Browsing by Subject "INORGANIC NUTRIENTS"

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  • Figueroa, D.; Rowe, O. F.; Paczkowska, J.; Legrand, C.; Andersson, A. (2016)
    Heterotrophic bacteria are, in many aquatic systems, reliant on autochthonous organic carbon as their energy source. One exception is low-productive humic lakes, where allochthonous dissolved organic matter (ADOM) is the major driver. We hypothesized that bacterial production (BP) is similarly regulated in subarctic estuaries that receive large amounts of riverine material. BP and potential explanatory factors were measured during May-August 2011 in the subarctic RAyenne Estuary, northern Sweden. The highest BP was observed in spring, concomitant with the spring river-flush and the lowest rates occurred during summer when primary production (PP) peaked. PLS correlations showed that similar to 60 % of the BP variation was explained by different ADOM components, measured as humic substances, dissolved organic carbon (DOC) and coloured dissolved organic matter (CDOM). On average, BP was threefold higher than PP. The bioavailability of allochthonous dissolved organic carbon (ADOC) exhibited large spatial and temporal variation; however, the average value was low, similar to 2 %. Bioassay analysis showed that BP in the near-shore area was potentially carbon limited early in the season, while BP at seaward stations was more commonly limited by nitrogen-phosphorus. Nevertheless, the bioassay indicated that ADOC could contribute significantly to the in situ BP, similar to 60 %. We conclude that ADOM is a regulator of BP in the studied estuary. Thus, projected climate-induced increases in river discharge suggest that BP will increase in subarctic coastal areas during the coming century.
  • Andersson, A.; Brugel, S.; Paczkowska, J.; Rowe, O.F.; Figueroa, D.; Kratzer, S.; Legrand, C. (2018)
    Phytoplankton and heterotrophic bacteria are key groups at the base of aquatic food webs. In estuaries receiving riverine water with a high content of coloured allochthonous dissolved organic matter (ADOM), phytoplankton primary production may be reduced, while bacterial production is favoured. We tested this hypothesis by performing a field study in a northerly estuary receiving nutrient-poor, ADOM-rich riverine water, and analyzing results using multivariate statistics. Throughout the productive season, and especially during the spring river flush, the production and growth rate of heterotrophic bacteria were stimulated by the riverine inflow of dissolved organic carbon (DOC). In contrast, primary production and photosynthetic efficiency (i.e. phytoplankton growth rate) were negatively affected by DOC. Primary production related positively to phosphorus, which is the limiting nutrient in the area. In the upper estuary where DOC concentrations were the highest, the heterotrophic bacterial production constituted almost 100% of the basal production (sum of primary and bacterial production) during spring, while during summer the primary and bacterial production were approximately equal. Our study shows that riverine DOC had a strong negative influence on coastal phytoplankton production, likely due to light attenuation. On the other hand DOC showed a positive influence on bacterial production since it represents a supplementary food source. Thus, in boreal regions where climate change will cause increased river inflow to coastal waters, the balance between phytoplankton and bacterial production is likely to be changed, favouring bacteria. The pelagic food web structure and overall productivity will in turn be altered. (C) 2018 The Authors. Published by Elsevier Ltd.
  • Ylöstalo, Pasi; Seppälä, Jukka; Kaitala, Seppo; Maunula, Petri; Simis, Stefan (2016)
    We studied the loadings of dissolved organic matter (DOM) and nutrients from the Neva River into the Eastern Gulf of Finland, as well as their distribution within the salinity gradient. Concentrations of dissolved organic carbon (DOC) ranged from 390 to 840 mu M, and were related to absorption of colored DOM (CDOM) at 350 nm, a(CDOM)(350), ranging from 2.70 to 17.8 m(-1). With increasing salinity both DOC and a(CDOM) decreased, whereas the slope of a(CDOM) spectra, S-CDOM(300-700), ranging from 14.3 to 21.2 mu m(-1), increased with salinity. Deviations of these properties from conservative mixing models were occasionally observed within the salinity range of approximately 1-4, corresponding to the region between 27 and 29 degrees E. These patterns are suggested to mostly reflect seasonal changes in properties of river end-member and hydrodynamics of the estuary, rather than non-conservative processes. On the other hand, observed nonlinear relationships observed between a(CDOM)*(350) and S-CDOM(275-295) emphasized the importance of photochemistry among various transformation processes of DOM. Dissolved inorganic nitrogen was effectively transformed in the estuary into particulate organic nitrogen (PON) and dissolved organic nitrogen (DON), of which DON was mostly exported from the estuary, enhancing productivity in nitrogen limited parts of the Gulf of Finland. DON concentrations ranged from 12.4 to 23.5 mu M and its estuarine dynamics were clearly uncoupled from DOC. In contrast to DOC, estuarine DON dynamics suggest that its production exceeds losses in the estuary. Total nitrogen (TN) and phosphorus (TP) loadings from the Neva River and St. Petersburg were estimated as 73.5 Gg N yr(-1) and 4.2 Gg P yr(-1), respectively. Approximately 59% of TN and 53% of TP loads were in organic forms. DOC and DON loadings were estimated as 741.4 Gg C yr(-1) and 19.0 Gg N yr(-1), respectively. Our estimate for DOC loading was evaluated against a previously published carbon budget of the Baltic Sea. According to the updated model, the Baltic Sea could be identified as a weak source of carbon into the atmosphere. (C) 2016 The Authors. Published by Elsevier B.V.
  • Rowe, Owen F.; Dinasquet, Julie; Paczkowska, Joanna; Figueroa, Daniela; Riemann, Lasse; Andersson, Agneta (2018)
    Dissolved organic matter (DOM) in marine waters is a complex mixture of compounds and elements that contribute substantially to the global carbon cycle. The large reservoir of dissolved organic carbon (DOC) represents a vital resource for heterotrophic bacteria. Bacteria can utilise, produce, recycle and transform components of the DOM pool, and the physicochemical characteristics of this pool can directly influence bacterial activity; with consequences for nutrient cycling and primary productivity. In the present study we explored bacterial transformation of naturally occurring DOM across an extensive brackish water gradient in the Baltic Sea. Highest DOC utilisation (indicated by decreased DOC concentration) was recorded in the more saline southerly region where waters are characterised by more autochthonous DOM. These sites expressed the lowest bacterial growth efficiency (BGE), whereas in northerly regions, characterised by higher terrestrial and allochthonous DOM, the DOC utilisation was low and BGE was highest. Bacterial processing of the DOM pool in the south resulted in larger molecular weight compounds and compounds associated with secondary terrestrial humic matter being degraded, and a processed DOM pool that was more aromatic in nature and contributed more strongly to water colour; while the opposite was true in the north. Nutrient concentration and stoichiometry and DOM characteristics affected bacterial activity, including metabolic status (BGE), which influenced DOM transformations. Our study highlights dramatic differences in DOM characteristics and microbial carbon cycling in sub-basins of the Baltic Sea. These findings are critical for our understanding of carbon and nutrient biogeochemistry, particularly in light of climate change scenarios.
  • Hornick, Thomas; Bach, Lennart T.; Crawfurd, Katharine J.; Spilling, Kristian; Achterberg, Eric P.; Woodhouse, Jason N.; Schulz, Kai G.; Brussaard, Corina P. D.; Riebesell, Ulf; Grossart, Hans-Peter (2017)
    The oceans absorb about a quarter of the annually produced anthropogenic atmospheric carbon dioxide (CO2), resulting in a decrease in surface water pH, a process termed ocean acidification (OA). Surprisingly little is known about how OA affects the physiology of heterotrophic bacteria or the coupling of heterotrophic bacteria to phytoplankton when nutrients are limited. Previous experiments were, for the most part, undertaken during productive phases or following nutrient additions designed to stimulate algal blooms. Therefore, we performed an in situ large-volume mesocosm (similar to 55 m(3)) experiment in the Baltic Sea by simulating different fugacities of CO2 (fCO(2)) extending from present to future conditions. The study was conducted in July-August after the nominal spring bloom, in order to maintain low-nutrient conditions throughout the experiment. This resulted in phytoplankton communities dominated by small-sized functional groups (picophytoplankton). There was no consistent fCO(2)-induced effect on bacterial protein production (BPP), cell-specific BPP (csBPP) or biovolumes (BVs) of either free-living (FL) or particle-associated (PA) heterotrophic bacteria, when considered as individual components (univariate analyses). Permutational Multivariate Analysis of Variance (PERMANOVA) revealed a significant effect of the fCO(2) treatment on entire assemblages of dissolved and particulate nutrients, metabolic parameters and the bacteria-phytoplankton community. However, distance-based linear modelling only identified fCO(2) as a factor explaining the variability observed amongst the microbial community composition, but not for explaining variability within the metabolic parameters. This suggests that fCO(2) impacts on microbial metabolic parameters occurred indirectly through varying physicochemical parameters and microbial species composition. Cluster analyses examining the co-occurrence of different functional groups of bacteria and phytoplankton further revealed a separation of the four fCO(2)-treated mesocosms from both control mesocosms, indicating that complex trophic interactions might be altered in a future acidified ocean. Possible consequences for nutrient cycling and carbon export are still largely unknown, in particular in a nutrient-limited ocean.
  • Paczkowska, Joanna; Brugel, Sonia; Rowe, Owen; Lefebure, Robert; Brutemark, Andreas; Andersson, Agneta (2020)
    Climate change scenarios project that precipitation will increase in northern Europe, causing amplified inflows of terrestrial matter (tM) and inorganic nutrients to coastal areas. How this will affect the plankton community is poorly understood. A mesocosm experiment was carried out to investigate the influence of two levels of tM inputs on the composition, size-structure and productivity of a natural coastal phytoplankton community from the northern Baltic Sea. The tM addition caused browning of the water and decreased underwater light levels, while the concentrations of dissolved organic carbon (DOC) and inorganic nutrients increased. Microphytoplankton were promoted by tM addition, while in the controls picophytoplankton dominated the phytoplankton community. Inorganic nutrient availability was instrumental in defining the phytoplankton community composition and size-structure. As a response to tM addition, the phytoplankton increased their chlorophyll a content. This physiological adaptation helped to maintain high primary production rates at the low tM enrichment, but at the high tM load the primary production decreased as did the biomass of mesozooplankton. The ciliate biomass was high when the mesozooplankton biomass was low, indicating that a trophic cascade occurred in the system. Structural equation modeling showed that tM borne DOC promoted ciliates, while primary and bacterial production were disfavored. Thus, DOC originating from soils had an indirect negative effect on the mesozooplankton by reducing their food availability. Although, a positive correlation between heterotrophic bacteria and phytoplankton suggested coupling between phytoplankton produced carbon and heterotrophs growth. The results from our study indicate that river-borne DOC and inorganic nutrients have a large impact on the phytoplankton community, driving the system to the dominance of large diatoms. However, since river-borne humic substances cause browning of the water, phytoplankton increase their light harvesting pigments. At moderate inflow this helps to support the primary production, but at high inflows of terrestrial material the primary production will decrease. As high river inflows have been projected to be a consequence of climate change, we foresee that primary production will decrease in coastal areas in the future, and the impacts of such changes on the food web could be significant.