Freshwater Marsh Research Articles

Two Dimensional Model for Backwater Geomorphology: Darby Creek, PA

Predicting morphological alterations in backwater zones has substantial merit as it potentially influences the life of millions of people by the change in flood dynamics and land topography. While there is no two-dimensional river model available for predicting morphological alterations in backwater zones, there is an absolute need for such models. This study presents an integrated iterative two-dimensional fluvial morphological model to quantify spatio-temporal fluvial morphological alterations in normal flow to backwater conditions. The integrated model works through the following steps iteratively to derive geomorphic change: (1) iRIC model is used to generate a 2D normal water surface; (2) a 1D water surface is developed for the backwater; (3) the normal and backwater surfaces are integrated; (4) an analytical 2D model is established to estimate shear stresses and morphological alterations in the normal, transitional, and backwater zones. The integrated model generates a new digital elevation model based on the estimated erosion and deposition. The resultant topography then serves as the starting point for the next iteration of flow, ultimately modeling geomorphic changes through time. This model was tested on Darby Creek in Metro-Philadelphia, one of the most flood-prone urban areas in the US and the largest freshwater marsh in Pennsylvania.

Effect of Sulphur Oxidizing Bacteria (SOB) on sulphur nutrition in Sesame (Sesamum indicum)

Sulphur (S) plays an important role particularly in the nutrition of Oilcrops as it is a key element of S containing amino acids. Sulphur is a constituent of three amino acids commonly found in plants viz., cystine, cysteine, and methionine, which are essential components of proteins. Sulphur increase the oil content and gives pungency to oil as it forms certain disulphide linkages. Oil seeds crops like sesame, sunflower, groundnut etc., require more sulphur than cereals as their oil storage organs are mostly protein, rich in sulphur. Certain types of bacteria are able to oxidize, reduced form of sulphur which is unavailable to plants into available form. These types of bacteria are called as Sulphur Oxidizing Bacteria (SOB), which can live in very different environments, from deep in the ocean to freshwater marshes. One of the best examples of SOB is a genus Thiobacillus i.e., Thiobacillus thiooxidans, Thiobacillus ferrooxidans, Thiobacillus thioparus, Thiobacillus novellus. SOB generally improves the production or the conversion of the elemental sulphur to the sulphate (SO4-2) for absorption and results in the plant growth promotion and production process. Because of applying Sulphur Oxidizing Bacteria (SOB) to oilcrops, an amount of available sulphur to the plant is increased, this in turn helps to enhance the oil seed production and productivity.

The Role of Seed Bank and Germination Dynamics in the Restoration of a Tidal Freshwater Marsh in the Sacramento–San Joaquin Delta

Liberty Island, California, is a historical freshwater tidal wetland that was converted to agricultural fields in the early 1900s. Liberty Island functioned as farmland until an accidental levee break flooded the area in 1997, inadvertently restoring tidal marsh hydrology. Since then, wetland vegetation has naturally recolonized part of the site. We conducted a seed bank assay at the site and found that despite a lack of germination or seedling recruitment at the site, the seed bank contained a diverse plant community, indicating that the site’s continuous flooding was likely suppressing germination. Additionally, the frequency of germinating seeds in the seed bank did not represent the dominant adult plant community. We conducted a cold stratification study to determine if this observed disparity could be explained by seed germination dynamics, and whether germination could be enhanced using a pre-germination cold exposure, particularly for species of concern for wetland restoration. The cold stratification study showed that longer durations of pre-germination cold enhanced germination in Schoenoplectus acutus, but reduced germination in Schoenoplectus californicus, and had no effect on Typha latifolia. Overall, germination of S. californicus and S. acutus was much lower than T. latifolia. Our findings suggest that seeding may not be an effective restoration technique for Schoenoplectus spp., and, to improve restoration techniques, further study is needed to more comprehensively understand the reproduction ecology of important marsh species.

Experimental Saltwater Intrusion Drives Rapid Soil Elevation and Carbon Loss in Freshwater and Brackish Everglades Marshes

Increasing rates of sea-level rise (SLR) threaten to submerge coastal wetlands unless they increase soil elevation at similar pace, often by storing soil organic carbon (OC). Coastal wetlands face increasing salinity, marine-derived nutrients, and inundation depths from increasing rates of SLR. To quantify the effects of SLR on soil OC stocks and fluxes and elevation change, we conducted two mesocosm experiments using the foundation species sawgrass (Cladium jamaicense) and organic soils from freshwater and brackish Florida Everglades marshes for 1 year. In freshwater mesocosms, we compared ambient and elevated salinity (fresh, 9 ppt) and phosphorus (ambient, + 1 g P m−2 year−1) treatments with a 2 × 2 factorial design. Salinity addition reduced root biomass (48%), driving 2.8 ± 0.3 cm year−1 of elevation loss, while soil elevation was maintained in freshwater conditions. Added P increased root productivity (134%) but also increased breakdown rates (k) of roots (31%) and leaves (42%) with no effect on root biomass or soil elevation. In brackish mesocosms, we compared ambient and elevated salinity (10, 19 ppt) and inundated and exposed conditions (water level 5-cm below and 4-cm above soil). Elevated salinity decreased root productivity (70%) and root biomass (37%) and increased k in litter (33%) and surface roots (11%), whereas inundation decreased subsurface root k (10%). All brackish marshes lost elevation at similar rates (0.6 ± 0.2 cm year−1). In conclusion, saltwater intrusion in freshwater and brackish wetlands may reduce net OC storage and increase vulnerability to SLR despite inundation or marine P supplies.

Food Resources for Wintering and Spring Staging American Black Ducks

Abstract Habitat restoration and enhancement objectives for wintering waterfowl are typically derived by a bioenergetics modeling approach. This approach has been developed as a planning tool to identify the amount of foraging habitat required to meet North American Waterfowl Management Plan population objectives. Our objective was to provide the energetic supply component of the bioenergetics model at an important wintering area for American black ducks Anas rubripes in the Atlantic Flyway, the Eastern Shore of Virginia. We estimated food availability among four main wetland cover types used by overwintering American black ducks: brackish water, freshwater, mudflat, and salt marsh. Mudflat (221 ± 50 kg/ha) and salt marsh (728 ± 175 kg/ha) had the highest amounts of available invertebrate food density, and freshwater (42 ± 9 kg/ha) had the highest amounts of available seed biomass. Our results suggest that seed density found in freshwater wetlands on the Eastern Shore of Virginia is considerably lower than densities found in inland freshwater cover types used by dabbling ducks. We also found that levels of invertebrate density found in Virginia mudflat and salt marsh are considerably lower than levels on Long Island, New York, and in southern New Jersey. Lower levels of food density compared with both more inland and northern wintering areas suggest that American black ducks wintering in Virginia are more likely to be limited by forage availability than American black ducks and other dabbling ducks wintering both inland and in the northern portion of the wintering range.

Chronic but not acute saltwater intrusion leads to large release of inorganic N in a tidal freshwater marsh

Sea level rise is expected to increase inundation and saltwater intrusion into many tidal freshwater marshes and forests. Saltwater intrusion may be long-term, as with rising seas, or episodic, as with low river flow or storm surge. We applied continuous (press) and episodic (pulse) treatments of dilute seawater to replicate 2.5 × 2.5 m field plots for three years and measured soil attributes, including soil porewater, oxidation-reduction potential, soil carbon (C), and nitrogen (N) to investigate the effects of continuous and episodic saltwater intrusion and increased inundation on tidal freshwater marsh elemental cycling and soil processes. Continuous additions of dilute seawater resulted in increased porewater chloride, sulfate, sulfide, ammonium, and nitrate concentrations. Plots that received press additions also had lower soil oxidation-reduction potentials beginning in the second year. Episodic additions of dilute seawater during typical low flow conditions (Sept.-Oct.) resulted in transient increases in porewater chloride and sulfate that returned to baseline conditions once dosing ceased. Freshwater additions did not affect porewater inorganic N or soil C or N. Persistent saltwater intrusion in freshwater marshes alters the N cycle by releasing ammonium-N from sorption sites, increasing nitrification and severely reducing N storage in macrophyte biomass. Chronic saltwater intrusion, as is expected with rising seas, is likely to shift tidal freshwater marshes from a sink to a source of N whereas intermittent intrusion from drought may have no long term effect on N cycling.

Arsenic redistributive accretion in interdune marshes and its impact on groundwater contamination of coastal plains (southern Brazil)

Excessive concentrations of arsenic in aquifers have been presented for the first time in the southern Brazilian coastal plain. In this region, the shallow aquifers are mainly constituted by a mosaic distribution of marsh sediment lenses formed in the interdune depressions in past times and subsequently covered by eolian sands. The stratigraphic descriptions and analytical determinations in water (pH, conductivity, As) and sediment (organic carbon, As, Fe, Mn) were obtained in samples of an interdune freshwater marsh, an aquifer (a palaeo-freshwater marsh), and a modern eolic dune. Principal component analysis was applied to summarize the process of As immobilization. In sediments of the modern interdune marshes and under suboxic conditions, As is mobilized from the eolic sands and its redistribution occurs along sediment profile. Its maximum concentration (up to 1.7 mg kg−1 dw) occurred at the marsh’s sediments surface and was strongly coupled to Fe hydroxides. In pore water of marshes, As has been registered up to 79 µg L−1. This enrichment was driven by reductive dissolution of As-bearing Fe hydroxides in sediments, where the reduced environment has allowed their desorption from solids as Fe(II) and As(III) reduction. After the cover of the interdune marshes by eolic sands, turning them into current aquifers, the high As contents have been maintained above the sanitary limit of 10 μg L−1 for drinking water in groundwaters. The southern Brazilian coastal plain is probably an area with arsenic contamination problem for groundwater, which deserves more attention when it is used for drinking supply.

Plant defence allocation patterns following an increasing water level gradient in a freshwater wetland

Abstract Plant species are characterized by high adaptability to water level fluctuation in freshwater wetlands. Alteration in defence allocation patterns is one of the plant defence strategies in response to increasing water level gradients. Two dominant species, flood-sensitive species Deyeuxia angustifolia and flood-tolerant species Carex pseudocuraica, from freshwater marshes in the Sanjiang Plain were collected and treated with four water level gradients (–5, 0, 5, and 15 cm, relative to the soil surface), and both plant chemical (total polyphenols and condensed tannins) and structural (cellulose and lignin) defence compounds in leaves, stems and roots were measured. Increasing water level significantly decreased concentration of condensed tannins in C. pseudocuraica roots. For structural defence compounds, lignin concentration in C. pseudocuraica roots increased, which performed the contrary results in D. angustifolia roots and leaves. On the whole plant level, concentrations of chemical defence compounds in plant leaves were higher than that in stems and roots. Moreover, both the total phenols allocation to D. angustifolia leaves and condensed tannins allocation to C. pseudocuraica roots decreased with the increasing water level. Negative correlations between concentrations of condensed tannins and cellulose could be found in both D. angustifolia and C. pseudocuraica leaves. Plants adopt different defence strategies in response to the increasing water level, which provide us new purviews for revealing the plant distribution patterns in freshwater wetlands.

Significant Increase in Nutrient Stocks Following Phragmites australis Invasion of Freshwater Meadow Marsh but Not of Cattail Marsh

Invasive species are a threat to biodiversity and can cause ecological degradation, however, well-established invasive species may serve valuable ecological functions. For example, in the Laurentian Great Lakes, where nutrient pollution is a major issue, highly productive Phragmites australis (European Common Reed) may provide a nutrient retention service. Yet there is a lack of research comparing carbon and macronutrient stocks in P. australis with resident plant communities, such as cattail and meadow marsh. We quantified the effect of P. australis invasion on carbon and macronutrient standing stocks in a freshwater coastal marsh by comparing the above- and belowground biomass, tissue nutrient concentrations, and annual nutrient standing stocks in marsh invaded by P. australis with cattail marsh (dominated by Typha spp.) and meadow marsh (dominated by Calamagrostis canadensis), which are being displaced by P. australis in Lake Erie coastal marsh. We conclude that the effect of P. australis invasion on carbon and macronutrient standing stocks is dependent on the plant community being replaced. The annual standing stock of carbon, nitrogen, phosphorus, and potassium are consistent between cattail marsh and P. australis-invaded marsh, though cattail marsh contains more magnesium (112 % mean increase) and calcium (364 % mean increase). In contrast, when P. australis replaces meadow marsh, the standing stocks of all measured nutrients and carbon increase significantly (103 - 188 % mean increase). Our study highlights that plant invasions may create trade-offs between ecosystem services. In our case, the increase in nutrient standing stocks when P. australis invades meadow marsh should be weighed against the documented reductions in biodiversity and habitat value.

Community diversity and distribution of ammonia-oxidizing archaea in marsh wetlands in the black soil zone in North-east China

Since its first detection, ammonia-oxidizing archaea (AOA) have been proven to be ubiquitous in aquatic and terrestrial ecosystems. In this study, two freshwater marsh wetlands- the Honghe wetland and Qixinghe wetland — in the black soil zone in North-east China were chosen to investigate the AOA community diversity and distribution in wetland soils with different vegetation and depth. In the Honghe wetland, two sampling locations were chosen as the dominant plant transited from Deyeuxia to Carex. In the Qixinghe wetland, one sample location that was dominated by Deyeuxia was chosen. Samples of each location were collected from three different depths, and Illumina MiSeq platform was used to generate the AOA amoA gene archive. The results showed that the AOA amoA genes in the soils of the two wetlands were affiliated with three lineages: Nitrososphaera, Nitrosotalea, and Nitrosopumilus clusters. The different dominant status of these AOA lineages indicated their differences in adapting to acidic habitat, oxygenic/hypoxic alternation, organic matter, and other environmental factors, suggesting high diversity among AOA in marsh soils. The main driver of the AOA community was pH, along with organic carbon and ammonium nitrogen, which also played an important role combined with many other environmental factors. Thus, soil physiochemical characteristics, rather than vegetation, were the main cause of AOA community diversity in the wetlands in the black soil zone in China.

Testing the mid-Holocene relative sea-level highstand hypothesis in North Wales, UK

Accurate Holocene relative sea-level curves are vital for modelling future sea-level changes, particularly in regions where relative sea-level changes are dominated by isostatically induced vertical land movements. In North Wales, various glacial isostatic adjustment (GIA) models predict a mid-Holocene relative sea-level highstand between 4 and 6 ka, which is unsubstantiated by any geological sea-level data but affects the ability of geophysical models to model accurately past and future sea levels. Here, we use a newly developed foraminifera-based sea-level transfer function to produce a 3300-year-long late-Holocene relative sea-level reconstruction from a salt marsh in the Malltraeth estuary on the south Anglesey coast in North Wales. This is the longest continuous late-Holocene relative sea-level reconstruction in Northwest Europe. We combine this record with two new late-Holocene sea-level index points (SLIPs) obtained from a freshwater marsh at Rhoscolyn, Anglesey, and with previously published regional SLIPs, to produce a relative sea-level record for North Wales that spans from ca. 13,000 BP to the present. This record leaves no room for a mid-Holocene relative sea-level highstand in the region. We conclude that GIA models that include a mid-Holocene sea-level highstand for North Wales need revision before they are used in the modelling of past and future relative sea-level changes around the British Isles.

Feedback of coastal marshes to climate change: Long-term phenological shifts.

Coastal marshes are important carbon sinks facing serious threats from climatic stressors. Current research reveals that the growth of individual marsh plants is susceptible to a changing climate, but the responses of different marsh systems at a landscape scale are less clear. Here, we document the multi‐decadal changes in the phenology and the area of the extensive coastal marshes in Louisiana, USA, a representative of coastal ecosystems around the world that currently experiencing sea‐level rise, temperature warming, and atmospheric CO 2 increase. The phenological records are constructed using the longest continuous satellite‐based record of the Earth's ecosystems, the Landsat data, and an advanced modeling technique, the nonlinear mixed model. We find that the length of the growing seasons of the intermediate and brackish marshes increased concomitantly with the atmospheric CO 2 concentration over the last 30 years, and predict that such changes will continue and accelerate in the future. These phenological changes suggest a potential increase in CO 2 uptake and thus a negative feedback mechanism to climate change. The areas of the freshwater and intermediate marshes were stable over the period studied, but the areas of the brackish and saline marshes decreased substantially, suggesting ecosystem instability and carbon storage loss under the anticipated sea‐level rise. The marshes' phenological shifts portend their potentially critical role in climate mitigation, and the different responses among systems shed light on the underlying mechanisms of such changes.

Impacts of Saltwater Intrusion on Wetland Prey Production and Composition in a Historically Freshwater Marsh

Sea level rise is a fundamental driver of ecosystem change and has the potential to shift the spatial distributions of habitats more rapidly than species can adapt. Rapid sea level rise and associated saltwater intrusion have negative impacts on coastal environments, including loss of habitat for species such as sea turtles and shorebirds. In Florida’s largest wetland, the Everglades, the availability of small fishes that are prey for wading birds serve as an indicator of ecosystem health. In the southwestern part of the ecosystem, sea level rise and a reduction in freshwater flow have converted formerly freshwater marsh into an estuarine mangrove-dominated landscape. In this study, we sampled fish communities in this southwest portion of the Everglades exposed to a range of saline conditions. Biomass of native fishes was highest at a salinity value of approximately 25 parts per thousand, while non-native biomass decreased with increasing salinity. Applying salinity change scenarios, we determined that a 10% reduction from the salinity levels recorded in this study would be optimal for biomass of native fishes. The baseline data we collected on non-native fishes at the site will be useful for monitoring as restoration progresses and for managers working on invasive species control. This region has been actively undergoing ecosystem restoration for the last decade, but restored freshwater flow closer to historical conditions is still years away. Without increased freshwater inflow from hydrologic restoration, rising sea levels and saltwater intrusion may provide conservation challenges for wading birds and their prey-base fishes.

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.

The value of coastal wetland flood prevention lost to urbanization on the coastal plain of the Gulf of Mexico: An analysis of flood damage by hurricane impacts

Wetlands provide ecosystem services such as flood prevention; however, their transformation to housing developments limits the provision of these services. When tropical storms and hurricanes occur where coastal wetlands have undergone land use change (LUC), socioeconomic disaster results. Our objective was to estimate the economic value of flood prevention service provided by coastal wetlands. We quantified LUC and the loss of water retention capacity as a wetlands loss function and estimated the economic cost of flooding to households (lost appliances). The Veracruz-Boca del Rio-Medellin conurbation in Veracruz, Mexico, was used to evaluate these parameters during the floods caused by hurricane Karl in 2010. The total economic cost of losses to households was $150.85 million USD/2007. Between 1980 and 2010, the urban zone grew by 1,437.41 ha, resulting in the loss of 16.34 ha of water bodies, 455.41 ha of agriculture, and 965.66 ha of coastal wetlands (25.36 ha of mangroves, 152.95 ha of freshwater marshes and 787.35 ha of flooded grasslands). These results were used to obtain the economic value of flood prevention service and expressed as indirect-avoided cost. The economic values of flood prevention were: flooded grassland at $148,277 USD/ha/2007, freshwater broad-leaved marsh at $190,863 USD/ha/2007, and mangroves at $193,674 USD/ha/2007. The results of this study highlight the importance of protecting coastal wetlands and can be used by urban planning decision-makers when drawing up public policies in regional coastal contexts to protect human settlements and infrastructure.

Phosphorus alleviation of salinity stress: effects of saltwater intrusion on an Everglades freshwater peat marsh.

Saltwater intrusion and salinization of coastal wetlands around the world are becoming a pressing issue due to sea level rise. Here, we assessed how a freshwater coastal wetland ecosystem responds to saltwater intrusion. In wetland mesocosms, we continuously exposed Cladium jamaicense Crantz (sawgrass) plants and their peat soil collected from a freshwater marsh to two factors associated with saltwater intrusion in karstic ecosystems: elevated loading of salinity and phosphorus (P) inputs. We took repeated measures using a 2 × 2 factorial experimental design (n=6) with treatments composed of elevated salinity (~9ppt), P loading (14.66μmol P/d), or a combination of both. We measured changes in water physicochemistry, ecosystem productivity, and plant biomass change over two years to assess monthly and two-year responses to saltwater intrusion. In the short-term, plants exhibited positive growth responses with simulated saltwater intrusion (salinity + P), driven by increased P availability. Despite relatively high salinity levels for a freshwater marsh (~9 ppt), gross ecosystem productivity (GEP), net ecosystem productivity (NEP), and aboveground biomass were significantly higher in the elevated salinity + P treated monoliths compared to the freshwater controls. Salinity stress became evident after extended exposure. Although still higher than freshwater controls, GEP and NEP were significantly lower in the elevated salinity + P treatment than the +P treatment after two years. However, elevated salinity decreased live root biomass regardless of whether P was added. Our results suggest that saltwater intrusion into karstic freshwater wetlands may initially act as a subsidy by stimulating aboveground primary productivity of marsh plants. However, chronic exposure to elevated salinity results in plant stress, negatively impacting belowground peat soil structure and stability through a reduction in plant roots.

Adapting floating wetland design to advance performance in urban waterfronts

The great cities of the Mid-Atlantic, from Washington, DC to New York City, were strategically placed along the fall line where the Piedmont physiographic province transitions to the Coastal Plain. Situated at the head of the tide, this landscape position held important attributes for city building, including safe harbor for ships, local stone for construction, and proximity to steep streams suitable to run mills. But the head of tide is also an important ecological landscape threshold, where carbon, sediment and nutrients are delivered from the uplands by streams and rivers and deposited in tidal freshwater and brackish marsh systems. In undisturbed landscapes, those marshes uptake and transform pollutants in the water while providing refugia for aquatic fauna, spawning habitat for fish, and feeding grounds for migrating waterfowl. As human development has displaced these ecosystems, the connection facilitated by the beneficial ecosystem services of the tidal marsh systems has been severed.

Freshwater marsh classification in the Lower Paraná River floodplain: an object-based approach on multitemporal X-band COSMO-SkyMed data

A multitemporal approach to discriminate freshwater macrophyte vegetation types in the Lower Parana River floodplain is addressed. During a low-intensity flood pulse, seven X-band HH COSMO-SkyMed HImage images are acquired, covering a nine-month period. Scenes are segmented with a mean-shift segmentation algorithm. Objects are classified with an expectation maximization algorithm into clusters with different temporal signatures and are assigned to six information classes: water, bulrush marshes, short broad-leaf marshes, tall broad-leaf marshes, short grasslands and grass marshes, and tall grasslands and grass marshes. Class interpretation is based on backscatter dynamics, with focus on their correlation with hydrometric water level measured in the Parana River and/or with the floodplain area covered by water as estimated with a normalized difference vegetation index threshold criterion. The obtained product has a global accuracy of 75.4% and a kappa index of 67.2%. We point out the usefulness of X-band for flood monitoring and macrophyte vegetation type discrimination. However, we find limitations for the discrimination between high-biomass vegetation targets, such as tall broad-leaf marshes and tall grasslands. In a mosaic of herbaceous wetlands, the knowledge on the relation between vegetation and floods is essential for interpreting and predicting how backscattering coefficients and other synthetic aperture radar-derivated parameters vary with flooding.

Changes in bird assemblages in an afforestation landscape in the Lower Delta of the Paraná River, Argentina

ABSTRACTGlobal loss of wetlands has increased significantly in recent years. As a result, many wetlands have experienced changes in biotic communities, including birds. We compare the temporal variation in bird communities and the effects of land-use change on the structure and function of avian assemblages in the Lower Delta of the Paraná River (Argentina). We detected 28 families and 80 species of birds, with the highest richness, diversity and evenness in spring and summer because of the arrival of migratory species. Bird diversity, richness and evenness were significantly higher in secondary forests than in poplar plantations and cattle-grazing grasslands. Bird assemblages were related to structural differences of the habitat types and only generalist forest species were found in active plantations. Secondary forests exhibited species typical of the original riparian forest, practically extinct in the region. We speculate that abundance of guilds among habitat types is related to food supply and to plant composition. Our study shows for the first time how the conversion of wetlands into a Salicaceae plantation impacts on birds, particularly on wetland species. This demonstrates the need to implement management strategies to maintain a mosaic including secondary forests and freshwater marshes in order to conserve these species.

Exceptional rates and mechanisms of muddy shoreline retreat following mangrove removal

AbstractProbably the largest regular shoreline fluctuations on Earth occur along the 1500 km‐long wave‐exposed Guianas coast of South America between the mouths of the Amazon and Orinoco Rivers, the world's longest muddy coast. The Guianas coast is influenced by a succession of mud banks migrating northwestward from the Amazon. Migrating mud banks dissipate waves, partially weld onshore, and lead to coastal progradation, aided by large‐scale colonization by mangroves, whereas mangrove‐colonized areas between banks (inter‐bank areas) are exposed to strong wave action and undergo erosion. On large tracts of this coast, urbanization and farming have led to fragmentation and removal of mangroves, resulting in aggravated shoreline retreat. To highlight this situation, we determined, in a setting where mangroves and backshore freshwater marshes have been converted into rice polders in French Guiana, shoreline change over 38 years (1976‐2014) from satellite images and aerial orthophotographs. We also conducted four field experiments between October 2013 and October 2014, comprising topographic and hydrodynamic measurements, to determine mechanisms of retreat. The polder showed persistent retreat, at peak rates of up to ‐200 m/yr, and no recovery over the 38‐year period of monitored change. Notwithstanding high erosion rates, mangrove shorelines show strong resilience, with recovery characterized by massive accretion. Retreat of the polder results in a steep wave‐reworked shoreface with a lowered capacity for bank welding onshore and mangrove establishment. Persistent polder erosion is accompanied by the formation of a sandy chenier that retreats landwards at rates largely exceeding those in inter‐bank situations. These results show that anthropogenic mangrove removal can durably modify the morphodynamics of muddy shorefaces. This limits the capacity for shoreline recovery and mangrove re‐establishment even when there is no sustained long‐term deficit in mud supply, as in the case of the Amazon‐influenced Guianas coast. © 2019 John Wiley & Sons, Ltd.