Abstract:Energy (carbon) flows and element cycling are fundamental, interlinked principles explaining ecosystem processes. The element balance in components, interactions and processes in ecosystems (ecological stoichiometry; ES) has been used to study trophic dynamics and element cycling. This study extends ES beyond its usual limits of C, N, and P and examines the distribution and transfer of 48 elements in 16 components of a coastal ecosystem, using empirical and modeling approaches. Major differences in elemental c… Show more
“…microbial mats), as well as bacteria and fungi, may alleviate N and P shortage in the food web as a whole and contribute to a biomagnification of N and P at higher trophic levels, as described e.g. for the Baltic Sea ecosystem by Bradshaw et al (2012). Mangrove trees on Twin Cays also showed some degree of compensation for the different availability of nutrients through reabsorption of nutrients before leaf abscission .…”
Our study investigated the carbon:nitrogen:phosphorus (C:N:P) stoichiometry of mangrove island of the Mesoamerican Barrier Reef (Twin Cays, Belize). The C:N:P of abiotic and biotic components of this oligotrophic ecosystem was measured and served to build networks of nutrient flows for three distinct mangrove forest zones (tall seaward fringing forest, inland dwarf forests and a transitional zone). Between forest zones, the stoichiometry of primary producers, heterotrophs and abiotic components did not change significantly, but there was a significant difference in C:N:P, and C, N, and P biomass, between the functional groups mangrove trees, other primary producers, heterotrophs, and abiotic components. C:N:P decreased with increasing trophic level. Nutrient recycling in the food webs was highest for P, and high transfer efficiencies between trophic levels of P and N also indicated an overall shortage of these nutrients when compared to C. Heterotrophs were sometimes, but not always, limited by the same nutrient as the primary producers. Mangrove trees and the primary tree consumers were P limited, whereas the invertebrates consuming leaf litter and detritus were N limited. Most compartments were limited by P or N (not by C), and the relative depletion rate of food sources was fastest for P. P transfers thus constituted a bottleneck of nutrient transfer on Twin Cays. This is the first comprehensive ecosystem study of nutrient transfers in a mangrove ecosystem, illustrating some mechanisms (e.g. recycling rates, transfer efficiencies) which oligotrophic systems use in order to build up biomass and food webs spanning various trophic levels.
“…microbial mats), as well as bacteria and fungi, may alleviate N and P shortage in the food web as a whole and contribute to a biomagnification of N and P at higher trophic levels, as described e.g. for the Baltic Sea ecosystem by Bradshaw et al (2012). Mangrove trees on Twin Cays also showed some degree of compensation for the different availability of nutrients through reabsorption of nutrients before leaf abscission .…”
Our study investigated the carbon:nitrogen:phosphorus (C:N:P) stoichiometry of mangrove island of the Mesoamerican Barrier Reef (Twin Cays, Belize). The C:N:P of abiotic and biotic components of this oligotrophic ecosystem was measured and served to build networks of nutrient flows for three distinct mangrove forest zones (tall seaward fringing forest, inland dwarf forests and a transitional zone). Between forest zones, the stoichiometry of primary producers, heterotrophs and abiotic components did not change significantly, but there was a significant difference in C:N:P, and C, N, and P biomass, between the functional groups mangrove trees, other primary producers, heterotrophs, and abiotic components. C:N:P decreased with increasing trophic level. Nutrient recycling in the food webs was highest for P, and high transfer efficiencies between trophic levels of P and N also indicated an overall shortage of these nutrients when compared to C. Heterotrophs were sometimes, but not always, limited by the same nutrient as the primary producers. Mangrove trees and the primary tree consumers were P limited, whereas the invertebrates consuming leaf litter and detritus were N limited. Most compartments were limited by P or N (not by C), and the relative depletion rate of food sources was fastest for P. P transfers thus constituted a bottleneck of nutrient transfer on Twin Cays. This is the first comprehensive ecosystem study of nutrient transfers in a mangrove ecosystem, illustrating some mechanisms (e.g. recycling rates, transfer efficiencies) which oligotrophic systems use in order to build up biomass and food webs spanning various trophic levels.
“…The marine ecosystems at the site and other important site data are described in Aquilonius (2010), who summarizes site data such as hydrodynamics, chemical and physical characteristics, biota types and biomass, as well as quantification of ecosystem processes. Elemental transfers in this area have also been studied (Bradshaw et al 2012). Fig.…”
In safety assessments of underground radioactive waste repositories, understanding radionuclide fate in ecosystems is necessary to determine the impacts of potential releases. Here, the reliability of two mechanistic models (the compartmental K-model and the 3D dynamic D-model) in describing the fate of radionuclides released into a Baltic Sea bay is tested. Both are based on ecosystem models that simulate the cycling of organic matter (carbon). Radionuclide transfer is linked to adsorption and flows of carbon in food chains. Accumulation of Th-230, Cs-135, and Ni-59 in biological compartments was comparable between the models and site measurements despite differences in temporal resolution, biological state variables, and partition coefficients. Both models provided confidence limits for their modeled concentration ratios, an improvement over models that only estimate means. The D-model enables estimates at high spatio-temporal resolution. The K-model, being coarser but faster, allows estimates centuries ahead. Future developments could integrate the two models to take advantage of their respective strengths.Electronic supplementary materialThe online version of this article (doi:10.1007/s13280-013-0398-2) contains supplementary material, which is available to authorized users.
“…Persson et al, 2010). The degree of homeostasis has been shown to vary depending on whether elements are macronutrients, essential micronutrients, or non-essential elements (Karimi and Folt, 2006;Bradshaw et al, 2012). Organisms often take up the necessary amounts of trace elements from their food within the 'window of essentiality' (Hopkin, 1989) to ensure essential levels but avoid toxic concentrations in the body.…”
Section: Natural Variation In Element Compositionmentioning
confidence: 98%
“…For example, for autotrophs, extrapolation from environmental concentrations or ratios is probably more appropriate, whereas for heterotrophs, extrapolation within taxonomic groups may be more relevant (Karimi and Folt, 2006;White et al, 2012). Higher trophic levels may have a more similar elemental composition to their food than lower trophic levels, and stoichiometric ratios may shift between abiotic-biotic components and from primary producers to primary consumers (Bradshaw et al, 2012). In cases of homeostasis, element ratios will be constrained by the biology and ecology of the organism/ecosystem.…”
Section: Natural Variation In Element Compositionmentioning
confidence: 98%
“…Radionuclide or element concentrations in ecosystem components are normalised to their C content, i.e. element:C ratios are calculated, based on the assumption that many elements are stoichiometrically related to the carbon content because of their role in metabolism and structural components of the organism (Elser et al, 2000;Bradshaw et al, 2012). Ecosystem models based on carbon flows are thus constructed as the basis for radionuclide/element transfer models, using CR values based on Cnormalised element concentrations (Kumblad et al, 2006;Bradshaw et al, 2012;Konovalenko et al, 2014).…”
We will never have data to populate all of the potential radioecological modelling parameters required for wildlife assessments. Therefore, we need robust extrapolation approaches which allow us to make best use of our available knowledge. This paper reviews and, in some cases, develops, tests and validates some of the suggested extrapolation approaches. The concentration ratio (CRproduct-diet or CRwo-diet) is shown to be a generic (trans-species) parameter which should enable the more abundant data for farm animals to be applied to wild species. An allometric model for predicting the biological half-life of radionuclides in vertebrates is further tested and generally shown to perform acceptably. However, to fully exploit allometry we need to understand why some elements do not scale to expected values. For aquatic ecosystems, the relationship between log10(a) (a parameter from the allometric relationship for the organism-water concentration ratio) and log(Kd) presents a potential opportunity to estimate concentration ratios using Kd values. An alternative approach to the CRwo-media model proposed for estimating the transfer of radionuclides to freshwater fish is used to satisfactorily predict activity concentrations in fish of different species from three lakes. We recommend that this approach (REML modelling) be further investigated and developed for other radionuclides and across a wider range of organisms and ecosystems. Ecological stoichiometry shows potential as an extrapolation method in radioecology, either from one element to another or from one species to another. Although some of the approaches considered require further development and testing, we demonstrate the potential to significantly improve predictions of radionuclide transfer to wildlife by making better use of available data.
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