Phytoplankton Dynamics and Urbanization Gradients Reshape Dissolved Organic Matter and Microbial Networks across a Freshwater Estuary
- 1Integrated Discovery Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, USA
Abstract
Freshwater estuaries process contaminants, cycle nutrients, and support biodiversity. However, watershed development degrades water quality, alters organic matter (OM) composition, and reshapes microbial and phytoplankton communities. Understanding how anthropogenic land use shapes estuarine ecosystem function remains a key challenge. We evaluated relationships among benthic and pelagic biogeochemistry, algal, and microbial communities across six sites along an urbanization gradient, combining FTICRMS characterization of water and sediment OM, with 16S and 18S rRNA gene amplicon sequencing of bacterial/archaeal and algal assemblages, alongside measurements of nutrients, ions, turbidity, temperature, phytoplankton biovolume, and land use. Pelagic OM and microbial variation tracked seasonal gradients and transient phytoplankton dynamics modulated by urban inputs, whereas sediments responded directly to urbanization: urban sediments were N-rich with protein, and amino-sugar-like OM, while rural sediments carried aromatic, terrestrial, plant-derived signatures. Both compartments showed non-linear responses, with microbial, algal, and OM abundances shifting abruptly across urbanization thresholds. Strong associations between sediment microbial dissimilarity and phytoplankton biovolume indicate benthic-pelagic coupling, whereby urban nutrients putatively stimulate phytoplankton growth and subsequent OM deposition restructures benthic assemblages. Thus, pelagic communities capture transient urban effects mediated by phytoplankton, whereas benthic communities integrate chronic impacts, highlighting the value of compartment-specific monitoring in estuarine ecosystems.
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BibTeX
@misc{ayalaortiz2026phytoplankton,
title = {{Phytoplankton Dynamics and Urbanization Gradients Reshape Dissolved Organic Matter and Microbial Networks across a Freshwater Estuary}},
author = {C. O. Ayala-Ortiz and P. A. Birschbach and J. Rodriguez-Ramos and W. Petersen and C. G. Simonsen and A. T. Townsend and I. Stohel and Y. Farris and A. Santosh Deshpande and A. Turetcaia and T. W. O. Wietsma and W. R. Kew and R. Chu and E. Reavie and C. T. Filstrup and H. Nicklay and E. B. Graham},
howpublished = {bioRxiv},
year = {2026},
month = oct,
doi = {10.64898/2026.10.26.761939},
url = {https://www.biorxiv.org/content/10.64898/2026.10.26.761939v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Phytoplankton Dynamics and Urbanization Gradients Reshape Dissolved Organic Matter and Microbial Networks across a Freshwater Estuary
AU - C. O. Ayala-Ortiz
AU - P. A. Birschbach
AU - J. Rodriguez-Ramos
AU - W. Petersen
AU - C. G. Simonsen
AU - A. T. Townsend
AU - I. Stohel
AU - Y. Farris
AU - A. Santosh Deshpande
AU - A. Turetcaia
AU - T. W. O. Wietsma
AU - W. R. Kew
AU - R. Chu
AU - E. Reavie
AU - C. T. Filstrup
AU - H. Nicklay
AU - E. B. Graham
PY - 2026
DA - 2026/10/26
PB - bioRxiv
DO - 10.64898/2026.10.26.761939
UR - https://www.biorxiv.org/content/10.64898/2026.10.26.761939v1
AB - Freshwater estuaries process contaminants, cycle nutrients, and support biodiversity. However, watershed development degrades water quality, alters organic matter (OM) composition, and reshapes microbial and phytoplankton communities. Understanding how anthropogenic land use shapes estuarine ecosystem function remains a key challenge. We evaluated relationships among benthic and pelagic biogeochemistry, algal, and microbial communities across six sites along an urbanization gradient, combining FTICRMS characterization of water and sediment OM, with 16S and 18S rRNA gene amplicon sequencing of bacterial/archaeal and algal assemblages, alongside measurements of nutrients, ions, turbidity, temperature, phytoplankton biovolume, and land use. Pelagic OM and microbial variation tracked seasonal gradients and transient phytoplankton dynamics modulated by urban inputs, whereas sediments responded directly to urbanization: urban sediments were N-rich with protein, and amino-sugar-like OM, while rural sediments carried aromatic, terrestrial, plant-derived signatures. Both compartments showed non-linear responses, with microbial, algal, and OM abundances shifting abruptly across urbanization thresholds. Strong associations between sediment microbial dissimilarity and phytoplankton biovolume indicate benthic-pelagic coupling, whereby urban nutrients putatively stimulate phytoplankton growth and subsequent OM deposition restructures benthic assemblages. Thus, pelagic communities capture transient urban effects mediated by phytoplankton, whereas benthic communities integrate chronic impacts, highlighting the value of compartment-specific monitoring in estuarine ecosystems.
ER -