Modelling the effects of litter decomposition on tree diversity patterns

Current theories may not fully explain why latitudinal patterns of plant diversity differ between terrestrial and flooded ecosystems. Moreover, the co-occurrence of hyper diverse stands in lowland tierra firma (not inundated) forests and almost monospecific stands in mangroves and gallery riparian vegetation within the tropics remains enigmatic. Building on evidence from ecology and agriculture, we present a new model investigating the hypothesis that, besides the general positive feedback of plant growth by nutrients release, litter decomposition builds up an intra-specific negative feedback functionally linked with tree diversity. The model results were compared with extensive published data sets both across and within latitudinal zones. The model predicts correctly the biomass production and decomposition process, as well as the number of tree species, their relative abundance in all environmental conditions providing a novel, putative explanation also for the diversity variations observed within the tropics. The model demonstrates a possible mechanistic link between the carbon cycle and biodiversity patterns, which is interesting in the debate about advancing in the direction of a unifying ecosystem theory.     

Modelling the interactions between nutrients and the submersed vegetation in the Orbetello Lagoon

The main problem in the Orbetello Lagoon is the control of the submersed vegetation, both in biomass and inventory, to manage a problematical coexistence between macroalgae and macrophytes. While macroalgae are liable to cause dystrophic crises, macrophytes oxygenate and stabilise the sediment and thus control the nutrient flux into the water. A mathematical model was required by the Orbetello Lagoon Managerial Office to predict the development of both groups and test the actions to favour macrophytes over macroalgae, in the context of a decision support system. This model, developed for this need, takes into account the interactions between nutrients and the submersed vegetation in a 2D spatial context including a hydrodynamic model for the water movements and an ecological model describing the interactions between nutrients and the submersed vegetation. In the spatial grid the model operates with two interlocked modules: each cell implements the kinetics of nutrients, vegetation and their interactions, running on an hourly basis to keep track of the circadian cycles, whereas an advection/diffusion mechanism running on a daily basis exchanges information among all the grid cells. The model output consists of daily variations in nutrient concentrations and vegetation biomass showing the relative abundance of either group as a consequence of environmental conditions. After a sensitivity assessment, the model has been calibrated with data from the Orbetello Lagoon, where it can now be used as a forecasting tool to predict the development of vegetation and the relative advantage that macrophytes may have upon macroalgae.     

Sulfate radical-induced incorporation of NO2 group into chlorophenols

Environmental Chemistry Letters - Sulfate radical ( $${\text{SO}}_{4}^{ \cdot - }$$ )-based advanced oxidation processes (SR-AOPs) are promising in situ chemical oxidation technologies that...     

Nonparametric MLE incorporation of heterogeneity and model testing into premarked cohort studies

We utilize mixture models and nonparametric maximum likelihood estimation to both develop a likelihood ratio test (lrt) for a common simplifying assumption and to allow heterogeneity within premarked cohort studies. Our methods allow estimation of the entire probability model and thus one can not only estimate many parameters of interest but one can also bootstrap from the estimated model to predict many things, including the standard deviations of estimators. Simulations suggest that our lrt has the appropriate protection for Type I error and often has good power. In practice, our lrt is important for determining the appropriateness of estimators and in examining if a simple design with only one capture period could be utilized for a future similar study.     

Linking marine resources to ecotonal shifts of water uptake by terrestrial dune vegetation

As evidence mounts that sea levels are rising, it becomes increasingly important to understand the role of ocean water within terrestrial ecosystem dynamics. Coastal sand dunes are ecosystems that occur on the interface of land and sea. They are classic ecotones characterized by zonal distribution of vegetation in response to strong gradients of environmental factors from the ocean to the inland. Despite the proximity of the dune ecosystem to the ocean, it is generally assumed that all vegetation utilizes only freshwater and that water sources do not change across the ecotone. Evidence of ocean water uptake by vegetation would redefine the traditional interpretation of plant-water relations in the dune ecosystem and offer new ideas for assessing maritime influences on function and spatial distribution of plants across the dune. The purpose of this study was to identify sources of water (ocean, ground, and rain) taken up by vegetation using isotopic analysis of stem water and to evaluate water uptake patterns at the community level based on the distribution and assemblage of species. Three coastal dune systems located in southern Florida, USA, and the Bahamian bank/platform system were investigated. Plant distributions across the dune were zonal for 61-94% of the 18 most abundant species at each site. Species with their highest frequency on the fore dune (nearest the ocean) indicate ocean water uptake as evidenced by delta 18O values of stem water. In contrast, species most frequent in the back dune show no evidence of ocean water uptake. Analysis of species not grouped by frequency, but instead sampled along a transect from the ocean toward the inland, indicates that individuals from the vegetation assemblage closest to the ocean had a mixed water-harvesting strategy characterized by plants that may utilize ocean, ground-, and/or rainwater. In contrast, the inland vegetation relies mostly on rainwater. Our results show evidence supporting ocean water use by dune vegetation and demonstrate an exciting relationship between seawater and ecotonal shifts in plant function of a terrestrial ecosystem.     

Modelling forest management within a global vegetation model—Part 1: Model structure and general behaviour

This article describes a new forest management module (FMM) that explicitly simulates forest stand growth and management within a process-based global vegetation model (GVM) called ORCHIDEE. The net primary productivity simulated by ORCHIDEE is used as an input to the FMM. The FMM then calculates stand and management characteristics such as stand density, tree size distribution, tree growth, the timing and intensity of thinnings and clear-cuts, wood extraction and litter generated after thinning. Some of these variables are then fed back to ORCHIDEE. These computations are made possible with a distribution-based modelling of individual tree size. The model derives natural mortality from the relative density index (rdi), a competition index based on tree size and stand density. Based on the common forestry management principle of avoiding natural mortality, a set of rules is defined to calculate the recurrent intensity and frequency of forestry operations during the stand lifetime. The new-coupled model is called ORCHIDEE-FM (forest management).The general behaviour of ORCHIDEE-FM is analysed for a broadleaf forest in north-eastern France. Flux simulation throughout a forest rotation compare well with the literature values, both in absolute values and dynamics.Results from ORCHIDEE-FM highlight the impact of forest management on ecosystem C-cycling, both in terms of carbon fluxes and stocks. In particular, the average net ecosystem productivity (NEP) of 225 gC m⁻² year⁻¹ is close to the biome average of 311 gC m⁻² year⁻¹. The NEP of the “unmanaged” case is 40% lower, leading us to conclude that management explains 40% of the cumulated carbon sink over 150 years. A sensitivity analysis reveals 4 major avenues for improvement: a better determination of initial conditions, an improved allocation scheme to explain age-related decline in productivity, and an increased specificity of both the self-thinning curve and the biomass-diameter allometry.     

Acetate incorporation into the lipids of the anemone Anthopleura elegantissima and its associated zooxanthellae

Anthopleura elegantissima containing zooxanthellae, as well as isolated zooxanthellae, incubated with acetate-1-¹⁴C under both light and dark conditions readily incorporate radioactivity into their total lipid pools. In both cases, the specific activity was greatly increased in the light. Dark-incubated anemones and isolated zooxanthellae incorporate activity predominantly into polar lipid; the remainder being present principally in the triglyceride moiety. Light-incubated organisms, however, show a dramatic redistribution of isotope towards greatly increased triglyceride and was ester incorporation, with a concomitant drop in polar lipid. onder light conditions, 70 to 75% of the radioactivity found in the fatty acids of the total zooxanthellae lipid was present in hexadecanoic (16:0) and octadecenoic (18:1) fatty acids. These are also the two major fatty acids by mass. Octadecanoic acid (18:0) is less than 5% by mass. Isotope incorporation patterns suggest that octadecenoic acids arise by elongation of hexadecenoic acids and that this conversion is blocked in the dark. Isotope incorporation patterns for anemones suggest that fatty acids, primarily in the form of saturated or monoenoic fatty acids, are translocated from algal to animal cells. No activity was found in either octadecadienoic (18:2) or octadecatrienoic (18:3) acids. The significance of these data is discussed.     

Pathways of arsenic uptake and incorporation in estuarine phytoplankton and the filter-feeding invertebrates Eurytemora affinis,Balanus improvisus and Crassostrea virginica

Arsenic uptake from water and from phytoplankton was followed in the copepod Eurytemora affinis and the barnacle Balanus improvisus collected from the Patuxent River estuary, Chesapeake Bay, eastern coast of the USA in 1987, and in the oyster Crassostrea virginica obtained from a hatchery on the shore of Chesapeake Bay in 1987. Dissolved arsenic was readily taken up by phytoplankton and by shell material of B. improvisus and C. virginica; however, no dissolved arsenic was incorporated into the invertebrate tissues. When E. affinis, B. improvisus and C. virginica were fed phytoplankton containing elevated arsenic contents, significant arsenic incorporation occurred. Juvenile B. improvisus incorporated relatively more arsenic than adults of all three species. Compared to the 100 to 200% increase in arsenic content by phytoplankton exposed to dissolved arsenic, the 25 to 50% increase in these invertebrate species via trophic transfer is relatively small. Even though the trophic pathway for arsenic transfer is the major one for higher trophic levels within an ecosystem, the potential for direct arsenic impact to trophic levels other than phytoplankton appears to be minimal.     

Model of turbulence penetration into a suspension layer on a sediment bed and effect on vertical solute transfer

The vertical diffusional mass (solute) transfer through a suspended sediment layer, e.g. at the bottom of a lake, reservoir or estuary, by the propagation of velocity fluctuations from above was investigated. The attenuation of the velocity fluctuations in the suspension layer and the associated effect on solute transfer through the suspension layer was simulated. To represent large eddies traveling downstream in water over a high-concentration suspended sediment layer, a streamwise velocity fluctuation moving in downstream direction was imposed along the upper boundary of the suspension layer. Velocity fluctuations and downstream velocity were normalized by the shearvelocity (U_*) at the top of the suspension layer. Streamwise and vertical velocity components inside the suspension layer, were obtained from the 2-D continuity and the Navier–Stokes equations. The persistence of turbulence with depth—as it penetrates from the overlying water into the suspension layer—was found to depend on its amplitude, its period, and on the apparent viscosity of the suspension. The turbulence was found to propagate efficiently into the suspension layer when its frequency is low, and the apparent viscosity of the suspension is high. Effects on vertical mass transfer were parameterized by penetration depth and effective diffusion coefficient, and related to apparent viscosity of the suspension, Schmidt number and shear velocity on top of the suspension layer. The enhancement of turbulence penetration by viscosity is similar to the flow near an oscillating flat plate (Stokes’ second problem), but is opposite to turbulence penetration into a stationary porous and permeable sediment bed. The information is applicable to water quality modeling mear the sediment/water interface of lakes, river impoundments and estuaries.     

Uptake and incorporation of mercury into mercury-binding proteins of gills of Mytilus edulis as a function of time

Individuals of Mytilus edulis (collected from Sequim Bay, Washington, in April and August, 1980) were exposed to 5 g l^-1 mercury as HgCl₂ for 28 d. Gill mercury accumulation, mercury incorporation into the soluble fraction and low molecular weight, mercury-binding proteins of gills, and induction of these mercury-binding proteins were determined as a function of time. Short-term mercury uptake rates of excised gills were also determined for mussels sampled at intervals during exposure. Gill mercury accumulation occurred in three phases, represented by net uptake phases initially (up to Day 4) and toward the end of the exposure (Days 15 to 28), and an intermediate stable phase (Days 4 to 15). The stable phase was associated with induction of the predominant mercury-binding proteins and mercury incorporation into the proteins. After Day 15, the mercury-binding proteins were saturated and spillover of mercury into high molecular weight proteins had occurred. This was associated with saturation of the soluble fraction, increases of mercury on particulate fractions, and a loss of the ability of gills to maintain stable mercury concentrations. Mercury uptake rates of gills were not affected by the 28 d exposure of the whole organism.     

Modelling forest management within a global vegetation model—Part 2: Model validation from a tree to a continental scale

The construction of a new forest management module (FMM) within the ORCHIDEE global vegetation model (GVM) allows a realistic simulation of biomass changes during the life cycle of a forest, which makes many biomass datasets suitable as validation data for the coupled ORCHIDEE-FM GVM. This study uses three datasets to validate ORCHIDEE-FM at different temporal and spatial scales: permanent monitoring plots, yield tables, and the French national inventory data. The last dataset has sufficient geospatial coverage to allow a novel type of validation: inventory plots can be used to produce continuous maps that can be compared to continuous simulations for regional trends in standing volumes and volume increments. ORCHIDEE-FM performs better than simple statistical models for stand-level variables, which include tree density, basal area, standing volume, average circumference and height, when management intensity and initial conditions are known: model efficiency is improved by an average of 0.11, and its average bias does not exceed 25%. The performance of the model is less satisfying for tree-level variables, including extreme circumferences, tree circumference distribution and competition indices, or when management and initial conditions are unknown. At the regional level, when climate forcing is accurate for precipitation, ORCHIDEE-FM is able to reproduce most productivity patterns in France, such as the local lows of needleleaves in the Parisian basin and of broadleaves in south-central France. The simulation of water stress effects on biomass in the Mediterranean region, however, remains problematic, as does the simulation of the wood increment for coniferous trees. These pitfalls pertain to the general ORCHIDEE model rather than to the FMM. Overall, with an average bias seldom exceeding 40%, the performance of ORCHIDEE-FM is deemed reliable to use it as a new modelling tool in the study of the effects of interactions between forest management and climate on biomass stocks of forests across a range of scales from plot to country.     

Diel patterns of carbon incorporation into biochemical constituents of Synechococcus spp. and larger algae in the Northwest Atlantic Ocean

Diel patterns of ¹⁴C-bicarbonate incorporation in>5 m algal communities were compared with those in cyanobacterial populations of Synechococcus spp. (0.6 to 1.0 m), collected from the surface and/or chlorophyll maximum at three stations in the Northwest Atlantic Ocean (a neritic front; in Warm-Core Eddy 84-E; and Wilkinson's Basin) from 21 July to 8 August, 1984. Cell constituents were chemically separated into four fractions: lipids, low molecular weight (LMW) metabolites, polysaccharides/nucleic acids, and proteins. The in situ diel pattern of ¹⁴C assimilation was virtually the same for >5 m algal communities adapted to different environments. Protein synthesis appeared to continue at a reduced rate at night using energy derived from the catabolism of polysaccharides and the mobilization of LMW compounds. Synechococcus spp. populations exhibited inherent physiological differences in their in situ diel pattern of carbon fixation from that in>5 m algal communities taken from the same water mass. There was no nighttime protein-synthesis in Synechococcus spp. The relative proportion of ¹⁴C-protein remained constant over night, while that of ¹⁴C-polysaccharides/nucleic acids declined and that of labelled LMW metabolites increased. Daytime light-intensity manipulations did not alter the diel pattern of carbon fixation in any of the>5 m algal assemblages, while changes in the carbon metabolism of surface and shadeadapted Synechococcus spp. populations could be rapidly induced by altering the light intensity.Bigelow Laboratory Contribution No. 86004     

不同人工林分枯落物和土壤持水能力研究

对大岭山林场尾叶桉、马占相思、黑木相思、厚荚相思、卷荚相思、杉木和马尾松林分的枯落物和土壤持水功能进行研究。结果表明,林地枯落物持水量的大小顺序为:马占相思林>杉木林>厚荚相思林>黑木相思林>尾叶桉林>马尾松林>卷荚相思林;土壤持水量大小则为:杉木林>厚荚相思林>卷荚相思林>马尾松林>尾叶桉林>马占相思林>黑木相思林。对于尾叶桉林来说,随着林分年龄的增加,其枯落物持水能力增加,但持水量降低。     

Energy use and animal abundance in litter and soil communities

Tools from metabolic scaling and food web theory were used to construct a general model of carbon flux by litter and soil invertebrates. The flux model was used to explore the energetic basis of invertebrate abundance and predicted that abundance should (1) scale linearly with net primary production; (2) be related to the body mass of animals as a power function, with an exponent between -0.65 and -0.85; (3) be related to the average body temperature of animals according to the Boltzmann factor, with an activation energy between 0.27 and 0.79 eV; and (4) decrease by a factor of 0.05 to 0.15 across trophic levels due to gross production efficiency of prey. Model predictions were generally supported by a global data set on invertebrate abundance that was amassed during the International Biological Programme, indicating that fundamental energetic principles explain a large degree of variation in invertebrate abundance across the globe.     

Using biochemical and isotopic tracers to characterise organic matter sources and their incorporation into estuarine food webs (Rufiji delta,Tanzania)

Fatty acid biomarkers and stable isotope signatures were used to identify the sources of particulate and sedimentary organic matter and its input into the food web through the dominant consumer within the mangrove-dominated Rufiji estuary, Tanzania. Specific fatty acids were used to identify the preferred basal sources of dominant fauna (i.e. filter feeder bivalves, snails, crabs, shrimps, and three fish species), and their presence in the water and sediment samples in the estuary. Both fatty acid and stable isotope results revealed that food web in the Rufiji estuary depended on a variety of carbon sources (mangroves, allochthonous terrestrial inputs, macroalgae, and phytoplankton), contributing to a different degree into the diets of primary consumers and members of near-shore fish, but none of them were obligatory for the survival of these species. The δ¹⁵N values of major primary producers and consumers/predators revealed a trend for δ¹⁵N enrichment with increasing trophic level. The ratio of docosahexaenoic acid to eicosapentaenoic acid (DHA:EPA) decreased from pelagic to benthic feeding fish. This indicated that fish with different feeding modes derived their fatty acids from different primary sources of nutrition, and suggested that the DHA:EPA ratio may be a useful indicator of feeding mode.     

Analysing the incorporation of sustainability themes into the university curricula: a case study of a Spanish public university

From an international view, several papers have analysed how sustainability themes are integrated into the university curricula. In Spain, few studies to date have examined the extent to which universities are incorporating sustainability themes into their curricula. In view of such considerations, this article examines the extent to which sustainability themes are being incorporated into the curricula of a Spanish public university strongly committed to signing sustainability policies and declarations. In addition, this study analyses the main barriers to the incorporation of sustainability themes into the curricula of this university. To accomplish this task, this article uses different methodological instruments over three phases through a case study approach. The findings of this study suggest how the university examined has many difficulties in incorporating, holistically or separately, sustainability themes in its formal courses despite having so many policies, regulations and a commitment to sustainability.     

Modelling and analysis of recruitment distributions

Recruitment data for 18 marine fish stocks are smoothed using 10 parametric families of probability distributions. Comparative fit of the 10 families is assessed by means of the maximized log-likelihood. Results indicate that the gamma distribution provides an overall good fit in the right-hand tail of the data, but that some adjustment to the gamma distribution is called for in the left-hand tail. Weight functions and weighted distributions are suggested as one means of achieving the needed adjustment.     

Diel variation of bacterial productivity in seagrass (Zostera capricorni) beds measured by rate of thymidine incorporation into DNA

Diurnal variations occurred in bacterial growth rates in the sediment and water column associated with seagrass (mainly Zostera capricorni Aschers) beds in Moreton Bay, Queensland, Australia. Studies were carried out in March and June 1981. Cell production rates increased by 5- to 10-fold during the morning and decreased during the afternoon. No nocturnal variation was observed. Daily bacterial cell production rate in the aerobic zones of the seagrass bed was estimated to be 43 mg C m^-2. A minimum of 100 mg C m^-2 d^-1 would be required to support the bacterial production. This represents about 10% of net primary production. The incorporation of tritiated thymidine into DNA was used to measure bacterial growth. The validity of the method is discussed.     

Collection and analysis of baseline vegetation data

Vegetation baseline studies are dependent on the use of an adequate classification of vegetation, which structures all further study. The reliable and careful execution of sampling techniques is as important as choosing a sound sampling scheme. In order for vegetation mapping to represent the vegetation accurately, significant community gradation and anomalous communities should be portrayed. Data analysis should distinguish between precision and accuracy, include an indication of the statistical reliability of estimates, and explain and interpret findings.