RESUMEN

Microplastic (plastics <5 mm; MPs) contamination of the marine environment has garnered global attention in recent years, not only because of continuous accumulation of MPs but also due to the serious threats they pose to the ecosystems. This review evaluates patterns of MPs accumulation in three coastal habitats: seagrasses, mangroves and saltmarshes with the aim of providing a more integrated view of MPs pollution. These habitat-forming ecosystems are known to enhance deposition of suspended particles, including MPs. Studies regarding sources, distribution characterization, and fate of MPs in the different environmental compartments of these habitats have been reported since 2011. We found an unequal geographic distribution with most studies performed in the Northern hemisphere and in mangrove forests, which exhibit the highest MPs concentrations in comparison to saltmarshes and seagrass beds, particularly near urban centers and fishing zones. Almost 40 % of the outcomes of our meta-analysis reported a higher accumulation in vegetated than unvegetated sites. Also, degraded and highly-degraded sites exhibited higher amounts of MPs compared to less-degraded sites. In addition, fibers and fragments (secondary MPs) are the dominant form of MPs found in these habitats. The less dense polymers (polyethylene polystyrene and polypropylene) were the more abundant, appearing in all the systems and blue, black and transparent were the most abundant colors. Methodological considerations highlight the variability in reporting units, sampling depths, and extraction methods, all of which makes the studies less comparable and increase variability of results. This review offers a comprehensive understanding of the current state of MP research in coastal ecosystems, revealing critical gaps in knowledge influencing MPs distribution, including vegetation density and diversity, or hydrodynamism, and emphasizing the importance of using standardized methodologies for accurate comparisons.

RESUMEN

Nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) is an important methane (CH4) consumption and nitrogen (N) removal pathway in estuarine and coastal wetlands. Antibiotic contamination is known to affect microbially mediated processes; however, its influences on n-DAMO and the underlying molecular mechanisms remain poorly understood. In the present study, using 13CH4 tracer method combined with molecular techniques, we investigated the responses of n-DAMO microbial abundance, activity, and the associated microbial community composition to sulfamethazine (SMT, a sulfonamide antibiotic, with exposure concentrations of 0.05, 0.5, 5, 20, 50, and 100 µg L-1). Results showed that the effect of SMT exposure on n-DAMO activity was dose-dependent. Exposure to SMT at concentrations of up to 5 µg L-1 inhibited the potential n-DAMO rates (the average rates of nitrite- and nitrate-DAMO decreased by 92.9 % and 79.2 % relative to the control, respectively). In contrast, n-DAMO rates tended to be promoted by SMT when its concentration increased to 20-100 µg L-1 (the average rates of nitrite- and nitrate-DAMO increased by 724.1 % and 630.1 % relative to the low-doses, respectively). Notably, low-doses of SMT suppressed nitrite-DAMO to a greater extent than nitrate-DAMO, indicating that nitrite-DAMO was more sensitive to SMT than nitrate-DAMO. Molecular analyses suggest that the increased n-DAMO activity under high-doses SMT exposure may be driven by changes in microbial communities, especially because of the promotion of methanogens that provide more CH4 to n-DAMO microbes. Moreover, the abundances of n-DAMO microbes at high SMT exposure (20 and 50 µg L-1) were significantly higher than that at low SMT exposure (0.05-5 µg L-1). These results advance our understanding of the ecological effects of SMT on carbon (C) and N interactions in estuarine and coastal wetlands.

Asunto(s)

RESUMEN

The "Shadegan International Wetland" (SIW) is one of the wetlands internationally recognized in the Ramsar convention. The vegetation of this wetland ecosystem consists of mostly grasses and shrubs that host a large number of fungi including endophytes. In this study, Nigrospora isolates were obtained from healthy plants of this wetland and its surrounding salt marshes and identified based on morphological features and multilocus phylogenetic analyses based on three DNA loci, namely the internal transcribed spacer regions 1 and 2 including the intervening 5.8S nuclear ribosomal DNA (ITS), ß-tubulin (tub2), and elongation factor 1-α (tef1-α). Accordingly, the following Nigrospora species were identified: N. lacticolonia, N. oryzae, N. osmanthi, N. pernambucoensis and a novel taxon N. shadeganensis sp. nov., which is described and illustrated. To the best of our knowledge, 10 new hosts for Nigrospora species are here reported, namely Aeluropus lagopoides, Allenrolfea occidentalis, Anthoxanthum monticola, Arthrocnemum macrostachyum, Cressa cretica, Halocnemum strobilaceum, Seidlitzia rosmarinus, Suaeda vermiculata, Tamarix passerinoides, and Typha latifolia. Moreover, the species N. lacticolonia and N. pernambucoensis are new records for the mycobiota of Iran.

Asunto(s)

RESUMEN

Marshes are an important ecosystem, acting as a biodiversity hotspot, a carbon sink and a bioremediation site, breaking down anthropogenic waste such as antibiotics, metals and fertilizers. Due to their participation in these metabolic activities and their capability to contribute to primary productivity, the microorganisms in such habitats have become of interest to investigate. Since Proteobacteria were previously found to be abundant and the waters are well aerated and organic-rich, this study on the presence of anoxygenic phototrophic bacteria, purple non-sulfur bacteria and aerobic anoxygenic phototrophs in marshes was initiated. One sample was collected at each of the seven Manitoban sites, and anoxygenic phototrophs were cultivated and enumerated. A group of 14 strains, which represented the phylogenetic diversity of the isolates, was physiologically investigated further. Aerobic anoxygenic phototrophs and purple non-sulfur bacteria were present at each location, and they belonged to the α- and ß-Proteobacteria subphyla. Some were closely related to known heavy metal reducers (Brevundimonas) and xenobiotic decomposers (Novosphingobium and Sphingomonas). All were able to synthesize the photosynthetic complexes aerobically. This research highlights the diversity of and the potential contributions that anoxygenic phototrophs make to the essential functions taking place in wetlands.

RESUMEN

Herbaceous marshes are widely distributed in China and are vital to regional ecological security and sustainable development. Vegetation net primary productivity (NPP) is a vital indicator of vegetation growth. Climatic change can significantly affect NPP, but variations in NPP of herbaceous marsh and their responses to climate change in China remain unclear. Using meteorological data and MODIS NPP data during 2000-2020, this study analyzed the spatial and temporal variations of NPP and their responses to climate change in Chinese herbaceous marshes. We found that the annual NPP of herbaceous marshes in China increased significantly at a rate of 3.34 g C/m2/a from 2000 to 2020, with an average value of 336.60 g C/m2. The increased annual total precipitation enhanced the national average NPP, whereas annual mean temperature had no significant effect on the national average NPP. Regionally, precipitation had a significant positive effect on the NPP in temperate semi-arid and arid and temperate semi-humid and humid marsh regions. For the first time, we discovered asymmetry effects of daytime and nighttime temperatures on NPP in herbaceous marshes of China. In temperate humid and semi-humid marsh regions, increased summer daytime temperature decreased the NPP while increased summer nighttime temperature increased the NPP. In the Tibetan Plateau, increased autumn daytime temperature, as well as summer daytime and nighttime temperatures could increase the NPP of herbaceous marshes. This study highlights the different influences of seasonal climate change on the NPP of herbaceous marshes in China and indicates that the differential effects of daytime and nighttime temperatures should be considering in simulating the NPP of herbaceous marshes in terrestrial ecosystem models, especially under the background of global asymmetric diurnal warming.

RESUMEN

The Paraná River Delta in South America, a large wetlands macromosaic, faces threats from climate change, human activities like livestock intensification, and hydrological modifications driven by the construction of water management infrastructure to prevent flooding in productive lands. Macroinvertebrates, essential for wetland health, are affected by cattle-induced changes in water quality, nutrient enrichment, and trampling, posing challenges to the ecosystem's ecological balance and long-term survival of these organisms. In this study, we analyzed the impact of two categories of cattle stocking rates (low and high) on the taxonomic and functional structure of the aquatic macroinvertebrate community in freshwater marshes. In addition, we compare the influence of cattle stocking rate on macroinvertebrates in natural and modified freshwater marshes, and, finally, the effect of cattle stocking rate in three contrasting hydrometeorological periods: a drier, a humid, and an extreme drought period. Samplings were conducted in 16 freshwater habitats of the Lower Paraná River Delta, examining variables such as temperature, pH, dissolved oxygen, coliforms, and nutrient concentrations. Macroinvertebrates were collected and functional and taxonomic metrics were estimated. Statistical analyses, including ANOVA and Kruskal-Wallis tests, were conducted to evaluate the effects of cattle stocking rates, hydrological modifications, and hydrometeorological periods on macroinvertebrate metrics and environmental variables. RDA, PERMANOVA, and SIMPER analyses explored the relationships between assemblage composition and environmental factors. High stocking rate altered the community structure, modifying its composition and decreasing the density, taxonomic and functional richness. Moreover, hydrological alterations exacerbated these negative impacts of cattle overstocking in macroinvertebrates. Under severe drought conditions, only tolerant species can survive cattle overstocking conditions. Our findings provide relevant insight into the ecological risks associated with cattle overstocking in natural and modified freshwater marshes and underscore the need to control cattle stocking rates in extreme drought to avoid loss of ecological functions.

Asunto(s)

RESUMEN

The role of facilitation in shaping natural communities has primarily been studied in the context of plant assemblages, while its relevance for mobile animals remains less understood. Our study investigates whether reciprocal interspecific facilitation may exist between fire ants (Solenopsis richteri) and cavies (Cavia aperea), two mobile animals, in the SW Atlantic coast brackish marshes. Field samples showed a spatial association between ant mounds and cavies, and that ants prefer to use cavy runways for movement within the marsh. Through experiments involving transplanting the dominant plant, cordgrass (Spartina densiflora), and manipulating cavy presence in areas with and without ant mounds, we observed that cavies forage extensively (and defecate more) near ant mounds. The ants actively remove cavy droppings in their mound vicinity. These ant activities and interactions with cavy droppings led to reduced moisture and organic content while increasing nitrate and phosphate levels in marsh sediment. Consequently, this enhanced plant growth, indirectly facilitating the cavies, which preferred consuming vegetation near ant mounds. These cascading indirect effects persisted over time; even four months after cavies left the marshes, transplanted plants near ant mounds remained larger and exhibited more leaf senescence when exposed to cavy herbivory. Therefore, the networks of positive interactions appear to generate simultaneous selection among species (populations), promoting coexistence within the community. Although complex, these reciprocal facilitative effects among mobile animals may be more common than currently believed and should be further studied to gain a better understanding of the underlying mechanisms driving species coexistence in natural communities.

Asunto(s)

RESUMEN

Quantifying ecosystem resilience to disturbance is important for understanding the effects of disturbances on ecosystems, especially in an era of rapid global change. However, there are few studies that have used standardized experimental disturbances to compare resilience patterns across abiotic gradients in real-world ecosystems. Theoretical studies have suggested that increased return times are associated with increasing variance during recovery from disturbance. However, this notion has rarely been explicitly tested in field, in part due to the challenges involved in obtaining long-term experimental data. In this study, we examined resilience to disturbance of 12 coastal marsh sites (five low-salinity and seven polyhaline [=salt] marshes) along a salinity gradient in Georgia, USA. We found that recovery times after experimental disturbance ranged from 7 to >127 months, and differed among response variables (vegetation height, cover and composition). Recovery rates decreased along the stress gradient of increasing salinity, presumably due to stress reducing plant vigor, but only when low-salinity and polyhaline sites were analyzed separately, indicating a strong role for traits of dominant plant species. The coefficient of variation of vegetation cover and height in control plots did not vary with salinity. In disturbed plots, however, the coefficient of variation (CV) was consistently elevated during the recovery period and increased with salinity. Moreover, higher CV values during recovery were correlated with slower recovery rates. Our results deepen our understanding of resilience to disturbance in natural ecosystems, and point to novel ways that variance can be used either to infer recent disturbance, or, if measured in areas with a known disturbance history, to predict recovery patterns.

Asunto(s)

RESUMEN

Combating the current biodiversity crisis requires the accurate documentation of population responses to human-induced ecological change. However, our ability to pinpoint population responses to human activities is often limited to the analysis of populations studied well after the fact. Museum collections preserve a record of population responses to anthropogenic change that can provide critical baseline data on patterns of genetic diversity, connectivity, and population structure prior to the onset of human perturbation. Here, we leverage a spatially replicated time series of specimens to document population genomic responses to the destruction of nearly 90% of coastal habitats occupied by the Savannah sparrow (Passerculus sandwichensis) in California. We sequenced 219 sparrows collected from 1889 to 2017 across the state of California using an exome capture approach. Spatial-temporal analyses of genetic diversity found that the amount of habitat lost was not predictive of genetic diversity loss. Sparrow populations from southern California historically exhibited lower levels of genetic diversity and experienced the most significant temporal declines in genetic diversity. Despite experiencing the greatest levels of habitat loss, we found that genetic diversity in the San Francisco Bay area remained relatively high. This was potentially related to an observed increase in gene flow into the Bay Area from other populations. While gene flow may have minimized genetic diversity declines, we also found that immigration from inland freshwater-adapted populations into tidal marsh populations led to the erosion of divergence at loci associated with tidal marsh adaptation. Shifting patterns of gene flow through time in response to habitat loss may thus contribute to negative fitness consequences and outbreeding depression. Together, our results underscore the importance of tracing the genomic trajectories of multiple populations over time to address issues of fundamental conservation concern.

Asunto(s)

RESUMEN

Sea-level rise is particularly concerning for tidal wetlands that reside within an area with steep topography or are constrained by human development and alteration of sedimentation. Sediment augmentation to increase wetland elevations has been considered as a potential strategy for such areas to prevent wetland loss over the coming decades. However, there is little information on the best approaches and whether adaptive management actions can mimic natural processes to build sea-level rise resilience. In addition, the lack of information on long-term marsh characteristics, processes, and variability can hamper development of effective augmentation strategies. Here, we assess a case study in a southern California marsh to determine the nature of the pre-existing sediments and variability of the site in relation to sediments applied during an augmentation experiment. Although sediment cores revealed natural variations in the grain size and organic content of sediments deposited at the site over the past 1500 years, the applied sediments were markedly coarser in grain size than prehistoric sediments at the site (100% maximum sand versus 76% maximum sand). The rate of the experimental sediment application (25.1 ± 1.09 cm in ~2 months) was also much more rapid than natural accretion rates measured for the site historically. In contrast, post-augmentation sediment accretion rates on the augmentation site have been markedly slower than pre-augmentation rates or current rates on a nearby control site. The mismatch between the characteristics of the applied sediment and thickness of application and the historic conditions are likely strong contributors to the slow initial recovery of vegetation. Sediment augmentation has been shown to be a useful strategy in some marshes, but this case study illustrates that vegetation recovery may be slow if applied sediments are not similar or at a thickness similar to historic conditions. However, testing adaptation strategies to build wetland elevations is important given the long-term risk of habitat loss with sea-level rise. Lessons learned in the case study could be applied elsewhere.

Asunto(s)

RESUMEN

China's coastal wetlands have experienced large losses and gains with rapid coastal reclamation and restoration since the end of the 20th century. However, owing to the difficulties in mapping soil organic carbon (SOC) in blue carbon stocks of coastal wetlands on a national scale, little is known about the spatial pattern of SOC stock in China's coastal wetlands and the loss and gain of SOC stock following coastal reclamation, conservation, and restoration over the past decades. Here, we developed a SOC stock map in China's coastal wetlands at 30 m spatial resolution, analyzed the spatial variability and driving factors of SOC stocks, and finally estimated SOC losses and gains due to coastal reclamation and wetland management from 1990 to 2020. We found that the total SOC stocks in China's coastal wetlands were 77.8 Tg C by 2020 with 3.6 Tg C in mangroves, 8.8 Tg C in salt marshes, and 65.4 Tg C in mudflats. Temperature, rainfall, and seawater salinity exerted the highest relative contributions to SOC spatial variability. The spatial trend of SOC density gradually decreased from south to north except for Liaoning province, with the lowest density in Shandong province. About 24.9% (19.4 Tg C) of SOC stocks in China's coastal wetlands were lost due to high-intensity reclamation, but SOC stock gained from conservation and restoration offset the reclamation-induced losses by 58.2% (11.3 Tg C) over the past three decades. These findings demonstrated the great potential of conservation and restoration of coastal wetlands in reversing the loss trend of blue carbon and contributing to the mitigation of climate change toward carbon neutrality. Our study provides significant spatial insights into the stocks, sequestration, and recovery capacity of blue carbon following rapid urbanization and management actions, which benefit the progress of global blue carbon management.

Asunto(s)

RESUMEN

This study delves into the magnitude and attributes of plastic pollution in the salt marshes of the Bahía Blanca Estuary, Argentina, with a specific focus on its spatial distribution. The investigation included the evaluation of microplastics (1-5 mm), mesoplastics (5-25 mm) and macroplastics (25-100 mm), discovering elevated levels along the high salt marsh strandline compared to low salt marsh and mudflat areas. Notably, the abundance of plastic reached staggering levels, reaching up to 20,060 items/m2 in the vicinity of an illegal dumpsite. Microplastics, particularly in the 2-4 mm range, were dominant, and the main plastic components were high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS). Plastic films emerged as the predominant plastic type, while the presence of pellets hinted at potential sources such as illegal dumping and port-related activities. This contamination could be largely attributed to inappropriate waste management practices and urban runoff, which pose a substantial ecological threat to these ecosystems. Urgent remedial action is essential to protect these marshes, underscoring the critical need for comprehensive wetland management and educational initiatives to ensure their long-term sustainability.

RESUMEN

Soil metal pollution has been widely studied in salt marshes but mainly regarding non-essential metals. The aim of this study was to assess the levels of two essential metals (Fe and Mn) and one non-essential one (Cd) in Spartina alterniflora salt marshes in a South American estuary in order to evaluate the potential of this species as a phytoremediator and/or bioindicator of Fe, Mn and Cd and to analyze the distribution of these metals according to the edaphic conditions. The metals present in the soils varied among the three sites studied according to the content of organic matter and fine sediments. In comparison with other Spartina-dominated salt marshes worldwide, in this study Fe and Mn were approximately in the same range, whereas Cd levels were always lower, with a high number of samples below the method detection limit (MDL). All metals were highly correlated with each other suggesting an association of Cd with Mn and Fe oxides/hydroxides or sulfides and/or a common anthropogenic source. Metals in plant tissues also varied from site to site and between the aboveground and belowground tissues. Compared to the metal levels in Spartina tissues in other salt marshes, our levels of Fe and Mn were in the same range, whereas the Cd levels were lower, among most samples, especially those from aboveground tissues that were below the MDL. The bioconcentration factor (metal in belowground tissues/metal in soil) was always lower than one for Fe and Mn meaning that there is no accumulation of these metals in belowground tissues, but this factor for Cd was sometimes higher than one, even as high as 3.45, implying that S. alterniflora can accumulate this metal in its tissues, pointing to a potential role of this species in Cd phytoremediation. Translocation factors (metal in aboveground tissues/metal in belowground tissues) were always lower than one for Fe and could not be calculated for Cd but were usually higher than one for Mn, showing the role of this element in photosynthetic tissues and a possible function of this species for phytoextraction of Mn. In most samples the Fe levels in plant tissues were higher than the permissible levels reported in the literature, suggesting a potential role of S. alterniflora in Fe phytoremediation. No correlation was observed between metal concentrations in soils and aboveground tissues; therefore, S.alterniflora is not a good bioindicator for the metals studied. Although our results are not conclusive, they reinforce the importance of local edaphic conditions on the behavior of metals in salt marshes and shed light on the potential role of S. alterniflora in the phytoremediation of highly toxic metals such as Cd or poorly studied metals such as Fe and Mn.

Asunto(s)

RESUMEN

Continuous nitrogen (N) loading alters plant growth and subsequently has the potential to impact soil organic carbon (SOC) accumulation in salt marshes. However, the knowledge gap of photosynthesized carbon (C) allocation in plant-soil-microbial systems hampers the quantification of C fluxes and the clarification of the mechanisms controlling the C budget under N loading in salt marsh ecosystems. To address this, we conducted an N fertilization field observation combined with a 5 h 13C-pulse labeling experiment in a salt marsh dominated by Suaeda. salsa (S. salsa) in the Yellow River Delta (YRD), China. N fertilization increased net 13C assimilation of S. Salsa by 277.97%, which was primarily allocated to aboveground biomass and SOC. However, N fertilization had little effect on 13C allocation to belowground biomass. Correlation analysis showed that 13C incorporation in soil was significantly and linearly correlated with 13C incorporation in shoots rather than in roots both in a 0 N (0 g N m-2 yr-1) and +N (20 g N m-2 yr-1) group. The results suggested that SOC increase under N fertilization was mainly due to an increased C assimilation rate and more efficient downward transfer of photosynthesized C. In addition, N fertilization strongly improved the 13C amounts in the chloroform-labile SOC component by 295.26%. However, the absolute increment of newly fix 13C mainly existed in the form of residual SOC, which had more tendency for burial in the soil. Thus, N fertilization enhanced SOC accumulation although C loss increased via belowground respiration. These results have important implications for predicting the carbon budget under further human-induced N loading.

Asunto(s)

RESUMEN

Salt marshes sit at the terrestrial-aquatic interface of oceans around the world. Unique features of salt marshes that differentiate them from their upland or offshore counterparts include high rates of primary production from vascular plants and saturated saline soils that lead to sharp redox gradients and a diversity of electron acceptors and donors. Moreover, the dynamic nature of root oxygen loss and tidal forcing leads to unique biogeochemical conditions that promote nitrogen cycling. Here, we highlight recent advances in our understanding of key nitrogen cycling processes in salt marshes and discuss areas where additional research is needed to better predict how salt marsh N cycling will respond to future environmental change.

RESUMEN

Given the decline of global salt marshes, there is a pressing need to pinpoint the key processes that limit and facilitate seed-based pioneer recruitment. Secondary seed dispersal, in the form of short-distance submerged movement, is a prerequisite for initiating pioneer establishment in adjacent tidal flats but has not been fully appreciated and understood. In this study, using a settling tube and race-track flume, seeds of four global occurring saltmarsh species were studied in terms of their settlement speed and trapping opportunity to understand how seed traits and physical settings affect submerged dispersal behavior and thus seed-based saltmarsh recruitment. Present study led to the following novel insights: 1) Seeds have density-dependent settling speeds, which are comparable to that of fine sand, but much faster than that of very fine sand and silt. Since the latter is the type of sediment commonly found in many estuaries worldwide (such as the Scheldt), seeds will typically settle faster than local sediments. A sufficiently long hydrodynamic-calm period allows slowly settling sediment to bury settled seeds, otherwise, seeds will remain uncovered if the period is short. 2) Seed trapping ratio increased linearly with surface roughness (a proxy for local topographic complexity), but this effect becomes smaller with increasing hydrodynamic intensity. Seed drag coefficient was identified as the key biotic factor contributing to interspecies variability in trapping ratio. Overall, present results suggest that submerged seed dispersal may form a primary bottleneck for salt marsh recruitment by limiting seed availability via two mechanisms: i) reduced chance of seed burial through asynchronous settling of seeds and sediment particles; ii) reduced probability of seed trapping due to encountering smooth tidal flat surfaces. This study provide mechanistic and data basis for the targeted application of biophysical models in predicting outcomes of saltmarsh recruitment and long-term maintenance, thereby informing seed-based conservation and restoration.

Asunto(s)

RESUMEN

Wetlands in arid and semi-arid regions are characterized by dry- and wet-phase vegetation expression which responds to variable water resources. Monitoring condition trends in these wetlands is challenging because transitions may be rapid and short-lived, and identification of meaningful condition change requires longitudinal study. Remotely-sensed data provide cost effective, multi-decadal information with sufficient temporal and spatial scale to explore wetland condition. In this study, we used a time series of Enhanced Vegetation Index (EVI) derived from 34 years (1988-2021) of Landsat imagery, to investigate the long-term condition dynamics of six broad vegetation groups (communities) in a large floodplain wetland system, the Macquarie Marshes in Australia. These communities were persistently mapped as River Red Gum wetland, Black Box/Coolibah woodland, Lignum shrubland, Semi-permanent wetland, Terrestrial grassland and Terrestrial woodland. We used generalized additive models (GAM) to explore the response of vegetation to seasonality, river flow and climatic conditions. We found that EVI was a useful metric to monitor both wetland condition and response to climatic and hydrological drivers. Wetland communities were particularly responsive to river flow and seasonality, while terrestrial communities were responsive to climate and seasonality. Our results indicate asymptotic condition responses, and therefore evidence of hydrological thresholds, by some wetland communities to river flows. We did not observe a long-term trend of declining condition although an apparent increase in condition variability towards the end of the time series requires continued monitoring. Our remotely-sensed, landscape-scale monitoring approach merits further ground validation. We discuss how it can be used to provide a management tool which continuously assesses short and long-term wetland condition and informs conservation decisions about water management for environmental flows.

RESUMEN

Introduction: Grazing prohibition is an effective management practice to restore salt marsh functioning. However, the effects of grazing exclusion on denitrifying microbial communities and their controlling factors in salt marshes remain unclear. Methods: In this study, we surveyed soil physicochemical properties and above- and below-ground biomass and using quantitative polymerase chain reaction and Illumina MiSeq high-throughput sequencing technology to determine the relative abundance, composition, and diversity of nitrite reductase nirS- and nirK-type denitrifying bacterial communities associated with grazing prohibition treatments and elevations. Results: The abundance of nirS-type denitrifiers increased with grazing prohibition time, whereas the abundance of nirK-type denitrifiers remained unaltered. Moreover, nirS-type denitrifiers were more abundant and diverse than nirK-type denitrifiers in all treatments. Grazing prohibition significantly altered the operational taxonomic unit richness, abundance-based coverage estimator, and Chao1 indices of the nirS-type denitrifying bacterial communities, whereas it only minimally affected the structure of the nirK-type denitrifying bacterial community. Discussion: The results imply that the nirS community, rather than nirK, should be the first candidate for use as an indicator in the process of salt marsh restoration after grazing prohibition. Substances of concern, total nitrogen, and salinity were the key environmental factors affecting the abundance and community composition of nirS and nirK denitrifiers. The findings of this study provide novel insights into the influence of the length of grazing prohibition and elevation on nirS- and nirK-type denitrifying bacterial community composition in salt marshes.

RESUMEN

Coastal marshes are efficient ecosystems providing a multitude of benefits for invertebrates, birds, fish and humans alike. Yet despite these benefits, wetlands are threatened by anthropogenic inputs such as human wastewater which contain high levels of nitrogen (N). Increased nitrogen loads cause eutrophication and hypoxia in estuaries leading to further degradation of these valuable ecosystems that are already stressed by sea level rise and climate change. Policies to protect wetlands via wastewater treatments are reactive rather than proactive and a growing body of research shows that characteristics associated with population health and economic activity can be identified in wastewater. Analysis of a 2-m salt marsh sediment core reveals δN15 signatures indicative of human population rise and connects human impact to ecosystem health. Using key X-ray fluorescence (XRF), pollen, sediment and nitrogen signatures along the core, a robust chronology was produced dating back to 1700. This result was coupled with population data to observe the relationship between δN15 levels and population over three centuries. There is a statistically significant positive correlation between δN15 and population. Other external factors such as federal government policies (regulating clean water) show a clear reduction in this association but the use of synthetic nitrogen fertilizer masks the strength of this relationship. Further research to refine the relationship between population and δN15 could be beneficial in predicting nitrogen loads as human population grows, which in turn would create a proactive system to protect our coastal ecosystems.

Asunto(s)

RESUMEN

Hurricane Katrina (category 5 with maximum wind of 280 km/h when the eye is in the central Gulf of Mexico) made landfall near New Orleans on August 29, 2005, causing millions of cubic meters of disaster debris, severe flooding, and US$125 billion in damage. Yet, despite numerous reports on its environmental and economic impacts, little is known about how much debris has entered the marine environment. Here, using satellite images (MODIS, MERIS, and Landsat), airborne photographs, and imaging spectroscopy, we show the distribution, possible types, and amount of Katrina-induced debris in the northern Gulf of Mexico. Satellite images collected between August 30 and September 19 show elongated image features around the Mississippi River Delta in a region bounded by 92.5°W-87.5°W and 27.8°N-30.25°N. Image spectroscopy and color appearance of these image features indicate that they are likely dominated by driftwood (including construction lumber) and dead plants (e.g., uprooted marsh) and possibly mixed with plastics and other materials. The image sequence shows that if aggregated together to completely cover the water surface, the maximal debris area reached 21.7 km2 on August 31 to the east of the delta, which drifted to the west following the ocean currents. When measured by area in satellite images, this perhaps represents a historical record of all previously reported floating debris due to natural disasters such as hurricanes, floodings, and tsunamis.

Asunto(s)