Allochthonous carbon is a major driver of the microbial food web - A mesocosm study simulating elevated terrestrial matter runoff

Progress in the interaction of dissolved organic matter and microbes (1991-2020): a bibliometric review

Dissolved organic matter (DOM) and microbes are key in the planetary carbon cycle, and research on them can lead to a better understanding of the global carbon cycle and an improved ability to cope with environmental challenges. Several papers have reviewed one or several aspects of the interaction of DOM and microbes, but no overall review has been performed. Here, we bibliometrically analyzed all publications from the Web of Science on DOM and microbes (1991-2020). The results showed that studies on DOM and microbes grew exponentially during this period; the USA contributed the most to the total publications, and China has had the fastest increasing rate since 2010. Moreover, we used the Latent Dirichlet Allocation model to identify topics and determine their (cold or hot) trends by analyzing the abstracts of 9851 publications related to DOM and microbes. A total of 96 topics were extracted, and these topics that are related to the source, composition, and removal path of DOM and the temporal-spatial patterns of DOM and microbes consistently rose from 1991 to 2020. Most studies have used accurate and rapid methods combined with microbiological genetic approaches to study the interaction of DOM and microbes in terrestrial and aquatic ecosystems. The results also showed that the impacts of climate change and land use on the interaction of DOM and microbes, and topics related to human health have received considerable attention. In the future, the interaction mechanism of DOM and microbes and its response to environmental change should be further elucidated.

Ecosystem Capacity for Microbial Biodegradation of Munitions Compounds and Phenanthrene in Three Coastal Waterways in North Carolina, United States

Munitions compounds (i.e., 2,4,6-trinitrotoluene (TNT), octahy-dro-1,3,5,7-tetranitro-1,3,5,7-tetrazocin (HMX), and hexadydro-1,3,5-trinitro-1,3,5-triazin (RDX), also called energetics) were originally believed to be recalcitrant to microbial biodegradation based on historical groundwater chemical attenuation data and laboratory culture work. More recently, it has been established that natural bacterial assemblages in coastal waters and sediment can rapidly metabolize these organic nitrogen sources and even incorporate their carbon and nitrogen into bacterial biomass. Here, we report on the capacity of natural microbial assemblages in three coastal North Carolina (United States) estuaries to metabolize energetics and phenanthrene (PHE), a proxy for terrestrial aromatic compounds. Microbial assemblages generally had the highest ecosystem capacity (mass of the compound mineralized per average estuarine residence time) for HMX (21-5463 kg) > RDX (1.4-5821 kg) ≫ PHE (0.29-660 kg) > TNT (0.25-451 kg). Increasing antecedent precipitation tended to decrease the ecosystem capacity to mineralize TNT in the Newport River Estuary, and PHE and TNT mineralization were often highest with increasing salinity. There was some evidence from the New River Estuary that increased N-demand (due to a phytoplankton bloom) is associated with increased energetic mineralization rates. Using this type of analysis to determine the ecosystem capacity to metabolize energetics can explain why these compounds are rarely detected in seawater and marine sediment, despite the known presence of unexploded ordnance or recent use in military training exercises. Overall, measuring the ecosystem capacity may help predict the effects of climate change (warming and altered precipitation patterns) and other perturbations on exotic compound fate and transport within ecosystems and provide critical information for managers and decision-makers to develop management strategies based on these changes.

Indirect link between riverine dissolved organic matter and bacterioplankton respiration in a boreal estuary

Increasing loading of terrestrially derived dissolved organic matter tends to enhance bacterioplankton respiration (BR) in boreal estuaries, but knowledge on the mechanisms behind this effect is not complete. We determined the stable isotopic signature of the reactive estuarine dissolved organic carbon (DOC) in the Öre estuary (Baltic Sea) by using the Keeling plot method. The δ¹³C ratio of the estuarine labile DOC varied from -26.0‰ to -18.7‰ with most values resembling those typical for DOC of coastal phytoplanktonic origin (-18 to -24‰), while being distinctly higher than those of DOC from ter-res-trial sources (-28‰ to -27‰). Furthermore, the δ¹³C of the respired carbon was positively correlated to DOC concentrations, indicating that carbon of marine origin increasingly dominated the reactive substrates when input of organic matter into the estuary became higher. This suggests that riverine organic matter mainly affects BR indirectly, by providing nutrients that stimulate the production of phytoplankton-derived reactive DOC in the estuary. Thus, riverine derived DOC per se may not be as important for coastal CO₂ emissions as previously thought.