Sulfate reduction and S-oxidation in a moorland pool sediment

In an oligotrophic moorland pool in The Netherlands, S cycling near the sediment/water boundary was investigated by measuring (1) SO₄ ^2– reduction rates in the sediment, (2) depletion of SO₄ ^2– in the overlying water column and (3) release of³⁵S from the sediment into the water column. Two locations differing in sediment type (highly organic and sandy) were compared, with respect to reduction rates and depletion of SO₄ ^2– in the overlying water.Sulfate reduction rates in sediments of an oligotrophic moorland pool were estimated by diagenetic modelling and whole core³⁵SO₄ ^2– injection. Rates of SO₄ ^2– consumption in the overlying water were estimated by changes in SO₄ ^2– concentration over time in in situ enclosures. Reduction rates ranged from 0.27–11.2 mmol m^–2 d^–1. Rates of SO₄ ^2– uptake from the enclosed water column varied from –0.5, –0.3 mmol m^–2 d^–1 (November) to 0.43–1.81 mmol m^–2 d^–1 (July, August and April). Maximum rates of oxidation to SO₄ ^2– in July 1990 estimated by combination of SO₄ ^2– reduction rates and rates of in situ SO₄ ^2– uptake in the enclosed water column were 10.3 and 10.5 mmol m^–2 d^–1 at an organic rich and at a sandy site respectively.Experiments with³⁵S^2– and³⁵SO₄ ^2– tracer suggested (1) a rapid formation of organically bound S from dissimilatory reduced SO₄ ^2– and (2) the presence of mainly non SO₄ ^2–-S derived from reduced S transported from the sediment into the overlying water. A³⁵S^2– tracer experiment showed that about 7% of³⁵S^2– injected at 1 cm depth in a sediment core was recovered in the overlying water column.Sulfate reduction rates in sediments with higher volumetric mass fraction of organic matter did not significantly differ from those in sediments with a lower mass fraction of organic matter.Corresponding author     

The Abundance of Different Peritrich Ciliates on Stone Surfaces in Contrasting Lowland Streams Throughout the Year

ABSTRACT. Pentrich ciliates attached to small stones from the beds of two streams, one large with hard water, the other small with soft water, were enumerated throughout an annual cycle. Throughout the year, Platycola was the dominant peritrich in both streams, except for a brief period during the spring when Vorticella and Carchesium predominated. Vorticella reached peak levels of 89 ciliates cm² of stone surface, and up to 102 Platycola per cm² of stone surface were found. Mean volumes of samples of the main species were calculated, and used to estimate the standing stock biomasses. using a standard value of dry weight per unit volume. Published values of the growth rates of representatives of the main genera were used to estimate production values, which totalled about 6.5 g dry weight of peritrich cytoplasm/m² of stream bed per annum in the large stream (mean annual density = 8.3 peritrichs/cm² of stone surface), and 33 g dry weight/m² of stream bed per annum in the small stream (mean annual density = 47 peritrichs/cm² of stone surface). Food supply, temperature and predation were the primary factors determining peritrich abundance     

Effects of planktivore abundance on chlorophyll-a and Secchi depth

We used two analyses to test the hypothesis that planktivore abundances contribute to the residual variations of Secchi depth or chlorophyll-a plotted with respect to mean summer epilimnetic total phosphorus. The first analysis involved 15 lake years of data from six lakes. The data set comprised mark-recapture assessments of piscivore and planktivore numbers and estimates of mean summer chlorophyll-a, total phosphorus and Secchi depth. We found that residual chlorophyll-a variation was not significantly (p>0.05) correlated with planktivore densities, but that planktivore densities did contribute (p<0.02) to the residual variation of Secchi depth on mean total phosphorus. The second analysis included all of the data used in the first plus an additional 13 lake years of data from the literature. These data showed that the percentage of the total fish community comprising planktivores did not significantly (p>0.05) contribute to the residual variation in chlorophyll-a with respect to mean summer total phosphorus. Together, our results suggest that planktivore abundance has a significant cascading impact on water clarity, but no long term statistically significant impact on mean summer chlorophyll-a concentration.     

Observations on Schizothrix mexicana Gomont (Cyanophyta) under culture conditions

Using agar gel électrophoresis, the number and relative mobility of seric protein fractions has been determined for twelve species of fishes belonging to the Elasmobranchii, Dipnoi and Actinopterygii.The study of relative mobilities has shown both similitudes and divergences between some of the proteinograms. Immunoelectrophoretic cross tests using the twelve sera and five antisera have shown that these similitudes did not result from protein homology and thus agar gel electrophoresis could not be used to determine phylogenetic relationships between the species considered.

Laboratoire d'Hydrobiologie et de Pisci culture, Université de Kinshasa (Zaïre)     

A study on biological activity measurements and heterotrophic bacteria in a small freshwater lake

A 6-m-deep lake has been sampled to measure the temporal and depth-wise distribution of heterotrophic bacteria and biological activity in the water. Surface, mid-depth and bottom waters were analysed at monthly intervals for a period of one year. The coefficient of heterotrophic activity, alkaline phosphatase activity and biological oxygen demand are used as an index of biological activity. The bacterial community was at maximum during spring, coinciding with high values of biological activity. Highest biological activity was observed in the bottom waters. Dissolved organic carbon showed a significant positive correlation with most of the biological activity parameters. This suggests that biological activity, as measured by the coefficient of heterotrophic activity, was more closely related to the concentration of substrates than to population density of heterotrophic bacteria.     

The ecology of the Turbellaria with special reference to the freshwater triclads

To attempt a complete review of turbellarian ecology in the time and space available would result in superficiality. Therefore, I have restricted this account to the four basic ecological processes which have and continue to determine flatworm distribution and abundance. These are: (1) historical or zoogeographical events which permit or prevent a species from reaching a habitat; (2) physiological limitations of the species vis à vis the habitat; (3) access to suitable energy sources and (4) the effects of competition, predation and parasitism, referred to collectively as bionomic processes.     

The freshwater calanoida (crustacea : copepoda) of Singapore and Peninsular Malaysia

The systematics and geographical distribution of Malaysian and Singapore freshwater calanoid copepods are discussed in details. Neodiaptomus handeli Brehm, N. laii Kiefer, N. blachei (Brehm), N. botulifer Kiefer, N. mephistopheles Brehm, Pseudodiaptomus (Schmackeria) dauglishi Sewell, P. (S.) tollingerae Sewell and Tropodiaptomus spp. Kiefer are all present in the northwestern part of the Peninsula. There are only 4 species, namely, N. handeli, N. botulifer, N. meggitti Kiefer and Tropodiaptomus sp. in the southern half of the Peninsula. The whole of the east coast also has 4 species, i.e. N. handeli, N. malaindosinensis (n.n.), P. (S.) tollingerae and one species of Tropodiaptomus. The only species that cut across a wide range of geographical barriers are N. handeli and Tropodiaptomus.     

Functional morphology of the caudal skeleton in teleostean fishes

The basic function of the caudal skeleton in teleostean fishes is to support the caudal fin, but its parts contribute to this function in somewhat different ways. The main axis for this support is the upturned terminal end of the vertebral column, which ends at the base of the uppermost principal rays. The uroneural struts just ahead of this axis provide support for it. The parts of the caudal skeleton behind and below this upturned axis, the hypurals and parhypural, not only support the caudal rays but also provide a means for differential movements between the upper and lower parts of the fin base. This basic caudal skeleton varies with the position of the fish in the sequence of teleosten evolution, the way in which the fish uses its caudal fin, and to some extent with the shape of the fin.