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Table 2
Algae characteristics of study lakes.
| Time, AD | Ķikuru | Lilaste | Āraišu | Trikātas | Lielais Svētiņu |
|---|---|---|---|---|---|
| 1850 – present | Distinct dominance of Tetraëdron minimum suggesting switch in trophic state towards eutrophic conditions with increased nutrient load. | Rapid increase of small Fragilaria spp. and periphytic diatoms (Amphora pediculus, Cocconeis neothumensis, Geissleria schoenfeldii) suggest lake trophic alteration over the last century. | Since 1950s increase of Stephanodiscus parvus shows distinct nutrient loading thus eutrophic to hypertrophic lake conditions. | Stephanodiscus parvus, S. hantzschii and Lindavia comta point to hypertrophic lake that switch from a clear-water to a turbid phytoplankton dominated state of the aquatic ecosystem. | Slight increase of Cyanophyta towards the present-day. Coelastrum and Cyanophyta are the most common algae. |
| 1200 − 1850 | Change in algae composition that is evident by increased Tetraëdron minimum and Pediastrum boryanum var. boryanum suppressing previously dominating species. | Gradual increase in small Fragilaria spp. suggests higher turbidity level in the water column. | Significant variations in diatom, green algae and cyanobacteria composition. Aulacoseira ambigua suggests higher turbulence and mixing of the water column. | More abundant planktonic diatom community that switched to more eutrophic conditions. Aulacoseira ambigua, Cyclostephanos dubius and Platessa holsatica were found this period. | Cyanophyta decrease and composition switch in algae by dominance of Coelastrum reticulatum and C. polychordum suggesting additional nutrient loading to the lake. |
| 1 − 1200 | Algae composition suggests eutrophic conditions as Coelastrum and Chlamydomonas overwhelmingly dominate. | Aulacoseira ambigua and A. granulata form the most common algae. | Rather stable assemblage of phytoplankton indicating mesoeutrophic conditions until AD 700. Increased amount of Cyanophyta and Stephanodiscus parvus and increase of small Fragilaria spp. indicate in-lake nutrient enrichment since AD 800. | Periphytic diatoms, e.g., Sellaphora vitabunda, Platessa holsatica, suggest a shallow hard-water lake with oligo-/mesotrophic conditions. Although dominance of Staurosira construens and S. venter might show unstable conditions and higher turbidity level. | Aphanizomenon and Anabaena dominates with increased prevalence of Gloeotrichia pisum suggesting Cyanophyta dominance within the lake. |
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