Particulate Organic Phosphorus Research Articles

"Load-Unload" Effect of Manganese Oxides on Phosphorus in Surface Water of the Pearl River Estuary

Phosphorus (P) conveyed by surface runoff plays an essential role in regulating nutrient balance and primary production in estuarine waters. In this study, basic physiochemical properties, total phosphorus (TP, including speciation), particulate iron (PFe), particulate manganese (PMn), and particulate aluminum (PAl) of the surface water in the Pearl River Estuary (PRE) in different seasons were determined to investigate the spatiotemporal distribution characteristics of P and to identify the crucial factor controlling P migration and transformation in the freshwater-saltwater interaction zone. TP concentrations (28.88-233.68 μg·L-1) decreased with increasing salinity gradient owing to deposition and dilution. The proportions of P speciation followed a decreasing order as dissolved inorganic phosphorus (DIP, 37.3%) > particulate inorganic phosphorus (PIP, 22.7%) > dissolved organic phosphorus (DOP, 21.0%) > particulate organic phosphorus (POP, 19.0%). PIP was positively related to PFe, PMn, and PAl (P < 0.05), confirming their concurrent migration behaviors. In addition, the increase in salinity promoted the desorption of phosphate on the suspended particulate matters, which mainly took place near the freshwater-saltwater interface. A significant positive correlation (P < 0.001) between the solid-liquid phase partitioning coefficient (Kd) of phosphate and salinity indicated that PIP was present mainly in more stable forms in the brackish water. Most importantly, a better relationship between Kd and PMn (P < 0.01) supported our scientific hypothesis of the "load-unload" effect of Mn oxides on P:particulate-carrying phosphates transported from the freshwater zone tend to be desorbed and released into the brackish water.

Depth Variance of Organic Matter Respiration Stoichiometry in the Subtropical North Atlantic and the Implications for the Global Oxygen Cycle

AbstractClimate warming likely drives ocean deoxygenation, but models still cannot fully explain observed declines in oxygen. One unconstrained parameter is the oxygen demand per carbon respired for complete remineralization of organic matter (i.e., the total respiration quotient, rΣ‐O2:C). Here, we tested if rΣ‐O2:C declined with depth by quantifying suspended concentrations of particulate organic carbon (POC), particulate organic nitrogen (PON), particulate organic phosphorus (POP), particulate chemical oxygen demand (PCOD), and total oxygen demand (Σ‐O2 = PCOD + 2PON) down to a depth of 1,000 m in the Sargasso Sea. The respiration quotient (r‐O2:C = PCOD:POC) and total respiration quotient (rΣ‐O2:C = Σ‐O2:POC) declined with depth in the euphotic zone, but increased vertically in the disphotic zone. C:N and rΣ‐O2:N changed with depth, but surface values were similar to values at 1,000 m. C:P, N:P, and rΣ‐O2:P mostly decreased with depth. We hypothesize that rΣ‐O2:C is linked to multiple environmental factors that change with depth, such as phytoplankton community structure and the preferential production/removal of biomolecules. Using a global model, we show that the global distribution of dissolved oxygen is equally sensitive to r‐O2:C varying between surface biomes versus vertically during remineralization. Additionally, adjusting the model's r‐O2:C with depth to match our observations resulted in less dissolved oxygen throughout the upper ocean. Most of this loss occurred in the tropical Pacific thermocline, where oxygen models underestimate deoxygenation the most. This study aims to improve our understanding of biological oxygen demand as warming‐induced deoxygenation continues.

Metagenome-assembled genomes from particle-associated microbial communities in the mesopelagic zone of the Pacific Ocean.

We report 10 particle-associated metagenome-assembled genomes (MAGs) from the mesopelagic zone of Pacific Ocean seawaters. MAGs comprise members of Flavobacteria Halomonas, Blastomonas, Brevundimonas, Alteromonas, Shingomonas, Sphingopyxis, Tabrizicola, Proteobacteria, and Gammaproteobacteria. Functional annotation suggests that these bacteria are involved in central particulate organic carbon conversion, nitrogen cycling, and phosphorus cycling.

Exploring the role of different data types and timescales in the quality of marine biogeochemical model calibration

Abstract. Global biogeochemical ocean models help to investigate the present and potential future state of the ocean, its productivity and cascading effects on higher trophic levels such as fish. They are often subjectively tuned against data sets of inorganic tracers and surface chlorophyll and only very rarely against organic components such as particulate organic carbon or zooplankton. The resulting uncertainty in biogeochemical model parameters (and parameterisations) associated with these components can explain some of the large spread of global model solutions with regard to the cycling of organic matter and its impacts on biogeochemical tracer distributions, such as oxygen minimum zones (OMZs). A second source of uncertainty arises from differences in the model spin-up length as, so far, there seems to be no agreement on the required simulation time that should elapse before a global model is assessed against observations. We investigated these two sources of uncertainty by optimising a global biogeochemical ocean model against the root-mean-squared error (RMSE) of six different combinations of data sets and different spin-up times. Besides nutrients and oxygen, the observational data sets also included phyto- and zooplankton, as well as dissolved and particulate organic phosphorus (DOP and POP, respectively). We further analysed the optimised model performance with regard to global biogeochemical fluxes, oxygen inventory and OMZ volume. Following the optimisation procedure, we evaluated the RMSE for all tracers located in the upper 100 m (except for POP, for which we considered the entire vertical domain), regardless of their consideration during optimisation. For the different optimal model solutions, we find a narrow range of the RMSE, between 14 % of the average RMSE after 10 years and 24 % after 3000 years of simulation. Global biogeochemical fluxes, global oxygen bias and OMZ volume showed a much stronger divergence among the models and over time than RMSE, indicating that even models that are similar with regard to local surface tracer concentrations can perform very differently when assessed against the global diagnostics for oxygen. Considering organic tracers in the optimisation had a strong impact on the particle flux exponent (Martin b) and may reduce much of the uncertainty in this parameter and the resulting deep particle flux. Independent of the optimisation setup, the OMZ volume showed a particularly sensitive response with strong trends over time, even after 3000 years of simulation time (despite the constant physical forcing); a high sensitivity to simulation time; and the highest sensitivity to model parameters arising from the tuning strategy setup (variation of almost 80 % of the ensemble mean). In conclusion, calibration against observations of organic tracers can help to improve global biogeochemical models even after short spin-up times; here especially, observations of deep particle flux could provide a powerful constraint. However, a large uncertainty remains with regard to global OMZ volume and its evolution over time, which can show very dynamic behaviour during the model spin-up, which renders temporal extrapolation to a final equilibrium state difficult if not impossible. Given that the real ocean shows variations on many timescales, the assumption of observations representing a steady-state ocean may require some reconsideration.

Long-term remote observations of particulate organic phosphorus concentration in eutrophic Lake Taihu based on a novel algorithm

Monitoring the long-term spatiotemporal variations in particulate organic phosphorus concentration (CPOP) is imperative for clarifying the phosphorus cycle and its biogeochemical behavior in waters. However, little attention has been devoted to this owing to a lack of suitable bio-optical algorithms that allow the application of remote sensing data. In this study, based on Moderate Resolution Imaging Spectroradiometer (MODIS) data, a novel absorption-based algorithm of CPOP was developed for eutrophic Lake Taihu, China. The algorithm yielded a promising performance with a mean absolute percentage error of 27.75% and root mean square error of 21.09 μg/L. The long-term MODIS-derived CPOP demonstrated an overall increasing pattern over the past 19 years (2003–2021) and a significant temporal heterogeneity in Lake Taihu, with higher value in summer (81.97 ± 3.81 μg/L) and autumn (82.07 ± 3.8 μg/L), and lower CPOP in spring (79.52 ± 3.81 μg/L) and winter (78.74 ± 3.8 μg/L). Spatially, relatively higher CPOP was observed in the Zhushan Bay (85.87 ± 7.5 μg/L), whereas the lower value was observed in the Xukou Bay (78.95 ± 3.48 μg/L). In addition, significant correlations (r > 0.6, P < 0.05) were observed between CPOP and air temperature, chlorophyll-a concentration and cyanobacterial blooms areas, demonstrating that CPOP was greatly influenced by air temperature and algal metabolism. This study provides the first record of the spatial-temporal characteristics of CPOP in Lake Taihu over the past 19 years, and the CPOP results and regulatory factors analyses could provide valuable insights for aquatic ecosystem conservation.

Effect of Rational Fertilizer for Eggplants on Nitrogen and Phosphorus Pollutants in Agricultural Water Bodies

Excessive fertilizer application in the cropping industry leads to excessive nitrogen and phosphorus in surrounding water bodies, which causes farmers to increase economic cost and damage the environment. To address the problem, we built a crop-soil runoff soil column test system, setting eight fertilizer application levels for eggplants. Then, crop yield, soil fertility and pollutant concentrations in the receiving water bodies were measured. The process of fertilizer application on the water quality of surrounding receiving water bodies and the rationality of fertilizer application were analyzed. The results showed that crop yield, soil fertility, and pollutant concentrations in the receiving water increased with the increase in fertilizer application. The crop yield stabilized when the fertilizer application amount was higher than 0.12 kg/m2; the concentrations of total nitrogen (TN) and total phosphorus (TP) in the water increased significantly with the increase in fertilizer application, where particulate nitrogen (PN) and organic phosphorus (OP) were the key pollutants. In addition, crop growth had an interception effect on pollutant migration. The concentration of pollutants in the water was significantly lower in the late crop growth period (after flowering) than in the early. The crop had the best interception effect on pollutants when the fertilizer application was 0.12 kg/m2. The concentrations of TN and TP in the water were 29.7% and 22.3% after the flowering period, being lower than those before the flowering period. Therefore, a reasonable value of 0.12 kg/m2 is recommended for fertilizer application in this article. It can provide a reference for the fertilization system of eggplant planting in North China and theoretical support for the realization of clean production in small rural watershed planting.

Global Ocean Particulate Organic Phosphorus, Carbon, Oxygen for Respiration, and Nitrogen (GO-POPCORN)

Concentrations and elemental stoichiometry of suspended particulate organic carbon, nitrogen, phosphorus, and oxygen demand for respiration (C:N:P:−O2) play a vital role in characterizing and quantifying marine elemental cycles. Here, we present Version 2 of the Global Ocean Particulate Organic Phosphorus, Carbon, Oxygen for Respiration, and Nitrogen (GO-POPCORN) dataset. Version 1 is a previously published dataset of particulate organic matter from 70 different studies between 1971 and 2010, while Version 2 is comprised of data collected from recent cruises between 2011 and 2020. The combined GO-POPCORN dataset contains 2673 paired surface POC/N/P measurements from 70°S to 73°N across all major ocean basins at high spatial resolution. Version 2 also includes 965 measurements of oxygen demand for organic carbon respiration. This new dataset can help validate and calibrate the next generation of global ocean biogeochemical models with flexible elemental stoichiometry. We expect that incorporating variable C:N:P:-O2 into models will help improve our estimates of key ocean biogeochemical fluxes such as carbon export, nitrogen fixation, and organic matter remineralization.

Isotopic compositions of copper and zinc in plankton from the Mediterranean Sea (MERITE-HIPPOCAMPE campaign): Tracing trophic transfer and geogenic inputs

This study uses Cu and Zn isotopic compositions as proxies of sources and metal transfers in the planktonic food webs from the Mediterranean Sea. Plankton was collected in spring 2019 in the deep chlorophyll maximum (DCM) along a North-South transect including coastal and offshore zones (MERITE-HIPPOCAMPE campaign). δ65Cu and δ66Zn were determined on four planktonic size fractions from 60 to 2000 μm. Combined δ65Cu and δ66Zn with geochemical tracers (Ti, particulate organic phosphorus) showed that geogenic particles were ubiquitous with plankton assemblages. The δ15N ecological tracer showed that planktonic food web was enriched in heavy isotopes of Cu and Zn in the higher trophic levels. δ65Cu were correlated with picoplankton in the offshore zone, and with zooplankton in the southern coastal zone. Firmicutes bacteria were found correlated with δ66Zn in northern and southern coastal zones suggesting decomposition of particulate matter at the DCM. These findings suggest that biogeochemical process may impact Cu and Zn isotopy in the planktonic community.

The composition of organic phosphorus in a river during the springtime irrigation period

Study regionThe study region was the Sakura River, a tributary of Lake Kasumigaura, Japan. Study focusWe asked whether particulate organic phosphorus (POP) contributed to the P cycle in rivers. Previous studies have focused on the interaction between PO43– and particulate inorganic P (PIP), but our study focused on whether POP could also be the source of PO43–. New hydrological insights for the regionAfter rain events during irrigation, concentrations of suspended particles and particulate P (PP) increased. POP accounted for 42.4 % of PP concentrations. The PIP and POP concentrations were both positively correlated with suspended particle concentrations. The PO43– concentrations were significantly higher during decomposition experiments when suspended particles were present in the water. Decomposition experiments revealed that the P composition changed and the proportion of organic P decreased as DNA-P disappeared from the PP. The fact that the DOP concentration was significantly lower in the treatment with suspended particles than without suspended particles suggested that DOP mineralization rates were increased by the presence of suspended particles. In addition to mineral-sorbed P, the POP derived from the irrigation of paddy fields may also be bioavailable.

Biogeochemical dynamics of particulate organic phosphorus and its potential environmental implication in a typical “algae-type” eutrophic lake

Organic phosphorus (Po) plays a very important role in the process of lake eutrophication, but there is still a lack of knowledge about the internal cycle of Po in suspended particulate matter (SPM) dominated by algal debris. In this study, the characterization of bioavailable Po by sequential extraction and enzymatic hydrolysis showed that 45% of extracted TP was Po in SPM of Lake Dianchi, and 43–98% of total Po in H2O, NaHCO3 and NaOH fractions was enzymatically hydrolyzable Po (EHP, H2O−EHP: 31–53%). Importantly, labile monoester P was the main organic form (68%) of EHP, and its potential bioavailability was higher than that of diester P and phytate-like P. According to the estimation of P pools in SPM of the whole lake, the total load of Pi plus EHP in the H2O extract of SPM was 74.9 t and had great potential risk to enhance eutrophication in the lake water environment. Accordingly, reducing the amount of SPM in the water during the algal blooming period is likely to be a necessary measure that can successfully interfere with or block the continuous stress of unhealthy levels of P on the aquatic ecosystem.

C, N, and P Mass Balances in the Bottom Seawater–Surface Sediment Interface in the Reducing Environment due to Anoxic Water of Gamak Bay, Korea

Current mass balances of C, N, and P were estimated using a model (Fluxin = Fluxout + ΔFlux) from Gamak Bay, Korea, in August 2017, where eutrophication and reducing conditions are prevalent. To examine the current fluxes of particulate organic carbon (POC), nitrogen (PON), and phosphorus (POP), sinking and re-floating sediment traps were deployed, a sediment oxygen demand (SOD) chamber experiment and ex-situ nutrient incubation experiment were conducted, and Fick’s first law of diffusion was applied. The principal component analysis and cluster analysis were performed to identify the three groups of water masses based on the characteristics of the bay, including the effects of the reducing environment due to the anoxic water mass using 14 bottom water quality parameters. In the reducing environment (sampling point GA4), the SOD20 flux was 3047.2 mg O2/m2/d. Additionally, the net sinking POC flux was 861.0 mg C/m2/d, while 131.8% of the net sinking POC flux (1134.5 mg C/m2/d) was removed toward the overlying water. This indicates that the organic matter that had been deposited was decomposed as a flux of 273.6 mg C/m2/d. The net sinking PON flux was 187.9 mg N/m2/d, whereas 15.8% of the net sinking PON flux was eluted, and 84.2% remained in the surface sediments. The dissolved inorganic nitrogen (DIN) elution flux from the surface sediments consisted of NH4+ elution (33.7 mg N/m2/d) and NOx− elution (−4.1 mg N/m2/d) fluxes. Despite the net sinking POP flux being 26.0 mg P/m2/d, the 47.7 mg P/m2/d of DIP elution flux (179.5% of the net sinking POP flux) was eluted to the overlying water. Similar to C mass balance, the additional elution flux occurred. Therefore, severe eutrophication (16.5 of the Okaichi eutrophication index) with the lowest N:P ratio (2.6) in GA4 was noted. This indicates that not only the freshly exported organic matter to the surface sediments but also the biochemical processes under anoxic conditions played an essential role as a remarkable nutrient source–particularly P–for eutrophication in Gamak Bay, Korea.

A Century‐Long Trajectory of Phosphorus Loading and Export From Mississippi River Basin to the Gulf of Mexico: Contributions of Multiple Environmental Changes

AbstractPhosphorus (P) control is critical to mitigating eutrophication in aquatic ecosystems, but the effectiveness of controlling P export from soils has been limited by our poor understanding of P dynamics along the land‐ocean aquatic continuum as well as the lack of well‐developed process models that effectively couple terrestrial and aquatic biogeochemical P processes. Here, we coupled riverine P biogeochemical processes and water transport with terrestrial processes within the framework of the Dynamic Land Ecosystem Model to assess how multiple environmental changes, including fertilizer and manure P uses, land use, climate, and atmospheric CO2, have affected the long‐term dynamics of P loading and export from the Mississippi River Basin to the Gulf of Mexico during 1901–2018. Simulations show that riverine exports of dissolved inorganic phosphorus (DIP), dissolved organic phosphorus, particulate organic phosphorus (POP), and particulate inorganic phosphorus (PIP) increased by 42%, 53%, 60%, and 53%, respectively, since the 1960s. Riverine DIP and PIP exports were the dominant components of the total P flux. DIP export was mainly enhanced by the growing mineral P fertilizer use in croplands, while increased PIP and POP exports were a result of the intensified soil erosion due to increased precipitation. Climate variability resulted in substantial interannual and decadal variations in P loading and export. Soil legacy P continues to contribute to P loading. Our findings highlight the necessity to adopt effective P management strategies to control P losses through reductions in soil erosion, and additionally, to improve P use efficiency in crop production.

Short term assessment of nutrients and physicochemical parameters considering different depths in a hypersaline lagoon – Araruama Lagoon –RJ

The Araruama lagoon water quality has deteriorated at an accelerated pace during the last decades, mainly due to an expansion of urban occupation. The nutrients input increased by domestic effluents could reach eutrophication, which may cause episodes of algal blooms and fish mortalities. The aim of this study was to evaluate the stratification of water parameters in the same sampling campaign. Eleven water samples were collected at the surface, middle, and bottom along the lagoon. For each sample, the following parameters were analyzed: biochemical oxygen demand (BOD5), dissolved oxygen (DO), turbidity, particulate organic carbon (POC), nitrogen and phosphorus (dissolved and particulate). The hydrodynamic characterization showed that regardless the connection with the ocean, a large part of the lagoon is more influenced by winds than tides. In general, parameters showed a homogeneous behavior along the water column. The results of DO and BOD5 confirmed that the lagoon is highly oxygenated. High phosphorus values combined with the result of the rates of nitrogen to phosphorus ratio (N:P) show that P is the limiting factor. The concentrations of BOD5, total nitrogen and total phosphorus, chlorophyll-a and phaeopigments corroborate this result.

Long-Term Remote Observations of Particulate Organic Phosphorus Concentration in Eutrophic Lake Taihu Based on a Novel Algorithm

Long-Term Remote Observations of Particulate Organic Phosphorus Concentration in Eutrophic Lake Taihu Based on a Novel Algorithm

Phosphorus compounds in the dissolved and particulate phases in urban rivers and a downstream eutrophic lake as analyzed using 31P NMR

Phosphorus (P) discharges from human activities result in eutrophication of lakes. We investigated whether the forms of phosphorus (P) in rivers with high effluent loads flowing through urban areas of Sapporo, Japan, were transformed when transported downstream into a eutrophic lake, namely Lake Barato. We hypothesized that the inorganic P supplied from the rivers might be transformed to organic forms in the lake. The results showed that soluble reactive phosphorus (SRP) and particulate inorganic phosphorus (PIP) dominated in the river discharge to the lake. Suspended solids in the rivers were rich in iron (Fe) so PIP was associated with Fe. A comparison of the concentrations at the river mouth and 4.5 km downstream showed that the concentrations of SRP and PIP were lower at 4.5 km downstream than at the river mouth, whereas the concentrations of organic P (i.e., dissolved organic phosphorus and particulate organic phosphorus) were similar. The results from solution 31P nuclear magnetic resonance spectroscopy of lake water showed that pyrophosphate was only present in the particulate fraction, while orthophosphate diesters (DNA-P) were only present in the dissolved fraction. Riverine samples contained orthophosphate (ortho-P) only, while lake samples contained ortho-P, orthophosphate monoesters, and DNA-P. The results suggest that the P forms, particularly those of dissolved P, shifted from inorganic to organic forms as the water was discharged from the river to the lake.

Limnological changes in Lake Victoria since the mid‐20th century

Abstract Lake Victoria experienced a strong degradation of water quality between the 1960s and the 1990s and, as a consequence of eutrophication, the dominant phytoplankton group changed from diatoms to N2‐fixing cyanobacteria and there was a 2‐ to 10‐fold increase in chlorophyll‐a. The goal of this study is to determine whether the 2018–2019 physical (light, stratification) and ecological (nutrient, chlorophyll‐a, phytoplankton composition) conditions in Lake Victoria changed from the 1990s. Samples were collected in 2018–2019 in nearshore and offshore waters (Uganda), during three contrasting seasons: heavy rains (March), low rains (October), and dry (June), which corresponded to distinct water column mixing regimes, respectively, late‐stratified, early‐stratified, and mixed regimes. At each station (48 nearshore and 25 offshore), we measured vertical profiles of temperature, oxygen, phytoplankton biomass and composition, inorganic nutrients, and particulate organic carbon, particulate nitrogen (N), and phosphorus (P). Chlorophyll‐a concentrations in 2018–2019 were 10.3 ± 7.1 and 2.8 ± 1.1 µg/L in the nearshore and offshore surface waters, respectively, close to those measured in the 1960s before eutrophication, but distinctly lower than those measured in the 1990s (71 ± 100 and 14 ± 6 µg/L). The phytoplankton of Lake Victoria in 2018–2019 still appears dominated by diatoms and cyanobacteria. However, we observed more non‐heterocystous filamentous and coccal/colonial cyanobacteria taxa that are better adapted to mixing conditions than gas‐vacuolated heterocystous taxa, which were dominant in the 1990s. Particulate N was significantly lower in 2018–2019 than in the 1990s, indicative of less efficient N fixation. The dissolved silica concentrations in 2018–2019 were significantly higher with the concomitant reappearance of Aulacoseira spp., which was not observed in the 1990s, presumably due to low dissolved silica concentrations. As data from long‐term monitoring are absent, the reasons for the lower chlorophyll‐a concentrations in 2018–2019 compared to the 1990s are unclear. However, climatic controls (El Niño/La Niña conditions) may be an important factor influencing the historical trend in chlorophyll‐a. Higher wind in 2018–2019 promoted vertical mixing, resulting in a deeper thermocline and surface mixed layers, which eventually lowered phytoplankton production in comparison to the 1990s. In contrast, the thermocline and surface mixed layers in the 1990s were shallower, enabling phytoplankton to stay suspended in the upper well illuminated water, allowing greater productivity. The lake in 2018–2019 is still P saturated, suggesting that another episode of high chlorophyll‐a concentrations could develop if less windy conditions occur in future, or if continued warming of surface waters eventually overcomes the mixing from present windy conditions. This study gives insights about the present ecological functioning of Lake Victoria and emphasises the impacts of variations in climate on lake physics that changes the light environment for phytoplankton. A possible less windy period in the future resulting from a new El Niño phase or from climate change, will probably lead to another episode of eutrophication in Lake Victoria. As in 2018–2019 the lake was still saturated by nutrients, there is need to reduce the nutrient concentrations (especially P) to prevent future destructive eutrophic periods caused by reduced mixing.

First report of lytic and lysogenic viral production rates in the vicinity of fish farms (Mediterranean Sea)

The vital role of viruses in organic matter recirculation has been rarely studied in the coastal zone and never before in aquaculture areas. In this study, we examine for the first time viral lytic and lysogenic production in the vicinity of fish farms in the Mediterranean Sea. Viral production rates were determined based on the viral reduction approach at two impacted stations (including two downstream distances from cages, i.e. 50 and 100 m, and various depths in the water column, i.e. from the surface down to 50 m) and one control site. We highlight that lytic production rates were significantly higher at 50 and 100 m distances from the cages compared to the control. Maximum levels (up to 1.1 × 107 released virus-like particles mL−1 h−1) were seen at the bottom waters of the impacted sites. Interestingly, lytic production was significantly correlated with the concentrations of chlorophyll a, phaeophytin and particulate organic phosphorus, confirming the role of primary producers in fuelling prokaryotic, thus viral activity too. On the other hand, lysogenic production was not correlated with any environmental variable examined here, and did not differ between stations. We propose that viruses, acting in parallel to grazers and dilution processes, may lead to extensive “disappearance” of suspended particulate matter that is produced due to nutrient additions near fish cages. Further, we provide insights into the possibly-involved mechanisms of this viral activity.

Factors affecting behavior and distribution of dissolved organic matter in an artificial coastal reservoir

Measurements were conducted in each season (four times) during 2019 at thirteen sites within the Saemangeum Reservoir, which is an artificially constructed reservoir located in a coastal region, to determine factors affecting the behavior and distribution of dissolved organic matter (DOM). The spatial distributions of particulate organic nitrogen, particulate organic phosphorus, and Chlorophyll-a indicate addition reactions in the low salinity region of the reservoir. Results of principal components analysis showed an increase in the amount of allochthonous DOM with a decrease in salinity. The changes in particulates and DOM imply an increase in dissolved organic and inorganic matter, which is attributed to the degradation of particulate organic matter. Therefore, the organic matter distribution is influenced both by dilution from the external upstream origin and the artificial operation of the sluice gate. In addition, the restricted mass transfer relating to salinity stratification from the bottom to the surface causes an increase in inorganic nutrients.

The Combined Effects of Increased pCO2 and Warming on a Coastal Phytoplankton Assemblage: From Species Composition to Sinking Rate

In addition to ocean acidification, a significant recent warming trend in Chinese coastal waters has received much attention. However, studies of the combined effects of warming and acidification on natural coastal phytoplankton assemblages here are scarce. We conducted a continuous incubation experiment with a natural spring phytoplankton assemblage collected from the Bohai Sea near Tianjin. Experimental treatments used a full factorial combination of temperature (7 and 11°C) and pCO2(400 and 800 ppm) treatments. Results suggest that changes in pCO2and temperature had both individual and interactive effects on phytoplankton species composition and elemental stoichiometry. Warming mainly favored the accumulation of picoplankton and dinoflagellate biomass. Increased pCO2significantly increased particulate organic carbon to particulate organic phosphorus (C:P) and particulate organic carbon to biogenic silica (C:BSi) ratios, and decreased total diatom abundance; in the meanwhile, higher pCO2significantly increased the ratio of centric to pennate diatom abundance. Warming and increased pCO2both greatly decreased the proportion of diatoms to dinoflagellates. The highest chlorophyllabiomass was observed in the high pCO2, high temperature phytoplankton assemblage, which also had the slowest sinking rate of all treatments. Overall, there were significant interactive effects of increased pCO2and warming on dinoflagellate abundance, pennate diatom abundance, diatom vs. dinoflagellates ratio and the centric vs. pennate ratio. These findings suggest that future ocean acidification and warming trends may individually and cumulatively affect coastal biogeochemistry and carbon fluxes through shifts in phytoplankton species composition and sinking rates.

Cover Crop Complements Flue Gas Desulfurized Gypsum to Improve No-till Soil Quality

ABSTRACT Integration of flue gas desulfurized gypsum (FGD-gypsum) with cover crops is expected to improve soil quality (SQ). Our objectives were to evaluate the impact of FGD-gypsum and rye on SQ and the contribution of core indicators to account for SQ variability in a rainfed corn-soybean system. A completely randomized design (CRD) with two FGD-gypsum rates (control vs. 1,120 kg/ha) x two cover crops (control vs. rye) was conducted. Results showed that both FGD-gypsum and cover crop variably affected soil properties; however, their impact on SQ was more pronounced when integrated. Soil bio-efficiency increased via a large microbial biomass (SMB) pool and higher enzyme activities with a decrease (38%) in microbial catabolism (qCO2). Soil chemical balancing increased 15% by active carbon (AC), 26% by active nitrogen (AN), 50% by particulate organic carbon (POC), 58% by particulate organic nitrogen (PON) and 53% by particulate organic phosphorus (POP) contents. Improved physical stability increased aggregate stability (>250 µm) contributed to higher POC, PON, and POP enrichment within aggregates. The increased bio-efficiency, chemical balancing, and physical stability as impacted by FGD-gypsum and cover crop consequently improved SQ. Principal components analysis (PCA) identified eight indicators to calculate for minimum dataset SQ index (SQIMDS), which explained for 86% of the variability in generalized SQI (SQIgen). A lack of non-significant difference between SQIg and SQIMDS suggesting that SQIMDS can be consistently used to quantify, compare, and predict SQ. A greater use of FGD-gypsum with cover crops will be important for proactive recycling of industrial by-products for growing crops.