Macroinvertebrates in the Demmerik ditches (The Netherlands): The role of environmental structure

The relation between the different microhabitats and habitats and the quantitative distribution of macroinvertebrates was investigated as well as the applicability of different sampling devices. Data processing took place by means of multivariate analysis (Flexclus, Canoco). It was concluded that the spatial-physical structure is more important to macroinvertebrates than the plant species. In fact, this spatial physical structure can be indicated as the mesh size of a (micro-)habitat. In order from open vegetation, shore/dense vegetation, artificial substrate, bottom material, and filamentous algae the mesh size decresed. It is advisable to use different sampling devices to sample a macroinvertebrate community.     

Fossil spores of Zygnemataceae in ditches of a pre-historic settlement in Hoogkarspel (The Netherlands)

A palynological investigation of the ditch-fill from a Bronze-Age settlement gave a negative result with regards to pollen. However, from observations of zygospores (or possibly aplanospores) of Zygnemataceae (Algae) it is possible to gain an impression of the prevailing conditions in these drainage ditches at the time of their use. Since such zygospores have until now been unjustifiably ignored by palynologists, it seemed expedient to the author to describe and show photographs of these microfossils.     

The application of algal growth potential tests (AGP) to the canals and lakes of western Netherlands

Four hundred and forty bioassays with Scenedesmus quadricauda (Turp.) Bréb. as a test organism have been carried out with samples from canals and lakes in the western part of the Netherlands. The results are used to assess the algal growth potential (AGP) and to determine the limiting nutrient(s) for maximum biomass production. Special attention has been paid to the effects of deep-freezing and autoclaving as pretreatment of water samples on pH and nutrient concentrations.The AGP ranged from very low in the relatively isolated polder lakes to very high in canals and lakes, which form part of the basin system of Rijnland. The lowest yields are observed in nitrogen and phosphorus co-limited waters, while the highest are found in waters limited by nitrogen alone. AGP proved to be primarily determined by the amount of nitrogen, especially nitrate, in the samples and only secondarily by the amount of phosphorus.The observed ranges indicating phosphorus limitation, > 50 for inorganic and > 30 for total N/P ratios, lie considerably higher than reported so far. It is concluded that, once the relations between AGP and nutrients are established, AGP tests do not have to be carried out routinely, but still can be very useful in special studies, e.g. in lake restoration projects.     

Diatoms and water quality in lowland streams in the province of northern Brabant (The Netherlands)

Summary The diatoms of two Dutch lowland streams were studied. The stream Beerze is heavily polluted by the effluent of a sewage treatment plant, causing a change in the pH from less than 4 to more than 6. The acidobiontic diatomEunotia exigua is replaced by more alkaline and eutraphentic species such asGomphonema parvulum, Cyclotelia meneghiniana andFragilaria capucina. The Simpson diversity index rises from 0.2 in the upper course to 0.9 in the middle course and maintains this level in the lower course.From stream Rosep samples of 1919–1930 and recent ones were studied. This stream is polluted now by agriculture. In the earlier samples oligo-mesotraphentic species dominated (Eunotia spp.,Melosira distans). In 1976 the species of organically polluted waters were most abundant. The oligo-mesotraphentic species were hardly recovered.In spite of the severe pollution the number of rare species in both streams is still high, compared with that in stagnant waters. Only in mesotrophic moorland pools and mesotrophic quivering bogs, which are situated in trophic gradients just like both streams, a comparable number of rare species may be found.     

Effects of laundry wastewater on benthic algae in ditches in the Netherlands

Summary A modified, artificial substrate method was used to study the effects of laundry wastewater on benthic algae in a polder in the western part of the Netherlands. In a polluted ditch a clear chemical gradient was found with regard to the parameters conductivity, B.O.D., C.O.D., NH₄, ortho-P, total-P and Cl, showing decreasing values with increasing distance from the polluting source. pH and oxygen values showed the opposite. Algae, such asEuglena viridis, Nitzschia palea andOscillatoria spp. were positively correlated with the amount of pollution, while others, such asChrysochaete brittannica, Chrysophaera gallica, Cocconeis placentula andSynedra ulna showed a negative correlation with the amount of pollution. The results of algal counts are evaluated by means of diffenent methods,e.g. similarity coefficients, species abundance curves, diversity and saprobity indices. In different seasons benthic algal biomass proved to be a good indicator of pollution, except very close to the polluting source. The role of algal periodicity, influencing species composition, diversity and saprobity values, and biomass growth, has been discussed. The need of revising the saprobity system for stagnant ditches in the Netherlands, using artificial substrates, has been stressed.     

Perinatal mortality in Utrecht, The Netherlands, 1880–1940

The secular trend of perinatal mortality in Utrecht between 1880 and 1940 and its causes are examined in this study, based on patient records of two maternity clinics, those of the city's academic hospital, and of its outpatient clinic. The sample includes 17,111 deliveries. Over the period the proportion of births in the city occurring in the two institutions rose from 3 to 90%. The perinatal mortality rate in the hospital declined and then rose slightly at the end of the 19th century, but remained constant, even if cyclical, thereafter in both the hospital and the outpatient clinic. Rates differed substantially between the two maternity services. Logistic regression analysis reveals a cluster of factors related to perinatal death. Low birth weight had a powerful association with perinatal mortality in both samples. Most of the other factors associated with perinatal mortality were related to the health of the patients, to obstetric problems related to deliveries, and to infant sex and maternal age. Relationships between perinatal mortality and other measures of human welfare in The Netherlands are explored.     

Vegetation history and agriculture in the cover-sand area west of Breda (province of Noord-Brabant, The Netherlands)

Botanical investigation of archaeological sites situated in the northwest of the region bounded by the rivers Maas, Scheldt and Demer (‘MSD region’), west of the city of Breda, has provided a great deal of evidence about the landscape and its use in the period between 2000 b.c. and a.d. 1500. From pollen analysis, it appears that this cover-sand area gradually lost its woodlands through human activity after the beginning of the Bronze Age (ca. 2000 b.c.). Patches of woodland did survive there, however, until the early Middle Ages. In contrast to the cover-sand area in the vicinity of ’s-Hertogenbosch and Oss-Ussen in the northeast of the MSD region, the first large heathlands in the Breda area did not evolve until the early Middle Ages. In late prehistory, land use in this area was not much different from that in the micro-region of ’s-Hertogenbosch and Oss-Ussen. In the Bronze Age, Hordeum vulgare ssp. vulgare (hulled six-row barley) and Triticum dicoccon (emmer wheat) were grown. During the Iron Age, Panicum miliaceum (common millet) and T. spelta (spelt wheat) were introduced, but these crops disappeared during the Roman period. The Roman period is remarkable because of the lack of any Mediterranean culinary herbs or exotic fruits. Only pollen of Juglans regia (walnut), found around the transition from the Roman period to the early Middle Ages, indicates the introduction of an exotic tree into the region. From the early Middle Ages onwards, Secale cereale (rye) was the most important cereal, which was grown as a winter crop. In the course of the Middle Ages, arable weeds of the Sclerantho annui-Arnoseridetum plant community appeared, which is associated with the continuous growing of rye.     

Dominant diatoms in Tjeukemeer (The Netherlands)

A situation is described where silicon depletion affected a population of diatoms, mainly Diatoma elongatum and Melosira spp., in the shallow lake Tjeukemeer (The Netherlands). After Si-deficiency the numbers of cells dropped quickly, whereas at least for the upper layer (0–1 m) a big increase in the percentage of biprotoplastic D. elongatum cells was observed. Probably the major part of the D. elongatum population arrived alive at the bottom. Heavy winds occurring 2 weeks later stirred up considerable numbers of both diatoms. The numbers of dead D. elongatum cells was then 40–50%, presenting some evidence that a large scale dying of D. elongatum cells occurs rather shortly after arrival at the bottom of Tjeukemeer. In the following weeks, at low Si-concentration, numbers of D. elongatum almost doubled with once again a relatively high percentage of biprotoplastic cells, whereas numbers of Melosira spp. decreased. In the relevant conditions it seems that D. elongatum can take up silicon faster than Melosira spp.     

Synuraceae (Chrysophyceae) in the Netherlands

Summary Investigations of phytoplankton biomass development and species succession in the Oude Waal near Nijmegen revealed the importance of the Chrysophyceae (Table I).Submicroscopical structures of the Chrysophyceae are known to be species-specific. So electronmicroscopical observations have been introduced into the research program. Special attention has been paid to the (scale-bearing) Synuraceae. The analysis of weekly taken samples in the year 1979 revealed a typical temporal distribution pattern of the Synuraceae, mainly controlled by temperature. Particulary the genusSynura showed a succession of four species:S. uvella dominated at water temperatures from 10–14°C,S. glabra from 14–16°C,S. curtispina from 10–19°C andS. petersenii occurred at water temperatures ranging from 0–21°C.     

Biological Assessment of the Water Quality in South-Holland (The Netherlands)

A hydrobiological study was carried out to elaborate the water quality classification system of CASPERS & KARBE (1966, 1967) for the larger stagnant bodies of water in the western part of the Netherlands. Significant correlations have been established between different physical and chemical parameters and phytoplankton community structures such as diversity and saprobity. From this a proposal is developed to quantify the water quality classes in CASPERS & KARBE'S scheme on parameters measuring the bioactivity, oxygen regime and phytoplankton community structure. The scheme is now incorporated in the practical water quality assessment in North- and South-Holland both for routine monitoring as well as for special water quality studies.     

Macroinvertebrates in Dutch ditches: A typological characterization and the status of the Demmerik ditches

Different aspects of using a new multivariate analysis technique namely detrended canonical correspondence analysis (DCCA), for the elaboration of macrofaunal data from Dutch ditches are shown. In this technique a graphic representation is given of combined main biotic and abiotic parameters. Especially for typological purposes, this technique is promising. A typological scheme resulted from typifying small, stagnant, line-shaped waters' or ditches in the province of Overijssel. All ditches were separated into eight major clusters. The most important related variables were acidity, drought, and stream velocity within which nutrient content/organic load diversified. The Demmerik ditches (see Hpigler and Verdonschot, 1989) represent larger sized ditches on a peaty substrate. They belong to the real ditches. Their taxon composition is most similar to that of clear, eutrophic, permanent ditches with a densely developed vegetation.     

The aerobic mineralization of organic compounds in the saline Lake Grevelingen (The Netherlands) (VI)

Summary During a one year period the uptake of aspartic acid and of a mixture of amino acids was determined using¹⁴C-labeled substrates as described by WRIGHT and HOBBIE (1966). By this technique the activity is analyzed of that part of the bacterial population which is able to utilize the added substrate. For comparison purposes the activity of the total heterotrophic bacterial population was determined by measurement of the oxygen consumption rate. From the oxygen consumption rate (mg O₂.l^–1.h^–1) the carbon mineralization rate (mg C.l^–1.h^–1) was calculated by applying a conversion factor of 0.29.Aspartic acid was respired for 80% and the amino acid mixture for 43%. From the maximum uptake rates, the potential yearly uptake of the substrate in question can be calculated. These data indicate the relative importance of the several subpopulations in the carbon mineralization process as a whole. The highest value of the potential yearly uptake was obtained for the amino acid mixture; the comparable value for the uptake of aspartic acid was slightly lower.The carbon mineralization rate as calculated from the oxygen uptake experiments was about 150–200 g C.m^–2.year^–1. The potential yearly uptake as determined with the¹⁴C-labeled amino acid mixture was only 2.8% of the amount of mineralized carbon, as calculated from the oxygen uptake experiments. This percentage is very low in view of the fact that 35–55% of the organic carbon of living phytoplankton and zooplankton consists of protein (HAGMEIER, 1961) and that the aerobic mineralization of amino acids is a very common property among the heterotrophic bacterial population (SEPERS, 1979). The value of the applied activity measurements was investigated in order to obtain information about the relation between the uptake process as measured with¹⁴C-labeled substrates and the activity of the bacterial population in situ. The results of this study have been published bij SEPERS and VAN ES (1979).     

Past and present distribution of stoneworts (Characeae) in The Netherlands

Across the world there is a prevailing view that freshwater algae are cosmopolitan. The notion has seldom been tested and is unlikely to be true in genetic terms. Nonetheless, some morphospecies of several groups of algae do have a worldwide distribution. Others have restricted distributions and may be regarded as endemic to a region. However there is always the possibility that they will be discovered in far away places. Australia has a rather large element of endemicity in its algal flora. From the early days of Australian phycology many new genera and species of freshwater algae have been described. Some are of such distinctive appearance or novelty as to be regarded as ‘flagship’ taxa. There is little doubt about their endemicity and their existence increases the probability of less-distinguished species also being endemic. The degree of endemicity is probably masked by the ‘force-fitting’ of European names to Australian species. Some Australian endemics are robust and are widely distributed in a variety of types of water body. Others, the frail endemics, the ones of greatest novelty and phylogenetic significance, have a very restricted range with their strongholds in dystrophic coastal lagoons where tracts or remnant patches of native vegetation survive. Their survival and the conservation of their biodiversity depends on recognition of the significance of coastal lagoons and swamps.