Chemical speciation, reactivity, and long-term burial of sedimentary phosphorus in Green Bay, a seasonally hypoxia-influenced freshwater estuary

• Published in: The Science of the total environment 2024-10, Vol.948, p.174957, Article 174957
• Main Authors: Lin, Peng, Klump, J. Val, Guo, Laodong
• Format: Article
• Language: English
• Subjects: Accumulation rate; Chemical speciation; Green Bay; Phosphorus cycling; Potentially bioavailable sedimentary P; Sediment-water interface
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2024.174957

Sediment cores were collected along a trophic gradient in Green Bay, a seasonally hypoxia-influenced freshwater estuary in Lake Michigan, to measure various phosphorus (P) species, including exchangeable-P (Ex-P), iron-bound-P (Fe-P), biogenic-apatite and/or CaCO3-associated-P (CFA-P), organic-P (Org-P) and detrital-apatite-P (Detr-P). Although total phosphorus (TP) decreased with increasing depth, different P species exhibited distinct vertical distribution patterns with different post-depositional behaviors. The Ex-P, Fe-P and CFA-P species were identified as potentially bioavailable-P (BAP). Little variation was observed for Org-P and Detr-P species, especially below the upper-active-layer, both serving as the primary sink for P in sediment. Detr-P% decreased consistently from the near river plume station to the open bay in the north. P accumulation rates were estimated at 25.1 mmol-P/m2/yr (779 mg-P/m2/yr) in the south, 10.9 mmol-P/m2/yr (338 mg-P/m2/yr) in the central region, and 8.1 mmol-P/m2/yr (252 mg-P/m2/yr) in the north of Green Bay, showing a decrease in the depth of the upper active layer for P regeneration along the south-north transect. The overall potential P regeneration back into the water column increased from 2.8 mmol-P/m2/yr (87 mg-P/m2/yr) in the south, and 3.3 mmol-P/m2/yr (101 mg-P/m2/yr) in the central region to 5.6 mmol-P/m2/yr (173 mg-P/m2/yr) in the north of the bay, corresponding to P burial efficiencies of ∼89 %, 70 % and 31 % along the trophic gradient. The recent decrease in Detr-P and thus the increase in BAP over the last 2–3 decades could be related to anthropogenic activities, such as damming and implementation of agricultural conservation practices. Conversely, a recent increase in TOC/TOP ratios may reflect the increased extent of trophic status and seasonal hypoxia in bottom waters and enhanced regeneration and recycling of particulate P in Green Bay since the 1960s. New results from this study provide an improved understanding of the linkage between sources, internal cycling, and long-term burial of P in the basin. [Display omitted] •Post-depositional behavior of sedimentary P species was examined.•Organic-P and detrital apatite were the main sedimentary P sink in Green Bay.•P-regeneration occurred mostly from internal cycling of potentially bioavailable P.•Estimated fluxes of regenerated P increased along the river-lake transect.•Variations in detrital apatite may serve as an indicator of anthropogenic impact.