A Holocene high‐resolution record of aquatic productivity, seasonal anoxia and meromixis from varved sediments of Lake Łazduny, North‐Eastern Poland: insight from a novel multi‐proxy approach

Abstract

Anthropogenic eutrophication and spreading anoxia in freshwater systems is a global concern. Little is known about anoxia in earlier historic times under weaker human impact, or under prehistoric natural conditions with different trophic, land cover and climatic regimes. We use a novel approach that combines high-resolution hyperspectral imaging with µ-XRF and HPLC-pigment data, which allows us to assess chloropigments (productivity) and bacteriopigments (anoxia) at seasonal subvarve-scale resolution. Our~9700 cal a BP varved sediment record from NE Poland suggests that productivity increased stepwise from oligotrophic Early Holocene conditions (until 9200 cal a BP) to mesotrophic conditions in the Mid-and Late Holocene. Natural eutrophication was mainly a function of progressing landscape evolution with intense weathering under dense forest and warm-moist climatic conditions. Generally, anoxia increased with increasing productivity. Seasonal anoxia and some multi-decadal periods of meromixis were the common mixing patterns throughout the Holocene except for a period of persisting meromixis between~5200 and 2000 cal a BP. Anthropogenic deforestation around 400 cal a BP resulted in substantially better lake oxygenation despite high productivity. In this small lake, aquatic productivity and lakeshore forest cover (wind shield) were more important factors controlling oxic/anoxic conditions than Holocene temperature variability.

Scanning Hyperspectral Imaging for In Situ Biogeochemical Analysis of Lake Sediment Cores: Review of Recent Developments

“…Other groups of pigments can also be estimated using the same principle. Bacteriopheophytin a (a derivative of bacteriochlorophyll a and a biomarker for anoxygenic phototrophic purple sulfur bacteria [ 67 ]) absorbs light at approximately 845 nm [ 6 , 13 , 68 ], and the RABD 845 index has successfully been calibrated to concentrations of bacteriopheophytin a in several studies of lake sediments [ 6 , 43 , 49 , 50 , 51 , 53 ]. Additionally, an absorption band at 615 nm has been identified as phycocyanin (pigment produced by cyanobacteria [ 44 , 69 ]), and an absorption band at 510 nm has been interpreted as a proxy for carotenoid pigments [ 9 , 23 ].…”

“…HSI has been applied to lake sediments from across the globe, with the majority of sites being in Europe. The most common application has been the reconstruction of past aquatic productivity based on the absorbance of chloropigments [ 12 , 13 , 14 , 43 , 44 , 45 , 47 , 49 , 50 , 51 , 53 , 66 , 73 , 74 , 75 ]. Other sedimentary variables interpreted from HSI include bacteriopheophytin a [ 6 , 12 , 13 , 43 , 44 , 45 , 47 , 49 , 50 , 51 , 53 , 75 ], phycocyanin [ 44 ], bulk organic matter [ 11 , 55 ], aromatic organic matter [ 44 ], charcoal [ 12 , 62 ], tephra [ 54 ], flood layers [ 17 , 18 ], particle size [ 15 , 16 ], calcite [ 12 , 47 ], and lithogenic minerals [ 12 , 45 , 46 ].…”

“…Several studies have used the seasonal pattern of bacteriopheophytin a to reconstruct past lake mixing regimes. Detectable concentrations of Bphe throughout the varve year indicate the continuous growth of purple sulfur bacteria and are interpreted as being indicative of year-round water-column stratification [ 43 , 49 , 51 ].…”

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

“…Eutrophication and subsequent oxygen depletion have become primary water quality issues for most freshwater and coastal marine ecosystems globally (Schindler, 2006;Jenny et al, 2016a). Rising mean global temperature can potentially worsen lake anoxia by enhancing water stratification and algal blooms (Adrian et al, 2009;Woolway and Merchant, 2019).…”

Late Holocene Paleonvironmental Evolution of Two Coastal Lakes in Mediterranean Chile and Its Implications for Conservation Planning

“…However, few studies focused on long-term changes in the entire phytoplankton community have been considered in Chilean coastal lakes to explain their response to environmental conditions [6,9,[28][29][30]. Sedimentological and biological proxies such as (sub)fossil remains, total organic carbon concentration, C and N stable isotopes and phytoplankton pigments can provide valuable information on past changes in primary production and the phytoplankton community structure [6,7,[31][32][33][34][35][36][37][38][39]. Phytoplankton pigments have the advantages that they also allow for the study of soft-bodied organisms which do not readily fossilise.…”