202 research outputs found
Tidal flooding diminishes the effects of livestock grazing on soil micro-food webs in a coastal saltmarsh
Livestock grazing not only has a direct impact on plant productivity but also exerts an indirect influence on soil biota via various pathways. However, little is known about the effects of livestock grazing on soil food webs in saltmarsh ecosystems that are subject to regular tidal inundation stress. By exclosure experiments established at a frequently inundated middle marsh and a less inundated high marsh of Chongming Island (China), the responses of soil micro-food web components (microorganisms, protozoa, and nematodes) to cattle grazing in intertidal marshes were investigated. In the high marsh, cattle grazing significantly increased the biomass of soil microorganisms, protozoa, and the abundance of total nematodes by 30.0%, 97.3% and 76.2%, respectively, but did not significantly affect their biomass or abundance in the middle marsh. For low-trophic-level nematodes, the abundance of bacterial-feeding and algal-feeding nematodes increased more in the high marsh than in the middle marsh, and that of plant-feeding nematodes decreased more in the high marsh than in the middle marsh under grazing. In contrast, carnivorous and omnivorous nematodes at high trophic levels did not respond to cattle grazing along an elevational gradient. The nematode maturity index and structure index based on nematode functional guilds significantly decreased under grazing along the elevational gradient, suggesting that cattle grazing caused a more simplified and unstable soil micro-food web structure. Overall, low trophic levels in soil micro-food webs were most vulnerable under grazing and the response was strongest in the less inundated high marsh. Thus, cattle grazing leads to different changes in soil ecosystem processes at different elevations. These results indicate that the strength of the biotic grazing effect on soil micro-food webs and ecological functions might also depend on local abiotic disturbance such as tidal inundations in the saltmarsh
Elymus athericus encroachment in Wadden Sea salt marshes is driven by surface elevation change
Questions What are the main drivers of vegetation succession and the encroachment of Elymus athericus (Link) KerguĂ©len in ungrazed Wadden Sea salt marshes? Is (a) elevation, a proxy for tidal inundation and thus abiotic conditions, limiting the expanse of Elymus. Does sedimentation increase the spread of Elymus by (b) leading to surface elevation change or does it (c) add nitrogen and thereby allows Elymus to grow in lower elevation? Location Salt marsh at SönkeâNissenâKoog, Wadden Sea National Park SchleswigâHolstein, Germany. Methods The experiment was established in 2007 in the high marsh and consisted of four blocks of 12 m Ă 8 m. The blocks differed in surface elevation change during the experiment. Each block was subdivided into 24 plots of 1 m Ă 1 m. The original elevation of all plots in relation to the German ordnance datum (NHN) was assessed at the start of the experiment. Plots within the blocks were randomly assigned to one of the three N fertilization treatments. Within each plot we planted five randomly chosen individuals of Elymus. After four years of treatment, the vegetation composition and cover were recorded in all plots and aboveground biomass was collected. Results Original elevation was found to be a main driver of succession favouring Elymus and other lateâsuccessional plants. There was no effect of N fertilization, but a positive effect of surface elevation change on Elymus cover was detected. Conclusions We can conclude that the positive effect of surface elevation change on Elymus is based on the resulting higher elevation and more favourable abiotic conditions caused by sedimentation, but not by the addition of nitrogen with the freshly deposited sediment. This case, therefore, is an example for an ecosystem in which encroachment is driven by a natural factor, rather than anthropogenic eutrophication
A Hierarchy of DSMLs in Support of Product Life-Cycle Assessment
To support understanding and analysis of sustainability related aspects in organizations (e.g., via an assessment of a productâs life-cycle from the cradle to the grave), various instruments, among others, in the field of conceptual modeling, have been proposed. Although existing tools and languages are, to some extent, indeed supporting the product Life-Cycle Assessment (LCA), our investigations show that a hierarchy of Domain-Specific Modeling Languages(DSMLs) is needed to satisfy advanced requirements. In this paper, as an innovation for the field of LCA, we propose an application of multi-level language architecture to design a hierarchy of DSMLs encompassing concepts for LCAs that can be detailed to specific industrial domains and local needs of enterprises. This enables a new generation of instruments allowing users to use and refine concepts, corresponding to their specific needs
Efficiency of Varying Sediment Traps under Experimental Conditions Simulating Tidal Inundations
Accelerated sea-level rise (SLR) is threatening tidal marshes worldwide. An important control of tidal marsh survival under accelerated SLR is sediment deposition. Therefore, factors affecting sediment deposition rates (SDRs) have been studied extensively using various types of sediment traps. The efficiency of various sediment traps has been compared in several studies, but most of these were conducted in shallow lakes or rivers. In contrast, the efficiency of different sediment traps in tidal marshes is unknown. Therefore, the aim of this study was to compare the trapping efficiency of four frequently used sediment traps, namely flat traps constructed of either tiles or floor mat and circular traps with and without a lid, under controlled experimental conditions simulating tidal inundations in a flume. The strong differences between circular sediment traps (high efficiency) and both flat-surface sediment trap methods (low efficiency) found in this study were remarkable. Additionally, further evidence was found for decreases in SDRs with increasing distance to the inflow of the flume (sediment source) and with decreasing suspended sediment concentration. These findings indicate that trap design has a large influence on sedimentation rate and that studies using different types of sediment traps are not directly comparable
Livestock grazing reduces sediment deposition and accretion rates on a highly anthropogenically altered marsh island in the Wadden Sea
Coastal salt marshes and their provided ecosystem services are threatened by rising sea levels all over the world. In the Northern Wadden Sea region, a sea-level rise of 4âŻmm yâ1 was recorded for recent years. Identifying and understanding factors that affect sediment deposition and determine vertical accretion of salt marshes is crucial for the management of these ecosystems. Even though major processes contributing to sedimentation and accretion have already been identified, the influence of reduced canopy heights due to livestock grazing is still debated. On a highly anthropogenically altered marsh island in the Wadden Sea, sediment deposition, accretion and suspended sediment concentration was analyzed on grazed and adjacent ungrazed plots both at the marsh edge and at the marsh interior. Due to a low seawall (a so-called âsummer dikeâ), flooding frequency on the island is reduced and flooding mainly takes place during storm surges. After five flooding events within a year, mean sediment deposition and accretion were found to be up to seven times higher on ungrazed plots compared to grazed plots, but only at the marsh edges. This result was not explained by the overmarsh suspended sediment concentration (SSC), which was found to be twice as high on grazed plots compared to ungrazed plots. It is concluded that grazing has a negative effect on sediment deposition and accretion on Wadden Sea marsh islands and areas with similar conditions (e.g. presence of a summer dike) by reducing the sediment trapping capacity of those marshes. Overall, vertical marsh accretion ranged from 0.11âŻÂ±âŻ0.09âŻmm yâ1 on a grazed plot at the marsh edge to 1.12âŻÂ±âŻ0.71âŻmm yâ1 on an ungrazed plot at the marsh edge. By increasing the discrepancy between accretion and sea-level rise, livestock grazing can lead to higher inundation levels and in turn to increased hydrodynamic forces acting on these anthropogenically altered marshes
Unrecognized controls on microbial functioning in Blue Carbon ecosystems: The role of mineral enzyme stabilization and allochthonous substrate supply
Tidal wetlands are effective carbon sinks, mitigating climate change through the longâterm removal of atmospheric CO2. Studies along surfaceâelevation and thus floodingâfrequency gradients in tidal wetlands are often used to understand the effects of accelerated seaâlevel rise on carbon sequestration, a process that is primarily determined by the balance of primary production and microbial decomposition. It has often been hypothesized that rates of microbial decomposition would increase with elevation and associated increases in soil oxygen availability; however, previous studies yield a wide range of outcomes and equivocal results. Our mechanistic understanding of the elevationâdecomposition relationship is limited because most effort has been devoted to understanding the terminal steps of the decomposition process. A few studies assessed microbial exoâenzyme activities (EEAs) as initial and rateâlimiting steps that often reveal important insight into microbial energy and nutrient constraints. The present study assessed EEAs and microbial abundance along a coastal ecotone stretching a flooding gradient from tidal flat to high marsh in the European Wadden Sea. We found that stabilization of exoâenzymes to mineral sediments leads to high specific EEAs at low substrate concentrations in frequently flooded, sedimentârich zones of the studied ecotone. We argue that the high background activity of a mineralâassociated enzyme pool provides a stable decomposition matrix in highly dynamic, frequently flooded zones. Furthermore, we demonstrate that microbial communities are less nutrient limited in frequently flooded zones, where inputs of nutrientârich marine organic matter are higher. This was reflected in both increasing exoâenzymatic carbon versus nutrient acquisition and decreasing fungal versus bacterial abundance with increasing flooding frequency. Our findings thereby suggest two previously unrecognized mechanisms that may contribute to stimulated microbial activity despite decreasing oxygen availability in response to accelerated seaâlevel rise
Effects of small-scale patterns of vegetation structure on suspended sediment concentration and sediment deposition in a salt marsh
Salt marshes contribute to coastal protection by attenuating waves and reducing flow velocities. Nevertheless, coastal salt marshes are threatened by rising sea levels. In order to keep pace with rising sea levels, salt marshes need to grow vertically by sediment input. Although major processes contributing to sediment deposition in salt marshes are known, there is still a lack of understanding of the influence of canopy height and biomass on suspended sediment concentration and sediment deposition and on the spatial scale beyond which an influence of vegetation on sediment deposition comes into effect. Furthermore, vegetation can be heterogenous and little is known on the role of small-scale patterns of vegetation structure on suspended sediment concentration and sediment deposition. We investigated the effects of small-scale patterns of vegetation on suspended sediment concentration and sediment deposition in a field experiment with two vegetation types (i.e. Spartina anglica in the low marsh and Elymus athericus in the high marsh). Partial mowing of the vegetation resulted in a pattern of mown subplots and control subplots with a size of 4âŻm2 in various combinations adjacent to a creek. Based on the results, it can be concluded that on the spatial scale of 4âŻm2, there is no effect of the vegetation on water flow as the sediment deposition between mown and control subplots did not differ in both the high and the low marsh. Furthermore, a mown or a control subplot next to the creek had no influence on the sediment deposition on a mown or control subplot behind. In summary, based on the results of our study, it can be concluded that the presence of salt marsh vegetation not automatically leads to higher sediment deposition on vegetated patches compared to mown patches in both the low and high marsh
Assessing the longâterm carbonâsequestration potential of the semiânatural salt marshes in the European Wadden Sea
Salt marshes and other blue carbon ecosystems have been increasingly recognized for their carbon (C)âsink function. Yet, an improved assessment of organic carbon (OC) stocks and Câsequestration rates is still required to include blue C in Câcrediting programs. Particularly, factors inducing variability in the permanence of sequestration and allochthonous contributions to soil OC stocks require an improved understanding. This study evaluates the potential for longâterm C sequestration in the semiânatural salt marshes of the European Wadden Sea (WS), conducting deep (1.3 m) downâcore OCâdensity assessments in sites with known site histories and accretion records. Because these young marshes have developed from tidalâflat ecosystems and have undergone rapid succession during the last 80â120 yr, the identification of different ecosystem stages downâcore was crucial to interpret possible changes in OC density. This was conducted based on the downâcore distribution of different foraminiferal taxa and grain sizes. Comparisons of historic and recent accretion rates were conducted to understand possible effects of accretion rate on downâcore changes in OC density. ÎŽ13C in OC was used to assess the origin of accumulated OC (autochthonous vs. allochthonous sources). We show that large amounts of shortâterm accumulated OC are lost downâcore in the wellâaerated marsh soils of the WS region and thus emphasize the importance of deep sampling to avoid overestimation of C sequestration. Despite steep declines in OCâdensity downâcore, minimum values of OC density in the saltâmarsh soils were considerably higher than those of the former tidalâflat sediments that the marshes were converted from, illustrating the greater Câsequestration potential of the vegetated ecosystem. However, our data also suggest that marineâderived allochthonous OC makes up a large fraction of the effectively, longâterm preserved OC stock, whereas atmospheric CO2 removal by marsh vegetation contributes relatively little. The implication of this finding for Câcrediting approaches in blue C ecosystems has yet to be clarified
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