Coupling pathway prediction and fluorescence spectroscopy to assess the impact of auxiliary substrates on micropollutant biodegradation.

Some bacteria can degrade organic micropollutants (OMPs) as primary carbon sources. Due to typically low OMP concentrations, these bacteria may benefit from supplemental assimilation of natural substrates present in the pool of dissolved organic matter (DOM). The biodegradability of such auxiliary substrates and the impacts on OMP removal are tightly linked to biotransformation pathways. Here, we aimed to elucidate the biodegradability and effect of different DOM constituents for the carbofuran degrader Novosphingobium sp. KN65.2, using a novel approach that combines pathway prediction, laboratory experiments, and fluorescence spectroscopy. Pathway prediction suggested that ring hydroxylation reactions catalysed by Rieske-type dioxygenases and flavin-dependent monooxygenases determine the transformability of the 11 aromatic compounds used as model DOM constituents. Our approach further identified two groups with distinct transformation mechanisms amongst the four growth-supporting compounds selected for mixed substrate biodegradation experiments with the pesticide carbofuran (Group 1: 4-hydroxybenzoic acid, 4-hydroxybenzaldehyde; Group 2: p-coumaric acid, ferulic acid). Carbofuran biodegradation kinetics were stable in the presence of both Group 1 and Group 2 auxiliary substrates. However, Group 2 substrates would be preferable for bioremediation processes, as they showed constant biodegradation kinetics under different experimental conditions (pre-growing KN65.2 on carbofuran vs. DOM constituent). Furthermore, Group 2 substrates were utilisable by KN65.2 in the presence of a competitor (Pseudomonas fluorescens sp. P17). Our study thus presents a simple and cost-efficient approach that reveals mechanistic insights into OMP-DOM biodegradation.

Remediation of marine dead zones by enhancing microbial sulfide oxidation using electrodes.

Marine dead zones caused by hypoxia have expanded over the last decades and pose a serious threat to coastal marine life. We tested sediment microbial fuel cells (SMFCs) for their potential to reduce the release of sulfide from sediments, in order to potentially protect the marine environment from the formation of such dead zones. Steel electrodes as well as charcoal-amended electrodes and corresponding non-connected controls of a size of together 24 m2 were installed in a marine harbour, and the effects on water quality were monitored for several months. Both pure steel electrodes and charcoal-amended electrodes were able to reduce sulfide concentrations in bottom water (92 % to 98 % reduction, in comparison to disconnected control steel electrodes). Also phosphate concentrations and ammonium were drastically reduced. SMFCs might be used to eliminate hypoxia at sites with high organic matter deposition and should be further investigated for this purpose.

Removal of dissolved organic matter from the woodchip bioreactor start-up by foam fractionation.

Denitrifying woodchip bioreactors are passive, low-tech systems primarily designed to remove nitrate from shallow ground waters as well as point source discharges. Despite their capacity to achieve constant nitrate removal over several years, natural aquatic environments may be affected by the leaching of dissolved organic matter (DOM) from fresh woodchips during start-up. Simple on-site measures might reduce the woodchip leachate during start-up and thus add to the overall environmental sustainability of woodchip bioreactor installations. The aim of the study was to investigate whether foam fractionators could provide an effective solution. Water was flowed through fresh laboratory-scale woodchip bioreactors and recirculated through foam fractionators for 11 days. The bioreactors removed nitrate but increased phosphate and ammonia, which were not effectively removed via foam fractionation. However, foam fractionation did remove 37.8 ± 4.7% of the dissolved chemical oxygen demand (CODdiss) leached during the first 11 days of operation. Fluorescence spectroscopy revealed that the DOM composition differed between the foam and water, where the foam fraction contained higher amounts of DOM associated with the highest bioavailability and hence the greatest potential environmental impact. Optimised foam fractionators could therefore help to reduce the environmental impact of DOM leachate from woodchip bioreactors during start-up.

Coastal freshening drives acidification state in Greenland fjords.

Greenland's fjords and coastal waters are highly productive and sustain important fisheries. However, retreating glaciers and increasing meltwater are changing fjord circulation and biogeochemistry, which may threaten future productivity. The freshening of Greenland fjords caused by unprecedented melting of the Greenland Ice Sheet may alter carbonate chemistry in coastal waters, influencing CO2 uptake and causing biological consequences from acidification. However, few studies to date explore the current acidification state in Greenland coastal waters. Here we present the first-ever large-scale measurements of carbonate system parameters in 16 Greenlandic fjords and seek to identify the drivers of acidification state in these freshening ecosystems. Aragonite saturation state (Ω), a proxy for ocean acidification, was calculated from dissolved inorganic carbon (DIC) and total alkalinity from fjords along the east and west coast of Greenland spanning 68-75°N. Aragonite saturation was primarily >1 in the surface mixed layer. However, undersaturated-or corrosive--conditions (Ω < 1) were observed on both coasts (west: Ω = 0.28-3.11, east: Ω = 0.70-3.07), albeit at different depths. West Greenland fjords were largely corrosive at depth while undersaturation in East Greenland fjords was only observed in surface waters. This reflects a difference in the coastal boundary conditions and mechanisms driving acidification state. We suggest that advection of Sub Polar Mode Water and accumulation of DIC from organic matter decomposition drive corrosive conditions in the West, while freshwater alkalinity dilution drives acidification in the East. The presence of marine terminating glaciers also impacted local acidification states by influencing fjord circulation: upwelling driven by subglacial discharge brought corrosive bottom waters to shallower depths. Meanwhile, discharge from land terminating glaciers strengthened stratification and diluted alkalinity. Regardless of the drivers in each system, increasing freshwater discharge will likely lower carbonate saturation states and impact biotic and abiotic carbon uptake in the future.

Vertical redistribution of principle water masses on the Northeast Greenland Shelf.

The Northeast Greenland shelf (NEGS) is a recipient of Polar Water (PW) from the Arctic Ocean, Greenland Ice Sheet melt, and Atlantic Water (AW). Here, we compile hydrographical measurements to quantify long-term changes in fjords and coastal waters. We find a profound change in the vertical distribution of water masses, with AW shoaling >60 m and PW thinning >50 m since early 2000's. The properties of these waters have also changed. AW is now 1 °C warmer and the salinity of surface waters and PW are 1.8 and 0.68 lower, respectively. The AW changes have substantially weakened stratification south of ~74°N, indicating increased accessibility of heat and potentially nutrients associated with AW. The Atlantification earlier reported for the eastern Fram Strait and Barents Sea region has also propagated to the NEGS. The increased presence of AW, is an important driver for regional change leading to a likely shift in ecosystem structure and function.

Glacial meltwater determines the balance between autotrophic and heterotrophic processes in a Greenland fjord.

Global warming accelerates melting of glaciers and increases the supply of meltwater and associated inorganic particles, nutrients, and organic matter to adjacent coastal seas, but the ecosystem impact is poorly resolved and quantified. When meltwater is delivered by glacial rivers, the potential impact could be a reduction in light and nutrient availability for primary producers while supplying allochthonous carbon for heterotrophic processes, thereby tipping the net community metabolism toward heterotrophy. To test this hypothesis, we determined physical and biogeochemical parameters along a 110-km fjord transect in NE Greenland fjord, impacted by glacial meltwater from the Greenland Ice Sheet. The meltwater is delivered from glacier-fed river outlets in the inner parts of the fjord, creating a gradient in salinity and turbidity. The planktonic primary production was low, 20-45 mg C m-2 d-1, in the more turbid inner half of the fjord, increasing 10-fold to around 350 mg C m-2 d-1 in the shelf waters outside the fjord. Plankton community metabolism was measured at three stations, which displayed a transition from net heterotrophy in the inner fjord to net autotrophy in the coastal shelf waters. Respiration was significantly correlated to turbidity, with a 10-fold increase in the inner turbid part of the fjord. We estimated the changes in meltwater input and sea ice coverage in the area for the last 60 y. The long-term trend and the observed effects demonstrated the importance of freshwater runoff as a key driver of coastal ecosystem change in the Arctic with potential negative consequences for coastal productivity.

Assessing the substrate specificity of a micropollutant degrading strain: generalist or specialist?

Natural dissolved organic matter (DOM) can serve as an additional substrate for organic micropollutant (OMP) degrading bacteria, thus influencing OMP biodegradation in aquatic systems. DOM biodegradation depends on the OMP degrader's ability to grow on different DOM constituents, and on its capability to compete for DOM constituents against the rest of the resident aquatic microbial community. This study aimed to investigate the growth of a model OMP degrader strain, Novosphingobium sp. KN65.2 (assumed specialist), isolated for its ability to mineralize carbofuran, on thirteen DOM constituents; compare its metabolic capabilities to those of a common freshwater strain (Pseudomonas fluorescens sp. P17) (generalist); and to evaluate competition for specific compounds. Growth experiments were carried out in pure- and mixed culture batch experiments. The DOM constituents tested included aromatic amino acids and a range of phenolic acids (lignin derivatives). The OMP degrader could biodegrade approximately half of the tested compounds. It showed a high specialization for substrates containing a hydroxyl-group in the para-position of the primary aromatic ring substituent. However, its broad substrate range enabled the strain to grow on the same number of auxiliary substrates as the generalist. Moreover, the OMP degrader was able to successfully compete against the generalist for the biodegradation of one (4-hydroxybenzaldehyde) out of three substrates (4-hydroxybenzoic acid, 4-hydroxybenzaldehyde, L-tyrosine), which were biodegraded by both strains. The study results provide insight on the substrate specificity of a model OMP degrader, which can inform development of modeling frameworks investigating the influence of DOM on OMP biodegradation.

Tracing Atlantic water transit time in the subarctic and Arctic Atlantic using 99Tc-233U-236U.

The pathway and transport time of Atlantic water passing northern Europe can be traced via anthropogenic radioisotopes released from reprocessing of spent nuclear fuels at Sellafield (SF) and La Hague (LH). These reprocessing derived radioisotopes, with extremely low natural background, are source specific and unique fingerprints for Atlantic water. This study explores a new approach using 99Tc-233U-236U tracer to estimate the transit time of Atlantic water in the coast of Greenland. We isolate the reprocessing plants (RP) signal of 236U (236URP) by incorporating 233U measurements and combine this with 99Tc which solely originates from RP, to estimate the transit time of Atlantic water circulating from Sellafield to the coast of Greenland-Iceland-Faroe Islands. Both being conservative radioisotopes, the temporal variation of 99Tc/236URP ratio in Atlantic water is only influenced by their historic discharges from RP, thus 99Tc/236URP can potentially be a robust tracer to track the transport of Atlantic water in the North Atlantic-Arctic region. Based on our observation data of 99Tc-233U-236U in seawater and the proposed 99Tc/236URP tracer approach, Atlantic water transit times were estimated to be 16-22, 25 and 25 years in the coast of Greenland, Iceland and Faroe Island, respectively. Our estimates from northeast Greenland coastal waters agree with earlier results (17-22 years). Therefore, this work provides an independent approach to estimate Atlantic water transit time with which to compare estimates from ocean modelling and other radiotracer approaches.

Anthropogenic 236U and 233U in the Baltic Sea: Distributions, source terms, and budgets.

The Baltic Sea receives substantial amounts of hazardous substances and nutrients, which accumulate for decades and persistently impair the Baltic ecosystems. With long half-lives and high solubility, anthropogenic uranium isotopes (236U and 233U) are ideal tracers to depict the ocean dynamics in the Baltic Sea and the associated impacts on the fates of contaminants. However, their applications in the Baltic Sea are hampered by the inadequate source-term information. This study reports the first three-dimensional distributions of 236U and 233U in the Baltic Sea (2018-2019) and the first long-term hindcast simulation for reprocessing-derived 236U dispersion in the North-Baltic Sea (1971-2018). Using 233U/236U fingerprints, we distinguish 236U from the nuclear weapon testing and civil nuclear industries, which have comparable contributions (142 ± 13 and 174 ± 40 g) to the 236U inventory in modern Baltic seawater. Budget calculations for 236U inputs since the 1950s indicate that, the major 236U sources in the Baltic Sea are the atmospheric fallouts (∼1.35 kg) and discharges from nuclear reprocessing plants (> 211 g), and there is a continuous sink of 236U to the anoxic sediments (589 ± 43 g). Our findings also indicate that the limited water renewal endows the Baltic Sea a strong "memory effect" retaining aged 236U signals, and the previously unknown 236U in the Baltic Sea is likely attributed to the retention of the mid-1990s' discharges from the nuclear reprocessing plants. Our preliminary results demonstrate the power of 236U-129I dual-tracer in investigating water-mass mixing and estimating water age in the Baltic Sea, and this work provides fundamental knowledge for future 236U tracer studies in the Baltic Sea.

Classification and Quantification of Microplastics (<100 µm) Using a Focal Plane Array-Fourier Transform Infrared Imaging System and Machine Learning.

Microplastics are defined as microscopic plastic particles in the range from few micrometers and up to 5 mm. These small particles are classified as primary microplastics when they are manufactured in this size range, whereas secondary microplastics arise from the fragmentation of larger objects. Microplastics are widespread emerging pollutants, and investigations are underway to determine potential harmfulness to biota and human health. However, progress is hindered by the lack of suitable analytical methods for rapid, routine, and unbiased measurements. This work aims to develop an automated analytical method for the characterization of small microplastics (<100 µm) using micro-Fourier transform infrared (µ-FTIR) hyperspectral imaging and machine learning tools. Partial least squares discriminant analysis (PLS-DA) and soft independent modeling of class analogy (SIMCA) models were evaluated, applying different data preprocessing strategies for classification of nine of the most common polymers produced worldwide. The hyperspectral images were also analyzed to quantify particle abundance and size automatically. PLS-DA presented a better analytical performance in comparison with SIMCA models with higher sensitivity, sensibility, and lower misclassification error. PLS-DA was less sensitive to edge effects on spectra and poorly focused regions of particles. The approach was tested on a seabed sediment sample (Roskilde Fjord, Denmark) to demonstrate the method efficiency. The proposed method offers an efficient automated approach for microplastic polymer characterization, abundance numeration, and size distribution with substantial benefits for method standardization.

Sediment alkaline-extracted organic matter (AEOM) fluorescence: An archive of Holocene marine organic matter origins.

Organic matter (OM) is comprised of a complex mixture of substrates, which are difficult to fully characterize. Therefore a range of analytical approaches is applied to provide a better understanding of the dynamics and biogeochemical cycling of aquatic system. One approach is UV-Visible spectroscopy, which includes measurements of spectral absorption and fluorescence of colored and fluorescent fractions of dissolved OM (DOM, CDOM and FDOM). In this study OM fluorescence is characterized by excitation-emission matrix spectroscopy on alkaline extracted DOM from a Baltic Sea sediment core that spanned 8500 years and fluctuating levels of hypoxia. Our results showed that three underlying fluorescence components had strong correlations with carbon, nitrogen content and δ15N. Our results demonstrate that optical properties of extracted OM from sediments reveal information about OM quality and quantity similar to those of biomarkers, which can be a useful additional tool for investigating OM deposition.

The Molecular Fingerprint of Fluorescent Natural Organic Matter Offers Insight into Biogeochemical Sources and Diagenetic State.

Investigating the biogeochemistry of dissolved organic matter (DOM) requires the synthesis of data from several complementary analytical techniques. The traditional approach to data synthesis is to search for correlations between measurements made on the same sample using different instruments. In contrast, data fusion simultaneously decomposes data from multiple instruments into the underlying shared and unshared components. Here, Advanced Coupled Matrix and Tensor Factorization (ACMTF) was used to identify the molecular fingerprint of DOM fluorescence fractions in Arctic fjords. ACMTF explained 99.84% of the variability with six fully shared components. Individual molecular formulas were linked to multiple fluorescence components and vice versa. Molecular fingerprints differed in diversity and oceanographic patterns, suggesting a link to the biogeochemical sources and diagenetic state of DOM. The fingerprints obtained through ACMTF were more specific compared to traditional correlation analysis and yielded greater compositional insight. Multivariate data fusion aligns extremely complex, heterogeneous DOM data sets and thus facilitates a more holistic understanding of DOM biogeochemistry.

Investigating Fluorescent Organic-Matter Composition as a Key Predictor for Arsenic Mobility in Groundwater Aquifers.

Dissolved organic matter (DOM) is linked to the heterogeneous distribution of elevated arsenic (As) in groundwater used for drinking and irrigation purposes, but the relationship between DOM characteristics and arsenic mobility has yet to be fully understood. Here, DOM from groundwater sampled in the Bengal Basin region was characterized using both conventional bulk emission-excitation (EEM) spectroscopy and high-performance size-exclusion chromatography coupled to spectroscopy (HPSEC-EEM). Notably, application of the novel HPSEC-EEM approach permitted the total fluorescence of individual samples to be independently resolved into its underlying components. This allowed the external validation of the bulk-sample fluorescence decomposition and offered insight into the molecular size distribution of fluorescent DOM. Molecular size distributions were similar for the UVA fluorescent (C310 and C340) as well as the three visible fluorescent (C390, C440, and C500) components. There was a greater visible fluorescence in shallow aquifer samples (10-33 m) with high As (SH, up to 418 µg/L) than in samples from the same depth with lower As (up to 40 µg/L). This indicated a link between DOM quality and As mobility within the shallow aquifer. The deep aquifer samples (170-200 m) revealed DOM characteristics similar to SH samples but had low As concentrations (<4 µg/L), signifying that the deep aquifer is potentially vulnerable to As contamination. These findings pave the way for a more comprehensive assessment of the susceptibility of drinking water aquifers, thereby supporting the management of groundwater resources.

Evidence of local and regional freshening of Northeast Greenland coastal waters.

The supply of freshwater to fjord systems in Greenland is increasing as a result of climate change-induced acceleration in ice sheet melt. However, insight into the marine implications of the melt water is impaired by lack of observations demonstrating the fate of freshwater along the Greenland coast and providing evaluation basis for ocean models. Here we present 13 years of summer measurements along a 120 km transect in Young Sound, Northeast Greenland and show that sub-surface coastal waters are decreasing in salinity with an average rate of 0.12 ± 0.05 per year. This is the first observational evidence of a significant freshening on decadal scale of the waters surrounding the ice sheet and comes from a region where ice sheet melt has been less significant. It implies that ice sheet dynamics in Northeast Greenland could be of key importance as freshwater is retained in southward flowing coastal currents thus reducing density of water masses influencing major deep water formation areas in the Subarctic Atlantic Ocean. Ultimately, the observed freshening could have implications for the Atlantic meridional overturning circulation.

The One-Sample PARAFAC Approach Reveals Molecular Size Distributions of Fluorescent Components in Dissolved Organic Matter.

Molecular size plays an important role in dissolved organic matter (DOM) biogeochemistry, but its relationship with the fluorescent fraction of DOM (FDOM) remains poorly resolved. Here high-performance size exclusion chromatography (HPSEC) was coupled to fluorescence emission-excitation (EEM) spectroscopy in full spectral (60 emission and 34 excitation wavelengths) and chromatographic resolution (<1 Hz), to enable the mathematical decomposition of fluorescence on an individual sample basis by parallel factor analysis (PARAFAC). The approach allowed cross-system comparisons of molecular size distributions for individual fluorescence components obtained from independent data sets. Spectra extracted from allochthonous DOM were highly similar. Allochthonous and autochthonous DOM shared some spectra, but included unique components. In agreement with the supramolecular assembly hypothesis, molecular size distributions of the fluorescence fractions were broad and chromatographically unresolved, possibly representing reoccurring fluorophores forming noncovalently bound assemblies of varying molecular size. Samples shared underlying fluorescence components that differed in their size distributions but not their spectral properties. Thus, in contrast to absorption measurements, bulk fluorescence is unlikely to reliably indicate the average molecular size of DOM. The one-sample approach enables robust and independent cross-site comparisons without large-scale sampling efforts and introduces new analytical opportunities for elucidating the origins and biogeochemical properties of FDOM.

Assessment of drinking water quality at the tap using fluorescence spectroscopy.

Treated drinking water may become contaminated while travelling in the distribution system on the way to consumers. Elevated dissolved organic matter (DOM) at the tap relative to the water leaving the treatment plant is a potential indicator of contamination, and can be measured sensitively, inexpensively and potentially on-line via fluorescence and absorbance spectroscopy. Detecting elevated DOM requires potential contamination events to be distinguished from natural fluctuations in the system, but how much natural variation to expect in a stable distribution system is unknown. In this study, relationships between DOM optical properties, microbial indicator organisms and trace elements were investigated for households connected to a biologically-stable drinking water distribution system. Across the network, humic-like fluorescence intensities showed limited variation (RSD = 3.5-4.4%), with half of measured variation explained by interactions with copper. After accounting for quenching by copper, fluorescence provided a very stable background signal (RSD < 2.2%) against which a ∼2% infiltration of soil water would be detectable. Smaller infiltrations would be detectable in the case of contamination by sewage with a strong tryptophan-like fluorescence signal. These findings indicate that DOM fluorescence is a sensitive indicator of water quality changes in drinking water networks, as long as potential interferents are taken into account.

Global distribution of dissolved organic matter along the aquatic continuum: Across rivers, lakes and oceans.

Based on an extensive literature survey containing more than 12,000 paired measurements of dissolved organic carbon (DOC) concentrations and absorption of chromophoric dissolved organic matter (CDOM) distributed over four continents and seven oceans, we described the global distribution and transformation of dissolved organic matter (DOM) along the aquatic continuum across rivers and lakes to oceans. A strong log-linear relationship (R2=0.92) between DOC concentration and CDOM absorption at 350nm was observed at a global scale, but was found to be ecosystem-dependent at local and regional scales. Our results reveal that as DOM is transported towards the oceans, the robustness of the observed relation decreases rapidly (R2 from 0.94 to 0.44) indicating a gradual decoupling between DOC and CDOM. This likely reflects the decreased connectivity between the landscape and DOM along the aquatic continuum. To support this hypothesis, we used the DOC-specific UV absorbance (SUVA) to characterize the reactivity of the DOM pool which decreased from 4.9 to 1.7m2 × gC-1 along the aquatic continuum. Across the continuum, a piecewise linear regression showed that the observed decrease of SUVA occurred more rapidly in freshwater ecosystems compared to marine water ecosystems, suggesting that the different degradation processes act preferentially on CDOM rather than carbon content. The observed change in the DOM characteristics along the aquatic continuum also suggests that the terrestrial DOM pool is gradually becoming less reactive, which has profound consequences on cycling of organic carbon in aquatic ecosystems.

Ecological effects of scrubber water discharge on coastal plankton: Potential synergistic effects of contaminants reduce survival and feeding of the copepod Acartia tonsa.

To meet the oncoming requirements for lower sulphur emissions, shipping companies can install scrubbers where the exhaust is sprayed with seawater and subsequently discharged to the sea. The discharge water has a pH around 3 and contains elevated concentrations of vanadium, nickel, lead and hydrocarbons. We investigated 1) the threshold concentrations of scrubber discharge water for survival, feeding and reproduction of the copepod Acartia tonsa, 2) whether the effects depend on the exposure route and 3) whether exposure to discharge water can be detected in field-collected organisms. A direct exposure to discharge water increased adult copepod mortality and reduced feeding at metal concentrations which were orders of magnitude lower than the lethal concentrations in previous single-metal studies. In contrast, reproduction was not influenced by dietary uptake of contaminants. Scrubber water constituents could have synergistic effects on plankton productivity and bioaccumulation of metals, although the effects will depend on their dilution in the marine environment.

The Effect of Increased Loads of Dissolved Organic Matter on Estuarine Microbial Community Composition and Function.

Increased river loads are projected as one of the major consequences of climate change in the northern hemisphere, leading to elevated inputs of riverine dissolved organic matter (DOM) and inorganic nutrients to coastal ecosystems. The objective of this study was to investigate the effects of elevated DOM on a coastal pelagic food web from the coastal northern Baltic Sea, in a 32-day mesocosm experiment. In particular, the study addresses the response of bacterioplankton to differences in character and composition of supplied DOM. The supplied DOM differed in stoichiometry and quality and had pronounced effects on the recipient bacterioplankton, driving compositional changes in response to DOM type. The shifts in bacterioplankton community composition were especially driven by the proliferation of Bacteroidetes, Gemmatimonadetes, Planctomycetes, and Alpha- and Betaproteobacteria populations. The DOM additions stimulated protease activity and a release of inorganic nutrients, suggesting that DOM was actively processed. However, no difference between DOM types was detected in these functions despite different community compositions. Extensive release of re-mineralized carbon, nitrogen and phosphorus was associated with the bacterial processing, corresponding to 25-85% of the supplied DOM. The DOM additions had a negative effect on phytoplankton with decreased Chl a and biomass, particularly during the first half of the experiment. However, the accumulating nutrients likely stimulated phytoplankton biomass which was observed to increase towards the end of the experiment. This suggests that the nutrient access partially outweighed the negative effect of increased light attenuation by accumulating DOM. Taken together, our experimental data suggest that parts of the future elevated riverine DOM supply to the Baltic Sea will be efficiently mineralized by microbes. This will have consequences for bacterioplankton and phytoplankton community composition and function, and significantly affect nutrient biogeochemistry.

Coupling Bacterioplankton Populations and Environment to Community Function in Coastal Temperate Waters.

Bacterioplankton play a key role in marine waters facilitating processes important for carbon cycling. However, the influence of specific bacterial populations and environmental conditions on bacterioplankton community performance remains unclear. The aim of the present study was to identify drivers of bacterioplankton community functions, taking into account the variability in community composition and environmental conditions over seasons, in two contrasting coastal systems. A Least Absolute Shrinkage and Selection Operator (LASSO) analysis of the biological and chemical data obtained from surface waters over a full year indicated that specific bacterial populations were linked to measured functions. Namely, Synechococcus (Cyanobacteria) was strongly correlated with protease activity. Both function and community composition showed seasonal variation. However, the pattern of substrate utilization capacity could not be directly linked to the community dynamics. The overall importance of dissolved organic matter (DOM) parameters in the LASSO models indicate that bacterioplankton respond to the present substrate landscape, with a particular importance of nitrogenous DOM. The identification of common drivers of bacterioplankton community functions in two different systems indicates that the drivers may be of broader relevance in coastal temperate waters.