Dissolved organic matter (DOM) serves as crucial nutrient for microorganisms in oligotrophic groundwater environment. This study investigated regional-scale variations in fluorescent DOMs (fDOM) across three major English aquifers: Jurassic limestone, Permo-triassic sandstone, and Cretaceous chalk, which display different dominant groundwater flow regimes ranging from karstic, intergranular and fractured respectively. Untreated groundwater samples from 134 public supply pumps were analysed using Fluorescence spectroscopy to characterize fDOM in these aquifers with distinct properties. Our aim was to find the baseline fDOM concentrations in uncontaminated groundwater and explore the associations between fDOM, DOC, and bacterial biomass. PARAFAC modelling of the Excitation Emission Matrices (EEMs) revealed two humic-like components (HLF): component-1 peak-C, and component-2 or peak-M; and two protein-like components: component-3 or peak-T (tryptophan like or TLF) and component 4 or peak-B (Tyrosine like). Humic-like components were predominant in groundwater, with median total HLF of 0.19 raman unit (RU). Bacterial cells were enumerated using flow cytometry. Absence of E. Coli in the samples suggested no surface microbial contamination. DOC concentration ranged from 0.76 to 1.11 mg/L, lower than the UK groundwater mean of 3.1 mg/L, implying a carbon-poor environment. Significant difference of fDOM and DOC across three aquifers were observed. Median DOC and HLF were significantly higher in limestone and chalk aquifers than in sandstone aquifers. Higher humification index in limestone (HIX=0.8) and chalk (HIX=0.74) aquifer suggested less complex and high H/C ratio fDOM was present in sandstone aquifer (HIX=0.68). Sandstone also exhibited higher β/α ratio (0.97) and fluorescence index (FI=1.53) than chalk (β/α=0.85, FI=1.4) and limestone aquifer ((β/α=0.75, FI=1.4) suggesting fresher and more microbially derived autochthonous fDOM in sandstone aquifer in contrast with more mature and allochthonous fDOM in limestone and chalk aquifers. Positive correlations between HLF, TLF, and total bacterial cell concentration (TCC) were observed across all aquifers. However, DOC was only correlated with TCC in sandstone aquifers. This emphasised that the type of DOM, rather than its quantity, closely associates with bacterial biomass. Median TCC in karstic limestone aquifer (2×104/ml) was nearly double that of intergranular sandstone (1×104/ml), and fractured chalk aquifer (8×103/ml). Despite relatively high fDOMs in chalk aquifers, TCC was significantly lower due to size exclusion of suspended bacteria through smaller pore-throats of the chalk. This also suggested that the correlation of TCC and fDOMs might not be due to more DOM promoting more bacterial productivity, but possibly due to their similar source. This study highlighted the carbon-poor nature of uncontaminated groundwater environments, with spatially distinct baseline values of fDOM, DOC, and TCC. Limestone and chalk aquifers have high permeability and surface connectivity and are therefore more vulnerable to quality degradation.

<p>The river Thames catchment  passes through rural and urban centres covering many different environments and land uses. Therefore, it is exposed to a range of stresses from sewage pollution to run off from agriculture. As such, UKCEH has been conducting water quality monitoring of the Thames since 1997, which later expanded into the Thames Initiative. The Thames Initiative collects a wide range of chemical and biological data, at 19 sites across the Upper Thames Catchment and its tributaries. For 18 months, in 2012-13, fluorescence spectroscopy and PARAFAC analysis was used to identify 4 components of fluorescent organic matter (FOM). This research focusses on the role of the fourth component, C4, which represents a tryptophan like FOM(TLF). The study is looking at the peak’s temporal variability at all 19 sites within the Thames catchment, alongside nutrient and biological data. This will enable greater understanding TLF’s sources and pathways by analysing TLF’s interaction with other nutrients and pollutants.  There is robust research linking TLF to sewerage pollution and more widely anthropogenic activity. However, the understanding of TLF as a product of insitu production from microorganisms is still in relative infancy, particularly when looking for evidence in the field at a catchment level. In this study multiple variate linear modelling using forward stepwise regression techniques have been applied to the data at each site to investigate the sources of C4 across the catchment to understand both catchment and instream processes. The possible predictors available to each model were dissolved potassium (DK), total dissolved nitrogen (TDN), dissolved calcium (DCa), total bacterial counts(TBC) and chlorophyll <em>a</em>. The models used between 2-3 predictors (σ=2.53, μ =0.678). DK was the most common (18 models),  followed by TBC (11 models), then DCa and TDN (both 8 models) and finally chlorophyll <em>a</em> (2 Models). These results suggest a dominant source of C4 across the catchment is from the wastewater as dissolved potassium is a sewerage indicator.  Secondly the occurrence of TDN or dissolved  calcium suggest a more dominate baseflow path of the fluorescence at these sites, as found in previous analysis of these sites.  However, most novelty is the regular occurrence of TBC in the models. This suggests  the C4 component has a bacteriological element as well, which means it is likely there is an important contribution of TLF by insitu-production from microorganisms.</p>

<p>The identification of novel terrestrial sites that are analogous for other planetary bodies is an active area of research within astrobiology, because of the logistical and financial difficulties in obtaining extraterrestrial samples for analysis. Characterisation of potential analogue sites is undertaken to assess how accurately they represent a specific extraterrestrial environment. Analysing their physicochemical conditions and microbial communities are key components of these studies to understand what metabolisms would be viable in such environments.</p> <p>One such novel analogue environment is the salt plains of Western Sahara. Western Sahara is one of the driest regions on Earth. It is located on the northwest coast of West Africa and is characterised by high UV exposure, low annual precipitation and water activity, subsurface water and high annual temperatures. These features make Western Sahara a potential analogue site for Mars during the Noachian-Hesperian transition period (3.5 – 3.8 Ga), when the atmosphere began to thin and surface water started evaporating (Warner et al., 2010), similar to other terrestrial deserts, such as the Atacama Desert and the McMurdo Dry Valleys.</p> <p>The hypersalinity, aridity and high UV radiation levels of the Western Sahara salt plains would also be appropriate to study whether dissimilatory sulfur metabolisms would be viable in a Noachian-Hesperian Mars analogue environment. Dissimilatory sulfur cycling refers to the use of inorganic sulfur compounds for energy conservation and it has been recognised as a metabolic strategy of interest for putative martian life (Macey et al., 2020). On Earth, evidence from stable sulfur isotope fractionation has suggested this metabolism emerged early in the history of life (~3.5 Ga). During this period, the conditions on Mars were predicted as being more habitable than present-day, with an active magnetic field, thicker atmosphere and liquid water on the surface.</p> <p>In this study, molecular and geochemical techniques were used to give first insights into the potential of the Western Sahara salt plains to serve as an analogue of Mars during the Noachian-Hesperian transition period. The microbiology was investigated through cultivation-independent and culture-dependent analyses of salt crystals, sediment and water samples obtained at three sites near Llaayoune (Fig. 1). The chemical nature of the samples was analysed through ion chromatography (IC) and inductively coupled plasma - optical emission spectrometry (ICP-OES).</p> <p>The geochemical characterisation confirmed the high salinity of the samples and identified that sodium, potassium, magnesium and sulfur were the most enriched elements within all samples. Cultivation-dependent work resulted in the enrichment of a wide range of metabolic strategies from the samples including aerobic heterotrophs, phototrophs and sulfate-reducers. The enrichments from the salt were dominated by strains of <em>Bacillus</em>, whereas sulfate-reducing strains of <em>Clostridium</em> were isolated from the sediment samples. Microscope analysis of phototroph-selective media also indicated that algae and Cyanobacteria were successfully enriched from the samples. 16S rRNA amplicon sequencing results will also be presented to gain further in-depth understanding of the microbial community composition. Additionally, results from quantitative polymerase chain reaction (qPCR) experiment targeting <em>sox</em> and <em>dsr</em> genes will be presented to identify the abundance of genes specific for dissimilatory sulfur metabolisms within the samples.</p> <p>Preliminary data shows that sulfur cycling is occurring in Western Sahara salt plains. Future characterisation of this environment will involve metagenomic analysis of the samples and genome sequencing of the isolates to identify the key metabolisms underpinning the survival and viability of the microbial community. Comparative studies with other Mars analogue environments will then be undertaken to identify metabolisms that may have been thermodynamically viable in ancient martian aqueous environments.</p> <p><img src="" alt="" width="628" height="373" /></p> <p>Figure 1. Location of the sample collection sites. Images were generated with Google Earth Pro.</p> <p><strong>References</strong></p> <p>Macey, M. C., Fox-Powell, M., Ramkissoon, N. K., Stephens, B. P., Barton, T., Schwenzer, S. P., . . . Olsson-Francis, K. (2020). The identification of sulfide oxidation as a potential metabolism driving primary production on late Noachian Mars. <em>Scientific Reports</em>,<em> 10</em>(1), 10941. https://doi.org/10.1038/s41598-020-67815-8</p> <p>Warner, N., Gupta, S., Lin, S.-Y., Kim, J.-R., Muller, J.-P., & Morley, J. (2010). Late Noachian to Hesperian climate change on Mars: Evidence of episodic warming from transient crater lakes near Ares Vallis [https://doi.org/10.1029/2009JE003522]. <em>Journal of Geophysical Research: Planets</em>,<em> 115</em>(E6). https://doi.org/https://doi.org/10.1029/2009JE003522</p>

Protocol for field based sampling of bacterial biomass or environmental DNA (eDNA) using Sterivex filters and syringes.