Anthropogenically driven changes of organic matter input to small shallow lake sediments in the Songnen Plain, Northeast China, over the past 200 years

Abstract

Analyzing organic matter (OM) input patterns to lake sediments influenced by various types and intensities of human activities is crucial for predicting lake organic carbon (OC) burial under future intensified human interventions. However, such studies remain scarce in small, shallow lakes, although these lakes have high OC burial potential. Here, historical transformation of OM input to sediments of four lakes (LJP, KQP, XLHP, and TLH) from the Songnen Plain (SNP) was determined by paleolimnological methods. A generally comparable OM input pattern was observed across the four lakes over the past ∼ 200 years with unique peculiarities in each lake. Before ∼ 1920 CE, low abundances of short- and middle-chain n-alkanes and high abundances of long-chain n-alkanes, coupled with low aquatic macrophyte input (Paq) values and high terrestrial/aquatic ratio (TAR) suggested dominant terrestrial inputs and limited autochthonous aquatic OM, likely due to minimal human impacts and low nutrient supply. During 1920–1950 CE, increased long-chain n-alkane abundances and TAR indicated amplified terrestrial OM input, driven by intensified soil runoff from agricultural expansion. In Lakes KQP and TLH, elevated short-chain n-alkane abundances indicated a greater input from phytoplankton, probably resulting from early lake eutrophication due to excessive input of nutrient-rich black soil. A further transformation of OM input was recorded since 1950 CE, rising short- and middle-chain n-alkane abundances and Paq values suggested increased inputs from phytoplankton and submerged macrophytes, driven by the notable lake eutrophication from intensified agriculture and fertiliser use. This trend peaked in 2000 CE, reflecting a further intensification of OM input from phytoplankton and submerged plants, probably a result of accelerated lake eutrophication due to aquaculture and tourism-related nutrient discharge. The anthropogenically driven complex and nonlinear transformation of OM inputs to lake sediments provides critical insights for predicting OC sequestration in small shallow lakes under future environmental scenarios.