Hyperspectral imaging sediment core scanning tracks high-resolution Holocene variations in (an)oxygenic phototrophic communities at Lake Cadagno, Swiss Alps
<p>Pigments produced by anoxygenic phototrophic bacteria are valuable proxies of past anoxia in lacustrine and marine environments. Pigment measurement typically requires time-consuming and costly chemical extractions and chromatographic analyses, which limits the temporal resolution of paleoe...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-06-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/20/2221/2023/bg-20-2221-2023.pdf |
| Summary: | <p>Pigments produced by anoxygenic phototrophic bacteria are valuable proxies
of past anoxia in lacustrine and marine environments. Pigment measurement
typically requires time-consuming and costly chemical extractions and
chromatographic analyses, which limits the temporal resolution of
paleoenvironmental reconstructions based on sedimentary pigments. Here, we
evaluate the potential of in situ hyperspectral imaging (HSI) core scanning as a
rapid, non-destructive method to document high-resolution changes in
oxygenic and anoxygenic phototrophic communities at meromictic Lake Cadagno,
Switzerland. Three distinct groups of pigments can be detected with the HSI
method in the sediments of Lake Cadagno; each pigment group represents a
different phototrophic community. Oxygenic phototrophs are indicated by
total chloropigments (TChl; chlorophyll <span class="inline-formula"><i>a</i></span>, <span class="inline-formula"><i>b</i></span>, and derivatives). Two types of
anoxygenic phototrophs were distinguished – purple sulfur bacteria (PSB),
represented by bacteriochlorophyll <span class="inline-formula"><i>a</i></span>, and green sulfur bacteria (GSB),
represented by bacteriochlorophyll <span class="inline-formula"><i>c</i></span>, <span class="inline-formula"><i>d</i></span>, and <span class="inline-formula"><i>e</i></span>. HSI pigment indices were
validated by pigment measurements performed on extracted samples using
spectrophotometer and high-performance liquid chromatography (HPLC).
Bacteriochlorophylls were present throughout the past 10 kyr, confirming
geochemical evidence of nearly continuous stratification and sulfidic
conditions at Lake Cadagno. Major shifts in the anoxygenic phototropic
communities are recorded at decadal to millennial scales. GSB and PSB
communities coexisted from 10.2–8.8 kyr BP. Dominance of PSB over GSB from
8.8–3.4 kyr BP indicates strongly stratified conditions in the lake and
strong light radiation at the chemocline. From 3.4–1.3 kyr BP, PSB were
mostly absent, and GSB became dominant, implying lower light intensity at
the chemocline due to a combination of factors including deforestation in
the lake surroundings, increased flood frequency, cooler climatic
conditions, and changes in groundwater solute concentrations. The
high-resolution HSI data show that frequent flood events and mass movements
disturbed the chemocline and the anoxygenic bacterial communities and that
the PSB were particularly sensitive and slow to recover following these
disturbance events. This study demonstrates for the first time that HSI can
detect GSB-related pigments, making the method uniquely valuable as a rapid
tool to study samples containing pigments of both oxygenic and anoxygenic
phototrophs.</p> |
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| ISSN: | 1726-4170 1726-4189 |