Factors affecting the bacterial community composition and heterotrophic production of Columbia River estuarine turbidity maxima

Abstract

Estuarine turbidity maxima (ETM) function as hotspots of microbial activity and diversity in estuaries, yet, little is known about the temporal and spatial variability in ETM bacterial community composition. To determine which environmental factors affect ETM bacterial populations in the Columbia River estuary, we analyzed ETM bacterial community composition (Sanger sequencing and amplicon pyrosequencing of 16S rRNA gene) and bulk heterotrophic production (3H‐leucine incorporation rates). We collected water 20 times to cover five ETM events and obtained 42 samples characterized by different salinities, turbidities, seasons, coastal regimes (upwelling vs. downwelling), locations, and particle size. Spring and summer populations were distinct. All May samples had similar bacterial community composition despite having different salinities (1–24 PSU), but summer non‐ETM bacteria separated into marine, freshwater, and brackish assemblages. Summer ETM bacterial communities varied depending on coastal upwelling or downwelling conditions and on the sampling site location with respect to tidal intrusion during the previous neap tide. In contrast to ETM, whole (>0.2 μm) and free‐living (0.2–3 μm) assemblages of non‐ETM waters were similar to each other, indicating that particle‐attached (>3 μm) non‐ETM bacteria do not develop a distinct community. Brackish water type (ETM or non‐ETM) is thus a major factor affecting particle‐attached bacterial communities. Heterotrophic production was higher in particle‐attached than free‐living fractions in all brackish waters collected throughout the water column during the rise to decline of turbidity through an ETM event (i.e., ETM‐impacted waters). However, free‐living communities showed higher productivity prior to or after an ETM event (i.e., non‐ETM‐impacted waters). This study has thus found that Columbia River ETM bacterial communities vary based on seasons, salinity, sampling location, and particle size, with the existence of three particle types characterized by different bacterial communities in ETM, ETM‐impacted, and non‐ETM‐impacted brackish waters. Taxonomic analysis suggests that ETM key biological function is to remineralize organic matter.

Assembly processes and source tracking of planktonic and benthic bacterial communities in the Yellow River estuary

“…These transitional ecosystems are important not only for our understanding of the shifts in microbiota from rivers to oceans but also for managing and improving estuarine ecosystems. Many studies have been performed on estuarine microbiota and their changes along environmental gradients, for example, the shifts in the aquatic bacterioplankton, archaeaplankton and phytoplankton communities of the Pearl River estuary (Liu et al ., 2014; Liu et al ., 2015; Li et al ., 2017; Zhu et al ., 2018), the Yaquina Bay estuary (Kieft et al ., 2018), the Baltic Sea (Herlemann et al ., 2011; Herlemann et al ., 2016; Rojas‐Jimenez et al ., 2019), the Columbia River estuary (Fortunato and Crump, 2011; Fortunato et al ., 2012; Herfort et al ., 2017), Delaware Bay (Campbell and Kirchman, 2013), a Pacific Northwest estuary (Bernhard et al ., 2005), the Amazon River estuary (Doherty et al ., 2017) and the Yangtze River estuary (Wu et al ., 2019). These studies demonstrated objective differences in these communities that were directly related to environmental or geographical changes.…”

Effects of surface water interactions with karst groundwater on microbial biomass, metabolism, and production

“…High correlation of heterotrophic production rates with DOC concentration (r = 0.86, p < 0.05) and quality (HIX, r = 0.86; BIX and FI, r = -0.85; p < 0.05) support that both the availability and characteristics of DOC influenced growth of the surface water and groundwater communities we investigated. In the organic matter-and DO-rich surface waters of River Sink, biomass was produced at rates exceeding those reported for the Amazon River (28 µg C L -1 d -1 ; Benner et al, 1995) and were comparable to values for high organic matter river systems such as the Columbia River estuary (3,120 to 114,240 μg C L -1 d -1 ; Herfort et al, 2017). Groundwater contributions to the sink-rise system are minimized when discharge rates are high (> 15 m 3 s -1 ), and while these hydrological conditions tend to increase DO and DOC concentration, the terrigenousderived DOC was generally of lower quality than that observed when groundwater is entering the conduits (Flint et al, 2023).…”

Stochastic processes shape the aggregation of free‐living and particle‐attached bacterial communities in the Yangtze River Estuary, China

“…Estuarine environments are complex systems that are affected by geological, hydrological, physical, chemical, and biological factors [1]. Estuaries are conduits for the transport, transformation, and production of organic carbon and nutrients [2], with unique physical, chemical, and biological characteristics [3]. The Yangtze River Estuary (YRE) is located at the entrance of the Yangtze River flowing into the East China Sea (ECS) [4], which accepts approximately 90% of terrestrial substances from the fresh water input of the Yangtze River [5].…”