Interaction Between Oxygen Consumption and Carbon Dioxide Emission in a Subtropical Hypoxic Reservoir, Southeastern China

Abstract

Construction of dams in the channels of rivers form artificial reservoirs which change the transit time of water flowing from the catchment to the coast (Bednarek, 2001;Dynesius & Nilsson, 1994;Fearnside, 2001). Human activities in river basins (such as livestock and poultry production, and excessive application of chemical fertilizers) increase the discharge of dissolved nutrients and organic matter (OM) into the river channels, and consequently can cause eutrophication of downstream systems such as reservoirs (

Hydrological dynamics drive the transition of antibiotic resistance genes between particle-attached and free-living lifestyles in a deep freshwater reservoir

“…Nutrients have been found to be correlated with the abundances of certain ARG types (e.g., tetracycline, MLSB, and sulfonamide) in a riverine ecosystem 34 , which could be due to their function in enhancing cell metabolisms and activities 35 . The particles containing ARGs in water columns may come from sediment resuspension during seasons with well-mixed water columns (i.e., January and April) 12 or upstream river deposits. Additionally, positive correlations between ARGs with different physico-chemical parameters, such as the relationship between sulfonamide resistance genes and NO 3 -N or soluble reactive phosphorus, the relationship between tetracycline resistance genes and DO, might be due to the seasonal variation of the microbial community carrying these ARGs 36 .…”

“…As a typical subtropical deep freshwater ecosystem, the SR experienced a seasonal vertical stratification water column starting from summer to fall 12 . Similarly, we observed a vertical differentiation of ARGs profile from the surface water to bottom water ( Fig.…”

“…4E & 4F ). During stratified seasons, the SR experienced phytoplankton blooms (chlorophyll-a > 10 µg/L) and vertical stratification leading to hypoxia conditions in the deep layer of water columns 12 . The micro-patches with low oxygen levels in particles have been found to be the critical factor regulating the PA microbial communities 37,44 .…”

“…However, the water columns were well-oxygenated in April 2017 and January 2018. Details on reservoir seasonal-vertical hydrodynamics of this sampling campaign were described elsewhere 12 . Water samples were collected at the depth of 0.5 m, 10 m, 20 m, and 40 m from sites S7 and S4, and water samples at the depth of 53 m were only collected from site S4 (Fig.…”

“…Unlike their shallow counterpart, deep reservoirs usually undergo a complete vertical mixing from winter to spring and a thermal stratification from summer to fall 11 . Due to the lack of vertical mixing of water columns in stratified seasons (e.g., summer and fall), temperature and dissolved oxygen (DO) significantly decrease with depth 12 . This phenomenon can subsequently result in dramatic changes in the composition and function of microbial communities between upper and deeper layers 13,14 .…”