Water depth and transparency drive the quantity and quality of organic matter in sediments of Alpine Lakes on the Tibetan Plateau

Abstract

Identifying primary environmental drivers mediating the quantity and quality of sedimentary organic matter (OM) in climate-sensitive alpine lakes is crucial to understanding the role of alpine lakes in greenhouse gas emissions and Earth's climate system. Here, we characterized various pools of OM of 20 alpine lakes across the Tibetan Plateau, including bulk OM, water-soluble OM and alkaline-extracted OM from surface sediments, and dissolved OM (DOM) from surface water. The total organic carbon (TOC) content in sediments was low (< 3%), and δ 13 C of TOC and C : N ratios indicated limited allochthonous carbon inputs. Sedimentary water-soluble OM and alkaline-extracted OM were both dominated by low-molecular-weight, low-aromaticity compounds with low contributions of terrestrial humic substances, suggesting that sedimentary leachable OM was primarily regulated by in-lake sources and processes. Redundancy analysis showed that water depth, water transparency, and total phosphorus concentration in water column explained $ 50% variance of sedimentary bulk and leachable OM, substantiating the importance of autochthonous sources and primary productivity in regulating the quantity and quality of sedimentary OM. Compared with lake surface water DOM, water-soluble OM and alkaline-extracted OM from sediments had higher proportions of terrestrial humic-like substances, suggesting preferential preservation of allochthonous materials in sediments. Our results are the first to demonstrate a clear link between physical attributes and sedimentary OM in Tibetan lakes. The associated relations predict that the amount of total OM and autochthonous carbon preserved in sediments would increase due to the lake enlargement under the scenarios of climate warming and precipitation enhancement, which may amplify greenhouse gas emissions from Tibetan lakes.

Methods for molecular characterization of dissolved organic matter in the alpine water environment: an overview

“…Disentangling the DOM composition and structure, such as microscopic morphology, molecular weight distribution, and chemical bond composition, is essential for understanding its reaction processes and mechanisms and feedback to environmental change. Various DOM characterization methods have been applied to the alpine water quality assessment and the evaluation of anthropogenic effects on DOM-induced biogeochemical cycling (Zhang et al, 2007;Mu et al, 2016;Ma et al, 2018;Wang et al, 2018;Zhou et al, 2019;Li et al, 2020;Du et al, 2022). Different characterization methods have their own advantages and disadvantages for the case of alpine water analysis (Table 1).…”

“…Up to November 2023, using alpine (plateau, alpine, or highland), water quality, and dissolved organic matter as keywords, ~500 articles were found in the Web of Science (WOS) database. Further screening found that ~70 papers focused on the DOM analysis and characterization methods for alpine water, among which most papers (~2/3) focused on the Tibetan Plateau (e.g., Hayakawa et al, 2004;Li et al, 2020;Du et al, 2022). Other study areas include Europe (Laurion et al, 2000;Mladenov et al, 2008;Singer et al, 2012), North America (Belzile et al, 2002;Morris and Hargreaves, 2003;Miller et al, 2009), and Antarctica (Guo et al, 2022).…”

Machine-learning based approach to examine ecological processes influencing the diversity of riverine dissolved organic matter composition

“…Currently, the processing rates of organic C degradation vary regionally and globally (Tiegs et al, 2019), likely arising from the differences in biotic (autotrophic production and heterotrophic microbial degradation) and abiotic (e.g., light) degradation of DOM across large spatial scales. Specifically, environmental factors such as temperature, precipitation, and solar irradiation, have been identified as important regulators of DOM compositions at both region and continental scales (Du et al, 2022(Du et al, , 2023. The variation in microbial community compositions, driven by environmental factors within and across stream ecosystems, also plays a role.…”

C/N Ratio of Resuspended Sediment Regulates Phytoplankton Growth in Shallow Eutrophic Lakes

“…Lake sediments are major sinks of organic matter and serve as pivots for the biogeochemical cycling of nutrients; thus, they are crucial for maintaining the stability and ecological functions of lake ecosystems. − Lake sediments worldwide are estimated to contain 820 Pg of organic carbon, and the annual organic carbon burial is 0.2–0.6 Pg C. − The accumulated sediment organic matter (SOM) can also be released into the overlying water body , to refuel the ambient nutrient stock, particularly in shallow lakes. Sediment organic nitrogen (SON), an important component of SOM, can be easily ammoniated to produce ammonium (NH 4 + –N), which subsequently supports harmful algal blooms .…”