In the examination of the phytoplankton communities from both sampling sites, they were classifid into 7 divisions and a total of 81 species and 79 species of phytoplankton were identifid (Appendix ; Table 5). In sampling site 1, the Chlorophyta was the most abundant species with 32.10%. There were 27.17% species of Euglenophyta, 19.76% of Cyanophyta, 9.87% of Bacillariophyta, 4.93% of Pyrrhophyta were found, Cryptophyta had 3.70% and Chrysophyta had 2.46%. Similarly in sampling site 2, the Chlorophyta was the richest in species with 31.65%. Euglenophyta was found to have 22.79%, Cyanophyta - 20.26%, Bacillariophyta - 13.92%, Pyrrhophyta - 5.06%, Cryptophyta - 3.79% and Chrysophyta - 2.53%, respectively (Figure 2). In sampling sites 1 and 2 were found the highest species of phytoplankton in Division Chlorophyta. According to Charzykowskie Lake in Poland (Wisniewska & Luscinska, 2012) and Mae Ngat Somboonchol Reservoir in Chiang Mai Province (Proongkiat, 1999) were found that the highest species of algae was in Division Chlorophyta. It was shown that there are an abundance of nitrate and phosphorus in the water when the Chlorophyta was the richest in water (Proongkiat, 1999). In sampling site 1, the highest phytoplankton biovolume was found at the depth of 1 meter ranging from 780.34-12,347.78 mm3.m-3 (The average was 4,267.09 mm 3 .m -3). At sampling site 2, phytoplankton biovolume ranged from 1,051.49-13,903.18 mm3.m-3 (The average was 4,967.10 mm3.m-3). The highest value of phytoplankton biovolume at both sampling sites was found in December 2011 to January 2012 due to the inflw of nutrients, organic and inorganic matters into the lake during the great flods causing algae bloom (Talling, 1962 ; Wetzel, 1975). In the study of phytoplankton biovolume at different depths of sampling site 1, the biovolume stratifiation at 1 meter from water surface tended to be higher than those at lower depths (Figures 3). It was found that 31.35% at the depth of 1 meter followed by at the depth of 5 meters and 10 meters representing 30.54% and 20.15%, respectively. The percentages of phytoplankton biovolume were low at the depth of 15 and 20 meters with 12.49% and 5.47%, respectively (Figure 4). The fiding showed signifiant differences (p<0.05) in the amount of biovolume in each depth of the lake because light is an essential factor for photosynthesis of phytoplankton. When the sunlight is able to penetrate through the water surface, phytoplankton will grow well and therefore increase the phytoplankton biovolume (Shirota, 1966). Likewise at sampling site 2, the phytoplankton biovolume at the depth of 1 meter was higher than that at 4 meters (Figure 5) but there were no signifiant differences (p>0.05). Comparing the amount of phytoplankton biovolume and chlorophyll a at the depth of 1 meter at both sampling sites, there were no signifiant differences (p>0.05) because of these sampling sites had the same physico-chemical variable. Therefore, the amount of phytoplankton biovolume and chlorophyll a were not different (Pekoh, 2002). Both sampling sites had the same dominant species such as Cylindrospermopsis raciborskii (Woloszynska) Seenayya & Subba Raju followed by, Peridiniopsis cunningtonii Lemmermann, Pseudanabaena limnetica (Lemmermann) Komárek and Trachelomonas volvocina (Ehrenberg) Ehrenberg, respectively. In this research, C. raciborskii, P. limnetica and P. cunningtonii had the highest biovolume in both sampling sites after flod disaster during December 2011 and January 2012 which indicator water in Rama IX Lake was in mesotrophic to eutrophic status. However, C. raciborskii can be found in every specifid depth of the lake because C. raciborskii is tolerant to low light availability and is able to assimilate and store phosphorus and to fi atmospheric nitrogen (Padisák, 1997) and very common in the tropical zone with an optimum temperature growth rate above 25˚C (Chiswell et al., 1997). Walsby (1992) reported that C. raciborskii has gas vacuoles which is nitrogen gas. Thus, it can be sink to the lower levels or flat up to the surface of the lake. After flod period from February to November 2012, it was found that P. cunningtonii which is dinoflgellate and T. volvocina were a dominant species in both sampling sites of the Rama IX Lake and indicated as mesotrophic status. According to Suravit (1996), who found Peridinium app. and Trachelomonas spp. Were to be the dominant species in Ratchaprapa reservoir in southern, Thailand and indicated as mesotrophic status. Therefore, the dominant species of phytoplankton can be used to indicator the trophic status in the Rama IX Lake.
การแปล กรุณารอสักครู่..