Effects of different chemical agents on changes in sediment phosphorus composition and the response of sediment microbial community.

Controlling the release of sediment phosphorus (P) using chemical agents is a promising method for controlling internal P in eutrophic lakes. However, mineral P formation and changes in the organic P composition after sediment amendment with P-inactivation agents remain poorly understood. Furthermore, little is known about the changes in the sediment microbial community composition after remediation. Here, various ratios of poly aluminum chloride (PAC) and lanthanum-modified bentonite (LMB) were added to nutrient-rich sediments and incubated. Sequential P extraction, solution/solid-state 31P nuclear magnetic resonance (NMR), and microbial analyses were periodically performed on the inactivated sediments. The results indicate that PAC and LMB effectively reduced sediment iron-bound P and organic P, respectively, markedly increasing the content of aluminum- and calcium-bound P in the sediment, respectively. Solid-state 31P NMR results confirmed the formation of rhabdophane (LaPO4. nH2O) in the LMB-amended sediment. Solution 31P NMR results showed that PAC preferentially reduced the organic P fractions of pyrophosphate, whereas LMB efficiently reduced the organic P fractions of orthophosphate, monoesters, and diesters in the sediment. Compared with the control sediment, PAC addition can cause short-term negative effects on sediment microbes at high doses, whereas LMB addition can increase bacterial diversity or richness in the sediment. These results provide a deeper understanding of the differences between PAC and LMB in internal sediment P control.

Distinct patterns of sedimentary phosphorus fractionation and mobilization in the seafloor of the Black Sea, Marmara Sea and Mediterranean Sea.

Phosphorus (P) is a key element to all life that is used for structural and functional component of all organisms. The cycling of sedimentary P may differ depending on the redox-conditions of the overlying waters affecting the dynamics, and distribution of P-fractions and the elements that are highly coupled to P cycle. Though biogeochemistry of water column in the three interconnected marine basins of Black, Marmara and Mediterranean Seas have been studied extensively, few studies were carried out to understand sedimentary P dynamics in these regions. In this study, therefore, the biogeochemical cycling of sedimentary P and related variables such as porewater nutrients, sedimentary organic carbon, nitrogen and reactive iron were studied in selected sites at the three interconnected marine basins: Black Sea, Marmara and Northeastern (NE) Mediterranean Sea. The pool of "potentially mobile P" was also determined for the studied sites. The study results showed that porewater and sediment biogeochemistry displayed great variability in the studied sites with the maximum concentrations of porewater phosphate, ammonium, reactive silicate, surface sediment organic carbon, nitrogen, phosphorus and total phosphorus (TP) measured in the hypoxic Marmara Sea and suboxic/anoxic Black Sea. The decline in the TP concentrations of all sediment core samples indicated P-mobilization to the overlying water. The pool of "potentially mobile P" varied between 0.023 and 0.148 mol/m2 in the studied sites with the maximum values recorded in suboxic and anoxic/sulfidic parts of the Black Sea. This study predicts that the deoxygenation and eutrophication would further lead to the preferential release of P in these three interconnected marine basins, hence changing the remineralization, N/P molar ratios and eventually transform the deep-water nutrient stocks with implications for internal N/P control on marine ecosystems.

In situ control of internal nutrient loading and fluxes in the confluence area of an eutrophic lake with combined P inactivation agents and modified zeolite.

In this study, a field in situ inactivation experiment was carried out to control the confluence area sediment nutrient loading and fluxes using modified zeolite (MZ) in combination with poly aluminum chloride (PAC) and lanthanum-modified bentonite (LMB). The results indicated that PAC + MZ and LMB + MZ can reduce 76% and 75% of the P flux and 20% and 27% of the N flux, respectively. These results are based on a comparison with a control treatment over four months under the influence of external loading. However, their control efficiency on sediment nutrient fluxes decreased largely during the summertime algal blooming season. Both of the treatments lost their N control efficiency at this time. In contrast, LMB + MZ can still reduce 27% of the P flux compared to the control treatment. Surface sediment extractable ammonium increased substantially from the PAC + MZ and LMB + MZ treatments, which is 1.8 and 2.2 times more than the extractable ammonium in the control sediment after 210 days of remediation. The P fractionation analysis indicated that, in the PAC + MZ and LMB + MZ, both NaOH-rP and HCl-P increased greatly at a rate of 1.5 and 3.9 times, respectively, compared to the control sediment. PAC + MZ and LMB + MZ reduced the mobile P by 21% and 43%, respectively compared with the control sediment after 210 days of remediation. Bacteria richness and diversity in the PAC + MZ and LMB + MZ treatments had no obvious distinction when compared with the control treatment after 210 days of remediation but had a transient decrease in the LMB + MZ and recovered as it returned back to the same level found in control after 60 days. The results indicated that the control efficiency of nutrient fluxes in sediment might vary with types of inactivation agents and dosing methods and can be largely reduced under the influence of external loading and algal blooms.

Dynamics of phosphorus composition in suspended particulate matter from a turbid eutrophic shallow lake (Lake Chaohu, China): Implications for phosphorus cycling and management.

Particulate phosphorus (P) dominates the total P (TP) content in lacustrine water columns and is a primary source of dissolved P in turbid eutrophic shallow lakes. However, the spatiotemporal variability of P compositions in suspended particulate matter (SPM) remains poorly understood. In this study, we applied chemical extraction and solution 31P nuclear magnetic resonance (31P NMR) to assess the seasonal variations of SPM P compositions from a shallow turbid lake (Lake Chaohu, China) and its main river tributaries. P fractionation analysis indicated that mobile P (the sum of labile-P, iron-bound P, and organic P) accounted for >60% of the TP in SPM and showed high spatiotemporal variability throughout the year-long field investigation. In most seasons, riverine SPM (in urban rivers or rivers with high flow) contained a higher mobile P content than that of the lake and was therefore a dominant source of lacustrine mobile particulate P. Solution 31P NMR identified five types of P compounds in SPM, with highest contributions from orthophosphate. Organic P components and concentrations showed high seasonal variability, and elevated p values occurred during the summer algal bloom. The correlation analysis between organic and inorganic P fractions inferred the possible degradation of organic P into reactive inorganic components of SPM. Consequently, biological or chemical processes would further transform the labile inorganic P into soluble reactive phosphorus, which is readily utilized by lacustrine algae. Our results suggest that the labile forms of P in SPM were highly dynamic and significantly contributed to the eutrophication of the turbid shallow lake.

Immobilization of mobile and bioavailable phosphorus in sediments using lanthanum hydroxide and magnetite/lanthanum hydroxide composite as amendments.

This work prepared lanthanum hydroxide (La-OH) and magnetite/lanthanum hydroxide composite (Mag-La-OH), and then La-OH and Mag-La-OH were used as sediment amendments to immobilize phosphorus (P) in sediments. The immobilization efficiency of mobile P (MobP) and bioavailable P (BIO-P) in sediments by La-OH and Mag-La-OH was investigated. Results showed that the addition of La-OH into sediment resulted in the transformation of loosely adsorbed P (LA-P) and redox sensitive P (RS-P) to sodium hydroxide extractable P (OH-P) and hydrochloride extractable P (HP) in the sediment, while the addition of Mag-La-OH into sediment led to the transformation of LA-P, RS-P and HP to OH-P and residual P (RESP) in the sediment. Both La-OH and Mag-La-OH can effectively immobilize Mob-P (LA-P + RS-P) in sediments, but La-OH had a higher Mob-P immobilization capacity than Mag-La-OH. The amendment of sediments with La-OH and Mag-La-OH both can reduce the amounts of different types of BIO-P including water soluble P (WA-P), algal available P (AL-P) and Fe oxide-paper extractable P (FE-P) in the sediments, and La-OH had a higher BIO-P immobilization capacity than Mag-La-OH. The immobilization of Mob-P in sediments by Mag-La-OH could be described by the equation: W = 0.333 × (∆Mob-P)-14.4, where ∆Mob-P (mg/kg) is the amount of Mob-P bounded in sediments and W (%) is the Mag-La-OH dosage. The immobilization of FE-P in sediments by Mag-La-OH could be described by the equation: W = 0.380 × (∆FE-P) + 1.14, where ∆FE-P is the amount of FE-P bounded in sediments. Considering that Mag-La-OH can be retrieved from the water bodies under the action of external magnetization fields after its application, Mag-La-OH could have high potential to be used as an amendment for the immobilization of Mob-P and BIO-P in sediments.

Performance of physical and chemical methods in the co-reduction of internal phosphorus and nitrogen loading from the sediment of a black odorous river.

The continuous release of nutrients from sediment is a major barrier to the remediation of black odorous rivers. This study used a long-term laboratory incubation experiment to investigate the effectiveness of sediment dredging, intermittent aeration, and in situ inactivation with modified clays to reduce the internal loading of sediment from a seriously polluted river. The results indicated that intermittent aeration and in situ inactivation were effective in reducing the TN and NH4+ concentrations in the water column. However, sediment dredging did not consistently reduce the TN and NH4+ concentrations in the water column. In contrast, the three methods were all effective in controlling the TP and PO43- concentrations in the water column. Except for dredging, >30% of NH4+ and 40% of PO43- fluxes from sediment were reduced when compared with a control sample after 120 days of remediation. Dredging induced a significant release of NH4+ from sediment. Dredging and aeration made nearly no change to the amount of extractable nitrogen in the sediment. However, inactivation may increase sediment-extractable ammonium in deep sediment layers with time due to vertical transportation of clay by intensive bioturbation. Dredging is the most effective way to reduce surface mobile phosphorus over time while the transported clays can reduce a large percentage of the mobile phosphorus in deeper sediment. The relative abundance of Nitrospira in the surface sediment increased significantly with each remediation measure, creating favorable conditions for the reduction of the ammonium released from sediment. Altogether, the results of this study indicated that clay inactivation is the best method for controlling the internal loading of both phosphorus and nitrogen in seriously polluted river sediment.

Internal phosphorus loading from sediments causes seasonal nitrogen limitation for harmful algal blooms.

It is proposed that the internal loading of phosphorus (P) from sediments plays an important role in seasonal nitrogen (N) limitation for harmful algal blooms (HABs), although there is a lack of experimental evidence. In this study, an eutrophic bay from the large and shallow Lake Taihu was studied for investigating the contribution of internal P to N limitation over one-year field sampling (February 2016 to January 2017). A prebloom-bloom period was identified from February to August according to the increase in Chla concentration in the water column, during which the ratio of total N to total P (TN/TP) exponentially decreased with month from 43.4 to 7.4. High-resolution dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) analysis showed large variations in the vertical distribution of mobile P (SRP and DGT-labile P) in sediments, resulting in the SRP diffusion flux at the sediment-water interface ranging from -0.01 to 6.76mg/m2/d (minus sign denotes downward flux). Significant and linear correlations existed between SRP and soluble Fe(II) concentrations in pore water, reflecting that the spatial-temporal variation in mobile P was controlled by microbe-mediated Fe redox cycling. Mass estimation showed that the cumulative flux of SRP from sediments accounted for 54% of the increase in TP observed in the water column during the prebloom-bloom period. These findings are supported by the significantly negative correlation (p<0.01) observed between sediment SRP flux and water column TN/TP during the same period. Overall, these results provide solid evidence for the major role of internal P loading in causing N limitation during the prebloom-bloom period.

A simple model for predicting aluminum bound phosphorus formation and internal loading reduction in lakes after aluminum addition to lake sediment.

The conversion of mobile phosphorus (P) to aluminum bound P (Al-P) after addition of Al to over 300 sub-samples from 35 sediment cores collected from 20 lakes in the upper Midwest, United States was investigated in this study. Consistent relationships between mobile P reduction and Al-P formation were detected across a broad range of mobile sediment P contents (0.04-2.8 g P m(-2) cm(-1) or 0.083-2.8 mg P g(-1)DW) and lake types. The conversion of mobile P to Al-P was dependent on the initial mobile sediment P content and the amount of Al added to the sediment. An empirical model was then developed to predict the formation of Al-P based on the amount of Al added relative to the initial mass of mobile P in the sediment. The results were compared to sediment collected from an Al treated lake and good agreement was found between the model and in-situ changes to sediment P fractions caused by Al treatment. The model developed in this study, unlike previous models with extreme, singular endpoints, allows for a continuum of estimates for mobile P conversion to Al-P, along with efficiency of P binding by Al, as Al dose varies. Model results can be used in conjunction with mobile sediment P based predictions for internal P loading to calculate an Al dose required to meet internal phosphorus loading goals for lake management and restoration without the need for expensive, time consuming Al additions to sediment.