Total Phosphorus Fluxes Research Articles

Changes in chlorophyll a and its response to nitrogen and phosphorus characteristics over the past three decades in Poyang Lake, China

AbstractIn this study, we explore the relationship between changes in chlorophyll a (Chl a) content, total nitrogen (TN) and total phosphorus (TP) characteristics from 1989 to 2018 in Poyang Lake, China, by applying Landsat Thematic Mapper/Enhanced Thematic Mapper (TM/ETM) image data in combination with in situ monitoring data. Results showed that the average Chl a content in water over this 30‐year period was 5.77 μg/L. Although the water quality status of the lake was generally healthy, proportional Chl a content >10 μg/L (E10) has gradually increased, and the water quality in some areas of the lake has subsequently deteriorated over the past 30 years. Additionally, E10 was significantly positively correlated to the TN/TP. Changes in Chl a content were significantly positively correlated to the ratio of TN flux to TP flux from tributaries into the lake, but negatively correlated to TP flux. Results indicated that Lake can be categorized as phosphorus‐sufficient and nitrogen limited.

Effects of particulate fractions on critical slope and critical rainfall intensity for runoff phosphorus from bare loessial soil

Slope and rainfall intensity are important factors affecting runoff phosphorus (P), but the dynamic mechanism of their coupled influence on P fractions in loessial bare sloping lands is not completely understood. The critical slope and critical rainfall intensity are thresholds associated with significant changes in runoff, erosion, and/or nutrient loss. In this study, 30 rainfall events (45, 60, 75, 90, 105 and 120 mm/h; 5°, 10°, 15°, 20° and 25°) were simulated to estimate the contribution of particulate P (PP) and soluble P (SP) fractions to P loss from bare loessial soils and identify the critical slope and critical rainfall intensity for different P forms and TP fluxes. The results indicate that: (i) total phosphorus (TP) and PP loss concentrations are significantly correlated to sediment yield and slope gradient, although there were close relationships between the average TP loss concentration and rainfall intensity at slopes of 20° and 25°; (ii) P in runoff from bare loessial soil consists almost entirely of the reactive PP form (96.6%), regardless of rainfall intensity and slope. The average PP fraction for different rainfall intensities increases with increasing slope, from 94.6% at a 5° slope to 98.0% at a 25° slope; and (iii) PP and TP have the same critical slope and critical rainfall intensity for bare loessial soil because of the dominance of PP in runoff P. The critical slope for the sharp increases in PP and TP was found to be in the range of 15–20° because the average losses at 20–25° increased about 1.67 times compared to 5–15°, and the critical rainfall intensity for significant increases in PP and TP was found to be in the range of 90–105 mm/h. The hydrological pathways transporting the various P fractions under storms may help to provide new insights needed to guide sloping farmland management in rainfed land agroecosystems of loess hilly regions.

Variation of net anthropogenic phosphorus inputs (NAPI) and riverine phosphorus fluxes in seven major river basins in China

The riverine phosphorus (P) import resulting from human activities is always a worldwide concern for environmental management due to the effect of eutrophication. In this study, we made modification of the NAPI method to make the results closer to the actual situation. We collected the data of seven major outflow rivers in China to have a comprehensive understanding of P export and P inputs and build the quantitative relationship between them. We estimated the net anthropogenic phosphorus inputs (NAPI), including fertilizer P (Pfert), net food and feed import P and non-food P using by human (Pim+nf), in seven major river basins in China and the corresponding riverine total phosphorus (TP) fluxes. The relationship between NAPI and riverine TP flux was also explored. NAPI in seven river basins presented an obvious uneven distribution. Huaihe River basin showed the highest NAPI of 4005.09 kg P km−2 yr−1 due to its highest intensities of human-activities, and the lowest NAPI was observed in Songhua River basin as 334.36 kg P km−2 yr−1. Pim+nf occupied a larger proportion of NAPI in the Pearl River and Liaohe River basins (> 65%), while Pfert contributed more to NAPI in the other basins (nearly 60%) with an exception of the Yangtze River basin (where Pim+nf and Pfert approximately contributed the same). Different contributions of NAPI components were mainly attributed to the different land uses. The total TP flux of all the seven rivers was 117.10 × 103 t P yr−1, with the highest flux in the Yangtze River (77.42 × 103 t P yr−1), contributed 72.88% to the total TP fluxes in China. Change in riverine TP flux could be well described by NAPI, river discharge, and percentage of lake area in the basin and this provided an effective way to predict TP fluxes in rivers.

Characteristics of effluents from trout farms and their impact on water quality and benthic algal assemblages of the receiving stream

In this study, characteristics of effluents from three flow-through rainbow trout farms in Turkey and their impact on water quality and epilithic algal communities of the receiving stream were investigated. Water samples were taken monthly from both inlets and outlets of three fish farms, while both water and epilithic algae samples were collected from two stations (upstream and downstream) in the stream. A significant increase from inlets to outlets was observed for chemical oxygen demand (COD), soluble reactive phosphorus (SRP), total suspended solids (TSS), NH4–N and total phosphorus (TP) (p < 0.05) due to no effluent treatment processes and high FCR at the fish farms. The daily average total nitrogen (TN) and TP fluxes of the fish farms predicted with the nutritional method were found close to those measured with the hydrological method. Although there were significant increases in COD, TSS, NH4–N, TN, NO3–N, NO2–N, TP and SRP concentrations at the downstream station compared to the upstream station of the receiving stream (p < 0.05), water quality of the downstream station remained in Class I in terms of examined parameters. Trophic Diatomic Index and Biological Diatom Index values indicated that the upstream station had a better water quality than the downstream station. Also, filamentous algae such as Cladophora glomerata, Ulothrix zonata and Stigeoclonium lubricum were observed at the downstream station. In view of the above findings, several suggestions were put forward to protect the water quality of the receiving stream.

The transborder flux of phosphorus in the Lancang-Mekong River Basin: Magnitude, patterns and impacts from the cascade hydropower dams in China

Nutrients are critical to the development of plant and animal life in the river ecological system. In recent years, more attentions have arisen on the impact of building hydropower dams to transborder nutrient flux in the Lancang-Mekong River Basin (LMRB). In this paper, phosphorus was taken as an example, which is considered as one of the most significant factors to limit biological activities in the river. The Soil and Water Assessment Tool (SWAT) was used to access the multisource loading pattern of Total Phosphorus (TP) under no-dam scenario, and various types of dam construction scenarios analyses were performed to investigate potential changes in the transborder TP flux from Lancang River Basin (LRB, Chinese part of LMRB) to lower LMRB (other parts of LMRB). The results showed that the Total Phosphorus load in the LRB is about 27,079 tons/year, of which 85% TP is collected from July to October. The annual TP export at the outlet of the LRB is 14,112 tons/year under no-dam scenario, which accounts for about 4.2% of the total TP loads in the lower LMRB. With seven to twenty-one dams included in experiments, TP flux at the outlet of the LRB decreased 50–59%, while the delivered ratio for the lower LMRB decreased 2.1–2.5%. As a summary, building dams has a significant impact on the TP transport pattern in the Chinese part of LMRB, but very limited effect in lower LMRB according to the modeling results, especially for the Mekong delta. Moreover, the existing dams (seven dams) seem to intercept much more phosphorus than those dams that are under construction.

Tempo-spatial and Retention Analysis of Total Phosphorus in the Three Gorges Reservoir

Phosphorus, as a limiting and vital macronutrient in water, circulates mainly with sediment through rivers. The construction and operation of large reservoirs can have a profound impact on the characteristics of phosphorus transportation and transformation. Based on measured hydrological and water quality data during 2008-2016 in the Three Gorges Reservoir (TGR), a statistical model of total phosphorus (TP) flux and sediment load in different periods was established. The formula of TP flux was established by analyzing the interpolation of unmeasured TP concentration, tempo-spatial characteristics, flux variation, and the retention effect of TP in the TGR. The results indicated that taking no account of the effects of TP inflows of tributaries, annual TP concentration in the TGR varied between 0.196 mg·L-1 and 0.290 mg·L-1 during 2008-2012, and inner-annual changes in TP concentration presented an "M" type with two obvious peaks. TP concentration decreased slowly from upstream to downstream of the TGR, and increased significantly from Cuntan to Qingxichang in some years. The average annual TP flux and retention rate of the TGR were 82300 t and 49.76% during 2008-2012, respectively. During 2013-2016, the average annual TP flux and retention rate decreased significantly, to about 47900 t and 12.03%, respectively.

Long-term (1980–2015) changes in net anthropogenic phosphorus inputs and riverine phosphorus export in the Yangtze River basin

Quantitative information on long-term net anthropogenic phosphorus inputs (NAPI) and its relationship with riverine phosphorus (P) export are critical for developing sustainable and efficient watershed P management strategies. This is the first study to address long-term (1980–2015) NAPI and riverine P flux dynamics for the Yangtze River basin (YRB), the largest watershed in China. Over the 36-year study period, estimated NAPI to the YRB progressively increased by ∼1.4 times, with NAPIA (chemical fertilizer input + atmospheric deposition + seed input) and NAPIB (net food/feed imports + non-food input) contributing 65% and 35%, respectively. Higher population, livestock density and agricultural land area were the main drivers of increasing NAPI. Riverine total phosphorus (TP), particulate phosphorus (PP) and suspended sediment (SS) export at Datong hydrological station (downstream station) decreased by 52%, 75% and 75% during 1980–2015, respectively. In contrast, dissolved phosphorus (DP) showed an increase in both concentration (∼7-fold) and its contribution to TP flux (∼16-fold). Different trends in riverine P forms were mainly due to increasing dam/reservoir construction and changes in vegetation/land use and NAPI components. Multiple regression models incorporating NAPIA, NAPIB, dam/reservoir storage capacity and water discharge explained 84% and 92% of the temporal variability in riverine DP and PP fluxes, respectively. Riverine TP flux estimated as the sum of DP and PP fluxes showed high agreement with measured values (R2 = 0.87, NSE = 0.84), indicating strong efficacy for the developed models. The model forecasted an increase of 50% and 7% and a decrease of 15% and 22% in riverine DP flux from 2015 to 2045 under developing, dam building, NAPIA and NAPIB reduction scenarios, respectively. This study highlights the importance of including enhanced P transformation from particulate to bioavailable forms due to river regulation and changes in land-use, input sources and legacy P pools in development of P pollution control strategies.

Effect of Optimized Fertilization and Biochar Application on Phosphorus Loss in Purple Soil Sloping Farmland

Phosphorus is an essential nutrient for crop growth, but the input of excess phosphorus is a significant cause of eutrophication. This study explored the relationship between fertilization methods and phosphorus loss in actual production, providing a theoretical basis for scientific fertilization and rational reduction of fertilizer application. In the experiment, a wild-type OD flow plot was used to monitor the occurrence of multiple rainfall runoff and sediment yield in purple soil sloping farmland in 2017-2018. Four different schemes of non-fertilizer treatment, conventional fertilization treatment, optimized fertilization treatment, and reduced fertilization combined with biochar were studied. The effects of soil flow, surface runoff, and sediment phosphorus loss on purple soil sloping farmland were analyzed. The results showed that:①The total yield of each treatment was optimized (20737.23 L) > conventional (18513.17 L) > CK (18134.58 L) > biochar (13594.85 L), and the total sediment yield of each treatment was CK (1998 kg·hm-2) > biochar (1884 kg·hm-2) > optimized (1681 kg·hm-2) > conventional (910 kg·hm-2). The middle stream of soil is the main type of runoff in the rainy season, accounting for 60.14%-87.34% of the total output flow. The total amount of sediment produced by each treatment was not significantly different from that of the conventional treatment (P>0.05). ②The flux of total phosphorus loss in each treatment was characterized by sediment > surface runoff > soil middle flow. Phosphorus lost through the middle stream of soil is the least, accounting for only 2.63%-12.91% of the flux of total phosphorus loss, while the flux of sediment loss of phosphorus can reach 63.74%-78.74%, and thus is the main output route of soil phosphorus loss. ③The application of biochar can effectively reduce the abortion flow in the soil of purple soil sloping land, and the loss flux of orthophosphate in the middle stream, which are 49.94% and 56.45% lower than the conventional treatment, respectively. However, the interception effect on surface runoff is not good, and there is no significant influence on the flux loss of particulate phosphorus. At the same time, the flux of total phosphorus in surface runoff and sediment is significantly increased by 73.28% and 123.53%, respectively, compared with conventional treatment (P<0.05). Therefore, to control the loss of phosphorus in purple soil sloping farmland in southwest China, we should focus on reducing the occurrence of soil sediment loss. Bio-carbon should be further optimized in the practical application of agricultural production with the phosphorus fertilizer input ratio.

Characteristics of Nitrogen and Phosphorus Output and Loss Flux in the Shipanqiu Watershed, Three Gorges Reservoir Area

As the source of non-point pollution in the Three Gorges Reservoir Area, small watershed is a key control object in alleviating deterioration of water quality. In the Three Gorges Reservoir Area, the Shipanqiu small watershed with various land-use types was selected as the research object, and the water quantity and quality of the outlet section of the watershed were continuously monitored. We carried out analysis of the small watershed runoff loss and nitrogen and phosphorus pollutants with concentration, analyzed the morphology change characteristics of runoff erosion, calculated the small watershed of pollutant emission flux, and analyzed the nitrogen and phosphorus nutrient loss and main human and natural factors, especially in the Three Gorges Reservoir Area of agriculture where nonpoint source pollution research has important practical significance. The results showed that the rainfall in the watershed varied significantly with the seasons, and the rainfall was mainly distributed from April to June, which was the main output period of nitrogen and phosphorus loss in the small watershed, accounting for 58.94% and 67.60% of the total nitrogen and phosphorus load, respectively, in the whole year. The total annual runoff in the Shipanqiu small watershed was 8.02×104 m3, and the annual total nitrogen loss flux was 5.04 kg·hm-2, of which nitrate nitrogen (2.54 kg·hm-2) was the main part. The total phosphorus output was 0.534 kg·hm-2, and the soluble total phosphorus (0.422kg·hm-2) accounted for 79.00% of the total phosphorus flux. The loss flux of total nitrogen was 9.51 times that of total phosphorus, and the non-point source pollution risk of nitrogen was much greater than that of phosphorus. Therefore, for the Shipanqiu small watershed, it is especially important to prevent nitrogen loss in paddy fields when fertilization and rainfall coincide.

Effect of water diversion from the Yangtze River to Lake Taihu on total phosphorus rebound after 2016

针对“引江济太”工程将总磷浓度偏高的长江水引入太湖后对2016年后太湖总磷反弹的影响，本文实测并收集整理了2016年前后“引江济太”调水入湖水量、磷通量及全太湖入湖水量、磷通量与太湖磷存量等数据，对2016年前后“引江济太”调水入湖水量、磷通量、磷形态与其他入湖河道水量、磷通量、磷形态以及全太湖的水质、受水区贡湖的水质进行了分析.结果表明：2016年前后，“引江济太”年均入湖磷通量为97.56 t，年均入湖水量为8.16亿m³，从调水量、入湖磷通量、调水后短期磷响应及各湖区磷增量来看，“引江济太”与2016年后太湖总磷反弹相关性不强.“引江济太”调水累计入湖磷通量为877.97 t，占太湖总入湖磷通量的4.58%，累计入湖水量占太湖累计入湖水量的7.36%，单位水量携带的磷通量仅为其他来水的一半左右，占比相对有限.与太湖主要入湖河流相比，“引江济太”调水属于优质来水，湖泊的入湖河流总磷浓度一般都高于湖泊本身的总磷浓度，“引江济太”调水总磷浓度偏高属于正常范围.目前“引江济太”工程在保证供水安全、缓解水华危机的同时对处于严重富营养化状态的太湖具有一定的改善效果，但未来引水量增加的情况下，必须继续关注引水带来的磷通量与太湖磷循环系统的关系，确保“引江济太”对太湖继续产生良性的影响.;In order to figure out the influence of the water diversion from the Yangtze River Project (WDP) on the rebound of total phosphorus (TP) concentration in Lake Taihu after 2016,this study analyzed the water quantity, phosphorus flux and phosphorus form of Yangtze River and other inflowing rivers including Lake Taihu and Gonghu Bay around 2016 based on the data of water quantity, phosphorus flux transfer from Yangtze River and the phosphorus stock in the lake. The result shows that the average annual phosphorus flux into the lake was 97.56 t and the average annual water inflow volume was 816 million m³ around 2016. From the perspective of water volume, phosphorus flux into the lake, short-term phosphorus response after water diversion and phosphorus increment in each lake area, the correlation between the WDP and the TP rebound in the lake after 2016 is not strong. The cumulative phosphorus flux from the WDP was 877.97 t, accounting for 4.58% of the total TP flux into the lake, and the accumulative amount of lake water accounted for 7.36% of the accumulative amount of lake water in Lake Taihu, the phosphorus flux per unit of water is only about half of that of other water, which accounts for a relatively limited proportion. Compared with the main inflow rivers of Lake Taihu, the water quality from Yangtze River is good. The TP concentration in the inflow rivers is generally higher than the TP concentration of the lake itself. At present, in addition to ensuring the safety of water supply and alleviating the water bloom crisis, the incoming water from the WDP has certain improvement effect when the lake is serious eutrophic. In the next step, we must pay attention to the relationship between the phosphorus flux brought by water diversion and the phosphorus circulation system in Lake Taihu, so as to ensure the ongoing WDP continue to have a positive impact.

Thin-layer fine-sand capping of polluted sediments decreases nutrients in overlying water of Wuhan Donghu Lake in China.

Capping water body sediments with a thin layer of sand is an effective technique to decrease nutrient concentrations in the water column and accelerate ecological restoration of eutrophic water bodies. However, long-term effects of thin-layer sand capping in shallow lakes are reported less often. Using clean fine sand and geotextile mats as capping materials for sediments collected from Wuhan Donghu Lake in China, we designed a 290-day tank experiment with 3 cm of sand capping at four percentages of sediment coverage from 25 to 100% and a control (no capping). We monitored total nitrogen (TN), total phosphorus (TP), nitrate (NO3-), ammonia (NH4+), and soluble reactive phosphorus (SRP) in the overlying water every 7 days. Mean TN and NO3- concentrations were significantly the lowest (P < 0.05) at 50% coverage. Further increase in coverage kept them slightly fluctuating. NH4+ concentration was significantly lowest (P < 0.05) at 75% coverage. The relation between coverage and mean TP and SRP concentrations indicated that 75% coverage significantly decreased (P < 0.05) them, and increasing coverage to 100% decreased them even more. The fluxes of TN and TP estimated between sediments and overlying water showed that the thin fine-sand layer significantly increased the function of sediments as a sink of TN from overlying water and the potential of a sand layer to block release of TP from sediments (P < 0.05). Our results suggested that if thin-layer sand capping were applied to Wuhan Donghu Lake, more than 50% coverage is required to decrease nutrients in the lake's water.

Investigation of watershed nutrient export affected by extreme events and the corresponding sampling frequency

Although the real-time monitoring technique has been widely applied due to the improvement of sensors, development of traditional sampling methods is still worth of being discussed due to the economically feasibility. Currently, extreme events (e.g. extreme rainfall caused by climate change) play a relatively important role in nutrient export. However, impacts of extreme events on the optimization of sampling strategy is still not well addressed despite the uncertainty of different frequency sampling programs has been sufficiently discussed in previous studies. Therefore, the corresponding impact of extreme events impact on the optimization of sampling strategy was investigated by examining temporal (i.e., inter-annual and seasonal) variations of available data. Uncertainty of nutrient flux estimates under different sampling frequencies was explored by subsampling daily monitoring data. Results showed that uncertainty in flux estimates differed between nitrogen and phosphorus. The relative error (RE) in annual TN flux estimates ranged from −4.2% to 2.4% (once per three-day) to −21.4–31.1% (monthly sampling), while the RE in annual TP flux estimates varied from −14.1% to 8.2% (once per three-day) to −65.9%–163.4% (monthly sampling). Biweekly and weekly sampling routines are considered the optimal sampling program for total nitrogen (TN) and for total phosphorus (TP) when the extreme events impact were not been considered. The uncertainty of flux estimates with different sampling frequencies increased with the increasing extreme events. High level of uncertainty occurred in years with the most extreme events in 2012 (RE: 21.4–69.0% for TN, 33.3–96.6% for TP), while the lowest can be found in 2011 (RE: 0–20.7% for TN, 0–48.3% for TP) (with the fewest extreme events). In addition, uncertainty in TN and TP flux estimates was generally greater during summer season than during other seasons. These results highlighted the important role of extreme events in nutrient export. Approximately half of the annual TN and TP flux occurred in some extreme days that only accounted for less than 20% in the same year. The onset of these extremes of nutrient export was likely due to the stormflow with addition of external fertilizer and the direct discharge of surface ponding water from paddy fields during special periods of time. These results would be helpful for the optimization of sampling strategy.

Modelling historical variability of phosphorus and organic carbon fluxes to the Mackenzie River, Canada

AbstractThis study provides an improved statistical modelling framework for understanding historical variability and trends in water constituent fluxes in subarctic western Canada. We evaluated total phosphorus (TP) and dissolved organic carbon (DOC) fluxes for the Hay, Liard and Peel tributaries of the Mackenzie River. The TP and DOC concentrations primarily exhibit chemodynamic relationships with discharge, with the exception of the chemostatic relationship between DOC and discharge for the Hay River. With this understanding, we explored a number of enhancements in the load estimation model that included the use of (i) linear regression and logarithmic models, (ii) air-temperature as an alternate input variable and (iii) quantile mapping for bias-correction. Further, we evaluated uncertainties in the simulation of fluxes and trends by using a bootstrapping method. The modelled TP and DOC fluxes show considerable seasonal and interannual variability that generally follow the runoff dynamics. The annual and seasonal trends are mostly small and insignificant, with the largest significant increases occurring in the winter months. These trends are amplified compared with discharge, suggesting the possibility of pronounced changes with large changes in discharge. Additionally, the results provide evidence that directly using limited water constituent samples for trend analysis can be problematic.

Estimation of phosphorus flux into the sea through one reversing river using continuous turbidities and water quality modeling

Based on continuous turbidity values (T) and water quality modeling, one methodology was proposed to estimate phosphorus (P) flux into the sea through the river. There are three steps in the procedure: (1) analyzing the relationship of P and total suspended solid (TSS), TSS and T; (2) estimating P concentrations with high temporal and spatial density along the river; and (3) calculating the amount of phosphorus flux into the sea. From September 2014 to December 2016, 224 data sets were collected at eight sites along the Tonglv River which feeds into the Yellow Sea, China. The linear regression of TSS and T provided a fit with R2 = 0.944, and TP and TSS presented linear relationship with R2 = 0.884. It was estimated that about 30,227 kg total phosphorus (TP) flows from the river into the sea from September 2014 to August 2015. It is practicable and credible to use T values and water quality modeling to estimate the process of phosphorus flux. Besides, the procedure proposed could be also applied in analyzing the influence on TP fluxes brought by pollution loading changes. Thus, to facilitate long-term pollutants’ fluxes estimation, combining the regression models with water quality modeling might be an effective technique.

Nutrient dynamics in the Changjiang and retention effect in the Three Gorges Reservoir

2009 ∼ 2010 was a critical period for the Three Gorges Reservoir (TGR) transition from staged impoundment to full operation. This study reports on the composition of nutrients in the whole Changjiang and retention effect of the reservoir during the transitional period, and the potential impact of the reservoir impoundment on the eutrophication of the TGR and estuary. Water samples were collected in the mainstream and tributaries of Changjiang from August to October 2009 and June 2010 to analyze the concentrations of dissolved and particulate nutrients, and suspended particulate matter (SPM). The Changjiang was enriched with dissolved inorganic nitrogen (DIN), dissolved silicate (DSi) and SPM, but depleted in PO43− and biogenic silica (BSi), with higher DIN:PO43− and DSi:PO43− ratios. DIN and PO43− concentrations were lower in the Jinshajiang, but increased in the Mid-downstream of the Changjiang due to high human activities and nutrients import from major tributaries. DSi concentration varied little along the Changjiang, and was relatively low in the TGR. Particulate inorganic phosphorus (PIP), total particulate phosphorus (TPP) and BSi concentrations were very high in the Jinshajiang, and then dramatically decreased with the SPM in the TGR. The northern tributaries contributed more nutrients to the Changjiang than the southern tributaries. Depending on the nutrients input-output mass balance model, the retention of nutrients in the TGR were higher for TPP and BSi, lower for dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP). Total dissolved nitrogen (TDN), total phosphorus (TP) and DSi retained in the reservoir accounted for 15%, 12% and 1%, respectively of the TDN, TP and DSi fluxes in the Datong station near the estuary. Historical data showed that the impoundment of the TGD greatly contributed to the eutrophication of the reservoir and estuary. Since 2003, algal blooms were likely to occur in the TGR, estuary and adjacent seas, but the outbreak frequency and area of red tides in the East China Sea (ECS) dramatically decreased. Therefore, further study is required to estimate the response of estuarine ecosystem on the dispatching mode of the TGR.

The Transport Process of Total Suspended Substance and Its Influence on TN and TP Fluxes in Urban River: A Case Study of Baoxiang River, Yunnan China

To reveal the characteristics of solid phase TSS (Total suspended substance) distribution and transported flux in urban river, and explore its effect on TN (Total nitrogen) and TP (Total phosphorus) transported fluxes. The TSS concentrations and flux, TN flux and TP flux, river runoff flux were be monitored and calculated systematically in Baoxiang River, the results shows that: (1) the annual TSS quantity transported by Baoxiang River into Dianchi Lake was 578.86t. Urban areas were the major transported areas of TSS, and summer and autumn were the main transported periods. (2) TSS has a certain correlation with TN (R2=0.28, P<0.01, n=72) and TP (R2=0.34, P<0.01, n=72), but there correlations were not significant. However, the correlations of river runoff flux with TN and TP were significant, it indicated that liquid phase was the main factor affecting TN TP fluxes, priority should be given to liquid phase when dealing with TN and TP pollution. The results can provide a basis for eutrophication control of urban rivers and nonpoint pollution management of Dianchi Lake River basin.

Quantifying model uncertainty using Bayesian multi-model ensembles

Watershed models are essential tools to understand, quantify, and predict hydrologic processes and water quality responses from scales ranging from field to large river basins. However, the reliability of watershed models in a management context depends largely on inherent uncertainties in model predictions. The objective of this study is to quantify prediction uncertainty for flow, sediment, total nitrogen (TN), and total phosphorus (TP) resulting from model structure. We do this using using three process-based models: the Soil and Water Assessment Tool-Variable Source Area model (SWAT-VSA), the standard Soil and Water Assessment Tool (SWAT-ST), and the Chesapeake Bay Program’s Phase 6 Watershed Model (CBP-Model). We initialize each of the models using meteorological, soil, and land use data, and analyze outputs of flow, sediment, TN, and TP fluxes at the U.S. Geological Survey stream gauge at the downstream end of the Susquehanna River Basin in Conowingo, Maryland. Using these three models, we develop and compare two types of Bayesian models, a Bayesian Generalized (Non-) Linear Multilevel Model (BGMM), and a Bayesian Model Averaging (BMA) for flow, sediment, TN, and TP and 95% credible intervals. We compare the Bayesian models results against the individual model results, and straight model averaging (SMA) using a split time period analysis to assess their predictive strengths. Both Bayesian models provided substantially better predictions than the individual process-based models, and estimates of prediction uncertainty, which can enhance decision-making and improve watershed management by providing a risk based assessment of outcomes.

Changes in lateral floodplain connectivity accompanying stream channel evolution: Implications for sediment and nutrient budgets

Floodplain storage commonly represents one of the largest sediment fluxes within sediment budgets. In watersheds responding to large scale disturbance, floodplain-channel lateral connectivity may change over time with progression of channel evolution and associated changes in channel geometry. In this study we investigated the effects of channel geometry change on floodplain inundation frequency and flux of suspended sediment (SS) and total phosphorus (TP) to floodplain storage within the 52.2 km2 Walnut Creek watershed (Iowa, USA) through a combination of 25 in-field channel cross section transects, hydraulic modeling (HEC-RAS), and stream gauging station-derived water quality and quantity data. Cross sectional area of the 25 in-field channel cross sections increased by a mean of 17% over the 16 year study period (1998–2014), and field data indicate a general trend of degradation and widening to be present along Walnut Creek's main stem. Estimated stream discharge required to generate lateral overbank flow increased 15%, and floodplain inundation volume decreased by 37% over study duration. Estimated annual fluxes of SS and TP to floodplain storage decreased by 61 and 62% over study duration, respectively. The estimated reductions in flux to floodplain storage have potential to increase watershed export of SS and TP by 9 and 18%, respectively. Increased contributions to SS and TP export may continue as channel evolution progresses and floodplain storage opportunities continue to decline. In addition to loss of storage, higher discharges confined to the channel may have greater stream power, resulting in further enhancement of SS and TP export through accelerated bed and bank erosion. These increased contributions to watershed loads may mask SS and TP reductions achieved through edge of field practices, thus making it critical that stage and progression of channel evolution be taken into consideration when addressing sediment and phosphorus loading at the watershed scale.

SWAT model uncertainties and cumulative probability for decreased phosphorus loading by agricultural Best Management Practices

Effects of mitigation measures in agriculture on abating eutrophication are difficult to evaluate by assessments of catchment monitoring data. Estimates of improved water quality by specific agricultural Best Management Practices (BMPs) are therefore often dependent on simulation modeling. A main objective was thus to assess the probable reductions in total phosphorus (TP) loading achieved by implemented agricultural mitigation measures. The case-study site was a catchment in southeastern Norway. Simulation modeling was conducted by use of The Soil and Water Assessment Tool (SWAT). The aim of this present study was to understand the model uncertainty associated both with calibration/validation (baseline) and TP loading scenarios based on BMP. The modeled decrease in TP loading by the set of implemented BMPs was assessed by comparing simulated baseline output with output where the set of abatement actions were removed.The model was set up for the years 2006–2010 and calibrated against observed monitoring data, including daily discharge, sediment- and TP fluxes. Model simulations were performed including and excluding the implemented set of mitigation measures. The simulated set of mitigation measures include decrease in amount of phosphorus fertilization, establishment of vegetated buffer strips along streams and constructed wetlands in the water courses, no autumn tilling and removal of point TP sources from scattered dwellings. Model calibration and uncertainty estimation are performed using an algorithm for Sequential Uncertainty Fitting (SUFI2; ver. 2).Probabilistic risk for given magnitudes of increased TP loading if existing BMPs were not implemented was assessed. Using this novel approach it was possible to state, with a 80th percentile confidence level, that the average annual TP loading would have been about 26% higher if no mitigation measures were implemented in the catchment. This was possible to assess even though the difference between baseline and BMP scenario was not significant.

The influence of dam construction on water quality in the lower Geum River, Korea

AbstractThe Geum River has been faced with extreme environmental change due to the construction of three dams in midstream since 2012 (Four Major River Restoration Project). We hypothesized that suspended solids (SS) and total particulate phosphorus (TPP) decreased after the dam construction. To test our hypothesis, we investigated the influence of the dam construction on water quality by measuring possible impacts of decreasing SS, total phosphorus (TP), and TPP on the ecosystem in the lower Geum River and the Geum River estuary. For this study, we chose one site to compare the monthly water quality data pre‐construction (2008) and post‐construction (2015). Dissolved oxygen and pH were not significantly different between pre‐ and post‐construction, while electric conductivity (EC) increased. The increase in the EC may be related to a decrease in river discharge (RD) after the dam construction. As we expected, TP and TPP decreased post‐construction, but SS did not show significant differences between pre‐ and post‐construction. This suggests that the decline of TPP concentrations post‐construction were not related to SS levels. The explosive algal bloom and sedimentation of the algae may be an important factor in explaining the decrease in TP and TPP. The decline of SS, TP, and TPP flux to the lower Geum River was observed. This could be a potential reason for the erosion of the mud flat of the Geum River estuary in the future. Therefore, to determine the long‐term effects of the SS and the phosphorus fluxes to the lower Geum River, these factors should be monitored periodically over longer periods of time than this study.