چكيده انگليسي :
The aim of this study was to investigate the quantitative and qualitative effects of Gragar river fish farming and its impact on Karun River health. Field sampling started from February 2015 and continued for a year in the studied area. From 7 stations (1 station before river dividing in Shushtar city and 4 stations along the Gargar River and 1 station from the Shutait Karun Branch and finally 1 station in Large Karoon after the connecting the three branches of Shutait , Gargar and Dez). Stations 3 and 4 were located at the point of discharge of effluent
from fish farms. Mmonthly regular sampling of water, coliforms, sediment ,macrobenthos and phytoplankton were carried out. Many types of quality indices based on water, sediment and biotic communities have been used to assess river quality statuss. Based on the results, aquaculture wastewater influences the water quality of the river, but the meagnitude of this effects as the only source to produce a significant effect on the river ecosystem is less and the more meaningful effects are observed in the discharge points. The most important
effects of fish farms drainage on water resources, are increasing the amount of nutrients and the growth rate of algae, which ultimately leading to occuring eutrophication in the river, in which the algal bloom were not observed in this study. Considering the importance of phosphorus as a limiting parameters of primary production in freshwater sources, the amount of phosphorus in the river was much lower than the eutrophy threshold (2-4
mg / l). According to the results of the Streeter-Phelps self purification equation, in the interval between wastewater drainage and the final station, it is concluded that if aquaculture waste was continuously entered into the Gargar branch with current conditions , due to the aeration velocity and river self-purification, the oxygen deficite from oxygen consumption in oxygenated activities does not pose a risk to river life, and the level
of dissolved oxygen in the river is higher than the minimum of aquatic life standard l (4 milligrams per liter). The results showed that Station 2, after the wastewater discharge site in Shushtar, has the highest of the total bacterial count and generally, in all stations are higher than the standard limit. Also, the total number of coliform
and fecal coliform in all stations was higher than the allowable discharge of wastewater and different uses, which suggests that the sources of pollutants in the river are numerous in terms of the total bacterial count and is not limited to waste water from fish farms. It can be concluded that, although water bacterial flora is affected by
human and agricultural activities, fish farms effluent is not considered as the only source of bacterial
contamination for the river. The numerical value of the Saprobic index based on phytoplankton, which is the most relevant biological index with water nutrient content, all stations are classified in the qualitative class (II), or beta mesosaprob with a moderate level of contamination, and the results of Palmer index showed , stations 3,
4, 5 and 7 are categoried in the group of organic materials contamination. According to the results of biological indices based on Benthic communities (BMWP, ASPT, HFBI), the quality of the Gregar River was classified in unfavorable and poor condition, which is obviously due to the burden of human intervention on the river's body and is not necessarily due to fish wastewater, because The eutrophy condition due to the entry of nutrients from the farm effluent in an y of the studied stations have not been observed. Since the indices associated with
sediment parameters can express a longer history of river quality, and since the source of organic contamination of the river can not be solely due to fish waste, It can indicate different sources that affect on quality of the river in addition to aquaculture. Also , station 6 located in shutate branch without any aquaculture activity
showed similar qualitative result. Fish-farming ponds can be one of the sourcess contributing to increasing
nutrient concentrations in the Gargar river. Of course, in this case, other factors such as increasing temperature
and evaporation, reducing water volume of the river, entering urban and rural wastewater and agriculture also
affect the concentration of pollutants in the aquatic environment. Therefore, reducing the water quality and
increasing the nutrient content in the Gargar River is not attributed solely to the effluent from the fish farms. The
quality status of the Gargar River water is classified in the qualitative class of 2-3 which describes the low
pollution and the results of the WQI, except for station 4 in the wastewater entry point, which has a moderate
quality, all other stations are categoried in good quality class It is recommended that wastewater treatment systems must be used to reduce pollutants and not be necessarily reduced aquaculture production volumes. It is also suggested that must be pay attention to the capacity of river dilution and self-purification for issuing permits. It should be noted that other factors, such as the type of water using , also affect water quality and their impact on water quality can not be ignored for assessment and all changes in the communities and water quality are not solely effected by aquaculture.
