Surface Scum Research Articles

Microcystis changes its buoyancy in response to the average irradiance in the surface mixed layer

A population of buoyant colonies of Microcystis sp. dominated the phytoplankton of the small Vinkeveen Lake, in the Netherlands. The Microcystis colonies were circulated within the surface mixed layer whose depth (usually 2 to 4 m) usually exceeded the euphotic depth (usually less than 1.5 m) in this wind-exposed lake. Colonies held in bottles at the lake surface responded to the high irradiance by losing their buoyancy, while those kept at greater depths remained buoyant. For colonies circulating within the surface layer the degree of buoyancy loss that occurred during the day depended on the mean irradiance to which they were exposed, which could be determined from the average surface irradiance, the mixed depth and the vertical extinction coefficient. Buoyancy loss was also correlated, but less strongly, with the proportion of the daytime spent by colonies within the euphotic zone. Surface scums were usually prevented from forming by wind mixing.

Light‐dependence of photosynthesis and growth in cyanobacteria: Implications for their dominance in eutrophic lakes

Abstract In eutrophic lakes cyanobacteria are favoured relative to other phytoplankton, both under stratified and mixed conditions. During stratification, gas vacuole formation allows the accumulation of dense surface scums which attain the highest possible area‐specific photosynthetic rates in aquatic environments owing to high irradiances, near‐complete harvesting of impinging light, and minimal light inhibition and photo‐oxidation. During moderate mixing, high yields of biomass can be achieved by effective light harvesting for photosynthesis (aided by phycobilin pigments) and low maintenance energy requirements at low mean irradiances. Howevrr, nitrogen fixation competes for energy and reductant with photosynthesis, and leads to a decline of light‐saturated maximum growth rates. Wind‐driven vertical mixing and lateral advection are the main causes for the instability of cyanobacterial blooms in hyper‐eutrophic lake ecosystems.

Partitioning of CO 2 Fixation in the Colonial Cyanobacterium Microcystis aeruginosa : Mechanism Promoting Formation of Surface Scums

Constraints on inorganic carbon (C(i)) availability stimulated buoyancy in natural, photosynthetically active populations of the colonial blue-green alga (cyanobacterium) Microcystis aeruginosa. In nonmixed eutrophic river water and cultures, O(2) evolution determinations indicated C(i) limitation of photosynthesis, which was overcome either by CO(2) additions to the aqueous phase or by exposure of buoyant colonies to atmospheric CO(2). Microautoradiographs of M. aeruginosa colonies revealed partitioning of CO(2) fixation and photosynthate accumulation between peripheral and internal cells, particularly in large colonies. When illuminated colonies were suspended in the aqueous phase, peripheral cells accounted for at least 90% of the CO(2) assimilation, whereas internal cells remained unlabeled. However, when CO(2) was allowed to diffuse into colonies 15 min before illumination, a more uniform distribution of labeling was observed. Resultant differences in labeling patterns were most likely due to peripheral cells more exclusively utilizing CO(2) when ambient C(i) concentrations were low. Among colonies located at the air-water interface, internal cells showed an increased share of photosynthate production when atmospheric CO(2) was supplied. This indicated that C(i) transport was restricted in large colonies below the water surface, forcing internal cells to maintain a high degree of buoyancy, thus promoting the formation of surface scums. At the surface, C(i) restrictions were alleviated. Accordingly, scum formation appears to have an ecological function, allowing cyanobacteria access to atmospheric CO(2) when the C(i) concentration is growth limiting in the water column.

Partitioning of CO2 Fixation in the Colonial Cyanobacterium Microcystis aeruginosa: Mechanism Promoting Formation of Surface Scums

Partitioning of CO2 Fixation in the Colonial Cyanobacterium Microcystis aeruginosa: Mechanism Promoting Formation of Surface Scums

Photosynthetic microbial communities in aquatic ecosystems

A critical reappraisal of our knowledge on the photosynthetic communities of the open oceans and large lakes, and the development of new approaches to measurement of their activity in situ have greatly influenced our present views on the structure and function of these communities. Based on the accumulated knowledge of the physiology and molecular biology of the photosynthetic organisms involved we can now understand some of the mechanisms underlying adaptive processes operative in Nature. The distribution pattern of the photosynthetic communities in the photic zone of aquatic ecosystems is controlled by the nature of the photosynthetic apparatus, the range of antenna pigments formed by the different organisms, and their ability to regulate quantitatively and qualitatively pigment synthesis in response to light intensity and spectral composition. An additional factor controlling distribution is the ability of many of the photosynthetic organisms to escape the oligotrophic conditions prevailing in the water column by adherence to interfaces such as the benthos or the neuston. A major factor governing the ability of organisms to adhere to these interfaces is the hydrophobicity of their cell envelope. Planktonic organisms, on the other hand, have highly hydrophilic envelopes. Benthic organisms have evolved mechanisms for dispersal, which in many cases involves the formation by the hydrophobic adherent parent cells of hydrophilic progeny cells. This has been confirmed for several hormogonia-producing cyanobacteria. Benthic photosynthetic organisms must in addition be capable of phototactic motility and have versatile metabolic patterns to adapt to the rapid fluctuations in their environment. The photosynthetic organisms of the neuston and the cyanobacteria that form surface scum share mechanisms enabling the cells to withstand conditions of photo-oxidation, lethal to most non-resistant organisms.

Blue‐green algal scums: An explanation for their occurrence during freshwater blooms1

Nuisance blue‐green algal (cyanobacterial) scums are a sign of advanced eutrophication in aquatic systems. Previous workers have concluded that scums arc a sign of cyanobacterial senescence, or uncontrollable buoyancy. Our studies, however, indicate that scum formation may represent a mechanism by which the cyanobactcria can dominate surface waters. The mechanism is based on a preference for CO2 over HCO3− and CO32− as a photosynthetic carbon source, particularly in poorly buffered (low total inorganic carbon) waters. On calm days, when surface waters are thermally stratified, supplies of free CO2 are depleted, resulting in an increase in ambient pH. In response to CO2 depletion, cyanobacteria form surface scums, enabling them to use CO2 at the air‐water interface. This also promotes optimal photosynthetic growth and N2 fixation while simultaneously shading underlying noncyanobacterial phytoplankton.

Multiformulation dips for controlling storage disorders of apples and pears. III. Throughput limitations in dip application

Effectiveness of post-harvest diphenylamine (DPA) dip treatments for superficial scald (scald) control is dependent on application method, DPA formulation, dip age, quantity of fruit throughput and the inclusion of additives (calcium chloride and fungicides). With bin-immersion systems, throughput up to 100 × 18 kg cases per 561 of dip, caused no loss of DPA. However, with an Australian miscible oil formulation DPA (M.O. Aust.) containing additives there was increased scald and lenticel spot (spot) after 50-case throughput, and with a wettable powder formulation DPA (P) there was increased spot after 50-case throughput, but these limitations were not apparent with an American miscible oil formulation DPA (M.O. U.S.). Replacing lost dip-volume with normal strength DPA after 50-case throughput prevented the occurrence of these disorders with further throughput. Dips which had had prior throughput and were then aged for 1–2 weeks were effective provided they were agitated before use. With bin-flooding systems using DPA (M.O. Aust.) or DPA (P), effective scald control was limited to the case throughput which was treated in 40–75 min. Exceeding this limitation caused the DPA (M.O. Aust.) emulsion to break down due to mechanical agitation in pumping, and DPA (P) to form a surface scum of DPA ingredient in the return tank. The DPA (M.O. U.S.) formulation was stable and effective in this system for at least 100 min pumping.

Plant Development and Sequence in Artificial Ponds with or without Phosphorus-Enriched Sediments

Plant Development and Sequence in Artificial Ponds with or without Phosphorus-Enriched Sediments

Die-offs of the blue-green alga, Anabaena variabilis, in fish ponds

Dense populations of the blue-green alga, Anabaena variabilis, frequently develop in fish ponds at Auburn, Alabama, during windy weather in March and early April. Massive die-offs of this alga can be expected when it forms surface scums during prolonged periods of calm, clear, warm weather between mid April and mid May. Dissolved oxygen concentrations decline following die-offs and fish kills may result.

Dislocation-free copper: A case history

Dislocation-free copper crystals have been produced under conditions which were once considered too severe, i.e. without an afterheater and without rotation. Attention is paid to the elimination of such technological problems as melt surface scum and melt vibration; and with the aid of X-ray diffraction topographs it is shown what effect these phenomena have on crystal perfection. Evidence is then presented to illustrate how dislocation propagation (e.g. from the neck) and generation (e.g. from thermal shock) can be controlled.

Sudden Mortality of a Massive Phytoplankton Bloom

A dense bloom of the blue-green alga,Anabaena variabilisKuetzing suddenly died in a pond heavily stocked with channel catfish (Ictalurus punctatusL.). Low light intensity caused the formation of gas vacuoles inA. variabilis. The buoyant filaments accumulated at the surface in large numbers during a period of calm, warm weather. Light injury to cells in the surface scum apparently triggered the mass mortality of phytoplankton. Decomposition of dead algae quickly resulted in depletion of dissolved oxygen. Concentrations of CO2and ammonia increased to high levels and the pH declined following the phytoplankton die-off. A period of 7 days was required for re-establishment of a phytoplankton community and little improvement in water quality occurred until high densities of healthy phytoplankters were present. Massive mortality of fish was prevented by pumping oxygenated water into the pond at two sites and by mechanically agitating surface water in a limited area.

An experiment on the culture of Tilapia esculenta (Graham) and Tilapia zillii (Gervais) (Cichlidae) in fish ponds

Segregated populations of Tilapia zillii and Tilapia esculenta were kept in artificial ponds. Supplementary food was given and phytoplankton was encouraged by the addition of superphosphate and ammonium sulphate fertilisers. The fry were cropped regularly in an attempt to control population size. A control population of T. zillii was also established in which none of these procedures were carried out.The growth of T. esculenta was found to be dependent upon the phytoplankton density of the pond whilst T. zillii successfully utilized the supplementary food and grew well. The T. esculenta population also produced more fry than the T. zillii population. The comparative advantages of planktrvorous/brooders and herbivorous/guarders in fish culture are considered.Despite the fecundity of the species used a population of known composition was maintained by manual cropping of the fry.The addition of ammonium sulphate to the ponds caused blooms of phytoplankton which in turn had effects upon the base reserves and pH of the water, and probably caused some reduction of oxygen concentration beneath surface scums. This last point is used to explain the changes in phosphate and calcium content of the water also observed.The low oxygen concentration frequently noted in the mornings probably affected the feeding behaviour of the fishes, and was low enough to have affected metabolism directly.

Investigation of Drag Reduction by Certain Algae

INVESTIGATIONS were carried out between March and September 1969 to determine the drag reduction effects produced by certain species of algae in No. 3 towing tank at the Ship Division of the National Physical Laboratory. The tank is 48 feet wide, 25 feet deep and 1,300 feet long and contains the water added in August-September 1957. Small additions are regularly made to compensate for evaporation losses. The tank is constantly used for hydrodynamical experiments and is daily skimmed by towing a plastic tube along the tank to remove surface scum. The tube extends across the width of the tank and below it is suspended a muslin curtain. Samples from this scum were studied and species were tested, for drag reduction effects.

Two Electrical Phenomena on Liquid Germanium Surfaces

This paper describes some experiments in which an electric discharge, between the surface of a molten pool of germanium and a nearby solid germanium electrode, was found to repel surface scum from the vicinity of the discharge. It also reports some experiments in which it was found possible to produce crystal nucleation by the application of a relatively low electric field to the surface of a supercooled germanium melt. No explanation for either of these phenomena is proposed.