CHAPTER 1 

 INTRODUCTION 



The Concept of Trophic State in Lakes 



Primary productivity in lakes can be defined as the rate at 

 which new organic matter is formed by photosynthesis in autotrophs 

 such as phytoplankton and macrophytes. Annual productivity is 

 typically expressed as the number of grams of carbon fixed per unit 

 of lake surface area per year. Lake productivity, however, has been 

 more traditionally thought of in conceptual terms referred to as 

 trophic state, and typologically described using categories ranging 

 from ultraoligotrophic at the low end of productivity to 

 hypereutrophic at the high end (cf. Shannon and Brezonik 1972). 



Several trophic state indices (TSI) have been developed that 

 permit numerical expression of trophic state using biological, 

 physical and chemical characteristics. Shannon and Brezonik (1972), 

 for instance, used principal components analysis to reduce seven 

 variables including chlorophyll a (Chi a), primary productivity, and 

 total P to a single variable that described the trophic status of lakes. 

 Although it was inclusive, this TSI has been regarded as 

 cumbersome, especially because of the difficulty in obtaining 

 primary productivity values. Carlson (1977) sought a single, easily 

 obtained measure to describe lake trophic state, and he selected 



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