جستجوی مقالات مرتبط با کلیدواژه "trophic index" در نشریات گروه "شیلات"

The spatial salinity patterns which give a picture of the area affected by eutrophication and trophic status changes at the ecosystem. The aim of this study was to determine the area affected by freshwater eutrophication using trophic level (TRIXcs), the risk of eutrophication (UNTRIX) and the nutrient-salinity scatter diagram. Also, the data of the present study are compared with previous year of studies. This research was conducted during 2018 to 2019 in eight transects and at 5, 10 and 30 meter depths of Iranian coasts of southern Caspian Sea. The results showed that mean seasonal changes of TRIXcs and UNTRIXcs were 4.94-5.59 and 3.57-4.17, respectively, which the highest trophic level and risk of eutrophication was observed in summer season. In addition to, trophic level (TRIXcs) risk of eutrophication (NUTRIX=4.30) of near the coast (5m depth) were high. Mean of TRIXcs and UNTRIX between different regions (western, middle and eastern) were not significant. In the present study, the maximum amounts of ammonium and soluble silica near the west coast were recorded in Anzali transect and also under the influence of the largest river Sefidrud in the southern shores of the Caspian Sea, but the points with maximum NOx and phosphate values were observed in the east (Amirabad and Bandar-e-Turkmen transects). The nonlinear relationship between NOx, NH4, DIP and DSi with salinity indicates that river flow and water mixing were affected nutrient concentration and changes of trophic levels in the study area.

This study was designed to determine the effect of rainbow trout cage culture on the chlorophyll-a content and trophic index value in the Abbas Abad area, southern Caspian Sea. For this purpose, water samples were collected by a distances of 5, 50, 100 and 1000 m from the cages during December 2014 (before rearing period), March and April (during rearing) and August 2015 (post rearing period). In this study, a totalof 42 species of phytoplankton belonging to five phyla (with the dominance of Bacillariophyta) were identified. Chlorophyll-a content varied significantly in different periods and stations (P<0.05). The highest and lowest chlorophyll-a content was recorded in March and station 5 m (2.13 μg/l) and May and station 1000 m (0.44 μg / l) away from cages, respectively. The Trophy State Index (TSI) was significantly different between the sampling periods (P<0.05). The highest TSI (42.18) was observed in March and then in August (40.47) and this differences were significant between different periods (P<0.05), whereas, it was not affected by the distance from the cages (P<0.05). It seems that the rainbow trout cage culture in the Abbas Abad region no remarkable effect on Chlorophyll-a and trophic index in the vicinity of fish cages due to the small scale and short duration of cage culture activity and strong water currents, so that observed changes were more associated with seasonal fluctuant.

Determining the relationship between biotic and abiotic factors and their effects on water quality and eutrophication plays important roles in managing and optimizing the efficiency of dams. Therefore, in the present article, the above relations with emphasis on the results of one-way and multivariate statistical analysis were investigated in Sanandaj Azad dam. Monthly Sampling was carried out in 5 stations in 2015-2016. All environmental parameters (Water temp.,Secchi disk, Turbidity, pH, DO, DO%, BOD5, COD, EC, NO3-, PO43-, Chl-a) and microbs (Total counts, Total coliform,  Fecal coliform and   Fecal Streptococcus) were analyzed based on standard methods. (According to the results, low numbers (less than 0.1 CFU / 100 ml),  of streptococcus and fecal coliform in all samples were a good sighn of fine water quality in terms of non-contamination with fecal (resistant and old) and (fresh) microbes. In the step wise linear regression test, the coefficient effect of trophic state, based on chlorophyll-a and transparency depth on the total trophic index was obtained more than the nutrients trophic index. According to the principal component analysis (PCA), the trophic state index and chlorophyll-a concentration (in the first component) were the most important factors on quality of the water. While the water quality index and its parameters (inorganic phosphorus, BOD5 and coliform) were included in the second component. Among the environmental parameters affecting the quality of water, the percentage of saturated dissolved oxygen and then BOD5 were in the first priority. As a conclusion, according to the the trophic state index, this dam is suitable for the development of rough fish (cyprinidae). In other words, according to the WQI index, the Azad Dam is suitable for farming of salmonids fish, but based on trophic stae index, condition is not very favorable.