摘要:

AbstractSinking terminal velocities ofD. middendorffiana(with and without tail spine) were measured and correlated with morphological parameters and water temperature. The main dimensions of the body showed positive growths rate correlations with the body weight. In turn, negative allometric variation was observed in the tail‐spine length. The density ofD. middendorffianawas age specific, and decreased as the individual grew. No differences in the sinking terminal velocities and trajectories between individuals with and without tail spine were observed. The observed hydrodynamic characteristics ofD. middendorffianawere simulated by means of a model based on equivalent ellipsoids and spheres. The analysis showed that the effects of shape and the body projections are negligible on the sinking rates ofD. middendorffian

ISSN:1434-2944    

DOI:10.1002/iroh.19980830402

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

ISSN:1434-2944    

DOI:10.1002/iroh.19980830403

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractAn analysis of plankton seasonal succession in large shallow eutrophic lake Võrtsjärv (270 km2, mean depth 2.8 m, max. depth 6 m) is presented. Weekly samples for 1995 have been analysed using the PEG model approach. In winter, light was the main factor controlling phytoplankton growth. In early spring phytoplankton was mainly resource‐controlled, competition for phosphorus being the main driving force. Ciliates (Paradileptussp.,Strobilidiumsp. andVorticellasp.) were the first herbivores which started to increase in April causing a twofold decline of phytoplankton biomass. The annual maximum of primary production (PP) in early May was probably caused by soluble reactive phosphorus (SRP), regenerated by herbivores, and stirred up from bottom sediments as a result of strong wind stress. This primary production peak provided substrate for further increase of bacterial biomass. The more abundant food supply supported the development of the second spring peak of herbivores (ciliates, rotifers, juvenile copepods) which was followed by the second modest “clear water phase” in late May. Silicon was depleted by the end of May causing a strong decrease in primary production of the diatom‐dominated community, whereas the biomass of the cyanophytes increased under the improved nutrient conditions. Some weeks later, inorganic N was depleted and the period of N limitation with the appearance of N‐fixing cyanophytes began. The ciliate collapse at the beginning of June coincided with the start of the cladoceran development and with the increase of other metazooplankton groups. This explains the further decrease of the biomass of phytoplankton and bacteria in spite of their high production. Beginning from late June, silicon appeared again and SRP started to occur periodically, while inorganic N remained close to zero until November. During this period, phytoplankton development relied to a great extent on the N‐fixation and N‐regeneration potential. The collapse of the ciliate community in September removed the top‐down control from bacteria and their biomass increased, while the development of cladocerans still suppressed phytoplankton biomass in spite of a quite high PP. In October phytoplankton biomass and chlorophylla(Chla) increased, SRP was completely depleted by the middle of October reflecting a slow regeneration due to the declined activity of zooplankton in cold water. In November nitrates appeared again, and silicon reached the same level as in spring. The biomass of N‐fixingAphanizomenon skujaedecreased whileLimnothrix redekeiandL. planctonicawere quite abundant to

ISSN:1434-2944    

DOI:10.1002/iroh.19980830404

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe growth and biochemical composition ofScenedesmus bijugatusgrown in normal and nutrient enriched Narendra Pond water was evaluated at different levels of salinity. In normal pond water (NPW) the growth was enhanced when the initial salinity of the water was doubled (to 7.2 mmol/l) but further salinity increase caused growth retardation. In nutrient enriched pond water (NEW), however, the maximum growth occurred in the culture containing 29 mmol/l of NaCl. At growth retarding salt concentrations the chlorophyll, carbohydrate, protein and lipid contents per cell decreased in both NPW and NEW while the proline content first increased and was then reduced. All nutrients, taken separately or in combination, caused growth enhancement of the alga at the three selected salinity levels. The alga showed a better halotolerance when enriched with nitrogen or phosphorus.

ISSN:1434-2944    

DOI:10.1002/iroh.19980830405

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractTwo‐hundred and fourty‐six freshwater and saline‐alkaline waters in Inner Mongolia, P.R. China were surveyed for Brachionidae. Twenty‐nine brachionid morphospecies (33 taxa) are recorded, four are new to China. Some data on their distribution, and comments on selected taxa are provided.Brachionus asplanchnoides(stat.nov.) is reinstated at the morphospecies level. We suggest that this taxon may be used in aquaculture, considering that, by its large size, it extends the size range of brackish‐water Rotifera potentially available as food for fi

ISSN:1434-2944    

DOI:10.1002/iroh.19980830406

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractTemporal and spatial changes of epibenthic macroinvertebrates (EMI) were described from a ten‐year (1985–1995) trawl study on the San Pedro Shelf, California. Community measures including number of species, individuals, biomass, dominance (DI), evenness (J'), and diversity (H' and SR) per trawl were computed for eight trawl stations representing four isobaths. Two reference stations and a test station (located at an ocean outfall) were featured in statistical analyses examining whether the outfall had any effect on EMI. During the ten‐year period 127,389 individuals provided 106 EMI taxa. Water depth was the most important factor affecting EMI composition. Although some statistically significant differences in EMI community measures among trawl stations were found. differences between the outfall and both reference stations were either insignificant or inconsistent, providing no obvious ecological impacts attributable to the ou

ISSN:1434-2944    

DOI:10.1002/iroh.19980830407

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractTo quantify bioturbation activity in Tikehau lagoon, a tracer made of black basaltic sand was poured over the natural white calcareous sediment surface. Three stations respectively located on the inner flat (‐3m), the inner slope (‐9m), and the lagoon floor (‐19m), were studied for short periods of time (48 hours). Bioturbation by macrofauna was quantified by volume of sediment ejected onto the experimental surface and by volume of tracer incorporated into sediment. The results showed a rapid incorporation of sedimented particles at the interface by way of the funnels and burrows of surface deposit feeders and carnivores. Expelled quantities varied with respect to site location: 213 cm3· m−2· 24 h−1in the inner flat; 98.9 cm3· m−2· 24 h−1in the inner slope; 7.9 m3· m−2· 24 h−1in the lagoon floor. Bioturbation by decapod megafauna appeared to be important in the dynamics of the sediments in the deepest areas of the lagoon. In these areas, with almost no hydrodynamical impacts on sediments, bioturbating events were responsible for sediment mixing (despite lower absolute rates than in shallow area). Hydrodynamics controlled the spatial distribution of macroinvertebrate trophic groups by its e

ISSN:1434-2944    

DOI:10.1002/iroh.19980830408

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

ISSN:1434-2944    

DOI:10.1002/iroh.19980830409

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe relation between environmental conditions and the species composition and individual abundance of crustaceans was investigated in a shallow alluvial aquifer, located in the Danube wetlands (Lobau, Austria). Samples, consisting of groundwater, sediment, and fauna, were taken from permanent installed wells by means of a piston pump five times in a year cycle.The results show that the spatial and temporal distribution, individual abundance, and species richness of crustacean fauna is related to hydrological conditions, oxygen concentrations, and geologic structures in the alluvial aquifer. Therefore, crustaceans, divided in stygoxene, stygophile, and stygobite species, can be used as bioindicators of these environmental conditions in an aquifer. It is suggested that beside physicochemical analyses also the crustacean fauna should be considered to characterise a groundwater ecosystem.

ISSN:1434-2944    

DOI:10.1002/iroh.19980830410

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

ISSN:1434-2944    

DOI:10.1002/iroh.19980830401

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY