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To estimate a watershed's response to climate change, it is crucial to understand how human activities and climatic extremes have interacted over time. Over the last century, the Zarivar Lake watershed, Iran, has been subjected to various anthropogenic activates, including deforestation and inappropriate land-management practices alongside the implementation of conservation measures like check dams. To understand the effects of these changes on the magnitude of sediment, organic carbon (OC), and phosphorus supplies in a small sub-watershed connected to the lake over the last century, a lake sediment core was dated using 210Pbex and 137Cs as geochronometers. The average mass accumulation rate (MAR), organic carbon accumulation rates (OCAR), and particulate phosphorus accumulation rates (PPAR) of the sediment core were determined to be 6498 ± 2475, 205 ± 85, and 8.9 ± 3.3 g m-2 year-1, respectively. Between the late 1970s and early 1980s, accumulation rates were significantly higher than their averages at 7940 ± 3120, 220 ± 60, and 12.0 ± 2.8 g m-2 year-1 respectively. During this period, the watershed underwent extensive deforestation (12%) on steep slopes, coinciding with higher mean annual precipitations (more than double). Conversely, after 2009, when check dams were installed in the sub-watershed, the sediment load to the lake became negligible. The results of this research indicate that anthropogenic activities had a pronounced effect on MAR, OCAR, and PPAR, causing them to fluctuate from negligible amounts to values twice the averages over the last century, amplified by climatic factors. These results imply that implementing climate-smart watershed management strategies, such as constructing additional check dams and terraces, reinforcing restrictions on deforestation, and minimum tillage practices, can facilitate protection of lacustrine ecosystems under accelerating climate change conditions.

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Phosphorus (P) is an essential biogenic element in ecosystems; but excessive or insufficient P in coastal waters caused by human activities has led to serious ecological issues. However, the understanding of the dynamic processes of different P forms in high turbidity estuaries/bays, as well as their impact on eutrophication and coastal algal blooms, is still relatively limited. To address this issue, we analyzed P dynamics and their impact on eutrophication in Hangzhou Bay (HZB), which is typical of eutrophic and turbid bay worldwide. The concentration of particulate P (PTP) was 3-5 times higher than that of dissolved inorganic phosphorus (DIP). Seasonal sediment resuspension led to the accumulation of suspended particulate matter (SPM) and PTP with regional variation, both maintaining DIP concentrations above 1 µmol/L within the bay. Furthermore, 3000 tons of bioavailable P were retained in the fine-grained SPM, with the potential for outward transport, fueling subsequent harmful algal blooms. A comparative analysis of global coastal waters highlighted that different turbidity levels significantly affect P cycling. Therefore, understanding the relationship between SPM and P in highly turbid waters is crucial for effective management of eutrophication.

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The necessity on controlling internal P pollution has been widely reported for lake restoration; thus far, cutting the migrations of soluble P from sediment to overlying water, especially under anoxic condition, is the main target of the internal P pollution control to achieve favorable ecological responses in lake. Here, according to the types of P directly available by phytoplankton, phytoplankton-available suspended particulate P (SPP) pollution, which mainly occurs under aerobic condition and due to sediment resuspension and soluble P adsorption by suspended particle, is found to be the other kind of internal P pollution. The SPP has long been a key index for environmental quality assessment, which could be indirectly reflected by the developed various methods for phytoplankton-available P pool analysis; also, the P has been demonstrated to be a major cause of phytoplankton breeding, typically in shallow lakes. Importantly, compared to the soluble P, SPP pollution clearly has more complicated loading pathways and P activation mechanisms and involves in different fractions of P, even part of which are with relatively high stability in sediment and suspended particle, leading to the potential control measures for the pollution being more complex. Considering the potential differences of internal P pollution among various lakes, this study is therefore calling for more research to focus on regulating phytoplankton-available SPP pollution. Recommendations are also offered to bridge knowledge gap of the regulation to design proper measures for lake restoration.

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The classical lake internal phosphorus (P) pollution control using P-inactivating materials is typically carried out by reducing the release of soluble P from sediments to overlying water; however, particulate P loading through sediment resuspension could also cause internal P pollution for algae breeding. Therefore, based on lanthanum modified bentonite clay (Phoslock®) and drinking water treatment residues (DWTR), the effect of P inactivating materials on sediment resuspension and settlement were comprehensively investigated to assess the variations in particulate P pollution from sediment. Results showed that both materials could effectively control soluble P pollution from sediment, while both had limited effect on the supplement of particulate P to overlying water. The reason may be that hydrodynamic disturbance was the key factor regulating sediment resuspension and settlement. The disturbance induced the resuspension of different sized sediments, especially <8 µm fractions, while increasing disturbing intensities promoted resuspension of relatively larger sized sediments (e.g., <63 µm). Further analysis suggested that after resuspension and settlement, the efficiencies of reducing bioavailable P by Phoslock® in relatively large sized sediment fraction (e.g., <63 µm) were substantially less than those in relatively small sized sediment (<8 µm). Although the reducing efficacies of DWTR had limited changes in different sized sediments, the remaining bioavailable P were clearly higher in smaller sized sediments with DWTR. The different performances on bioavailable P reduction mainly resulted from the distributions of materials and original P in different sized sediments. These findings indicated the potential supplement of particulate P for algal growth during resuspension and settlement of sediments amended by P inactivating materials. Overall, understanding the sediment P bioavailability and hydraulic properties at different sizes and the lake hydrodynamic conditions is essential to develop appropriate methods to control lake internal P pollution.

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Shallow lakes have a tendency to settle into turbid or clear-water states, the latter having lower concentrations of total phosphorus (TP). However, how P-cycling is affected by and perhaps contributes to maintaining the different states is not well understood, in part because quantifying the processes involved by traditional methods is difficult. To elucidate these processes, we conducted experiments using 32P-PO4 as a tracer on samples collected from the unrestored, unvegetated sections of Huizhou West Lake where turbid water prevails as well as the restored, clear-water, macrophyte-rich waters of the lake. We measured PO4 uptake rates, 32P-PO4 accumulation by various plankton size-fractions (picoplankton (0.2-2 µm), nanoplankton (2-20 µm) and microplankton (>20 µm)) as well as release rates of 32P-PO4 by labelled plankton. Our results revealed slow PO4 uptake in the turbid state due to low PO4 concentration, slow recycling of the high particulate P, and high levels of particulate 32P which may allow for continuous high growth and biomass of phytoplankton. In contrast, in the clear water state, the uptake of PO4 was rapid due to a higher PO4 concentration, the recycling rates of particulate 32P were high and the levels of particulate 32P were low, potentially constraining the phytoplankton growth. A greater proportion of particulate 32P was in the microplankton fraction in clear waters, suggesting that grazing by microplankton may play an important role in the rapid P recycling in clear-waters. Our results provide some evidence for a reinforcement of the turbid conditions (low recycling rate) when the lake is in a turbid state and vice versa when in the clear water state. The results add new knowledge to the understanding of P cycling in shallow lakes and illustrate the utility of using P-kinetics in contrasting states in plankton communities.

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As a promising soil amendment, biochar has demonstrated its potential for influencing soil nutrient transformations. The effects of biochar on soil phosphorus (P) transformations have received much less attention than its effects on carbon cycling. A review of the literature reveals that biochar applications to soils may have notable effects on the abundance, speciation, availability, and leaching loss of soil P. However, a comprehensive and systematic understanding of the biochar-induced environmental behavior of soil P has not been obtained so far. Therefore, in this review, we analyzed and identified the known and potential mechanisms through which biochar affects P behavior in soils: (1) biochar as a source of P provides soluble and exchangeable P to soil; (2) biochar enhances the availability of endogenic soil P by influencing P-related complexation and metabolism effects; and (3) biochar affects P leaching losses directly or indirectly by adsorbing P, improving P retention by soil, and facilitating P assimilation by plants. By presenting a broad and detailed illustration of P behaviors in biochar-amended soils, this paper suggests that the application of biochar to soils will help enlarge soil P pools, increase soil P availability, and decrease P leaching losses from soil. Additional studies are needed to further elucidate the long-term effects of biochar addition on soil P transformations, explore how biochar-derived dissolved organic matter (BDOM) affects the mobility and availability of soil mineral-associated P, and examine the transport of particulate P in biochar-amended soils.

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Subsurface storm flow of phosphorus (P), including particulate P, has been recently discussed as an important P transport path in contrast to typical surface runoff events. However, P speciation, and P concentration during storm events has not been extensively investigated; therefore, its contribution to the water quality is not clearly understood. In this study, the physicochemical properties of particulate P in tile water samples during a high flow event were investigated in Midwestern agricultural lands using wet chemical methods, 31P Nuclear Magnetic Resonance spectroscopy and P K-edge X-ray absorptions near edge structure spectroscopy. In slightly alkaline pH tile water, total P was ranging from ∼0.06 to 0.22 mg L-1, which is significantly greater than dissolved reactive P (DRP) (∼0.02-0.08 mg L-1). The tile water contains P enriched particulate matters (∼200-660 mg L-1). Total P in the colloidal fraction was from 1013 to 2270 mg kg-1. Phosphate and organic P species, especially monoesters, are sorbed in soil colloids like calcite, and iron oxides, and colloids are effective carriers of P in the subsurface transport process during storm events. The results of this study show that storm events can accelerate the subsurface transport of P with soil particles in addition to DRP.

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Different phosphorus fractions, including total dissolved P (TDP), dissolved inorganic P (DIP), total particulate P (TPP), and particulate inorganic P (PIP), were analyzed in the Danshuei River Estuary (DRE), northern Taiwan to study the P partitioning within the estuary. Relatively higher concentrations of TDP (4.3-12.4 µM) and TPP (2.3-8.7 µM) were generally found in the upper estuary, salinity <5 region, during the four surveys. The DIP concentration generally dominated the total P pool (TDP + TPP) within the estuary. However, dissolved organic P (DOP) became the important fraction in the salinity >25 region, probably attributed to phytoplankton production because the higher DOP concentration was generally accompanied with a higher Chl. a concentration. The TPP concentrations generally correlated well with the total particulate Fe and Mn concentrations, suggesting that particulate Fe and Mn played crucial roles influencing the P distribution within the DRE.

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PURPOSE: Phosphorus (P) lost from agricultural land by erosion, runoff, throughflow and leaching is of major concern for water resource managers worldwide. Previous study on soils from cropping land of southwest Western Australia suggested P loss as dissolved unreactive P (DURP) via leaching, but the implications for processes and rates of P transport in soils are not known. MATERIAL AND METHODS: Two contrasting soil profiles (sand and loam) from cropping land of southwest Western Australia were exposed to artificial rain in packed boxes and field runoff plots to examine P forms and fluxes in runoff, throughflow, leachate and soil solution after three P rates of application (equivalent to 0, 20 and 40kg P/ha). Solutions were analyzed for total P (TP), dissolved reactive P (DRP) and total dissolved P (TDP). Particulate P (PP) and DURP were calculated by subtracting DRP from TP and TDP respectively. RESULT AND DISCUSSION: In the sand profile, about 90% or more of P losses via runoff and leachate were in DURP and PP forms, whereas DRP was a minor contributor. Phosphorus load in soil solution, throughflow, leachate and run-off increased with increasing P rate. The relatively higher affinity of soil for DRP compared to DURP might cause the latter to be more mobile through profile in association with colloidal compounds <0.2µm. Higher PP concentration for loam soil via throughflow is exacerbated by dispersed clay, which could be an additional process influencing P mobility in loam and duplex soils. CONCLUSION: The DRP played a limited role in P transport compared to PP and DURP that both appeared to be associated with soil particles or soil colloids in runoff, throughflow, leachate and soil solution. Further characterization of the latter forms of P is needed so that management practices can be developed to minimize P losses.

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We tested the hypothesis that in shallow, eutrophic Lake Kasumigaura, the concentration of particulate phosphorus (PP) is controlled by biogenic P (P in living or dead phytoplankton and bacterial cells), rather than by resuspension of inorganic P in sediment. Increases in wind velocity and turbidity were associated with bottom shear stress exceeding the critical value for the lake (τc=0.15Nm(-2)); this increased turbidity was due to sediment resuspension. However, concentrations of PP; HCl-extractable, reactive P in PP (P-rP); and HCl-extractable, non-reactive P in PP (P-nrP) were not correlated with wind velocity (PP vs. wind velocity: r=0.40, p>0.05). Rather, the P-nrP concentration accounted for approximately 79% of PP, and the concentrations of PP, P-rP, and P-nrP were correlated with the particulate organic carbon (POC) concentration (POC vs. PP: r=0.90, p<0.01; POC vs. P-rP: r=0.82, p<0.01; POC vs. P-nrP: r=0.86, p<0.01). In our (31)P nuclear magnetic resonance spectroscopy results, mononucleotides accounted for the largest proportion among the detected P compound classes. In addition, concentrations of mononucleotides, orthophosphate, and pyrophosphate were significantly higher in samples with high POC concentrations, whereas the DNA-P concentration was not. These results suggest that biogenic P affects PP concentrations more strongly than does sediment resuspension, and the production of biogenic P creates a pool of mononucleotides, a class of easily degradable P, even in shallow, eutrophic Lake Kasumigaura.

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