Leaf Elemental Concentrations, Stoichiometry, and Resorption in Guam’s Coastal Karst Forests

Greater knowledge concerning the interspecific diversity of the plant leaf ionome is required to effectively understand the spatiotemporal dynamics of biogeochemistry, but Micronesia has been ignored in this literature. The objectives of this study were to quantify the leaf ionome, resorption efficiency, and stoichiometry of leaves from 25 plant species representing Guam’s coastal karst forests. Carbon and nitrogen were quantified by dry combustion, and other minerals and metals were quantified by spectrometry. Nitrogen and calcium concentrations in Guam’s green leaves exceeded the published global means, but manganese and copper concentrations were less than the global means. The remainder of the elements were within the expected ranges. Nutrient resorption rates exhibited a decreasing order of potassium > phosphorus > nitrogen > zinc > copper. The term “accretion efficiency” is introduced to describe the accumulation of an element throughout leaf aging and senescence, and calcium and iron exhibited substantial accretion efficiency in this study. Stoichiometry relations indicated that Guam’s karst forest is most limited by phosphorus and then secondarily limited by nitrogen, although several individual taxa exhibited co-limitation by potassium. Five of the species are officially listed on extinction threat lists. Of these, the Malvaceae tree Heriteria longipetiolata exhibited leaf traits depicting the most recalcitrant litter characteristics, and the Fabaceae tree Serianthes nelsonii exhibited leaf traits depicting the most labile litter characteristics. The contributions of these two tree species to spatiotemporal diversity in biogeochemistry appear to be profound, indicating species recovery efforts are of paramount importance for maintaining ecosystem function and soil heterotroph biodiversity in northern Guam.

Review of the most significant caves in Montenegro

The most significant caves in Montenegro were distinguished in response to their physical-geographic, biological, archeological and morphometric characteristics (length and depth). Caves distribute in four distinctive regions: coastal karst, karst plateau (relict valley system), fluvial karst (recent hydrologic systems) and the high mountainous karst area. The most outstanding within the last, due to abundances of the major caves with depths from a few hundred meters to 1,162 m, are four mountain regions: Mt. Durmitor, Mt. Lovćen-Orjen, Mt. Maganik and Mt. Bjelič.

The VIOLA Project: Functional responses of groundwater microbial community across the salinity gradient in a coastal karst aquifer

<p>The vulnerability to salinization is a major issue for coastal aquifers. The resulting rapid modifications of hydro-geochemical characteristics, driven by the different origin of water inputs, can modify the properties of the resident biological communities. The study of structural and functional properties of groundwater microbial community, posed at the base of the heterotrophic food web, assumes an increasing importance to describe the effect of water quality on C-cycling and the resilience of groundwater systems to changes.</p><p>Within the framework of the VIOLA project, this study was entailed to explore the groundwater quality and the functional responses of the microbial community across the gradient of salinity in a coastal karst aquifer located in Apulia Region (Southern Italy). The investigated area (1227 km<sup>2</sup>) is located in a semi-arid climate region with predominantly agricultural vocation. In this area, an excess of withdrawals for irrigation and other uses, often results in a significant decline of the water table, facilitating saline intrusion.</p><p>The main physical-chemical parameters of 47 groundwater sampling sites (T, pH, oxidation-reduction potential, electrical conductivity, major anions/cations, trace elements, dissolved oxygen, ammonia, nitrites, cyanides and dissolved organic carbon) were measured, along with microbial community analyses including the total cell abundance, the High Nucleic Acid and Low Nucleic Acid content cell ratio (Flow Cytometry), the total coliform and Escherichia Coli contamination (Colilert-18 assay), the microbial metabolic potential (Biolog EcoPlates), and the microbial respiration (Biolog MT2 MicroPlates). The preliminary results allowed identifying two major groups of waters with different salinity levels and concentrations of Cl, Na, Mg and SO<sub>4</sub>. Prokaryotic cell abundance (mean 3.5 x 10<sup>4</sup> ± 4.6 x 10<sup>4</sup> cells/ml) showed higher values in saline waters, so as HNA cell percentages and total coliforms. Saline waters were also characterised by relatively higher metabolic potential and respiration values. In conclusion, the observed groundwater quality changes induced the stimulation of the functional microbial properties and the functional diversity. These changes in the metabolic potential of the resident communities could alter the ability to exploit the available resources and modify the related groundwater biogeochemical cycling.</p>

Analysis of the Saltwater Wedge in a Coastal Karst Aquifer with a Double Conduit Network, Numerical Simulations and Sensitivity Analysis

We investigate the long-distance salinity in a dual permeability coastal karst aquifer with a double conduit network using a three-dimensional variable-density groundwater flow and multispecies transport SEAWAT model. Sensitivity analyses were used to evaluate the impact of the parameters and boundary conditions on the modeling saltwater wedge in a karstic aquifer situated in the Cuban land territory, including hydraulic conductivity, vertical anisotropy and salinity concentration; both in the conduits network and the fractured medium. These analyses indicated that hydraulic conductivity of the fractured medium and salt concentration were the ones that have a stronger effect on saltwater intrusion in a karstic aquifer. We also show results of the three-dimensional numerical simulations on groundwater salinity for different scenarios with the variabilities of the important parameters and compare results with electric conductivity profiles measured in a well.