Determining the carbon-to-chlorophyll ratio of natural phytoplankton

For field samples, regression analyses of plots of chemically determined particulate organic carbon on chlorophyll are often employed to estimate the algal carbon-to-chlorophyll ratio (F) in the presence of appreciable amounts of nonalgal particulate organic carbon. Spurious results will be obtained, however, if the temporal rate of change of the algae or the nonplant matter reverses its sign during the sampling interval and the samples cannot be ordered correctly in time or space. Previously recognized sources of bias inherent in the chemical approach are also discussed. The great uncertainty of our present knowledge of F is pointed out. It is shown that the concentration of microscopically visible, nonliving particles in the sea isnot known. Renewed studies are suggested as a means of improving on the chemical approach to determining F. The general argument holds for the ratios of nitrogen (particle volume, etc.)-to-chlorophyll, carbon (nitrogen, particle volume, etc.)-to-ATP, and similar conversion factors.Contribution No. 932 from the Department of Oceanography, University of Washington, Seattle, Washington 98195, USA. The article is a revised and expanded version of a paper contributed at the Joint Oceanographic Assembly, September 1976, at Edinburgh, Scotland, UK.     

Environmental prevalence,fate, impacts,and mitigation of microplastics—a critical review on present understanding and future research scope

Environmental Science and Pollution Research - Microplastics are considered to be ubiquitous and widespread emerging contaminants. They are persistent in the nature and pose considerable harm to...     

Modelling episodic acidification of surface waters: the state of science

Field studies of chemical changes in surface waters associated with rainfall and snowmelt events have provided evidence of episodic acidification of lakes and streams in Europe and North America. Modelling these chemical changes is particularly challenging because of the variability associated with hydrological transport and chemical transformation processes in catchments. This paper provides a review of mathematical models that have been applied to the problem of episodic acidification. Several empirical approaches, including regression models, mixing models and time series models, support a strong hydrological interpretation of episodic acidification. Regional application of several models has suggested that acidic episodes (in which the acid neutralizing capacity becomes negative) are relatively common in surface waters in several regions of the US that receive acid deposition. Results from physically based models have suggested a lack of understanding of hydrological flowpaths, hydraulic residence times and biogeochemical reactions, particularly those involving aluminum. The ability to better predict episodic chemical responses of surface waters is thus dependent upon elucidation of these and other physical and chemical processes.     

Chlorinated hydrocarbon contaminants in Hong Kong surficial sediments.

Twenty surficial sediments were sampled from nearshore Hong Kong waters during 1997-1998, and analyzed for a range of chlorinated pesticides and polychlorinated biphenyls (PCBs). Results showed that concentrations (on a dry weight basis) of total HCHs were in the range 0.1-16.7 ng g-1, and total DDTs 0.3-14.8 ng g-1. PCBs, measured as an Aroclor 1242, 1248, 1254, 1260 (1:1:1:1) mixture, were found to be in a range of 0.5-97.9 ng g-1, and were at highest concentrations in Victoria Harbour. Results indicated that chlorinated pesticides and PCBs in Hong Kong nearshore sediments were most likely derived from waste discharge from a variety of sources, including agricultural, sewage, industrial waste disposal and shipping-related activities. In addition, as the north and west sides of Hong Kong are subject to influence from the Pearl River (due mainly to agricultural activities in the Pearl River Delta, and to a lesser extent developments around the Shenzhen Special Economic Zone), these inputs are also thought to be likely sources of contamination.     

Bioavailability of persistent organic pollutants in soils and sediments--a perspective on mechanisms, consequences and assessment

It has been observed that as soil-pollutant contact time increases, pollutant bioavailability and extractability decreases. This phenomenon has been termed 'ageing'. Decreased chemical extractability with increased soil-chemical contact time is evident where both 'harsh' techniques, e.g. dichloromethane Soxhlet extraction, and 'non-exhaustive' techniques, e.g. butanol shake extraction, have been used. It has also been observed that the amount of chemical extracted by these techniques varies considerably over time. Similarly, decreases in bioavailability with increased soil-pollutant contact time have been described in bacterial, earthworm and other organism studies. From these investigations, it has been shown that the fraction of pollutant determined to be bioavailable can vary between organisms. Thus, there is an immediate definition problem, what is bioavailability? Additionally, if bioavailability is to be assessed by a chemical means, which organisms should (or can) be mimicked by the extraction procedure? This review provides a background to the processes inherent to ageing, a discussion of its consequences on bioavailability and ends with some reflections on the appropriateness of chemical extraction techniques to mimic bioavailability     

Mycotoxins of Aspergillus fumigatus in pure culture and in native bioaerosols from compost facilities

Exposure to secondary metabolites of airborne fungi in waste handling facilities is discussed in regard to potential toxic impacts on human health. The relevance of mycotoxins has been intensely studied in connection with contamination of food and feed. Toxic secondary metabolites are expected to be present in airborne spores, but exposure to mycotoxins in bioaerosols has not been studied sufficiently. Aspergillus fumigatus is one of the most frequent species in the air of compost plants. A wide range of secondary metabolites was found in pure cultures of freshly isolated strains of A. fumigatus. Tryptoquivaline, a compound with tremorgenic properties, and trypacidin, for which no toxic properties are described, were found in native bioaerosols in a compost facility. The highly toxic metabolites gliotoxin and verruculogen were not found in the bioaerosols.     

Evaluating unintended consequences of intentional species introductions and eradications for improved conservation management

Increasingly intensive strategies to maintain biodiversity and ecosystem function are being deployed in response to global anthropogenic threats, including intentionally introducing and eradicating species via assisted migration, rewilding, biological control, invasive species eradications, and gene drives. These actions are highly contentious because of their potential for unintended consequences. We conducted a global literature review of these conservation actions to quantify how often unintended outcomes occur and to elucidate their underlying causes. To evaluate conservation outcomes, we developed a community assessment framework for systematically mapping the range of possible interaction types for 111 case studies. Applying this tool, we quantified the number of interaction types considered in each study and documented the nature and strength of intended and unintended outcomes. Intended outcomes were reported in 51% of cases, a combination of intended outcomes and unintended outcomes in 26%, and strictly unintended outcomes in 10%. Hence, unintended outcomes were reported in 36% of all cases evaluated. In evaluating overall conservations outcomes (weighing intended vs. unintended effects), some unintended effects were fairly innocuous relative to the conservation objective, whereas others resulted in serious unintended consequences in recipient communities. Studies that assessed a greater number of community interactions with the target species reported unintended outcomes more often, suggesting that unintended consequences may be underreported due to insufficient vetting. Most reported unintended outcomes arose from direct effects (68%) or simple density-mediated or indirect effects (25%) linked to the target species. Only a few documented cases arose from more complex interaction pathways (7%). Therefore, most unintended outcomes involved simple interactions that could be predicted and mitigated through more formal vetting. Our community assessment framework provides a tool for screening future conservation actions by mapping the recipient community interaction web to identify and mitigate unintended outcomes from intentional species introductions and eradications for conservation.