The influence of the diel climatic cycle on the depth-time distribution of phytoplankton and photosynthesis in a shallow equatorial lake (Lake Baringo,Kenya)

Lake Baringo is a shallow equatorial lake. This paper reports a diel study of the depth-time distribution of phytoplankton and photosynthesis at one location in Lake Baringo on 10 March 1989. The water column shows a pattern of diurnal stratification probably accentuated by the high turbidity of the water and therefore rapid attenuation of solar energy. This stratified pattern breaks down at night due to atmospheric cooling and the regular onset of winds in the early evening. The phytoplankton is dominated byMicrocystis aeruginosa with some associated epiphytes. It concentrates in the narrow euphotic zone during the diurnal period of stratification due to buoyancy of theMicrocystis; evening breakdown of the thermocline results in the phytoplankton being mixed throughout the water column. A series of measurements of photosynthesis throughout the diurnal period gives an areal rate of 3.8 g O₂ m⁻² d⁻¹. The relationship between this value and the level of fish exploitation in Lake Baringo is discussed. The diel cycle in Lake Baringo is interpreted as dominating over any seasonal limnological cycle in the lake.     

Floristic studies on freshwater algae of Lake Gondwana,Northern Victoria Land (Antarctica)

Benthic algal mats and phytoplankton of Lake Gondwana (Northern Victoria Land, Antarctica) were investigated. Biomass, chlorophyll content and floristic analyses were carried out on algal mats. The mats are composed of two layers different in colour, floristic composition and chlorophyll content. The algal flora of the mats amount to 34 taxa (19 Cyanophyta, 7 Bacillariophyta, 8 Chlorophyta). The phytoplankton community is species-poor (only 5 taxa). Crytophyta account for about 98% of total algal density.     

Hydrological cycle and interannual variability of the aquatic community in a temporary saline lake (Fuente de Piedra,Southern Spain)

Fuente de Piedra is a shallow, temporary saline lake whoseseasonal behavior is strongly dependent on the annual hydrologicalbudget. In this study, we outline the characteristics of Fuente dePiedra Lake for two years that had different hydrological budgets.The high precipitations in 1989–90 caused the lake not to dry asusual, and decreased both salinity and the amplitude of changes.There were also differences in nutrient dynamics, with generallylower concentrations of soluble reactive phosphorus and ammonium,whereas in the more humid year nitrate showed a distinct maximum inwinter. Winter bloom chlorophyll a concentrations were alsomuch higher in 1989–90 (>600 g l-1) but there wasalso a winter productive phase that was presumably poorly coupledwith consumption processes that predominate in spring. Planktonicassemblages were different between years. Highly halotolerantphytoplankton species (Dunaliella salina and D. viridis) became scarcer, and especially two previouslyunrecorded diatoms (Cyclotella sp. and Chaetoceros sp.)became dominant in the bloom time in the wet year. The speciesrichness of the zooplankton increased in the wet year, with newspecies appearing that were not collected during 1987–88(Branchinectella media, Daphnia mediterranea, Macrothrix sp.,Arctodiaptomus salinus, Cyclops sp., Sigara sp...).There was also a much higher development of macrophytes (Ruppiadrepanensis, Althenia orientalis, Lamprothamnium papulosum)and bird populations, especially flamingoes (Phoenicopterusruber).Important interannual variations in this sort of system pointto the need for long term studies to observe the whole range ofstates that define the lake as an entity.     

Summer zooplankton dynamics in the limnetic and littoral zones of a humic acid lake

The limnetic and littoral zooplankton were studied during summer 1989 in Triangle Lake, a humic acid (pH 4.9) bog lake in Ohio, USA. The limnetic zooplankton showed low species richness and biomass, and dominance by the rotifers Kellicottia bostoniensis and Polyarthra vulgaris. In the littoral, species richness and biomass were markedly higher, and the crustaceans Alona guttata, Ceriodaphnia quadrangula, Chydorus sphaericus, Simocephalus serrulatus and Tropocyclops prasinus, and the rotifer Ascomorpha ecaudis were the dominants. The extreme rotifer dominance and lack of cladocerans in the limnetic zone were likely the result of Chaoborus predation. A pronounced mid-summer decline in cladoceran biomass in the littoral was likely due to predation by T. prasinus and Utricularia (bladderwort).     

An environmental history of two freshwater lakes in the Larsemann Hills,Antarctica

The Larsemann Hills are a series of rocky peninsulas and islands in Prydz Bay at 69° 24 S and 76° 20 E. There is about 2000 km² of ice free land with well over 150 freshwater lakes spread evenly over the granite and gneiss hills. The nearshore islands were ice free by 9500 BP, while the present coastline was exposed by 4500 BP. A relatively steady rate of ice retreat is indicated, around 0.3 ma^–1. The two freshwater lakes studied so far have evolved from oligotrophic, proglacial lagoons to fresh or brackish lakes affected by periodic influxes of salt water from sea spray and surges produced by glacial calving. The diatom assemblages increase in species diversity following marine incursion or influence. The major changes are therefore due to the postglacial recovery of sea level, rather than any intrinsic chemical evolution of the lake waters.     

The sediment column as a record of trophic status: examples from Bosherston Lakes,SW Wales

Bosherston Lakes are a series of interconnected, mesotrophic to hypereutrophic, artificially-created coastal marl lakes in Dyfed, South West Wales. Progressive eutrophication of the lake system has been produced by a high external phosphorus loading which includes phosphorus-rich effluent from a sewage treatment works (STW) in the catchment of the Lakes.Cores were taken from four sites of varying eutrophic status within the Lakes. In the surface sediment layer, organic C, N and P concentrations generally correlate directly with trophic status and reflect distance from the source of P input. At one site, sediment stratigraphy records a clear transition at 20–15 cm depth, marked by a sharp upward increase in porosity, organic C, N, and P, and iron-associated-P; decreases in organic matter C/N, C/P and N/P ratios; a sharp decrease in carbonate, and a change in the subfossil diatom assemblage. Lead-210 dating indicates that this change occurred in the period 1919 to 1938.The diatom stratigraphy and sediment geochemistry suggest that this transition reflects an increase in trophic status at this site, probably as a result of the influx of nutrient-rich water. This took place when the management of the Stackpole estate surrounding the lake system, fell into decline during the period 1919–1938.     

Nutrient enrichment experiments in three central Florida lakes of different trophic states

Seasonal nutrient enrichment experiments (short-term bioassays) were conducted in three Florida lakes of different trophic states to determine the effects of addition of various nutrient combinations upon chlorophyll a and phytoplankton standing crops. Nutrient enriched surface water samples with crustacean zooplankton removed were incubated in situ in clear polyethylene bags for 3 to 6 days. The 2⁵ factorial design employed two levels (ambient and enriched) of each of five nutrients [NH₄ ⁺, PO _inf4 ^sup3− , Fe⁻ -EDTA, SiO _inf3 ^sup2− and a cation (Ca²⁺ or K⁺) or trace elements]. Ammonium produced significant increases in chlorophyll a and phytoplankton standing crops in all experiments. Phosphate produced similar results in the mesotrophic lake, but the eutrophic lakes had both positive and nonsignificant responses which varied seasonally between lakes. Iron increased chlorophyll a in most experiments but affected total phytoplankton standing crop only during the summer and fall. Silicon had negative effects in some experiments. Cations and trace elements produced marked differences between lakes for chlorophyll a, but total phytoplankton standing crop showed few significant responses. Synergistic responses to two- and three-factor interactions were observed in all lakes. Differences in the responses of phytoplankton taxonomic divisions to enrichment may be responsible for much of the between lake variation in chlorophyll a and total phytoplankton volume responses. Nutrient limitations in these lakes are discussed and related to limnological factors and predictive models.     

Inland salt waters of southern Africa

Inland salt lakes are widely distributed in southern Africa: they are particularly common in South Africa, but many occur in Namibia and Botswana. All are shallow, and most are ephemeral with salinities that are not very high (mostly < 50 g l⁻¹). Fringing zones of halophytes or submerged macrophytes are neither well-developed nor taxonomically diverse. The Cyanobacteria, especially Nodularia spumigena, often dominate the phytoplankton. The fauna of the Makgadikgadi area (northeast Botswana) is diverse and is similar to that of East African salt lakes. The aquatic fauna of salt water south of the Makgadikgadi Basin, on the other hand, is extremely depauperate, has no well-defined assemblage confined to saline waters, and appears mostly to comprise tolerant freshwater forms. Lovenula falcifera and Metadiaptomus transvaalensis (diaptomid copepods), Moina micrura (Cladocera) and Brachionus plicatilis (Rotifera) are frequently encountered zooplankton species, a few species of insects (Anisops sp., beetles, chironomids and ephydrids) are the principal non-planktonic macroinvertebrates. Artemia ‘salina’ is occasionally present, but may be an introduced form. The avifauna, in contrast to the aquatic macroinvertebrate fauna, is rich, with the greater and lesser flamingo often common.     

Burrowing beetles of the genus Bledius (Staphylinidae) as agents of bioturbation in the emergent areas and shores of an athalassic inland lake (Fuente de Piedra,southern of Spain)

Bledius (Elbidus) bicornis (Germ.) and B. (Eucerotobledius) furcatus (Oliv.) (Coleoptera: Staphylinidae) are the most important burrowing species in the emergent areas and shores in the athalassic lake of Fuente de Piedra (Málaga, S. of Spain). A first estimate of the importance of these organisms in this system is presented. These insects kick out sediment during their burrowing activity, which accumulates on the surface near the burrows as tumuli which can be easily eroded. The lake perimeter (17 km) is densely colonized (usual densities from 1700 to 2500 ind m⁻²). The amount of granulated material that can be potentially kicked out was 46.22 g dry wt m⁻² day⁻¹. At the same time, the material that constitutes the tumuli shows different characteristics from the compact ground below the surface. Thus, it is relatively enriched with organic matter (6.15 g per square meter), soluble phosphate (406.5 μg m⁻²) and ammonium (4856 μg m⁻²), whereas it lacks nitrate. Results of a transect from uninhabited areas to zones of maximum population density also show a similarity between the higher ground level of ammonium and phosphate concentrations and population density.     

Weichselian chironomid and cladoceran assemblages from maar lakes

Sediments from maar lakes in the periglacial area were analysed to obtain information about the limnetic fauna of Pleniglacial lakes. On the basis of abundance and species composition of the subfossil chironomid and cladoceran assemblages, three major zones were biostratigraphically separated: the Upper Pleniglacial, the Middle Pleniglacial, and the Eem Interglacial.