Dissolved Inorganic Phosphate Research Articles

The biogenic elements retention in reservoirs of the Yangtze River basin and effect on the nutrient flux into the sea

The Yangtze River catchment is among the most human-impacted basins globally, with a population of approximately 590 million and over 60,000 dams constructed by 2020. While the effect of reservoir dams on runoff and sediment has been extensively studied, assessing the impact of biogenic element retention in reservoirs on nutrient flux into the sea remains a challenge. This study analyzed the total organic carbon (TOC), total organic nitrogen (TN), biogenic silica (BSi), grain size, and 210Pb chronology of sediment cores collected from the Pengshui, Wuqiangxi, Three Gorges, and Danjiangkou reservoirs. The analysis was combined with the database of annual reservoir area and nutrient flux into the sea of the Yangtze River. The results showed that the average annual sedimentary retention of TOC, TN, and BSi in the four reservoirs increased by 16%, 18%, and 26% after dam construction and rapid eutrophication. The total water area of large reservoirs increased from 30 to 132,000 km2 between 1960 and 2016, resulting in total accumulated retention increments of TOC, dissolved inorganic nitrogen (DIN), dissolved inorganic phosphate (DIP), and dissolved silicon (DSi) in reservoirs reaching 27, 3.5, 0.1, and 27.2 million tons, respectively. The retention increments accounted for 20.6%, 7.0%, 8.8%, and 12.1% of the total flux of TOC, DIN, DIP, and DSi into the sea during the same period, respectively. The retention of TOC and DSi in reservoirs led to a decrease in their annual flux into the sea by 67.2% and 61.4% in 2016 compared to 1960. However, the retention of DIN and DIP increased their annual flux by 6.4-fold and 4.2-fold in 2016 compared to 1960, which was attributed to the substantial emission of fertilizer and sewage in the downstream catchment area of dams. These findings provide valuable insights into biogenic element retention in reservoir catchments and their impact on nutrient flux into the sea.

Variability in water quality of two meso-tidal estuaries of Odisha, East Coast of India

The increasing human population and rapid development along the east coast of India pose potential threats to coastal water quality. To assess the water quality of two tropical estuaries of Odisha, India, diurnal and seasonal variations along with the influence of differential anthropogenic impacts have been studied. From the results, it was evident, the seasonal variations in the water quality were largely influenced by anthropogenic sources at both the estuaries. Relatively lower seasonal variations in salinity were recorded in Mahanadi compared to Dhamara. Dissolved inorganic nitrogen (DIN) concentrations were found to be higher in the Dhamara estuary when compared to the Mahanadi estuary that can be attributed to decay of organic materials followed by the nitrification process. A reverse trend was recorded for dissolved inorganic phosphate (DIP), with significantly higher values recorded in Mahanadi. The partial pressure of carbon dioxide (pCO2) showed strong temporal variations in both the estuaries dominated by moderate CO2 supersaturation with respect to the atmosphere. The mean annual pCO2 was higher in the Mahanadi estuary and was largely attributed to its significant increase during the post-monsoon season. This study indicated the stronger influence of freshwater input and tidal activities compared to that of in situ biological processes in regulating the temporal variations in water quality of both the estuaries. The present study is helpful in understanding the natural state of the estuarine water and protection of ecosystems resources to fulfil the sustainable development at the regional level.

Key determinants controlling the seasonal variation of coastal zooplankton communities: A case study along the Yellow Sea

Zooplankton play key top-down and bottom-up regulatory roles in aquatic food webs, and are also ecologically indicative in marine ecosystems. However, there are relatively limited data on the effects of environmental changes on natural zooplankton communities, especially in coastal ecosystems. In the present study, we systematically evaluated the potential effects of various environmental variables, such as temperature, salinity, and nutrients, on the zooplankton communities along the coastal Yellow Sea during spring, summer, and fall. The results showed that the average abundance of zooplankton decreased in general from spring to autumn, but the biomass exhibited a different seasonal variation trend, with the highest in summer and the lowest in fall. Throughout the three seasons, copepods were the most dominant species within the zooplankton communities, followed by Pelagic larvae and Hydromedusae. However, Noctiluca miliaris accounted for a large proportion of zooplankton abundance during spring. Moreover, the correlation analysis was applied to explore the potential effects of environmental factors on the seasonal variation of zooplankton communities. The results showed that chlorophyll a (Chl a) and salinity were significantly correlated with zooplankton abundance and biomass during spring. The implication is that high phytoplankton biomass (expressed as Chl a) and salinity would benefit the growth of zooplankton in spring. During summer and fall, the effects of dissolved inorganic phosphate (DIP) on the zooplankton abundance and biomass showed a significant positive correlation, indicating that zooplankton were better able to tolerate high DIP during summer and fall. Taken together, Chl a, salinity, and DIP may be the key determinants controlling the seasonal dynamics of zooplankton communities in the coastal Yellow Sea.

New insights into the mechanism of phosphate release during particulate organic matter photodegradation based on optical and molecular signatures

Phosphate release from particulate organic matter (POM) dominates phosphorus (P) cycling in aquatic ecosystems. However, the mechanisms underlying P release from POM remain poorly understood because of complex fractionation and analytical challenges. In this study, the release of dissolved inorganic phosphate (DIP) during POM photodegradation was assessed using excitation–emission matrix (EEM) fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). POM in suspension was significantly photodegraded under light irradiation, concomitantly with the production and release of DIP in the aqueous solution. Chemical sequential extraction revealed that organic phosphorus (OP) in POM participated in photochemical reactions. Moreover, FT-ICR MS analysis revealed that the average molecular weight of P-containing formulas decreased from 374.2 to 340.1 Da. Formulas containing P with a lower oxidation degree and unsaturation were preferentially photodegraded, generating oxygen-enriched and saturated formula compounds, such as protein- and carbohydrate-like P-containing formulas, benefiting further utilization of P by organisms. Reactive oxygen species played an important role in the photodegradation of POM, and excited triplet state chromophoric dissolved organic matter (3CDOM*) was mainly responsible for POM photodegradation. These results provide new insights into the P biogeochemical cycle and POM photodegradation in aquatic ecosystems.

Spatial and temporal variation of physicochemical parameters of coastal waters in the southwestern region of Sri Lanka

Physicochemical parameters of coastal water in the southwestern area of Sri Lanka were studied from January to November 2016. Surface water samples from 15 selected locations were analysed according to standard methods. The ranges of the values recorded were; water temperature (WT) 26.5-33.9 ºC, pH 7.1-8.4, dissolved oxygen (DO) 4.4-7.4 mg L-1, salinity 14-38 ppt, electrical conductivity (EC) 27.1-53.8 mS cm-1, total suspended solids (TSS) 50.2-403.4 mg L-1, turbidity 1.2-64.9 NTU, nitrate nitrogen (NO3--N) 0.00-0.57mg L-1, nitrite nitrogen (NO2--N) 0.00-0.035mg L-1, ammoniacal nitrogen (NH4+-N) 0.00-1.72mg L-1, dissolved inorganic phosphorous (DIP) 0.00-0.65 mg L-1, biochemical oxygen demand (BOD) 0.1-11.6 mg L-1 and chemical oxygen demand (COD) 40-768 mg L-1. Results of Two-way ANOVA showed that there was a seasonal variability in parameters such as water temperature (p<0.001), dissolved oxygen (p<0.001), BOD (p<0.001), COD (p<0.001), nitrite nitrogen (p<0.001), nitrate nitrogen (p<0.001), dissolved inorganic phosphorous (p<0.001), turbidity (p<0.001), TSS (p<0.001) and Chlorophyll a (p<0.001). Spatial variation was identified in parameters, pH (p<0.001), turbidity (p<0.001), dissolved oxygen (p=0.004) and nitrite nitrogen (p<0.001) whereas the interaction between time and location was significant in pH (p=0.005) and turbidity (p=0.007). However, EC, salinity and ammoniacal nitrogen were not significant by either of the factors of consideration. In conclusion, the physicochemical characteristics of water are highly variable over time and location due to both natural and human factors. Water quality near fish processing areas such as fishery harbours and fish markets relatively deteriorated in terms of pH, DO, turbidity and nitrite nitrogen compared to recreational beaches. It is recommended to regulate any discharges of sewage and industrial wastewater directly into the sea. A long-term coastal water quality monitoring programme is vitally important to comprehensively characterise the coastal segments for a long-term strategic plan for sustainable development.

First Measurements on Triple Oxygen Isotopes of Dissolved Inorganic Phosphate in the Hydrosphere.

Although dissolved inorganic phosphate (DIP) is an important nutrient in the hydrosphere, it is difficult to quantitatively clarify the dynamics of DIP in the hydrosphere using the δ18O value of DIP as a tracer. In this study, we quantified the triple oxygen isotopic compositions (Δ'17O) of DIP relative to VSMOW with the reference line with a slope of 0.528 as an additional tracer to clarify the sources and dynamics of DIP in the hydrosphere. We found significant variation in the Δ'17O values of riverine DIP in urban areas, ranging from -107 × 10-6 to +3 × 10-6, while those of DIP in the effluents from wastewater treatment plants (WWTP) and DIP extracted from the chemical fertilizers showed -56 ± 5 × 10-6 (1SD) and -98 ± 5 × 10-6, respectively. We conclude that both the DIP supplied directly from the artificial loads (the WWTP effluent and chemical fertilizers) showing 17O-depleted Δ'17O values and the DIP turned over via the aquatic biosphere showing 17O-enriched Δ'17O values similar to ambient H2O were the major sources of riverine DIP. High-precision determination of the Δ'17O value of DIP can contribute to quantitative clarification of the dynamics of DIP in the hydrosphere.

Portable All-in-One Electrochemical Actuator-Sensor System for the Detection of Dissolved Inorganic Phosphorus in Seawater.

We present a methodology for the detection of dissolved inorganic phosphorous (DIP) in seawater using an electrochemically driven actuator-sensor system. The motivation for this work stems from the lack of tangible solutions for the in situ monitoring of nutrients in water systems. It does not require the addition of any reagents to the sample and works under mild polarization conditions, with the sample confined to a thin-layer compartment. Subsequent steps include the oxidation of polyaniline to lower the pH, the delivery of molybdate via a molybdenum electrode, and the formation of an electroactive phosphomolybdate complex from DIP species. The phosphomolybdate complex is ultimately detected by either cyclic voltammetry (CV) or square wave voltammetry (SWV). The combined release of protons and molybdate consistently results in a sample pH < 2 as well as a sufficient excess of molybdate, fulfilling the conditions required for the stoichiometric detection of DIP. The current of the voltammetric peak was found to be linearly related to DIP concentrations between 1 and 20 μM for CV and 0.1 and 20 μM for SWV, while also being selective against common silicate interference. The analytical application of the system was demonstrated by the validated characterization of five seawater samples, revealing an acceptable degree of difference compared to chromatography measurements. This work paves the way for the future DIP digitalization in environmental waters by in situ electrochemical probes with unprecedented spatial and temporal resolution. It is expected to provide real-time data on anthropogenic nutrient discharges as well as the improved monitoring of seawater restoration actions.

What controls the future phytoplankton change over the Yellow and East China Seas under global warming?

The Yellow and East China Seas (YECS) are productive continental shelves where essential nutrients for phytoplankton growth are mainly supplied by the intrusion of the Kuroshio Current, riverine inputs, and atmospheric deposition. Surface temperatures in YECS are increasing due to global warming, and are projected to increase further. In this study, future changes in YECS biogeochemical processes were evaluated using Coupled Model Intercomparison Project Phase 6 (CMIP6) Earth System Models. We found a great diversity in predictions of future changes in chlorophyll-a over the YECS region. This diversity was determined to be closely related to the extent of phosphorus (P) limitation for phytoplankton growth. Models simulating positive chlorophyll changes tend to simulate increased Dissolved Inorganic Phosphate (DIP) supplies under future global warming. Our study also demonstrated that the intrusion of the Kuroshio Current into the YECS plays a critical role in future changes in DIP and chlorophyll-a by transporting relatively DIP-rich subsurface water from the Kuroshio Current into the marginal sea.

Fjords of the western and northern regions of Svalbard harbour distinct bacterioplankton community structures.

Fjords are highly dynamic ecosystems that are known to be sentinels to climate change due to increased glaciomarine interactions. The convergence and mixing of warm Atlantic water (AtW) and cold Arctic water (ArW) is known to influence the hydrodynamics and ecology of the Arctic fjords. However, most past studies were limited to single-fjord ecosystems, determining the baseline knowledge of inter-fjord comparison on bacterioplankton diversity and distribution patterns. In the present study, we investigated the bacterial diversity and community composition across three Arctic fjords located in the western and northern regions of Svalbard. Our observations show that the bacterial community structure varied significantly among the fjords, while abundant Operational Taxonomic Units (OTUs) were widespread (n = 100) between all the samples and rare OTUs (n = 2221) mainly contributed to these differences. Phylogenetic classification revealed that Alpha (27.3-55%) and Gamma-proteobacteria (16-51.3%), followed by Bacteroidota (17-35.7%) were dominant in the St.Jonsfjorden and Magdalenefjorden, while Verrucomicrobiota (up to 84.19%) and Actinobacteriota (up to 76.5%) were predominant in the Raudfjorden. Temperature, dissolved inorganic phosphate (DIP) and depth were found to significantly influence the community composition of abundant bacterial groups, whereas the rare bacterial groups were affected by temperature, DIP, dissolved inorganic nitrate (DIN), ammonium and depth. A comparative meta-analysis along with Kongsfjorden and Krossfjorden also showed that each fjord had a significantly different bacterioplankton community structure.

Uptake of inorganic and organic phosphorus compounds by two marine sponges and their associated bacterial communities in aquaria.

Marine sponges are abundant filter-feeders in benthic ecosystems and many host copious microorganisms. Sponges and their symbionts have emerged as major players within marine biogeochemical cycles, facilitating uptake and release of carbon, nitrogen, and sulfur. Sponge holobionts' role in transforming dissolved carbon and nitrogen is well established; however, the same depth of understanding has not yet been extended to phosphorus. In this aquaria-based study, 32 P-labelled orthophosphate and ATP were used to determine that two sponges, Lendenfeldia chondrodes and Hymeniacidon heliophila, both take up ambient dissolved inorganic phosphate (DIP) and dissolved organic phosphorus (DOP). Subsequent genetic analyses and chemical extraction showed that sponge symbionts have the potential to synthesise polyphosphate (poly-P) and that this energy-rich form of stored phosphorus is present in both sponges. L. chondrodes, an oligotrophic sponge with a microbiome dominated by cyanobacteria, stores more phosphorus as poly-P (6%-8% of total phosphorus) than H. heliophila (0.55%), a eutrophic sponge with low cyanobacterial abundance. DIP/DOP uptake, as well as poly-P storage, may be driven by two factors: cyanobacterial abundance and nutrient availability. Considering their prevalence in phosphorus-limited ecosystems and their ability to pump large amounts of seawater, sponge holobionts are likely to be key players within benthic phosphorus cycles.

Impacts of Mesoscale Eddies on Biogeochemical Variables in the Northwest Pacific

Mesoscale eddies play an important role in regulating biogeochemical cycles. However, the response of biogeochemical variables to cold and warm eddies has not been well elucidated, mainly due to most previous studies relying on remote sensing techniques and lacking in situ observations below the surface water. Here, we used hydrographic and biochemical data from one survey in the northwestern Pacific to document the vertical biogeochemical structure of one cold and two warm eddies. We first compared the changes of key variables in the eddy core relative to eddy outside, explained the role of key layers (the mixing depth, pycnocline, nutricline, euphotic) in causing these changes, and then analyzed the main environmental factors affecting chlorophyll a (Chla) and phytoplankton communities. Finally we focused on the response mechanisms of key biogeochemical variables to the cold and warm eddies. The results showed that biological variables (Chla, microphytoplankton, picophytoplankton), salinity, dissolved inorganic nitrogen (DIN), dissolved inorganic phosphate (DIP), and dissolved inorganic silicate (DSi) in the cold eddy core increased by 0.2–134%, while in the warm eddy core, they decreased by 0.2–70% relative to the eddy outside. The cold and warm eddies were able to force the deep chlorophyll maximum (DCM), which rose or fell with the pycnocline, nutricline and euphotic depth (Zeu) as a whole. Cold eddies with a raised thermocline could lead to about 20 m elevated DCM and enhanced phytoplankton biomass when the nutricline and thermocline were coincident. In contrast, warm eddies drove isopycnals downward, resulting in a 10–25 m drop in DCM and a decrease in nutrient and Chla concentrations at the center of the eddies. The significant difference in the vertical structure of the phytoplankton community between the center and the outside of the eddy might be explained by the direct influence of both nutrient concentrations and stoichiometry changes. The contribution of microphytoplankton to total biomass was much smaller than that of picophytoplankton in oligotrophic waters where the DIN:DIP and DSi:DIN ratios are significantly low. Compared to nutrients, photosynthetically active radiation (PAR) might not be the main factor controlling phytoplankton biomass and abundance attributed to Zeu being consistently deeper than the mixed depth (Zm), whereas it was likely to be the key limiting factor affecting the vertical distribution of the phytoplankton community.

Spatial and temporal distribution of phytoplankton community in relation to environmental factors in the southern coastal waters of Korea

The spatial and temporal environmental conditions in the southern coastal waters of Korea (SCWK) as a complex area, which is influenced by both ocean currents and anthropogenic nutrient inputs, are highly variable. The impacts of environmental factors on the distribution of phytoplankton community structure in the SCWK remain unclear. Based on high-performance liquid chromatography (HPLC) analysis of a variety of photosynthetic pigments, spatial and temporal variations in phytoplankton community compositions were investigated in the SCWK. Cluster analysis, correlation analysis, and generalized additive models (GAMs) were used to explore the major phytoplankton groups and their response patterns to temperature, salinity, depth, and macronutrients. The results indicated that diatoms were the absolute dominant groups in the SCWK for all seasons, especially in cold seasons. Diatoms mainly concentrated at 1% light depths, while high chlorophyll-a concentrations (&amp;gt;3 µg/L) occurred at 100% and 30% light depths with good light conditions. Both clustering and correlation analyses showed that diatoms had a strong positive correlation with macronutrients such as dissolved inorganic nitrogen (DIN), dissolved inorganic phosphate (DIP), and dissolved silica (DSi). The temperature and salinity discrepancy between surface and bottom layers in summer caused a strong water stratification resulting in blocking nutrient-rich bottom water upwelling and leading cyanobacteria to become the dominant groups at 100% and 30% light depths in summer. Consistently, the cyanobacteria were highly associated with high temperature and low salinity in the correlation analysis and GAM results. Compared with diatom-predominant sites, cryptophytes and diatom-dominated sites are characterized by higher average excess nitrate (ExN). Further research on the responses of small-sized prokaryotic phytoplankton especially cyanobacteria to environmental variations and their primary production contributions would warrant a better understanding of the SCWK ecosystem.

Spatiotemporal assessments of nutrients and water quality in coastal areas using remote sensing and a spatiotemporal deep learning model

Revealing the spatiotemporal variations of nutrients in coastal waters is crucial to the understanding and evaluation of coastal environment, thereby providing efficient guidance for the aquatic environmental treatment. This study proposed a spatiotemporal-incorporated deep learning model, which is easily applicable to establish the quantitative relationships between measured environmental factors and large-scale satellite maps, and can reduce estimation errors by more than 40% compared with non-spatiotemporal-incorporated deep learning model. The spatiotemporal distributions of dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphate (DIP) over 44400 km2 of the East China Sea on 8-day scale from 2010 to 2018 were obtained. Based on the spatiotemporal variations, the water quality patterns were depicted, and the fluctuation variations of the two essential nutrients were found in the harbors with complex anthropogenic influences, in the typical estuaries with multiple river inputs, and in the open seas with important fisheries. Although the concentration of DIN and DIP decreased by 24% and 19% in 9 years, respectively, the water quality level in the inshore sea has not been significantly improved, especially in autumn and winter. Further, we quantitatively analyzed the main factors of deteriorated water and provided scientific suggestions for targeted monitoring and regional cooperative governances.

Summer Distributional Characteristics of Surface Phytoplankton Related with Multiple Environmental Variables in the Korean Coastal Waters

Multiple environmental variables related to ocean currents, freshwater runoff, and upwelling in a coastal area have complex effects on the phytoplankton community. To assess the influence of environmental variables on the phytoplankton community structure during the summer of 2019, we investigated the various abiotic and biotic factors in Korean coastal waters (KCWs), separated into five different zones. Summer environmental factors in KCWs were strongly influenced by Changjiang Diluted Water (CDW) in St. SO (Southern Offshore) 1 and 2, upwelling in St. SI (Southern Inshore) 2–4, and Nakdong River discharge in St. SI 12. In particular, low–salinity water masses (p &lt; 0.05 for nearby locations) of CDW gradually expanded from the East China Sea to southwestern KCWs from June to July. In addition, there were high levels of nutrients following freshwater runoff from the Nakdong River in southeastern KCW, which led to the dominance of Cryptomonas spp. (81%), a freshwater and brackish water algae. On the other hand, upwelling areas in southwestern KCW were dominated by diatoms Skeletonema spp., and are characterized by high phosphate concentrations (p &lt; 0.05) and low temperatures (p &lt; 0.05) compared to nearby locations. Leptocylindrus danicus (20%) was dominant due to the effect of water temperature in the SE (Southeastern area) zone. Low nutrient concentrations were maintained in the East Sea (dissolved inorganic nitrogen (DIN) = 0.39 ± 0.40 μM; dissolved inorganic phosphate (DIP) = 0.09 ± 0.03 μM) and the Yellow Sea (DIN = 0.40 ± 0.07 μM; DIP = 0.04 ± 0.02 μM), which were characterized by low levels of chlorophyll a and dominated by unidentified small flagellates (35, 40%). Therefore, our results indicated that hydro–oceanographic events such as upwelling and freshwater run–off, but not ocean currents, provide nutrients to the euphotic layers of the coastal environment and play important roles in determining the phytoplankton community structure during summer in the KCWs.

Change of the Long-Term Nitrogen and Phosphorus in the Changjiang (Yangtze) River Estuary

The concentration and structure of nutrients play a key role in sustaining marine ecosystems. In recent decades, the change in nutrient input from land has led to significant changes in nutrient concentration and structure in the marginal sea and has had an important impact on the coastal ecosystem. Based on historical data from 1984 to 2016, the long-term variations in nutrients and their potential influencing factors, were analyzed in the Changjiang River Estuary. The concentration of dissolved inorganic nitrogen (DIN) increased gradually from 1984 to 2003, but after 2003 the concentration began to decrease. Compared with DIN, the change in dissolved inorganic phosphate (DIP) had a delayed effect and has exhibited a slow downward trend since 2005. The decreases in DIN and DIP are mainly due to the improvement of wastewater treatment efforts and chemical fertilizer use efficiency in recent years. The retention of nutrients by the Three Gorges Reservoir (TGR) has been another important factor since its completion in 2003, especially because the large amount of particulate phosphorus retained by the TGR has led to a significant decrease in the total phosphorus flux into the sea, which is the main reason for the decrease in DIP. The vatiations of DIP and DIN have been instrumental in causing the observed changes of phytoplankton community in the Changjiang River Estuary.

Interannual Variation in Phytoplankton Community Driven by Environmental Factors in the Northern East China Sea

The relative importance of interannual environmental changes in shaping phytoplankton community structure remains unclear in the East China Sea (ECS), which is the largest marginal sea in the western North Pacific Ocean. Based on high-performance liquid chromatography (HPLC) analysis of a variety of photosynthetic pigments, we investigated spatiotemporal variations in the phytoplankton community in the northern East China Sea (NECS) from 2018 to 2020 to understand biomass and compositional responses to environmental conditions in a complex current system. Correlation heatmaps and generalized additive models (GAMs) were used to explore the variations in major phytoplankton groups and their relationships to temperature, salinity, depth, and nutrients. The results indicated that the phytoplankton community structure was significantly different between 2018/2019 and 2020. Under the conditions of high dissolved inorganic nitrogen (DIN) and low dissolved inorganic phosphate (DIP) concentrations in winter 2020, cryptophytes replaced diatoms as the dominant species and were observed for the first time in this study area. Dinoflagellates predominated throughout the euphotic zone in spring 2020, and statistical analysis showed that dinoflagellates tended to prevail at low DIP and high DIN conditions compared with diatoms. Summer was the only season with strong water stratification that reoccurred every year, and diatoms were mainly concentrated at nutrient-enriched 1% light depths in the summers of 2018/2019. However, a large amount of Changjiang River Diluted Water (CDW) from the surface and western part of the study area affected all sampling sites eastward to 126°E in 2020, allowing diatoms to be dominant at 100% and 30% light depths in the westernmost stations in the NECS. In autumn 2020, diatoms decreased significantly because of DIP-limited environmental conditions and were replaced by small phytoplankton. Under expected warming ocean scenarios with human-induced nutrient inputs, small phytoplankton will become dominant, while spring dinoflagellate blooms will occur more frequently in the NECS. International monitoring programs for marine ecosystems are currently needed in the ECS.

Oxygen isotope exchange rates between phosphate and water catalyzed by inorganic pyrophosphatase: Implications for the biogeochemical cycle of phosphorus

The oxygen isotope composition of phosphate (δ18OPO4) has been widely used as (paleo)temperature and bio-signature proxies and a tracer of biogeochemical cycling of phosphorus (P). In natural aqueous systems, reactive inorganic phosphorus is dominantly present as dissolved inorganic phosphate (DIP), and reactions involving DIP are primarily carried out by microorganisms and catalyzed by enzymes. One enzyme suggested to dominate P-cycling in nature is inorganic pyrophosphatase (PPase), a ubiquitous intracellular enzyme that catalyzes oxygen (O) isotope exchange between DIP and water. Herein, we determined PPase-catalyzed O-isotope exchange rates between DIP and water over the range of typical Earth surface temperatures (3 - 37°C) using isotope ratio mass spectrometry (IRMS). Exchange rates determined at pH 7.4 and between 3 and 37°C, were described by first-order reaction kinetics (rate constant k = 1.51E-05 to 3.13E-04 sec−1; half-life of reaction t1/2 = 37 to 765 minutes), and strongly dependent on temperature. The temperature dependence of the exchange reaction was fitted by the Arrhenius equation, with an activation energy of 61.8 kJ/mole. The rate of PPase-catalyzed O-isotope exchange is ca. 7 - 8 orders of magnitude faster than the rate of abiotic reactions (pH 5) at 37°C calculated by the extrapolation of high-temperature rate data. The results of this study can be used to improve the interpretation of measured δ18O values of phosphate preserved in the rock record or during biogeochemical reactions (e.g., deconvolution of simultaneous abiotic and enzymatic/microbial processes).

The Importance of Benthic Nutrient Fluxes in Supporting Primary Production in the Laptev and East Siberian Shelf Seas

AbstractThis study presents an assessment of benthic nutrient regeneration and its role for the nutrient budget of the outer Laptev and East Siberian shelf sea. Porewater profiles of the major nutrients dissolved silica (DSi), dissolved inorganic nitrogen (DIN), and dissolved inorganic phosphate (DIP) as well as total dissolved iron (DFe) were evaluated with a one‐dimensional reaction transport model to derive net reaction rates and benthic nutrient fluxes from shelf and slope 16 stations. Integrated over the shelf area the benthic fluxes of DSi, DIN, and DIP were found to be 7.1, 1.2, and 0.5 Gmol/year in the Laptev Sea and 29.8, 9.5, and 2.8 Gmol/year in East Siberian Sea, respectively. A comparison of the ratios of the benthic nutrient fluxes with marine and riverine inputs and Arctic plankton stoichiometry indicate substantial benthic nitrogen loss likely due to denitrification relative to DIP and DSi. Our benthic flux estimation is likely a low estimate of benthic nutrient fluxes considering potentially higher regeneration rates of nutrients from more productive, bioturbated near‐shore sediments. The estimate emphasizes the role of benthic nutrient fluxes by returning nutrients with a fundamentally different stoichiometry to bottom waters from that of Arctic marine phytoplankton, riverine sources, and open water inflow. With a simple box model, we provide a snapshot of today's nutrient budget in the two seas and estimate that about 10%–20% of nutrients required by primary production are derived from sediments. This proportion is expected to increase for a future warmer Arctic continental shelf in response to increasing primary production.

Oxygen isotopic fingerprints on the phosphorus cycle within the deep subseafloor biosphere

Phosphorus (P) is essential for all known forms of life. The oxygen isotopic composition of phosphate can carry a strong imprint from the metabolic processes in Earth’s surface environments, including the deep subseafloor biosphere extending to > 1 km beneath the seafloor. Here, we report the 18O/16O ratios (δ18O) of dissolved inorganic phosphate (DIP) to identify different pathways of P cycling in deep-sea sediments sampled up to 200 meters below the seafloor during Ocean Drilling Program (ODP) Leg 201. Our results, along with a diagenetic model, indicate that the δ18O of DIP (δ18ODIP) is mainly controlled by three pathways of P cycling at Site 1230: (1) release of DIP by extracellular enzymatic degradation of organic matter (i.e., organophosphate), (2) precipitation of authigenic apatite, (3) enzyme-catalyzed oxygen isotopic exchange between phosphate and water. Our diagenetic model quantitatively deconvolves the rates of the three P cycling pathways. In particular, a shift of δ18ODIP towards equilibrium around 140 m below the seafloor corresponds well with a shift in microbial communities, suggesting that δ18ODIP has potential as a proxy for microbial activities in the deep subseafloor biosphere. We also find that the rate of oxygen isotopic exchange can be scaled with the rate of organic matter degradation, suggesting microbially controlled oxygen isotopic exchange. Further, the pattern of variation between authigenic phosphate in sediments and DIP in porewaters bolsters the case that authigenic phosphate (authigenic apatite and Fe-bound phosphate) should reflect the oxygen isotopic composition of contemporaneous porewater DIP and thus can be used to track biogeochemical cycling of P.

Approximation of submarine groundwater discharge and allied nutrient fluxes to the Bay of Bengal, India using nutrient mass balance

The magnitude of terrestrial (fresh) and recirculated (saline) submarine Groundwater Discharge (SGD) derived nutrient fluxes were estimated to transact parallel in Coleroon estuary from surface water, pore water, and groundwater samples. The dissolved nutrients fluxes observed were 1656.0 μ mol day−1 for Dissolved Inorganic Nitrogen (DIN), 127.4 μ mol day−1 for dissolved inorganic phosphate (DIP), and 534.4 μ mol day−1 for dissolved silica (DSi), suggesting sources due to fertilizers, ion exchange, and degree of weathering irrespective of tides and sampling locations. Groundwater supplied nutrients were higher than streams, rivers, and pore water, other water bodies supplied nutrients. Location A recorded a higher Redfield ratio (4274.3) and was found declining towards the coast which suggests anoxic seawater mixing with oxic groundwater, and lower ratio recorded in location C groundwater samples (1.5) suggests anoxic aquifers due to salinization. Mass balance calculated net nutrient production was 1656.0 µ mol day−1 for DIN, 127.4 µ mol day−1 for DIP, and 534.4 µ mol day−1 for DSi, suggesting SGD as sources for algal blooms and hypoxia.