TP Concentrations Research Articles

Deep learning based soft sensor for microbial wastewater treatment efficiency prediction

With the swift industrial development, the pollution of water bodies by industrial effluent is becoming more widespread and serious. To achieve a more effective and intelligent control strategy to deal with the risk of standard-exceeding of water quality, it is crucial to develop a soft sensor to meet the demand of water quality prediction of IETP. Therefore, this paper proposes a CEEMD-ReliefF-CNNGA soft sensor for water quality prediction. The soft sensor firstly combines CEEMD and ReliefF algorithms to optimize the feature structures. CEEMD decomposes mode mixing between signals efficiently, and ReliefF intensifies the weights of signals with positive effects adaptively. Then, the soft sensor selects feature combinations as the input of CNNGA model. CNNGA calibrates the signal features most relevant for the predicted target by means of multi-layer iterative convolutions, embeds the pooling layers to prevent overfitting, and introduces Bidirection-GRU to adaptively capture the bidirectional dependencies of different temporal scales in the signal features. To avoid Bidirection-GRU holds the same attention on all signal features, an attention mechanism is introduced to strengthen time-dependent influences of key information, so as to improve the soft sensor performance effectively. To evaluate the soft sensor performance, the experiment adapts microbial wastewater data from IETP to forecast the concentrations of COD, NH3-N, TN, and TP in the real effluent. Results show the proposed soft sensor performs better than the other advanced models, and the soft sensor has a certain validity and stability in the actual prediction requirements of IETP.

Evolution Characteristics of Water Quality in Plain Reservoirs and Its Relationship with the Economic Development Response: A Case Study of Daheiting Reservoir in Northern China

In order to explore the evolution characteristics of TP and NH3-N in Daheiting reservoir since its construction, and their response to economic development, the monitoring data of water quality from 1992 to 2018 and statistical data of socio-economic development in Qianxi County were analyzed to examine the interannual evolution of TP and NH3-N and their correlation with upstream water quality, various economic indicators, and the scale of cage fish culture. The results show that, influenced by economic development, the evolution process of TP and NH3-N in Daheiting reservoir can be divided into three stages. In Stage I, the economic development of Qianxi County was slow, and the water quality of upstream water and the reservoir was good, with TP and NH3-N concentrations remaining relatively stable. In Stage II, Qianxi County entered a period of rapid economic development, and the TP and NH3-N in upstream water and Daheiting reservoir both increased significantly, with TP exceeding the standard limit. In Stage III, the intensity of external pollution control increased, and all cages were removed from the reservoir. Both TP and NH3-N showed a downward trend, but TP still exceeded the standard limit. Pearson correlation analysis and RDA analysis revealed that the levels of TP and NH3-N in Daheiting reservoir were mainly affected by the water quality of upstream water and the development of primary industry (including cage fish culture).

The Influence of Tomato and Pepper Processing Waste on Bread Quality

Worldwide, there is a significant amount of food waste, highlighting the need to reduce waste throughout the production process. This study investigated the impact of incorporating vegetable processing waste from tomatoes (TP) and bell peppers (PB) on dough characteristics and bread quality, with concentrations of TP and PB ranging from 3% to 12% based on flour weight. The addition of TP and PB influenced the farinograph characteristics, increasing water absorption, dough development, and softening while reducing stability time. However, the changes in bread quality, including baking yield, loss, volume, and crumb porosity, were not significant. The texture properties, such as hardness, chewiness, and cohesiveness of the crumb, showed no significant changes within the supplemented levels up to 9%. Additionally, the TP and PB had a significant impact on the color of the bread crumb, increasing redness and yellowness, particularly with PB. Fortification with TP and PB up to 9% resulted in baking characteristics comparable to 100% wheat bread. The addition of TP and PB changed nutrient content, particularly dietary fiber, without significantly altering the caloric value of the bread. However, semi-consumer sensory evaluation indicated a decrease in aroma and taste when PB exceeded 9%, and a similar effect on taste was indicated when TP exceeded 9%. In conclusion, TP and PB at supplementation levels up to 9% can enhance the nutritional profile of bread and maintain its baking quality.

Stimulating effects of whooper swans’ behaviors on nutrient releasing from the sediments caused by different human feeding intensities in the swan Lake, China

In many shallow water lakes of China, as the numbers of tourists observing waterflow increases, the amount of supplemental food provided to waterflow also increases. However, little attention has been paid to the role of waterfowl’s behavior perturbation in N and P nutrients releasing from the sediment. In this study, five feeding experiments were undertaken in the Swan Lake (Shandong Province, northern China) during the wintering season and a noticeable release of nutrients in all experiments was found by the disturbance of the swan behaviors. The release of TN and TP was through three stages including the non-release stage, the rapid release stage, and the stable release stage. Moreover, supplemental food also influenced the swan behavior changes and triggered the frequency of the swans’ grazing and aggression. The aggressive behaviors among the swans stirred nutrient (N & P) releasing from sediments and altered TN and TP concentrations in the water columns, indicating that the aggressive behaviors may be a significant factor in affecting the TN and TP releasing from the sediment. Human feeding intensity (HFI) suggested > 850 g of supplemental corn can be an optimal way to aid in avoiding foraging competition among the swans to control nutrient release by three levels of human feeding intensity assessment. Our findings demonstrate that under the swans’ optimal foraging need in natural versus artificial feeding scenarios, the swans acted as biological pumps to increase nutrient release. There is a need for a systematic and evidence-based feeding strategy for swans, with greater restrictions on the provision of small food items scattered by visitors. Our study provided novel insights into the release mechanism of N and P from bioturbation and could help to inform a whooper swan conservation strategy in coastal wetlands and nature reserves.

Field Baseflow Eluting SOM-Rich Sandy Soil to Exacerbate Non-Point Source Pollution of Lake Erhai, Southwest China

Excessive nutrient loss from farmland located on the west bank of Erhai Lake has resulted in significant non-point source pollution within the Lake Erhai basin. However, mitigating this issue proves challenging due to the intricate nature of soil properties and environmental factors. Here, during the rainy season in the Lake Erhai basin, we collected and analyzed soil profile samples, 35 topsoil (0–20 cm) samples, and more than 300 field baseflow samples. Our objective was to explore the influences of soil properties, field baseflow, and agricultural management measures on the spatiotemporal migration of nutrients. The results indicated that the concentration of soil organic matter (SOM) has a significant impact on the spatial patterns of nutrient distribution in sandy soil. Consequently, this leads to a substantial reduction in the potential for nutrient loss in the Lake Erhai basin. The vegetable-field baseflow exhibited the highest concentrations of nitrogen and phosphorus when subjected to high fertilization and flood irrigation. The concentrations of TN and TP in baseflow increase by a factor of 2 and 7.7, respectively, during rainfall compared to periods of no rainfall. Optimizing agricultural measures, such as replacing chemical fertilizers with organic fertilizers and modifying irrigation methods to enhance the organic content of sandy soil and minimize baseflow elution, has a beneficial impact on mitigating agricultural non-point source pollution in the Erhai Lake basin. The research results can enable us to have a more systematic understanding of the problem of non-point source pollution in the Erhai River Basin, and provide a theoretical basis for developing targeted agricultural non-point source pollution mitigation plans. Simultaneously, optimizing agricultural management models to strike a balance between agricultural economic development and ecological protection issues holds significant practical significance for managers.

Comparing Drivers of Spatial Variability in U.S. Lake and Stream Phosphorus Concentrations.

Decision makers need to know the drivers of surface water phosphorus (P) concentrations, the environmental factors that mediate P loading in freshwater systems, and where pollution sources and mediating factors are co-located to inform water quality restoration efforts. To provide this information, publicly available spatial data sets of P pollution sources and relevant environmental variables, like temperature, precipitation, and agricultural soil erodibility, were matched with >7,000 stream and lake total P observations throughout the conterminous United States. Using three statistical approaches, consisting of (a) correlation, (b) regression, and (c) machine learning techniques, we identified likely drivers of P concentrations. Surface water concentrations in streams were more strongly correlated and effectively predicted by annual fertilizer and manure input rates and agricultural legacy sources compared to that of lakes. This observation suggests that streams may be more immediately responsive to improvements in agricultural nutrient management. In contrast, lake concentrations, though still positively associated with agricultural input and surplus variables, may be more influenced by historic erosional inputs, internal lake recycling, and other environmental factors. Thus, lake TP concentrations may not be as immediately responsive as streams to improvements in phosphorus management. Both stream and lake P concentrations will potentially increase because of warming temperatures and forest recovering from past acidification, putting even further pressure on existing water quality restoration efforts to meet nutrient loading reduction targets. The identified spatial data sets and relationships elucidated in this effort can inform the placement and development of watershed restoration strategies to reduce excess P in aquatic systems.

Top-down and bottom-up control of plankton structure and dynamics in hypertrophic fishponds

We investigated the effects of strong top-down control by high fish stock on structure and seasonal dynamics of plankton in nine fishponds under conventional fishery management based on auxiliary feeding during two vegetation seasons. Mean concentrations of total nitrogen, phosphorus, and high densities of phytoplankton, bacteria, heterotrophic nanoflagellates, and ciliates indicated hypertrophic state of the fishponds, as well as a markedly reduced control of these microbial food web components by crustacean zooplankton. Mean seasonal densities of zooplankton varied within one order of magnitude for cladocerans, copepods, nauplii, and rotifers. Daphnia were found in most fishponds in densities up to 630 ind. l−1 (median: 53 ind. l−1). While TN and TP concentrations were high, dissolved inorganic N (median: 29 µg l−1) and reactive P (median: 11 µg l−1) indicated possible nutrient deficiency. The fish stock index (defined as the product of biomass and square root of densities) was used as a proxy for fish predation pressure. Multivariate analysis revealed that nutrients and high fish stocks (market carp, carp fry, and/or undesirable small planktivorous fishes) were the main driving forces shaping the fishpond plankton. The resulting trophic structure thus severely reduced the herbivorous zooplankton–fish link during a vegetation season.

Removal effect of typical pollutants from stormwater runoff in ecological ditches.

Ecological ditches are a typical ecological facility for controlling road stormwater runoff pollution; they mainly remove harmful pollutants from runoff through plant absorption, retention and sedimentation, ecological adsorption, and microbial action. In this paper, according to the transport form of rainwater in the ditches, the removal effects of two different types of ditches on nitrogen, phosphorus, heavy metals, and other pollutants were simulated under three conditions of rainfall, slow flow, and still water, respectively, and their operating characteristics were analyzed. The results showed that the removal rate of TN in the two ecological ditches under slow flow conditions showed a downward trend as a whole with the increase of hydraulic load, and the suitable hydraulic load for TN removal should be selected as 0.3 m3/(m2 day). Under the simulated rainfall conditions, the TN removal rates of no. 1 and no. 2 ditches were 26.1-37.2% and 24.9 ~ 52.5%, respectively, and the TP removal rates were 44.6 ~ 63.3% and 36.1 ~ 62.1%. After 19.4h and 22.1h in the static state, the TP concentration in no. 1 ditch and no. 2 ditch reached the surface V water standard, and the average removal rate of TP was 74.7% and 53.7%, respectively. This paper provides a reference for selecting suitable parameters and optimizing the operational performance of ecological ditches to reduce runoff pollutants more effectively.

How the land use/cover changes and environmental factors at different scales affect lake water quality in arid and semi-arid regions

The quantitative relationship between land use/cover change (LUCC) within basins, lake water environmental factors, and water quality has long been a popular research area. In this study, we investigated three typical basins (Ulansuhai Basin, Daihai Basin, and Dalinor Basin) in arid and semi-arid areas of China. The assessment was based on the China Land Cover Dataset (CLCD), which was used to calculate the land use dynamic degree index and Markov transfer matrix. Moreover, an econometric analysis model and a hybrid evolutionary algorithm (HEA) model were used to explore the quantitative relationship between LUCC and environmental factors on the lake water quality. The results showed that the LUCC of the three lake basins was dominated by cultivated land and grassland over the past 20 years. In all of the basins, grassland and water area were converted into cultivated land, water area decreased to varying degrees, and impervious surface area increased continuously. Moreover, the concentration of TN and TP were generally proportional to chemical oxygen demand concentration (COD), biochemical oxygen demand concentration (BOD5), and dissolved oxygen concentration (DO), but inversely proportional to water depth and transparency; the relationship between Nutrient concentration and pH was usually related to the ecological threshold. On the basin scale, the grassland and forestland played positive roles in improving water quality, while cultivated land and impervious surface were the main factors contributing to water pollution. Overall, this study provides a scientific theoretical basis for the rational utilization of land resources, improvement of lake water quality, and ecological protection of typical lake basins in arid and semi-arid regions.

Mesocosm experimental study on sustainable riparian restoration using sediment-modified planting eco-concrete

The continued deterioration of riparian ecosystems is a worldwide concern, which can lead to soil erosion, plant degradation, biodiversity loss, and water quality decline. Here, taking into account waste resource utilization and eco-environmental friendliness, the sediment-modified planting eco-concrete with both H. verticillata and T. orientalis (SEC-H&T) was prepared and explored for the first time to achieve sustainable riparian restoration. Concrete mechanical characterizations showed that the compressive strength and porosity of SEC with 30% sediment content could reach up to 15.8 MPa and 21.25%, respectively. The mechanical properties and the sediment utilization levels of SEC were appropriately balanced, and potentially toxic element leaching results verified the environmental safety of eco-concrete modified with dredged sediments. Plant physiological parameters of both aquatic plants (biomass, chlorophyll, protein and starch) were observed to reach the normal levels in SEC during the 30-day culture period, and T. orientalis seemed better adapted to SEC environment than H. verticillate. Importantly, compared to SEC-H and SEC-T, SEC-H&T could effectively reduce the concentrations of COD, TN and TP by 58.59%, 74.00% and 79.98% in water, respectively. Notably, water purification mechanisms by SEC-H&T were further elucidated from the perspective of microbial community responses. Shannon index of bacterial diversity and proliferation of specific populations dominating nutrient transformation (such as Bacillus and Nitrospira) was increased under the synergy of SEC and aquatic plants. Correspondingly, functional genes involved in nitrogen and phosphorus transformation (such as nosZ and phoU) were also enriched. Our study can not only showcase an effective and flexible approach to recycle dredged sediments into eco-concrete with low environment impacts, but also provide a promising alternative for sustainable riparian restoration.

Short-term climate change influence on surface water quality impacts from agricultural activities.

Climate change is a global phenomenon that directly affects agriculture by altering crop yield, nutritional quality, pests, and plant diseases. The North Aegean Basin located in Turkey has considerable agricultural importance due to its fertile soils. Agricultural activities have increased significantly and uncontrollably in the last decade, resulting in dramatic changes in nitrate and phosphorus levels in surface water within the watershed. Changes in climatic conditions have the potential to impact the quantity and quality of water resources. Best management practices (BMPs) are presently utilized as a planning tool to enhance the quality of water resources. To develop policies in this regard, it is necessary to evaluate the effectiveness of BMPs. To this end, this study aims to investigate the potential effect of climate change on the surface water quality of the North Aegean Basin. For the period between 2010 and 2030, global climate data retrieved from Concentration Pathway (RCP) scenarios 4.5 and 8.5 and regionally downscaled were used to feed the Soil and Water Assessment Tool (SWAT) model. The various potential BMP scenarios were developed and simulated in the hydrological model by considering the effects of climate change. The RCP4.5 scenario reduced the precipitation by 15.11%, while the RCP8.5 scenario reduced the precipitation by 10.97%. Decreased precipitation also affected the runoff and the nutrient loads and concentrations. As a result of the RCP4.5 simulation, TP and TN concentrations increased by 24.42% and 58.45%, respectively, in the IST_KEN014 station. Improvements were observed in TN and TP concentrations with the effect of applied BMP simulations. Also, the results revealed that the applied BMP scenarios may contribute to considerable reductions in nutrient loads. Considering the RCP4.5 scenario, BMPs reduced TN loads in the basin by 2.42-10.97%, while reducing TP loads by around 3.60-16.81%. Considering the RCP8.5 scenario, the BMPs reduced the TN loads in the basin between 2.21 and 10.04%, while they reduced the TP loads between 3.57 and 16.67%.

Impacts of dyke systems on the distribution of benthic invertebrate communities and physicochemical characteristics of surface water in An Giang, Vietnam.

The dyke system plays a vital role in cultivating rice intensively in the Vietnamese Mekong Delta, which protects rice paddy fields from annual floods. This study aimed to examine whether the full-dyke system (FD, which restricts water exchange for a long time) can cause degradation of surface water quality and reduction in benthic invertebrate biodiversity. The surface water quality and benthic invertebrate community were compared between the FD and semi-dyke systems (SD, which permits water exchange during flooding season) using a large number of samples collected seasonally in 2019. The results showed that the surface water quality within the FD system had significantly higher concentrations of TSS, COD, BOD5, N-NO3-, N-TKN, P-PO43-, and TP than compared to the SD system (p < 0.05), indicating greater pollution levels. The benthic invertebrate community was less diverse in the FD system than in the SD system. Only 17 species (belonging to 4 families) were detected in the FD system, and 30 species (belonging to 5 families) were detected in the SD system. The benthic invertebrate community structure changes and biodiversity loss were associated with degraded water quality. The P-PO43- and TP parameters were negatively correlated with the number of species, density, and biomass in the FD system and with the Shannon-Wiener (H') index in the SD system. In conclusion, the FD system has been degrading water quality and causing biodiversity loss.

Removal and Adsorption Mechanisms of Phosphorus, Cd and Pb from Wastewater Conferred by Landfill Leachate Sludge-Derived Biochar

There is a high treatment cost and secondary pollution to the environment due to the high organic content and complex composition in landfill leachate sludge in refuse incineration power plants. Landfill leachate sludge-derived biochar (LLSDB) was prepared via pyrolysis in order to realize its resource utilization and remove pollutants from wastewater. The study focused on the removal of nutrients phosphorus and heavy metals (Cd(II) and Pb(II)) from wastewater through the adsorption process using LLSDB. The investigation also looked into the kinetics and thermodynamics of the adsorption process. It was found that the Freundlich–Temkin–Langmuir model was the best model for describing the initial concentration of total phosphorus, (TP) 0–1.0, 1.0–20, and 20–120 mg/L, respectively, while the Freundlich–Langmuir model was the best model for Cd(II) 100–500 mg/L, Pb(II) 500–5000 mg/L, respectively. Additionally, while the exothermic entropy reduction process for TP (˂1.0 mg/L) was spontaneous, the endothermic entropy increment processes for TP (≥1.0 mg/L), Pb(II) and Cd(II) in wastewater increased with the adsorption temperature. It was inferred for the adsorption mechanism of LLSDB that the adsorption of low concentrations of TP, Cd(II) and Pb(II) from wastewater was mainly physical adsorption, following a linear distribution, while that of high concentrations was mainly chemical adsorption because of a series of chemical reactions; TP, Cd(II) and Pb(II) from wastewater were nicely adsorbed and removed by LLSDB600, which was an incredibly superior strategy for controlling waste with waste.

Variations in the morphological phosphorus in a full‐scale A2O + MBR process with heavy chemical P removal addition dosing

AbstractThe removal of biological phosphorus (P) removal along with chemical P removal additions is significantly important role in removing P at full‐scale wastewater treatment plants (WWTPs). Few research groups have recently reported the use of P forms in these WWTPs. The current study mainly presents the varied forms of morphological phosphorus and the fate of chemical P removal agents in a full‐scale WWTP that has adopted the A2O + MBR process. With time, the TP concentration in the liquid phase and the solid phase reaches the minimum (0.27 mg/L) and maximum values (1.75 mg/g), respectively. At this point, the TP concentration at the end of the aerobic and membrane pool becomes nearly constant. This indicates the complete removal of effluent TP from in the system. The heavy chemical P removal and addition dosing result in Al–P being the predominant P form in the solid phase. The fate of the chemical P removal and agents was determined by investigating the valences of the surface elements in freeze‐dried MLSS at the membrane pool.

Controlled mechanism and removal performance of phosphorus in black and odorous water bodies by Fe-based layered double hydroxides

The effective approach for controlling internal phosphorus loading remains a longstanding challenge to the maintenance of remediated black and odorous water bodies. Here, three Fe-based LDHs materials were developed for alleviating the phosphorus pollution in black and odorous water through synergistic functions of phosphate adsorption, controlled release of phosphorus, and microbial metabolism. The mechanism of phosphate removal in overlying water is mainly specific electrostatic attraction and coordination. After the addition of Fe-based LDHs, the water quality indexes of black and odorous water bodies were significantly improved, including TP concentration (from 0.8 to 0.2 mg/L), the dissolved oxygen content (from 0.1 to 3.0 mg/L), COD, turbidity (from 34 to 18 FTU), and redox potential. Moreover, the morphology and physicochemical properties of sediments were regulated by Fe-based LDHs. Fluffier and smaller sediments particles due to the destruction of extracellular polymeric substances structure, which was beneficial to the release of endogenous phosphorus. Furthermore, the results of microbial community structure analysis illustrated that Proteobacteria and Dechloromonas played the most important role in phosphorus elimination in Fe-based LDHs system. That is, based on the biocompatibility of Fe-based LDHs, which act as a medium of the electron transfer in the microbial metabolism, combining with microorganisms for the synergistic remediation of black and odorous water bodies. Our study emphasizes the feasibility of Fe-based LDHs materials for the remediation of internal phosphorus loads in black and odorous water bodies, towards sustainable control.

The interaction of tide and river flow on water quality in Hai Phong coastal waters (Lach Huyen - Do Son) drawn from field observation

This paper presents the results of a study on the impacts of the interaction of tide and river flow on water quality at the Hai Phong coastal water, outside the Nam Trieu estuary and Lach Huyen, drawn from field observation from October 14, 2022, to October 17, 2022. During the field observation, the dissolved oxygen concentration was measured, and water samples were taken at the surface, mid-depth, and bottom of 8 observational points at 1:00, 7:00, 13:00, and 19:00 h. Five sewage wastewater samples at Do Son coast and 6 coastal and river water samples were also taken. The collected seawater samples were laboratory analyzed to determine the concentration of BOD5, COD, TN, and TP. Additionally, the concentration of ions NH4+, NO2-, NO3-, and PO43- are determined by analyzing collected coastal, river, and sewage water samples and seawater samples at mid-depth at all observational points in a laboratory. It was found that the concentration of essential nutrients and other environmental components in wastewater samples generally does not exceed those specified in Vietnam regulations. The discharge of wastewater during the field observation was minimal. Thus it could be expected that the wastewater would not have a notable influence on seawater quality in the marine study area. Consequently, the study area’s primary source of nutrient pollutants was rivers. Time variation of the concentration of environmental components reveals that the nutrient concentration in the marine study area strongly influences by the interaction of the tide and river flow. The concentration of dissolved oxygen and major nutrient components in seawater at 8 points was within the limit of Vietnam standard for coastal water. However, significant nutrient concentration exceeds thresholds for eutrophication.

No lukewarm diatom communities—the response of freshwater benthic diatoms to phosphorus in streams as basis for a new phosphorus diatom index (PDISE)

In the present study, we developed a new Swedish phosphorus diatom index (PDISE) to improve the poor fit of existing indices to match the needs of water managers to detect and mitigate eutrophication. We took advantage of a large amount of data (820 Swedish stream sites) collected in recent years. During our work, we found an unexpected bimodal response of the diatom assemblages to phosphorus. The taxa clustered either into an assemblage with a low or with a high site-specific averaged TP optimum (a calculated value comprised of the diatom taxa-specific optima). We could not find a characteristic diatom assemblage for sites with intermediate site-specific averaged TP optima. To our knowledge, this bimodal community response has not been shown earlier. The PDISE correlated more strongly than the currently used TDI to changes in TP concentrations. Thus, the PDISE should replace the TDI in the Swedish standard method. The modeled TP optima (expressed as categories) were different compared to the TDI for most of the taxa included in the index, indicating that the realized niche for these morphotaxa was different between Sweden and the UK where the TDI was developed originally. With a r2 of 0.68, the correlation of the PDISE to TP is among the highest reported for other diatom nutrient indices globally; thus, we believe that it might be worth to test it for other bioregions with similar geography and climate.

Determining the main contributing factors to nutrient concentration in rivers in arid northwest China using partial least squares structural equation modeling

Understanding the main driving factors of oasis river nutrients in arid areas is important to identify the sources of water pollution and protect water resources. Twenty-seven sub-watersheds were selected in the lower oasis irrigated agricultural reaches of the Kaidu River watershed in arid Northwest China, divided into the site, riparian, and catchment buffer zones. Data on four sets of explanatory variables (topographic, soil, meteorological elements, and land use types) were collected. The relationships between explanatory variables and response variables (total phosphorus, TP and total nitrogen, TN) were analyzed by redundancy analysis (RDA). Partial least squares structural equation modeling (PLS-SEM) was used to quantify the relationship between explanatory as well as response variables and fit the path relationship among factors. The results showed that there were significant differences in the TP and TN concentrations at each sampling point. The catchment buffer exhibited the best explanatory power of the relationship between explanatory and response variables based on PLS-SEM. The effects of various land use types, meteorological elements (ME), soil, and topography in the catchment buffer were responsible for 54.3% of TP changes and for 68.5% of TN changes. Land use types, ME and soil were the main factors driving TP and TN changes, accounting for 95.56% and 94.84% of the total effects, respectively. The study provides a reference for river nutrients management in arid oases with irrigated agriculture and a scientific and targeted basis to mitigate water pollution and eutrophication of rivers in arid lands.

Assessment of Nutrient Removal in Surface Flow Constructed Wetland Treating Secondary Effluent with Low Organic, Nitrogen and Phosphorus Loads

Nutrient loads must be reduced to safe levels to protect sensitive receiving environments. This work presents the results of a 15-month monitoring program of a surface flow-constructed wetland (SFCW) in Queensland, Australia. The SFCW reduced the influent TN concentration by 54% and was able to retain 80% of the TN load, mainly due to the efficient removal of NOx and ammonium (92–100%). TP removal was negative due to the unaccounted loads from wildlife activity. During occasions of high loads, the wetland reduced TP concentrations by 77%. The hydraulic loading rate (HLR) correlated poorly to the TSS and TVS loads (r &lt; 0.55); however, when adjusted to account for precipitation and evapotranspiration, stronger correlations (r &gt; 0.78) were revealed. Strong correlations were revealed between adjusted HLR and TP (r = 0.87) and TN (r = 0.93). TN removal was highly governed by the inflow of TN concentration. TN removal could be predicted from the inflow concentration using the first-order plug-flow model (R2 = 0.72). The model suggests that the system has an irreducible threshold TN load of 0.115 kg-N per m2 per month. This work shows that SFCW can be effective in managing the nutrient loads even in systems that receive low organic and nutrient loads.

Lowland artificial watersheds with unique nutrient transport: Response to natural and anthropogenic drivers

Excess nitrogen (N) and phosphorus (P) from watersheds is a key factor causing eutrophication and water quality deterioration in downstream lakes/rivers. However, tracking N & P loss and transport at a watershed scale is challenging especially in lowland artificial watersheds (polders) with complex hydrological processes. To address this challenge, this study selected 171 polders in lower reach of Yangtze River in China as the study area, and investigated the response of N & P loss to both natural and anthropogenic drivers using two process-based models (PDP & NDP) specifically developed for polders. Our modelling practices revealed that these polders had a high N & P loss intensity of 38.37 and 1.75 kg/ha/yr, respectively. Rainy-season precipitation and TN & TP concentrations in connected-rivers were characterized as sensitive factors determining polder N & P loss with a threshold value of 950 mm/yr, 0.2 and 0.02 mg/L, respectively. Compared with annual precipitation, rainy-season precipitation more highly (P < 0.001, R2 >0.8) determined polder N & P loss, with a loss-intensity increase of 6.05 and 0.28 kg/ha/yr for 100 mm increase of rainy-season precipitation. Polder N & P loss was highly related (P < 0.001) to the area of farmland and surface water within these polders. This study can potentially improve our understanding of N & P cycling for lowland polders, and can thus support N & P control in water management practices.