Water Column Primary Production Research Articles

Subsidy-stress responses of ecosystem functions along experimental freshwater salinity gradients

AbstractHuman activity is increasing salt concentrations in freshwaters worldwide, but effects of freshwater salinity gradients on biogeochemical cycling are less understood than in saline, brackish, or marine environments. Using controlled microcosm experiments, we characterized (1) short-term (one to five days) biogeochemical responses and (2) water column metabolism along a freshwater salinity gradient of multiple salt types. After one day, microcosms were oxic (4.48–7.40 mg O2 L−1) but became hypoxic (1.20–3.31 mg L−1) by day five. After one day in oxic conditions, microbial respiration in magnesium-, sodium-, and sea salt-based salinity treatments showed a subsidy-stress response, with respiration increasing by over 100% as salinity increased from 30 to 350–800 µS cm−1. Conversely, respiration consistently increased along a calcium-based salinity gradient, peaking at 1500 µS cm−1. By day five, an inverse subsidy-stress response was observed with elevated respiration at upper or lower ends of the gradient except for the magnesium treatment, which had the lowest respiration at the highest salinity. Calcium- and magnesium-based salinity treatments also caused considerable changes in phosphorus concentrations and C:P and N:P. In a separate experiment, microbial respiration and water column primary production also displayed subsidy-stress responses, but imbalances in effect sizes caused consistently declining net community production with increasing salinity. Collectively, our results establish that short-term exposure to different salt ion concentrations can enhance freshwater biogeochemical cycling at relatively low concentrations and alter resource stoichiometry. Furthermore, the nature of effects of freshwater salinization may also change with oxygen availability.

Influence of land-terminating glacier on primary production in the high Arctic fjord (Blagopoluchiya Bay, Novaya Zemlya archipelago, Kara Sea)

Glaciers retreat linked with rapid Arctic warming changes bioproductivity in the bays and coastal areas of the Arctic Ocean (AO). The impact of different types of glaciers shrinking on water column primary production (IPP) is widely discussed. This work studied the influence of the land-terminating glacier on IPP and chlorophyll a concentration (Chlph) in Blagopoluchiya Bay (Novaya Zemlya archipelago). It is known that meltwater runoff from land-terminating glaciers enriches coastal waters with inorganic suspended matter and nutrients. The aim of the present study was to establish the main environmental factor determining IPP in the bay influenced by the glacier. During summer and autumn, IPP in the bay was low. The medians of IPP were 69 and 26 mgC m−2 day−1, respectively, which was 1.7- and 1.9-fold lower than in open waters of the Kara Sea in the vicinity of the bay. Generally, IPP increased from the inner part, close to the glacier, to the outer part of the bay. In summer, IPP and Chlph depend on both nutrient concentrations in the photosynthetic layer and the parameters of water transparency. On the contrary, in autumn, IPP and Chlph depend only on the optical properties of the subsurface layer. It can be concluded that low IPP in Blagopoluchiya Bay is determined mainly by unfavorable conditions of underwater PAR formed by meltwater discharge from the glacier. Thus, the fast melting of the land-terminating glaciers linked with climate warming can lead to a decrease in the biological productivity of the AO bays.

A decadal perspective on north water microbial eukaryotes as Arctic Ocean sentinels

The North Water region, between Greenland and Ellesmere Island, with high populations of marine birds and mammals, is an Arctic icon. Due to climate related changes, seasonal patterns in water column primary production are changing but the implications for the planktonic microbial eukaryote communities that support the ecosystem are unknown. Here we report microbial community phenology in samples collected over 12 years (2005–2018) from July to October and analysed using high throughput 18S rRNA V4 amplicon sequencing. Community composition was tied to seasonality with summer communities more variable than distinct October communities. In summer, sentinel pan-Arctic species, including a diatom in the Chaetoceros socialis-gelidus complex and the picochlorophyte Micromonas polaris dominated phytoplankton and were summer specialists. In autumn, uncultured undescribed open water dinoflagellates were favored, and their ubiquity suggests they are sentinels of arctic autumn conditions. Despite the input of nutrients into surface waters, autumn chlorophyll concentrations remained low, refuting projected scenarios that longer ice-free seasons are synonymous with high autumn production and a diatom dominated bloom. Overall, the summer sentinel microbial taxa are persisting, and a subset oceanic dinoflagellate should be monitored for possible ecosystem shifts as later autumn ice formation becomes prevalent elsewhere.

Role of emergent and submerged vegetation and algal communities on nutrient retention and management in a subtropical urban stormwater treatment wetland

A 4.6-ha urban stormwater treatment wetland complex in southwest Florida has been investigated for several years to understand its nutrient retention dynamics. This study investigates the role of aquatic vegetation, both submerged vegetation (such as benthic macrophytic and algal communities) and emergent plant communities, on changes in nutrient fluxes through the wetlands. Gross and net primary productivity of water column communities and net primary productivity of emergent macrophytes were used to estimate nutrient fluxes through vegetation in these wetlands using biannual biomass, nutrient concentrations of plant material, and areal coverage data. Emergent macrophyte net primary productivity was estimated as the difference between the increase of productivity during the wet season and the loss during the dry season which, in turn, suggested approximately 0.11g-N m− 2 y− 1 and 0.09g-P m− 2 yr− 2 being removed, primarily from the soil, by emergent vegetation. Water column primary productivity accounted for a much larger flux of nutrients with approximately 39.6g-N m− 2 yr− 1 and 2.4g-P m− 2 yr− 1 retained in algal communities. These fluxes, combined with measurements in parallel studies, allowed us to develop preliminary nutrient budgets for these wetlands and identify gaps, or missing fluxes, in our models for these wetlands. The results further validated previous findings that suggested that there are large inputs of nitrogen (up to 62.3g-N m− 2 yr− 1) that are not accounted for by the pumped inflow. Additionally, management suggestions are provided to improve water quality by identifying vegetative species that are most effective at retaining nutrients.

Seasonal Variability and Estimation of Annual East Siberian Sea Phytoplankton Primary Production and Comparison with the Other Siberian Seas

Studies of seasonal variability of the East Siberian Sea (ESS) water column primary production (IPP) and evaluation of its total annual value (PPtot) were performed using MODIS-Aqua data (2002–2018). Region-specific primary production and chlorophyll algorithms were used for the first time to achieve that result. Northeastern and Southwestern regions were distinguished in ESS based on multiyear average daily primary production. Seasonal variations in IPP in the Northeastern region were characterized by the maximum in June (273 mgC m–2 d–1). The maximum of water column primary production value in the Southwestern region was recorded in May (311 mgC m–2 d–1). The maximum of IPP for the entire ESS was registered in June (273 mgC m–2 d–1). Values of daily primary production and PPtot in the Southwestern region were, respectively, 1.8 and 2 fold higher than in the Northeastern region. The multiyear averaged value of ESS IPP was equal to 91 mgC m–2 d–1 and PPtot value was equal to 9 TgC. Productivity of the Siberian seas decreased eastward.

Nutrient cycling and primary production in Peninsular Malaysia waters; regional variation and its causes in the South China Sea

This multidisciplinary survey investigated the combined influence of riverine nutrient input, physical oceanography and monsoon season on water column primary production and nutrient cycling in east coast Peninsular Malaysia waters. Although the combined nutrient load of the regional rivers was similar to major rivers in the northern South China Sea, its influence on primary production was restricted to coastal stations. In the wet season (October–March) the higher riverine nutrient input and a generally well-mixed water column resulted in estimated primary production up to 82.9 μg C L−1 h−1. During the dry season (April–September) primary production (average 7.3 μg C L−1 h−1) was driven by locally upwelled nutrient input in offshore southern waters and Gulf of Thailand-derived input in offshore northern waters. Dry season decoupling of dissolved organic nutrient production and consumption in seasonally stratified offshore waters resulted in its accumulation with the potential to act as a nutrient reservoir. This study therefore provides new insights into how the interplay of physical processes, meteorology and nutrient source influence primary production and associated biogeochemical cycles in this understudied region.

Seasonal patterns of benthic-pelagic coupling in oyster habitats

Oysters enhance benthic-pelagic coupling in coastal systems by moving large quantities of suspended particulates to the sediments, stimulating biogeochemical processes. Recent research efforts have focused on quantifying the impact of oysters on coastal biogeochemical cycling, yet there is little consensus on how oysters influence processes across systems. A potential driver of this variance is availability of organic material suspended in the water column and subsequent loading to sediment by oysters. Here, we measured fluxes of sediment di-nitrogen (N2-N), ammonium (NH4+), combined nitrate-nitrite (NOx), and phosphate (PO43-) in spring, summer, and fall at 2 oyster reefs and 1 farm in a temperate estuary (Narragansett Bay, Rhode Island). We then linked these fluxes with patterns of water column primary production. Nitrogen removal from the system was highest in spring, when we detected net sediment denitrification (48.8 µmol N2-N m-2 h-1) following a winter-spring diatom bloom. In contrast, we measured sediment N2 fixation in fall (-44.8 µmol N2-N m-2 h-1) at rates nearly equivalent to spring denitrification. In the summer, we measured a nearly net zero sediment N2-N flux (-2.7 µmol N2-N m-2 h-1). Recycling of nitrogen to the water column was consistent across seasons, composed almost exclusively of NH4+. These results demonstrate that sediment nitrogen cycling in oyster habitats is dynamic and can change rapidly based on seasonal patterns of productivity. At carrying capacity, the impact of oysters on nitrogen cycling is large and should be considered during efforts to increase oyster populations through aquaculture or reef restoration.

Seasonal variability and annual Laptev sea phytoplankton primary production using MODIS-aqua data

Studies of seasonal variability of Laptev Sea water column primary production and evaluation of its annual values were performed using MODIS-Aqua data (20022018). To reach that result regional-specific primary production and chlorophyll algorithms were used for the first time. Based on multiyear averaged daily primary production Northwestern and Southeastern regions were distinguished in the Laptev Sea. Seasonal variations in water column primary production in the Northwestern region were characterized by the maximum in June (245 mgC m‑2 d‑1). In the Southeastern region and for all Laptev Sea the maximum water column primary production values were denoted from May to July, 273282 mgC m‑2 d‑1 and 256281 mgC m‑2 d‑1, respectively. Daily primary production and annual values of total primary production in the Southeastern region were, respectively, 1.9 and 3 fold higher than in the Northwestern region. Multiyear averaged value of Laptev Sea water column primary production was equal to 125 mgC m‑2 d‑1 and total annual primary production was equal to 8 1012 gC.

Spatial variability of primary production and chlorophyll in the Laptev sea in august–september

Spatial distribution of phytoplankton primary production and chlorophyll was studied based on the data of three cruises carried out in AugustSeptember of 2015, 2017 and 2018. The average value of water column primary production (IPP) along the transect from Lena`s mouth to the continental slope was 2.8 fold higher than that one along the transect from Khatanga`s mouth, which was explained by the level of incident radiation and nutrients concentration. Along the cross-slope transects increasing of photosynthetically layer integrated chlorophyll (Chlph) occurred due to developing of deep maxima. IPP and Chlph increasing was registered in the vicinity of the continental slope. In AugustSeptember the averaged IPP value was 100 mgC m-2 d-1 that is the evidence of oligotrophy of the Laptev Sea at the end of summer and at the beginning of autumn.

Primary production and associated environmental conditions in the East Siberian Sea in autumn

Spatial variability of primary production (PP) was study on vast area of East Siberian Sea in autumn 2017. Water column PP (IPP) value was equal to 28±13 mgC m-2 day-1 on average that testify ultraoligotrophic conditions. IPP was limited by low incident and underwater photosynthetically available radiation and nitrate concentration. Ammonium concentration partly compensates lack of dissolved nitrogen.

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.

Primary Production and Associated Environmental Conditions in the East Siberian Sea in Autumn

The spatial variability of primary production in the East Siberian Sea over a large-scale aquatic area was characterized for the first time by the data of cruise 69 of R/V Akademik Mstislav Keldysh in September 2017. The value of the water column primary production IPP amounted to 28 ± 13 mg C/m2 per day, which pointed to extreme oligotrophy of the treated areas during the autumn. The IPP value was limited by low incident and subsurface insolation, as well as by the concentration of nitrates. The shortage of inorganic nitrogen was partially compensated by ammonium, which also constituted the buffer preventing a phytoplankton deficiency in nitrogen.

Comparing static and dynamic incubations in primary production measurements under different euphotic and mixing depths

Since phytoplankton production is usually estimated from static incubations (fixed depths or light levels), a mesocosm study was performed to evaluate the significance of mixing depth, mixing intensity and load of humus of natural phytoplankton assemblages. Vertically rotated (dynamic) incubations usually gave higher results than static incubations in humus-rich water. Mixing intensity was of significant importance in one of 2 years tested, but strong interaction effects with humus complicated the explanation. Differences in primary production between dynamic incubations did not fully reflect the received PAR dose, and increased humus and increased mixing depth increased the photo-assimilation efficiency. Different single-depth incubations did not provide a shortcut method to measure water-column primary production with high accuracy. Results diverged from theoretical estimates based on recent combined photo-biological and physical environmental models. The large variability in responses to mixing is supposed to reflect species-specific adaptations and pre-history regarding quantity (photons) and quality (spectral distribution) of the optical environment in an assemblage of different species. The proportional abundance of each species with its specific characters will therefore strongly influence bulk primary production. Due to such variable responses, clear guidelines for a “best practice” in primary production measurements cannot be given, based on the present results.

ПЕРВИЧНАЯ ПРОДУКЦИЯ И ХЛОРОФИЛЛ В СЕВЕРНОЙ АТЛАНТИКЕ ПО МАТЕРИАЛАМ 44 РЕЙСА НИС «АКАДЕМИК ИОФФЕ» В ИЮЛЕ 2014

Data were obtained during 44th cruise of «Akademik Ioffe» from 4 to 15 of July 2014 along 59.5°N. Surface chlorophyll concentration changed by more than one order of magnitude, from 0.06 to 2.12 mg/m3. Surface primary production varied from 2.88 to 31.44 mgC/m3 per day. Water column primary production changed from 32 to 443 mgC/m2 per day and the average value of this parameter was equal to 265 mgC/m2 per day. Euphotic layer integrated chlorophyll concentration varied from 6.11 to 64.60 mg/m3. High water column stratification restricted nutrient flux to the euphotic layer in the investigated area in the middle of summer.

Satellite remote-sensing observations for definitions of areas for marine conservation: Case study of the Scotian Slope, Eastern Canada

Characterizing offshore areas for marine conservation faces impediment from logistics and costs of in situ data collection. This study leveraged the high spatial and temporal coverage provided by remote-sensing ocean colour products, and the concept of biogeographical classification to delineate areas in the pelagic environment with application to marine conservation. Satellite-derived and modelled biogeophysical data were used to delineate an area of biological and physical homogeneity spatially consistent with the static boundaries of the Scotian Slope Ecologically and Biologically Significant Area (EBSA), off eastern Canada. We used iterative cluster analysis applied to an archive (2004–2014) that consisted of remotely-sensed Chlorophyll a, sea-surface temperature, and primary production derived from the Moderate resolution Imaging Spectroradiometer (MODIS), and simulated mixed layer depth to define “dynamic” boundaries of the EBSA at bi-weekly, seasonal and annual resolutions. The final cluster extended further east than the static EBSA in summer and fall, indicating that characteristics of the static EBSA environment persist beyond the current boundaries in these seasons. In winter and spring, the final areas derived by our analysis was smaller than the static EBSA, but again showed extension beyond the current eastern boundary. Both ice and cloud cover affecting remotely-sensed data and the extent of water column mixing were important in determining the size of the final cluster. The dynamic cluster east of the original static boundary incorporated an area of lower Chlorophyll a and water column primary production in the spring, but higher values in the autumn relative to the static area. Overall physical and biological characteristics of the static and dynamic EBSA considered in this research were similar within and across years. This methodology incorporates ocean-colour data and modelled estimates of multiple biological and physical characteristics to objectively refine areas of ecological interest at a spatial scale relevant for the management of marine conservation areas.

Long-term patterns of benthic irradiance and kelp production in the central Beaufort sea reveal implications of warming for Arctic inner shelves

This study synthesizes a multidecadal dataset of annual growth of the Arctic endemic kelp Laminaria solidungula and corresponding measurements of in situ benthic irradiance from Stefansson Sound in the central Beaufort Sea. We incorporate long-term data on sea ice concentration (National Sea Ice Data Center) and wind (National Weather Service) to assess how ice extent and summer wind dynamics affect the benthic light environment and annual kelp production. We find evidence of significant changes in sea ice extent in Stefansson Sound, with an extension of the ice-free season by approximately 17 days since 1979. Although kelp elongation at 5–7 m depths varies significantly among sites and years (3.8–49.8 cm yr−1), there is no evidence for increased production with either earlier ice break-up or a longer summer ice-free period. This is explained by very low light transmittance to the benthos during the summer season (mean daily percent surface irradiance ± SD: 1.7 ± 3.6 to 4.5 ± 6.6, depending on depth, with light attenuation values ranging from 0.5 to 0.8 m−1), resulting in minimal potential for kelp production on most days. Additionally, on month-long timescales (35 days) in the ice-free summer, benthic light levels are negatively related to wind speed. The frequent, wind-driven resuspension of sediments following ice break-up significantly reduce light to the seabed, effectively nullifying the benefits of an increased ice-free season on annual kelp growth. Instead, benthic light and primary production may depend substantially on the 1–3 week period surrounding ice break-up when intermediate sea ice concentrations reduce wind-driven sediment resuspension. These results suggest that both benthic and water column primary production along the inner shelf of Arctic marginal seas may decrease, not increase, with reductions in sea ice extent.

Extended Formulations and Analytic Solutions for Watercolumn Production Integrals

The effect of biomass dynamics on the estimation of watercolumn primary production is analysed, by coupling a primary production model to a simple growth equation for phytoplankton. The production model is formulated with depth- and time-resolved biomass, and placed in the context of earlier models, with emphasis on the canonical solution for watercolumn production. A relation between the canonical solution and the general solution for the case of an arbitrary depth-dependent biomass profile was derived, together with an analytical solution for watercolumn production in case of a depth dependent biomass profile described with the shifted Gaussian function. The analysis was further extended to the case of a time-dependent, mixed-layer biomass and two additional analytical solutions to this problem were derived, the first in case of increasing mixed-layer biomass and the second in case of declining biomass. The solutions were tested with Hawaii Ocean Time-series data. The canonical solution for mixed-layer production has proven to be a good model for this data set. The shifted Gaussian function was demonstrated to be an accurate model for the measured biomass profiles and the shifted Gaussian parameters extracted from the measured profiles were further used in the analytical solution for watercolumn production and results compared with data. The influence of time-dependent biomass on mixed-layer production was studied through analytical solutions. Re-examining the Critical Depth Hypothesis we derived an expression for the daily increase in mixed-layer biomass. Finally, the work was placed in a remote sensing context and the time-dependent model for biomass related to the remotely sensed-biomass.

Enhanced primary production in summer and winter-spring seasons in a populated NW Mediterranean coastal ecosystem

Populated coastal ecosystems in the NW Mediterranean present three main characteristics that distinguish them from the open water ecosystem: a sea-land interaction, with freshwater influence from river mouths; a shallow seabed, which facilitates the interaction between the euphotic water column and the sediments; and high anthropogenic pressure, due to submarine sewage discharges. As a result, relatively high nutrient concentrations are measured in these ecosystems, with ammonia being an important fraction. These characteristics entail a different scenario from the open water ecosystem.Here, we present the distribution of phytoplankton primary production in the Barcelona coastal waters during summer and winter-spring seasons, by means of photosynthesis-irradiance experiments using the 14C technique. In winter-spring, stratification of the water column may begin earlier than in open water due to freshwater inputs. Therefore, with the water-column slightly stratified, chlorophyll-a and primary production become localised in the surface layers, due to the lower daily irradiance during this season. In these conditions, Total Primary Production (TPP) values measured ranged between 0.27 and 14.52mgCm−3h−1. As spring progresses and the stratification develops, surface waters tend to become nutrient depleted and nutrients are mainly localised in bottom waters between the thermocline and the seafloor. Under these conditions, high chlorophyll layers develop near the bottom. With the exception of their nutrient enrichment, these structures, referred to as coastal deep chlorophyll maxima, are comparable to the oceanic deep chlorophyll maxima in temperate oligotrophic seas. The nutrient enrichment is the result of the sediment resuspension from the seabed and the presence of sewage water discharged from the submarine outfall. These structures are highly productive (ca. 60% of water column primary production), comparable to the winter-spring bloom, and are sustained throughout the stratified season. In this period, TPP values measured ranged between 0.25 and 9.02mgCm−3h−1.The primary productivity structures studied play a leading role in processing nutrients from terrestrial sources, thus providing an important ecosystem service.

Measurement of water column primary production using photosynthesis-irradiance relations for surface phytoplankton, the vertical chlorophyll profile, and underwater light intensity

A method has been developed to measure water column integrated primary production (PPint) in the water column using photosynthesis-irradiance relations for surface phytoplankton, the vertical profile of chlorophyll a concentration, and the underwater light intensity. Good correlation has been found for the results calculated with this method and light dependences in situ. The advantages of this method are the independence of PPint calculation from CTD profiling and water sampling, and thus optimization (reduction) of the station working time.

Modeling the Relative Importance of Nutrient and Carbon Loads, Boundary Fluxes, and Sediment Fluxes on Gulf of Mexico Hypoxia.

The Louisiana continental shelf in the northern Gulf of Mexico experiences bottom water hypoxia in the summer. In this study, we applied a biogeochemical model that simulates dissolved oxygen concentrations on the shelf in response to varying riverine nutrient and organic carbon loads, boundary fluxes, and sediment fluxes. Five-year model simulations demonstrated that midsummer hypoxic areas were most sensitive to riverine nutrient loads and sediment oxygen demand from settled organic carbon. Hypoxic area predictions were also sensitive to nutrient and organic carbon fluxes from lateral boundaries. The predicted hypoxic area decreased with decreases in nutrient loads, but the extent of change was influenced by the method used to estimate model boundary concentrations. We demonstrated that modeling efforts to predict changes in hypoxic area on the continental shelf in relationship to changes in nutrients should include representative boundary nutrient and organic carbon concentrations and functions for estimating sediment oxygen demand that are linked to settled organic carbon derived from water-column primary production. On the basis of our model analyses using the most representative boundary concentrations, nutrient loads would need to be reduced by 69% to achieve the Gulf of Mexico Nutrient Task Force Action Plan target hypoxic area of 5000 km(2).