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Gashtrudkhan River is located in the western drainage basin of Guilan Province. Monthly sampling of macroinvertebrates was carried out in five stations by using a surber sampler with Dimensions of 30.5 cm ×30.5 cm and 360 micron mesh size for eight months in different seasons from autumn 2019 to spring 2020. Moreover, some physicochemical parameters of water, i.e., pH, EC, TDS, DO, temperature and salinity were measured, so that these parameters showed significant differences in different seasons. In addition, diversity indices (Simpson and Shannon), species richness, EPT, EPT/Chir, biological indices (Hilsenhoff and BMWP) and the WQI index were studied and calculated. During the sampling period, a total of 1017 macroinvertebrates were isolated and identified from different stations, belonging to one Phylum, one Kingdom, four orders, 19 families and 22 genera in this river. EPT and EPT/CHIR indices were the highest in spring and the lowest in winter. Also, the highest and lowest values of Shannon's diversity and species richness indices were observed in autumn and spring, respectively. The water quality status in the studied period was classified as good to excellent based on the Hilsenhof biological index. Furthermore, the water quality status was evaluated based on the BMWP and WQI indicators as clean and average, respectively. According to the investigated area in Gashtroudkhan River, located in a forest area with gravel and stone beds, no significant differences were observed in many of the studied indicators.

The seasonal succession of phytoplankton communities in Yamchi dam constructed on Balikhli River, Ardabil province was studied from October 2014 to November 2015. Monthly sampling was carried out in three stations at the depths of 0, 5 and 10 m in station number 1 and the depths of 0 and 5 m in stations number 2 and three. In this survey, 41 species belonging to 35 genera, 8 classes and 6 phylla of algae were studied. The phyla Chlorophyta and Bcillariophyta contained the highest number of species (14 and 13 species, respectively). The highest density of phytoplanktons was observed in station 1 at the depth of 10 m in September (2.4 × 104 cell.ml -1) and the lowest density was identified at station 1 at the depth of 5 m in May (2 × 103 cell.ml -1). In total, the highest densities belonged to Chlorophyta with the maximum densities in spring and summer (the highest was 1.2 × 103 cell.ml -1). In studying the seasonal succession, diatoms were dominant in autumn and early spring assemblages. In summer, green algae and dinoflagellates and in late summer cyanobacteriae were the most dominant groups. The seasonal succession observed in Yamchi dam reservoir is characteristic of eutrophic alkaline lakes. Results of ordination analysis (PCA) revealed that the temperature, silicate, sulphate and BOD, and COD were the main factors affecting phytoplankton assemblages in this lake.

This study aimed to assess the ecological status of Khamir, Tiyab and Jagin creeks and the impact of human activities on the studied ecosystems using AMBI biological indicator. During the study period, 165 macro-benthos taxa belong to seven phyla including Annelids (65 taxa), Mollusca (65 taxa), Arthropods (28 taxa), Echinoderms (3 taxa), Hydrozoans (2 taxa), Nemertea (1 taxon) and Nematoda (1 taxon) were identified. For the total abundance, Polychaeta showed the richest taxonomic feature with 62 species, contributed 37.57% of the total abundance. The average values of AMBI in the four seasons ranged from 1.12±0.09 (spring) to 5.08±0.15 (autumn). The highest values occurred at station 6 (spring, 4.12±0.81; summer, 5.01±0.56; autumn, 5.08±0.15; winter, 4.42±0.38), and the lowest values occurred at stations 7 (spring, 1.12±0.09; summer, 1.24±0.07), and 1 (autumn, 1.25±0.07; winter, 1.33±0.24). Results from ecological status of studied creeks using AMBI index throughout the year showed that Khamir creek classified as "slightly polluted" to "moderately polluted", Tiyab creek classified as "slightly polluted" to "heavily polluted" and Jagin creek classified as "slightly polluted". The findings of this study revealed that the AMBI index is suitable for separation of areas with less impacted by human activities from areas affected by these activities and could be used as a robust management tool for monitoring programs.