Paper : 12 Principles of Ecology Module : 21 Types of Ecosystems: Aquatic Ecosystem - Fresh Water Ecosystem: Part 1 Development Team Principal Investigator : Prof. Neeta Sehgal Department of Zoology, University of Delhi Co-Principal Investigator : Prof. D.K. Singh Department of Zoology, University of Delhi Paper Coordinator : Prof. D.K. Singh Department of Zoology, University of Delhi Content Writer : Dr. Sushma Bhardwaj , Deshbandhu College, DU Ms. Harshita Mishra, Research Scholar, DU Content Reviewer : Prof. K.S. Rao Department of Botany, University of Delhi 1 Principles of Ecology ZOOLOGY Aquatic Ecosystem – Fresh Water Ecosystem: Part 1 Description of Module Subject Name ZOOLOGY Paper Name Principles of Ecology Module Name/Title Types of Ecosystems Module Id M21: Aquatic Ecosystem: Freshwater Ecosystem: Part 1 Keywords Ecosystem, Freshwater ecosystem, limnology, lake, river, stream Contents 1. Learning Objectives 2. Introduction 3. Structure of Ecosystem 3.1. Trophic Structure of the Ecosystem 3.2. Components of Ecosystem 4. Types of Ecosystem 5. Freshwater Ecology 5.1. Freshwater Habitat 5.2. Types of Freshwater Habitat 5.3. Limiting Factors of Freshwater Ecosystems 5.3.1. Temperature 5.3.2. Transparency 5.3.3. Current 5.3.4. Concentration of respiratory gases 5.3.5. Concentration of biogenic salts 5.3.6. Isolation due to land barriers 5.3.7. Osmoregulation 6. Summary 2 Principles of Ecology ZOOLOGY Aquatic Ecosystem – Fresh Water Ecosystem: Part 1 1. Learning Objectives After the end of this module you will be able to Understand the structure, function and composition of an ecosystem Differentiate between ecosystem, ecology and environment List the different type of ecosystems and their characteristics. Know the characteristics of Freshwater Ecosystem Explain the limiting factors of Freshwater Ecosystem 2. Introduction Any assemblage of plants and animals able to exist within an area will in time, form a biotic community. In this community, the different species tend to interact with one another and to modify the conditions of life within which each exists. They therefore develop the inter- relationships and inter-dependences which constitutes an ecosystem. All ecosystems of the earth, together, form the biosphere. The biosphere is that portion of the earth within which life exists. It includes all oceans and freshwater, lower layers of the atmosphere and the outer skin of the earth‘s crust- the rocks and soil of the earth‘s surface. The term ecosystem was proposed by A.G. Tansley in 1935, who defined it as ‗the system resulting from integration of all the living and non-living factors of environment‘. An ecosystem is an overall integration of whole mosaic of interacting organisms and their environment. It is normally an open system with a continuous, but variable, influx and loss of materials and energy. It is a basic, functional unit with no limits of boundaries, consisting of both biotic and abiotic components interacting with each other, both necessary for maintenance of life upon earth. Therefore, it represents the highest level of energy based ecological interaction. 3 Principles of Ecology ZOOLOGY Aquatic Ecosystem – Fresh Water Ecosystem: Part 1 Fig.1: Schematic Representation of an Ecosystem 3. Structure of Ecosystem 3.1. Trophic Structure of the Ecosystem Based on the trophic structure (trophe = ‘nourishment‘), ecosystem is two layered. 1. Autotrophic (―self-nourishing‖) Stratum is the upper layer, also called the ‗green belt‘ of chlorophyll containing plants. This stratum is predominated by fixation of light energy, use of simple inorganic substances, and the buildup of complex substances. 2. Heterotrophic (―other- nourished‖) Stratum is the second layer, also known as the ―brown belt‖ of soil and sediments, decaying matter, roots, etc. This level is dominated by the use, rearrangement and decomposition of complex materials. 3.2. Components of Ecosystem Living organisms and their non-living environment are in-separable and interact with each other in an ecosystem (Fig. 2). Therefore, they constitute the two major components of an ecosystem: a. Abiotic (Non- Living) component b. Biotic (Living) component 4 Principles of Ecology ZOOLOGY Aquatic Ecosystem – Fresh Water Ecosystem: Part 1 Abiotic Component: It includes Inorganic compounds: Substances like, P, S, C, N, H, etc. which are involved in mineral cycling. The amount of these substances present in the ecosystem at any point of time is the indicator of its standing quality. Organic Substances: Substances like proteins, carbohydrates, lipids etc., present either in the biomass or in the environment i.e., biochemical structure. Amount and distribution of inorganic chemicals such as chlorophyll and organic substances, links the biotic and abiotic components of the ecosystem. Air, water and substrate environment, including the climate regime and other physical factors. Biotic Components: It is the living component of an ecosystem and gives the trophic level (nutritional structure) to an ecosystem. The biotic components comprise of: Producers: They convert the sun‘s energy into chemical or food energy (usually green plants). Phagotrophs (phago = ―to eat‖) or Consumers: They depend upon the producers for food/energy. They may be herbivorous, carnivorous, etc. Saprotrophs (sapro + ―to ecompose‖) or Decomposers: They breakdown the complex compounds of dead or living protoplasm into simpler forms and release inorganic nutrients in the environment, which can be reused by the autotrophs. They are also referred as microconsumers and chiefly include bacteria, actinomycetes and fungi. 5 Principles of Ecology ZOOLOGY Aquatic Ecosystem – Fresh Water Ecosystem: Part 1 Fig. 2: Schematic diagram of Ecosystem Function Ecosystem is a functional unit. It includes environment (biotic + abiotic) and the inter- relationship of living organisms with each other and the environment. Ecosystem can be as big as our Earth or as small as a drop of water (water + micro-organisms). Ecosystem is thus a subset of ecology which is a vast subject area. 4. Types of Ecosystem There are four major habitats in the biosphere, i.e., terrestrial, fresh water, marine and estuarine. Based on these habitats, the ecosystem study is classified under different categories. The ecosystem study based on habitat approach helps in developing an understanding of the organisms and physical factors associated with that particular ecosystem. This helps mitigate the pitfalls that may follow excessive generalization (Odum, 1996). Such studies also provide insight into the methods, instrumentation, and technical difficulties applicable to specific situations. 6 Principles of Ecology ZOOLOGY Aquatic Ecosystem – Fresh Water Ecosystem: Part 1 Fig. 3: Classification of Ecosystem 5. Freshwater Ecology According to scientific postulates, life began in ocean. Therefore, it would be logical to start the ecosystem study with marine habitat. However, in actual practice, it is best to start the study with the fresh water ecosystems for several reasons. Primarily, examples for fresh water ecosystems are in close vicinity of man and therefore, it can be easily studied and identified with. Secondly, these are relatively small ecosystems, and hence easily accessible with the use of relatively simple instruments. Finally, the comparatively small biodiversity of the fresh water ecosystem makes it easier for the beginner to understand the dynamics of the natural system. 7 Principles of Ecology ZOOLOGY Aquatic Ecosystem – Fresh Water Ecosystem: Part 1 5.1. Freshwater Habitat Any waterbody having a low salt concentration — usually less than 1% is called a freshwater body. Animals as well as plants in these freshwaters are adapted to the low salt concentrations and are unable to survive high concentration of salt present in oceans. The study of relationship between living organisms and the fresh water environment constitutes the freshwater ecology. The study of physical, chemical, geological and biological aspects of freshwaters is called limnology. In the year 1989, F.A. Forel, a Swiss physician, a naturalist and a professor at the University of Lausanne, published a paper describing the bottom of the fauna of Lac Leman, now called Lake Geneva. This publication of Forel‘s paper is now considered as the beginning of the scientific study of lakes. Forel earned himself an ever-lasting regard as the founder of limnology. The study includes many disciplines, such as geology, chemistry, physics and biology, which constituted the core for the study of the inland waters. By 1900 limnology had gained a strong ecological approach. A paper published by S.A. Forbes, a naturalist and entomologist, in 1997, titled ―The lake as a microcosm,‖ had described the lake as a ―small world‖ in which environmental features and living organisms are in complex interrelationships and bound together by a web of interdependence. Fig. 4: Lake Geneva 8 Principles of Ecology ZOOLOGY Aquatic Ecosystem – Fresh Water Ecosystem: Part 1 Although the term limnology originally applied only to the study of lakes, in its current use it also refers to the study of streams. As we will see, these two types of water systems differ in many ways. The term potamology is frequently used for studying the river systems. The word stream is used to indicate any mass of water with unidirectional flow; mountain brooks, spring brooks, creeks and rivers. In recent years, ecologists, hydrologists and engineers have been giving special attention to stream systems. 5.2. Types