Environmental limitations on recruitment from seed in invasive Spartina densiflora on a southern European salt marsh

The South American cordgrass, Spartina densiflora, has invaded a range of different habitats that can support different native species assemblages on salt marshes in the Gulf of Cadiz, Spain. Little is known about the mechanisms of invasion. We examined the potential for seed germination and recruitment in a field transplant experiment, representing a wide range of environments, on elevational gradients across marshes with muddy and sandy sediments. The biotic resistance of native, perennial vegetation (where present) to recruitment of the alien was also investigated. Spartina densiflora seeds were able to germinate over a greater than 2-m range of elevation in the tidal frame. Germination success on unvegetated muddy sediments was related to sediment redox potential, with poor germination at strongly negative redox potentials on the lower sites. On sandy, well-drained sediments, germination was apparently constrained by water availability at the highest elevations. Comparison of vegetated and cleared plots on the upper marsh showed that there was a negative relationship between the presence of Atriplex portulacoides and germination on the muddy sediments. Recruitment (survival of seedlings for 12 weeks) was seen only on unvegetated muddy sediments at the highest elevation. Hence the invasive success and wide elevational tolerance of S. densiflora on the marshes of the Gulf of Cadiz are not reflected in its short-term ability to become established from its prolific seed production. Colonization of sub-optimal habitats may be largely by vegetative propagules and clonal growth.     

Distribution of benthic flora in the lower course of the Valdivia River,Chile

The Valdivia River (Lake Region, Chile) originates in Riñihue Lake and flows into the sea at Corral Bay (39°52′S latitude), changing names several times along its course. The aquatic benthic flora (algae and aquatic plants) of the Valdivia River was characterized, based on 22 sites sampled and 124 plant species collected. Four benthic vegetation zones were established using presence-absence data: a freshwater zone and a marine zone were found at the extremes of the transect; an estuarine zone and a discontinuity zone were detected in the middle of this transect. The freshwater zone was characterized by a relatively diverse assemblage of vascular plants, the marine zone was dominated by algae and was rich in species. By contrast the estuarine zone was inhabited by only a few species but in great abundance, while the discontinuity zone was poor, in species and low in cover vegetation.     

Spatial and temporal variations in aboveground and belowground biomass of Spartina maritima (small cordgrass) in created and natural marshes

Spartina species are commonly used for salt marsh manipulative projects, where aboveground and belowground biomasses are functional traits that play important roles, showing high spatial and temporal variations. This work analyses variations in AGB and BGB of Spartina maritima and abiotic environmental parameters along a chronosequence of six marshes created from 1997 to 2003 with disparate sediment dynamics, and adjacent natural marshes and unvegetated tidal flats. S. maritima behaved as an autogenic engineer, as its colonization of bare sediments yielded abiotic environmental changes: specifically, bed level rise accompanied by higher oxygenation and salinity. These modifications of the environment were site-specific, depending mainly on sedimentary dynamics. At the same time, abiotic environmental changes determined biomass production rates of S. maritima that were higher in more-accreting marshes; however, AGB was kept constant from early in its development (2 years). The increase in BGB with elevation seemed to be related to the inhibition of subsurface tissue development in anoxic sediments. Biomass accumulation and production varied markedly, depending on the spatial scale, indicating the relevance of the plot size chosen for the analysis of biomass of cordgrasses. Our results show that managers of salt marshes should consider sedimentary dynamics carefully when setting realistic expectations for success criteria of created and restored wetlands.     

Grass cover density and metal speciation in profiles of a tailings-pile from a mining zones in Zacatecas,North-Central Mexico

The 7-year-old mine tailings pile P2 from Concepción del Oro has been revegetated spontaneously by xerophyte grasses, covering about the 30% of its surface. To elucidate the effect of the grass cover in the geochemical behavior of the sulfide minerals (SM) and metals, the strata of four selected profiles (P2-I, P2-II, P2-III and P2-IV, with high, middle, low, and null grass cover, respectively) were analyzed mineralogically and chemically, using scanner electron microscopy, X-ray diffractometer and performing a six-step sequential extraction method. An older (50-year-old) and uncovered (without grass cover) profile of the tailings pile P3 was also analyzed. In all the profiles from P2, the SM oxidation is not yet an extended process; however, the samples from the uncovered profile P2-IV showed evidences of SM (pyrite and chalcocite) oxidation, as well as the presence of gypsum and Fe oxides, as the major secondary phases resulted from the SM oxidation. Additionally, the carbonate content and pH values in P2-IV were lower than in the covered profiles from P2. The oldest and uncovered P3-I profile showed an extensive oxidation of sulfurs which resulted in the depletion of carbonates and a pH 2. Another distinctive characteristics of the covered profiles was that Pb, Cu, and Zn were mainly associated with the reducible fractions (carbonates and/or amorphous oxides); meanwhile, in the uncovered (P2-IV and P3-I) such metals were mainly associated with the oxidizable fraction (crystalline oxides). The results suggest that the mineralogical transformations control metal stability in plant-covered impoundments (phytostabilization): the occurrence of a thick grass cover, with an efficient water usage and retention, seems to shun both the acidic dissolution of carbonates and the reductive dissociation of the formerly present oxyhydroxides, which is desired for remediation tasks. This is the first report about the effects of grass cover for a carbonaceous and unsaturated mine tailings from a semiarid region, that can help in a better understanding of the scope of phytoremediation in such conditions.     

Field investigation of siltation at a tidal harbor: North Port of Incheon,Korea

Ocean Dynamics - To understand siltation processes within the North Port of Incheon, Korea, this study estimated the sedimentation rate and then determined the dominant mechanisms for the...     

Effect of nutrient supply on photosynthesis and pigmentation to short-term stress (UV radiation) in Gracilaria conferta (Rhodophyta)

The effects of increased photosynthetic active radiation (PAR), UV radiation (UVR), and nutrient supply on photosynthetic activity, pigment content, C:N ratio and biomass yield were studied in tank cultivated Gracilaria conferta (Rhodophyta). Electron transport rate (ETR) and biliprotein content were higher under high nutrient supply (HNS), obtained from fishpond effluents, compared to low nutrient supply (LNS), in contrast to mycosporine-like amino acids (MAAs) dynamic. The high MAA content in LNS-algae could be explained by higher UVR penetration in the thallus and by the competition for the use of nutrients with other processes. Effective quantum yield decreased after short-term exposure to high irradiance whereas full recovery in shade was produced only under slightly heat shock. UVA radiation provoked an additional decrease in photosynthesis under high water temperature. UVB radiation reversed UVA’s negative effect mainly with HNS. Results support that nutrient-sufficiency help G. conferta to resist environmental changes as short-term temperature increase.     

Petrology of pumices of April 1993 eruption of Lascar (Atacama, Chile)

Lascar Volcano (Atacama, Chile) erupted on 18–20 April 1993. Several sub-Plinian explosions occurred, and some were mushroom-shaped. The highest column rose up to 23 km. Ash clouds crossed South America eastwards. Dacite pumice falls made of blocks and ashes were deposited on the flanks of the volcano as a result of collapsed columns. The pumice contains phenocrysts of plagioclase, enstatite, augite, biotite, magnetite and ilmenite and small crystals of apatite. The 1992 previous andesite dome inside the crater was destroyed. Banded blocks resulting from mingling of the dacitic pumice and andesite from the dome are found in the pumice flow. Both the lava dome and the pumice are representative of the Lascar high-K magma unit. Dacitic pumice is a product of crystal fractionation of the andesitic magma.     

Microstructure measurements in natural waters: Methodology and applications

Modern approaches to microstructure data processing, including wavelet denoising, are discussed. The wavelet procedure is applied to small-scale shear signals before estimating the dissipation rate ε and to the temperature/density profiles used to calculate Thorpe scales. Microstructure data obtained on the Mediterranean shelf of Catalonia are used to illustrate various approaches to the Thorpe displacement calculations. It is suggested that the Weibull probability function is an appropriate model for the Thorpe scale distribution. Microstructure measurements from the upper layer of the Boadella reservoir (Catalonia, Spain) support this finding.A new analytical approximation for the 1D Panchev–Kesich spectrum is deduced and the results of ε computation are compared with spectral fitting by the widely used Nasmyth spectrum. Applying the Kraichnan spectral model to compute ε from temperature spectra in the convective-viscous sub-range is examined as an alternative to the Batchelor spectrum. Microstructure measurements taken in Lake Banyoles (Catalonia, Spain) and in the North Atlantic were used for spectral calculations.Statistical analysis of eddy K_b and thermal K_θ diffusivities measured on a shallow shelf of the Black Sea shows the importance of process-orientated domain averaging of the diffusivities in obtaining good correspondence between K_b and K_θ in active turbulent regions. In weakly turbulent, stratified interior layers, the averaged K_b and K_θ differ significantly, which may point to the inapplicability of isotropic formulae used for ε and temperature dissipation χ_θ estimates, as well as to a dependence of the mixing efficiency γ on the Richardson number or in some cases on regions of fossil turbulence.     

The physical structure of a cold filament in a Chilean upwelling zone (Península de Mejillones, Chile, 23°S)

Cold filaments associated with Eastern Boundary Currents are typically narrower than 100 km but can be several hundred kilometers long, extending from the coast to the open ocean in upwelling areas. One such structure, observed off Península de Mejillones (23°S, Chile), was studied with both satellite images and two 5-days hydrographic cruises carried out during January 1997. The study used a coastal grid of 31 stations in an area of 165 ×155 km², approximately. The spatial distribution of the filament and its change between cruises are described from the horizontal distributions of dynamic height, temperature, salinity and dissolved oxygen. The filament was a shallow feature (thickness <100 m) and extended at least 165 km toward the open ocean. A meandering northward current flowed at the borders of the filament, separating oceanic and coastal waters of different physical properties. Comparisons of cross sections of the filament near the coast and in the oceanic zone show the ascent of the shallow salinity minimum (SSM), and its extension toward the ocean, bound to the filament. It is concluded that Subantarctic Water ((SAAW) distinguish by low salinity, high dissolved oxygen) and Equatorial Subsurface Water ((ESSW) high salinity, low dissolved oxygen, high nutrient content) form this filament, and that their relative proportions depend on the strength of the coastal upwelling. Thus, the knowledge of the dynamics of these structures is fundamental to better understanding of the spatial distribution of important biological variables, such as nutrients and chlorophyll, in the coastal ecosystem.