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A 150-year record of phytoplankton 1 community succession controlled by hydroclimatic variability in a tropical lake
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.
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2016 (English)In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, no 13, 3971-3980 p.Article in journal (Refereed) Published
Abstract [en]

Climate and human-induced environmental change promotes biological regime shifts between alternate stable states, with implications for ecosystem resilience, function and services. While this has been shown for recent microbial communities, the long-term response of microbial communities has not been investigated in detail. This study investigated the decadal variations in phytoplankton communities in a ~150 year long sedimentary archive of Lake Nong Thale Prong (NTP), southern Thailand using a combi nation of DNA and lipid biomarkers techniques. Reconstructed drier climate from ~1857-1916 Common Era (CE) coincided with oligotrophic lake water conditions and dominance of the green algae Botryococcus braunii, producing characteristic botryococcene lipids. A change to higher silica (Si) input ~1916 CE, which was related to increased rainfall concurs with an abrupt takeover by diatom blooms lasting for 50 years. Since the 1970s more eutrophic conditions prevailed, which was likely caused by increased levels of anthropogenic phosphate (P), aided by increased lake stratification caused by somewhat dryer conditions. The eutrophic conditions led to increased primary productivity consisting again of a Botryococcus sp., though this time not producing the botryococcene lipids. Moreover, Cyanobacteria became dominant. Our results indicate that a combined DNA and lipid biomarker approach provides an efficient way to allow tracking centennial-scale hydroclimate and anthropogenic feedback processes in lake ecosystems.

Place, publisher, year, edition, pages
2016. Vol. 13, no 13, 3971-3980 p.
National Category
Environmental Sciences
Research subject
Geochemistry
Identifiers
URN: urn:nbn:se:su:diva-129481DOI: 10.5194/bg-2015-633OAI: oai:DiVA.org:su-129481DiVA: diva2:922534
Available from: 2016-04-22 Created: 2016-04-22 Last updated: 2016-09-14Bibliographically approved
In thesis
1. A combined carbon and hydrogen isotope approach to reconstruct the SE Asian paleomonsoon: Impacts on the Angkor Civilization and links to paleolimnology
Open this publication in new window or tab >>A combined carbon and hydrogen isotope approach to reconstruct the SE Asian paleomonsoon: Impacts on the Angkor Civilization and links to paleolimnology
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Changes in monsoon patterns not only affect ecosystems and societies but also the global climate system in terms of heat energy and humidity transfer from the equator to higher latitudes. However, understanding the mechanisms that drive monsoon variability on longer timescales remains a challenge, partly due to sparse paleoenvironmental and paleoclimatic data.

This thesis, which contributes new hydroclimate data sets for the Asian monsoon region, seeks to advance our understanding of the mechanisms that contributed to Southeast Asian summer monsoon variability in the past. Moreover, it explores how past climatic conditions may have impacted societies and ecosystems. In this study lake sediment and peat sequences from northeastern and southern Thailand have been investigated using organic geochemistry, and more specifically the stable carbon and hydrogen isotopic composition of specific biomarkers (n-alkanes, botryococcenes, and highly branched isoprenoids).

The hydrogen isotopic composition of leaf waxes (δDwax) in Thailand was shown to relate to the amount of precipitation and the extent of the El Niño Southern Oscillation.  Higher values of δDwax can be interpreted as reflecting relatively dry climatic conditions, whereas lower values relate to wetter conditions.

The hydroclimate reconstruction for northeastern Thailand, based on the sedimentary record of Lake Kumphawapi, suggests higher moisture availability between ca. 10,700 cal. BP and ca. 7,000 cal. BP likely related to a strengthened early Holocene summer monsoon. Moisture availability decreased during the mid-Holocene, but seems to have increased again around 2,000 years ago and has fluctuated since. The high-resolution Lake Pa Kho peat sequence, which allows for a sub-centennial reconstruction of moisture availability, indicates that the wettest period occurred between ca. 700 and ca. 1000 CE whereas driest intervals were from ca. 50 BCE to ca. 700 CE and from ca. 1300 to ca. 1500 CE. Hydroclimate comparison of Pa Kho’s δDwax record with other paleoclimate records from the Asian-Pacific region suggests that El Niño-like conditions led to Northeastern Thailand being wetter, whereas La Niña-like conditions led to drier conditions.

Regional hydroclimate variability also greatly influenced the Angkor Civilization, which flourished between ca. 845 and ca. 1450 CE. The shift from drier to wetter conditions coincided in time with the rise of the Angkor Civilization and likely favored the intense agriculture needed to sustain the empire. The gradual decline in moisture availability, which started after ca. 1000 years CE, could have stretched the hydrological capacity of Angkor to its limit. It is suggested that Angkor’s population resorted to unconventional water sources, such as wetlands, as population growth continued, but summer monsoon rains weakened.

The 150-year long record of Lake Nong Thale Prong in southern Thailand offers insights into decadal-scale hydroclimatic changes that can be connected to the instrumental record. δDwax-based hydroclimate was drier from ~1857 to 1916 CE and ~1970 to 2010 CE and wetter from ~1916 to 1969 CE. Drier climatic conditions between ~1857 and 1916 CE coincided with oligotrophic lake waters and a dominance of the green algae Botryococcus braunii. Higher rainfall between ~1916 and 1969 CE concurred with an increase in diatom blooms while eutrophic lake water conditions were established between ~1970–2010 CE.

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University, 2016
Series
Meddelanden från Stockholms universitets institution för geologiska vetenskaper, 363
Keyword
Holocene, summer monsoon, biomarkers, hydrogen isotopes, lake sediment, peat, Thailand
National Category
Geosciences, Multidisciplinary
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-128736 (URN)978-91-7649-378-6 (ISBN)
Public defence
2016-05-20, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 13:30 (English)
Opponent
Supervisors
Projects
Monsoon project
Funder
Swedish Research Council, 621-2011-4916Swedish Research Council, 348-2008-6071Swedish Research Council, 621-2008-2855
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Manuscript.

Available from: 2016-04-27 Created: 2016-04-01 Last updated: 2016-04-28Bibliographically approved

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