DOM Biological Lability in an Estuarine System in Two Contrasting Periods

Simona Retelletti Brogi,Chiara Santinelli,Margherita Gonnelli,Stefano Vestri,Benjamin Misson,Cecilia Balestra,Raffaella Casotti

doi:10.3390/jmse9020172

Abstract

Estuarine processes play a key role in determining the amount and quality of land-derived dissolved organic matter (DOM) reaching the oceans. Microbial-mediated reactions can affect the concentration, quality, and bioavailability of DOM within an estuary. In this study, we investigated biological DOM removal in a small estuary and its variability in two contrasting seasons (spring and autumn) characterized by natural differences in the concentration and quality of the riverine DOM. Two incubation experiments were carried out using natural DOM and heterotrophic prokaryotes community collected at the estuary in March and September. Dissolved organic carbon (DOC) concentration, DOM fluorescence, and the heterotrophic prokaryotes abundance (HPA) showed marked differences between the two seasons. These parameters were followed through time for up to two months. Despite the marked differences in the initial conditions, the DOC removal rates were surprisingly similar in the two periods (16 µM DOC month−1 in March and 18 µM DOC month−1 in September), with the biggest removal in the first 48 h. The trend of fluorescent DOM (FDOM) during the incubation showed marked differences between the two periods. In March, the net removal of all the FDOM components was observed consistently with the decrease in DOC; whereas, in September, the net production of humic-like substances was observed.

Highlights

A large amount of dissolved organic matter (DOM) is continuously exported from the land to the oceans through rivers and estuaries
The results of this study show similar dissolved organic carbon (DOC) removal rates in the Arno River estuary in spring and autumn, despite the marked difference in DOC initial concentration, heterotrophic prokaryotes abundance (HPA), and environmental conditions
8–9% of the initial DOC was removed after 48 h, suggesting that it is labile on the short temporal scale

Summary

Introduction

A large amount of dissolved organic matter (DOM) is continuously exported from the land to the oceans through rivers and estuaries. The delivery of organic matter from rivers to the coastal ocean via estuaries is recognized as an important component of the global C budget [3,4,5,6]. A variety of biogeochemical reactions determine the quantity and quality of DOM reaching the oceans. These reactions include flocculation, adsorption on suspended matter, photochemical and microbial processes [2,7,8,9], and can affect both the concentration and quality of the DOM transported to the coastal area [10]

Methods

Results

Conclusion