Other language confidence: 0.8216509329130032
In all abyssal stations, densities are never over an average of c. 3100 individuals m−2 (Fig. 3, Table 1). In contrast, the shallow station (CON01-427, Posolskoe Bank) harbours the highest observed densities (oligochaetes reach densities as high as 13573 individuals m−2 on average). Gammarids are present in this latter station at 128 m deep, while they are absent from all deep stations. The presence of some groups is anecdotal, such as Hydrachnidia (one specimen in a core at 388 m and two specimens in a core at 625 m) and chironomid larvae (two larvae in a core at 625 m). Interestingly, the two deepest Vydrino cores (CON01-105-7, 600 m, and CON01-106-3, 700 m) are virtually free from animals, suggesting that these stations are perhaps the best choice for the study of stratigraphy and climate proxies.
Calculations were based on factors established for 89 water samples across Lake Baikal in July 2001 (see text). The traps were deployed for about 16 months and the core top spanned c. 7 years (see text).According to the contribution to the chlorophyll a-model shown in Eq. (1), the chlorophyll a content in the water of the south basin in July 2001 was composed of 30% Bacillariophyceae plus Chrysophyceae, 44% Chlorophyta, and 26% cyanobacterial picoplankton. In the 40-m trap, in contrast, 87% of the chlorophyll a originated from Bacillariophyceae plus Chrysophyceae, 11% from Chlorophyta, and 2% from cyanobacterial picoplankton (Fig. 5). The percentage contribution did not change with the water depth, as the same composition was found in the deepest traps (Fig. 5).
During 16 months of deployment, 239 g m−2 dry matter settled in the 40-m trap, with an average flux of 14.9 g m−2 month−1 (Table 2 and Fig. 2). The content of organic carbon was 21.9% at that depth and that of total nitrogen 1.6% (Table 2 and Fig. 2). The resulting atomic C/N ratio of 15 indicated that the sedimented material resulted from the autochthonous production by suspended phytoplankton and that terrigenous input is likely to be negligible at that site. The amount of pigments gathered during the 16 months deployment in the 40-m trap was 193.1 μmol m−2 for chlorophyll a and 797 μmol m−2 for chlorophyllide a+pheopigment a. The average flux was hence 61.8 μmol m−2 month−1 settled chlorophyll a+chlorophyllide a+pheopigment a (Table 1). It is worth noting that the replicate samples of the 40-m trap deviated strongly (coefficient of variation: 60.5%), whereas the coefficients of variation for the replicate samples in the traps
Fig. 4 visualises differences in the degradation between the organic compounds, chlorophylls, and carbon. The chlorophyll a/carbon ratio decreased with depth, indicating that organic carbon is more slowly degraded than chlorophyll a (Table 6 and Fig. 4), whereas the pheophytin a/carbon ratio and the pyropheophytin a/carbon ratio increased with the depth, indicating the formation of pheophytin and pyropheophytin with depth (Table 6 and Fig. 4). Best fits for the chlorophyllide a/carbon ratio and pheophorbide a/carbon ratio vs. depth were also linear regression models, but they were not significant (Fig. 4).
The traps were deployed for about 16 months. The respective regression equations and its coefficients of determination (r2) are reported in Table 5.In the 40-m trap, fucoxanthin was the dominant carotenoid (Table 1 and Fig. 3). Other pigments of Bacillariophyceae plus Chrysophyceae (chlorophyll c, diadinoxanthin, and diatoxanthin) as well as the cyanobacterial zeaxanthin also showed high sedimentation rates, whereas the chlorophyte chlorophyll b and lutein, as well as the cryptophyte alloxanthin, sedimented only in low amounts (Table 1 and Fig. 3). Abbreviations: Chl—chlorophyll, Fuco—fucoxanthin, Zea—zeaxanthin, β-car—β-carotene, Allo—alloxan
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