Phytoplankton Primary Production Research Articles

Relevance of Nutrient-Limited Phytoplankton Production and Its Bacterial Remineralization for Carbon and Oxygen Fluxes in the Baltic Sea

The Baltic Sea is prone to oxygen deficiency due to the restricted water exchange with the North Sea in coincidence with a high biological oxygen demand. The partitioning of organic carbon between respiration, accumulation and export is co-determined by phytoplankton primary production and its subsequent bacterial remineralization. Here, we investigated net phytoplankton primary production, heterotrophic bacterial biomass production and dark CO2 fixation by on-board incubations with radiolabeled tracers in the Baltic Proper and in the Gulf of Riga after the main spring bloom. Results show that low phytoplankton standing stocks of ≤1.6 µg chlorphyll a L-1 sustained net primary production of 161-724 mg C m-2 d-1 under nitrogen limitation. Estimates of bacterial carbon remineralization suggest that freshly produced organic carbon was supplied to the aphotic zone at all stations. In the southern Baltic Proper, net primary production exceeded the bacterial carbon demand in the upper mixed layer, suggesting that organic matter derived from nutrient-limited primary production was available for export to bacterial communities below the oxycline. On average, 46% of heterotrophic bacterial production was mediated in oxygen minimum zones, revealing the high importance of organic matter recycling under hypoxic and anoxic conditions for the carbon budget. Dark CO2 fixation of up to 4.33 µg C L-1 d-1 in sulfide-free waters equaled 9-54% of the co-inciding heterotrophic bacterial carbon demand and may have provided another organic carbon source for heterotrophic activity. Substantially higher dark CO2 fixation up to 25.46 µg C L-1 d-1 was determined in sulfidic waters. Since our study was conducted five months after the major Baltic inflow event in winter 2014/2015, potential effects of deep water ventilation could be investigated. In the Gotland Basin, heterotrophic bacterial production in renewed oxygen-rich bottom water was similar to that in the uplifted oxygen-deficient former bottom water, while it was significantly reduced in sulfidic waters. Hence, our results suggest that the removal of hydrogen sufide by inflow events has a high potential to increase bacterial carbon remineralization.

Ideas and perspectives: Is dark carbon fixation relevant for oceanic primary production estimates?

Abstract. About half of the global primary production (PP) is generated in the euphotic layer of the ocean. The 14C method developed by Steemann Nielsen (Nielsen, 1952) more than half a century ago has been the most frequently used method to determine PP in all aquatic systems. This method includes dark incubations to exclude the non-phototrophic dissolved inorganic carbon (DIC) fixation. The presence of significant dark DIC fixation rates has been habitually used to suggest the inaccuracy of the 14C method to determine autotrophic phytoplankton primary production. However, we suggest that the dark DIC fixation rates should be incorporated into global oceanic carbon production estimates since the total production of organic matter does not originate only from photosynthesis but also from other processes such as chemoautotrophic and anaplerotic processes. Here we analyzed data collected over almost 30 years from the longest available oceanic time series and calculated that the inclusion of dark DIC fixation would increase oceanic PP estimates by 5 %–22 % when total dark DIC fixation is included or by 2.5 %–11 % when only considering the nighttime DIC fixation. We conclude that dark DIC fixation should be included into global oceanic primary production estimates as it represents newly synthesized organic carbon (ca. 1.2–11 Pg C yr−1) available for the marine food web.

Potential influence of the Deepwater Horizon oil spill on phytoplankton primary productivity in the northern Gulf of Mexico

Nine years after the Deepwater Horizon (DwH) oil spill (20 April–15 July 2010), the recovery of primary productivity at the ocean surface remains to be investigated. Here, we used the normalized fluorescence line height (nFLH) from the Moderate Resolution Imaging Spectroradiometer as an indicator of chlorophyll a concentration (Chl a). First, from the spatiotemporal variations of nFLH between 2001 and 2017, a reduction of nFLH after the DwH oil spill was observed (for a relatively long period, from 2011 to 2014). Second, a stepwise multiple regression model was used to examine which of the following environmental factors could explain the annual variations in nFLH: river discharge, total nitrogen load, total phosphorus load, photosynthetically available radiation, sea surface temperature and wind speed. Results show that river discharge, sea surface temperature and wind speed are the primary factors that regulated the annual nFLH variations in the DwH area during the pre-spill years. In contrast, this same model could not explain the reduction of nFLH for the four years after the DwH oil spill. After 2015, nFLH appears to have resumed to the pre-spill concentrations. Here we suggest that the nFLH reduction between 2011 and 2014 could have originated from the DwH oil spill, although the exact mechanism is yet to be determined.

Sensitivity of Phytoplankton Primary Production Estimates to Available Irradiance Under Heterogeneous Sea Ice Conditions

AbstractThe Arctic ice scape is composed by a mosaic of ridges, hummocks, melt ponds, leads, and snow. Under such heterogeneous surfaces, drifting phytoplankton communities are experiencing a wide range of irradiance conditions and intensities that cannot be sampled representatively using single‐location measurements. Combining experimentally derived photosynthetic parameters with transmittance measurements acquired at spatial scales ranging from hundreds of meters (using a remotely operated vehicle, ROV) to thousands of meters (using a surface and underice trawl, SUIT), we assessed the sensitivity of water column primary production estimates to multiscale underice light measurements. Daily primary production calculated from transmittance from both the ROV and the SUIT ranged between 0.004 and 939 mgC·m−2·day−1. Upscaling these estimates at larger spatial scales using satellite‐derived sea ice concentration reduced the variability by 22% (0.004–731 mgC·m−2·day−1). The relative error in primary production estimates was two times lower when combining remote sensing and in situ data compared to ROV‐based estimates alone. These results suggest that spatially extensive in situ measurements must be combined with large‐footprint sea ice coverage sampling (e.g., remote sensing, aerial imagery) to accurately estimate primary production in ice‐covered waters. Also, the results indicated a decreasing error of primary production estimates with increasing sample size and the spatial scale at which in situ measurements are performed. Conversely, existing estimates of spatially integrated phytoplankton primary production in ice‐covered waters derived from single‐location light measurements may be associated with large statistical errors. Considering these implications is important for modeling scenarios and interpretation of existing measurements in a changing Arctic ecosystem.

Ecosystem responses to increased organic carbon concentration: comparing results based on long-term monitoring and whole-lake experimentation

ABSTRACTRecent increases in terrestrial dissolved organic carbon (DOC) concentrations in northern inland waters have many ecological consequences. We examined available data on carbon cycles and food webs of 2 boreal headwater lakes in southern Finland. Basic limnology and catchment characteristics of a pristine lake, Valkea-Kotinen (VK), were monitored over the past 25 years while the lake has undergone browning and DOC increased from ∼11 to 13 mg L−1. Pronounced changes in the early 2000s represent a regime shift in DOC concentration and color. Lake Alinen Mustajärvi (AM) was manipulated for 2 years by additions of labile DOC (cane sugar), raising the DOC concentration from ∼10 to 12 mg L−1, but not changing light conditions. The 2 different approaches both revealed increased concentrations and efflux of carbon dioxide (CO2) from the lakes and thus net heterotrophy and changes in the pelagic community structure following an increase in DOC concentration. Long-term monitoring of VK revealed a decline in phytoplankton primary production (PP) along with browning, which was reflected in retarded growth of young (1–2-year-old) perch. In the experimentally manipulated lake (AM), PP was not affected, and the growth of young perch was more variable. The results suggested the importance of a pathway from labile DOC via benthic invertebrates to perch. Although provided with this extra resource, the food chain based on DOC proved inefficient. Long-term monitoring and whole-lake experimentation are complementary approaches for revealing how freshwater ecosystems respond to climate and/or atmospheric deposition-induced changes, such as browning.

ТРАНСФОРМАЦИЯ И ЭФФЕКТЫ ВНУТРЕННИХ ВОЛН В ПРИБРЕЖНОЙ ЗОНЕ МОРЯ

Analysis of results of field experiments in the near-shore region of the Peter the Great Bay (the Sea pf Japan) is made from the point of view of internal waves (IW) influence on biological and geomorphologic processes in the shelf zone of sea. The main measured parameters were fluctuations of temperature, pressure and current velocity in the near-bottom layer in the near-shore region with bottom depth of 20–30 m. Fluctuations of temperature were measured with the help of anchored strings of 20–30 thermistors with 0.5 m interval, fluctuations of current velocity were measured at 10–15 levels with 1–3 m intervals. The typical for shoreward propagated IW was their nonlinear transformation with formation of stable discreet boluses - water volumes with cold cores, separated from surrounding medium by high-gradient layers. Propagating into shallow regions, IW stimulate mixing, bottom sediments resuspension and near-shore region ventilation. The boluses can propagate farther into shallow regions where continuous picnocline is absent, supplementing effects of IW and amplifying them. It is shown that biological effects of IW and boluses are caused by their considerable impact on the main parameters defining primary production of phytoplankton: biogens concentration, illumination, and fluctuations of temperature.

The influence of geostrophic strain on oceanic ageostrophic motion and surface chlorophyll

Oceanic submesoscale ageostrophic processes have been progressively recognized as an important upwelling mechanism to close the nutrient budget and sustain the observed primary production of phytoplankton in the euphotic layer. Their relatively small spatio-temporal scales (of 1~10 km and a few days) have hindered a systematic observational quantification of the submesoscale ageostrophic flow variability and its impact on ocean biogeochemistry. By combining surface drifters, satellite altimetry and satellite ocean-color data, we detect that when the strain rate of mesoscale surface geostrophic flow is strong, it favors a higher ageostrophic kinetic energy level and an increase in surface chlorophyll concentration. The strain-induced frontal processes are characterized by a surface chlorophyll increase and secondary ageostrophic upwelling along the light side of the oceanic density front. Further analysis indicates that the balanced ageostrophic motions with longer time scales are more effective in inducing chlorophyll increase than the unbalanced shorter time-scale wave motions.

Plant detritus is selectively consumed by estuarine copepods and can augment their survival

Particulate material comprising the detrital remains of terrestrial plants and macrophytes is a substantial source of organic matter to estuaries and therefore has the potential to support the energy demands of the pelagic aquatic food web. Despite the prevalence of macrophytic or terrestrial particulate organic carbon (tPOC), phytoplankton are nutritionally superior and are thought to be the primary food resource for zooplankton. However, estuarine phytoplankton primary productivity abundances can wax and wane, and often production cannot meet heterotrophic energy needs. In this study, we examined how tPOC (detritus of macrophytes and grasses) may affect survival of a calanoid copepod (Eurytemora affinis) common in the San Francisco Estuary (SFE), an estuary with relatively low phytoplankton primary productivity. Using chemical biomarkers and a targeted DNA metagenomic methodology, we show that E. affinis consumed tPOC (dominated by Schoenoplectus sp., or tule) even when phytoplankton were abundant and tPOC was scarce. Furthermore, we found that a mixed diet of phytoplankton and terrestrial material (1:3 carbon ratio) enhanced the survival of E. affinis over a diet of phytoplankton alone. These data show that tPOC can be a vital supplementary food source for zooplankton, perhaps extending survival during low phytoplankton periods, and may help explain elevated zooplankton abundances in tidal wetlands and other detrital-dominated regions.

Seasonal and interannual fluctuations of phytoplankton primary production in the rybinsk water reservoir: effect of the weather and climatic changes

Seasonal and multi-annual dynamics of phytoplankton primary production were examined in the Rybinsk water reservoir (Upper Volga) in 2005–2014. Positive links were detected between the average values of plankton primary production during the vegetation period and abiotic factors of the water environment (temperature, solar irradiation, and concentration of biogenic elements), as well as between the primary production and the index of the North Atlantic Oscillation, excluding the data for the abnormally hot summer in 2010. Water temperature increase (up to 27.9°С) in summer 2010 caused a significant increase in phytoplankton production. Significant increase of phytoplankton primary production was noted in the Rybinsk water reservoir during the analysis period.

Improving the Accuracy of Single Turnover Active Fluorometry (STAF) for the Estimation of Phytoplankton Primary Productivity (PhytoPP)

Photosystem II (PSII) photochemistry is the ultimate source of reducing power for phytoplankton primary productivity (PhytoPP). Single turnover active chlorophyll fluorometry (STAF) provides a non-intrusive method that has the potential to measure PhytoPP on much wider spatiotemporal scales than is possible with more direct methods such as 14C fixation and O2 evolved through water oxidation. Application of a STAF-derived absorption coefficient for PSII light-harvesting (aLHII) provides a method for estimating PSII photochemical flux on a unit volume basis (JVPII). Within this study, we assess potential errors in the calculation of JVPII arising from sources other than photochemically active PSII complexes (baseline fluorescence) and the package effect. Although our data show that such errors can be significant, we identify fluorescence-based correction procedures that can be used to minimize their impact. For baseline fluorescence, the correction incorporates an assumed consensus PSII photochemical efficiency for dark-adapted material. The error generated by the package effect can be minimized through the ratio of variable fluorescence measured within narrow wavebands centered at 730 nm, where the re-absorption of PSII fluorescence emission is minimal, and at 680 nm, where re-absorption of PSII fluorescence emission is maximal. We conclude that, with incorporation of these corrective steps, STAF can provide a reliable estimate of JVPII and, if used in conjunction with simultaneous satellite measurements of ocean color, could take us significantly closer to achieving the objective of obtaining reliable autonomous estimates of PhytoPP.

Spatial variability of phytoplankton primary production characteristics in the North Atlantic in summer 2013

Spatial variability of phytoplankton primary production characteristics has been studied along the transects between Shetland Islands and Iceland (transect I) and along 59.5° N (transect II) from 30 June to 16 July 2013. It has been shown that surface chlorophyll a concentration (Chl0) varied more than two order of magnitude from 0.07 to 6.67 mg/m3 (transect I) and from 0.02 to 3.63 mg/m3 (transect II). Water column integrated primary production (IPP) changed by a factor of 3.8 from 273 to 1040 and by a factor of 5.6 from 68 to 379 mgC/m2 per day along transects I and II, respectively. It has been established that spatial variability of Chl0 and IPP was consistent with distribution of the main surface flows and thermohaline fronts. That conclusion was made on the basis of reliable positive correlation between Chl0 and the zonal potential temperature gradient (R = 0.43, p < 0.01, N = 65). Phytoplankton assimilation activity along transect II depends on nutrients concentration. That conclusion was confirmed by reliable positive correlation between optimum chlorophyll specific carbon fixation rate (Pbopt) and phosphate concentration (R = 0.58, p < 0.05, N = 76) and between Pbopt and dissolved silica (R = 0.51, p < 0.05, N = 76).

Linking phytoplankton primary production and chromophoric dissolved organic matter in the sea

The link between phytoplankton primary production (PPP) and chromophoric dissolved organic matter (CDOM) has been demonstrated indirectly in the laboratory, but not directly in the sea. Here, for the first time, we report a strong link between PPP and CDOM in a study carried out in coastal marine waters around Barcelona (NW Mediterranean) in contrasting seasons. We measured relevant correlations between a254 CDOM concentration and both PPP (r = 0.89, p < 0.001, n = 16; r = 0.76, p < 0.01, n = 10; and r = 0.68, p < 0.001, n = 26; for summer, winter–spring and both seasons together, respectively) and the specific production rate at optimal light intensity (PmB; r = 0.77, p < 0.001, n = 16; r = 0.86, p < 0.01, n = 10; and r = 0.85, p < 0.001, n = 26; for the same seasons). Based on our findings, we design a model that predicts PPP very well, using a254 CDOM, water temperature and photosynthetically active radiation (PAR) (R2 = 0.84, p < 0.001, n = 26).Relationships between CDOM concentration parameters (measured at wavelengths of 280, 300, 340, 355, 375, 412 and 460 nm) and variables associated to CDOM processes (chlorophyll-a, bacterial abundance, turbidity related to sediment resuspension and PAR) were also evaluated. Bacterial abundance is significantly correlated with CDOM concentration measured at higher wavelengths when all samples are considered (e.g., r = 0.82, p < 0.001, n = 26, for a355 CDOM). However, in seasonal data analysis, the correlations decrease slightly (summer season: e.g., r = 0.79, p < 0.001, n = 16, for a355 CDOM) or become non-significant (winter–spring season: e.g., r = -0.02, p = 0.95, n = 10, for a355 CDOM). Sunlight photobleaching and sediment resuspension processes significantly influence CDOM dynamics in the summer (for a300 CDOM: r = -0.72, p < 0.001, n = 16; and r = 0.67, p < 0.01, n = 16, respectively).

Fast Repetition Rate Fluorometry (FRRF) Derived Phytoplankton Primary Productivity in the Bay of Bengal

The approach of fast repetition rate fluorometry (FRRF) requires a conversion factor (Φe : C/nPSII) to derive ecologically-relevant carbon uptake rates (PPz,t). However, the required Φe : C/nPSII is commonly measured by 14C assimilation and varies greatly across phytoplankton taxonomy and environmental conditions. Consequently, the use of FRRF to estimate gross primary productivity (GPz,t), alone or in combination with other approaches, has been restricted by both inherent conversion and procedural inconsistencies. Within this study, based on a hypothesis that the non-photochemical quenching (NPQNSV) can be used as a proxy for the variability and magnitude of Φe : C/nPSII, we thus proposed an independent field model coupling with the NPQNSV-based Φe : C/nPSII for FRRF-derived carbon, without the need for additional Φe : C/nPSII in the Bay of Bengal (BOB). Therewith, this robust algorithm was verified by the parallel measures of electron transport rates and 14C-uptake PPz,t. NPQNSV is theoretically caused by the effects of excess irradiance pressure, however, it showed a light and depth-independent response on large spatial scales of the BOB. Trends observed for the maximum quantum efficiency (Fv/Fm), the quantum efficiency of energy conversion (/) and the efficiency of charge separation (/) were similar and representative, which displayed a relative maximum at the subsurface and were collectively limited by excess irradiance. In particular, most observed values of Fv/Fm in the BOB were only about half of the values expected for nutrient replete phytoplankton. FRRF-based estimates of electron transport at PSII (ETRRCII) varied significantly, from 0.01 to 8.01 mol e− mol RCII−1 s−1, and showed profound responses to depth and irradiance across the BOB, but fitting with the logistic model. N, P, and irradiance are key environmental drivers in explaining the broad-scale variability of photosynthetic parameters. Furthermore, taxonomic shifts and physiological changes may be better predictors of photosynthetic parameters, and facilitate the selection of better adapted species to optimize photosynthetic efficiency under any particular set of ambient light condition.

Seasonal and Year-to-Year Variations of Phytoplankton Primary Production in the Rybinsk Reservoir: The Effect of Weather and Climate Variations

The seasonal and long-term dynamics of phytoplankton primary production has been studied in the Rybinsk Reservoir (Upper Volga) in 2005–2014. A positive correlation has been found to exist between the values of plankton primary production, averaged over vegetation period, and the abiotic factors of the water medium (temperature, solar radiation, and nutrient concentrations), as well as, excluding the data on the anomalously hot summer of 2010, between the primary production and the index of North Atlantic Oscillation. The increase in water temperature (up to 27.9°C) in the summer of 2010 has caused a considerable increase in phytoplankton production. A considerable increase in phytoplankton primary production has been revealed in the Rybinsk Reservoir in the period under study.

The Seasonal Dynamics of Biosedimentation and Primary Production in Sevastopol Bay: Assessment of the Relationship Using 234Th and 40K

The seasonal dynamics of biogenic sedimentation in Sevastopol Bay, Black Sea, was studied using thorium-234 (234Th) as a natural radiotracer. The percentage content of biogenic particulate matter in bottom sediments was determined based on the 40K radionuclide according to the previously developed method. Two major maxima of the rate of bottom sedimentation have been recorded: in April–June and in the second half of the summer. In the former case, the peak can apparently be attributed to a more intensive flux of terrigenous particulate matter in the spring; in the latter case, it can apparently be attributed to high values of phytoplankton primary production in the late summer. The results obtained by applying this method provide a more accurate estimate of the mean annual biosedimentation rate, which is required to calculate deposition fluxes of biogenic matter and pollutants to bottom sediments of coastal waters.

Exploring effects of dredging and organic waste on the functioning and the quantitative biomass structure of the Ems estuary food web by applying Input Method balancing in Ecological Network Analysis

Detailed food webs of the three main Ems estuary reaches (Lower Reaches/LR, Middle Reaches/MR and Dollard/DO) representing the 1975–1980 period, were used for explorations. The effects of turbidity and organic waste were explored for ∼1955 (waste loads and low suspended matter) and ∼2005 (no waste loads and high suspended matter) by applying the Input Method-based balancing as part of the Ecological Network Analysis (ENA) package to analyse food web carbon flows. The total phytoplankton primary production (sum of true phytoplankton and resuspended microphytobenthos) of the LR in 2005 is reduced by 56% compared to 1955. For MR and DO the primary production reduction over the same period is ∼70%. Expressed in tons carbon the 2005 total primary production (including microphytobenthos) of the entire estuary is 59% of that in 1955. In 2005 the total (all living compartments) estuarine biomass is 63% of that in 1955. The data suggest a further fast future biomass decline. Compared to 1955 the relative biomass changes of the living compartments are in 2005 −71.1% for LR, −66.7% for MR and −70% for the Dollard. Results are in line with independent monitoring. The biomass changes per species range for LR from −1.3% (microzooplankton) and −1.5% (intertidal bivalves) to −71.7% (pelagic bacteria), for MR from −15.3% (mesozooplankton, Sprattus sprattus, Clupea harengus) to −90.5% (pelagic bacteria) and for DO from −6.6% (Chelon labrosus) to −97.4% (pelagic bacteria). The relative mean total biomass changes caused by the sanitation of the organic waste loads are −1.5% for LR, −5.0% for MR and −12.5% for DO. The IM-based balancing results in an increasing ratio between detritivory and herbivory and increase of the carbon cycling. The effects are strongest for the LR. The described changes are driven by i) the combination of changed system boundary conditions and the species specific diets and ii) the absence of international political collaboration because of a disputed border that results in the absence of an internationally agreed integral solution via one master plan Ems estuary. The varying changes at the species level and the strong connection of pelagic and benthic systems in intertidal flat estuaries demand an integral approach for assessments and management.

Insensitivities of a subtropical productive coastal plankton community and trophic transfer to ocean acidification: Results from a microcosm study

Ocean acidification (OA) has potential to affect marine phytoplankton in ways that are partly understood, but there is less knowledge about how it may alter the coupling to secondary producers. We investigated the effects of OA on phytoplankton primary production, and its trophic transfer to zooplankton in a subtropical eutrophic water (Wuyuan Bay, China) under present day (400 μatm) and projected end-of-century (1000 μatm) pCO2 levels. Net primary production was unaffected, although OA did lead to small decreases in growth rates. OA had no measurable effect on micro-/mesozooplankton grazing rates. Elevated pCO2 had no effect on phytoplankton fatty acid (FA) concentrations during exponential phase, but saturated FAs increased relative to the control during declining phase. FA profiles of mesozooplankton were unaffected. Our findings show that short-term exposure of plankton communities in eutrophic subtropical waters to projected end-of-century OA conditions has little effect on primary productivity and trophic linkage to mesozooplankton.

Spatial Variability of Phytoplankton Primary Production Characteristics in the North Atlantic in Summer 2013

Spatial Variability of Phytoplankton Primary Production Characteristics in the North Atlantic in Summer 2013

How light conditions influence theoretical pelagic to benthic primary production ratios in small lakes

AbstractTheoretical pelagic primary production of phytoplankton and benthic primary production of periphyton were modelled for two small lakes in Estonia (Northeast Europe). Although located only 500 m apart, the water colour and light attenuation of these two lakes differed markedly. The Secchi depth (SD) in the clear‐water lake was 4.5 m and only 0.47 m in the dark‐water lake. The total phosphorus (TP) concentrations were, respectively, 15 μg/l and 28 μg/l. An empirical model whose inputs were morphometric, light conditions and dissolved organic carbon parameters obtained from in situ measurements was employed for the present study. The model calculated primary production with a time‐step of 10 min, and a spatial resolution of 10 cm, from sunrise to sunset and from lake surface to lake bottom. The primary production of periphyton and phytoplankton was almost equal in the clear lake, whereas only phytoplankton contributed to whole‐lake primary production in the dark lake because of the stronger light attenuation in the water column. The results of the present study indicated the depth‐distribution profiles differed dramatically between the two lakes. The clear lake had a deep, U‐shaped curve, with the productive layer reaching considerable depth soon after sunrise and maintaining a similar profile throughout the light hours. In contrast, the dark lake production declined rapidly with increasing depth, whereas the profile changed over the day reaching the greatest depth at noon.

Temporal-spatial variation in phytoplankton primary production and its influencing factors in Lake Chenghai on the Yunnan Plateau, China

Temporal-spatial variation in phytoplankton primary production and its influencing factors in Lake Chenghai on the Yunnan Plateau, China