Limnologica最新文献

Worldwide, the exacerbation of global warming has accelerated the growth of submerged macrophytes in wetlands, thereby substantiating the supply of labile substrates for carbon (CH₄ and CO₂) emissions. Nevertheless, limited studies have been conducted on carbon emission from tropical wetlands with submerged macrophytes. In the current study an attempt has been made to reveal the role of submerged macrophytes in influencing carbon flux from a natural wetland in the Indo-Burma Biodiversity hotspots. The submerged macrophytes colonising the shallow freshwater wetland of Keibul Lamjao comprise of Hydrilla verticillata, Ceratophyllum demersum, and Potamogeton crispus, with primary productivity at community level ranging between 20.72 and 152.53 g m^-2 d^-1 (mean, 95.6 ± 54.66 g m^-2 d^-1). This study gives a comparative analysis of the carbon gases (CH₄ and CO₂) emission in two distinct zones of the wetland: areas with profuse submerged macrophytic growth and water free of macrophytes. The mean CO₂ and CH₄ emissions from the zone with submerged macrophytes were 8362.64 ± 2935.57 and 227.90 ± 73.50 mg m^-2 d^-1, respectively, compared to 5558.07 ± 1222.05 and 149.72 ± 20.44 mg m^-2 d^-1 from those without macrophytes. The CO₂ and CH₄ emissions peak during the summer and wane in the following seasons, with minimum emissions occurring during the winter. It is apparent from the results that the generation of the gases in the wetland was temperature dependent, plus the macrophytic detritus availability. The carbon emissions were significantly correlated with the physicochemical properties of the water and the lake bottom sediment. A significantly positive correlation between carbon emission and dissolved organic carbon (DOC) and organic matter (OM) was established in the zone with macrophytes, thereby revealing that the growth of submerged macrophytes in the wetland enhances atmospheric carbon emissions.

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Negative interactions between macroconsumers and detritivores can influence organic matter processing in streams. We evaluated how the shrimp Macrobrachium potiuna affects the shredding activity and survival of larvae of Phylloicus major and Triplectides gracilis, two caddisfly species that build cases with leaf pieces and tree sticks, respectively. We also evaluated whether the shredding activity of the shrimp changes in the presence of potential prey. We hypothesized that (i) M. potiuna would constrain the rates of leaf consumption and FPOM production of P. major more than T. gracilis and (ii) the shredding activity of the shrimp would increase in the presence of larvae. Laboratory trials were carried out in feeding arenas containing one shrimp, three larvae of one caddisfly species, and leaf discs of Miconia chartacea as food. The visual and chemical stimuli from the shrimp did not change the rates of leaf consumption and FPOM production of either larva. However, when physical contact was allowed, the survival rate of P. major was 35.7 %, while all individuals of T. gracilis remained alive. The shredding activity of M. potiuna was low and observed only in the presence of P. major. These results suggest that although larvae of P. major are less protected against predation, M. potiuna does not constrain the activity of either shredder. Therefore, top-down effects of this macroconsumer on detritus-based food webs dominated by case-building caddisfly shredders are likely context dependent.

Noble crayfish (Astacus astacus) are endangered in many parts of Europe. Conservation efforts, including stocking measures, are widely conducted to safeguard the species and associated ecosystem functions. Due to limited availabilities of adult crayfish, juvenile noble crayfish are frequently released into lakes and rivers during autumn, usually without information on their fate and growth during the following winter. To investigate size- and density dependence of winter mortality and growth of newly stocked noble crayfish we conducted a mesocosm experiment in a small artificial lake in northern Germany. The experiment was carried out at water temperatures between 0.7 °C and 9.1 °C from mid-December until mid-March and simulated stocking densities of 20, 60, and 120 crayfish per square meter with unlimited food availability. Winter mortality rates were generally low and strongly size dependent. Specifically, a winter mortality rate of 9.2% was observed and crayfish with a total length (TL) above 34 mm all survived. The relative risk of mortality in dependence of TL increased by 41–94% (95% CI) with every decreasing centimetre of TL at the onset of winter. Increasing density had no effect on winter survival, but tended to reduce growth. Our work indicates that stocking measures of noble crayfish for conservation reasons can decrease costs and increase prospects of success if juveniles larger than 30 mm TL are used as stocking material.