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Nutrient Recycling (nutrient + recycling)
Selected AbstractsA cross-system synthesis of consumer and nutrient resource control on producer biomassECOLOGY LETTERS, Issue 7 2008Daniel S. Gruner Abstract Nutrient availability and herbivory control the biomass of primary producer communities to varying degrees across ecosystems. Ecological theory, individual experiments in many different systems, and system-specific quantitative reviews have suggested that (i) bottom,up control is pervasive but top,down control is more influential in aquatic habitats relative to terrestrial systems and (ii) bottom,up and top,down forces are interdependent, with statistical interactions that synergize or dampen relative influences on producer biomass. We used simple dynamic models to review ecological mechanisms that generate independent vs. interactive responses of community-level biomass. We calibrated these mechanistic predictions with the metrics of factorial meta-analysis and tested their prevalence across freshwater, marine and terrestrial ecosystems with a comprehensive meta-analysis of 191 factorial manipulations of herbivores and nutrients. Our analysis showed that producer community biomass increased with fertilization across all systems, although increases were greatest in freshwater habitats. Herbivore removal generally increased producer biomass in both freshwater and marine systems, but effects were inconsistent on land. With the exception of marine temperate rocky reef systems that showed positive synergism of nutrient enrichment and herbivore removal, experimental studies showed limited support for statistical interactions between nutrient and herbivory treatments on producer biomass. Top,down control of herbivores, compensatory behaviour of multiple herbivore guilds, spatial and temporal heterogeneity of interactions, and herbivore-mediated nutrient recycling may lower the probability of consistent interactive effects on producer biomass. Continuing studies should expand the temporal and spatial scales of experiments, particularly in understudied terrestrial systems; broaden factorial designs to manipulate independently multiple producer resources (e.g. nitrogen, phosphorus, light), multiple herbivore taxa or guilds (e.g. vertebrates and invertebrates) and multiple trophic levels; and , in addition to measuring producer biomass , assess the responses of species diversity, community composition and nutrient status. [source] Effect of environmental variables on eukaryotic microbial community structure of land-fast Arctic sea iceENVIRONMENTAL MICROBIOLOGY, Issue 3 2010Brian Eddie Summary Sea ice microbial community structure affects carbon and nutrient cycling in polar seas, but its susceptibility to changing environmental conditions is not well understood. We studied the eukaryotic microbial community in sea ice cores recovered near Point Barrow, AK in May 2006 by documenting the composition of the community in relation to vertical depth within the cores, as well as light availability (mainly as variable snow cover) and nutrient concentrations. We applied a combination of epifluorescence microscopy, denaturing gradient gel electrophoresis and clone libraries of a section of the 18S rRNA gene in order to compare the community structure of the major eukaryotic microbial phylotypes in the ice. We find that the community composition of the sea ice is more affected by the depth horizon in the ice than by light availability, although there are significant differences in the abundance of some groups between light regimes. Epifluorescence microscopy shows a shift from predominantly heterotrophic life styles in the upper ice to autotrophy prevailing in the bottom ice. This is supported by the statistical analysis of the similarity between the samples based on the denaturing gradient gel electrophoresis banding patterns, which shows a clear difference between upper and lower ice sections with respect to phylotypes and their proportional abundance. Clone libraries constructed using diatom-specific primers confirm the high diversity of diatoms in the sea ice, and support the microscopic counts. Evidence of protistan grazing upon diatoms was also found in lower sections of the core, with implications for carbon and nutrient recycling in the ice. [source] Bioethanol from agricultural waste residuesENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 1 2008Pascale Champagne Abstract Under the Kyoto Protocol, the Government of Canada has committed to reducing its greenhouse gas emissions by 6% from 1990 levels between 2008 and 2012. Ethanol-blended gasolines have the potential to contribute significantly to these emission reductions. Ethanol is derived from biologically renewable resources and can be employed to replace octane enhancers and aromatic hydrocarbons or oxygenates. To date, the ethanol production industry in Canada is comprised mainly of small-scale plants producing ethanol primarily from agricultural crops as feedstock. Research interests in the area of bioethanol production from organic waste materials emerged in the late 1980. Significant advances in lignocellulosic material extraction and enzymatic hydrolysis have been reported in the last decade, however, continued research efforts are essential for the development of technically feasible and economically viable large-scale enzyme-based biomass-to-ethanol conversion processes. This research aims to develop and test an enzyme-based biomass-to-ethanol conversion process, which employs organic waste materials, such as livestock manures, as alternative sources of cellulosic material feedstock. The source of the livestock manure, manure management practices and cellulose extraction procedures have a significant impact on the quantity and quality of the cellulosic materials derived. As such, raw feedstock materials must be carefully characterized to assess the impact of these factors on the yield of bioethanol and residual end products. The success of cellulose-to-ethanol conversion processes for cellulose extracted from these waste materials as feedstock is generally a function of cellulose fiber pretreatment, enzyme selection and operating conditions. These will differ depending on the source of the waste material feedstock. The long-term benefits of this research will be to introduce a sustainable solid waste management strategy for a number of livestock manure and other lignocellulosic waste materials; contribute to the mitigation in greenhouse gases through sustained carbon and nutrient recycling; reduce the potential for water, air, and soil contamination associated with land disposal of organic waste materials; and to broaden the feedstock source of raw materials for the ethanol production industry. © 2007 American Institute of Chemical Engineers Environ Prog, 2008 [source] Bacterivorous grazers facilitate organic matter decomposition: a stoichiometric modeling approachFEMS MICROBIOLOGY ECOLOGY, Issue 2 2009Hao Wang Abstract There is widespread empirical evidence that protist grazing on bacteria reduces bacterial abundances but increases bacteria-mediated decomposition of organic matter. This paradox has been noted repeatedly in the microbiology literature but lacks a generally accepted mechanistic explanation. To explain this paradox quantitatively, we develop a bacteria-grazer model of organic matter decomposition that incorporates protozoa-driven nutrient recycling and stoichiometry. Unlike previous efforts, the current model includes explicit limitation, via Liebig's law of minimum, by two possible factors, nutrient and carbon densities, as well as their relative ratios in bacteria and grazers. Our model shows two principal results: (1) when the environment is carbon limiting, organic matter can always be decomposed completely, regardless of the presence/absence of grazers; (2) when the environment is nutrient (such as nitrogen) limiting, it is possible for organic matter to be completely decomposed in the presence, but not absence, of grazers. Grazers facilitate decomposition by releasing nutrients back into the environment, which would otherwise be limiting, while preying upon bacteria. Model analysis reveals that facilitation of organic matter decomposition by grazers is positively related to the stoichiometric difference between bacteria and grazers. In addition, we predict the existence of an optimal density range of introduced grazers, which maximally facilitate the decomposition of organic matter in a fixed time period. This optimal range reflects a trade-off between grazer-induced nutrient recycling and grazer-induced mortality of bacteria. [source] POSITIVE FEEDBACK AND THE DEVELOPMENT AND PERSISTENCE OF ECOSYSTEM DISRUPTIVE ALGAL BLOOMS,JOURNAL OF PHYCOLOGY, Issue 5 2006William G. Sunda Harmful algal blooms (HABs) have occurred with increasing frequency in recent years with eutrophication and other anthropogenic alterations of coastal ecosystems. Many of these blooms severely alter or degrade ecosystem function, and are referred to here as ecosystem disruptive algal blooms (EDABs). These blooms are often caused by toxic or unpalatable species that decrease grazing rates by planktonic and benthic herbivores, and thereby disrupt the transfer of nutrients and energy to higher trophic levels, and decrease nutrient recycling. Many factors, such as nutrient availability and herbivore grazing have been proposed to separately influence EDAB dynamics, but interactions among these factors have rarely been considered. Here we discuss positive feedback interactions among nutrient availability, herbivore grazing, and nutrient regeneration, which have the potential to substantially influence the dynamics of EDAB events. The positive feedbacks result from a reduction of grazing rates on EDAB species caused by toxicity or unpalatability of these algae, which promotes the proliferation of the EDAB species. The decreased rates also lower grazer-mediated recycling of nutrients and thereby decrease nutrient availability. Since many EDAB species are well-adapted to nutrient-stressed environments and many exhibit increased toxin production and toxicity under nutrient limitation, positive feedbacks are established which can greatly increase the rate of bloom development and the adverse effects on the ecosystem. An understanding of how these feedbacks interact with other regulating factors, such as benthic/pelagic nutrient coupling, physical forcing, and life cycles of EDAB species provides a substantial future challenge. [source] | ||||||||||