Impact of biological activity on detritus transported in the lower river Rhine: an exercise in ecosystem analysis

SUMMARY. 1. Published data are used to construct a tentative carbon budget for the ecosystem of the lower river Rhine and its sedimentation areas in The Netherlands.
2. It is estimated that 287 × 10⁶kg Cy⁻¹ of particulate organic material is transported by the river Rhine, and 100 × 10⁶ kgCy⁻¹ of this material is deposited in the delta.
3. Phytoplankton and nitrifying bacteria seem to contribute significantly to the carbon budget, by producing c. 78 × 10⁶kgCy^−l.
4. The mineralization in the water (estimated from routine determinations of biological oxygen demand and from in situ diurnal fluctuations of oxygen) and in the bottom (estimated from the denitrification rates in the delta, from the production rate of methane and from overall oxygen consumption) is shown to degrade c. 50% of the carbon input plus autochthonous production.
5. The carbon budget and oxygen regime in the lower Rhine suggest that after decades of severe organic pollution the river has more or less resumed the normal, slightly heterotrophic state of a large lowland river.     

Growth Cycle-Dependent Overproduction and Accumulation of Protoporphyrin IX in Tetrahymena: Effect of Heavy Metals1

Cells of the ciliate Tetrahymena pyriformis GL overproduce and accumulate massive quantities of the heme intermediate, protoporphyrin IX. Protoporphyrin is localized intracellularly in discrete membranous compartments. The amount of porphyrin stored in the cell changes dramatically as cells progress through the growth cycle. Porphyrin overproduction is stimulated by δ-aminolevulinic acid, but only during the mid-stationary phase. Overproduction of protoporphyrin IX apparently results from an increase, late in the growth cycle, of activities subsequent to δ-aminolevulinic acid synthetase. Feedback inhibition in the pathway by accumulated protoporphyrin IX does not occur. The presence of Co²⁺ completely inhibits accumulation of protoporphyrin IX in a manner reversed by δ-aminolevulinic acid. Sn⁴⁺ stimulates protoporphyrin IX accumulation in the culture.     

Differences in the mating behaviour of the rat flea Nosopsyllus fasciatus (Bosc)

An account is given of differences in development at emergence in two strains of Nosopsyllus fasciatus, and of consequent differences in mating behaviour.     

TRIADs: a new class of proteins with a novel cysteine-rich signature.

Triad1 was recently identified as a nuclear RING finger protein, which is up-regulated during retinoic acid induced granulocytic differentiation of acute leukemia cells. Here we show that a cysteine-rich domain (C6HC), present in Triad1, is conserved in at least 24 proteins encoded by various eukaryotes. The C6HC consensus pattern C-x(4)-C-x(14-30)-C-x(1-4)-C-x(4)-C-x(2)-C-x(4)-H-x(4)-C defines this structure as the fourth family member of the zinc-binding RING, LIM, and LAP/PHD fingers. Strikingly, in 22 of 24 proteins the C6HC domain is flanked by two RING finger structures. We have termed the novel C6HC motif DRIL (double RING finger linked). The strong conservation of the larger tripartite TRIAD (two RING fingers and DRIL) structure indicates that the three subdomains are functionally linked and identifies a novel class of proteins.     

Eucalyptus leachate inhibits reproduction in a freshwater fish

1. Dissolved organic carbon (DOC) can induce lethal and sub‐lethal effects in exposed biota via hypoxic blackwater events and the toxicity of leached compounds. Little is known of how DOC exposure affects fish reproduction despite the fact that its release can coincide with spawning‐associated flow pulses. 2. River red gum (Eucalyptus camaldulensis) leaf leachate is a major source of DOC in Australian freshwaters and includes the toxic plant secondary metabolites polyphenols and tannins. High concentrations of leachate are released when leaves on floodplains or dry stream channels are inundated by water. 3. Southern pygmy perch (Nannoperca australis) from naturally high and naturally low Eucalyptus leachate environments in south‐east Australia were exposed to elevated leachate levels to investigate the effects of DOC on reproduction and to explore whether response patterns were consistent with populations becoming locally adapted to historical leachate levels. 4. Fish exposed to leachate were half as likely to reach sexual maturity as control fish. Fish from a naturally high‐exposure population tended to reach sexual maturity earlier than those from a naturally low‐exposure population. Leachate exposure had no effect on either egg size or fecundity. 5. Our results suggest that leachate‐exposed mothers did not reproduce because they were physiologically stressed or perceive the environment to be unsuitable, which raises the potential of plastic or adaptive responses to this stressor. The negative sub‐lethal effects observed have important fitness implications for individuals, the viability of populations and the management of environmental flows and riparian zones.     

Phosphorus inactivation in a eutrophic lake by the direct addition of ferric aluminium sulphate: impact on iron and phosphorus

SUMMARY.

• 1 Following addition of ferric aluminium sulphate (FAS) in February 1980 to a eutrophic lake, White Lough, Northern Ireland, the cycles of phosphorus (P) and iron (Fe) over 34 months were compared to those in the 18 months preceding the application.
• 2 During the summer of 1980, P release to the hypolimnion was reduced by 92% compared to 1979 but by 1982 had returned to pre-treatment levels. Phosphorus budget calculations for the post- treatment period indicated that P was accumulating in the sediment at a rate sufficient to permit the recovery of P release.
• 3 In the three summers following FAS addition, Fe released into the hypolimnion increased by 56–71% compared to 1979 but this increase represented less than 10% of Fe added in the FAS.
• 4 Prior to FAS treatment, hypolimnetic Fe and P were mixed throughout the lake at overturn, resulting in high winter concentrations, but after treatment, overturn was accompanied by large reductions in the lake Fe and P content due to precipitation. As a result, overwintering P concentrations in 1980/81 and 1981/82 were in the range 31–53μg P1^-1 compared to 111–194μg P1^-1in 1978/79 and 1979/80.
• 5 The reduction of hypolimnetic P release in 1980 and 1981 and lower overwintering P had little impact on summer epilimnetic P concentrations which for 1979–82 were 51, 36, 47 and 48μg P1^-1respectively. Phosphorus concentrations in the epilimnion were raised between April and June in each year by a release of P into the epilimnion. August and September was the only period when reductions in hypolimnetic P were reflected in lower P concentrations in the epilimnion.

     

An analysis of the total phosphorus cycle in some temperate lakes: the response to enrichment

• 1 Total phosphorus (TP) cycles were examined in seventeen lakes from the Scottish lowlands and Northern Ireland, which varied in annual mean TP from 17 to 192 μg Pl^-1.
• 2 It is clear from the data that the annual range of TP concentrations increases as the annual maximum TP increases. Although the annual minimum TP increases somewhat with increasing annual maxima, even enriched lakes show a pronounced TP minimum. As a result, the annual maximum values are highly correlated with the ranges and means, but less so with the annual minima.
• 3 The data are discussed in relation to a conceptual sine wave model and it is suggested that enrichment modulates the amplitude of the sine wave.
• 4 Mechanisms conditioning the maximum and minimum values are reviewed.

     

Soil and litter respiration in rainforests of contrasting nutrient status and physiognomic structure near Lake Eacham,north-east Queensland

Soil and litter respiration and nutrient concentrations (N, P, Ca, Mg and K) were measured in two adjacent rainforests near Lake Eacham on the Atherton Tableland in north-east Queensland. One forest had soil formed on basalt and, in physiognomic-structural classification of Webb (1968, 1978), was structurally complex. The other had soil formed on metamorphic rock and was structurally simple. Respiration was measured by the alkali trap method on 16 monthly occasions in 1986 and 1987. Soil and litter nutrient concentrations were higher in the complex forest (with the exception of soil N). The relative differences were greater for soil than litter and more pronounced for P and Ca (and also soil Mg) than other nutrients. Litter polyphenol concentrations were lower in the complex forest. Rates of litter respiration in the complex forest were, on average, nearly twice those of the simple forest. Soil respiration rates were occasionally slightly lower in the complex forest during the wet season but did not differ between the forests during the dry season. Highest rates of respiration were measured during the wet season although high rates for litter occasionally occurred during the dry season. Cumulative CO₂ release from the soil and overlying litter did not differ between forests and averaged 5134 ± 96 g CO₂ m^-2 per year (mean ± s.e.m.) (1400 g C m^-2 per year). Litter respiration accounted for 14% of the annual release in the complex forest and 11% in the simple forest. The association between site nutrient status and forest physiognomic structure at Lake Eacham represents a more general pattern in rainforests of north-east Queensland. Further study is needed to ascertain whether the results from this study apply more generally in both primary and secondary rainforests.