F. W. B. van den Brink

Growth and morphological responses of four helophyte species in an experimental water-depth gradient

Abstract The distribution on shorelines of four helophyte species (two gramineous species, viz. Phalaris arundinacea L. and Phragmites australis (Cav.) Trin. ex Steudel and two cyperacean species, viz. Scirpus maritimus L. and S. lacustris L.) was studied in relation to growth responses in the water-depth gradient. Stands of S. lacustris were found at lower depths relative to the mean water level (average fringe depth 69 ± 19 cm) than stands of Phragmites australis (av. 45 ± 20 cm), S. maritimus (av. 36 ± 8 cm) and Phalaris arundinacea (av. 25 ± 8 cm). The growth responses to a gradient of water depth were studied by planting the four species at five distinct water depths in outdoor basins, and determining morphological parameters and biomass distributions of the species grown for two consecutive years. The biomass of Phalaris arundinacea was reduced below 30 cm water depth, while Phragmites australis and S. maritimus showed reduced biomass at 80 cm water depth. S. lacustris showed no biomass reduction even at 80 cm water depth. An increased above-ground: below-ground biomass ratio in deeper water was demonstrated for each of the species under study; however, the modification of biomass distribution in the gramineous species occurred abruptly in very shallow water contrary to the cyperacean species. Mean basal stem diameter increased with water depth in all four species. Mean stem length increased with water depth in three of the four species. Stem elongation with increasing water depth was strongest in the cyperacean species. The gramineous species showed enhanced formation of adventitious roots at submerged nodes. The similarity of responses to water depth was greatest within each of the groups of gramineous and cyperacean species. The responses reflect the zonation of the species along the water-depth gradient: S. lacustris in relatively deep water, Phragmites australis and S. maritimus in shallower water, and Phalaris arundinacea in very shallow water.

Impact of hydrology on the chemistry and phytoplankton development in floodplain lakes along the Lower Rhine and Meuse

The impact of hydrology (floods, seepage) on the chemistry of water and sediment in floodplain lakes was studied by a multivariate analysis (PCA) of physico-chemical parameters in 100 lakes within the floodplains in the lower reaches of the rivers Rhine and Meuse. In addition, seasonal fluctuations in water chemistry and chlorophyll-a development in the main channel of the Lower Rhine and five floodplain lakes along a flooding gradient were monitored. The species composition of the summer phytoplankton in these lakes was studied as well.At present very high levels of chloride, sodium, sulphate, phosphate and nitrate are found in the main channels of the rivers Rhine and Meuse, resulting from industrial, agricultural and domestic sewage. Together with the actual concentrations of major ions and nutrients in the main channel, the annual flood duration determines the physico-chemistry of the floodplain lakes. The river water influences the water chemistry of these lakes not only via inundations, but also via seepage. A comparison of recent and historical chemical data shows an increase over the years in the levels of chloride both in the main channel of the Lower Rhine and in seepage lakes along this river. Levels of alkalinity in floodplain lakes showed an inverse relationship with annual flood duration, because sulphur retention and alkalinization occurred in seepage waters and rarely-flooded lakes. The input of large quantities of nutrients (N, P) from the main channel has resulted, especially in frequently flooded lakes, in an increase in algal biomass and a shift in phytoplankton composition from a diatom dominated community towards a community dominated by chlorophytes and cyanobacteria.

Ecological aspects, explosive range extension and impact of a mass invader, Corophium curvispinum Sars, 1895 (Crustacea: Amphipoda), in the Lower Rhine (The Netherlands)

A few years after it invaded, the amphipod Corophium curvispinum Sars appeared to be the most numerous macroinvertebrate species in the River Rhine. From 1987 to 1991 the densities of this species on the stones of groins in the Lower Rhine at a depth of 0.5 m increased from 2 to 200000 specimens per m2. In the Lower Rhine and its branches the densities of C. curvispinum increased with increasing current velocities and with increasing water depths. So far, a maximum population density of 750000 specimens per m2 has been found in the Lower Rhine, which is many times the densities recorded elsewhere. Population parameters, densities and distribution of C. curvispinum were studied in the Lower Rhine and its branches, using artificial substrates and sampling stones from groins. The success of this immigrant is related to its competitive strategy, which shows several aspects of a r-strategy. In addition, the heavily eutrophicated Lower Rhine provides abundant food (phytoplankton, suspended organic matter) for this opportunistic filter-feeder. The increased salinity and water temperatures in the Lower Rhine resulting from industrial discharges have contributed to the current success of this southern species originating in brackish waters. The very high densities of C. curvispinum might have an enormous impact on the river ecosystem by changing food webs.A few years after it invaded, the amphipod Corophium curvispinum Sars appeared to be the most numerous macroinvertebrate species in the River Rhine. From 1987 to 1991 the densities of this species on the stones of groins in the Lower Rhine at a depth of 0.5 m increased from 2 to 200000 specimens per m2. In the Lower Rhine and its branches the densities of C. curvispinum increased with increasing current velocities and with increasing water depths. So far, a maximum population density of 750000 specimens per m2 has been found in the Lower Rhine, which is many times the densities recorded elsewhere. Population parameters, densities and distribution of C. curvispinum were studied in the Lower Rhine and its branches, using artificial substrates and sampling stones from groins. The success of this immigrant is related to its competitive strategy, which shows several aspects of a r-strategy. In addition, the heavily eutrophicated Lower Rhine provides abundant food (phytoplankton, suspended organic matter) for this opportunistic filter-feeder. The increased salinity and water temperatures in the Lower Rhine resulting from industrial discharges have contributed to the current success of this southern species originating in brackish waters. The very high densities of C. curvispinum might have an enormous impact on the river ecosystem by changing food webs.

Growth and morphology of four freshwater macrophytes under the impact of the raised salinity level of the Lower Rhine

Abstract The growth and morphology of Potamogeton lucens L., Potamogeton perfoliatus L., Potamogeton nodosus Poir. and Ranunculus circinatus Sibth. were studied in relation to salinity. Plants were grown for 8 weeks in microcosms under ambient climatic conditions at (sodium) chloride concentrations which presently occur in the main channel of the Lower Rhine and its connected lakes (7.0 mmol l−1 Cl−), which have a poorly developed vegetation, and at concentrations which presently occur in infrequently flooded lakes (1.4 mmol l−1 Cl−1) within the floodplain of the Lower Rhine, which are rich in aquatic macrophytes. The sodium chloride level of the main channel negatively affected biomass production and growth rates for all three Potamogeton species, but not for R. circinatus. The reductions in biomass and growth rates of the Potamogeton species concurred with a decline in their leaf ratios, suggesting that the growth reduction might be related to a reduced leaf cell expansion. Root:shoot ratios increased in all selected species, whereas flowering decreased in response to higher salinity. The relevance of salinity as a stress factor is discussed in relation to the occurrence of these macrophytes in the Lower Rhine and its floodplain lakes.

Observations on the seasonal and yearly occurrence and the distribution ofAtyaephyra desmaresti (Millet, 1831) (Crustacea, Decapoda, Natantia) in The Netherlands

SummaryThe seasonal occurrence ofAtyaephyra desmaresti in The Netherlands has been studied by sampling the cooling-water filtering screens of power stations situated along the rivers Rhine and Meuse. The shrimps were only found in large numbers at the two power stations with vegetation in the cooling-water intake areas. Fluctuations in the seasonal occurrence showed great similarity for these two localities. Highest numbers of shrimps were impinged in November. High numbers also occurred in September, while a lower peak in numbers was found in May.Changes in the numbers of records during the last 30 years in The Netherlands were compared with climatological fluctuations (severe or mild winters), indicating that this mainly southern-European species is living here at the limits of its ecological and geographical range.The distribution in The Netherlands reveals thatAtyaephyra desmaresti mainly occurs in freshwater habitats, although it tolerates higher chlorinities.

IS THE MERCURY-INDUCED DECREASE OF THE Na+ AND Cl− CONCENTRATION IN THE BLOOD OF RAINBOW TROUT (SALMO GAIRDNERI) ATTRIBUTABLE TO A DECREASED ACETAZOLAMIDE-SENSITIVE ESTERASE (CARBONIC ANHYDRASE) ACTIVITY OF THE GILL EPITHELIAL CELLS?

Freshwater fish compensate for urinary and diffusional loss of Na+ and Cl − by independent uptake of these ions via the gills. Mercury compounds at sublethal concentrations in water cause significant decreases in the Na + and Cl − concentrations in the blood of rainbow trout. This chapter discusses whether the mercury-induced decrease of the Na + and Cl − concentration in the blood of rainbow trout is attributable to a decreased acetazolamide-sensitive esterase activity of the gills epithelial cells or to an increased osmotic water uptake by these organs. It is assumed that if carbonic anhydrase is inhibited, the reversible hydration of CO 2 will also be reduced resulting in fewer available counter ions for exchange with Na + and Cl − . Lethal but not sublethal concentrations of mercury affect the carbonic anhydrase activity of the gill epithelial cells and that of the red blood cells. Conversely, much lower mercury concentrations cause an increased permeability of the gills for water. It is concluded, therefore, that a change in the permeability characteristics of the cell membrane for water and possibly for ions rather than inhibition of carbonic anhydrase of the gills is the primary reason for the decreased Na + and Cl − concentrations in the blood of mercury treated trout.