Variability Of Phytoplankton Biomass Research Articles

Combined Generalized Additive model and Random Forest to evaluate the influence of environmental factors on phytoplankton biomass in a large eutrophic lake

The over-proliferation of phytoplankton has been a public concern for the last several decades. To evaluate the importance of different environmental factors on phytoplankton biomass variations with their complex response relationships in the large eutrophic Lake Okeechobee, the nonlinear methods including Generalized Additive Model (GAM) and Random Forest (RF) algorithm were employed. A long-term monitoring dataset of 8 sampling sites ranging from January 1996 to December 2010 was applied to explore the driven factors and response relationships of phytoplankton biomass from the different scales in Lake Okeechobee. Results showed a spatially heterogeneous distribution of phytoplankton biomass there, and the western and southern littoral zones occurred heavier algal blooms than the central pelagic zones. Spearman’s correlation results denoted Chlorophyll a (Chla) was negatively correlated with phosphorus in different scales. In the aspect of temporal variations, phytoplankton biomass appeared a three-peak-two-valley variation trend there, which peaked in 1997, 2003, and 2010, respectively. On the lake-wide scale, the RF model indicated that the inorganic nutrients were the primary predictors of phytoplankton biomass, while underwater light availability factors were followed to play essential roles in the prediction. On the local scale, total nitrogen (TN) was the top predictor in the western near-shore zone, while other zones were nitrate and nitrite (NO23) or phosphate (PO4). GAM results suggested that phytoplankton biomass had positive response to TN increase in both lake-wide and local scales. However, its response to water temperature (WT) appeared spatial heterogeneity. This study provided a new perspective to evaluate the primary predictors of phytoplankton biomass with their response relationships from lake-wide scale and local scale in the large shallow eutrophic lake, and the importance of taking spatial heterogeneity into account for lake water quality management was stressed.

Long-term trend of heat waves and potential effects on phytoplankton blooms in Lake Qiandaohu, a key drinking water reservoir.

Global warming is increasing the frequency and duration of heat waves, which is defined as when air temperature exceeds a threshold for more than specific consecutive days. Ecosystem around the globe will be impaired by heat waves just like the exposures to dangerously high temperatures as a public health threat to human. However, the knowledge of the response of lake and reservoir ecosystem to heat waves is largely unknown although it has been argued that climate warming may increase the incidence of harmful algal blooms. We examined the long-term trend of heat waves and how the variability of phytoplankton biomass responds to lake heat waves on a deep reservoir (Lake Qiandaohu). Long-term (1980–2020) meteorological observation in the lake watershed showed a significant warming trend of 0.36 °C per decade for the yearly average of daily average air temperature and the yearly average of daily maximum air temperature of 18.32 °C was observed in 2016. Meanwhile, a significant increasing number of heat wave events lasting longer was observed, and Lake Qiandaohu suffered an unusually severe lake heat wave in summer 2016. Significant correlations were found between the yearly average of daily maximum air temperature and heat days, heat wave events, and heat wave days. Nuisance phytoplankton bloom was found in Lake Qiandaohu by high frequency observation and remote sensing monitoring in summer 2016. Remote sensing estimation from two Landsat 8 Operational Land Imager (OLI) images showed that the average chlorophyll a (Chla) was 7.45 ± 4.89 μg/L on July 18 before heat wave and 18.96 ± 0.98 μg/L on August 19 during the heat wave. Two heat wave events lasting from July 20 to August 2 and August 11 to 26 with average surface water temperature of 29.93 and 31.99 °C promoted two marked phytoplankton blooms with average Chla concentrations of 11.75 ± 4.08 and 10.53 ± 1.65 μg/L in the central lake region, respectively, as evidenced by high-frequency buoy data. These findings suggest that heat waves are likely to yield an increased threat of harmful algal bloom in freshwater ecosystems. With lake heat waves projected to increase in frequency, duration, and spatial extent with global climate change, more studies are needed to improve our understanding of lake heat waves and their potential effects on the species, communities, frequency of phytoplankton bloom, and also help providing advanced schemes of water quality management.

Long-term and regional variability of phytoplankton biomass and its physical oceanographic parameters in the Yellow Sea, China

Spatio-temporal variation of phytoplankton biomass were analyzed for five typical regions in the Yellow Sea (YS) during 2003–2018, using monthly long-term satellite data. The correlation between phytoplankton biomass and physical oceanographic parameters were explored using multiwavelet coherence for each region. The results showed the phytoplankton biomass decreased from the inshore to the center of the YS. There were opposing trends observed for phytoplankton biomass in the coastal area and the middle of the YS. The phytoplankton biomass varied seasonally for five the different regions due to the influence of sea surface temperature (SST), photosynthetically active radiation (PAR), and mix layer depth (MLD). The highest and lowest phytoplankton biomass occurred in April and July in most of regions. The phytoplankton biomass increased in the spring and decreased in winter for all five regions during 2003–2018. The SST, PAR and MLD also increased in most regions during the study periods. The Chlorophyll-a (Chl-a) had an interannual periodicity, mostly influenced by the MLD among the physical oceanographic parameters explored. The Chl-a showed a negative correlation with the SST and the PAR, and a positive correlation with the MLD. Among the physical oceanographic parameters explored, the PAR and the MLD were the key factors that influenced the variation of phytoplankton biomass in the estuary of the Yangtze River (EYR) and the North Yellow Sea (NYS), while the SST and the PAR were the main factors in the Jiangsu Shoal (JSS). In the Yellow Sea Cold Water Mass (YSCWM) and the south coast of Shandong Peninsula (SCSDP), the SST and the MLD were the main factors influencing for the phytoplankton biomass among the physical oceanographic parameters explored, respectively. The best three-factor combination all included Niño 3.4 in each region, which suggest that El Niño had a certain influence on the variation of the Chl-a in the YS over a long time scale.

Spatio-temporal variability of chlorophyll-a in response to coastal upwelling and mesoscale eddies in the South Eastern Arabian Sea

ABSTRACT The influence of mesoscale dynamics on variability of phytoplankton biomass in terms of chlorophyll-a (chl-a) concentration was studied in the coastal waters of the South Eastern Arabian Sea (SEAS) using long-term satellite data. Satellite-derived chl-a, sea level anomaly, sea surface temperature, and sea surface wind data for the period 1998–2016 were compiled from various sources and analysed to investigate the chl-a variability associated with coastal upwelling and mesoscale eddies. The Empirical Orthogonal Function and Morlet wavelet analyses were performed to estimate the quantitative variability and the result showed strong seasonal and interannual modulation in chl-a concentration and associated environmental variables. The Okubo–Weiss criterion was applied for the identification of mesoscale eddies. The results indicated the presence of cyclonic (cold core) eddies during the summer monsoon season (June–September). The wind-induced upwelling and the cyclonic eddies were most intense during the summer monsoon season, causing higher values of chl-a compared with other season. It is revealed that the variability of chl-a, which might be attributed to seasonal and interannual differences in the surface and sub-surface nutrients, is caused either by coastal upwelling or cyclonic eddies. In particular, the wind-induced upwelling strongly controls the spatial and temporal variability of chl-a compared with mesoscale eddies along the SEAS. The regression model we adopted points out the dominant role played by the wind and its forcing bring about variability in chl-a. The occurrence of extreme climatic events such as El Niño, La Niña and Indian Ocean Dipole (IOD) was noticed during the study period and particularly taken into account to understand the interannual fluctuations in chl-a and associated environmental variables. The relative variability in chl-a concentration was prominent during strong El Niño, La Niña, and IOD. We have attempted to determine the relationship between chl-a with coastal upwelling and mesoscale eddies, the overall importance of such physical forcings, and their influence on bio-production in the SEAS.

Applying transport rate for quantifying local transport conditions in estuarine and coastal systems

Abstract Transport rate, as a scale complementary to commonly used transport timescales, is useful for quantifying local transport conditions in estuarine and coastal systems. A specific transport rate computed based on tracer release is highlighted for quantifying the local transport condition for long-standing autochthonous constituents originating from the system. The overall flushing capability of the constituents can be quantified by the material turnover time, an analog of turnover time, which can be conveniently computed using transport rate. The transport rate is computed in the James River, a tributary of Chesapeake Bay, U.S.A., which clearly describes the temporal and spatial variations of local transport conditions and provides an example to evaluate the contribution of physical transport to variations in phytoplankton biomass. The transport rate can also be used to diagnose the relative importance of physical transport against other environmental factors to the dynamics of reactive autochthonous constituents. Given the advantages, the transport rate provides an efficient tool for diagnosing local transport conditions modulating dynamics of autochthonous constituents in estuarine and coastal systems.

Spatial-Temporal Change of Phytoplankton Biomass in the East China Sea with MODIS Data

A ten-year chlorophyll-a concentration dataset from Moderate Resolution Imaging Spectro-radiometer (MODIS) were used to analyze the variation of phytoplankton biomass and its potential relation with climate in the East China Sea. The result indicated that the phytoplankton biomass generally had a regular pattern every year, and phytoplankton bloom mainly occurred between May and July. The highest phytoplankton biomass appeared near the Yangtze River Estuary. The lowest phytoplankton biomass located near the Taiwan Strait. In general, the starting bloom time was earlier in the south than in the north, and the span time of the former was also longer. During the recent ten years, the phytoplankton biomass around the Yangtze River Estuary decreased obviously. The change of phytoplankton biomass was found to be related with the Nino 3.4 Index. The correlation between the intensity of phytoplankton bloom with the number and square of red tide were 0.63 and 0.74, respectively.

Coastal upwelling and seasonal variation in phytoplankton biomass in the Pemba Channel

This study was conducted in the Pemba Channel off Tanga Region in northern Tanzania to investigate physical and chemical factors that drive changes in phytoplankton biomass. Three transects off Mwaboza, Vyeru and Sahare were selected. For each transect, ten stations were sampled. Phytoplankton biomass was determined as chlorophyll-a (Chl-a) concentration. Similarly, physico-chemical variables (temperature, salinity, dissolved oxygen, pH and nutrients) were determined. It was observed that the Chl-a concentration was significantly higher during the northeast monsoon (median 1.44 mg m-3) as compared to the southeast monsoon (median 1.19 mg m-3; W = 2216, p = 0.029). The higher productivity during the northeast monsoon is attributed to the presence of high-nutrient water caused by coastal upwelling. It is concluded that indication of upwelling, observed through relatively low temperatures during the northeast monsoon season, could be responsible for bringing nutrient-rich waters to the surface, which in turn stimulated the increase in Chl-a concentration.

Reconsideration of the phytoplankton seasonality in the open Black Sea

AbstractChlorophyll a (Chl a) observations from satellites exhibit a unimodal seasonal variation in the open Black Sea that peaks during winter, which has led to the hypothesis that phytoplankton production is sustained by convective mixing of nitrate from deeper layers. We compiled in situ carbon‐to‐Chl a ratios for the entire year, displaying an expected seasonal pattern ranging from 46 in February to 195 mg C mg Chl−1 in September. We combined monthly ratios with satellite Chl a to obtain a comprehensive proxy data set for phytoplankton carbon biomass, and used this to examine the seasonal variation in phytoplankton biomass and bloom occurrences. Contrary to current understanding, our results showed that phytoplankton accumulation is predominantly taking place from July to September, when biomass increased threefold despite nitrate transport from below being negligible. We hypothesize that nitrate harvesting at depths and endosymbiont nitrogen fixation by large diatoms could be important, albeit unexplored mechanisms.

Spatiotemporal Variability of Surface Phytoplankton Carbon and Carbon-to-Chlorophyll a Ratio in the South China Sea Based on Satellite Data

The spatiotemporal variability of phytoplankton biomass has been widely studied because of its importance in biogeochemical cycles. Chlorophyll a (Chl-a)—an essential pigment present in photoautotrophic organisms—is widely used as an indicator for oceanic phytoplankton biomass because it could be easily measured with calibrated optical sensors. However, the intracellular Chl-a content varies with light, nutrient levels, and temperature and could misrepresent phytoplankton biomass. In this study, we estimated the concentration of phytoplankton carbon—a more suitable indicator for phytoplankton biomass—using a regionally adjusted bio-optical algorithm with satellite data in the South China Sea (SCS). Phytoplankton carbon and the carbon-to-Chl-a ratio (θ) exhibited considerable variability spatially and seasonally. Generally, phytoplankton carbon in the northern SCS was higher than that in the western and central parts. The regional monthly mean phytoplankton carbon in the northern SCS showed a prominent peak during December and January. A similar pattern was shown in the central part of SCS, but its peak was weaker. Besides the winter peak, the western part of SCS had a secondary maximum of phytoplankton carbon during summer. θ exhibited significant seasonal variability in the northern SCS, but a relatively weak seasonal change in the western and central parts. θ had a peak in September and a trough in January in the northern and central parts of SCS, whereas in the western SCS the minimum and maximum θ was found in August and during October–April of the following year, respectively. Overall, θ ranged from 26.06 to 123.99 in the SCS, which implies that the carbon content could vary up to four times given a specific Chl-a value. The variations in θ were found to be related to changing phytoplankton community composition, as well as dynamic phytoplankton physiological activities in response to environmental influences; which also exhibit much spatial differences in the SCS. Our results imply that the spatiotemporal variability of θ should be considered, rather than simply used a single value when converting Chl-a to phytoplankton carbon biomass in the SCS, especially, when verifying the simulation results of biogeochemical models.

Drivers assessment of zooplankton grazing on phytoplankton under different scenarios of fish predation and turbidity in an in situ mesocosm experiment

Zooplankton play a key role in energy transfer within lake food webs, but we have a poor knowledge concerning their role as phytoplankton grazers in shallow subtropical lakes. In this study, we aimed to determine how zooplankton grazing upon phytoplankton is altered in different scenarios of fish predation and turbidity, and we explored the relevance of grazing compared to other environmental variables, to explain phytoplankton biomass changes. A mesocosm experiment was conducted by including the following treatments: fish, turbidity, fish + turbidity, and a control (without fish or varying turbidity). The experiment lasted 21 days, and samples were taken four times. Zooplankton grazing was only effective for the microphagous group upon Cryptophyceae, while large Chlorophyceae and small pennate Bacillariophyceae biomass were benefited in the presence of copepods and cladocerans, being negatively affected by depletions in nitrogen availability. In the turbidity treatment, a reduction in phytoplankton biomass was obtained, artificially increasing zooplankton grazing on phytoplankton, while fish presence inhibited grazing of adult copepods and cladocerans. The other groups of phytoplankton were only influenced by the environment. This experiment suggests that phytoplankton biomass variations would be more affected by the environment than by zooplankton grazing in shallow lakes from the Parana River.

Phytoplankton phenology in algerian continental shelf and slope waters using remotely sensed data

Understanding the dynamics of phytoplankton provides important information on the health and richness of a marine ecosystem. In the Mediterranean Sea, significant phytoplankton variability has been observed between the western and eastern basins and between open ocean and coastal waters. In this study, we used eleven years' (2003–2013) MERIS and MODIS sea surface chlorophyll-a (Chla) data to investigate the spatial and temporal variability of phytoplankton in the Algerian shelf and slope waters (ASW), in the southwestern part of the Mediterranean Sea. We assessed the inter-annual and seasonal variability of phytoplankton biomass, retrieved thirteen pixel-based phenology metrics using TIMESAT algorithms, and determined the influence of precipitation on phytoplankton dynamics. Our results reveal differences between the western and eastern parts of ASW. In the eastern part of the coast, the production season starts one month later than in the western region. It also peaks about 15 days earlier and ends one month earlier as compared to the west. As a result, the productive season is shorter in the east than in the west. The area between Béjaïa and Skikda stands out, with the highest Chla values and the highest variability. These findings show that the phytoplankton dynamics varies also at the scale of ASW in timing and magnitude, which is complementary with studies previously conducted at the Mediterranean Sea scale. Correlation analysis shows that rainfall influences phytoplankton biomass and some phenology metrics’ variability. However, other physical and biogeochemical variables should be investigated for a more complete understanding of the plankton dynamics and to assess the impact of this variability on species abundance and diversity.

Spatial Variations of Phytoplankton Biomass Controlled by River Plume Dynamics Over the Lower Changjiang Estuary and Adjacent Shelf Based on High-Resolution Observations

Phytoplankton biomass in estuarine and continental shelf regions are regulated and modified by physical processes, but these interactions have mostly been investigated at a scale of tens of kilometers, and the role of meso- to sub-mesoscale dynamical processes of freshwater plumes in regulating the spatial and temporal variations of algal biomass is largely unknown. To assess the importance of features at these scales, high-resolution (horizontal spacing smaller than 1 km) cross-sectional profiles of hydrographic and biogeochemical variables were collected in the lower Changjiang Estuary and adjacent continental shelf with a towed, undulating vehicle equipped with sensors measuring fluorescence, turbidity and irradiance. Discrete stations were also occupied to allow for the characterization of nutrients. Multiple physical features at different scales regulated the spatial variation of phytoplankton biomass. Phytoplankton biomass was initialized by an improved irradiance field driven by reduced turbidity together with a rapid development of subsurface stratification at the main plume front (isohaline of 23) downstream from the turbidity maximum zone. Phytoplankton blooms did not occur until outcrops located within the main front that were characterized by surface convergence and downwelling, which contributed to large algal biomass by mass trapping and enhanced light penetration. Wave-like features were detected seaward of the main front, coinciding with deacceleration of currents, indicating that they are front-released internal waves that increase algal retention time. This study revealed the critical role of small-scale processes near the plume front in triggering phytoplankton blooms under the large-scale context of improved light conditions, coastal upwelling and nutrient additions from intruding oceanic waters.

Year-to-year variation in phytoplankton biomass in an anthropogenically polluted and complex estuary: A novel paradigm for river discharge influence

We examined the effects of nutrient availability and turbidity on phytoplankton biomass over 9 years in Gwanyang Bay, Korea, which is an anthropogenically polluted and complex estuary. While dredging and reclamation shaped geochemical features, river discharge with low-turbidity water and sewage treatment plants contributed to nutrient loading. The replete levels of nutrients and short water-residence time suggest the inapplicability of the washout theory, whereas the presence of NH4+ suppressed the growth of phytoplankton. A reduction in the river discharge caused a concomitant decline in the loading and dilution of suspended particles. All these features led to an increase in SPM, light limitation, and NH4+ concentration. GLM estimates revealed negative effects of NH4+ and SPM on chlorophyll a over 9 years while SEM verified synergistic effects of NH4+ and SPM compared with positive effects of NO2 + NO3−. Our findings provide new insights into phytoplankton bloom dynamics in Gwangyang Bay.

The impact of temporal variability in light-climate on time-averaged primary production and a phytoplankton bloom in a well-mixed estuary

Phytoplankton primary production (PP) in turbid estuaries is often limited by light-availability. Two important factors altering light-climate are solar irradiance at the water surface and exponential light-extinction coefficient within the water column. Additionally, the depth of the water body changes the light-climate and corresponding PP by altering the ratio of the euphotic and mixing depth in a well-mixed estuary. These three parameters are highly variable yet are often assumed to be constant by both experimental scientists and modelers because of a lack of data or to reduce complexity. Because assuming constant parameters introduces an error, we utilize an idealized model of depth-integrated primary production to analyze the (individual) impact of temporal variability in these three parameters. We only consider the main tidal and solar constituents in temporal variability of the forcings and apply a second-order moment approximation to analyze the bias introduced to time-averaged PP estimates by neglecting temporal fluctuations. We demonstrate that the sign and magnitude of this bias are system-specific and depend on two non-dimensional parameters that characterize the system. The first is equivalent to the ratio of mixing and photic depth. The second accounts for typical incident irradiance and the photosynthetic parameters of the phytoplankton population present. To demonstrate the applicability of our approach, we apply the model to two cases in the Scheldt estuary (Belgium) in the brackish and freshwater part. In the first application, we study the impact of fluctuations on phytoplankton in dynamic equilibrium, where biomass is assumed to be constant. We show that variability in solar irradiance has the largest impact on time-averaged PP in dynamic equilibrium, resulting in a 30 percent decrease compared to time-invariant forcing. By comparing with a numerical integrator, we show that a second-order moment approximation correctly predicts the order of magnitude of the impact of temporal variability of the individual parameters. In the second application, we study the impact of fluctuations on unbounded exponential phytoplankton growth. Also here, fluctuations in solar irradiance have the largest impact and lead to a significant decrease in exponential growth. In this case study, we show that temporal fluctuations delay the onset of the biomass by two weeks and decrease the biomass by a factor 14 after two weeks compared to time invariant forcing. Additionally, we show that the temporal fluctuations induce low-frequency variability in phytoplankton biomass with similar periodicity as the spring-neap cycle, making it difficult to observe these phenomena in real-world time series.

Correction to 'Inter-decadal variability of phytoplankton biomass along the coastal West Antarctic Peninsula'.

You have accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Kim Hyewon, Ducklow Hugh W., Abele Doris, Ruiz Barlett Eduardo M., Buma Anita G. J., Meredith Michael P., Rozema Patrick D., Schofield Oscar M., Venables Hugh J. and Schloss Irene R. 2020Correction to ‘Inter-decadal variability of phytoplankton biomass along the coastal West Antarctic Peninsula’Phil. Trans. R. Soc. A.3782020028120200281http://doi.org/10.1098/rsta.2020.0281SectionYou have accessCorrectionCorrection to ‘Inter-decadal variability of phytoplankton biomass along the coastal West Antarctic Peninsula’ Hyewon Kim Hyewon Kim Google Scholar Find this author on PubMed Search for more papers by this author , Hugh W. Ducklow Hugh W. Ducklow Google Scholar Find this author on PubMed Search for more papers by this author , Doris Abele Doris Abele Google Scholar Find this author on PubMed Search for more papers by this author , Eduardo M. Ruiz Barlett Eduardo M. Ruiz Barlett Google Scholar Find this author on PubMed Search for more papers by this author , Anita G. J. Buma Anita G. J. Buma Google Scholar Find this author on PubMed Search for more papers by this author , Michael P. Meredith Michael P. Meredith Google Scholar Find this author on PubMed Search for more papers by this author , Patrick D. Rozema Patrick D. Rozema Google Scholar Find this author on PubMed Search for more papers by this author , Oscar M. Schofield Oscar M. Schofield Google Scholar Find this author on PubMed Search for more papers by this author , Hugh J. Venables Hugh J. Venables Google Scholar Find this author on PubMed Search for more papers by this author and Irene R. Schloss Irene R. Schloss Google Scholar Find this author on PubMed Search for more papers by this author Hyewon Kim Hyewon Kim Google Scholar Find this author on PubMed Search for more papers by this author , Hugh W. Ducklow Hugh W. Ducklow Google Scholar Find this author on PubMed Search for more papers by this author , Doris Abele Doris Abele Google Scholar Find this author on PubMed Search for more papers by this author , Eduardo M. Ruiz Barlett Eduardo M. Ruiz Barlett Google Scholar Find this author on PubMed Search for more papers by this author , Anita G. J. Buma Anita G. J. Buma Google Scholar Find this author on PubMed Search for more papers by this author , Michael P. Meredith Michael P. Meredith Google Scholar Find this author on PubMed Search for more papers by this author , Patrick D. Rozema Patrick D. Rozema Google Scholar Find this author on PubMed Search for more papers by this author , Oscar M. Schofield Oscar M. Schofield Google Scholar Find this author on PubMed Search for more papers by this author , Hugh J. Venables Hugh J. Venables Google Scholar Find this author on PubMed Search for more papers by this author and Irene R. Schloss Irene R. Schloss Google Scholar Find this author on PubMed Search for more papers by this author Published:31 August 2020https://doi.org/10.1098/rsta.2020.0281This article corrects the followingResearch ArticleInter-decadal variability of phytoplankton biomass along the coastal West Antarctic Peninsulahttps://doi.org/10.1098/rsta.2017.0174 Hyewon Kim, Hugh W. Ducklow, Doris Abele, Eduardo M. Ruiz Barlett, Anita G. J. Buma, Michael P. Meredith, Patrick D. Rozema, Oscar M. Schofield, Hugh J. Venables and Irene R. Schloss volume 376issue 2122Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences14 May 2018Phil. Trans. R. Soc. A376, 20170174 (Published online 14 May 2018) (doi:10.1098/rsta.2017.0174)This correction article concerns the Data accessibility statement. The link should be updated from https://issues.pangaea.de/browse/PDI-14850 to https://doi.pangaea.de/10.1594/PANGAEA.874862. The paper has been updated. Previous Article VIEW FULL TEXT DOWNLOAD PDF FiguresRelatedReferencesDetailsRelated articlesInter-decadal variability of phytoplankton biomass along the coastal West Antarctic Peninsula14 May 2018Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences This Issue02 October 2020Volume 378Issue 2181 Theme issue 'The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning' compiled and edited by Martin Solan, Philippe Archambault, Paul E. Renaud and Christian März Article InformationDOI:https://doi.org/10.1098/rsta.2020.0281PubMed:32862807Published by:Royal SocietyPrint ISSN:1364-503XOnline ISSN:1471-2962History: Published online31/08/2020Published in print02/10/2020 License:© 2020 The Author(s)Published by the Royal Society. All rights reserved. Citations and impact Subjectsbiogeochemistryoceanography

Biophysical Control on Variability in Phytoplankton Production and Composition in the South-Western Tropical Indian Ocean During Monsoon 2014

The existing oligotrophic conditions in the southwest tropical Indian Ocean (SWTIO) is believed to be one of the causes for low phytoplankton productivity (PP) observed in this area. Though many remote sensing based studies on PP have been carried out in SWTIO; studies on in situ estimation of PP and its cause(s) of variability are scarce. Thus, to understand the controlling environmental forcings on the variability in phytoplankton biomass (chlorophyll-a; Chl-a), community structure and productivity, time series (TS; @6h intervals for 10 days) plus point measurements (RT) were carried out in the SWTIO during southwest monsoon (June) of 2014. Strong thermohaline stratification resulted in shallow (35-40m) mixed layer (ML). Subsurface Chl-a maximum (SCM) was observed to oscillate within 40-60m with majority of peaks at ~50m, and existed just beneath the ML depth. Light availability at the time of sampling was highly conducive for algal growth; whereas nutrient ratios indicated N- and Si-limitation suggesting unfavourable conditions for diatoms and/or silicoflagellates growth within the ML. Furthermore, HPLC-based pigments analysis confirmed dominance of nano-sized plankton (53%) followed by pico-plankton (25%) and micro-plankton (22%). Column integrated production (IPP) varied from 176 - 268 (241+43 mgC m-2 d-1) and was relatively stable during the observation period, except a low value on 11-June, which was ascribed to the drastic dropdown in the daily incident PAR due to overcast sky. Vertical profiles of PP and Chl-a resembled each other and maximum PP usually corresponded with SCM depths. The Chl-a-specific PP (PB) was mostly higher within the ML and showed no surface photoinhibition, due to the dominance of smaller phytoplankton (less prone to pigment packaging effect) in the surface layer. Comparatively, higher PB within the ML is indicative of phytoplankton healthiness during the sampling time, whereas low PB below the SCM was due to light limitation. Highest integrated Chl-a (39 mg m-2) and IPP (328 mgC m-2 d-1) observed at RT-2 was clearly linked to low sea surface height anomaly (SSHA), cyclonic disturbance and associated positive Ekman pumping. Conversely, high SSHA and strong stratification conditions prevailed at TS, RT-4 and RT-6 stations leading to comparatively low IPP.

Spatio-Temporal Variability of Chlorophyll-A and Environmental Variables in the Panama Bight

The analysis of synoptic satellite data of total chlorophyll-a (Chl-a) and the environmental drivers that influence nutrient and light availability for phytoplankton growth allows us to understand the spatio-temporal variability of phytoplankton biomass. In the Panama Bight Tropical region (PB; 1–9°N, 79–84°W), the spatial distribution of Chl-a is mostly related to the seasonal wind patterns and the intensity of localized upwelling centers. However, the association between the Chl-a and different physical variables and nutrient availability is still not fully assessed. In this study, we evaluate the relationship between the Chl-a and multiple physical (wind, Ekman pumping, geostrophic circulation, mixed layer depth, sea level anomalies, river discharges, sea surface temperature, and photosynthetically available radiation) and chemical (nutrients) drivers in order to explain the spatio-temporal Chl-a variability in the PB. We used satellite data of Chl-a and physical variables, and a re-analysis of a biogeochemical product for nutrients (2002–2016). Our results show that at the regional scale, the Chl-a varies seasonally in response to the wind forcing and sea surface temperature. However, in the coastal areas (mainly Gulf of Panama and off central-southern Colombia), the maximum non-seasonal Chl-a values are found in association with the availability of nutrients by river discharges, localized upwelling centers and the geostrophic circulation field. From this study, we infer that the interplay among these physical-chemical drivers is crucial for supporting the phytoplankton growth and the high biodiversity of the PB region.

Environmental factors driving phytoplankton biomass and diversity in a tropical reservoir

We determined the spatial and temporal variation of phytoplankton biomass and diversity in 10 fortnightly sampling journeys verifying five sampling sites in El Peñol-Guatapé reservoir located in Antioquia, Colombia. In situ and ex situ physical and chemical variables were measured and phytoplankton samples were taken. Richness was dominated by Chlorophyta and biomass by Dinophyta. This variable was higher in the transition zone while in the riverine zone it showed average values, the lowest were registered in the lacustrine zone. Diversity was lower in the riverine zone, but it increased considerably in the transition zone and in the lacustrine zone where it showed similar values. At the vertical scale, biomass and diversity did not vary widely. Biomass showed a differential response to the effect of precipitation changes and water levels in the reservoir zones. Due to the low variability in environmental conditions, diversity was homogeneous time-wise. These results suggest that factors related to the hydrodynamic such as precipitation and water level resulting from the dam operation and inflow have a slight influence on the temporal variations of phytoplankton biomass and structure. There was a direct relationship between these attributes and physical variables such as turbidity and nutrients concentration at spatial scale while at the vertical scale, mixing patterns and the influence of the wind explained the absence of the vertical gradient of biomass and phytoplankton structure.

Environmental gradients along the tropical coast drive plankton biomass and alter food web interactions.

Traditionally, the Bay of Bengal is considered as a less productive basin when compared with the neighbouring Arabian Sea. However, limited information is available for a comparative study between these two basins on plankton with relation to environmental properties of inshore waters. In order to understand the spatial variability in plankton biomass along tropical coastal waters, the analysis was carried out by collecting samples from 8 locations, covering both east and west coasts of India during dry and wet periods during 2011. Salinity showed considerable seasonal variability along west coast of India (WCI) and east coast of India (ECI); it has highly fluctuated during wet period along ECI. Suspended solids (SSC) and nitrate showed their concentrations along ECI than WCI. Phosphate and silicate exhibited significant seasonality along WCI, whereas insignificant along ECI. Inconsistency in the monsoonal runoff, physical processes and anthropogenic and terrestrial sources seems to be the major driving forces for these parameters. Nearly 3-fold higher phytoplankton biomass was noticed along WCI than ECI due to low SSC in the former region. Though the zooplankton population also followed the same pattern as phytoplankton, the difference between WCI and ECI is lesser than phytoplankton. Zooplankton abundance showed significant relation with phytoplankton and SSC along WCI and ECI, respectively. The present study reveals irrespective of nutrient concentrations; phytoplankton was dominantly constrained by light availability followed by grazers. Moreover, mesozooplankton was supported by not only phytoplankton but also alternative carbon sources; hence, variability in phytoplankton biomass and SSC leads to alterations in trophic interactions.

Limited evidence for common interannual trends in Baltic Sea summer phytoplankton biomass.

The Baltic Sea summer phytoplankton community plays an important role in biogeochemical cycling and in the transfer of energy through the food web via zooplankton. We aimed to improve the understanding of the degree to which large-scale versus local environmental dynamics regulate phytoplankton dynamics by analyzing time series at the Baltic Sea scale. We used dynamic factor analysis to study if there are common patterns of interannual variation that are shared (“common trends”) among summer phytoplankton total and class-level biomass time series observed across Baltic Sea latitudinal gradients in salinity and temperature. We evaluated alternative hypotheses regarding common trends among summer phytoplankton biomass: Baltic Sea-wide common trends; common trends by geography (latitude and basin); common trends differing among functional groups (phytoplankton classes); or common trends driven by both geography and functional group. Our results indicated little support for a common trend in total summer phytoplankton biomass. At a finer resolution, classes had common trends that were most closely associated with the cryptophyte and cyanobacteria time series with patterns that differed between northern and southern sampling stations. These common trends were also very sensitive to two anomalous years (1990, 2008) of cryptophyte biomass. The Baltic Sea Index, a regional climate index, was correlated with two common class trends that shifted in mean state around the mid-1990s. The limited coherence in phytoplankton biomass variation over time despite known, large-scale, ecosystem shifts suggests that stochastic dynamics at local scales limits the ability to observe common trends at the scale of monitoring data collection.