Small Ponds as Hotspots of Carbon Burial in Agricultural Landscape

Abstract

Carbon (C) cycling in small ponds within agricultural landscapes is of increasing concern due to its high retention capacity during terrestrial C transport. However, quantifying C cycling processes has remained a challenge due to its complex mechanisms and the strong influence of intensive human activities. To bridge this gap, a daily process-based model (Pond-C) was specifically developed to describe the dynamics of diverse C components including dissolved inorganic C, particulate organic C and dissolved organic C, and to quantify C cycling within agricultural ponds. To evaluate the model performance, a five-year (2018-2022) biweekly sampling program was conducted at a typical agricultural pond in the lowland area of Lake Taihu Basin, eastern China. The model achieved a model fit of Nash-Sutcliffe efficiency (NS) higher than 0.3. Our modeling practices revealed that the agricultural pond served as a hotspot for C burial, with a rate of 1273.6 g C·m-2·yr-1 through C settling. Phytoplankton played a critical role in accelerating C cycling within the pond, with key processes including photosynthesis and settling. The studied pond released 184.38 g C·m-2·yr-1 through water-air interface. This study provided quantitative evidences for small agricultural ponds as hotspots of C burial. Compared with previous studies in C-flux estimation, the newly-developed model (Pond-C) provided an avenue for quantifying C flux for each process, and thus enhanced our understanding of C cycling within the agricultural pond ecosystems.

Keywords: Carbon cycling, Carbon dynamic model, Primary production, Lake Taihu Basin