Publications of Sigee, D.C.

Modelling of elemental associations in Anabaena

Changes in the elemental composition of the blue-green alga Anabaena at Rostherne Mere (Cheshire, U.K.) were studied over an extended bloom period in 1996. Elemental analysis was carried out in relation to intracellular concentrations, intracellular elemental correlations, time series correlations and total quantities of elements in lake water. Most of the intracellular elements showed considerable variation both between and within samples. Correlations between these elements also varied considerably, though certain pairs – K/Cl, K/Mg, P/K and P/Mg were significantly correlated in at least 50% of the samples. Analysis of the time series demonstrated clear correlations between lake water P and intracellular P and Mg. The growth of Anabaena coincided with a considerable increase in the overall amount of chemicals contained in its population. The total amounts of chemicals in the lake water, however, always substantially exceeded those present in the population of Anabaena cells. Elemental relationships within cells are considered in relation to an elemental correlation pattern, consisting of three main groupings – Mg-K-P, Na-S and Ca-Cl. The structural model of intracellular elemental associations presented here may be helpful in the investigation of algal response to changes in environmental parameters.The incorporation of this model into a dynamic model simulating phytoplankton–environmental interactions is discussed.

Elemental concentrations, correlations and ratios in micropopulations of Ceratium hirundinella (Pyrrhophyta): an X-ray microanalytical study

The elemental composition of <e1>Ceratium hirundinella</e1> was determined in mixed phytoplankton samples collected over a 2-month period (late June to early September 1995). Electron probe X-ray microanalysis spectra of single cells routinely showed clear peaks of monovalent (Na, K) and divalent (Mg, Ca) cations, plus Si, P, S and Cl. Considerable variation in elemental concentrations occurred both within and between samples (20 cells). The overall ratio of monovalent to divalent cations was relatively constant at about 1.3. Intracellular concentrations of anions/cations and electronegative/electropositive elements were significantly correlated in most samples, suggesting a controlled internal balance of these ionic groups. Correlation analysis of elemental concentrations revealed clear patterns of statistical association within individual samples, with significant positive correlations between particular pairs of elements (Mg–P, K–Cl and K–P). Some pairs of highly correlated elements (particularly Mg–P) occurred in defined ratios throughout the samples, while others (e.g. K–Cl, Na–Mg) were variable. Factor analysis showed that elemental associations were determined by two Principal Factors in most samples, possibly related to insoluble and soluble components of cells. Decrease in the level of available P in lake water was associated with a sharp decrease in the intracellular P concentration and the concentration of other correlated elements. The estimated C/P ratio markedly differed from the classical (Redfield) value at times of low P availability. The concentration of P in cells of <e1>Ceratium</e1> was approximately 10⁴ times greater than in the surrounding water medium (total P) compared with values of 10²–10³ for K.

Elemental composition of phytoplankton in a subtropical lake: X-ray microanalytical studies on the dominant algae Spirulina platensis (Cyanophyta) and Cyclotella meneghiniana (Bacillariophyceae)

Studies were carried out on the phytoplankton of a subtropical polluted lake (Lake Maryut, Egypt) over a 1 year sampling period. The elemental composition of two major algal constituents-Spirulina platensis (Cyanophyta) and Cyclotella meneghiniana (Bacillariophyceae) – was determined from mixed plankton samples using electron-probe X-ray microanalysis. X-ray emission spectra obtained from S. platensis revealed a wide range of detectable elements. Clear positive (e.g. K-P, Na-Cl) and negative (e.g. Na-S, P-Cl) statistical correlations were interpreted in terms of elemental associations and compartmentation within the cell. C. meneghiniana had a broadly similar range of elements, but differed in the additional presence of Al and frequent peaks of Fe and Cu. The high concentration of Si reduced the detectability of other elements, causing a general reduction in mass fraction levels. Comparison of correlation coefficients derived from four sets of data revealed a clear pattern of elemental occurrence in the cell. There were two major groupings (involving divalent and monovalent cations) which may relate respectively to the frustule and protoplasmic compartments of the cell. Uptake of metal pollutants and P was investigated by comparison of cellular and environmental levels. Although metal pollution in the lake was high, no significant uptake was detected in S. platensis and only limited uptake (of Fe and Cu) occurred in C. meneghiniana. In this alga, cell loading with Fe and Cu did not relate to concentrations in contemporary water samples, suggesting that metal accumulation may not be in synchrony with environmental changes. Similar considerations apply to P, since neither S. platensis nor C. meneghiniana showed clear or consistent correlations between cellular and environmental concentrations.