Meadow Structure Research Articles

The interaction between vegetation patchiness and tidal flows in a shortleaf seagrass meadow

AbstractSeagrasses are critical coastal habitats that provide numerous ecosystem services. The inherent patchiness within meadows exerts a significant influence on the flow‐vegetation interaction, which, in turn, affects the array of services provided by these environments. We present field observations of vegetation distribution and hydrodynamic measurements within and surrounding an approximately 2 m diameter gap (bare sediment) in a fragmented seagrass meadow. We show that variability in mean flows and turbulence is correlated with meadow structure at small (O (100 m)) and large (O (102 m)) spatial scales. Our observations reveal that bare gaps within seagrass meadows lead to faster flows and lower bed elevations. Despite slower flow speeds above the dense seagrass adjacent to the gap, the rates of dissipation of turbulent energy above the vegetation are typically around an order of magnitude larger than above the bare bed. Associated with this enhanced dissipation of turbulent energy, we observed a dominance of down‐deceleration events promoting fluid exchange and mixing and driving mass flux into the canopy. Analysis of directional variograms demonstrates that the major continuity axis within NDVI (normalized difference vegetation index) imagery (used as a proxy for vegetation biomass) coincides with the major axis of flow on both gap and meadow scales. Conversely, along the axis of minor flow variance, vegetation remains dense and exhibits greater uniformity. These findings indicate a feedback mechanism between seagrass meadow patchiness and spatial structure through flow modification, which may be beneficial for plant development.

Combined exposure to CO2 and H2S significantly reduces the performance of the Mediterranean seagrass Posidonia oceanica: Evidence from a volcanic vent

AbstractAlthough seagrasses are expected to thrive in future acidified oceans by overcoming low CO2 diffusion into plant tissues, the co‐occurrence of environmental stressors may affect their growth. Volcanic CO2 vents are often associated with toxic gases and metal‐rich fluids representing ideal sites to assess the effects of multiple stressors. We evaluated the response of Posidonia oceanica growing near shallow CO2 vents characterized by H2S spill‐out by comparing meadow structure and phenology to an area with no gas emissions. Seagrass descriptors at meadow, shoot and leaf level indicated that P. oceanica experienced stressful conditions at the vent area, in clear contrast to the flourishing features of P. oceanica previously described at CO2 vents with no evidence of toxic inputs. Furthermore, the reduction in both leaf δ34S and growth at the vent area indicates that sulfide intrusion occurs and affects seagrass growth performance, dampening the expected beneficial effects of high CO2 levels.

The noise is the signal: spatio-temporal variability of production and productivity in high elevation meadows in the Sierra Nevada mountain range of North America

There are expectations that increasing temperatures will lead to significant changes in structure and function of montane meadows, including greater water stress on vegetation and lowered vegetation production and productivity. We evaluated spatio-temporal dynamics in production and productivity in meadows within the Sierra Nevada mountain range of North America by: (1) compiling Landsat satellite data for the Normalized Difference Vegetation Index (NDVI) across a 37-year period (1985–2021) for 8,095 meadows >2,500 m elevation; then, (2) used state-space models, changepoint analysis, geographically-weighted regression (GWR), and distance-decay analysis (DDA) to: (a) identify meadows with decreasing, increasing or no trends for NDVI; (b) detect meadows with abrupt changes (changepoints) in NDVI; and (c) evaluate variation along gradients of latitude, longitude, and elevation for eight indices of temporal dynamics in annual production (mean growing season NDVI; MGS) and productivity (rate of spring greenup; RSP). Meadows with no long-term change or evidence of increasing NDVI were 2.6x more frequent as those with decreasing NDVI (72% vs. 28%). Abrupt changes in NDVI were detected in 48% of the meadows; they occurred in every year of the study and with no indication that their frequency had changed over time. The intermixing of meadows with different temporal dynamics was a consistent pattern for monthly NDVI and, especially, the eight annual indices of MGS and RSP. The DDA showed temporal dynamics in pairs of meadow within a few 100 m of each other were often as different as those hundreds of kilometers apart. Our findings point strongly toward a great diversity of temporal dynamics in meadow production and productivity in the SNV. The heterogeneity in spatial patterns indicated that production and productivity of meadow vegetation is being driven by interplay among climatic, physiographic and biotic factors at basin and meadow scales. Thus, when evaluating spatio-temporal dynamics in condition for many high elevation meadow systems, what might often be considered “noise” may provide greater insight than a “signal” embedded within a large amount of variability.

Loss of POC and DOC on seagrass sediments by hydrodynamics

Coastal development and climate change are sparking growing concern about the vulnerability of the organic carbon (OC) stocks in marine sediments to remineralization, especially in high threaten coastal ecosystems like seagrass meadows. Uncertainties still exist regarding the role played by hydrodynamics, seagrass canopies and sediment properties in OC resuspension and remineralization. A set of laboratory experiments were conducted to assess, for the first time, the mechanisms by which the particulate and dissolved organic carbon (POC and DOC) may be released and remineralized under hydrodynamic conditions (i.e., unidirectional and oscillatory flows) in two eelgrass densities and sediments properties (i.e., grain size and OC content). After a gradually increase in hydrodynamic forces, our results demonstrated that the presence of eelgrass reduced sediment erosion and OC loss in high-density canopies, while low-density canopies promote OC resuspension (on average, 1.8-fold higher than high-density canopies). We also demonstrated that unidirectional and oscillatory flows released similar DOC from surface sediments (on average, 15.5 ± 1.4 and 18.4 ± 1.8 g m−2, respectively), whereas oscillatory flow released significantly more POC than unidirectional flows (from 10.8 ± 1.1 to 32.1 ± 5.6 g m−2 for unidirectional and oscillatory flows, respectively). POC and DOC released was strongly influenced by both seagrass meadow structure (i.e., lower eelgrass density and shoot area) and sediment properties (i.e., lower mud and higher sediment water content). We found that, although >74 % of OC in upper sediments was remineralized within 30 days, a relatively high amount of OC in high-density canopies is recalcitrant, highlighting its potential for the formation of blue carbon deposits. This study highlights the vulnerability of OC deposits in seagrass sediments to resuspension if the meadow is degraded and/or the climate change yield stronger storms, which could potentially weaken the seagrass meadows' service as blue carbon ecosystem in the future.

Global dataset on seagrass meadow structure, biomass and production

Abstract. Seagrass meadows provide valuable socio-ecological ecosystem services, including a key role in climate change mitigation and adaption. Understanding the natural history of seagrass meadows across environmental gradients is crucial to deciphering the role of seagrasses in the global ocean. In this data collation, spatial and temporal patterns in seagrass meadow structure, biomass and production data are presented as a function of biotic and abiotic habitat characteristics. The biological traits compiled include measures of meadow structure (e.g. percent cover and shoot density), biomass (e.g. above-ground biomass) and production (e.g. shoot production). Categorical factors include bioregion, geotype (coastal or estuarine), genera and year of sampling. This dataset contains data extracted from peer-reviewed publications published between 1975 and 2020 based on a Web of Science search and includes 11 data variables across 12 seagrass genera. The dataset excludes data from mesocosm and field experiments, contains 14 271 data points extracted from 390 publications and is publicly available on the PANGAEA® data repository (https://doi.org/10.1594/PANGAEA.929968; Strydom et al., 2021). The top five most studied genera are Zostera, Thalassia, Cymodocea, Halodule and Halophila (84 % of data), and the least studied genera are Phyllospadix, Amphibolis and Thalassodendron (2.3 % of data). The data hotspot bioregion is the Tropical Indo-Pacific (25 % of data) followed by the Tropical Atlantic (21 %), whereas data for the other four bioregions are evenly spread (ranging between 13 and 15 % of total data within each bioregion). From the data compiled, 57 % related to seagrass biomass and 33 % to seagrass structure, while the least number of data were related to seagrass production (11 % of data). This data collation can inform several research fields beyond seagrass ecology, such as the development of nature-based solutions for climate change mitigation, which include readership interested in blue carbon, engineering, fisheries, global change, conservation and policy.

Plant and Meadow Structure Characterisation of Posidonia oceanica in Its Westernmost Distribution Range

Posidonia oceanica is an endemic seagrass species from the Mediterranean Sea that provides critical ecological services to coastal environments. This species is distributed from the Turkish to the Spanish coast, where its westernmost record was documented in Punta Chullera, Malaga (36°18′36.45′′ N, 5°14′54.31′′ W). Nevertheless, previous studies suggested that its distribution was even further west, although these populations were never described. In this study, we documented and characterised the only known P. oceanica population on the coast of Cadiz, in Cala Sardina (36°18′38.80′′ N, 5°15′15.13′′ W). The newly documented population of P. oceanica presented a fragmented structure, consisting of nine patches found in a rocky shallow area surrounded by the invasive algae Rugulopteryx okamurae, with a total size of 61.14 m2. Shoots had a relatively small size (21.0 ± 2.9 cm) in comparison with centrally-distributed populations. The relatively small size of the plants, alongside the observed low shoot density (437 ± 42 shoots m−2) and leaf area index (4.8 ± 0.7 m2 m−2), may indicate that this meadow could be exposed to sub-optimal environmental conditions for plant development. By contrast, the meadow showed relatively high production rates (0.03 ± 0.01 leaf day−1 shoot−1) in comparison with other Mediterranean populations. The percentage of carbon in plant leaves was 38.73 ± 1.38%, while the nitrogen and C/N were 1.38 ± 0.37% and 29.93 ± 6.57, respectively. The documentation of this meadow extends the distribution of this species to the Mediterranean coast of Cadiz, making this region the place with the highest seagrass biodiversity (four species) in the Iberian Peninsula, and potentially in Europe. This exploratory study provides a baseline to examine the potential effects of climate change, anthropogenic disturbances or the presence of invasive species.

Mapping the structure of mixed seagrass meadows in the Mexican Caribbean

The physical and ecological importance of seagrass meadows in coastal processes is widely recognized, and the development of tools facilitating characterization of their structure and distribution is important for improving our understanding of these processes. Mixed (multi-specific) meadows in a Mexican Caribbean reef lagoon were mapped employing a multiparameter approach, using PlanetScope remote sensing images, and supervised classification based on parameters related to the structure of the seagrasses meadows, including the cover percentages of seagrass/algae/sediment, algae thalli and seagrass shoot densities, canopy heights and estimated leaf area index (LAI). The cover, seagrass and algae densities, and seagrass canopy heights were obtained using ground truth sampling, while the LAI was estimated using data obtained from long-term monitoring programs. The maps do not show the differentiation of seagrass species, but ground truthing contemplated characterization of the density of Thalassia testudinum, Syringodium filiforme and Halodule wrightii and their respective LAIs. S. filiforme was the dominant species in terms of shoot density, and T. testudinum was dominant in terms of LAI. In the multiparameter-based map four classes were defined, based on the cover and structural characteristics, and its overall accuracy was very high (~90%). Maps based on sediment cover and LAI alone also had 4 classes, but they were less accurate than the multiparameter-based map (~70% and ~80%, respectively). The multiparameter-based seagrass map provided spatially-explicit data on the abundance and structure of seagrasses, useful for future monitoring of the changes in the meadows, and also for studies of that require data of large-scale meadow structure, such as inventories of associated biota, blue carbon storage, or modelling of the local hydrodynamics.

Stochastic Processes Drive Plant Community Assembly in Alpine Grassland during the Restoration Period

Enclosure (prohibition of grazing) is an important process to restore alpine grassland on the Qinghai-Tibetan Plateau. However, few studies have quantified the extent to which the long-term enclosure may contribute to the changes in plant phylogenetic diversity and community assembly in alpine grassland under environmental change. In this study, based on an 11-year fencing experiment along an altitudinal gradient ranging from 4400 m to 5200 m in central Tibet, we conducted an observation of species composition and coverage within and outside the fences in the fifth, eighth and eleventh year, and monitored the related climate and soil factors at 7 sites. Our aim is to quantify the relative effects of environmental change and grassland management on the alpine plant community assemblage. The results were: (1) the overall phylogenetic structure (NRI) of the alpine plant communities, whether inside or outside the enclosure, was divergent at altitudes where the environment was relatively unextreme (4800–5100 m), but aggregative at altitudes with low precipitation (4400–4650 m) or with low temperature (5200 m). (2) The phylogenetic structure of the nearest taxon of species (NTI) was more aggregative along the whole gradient. (3) Precipitation was the dominant factor driving the changes in species richness, phylogenetic diversity and community α-phylogenetic structure indices (NRI and NTI), followed by enclosure duration and soil C:N ratio. (4) The phylogenetic structure of the communities was similar at higher altitudes under grazing or enclosure treatments, and was opposite at lower sites. Stochastic processes have driven the changes in the communities between inside and outside the fences at all altitudes. In addition, homogeneous dispersal occurred in communities at higher sites. In summary, the 11-year enclosure had little effect on community structure of alpine meadows where the grazing pressure is relative lower, whereas it could help restore the community of steppe meadow at lower altitudes where the grazing pressure is extensively higher. This study may provide a vital theoretical support for the formulation of differential management for alpine grassland on the Tibetan Plateau.

Variation in Fish Abundance, Diversity and Assemblage Structure in Seagrass Meadows across the Atlanto-Mediterranean Province

Seagrasses worldwide provide key habitats for fish assemblages. Biogeographical disparities in ocean climate conditions and seasonal regimes are well-known drivers of the spatial and temporal variation in seagrass structure, with potential effects on associated fish assemblages. Whether taxonomically disparate fish assemblages support a similar range of ecological functions remains poorly tested in seagrass ecosystems. In this study, we examined variation in the abundance, diversity (from a taxonomic and functional perspective), and assemblage structure of fish community inhabiting nine meadows of the seagrass Cymodocea nodosa across three regions in the Mediterranean (Mallorca and Alicante) and the adjacent Atlantic (Gran Canaria), and identified which attributes typifying the structure of meadows, and large-scale variability in ocean climate, contributed most to explaining such ecological variation. Despite a similar total number of species between Mallorca and Gran Canaria, the latter region had more taxonomically and functionally diverse fish assemblages relative to the western Mediterranean regions, which translated into differences in multivariate assemblage structure. While variation in the abundance of the most conspicuous fish species was largely explained by variation in seagrass structural descriptors, most variation in diversity was accounted for by a descriptor of ocean climate (mean seasonal SST), operating at regional scales. Variation in fish assemblage structure was, to a lesser extent, also explained by local variability in seagrass structure. Beyond climatic drivers, our results suggest that lower temporal variability in the canopy structure of C. nodosa meadows in Gran Canaria provides a more consistent source of food and protection for associated fish assemblages, which likely enhances the more abundant and diverse fish assemblages there.

Seasonal plant development and meadow structure of Irish and southern Spanish seagrass populations

Zostera marina and Z. noltii are two dominant meadow-forming seagrass species in temperate regions in the northern hemisphere. Seagrass meadows provide several goods and ecological services and rank amongst the most valuable ecosystems worldwide. Phenological shifts in Zostera species occur along latitudinal or temperature gradients, leading to an expectation for distinct seasonal dynamics and annual production in Spain and Ireland. Despite their global ecological importance, seasonal seagrass traits of populations exposed to contrasting climate settings from Ireland and southern Spain are poorly described. To address this gap, we evaluated the seasonal vegetative development (morphology, population structure, and productivity) of Z. marina and Z. noltii populations exposed to cold (western Ireland) and warm (southern Spain) temperatures over a year-long period. Our results highlight contrasting dynamics of Z. marina populations across their temperature range. The Irish population exhibited maximal growth during warmer months while the Spanish population revealed signs of growth reduction under maximum annual temperatures. Our results suggest that plants of Z. marina in Ireland were temperature-limited at most times, but in southern Spain exceeded their optima temperature for growth during summer. In addition, Irish and Spanish Z. noltii populations displayed differential vegetative dynamics and population structures, likely related to the contrasting local temperature regimes. These differences were particularly evident in summer when shoot size and growth rates were reduced in warm-temperate locations. This study represents an essential comparative baseline for future assessments of ecological status, and anticipated growth stress induced by climate change across the distributional gradient, of these important Zostera species.

The contribution of the spatial hydrological niche to species diversity in rare plant communities of English floodplain meadows

The hydrological niche is one of the few below ground spatial environmental niches, which has been shown to structure English floodplain meadows and other European and African herbaceous ecosystems. However, both the relative contribution of hydrological heterogeneity to the structure of English floodplain meadows across spatial scales and the forms of the individual species’ responses to hydrological heterogeneity remain largely unknown. Here, we use a survey database of 2440 evaluation units sampled in 15 English floodplain meadows to dissect the spatial architecture of this metacommunity and describe the relationship between the abundance of individual species and hydrological heterogeneity. Of the tested species, 65% responded to spatial hydrological heterogeneity, with both monotonic and hump-shaped responses. We found that between-site beta-diversity is much stronger than within-site beta-diversity, with between-site scale hydrological variation explaining twice as much variation in community structure as within-site scale. This leads to the conclusion that a conservation strategy of rare plant communities should include not only the preservation of the diversity of local hydrological regimes, but also, specially, the inclusion in the conservation system of as many and environmentally varied local plant communities as possible.

Shrub encroachment impaired the structure and functioning of alpine meadow communities on the Qinghai–Tibetan Plateau

AbstractShrub encroachment has been rapidly occurring due to climate change, with profound ecological consequences for the alpine meadows of the Qinghai–Tibetan Plateau. Here, we conducted field surveys along a shrub coverage gradient to examine the effects of shrub encroachment on the structure and functioning of alpine meadows' plant communities. Our results showed that the overall coverage, density, aboveground biomass, species richness, and diversity of meadow community gradually declined with increasing levels of shrub encroachment, especially when shrub coverage exceeded 60%. Aboveground ecosystem multifunctionality also decreased along the shrub coverage gradient. With 90% shrub coverage, the relative importance value of the forbs functional group significantly increased while the Cyperaceae functional group showed the opposite trend: the originally dominant sedges Carex moorcroftii and Kobresia myosuroides were replaced by the forbs Androsace umbellate and Polygonum sparsipilosum. Additionally, shrub encroachment had a strong effect on nonrandom herb species extinction and colonization. At shrub coverages higher than 60%, there were 9 herb species absent and 18 new species colonizing—7 of which were only observed in meadows with 90% shrub coverage. Rare species and those with lower stature were more likely to go extinct, while taller and shade‐tolerant species tended to colonize areas with increasing shrub coverage. Overall, our results indicate that shrub encroachment negatively affects herbaceous community structure and functioning, which has important implications for the management of alpine meadows of the Qinghai–Tibetan Plateau under ongoing climate change.

Effects of Waterbird Herbivory on Dominant Perennial Herb Carex thunbergii in Shengjin Lake

Abundant food resources in riparian zones provide efficient foraging sites for waterbirds. Herbivory is a key ecosystem process that has widely recognized effects on primary production and vegetation structure and composition. However, there is limited understanding of impacts of waterbird herbivory on riparian zone vegetation. In this study, a bird exclosure experiment with five levels of foraging intensities (no foraging, very little foraging, light foraging, moderate foraging and heavy foraging) was set up in Shengjin Lake to study the effects of waterbird foraging on the community structure of sedge meadows and individual traits of the dominant plant Carex thunbergii. Foraging intensity had little effect on community structure. The dry mass of C. thunbergii decreased with the increasing foraging time. Waterbird foraging reduced leaf dry mass under heavy foraging by 27.7% and root dry mass by 45.6% compared to CK (no foraging). Waterbird foraging increased allocation to shoot growth but had a weak effect on elemental allocation of C. thunbergii. The foraging intensity significantly affected the morphological traits of C. thunbergii. The results of structural equation modeling showed that RSR (root: shoot ratio represents the ratio of dry mass) and RL (root length) are key traits in driving the dry mass decline in the presence of bird foraging. This study may contribute to a better understanding of the adaptability of perennial herb plants to waterbird foraging and maintain the healthy development of wetland ecosystems.

Detection of grassland mowing frequency using time series of vegetation indices from Sentinel-2 imagery

ABSTRACT Management intensity deeply influences meadow structure and functioning, therefore affecting grassland ecosystem services. Conservation and management measures, including European Common Agricultural Policy subsidies, should therefore be based on updated and publicly available data about management intensity. The mowing frequency is a crucial trait to describe meadows management intensity, but the potential of using vegetation indices from Sentinel-2 imagery for its retrieval has not been fully exploited. In this work we developed on the Google Earth Engine platform a four-phases algorithm to identify mowing frequency, including i) vegetation index time-series computing, ii) smoothing and resampling, iii) mowing detection, and iv) majority analysis. Mowing frequency during 2020 of 240 ha of grassland fields in the Italian Alps was used for algorithm optimization and evaluation. Six vegetation indexes (EVI, GVMI, MTCI, NDII, NDVI, RENDVI783.740) were tested as input to the proposed algorithm. The Normalized Difference Infrared Index (NDII) showed the best performance, resulting in mean absolute error of 0.07 and 93% overall accuracy on average at the four sites used for optimization, at pixel resolution. A slightly lower accuracy (mean absolute error = 0.10, overall accuracy = 90%) was obtained aggregating the maps to management parcels. The algorithm showed a good generalization ability, with a similar performance between global and local optimization and an average mean absolute error of 0.12 and an overall accuracy of 89% on average on the sites not used for parameters optimization. The lowest accuracies occurred in intensively managed grasslands surveyed by one satellite orbit only. This study demonstrates the suitability of the proposed algorithm to monitor very fragmented grasslands in complex mountain ecosystems. Google Earth Engine was used to develop the model and will enable researchers, agencies and practitioners to easily and quickly apply the code to map grassland mowing frequency for extensive grasslands protection and conservation, for mowing event verification, or for forage system characterization.

Determining and quantifying the historical traces of spatial land arrangements in rural landscapes of Central and Eastern Europe

The article attempts to define and determine the intangible components of cultural heritage related to the spatial structure of land in a comprehensive way using computational methods. The components were quantified and a method of empirical evaluation of landscape durability was proposed for agricultural areas of significant cultural and historical value with an evident mosaic structure of fields, baulks, ponds, meadows, and forests. This method allows us to identify places more resistant to political transformation and those with greater cultural potential. The paper proposed an integrated approach to the measuring of the degree of preservation of spatial arrangements in the landscape based on a set of objects that describe the spatial land structure. The article classifies areas by the degree of preservation of rural spatial arrangements of land. The spatial analysis employed facilitated a synthetic quantification of the multi-criteria process. Three groups of factors were used: spatial assessment of land-cover type persistence (u), agricultural land structure persistence (w), and persistence of settlement buildings (z). The final results pinpointed areas in need of strategic intervention to sufficiently protect the rural cultural heritage, properly consider them in zoning planning, and ensure their sustainable development. The proposed tool can be used to monitor the degree of changes in the landscape layout structure when multiple time points are analysed as well.

Trait gradients inform predictions of seagrass meadows changes to future warming

Comparing populations across temperature gradients can inform how global warming will impact the structure and function of ecosystems. Shoot density, morphometry and productivity of the seagrass Posidonia oceanica to temperature variation was quantified at eight locations in Sardinia (western Mediterranean Sea) along a natural sea surface temperature (SST) gradient. The locations are spanned for a narrow range of latitude (1.5°), allowing the minimization of the effect of eventual photoperiod variability. Mean SST predicted P. oceanica meadow structure, with increased temperature correlated with higher shoot density, but lower leaf and rhizome width, and rhizome biomass. Chlorophyll a (Chl-a) strongly impacted seagrass traits independent of SST. Disentangling the effects of SST and Chl-a on seagrass meadow shoot density revealed that they work independently, but in the same direction with potential synergism. Space-for-time substitution predicts that global warming will trigger denser seagrass meadows with slender shoots, fewer leaves, and strongly impact seagrass ecosystem. Future investigations should evaluate if global warming will erode the ecosystem services provided by seagrass meadows.

Seagrass contribution to blue carbon in a shallow karstic coastal area of the Gulf of Mexico.

Seagrass meadows provide multiple ecosystem services, including carbon sequestration. However, seagrass meadows are among the most threatened ecosystems worldwide. Determining the magnitude of the carbon stocks in seagrass meadows at the regional scale allows for the estimation of their global magnitude and identification of their importance in regional environmental mitigation strategies. The objective of the present study was to determine the structure of seagrass meadows in the Los Petenes Biosfera Reserve (LPBR) and evaluate their contributions to sinks of carbon in this system, located in Yucatan, which is considered the region with the largest seagrass extension in Mexico. Analyses of the seagrass meadows were executed following standardized protocols (spectral analysis, and isotope and carbon stock analyses). The LPBR stores an average of 2.2 ± 1.7 Mg C ha−1 in living biomass and 318 ± 215 Mg C ha−1 in sediment (top 1 m), and this carbon stock decreases with water depth. The seagrass community extends 149,613 ha, which represents the largest organic carbon stock (47 Tg C) documented in seagrass meadows in Mexico. Macroalgae and seagrass represent 76% of the organic carbon stored in sediment. If LPBR seagrass meadows are lost due to natural or anthropogenic impacts, 173 Tg CO2eqemissions could be released, which corresponds to the emissions generated by fossil fuel combustion of 27% of the current Mexican population. This information emphasizes the importance of seagrass meadows as a carbon sink in the region and their contribution to climate change mitigation, thus allowing for the implementation of necessary conservation strategies.

Eutrophication reduces seagrass contribution to coastal food webs

AbstractFood sources and food web structure in seagrass meadows are important determinants of ecosystem functions and services. However, there is little information on the effect of eutrophication on food source contributions and food web structure in seagrass meadows. Here we used stable isotopes of carbon and nitrogen (δ13C and δ15N) to investigate how do different levels of nutrient enrichment affect the diets of consumers and food web structure within tropical seagrass meadows. We found that the diet contributions of macroalgae (mean 24% ± 12% for fish, 21% ± 5% for invertebrates), particulate organic matter (mean 19% ± 12% for fish, 18% ± 8% for invertebrates), and sediment organic matter (mean 24% ± 13% for fish, 21% ± 8% for invertebrates) to fish and invertebrates were all higher in seagrass meadows with higher nutrient concentrations, while seagrass and epiphytes contributed more to consumers in seagrass meadows with lower nutrient concentrations. Meanwhile, higher nutrient concentrations decreased the trophic position (mean 2.6 ± 0.5 in high‐nutrient level, 3.4 ± 0.6 in low‐nutrients level) of consumers and food chain length (2.5 in high‐nutrient level, 2.9 in low‐nutrients level). Higher nutrient concentrations reduced the contribution of seagrass carbon to consumers through the grazing food chain, but enhanced the flow of macroalgal carbon to consumers through the grazing food chain. Overall, eutrophication modified the food web structure of seagrass meadows. We recommend that measures be taken to decrease nutrient input into seagrass ecosystems to maintain its important functions and services.

Evaluation of the impact of freeze–thaw cycles on the soil pore structure of alpine meadows using X‐ray computed tomography

AbstractFreeze–thaw cycle (FTC) is an extremely complex soil surface process in cold regions, and quantifying the changes in soil pore structure during successive FTCs remains challenging. This study investigated response of soil pore structure to FTCs and revealed the underlying influence on soil water infiltration through an FTC simulation experiment (0, 1, 3, 5, and 10 cycles) and computed tomography (CT) scanning of undisturbed soil cores in an alpine meadow. One FTC involved soil freezing at −10 °C for 12 h, followed by thawing at 20 °C for 12 h. The results showed that CT‐measured soil porosity presented a variation trend of increase–decrease during successive FTCs. With increasing number of FTCs, soil porosity first increased and then decreased in the 0‐to‐75‐mm soil layer, decreased after five FTCs in the 75‐to‐150‐mm soil layer, and gradually decreased in the 150‐to‐280‐mm soil layer. Pore structures of different soil layers responded differently to FTCs, which was attributed to soil texture. The connectivity of soil pores and soil water infiltration rate decreased considerably after 10 FTCs. Therefore, FTCs changed soil pore structure of the alpine meadow, which was not conducive for soil water infiltration to deep soil layers.

Effects of plant species identity override diversity effects in explaining sedimentation within vegetation in a flume experiment

AbstractDuring floods, sediments suspended in river water deposit on floodplains. Thus, floodplains are a key to improving river water quality. Yet, the factors that determine the amount of fine sediment that deposits on floodplains are largely unknown. Plant diversity typically increases structural diversity, whereas the vegetation structure and the structural characteristics of individual species are known to influence sedimentation. We hypothesised that species diversity, in addition to species identity, may promote sediment retention. Our study aimed to disentangle the effects of species richness and species identity, via differences in vegetation structure, on sediment retention within herbaceous vegetation patches. In a flume experiment, we investigated sedimentation on 30 vegetation patches (40 × 60 cm2). We created patches with five different species‐richness levels (3, 4, 6, 8, and 11 species), each replicated six times. Species were randomly selected from 14 common floodplain species. We inundated the patches with silt‐ and clay‐rich water and measured the amount of accumulated sediment on the vegetation and on the ground underneath it. Species richness significantly increased sedimentation underneath the vegetation (R2 = 0.17). However, including species identity effects in a structural equation model, we showed that individual species' presence largely drove these effects. Alopecurus pratensis had a direct negative effect on sedimentation on the vegetation, whereas Bromus inermis and Elymus repens had indirect positive effects through an increase in total biomass (R2 = 0.42). Elymus repens had a direct negative, and Urtica dioica a direct positive effect on sedimentation underneath the vegetation (R2 = 0.38). Our results indicate that selecting the most effective species, rather than as many species as possible, may have the greatest benefits for promoting sedimentation. Overall, we conclude that floodplain management that aims to increase sediment retention should alter the vegetation structure of meadows by increasing vegetation biomass.