Comparative studies of the global ecological state variation of the aquatic environment in the Crişuri Hydrographic Space between 2007 and 2009

The paper presents a comparative study regarding the evolution across time of the quality of aquatic eco-systems in the Crişuri Hydrographic Space (CHS), between 2007 and 2009. Having as a goal a real and complete image of the quality of the environment in the CHS, the ecological monitoring conducted was meant to observe the structure of the aquatic communities (macrozoobenthos, microphytobenthos, phytoplankton) and the biotope characteristics (physical and chemical parameters of water: pH, conductivity, dissolved oxygen, CBO5, CCO-Mn, CCO-Cr, nitrites, nitrates, phosphates, amonium, chlorophyll "a", chlorides, sulphates, fix residues, As, Hg, Cu, Zn, Mn, phenols, detergents etc). The choosing of the monitoring sections, their identification and geographical position were accomplished in 2006. The basic criterion in the choice of the monitoring sections was the identification of all aspects that can influence the quality state of the waters. The monitoring of the quality state of the waters in the CHS was conducted in 40 sections, both on the main courses and their affluents, over a 3year period. After the results of the analyses of physico-chemical and biological samples were obtained, the categorization of the prelevation sections in quality classes followed; depending on these classes, the modelation of the global ecological states of the watercourses in the CHS was realized by means of mapping techniques (GIS). Most of the monitoring sections were in the good ecological state category. The very good ecological state was determined only for those sections upstream all polluting sources. Nevertheless, some of the prelevation points exceeded both physico-chemically and biologically the limits of the good quality state, entering the category of moderate quality state. No watercourse in the CHS was determined for poor or bad quality state. Generally, a "preservation" of the quality state of the waters from one year to the following was noticed, although some monitoring points registered an improvement of the global ecological state, whereas others, a degradation. The improvement (eg. prelevation sections Râbiţa on Crişul Alb, Pădurea Neagră on Barcău or upstream Huedin on Crişul Repede) is mainly due to the lower quantity of mis-/untreated residual water upstream the monitoring sections. The modernization of waste-water purifying stations as well the connection of the urban areas to these stations finally contributed to the improvement of the water quality