Interplay between eutrophication and climate warming on bacterial communities in coastal sediments differs depending on water depth and oxygen history

Stephanie Turner,Mark Dopson,Magnus Ståhle,Laura Seidel,Elias Broman

doi:10.1038/s41598-021-02725-x

Stephanie Turner, Mark Dopson + Show 3 more

Open Access

https://doi.org/10.1038/s41598-021-02725-x

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Journal: Scientific Reports	Publication Date: Dec 1, 2021
Citations: 6	License type: open-access

Affiliation: Linnaeus University, Stockholm University

Abstract

Coastal aquatic systems suffer from nutrient enrichment, which results in accelerated eutrophication effects due to increased microbial metabolic rates. Climate change related prolonged warming will likely accelerate existing eutrophication effects, including low oxygen concentrations. However, how the interplay between these environmental changes will alter coastal ecosystems is poorly understood. In this study, we compared 16S rRNA gene amplicon based bacterial communities in coastal sediments of a Baltic Sea basin in November 2013 and 2017 at three sites along a water depth gradient with varying bottom water oxygen histories. The shallow site showed changes of only 1.1% in relative abundance of bacterial populations in 2017 compared to 2013, while the deep oxygen-deficient site showed up to 11% changes in relative abundance including an increase of sulfate-reducing bacteria along with a 36% increase in organic matter content. The data suggested that bacterial communities in shallow sediments were more resilient to seasonal oxygen decline, while bacterial communities in sediments subjected to long-term hypoxia seemed to be sensitive to oxygen changes and were likely to be under hypoxic/anoxic conditions in the future. Our data demonstrate that future climate changes will likely fuel eutrophication related spread of low oxygen zones.

Highlights

Coastal aquatic systems suffer from nutrient enrichment, which results in accelerated eutrophication effects due to increased microbial metabolic rates
The temperature increased by several degrees independent of the depth of the coastal bottom waters (Supplemental Fig. S1) along with a trend in oxygen decline (Supplemental Fig. S1)
Of the 1.1% of significantly different amplicon sequence variants (ASVs) with a relative abundance over 0.5%, the Proteobacteria and Campylobacterota decreased while Chloroflexota and Cyanobacteria increased

Summary

Introduction

Coastal aquatic systems suffer from nutrient enrichment, which results in accelerated eutrophication effects due to increased microbial metabolic rates. Warming of northern hemisphere water bodies, like the Baltic Sea, has accelerated two to four times greater than the global mean rate[9] and how the seas respond is strongly influenced by interactions with other human-driven changes on the marine system, including overfishing and industrial plus household discharges[10,11] These effects might result in a more fragile marine ecosystem, to what extent this will happen remains uncertain. Prolonged higher temperatures will likely further accelerate these eutrophication effects such as hypoxic ( O2 < 2 mg/L) or anoxic (O2 = 0 mg/L) conditions in coastal bottom waters, which are derived from organic matter d ecomposition[15] These so called ‘dead zones’ have increased ten-fold compared to 100 years ago in the Baltic Sea[13]. The Helsinki Commission (HELCOM) proposed routines to reduce nutrient intake that has led to a Scientific Reports | (2021) 11:23384

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