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Institute
Landscapes can be viewed as spatially heterogeneous areas encompassing terrestrial and aquatic domains. To date, most landscape carbon (C) fluxes have been estimated by accounting for terrestrial ecosystems, while aquatic ecosystems have been largely neglected. However, a robust assessment of C fluxes on the landscape scale requires the estimation of fluxes within and between both landscape components. Here, we compiled data from the literature on C fluxes across the air–water interface from various landscape components. We simulated C emissions and uptake for five different scenarios which represent a gradient of increasing spatial heterogeneity within a temperate young moraine landscape: (I) a homogeneous landscape with only cropland and large lakes; (II) separation of the terrestrial domain into cropland and forest; (III) further separation into cropland, forest, and grassland; (IV) additional division of the aquatic area into large lakes and peatlands; and (V) further separation of the aquatic area into large lakes, peatlands, running waters, and small water bodies These simulations suggest that C fluxes at the landscape scale might depend on spatial heterogeneity and landscape diversity, among other factors. When we consider spatial heterogeneity and diversity alone, small inland waters appear to play a pivotal and previously underestimated role in landscape greenhouse gas emissions that may be regarded as C hot spots. Approaches focusing on the landscape scale will also enable improved projections of ecosystems’ responses to perturbations, e.g., due to global change and anthropogenic activities, and evaluations of the specific role individual landscape components play in regional C fluxes. WIREs Water 2016, 3:601–617. doi: 10.1002/wat2.1147
Microcystins do not necessarily lower the sensitivity of Microcystis aeruginosa to tannic acid
(2016)
Different phytoplankton strains have been shown to possess varying sensitivities towards macrophyte allelochemicals, yet the reasons for this are largely unknown. To test whether microcystin (MC) is responsible for strain-specific sensitivities of Microcystis aeruginosa to macrophyte allelochemicals, we compared the sensitivity of 12 MC- and non-MC-producing M. aeruginosa strains, including an MC-deficient mutant and its wild type, to the polyphenolic allelochemical tannic acid (TA). Non-MC-producing strains showed a significantly higher sensitivity to TA than MC-producing strains, both in Chlorophyll a concentrations and quantum yields of photosystem II. In contrast, an MC-deficient mutant displayed a higher fitness against TA compared to its wild type. These results suggest that the resistance of M. aeruginosa to polyphenolic allelochemicals is not primarily related to MCs per se, but to other yet unknown protective mechanisms related to MCs.
The importance of ciliates as herbivores and in biogeochemical cycles is increasingly recognized. An opportunity to observe the potential consequences of zooplankton dominated by ciliates arose when winter fish kills resulted in strong suppression of crustaceans by young planktivorous fish in two shallow lakes. On an annual average, ciliates made up 38-76% of the total zooplankton biomass in both lakes during two subsequent years. Consequently, ciliate biomass and their estimated grazing potential were extremely high compared with other lakes of various trophic states and depths. Grazing estimates based on abundance and size suggest that ciliates should have cleared the water column of small (<5 mu m) and intermediate (5-50 mu m) sized phytoplankton more than once a day. Especially, small feeders within the ciliates were important, likely exerting a strong top-down control on small phytoplankton. Particle-attached bacteria were presumably strongly suppressed by intermediate-sized ciliate feeders. In contrast to other lakes, large phytoplankton was proportionately very abundant. The phytoplankton community had a high evenness, which may be attributed to the feeding by numerous fast growing and selective ciliate species. Our study highlights ciliates as an important trophic link and adds to the growing awareness of the role of winter processes for plankton dynamics.
Groundwater influx can significantly contribute to nutrient and carbon budgets of lakes, and its influence is the strongest in littoral areas dominated by macrophytes and periphyton. We have reviewed the effects of groundwater-borne nitrogen and phosphorus and dissolved inorganic and organic carbon (DIC, DOC) on these benthic primary producers in lakes. We develop a hypothesis for groundwater effects including the less studied impacts of periphyton shading on macrophytes. Groundwater-borne nutrients and DIC promote both macrophytes and periphyton. Direct studies on groundwater-borne DOC effects are lacking, but coloured DOC contributes to light attenuation and thus can restrict the growth of benthic primary producers. We predict that above certain threshold levels of nutrient influx by groundwater, periphyton and macrophyte biomass should decline owing to shading by phytoplankton and periphyton, respectively. However, because of their higher light requirements, those thresholds should be lower for macrophytes. For macrophytes, a threshold level is also predicted for a shift from DIC limitation to light limitation. Differences in light requirements are expected to result in lower thresholds of DOC loading for declines of macrophytes than periphyton.