Typology of shallow lakes of the Salado River basin (Argentina), based on phytoplankton communities

The phytoplankton communities of eleven shallow lakes from Buenos Aires Province, Argentina, were studied seasonally from 1987 to 1989. Several physical and chemical properties were measured in each lake (pH, temperature, dissolved oxygen, transparency, nutrients), in order to interpret the structural and dynamic traits of the phytoplankton community.Important differences between the lakes studied were put in evidence by means of multivariate techniques (Cluster Analysis and PCA). The shallow lakes densely populated by macrophytes hosted lowest phytoplanktonic densities, with average values ranging from 690 to 16500 algae ml^–1. High species diversities were observed in these lakes (4.0–4.8). Lakes less colonized by macrophytes had higher phytoplankton densities. In some of them important blooms of Cyanophyceae were recorded, with between 60 000 and 179 000 algae ml^–1, and concomitant low diversities.The results of this investigation support the hypothesis that the phytoplankton community is strongly influenced by the macrophytes, by direct competition and/or by competition from periphytic algae associated with higher plants.     

Environmental control of phytoplankton productivity in turbulent turbid systems

Factors affecting phytoplankton productivity are analysed in turbid systems, such as shallow lakes and rivers. When resuspension from the sediment or loading from the catchment significantly increases inorganic (non-algal) turbidity and hence light attenuation potentials for high production are not realised. Energy available for phytoplankton growth is strongly regulated by underwater light availability which depends on the critical mixing depth, fluctuating light intensities and algal circulation patterns. Higher production rates in shallow waters are often compensated by greater algal respiration due to higher water temperatures when compared to deeper lakes.Total daily integral production of turbulent, turbid environments can be predicted from a combination of easily measured variables such as maximum photosynthetic rates, algal biomass, surface irradiance and some measure of underwater light attenuation.     

Acidification of small mountain lakes in the High Tatra Mountains,Poland

A hydrochemical investigation was carried out on eight small High Tatra mountain lakes (Poland). When comparing recent data with those from the period 1935–1965, a constant process of acidification of the lakes is found. The average pH of precipitation is 4.8 in the study area, but the lakes are in two stages of acidification: weak (pH 6.0–6.5) and intermediate (pH 5.5–5.8). The differences are due to differences in water sources.     

Comparative limnology,species diversity and biomass relationship of zooplankton and phytoplankton in five freshwater lakes in Kenya

Comparative studies on the limnology, species diversity and standing stock biomass of phytoplankton and zooplankton in five freshwater lakes, Naivasha and Oloidien, Ruiru, Masinga and Nairobi reservoirs, were undertaken. Phytoplankton chlorophyll a, dissolved oxygen and temperature were also measured. Thermocyclops oblongatus (Copepoda) was dominant in all the lakes. Ceriodaphnia cornuta and Diaphanosoma excisum (Cladocera) dominated in lakes Naivasha and Oloiden, whereas in Ruiru, Masinga and Nairobi reservoirs, Brachionus angularis and Hexarthra mira (Rotifera) were the dominant zooplankters. Phytoplankton biomass as chlorophyll a was lowest in Ruiru dam 5.64 ± 4.0 µg l^-1 and highest in the eutrophic Nairobi dam 71.5 ± 12.02 µg l^-1. The endorheic lakes Naivasha and Oloidien showed medium values of 24.5 ± 4.0 µg l^-1.     

Composition and distribution of bottom oligochaete fauna of a north Italian eutrophic lake (Lake Ledro)

The profundal macroinvertebrates, particularly the oligochaetes, of Lake Ledro (Trento, Italy), that has recently undergone eutrophication, were studied.A statistical approach of random sampling was used to study the distribution and abundance of the oligochaete species. The optimum sample number was calculated from a preliminary sample series. The oligochaete community was made up of five tubificid species, one naidid and one lumbriculid species that on average represents more than 80% of the macrobenthic community. Population density was correlated with depth and decreasing oxygen concentration. The role of Tubifex tubifex as a eutrophic, tolerant species was confirmed; and in fact it was the only species found (although at low density) in the deepest and anoxic zone. No comparable data are available for the lake prior to eutrophication, but these data will be valuable for future comparison once a remediation program for the lake has been implemented.     

Differential expression inArabidopsis ofLhca2, a PSI cab gene

A cDNA clone of the geneLhca2 encoding a photosystem I (PSI) type II chlorophylla/b-binding protein was isolated fromArabidopsis thaliana. The isolation of this, the fourth PSI cab gene fromArabidopsis, confirms a previous report [1] that indicatedArabidopsis may contain all four PSI cab genes identified in other plant species.Lhca2 is a single-copy gene as are the other knownArabidopsis PSI cab genes. The patterns of developmental expression and tissue-specific regulation ofLhca2 are similar to those of other PSI and PSII cab genes, but the light induction pattern and the steady-state mRNA level ofLhca2 are distinct. This suggests that a different mechanism may be employed to regulate the expression ofLhca2.     

Fine root growth phenology,production, and turnover in a northern hardwood forest ecosystem

A large part of the nutrient flux in deciduous forests is through fine root turnover, yet this process is seldom measured. As part of a nutrient cycling study, fine root dynamics were studied for two years at Huntington Forest in the Adirondack Mountain region of New York, USA. Root growth phenology was characterized using field rhizotrons, three methods were used to estimate fine root production, two methods were used to estimate fine root mortality, and decomposition was estimated using the buried bag technique. During both 1986 and 1987, fine root elongation began in early April, peaked during July and August, and nearly ceased by mid-October. Mean fine root ( 3 mm diameter) biomass in the surface 28-cm was 2.5 t ha^–1 and necromass was 2.9 t ha^–1. Annual decomposition rates ranged from 17 to 30% beneath the litter and 27 to 52% at a depth of 10 cm. Depending on the method used for estimation, fine root production ranged from 2.0 to 2.9 t ha^–1, mortality ranged from 1.8 to 3.7 t ha^–1 yr^–1, and decomposition was 0.9 t ha^–1 yr^–1. Thus, turnover ranged from 0.8 to 1.2 yr^–1. The nutrients that cycled through fine roots annually were 4.5–6.1 kg Ca, 1.1–1.4 kg Mg, 0.3–0.4 kg K, 1.2–1.7 kg P, 20.3–27.3 kg N, and 1.8–2.4 kg S ha^–1. Fine root turnover was less important than leaf litterfall in the cycling of Ca and Mg and was similar to leaf litterfall in the amount of N, P, K and S cycled.     

Changes in diatom assemblages in the profundal sediments of two large oligohumic lakes in eastern Finland

Sedimentary diatom assemblages in two large oligotrophic clear-water lakes were analysed, to assess their present ecological state and possible eutrophication due to diffuse nutrient loading. The lakes Pyhäjärvi and Puruvesi (Finnish lake district) are proportionally large for their catchment areas which accounts for their long retention times (ca 7 and 11 yr) and oligohumic character. Pyhäjärvi was studied by pairwise comparison of surface sediment diatom assemblages collected in 1985 and 1990 at 12 sites from different parts of the lake. In Puruvesi, the stratigraphy of diatoms was analysed in two short cores from 8 m and 32 m depths.The diatom assemblages of the two lakes are rather similar, and quite distinct from the assemblages of the mesohumic large lakes of the area. Cyclotella kuetzingiana is the most common planktonic dia- tom, but Aulacoseira ambigua abounds in Pyhäjärvi at sites with local sources of eutrophication. A diverse assemblage of benthic forms, especially Fragilaria and Achnanthes spp. characterizes the shallow bottoms in both lakes.There was little change within the short-core diatom profiles of Puruvesi, but the floral composition of the 8-m and 32-m sites differed markedly. The 8-m site, with 60–70% of benthic forms, represents illuminated bottom, on which much of the buried algae have lived in situ, while the deeper site is true profundal, dominated by sedimented planktonic algae.In Pyhäjärvi there was a slight increase in the benthic diatoms from 1985 to 1990, coinciding with increased phosphorus and chlorophyll concentrations as well as Secchi depth lowering. We interprete this observation as a very early step of eutrophication, of which first the sessile algal communities of the illuminated bottom areas have benefited.     

Benthic invertebrates of some saline lakes of the Sud Lipez region,Bolivia

The benthic invertebrates fauna of most of the saline lakes of the Sud Lipez region (Bolivia, Altiplano) has been until now quite unstudied. Samples collected during an extensive survey of 12 lakes and two small inflow rivers allow a first list of the main macroinvertebrates living in these biotopes.The heterogeneous nature of these saline lakes with their freshwater springs and phreatic inflows offers a variety of habitats to macroinvertebrates. The benthic fauna in lakes with salinities > 10 g l^–1 is not so low in density but includes few species and is dominated by Orthocladiinae and Podonominae larvae. In contrast, the freshwater springs and inflows are colonized by a diverse fauna, with a mixture of both freshwater and saline taxa, but dominated by Elmidae and Amphipoda. The lakes are quite isolated and, apart from some cosmopolitan organisms, their fauna can be quite distinctive.     

Morphology,distribution, and preservation potential of microbial mats in the hydromagnesite-magnesite playas of the Cariboo Plateau,British Columbia,Canada

Benthic microbial mats are common in the alkaline hydromagnesite-magnesite playa lakes of Interior British Columbia. Four main zones are recognized based on mat morphology that can be related to the type and duration of wetting. From the basin margin toward the playa centre they are: (i) vegetated hummocky ground; (ii) polygonal hummocky ground; (iii) low-domal and stratiform mats, and (iv) laterally continuous and pustular mats. Mats in peripheral mudflats are commonly mineralized by hydromagnesite, mostly precipitated by capillary evaporation of shallow groundwaters. Mats forming in the ephemeral lake tend to have lower carbonate content.Although widespread, the mats are poorly preserved in the Holocene sedimentary record. Underlying sediments are commonly weakly bedded, disturbed or massive. Desiccation, dehydration, wetting-drying cycles, and grazing by invertebrates cause fragmentation of mats at the surface, facilitating erosion. Cryogranulation, interstitial mineral precipitation, vesiculation, bioturbation, compaction, and volume changes associated with diagenesis, disrupt and destroy lamination in the upper few centimetres. Most surviving organic matter is lost by early microbial degradation.