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This paper presents the results of frequent observations of the intensity of production processes in the surface water layer in the Krasnovidovo pool of the Mozhaysk Reservoir from June 17, 2018 to September 26, 2018. Measurements were carried out using an automatic production meter developed by A.V. Goncharov, a system of water temperature recorders, subaquatic illumination, photosynthetically active radiation (PAR), and meteorological characteristics. No statistically significant relationship between gross production and the main predictors determining its value have been recorded throughout the measurement period, while its relationships with water temperature and illumination proved to be statistically significant for the period with no limitation of biogenic elements and for the autumn cooling period. According to the results, an important factor determining the amount of gross production is dynamic mixing. [ABSTRACT FROM AUTHOR]

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Phytoplankton contribute half of the primary production (PP) in the biosphere and are the major source of energy for the Arctic Ocean ecosystem. While PP measurements are therefore fundamental to our understanding of marine biogeochemical cycling, the extent to which current methods provide a definitive estimate of this process remains uncertain given differences in their underlying approaches, and assumptions. This is especially the case in the Arctic Ocean, a region of the planet undergoing rapid evolution as a result of climate change, yet where PP measurements are sparse. In this study, we compared three common methods for estimating PP in the European Arctic Ocean: (1) production of 18O-labeled oxygen (GPP-18O), (2) changes in dissolved oxygen (GPP-DO), and (3) incorporation rates of 14C-labeled carbon into particulate organic carbon (14C-POC) and into total organic carbon (14C-TOC, the sum of dissolved and particulate organic carbon). Results show that PP rates derived using oxygen methods showed good agreement across season and were strongly positively correlated. While also strongly correlated, higher scatter associated with seasonal changes was observed between 14C-POC and 14C-TOC. The 14C-TOC-derived rates were, on average, approximately 50% of the oxygen-based estimates. However, the relationship between these estimates changed seasonally. In May, during a spring bloom of Phaeocystis sp., 14C-TOC was 52% and 50% of GPP-DO, and GPP-18O, respectively, while in August, during post-bloom conditions dominated by flagellates, 14C-TOC was 125% of GPP-DO, and 14C-TOC was 175% of GPP-18O. Varying relationship between C and O rates may be the result of varying importance of respiration, where C-based rates estimate net primary production (NPP) and O-based rates estimate gross primary production (GPP). However, uncertainty remains in this comparison, given differing assumptions of the methods and the photosynthetic quotients. The median O:C ratio of 4.75 in May is within the range of that observed for other regions of the world’s ocean. However, the median O:C ratio for August is

Abstract: A device for the automated determination of the primary production (PP) and destruction (D) of organic matter in a water body by the oxygen method is presented. It consists of light and dark bottles with optical dissolved oxygen sensors (Onset, YSI) and the pump changing water in bottles through a predetermined period (3 h). Results of 3-day measurements performed in the Mozhaisk Reservoir have shown that the device describes the studied processes fairly well, significantly facilitating field research. The gross PP obtained during the experiment constituted about 4 mg O2/(L day), which corresponds to the eutrophic status of the reservoir. The device can be used for studying the functional characteristics of aquatic ecosystems under changing environmental factors such as temperature, illumination, and content of biogenic elements. [ABSTRACT FROM AUTHOR]

Saldanha Bay is a narrow-mouth bay on the west coast of South Africa linked to the southern Benguela upwelling system. Bay productivity was investigated by use of the conventional light-and-dark bottle oxygen method, and, for comparison, through assimilation of the stable isotope tracer13C. Gross community production GCP and net community production NCP, as determined from the oxygen method, were respectively 2.6 and 2.4 times higher than estimates determined from the stable isotope method. Chlorophylla(Chla) concentrations increased with the onset of spring and well-defined subsurface maxima developed in association with increasingly stratified conditions (mean water column Chlaconcentrations ranged from 5.4 to 31.5 mg m−3[mean 15.5 mg m−3; SD 7.6]). A sharp decline in photosynthetic ratesP* (GCP normalised to Chlaconcentration) with depth was attributed to light limitation, as demonstrated by the high vertical attenuation coefficients for downward irradianceKd, which varied from 0.29 to 0.70 m−1(mean 0.48 m−1; SD 0.12). Productivity maxima were consequently near-surface despite the presence of deeper subsurface biomass maxima. The community compensation depthZcc, where gross community production balances respiratory carbon loss for the entire community, ranged from 2.9 to 9.2 m (mean 5.8 m; SD 2.2), and was typically shallower than the 1% light depth for PAR (photosynthetically available radiation),Z1%PAR, which is traditionally assumed to be the depth of the euphotic zone and which ranged from 6.6 to 15.9 m (mean 9 m; SD 2.6). Autotrophic communities, where organic matter is produced in excess of respiratory demand, were confined on average to the upper 5.8 m of the water column, and often excluded the bulk of the phytoplankton community, where light limitation is considered to lead to heterotrophic community metabolism. Estimates of integrated water column productivity ranged from 0.84 to 8.46 g C m–2 d−1(mean 3.35 g C m−2d−1; SD 1.9). [ABSTRACT FROM AUTHOR]

Abstract: The main photosynthesis and respiration parameters (dark respiration rate, light saturated production rate, saturation irradiance, photosynthetic efficiency) were measured on a total of 23 macrophytes of the Thau lagoon (2 Phanerogams, 5 Chlorophyceae, 10 Rhodophyceae and 6 Phaeophyceae). Those measurements were performed in vitro under controlled conditions, close to the natural ones, and at several seasons. Concomitantly, measurements of pigment concentrations, carbon, phosphorous and nitrogen contents in tissues were performed. Seasonal intra-specific variability of photosynthetic parameters was found very high, enlightening an important acclimatation capacity. The highest photosynthetic capacities were found for Chlorophyceae (e.g. Monostroma obscurum thalli at 17°C, 982μmol O2 g−1 dwh−1 and 9.1μmolO2 g−1 dwh−1/μmolphotonsm−2 s−1, respectively for light saturated net production rate and photosynthetic efficiency) and Phanerogams (e.g. Nanozostera noltii leaves at 25°C, 583μmolO2 g−1 dwh−1 and 2.6μmolO2 g−1 dwh−1/μmolphotons m−2 s−1 respectively for light saturated net production rate and photosynthetic efficiency). As expected, species with a high surface/volume ratio were found to be more productive than coarsely branched thalli and thick blades shaped species. Contrary to R d (ranging 6.7–794μmolO2 g−1 dwh−1, respectively for Rytiphlaea tinctoria at 7°C and for Dasya sessilis at 25°C) for which a positive relationship with water temperature was found whatever the species studied, the evolution of P/I curves with temperature exhibited different responses amongst the species. The results allowed to show summer nitrogen limitation for some species (Gracilaria bursa-pastoris and Ulva spp.) and to propose temperature preferences based on the photosynthetic parameters for some others (N. noltii, Zostera marina, Chaetomorpha linum). [Copyright &y& Elsevier]