Practical Notes of Aquatic Ecology PDF

Practical notes of aquatic ecology Ecology is the Greek word, oikos meaning house and logos meaning science Ecology is the study of the interactions of organisms with each other and with their environment It consists of: - Species e.g., Nile tilapia, red tilapia, tilapia zillii, mirror carp. Popul...

Practical notes of aquatic ecology Ecology is the Greek word, oikos meaning house and logos meaning science Ecology is the study of the interactions of organisms with each other and with their environment It consists of: - Species e.g., Nile tilapia, red tilapia, tilapia zillii, mirror carp. Population e.g., Tilapia only or Carp only = species + species +species, etc. Community e.g., Tilapia with carp ‫ مبروك‬with mullets ‫ = بورى‬population + population, etc. Ecosystem e.g., water with sand with clay with oxygen with plankton + community, So Biosphere includes different ecosystems with each other e.g., aquatic ecosystem, plant ecosystem, etc. Fig.1 summary of biosphere Our targeting is aquatic ecosystem or aquatic ecology 1 Practical notes of aquatic ecology Aquatic ecology is branch of the science of ecology which focuses on the study of aquatic ecosystem and has two main divisions freshwater ecology and marine ecology and from mixture of two consists brackish ecology which called estuaries Freshwater ecology involves rivers, lakes, streams Marine ecology involves the seas and oceans Estuaries where freshwater meets saltwater Why must we study and understand aquatic ecology? Because changes in one part of the system often cause changes whether large or small throughout the system. This concept can be understood through this example: The pond with aquatic plants, a healthy largemouth bass population and bluegill fish. When all plants are eliminated from the pond in an effort to improve angling access, bluegill fish lose their protective cover and are exposed to excessive predation by largemouth bass. The largemouth bass fish initially respond by growing and reproducing rapidly, but the bluegill fish population declines, finally the Largemouth bass population limited by decreasing food supplies and becomes small and stunted. Some definitions Nutrients: elements and compounds such as phosphate and nitrate needed by organisms e.g., algae, aquatic plants in order to grow. Plankton: free floating plants and animals most microscopic and include phytoplankton and zooplankton. Phytoplankton: free floating microscopic plants e.g., microalgae Zooplankton: free floating microscopic animals e.g., larva, young crabs, shrimp, daphnia, or other crustaceans Oligotrophic: describing a body of water in which nutrients are in low supply. Eutrophic: waters with a good supply of nutrients. Successional cycle of ponds and lakes The aquatic ecosystem is a dynamic, changing environment, changes in water chemistry and the species composition. Ponds and lakes go through a cycle of changes over time. The cycle starts by oligotrophic waters which have very little 2 Practical notes of aquatic ecology nutrients, a small phytoplankton population and consequently clear water but it can be colored by dissolved or suspended minerals. With time the pond ages, leaves and other materials from terrestrial habitat wash into it through the rains, winds and climate changes and plants and animals of the pond over the time may die and decay and this pond called mesotrophic pond then gradually the amount of nutrients available to the ecosystem and the phytoplankton communities increase and the water becomes less clear and greener. vascular aquatic plants colonize the shoreline and extend into the water as nutrients become available. ponds or lakes with high levels of nutrients called eutrophic in this case the pond has reached a mature stage of development. With the frequent releasing of plant nutrients through rains, winds into pond over the time in addition to realizing farm fertilizers, livestock manure, some detergent these cause the appearance noxious algae blooms and excessive phytoplankton production in this case the lake is highly eutrophic or polluted. over time leaves, dead plants and other detritus accumulates on the pond bottom and aquatic vegetation covers the water's surface. The pond has reached the age of senescence. Willows, cypress, cattail and other shoreline plants advance toward the ponds center. Eventually dry land trees begin to invade areas and the pond becomes a bog or marsh. Surrounding terrestrial vegetation replaces aquatic and semi aquatic plant species and succession is complete. N.B. Successional cycle can be disrupted at any time by natural events e.g., floods that can deepen and rejuvenate the pond. Human activity e.g., draining and dredging the pond also can interrupt the successional cycle. Determining the Trophic State Index (T.S.I) of the lakes or ponds This measuring is more valuable to compare changes in one lake's quality over the years or to compare between lakes or to take a picture for good and bad lakes. T.S.I can be calculated through 1. secchi disk depth (SD) 2. the total phosphorus concentration at the surface of the lake (TP) 3. the chlorophyll a concentration at the surface of the lake (chl a) 3 Practical notes of aquatic ecology N.B. Either average one day's values or, preferably, average values over the summer can be used. 1. Secchi disk depth (SD): T.S.I = 60 – 14.41 (ln SD) The value of SD in m 2. the total phosphorus concentration at the surface of the lake (TP) T.S.I = 14.42 (ln TP) + 4.15, value of TP in µg/L 3. the chlorophyll a concentration at the surface of the lake (chl a) T.S.I = 9.81(ln chl a) + 30.6, value of chl a in µg/L N.B. Chlorophyll a is the best indicator to use if using data from the summer months TP is the best indicator to use if using data from the rest of the year You should be aware that you will not calculate the same T.S.I value with each of the parameters The scale to know the trophic state of the lake 0 - 40 oligotrophic 40 - 60 mesotrophic 60 - 100 eutrophic The description of each state Oligotrophic Modern Transparent high O2 high Bacteria low Nutrients and plankton 4 Practical notes of aquatic ecology Mesotrophic Moderate between modern and older Transparent moderate O2 moderate Bacteria moderate Nutrients and plankton moderate Eutrophic Older Transparent low O2 low Bacteria high Nutrients and plankton high Example calculate T.S.I when TP average concentration is 500 µg/L in summer and determine the state of the lake and Is this the best indicator? And if not say what is better in this case? The solution T.S.I = 14.42 (In TP) + 4.15 TP = 500 µg/L T.S.I = 14.42 (In 500) + 4.15 = 93 Since T.S.I = 93, the lake state is eutrophic TP is not the best indicator in summer Chlorophyll a is best indicator in summer Assignment 1 will deliver the next section, anyone delay don’t take the degree of her calculate T.S.I when (chl a) average concentration is 100 µg/L in summer and determine the state of the lake and Is this the best indicator? And if not say what is better in this case? 5