Phosphorus cycling in a subterranean estuary seepage face: A seasonal view on inventory composition and linkage with nitrate transformations

Danqing Sun; Juan Severino Pino Ibánhez; Jing Zhang; Guosen Zhang; Shan Jiang

doi:10.1016/j.scitotenv.2024.171473

Phosphorus cycling in a subterranean estuary seepage face: A seasonal view on inventory composition and linkage with nitrate transformations

Sci Total Environ. 2024 May 10:924:171473. doi: 10.1016/j.scitotenv.2024.171473. Epub 2024 Mar 6.

Authors

Danqing Sun¹, Juan Severino Pino Ibánhez², Jing Zhang³, Guosen Zhang¹, Shan Jiang⁴

Affiliations

¹ State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200241, China.
² Instituto de Investigacións Mariñas, Consejo Superior de Investigaciones Científicas (IIM-CSIC), Eduardo Cabello 6, 36208 Vigo, Spain.
³ State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200241, China; School of Oceanography, Shanghai Jiao Tong University, 200240, China.
⁴ State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200241, China. Electronic address: sjiang@sklec.ecnu.edu.cn.

PMID: 38458462
DOI: 10.1016/j.scitotenv.2024.171473

Abstract

Seasonal field surveys (April 2018 to February 2019) were conducted in a subterranean estuary (STE) seepage face in Sanggou Bay (China) aiming to explore the transport and reactivity of phosphorus (P) and biogeochemical linkages with the cycling of nitrogen (N) prior to discharge. Porewater dissolved inorganic phosphorus (DIP) and dissolved organic phosphorus (DOP) together with different fractions of sedimentary P were analyzed in the upper, middle and lower intertidal covering the top 20 cm of sediment (1-4 cm, 5-8 cm, 9-12 cm, 13-16 cm and 17-20 cm depth). The accumulation of sedimentary organic P stimulated the growth of phosphate-solubilizing microorganisms and led to porewater DOP enrichment during spring. During summer, total P (TP), porewater DIP and DOP concentrations decreased, potentially due to enhanced mineralization driven by high ambient temperature. From autumn to winter, pelagic organic matter into the STE lowered, triggering a drop of TP standing stocks. Compared with the significant seasonality, sedimentary P storage was statistically identical along the intertidal. Such spatial homogeneity likely results from the rebalance driven by P adsorption dynamics and pelagic organic matter delivered by tide and wave setup. The vertical distribution of DIP, DOP, and sedimentary TP were linked to nitrate transformations. In the sediment layer with active mineralization and nitrification, concentrations of DOP, sedimentary redox and clay P increased. In the layer with active nitrate removal (2-5 cm depth), both DIP and DOP concentrations decreased. The sedimentary loosely-bound and organic P were also lower there. Notably, a substantial quantity of soluble P seeped out, acting as an important contributor to the dissolved P pool of the receiving waters. The spatial and temporal overlap of high concentrations of N and P in STEs adds variabilities and uncertainties in P out-drainage fluxes and nutrient stoichiometry balances, which should draw attention from coastal researchers and stakeholders.

Keywords: Benthic microbiota; Phosphorus; Seepage face; Submarine groundwater discharge; Subterranean estuary.