Marisia - Maros Megyei Múzeum Évkönyve 32/1. (2012)
Zoology
Gabriela GRIGORAS, Marcela ROSCA basins with lush populations of aquatic plants as result of outflow of groundwater with high nutrients supply but nearly oxygen-free. A detailed analysis of our results and other scientific references do not confirm the above theory: • The respiratory intensity of higher aquatic plants increases when the DO content tends to saturation limit (Gessner, 1959 quoted by Kasselmann, 2003) and also the aeration of the substrate acts as limiting factor on the respiration of the roots. The respiratory processes represent an indicator of plant metabolism and its growing rate. • The aquatic biocoenosis from tropical area are characterized by a large range of dissolved oxygen content, 4—14 mg/1 frequently tending over saturation limit. • During the dark phase of their metabolism, the aquatic plants use the dissolved oxygen for photosynthesis and an optimum content of oxygen has a positive effect especially on the fast-growing plants species that can be considered an indicator of a good balanced environment from the physical, bio-chemical point of view. • It can be considered as optimum a saturation level between 70—130%. • An optimum content of dissolved oxygen could also have an inhibitory effect on bluegreen algae developing (Kasselmann, 2003). Into an aquarium with an optimum nutrient supply rate and high amount of light, the algae blossom is one of the risk factor that can inhibit the plants growing. • The oxygen is important for both heterotrophic and chemoautotrophic bacteria that use the atom as electron acceptor for respiration. The oxidation reduction potential (ORP) depends on DO water content but also several factors determine a certain level of ORP value. The intensity of redox processes from water is a measure of a well balanced and healthy aquatic environment. A value of 700 - 800 mV shows an oxidized environment (strong oxidizing agents that can withdraw electrons from bacteria killing them, are ozone, chlorine, chloramine and hydrogen peroxide) while a redox of — 250 h- - 350 mV is typical for reduced water (reducing agents such as magnesium, calcium, sodium or organic matter readily donats its electrons to oxygen radicals and blocks interaction of the active oxygen with various molecules). The substances that have the ability to counteract active oxygen by supplying electrons are called scavengers. The photosynthesis involves oxidation and reduction both and our redox potential dynamic measured into experimental tanks is influenced by the optimum level of this biological process, organic matter mineralization and all biochemical reaction from water, weak acid pH, UV-C radiation (that has sterilization effect but also acts in the same way as ozone), addition of new minerals (fertilization) or partially water change (with new ions supplying and electrolytes balancing). Fig. 15: The water oxidation reduction potential (mV) during aquarium set up (first stage of artificial ecosystem start-up) 128
