Effects of changes in catchment vegetation and land-use on phosphorus species and primary producers in a small Danish lake during the Holocene

Anna-Marie Klamt, Sofie P. Poulsen, Bent Vad Odgaard, Thomas Hübener, Suzanne McGowan, Henning S. Jensen, Kasper Reitzel

Publikation: Konferencebidrag uden forlag/tidsskriftKonferenceabstrakt til konferenceForskningpeer review

Abstrakt

This study aims to link long-term changes in catchment vegetation and land-use with changes in sedimentary phosphorus (P) species and response of primary producers in a small Danish lake. We investigated pollen, P pools (sequential P extraction), biogenic P forms (31P NMR), primary producers (diatoms, chlorophyll and carotenoid pigments), stable nitrogen (δ15N) isotopes and plant macrofossils in a 14C-dated sediment record spanning the Holocene. Initially, predominantly minerogenic P forms (Ca bound) were washed into the lake from the bare soils. Then, after the development of vegetation and soils, accumulation rates (ARs) of Fe- and Al-bound P forms as well as organic P, humic acid associated P and refractory organic P gradually increased. Sporadic occurrence of purple sulphur bacteria (highest abundances in the oldest/deepest sediment layers) suggest anoxic conditions. Chlorophytes and cyanobacteria were common throughout the entire profile and diatom assemblages were dominated by eutrophic species, suggesting nutrient-rich conditions even from the beginning of the lake’s development. Allochthonous inputs increased with the introduction (~ 3,800 BC) and the intensification (~ 1,000 BC) of farming, mainly animal husbandry, and this boosted the lake’s planktonic productivity (indicated by increased δ15N values). Biogenic P forms (neo-IP6, DNA and phospholipids) are preserved in the sediments as old as ~ 2,500 years. Forest regrowth between AD 200 and AD 1,000 clearly reduced external input and productivity. A drastic change occurred when the wheel plough was introduced and when the lake was used for hemp (Cannabis sativa) and flax (Linum usitatissimum) retting. High productivity in the lake led to unprecedented high burial of organic material in the sediments. All P forms, including monoesters, showed maximum ARs during the retting period. The preservation of biogenic P forms in such old and deep sediment layers has never been shown before and raises questions about their long-term storage capability.
OriginalsprogEngelsk
Publikationsdatoaug. 2018
StatusUdgivet - aug. 2018
BegivenhedSIL 2018: The International Society of Limnology - Nanjing, Kina
Varighed: 19. aug. 201824. aug. 2018

Konference

KonferenceSIL 2018: The International Society of Limnology
Land/OmrådeKina
ByNanjing
Periode19/08/201824/08/2018

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