Longitudinal Spatial Patterns of Bacterial Production and Respiration in a Large River–Estuary: Implications for Ecosystem Carbon Consumption

Abstract

Rivers and estuaries transport organic carbon (C) from terrestrial and freshwater ecosystems to the marine environment. During this transit, bacteria actively utilize and transform organic C, but few studies have measured detailed spatial variation in rates of bacterial respiration (BR) and production (BP). We measured BP at 39 stations and BR at 12 stations at monthly intervals along a 200-km reach of the tidal Hudson River. We observed strong repeatable spatial patterns for both BP and BR, with rates declining in the downstream direction. Bacterial Production had much greater dynamic range of spatial variation than BR. We used the detailed seasonal and spatial data on BP and BR to measure the total C demand of bacteria at several scales. We calculated volumetric and areal rates for 12 sections of the Hudson, as well as the total C utilization. Volumetric BR averaged 20 g-C-m–3 y–1, but it was highest in the most upstream section at 30 g C m–3 y–1. Areal rates averaged over the entire river were 174 g C m–2 y–1, but they were 318 g C m–2 y–1 in the deepest section of the river, indicating the importance of morphometric variation. Total bacterial C demand increased downriver with increasing total volume. Overall, bacteria in the freshwater section of the river consumed approximately 18–25.5 × 109 g C y–1, about 20% of the total organic C load.