Microbial communities play vital roles in the biogeochemistry of nutrients in coastal saltmarshes, ultimately controlling water quality, nutrient cycling, and detoxification. We determined the structure of microbial populations inhabiting coastal saltmarsh sediments from northern Barataria Bay, Louisiana, USA to gain insight into impacts on the biogeochemical cycles affected by Macondo oil from the 2010 Deepwater Horizon well blowout two years after the accident. Quantitative PCR directed toward specific functional genes revealed that oiled marshes were greatly diminished in the population sizes of diazotrophs, denitrifiers, nitrate-reducers to ammonia, methanogens, sulfate-reducers and anaerobic aromatic degraders, and harbored elevated numbers of alkane-degraders. Illumina 16S rRNA gene sequencing indicated that oiling greatly changed the structure of the microbial communities, including significant decreases in diversity. Oil-driven changes were also demonstrated in the structure of two functional populations, denitrifying and sulfate reducing prokaryotes, using nirS and dsrB as biomarkers, respectively. Collectively, the results from 16S rRNA and functional genes indicated that oiling not only markedly altered the microbial community structures, but also the sizes and structures of populations involved in (or regulating) a number of important nutrient biogeochemical cycles in the saltmarshes. Alterations such as these are associated with potential deterioration of ecological services, and further studies are necessary to assess the trajectory of recovery of microbial-mediated ecosystem functions over time in oiled saltmarsh sediment.

The puddle Slatina is the old meander of the river Tamis. It is periodically fill with moderate salt and high alkaline (pH 9) water. During our investigation it was determined 65 algal taxa from 5 divisions. Qualitative analysis points out on the domination of Cyanophyta, Euglenophyta and Chlorophyta, while quantitative analysis indicate the dominance of Cyanophyta. During spring 2003, total number of algae was 1.026 x 10**6 cel/l. High values of chlorophyll a (20 microgram/l) and total number of algae, as well as low transparency point out the progressive eutrophication.