Coastal uses and contaminant spread in the desert coastal region of Atacama

Dissolved greenhouse gases and benthic microbial communities in coastal wetlands of the Chilean coast semiarid region

Coastal wetlands are ecosystems associated with intense carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) recycling, modulated by salinity and other environmental factors that influence the microbial community involved in greenhouse gases production and consumption. In this study, we evaluated the influence of environmental factors on GHG concentration and benthic microbial community composition in coastal wetlands along the coast of the semiarid region. Wetlands were situated in landscapes along a south-north gradient of higher aridity and lower anthropogenic impact. Our results indicate that wetlands have a latitudinal variability associated with higher organic matter content at the north, especially in summer, and higher nutrient concentration at the south, predominantly in winter. During our sampling, wetlands were characterized by positive CO₂ μM and CH₄ nM excess, and a shift of N₂O nM excess from negative to positive values from the north to the south. Benthic microbial communities were taxonomically diverse with > 60 phyla, especially in low frequency taxa. Highly abundant bacterial phyla were classified into Gammaproteobacteria (Betaproteobacteria order), Alphaproteobacteria and Deltaproteobacteria, including key functional groups such as nitrifying and methanotrophic bacteria. Generalized additive model (GAM) indicated that conductivity accounted for the larger variability of CH₄ and CO₂, but the predictions of CH₄ and CO₂ concentration were improved when latitude and pH concentration were included. Nitrate and latitude were the best predictors to account for the changes in the dissolved N₂O distribution. Structural equation modeling (SEM), illustrated how the environment significantly influences functional microbial groups (nitrifiers and methane oxidizers) and their resulting effect on GHG distribution. Our results highlight the combined role of salinity and substrates of key functional microbial groups with metabolisms associated with both carbon and nitrogen, influencing dissolved GHG and their potential exchange in natural and anthropogenically impacted coastal wetlands.

Seasonal distribution of antibiotic resistance genes under the influence of land-ocean interaction in a semi-enclosed bay

The irrational use of antibiotics has given rise to the proliferation of antibiotic resistance genes (ARGs) in coastal bays. There were few reports on the seasonal distribution of ARGs under the influence of land-ocean interaction in coastal bay. This work studied the seasonal and spatial proliferation of ARGs under the influences of land-ocean interaction in the Sishili Bay. Ten ARGs including tetB, tetG, tetX, sul1, sul2, qnrA, qnrB, qnrS, ermF, ermT and class 1 integron-integrase gene (intI1) were detected and quantified. The relative abundances of intI1 and most of ARGs were in orders of magnitude of 1 × 10^-7-2 copies/16S rRNA copies. The abundances of total ARGs in autumn and summer were much higher than those in the other seasons. Estuary, port and aquaculture farms were important reservoirs of ARGs in the bay. The nutrient levels in coastal water were positively associated with most of the ARGs and intI1, indicating that the water quality was an important driver of ARGs and their transmission. The land-based discharge and seawater stratification were proved to be the dominant driving factors for the seasonal distribution of ARGs in the coastal bay. The land-based discharge and seawater stratification were enhanced from spring to summer, which led to the sharp increase in ARGs in the surface water of the bay.