Holocene phototrophic community and anoxia dynamics in meromictic Lake Jaczno (NE Poland) using high-resolution hyperspectral imaging and HPLC data

Abstract

Abstract. Global spread of hypoxia and altered mixing regimes in freshwater systems is a growing major environmental concern. Climate change and human impact are expected to increasingly deteriorate aquatic ecosystems. The study of processes and drivers of such changes in the past provides a great asset for prevention and remediation in the future. We used a multi-proxy approach combining high-resolution Hyperspectral Imaging (HSI) pigment data, with specific HPLC chlorophylls and carotenoids to examine Holocene trophic state changes and anoxia evolution in meromictic Lake Jaczno, NE Poland. A redundancy analysis RDA including pollen-inferred vegetation cover, temperature and human impacts provides insight into specific conditions and drivers of changing trophic and redox states in the lake. Anoxic and sulfidic conditions established in Lake Jaczno after initial basin infilling 9500 years ago. Until 6700 cal BP, lake trophy was relatively low, water turbidity was high, and green sulfur bacteria (GSB) were abundant within the phototrophic community, suggesting a deep oxic–anoxic boundary and weak stratification. The period between 6700–500 cal BP is characterized by constantly increasing lake production and a gradual shift from GSB to purple sulfur bacteria (PSB), suggesting a shallower oxic–anoxic boundary and pronounced stratification. Yet, the presence of spheroidene and speroidenone in the sediments indicates intermittent anoxia. After 500 cal BP, increasing human impact, deforestation and intensive agriculture promoted lake eutrophication, with a shift to PSB dominance and establishment of permanent anoxia and meromixis. Our study unambiguously documents the legacy of human impact on processes determining eutrophication and anoxia.

Tracking fire activity and post-fire limnological responses using the varved sedimentary sequence of Lake Jaczno, Poland

“…At the top of this zone, nine thin, homogeneous layers (a total thickness of approx. 45 mm) were observed, forming sharp but non-erosive horizons which were recognized as flood layers (Makri et al, 2021).…”

“…At the top of this zone, nine thin, homogeneous layers (a total thickness of approx. 45 mm) were observed, forming sharp but non-erosive horizons which were recognized as flood layers (Makri et al, 2021). • • JAC-4 (90-64 cm) -dark olive-brown, varved sediment with a typical varve structure consisting of calcite and clay.…”

“…75 mm) homogeneous layers were observed in this zone. Similarly to zone 3, they were recognized as flood layers (Makri et al, 2021).…”

“…Lake Jaczno is located in one of these forms (Smolska, 2011) where the lacustrine sedimentation started ca. 9500 cal BP (Makri et al, 2021). The slopes surrounding the northern part of the lake are steep (up to 40°; Figure 1c) which favors erosion processes; the steepness of the slopes on the southern part do not exceed 10°.…”

“…This study is of Lake Jaczno, located in northeast Poland. Sediments of this lake have been studied in detail by several authors (Butz et al, 2015(Butz et al, , 2017Gałka et al, 2019;Makri et al, 2021;Poraj-Górska et al, 2017;Weisbrodt et al, 2016), revealing an excellent varve record, which combined with a well-documented human impact history in this region yields a unique opportunity for further investigations supported by available data.…”