Salt marsh accretion with and without deep soil subsidence as a proxy for sea-level rise

The relation between salt marsh accretion and flooding regime was quantified by statistical analysis of a unique dataset of accretion measurements using sedimentation-erosion bars, on three barrier islands in the Dutch Wadden Sea over a period of c. 15 years. On one of the islands, natural gas extraction caused deep soil subsidence, which resulted in gradually increasing flooding frequency, duration, and depth, and can thus be seen as a proxy for sea-level rise. Special attention was paid to effects of small-scale variation e.g., in distance to tidal creeks or marsh edges, elevation of the marsh surface, and presence of livestock. Overall mean accretion rate was 0.44 ± 0.0005 cm year−1, which significantly exceeded the local rate of sea-level rise of 0.25 ± 0.009 cm year−1. A multiple regression approach was used to detect the combined effect of flooding regime and the local environment. The most important flooding-related factors that enhance accretion are mean water depth during flooding and overall mean water depth, but local accretion strongly decreases with increasing distance to the nearest creek or to the salt marsh edge. Mean water depth during flooding can be seen as an indicator for storm intensity, while overall mean water depth is a better indicator for storm frequency. The regression parameters were used to run a simple model simulating the effect of various sea-level scenarios on accretion and show that, even under extreme scenarios of sea-level rise, these salt marshes can probably persist for the next 100 years, although the higher parts may experience more frequent inundation

change from species composition data by nonlinear reduced-rank models. In: van

On inferring past environmental change from species composition data by nonlinear reduced-rank models

Species-rich grassland can persist under nitrogen-rich but phosphorus-limited conditions

Aim: Deposition of nitrogen is assumed to cause loss of botanical diversity, probably through increased production and exclusion of less competitive species. However, if production is (co-)limited by phosphorus, acceleration of the phosphorus cycle may be responsible for the diversity loss and, where that is the case, nitrogen emission reduction may turn out to be an ineffective mitigation strategy. Here we study the feasibility of this mechanism through adding potassium and phosphorus to grassland where nitrogen limitation is absent. Methods: We made vegetation relevés in a long-term agricultural fertilisation experiment where potassium, phosphorus and nitrogen were being added to grassland on drained peat where nitrogen availability was high, even in unfertilised plots. We applied a multivariate analysis to investigate the effect of additions of K, K + P and K + P + N on the species composition. Results: Unfertilised plots had a very low biomass production and were rich in plant species despite their high nitrogen availability. Addition of potassium led to a strongly increased production but did not result in a reduction of species numbers. Phosphorus in addition to potassium increased production still further and decreased species numbers, most notably the number of endangered species. Conclusions: Even under nitrogen rich conditions species richness may be high in grasslands where phosphorous provides a limitation to plant growth. Phosphorus limitation and phosphorus enrichment are both common in grassland, at least in north-western Europe. Part of the general decrease in species numbers that is commonly ascribed to nitrogen enrichment may therefore be due to phosphorus enrichment. If phosphorus and nitrogen are co-limiting (which is often the case) the current nitrogen emission reduction policies may be effective, but not sufficient to restore grassland diversity to its pre-industrial level.</p

MAPPING DUNE VEGETATION USING IMAGING SPECTROSCOPY FOR AMELAND, THE NETHERLANDS

ABSTRACT The possibility to map vegetation types using imaging spectroscopy in a coastal area was investigated. This landscape is under the influence of changing salt water inundation regimes, resulting in a heterogeneous composition of the vegetation structure. The species composition in the area of interest was described by means of vegetation relevees. A vegetation typology used in former studies was adopted to perform the hyperspectral image classification. The vegetation classes to be derived from image classification were identified as wet brackish dune valleys, dune shrub, beach grass dunes (white dunes) and grassy dunes (grey dunes). The commonly used maximum likelihood classification (MLHC) was used to classify a hyperspectral image, acquired by the AHS sensor. A new method of data reduction was explored, namely the redundancy analysis (RDA) in the software package CANOCO. The RDA was used to reduce the spectral data dimensionality and to determine which bands of the hyperspectral imagery had the most predictive power to distinguish the selected vegetation types. The band selection from the vegetation observation dataset was used to perform a MLHC and was then compared to a MLHC using a PCA transformation. A maximum classification accuracy of 64.8% was found when MLHC was employed for differentiation of the four vegetation types. The influence of soil background was an important source of variation in the hyperspectral dataset making separation of the different vegetation classes more difficult. Mapping and monitoring dune vegetation using hyperspectral imagery could further be enhanced when ancillary data (e.g. digital elevation models or multi-temporal imagery) is included in the analyses

Millennial multi-proxy reconstruction of oasis dynamics in Jordan, by the Dead Sea

Vegetation reconstructions in the Dead Sea region based on sediment records are potentially biased, because the vast majority of them derive from the western side of the sea, and only focus on large areas and time spans, while little is known about extra-local (< 1,000 m radius) to local (< 20 m radius) changes. To fill this gap, we compared a vegetation survey with modern pollen assemblages from the “Palm Terrace” oasis ca. 300 m b.s.l. (below sea level), at the eastern edge of the Dead Sea. This revealed how the oasis vegetation is reflected in pollen assemblages. In addition, two sediment cores were collected from the centre and the edge of a mire at the oasis to reconstruct past vegetation dynamics. We analysed sedimentary pollen and microscopic charcoal, as well as the sediment chemistry by X-ray fluorescence (XRF) and conductivity, focusing on the past ~ 1,000 years. Pollen results suggest that mesophilous Phoenix dactylifera (date palm) stands and wetland vegetation expanded there around ad 1300–1500 and 1700–1900. During the past ca. 100 years, drought-adapted Chenopodiaceae gained ground, partly replacing the palms. Results from elemental analysis, especially of elements such as chlorine, provide evidence of enhanced evaporative salinization. Increasing desertification and the associated decline of mesophilous date palm stands during the past ca. 50 years is probably related to a decrease in annual precipitation and also corresponds to decreasing water levels in the Dead Sea. These have mainly been caused by increasing extraction of fresh water from tributaries and wells, mainly for local agriculture and industry. In the future, with hotter and drier conditions as well as increased use of water, oasis vegetation along the Dead Sea might be at further risk of contraction or even extinction

Millennial multi-proxy reconstruction of oasis dynamics in Jordan, by the Dead Sea

Vegetation reconstructions in the Dead Sea region based on sediment records are potentially biased, because the vast majority of them derive from the western side of the sea, and only focus on large areas and time spans, while little is known about extra-local (< 1,000 m radius) to local (< 20 m radius) changes. To fill this gap, we compared a vegetation survey with modern pollen assemblages from the “Palm Terrace” oasis ca. 300 m b.s.l. (below sea level), at the eastern edge of the Dead Sea. This revealed how the oasis vegetation is reflected in pollen assemblages. In addition, two sediment cores were collected from the centre and the edge of a mire at the oasis to reconstruct past vegetation dynamics. We analysed sedimentary pollen and microscopic charcoal, as well as the sediment chemistry by X-ray fluorescence (XRF) and conductivity, focusing on the past ~ 1,000 years. Pollen results suggest that mesophilous Phoenix dactylifera (date palm) stands and wetland vegetation expanded there around ad 1300–1500 and 1700–1900. During the past ca. 100 years, drought-adapted Chenopodiaceae gained ground, partly replacing the palms. Results from elemental analysis, especially of elements such as chlorine, provide evidence of enhanced evaporative salinization. Increasing desertification and the associated decline of mesophilous date palm stands during the past ca. 50 years is probably related to a decrease in annual precipitation and also corresponds to decreasing water levels in the Dead Sea. These have mainly been caused by increasing extraction of fresh water from tributaries and wells, mainly for local agriculture and industry. In the future, with hotter and drier conditions as well as increased use of water, oasis vegetation along the Dead Sea might be at further risk of contraction or even extinction.</p

Appendix C. PCA ordination of plant traits.

PCA ordination of plant traits

Appendix A. Site information and climatic data.

Site information and climatic data

Appendix B. Summary of all mixed models tested for the data set "all species" and "sunlit species".

Summary of all mixed models tested for the data set "all species" and "sunlit species"