TOC fluctuations in a humic lake as related to catchment acidification, season and climate

Studies of fluctuations in total organic carbon (TOC) were performedin both the reference basin and the acidified basin of experimental LakeSkjervatjern, in order to separate effects of various catchment and in-lakeprocesses. Nearly five years of catchment acidification did not inducesignificant changes in TOC. TOC concentrations was not related clearly toprecipitation or runoff. In both basins, there was a regular, seasonal patternwith a gradual increase in TOC concentrations from spring to late autumn.Minima in concentrations occurred during periods with frozen ground inwinter, irrespective of discharge patterns. The decrease from 10 mg C l^-1 in autumn to 1--2 mg C l^-1 in latewinter, was only seen in surface layers. Runoff was the major loss routefor surface TOC in the lake. Photo-oxidation, bacterial oxidation, andsedimentation combined yielded maximum loss rates of 3%of surface TOC d^-1. Below a depth of 1 m 0.5%d^-1 was lost to these same processes. The surface microlayerhad 5--10 times more TOC than the bulk water on average, and could haveeffects on gas exchange and sub-surface light. Despite the oxidation ofTOC, the short residence time of the lake and rapid replacement of TOCfrom the catchment was the major determinant of lake water TOC.     

Effects of gravity and blood volume shifts on cardiogenic oscillations in respired gas.

During the cardiac cycle, cardiogenic oscillations of expired gas (x) concentrations (COS([x])) are generated. At the same time, there are heart-synchronous cardiogenic oscillations of airway flow (COS(flow)), where inflow occurs during systole. We hypothesized that both phenomena, although primarily generated by the heartbeat, would react differently to the cephalad blood shift caused by inflation of an anti-gravity (anti-G) suit and to changes in gravity. Twelve seated subjects performed a rebreathing-breath-holding-expiration maneuver with a gas mixture containing O2 and He at normal (1 G) and moderately increased gravity (2 G); an anti-G suit was inflated to 85 mmHg in each condition. When the anti-G suit was inflated, COS(flow) amplitude increased (P = 0.0028) at 1 G to 186% of the control value without inflation (1-G control) and at 2 G to 203% of the control value without inflation (2-G control). In contrast, the amplitude of COS of the concentration of the blood-soluble gas O2 (COS([O2/He])), an index of the differences in pulmonary perfusion between lung units, declined to 75% of the 1-G control value and to 74% of the 2-G control value (P = 0.0030). There were no significant changes in COS(flow) or COS([O2/He]) amplitudes with gravity. We conclude that the heart-synchronous mechanical agitation of the lungs, as expressed by COS(flow), is highly dependent on peripheral-to-central blood shifts. In contrast, COS([blood-soluble gas]) appears relatively independent of this mechanical agitation and seems to be determined mainly by differences in intrapulmonary perfusion.     

Inter‐ and intraspecific variation in body‐ and genome size in calanoid copepods from temperate and arctic waters

The tendency of ectotherms to get larger in the cold (Bergmann clines) has potentially great implications for individual performance and food web dynamics. The mechanistic drivers of this trend are not well understood, however. One fundamental question is to which extent variation in body size is attributed to variation in cell size, which again is related to genome size. In this study, we analyzed body and genome size in four species of marine calanoid copepods, Calanus finmarchicus, C. glacialis, C. hyperboreus and Paraeuchaeta norvegica, with populations from both south Norwegian fjords and the High Arctic. The Calanus species showed typical interspecific Bergmann clines, and we assessed whether they also displayed similar intraspecific variations—and if correlation between genome size and body size differed between species. There were considerable inter‐ as well as intraspecific variations in body size and genome size, with the northernmost populations having the largest values of both variables within each species. Positive intraspecific relationships suggest a functional link between body and genome size, although its adaptiveness has not been settled. Impact of additional drivers like phylogeny or specific adaptations, however, was suggested by striking divergences in body size – genome size ratios among species. Thus, C. glacialis and C. hyperboreus, had fairly similar genome size despite very different body size, while P. norvegica, of similar body size as C. hyperboreus, had the largest genome sizes ever recorded from copepods. The inter‐ and intraspecific latitudinal body size clines suggest that climate change may have major impact on body size composition of keystone species in marine planktonic food webs.     

A limnological investigation of the tarn Syslaktjønn, W Norway

An investigation covering hydrography, chemistry, vascular and cryptogamic plants, nitrogen fixation, phytoplankton biomass and production, and zooplankton was carried out from April to November 1976 in tarn in W Norway, The volume of the tarn was 18000 m³ and the turnover time about 30 d. Temperature ranged between 3.6 and 23.4°C and pH between 4.8 and 5.5. Nuphar luteum and Carex rostrata were the two dominating vasculars-with biomasses of 117 and 97 g m⁻², respectively The biomass of the bryophytes ( Sphagnum spp.) was about 510 g m⁻² and the production of the order 0.2–2.1 μg (mg d.w.)⁻¹h⁻¹. Nitrogen fixation in association with Sphagnum spp. was estimated at 25 g yr⁻¹ for the whole tarn. Phytoplankton was dominated by diatoms, green algae and chrysophyceans. The chlorophyll a content ranged from 2 to 20 mg m⁻³ and the carbon assimilation rates from 0.03 to 20 mg C m⁻³h⁻¹ at 0–4 m depths. Production in the period was of the magnitude 22 g C m⁻². The copepod Eudiaptomus gracilis was the most common netzooplankter. Large numbers of rotationrians were found during summer.     

TEMPERATURE-HUMIDITY “ORGAN” EXPERIMENTS WITH THREE SPECIES OF GRASSHOPPER BELONGING TO THE FAMILY OF ACRIDIDAE

Three ecologically well-differentiated species of grasshoppers were studied in a temperature-humidity organ. No statistically certain differences between the species were demonstrated.

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Zusammenfassung Drei ökologisch gut abgegrenzte Heuschreckenarten wurden untersucht. Die üblichen Methoden, an Hand derer man die Versuchsresultate der Temperatur-Feuchtigkeits-Orgel beurteilt, wurden kritisiert. Eine Arbeitsweise, statistisch analysierbare Werte zu erhalten, wird in dem vorliegenden Artikel aufgezeigt und angewandt. Zwischen den drei Arten wurden keine statistisch gesicherten Unterschiede erzielt. Die drei Arten zeigen nicht einmal eine Tendenz, sich in der Orgel auf eine Weise zu verteilen, die ihrere Verteilung im Verhältnis zum Temperaturfaktor in ihrer natürlichen Umgebung entspricht.

     

Morphogenesis of the hatching gland of Atlantic halibut (Hippoglossus hippoglossus)

Summary The halibut hatching gland (HG) cells are first observed as a cellular disc in front of the embryonic head around the midpoint of intra ovo development. The disc is subsequently transformed into a loop of increasing diameter as the HG cells migrate over the anterior part of the yolk sac. When the HG disc is transformed into a loop, the density of HG cells is highest at the migratory front. Some HG cells lag behind the migrating front at the early stages of HG development. At maturity, all cells are contained in a narrow belt which is about 10 cells wide. The HG belt structure consists of a monolayer of HG cells, and is maintained while the cells migrate between the two epidermal cell layers. Migration is halted about 2 days before normal hatching when the HG cells reach a destination at about a right angle to on the embryonic axis. Under the scanning electron microscope, the differentiating HG cells protrude as a ridge the yolk sac surface. The HG cells immunostain with antiserum to hatching enzyme when the HG is observed as a crescent structure around the embryonic head. By counting the number of immunostaining cells in composite photos of the entire yolk sac membrane, we found that the HG belt consists of approximately 2000 secretory cells at maturity. This cell number stays fairly constant throughout the period of HG cell migration. Accordingly, mitoses of the halibut HG cells have generally ceased prior to morphogenesis, and cytodifferentiation is already quite advanced when cell migration starts. Offprint requests to: J.V. Helvik     

Calcium limitation in Daphnia magna

The role of ambient calcium concentrations on survival, moulting,growth and egg production was assessed in the cladoceran Daphniamagna. A threshold for survival was found in the range 0.1–0.5mg Ca l^–1, even when ionic strength of the medium waskept constant. Accumulated length and length specific dry weightwas retarded at low Ca (0.5–1.0 mg Ca l^–1) at foodconcentrations above incipient limiting level. For lower foodlevels, the effect of Ca on growth was less clear. The effectof low Ca on growth rate was most manifest during the firstdays after hatching, reflecting the higher Ca demands of theearly juveniles. Age-specific egg production was strongly reducedat Ca concentrations <10 mg Ca l^–1. This was partlyan indirect effect of reduced growth rates, but could also bean effect of higher energetic costs associated with Ca uptakein a Ca-poor medium. The high Ca demands in D.magna may notbe representative of other Daphnia species. Nevertheless, highspecific Ca content seems to be a common property of Daphniaspp. and Ca deficiency could be a major determinant of speciessuccess and community structure among crustacean zooplankton;it also puts constraints on carbon sequestration in the pelagicfood web of softwater lakes.     

The post-glacial sediments of Øvre Heimdalsvatn

Two sediment cores, 143 cm and 268 cm in length, have been investigated. The oldest dating is 8240 ± 500 radiocarbon years B.P. The variation in the composition of the sediments is probably caused solely by climatic changes. The organic fraction is small, never exceeding 20%, reflecting the low primary production and rapid decomposition of allochthonous organic matter within the lake. The proportions of inorganic constituents indicate that the mineral fraction consists of clay and silt particles flushed into the lake from the drainage area.