Water quality effects of peat rewetting and leftover conifer brash, following peatland restoration and tree harvesting.

Harvesting of plantation conifers on peatlands is carried out as part of restoration and forestry operations. In particular, in the UK and Ireland, conifer plantations on drained ombrotrophic blanket and raised bogs are increasingly being removed (by harvesting), along with blocking of drainage ditches to help raise water tables to reinitiate and restore bog vegetation and function. However, both tree harvesting and peatland restoration operations can have significant impacts on water quality at local and catchment scales. Previous research has suggested that leaching from leftover decomposing brash (tree tops and branches, including wood and needles) is the primary cause, while other work has suggested that release from rewetted peat also contributes to water quality changes. This research investigates the relative importance of peat rewetting, needles and branches on water quality using mesocosm experiments, to help elucidate the mechanisms behind water quality changes following restoration and harvesting operations. Peat and brash were collected from a drained afforested blanket bog in the Flow Country, Scotland. Short-term mesocosm experiments were conducted by incubating peat, peat + needles and peat + needles + branches with rainwater in quadruplicate. Brash from Sitka spruce (Picea sitchensis) and lodgepole pine (Pinus contorta) was investigated separately, while we also conducted experiments with fresh and aged (∼18 months) brash. Peat, needles and branches all significantly impacted water quality in the order of branches > needles > peat, while concentrations of DOC, PO43-, NH4+, K and Mn were most impacted. Water quality impacts of spruce brash appeared generally greater than pine, while fresh brash had larger effects than aged brash. In our mesocosms, relative contributions to water quality changes were estimated by elemental yields. On average, peat contributed 25.4% (range 0.6-72.3%), while needles and brash contributed 19.7% (range 3.0-37.0%) and 54.9% (range 22.1-70.2%) to yields, respectively. We further estimate that 267 kg C ha-1 (255.8 kg as DOC, 10.7 kg as DIC), 27.4 kg K ha-1, 5.8 kg P ha-1 (as PO43-) and 0.5 kg N ha-1 (as NH4+) could be released from brash, over nine days.

Comparing DNA isolation and sequencing strategies for 16S rRNA gene amplicon analysis in biofilm containing environments.

Bacteria are primarily responsible for biological water treatment processes in constructed wetland systems. Gravel in constructed wetlands serves as an essential substrate onto which complex bacterial biofilms may successfully grow and evolve. To fully understand the bacterial community in these systems it is crucial to properly isolate biofilms and process DNA from such substrates. This study looked at how best to isolate bacterial biofilms from gravel substrates in terms of bacterial richness. It considered factors including the duration of agitation during extraction, extraction temperature, and enzyme usage. Further, the 16S taxonomy data subsequently produced from Illumina MiSeq reads (using the SILVA 132 ribosomal RNA (rRNA) database on the DADA2 pipeline) were compared with the 16S data produced from Oxford Nanopore Technologies (ONT) MinION reads (using the NCBI 16S database on the EPI2ME pipeline). Finally, performance was tested by comparing the taxonomy data generated from the Illumina MiSeq and ONT MinION reads using the same (SILVA 132) database. We found no significant differences in the effective number of species observed when using different bacterial biofilm detachment techniques. However, enzyme treatment enhanced the total concentration of DNA. In terms of wetland community profiles, relative abundance differences within each sample type were clearer at the genus level. For genus-level taxonomic classification, MinION sequencing with the EPI2ME pipeline (NCBI database) produced bacterial abundance information that was poorly correlated with that from the Illumina MiSeq and DADA2 pipelines (SILVA132 database). When using the same database for each sequencing technology (SILVA132), the correlation between relative abundances at genus-level improved from negligible to moderate. This study provides detailed information of value to researchers working on constructed wetlands regarding efficient biofilm detachment techniques for DNA isolation and 16 s metabarcoding platforms for sequencing and data analysis.

A comparison between constructed wetland substrates: Impacts on microbial community and wastewater treatment.

Constructed wetlands (CWs) can play a crucial role in treating wastewater, and in the context of this study, the distillation byproduct of the whisky industry known as 'spent lees'. Here, we assess several different CW substrates (pea gravel, LECA and Alfagrog), with and without the addition of 20% biochar, in mesocosms set up to treat spent lees. Among the substrates tested, LECA + biochar and gravel + biochar showed promising results, with greater dissolved copper (dissCu) reduction, chemical oxygen demand (COD) removal, organic carbon (OC) reduction, and pH modulation. These findings indicate a potentially beneficial role for biochar in enhancing treatment efficacy, particularly in facilitating dissCu remediation and the removal of organic pollutants. In terms of microbial diversity, mesocosms including biochar generally had reduced bacterial alpha diversity, suggesting that 'fresh' (uncolonized) biochar may negatively affect microbial diversity in wetland ecosystems in the short term. After continuously supplying spent lees to mesocosms for 2-months, microbial diversity in each mesocosm dropped substantially, and moderate levels of bacterial community differentiation and high levels of fungal community differentiation were detected among mesocosms. The bacterial and fungal communities were also found to differ between the substrate and outlet water samples. Among the bacterial classes present in the mesocosms that may play a crucial role in water treatment performance, Gammaproteobacteria, Bacteroidia and Alphaproteobacteria should be further investigated. In terms of fungal classes, the role of Sordariomycetes should be explored in greater depth.