Comparison of phytoplankton community structure of Kizilirmak delta lakes with environmental factors

Lakes and reservoirs constitute a significant portion of the Earth's freshwater. Lakes are unique ecosystems characterized by their own physical, chemical and biological properties. Lagoons, which are located within lake systems and have ecological importance, generally cover coastal wetlands that are connected to the sea, have shallow waters and are completely or partially separated from the sea or ocean as a result of sedimentation. Coastal lagoons are between the sea and the land surface and their ecosystems carry the characteristics of marine and terrestrial factors. The Kızılırmak Delta, formed by the alluviums carried by the Kızılırmak River, is one of the largest deltas in our country. It is located on the Black Sea coast and is a wetland that has preserved its natural characteristics. It provides an important biological contribution to the Bafra Bird Paradise in terms of richness and diversity due to the coexistence of ecosystems such as marsh, reed, lake, sea, forest and agricultural areas. The wetland ecosystems in the delta were fed by the regular floods of the Kızılırmak River and the waters entering from the sea connections in the past, but the floods have been prevented and their natural feeding has stopped due to the dams and flood prevention dams built on the river. Especially after the construction of the interception channels and the discharge of drainage waters to the sea through the transmission channel, the water in the lakes has gradually receded and the risk of drying has increased due to inadequate feeding. Apart from the Kızılırmak River, the permanent streams in the delta are the Engiz and Piliç Streams in the east of the Bafra Plain, the Darboğaz and Mera Streams, the İlyaslı Stream in the west, and the Bedeş, Gökçesu, Söğütlük, Gökçeboğaz and Uluçay (Alaçam) Streams In this study, sampling was carried out from the stations determined in seven lagoons in the Kızılırmak Delta in June, July, September 2020 and February, May, July 2021. Karaboğaz lagoon is a shallow lagoon. It was sampled from three points: from the part of the lake near the sea (KB3), from the part near the middle of the lake (KB2) and from the point where the lake meets the canal (KB1). In other lagoons, water samples for phytoplankton and environmental parameters were taken from the deepest point of Çernek Lagoon (CER); from the deepest point in Liman Lagoon (LIM); from the deepest point of Gıcı Lagoon (GICI), from the deepest point of Tatlı Lagoon (TAT), two points in Uzun Lagoon (UZ1 and UZ2) and three points in Ulu Lagoon (ULU1, ULU2 and ULU3). Temporal and spatial changes in phytoplankton biovolume, species richness, diversity and Reynolds functional groups (FGs) with the effects od different environmental variables (salinity, temperature, pH, dissolved oxygen, electrical conductivity salinity, temperature, pH, dissolved oxygen, electrical conductivity, nitrate-nitrogen, nitrite-nitrogen, sulfate, dissolved silica, ortho-phosphate, total nitrogen, total phosphorus, nitrate-nitrogen, nitrite-nitrogen, sulfate, dissolved silica, ortho-phosphate, total nitrogen, total phosphorus) were investigated seasonally in 2020 and 2021 in Ulu (ULU), Uzun (UZ) Tatlı (TAT), Gıcı (GIC), Çernek (CER), Liman (LİM) and Karaboğaz (KB) lagoons in the Kızılırmak Delta (Samsun, Türkiye). Also known as Balıklı Lake, Ulu Lake Lagoon is located east of the Kızılırmak River. It is surrounded by 19 Mayıs and Bafra districts. Agriculture and animal husbandry are developed in the villages belonging to the districts. Uzun Lake Lagoon is another lake located east of the Kızılırmak Delta. It is surrounded by Bafra and 19 Mayıs districts. Rice farming and buffalo husbandry are carried out in the surrounding villages. There is a canal connection with Ulu Lake. It is a shallow lakeTatlı Lake Lagoon is another lake located east of the Kızılırmak River. The lake is located on the border of 19 Mayıs and Bafra districts. Agriculture, animal husbandry and fishing are developed around the lake. Fish cooperatives allow hunting during certain periods. Especially Israeli Carp has become an invasive species in the lake. Gıcı Lake Lagoon is another lake located east of the Kızılırmak River. The lake is surrounded by 19 Mayıs and Bafra districts. Seasonal fishing is done in the lake. It is connected to Tatlı Lake via a canal. Liman Lake Lagoon is another lake located east of the Kızılırmak River. The lake is very close to the sea. There are savannas around it. In addition, a large canal empties its waters into the lake. Fishing is done in the lake. It is called by many names such as Çernek Lake Lagoon, Cernek, Görnek, etc. Çernek Lake has the characteristics of flooded forests by increasing its water surface area in rainy periods. In dry periods, the water volume decreases and shrinks. Buffalo husbandry is intensively done around it. Karaboğaz Lake Lagoon is a long lagoon lake located in the west of the Kızılırmak River. There is a canal that connects the lake to the sea at its end point close to the sea. This canal is opened at certain times and the lake water is combined with the sea. In addition, water is emptied into the lake through a canal. Agriculture and fishing are very developed in the villages around the lake. Since the average depth of the lakes was below 5 meters, water samples were taken 0,5 meters below the surface for physico-chemical analyses and phytoplankton identification. Salinity, temperature, pH, dissolved oxygen, total dissolved solid and electrical conductivity values were measured 0,5 meters below the water surface with YSI Proplus water quality probe. Ortho-phosphate (PO4-P), Nitrite Nitrogen (NO2-N), Nitrate Nitrogen (NO3-N), Dissolved Silica (SiO2), Sulphate (SO4), Total Nitrogen (TN) and Total Phosphorus (TP) were analyzed spectrophotometrically in the laboratory according to standard methods. Chlorophyll-a was measured spectrophotometrically using methanol extraction. Phytoplankton counts were made on an Olympus IX81 inverted microscope using a Utermöhl sedimentation circle. Identification keys were used for species identification and identified species were checked against the Algaebase species list. Water samples brought to the laboratory were shaken well to ensure homogeneous distribution of organisms and 50 mL of them were placed in graduated cylinders. For fixation, a solution containing KI + I and 4% formaldehyde was dropped and left to settle for at least 24 hours. When the sedimentation occurred at the bottom of the graduated cylinders, the excess water at the top was removed with a bull pipette and the 5 mL portion at the bottom of the cylinders was transferred to smaller bottles, the bottles were labeled and stored for analysis. There were no significant differences between the lakes in terms of temperature, pH and dissolved oxygen (p > 0,05), but there were significant differences between LIM and ÇER lakes in terms of electrical conductivity, between LIM and ÇER lakes in terms of salinity and between ULU and ÇER lakes in terms of zmix/zeu ratio (p < 0,05). In addition, there were no significant differences between the lakes in terms of NO2-N, NO3-N, PO4-P and TP (p > 0,05), while there were significant differences between ÇER and GIC in terms of TN, between ÇER and LIM in terms of SO4, and between ÇER and UZ in terms of SiO2 (p < 0,05). However, there was a significant difference between CER and ULU in terms of chlorophyll-a (p < 0,05). After the identification and counting, a total of 524 taxa belonging to 106 Bacillariophyta, 35 Charophyta, 165 Chlorophyta, 7 Cryptophyta, 87 Cyanobacteria, 77 Euglenozoa, 32 Miozoa, and 15 Ochrophyta divisions were recorded in Kızılırmak Delta Lakes. During the studied periods, 14 Functional Groups (FG) (codon-C, codon-D, codon-J, codon-Lo, codon-M, codon-MP, codon-P, codon-S1, codon-S2, codon-SN, codon-W1, codon-W2, codon-X1 and codon-X2) were evident in the total biovolume. Three Functional Groups (codon-C, codon-P and codon-SN) were found to be predominant only in KB, GIC and CER lagoons. Although phytoplankton biovolume did not show significant differences among the seven lagoons, mean biovolume values were lower in the saltiest LIM and KB lagoons. Moreover, the saltiest lagoons LIM, KB and CER had lower species richness and their species compositions were found to be different from less saline lagoons. In addition, the total number of taxa was lower in LIM and CER and contained a higher proportion of marine species. In addition, phytoplankton biomass and species richness were generally lower during spring. Phytoplankton biovolume and species richness were higher during the summer and fall periods of 2020. Based on pairwise comparisons of cluster analysis and β-diversity index, the phytoplankton community of the TAT and GIC lagoons, connected to each other by an artificial channel, was found to be closer. According to the results of the same two analyses, the phytoplankton community of UZ and ULU lagoons connected to each other by canals was similar. Pairwise comparisons of the β-diversity index also revealed a close similarity in the phytoplankton community between ULU and TAT lagoons. According to the Bray-Curtis cluster analysis, it was determined that the phytoplankton species compositions of the Tatlı Lake and Gıcı lagoons, which are connected to each other by artificial channels, are closer to each other, while the phytoplankton species compositions of the Ulu Lake and Uzun Lake lagoons, which are also connected to each other by artificial channels, are closer to each other. According to the results of RDA, the composition of FGs in the studied lagoons was also influenced by seasonality and hydrology and divided into spring (wet), summer (dry) and fall (transition) periods. Accordingly, TN and temperature were associated with summer months and codons J, Lo, M and X1; while NO3-N with codons W1 and P and mostly with spring periods; dissolved oxygen with codon W2 and mostly with fall periods; Si with codons S2 and SN and mostly with fall and spring periods. Moreover, FGs W1 and P were usually detected in spring periods, while codons J, Lo, M and X1 were usually detected in summer periods, and codons C, MP, W2 and X2 were the dominant groups in autumn periods. On the other hand, S1, S2, SN and D were found in lagoons during summer, spring and fall periods. Among the FGs, the dominant codons D, J, Lo, M, MP, S1, S2, W1, W2, X1 and X2 were more widely distributed in the lagoons. However, codon C in KB, codon P in GICI and codon SN in GICI and CER were dominant only in the indicated lagoons and their distribution was influenced by pH, NO3-N and low light availability (high zmix/zeu). As a result; during the periods examined, although phytoplankton biovolume did not show significant differences among the seven lagoons, the average biovolume values were found to be lower in the most saline Liman and Karaboğaz lakes. D, J, Lo, M, MP, S1, S2, W1, W2, X1 and X2 codons, which are dominant among FGs, were more widely distributed in the lagoons. Due to seasonality and hydrology, environmental parameters such as salinity (SAL), temperature (T), pH and nutrients generally differed in flood (spring), drought (summer) and transition (autumn) periods. Phytoplankton biovolume and taxa count were higher in the summer and autumn periods of 2020. In addition, W1 and P codons were generally detected in the spring periods, J, Lo, M and X1 codons were generally detected in the summer periods, while C, MP, W2 and X2 codons were the dominant groups in the autumn periods. On the other hand, S1, S2, SN and D codons were found in the lagoons during summer, spring and autumn periods.