Filamentous, nitrogen-fixing cyanobacteria form extensive summer blooms in the Baltic Sea. Their ability to fix dissolved N2 allows cyanobacteria to circumvent the general summer nitrogen limitation, while also generating a supply of novel bioavailable nitrogen for the food web. However, the fate of the nitrogen fixed by cyanobacteria remains unresolved, as does its importance for secondary production in the Baltic Sea. Here, we synthesize recent experimental and field studies providing strong empirical evidence that cyanobacterial nitrogen is efficiently assimilated and transferred in Baltic food webs via two major pathways: directly by grazing on fresh or decaying cyanobacteria and indirectly through the uptake by other phytoplankton and microbes of bioavailable nitrogen exuded from cyanobacterial cells. This information is an essential step toward guiding nutrient management to minimize noxious blooms without overly reducing secondary production, and ultimately most probably fish production in the Baltic Sea. 相似文献
Allograft reactions of the sponge Hymeniacidon heliophila Parker, 1910 have been studied and quantified at the cellular level in vitro. Cell-layer assays were used to record the timing of rejection between allogeneic individuals and to investigate changes in the cellular subpopulations of primmorphs belonging to different individuals and placed in direct contact. The initial contact on both cell layers and primmorphs was followed by partial fusion and ended by their isolation with formation of a defined barrier but without marked collagen deposition. Using cytospins, cellular subpopulations from primmorphs were morphologically distinguished based on overall shape and on nuclear and cytoplasmic characteristics. In the beginning of the cultures up to 17 cell types could be recognized. Within 5 days, following reaggregation and primmorph formation, populations of eight of these types suffered marked reduction, whereas nine other cell types were either maintained or reduced at a slower pace. When submitted to allogeneic contact, the cellular dynamics of the four remaining types were altered. Surprisingly, the percentage of archeocytes is reduced, probably depleted by differentiation into other, differentiated cell populations. Cellular responses to allogeneic contact were characterized mainly by a transient increase in globoferous cells, a larger participation of presumed collagen-secreting cells, and by a remarkable expansion of the collencyte population. The collencyte population remained altered after the isolation of the individuals by a collagen barrier, and this can represent a mechanism of short-term immune memory.Communicated by O. Kinne, Oldendorf/Luhe 相似文献
A one year field study of four stations in the Gulf of Bothnia during 1991 showed that the biomass was ca. two times, and primary productivity ca. four times, lower in the north (Bothnian Bay) than in the south (Bothnian Sea) during the summer. Nutrient addition experiments indicated phosphorus limitation of phytoplankton in the Bothanian Bay and the coastal areas in the northern Bothnian Sea, but nitrogen limitation in the open Bothanian Sea. A positive correlation between the phosphate concentration and the production/biomass ratio of phytoplankton was demonstrated, which partly explained the differences in the specific growth rate of the phytoplankton during the summer. Differences in photosynthetic active radiation between the stations also showed a covariation with the primary productivity. The relative importance of nutrient or light limitation for photosynthetic carbon fixation could not, however, the conclusively determined from this study. Marked differences in phytoplankton species composition from north to south were also observed. The number of dominating species was higher in the Bothnian Sea than in the Bothnian Bay. The distribution of some species could be explained as due to nutrient availability (e.g. Nodularia spumigena, Aphanizomenon sp.), while salinity probably limits the distribution of some limnic as well as marine species. The potentially toxic phytoplankton N. spumigena, Dinophysis acuminata and Chrysochromulina spp. were common in the Bothnian Sea but not in the Bothnian Bay. The pico- and nanoplankton biomass during late summer was higher than previously reported due to a revised carbon/volume ratio. 相似文献
Natural biofilms were simultaneously grown on granite, polished granite, andesite, polycarbonate and Plexi-glass substrata for six weeks in the Tisza River. Biofilm production and abundance of algae were influenced by the substratum. Magnitude of the substratum effect was andesite相似文献
This paper analyzes the human–nature interaction in a village in rural South Africa. It discusses preconditions, perceptions,
and consequences of natural resource use, and places these findings into a regional and historical context. Applying an interdisciplinary
perspective, the study uses interviews, questionnaires, remote sensing, and participatory mapping to analyze land cover changes
and local perceptions of the environment. The study area is located in a former homeland (Transkei), a setting where well-recorded
conflicts in the human–nature sphere have previously been triggered by population pressure, apartheid policies, and other
historical, political, and social reasons. A small-scale and subjective conceptualization of environmental security is used
as an approach to analyze local livelihood strategies in a selected village. The results indicate that the environment is
not the highest priority in local survival strategies. Instead, formal and informal jobs and governmental grants are the most
important security strategies. There are thus no major conflicts resulting from the interaction between the local population
and the natural resources in this specific area. Explanations to this pattern can partly be found in historical contexts,
which include apartheid policies, re-localizations, and a system of migrant labor. The study also suggests that general truths
about a region such as Transkei might be misleading in specific localities. For relevant and successful environmental management
and development planning however, it is crucial that decision-makers be able to get a clear picture of local situations and
adjust their plans accordingly. 相似文献
This paper describes a ‘win–win’ discourse on local sustainable development and global climate change mitigation regarding Kachung, a Swedish–Norwegian climate forestry investment in Uganda certified under the Clean Development Mechanism (CDM). In many ways, this investment is a typical example of how private interests and capital accumulation are prioritised over local concerns in natural resource management under neoliberalism. This study, however, indicated that investors had genuine intentions of creating mutual benefits for the global environment and local people. Drawing on Li (2007), we show that this ‘will to improve’ was nevertheless constructed in ways that resulted in prioritisation of global climate change mitigation over local context-specific concerns.
We identify three core factors making the win–win discourse around Kachung plantation especially resilient: (i) the perceived urgency of climate change mitigation, (ii) the apolitical framing of ‘sustainability’ as an environmental issue that can be fixed through external technical interventions and (iii) the devaluation of local and context-specific knowledge. We end by suggesting that research on the neoliberalisation of nature focus more on analysing the rationales behind specific interventions. This would leave us better equipped to suggest how such interventions should be modified to produce true wins for local contexts. 相似文献
2,4,7,9-tetramethyl-5-decyne-4,7-diol (TMDD) is a high-production volume chemical used in paper, ink, pesticide, and adhesive industries as a wetting and anti-foaming agent. The physicochemical properties and slow biodegradation rate of TMDD indicate a low bioaccumulation potential but a high prevalence in the environment. As a consequence, TMDD has been detected in several European rivers in the nanogram per liter and lower microgram per liter range; however, its environmental risk to aquatic organisms is considered low. Recent studies almost exclusively focused on acute effects by TMDD, little is known about cytotoxic and genotoxic effects, reproduction and developmental toxicity, endocrine disruption, and any kind of long-term toxicity and carcinogenicity so far. The present study aims to provide more specific baseline information on the ecotoxicological effects of TMDD in fish. For this end, cyto- and genotoxicity assays were carried out in vitro with the permanent fish cell line RTL-W1; in addition, in vivo studies were conducted with the early life stages of zebrafish (Danio rerio) in order to fill the data gaps in developmental toxicity and endocrine disruption. TMDD showed a cytotoxic and slight genotoxic potential in fish cell lines; moreover, various sublethal and lethal effects could be detected in developing zebrafish embryos. There was no evidence of endocrine-disrupting effects by TMDD; however, mortality following prolonged exposure to TMDD during fish sexual development test was clearly higher than mortality in the fish embryo test after 96-h exposure. Our results thus confirmed previous findings of laboratory screening tests, suggesting short-term toxic effects of TMDD in the intermediate, and long-term effects in the lower milligram per liter range. 相似文献