Dissolved Inorganic Phosphorus Concentrations Research Articles

Phosphorus cycling in a subterranean estuary seepage face: A seasonal view on inventory composition and linkage with nitrate transformations

Seasonal field surveys (April 2018 to February 2019) were conducted in a subterranean estuary (STE) seepage face in Sanggou Bay (China) aiming to explore the transport and reactivity of phosphorus (P) and biogeochemical linkages with the cycling of nitrogen (N) prior to discharge. Porewater dissolved inorganic phosphorus (DIP) and dissolved organic phosphorus (DOP) together with different fractions of sedimentary P were analyzed in the upper, middle and lower intertidal covering the top 20 cm of sediment (1–4 cm, 5–8 cm, 9–12 cm, 13–16 cm and 17–20 cm depth). The accumulation of sedimentary organic P stimulated the growth of phosphate-solubilizing microorganisms and led to porewater DOP enrichment during spring. During summer, total P (TP), porewater DIP and DOP concentrations decreased, potentially due to enhanced mineralization driven by high ambient temperature. From autumn to winter, pelagic organic matter into the STE lowered, triggering a drop of TP standing stocks. Compared with the significant seasonality, sedimentary P storage was statistically identical along the intertidal. Such spatial homogeneity likely results from the rebalance driven by P adsorption dynamics and pelagic organic matter delivered by tide and wave setup. The vertical distribution of DIP, DOP, and sedimentary TP were linked to nitrate transformations. In the sediment layer with active mineralization and nitrification, concentrations of DOP, sedimentary redox and clay P increased. In the layer with active nitrate removal (2–5 cm depth), both DIP and DOP concentrations decreased. The sedimentary loosely-bound and organic P were also lower there. Notably, a substantial quantity of soluble P seeped out, acting as an important contributor to the dissolved P pool of the receiving waters. The spatial and temporal overlap of high concentrations of N and P in STEs adds variabilities and uncertainties in P out-drainage fluxes and nutrient stoichiometry balances, which should draw attention from coastal researchers and stakeholders.

Comparison of nutrients status in Liaodong Bay and Northern Yellow Sea, China: Controlling factors and nutrient budgets

Under the dual stress of global warming and human interaction, Liaodong Bay (LDB) and northern Yellow Sea (NYS) are undergoing significant ecological changes. Little is known about the driving nutrients characteristics supporting fishery resource output in these areas. We carried out three field observations in 2019 to investigate nutrient status. Results showed that dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved silica (DSi) concentrations changed seasonally, with lowest values in spring, and highest values in autumn. High DIN, DIP, and DSi concentrations were detected in LDB and NYS's estuary areas. The Yellow Sea Cold Water Mass plays a role in the distribution and seasonal variation of nutrients. Exchanges across the sediment-water interface, SFGD, atmospheric deposition, and the adjacent sea input dominated DIN dynamics of these areas. DIP primarily came from the adjacent sea input and DSi mainly originated from sediment release and the adjacent sea input. NYS seawater invasion accounted for 13.8% of DIN, 63.4% of DIP, and 35.1% of DSi in LDB. These results provide new insights to better facilitate the formulation of nitrogen and phosphorus reduction and control policies in these marginal seas.

Prostorna i sezonska raspodjela partikularnog fosfora u obalnim vodama i otvorenom moru srednjeg Jadrana

The seasonal and spatial distributions of particulate phosphorus (PP) in the water column of the coastal area and open sea of the middle Adriatic Sea area were investigated for the first time. The relationship between PP and two other important forms of phosphorus (dissolved inorganic phosphorus (DIP), and organic phosphorus (P-ORG)), and the relationship between PP and other nutrients (nitrogen and silicon salts) and oceanographic parameters (temperature, salinity, oxygen saturation, chlorophyll a) from the water column were also examined. PP concentrations ranged from 0.007 μmol dm-3 in the open sea near Palagruža archipelago to 0.589 μmol dm-3 in the Krka River estuary. In the coastal area, PP concentrations were highest in autumn and lowest in winter. The vertical distribution of PP concentrations in the water column of the coastal area were highest in the surface layer during most of the year due to input of PP by freshwater inflows. In the open sea area, there were no significant seasonal or vertical differences in the distribution of PP concentrations in thewater column. Seasonal analysis of the total phosphorus pool (PP, DIP and P-ORG) in the water column indicated that PP and P-ORG concentrations were higher in the coastal area compared to the open sea, while DIP concentrations were comparable.The results further demonstrate that PP can be an important fraction of the total phosphorus pool. A significant positive correlation was found between PP and chlorophyll a, indicating that PP was mainly of biological origin, and with nutrient salts of nitrogen and silicon, while a negative correlation was found with salinity.

Vallisneria spiralis Promotes P and Fe Retention via Radial Oxygen Loss in Contaminated Sediments

Microbial respiration determines the accumulation of reduced solutes and negative redox potential in organic sediments, favoring the mobilization of dissolved inorganic phosphorus (DIP), generally coprecipitated with Fe oxyhydroxides. Macrophytes releasing oxygen from the roots can contrast DIP mobility via the oxidation of anaerobic metabolism end-products. In this work, the submerged macrophyte Vallisneria spiralis was transplanted into laboratory microcosms containing sieved and homogenized organic sediments collected from a contaminated wetland. Sediments with and without plants were incubated under light and dark conditions for oxygen and DIP fluxes measurements and pore water characterization (pH, oxidation-reduction potential, DIP, dissolved Mn, and Fe). Bare sediments were net DIP sources whereas sediments with V. spiralis were weak DIP sources in the dark and large sinks in light. V. spiralis radial oxygen loss led to less negative redox potential and lower Fe, Mn, and DIP concentrations in pore water. Roots were coated by reddish plaques with large amounts of Fe, Mn, and P, exceeding internal content. The results demonstrated that at laboratory scale, the transplant of V. spiralis into polluted organic sediments, mitigates the mobility of DIP and metals through both direct and indirect effects. This, in turn, may favor sediment colonization by less-tolerant aquatic plants. Further in situ investigations, coupled with economic analyses, can evaluate this potential application as a nature-based solution to contrast eutrophication.

Spatiotemporal Nutrient Patterns, Stoichiometry, and Eutrophication Assessment in the Tieshan Bay Coastal Water, China

Land-source inputs into coastal water have increased remarkably in recent years, resulting in the deterioration of water quality, eutrophication, and algae blooms. However, we have limited understanding of spatiotemporal nutrient patterns, stoichiometry, and eutrophication assessment in Tieshan Bay coastal water at present. To investigate the rapid development of the coastal areas in Tieshan Bay in the South China Sea, nutrients and other physicochemical parameters were observed in Tieshan Bay during the normal season (April), wet season (July), and dry season (October) in 2021. The results showed that the average concentrations of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and chemical oxygen demand (COD) in Tieshan Bay are 0.071 ± 0.115 mg/L, 0.008 ± 0.013 mg/L, and 0.71 ± 0.219 mg/L, respectively. DIN/DIP ratio ranges from 9.1–69.3, with an average value of 19.9 ± 19.2, which exceeds the Redfield value, behaving P limitations. In addition, the mean eutrophication index (EI) was low in Tieshan Bay, with an average value of 0.5 ± 1.5. Moreover, the hotspot coastal water with high DIN, DIP, and COD concentrations was located in the upper half of Tieshan Bay in all seasons. In addition to the DIN, DIP, and COD contributions to EI, the average contribution rates of DIN, DIP, and COD are 26.6%, 8.8%, and 64.6%, respectively, which leads to the largest contribution of COD to EI. Furthermore, the average comprehensive index (CI) of organic pollution in Tieshan Bay surface seawater ranged from −1 to 5.6. The seawater near Hepu in S8 station has organic pollution in wet and dry seasons, and Tieshan Bay’s middle region also has slight organic pollution. Additionally, the DIN, DIP, and COD had significant relationships with salinity (p < 0.05), suggesting that coastal water quality is affected by land-based sources input. To achieve the seawater quality target and mitigate regional eutrophication, it is critical to implement land-based source management across the river-bay-coastal water continuum.

Variations of dissolved inorganic nutrients and their influences on harmful algal blooms in Bohai Sea over the past thirteen years

The Bohai Sea (BHS) has been subjected to harmful algal blooms (HABs). In this study, we compiled and analyzed datasets of HABs and related environmental parameters in BHS from 2006 to 2018 including dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP). However, quarterly monitoring cannot give direct in-situ observations when HABs happened. Therefore, we reconstructed spatially discrete seasonal observations to a spatial resolution of 0.25° × 0.25° continuous monthly data from August 2006 to October 2019 using Chebyshev Polynomial Fitting (CPF) and seasonal decomposition methods. It was concluded that a coherent increasing trend of the DIN and DIN/DIP ratio transitioned to a decreasing trend from 2013, whereas the DIP concentration exhibited a consistent falling trend from 2012 to 2019. the occurrence of HABs was successfully controlled by the reduction of DIN and DIP, but the reduction may promote the occurrence or intensity of HABs events in some particular algal species.

Sources and long-term variation characteristics of dissolved nutrients in Maowei Sea, Beibu Gulf, China

Maowei Sea is a typical semi-enclosed subtropical bay where eutrophication has been rising due to human activities in recent years. At present, the source and long-term variability properties of nutrients are not well understood. This study investigated the dissolved inorganic nutrients in the riverine sections to the sea and the coastal areas from 2011 to 2017 in Qinzhou Bay (QZB), Beibu Gulf. Results showed that harmful blooms were frequent in the dry season due to rapid urbanization in recent years. During dry season, the concentrations of dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) increased by 67% and 150%, respectively. Most of the nutrients input to the bay were supplied by the adjoining rivers, followed by groundwater discharge according to the classical box model devised by the Land-Ocean Interactions in the Coastal Zone. High DIN concentrations in rivers were mainly caused by intensified agriculture, including urban and rural effluents, due to inadequate sanitary sewer systems. Maowei Sea (the inner bay of QZB) is a sink system for DIN but a strong source system for DIP, which surpassed riverine input, probably due to the discharge of DIP-containing effluent from the industries around the Maoling River mouth. The discrepancy in DIN and DIP sources resulted in different DIN/DIP ratios between the wet and dry seasons. P-limitation generally occurs in the wet season and is relieved in the dry season. The relief of P-limitation in the dry season may be crucial for the frequent harmful algal blooms, which may be further aggravated in the future with the rapid increase in DIP concentrations in the bay. Therefore, the results of this study provide a basis for the effective improvement of the ecological environment in the Maowei Sea.

Reconstruction of Monthly Surface Nutrient Concentrations in the Yellow and Bohai Seas from 2003–2019 Using Machine Learning

Monitoring the spatiotemporal variability of nutrient concentrations in shelf seas is important for understanding marine primary productivity and ecological problems. However, long time-series and high spatial-resolution nutrient concentration data are difficult to obtain using only on ship-based measurements. In this study, we developed a machine-learning approach to reconstruct monthly sea-surface dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved silicate (DSi) concentrations in the Yellow and Bohai seas from 2003–2019. A large amount of in situ measured data were first used to train the machine-learning model and derive a reliable model with input of environmental data (including sea-surface temperature, salinity, chlorophyll-a, and Kd490) and output of DIN, DIP, and DSi concentrations. Then, longitudinal (2003–2019) monthly satellite remote-sensing environmental data were input into the model to reconstruct the surface nutrient concentrations. The results showed that the nutrient concentrations in nearshore (water depth < 40 m) and offshore (water depth > 40 m) waters had opposite seasonal variabilities; the highest (lowest) in summer in nearshore (offshore) waters and the lowest (highest) in winter in nearshore (offshore) waters. However, the DIN:DIP and DIN:DSi in most regions were consistently higher in spring and summer than in autumn and winter, and generally exceeded the Redfield ratio. From 2003–2019, DIN showed an increasing trend in nearshore waters (average 0.14 μmol/L/y), while DSi showed a slight increasing trend in the Changjiang River Estuary (0.06 μmol/L/y) but a decreasing trend in the Yellow River Estuary (–0.03 μmol/L/y), and DIP exhibited no significant trend. Furthermore, surface nutrient concentrations were sensitive to changes in sea-surface temperature and salinity, with distinct responses between nearshore and offshore waters. We believe that our novel machine learning method can be applied to other shelf seas based on sufficient observational data to reconstruct a long time-series and high spatial resolution sea-surface nutrient concentrations.

Compound effect of land reclamation and land-based pollutant input on water quality in Qinzhou Bay, China

Based on a three-dimensional hydro-biogeochemical model, the compound and individual impacts of two types of human activities, i.e., land reclamation and land-based pollutant input, on coastal water quality were studied. In Qinzhou Bay (QZB), China, a total of 38.90 km2 of tidal flat was reclaimed between 2004 and 2019, and the Chemical Oxygen Demand (COD) in the wastewater was reduced by over 40%. However, the Dissolved Inorganic Nitrogen (DIN) was increased by above 40%, and the Dissolved Inorganic Phosphorus (DIP) was increased by about 17%, leading to the continuous deterioration of water quality in QZB. Correspondingly, the model results show that the bay's average COD decreased by 6.86%, but the DIN and DIP increased by 57.53% and 17.39%, respectively. Considering the individual effects, land reclamation contributed 72.73%, 75.38%, and 25.01% to the changes in the COD, DIN, and DIP concentrations in QZB, respectively; and the remainder was caused by the variations in the land-based pollutant input. By considering the compound effect of these two types of human activities, it was found that land reclamation can hinder the water quality improvement induced by the decrease in land-based pollutant input; and it can intensify the water quality deterioration induced by the increase in land-based pollutant input. These results indicate that the impact of land-based pollutant input on coastal water quality was modulated by land reclamation. However, the modulation did not affect the DIP since the phosphorus was the restrictive element in QZB. The comparison of different experimental results revealed that restoring hydrodynamics to enhance the bay-shelf exchange would be a more effective method of ecological restoration than solely reducing the pollutant input.

Nutrients across Time: Relationships with Climate, Hydrology, and Land Use in Four Rivers of the Pacific Northwest

AbstractUnderstanding the temporal dynamics and drivers of dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) provides a critical link to better management of nutrient‐related impacts such as eutrophication and harmful algal blooms (HABs). DIN and DIP are a primary control on persistent eutrophication and HABs in the Pacific Northwest (PNW). An understudied phenomenon, this paper examines multi‐decadal trends in DIN and DIP concentrations and loads, and their relationships to climatic and hydrologic factors (e.g., stream and air temperature, discharge, precipitation) in the PNW. Dissolved constituents act as a broad sentinel of linkages between watershed and in‐stream mechanisms such as nitrification, denitrification, nutrient use efficiency, evapotranspiration, hydrologic connectivity, groundwater extraction, irrigation, and land uses. As opposed to the total N and P often used in individual, autochthonous, lentic systems, DIN and DIP are used here as measures of multiscaled processes in allochthonous lotic systems with diverse flow paths. Time‐series data from public agencies were used for up to 20 years in river outlets from the Willamette, Salmon, Spokane, and Yakima watersheds. Seasonal Mann Kendall (SMK) tests suggest significant decreasing multi‐decadal trends in DIN and DIP loads for three out of four watersheds (for DIN, SMK = −0.104; for DIP, SMK = −0.081, −0.181, and −0.213), significant decreasing trends in DIN concentrations for one of the four watersheds (SMK = −0.144), and significant decreasing trends in DIP concentrations in three of the four watersheds (SMK = −0.120, −0.135, and −0.157). Multivariate regressions found significant relationships for concentrations, loads, and ratios when regressed against stream and air temperatures, precipitation, and discharge (16 significant regressions, with adjusted R2 values between 0.016 and 0.65). Highlights of these regression results are as follows: (1) precipitation, discharge, and water and air temperatures help to explain DIN and DIP concentrations and loads, (2) changes in DIN concentrations are sensitive to more hydroclimatic variables than DIP concentrations, and (3) DIP concentrations are positively correlated with stream temperature while DIP loads are negatively correlated with stream temperature. Furthermore, seasonal changes in nutrients — and their potential to alter aquatic productivity during a year — has received little attention in the literature. Regressions established significant seasonality or monthly variation of DIN and DIP concentrations and loads in all four watersheds (20 significant regressions, with adjusted R2 values between 0.038–0.65). Nutrient thresholds of DIN (0.3–0.5 mg/L) and DIP (0.05–0.005 mg/L) concentrations were used to analyze N‐ and P‐limitation. P‐limitation is known to occur in lakes, and N‐limitation is known to occur in rivers. Surprisingly, except for one watershed (Salmon), nutrient concentrations for both DIN and DIP in all watersheds were shown to be above the limitation thresholds across multiple seasons. In certain situations, such as where significant decreasing trends continue, the DIN:DIP ratio suggests seasonal switching between N‐ and P‐limited could create ideal conditions for HABs. The findings of this study have important implications for water resource management issues such as agriculture, land use development, fish populations, timber harvests, water quality, and public health.

Spatiotemporal nutrient patterns, composition, and implications for eutrophication mitigation in the Pearl River Estuary, China

Human activities and climate change have changed large river estuary ecosystems, which impacts nutrient enrichment in coastal waters. Enhanced nutrient levels lead to eutrophication, oxygen deficits, and frequent occurrences of harmful algal blooms. In this study, the spatiotemporal nutrient patterns and composition of dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP), as well as the relationships between DIN, DIP, eutrophication index (EI), and environmental factors were explored. The spatiotemporal pattern and composition of DIN and DIP in coastal water based on samples from fifteen stations in the Pearl River Estuary (PRE) were investigated during the dry (April), wet (July), and normal (October) seasons in 2018. The results showed that the average concentrations of DIN and DIP were 65.35 ± 47.72 μmol L−1 and 0.94 ± 0.70 μmol L−1 in the PRE, respectively. The concentration of DIN at most monitoring stations failed to reach the Grade IV national seawater quality standard, while the concentration of DIP did meet them. The ratio of DIN/DIP ranged from 4.33 to 242.50, with an average of 42.60 ± 47.06, exceeding the Redfield ratio. EI was high in the PRE, ranging from 0.01 to 67.19, with an average of 8.64 ± 11.94. Hotspots with high DIN and DIP concentrations were located in the upper PRE during all seasons. In addition, there were significant negative correlations among DIN, DIP, EI, and salinity (P < 0.05), except for DIP and EI in the wet water flow period, implying an impact from riverine nutrient input. Moreover, the DIN, DIP, and EI also had negative relationships with dissolved oxygen in all seasons (P < 0.05), indicating that eutrophication led to oxygen deficits in the PRE. Therefore, land–ocean integration management of PRE-associated nutrient criteria, composition, and sources should be introduced to effectively and efficiently mitigate eutrophication in the future.

Dynamics of phytoplankton groups in three contrasting situations of the open NW Mediterranean Sea revealed by pigment, microscopy, and flow cytometry analyses

A detailed study of phytoplankton composition and dynamics was carried out during three contrasting situations (cruises F1, F2, and F3) in the northwestern (NW) Mediterranean Sea. Haptophytes, diatoms, and green algae dominated in F1, during the spring bloom, with high nutrients and high phytoplankton biomass. In F2, the post-bloom situation with a still weak stratification and lower nutrient concentrations, we found a high spatial variability. Stations were clearly dominated by either Synechococcus, haptophytes or cryptophytes; with Synechococcus reaching the highest abundance (4 × 105 cells mL−1, 60% of the integrated chlorophyll a) reported to date for the open Mediterranean Sea. Cryptophytes accumulated close to the surface in very shallow mixed layer stations. In late summer, F3 revealed a fully developed stratification with low nutrients and a marked deep chlorophyll maximum (DCM). Prochlorococcus was present only during this cruise, mainly in deep layers together with haptophytes and pelagophytes, while haptophytes and Synechococcus dominated the upper mixed layer. Flow cytometry (FCM) and pigment-based abundance estimates for Prochlorococcus, Synechococcus and cryptophytes were well correlated, as happened also between small picoeukaryotes (FCM) and green algae (pigments), and between large picoeukaryotes (FCM) and haptophytes (pigments). Dinoflagellate abundance by microscopy and by pigments did not agree well, probably due to the presence of heterotrophic forms or because they contained pigments other than peridinin, the standard dinoflagellate marker. The decrease in size of the FCM large picoeukaryotes group with depth was presumably related to the increasing contribution of pelagophytes, with smaller cells than haptophytes, the other main component of this fraction. Cell size increase of Prochlorococcus and Synechococcus with depth suggests vertical segregation of genotypes or photoadaptation. The groups' ecological preferences are presented with respect to depth and nutrient concentrations. Synechococcus and cryptophytes occupied shallow layers; diatoms, green algae and Prochlorococcus showed a tendency for deep layers and pelagophytes for even deeper layers, while haptophyte and dinoflagellate allocations were less clear. As for nutrients, the maximum relative contributions of green algae and especially diatoms occurred when dissolved inorganic phosphorus (DIP) concentrations were highest, of Prochlorococcus, dinoflagellates and pelagophytes when lowest, and of Synechococcus and cryptophytes when DIP concentrations were low but not minimal. The contribution of haptophytes did not show a relationship with DIP concentration. These results from individual groups stand as significant exceptions to the general relationship between phytoplankton cell size and nutrient availability.

Heterotrophic bacteria outcompete diazotrophs for orthophosphate in the Mediterranean Sea

AbstractUnicellular photoautotrophic diazotrophs such as Crocosphaera spp. are ubiquitous in many oligotrophic and N‐limited oceans, as they can reduce N2 into bioavailable ammonia. The Mediterranean Sea is potentially an ideal environment for photoautotrophic diazotrophic activity, and yet N2‐fixation rates measured in the last two decades are typically very low and no diazotrophic blooms have been recorded in its offshore waters. Previous studies suggest that diazotrophs, as well as nondiazotrophic phytoplankton and heterotrophic bacteria, may be P‐limited, hence their low biomass and activity. Here, we amended surface seawater from six stations across a nutrient gradient in the Mediterranean Sea (east to west transect) with dissolved inorganic phosphorus (DIP), and with seawater‐acclimated inocula of Crocosphaera watsonii, a unicellular cyanobacterial diazotroph, to examine if DIP can stimulate diazotrophy. Our results demonstrate that C. watsonii are poor competitors for DIP relative to native nondiazotrophic heterotrophic microbial populations, especially in the ultraoligotrophic eastern Mediterranean basin, resulting in low N2‐fixation rates. Moreover, the results indicate that when the ambient DIP concentrations are &lt; 35 nmol L−1, unicellular photoautotrophic diazotrophs such as C. watsonii will likely be outcompeted for this macronutrient in the Mediterranean Sea, whereas above 35 nmol L−1 diazotrophy can be stimulated. Our findings support the “bypass theory” stating that photoautotrophs may be outcompeted by heterotrophic bacteria for DIP in nutrient‐poor regions such as the Mediterranean Sea.

Molecular responses to inorganic and organic phosphorus sources in the growth and toxin formation of Microcystis aeruginosa

Toxic cyanobacteria bloom is a ubiquitous phenomenon worldwide in eutrophic lakes or reservoirs. Microcystis, is a cosmopolitan genus in cyanobacteria and exists in many different forms. Microcystis aeruginosa (M. aeruginosa) can produce microcystins (MCs) with strong liver toxicity during its growth and decomposition. Phosphorus (P) is a typical growth limiting factor of M. aeruginosa. Though different forms and concentrations of P are common in natural water, the molecular responses in the growth and MCs formation of M. aeruginosa remain unclear. In this study, laboratory experiments were conducted to determine the uptake of P, cell activity, MCs release, and related gene expression under different concentrations of dissolved inorganic phosphorus (DIP) and dissolved organic phosphorus (DOP). We found that the growth of M. aeruginosa was promoted by increasing DIP concentration but coerced under high concentration (0.6 and 1.0 mg P/L) of DOP after P starvation. The growth stress was not related to the alkaline phosphatase activity (APA). Although alkaline phosphatase (AP) could convert DOP into algae absorbable DIP, the growth status of M. aeruginosa mainly depended on the response mechanism of phosphate transporter expression to the extracellular P concentration. High-concentration DIP promoted MCs production in M. aeruginosa, while high-concentration DOP triggered the release of intracellular MCs rather than affecting MCs production. Our study revealed the molecular responses of algal growth and toxin formation under different P sources, and provided a theoretical basis and novel idea for risk management of eutrophic lakes and reservoirs.

Concentrations and Patterns of Atmospheric Particulate Nitrogen and Phosphorus During Different Weather Conditions in Qingdao Coastal Region

Total suspended particulate (TSP) samples were continuously collected in the Qingdao coastal region from March 2018 to October 2019. The concentrations of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), dissolved total nitrogen (DTN), dissolved total phosphorus (DTP), total nitrogen (TN), and total phosphorus (TP) in the samples were (7.13±6.59) μg·m-3, (17.42±9.88) ng·m-3, (8.34±7.03) μg·m-3, (25.59±13.67) ng·m-3, (10.68±10.59) μg·m-3, and (76.34±51.79) ng·m-3, respectively. The results showed that the concentrations of different nitrogen and phosphorus species in aerosols varied significantly during the sampling period due to the influence of emission intensity, air mass source, and meteorological conditions. The concentrations of DIN, DTN, and TN were the highest in autumn followed by spring, winter, and summer, showing similar seasonal variations. However, TP showed the highest concentration in spring and the lowest in summer. The concentrations of DIN, DTN, and TN on haze days were 4.3, 3.8, and 4.5 times higher than on non-haze reference days, respectively, and DIP, DTP, and TP concentrations were 1.9, 1.9, and 1.2 times higher, respectively. During the heating period, the DIN/DTN ratio on haze days was (92.65±4.09)%, which was 8.87% higher than on non-haze days. During the non-heating period, the DIN/DTN ratio was (80.52±8.42)%, which was 4.83% higher than the reference days. However, the average DTN/TN ratio on haze days was significantly lower than on non-haze days; the average DTN/TN ratio on haze days was (73.41±12.18)% and (80.36±4.72)% during the heating and non-heating period, respectively, and were 13.35% and 5.92% lower, respectively, on non-haze days. The proportion of DIP to DTP on hazy days increased by only 1.47% relative to non-haze days, while the DIP/DTP ratio varied between hazy days. Due to the influence air mass sources, relative humidity, and atmospheric acidification process, the DTP/TP ratio on haze days increased by 10.58% relative to non-haze days. The concentrations of DIN, DTN, and TN in aerosols affected by dust events were 2.5, 2.6, and 2.6 times higher than on non-dust days, while DIP, DTP, and TP were 4.0, 2.8, and 7.2 times higher, respectively.

Traditional land use effects on nutrient export from watersheds to coastal seas

Land use features can have a significant impact on the flux and stoichiometry of nutrients from the watershed to the sea along the freshwater continuum. Traditional agricultural watersheds designated as a Globally Important Agricultural Heritage System (GIAHS) may have unique features on nutrient dynamics. Here, we conducted seasonal, high-resolution spatial surveys for concentrations of dissolved inorganic phosphorus (DIP) and nitrogen (DIN) and stable isotopes of water and nitrate of the GIAHS in Japan (Kunisaki Peninsula). The highest upstream DIN concentrations (mean = 83 μM) were observed in the non-irrigation period in autumn. 17O isotopes of nitrate suggested that microbial nitrification in forest soil was the primary source (> 95%) of total nitrate. Spatial differences in DIP and DIN concentrations among the upstream, midstream, and downstream waters were small, with high DIN/DIP ratios (> 50) were exported from the watershed to coastal seas. Nutrient concentrations exhibited different dynamics during summer when irrigation was taking place with average DIP concentrations increasing from upstream (0.5 μM) to downstream (2.1 μM) waters. A generalized linear model showed that the proportion of paddy fields, cultivated land, residential area as well as forest were the primary drivers of DIP concentrations. DIN concentrations decreased moving downstream likely due to denitrification in the anaerobic irrigation ponds and paddy fields. This study showed that the traditional agricultural landscapes mitigated the excess DIN loading from forested areas while supplying the essential DIP for coastal production, suggesting an important forest-river-sea connection system that manages nutrient inputs to coastal waters.

Influences of phosphorus concentration and porewater advection on phosphorus dynamics in carbonate sands around the Weizhou Island, northern South China Sea

A series of flow-through reactor experiments were undertaken to assess the potential effect of porewater advection and dissolved inorganic phosphorus (DIP) concentration on benthic DIP dynamics in permeable sediments collected from the Weizhou Island, northern South China Sea. The flux of DIP ranged from −0.13 to 0.05 mmol m−2 h−1, and the reversal from DIP efflux to influx occurred when the DIP concentration reached a threshold. DIP release from the sediment into the seawater peaked at intermediate advection rate, which perhaps provide optimum conditions for DIP release related to CaCO3 dissolution. Phosphorus limitation in seawater could be relieved by DIP release from the sediment, and CaCO3-bound P in carbonate sands may play a major role in benthic DIP release and decrease in the molar nitrogen/phosphorus ratio in seawater around the Weizhou Island.

Spatiotemporal river flux and composition of nutrients affecting adjacent coastal water quality in Hainan Island, China

Human activities have changed global nutrients cycling and appreciably altered marine ecosystems in riverine-estuarine systems. This is evident by the significant shifts in the supply of nitrogen and phosphorus. However, very little is known about the concentrations and fluxes and of these nutrients and their seasonal changes in Hainan Island, China. We examined Hainan Island, which is the second largest island in China, to assess the spatiotemporal concentrations and fluxes of nutrients using seasonal data on a whole-of-system scale covering river estuaries and adjacent coastal water (2017). The annual average total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) concentrations were 77.23 ± 31.36 μmol/L and 3.25 ± 1.67 μmol/L, respectively. The annual fluxes of pollutants from the discharge of coastal rivers on Hainan Island into coastal waters were 1.8 × 104 t for TDN and 1.1 × 103 t for TDP, respectively. The month with the largest contribution to the annual pollutants load was October, which contributed 13.60% of TDN and 17.79% of TDP. In addition, the largest river fluxes were Nandu River, which contributed 7.5 × 103 t of TDN and 364 t of TDP. The annual average concentrations of pollutants in the surface coastal water were 7.60 ± 10.71 μmol/L for dissolved inorganic nitrogen (DIN) and 0.24 ± 0.31 μmol/L for dissolved inorganic phosphorus (DIP). The annual average N/P ratios in coastal rivers and seawater were 30 and 65, which were significantly higher than the Redfield ratio (N/P = 16). The DIN and DIP concentrations of most monitoring stations met the national first-class seawater standards, but the problem of nutrient pollution in some local coastal water areas was still outstanding. The coastal water quality monitoring should consider the influence of tropical storms influence on Hainan Island. The effective improvement of coastal water quality should be based on land–ocean coordination monitoring of coastal water quality and the riverine nutrient flux of Hainan Island.

Groundwater‐controlled phosphorus release and transport from sandy aquifer into lake

AbstractAwareness of groundwater‐borne dissolved inorganic phosphorus (DIP) loadings into lakes and its role in lake eutrophication is increasing, albeit DIP of natural origin is often ignored. Release of geogenic DIP from an adjacent aquifer and its transport with groundwater into a eutrophic lake is described by combining hydrogeochemical data collected in this study (sampling of piezometers, hydrogeochemical profiles, and seepage meters) with groundwater flow and discharge rates from earlier studies. The major part of the DIP that entered the lake with discharging groundwater was mobilized from iron hydroxides reduced by organic matter buried in the sediments of the old lake bottom. This is indicated by the correlation between DIP and ferrous iron (Fe2+) concentrations, with a DIP/Fe2+ molar ratio of 0.06, and an increase in pH. One‐dimensional reactive transport modeling indicated that high discharge rates (&gt; 0.1 m d−1) of anoxic groundwater upwelling in areas adjacent to the lakeshore prevent downward diffusion of oxygen into the aquifer and do not leave enough time for DIP to become rebounding to the mineral phases at the sediment‐water interface. The groundwater‐controlled DIP input into the lake calculated along a two‐dimensional cross‐section averaged 0.01 mol DIP m−2 yr−1. A 2 m wide offshore high discharge zone delivered approximately 13% of the DIP into the lake. The continuous, external loading of geogenic DIP sustains lake eutrophication and explains the failure of two previous lake restoration attempts.

Exponential decay of between-month spatial dissimilarity congruence of phytoplankton communities in relation to phosphorus in a highland eutrophic lake.

Phytoplankton species composition has long been recognized to be structured by environmental filtering, but our knowledge of patterns of spatial dissimilarity congruence between the phytoplankton community and environmental divers is rather limited. Specifically, a study on whether there are specific temporal properties that could be more related to spatial dissimilarity remains to be seen. We examined the extent to how spatial dissimilarity changed with seasonal succession by measuring β-diversity in phytoplankton communities in Lake Erhai (from January 2012 to December 2014 at 15 sampling sites) as a function of different period conditions (high-density period and low-density period). We found that congruences of spatial dissimilarity in algal communities over time were neither stable in time nor showed a seasonal pattern. The spatial dissimilarity congruence between the phytoplankton community and dissolved inorganic phosphorus (DIP) concentration followed exponential decay patterns, and this congruence was led by algal cell density. This result implies that species and functions of phytoplankton are specialized, and DIP concentration drastically increases in high-density periods than in low-density periods. This means that DIP enrichment is related to the loss of algal diversity and functions and the increase of algal biomass in eutrophic lakes.