Isotopic and molecular distributions of biochemicals from fresh and buried <Emphasis Type="Italic">Rhizophora mangle</Emphasis> leaves†

Rhizophora mangle L. (red mangrove) is the dominant species of mangrove in the Americas. At Twin Cays, Belize (BZ) red mangroves are present in a variety of stand structures (tall >5 m in height, transition ~2–4 m and dwarf ~1–1.5 m). These height differences are coupled with very different stable carbon and nitrogen isotopic values[1] (mean tall δ ¹³C = -28.3‰, δ ¹⁵N = 0‰; mean tall δ ¹³C = -25.3‰, δ ¹⁵N = -10‰). To determine the utility of using these distinct isotopic compositions as 'biomarkers' for paleoenvironmental reconstruction of mangrove ecosystems and nutrient availability, we investigated the distribution and isotopic (δ ¹³C and δ ¹⁵N) composition of different biochemical fractions (water soluble compounds, free lipids, acid hydrolysable compounds, individual amino acids, and the residual un-extractable compounds) in fresh and preserved red mangrove leaves from dwarf and tall trees. The distribution of biochemicals are similar in dwarf and tall red mangrove leaves, suggesting that, regardless of stand structure, red mangroves use nutrients for biosynthesis and metabolism in a similar manner. However, the δ ¹³C and δ ¹⁵N of the bulk leaf, the biochemical fractions, and seven amino acids can be used to distinguish dwarf and tall trees at Twin Cays, BZ. The data support the theory that the fractionation of carbon and nitrogen occurs prior to or during uptake in dwarf and tall red mangrove trees. Stable carbon and nitrogen isotopes could, therefore, be powerful tools for predicting levels of nutrient limitation at Twin Cays. The δ ¹³C and δ ¹⁵N of biochemical fractions within preserved leaves, reflect sedimentary cycling and nitrogen immobilization. The δ ¹⁵N of the immobilized fraction reveals the overlying stand structure at the time of leaf deposition. The isotopic composition of preserved mangrove leaves could yield significant information about changes in ecosystem dynamics, nutrient limitation and past stand structure in mangrove paleoecosystems.     

Investigating Bermuda's pollution history through stable isotope analyses of modern and museum-held gorgonian corals

For centuries, Bermuda has been challenged with wastewater management for the protection of human and environmental health. By quantifying the δ¹⁵N of the common sea fan Gorgonia ventalina sampled from 30 sites throughout Bermuda we show that sewage-derived nitrogen is detectable on nearshore coral reefs and declines across the lagoon to the outer rim. We also sampled gorgonians from two museum collections representing a 50y time-series (1958–2008). These samples revealed an increase in δ¹⁵N of > 4.0‰ until the mid-1970s, after which δ¹⁵N values slowly declined by ~ 2.0‰. A δ¹⁵N chronology from a gorgonian skeleton exhibited a similar decline over the last 30–40 years of approximately 0.6‰. We conclude that policies have been effective in reducing sewage impacts to Bermudian reefs. However, significant sources of sewage pollution persist and are likely have a strong impact on harbor and nearshore coral communities and human health.     

Long‐term nitrogen and phosphorus fertilization effects on N2 fixation rates and nifH gene community patterns in mangrove sediments

The bioavailability of nutrients is important in controlling ecological processes and nitrogen cycling in oligotrophic mangrove forests, yet the variation of diazotrophic community structure and activity with nutrient availability in sediments remains largely unexplored. To investigate for the first time how nutrients in sediments affect spatial and temporal patterns of diazotrophic community structure and activity, the sedimentary environment of Twin Cays, Belize, was examined with respect to the effects of long‐term fertilization [treatments: control (Ctrl), nitrogen (N), and phosphorus (P)] on N₂ fixation rates and nifH gene community structure. We found that N₂ fixation rates were significantly higher at the P‐treatment, intermediate at the Ctrl‐treatment and lower in the N‐treatment (P: 4.2 ± 0.5, Crtl: 0.8 ± 0.1, N: 0.4 ± 0.1 nmol·N·g^?1·h^?1; P < 0.001) with spatial (Ctrl‐ and P‐treatments) and temporal (only P‐treatment) variability positively correlated with live root abundance (r² = 0.473, P < 0.001) and concentration (r² = 0.458, P < 0.0001). The community structure of diazotrophs showed larger spatial and temporal variability in the fertilized treatments than in the Ctrl‐treatment, with the relative abundance of OTUs (nifH operational taxonomic units) at the fertilized treatments inversely related to live root abundance. Overall, long‐term fertilization (with either N or P) affects not only nutrient levels in mangrove sediments directly, but also spatial and temporal patterns of both community structure and activity and likely plant‐microbe interactions as well. Our findings suggest that the maintenance of natural nutrient conditions in mangrove sediments is important to ensure the stability of microbial functional groups like diazotrophs.     

Comprehensive imaging and Raman spectroscopy of carbonate globules from Martian meteorite ALH 84001 and a terrestrial analogue from Svalbard

Abstract— We report a comprehensive imaging study including confocal microRaman spectroscopy, scanning electron microscopy (SEM), and 3‐D extended focal imaging light microscopy of carbonate globules throughout a depth profile of the Martian meteorite Allan Hills (ALH) 84001 and similar objects in mantle peridotite xenoliths from the Bockfjorden volcanic complex (BVC), Svalbard. Carbonate and iron oxide zoning in ALH 84001 is similar to that seen in BVC globules. Hematite appears to be present in all ALH 84001 carbonate‐bearing assemblages except within a magnesite outer rim found in some globules. Macromolecular carbon (MMC) was found in intimate association with magnetite in both ALH 84001 and BVC carbonates. The MMC synthesis mechanism appears similar to established reactions within the Fe‐C‐O system. By inference to a terrestrial analogue of mantle origin (BVC), these results appear to represent the first measurements of the products of an abiotic MMC synthesis mechanism in Martian samples. Furthermore, the ubiquitous but heterogeneous distribution of hematite throughout carbonate globules in ALH 84001 may be partly responsible for some of the wide range in measured oxygen isotopes reported in previous studies. Using BVC carbonates as a suitable analogue, we postulate that a low temperature hydrothermal model of ALH 84001 globule formation is most likely, although alteration (decarbonation) of a subset of globules possibly occurred during a later impact event.     

Elevation effects on rainfall: A stochastic model

The variation in point precipitation with elevation is investigated using an event-based stochastic model of thunderstorm rainfall and empirical data. Parameters of the model correspond to the number of events per unit of time and the depth of rainfall per event. An increase in precipitation with elevation may be due to an increase in the number of events, in the amount of rainfall per event or to some combination of both possibilities. The distribution of the number of events per season is assumed to be a Poisson variate while the distribution of point rainfall depths may be taken as geometric. The summation of a random number of random variables is used to represent seasonal point precipitation. Assuming that the two parameters of the model increase linearly with elevation, then total seasonal rainfall increases as a quadratic polynomial with elevation. The use of the model allows one to obtain the return period of storm rainfall of a given magnitude despite a short historical record. An independent set of data was used to verify the procedure.     

An event-based stochastic model of phosphorus loading into a lake

In most lakes, phosphorus (P) is the nutrient controlling the trophic state. Thus, for effective control of eutrophication, the uncertainty in P-loading should be encoded as a probability density function (pdf). Specifically, the pdf of P-loading Y from non-point agricultural sources is sought by means of an event-based stochastic model.P-loading events are triggered by precipitation events (X₁, X₂, T), in which X₁ is the rainfall amount, X₂ the duration, and T the interarrival time between events. (X₁, X₂) are dependent random variables, while T is assumed to be exponentially distributed. The precipitation event causes runoff, which carries dissolved P into the lake with a concentration C₁ and sediment yield, Z, which carries fixed or sorbed P into the lake in a fraction C₂ of Z. Seasonal loading of P is calculated by adding random numbers of random variables. The model accounts separately for dissolved P and sorbed P. Explicit expressions are given for the mean and variance of each type of P-loadings. The case study of a sub-watershed of Lake Balaton, Hungary, is used to illustrate the methodology. Precipitation data, empirical rainfall-runoff-sediment yield relationships and a small number of observations of events are used to calibrate the model and estimate the means and variances of loading per event and per season. Then a simulation method is used to estimate complete pdf of these random variables. Use of the model for alternative methods of controlling P-loading is briefly discussed, as well as the economics of control.     

Cycling of dissolved and particulate nitrogen and carbon in the Framvaren Fjord, Norway: stable isotopic variations

The reaction pathways of nitrogen and carbon in the Framvaren Fjord (Norway) were studied through stable isotope analysis (δ¹⁵N and δ¹³C) of dissolved inorganic and particulate organic matter (POM). The variations in the isotopic compositions of the various C and N pools within the water column were use to evaluate the historical deposition of material to the sediments. The high δ¹⁵N-NH₄⁺ at the O₂/H₂S interface, as a consequence of microbial uptake between 19 and 25 m, results in extremely depleted δ¹⁵N-particulate nitrogen (PN) of approximately 1‰ within the particulate maximum at approximately 19 m. The carbon isotopic distribution of dissolved inorganic carbon (DIC) and particulate organic carbon (POC) within the interface suggests that the distinct microbial flora (Chromatium sp. and Chlorobium sp.) fractionate inorganic carbon to different degrees. The extremely light δ¹³C-POC within the interface (−31‰) appears to be a result of carbon uptake by Chromatium sp. while δ¹³C-POC of −12‰ is more indicative of Chlorobium sp. Nitrogen isotopic mass balance calculations suggested that approximately 75% of the material sinking to the sediments was derived from the dense particulate maximum between 19 and 25 m. The sediment distribution of nitrogen isotopes varied from 2‰ at the surface to approximately 6‰ at 30 cm. The nitrogen isotopic variations with depth may be an indicator of the depth or position of the O₂/H₂S interface in the fjord. Low sediment δ¹⁵N indicated that the interface was within the photic zone of the water column, while more enriched values suggested that the interface was lower in the water column potentially allowing for less fractionation during biological incorporation of dissolved inorganic nitrogen. Results indicate that the dense layers of photo-autotrophic bacteria in the upper water column impart unique carbon and nitrogen isotopic signals that help follow processes within the water column and deposition to the sediments.     

Using evolutionary programming for modeling: an ocean acousticexample

The process of natural evolution is used as a basis for a search technique that can locate the extremum of complex response surfaces despite the existence of multiple local minima or maxima. Background on research in simulated evolution is offered. The fundamental properties of natural evolution are simulated for the purpose of modeling a set of ocean acoustic signals. The experimental results indicate that simulated evolution provides a method for estimating both the appropriate order and parameter values of a model. Some theoretical comparisons are made to standard estimation methods     

Solubility and solution mechanisms of C-O-H volatiles in silicate melt with variable redox conditions and melt composition at upper mantle temperatures and pressures

Solubility and solution mechanisms in silicate melts of oxidized and reduced C-bearing species in the C-O-H system have been determined experimentally at 1.5 GPa and 1400 °C with mass spectrometric, NMR, and Raman spectroscopic methods. The hydrogen fugacity, f_H2, was controlled in the range between that of the iron-wüstite-H₂O (IW) and the magnetite-hematite-H₂O (MH) buffers. The melt polymerization varied between those typical of tholeiitic and andesitic melts.The solubility of oxidized (on the order of 1-2 wt% as C) and reduced carbon (on the order of 0.15-0.35 wt% as C) is positively correlated with the NBO/Si (nonbridging oxygen per silicon) of the melt. At given NBO/Si-value, the solubility of oxidized carbon is 2-4 times greater than under reducing conditions. Oxidized carbon dioxide is dissolved as complexes, whereas the dominant reduced species in melts are CH₃-groups forming bonds with Si⁴⁺ together with molecular CH₄. Formation of complexes results in silicate melt polymerization (decreasing NBO/Si), whereas solution of reduced carbon results in depolymerization of melts (increasing NBO/Si).Redox melting in the Earth’s interior has been explained with the aid of the different solution mechanisms of oxidized and reduced carbon in silicate melts. Further, effects of oxidized and reduced carbon on melt viscosity and on element partitioning between melts and minerals have been evaluated from relationships between melt polymerization and dissolved carbon combined with existing experimental data that link melt properties and melt polymerization. With total carbon contents in the melts on the order of several mol%, mineral/melt element partition coefficients and melt viscosity can change by several tens to several hundred percent with variable redox conditions in the range of the Earth’s deep crust and upper mantle.