The effect on water chemistry and phytoplankton of artificial inflow of the River Radovna into Lake Bled (Yugoslavia)

From September 1978 till October 1979 limnological investigations of Lake Bled, Slovenia, were carried out at monthly intervals. Vertical profiles of physical and chemical variables and phytoplankton were determined. The effect of artificial inflow from the River Radovna on the lake was studied. The results indicate that the lake is still very eutrophic. During summer stratification the Radovna's inflow positively affects those variables whose dynamics depend on the lake's anaerobic conditions.     

Studies on the tributaries of Char Lake,Cornwallis Island,Canada

As part of studies on the production of arctic Char Lake in Cornwallis Island, the inflow of organic matter carried annually by tributaries into the lake, was investigated. In late June tremendous avalanches of snow, stones and slush make accurate measurements impossible, but afterwards drift could be estimated with nets, and benthic samples were gathered with scoops. Published data on erosion of similar streams were used to estimate the quantity of organic matter carried into the lake during the spring spate. About 600 kg of organic matter passes down stream from the watershed. The passage of organic matter during the brief season of free water provides the chief source of food for the limited benthic fauna, dominated by Chironomidae-Diamesa and Orthocladinae- and Enchytraeidae. The flora is dominated by diatoms. The biomass of the fauna of those parts of the stream investigated, amounted to 2.54 g/m². Some ecological features of animals living in running water in this extreme habitat were studied.Contribution No. 253 from the CCIBP (Char Lake Project No. 22)Contribution No. 253 from the CCIBP (Char Lake Project No. 22)     

Importance of soil cover box area for the determination of N2O emissions from arable soils

To obtain nutrients mineralised from organic matter in the soil, plants have to respond to its heterogeneous distribution. We measured the timing of nitrogen uptake by wheat from a localised, ¹⁵N labelled organic residue in soil, as well as the timing of changes in root length density. We calculated the rates of N uptake per unit root length (inflows) for roots growing through the residue and for the whole root system. A stimulated local inflow appeared to be the main mechanism of exploitation of the residue N during the first five days of exploitation. 8% of the N that the plants would ultimately obtain from the residue was captured in this period. Roots then proliferated in the residue. This, together with a rapidly declining N inflow, contributed to the capture, over the next seven days, of 63% of the N that the plants derived from the residue. After that time, massive root proliferation occurred in the residue, but relatively little further N was captured.     

Echocardiographic evidence of concentric left ventricular enlargement in female weight lifters

In this study we investigated resting left ventricular structure and function in elite female weight-lifters. Fifteen National Squad members [mean age (SD) 25 (6) years] were compared to a recreationally active control group [n = 46, 23 (3) years]. Subjects were matched for body mass, body surface area and fat free mass, but the controls were slightly taller (P<0.01). Athletes and controls demonstrated similar resting heart rates and blood pressures. Septal wall (ST), posterior wall (PWT) and left ventricular internal dimension in diastole and systole (LVIDd and LVIDs, respectively) were measured from M-mode echocardiograms. Calculations were made for left ventricular mass (LVM), mass-volume ratio (m:V), wall-thickness-cavity dimension ratio (h:R) and systolic function. Left ventricular filling velocities were determined via Doppler echocardiography. ST [9.0 (1.1) v.s. 7.7 (1.0) mm] and PWT [8.7 (1.4) v.s. 7.5 (1.3) mm] were greater, whereas LVIDd [46.2 (2.8) v.s. 48.4 (3.4) mm] was smaller in the weight-lifters (P<0.05). After allometrically adjusting for differences in height, the weight-lifters had a greater ST, PWT and LVM (P<0.05) and similar LVIDd. Both m:V and h:R were increased in the weightlifters (P<0.05). All functional data were within normal limits and no group differences were observed. The female weight-lifters demonstrated a concentric left ventricular enlargement that was not detrimental to left ventricular performance at rest.     

Root proliferation,nitrate inflow and their carbon costs during nitrogen capture by competing plants in patchy soil

The responses of roots to nitrogen- and phosphorus-rich patches of soil include proliferation of laterals and stimulation of nutrient inflow (uptake rate per unit root length) within the patch. Nitrate uptake from an N-rich patch is thereby maximised and, perhaps, compensates for an uneven supply of nitrate to the whole root system. Paradoxically, the often weak correlation between root length density and N uptake found in experiments on single plants and crop monocultures suggests that root proliferation in patches has only a minor compensatory influence on N capture. This paradox was resolved when it was realised that localised root proliferation during inter-specific competition for nitrate can lead to a strong association between root length density and nitrate capture. Here, a simple model of inter-specific competition is used to estimate the stimulation in inflow required in one plant to match the N capture of a competitor that responds only by root proliferation, and to estimate associated carbon costs. The model predicts that nitrate inflow must increase proportionally more than root length density to achieve the same N capture. For example, the N capture possible with a 10% increase in root length density can be matched by increasing N inflow by anything from 20% to 20-fold, depending on the initial conditions: the faster the rate of change in root length density, the greater the required relative increase in inflow. In those terms, proliferation would seem the better option, but one that may be more costly in terms of its carbon requirement.     

Influence of Pulsed Inflows and Nutrient Loading on Zooplankton and Phytoplankton Community Structure and Biomass in Microcosm Experiments Using Estuarine Assemblages

Productivity and community structure of phytoplankton and zooplankton are influenced by hydrologic disturbances in many ways. In a recent modeling study it was suggested that pulsed inflows might enhance zooplankton performance, curb accumulation of phytoplankton accumulated biomass, and promote phytoplankton species diversity. We tested these predictions by performing microcosm experiments on natural plankton assemblages from the Nueces Delta, TX, USA. On three occasions (March, June, and September 2001), experiments of semi-continuous and flow-through design were conducted using natural plankton assemblages. We investigated the effect of two different inflow and nutrient loading regimes on zooplankton biomass, and phytoplankton biomass and diversity, i.e., continuous and pulsed inflows of 3 day frequency. Despite differences in initial community structure on these three occasions, as well as the very different communities that arose between experimental designs, our findings showed that pulsed inflows altered plankton dynamics. In all cases, pulsed inflows resulted in greater zooplankton biomass. In most cases, pulsed inflows resulted in lower phytoplankton biomass and higher diversity. We speculate that greater phytoplankton diversity in the pulsed flow treatments favored selectively feeding zooplankton, whose better performance prevented higher accumulation of phytoplankton biomass.     

Advanced hepatic tissue destruction in ablative cryosurgery: potentials of intermittent freezing and selective vascular inflow occlusion

Recent studies indicate that cryosurgery represents a promising approach to treat non-resectable liver tumors. To improve parenchymal tissue destruction, a variety of modifications of the freeze-thaw procedure have been suggested, including repetitive freezing and portal-triad cross-clamping. The aim of the present study was to analyze whether intermittent freezing by application of a double freeze-thaw procedure or selective vascular inflow occlusion are more effective than a single freeze-thaw cycle to achieve complete hepatic tissue destruction. Using a porcine model, intrahepatic cryolesions were induced by freezing the hepatic tissue for a total of 15 min (n=6, SF). Additional animals (n=6) underwent a double freeze-thaw cycle of 7.5 min each (DF). A third group of animals (n=6) was treated by a single 15-min freeze-thaw cycle during selective vascular inflow occlusion (VO-SF). Seven days after freezing, DF did not change the volume of the cryolesion (25.4+/-1.7 cm(3)) compared to SF (29.9+/-3.7 cm(3)), however, resulted in enhanced destruction of hepatocyte nuclear morphology (DF-score: 2.4+/-0.2 versus SF-score: 1.1+/-0.3; p<0.05) and attenuated leukocyte infiltration within the margin of the cryolesion (DF-score: 1.5+/-0.2 versus SF-score: 2.8+/-0.1; p<0.05). VO-SF was also effective to significantly enhance destruction of hepatocyte nuclear morphology (2.8+/-0.1; p<0.05 versus SF), but, additionally, markedly increased the volume of the cryolesions (43.3+/-5.3 cm(3); p<0.05 versus SF and DF). Interestingly, VO-SF further increased the number of apoptotic cells, while leukocyte infiltration (2.3+/-0.3) was not affected compared to that after SF-treatment. Thus, our data indicate that both DF and VO-SF are effective to enhance parenchymal cell destruction within the margin of the cryolesion. VO-SF additionally increases the volume of the lesion and may therefore be most attractive for successful clinical application.     

Hedgehog signalling controls sinoatrial node development and atrioventricular cushion formation

Smoothened is a key receptor of the hedgehog pathway, but the roles of Smoothened in cardiac development remain incompletely understood. In this study, we found that the conditional knockout of Smoothened from the mesoderm impaired the development of the venous pole of the heart and resulted in hypoplasia of the atrium/inflow tract (IFT) and a low heart rate. The blockage of Smoothened led to reduced expression of genes critical for sinoatrial node (SAN) development in the IFT. In a cardiac cell culture model, we identified a Gli2–Tbx5–Hcn4 pathway that controls SAN development. In the mutant embryos, the endocardial-to-mesenchymal transition (EndMT) in the atrioventricular cushion failed, and Bmp signalling was downregulated. The addition of Bmp2 rescued the EndMT in mutant explant cultures. Furthermore, we analysed Gli2⁺ scRNAseq and Tbx5^−/− RNAseq data and explored the potential genes downstream of hedgehog signalling in posterior second heart field derivatives. In conclusion, our study reveals that Smoothened-mediated hedgehog signalling controls posterior cardiac progenitor commitment, which suggests that the mutation of Smoothened might be involved in the aetiology of congenital heart diseases related to the cardiac conduction system and heart valves.