Annual Total Phosphorus Loads Research Articles

Response of streamflow and nutrient loads in a small temperate catchment subject to land use change

The aim of this study was to quantify the effect of land use change (LUC) implemented to meet nutrient load targets for a freshwater lake in New Zealand. We used the Soil and Water Assessment Tool (SWAT) model in combination with a non-parametric statistical test to determine whether afforestation of 15% of a subcatchment area was adequate to meet assigned nutrient load targets. A regional management authority set nutrient load targets of reduction in total nitrogen (TN) by 0.9 t yr−1 and reduction in total phosphorus (TP) by 0.05 t yr−1 to avoid eutrophication in the receiving waters of a freshwater lake. The load reduction was designed to be achieved through 200 ha of LUC from pasture to trees. Analysis of nutrient loads before, during, and following LUC shows that a 15% increase in forest cover decreased the annual flow (7.2%), TP load (33.3%), and TN load (13.1%). As flow and water quality observations were discrete and at irregular intervals, we used a parametric test and the SWAT model as different lines of evidence to demonstrate the effect of afforestation on flow and water quality. Policymakers concerned with decisions about LUC to improve the quality of receiving waters can benefit from applying our findings and using a statistical and numerical modelling framework to evaluate the adequacy of land use change to support improvements in water quality.

Assessing hydrological and water quality responses to dynamic landuse change at watershed scale in Mississippi

The hydrology and water quality modeling in a watershed are affected by land use land cover (LULC) input. This study differs from numerous LULC change studies by introducing multi-year LULC input in a single simulation of Soil and Water Assessment Tool (SWAT) model. The proposed approach highlighted the outperformance of the model with dynamic LULC input (DM) over static LULC input (SM) based on the magnitude and direction of the hydrological responses. The difference between DM and SM outputs allowed for studying effects of historical LULC change. Additionally, agricultural management operation inputs enabled more realistic simulation of runoff, sediments, total nitrogen (TN), and total phosphorus (TP). The SM used static landuse data layers for 2009, and DM used landuse data layers for 2009, 2015, and 2018 to represent changes in LULC distribution over time. The expansion of agricultural land (0.9%) and forest cover (0.5%), as well as the reduction of grassland, water, and barren areas (1.4%), were the significant LULC changes from 2009 to 2018. Even though the expansion of forest cover was identified from 2009 to 2015, a declining trend was observed from 2015 to 2018. The agricultural land cover increased consistently from 2009 to 2018. The expansion of agricultural land increased average annual surface runoff, sediment yield, TN, and TP loads by 1.3%, 5.4%, 5.8%, and 5.9% respectively at watershed scale as determined by DM model simulation results. At sub-watershed scale, agricultural land expansion increased runoff, sediment, TN, and TP loads by up to 5%, 16%, 15%, and 15% respectively whereas, the expansion of forest cover resulted in reduction in same parameters by up to 5%, 15%, 23%, and 26% respectively. In general, the study determined that the integration of dynamic LULC and agricultural operations in SWAT allows a more accurate representation of agricultural watersheds for hydrological and water quality analysis.

Using a Multi‐Institutional Ensemble of Watershed Models to Assess Agricultural Conservation Effectiveness in a Future Climate

ABSTRACTThis study investigates the combined impacts of climate change and agricultural conservation on the magnitude and uncertainty of nutrient loadings in the Maumee River Watershed, the second‐largest watershed of the Laurentian Great Lakes. Two scenarios — baseline agricultural management and increased agricultural conservation — were assessed using an ensemble of five Soil and Water Assessment Tools driven by six climate models. The increased conservation scenario included raising conservation adoption rates from a baseline of existing conservation practices to feasible rates in the near future based on farmer surveys. This increased adoption of winter cover crops on 6%–10% to 60% of cultivated cropland; subsurface placement of phosphorus fertilizers on 35%–60% to 68% of cultivated cropland; and buffer strips intercepting runoff from 29%–34% to 50% of cultivated cropland. Increased conservation resulted in statistically significant (p ≤ 0.05) reductions in annual loads of total phosphorus (41%), dissolved reactive phosphorus (18%), and total nitrogen (14%) under the highest emission climate scenario (RCP 8.5). While nutrient loads decreased with increased conservation relative to baseline management for all watershed models, different conclusions on the true effectiveness of conservation under climate change may be drawn if only one watershed model was used.

Analysis on the variation of total phosphorus concentrations and loads of inflow and outflow rivers from different water resources zones around Lake Taihu

入出湖总磷负荷变化是影响太湖湖体磷收支平衡的关键因素.基于2012-2018年水质水量监测资料，计算全湖及各水资源分区河流入出湖总磷负荷，并以水量加权计算其总磷年平均浓度，探明其时空变化规律；运用双累积曲线法分析不同分区水污关系的变化规律；以月为时间尺度，利用Pearson相关系数，揭示入湖总磷负荷分别与入湖水量、入湖总磷浓度的相关关系；通过讨论分析，明确适用于太湖的入湖总磷平均浓度计算方法、总磷负荷影响因素及控制途径.研究结果表明：（1）水量加权法比算术平均法更加适用于太湖入湖总磷平均浓度的削减管理；环太湖河流入湖总磷浓度多年平均值为0.189 mg/L，明显高于出湖的0.079 mg/L，入湖总磷负荷多年平均值为2206.51 t，也高于出湖的873.73 t；2016年丰水年入、出湖及净入湖总磷负荷均最高，分别为2993.9、1341.1、1652.8 t.（2）湖西区河流入湖总磷浓度多年平均高于所有其他分区，其值为0.226 mg/L，浙西区、武澄锡虞区河流出湖总磷浓度多年平均分别为0.114和0.109 mg/L，均高于其他分区.不同水资源分区的水污关系呈现不同的年际变化规律，但除杭嘉湖区外，其他分区均未表现出入湖总磷得到有效控制的迹象.（3）湖西区和浙西区入湖总磷年负荷多年平均值分别为1748.71和278.61 t，两区各年入湖总磷负荷占总入湖负荷的比重位居前二，湖西区的都在67.88%以上；而浙西区在7%~19%之间变化；太浦河出湖总磷年负荷多年平均值为272.27 t，自2014年起其占出湖总磷年负荷的比重均在30%以上.（4）不同水资源分区月入湖总磷负荷均与入湖水量存在较好的相关关系，且除阳澄淀泖区外，其他分区月尺度入湖总磷负荷变化主要受入湖水量控制.（5）2016年丰水年湖西区入湖河流总磷浓度较高、入湖水量大的共同作用导致了其入湖总磷负荷的显著增加.研究成果可为太湖的磷外源负荷控制提供科学依据.;The variation in inflow and outflow total phosphorus (TP) loads is a key factor affecting the balance of the phosphorus budget for Lake Taihu. Based on the monitoring data of water quality and quantity from 2012 to 2018, the TP load of the rivers in each water resources zone around Lake Taihu were calculated, the flow-weighted mean annual concentrations of TP were attained, and their spatio-temporal variations were analyzed; the double accumulation curve method was adopted to analyze the relationships between water quantity and TP load in different zones; the Pearson correlation coefficient was utilized to reveal the correlation between the TP load and water quantity as well as TP concentrations of the inflow at the monthly time scale; through discussion and analysis, the calculation method of the average TP concentration of inflow applicable to Lake Taihu, the influencing factors of TP loads and measures of controlling the TP load were investigated. The results showed that:(1) The flow-weighted mean concentration of TP is the preferred approach for calculating average concentrations of tributaries with variable flows for Lake Taihu; The average annual TP concentration of inflow rivers of Lake Taihu was 0.189 mg/L, significantly higher than that of outflow rivers (0.079 mg/L). The average annual TP load of the inflow was 2206.51 t, which was also much higher than that of the outflow (873.73 t); in the high flow year of 2016, the TP loads of the inflow, outflow and net inflow of the lake were the largest among 2012-2018, and their values were 2993.9, 1341.1 and 1652.8 t, respectively. (2) The average annual TP concentration of inflow rivers in the Huxi zone was 0.226 mg/L, which was higher than that in other zones; the average annual TP concentrations of outflow rivers in the Zhexi and Wuchengxiyu zones were 0.114 and 0.109 mg/L, which were higher than those in other zones. The interannual variation of the relationships between water quantity and TP load in different water resources zones behaved differently, suggesting that TP pollution was not effectively controlled on the whole except in the Hangjiahu zone. (3) The average annual TP load of the inflow rivers in the Huxi zone and Zhexi zone were 1748.71 and 278.61 t, respectively. The Huxi zone accounted for above 67.88% of the annual total inflow TP load, and the percentage for the Zhexi zone was between 7% and 19%; the average annual outflow TP load of Taipu River was 272.27 t and accounted for more than 30% of the total outflow TP load since 2014. (4) There were good correlations between the monthly TP load and water quantity of the inflow in different water resources zones. Moreover, except in the Yangchengdianmao zone, the variation of monthly TP load of the inflow in other zones was mainly controlled by the water quantity of the inflow. (5) In the high flow year of 2016, the combined effect of high concentration of TP and large water quantity of inflow rivers in the Huxi zone led to a significant increase in the TP load of the inflow. The research results can provide a scientific basis for external phosphorus load control for Lake Taihu.

Exploring and Predicting the Individual, Combined, and Synergistic Impact of Land-Use Change and Climate Change on Streamflow, Sediment, and Total Phosphorus Loads

The present study predicts and assesses the individual, combined, and synergistic effect of land-use change and climate change on streamflow, sediment, and total phosphorus (TP) loads under the present and future scenarios by using the Soil and Water Assessment Tool (SWAT). To predict the impacts of climate and land-use change on streamflow, sediment, and TP loads, there are 46 scenarios composed of historical climate, baseline period climate, eight climate models of Coupled Model Intercomparison Project phase 5 (CMIP5) of two representative emission pathways (RCP4.5 and RCP8.5), after downscaled and bias-corrected, two observed land-use maps (LULC 1995, LULC 2015) and the projected two future land-use maps (LU2055 and LU 2075) with the help of CA-Markov model to be fed into SWAT. The central tendency of streamflow, sediment, and TP loads under future scenarios is represented using the annual average. The intra-/inter-annual variation of streamflow, sediment, and TP loads simulated by SWAT is also analyzed using the coefficient of variation. The results show that future land-use change has a negligible impact on annual streamflow, sediment, TP loads, and intra-annual and inter-annual variation. Climate change is likely to amplify the annual streamflow and sediment and reduce the annual TP loads, which is also expected to reduce its inter-/intra-annual variation of TP loads compared with the baseline period (2000–2019). The combined impact of land-use and climate change on streamflow, sediment, and TP loads is greater than the sum of individual impacts for climate change and land-use change, especially for TP loads. Moreover, the synergistic impact caused by the interaction of climate and land use varies with variables and is more significant for TP loads. Thus, it is necessary to consider the combined climate and land-use change scenarios in future climate change studies due to the non-negligible synergistic impact, especially for TP loads. This research rare integrates the individual/combined/synergistic impact of land-use and climate change on streamflow, sediment, and TP loads and will help to understand the interaction between climate and land-use and take effective climate change mitigation policy and land-use management policy to mitigate the non-point source pollution in the future.

Impacts of phosphorus loading temporal pattern on benthic algae growth in Lake Ontario

Nuisance growth of the alga Cladophora has been a critical issue in the Laurentian Great Lakes for decades. Although loading of total phosphorus (TP) has been below target values since the 1990s, the nearshore of the lakes still experience Cladophora blooms. This study explores the effects of TP loading temporal pattern on Cladophora growth in Rochester Embayment in Lake Ontario, where Cladophora blooms are frequently observed. Long-term TP loadings from the Genesee River, which is the primary tributary to the embayment, are calculated with a hydrological model, and Cladophora indicators based on beach closures and satellite data are collected for 2008–2017 to analyze the TP loading temporal patterns and their relation with Cladophora abundance. Using time series clustering for both TP loading and Cladophora indicators, it is found that besides total annual TP loading, the timing of high TP loading also plays an important role for Cladophora growth. High TP loading in mid-March to mid-June, compared to that in January to mid-March, is found to produce higher Cladophora abundance in summer. This finding is supported and explained using an integrated hydrodynamic and ecological modeling framework that includes a state-of-the-art Cladophora module. This study suggests that future Cladophora control should consider not only the total annual TP loading mass, but also the temporal loading patterns.

Quantify phosphorus transport distinction of different reaches to estuary under long-term anthropogenic perturbation.

Typical diffuse pollutants such as phosphorus (P) have long been a hot topic in the surface-water research field. As the fifth-largest river in the world, the Yellow River Basin (YRB) suffers from significant soil erosion and relatively high intensity of agricultural activities, which bring large amounts of P loads. However, owing to the large drainage area, few studies have investigated the transport and attenuation dynamic processes or provided a precise calculation of the total phosphorus (TP) load for the entire YRB. In this study, the SPAtially Referenced Regressions on Watershed Attributes (SPARROW) model was used to simulate and investigate the spatial variation and transport mechanism of P in the YRB. The YRB was divided into 60 sub-basins, and the data of drainage area, spatial attribute, streamflow, and monitored flux were integrated into the model correspondingly. Calculated R2 values confirm that 84% of the spatial variability in annual TP loads can represent regional processes. The estimated YRB TP load was 41,760 tons per year, contributed by farmland (64%), construction land (27%), grassland (5%), and forest (4%). In addition, the P transport dynamic process, contribution, and sensitivity of different P flux sources in different reaches were represented and identified. Our study highlights the significance of farmland as the most significant factor exacerbating TP pollution. As the study conducted the first attempt to develop a SPARROW model, integrated management strategies that consider the spatially varying P sources and associated TP transport were proposed. Additionally, to improve the ecological health of basin, it is critical to further increase P utilization efficiency and enhance cross-regional cooperation throughout the basin.

The Influence of the Modernization of the City Sewage System on the External Load and Trophic State of the Kartuzy Lake Complex

A study was carried out in the Kartuzy lake complex, which has been a receiver of raw domestic sewage since the 1950s. In 2018, the city’s sewage system of Kartuzy was modernized. An analysis of the water quality prior to the modernization of the sewage system revealed that the total phosphorus (TP) load that was introduced to the individual lakes from external sources substantially exceeded the dangerous load concentration (defined by Vollenweider) that causes accelerated eutrophication. The annual TP load introduced to the analyzed lakes in 2017 exceeded the critical load by 200% (Mielenko) to 1000% (Klasztorne Duże). Protective measures reduced the external loading of nutrients. In the case of Mielenko Lake, a 37% decrease in the external TP load was noted, and also a 32% decrease in the external TP load in Karczemne Lake, a 66% decrease in Klasztorne Małe Lake and a 54% decrease in Klasztorne Duże Lake was noted. The protective measures resulted in a slight decrease in the concentrations of phosphorus and nitrogen in the water. However, these changes did not improve the environmental conditions in the lakes. In a situation where the internal fertilization process in the lakes has started, the improvement of water quality will only be possible through restoration efforts with methods adjusted to the individual characteristics of each lake.

Spatial characteristics of total phosphorus loads from different sources in the Lancang River Basin

Lancang River, the upstream reach of Mekong River, is a hotspot region in the sustainable management of water resources and environment as it is currently facing the deterioration of aquatic ecosystems. Nutrient balance (i.e., Phosphorus) in the Lancang-Mekong River Basin has become a highly disputed issue in recent years due to the construction of cascade hydropower stations. However, the estimation of the total phosphorus (TP) load faces great difficulties and challenges due to the absent measured water quality data. This study estimates the TP load based on the social economic data, analyzes the spatial distribution of TP and the contribution of different TP sources in the Lancang River basin under the level of social-economic development in 2014. Results show that the annual average TP load in the Lancang River Basin is 1.6 × 104–3.9 × 104 tons, which is at a very low level compared with other large-scale basins in China. The TP load from natural soil erosion dominates all other sources, accounting for 69%, followed by agricultural production and fertilization. In general, the TP load increases from upstream to downstream, but heterogeneity also exits in different regions under the influence of various factors, such as rainfall intensity, soil properties and human activities. The results reveal a holistic picture of TP load in the Lancang River Basin, which could provide a new perspective on the trans-border international river management.

Calculation of total phosphorus loads from rivers around Lake Taihu and analysis of total phosphorus fluctuation in the lake in 2015-2016

太湖流域水环境综合治理力度空前，太湖总磷浓度却于2015、2016年重回升势，蓝藻大面积暴发情况也未得到有效遏制.本文从2015和2016年环太湖河道的进出太湖水量、总磷负荷量计算入手，结合雨情、水情、太湖调蓄以及人为影响等各方面因素，分别开展水量和总磷负荷质量的平衡分析.在此基础上，结合2010-2017年环太湖河流多年平均进出太湖总磷负荷量对比，分析太湖总磷的外源、内源变化趋势及来源，探讨2015和2016年太湖总磷升高的原因及控制重点方向.结果表明，2015和2016年为太湖流域丰水年，尤其是2016年发生特大洪水，太湖年内最高水位达4.87 m，仅次于1999年的4.97 m的历史最高水位.2015和2016年大量外源总磷负荷进入太湖，其中环太湖河道带入的总磷负荷量占年度太湖总磷负荷总量的66.8%和74.2%，成为进入太湖的总磷负荷的主要外源；加之，2015年太湖水生植物收割造成当年沉水植物面积较上年同期下降88.7%，水生植物骤减导致对磷的吸收转化能力下降，滞留在湖体中的总磷负荷量占年度太湖总磷负荷总量的21.5%和27.5%，成为影响太湖水体总磷浓度的重要内源.太湖总磷浓度升高又为太湖蓝藻暴发进一步提供了营养盐基础，亟需强化太湖总磷源头的控制、减少总磷入湖总量.;Government has strengthened the comprehensive management and restoration of the water environment in Taihu Basin. Despite the great efforts, the total phosphorus concentration in Lake Taihu rebounded in 2015-2016. Occurrence of cyanobacterial blooms has not been effectively inhibited. Thus, this essay is going to examine the reasons behind and figure out the key direction in controlling the total phosphorus in Lake Taihu. The water quantity balance analysis and the total phosphorus mass balance analysis will be carried out through the calculation of the total phosphorous fluxes and the water flows between Lake Taihu and the surrounding rivers. Affecting factors, including rainfall, lake storage regulation and human factors, will also be considered. Based on the analysis, we will investigate the sources of total phosphorus change in Lake Taihu as well as the reasons of variations. The results showed that Taihu Basin had abundant rainfall in 2015-2016, especially in 2016, there was a severe basin flooding. The maximum water level of Lake Taihu reached 4.87 m, only 0.1 m lower than that of the historical record in 1999. Enormous total phosphorus load flowed from the surrounding rivers to Lake Taihu, which became the main external source of Lake Taihu's total phosphorus load. The load from rivers occupied 66.8% and 74.2% of the annual total phosphorus load in Lake Taihu in 2015 and 2016, respectively. On the other hand, for internal source, the massive reduction of submerged plants played an important role in affecting the total phosphorus concentration in Lake Taihu. The area of submerged aquatic plants in Lake Taihu decreased by 88.7% in 2015. The large-scale harvest of aquatic plants hindered the phosphorus absorption and transformation capacity of the lake. In 2015 and 2016, the total phosphorus load retained in Lake Taihu accounted for 21.5% and 27.5% of the total phosphorus load. The increase in total phosphorus concentration in Lake Taihu provided a strong foundation for cyanobacterial blooms. It is urgent to lower the amount of total phosphorus into Lake Taihu and tighten the control of the total phosphorus sources.

A Phased Assessment of Restoration Alternatives to Achieve Phosphorus Water Quality Targets for Lake Okeechobee, Florida, USA

Achieving total phosphorus (TP) total maximum daily loads (TMDL) for Lake Okeechobee (Florida, FL, USA), a large freshwater lake, is a key component of the greater Everglades ecosystem restoration and sustainability of south Florida. This study was aimed at identification of a cost-effective restoration alternative using four TP control strategies—Best Management Practices (BMPs), Dispersed Water Management (DWM), Wetland Restoration, and Stormwater Treatment Areas (STAs)—to achieve a flow-weighted mean TP concentration of 40 µg/L at lake inflow points, through a phased scenario analysis approach. The Watershed Assessment Model was used to simulate flow and phosphorus dynamics. The 10-year (1998–2007) ‘Base’ scenario calibration indicated ‘acceptable’ to ‘good’ performance with simulated annual average flows and TP load of 2.64 × 109 m3 and 428.6 metric tons, respectively. Scenario results showed that TP load reduction without STAs would be around 11–40% with respect to Base compared to over 75% reduction requirement to achieve TMDL, indicating STAs as a necessary component to achieve restoration. The most cost-effective alternative to achieve TP target consisted of implementation of nutrient management BMPs, continuation of existing DWM projects, and the construction of ~200 km2 of STAs for a total project cost of US $4.26 billion.

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.

Spatial and seasonal variations in phosphorus speciation along a river in a lowland catchment (Warnow, Germany)

Losses of phosphorus (P) from arable land lead to P enrichment in surface waters and thus to eutrophication. To gain deeper insights into riverine P processing and transport, the temporal and spatial changes of P compounds along the lowland river Warnow and its tributaries were investigated. Surface water samples were taken monthly between August 2016 and August 2017 and analyzed for the four P fractions: dissolved reactive (DRP), dissolved nonreactive (DNP), particulate reactive (PRP) and particulate nonreactive (PNP) phosphorus. P-composition differed between the courses of the upper Warnow and the impounded middle Warnow due to differences in their hydrological conditions. In the catchment of the upper course, riverine lakes were the sources of PNP and DRP during the summer and autumn. From the catchment of the middle course, mainly PRP and DRP had been introduced into the river. The negative relationship between PRP and the chlorophyll (Chla) concentration (rho = −0.43, p < 0.001) indicated that this P fraction is potentially bioavailable. During the rainy summer of 2017, substantially higher amounts of DRP occurred in the whole Warnow river. The potentially bioavailable P fractions (DRP, PRP, DNP) supported phytoplankton growth in the middle course, and the PNP loads increased with increasing biomass. Total phosphorus (TP) loads increased along the Warnow flow path, due to increasing discharge volume. The annual TP load of 40 t to the estuary was dominated by DRP (32%) and PNP (31%), with smaller contributions by PRP and DNP (19% and 18%, respectively). Our results demonstrate that detailed information on P fractions are helpful to understand P-cycling in rivers and its influence on eutrophication processes. This knowledge should be included in the development of effective management strategies for the improvement of water quality.

The missing dead: The lost role of animal remains in nutrient cycling in North American Rivers

While leaf litter, wood, and other plant remnants are known to play a central role in lotic ecosystems, animal remains (carcasses, bones, shells) have received less attention. We propose a simple classification scheme for animal remains in rivers based on origin (authochthonous vs. allochthonous) and frequency (pulsed vs continuous). We then present case studies in which we estimate the former biomass of several taxonomic groups that are now diminished in abundance to determine whether their remains could have historically constituted a significant flux of nutrients in rivers of North America. We focus on bones and shells, which decompose slowly and could provide long-term reservoirs of nutrients. We find that carcasses of alligator snapping turtles, once abundant in southeastern rivers, could have provided an amount of phosphorus equivalent to about 1% of total phosphorus (TP) load at median flow, and more at low flows. Mussel shells could have contributed a similar amount (0.8% of TP) but the contribution of beaver carcasses, even at former abundances, was likely small. In contrast, a single documented mass drowning of bison in the Assiniboine River could have contributed half the annual TP load for that river. Such drownings could have been a common occurrence prior to the loss of most wild terrestrial megafauna in North America. We conclude that animal remnants, particularly allochthonous remains from terrestrial animals, formerly played a substantial role in nutrient cycling. Existing models of ecosystem function under reference conditions are incomplete without consideration of these lost animal legacies.

ASSESSING THE EFFECTS OF LAND USE CONVERSION ON RUNOFF AND NUTRIENT LOAD

An agricultural land with intensive cultivation, large catchments with extended rivers and agricultural population of high-density are the primary reasons for higher pollutant loads in freshwater. However, there are problems in pursuing nutrient losses since several parameters, such as variability in soils and climate are associated with heavy rainfall, especially in tropic regions; plant management, limited resources, and insufficient technical support are not consistent in every crop management. Changes in agricultural practices and unmonitored point sources discharge from watershed, have led to algal bloom in abundance, and thus generated eutrophication at the downstream. The complex watershed processes and forecasting the effects of land use change on water quality can be determined by using tools of watershed models. The Hydrological Simulation Programme-FORTRAN (HSPF) uses lumped parameters, continuous model to predict the long-term evaluation, and deterministic for simulating the water quality and quantity process that occur at the watershed. Pervious land segments (PERLND), impervious land segments (IMPLND), and channel reach (RCHRES) modules were used to determine the general water quality and quantity on Johor watershed. Based on calibration and validation, the HSPF model was capable of simulating different runoff seasons. An increment of 60% in agricultural land had increased the annual mean total phosphorus (TP) load and total nitrogen (TN) load by 3.82% and 5.34%, respectively. A 2-fold increase in agricultural land would result in an approximately 2-fold increase in the quantity of annual TN and TP loads. Between TN and TP loads, TP load has potentially increased more than TN load during the dry, wet, and base-flow years. Upon the long-term of water quality and quantity simulation, this study provides essential knowledge for a method-based runoff and nutrient management plan for the Johor watershed.

Quantifying the Role of Large Floods in Riverine Nutrient Loadings Using Linear Regression and Analysis of Covariance

This study analyzes the role of large river flow events in annual loads, for three constituents and for up to 32 years of daily data at multiple watersheds with different land-uses. Prior studies were mainly based on simple descriptive statistics, such as the percentage of nutrient loadings transported during several of the largest river flows, while this study uses log-regression and analysis of covariance (ANCOVA) to describe and quantify the relationships between large flow events and nutrient loadings. Regression relationships were developed to predict total annual loads based on loads exported by the largest events in a year for nitrate plus nitrite nitrogen (NO3-N + NO2-N, indicated as total oxidized nitrogen; TON), total phosphorus (TP), and suspended solids (SS) for eight watersheds in the Lake Erie and Ohio River basins. The median prediction errors for annual TON, TP, and SS loads from the top five load events for spatially aggregated watersheds were 13.2%, 18.6%, and 13.4%, respectively, which improve further on refining the spatial scales. ANCOVA suggests that the relationships between annual loads and large load events are regionally consistent. The findings outline the dominant role of large hydroclimatic events, and can help to improve the design of pollutant monitoring and agricultural conservation programs.

Evolution Characteristics of Surface Water Quality Due to Climate Change and LUCC under Scenario Simulations: A Case Study in the Luanhe River Basin.

It is of great significance to study the effects and mechanisms of the key driving forces of surface water quality deterioration—climate change and LUCC (land use and land cover change). The Luanhe River Basin (LRB) in north-eastern China was examined for qualitatively and quantitatively assessing the responses of total nitrogen (TN) and total phosphorus (TP) loads on different climate scenarios and LUCC scenarios. The results show that from 1963 to 2017, the TN and TP loads basically presented a negative correlation with the temperature change (except for winter), while showing a significant positive correlation with the precipitation change. The incidence of TN pollution is sensitive to temperature increase. From 2020 to 2050, the annual average loads of TN and TP were slightly lower than from 1963 to 2017. The contribution of rising temperature was more significant on nutrient loads. Also, the incidence of TN pollution is sensitive to the future climate change. Under LUCC scenarios, the TN and TP loads and pollution incidence increased correspondingly with the decrease of natural land. The evolution characteristics analysis can provide support for the effect and adaptation-strategies study of climate change and LUCC on surface water quality.

Optimizing best management practices to control anthropogenic sources of atmospheric phosphorus deposition to inland lakes

ABSTRACTExcessive phosphorus loading to inland freshwater lakes around the globe has resulted in nuisance plant growth along the waterfronts, degraded habitat for cold-water fisheries, and impaired beaches, marinas, and waterfront property. The direct atmospheric deposition of phosphorus can be a significant contributing source to inland lakes. The atmospheric deposition monitoring program for Lake Simcoe, Ontario, indicates roughly 20% of the annual total phosphorus load (2010–2014 period) is due to direct atmospheric deposition (both wet and dry deposition) on the lake. This novel study presents a first-time application of the genetic algorithm (GA) methodology to optimize the application of best management practices (BMPs) related to agriculture and mobile sources to achieve atmospheric phosphorus reduction targets and restore the ecological health of the lake. The novel methodology takes into account the spatial distribution of the emission sources in the airshed, the complex atmospheric long-range transport and deposition processes, cost and efficiency of the popular management practices, and social constraints related to the adoption of BMPs. The optimization scenarios suggest that the optimal overall capital investment of approximately $2M, $4M, and $10M annually can achieve roughly 3, 4, and 5 tonnes reduction in atmospheric P load to the lake, respectively. The exponential trend indicates diminishing returns for the investment beyond roughly $3M per year and that focusing much of this investment in the upwind, nearshore area will significantly impact deposition to the lake. The optimization is based on a combination of the lowest cost, most beneficial and socially acceptable management practices that develops a science-informed promotion of implementation/BMP adoption strategy. The geospatial aspect to the optimization (i.e., proximity and location with respect to the lake) will help land managers to encourage the use of these targeted best practices in areas that will most benefit from the phosphorus reduction approach.Implications: Excessive phosphorus loading to inland freshwater lakes around the globe has resulted in nuisance plant growth along the waterfronts, degraded habitat for cold water fisheries, and impaired beaches, marinas and waterfront property. This novel study presents a first-time application of the Genetic Algorithm methodology to optimize the application of best management practices related to agriculture and mobile sources to achieve atmospheric phosphorus reduction targets and restore the ecological health of the lake. The novel methodology takes into account the spatial distribution of the emission sources in the airshed, the complex atmospheric long-range transport and deposition processes, cost and efficiency of the popular management practices and social constraints related to the adoption of BMPs.

Spatio-temporal analysis of phosphorus concentrations in a North-Eastern German lowland watershed

Study regionThe Warnow River Basin, an agriculturally dominated lowland watershed in North-Eastern Germany with a considerable extent of artificial drainage. Study focusWe analyzed a 21-year data set (1990–2010) of dissolved reactive (DRP) and total phosphorus (TP) concentrations in surface waters to evaluate trends and seasonality of phosphorus (P) concentrations and pathways of P losses from soils. New hydrological insights for the regionPhosphorus concentrations were moderately spatially variable over the investigation period and mean DRP and TP concentrations ranged from 57 to 132 mg l−1 and 114 to 184 μg l−1 respectively. The mean annual DRP and TP loads ranged from 0.04 ± 0.01 to 0.15 ± 0.05 and 0.12 ± 0.05 to 0.27 ± 0.06 kg ha−1 a−1, respectively. We detected significant negative temporal trends of P concentrations and loads in the decade 1990–2000. In the 21st century, the TP concentrations and loads tend to increase moderately. The results underline the importance of baseflow for DRP export and storm flow events for TP export, and emphasize the importance of artificial drainage systems modifying the hydrological regime of soils and surface waters alike. The P export rates during storm events and the proportion of particulate phosphorus in artificial drainage systems should be monitored at a higher temporal resolution to obtain a comprehensive database necessary for developing management strategies to reduce P loads in agricultural used landscapes.

Assessing effectiveness of long-term forestry best management practices on stream water quality at a basin scale-a case study in Southern USA.

Forestry best management practices (BMPs) have proven to be very effective in protecting adjacent stream water quality at the plot scale. However, our knowledge is incomplete about the effectiveness of forestry BMPs in large watersheds where industrial forests are intensively managed. In this study, we compared long-term concentrations and loadings of total suspended solids (TSS), nitrate/nitrite nitrogen (NO3NO2-N), total Kjeldahl nitrogen (TKN), and total phosphorus (TP) before (1978-1988) and after extensive implementation of forestry BMPs (1994-2008) at the outlet of a 5000-km2 riverbasin that is predominately covered by intensively managed pine forests in Central Louisiana, USA. Our study shows that after extensive BMP implementation, both concentrations and loads of TSS in the basin outlet decreased significantly from 34 to 25mgL-1 and from 55,000 to 36,700tyear-1, respectively. However, no significant difference was found in NO3NO2-N, TKN, and TP concentrations between the two periods. The results of nutrient loadings varied, whereby the annual nitrogen loading declined without significant differences (from 1790 to 1600tyear-1 for TKN and from 176 to 158tyear-1 for NO3NO2-N, respectively) but the annual TP loading increased significantly (from 152 to 192tyear-1) after BMP implementation. Theincrease in TP loading is likely due to an increased application of phosphorus fertilizer, which offset BMPs' effects especially during high-flow conditions. These results strongly suggest that current forestry BMPs in this region are effective in reducing sediment loading, but current BMP guidelines for fertilization and nutrient management need to be reviewed and improved.