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The phytoplankton and productivity of the North American Great Lakes has been studied extensively by Fisheries and Oceans Canada during the past 15 years to monitor the impact of nutrient and contaminant loading on the plankton of the ecosystem. Lakewide cruises were conducted at monthly intervals mainly during the spring to fall period. This provided extensive biomass, species, size, productivity and nutrient concentration data for the Great Lakes. These data were collected using the Utermöhl inverted microscope technique together with standardized taxonomic, productivity and data-handling procedures. These standardized methodologies were applied to all the Great Lakes which resulted in a comprehensive phycological and ecological data base for the first time. These data form the basis for the evaluation of the complex phenomenon of seasonality.

Since the 1970's the management of aquatic habitats has changed from piecemeal monitoring to the ecosystem approach; this was initiated in the North American Great Lakes, comprising social, economic, and environmental aspects. The information included in this paper is based on the presentation made at the ‘Seminar On Ecosystem Approach To Water Management’ held in Oslo, Norway during 1991. Recently, the multidisciplinary, holistic, and integrated concept of ecosystem health has emerged, and is being advanced for the implementation of an ecosystem approach to environmental management, which has resulted in the formation of an international society (Aquatic Ecosystem Health & Management Society) and the publication of a primary journal (Journal of Aquatic Ecosystem Health). The information has been updated to incorporate new developments and recent progress about the Society and the journal since the Oslo Seminar.

Analyses by transmission electron microscopy (TEM) of the smallest organisms in surface waters can be used to assess ecosystem health; the evidence for this statement is reviewed and recommendations are made for optimal use of TEM technology in providing such assessments. Those groups of small organisms currently being considered as indicators of ecosystem health (viruses, bacteria, autotrophic picoplankton, and autotrophic nanoplankton) are reviewed briefly as subjects for monitoring by TEM. New information on direct counting by TEM of viral femtoplankton indicates that viruses can be present in numbers 103 to 107 times greater than previously estimated by the traditional counts of plaque-forming units using various host bacteria. Such concentrations indicate that virus infections may exert ecological control over planktonic microbes. Ultrastructural research on prokaryotic picoplankton suggests that TEM analyses of cells in ultra-thin sections can be used to speciate the picoplankton and to diagnose them for cytological modifications related to environmental stress. Considering their great importance, episodically, to primary productivity and to modulating the speciation of higher levels in the food web, such picoplankton ultrastructural analyses could be pursued with profit as a diagnostic tool. For decades, the ultrastructure of some eukaryotic nanoplankton has been known to vary in specific ways to specific stresses in laboratory experiments. An extension of these structure-function correlations is potentially a useful tool to provide indicators of ecosystem health. The barriers to progress in such research are now understood and can be overcome.

Seasonal abundance of phytoplankton has been discussed in three tropical ponds of Hyderabad, India during two years of investigation. The observed patterns have been characterized as seasonal maxima and minima during summer, monsoon and winter. The tropical patterns observed in the study ponds were typical but different from those observed in temperate regions. Most of the maxima were observed in winter and the minima during the monsoon or rainy season. Diatomeae dominated the phytoplankton of all the ponds in all seasons. An inverse relationship between Diatomeae and Cyanophyta, and Diatomeae and Euglenineae was observed. The phytoplankters have been grouped as perennial, summer, monsoon and winter species.

The ecology of Euglenineae was investigated for two years in certain polluted and unpolluted environments of Hyderabad, India. The paper includes discussions regarding the distribution and periodicity of euglenoid population in relation to the physicochemical complexes which existed in the three ponds during the period of investigation. Sewage and Garden Ponds were found to be considerably polluted, whereas, the Typha Pond was comparatively pure and less polluted. Sewage Pond exhibited the highest percentage of Euglenineae harbouring 13 species and Garden Pond harboured 2 species in large numbers. Typha Pond harboured typically Trachelomonas hispida and Euglena Sp. which were totally absent in the other two ponds. It seems that high average concentrations of free CO2 were favourable for euglenoid growth in Sewage Pond and the oxygen deficiency was helpful to trigger the oxygen-iron-phosphate complex, releasing larger quantities of phosphorus and iron. Higher average values of percent Cl + NO3 ratio were found to be responsible for the luxuriant growth of these flagellates and it was suggested that inorganic sources of nitrogen might be more important in their ecology as fluctuations of nitrate coincide closely with those of Euglenineae in all ponds. These flagellates were found to be abundant during the periods when water was not rich in total sulphides and concentrations higher than 2.0 ppm adversely effected the euglenoid development. These flagellates were found to develop usually after rains or during intermittent showers experiencing comparatively higher temperatures. A temperature range of 27° – 39°C was observed to be favourable for their growth. Higher concentrations of oxidizable organic matter showed a direct relationship to euglenoid population in Sewage Pond. It is suggested that certain species of Euglenineae, which very often developed in the polluted waters of Sewage Pond, could be used as biological indicators of pollution in the present investigation.

The paper is based on a two-year study of the distribution of phytoplankton in three freshwater, polluted and unpolluted ponds of Hyderabad, India. The distribution of several groups of algae likeVolvocales, Chlorococcales, Desmids, Diatoms, Dinoflagellates, blue-greens andEuglenineae exhibited interesting relationships to the physioo-chemical complexes of the ponds, and throws much light on the algal distribution in Indian waters. The discussion revolves around the yearly and overall averages of the ecological factors and the various groups of algae. Dissolved oxygen, oxidizable organic matter, free carbon dioxide, nitrates, phosphates, calcium and sulfides have been found to play a significant role. The fluctuations of certain ratios such as N : P : K, C/N, percent sodium, percent Cl + NO3 and Pearsall's basic ratio suggest distinctly important clues in the distribution of various groups of algae.

The limnology of three freshwater ponds, polluted and unpolluted was studied over a period of two years. The ponds studied, differed substantially in the degree of organic pollution. Physico-chemical complexes occurring in the ponds were analysed which exhibit interesting interrelationships. The investigation indicated certain important complexes operating in the ecosystem. The paper includes discussion on the interrelationships of the following sets of factors:1.Temperature and other physico-chemical factors.2.Oxygen and carbon dioxide.3.Carbon dioxide and the buffer system.4.Sodium and Chlorides.5.Temperature and other solids.6.Organic Matter and allied factors.7.Phosphates.8.Sulfur complex.9.Silicates.10.Nitrogen complex.