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Video screenshots showing abundant submerged macrophytes at the bottom of Lake Qinghai. (a) Abundant Potamogeton covers the shallow lake bottom at a water depth of ca. 3.2 m (a close-up image of the plant is shown in the upper right insertion). (b) The deep water lake bottom is covered mainly by the green alga Cladophora (a close up image of the alga is shown in the upper right insertion).
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The carbon isotope composition (δ13C values) of long chain n-alkanes in lake sediments has been considered a reliable means of tracking changes in the terrigenous contribution of plants with C3 and C4 photosynthetic pathways. A key premise is that long chain leaf wax components used for isotope analysis are derived primarily from terrigenous higher...
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... vegetation was surveyed at various water depths in Lake Qinghai and Lake Gahai by using an unmanned submerging video imaging system. Extensive submerged macrophytes were discovered to cover the lake bottom (Fig. 2). Two genera of flower- ing plants, Potamogeton L. and Ruppia L., dominate the shallow water (< 9 m), whereas the green alga Cladophora Kützing was found to cover the sediment surface in offshore settings exten- sively (Fig. ...
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... an unmanned submerging video imaging system. Extensive submerged macrophytes were discovered to cover the lake bottom (Fig. 2). Two genera of flower- ing plants, Potamogeton L. and Ruppia L., dominate the shallow water (< 9 m), whereas the green alga Cladophora Kützing was found to cover the sediment surface in offshore settings exten- sively (Fig. ...
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... influ- ence of aquatic macrophytes on sedimentary long chain com- pounds is minor in lakes, either due to the low biomass of aquatic macrophytes or because of the low relative abundance of the long chain compounds they produce. In the case of the Lake Qinghai region, however, we observed that aquatic macrophytes are abundant at the lake bottom ( Fig. 2) and additionally, the C 27 %, C 29 %, C 31 % and P aq values for surface sediments are inter- mediate in comparison with various sources (Fig. 4a-c). This evi- dence suggests a mixed input of long chain n-alkanes from terrigenous plants, submerged plants and Cladophora for these lakes. However, the contribution from Cladophora should ...
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... addition, Douglas et al. (2012) observed negative d 13 C values for Cladium jamaicense, a dominant wetland or emergent aquatic plant in South and Central American lakes; it seems that both C 4 -like and C 3 -like aquatic plants can be found from lakes on the slopes of Mt. Kenya, Africa (Ficken et al., 2000). These results indicate that C 3 -like and C 4 -like aquatic macrophytes might be abundant in lakes from other parts of the world. ...
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... in the deviation of d 13 C values between C 27 and C 31 as a gradual decline in the input from submerged plants (relative to a terrigenous source) with the increase in water depth. Based on our survey of aquatic macro- phytes in Lake Qinghai and Lake Gahai, the submerged plants were abundant only in shallow water but disappeared from deeper areas (Fig. 2). The decreasing P aq values (Fig. 6b) from 0.43 to 0.15 with increasing water depth also indicate that the input from long chain n-alkanes from submerged plants gradually decreases as the water becomes deeper. Therefore, in shallow areas, due to the con- tribution of submerged plants with more C 27 , sedimentary C 27 is more enriched ...
Citations
... The n-alkanes of nonemergent macrophytes are, on the contrary, strongly dominated by C 21 and C 23 homologues (Andrae et al., 2020), which, according to these authors, contain carbon enriched in 13 C. The carbon of С 27 , С 29 , and С 31 n-alkanes of aquatic vegetation is also enriched in 13 C (Liu et al., 2015). ...
The objects of study were bitumens of sedimentary rocks and paraffin oils of the Middle Devonian–lower Frasnian terrigenous complex of the Timan–Pechora basin. We studied the composition of biomarker hydrocarbons and the carbon isotope composition of individual n-alkanes of bitumens from the cores of the wells of the Omra–Lyzha saddle. The results were compared with similar data on the composition of paraffin oils from the south of the Pechora–Kozhva megaswell. The generation potential and thermal maturity of organic matter were studied by the Rock-Eval pyrolysis method. The maturity of organic matter in the rocks of the studied complex in the Omra–Lyzha saddle and the Pechora–Kozhva megaswell corresponds to the oil window. Data on the carbon isotopy of n-alkanes and on the composition of biomarker hydrocarbons do not contradict the possible genetic relationship between paraffin oils and the organic matter of the host sedimentary complex. Both the studied paraffin oils and the rock bitumens contain early eluting rearranged hopanes atypical of oils of other petroliferous complexes and show high contents of n-alkanes relative to iso-alkanes and polycyclic biomarkers. The content of 13C tends to decrease with an increase in the number of carbon atoms in the n-alkane molecule in both oils and bitumen rocks.
... However, the δ 13 C of aquatic plants was dominated by the fractionation of carbon isotopes during photosynthesis (Ménot & Burns, 2001), and the δ 13 C value of phytoplankton varies from − 34.4 to − 5.9‰, showing a wider range than that of terrestrial plants (Han & Wang, 2017). In water bodies dominated by authigenic organic matter, the carbon isotope of submerged plants is higher than that of emergent plants; thus, the δ 13 C value of the former is more positive (Liu et al., 2015). The δ 13 C values of submerged and emergent plants usually range from − 20.0 to − 12.0‰ and from − 30.0 to − 24.0‰, respectively (Aravena et al., 1992). ...
Methane (CH4) emissions from reservoir to the atmosphere depend on the balance of microbial CH4 production and oxidation, and temperature is an important factor to both processes by influencing directly the activity of microorganism. Six sediment cores of 30 cm were collected from the Meiziya Reservoir, China, a small water conservancy project with the maximum water depth of 9.7 m. The main input of reservoir was terrigenous organic matter, and the δ¹³C of organic matter in sediments ranged from − 27.5 to − 23.3‰. Using a self-made device for monitoring CH4 production rate, we measured the CH4 production and oxidation rates in sediment cores simultaneously at the range of 6–27 °C with an interval of 3 °C. The CH4 net production rates and oxidation rates in sediment cores varied in the range of (4.2–2489.0) × 10⁻³ µmol/L·h⁻¹ and (16.0–1287.5) × 10⁻³ µmol/L·h⁻¹, respectively. Increasing temperature enhanced the CH4 production and oxidation rates, and the former increased over temperature with an exponential trend. In the Meiziya Reservoir, a large proportion of CH4 (69.7–70.6%) that originated from sediments was depleted before escaping to the surface sediments. During the mineralization of organic matter in sediments, the release of CH4 accounted for 1.1–66.8% of gaseous carbon (calculated by the mass of C).
... ACL was first defined by Poynter et al. (1989), with the range from C 23 to C 33 n-alkanes, and it was later revised to C 27 to C 31 since this range is characteristic of terrestrial higher plants (Poynter and Eglinton, 1990). Recent studies have shown that submerged aquatic plants can also contribute to the sedimentary long chain nalkanes (e.g., C 27 and C 29 ) of QTP lakes, particularly in the littoral zone (Aichner et al., 2010;Liu et al., 2015;Liu and Liu, 2016). We conducted a literature survey to determine if this was commonly the case for other lakes across the QTP. ...
Long-chain n-alkanes are one of the most common organic compounds in terrestrial plants and they are well-preserved in various geological archives. nalkanes are relatively resistant to degradation and thus they can provide high-fidelity records of past vegetation and climate changes. Nevertheless, previous studies have shown that the interpretation of n-alkane proxies, such as the average chain length (ACL), is often ambiguous since this proxy depends on more than one variable. Both vegetation and climate could exert controls on the n-alkane ACL, and hence its interpretation requires careful consideration, especially in regions like the Qinghai-Tibet Plateau (QTP) where topography, biome type and moisture source are highly variable. To further evaluate the influences of vegetation and climate on the ACL in highelevation lakes, we examined the n-alkane distributions of the surface sediments of 55 lakes across the QTP. Our results show that the ACL across a climatic gradient is significantly affected by precipitation, rather than by temperature. The positive correlation between ACL and precipitation may be because of the effect of microbial degradation during deposition. Finally, we suggest that more caution is needed in the interpretation of ACL data in different regions.
... 71,72 The distributions of n-C 29 and n-C 31 alkane abundances are similar due to epicuticular waxes in both terrestrial and emergent plants. 43,68,72,73 For this reason, long-chain n-alkanes, in which odd-numbered carbon predominates over even-numbered carbon (such as n-C 27 or n-C 29 and n-C 31 ) in the studied coal samples, indicate an important contribution of aquatic emergent/terrestrial plant input. ...
... . In the KP1 seam in the Denis Formation, H/C ratios are between 0.07 and 0.14 (avg. 0.09) and O/C ratios are between 0.73 and 8.43 (avg. 3.05). ...
Organic geochemical (TOC, pyrolysis, biomarker) and petrographic (maceral analysis) investigations together with organic carbon isotope studies were carried out to characterize in detail the depositional environment, determine the organic matter type, and assess the hydrocarbon production potential of three coal seams (KP1-upper, KM3-middle, and KM2-lower) in the Soma (Manisa, Western Anatolia) coal field in Turkey. The total organic carbon value of the upper coal seam ranged between 11.7 and 55.75%, the middle coal seam between 20.12 and 62.86%, and the lower coal seam between 50.03 and 65.71%. Coals in all three seams are characterized by low hydrogen index (HI) values (<151 mg HC/g TOC), low bitumen index (BI) (<19 g HC/g TOC), and quality index (QI) between 23 and 156 mg HC/g TOC. According to Rock-Eval pyrolysis data, the organic matter type of the coals is type III kerogen. Huminite reflectance, Tmax, and biomarker data (22S/22S+22R (C32) sterane, ββ/(αα + ββ) (C29) sterane, and MPI-1) indicate that the organic matter is not thermally mature and that the Soma-Manisa coal has reached the sub-bituminous rank. Rock-Eval data shows that coal is gas-prone and has not reached the maturity threshold required for initial gas production. The dominant maceral group is huminite while liptinite and inertinite macerals have been found in minor amounts. Groundwater index (GWI), vegetation index (VI), tissue preservation index (TPI), and gelification index (GI) parameters indicate a transition from limnic-limno-telmatic to limno-telmatic-telmatic environment from the upper seam to the lower seam. N-Alkane distributions show that paleoclimatic conditions have changed from KP1 to KM2. The higher abundance of pristane compared to phytane and low C35/C31–C35 homohopane index values demonstrate that the coals were deposited in a suboxic–oxic environment. The predominance of n-alkanes with generally high carbon number, relative variable abundances of C27–C28–C29 steranes, δ¹³C values, C/N ratios, and very low gammacerane index indicate a terrestrial ecosystem with nonmarine influence, although algae and microorganisms also contributed to the biomass.
... Lignin phenol and n-alkane distributions alongside n-alkane δ 13 C spanning the last 23 ka in Lake Malawi reconstructed millennial-scale variability in vegetation linked to wet conditions in south-east Africa, and a dominance of higher plant signals in bulk δ 13 C was confirmed (Castañeda et al., 2009b). However, caution is required where there may be mixed aquatic/terrestrial or local/regional inputs in the same archive: contributions of aquatic C 27 and C 29 nalkanes to a lake sediment resulted in different δ 13 C variations compared to the terrestrial leaf wax δ 13 C 31 in the same core (Liu et al., 2015); varying inputs of local and more widely sourced leaf waxes to an estuarine sequence were identified by different δ 13 C signals recorded depending upon the n-alkane chain length (Carr et al., 2015). ...
To reconstruct past environmental changes, a range of indirect or proxy approaches can be applied to Quaternary archives. Here, we review the complementary and novel insights that have been provided by the analysis of chemical fossils (biomarkers). Biomarkers have a biological source that can be highly specific (e.g. produced by a small group of organisms) or more general. We show that biomarkers are able to quantify key climate variables (particularly water and air temperature) and can provide qualitative evidence for changes in hydrology, vegetation, human–environment interactions and biogeochemical cycling. In many settings, biomarker proxies provide the opportunity to simultaneously reconstruct multiple climate or environmental variables, alongside complementary and long‐established approaches to palaeoenvironmental reconstruction. Multi‐proxy studies have provided rich sets of data to explore both the drivers and impacts of palaeoenvironmental change. As new biomarker proxies continue to be developed and refined, there is further potential to answer emerging questions for Quaternary science and environmental change.
... Leaf wax n-alkanes are sensitive to ecological and climatic changes and provide information on changes in the vegetation type, biological productivity, and climatic conditions (Bourbonniere and Meyers, 1996;Ficken et al., 2000;Duan et al., 2014;Liu et al., 2015;Li et al., 2018;Liu et al., 2018). Our previous studies showed that the Neogene sediments of the Tianshui Basin, adjacent to the West Qinling orogenic belt, contain abundant n-alkanes (Peng et al., 2012;Peng et al., 2016). ...
... Specifically, ACL and Paq values of Stage Ⅲ are lower and higher than those of the other two stages, respectively. The published data in the CLP (Li et al., 2018) and NE TP (Gao et al., 2011;Duan et al., 2014;Liu et al., 2015; showed THP have the highest ACL and lowest Paq values, NEM have the lowest ACL and highest Paq values, and values of EMP distribute between THP and NEM ( Figure 5C, D5). In the Tianshui Basin, the ACL and Paq values of Stage Ⅲ are intermediate between NEM and EMP, while those of Stages Ⅰ and Ⅱ range between EMP and HTP, which indicates the increased contribution from aquatic plants during Stage Ⅲ (Figures 5C,D). ...
The Neogene fluvial–lacustrine sediments of the Tianshui Basin provide records of the interactions among tectonic activity, and climatic and ecological changes on the northeastern Tibetan Plateau (NE TP), from ∼12.4 to 2.6 Ma. We investigated the n-alkane record of a sedimentary sequence from the Tianshui Basin, which reveals shifts in the productivity and sources of n-alkanes. The productivity of n-alkanes doubled many times during ∼4.2–3.2 Ma, accompanied by the increased contribution from aquatic plants; in addition, non-emergent macrophytes occurred sporadically after ∼4.2 Ma but became a significant n-alkane source after ∼3.2 Ma. Changes in the inferred Late Miocene ecology of the region are consistent with the major climate transition in response to global cooling. The oscillations of the types and concentrations of n-alkanes during 4.2–3.2 Ma were likely related to the evolution of the East Asian monsoon (EAM), driven by the tectonic uplift of NE TP and global cooling. The major increase in aquatic plants and biological productivity of this region at ∼3.2 Ma may have been caused by the strengthening of the East Asian summer monsoon (EASM) and the regional tectonic uplift.
... Therefore, Botryococcus may not be excluded from having also contributed to the long-chain n-alkanes of the sedimentary archives of the Bale Mountains. According to published data, the ambiguity in the interpretation of sedimentary long-chain n-alkanes can be alleviated by compound specific δ13C values of the n-alkanes and through the application of isotopic mixing models (Aichner et al., 2010;Gao et al., 2011;Liu et al., 2015;Andrae et al., 2020;Yang and Bowen, 2022). Andrae et al. (2020) for instance have shown that in their case study from Australia aquatic macrophyte input significantly influenced the δ13C isotopic composition of the long-chain n-alkanes C27 and C29. ...
Organic matter in sedimentary archives is abundantly used to reconstruct paleoenvironmental and climate histories. Thereby, distinguishing between the terrestrial and aquatic origin of sedimentary organic matter is often a prerequisite for robust interpretations. In this case study, we use published data for modern plants and topsoils to identify the terrestrial versus aquatic source of n-alkane and sugar biomarkers in two afro-alpine sediment archives (Lake Garba Guracha and Depression B4) in the Bale Mountains, Ethiopia. The results of our comparative approach show that the long-chain n-alkanes C29, C31, and C33 in the sedimentary archives yielded patterns similar to those typical for the potential terrestrial input. By contrast, the relative abundances of the sedimentary mid-chain n-alkanes C23 and C25, and at least partly C27, are significantly increased compared to the plants and topsoils. This suggests that they are primarily produced by aquatic macrophytes and micro-organisms. The Paq ratio (C23 + C25)/(C23 + C25 + C29 + C31) is validated as a suitable source identification proxy in our study area. The sugar biomarkers xylose (xyl) and arabinose (ara) are abundant in the plant and topsoil samples. By comparison, high relative abundances of fucose (fuc) and rhamnose (rham) are generally only observed in sediments. This indicates that these sugar biomarkers are primarily produced by aquatic macrophytes or micro-organisms. Therefore, the ratio (fuc + rham)/(ara + xyl) is a suitable sugar biomarker proxy for organic matter source identification. The relative abundances of galactose and mannose are systematically decreasing and increasing, respectively, from leaves over O-layers to Ah-horizons. Furthermore, they are not significantly different from the abundances found in the sediments. This hinders terrestrial versus aquatic source identification using galactose and mannose.
... Somewhat higher contents of odd long-chain n-alkanes, particularly n-C 27 and n-C 29 (TAR, CPI, LSR, and OEP over 1, Table 1, Fig. 2a), along with Paq of 0.48 (Table 1), characterizes the OM of the immature sample, suggesting that vascular plants and submerged macrophytes partly contribute the petola's OM to some extent (Ficken et al., 2000;Aichner et al., 2010;Bush and McInerney, 2013;Liu et al., 2015). Since microorganisms, namely cyanobacteria, diatoms, and other microalgae, comprise the OM of the petola, higher portions of n-alkanes should have a pronounced microbial origin. ...
In Sečovlje Salina Nature Park, the therapeutic mud matured in the natural sedimentary environmental site. This work aimed to determine the influence of the peloid maturation process on the hydrocarbon and elemental distributions, as well as changes in morphology. For this purpose, the sample before and after maturation was examined using various methods. n-Alkanes were the most abundant among saturated hydrocarbons in both immature and mature peloid samples. The results showed that the maturation mainly influenced the change in distribution and concentration (from 378 to 1958 ppm) of n-alkanes. The organic matter (OM) of the immature peloid sample was characterized by a slight prevalence of long-chain and odd carbon-numbered n-alkanes, maximizing at n-C27. However, mature peloid's OM showed a similar share of short-, mid- and long-chain n-alkanes with a slight dominance of short-chain members, maximizing at n-C16. The origin of short-chain and even carbon-numbered n-alkanes was attributed to microbial precursors (e.g., Leptolyngbyaceae). Hopanes were considerably more dominant compared to steranes in both peloids. The hopane series of immature peloid was characterized by the dominance of 22,29,30-trinor-hop-5(6)-ene (C27 hopene), as well as the presence of C30-hop-22(29)-ene (diploptene), which are widespread in cyanobacterial species. The aromatic fraction of immature peloid pointed to the predominance of polycyclic aromatic hydrocarbons (PAHs). As peloid aging progressed, the sample was richer in methyl-branched alkanes, carboxylic acids, their methyl esters, and thermodynamically more stable hopanes and steranes. The presence of elements with toxicological relevance during maturation was reduced below the limits prescribed in most of the directives for cosmetic products. It specifically refers to: As, Ni and Se. A higher concentration of total sulfur in the mature peloid can be related to gypsum precipitation in the summer and/or more intensive microbial activity.
... Biomarkers in sediments are broadly used to reconstruct the paleoclimate, paleoenvironment, paleoecosystem, and paleoproduction [168][169][170]. Biomarkers related to aquatic macrophytes are mainly aliphatic hydrocarbons that are reliable markers for recording the origin of sediments due to their resistance to diagenesis and the specific source [171,172]. ...
... A proxy ratio (Paq) was proposed to reflect the composition of terrestrial and aquatic plants [173]. In addition, the combined applications of lipid biomarkers, stable isotopes, and spectroscopic indices are highly recommended and could more accurately trace the sediment origin and dynamics in aquatic ecosystems [169,173,174]. ...
Submerged macrophytes have attracted increasing attention in lake restoration due to the importance of their structuring communities and stabilizing functions in lake ecosystems. However, there is still a lack of systematic reviews on lake restoration with submerged macrophytes. Thus, we performed a systematic review based on a bibliometric analysis via analyzing and visualizing 934 published works from 1996 to 2023 from the Web of Science core collection. Publication characteristics were summarized, and keyword co-occurrence networks, reference co-citation analysis, and keyword burst tests were conducted. Our results suggest that the increasing attention in this field has partly resulted from the many water treatments and scientific schemes in Europe, China, and the USA and extensive international cooperation. The development of this field was divided into three stages based on keyword bursts (e.g., early, turning, and recent stages). Alternative stable states and biomanipulation laid the foundations of this field in the early stage. Progress in the field was discussed based on four aspects, the influence of environmental factors on submerged macrophytes, theory and mechanisms, targets, and evaluation and methods. Therefore, our results provide a new and comprehensive understanding of lake restoration with submerged macrophytes.
... However, previous studies considered the main peak carbon of terrestrial higher plants was nC 27 , nC 29 , nC 31 (Cranwell et al., 1987;Ficken et al., 2000;Gearing et al., 1976;Rieley et al., 1991). While several recent studies suggested that submerged aquatic plants with enriched δ 13 C might contribute to the concentrations of long-chain n-alkanes (nC 27 , nC 29 ), especially for Potamogeton and Ruppiaceae (Liu et al., 2015;, this may lead to an overestimation of the relative abundance of C 4 plants. Rao et al. (2014) determined the source of lake sediments by analyzing the linear relationship between δD 23 and δD 25 , δD 25 and δD 27 , δD 27 and δD 29 , and δD 29 and δD 31 of n-alkane in lake sediments of the Tibetan Plateau. ...
... Accordingly, here we estimated the C 4 abundance by δ 13 C 31 (Figure 5a), in which was proved a reliable proxy for C 4 and C 3 terrestrial vegetation composition Liu et al., 2015). Ultimately, the percentage of C 4 and C 3 plants was calculated using the following formula, in which X is the relative abundance C 3 plants. ...
The climate reconstruction of the Tibetan Plateau, which was called the Third Pole Environment, has been a research hotspot in recent years. However, there are few studies on C3 and C4 plants evolution and it is area of active debate on whether there are C4 plants exist on the Tibetan Plateau. In this study, the paleoclimate of the Hurleg Lake on the northeastern Tibetan Plateau is reconstructed based on n-alkanes induced indicators, while the C4 plant evolution history is established by compound specific isotope of long-chain n-alkanes since 14.1 cal kyr BP. The response of C4 plant evolution history to climate change on the northeastern margin of the Tibetan Plateau demonstrated that C3 and C4 plants were sensitive to local and global climate change. Solar radiation in summer, insolation-affected East Asian Monsoon and seasonal climate (including seasonal variation of the solar radiation, temperature and precipitation) had significant effects on the long-term growth of C4. On the other hand, factors such as temperature, precipitation and other potential factors affected the detailed variation of C4 plants in a relatively short-term. Our finding maintained the existence of C4 plants on the high-altitude region, and indicated that the abundance of C4 plants might increase significantly and the ecological pattern of vegetation on the Tibetan Plateau will change distinctly in the coming warmer climate condition.
