Current state of phytoplankton in the littoral area of Lake Baikal, spring 2017

Journal of Great Lakes Research xxx (xxxx) xxx

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Current state of phytoplankton in the littoral area of lake Baikal, spring 2017 N.A. Bondarenko, S.S. Vorobyova, N.A. Zhuchenko ⇑, L.P. Golobokova Limnological Institute SB RAS, 3, Ulan-Batorskaya St., 664033 Irkutsk, Russia

a r t i c l e

i n f o

Article history: Received 16 November 2018 Accepted 2 October 2019 Available online xxxx Communicated by Lars Rudstam

Keywords: Phytoplankton Species composition Abundance Structural change Nutrients New ecological equilibrium

a b s t r a c t To assess the current state of phytoplankton in the littoral area of Lake Baikal and provide a baseline for future comparisons, we sampled spring plankton communities from the 44 littoral and 3 pelagic stations
covering all three basins of the lake. The study examined chemical parameters of water (NH+4, NO
2 , NO3 , PO
3 4 , Si, COD), species composition, abundance, and biomass of phytoplankton in Lake Baikal during late spring 2017. Sharp spatial heterogeneity was observed in the distribution of phytoplankton biomass along the western (399 ± 72 mg/m3) and eastern (1319 ± 220 mg/m3) shores of the lake. The phytoplankton were diverse, with 79 species; dominant algae were different from site to site and from south to north throughout the lake. In Southern and Central Baikal, we recorded an intense bloom of the diatom Synedra acus subsp. radians (28–1400 cells/mL), similar to that observed for the past 10 years, while the chrysophyte Dinobryon cylindricum dominated in Northern Baikal. The diatoms Aulacoseira baicalensis, A. islandica, and Stephanodiscus meyeri that were dominant in the 1960s–1990s were not numerous in 2017 (0.5–10 cells/mL). This change in dominant species indicates structural changes in the phytoplankton of Lake Baikal, which have led to the disappearance of the main distinctive feature of the Baikalian phytoplankton – the alternation of extremely high (with the algal biomass over 1000 mg/m3) and extremely low (less than 100 mg/m3) productivity years. The ecological equilibrium appears to have shifted towards a new steady state. Ó 2019 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.

Introduction Large lakes are an important source of fresh water, and many of the world’s largest lakes are threatened by eutrophication (e.g. Barbiero and Tuchman, 2004; Munawar et al., 2017; Petrova et al., 2010; Schindler, 2006; Tekanova and Timakova, 2007). For example, local eutrophication has been recorded in such large lakes as Onega (Chekryzheva, 2008), Michigan (Kerfoot et al., 2008), Huron (Bierman et al., 2005), Erie, and Ontario (Scavia et al., 2014; Munawar et al., 2017). In these lakes, structural changes in the primary producer community are associated with changes in nutrient loading. Climate warming has also affected the ecology of large lakes and has resulted in changes in community structure, phytoplankton abundance, and food webs (e.g. Fedotov et al., 2016; Hampton et al., 2008, 2018; Izmest’eva et al., 2016; Reavie et al., 2017; Rühland et al., 2008).

⇑ Corresponding author. E-mail address: [email protected] (N.A. Zhuchenko).

Lake Baikal is the deepest (1642 m), most ancient lakes on Earth, over 30 million years old, and contains 20% of the world’s surface freshwater reserves. The Baikal shallow areas occupy approximately 7% of its total water area (Fialkov, 1983), but the processes taking place in this area affect the whole ecosystem. During recent years, the Baikalian shallow biota has changed, including changes in the structure of benthic macroalgae (Kravtsova et al., 2014; Timoshkin et al., 2015) and mass mortality of sponges due to a disease (Timoshkin et al., 2016). Cyanobacteria developed on the diseased and dead sponges and produced saxitoxinsneuroparalytic toxins (Belykh et al., 2016). According to Kravtsova et al. (2014) and Timoshkin et al. (2016), these ecosystem changes have been caused by biomass increases because of increasing concentrations of nutrients. Increased levels of phosphate have been detected in some lake areas because of the discharge of insufficiently treated sewage, and elevated recreational use of the lake. Monitoring of water chemistry in the littoral zone was initiated in the 1950s and lasted for 10 years (Votintsev and Glazunov, 1963). The Baikalian waters were found to be low in nutrients but rich in calcium hydrocarbonate and high oxygen content.

https://doi.org/10.1016/j.jglr.2019.10.001 0380-1330/Ó 2019 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.

Please cite this article as: N. A. Bondarenko, S. S. Vorobyova, N. A. Zhuchenko et al., Current state of phytoplankton in the littoral area of lake Baikal, spring 2017, Journal of Great Lakes Research, https://doi.org/10.1016/j.jglr.2019.10.001

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N.A. Bondarenko et al. / Journal of Great Lakes Research xxx (xxxx) xxx

Further studies were carried out from 2000 to 2007 (Golobokova et al., 2009). For the past 13 years, gas and chemical composition of the water have been studied at the research station of the Limnological Institute (LIN SB RAS) near the settlement Bolshie Koty (Domysheva et al., 2016). Since 2010, monitoring of the shallow waters has been carried out each year at the reference sites in all three basins of Lake Baikal at distances 1–2 km from shore (Tomberg et al., 2012; Volkova et al., 2012). A number of data on shallow water chemistry in the mouths of the main lake tributaries are also available (Khodzher et al., 2017). Khodzher et al. showed no abrupt changes in the nutrient load to the Baikalian waters when compared with the data obtained in the 1950s–1960s. The latter is used as the reference data for further studies. Phytoplankton of Lake Baikal have been studied since the beginning of the 20th century (Antipova, 1963a, 1963b, 1974, Popovskaya, 1987, 1991; Yasnitskiy, 1930; Yasnitskiy and Skabitshevskiy, 1957; Kozhova, 1956). Their structure and functioning in the pelagic zone have been analyzed using these longterm observations (Bondarenko and Evstafyev, 2006). These researchers found that the most striking feature of spring phytoplankton, represented primarily by diatoms and dinoflagellates, is the high inter-annual variability in phytoplankton biomass, with years of extremely high (with the algae biomass over 1000 mg/ m3) and extremely low (less than 100 mg/m3) biomass. High biomass years (‘Melosira years’ when algae of the genus Melosira now Aulacoseira dominate) appeared every 3–4 years or 6–8 years and so that three intervals between these ‘Melosira years’ covered 11 and 22 years correspondingly (Bondarenko and Evstafyev, 2006; Evstafyev and Bondarenko, 2007). Spring blooms started under the ice in early spring and ended in late May or early June. The same pattern was also observed in the shallow phytoplankton (Antipova, 1974; Bondarenko et al., 2012; Popovskaya, 1991). This periodicity was maintained until the beginning of the 21st century and then disappeared (Bondarenko and Logacheva, 2017) though some changes in the composition of the dominant complex of spring phytoplankton had already been recorded in the 1960s and 1970s (Antipova, 1974; Bondarenko, 1999; Popovskaya, 1991). Changes in the summer phytoplankton of the pelagic zone in the southern basin of Lake Baikal have been associated with climate warming (e.g. Hampton et al., 2008; Izmest’eva et al., 2016). This was caused by the increase of air temperature over Lake Baikal by 1.9 °C in winter and by 1.5 °C in spring over the past 100 years (Shimaraev and Domysheva, 2013). According to Hampton et al. (2008) and Izmest’eva et al., (2016), no widespread pelagic eutrophication was recorded in the three lake basins. However, the structure and functioning of the shallow spring phytoplankton changed: high and low productivity years disappeared while moderately productive years smoothed sharp fluctuations in algal development (Bondarenko and Logacheva, 2017). In recent years, the diatom Synedra acus subsp. radians has been abundant each spring, but the phytoplankton biomass during this period has been much lower than that in the previous productive years when the large-cell diatoms of the genus Aulacoseira Thw. dominated. Moreover, the nanoplankton alga Chlamydomonas Ehr., known as an indicator of organic water pollution, has been abundant in recent years in the shallow plankton, at over 103 cells/mL (Bondarenko and Logacheva, 2017). Phytoplankton are known to be informative indicators of an ecosystem’s current state as the high reproductive rates of algae allows these organisms to react to, and therefore reflect, current environmental conditions (Reynolds, 2006). Herein, we present the state of phytoplankton in the Baikal shallow waters during spring 2017. We discuss our findings as indicators of ecological changes in Lake Baikal with special attention to the possible impact of climate change and changes in the nutrient loading.

Materials and methods Study sites and sampling Studies of hydrochemical characteristics, structure, and quantitative parameters of phytoplankton were carried out in late May and early June 2017, at the 44 littoral and 3 pelagic stations throughout Lake Baikal (Table 1, Figs. 1 and 2a). Littoral stations 100 m from the coastline were located both close to and far from the settlements. At each littoral station, the lake water was sampled from the surface zone at a depth of 1 m, and from the deep near-bottom zone at a depth of 2–3 m from the bottom. The pelagic stations were located 3 km from the littoral stations toward the lake centre along the transects, which Limnological Institute used since 1960s (Table 1, Figs. 1 and 2a). At the pelagic sites, the samples were collected at the surface, 5, 10, 25, and 50 m. Water was collected with a water sampler (OTE model 110 standard PVC sample bottle). The temperature and transparency of water were measured using a TM – 10-2 meteorological glass thermometer and a Secchi disk, respectively. Water chemistry analyses Chemical analysis was performed using conventional freshwater water chemistry methods (Boeva, 2009; Khodzher et al., 2017; Wetzel and Likens, 1991). The water sample was divided into three parts. The first part was used for measurements on board the ship including pH and bicarbonate ions by the potentiometric method, conductivity by the conductometric method, and dissolved oxygen by the Winkler method (Boeva, 2009; Khodzher et al., 2017; Wetzel and Likens, 1991). The second part of the sample was filtered through a cellulose acetate membrane filter with a pore diameter of 0.45 lm, and filtrates were refrigerated. The third portion of the sample was frozen unfiltered. Further chemical analysis was carried out at the Laboratory of Hydrochemistry and Atmosphere Chemistry (LIN SB RAS) using the equipment of the Baikal Joint Instrumentation Centre ‘Ultramicroanalysis’. The nutrient content in the filtered water was measured using the following colorimetric methods: indophenol blue method for NH+4, Griss’s method for NO
2 , Deniges’s method for PO3
4 , and the ammonium molybdate method for Si (Khodzher et al., 2017). Nitrate NO
3 in the filtrates was quantified using ionic chromatography on an ICS-3000 ionic system (Dionex, USA). We used the dichromate method for determination of chemical oxygen demand (COD) measured in the unfiltered water. The following indicators were used: dissolved forms of inorganic phosphorus, Pinorganic, (the content of phosphate ions in the filtered water or soluble reactive phosphate phosphorus, Wetzel and Likens, 1991), and dissolved forms of inorganic nitrogen, Ninorganic, (the total nitrogen content or the sum of NO3–N, NO2–N, and NH4–N, Wetzel and Likens, 1991). The sum of ions in mg/L was calculated from the formula:
þ2 þ þ R ¼ HCO
3 þ SO
2 þ Mgþ2 ; 4 þ Cl þ Na þ K þ Ca



2 þ2 þ þ +2 where HCO
are the mean con3 ; SO4 ; Cl ; Na ; K ; Ca , and Mg centrations of ions in the water samples, mg/L.

Phytoplankton analyses For phytoplankton identification, we fixed 1 L of water with Lugol’s solution and then concentrated them by settling. Algae were counted twice in a 0.1 mL Nageotte chamber under ‘Peraval’ and ‘Amplival’ light microscopes with 720 and 2000 magnification. Algal biomass was calculated from the algal number using

Please cite this article as: N. A. Bondarenko, S. S. Vorobyova, N. A. Zhuchenko et al., Current state of phytoplankton in the littoral area of lake Baikal, spring 2017, Journal of Great Lakes Research, https://doi.org/10.1016/j.jglr.2019.10.001

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N.A. Bondarenko et al. / Journal of Great Lakes Research xxx (xxxx) xxx Table 1 List of site locations appearing in Figs. 1 and 2. Site number

Name of the geographical position

Description of the basin and the coast of Lake Baikal

Location of monitoring sites latitude

longitude

Southern Baikal

N51°49.10

E104°54.80

Elokhin-Davsha transect

Northern Baikal

N54°32.00

E108°42.50

Ukhan-Turka transect

Central Baikal

N52°59.10

E108°10.70

Littoral stations 1 Opposite the settlement Kultuk 2A Cape Polovinny

Southern Baikal, the western coast Southern Baikal, the western coast

51°43.10 51°47.80

103°43.10 104°21.10

2

Southern Baikal, the western coast

51°51.90

104°49.80

3 4 6

Baikal Ecological Museum, settlement Listvyanka Sennaya valley, settlement Listvyanka Listvenichny Bay Settlement Bolshie Koty

Southern Baikal, the western coast Southern Baikal, the western coast Southern Baikal, the western coast

51°51.80 51°50.70 51°53.90

104°50.60 104°52.50 105°03.90

7

Varnachka valley

Southern Baikal, the western coast

51°54.10

105°06.20

8

Settlement Bolshoe Goloustnoe

Southern Baikal, the western coast

52°01.30

105°25.10

9 10

Peschanaya Bay Settlement Buguldeyka

Southern Baikal, the western coast Southern Baikal, the western coast

52°15.50 52°31.80

105°42.30 106°04.20

11

Aya Bay

Central Baikal, the western coast

52°47.30

106°36.40

12

Malye Olkhonskiye Vorota

Central Baikal, the western coast

53°01.10

106°54.60

13 14 15

Mukhor Bay Settlement Sakhurta Settlement Khuzhir

Central Baikal, the western coast Central Baikal, the western coast Central Baikal, the western coast

53°02.20 53°01.20 53°12.30

106°48.50 106°53.40 107°19.60

16 17 18

Cape Arul Settlement Onguren Cape Rytyi

Central Baikal, the western coast Central Baikal, the western coast Northern Baikal, the western coast

53°28.00 53°37.20 53°49.80

107°33.70 107°37.40 108°02.00

19 20

Zavorotnaya Bay Cape Elokhin

Northern Baikal, the western coast Northern Baikal, the western coast

54°16.90 54°32.30

108°28.80 108°39.80

22

Cape Muzhinay

Northern Baikal, the western coast

54°51.00

108°54.20

23

Cape Kotelnikovskiy

Northern Baikal, the western coast

55°02.60

109°06.50

24

Cape Ludar

Northern Baikal, the western coast

55°21.40

109°12.70

25 26 27 28 29

Senogda Bay Settlement Zarechnoe Tyya River mouth Tyya River as the reference station Town Nizhneangarsk

Northern Northern Northern Northern Northern

55°34.00 55°35.30 55°35.40 55°38.20 55°46.00

109°13.70 109°18.70 109°20.70 109°21.90 109°34.30

30 31

Khakusy Bay Tompuda River

Northern Baikal, the eastern coast Northern Baikal, the eastern coast

55°21.70 55°07.60

109°48.80 109°43.50

32

Irinda River

Northern Baikal, the eastern coast

54°49.70

109°39.80

33

Settlement Davsha

Northern Baikal, the eastern coast

54°20.40

109°27.70

34

Chivyrkuy Bay

Northern Baikal, the eastern coast

53°47.40

109°07.50

35 36

Bolshoy Ushkaniy Island Settlement Maksimikha

Northern Baikal, the eastern coast Central Baikal, the eastern coast

53°51.90 53°18.40

108°40.00 108°44.30

Pelagic (deep-water) stations 5 Listvenichnoe-Tankhoy transect

21

38

Baikal, Baikal, Baikal, Baikal, Baikal,

the the the the the

western western western western western

coast coast coast coast coast

Depth of sampling, m

1 5 10 25 50 1 5 10 25 50 1 5 10 25 50 1 1 7 1 15 1 1 1 15 1 15 1 17 1 1 12 1 15 1 18 1 1 1 15 1 1 1 15 1 1 8 1 12 1 13 1 8 1 1 1 1 1 7 1 1 10 1 11 1 14 1 15 1 1 11 (continued on next page)

Please cite this article as: N. A. Bondarenko, S. S. Vorobyova, N. A. Zhuchenko et al., Current state of phytoplankton in the littoral area of lake Baikal, spring 2017, Journal of Great Lakes Research, https://doi.org/10.1016/j.jglr.2019.10.001

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Table 1 (continued) Site number

Name of the geographical position

Description of the basin and the coast of Lake Baikal

latitude

longitude

37

Settlement Turka

Central Baikal, the eastern coast

52°57.20

108°11.40

39

Cape Baklaniy

Central Baikal, the eastern coast

52°42.80

107°32.30

40

Border of Selenga shallow

Central Baikal, the eastern coast

52°23.90

106°32.10

41 42 43

Selenga shallow Town Babushkin Settlement Tankhoy

Central Baikal, the eastern coast Southern Baikal, the eastern coast Southern Baikal, the eastern coast

52°19.90 51°43.40 51°38.90

106°14.60 105°51.90 105°07.50

44

Opposite Baikalsk Pulp and Paper Plant

Southern Baikal, the eastern coast

51°31.40

104°11.40

45

Town Baikalsk

Southern Baikal, the eastern coast

51°31.70

104°08.10

46 47

Town Slyudyanka Settlement Kultuk

Southern Baikal, the eastern coast Southern Baikal, the eastern coast

51°39.90 51°42.5

103°43.50 103°43.50

individual cell volumes (Winberg, 1984). To determine biovolume, 100–200 cells of each species were measured. Algae were identified according to Matvienko and Litvinenko (1977), Starmach (1985), Gleser et al. (1988–1992), and Tsarenko (1990). To assess the current state of spring phytoplankton in the littoral zone of the lake, we compared the data for 2017 with the published data for previous years: 1950–1990 (Antipova, 1974; Kozhova, 1956; Popovskaya, 1987, 1991; Votintsev et al., 1975); and 1990–2016 (Bondarenko, 2009; Bondarenko et al., 2012; Bondarenko and Logacheva, 2017). The data for the comparison of the current state of Baikalian algae with 2013 and 2016 were taken from the archive of the first author. These data were obtained by similar methods and at similar times of the year, i.e. in May to June. For 2013 and 2016, the average values of biomass in the basins were obtained from 15 to 20 sites in each basin at the same stations. We used the archival data to examine temporal trends in spring phytoplankton going back to 1990. For statistical processing of the data (mean values, standard deviations, and correlation coefficients), we used Excel 2013 with incorporated statistical applications and STATISTICA 7 for Student’s t-test.

Results Water temperature and chemistry The studies were performed during ice breakup. In 2017, the northern basin of Lake Baikal was completely covered with ice on January 10, the central basin on January 12, and the southern basin after January 16. The ice breakup in the southern basin started on May 9 and slowly moved northward. The water temperature in Southern Baikal ranged from 3.1 to 5.4 °C and from 2.1 to 4.1 °C in the central basin while the northeastern part of the lake was still covered with ice fields, and the water temperature there varied from 1.0 to 4.5 °C. The water transparency measured by a Secchi disk was 5–19 m in Southern Baikal, 10–12 m in the central basin, and 2–11 m in the northern part of the lake. Rather low concentrations of dissolved silica of 0.21–0.75 mg/L (Fig. 1) and inorganic nitrogen, 0.03–0.11 mg/L, were observed throughout the southern basin, except at the sites adjacent to the delta of the Selenga River. This is typical for the ice breakup period in years with intensive development of diatoms. In the surface water layer at Cape Polovinny, nitrate nitrogen was lower than analytical detection and 94% of the total inorganic nitrogen con-

Location of monitoring sites

Depth of sampling, m

1 12 1 7 1 14 1 1 1 16 1 10 1 12 1 1 15

centrations of 0.02 mg/L consisted of ammonium nitrogen. Similar trends in the distribution of inorganic nitrogen were detected in the zone influenced by the Selenga delta and near the town of Babushkin, with a content of 0.02–0.03 mg/L, where contributions of ammonium nitrogen and nitrate nitrogen varied from 60% to 94% and from 37% to 0%, respectively. In the waters of Listvenichny Bay, the concentrations of ammonium nitrogen increased by up to 70–100% in the surface layer (1–6 m thick) at a distance of more than 1 km off shore where inorganic nitrogen varied from 0.02 to 0.03 mg/L. Inorganic phosphorus concentrations ranged from 0.002 to 0.011 mg/L, and chemical oxygen demand (COD) values varied between 0.7 and 7.6 mg/L. The silica concentrations in the central part of the lake was less variable, from 0.6 to 0.7 mg/L (see Fig. 1). The concentrations of inorganic nitrogen and phosphorus were low there, 0.07– 0.09 mg/L and 0.003–0.005 mg/L, respectively. In the Maloye More strait at sites 11, Malye Olkhonskiye Vorota, and 13, the settlement of Sukhurta, ammonium nitrogen predominated over nitrate nitrogen, at 70%–95% and 27%–0%, respectively. At site 15, Bolshiye Olkhonskiye Vorota, the relative concentrations of ammonium and nitrate fractions of inorganic nitrogen in the surface layer were close, 36% and 61%, respectively. At a depth of 12 m, the content of nitrate nitrogen increased, and ammonium nitrogen decreased towards average values generally typical for shallow waters, 77% and 23%. COD varied between 1.7 and 6.0 mg/L. In the northern basin of the lake (see Fig. 1), the silica concentrations were slightly higher, 0.48–0.87 mg/L, while inorganic nitrogen and phosphorus values were low, 0.05–0.09 mg/L and 0.002–0.009 mg/L, respectively. The phosphorus was 0.008– 0.017 mg/L, and COD was 1.3–12.5 mg/L. Maximal COD values were recorded in the mouths of the northern tributaries. Phytoplankton The late spring phytoplankton of Lake Baikal included 79 species with the most diverse groups being diatoms (21 species) and green algae (18 species). The spatial distribution of phytoplankton along the western and eastern shores of the lake was sharply heterogeneous (Fig. 2a): its average value along the eastern shore, 1319 ± 220 mg/m3 (here and elsewhere we used standard error values with a confidence level of 95%), was statistically higher than that along the western shore, 399 ± 72 mg/m3 (t = 1.867, df = 45, p < 0.05). The greatest contributions to the biomass were made by diatoms in the southern basin, diatoms and chrysophytes in the central basin, and chrysophytes in the northern basin (Fig. 2b).

Please cite this article as: N. A. Bondarenko, S. S. Vorobyova, N. A. Zhuchenko et al., Current state of phytoplankton in the littoral area of lake Baikal, spring 2017, Journal of Great Lakes Research, https://doi.org/10.1016/j.jglr.2019.10.001

N.A. Bondarenko et al. / Journal of Great Lakes Research xxx (xxxx) xxx

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Fig. 1. Hydrochemical parameters of Lake Baikal, June 2017 (see Table 1 for the location of sampling stations): a – inorganic nitrogen, b – dissolved silicon, c – inorganic phosphorus, d – chemical oxygen demand.

In the southern basin, phytoplankton were diverse, with 55 species. The diatom S. acus subsp. radians was a dominant species there (Table 2), 13%–90% of the total number and 31%–95% of the total biomass. Along the western shore, its number was 16– 93 cells/mL. Along the eastern shore, the abundance of this alga was much higher, from 414 to 1400 cells/mL. Its average value throughout the southern basin was 444 ± 113 cells/mL. Three diatom species of the Baikal algal complex were recorded in low numbers, i.e. spore-forming Aulacoseira islandica at 0.3–10 cells/mL, Stephanodiscus meyeri at 2.7–5.5 cells/mL, and Cyclotella minuta at 0.4–1.5 cells/mL. The numbers of nanoplanktonic flagellates were also low: from 0.5 to 32 cells/mL. The spring phytoplankton biomass had likely already reached maximal values at the sites along the western shore when these sites were sampled in 2017 because we found algae in deep layers of the water column. Such a vertical distribution of algae was demonstrated by sampling at discrete depths from 0 to 50 m at

the deep-water station of the transect Listvenichnoe–Tankhoy (Fig. 3). In the shallow zone, we registered low algal biomasses from 33 to 230 mg/m3. Along the eastern shore and in the very southern part of the lake (from the settlements of Kultuk to Babushkin), there was high biomass of planktonic algae, ranging from 860 to 3134 mg/m3. The maximum value (typical for mesotrophic conditions) was obtained near the town of Baikalsk. Phytoplankton in the central basin were almost evenly distributed within the 0–50 m layer (see Fig. 3) and diverse, with 60 species. Three algae species dominated (see Table 2, Fig. 2b), i.e. green Koliella longiseta, found at 187–543 cells/mL (294 ± 62 cells/ mL on average) representing 14% to 89% of the total number, the chrysophyte Dinobryon cylindricum, found at 141–246 cells/mL (175 ± 75 cells/mL on average), representing 14%–80% of the total number, and the diatom S. acus subsp. radians, present at 97– 114 cells/mL (45 ± 13 cells/mL on average), reaching up to 21% of the total number. In Maloye More and Chivyrkuy Bay, the numbers

Please cite this article as: N. A. Bondarenko, S. S. Vorobyova, N. A. Zhuchenko et al., Current state of phytoplankton in the littoral area of lake Baikal, spring 2017, Journal of Great Lakes Research, https://doi.org/10.1016/j.jglr.2019.10.001

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phytoplankton number. In the northern part of the lake, we found small amounts of the algae A. baicalensis, 0.6–1.5 cells/mL, and C. minuta, 0.5–10.4 cells/mL, which are considered Baikalian endemics. S. acus subsp. radians was present in smaller amounts than in the other two basins, up to 63 cells/mL. Analysing the relations between phytoplankton number and biomass and nutrients such as inorganic nitrogen, inorganic phosphorus, and dissolved silica at a depth of 1 m, we found weak negative correlations likely because phytoplankton growth decreased nutrient concentrations in the upper layer of the water column. The strongest correlation was with inorganic nitrogen:
0.53 ± 0.08 (p < 0.05) for phytoplankton number and
0.32 ± 0.09 (p < 0.05) for phytoplankton biomass. Phytoplankton biomass and number also correlated with silica:
0.44 ± 0.08 (p > 0.05) and
0.43 ± 0.08 (p < 0.05), respectively. Inorganic phosphorus was weakly correlated with phytoplankton number:
0.41 ± 0.08 (p < 0.05) and
0.35 ± 0.08 (p < 0.05) for phytoplankton biomass. Temporal changes in phytoplankton

Fig. 2. Phytoplankton biomass in Lake Baikal, June 2017 (see Table 1 for the location of sampling stations): a – spatial distribution, b – contributions of different algal taxonomic groups to the total biomass.

of D. cylindricum were much higher, up to 1374 cells/mL. Only at one of the sites investigated in 2017, Barguzin Bay, was there a significant number of the diatom A. islandica, at 100 cells/mL. In the Selenga shallow waters, phytoplankton were abundant with a total biomass of 1240 mg/m3. Synedra acus subsp. radians, Nitzschia graciliformis, and Stephanodiscus minutulus dominated, with 424, 493, and 1575 cells/mL, respectively. In the northern basin, 53 species of algae were found. In contrast to the southern part, here the biomass fluctuations along the western and eastern shores were smoother but a trend towards increased values along the eastern shore remained, from 60 to 765 mg/m3 near the western, and 413 to 1395 mg/m3 near the eastern shore (Fig. 2). Based on the vertical distribution of biomass, the algae were concentrated in the upper layers of the water column (Fig. 3), i.e. the spring growth period was still in progress. D. cylindricum dominated, with 25–516 cells/mL (238 ± 73 cells/ mL on average; Table 2), that was 11% to 86% of the total number. This mixotrophic flagellate actively migrates depending on light, temperature, and nutrient conditions. In insufficient nutrient conditions, this alga changes from autotrophy to mixotrophy (Rott, 1988). Subdominant were the green alga K. longiseta at 15– 55 cells/mL, up to 39% of the total density, and the diatom N. graciliformis at 10–69 cells/mL, contributing up to 57% of the total density. In the northwestern part of Lake Baikal and in Maloye More, significant amounts of cryptophytes were recorded, with the dominance of Rhodomonas pusilla with up to 33% of the total

Algae of the genus Aulacoseira did not develop high spring abundances in 2017 in contrast to their large blooms in the 1960s–2000 (Table 3). The main algal biomass was contributed by the smaller diatom S. acus subsp. radians, the green alga K. longiseta, and the chrysophyte D. cylindricum. Phytoplankton biomass in recent years 2013, 2016 and 2017 was lower than phytoplankton abundance in highly productive years (Fig. 4, Table 3). The 2014 and 2015 data obtained from a smaller number of sites (four or five sites in each lake basin), also showed that biomass of the shallow phytoplankton in the southern and central basins did not exceed 250 mg/m3 or 220 mg/m3 in the northern basin. This indicates that the present biomass of spring phytoplankton does not reach the formal criterion of a productive year in Lake Baikal, 1 g/m3, which was observed in 1950, 1953, 1957, 1960, 1964, 1968, 1974, 1976, 1979, 1982, 1990, 1994, 1997, 2000, and 2002 (Antipova, 1963a, 1963b, 1974; Bondarenko and Evstafyev, 2006; Popovskaya, 1987, 1991; Table 3). The phytoplankton development in shallow areas of the lake in 2017 corresponds to a moderately productive year. In recent years, the abundance of the main large-cell Baikalian diatom A. baicalensis has been low, 0.5–10 cells/mL (Fig. 5). This alga was replaced by a small-cell diatom, S. acus subsp. radians (Fig. 5). This is likely the reason the spring phytoplankton no longer exhibit the periodic phenomenon of highly productive years with biomass exceeding 1 g/m3 that was observed in the 20th century every 3–4 years or 6–8 years. Thus, the characteristic periodicity of Lake Baikal spring diatom blooms (three intervals between these ‘Melosira years’ (or highly productive years) covered 10–11 and 22 years) no longer occurs (Bondarenko and Evstafyev, 2006; Evstafyev and Bondarenko, 2007). Discussion The composition of littoral waters reflects changes in pelagic waters depending on physical (depth, bottom relief, and currents), hydrological (river and coastal runoff), climatic (wind, temperature, and insolation), and biological factors. The different nature of these processes, long-term changes, and shoreline alterations make the analysis and interpretation of the chemical and biological data obtained complicated. The studies were performed during the ice breakup in the lake. We call this period late biological spring and the beginning of Lake Baikal waters warming. The ice breakup in the southern basin of the lake starts usually in early May and slowly moves northward.

Please cite this article as: N. A. Bondarenko, S. S. Vorobyova, N. A. Zhuchenko et al., Current state of phytoplankton in the littoral area of lake Baikal, spring 2017, Journal of Great Lakes Research, https://doi.org/10.1016/j.jglr.2019.10.001

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N.A. Bondarenko et al. / Journal of Great Lakes Research xxx (xxxx) xxx Table 2 Average abundance (cells/mL ± standard error) of main algal species in the 0–1 m layer, Lake Baikal, late May–early June 2017 Taxon

Southern Baikal, May

Central Baikal, May

Northern Baikal, June

Maloye More, June

CHRYSOPHYTA Dynobrion cylindricum Imhof Dynobrion sociale Ehrenberg Cysts

32 ± 12 1±1 1±0

175 ± 75 4±3 5±4

238 ± 73 1±0 10 ± 3

229 ± 151 8±7 10 ± 8

CRYPTOPHYTA Rhodomonas pusilla (Bachm.) Javorn. Cryptomonas gracilis Skuja Cryptomonas marsonii Skuja Cryptomonas ovata Ehrenberg Cryptomonas erosa Ehrenberg

13 ± 4 0.5 ± 0.4 0.01 ± 0.01 0.22 ± 0.12 0.76 ± 0.43

29 ± 10 0.9 ± 0.6 1.02 ± 0.43 0.28 ± 0.24 0

48 ± 13 0.7 ± 0.5 0.13 ± 0.08 0 1.06 ± 0.98

46 ± 19 2±1 0.07 ± 0.07 0.61 ± 0.46 0

DINOPHYTA Gyrodinium helveticum (Penard) Y. Takano et T. Horiguchi Peridinium baicalense Kiselev et Cvetkov Glenodinium sp.

1.5 ± 0.5 0 4±1

4 ± 0.8 1 ± 0.6 3 ± 0.7

3 ± 0.7 1 ± 0.5 7±4

4±1 2±1 2 ± 0.6

0 1.4 ± 0.6 0.5 ± 0.2 29 ± 27

0.3 ± 0.1 12 ± 9 3 ± 0.7 52 ± 40

0.3 ± 0.1 2±1 3 ± 0.7 20 ± 9

0.4 ± 0.3 2.4 ± 0.6 4±1 114 ± 78

4±2 444 ± 113 0

14 ± 6 45 ± 13 7±5

3 ± 0.8 8±4 0

3±2 20 ± 8 16 ± 8

CHLOROPHYTA Koliella longiseta (Vischer) Hindak Monoraphidium arcuatum (Korsch.) Hindak Monoraphidium contortum (Thur.) Komarkova-Legnerova Elakotothrix genevensis (Reverdin) Hindak Chlamydomonas komma Pascher

63 ± 16 21 ± 21 6±6 0 2±2

294 ± 62 2±2 1±1 1±1 4±3

67 ± 13 0.3 ± 0.2 0 0 1±1

302 ± 89 4±3 2±1 2±2 7±6

HAPTOPHYTA Chrysochromulina parva Lackey

5±3

32 ± 13

5±2

52 ± 23

BACILLARIOPHYTA Aulacoseira baicalensis (K. Meyer) Simonsen Aulacoseira islandica (O. Mül l.) Simonsen Cyclotella minuta Antipova Nitzschia graciliformis Lange- Bertalot et Simonsen emend Genkal et Popovskaya Stephanodiscus meyeri Genkal et Popovskaya Synedra acus subsp. radians (Kütz.) Skabitsch. Asterionella formosa Hass.

The warming begins at the western shore followed by warming at the eastern shore. Wind speed is at its seasonal maximum at this time, which contributes to the rapid development of currents, surges, and intensive wind-induced water mixing. This time is regarded as the onset of the spring homothermy, with a duration of approximately 1 month for deep regions of the lake (Shimaraev, 1977). In the shallow waters and in bays, in areas influenced by river runoff, as well as in the littoral zones of Baikal, the homothermy duration is much shorter. After the ice breakup, enrichment of the photic zone with nutrients begins due to mixing of deep-water nutrients into surface water and through regeneration by the decomposition of dead plankton. At the same time, available nutrients are taken up by growing phytoplankton. In the 1950s, nutrient content in the upper layers reached a maximum in the winter period, with concentrations of 0.045– 0.080 mg/L for nitrate nitrogen, 0.030–0.040 mg/L for phosphate phosphorus, and 0.6–1.250 mg/L for silica (Votintsev, 1961). During the ice breakup, the concentration of nutrients was lower: nitrate nitrogen
0.030 to 0.070 mg/L, phosphate phosphorus – 0.008 to 0.020 mg/L, and silica
0.4 to 0.850 mg/L (Votintsev, 1961). In June 2017, the nitrogen concentrations varied from 0.020 to 0.070 mg/L (in near-bottom layers up to 0.14 mg/L), phosphorus from 0.002 to 0.017 mg/L, and silica from 0.003 to 0.015 mg/L. The content of nitrate nitrogen ranged from about 70%–85% of the total inorganic nitrogen while the share of ammonium nitrogen accounted for 15%–30%. At some sites, ammonium nitrogen concentrations were higher than the concentrations of nitrate nitrogen. Along the western shore, no nitrite nitrogen was detected, and low nitrite levels were observed throughout the eastern shore, 1–2% of the total inorganic nitrogen. Maximal contribution of nitrite nitrogen 3.5%–5.8%, were found in the areas of the Selenga

Delta, Aya Bay near Baikalsk, Babushkin, and Cape Polovinny locations close to settlements and tourist sites. We detected considerable spatial heterogeneity in the distribution of phytoplankton biomass with lower biomass along the western shore (399 ± 72 mg/m3) and higher biomass along the eastern shore (1320 ± 220 mg/m3) of the lake. Higher phytoplankton biomass near the eastern shore may be attributed to later water warming as well as to an increased nutrient load with more rivers near the eastern shore. For instance, in the waters of the Pereemnaya River, average sulphate and nitrate concentrations are two to three times higher than those in Lake Baikal (Obolkin et al., 2016). River runoff is the most important source of nutrients to Lake Baikal. The mixing zone of the river and lake waters occupies that part of the lake 3–4 km from the delta of the inflowing large rivers, two of which, Selenga and Barguzin, are located on the eastern shore, and small rivers mix their waters within a 1 km radius from the inlet (Sorokovikova et al., 2009). In addition, the eastern shore of the lake is relatively densely populated. The dominant species also differed throughout the lake. The diatom S. acus subsp. radians was one of the dominant species in the spring phytoplankton of the southern and central basins (see Table 2). Dinobryon phytoflagellates were dominant in the northern basin of the lake; but, despite the low concentrations of nutrients (Fig. 1), their abundance was significant across the basin (see Table 2). This flagellate is mobile and able to find optimal habitats within the water column. Moreover, Dinobryon can utilize bacterial phosphorus and carbon as an additional source of nutrition (Rott, 1988). In contrast, the abundance of the previously dominating Baikal diatom complex in the spring plankton was low in 2017, at 0.5–10 cells/mL. Despite the increase in abundance of some algae, their average basin biomass (547 ± 237 mg/m3 in the northern basin,

Please cite this article as: N. A. Bondarenko, S. S. Vorobyova, N. A. Zhuchenko et al., Current state of phytoplankton in the littoral area of lake Baikal, spring 2017, Journal of Great Lakes Research, https://doi.org/10.1016/j.jglr.2019.10.001

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N.A. Bondarenko et al. / Journal of Great Lakes Research xxx (xxxx) xxx

Fig. 3. Vertical distribution of phytoplankton biomass at the central stations of the transects Listvenichnoe-Tankhoy, Ukhan-Turka, and Elokhin-Davsha.

Table 3 Long-term dynamics of the phytoplankton biomass in the highly productive years, late May to early June, Southern Baikal. Period

Study area

Authors

Biomass, mg/m3

Dominant species

1961 1964 1968 1974 1976 1979 1982 1990 1994 1997 2000 2002 2007 2010

Bolshie Koty Bay Bolshie Koty Bay Listvenichny Bay Southern Baikal Southern Baikal Southern Baikal Southern Baikal Listvenichny Bay Listvenichny Bay Listvenichny Bay Listvenichny Bay Listvenichny Bay Listvenichny Bay Bolshie Koty Bay

Antipova (1974) Antipova (1974) Votintsev et al. (1975) Popovskaya (1987) Popovskaya (1987) Popovskaya (1987) Popovskaya (1987) Bondarenko (2009) Bondarenko (2009) Bondarenko (2009) Bondarenko (2009) Bondarenko (2009) Bondarenko (2009) Bondarenko et al. (2012)

2190 4469 2493 2380* 1575* 2365* 1394* 1470 1260 1320 1250 2500 1202 1180

Aulacoseira baicalensis A. baicalensis, A. islandica A. baicalensis, Stephanodiscus meyeri A. baicalensis A. islandica A. islandica A. baicalensis A. baicalensis A. baicalensis A. baicalensis A. islandica, A. baicalensis A. islandica S. meyeri, Synedra acus, A. baicalensis, A. islandica S. acus, S. meyeri, A. baicalensis, A. islandica

*The marked values are given as average values of the 14–16 sample sites throughout the southern basin of Lake Baikal due to absence of shallow biomass data.

841 ± 346 mg/m3 in the central basin, and 787 ± 440 mg/m3 in the southern basin) was lower than observed in past high productivity years (‘Melosira years’ > 1 g/m3) because of lower abundances of the dominants in recent years. Therefore, 2017 does not formally classify as a highly productive year. Similarly, 2013 and 2016, years with comparable data to 2017, and 2014–2015 (years with more limited data) all had lower biomass than 1 g/m3. Based on historic observations from the 1950s to 2000 s, we would have expected at least one highly productive year during this time period. This suggests substantial changes in the Baikal ecosystem. The ecological equilibrium appears to have shifted towards a new steady state.

Structural changes have been recorded in large lakes of the world, e.g. Onega Lake (Chekryzheva, 2008), and several bays in Lakes Michigan (Kerfoot et al., 2008), Huron (Bierman et al., 2005), Erie, and Ontario (Scavia et al., 2014; Munawar et al., 2017). Also it is well known that the invasion of the North American lakes by Dreissena polymorpha led to decreased phytoplankton (Barbiero and Tuchman, 2004; Kerfoot et al., 2008; Malkin et al., 2009; Mayer et al., 2014). Structural changes in ecosystems are often associated with eutrophication (e.g. Schindler, 2006, 2012; Smith and Schindler, 2009) caused by increasing inputs of nutrients from watersheds especially adjacent to settlements. In Onega Lake, Russia, eutrophication affected its large bays, mostly indus-

Please cite this article as: N. A. Bondarenko, S. S. Vorobyova, N. A. Zhuchenko et al., Current state of phytoplankton in the littoral area of lake Baikal, spring 2017, Journal of Great Lakes Research, https://doi.org/10.1016/j.jglr.2019.10.001

N.A. Bondarenko et al. / Journal of Great Lakes Research xxx (xxxx) xxx

Fig.4. Interannual dynamics of phytoplankton biomass by the average values, with their standard errors, in each lake basin (southern, central, northern) late May to early June in 2013, 2016, and 2017.

Fig. 5. Interannual abundance dynamics of Synedra acus subsp. radians and Aulacoseira baicalensis in Southern Baikal (each point reflects an average value with its standard error for 3 stations).

trialized and urbanized, but the main body of the lake remained oligotrophic (Chekryzheva, 2008; Tekanova and Timakova, 2007). In this lake, the species indicating eutrophication and water pollution were found to increase in number already in the 1950s. In Ladoga Lake, anthropogenic phosphorus pollution exceeded the critical level, leading to accelerated turnover of organic matter (Petrova et al., 2010). During the 1960s and 1970s, increased phosphorus inputs in Lake Erie degraded water quality and reduced central basin hypolimnetic oxygen levels which, in turn, eliminated thermal habitat vital to cold-water organisms and contributed to the extirpation of important benthic macro invertebrate prey species for fishes (Scavia et al., 2014). In the coastal zone of Lake Baikal near large settlements, booming house construction caused the transformation of biotopes (e.g.

9

Listvyanka village, Kultuk settlement, Babushkin town). In many areas, the littoral zone was subject to increasing recreational use and the discharge of insufficiently treated sewage. High algal biomass is observed in such areas. However, there were no abrupt changes in the overall nutrient load of the Baikal pelagic waters (Khodzher et al., 2017) compared to the data obtained in the 1950s and 1960s, the latter being reference data for further studies. Our studies also show comparative little change in the chemical characteristics of the littoral waters of Lake Baikal over the past 69 years (Table 4). The content of major ions has been consistently between 90 and 100 mg/L. Nutrient concentrations also show comparatively little change: 0.005–0.009 mg/L of inorganic phosphorus, 0.05–0.07 mg/L of inorganic nitrogen, and 0.5–1.1 mg/L of silica. Though the inorganic nitrogen content in the littoral waters was relatively constant, there were changes in the distribution of nitrogen fractions as the relative content of ammonium nitrogen in areas with a high anthropogenic load increased (Khodzher et al., 2018). An increase in the concentration of ammonium was also confirmed by our study. This increase led to an elevated number of mixotrophic flagellate forms in the plankton. The oligotrophic waters of the deep part of Lake Baikal are characterized by small concentrations of ammonium nitrogen and an almost complete absence of nitrite nitrogen; the nitrate nitrogen content increased from 0.01 to 0.07 mg/L in the surface layer to 0.14– 0.15 mg/L in the bottom layer (Khodzher et al., 2017). In general, the contribution of diatoms in aquatic ecosystems decreases with eutrophication, while the contribution of cyanobacteria, green algae, and euglenophytes increases (e.g. Chekryzheva, 2008; Munawar et al., 2017; Trifonova, 1990). Earlier, Bondarenko and Logacheva (2017) reported that a rise in elevated concentrations of dissolved organic matter in lake water caused an increase in the abundance of flagellated forms, primarily Chlamydomonas and Euglena, in the littoral zone and these algae were therefore indicators of organic water pollution. In 2017, we did not observe a dominance of those algae. The numbers of Chlamydomonas and Euglena in the surface water were small, 0.5–32 and 0.15–1.5 cells/mL, respectively. In 2010–2015, they were more numerous, with more than 102 cells/mL in the ice-free period and more than 103 cells/mL in the ice-covered period (Bondarenko and Logacheva, 2017). Notably, in the past (1950– 2000), Chlamydomonas was not detected in the lake, and species of the genus Euglena were rare in the plankton (Bondarenko and Logacheva, 2017). The highest concentrations of flagellates in 2017 were observed at the sites with increased COD values (areas with increased organic content) where the correlation coefficients ranged between 0.54 and 0.62. In recent years, many reports have been devoted to the influence of climate change on phytoplankton communities (e.g. Catalan and Ventura, 2002; Fedotov et al., 2016; Hampton et al., 2008; Izmest’eva et al., 2016; Kraemer et al., 2017; Reavie et al., 2017; Rühland et al., 2008; Sommaruga and Kandolf, 2014; Tolotti, 2001). Phytoplankton community changes include shifts in dominant species, which leads to changes in density and biomass that affect higher trophic levels in the ecosystem. Structural changes in diatom communities, such as decreases in the genus Aulacoseira and increases in smaller diatoms of the genus Cyclotella, have occurred in many lakes of North America and Europe (Kraemer et al., 2017; Reavie et al., 2017; Rühland et al., 2008). For example, a paleolimnological analysis of 10 sediment cores collected from deep locations throughout the Laurentian Great Lakes basin indicates a recent (30–50 year) reorganization of the diatom community to one characterized by elevated abundance of several species from the group Cyclotella sensu lato (Reavie et al., 2017). The researchers associated these changes with global warming resulting in the prolongation of the ice-free period, which has also been observed at Lake Baikal.

Please cite this article as: N. A. Bondarenko, S. S. Vorobyova, N. A. Zhuchenko et al., Current state of phytoplankton in the littoral area of lake Baikal, spring 2017, Journal of Great Lakes Research, https://doi.org/10.1016/j.jglr.2019.10.001

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Table 4 Long-term dynamics of total ions and nutrient content in the littoral waters, Lake Baikal. The underlined values for chemical parameters are- minimum and maximum values, the average values are below the line in each cell. Maximum, minimum and average values are calculated from data by Votintsev and Glazunov (1963) and Golobokova et al. (2009) and retrieved from graphic materials of Tomberg et al. (2012), Volkova et al. (2012) and Domysheva et al. (2016). Nitrate (NO3–N) was determined only in Votintsev and Glazunov (1963), Volkova et al. (2012) and Domysheva et al. (2016). Inorganic nitrogen, phosphorus and silicon were reported in the filtered water by Golobokova et al. (2009), Tomberg et al. (2012) and Volkova et al. (2012) and in unfiltered water by Votintsev and Glazunov. Period

Study area

Authors

Sum of ions (R), mg/L

Pinorganic, mg/L

Ninorganic, mg/L

Si, mg/L

1950–1960

Listvenichny Bay

Votintsev and Glazunov (1963)

93–99 95

0.005–0.012 0.009

0.01–0.10 0.07

0.9–1.3 1.1

2000–2007

Cape Beryozovy

Golobokova et al. (2009)

0.002–0.015 0.006

0.01–0.38 0.07

0.04–2.1 0.5

2004–2016

Bolshie Koty Bay

Domysheva et al. (2016)

91–106 97 No data

0.004–0.016 0.008

0.02–0.08 0.06

2011–2012

8 sites 100 m off the shore

Tomberg et al. (2012)

0.001–0.010 0.005

0.03–0.10 0.06

2010–2011

Bolshie Koty Bay

Volkova et al. (2012)

75–98 91 No data

0.4–0.7 0.6 <1.0

0.002–0.015 0.006

0.04–0.06 0.05

No data

June 2017

44 sites along the shoreline

Golobokova, Zhuchenko, the present report

77–117 93

0.001–0.012 0.005

0.02–0.14 0.07

0.2–1.5 0.6

Changes in climatic parameters in the 2000s were expressed by a rise of the surface water temperature throughout the entire Lake Baikal and a reduction of the ice-cover period. This period in Southern Baikal lasted 90 days in 2000s, which is 20–25 days shorter than in the 19th and 20th centuries (Troitskaya and Shimaraev, 2005). This trend was caused by a rise of the air temperature over Lake Baikal by 1.9 °C in winter and by 1.5 °C in spring over the past 100 years (Shimaraev and Domysheva, 2013). For this reason, abundance of the Baikalian complex (A. baicalensis, A. islandica, S. meyeri) decreased, because these algae spent a part of their life cycle in the interstitial ice water (Bondarenko et al., 2006). Large numbers of A. islandica were found in Barguzin Bay in 2017, but not at the other sites. This bay had been covered by ice earlier in 2017 than other parts of the lake, in November, while other parts were covered much later, (December and January) (http://geol. irk.ru/baikal/law/mlawecmon/mlawcosmmon, searched on 25 October 2017). Finally, Katz et al. (2015) have shown that Aulacoseira blooms have historically been correlated with ice duration and with early and severe winters. Therefore we conclude that the dramatic changes in the Baikal diatom complex are likely caused by climate warming. Our analysis of diatoms in the lake surface sediments supports the observation that the pelagic community is changing. This analysis showed that in the surface sediments, 0–1 cm thick, of Southern Baikal (5 km from Listvyanka), the number of S. acus subsp. radians increased almost by an order of magnitude, an increase iin relative abundance from 3.6% in 2003 to 35.5% in 2015 or 3.9 to 36.1  106 valves/g of dry sediment. The proportion of A. baicalensis valves decreased from 42% to 22%. Earlier paleoecological studies showed that changes in the structure of diatoms related to climate have occurred throughout the history of the lake (e.g. Bradbury et al., 1994; Khursevich et al., 2001; MacKay et al., 2006). Even though the change of the spring phytoplankton community structure in the pelagic zone of Lake Baikal are likely caused by climate warming (Bondarenko et al., 2019), the structural changes in the lake’s littoral area are most likely caused by both eutrophication and climate change. We found an increasing dominance of small-sized species that is one of the signs of eutrophication of the ecosystem. But we detected also a shift in the composition of cryophilic diatoms likely caused by warming.

throughout all the three lake basins characterizes the current (2017) state of spring phytoplankton in the lake. In the littoral zone, the concentrations of nutrients in the surface layers during the intensive development of the spring plankton were low. Concentrations of nitrogen ranged from 0.02 to 0.07 mg/L, phosphorus from 0.002 to 0.017 mg/L, and silica from 0.3 to 1.5 mg/L. Nitrate nitrogen varied from 70% to 85% of the total inorganic nitrogen while ammonium nitrogen contributed 15%–30%. At some sites, ammonium nitrogen prevailed over nitrate nitrogen. Nitrite nitrogen was negligible (near the analytical detection levels) along the western shore and showed a low content, about 1–2% of the total inorganic nitrogen along the eastern shore. We observed large differences in the distribution of phytoplankton biomass along the western and eastern shores of the lake that was caused by earlier water warming at the western shore. Earlier warming led to earlier sinking of the spring algal bloom in the west. In addition, high nutrient load through river runoff at the eastern shore, and more settlement likely increased eastern shore phytoplankton production. The changes in the phytoplankton community detected since the beginning of the current century continue. The abundance of the large-cell Baikalian diatoms A. baicalensis, A. islandica, and S. meyeri was not high, at 0.5–10 cells/mL. They were replaced by the small-cell diatom S. acus subsp. radians, green K. longiseta, and chrysophyte D. cylindricum. Due to this fact, spring phytoplankton stopped exhibiting the phenomenon of periodic highly productive years with biomass exceeding 1 g/m3 that was observed in the 20th century. Structural transformation in the plankton, decreasing the contribution of the typical Baikalian complex, changing of dominants, and intensive development of species of smaller sizes indicate a stress of the littoral zone in Lake Baikal. This part of the ecosystem requires further careful monitoring. Diatom analysis of the surface sediments of the lake also confirms the changes in the diatom community structure. The long-term observations on the phytoplankton are unfortunately rare worldwide, as such time series help us to identify small changes in the ecosystem of waterbodies, the causes of these changes (natural or anthropogenic), as well as to make future forecasts.

Conclusion

Declaration of Competing Interest

The study of chemical parameters of water, species composition, abundance, and biomass of phytoplankton in Lake Baikal in late spring of 2017 at the 44 littoral and 3 pelagic stations located

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Please cite this article as: N. A. Bondarenko, S. S. Vorobyova, N. A. Zhuchenko et al., Current state of phytoplankton in the littoral area of lake Baikal, spring 2017, Journal of Great Lakes Research, https://doi.org/10.1016/j.jglr.2019.10.001

N.A. Bondarenko et al. / Journal of Great Lakes Research xxx (xxxx) xxx

Acknowledgements Authors are grateful to anonymous reviewers for their useful comments and our special thanks to Dr. Lars Gosta Rudstam for his text editorial suggestions, which improved the quality of the article. Also we thank Dr. Ted Ozersky, Department of Biology University of Minnesota Duluth, for his references on the impact of climate on phytoplankton. The work was supported by the state projects of Siberian Branch of Russian Academy of Sciences Nos. 03452019-0009 (AAAA-A16-116122110067-8) (supporting the preparation of this paper, processing of phytoplankton sampling, and analysis of the material); 0345-2019-0006 (AAAA-A16116122110063-0) (supporting the field works, processing of the phytoplankton samples, analysis of the material, and preparation of this paper); 0345-2019-0008 (AAAA-A16-116122110065-4) (supporting the field works, processing of water chemistry samples, analysis of the material, and preparation of the water chemistry section of the paper).

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Please cite this article as: N. A. Bondarenko, S. S. Vorobyova, N. A. Zhuchenko et al., Current state of phytoplankton in the littoral area of lake Baikal, spring 2017, Journal of Great Lakes Research, https://doi.org/10.1016/j.jglr.2019.10.001