated sites produced the highest global warming potential, primarily driven by carbon dioxide and secondarily by nitrous oxide. We also found environmental drivers of gas rates varied notably between transect locations. Our findings indicate that seawater responses to soil and sediment inputs across coastal terrestrial-aquatic interfaces exhibit some consistent patterns and high intra- and inter-site variability, suggesting potential biogeochemical feedback loops as inundation regimes shift inland.

Floristic diversity, composition and dominance across Amazonian forest types respond differently to latitude

AbstractAimThe latitudinal biodiversity gradient is considered a first‐order biogeographical pattern for most taxonomic groups. Latitudinal variation in plant diversity is not always consistent, and this could be related to the particular characteristics of different forest types. In this study, we compare latitudinal changes in floristic diversity (alpha diversity), composition (beta diversity) and dominance across different tropical forest types: floodplain, terra firme and submontane forests.LocationWestern Amazonia (Ecuador, Peru and Bolivia).TaxonWoody plants.MethodsWe inventoried 1978 species and 31,203 individuals of vascular plants with a diameter at breast height ≥ 2.5 cm in 118 0.1‐ha plots over an 1800 km latitudinal gradient in three different forest types. The relationships between alpha diversity, latitude and forest type were analysed using generalised linear mixed models. Semi‐parametric permutational multivariate analysis of variance was used to investigate the effects of latitude and forest type on beta diversity. Dominant species abundances were correlated with non‐metric multidimensional scaling ordination axes to reflect their contributions in shaping changes in beta diversity.ResultsAlpha diversity increased towards equatorial latitudes in terra firme and submontane forests but remained relatively constant in floodplains. Beta diversity of all forest types changed with latitude, although less clearly in floodplains. Also, in floodplain forests, there were fewer dominant species contributing to beta diversity and more species homogeneous along the gradient.Main ConclusionsLatitudinal diversity patterns are manifested in alpha and beta diversity since latitude summarizes climatic and edaphic changes. However, we found different responses of each forest type. In floodplain forests, inundation regime is a stronger predictor than latitude, limiting floristic diversity and composition. Changes in dominant species abundance over gradients explained species composition, but floodplain forests harboured more homogeneous dominant species than well drained forests. It is key to study environmental trends and habitat characteristics of each forest type to understand their species diversity and dominance patterns.

Mechanical control inadvertently increases risk of alien plant invasion: influence of stem fragmentation and inundation regimes on Arundo donax regeneration in Neotropical savanna

Context Arundo donax L. is an exotic, perennial grass that has invaded dryland and wetland savannas of central Brazil. This species produces sterile flowers in its introduced range and propagates vegetatively via rhizomes and stem fragments. Aims We investigated bud sprouting capacity after fragmentation, which plays a major role in plant-proliferation ability, invasiveness and its escape from weed-control measures. Methods We evaluated the effects of size, different periods of desiccation (by exposure to air), submersion and water-column height on the regenerative capacity of single-node stem fragments. Key results Fragments of a minimum size of 3–4 cm successfully regenerated new plants. The regenerative capacity of single-node stem fragments (3–10 cm length) rapidly decreased after 1 week of air desiccation. Stem fragments that were submerged for 30 days resprouted and formed plants in a water column of 5, 10 or 15 cm, with no significant difference from the controls. However, leaves did not expand and shoot elongation was adversely affected in 15 cm of non-aerated water. This loss of performance was reversed when the newly formed plants were removed from the water and transferred to a moist substrate. Implications Our findings suggest that weed management, which involves cutting the plant to ground level without removing it from the site, is inefficient and can intensify the potential for invasion by A. donax, especially in the rainy season, when left-over stem fragments remain hydrated and capable of regeneration. Its establishment near riverbanks must be monitored because submerged propagules remain viable and able to resprout.

Comparison of leaf litter decomposition and microbial decomposer communities in fringe and riverine mangroves in French Guiana

Mangroves are highly productive and changing forests located in the intertidal zone of tropical regions. Leaf litter decomposition represents a substantial part of their carbon sink abilities. Little is known about the potential effect of climate change on this key process of ecosystem functioning. This study compared leaf litter microbial decay between fringe and riverine Avicennia germinans stands. A direct and reciprocal transplant experiment using litterbags was setup in French Guiana to test 3 hypotheses: (i) the activities and abundance of microbial decomposers are lowest in the fringe mangroves due to exposure to saline water and tidal immersion; (ii) for these reasons, litter decomposes faster in riverine stands; and (iii) according to the home-field advantage hypothesis, litter decomposes more rapidly in the environment from which it originates. Remaining litter masses, abundance of litter microbial community (phospholipid fatty acid signatures (PLFA)), and their functional capability (enzyme activities and Biolog) were assessed. Litter directly transplanted in riverine stands showed higher enzymatic activity (+ 77%), catabolic diversity (+ 10%), and microbial biomass (+ 60%) than litter transplanted directly in fringe stands. In contrast, both riverine and fringe derived litter showed faster decay at the fringe (14% mass loss) than riverine site (4% mass loss) between 30 and 45 days. Here, environmental conditions associated with different distances from the sea such as salinity and inundation regimes, rather than microbial features are suggested as main factors affecting decomposition process. Expected sea level rise in the coastal Guianas may therefore modify the mangroves productivity in the coming decades.

Estimating the Different Return Periods of Storm Impact Regimes on Beach and Foredune Systems Based in Hindcast Data: Applications to Exposed and Sheltered Beaches of Santa Catarina Island, Brazil

Prado, M.F.V.; Dalinghaus, C.; Gomes da Silva, P.; Weschenfelder, J., and Klein, A.H.F., 2022. Estimating the different return periods of storm impact regimes on beach and foredune systems based in hindcast data: Applications to exposed and sheltered beaches of Santa Catarina Island, Brazil. Journal of Coastal Research, 38(4), 844–859. Coconut Creek (Florida), ISSN 0749-0208. This paper presents an adapted methodology to estimate the different return periods of storm-induced impacts on beaches and foredune systems based on hindcast data, with examples of applications in areas exposed to and sheltered from the wave action. The methodology consists of using wave, tide, and surge reanalysis data to obtain large series of total water level, which are used to estimate the values related to different return periods (5,10, 25, and 50 years). Those levels are summed to the corresponding projection of sea level rise from the worst-case scenario projections. The final values are used to classify the beaches according to the coastal storm impact regime as (1) swash, (2) collision, (3) overwash, and (4) inundation. Finally, the limit between each regime is established based on the relation among dynamical and geomorphological parameters. The methodology was applied to the east (exposed beaches) and north (sheltered beaches) coasts of Santa Catarina Island (Florianópolis, Southern Brazil), a zone constantly submitted to extreme storm events and where large series of measured data are commonly missing. The results for Santa Catarina Island indicate that the storm impact regime in most of the exposed beaches is similar for different return periods (most of them classified as collision regime). Overwash regime is predominant on sheltered beaches. Sectors with an intense urban occupation are classified as under inundation regime for all return periods, while zones with well-developed foredune are classified as the collision regime. Some of those results could be qualitatively verified with observations from recent storm events, highlighting the value of this kind of methodology to estimate the impact of coastal storms in zones with an important lack of measurements.

Implications of Coastal Conditions and Sea-Level Rise on Mangrove Vulnerability: A Bio-Morphodynamic Modeling Study.

Mangrove forests are valuable coastal ecosystems that have been shown to persist on muddy intertidal flats through bio‐morphodynamic feedbacks. However, the role of coastal conditions on mangrove behavior remains uncertain. This study conducts numerical experiments to systematically explore the effects of tidal range, small wind waves, sediment supply and coastal slope on mangrove development under sea‐level rise (SLR). Our results show that mangroves in micro‐tidal conditions are more vulnerable because of the gentler coastal equilibrium slope and the limited ability to capture sediment, which leads to substantial mangrove landward displacement even under slow SLR. Macro‐tidal conditions with large sediment supply promote accretion along the profile and platform formation, reducing mangrove vulnerability for slow and medium SLR, but still cause rapid mangrove retreat under fast SLR. Small wind waves promote sediment accretion, and exert an extra bed shear stress that confines the mangrove forest to higher elevations with more favorable inundation regimes, offsetting SLR impacts. These processes also have important implications for the development of new landward habitats under SLR. In particular, our experiments show that landward habitat can be created even with limited sediment supply and thus without complete infilling of the available accommodation space. Nevertheless, new accommodation space may be filled over time with sediment originating from erosion of the lower coastal profile. Consistent with field data, model simulations indicate that sediment accretion within the forest can accelerate under SLR, but the timing and magnitude of accretion depend non‐linearly on coastal conditions and distance from the mangrove seaward edge.

Intertidal wetland geomorphology influences main channel hydrodynamics in a mature barrier estuary

Previous research utilising water level observations and hypsometric data has suggested that intertidal areas exert some control on main channel flow dynamics in estuaries, lagoons and tidal creeks. This has been demonstrated in more detail for saltmarsh and mangrove creeks utilising measurements of tidal velocity. However, understanding of relationships between tidal hydrodynamics and intertidal wetlands is still lacking for mature barrier estuaries. Improved understanding of hydrodynamics in these systems, as well as potential interactions with tidal wetlands, may facilitate their effective management and modelling.This study investigates relationships between main channel hydrodynamics and vegetated intertidal wetlands at Minnamurra River estuary, southeast Australia, using observations of tidal dynamics and wetland inundation regime. Tidal data was collected over five spring-neap cycles utilising tidal gauges and drag-tilt flow meters at six locations in the estuary's main channel, and 14 pressure transducers along three wetland transects. Comparison of stage-velocity plots and hypsometric curves indicates that estuarine flow dynamics were spatially variable and strongly influenced by the geomorphology of intertidal wetlands in the upper estuary, where water surface gradients developing during flood and ebb phases created velocity pulses. Spatiotemporal analysis of tidal asymmetry showed variability along the estuary, as well as between spring and neap conditions. The estuary studied displayed an ebb-dominated deeper main channel (velocity asymmetry) surrounded by wide shallow flood-dominated margins, indicating that caution should be adopted when interpreting an estuary's tidal asymmetry using a single asymmetry characteristic.Overall, results presented here demonstrate a strong connection between estuarine hydrodynamics and vegetated intertidal wetlands, which implies that integrated approaches considering estuarine hydrodynamics and vegetated intertidal wetlands simultaneously are required to manage and model mature barrier estuaries.

Impacts of a proposed water control project on the inundation regime in China's largest freshwater lake (Poyang Lake): Quantification and ecological implications

Study regionPoyang Lake, the largest freshwater lake in China, is connected to the Yangtze River and has been undergoing shrinkage over the past decade. Study focusThe Poyang Lake water control project (PLWCP) was proposed to protect the lake against rapid shrinkage. However, the quantitative impact of the project on the floodplain inundation regime is not yet clear. This study used a hydrodynamic model to quantify the influence of the PLWCP on the inundation regime of upstream floodplains in Poyang Lake. New hydrological insights for the regionPoyang Lake was characterised by high spatiotemporal heterogeneity in inundation patterns and that the northern lake areas were most affected, followed by the central and eastern lake areas. The western and southern lake areas were less affected. The water levels of the northern channels increased by a maximum of 4–5 m during the first recession period (16 Sep–31 Oct) and increased by 1–2 m during the impounding period (1 Sep–15 Sep). Most of the lake areas except the northern channels showed a water level increase of less than 0.5 m from November to March. The increased inundation areas were mostly 100–400 km2 (<20%) and reached greater than 800 km2 (~30%) from September to October, of which over 300 km2 (10%) lasted approximately 2 months. Potential suitable habitats in the northern, central and eastern lakes might be impacted.

Hindcasting Ecosystem Functioning Change in an Anthropogenized Estuary: Implications for an Era of Global Change

Understanding how altered hydrodynamics related to climate change and anthropogenic modifications affect ecosystem integrity of shallow coastal soft-sediment environments requires a sound integration of how species populations influence ecosystem functioning across heterogeneous spatial scales. Here, we hindcasted how intertidal habitat loss and altered hydrodynamic regimes between 1955 and 2010 associated with geomorphological change to accommodate expansion in anthropogenic activities in the Western Scheldt altered spatial patterns and basin-wide estimates of ecosystem functioning. To this end we combined an empirically derived metabolic model for the effect of the common ragworm Hediste diversicolor on sediment biogeochemistry (measured as sediment oxygen uptake) with a hydrodynamic and population biomass distribution model. Our integrative modeling approach predicted an overall decrease by 304 tons in ragworm biomass between 1955 and 2010, accounting for a reduction by 28% in stimulated sediment oxygen uptake at the landscape scale. Local gains or losses in habitat suitability and ecosystem functioning were primarily driven by changes in maximal current velocities and inundation regimes resulting from deepening, dredging and disposal practices. By looking into the past, we have demonstrated how hydro- and morphodynamic changes affect soft-sediment ecology and highlight the applicability of the integrative framework to upscale anticipated population effects on ecosystem functioning.

Dynamics of fortnightly water level variations along a tide-dominated estuary with negligible river discharge

Abstract. Observations indicate that the fortnightly fluctuations in the mean amplitude of water level increase in the upstream direction along the lower half of a tide-dominated estuary (the Guadiana Estuary), with negligible river discharge, but remain constant upstream. Analytical solutions reproducing the semi-diurnal wave propagation shows that this pattern results from reflection effects at the estuary head. The phase difference between velocity and elevation increases from the mouth to the head (where the wave has a standing nature) as the timing of high and low water levels come progressively closer to slack water. Thus, the tidal (flood–ebb) asymmetry in discharge is reduced in the upstream direction. It becomes negligible along the upper estuary half as the mean sea level remains constant despite increased friction due to wave shoaling. Observations of a flat mean water level along a significant portion of an upper estuary suggest a standing wave character and, thus, indicate significant reflection of the propagating semi-diurnal wave at the head. Details of the analytical model show that changes in the mean depth or length of semi-arid estuaries, in particular for macrotidal locations, affect the fortnightly tide amplitude and, thus, the upstream mass transport and inundation regime. This has significant potential impacts on the estuarine environment in terms of ecosystem management.

Inundation characteristics of mangrove and saltmarsh in micro-tidal estuaries

Tidal inundation is a principal driver in intertidal wetland functioning. A combination of surface elevation and its relation to tidal range creates inundation regimes that influence a range of abiotic factors that affect wetland species distribution. Hydroperiod is a term frequently used to describe inundation regimes; however, the term has been vaguely defined in the past and typically quantified using tide gauge data rather than empirical field observations. This study explores relationships between various characteristics, such as frequency, total duration, average duration, average depth, non-tidal exposure, and mangrove/saltmarsh distribution in micro-tidal estuarine settings of southeast Australia. Inundation was measured directly using 35 pressure transducers embedded into mangrove and saltmarsh substrates over a period of two lunar tidal cycles along six transects located at Clyde and Minnamurra River estuaries, New South Wales, Australia. Results indicated differences in wetland inundation characteristics between mangrove and saltmarsh that are a function of wetland microtopography and site-specific tidal regime (e.g. local tidal range). For example, mangroves were inundated approximately 15–70% of the time, and 0.9–2 times a day, whereas saltmarshes were submerged only <15% of the time and less than 0.9 times per day. Comparison of direct field measurements and tide gauge-derived estimates of wetland inundation regime revealed that nearby gauge data may provide an acceptable estimate; however, distant tide gauge data provided poor estimates due to the effect of tidal dampening and amplification, respectively. Detailed analysis of wetland inundation characteristics as presented in this study demonstrates a method for describing inundation regimes at local scale. Improved understanding of contemporary tidal inundation dynamics in mangrove and saltmarsh can support modelling of wetland response to sea-level rise, as well as restoration practises by providing estimates of inundation tolerances.

Spatiotemporal Heterogeneity of Mangrove Root Sphere under a Tropical Monsoon Climate in Eastern Thailand

Mangrove ecosystems under tropical monsoon climates experience changes in environmental factors, especially seasonal variations in salinity. These changes might have direct influences on the mangrove root sphere, which plays an important role in carbon dynamics and supports mangrove growth. We aimed to elucidate how the soil properties including salinity and nutrient budget affect the mangrove roots in the wet and dry seasons across the mangrove zonation (Avicennia, Rhizophora, and Xylocarpus zones). This area is in a secondary forest at the Trat River estuary, eastern Thailand. Root mass was observed at 0–10 and 10–20 cm depths across all zones and the living roots were separated into diameter classes. The soil water salinity was measured at a 10 cm depth. We analyzed the nitrogen, phosphorus, and carbon contents in the roots and soil. Spatiotemporal changes occurred due to the vegetation zonation and the variations in salinity and the content of soil available phosphorus that caused different root sphere conditions along the distance from the river. The highest root biomass was found in the riverward Avicennia zone, which was 4.8 times higher than that of the inland Xylocarpus zone in the wet season. The root necromass distribution along the zonation showed an opposite trend to that of biomass. Among seasons, the root size-class proportion differed, with high fine roots observed during the wet season. We confirmed that the root sphere showed both spatial and temporal heterogeneity. Mangrove roots, especially fine roots, interacted with changing salinity, inundation regime, and biological processes evoked by microtopographic gradients as a consequence of mangrove zonation and seasonal rainfall. Our findings indicate how the root sphere differed by specific vegetation structure in this mangrove forest. Therefore, these might provide an ecological perspective for the mangrove rehabilitation plans to facilitate below-ground carbon stock.

Large-scale variation in wave attenuation of oyster reef living shorelines and the influence of inundation duration.

One of the paramount goals of oyster reef living shorelines is to achieve sustained and adaptive coastal protection, which requires meeting ecological (i.e., develop a self-sustaining oyster population) and engineering (i.e., provide coastal defense) targets. In a large-scale comparison along the Atlantic and Gulf coasts of the United States, the efficacy of various designs of oyster reef living shorelines at providing wave attenuation was evaluated accounting for the ecological limitations of oysters with regard to inundation duration. A critical threshold for intertidal oyster reef establishment is 50% inundation duration. Living shorelines that spent less than one-half of the time (<50%) inundated were not considered suitable habitat for oysters, however, were effective at wave attenuation (68% reduction in wave height). Reefs that experienced >50% inundation were considered suitable habitat for oysters, but wave attenuation was similar to controls (no reef; ~5% reduction in wave height). Many of the oyster reef living shoreline approaches therefore failed to optimize the ecological and engineering goals. In both inundation regimes, wave transmission decreased with an increasing freeboard (difference between reef crest elevation and water level), supporting its importance in the wave attenuation capacity of oyster reef living shorelines. However, given that the reef crest elevation (and thus freeboard) should be determined by the inundation duration requirements of oysters, research needs to be refocused on understanding the implications of other reef parameters (e.g., width) for optimizing wave attenuation. A broader understanding of the reef characteristics and seascape contexts that result in effective coastal defense by oyster reefs is needed to inform appropriate design and implementation of oyster-based living shorelines globally.

Collembola (Hexapoda) as Biological Drivers between Land and Sea

Simple SummaryCollembola also represent one of the most abundant and important taxa of soil invertebrates inhabiting tundra soils. We focused on the structure and distribution patterns of the collembolan communities along the environmental gradient from costal tundra to live macroalgae and aged macroalgae debris deposited across the sub-Arctic coastline. Our results imply that environmental filtering influences collembolan species distributions across the gradient studied and the sorting of species according to their respective functional traits, including dispersal ability. We also suggest that the competition—colonisation trade-off mechanism, which affected the relative importance of competition and environmental filtering, probably determined Collembola community composition over the examined gradient. We believe that our results may become the basis for further study explaining the importance of Collembola as biological drivers of connectivity between land and sea.Macroalgae debris accumulated onshore function as points of interaction between marine and terrestrial ecological systems, but knowledge of the importance of detritivores facilitating the introduction of organic matter via the detritus pathway into neighbouring ecosystems, is still poorly understood. In particular, not much is known about biodiversity patterns and the colonisation of macroalgal debris by terrestrial, detritivorous soil microarthropods in the harsh environmental conditions in the subpolar Arctic region. We hypothesised that (i) soil microarthropods of the coastal tundra, including Collembola, can cross the ecosystem boundary and colonise decaying and freshly exposed macroalgae; and (ii) various inundation regimes by sea water, microhabitat stability and decaying of macroalgae drive distribution patterns of collembolan species. Our results suggest that environmental filtering influences collembolan species’ distributions across the examined gradient and induces sorting of species according to their functional traits, including dispersal ability, resistance to disturbance and environmental tolerance.

Characterization of storm surge deposits along the shore of the Gulf of Gdańsk (Baltic Sea) applying heavy mineral analysis

Recent studies along the southern Baltic Sea coast have revealed sedimentary records of catastrophic storm surges that significantly exceed the magnitude of storms documented by instrumental measurements. The present study aimed to apply heavy mineral analysis for storm surge deposits along coasts of Gulf of Gdańsk (southern Baltic), as well as for contemporary marine, beach, dune and coastal plain sediments, to test the applicability of the method and to provide new insights into the depositional processes and sediment sources of the storm deposits. The transparent, 0.125–0.25 mm heavy mineral fraction (>2.85 g/cm3) in 118 sediment samples was investigated, and the results were subjected to multivariate statistical analyses (cluster, PCA, LDA). Storm deposits showed higher concentrations of heavy minerals comprising enrichment in garnet, zircon, and rutile. General heavy mineral assemblage depended on regional provenance and primary sediment sources. However, flooding regime (overwash or inundation) played a key role in selective hydrodynamic sorting of grains and mineralogical composition of storm deposits. Interpretation of deposits formed in inundation regime was more certain than deposits formed in overwash regime. In the latter case, deposits showed more similarities to adjacent mineral provinces. Statistical analyses proofed that heavy minerals together with other sedimentological descriptors may be a promising proxy for recognition of deposits related to defined sedimentary environment or identification of particular sedimentological process, e.g. event layers resulted from storm surges.

High aqueous salinity does not preclude germination of invasive Iris pseudacorus from estuarine populations

AbstractEstuarine ecosystems are threatened by climate change and biological invasions. Among global changes, sea‐level rise is broadly impacting tidal wetlands, through increases in salinity and alteration of inundation regimes. Extant freshwater plant species are often presumed to be limited to reaches of estuaries with low salinity and narrow tidal ranges. However, the potential for invasive freshwater species (e.g., Iris pseudacorus) to persist and spread with increased salinity and flooding is poorly understood and can jeopardize native biodiversity and other wetland ecosystem services. The successful establishment of invasive plants will be dependent on their tolerance to salinity and inundation, starting with the germination life stage. Changes to abiotic estuarine gradients may alter the germination process of tidal wetland plant species that underlies significant patterns of plant community composition and biodiversity. We explored germination responses of seeds from two invasive I. pseudacorus populations from freshwater and brackish tidal sites in California’s San Francisco Bay–Delta Estuary. We tested germination dynamics under salinity levels ranging from freshwater to seawater (0, 12.5, 25, and 45 dS/m) and two hydrological conditions (moist and flooded). Salinity levels &gt;12.5 dS/m inhibited germination of seeds from both populations, consistent with viviparism and seedling emergence recorded at field sites. However, seeds exposed to seawater for 55 d germinated once exposed to freshwater. Germination velocity and seed buoyancy differed between populations, likely due to differences in seed coat thickness. Our results demonstrate that after 55 d in seawater, buoyant seeds of I. pseudacorus retain their ability to germinate, and germinate quickly with freshwater exposure. This suggests that invasive populations of I. pseudacorus can colonize new sites following potentially long‐distance dispersal of buoyant seeds with tidal currents. These findings inform risk assessments and highlight the need to prioritize the management of invasive I. pseudacorus in estuarine ecosystems impacted by rising sea level.

Morphodynamic modeling of a low-lying barrier subject to hurricane forcing: The role of backbarrier wetlands

Along much of the world's coastline, coastal barriers serve as the first line of defense against oceanic and meteorological forces. Extreme storms cause large morphological changes on coastal barriers through high sediment transport rates, which may degrade their defensive capabilities. The understanding of morphological impacts is therefore important for coastal resiliency, but is often challenged by site-specific characteristics, such as land cover and sediment availability, and their poorly understood impacts on the governing physical processes. The Caminada Headlands, Louisiana, USA presents unique considerations for morphodynamic modeling with regard to its low-lying topography, variable land cover, nearshore muddy substrate and sand deficiency. This study investigates the effects of land cover and limited sediment supply on low-lying barrier island morphology under storm conditions by using physics-based numerical models. A high-resolution, local-scale sediment transport/morphodynamic model (XBeach) of the Caminada Headlands is verified for Hurricane Gustav's (2008) impact using pre- and post-storm LIDAR surveys. When accurate input data are used to create physics-based numerical models these tools are robust in hindcasting storm impacts and provide a wealth of information as to the governing processes, which is otherwise difficult to obtain observationally. The simulation results show that a short-duration overwash regime dominates the morphological change in this low-lying barrier and is influenced by backbarrier wetland deterioration. The morphological response to overwash is modulated by backbarrier land cover and topography, as reduced accommodation space limits landward transport during the subsequent inundation regime. An intact backbarrier marsh reduces landward washover sediment transport distances and promotes deposition at supratidal elevations. In light of these findings, simultaneous restoration/creation of backbarrier wetlands in conjunction with subaerial beach renourishment may be an effective form of increasing the resiliency of low-lying barriers subject to frequent overwashing.