Total Phosphorus Losses Research Articles

How to effectively reduce sloping farmland nutrient loss and soil erosions in the Three Gorges Reservoir area

Fertilization and soil conservation measures play crucial roles in influencing nutrient loss and soil erosion on sloping farmlands. However, the long-term effects of these measures and the characterization of nutrient loss and sediment yield under different rainfall types and crop growth stages were not well studied. Therefore, we designed six treatments for sloping farmlands in the Three Gorges Reservoir Area with a field experiment. A field experiment included downslope cultivation with chemical fertilizer (DF), downslope cultivation with chemical fertilizer plus manure (DFM), cross-slope cultivation with chemical fertilizer plus manure (CFM), no-till straw cover with chemical fertilizer plus manure (NSFM), ridge plant hedges with chemical fertilizer plus manure (RFM), and biochar interception ditches with chemical fertilizer plus manure (BFM). The results indicated that soil and water conservation measures in association with manure substitution significantly reduced runoff depth (14.3–22.5 %), sediment yield (10.3–46.5 %), and total nitrogen (TN) loss (13.5–36.5 %) compared to DF. NSFM significantly reduced total phosphorus (TP) loss by 17.4 % and the TP loss from the other treatments did not show significant differences compared to DF. Rainfall intensity and runoff depth were identified as critical factors influencing nutrient loss and soil erosion. NSFM showed maximal nutrient reduction performance under different rainfall intensities, while DFM was not significantly effective. NO3--N and particulate P dominated the loss of TN and TP. The first 30 minutes of runoff generation and the seedling stage were identified as risk periods for N and P loss. The study suggests that the NSFM treatment was the appropriate method to prevent soil and water nutrient loss. This provides important insights for the precise control of nutrient loss and soil erosion on sloping farmlands.

Evaluating the Impacts of Fertilization and Rainfall on Multi-Form Phosphorus Losses from Agricultural Fields: A Case Study on the North China Plain

Excessive fertilizer application increases the risk of eutrophication and agricultural non-point source pollution (ANPS) in rivers near farmland. However, the processes and mechanisms of runoff and phosphorus losses, particularly in the interflow, under various fertilizer treatments and rainfall scenarios are not well understood. This study used orthogonal experimental methods to investigate the combined effects of fertilization schemes and rainfall intensity on multi-form phosphorus runoff losses and to establish statistical relationships and regression models between phosphorus losses and environmental factors in surface runoff and interflow. The results indicated that (1) the optimized fertilization scheme, compared with conventional fertilization, enhanced pak choi (Brassica rapa) growth while reducing phosphorus runoff losses. By reducing phosphorus fertilization by 35.7%, total phosphorus losses decreased by 29.3%, 34.2%, and 29.8% under light, moderate, and heavy rainfall, respectively. (2) Different fertilizer applications and rainfall intensities had varying effects on phosphorus losses through different pathways. Fertilizer application was the primary factor affecting phosphorus losses in surface runoff, while rainfall intensity mainly influenced phosphorus losses through interflow. (3) Surface runoff was the dominant pathway for phosphorus losses from farmland (>92.0%), with particulate phosphorus (>89.4%) being the predominant form. However, under high-intensity and long-duration rainfall, interflow became a significant pathway for phosphorus losses. This study highlights the importance of optimized fertilization in reducing phosphorus losses and improving fertilizer efficiency in agricultural fields. The findings will help develop strategies to mitigate ANPS and soil nutrient losses in the North China Plain.

Response of hydrology and nutrient losses to different extreme rainfall conditions in a coastal watershed influenced by orchards

Global warming is altering the frequency of extreme rainfall events and introducing uncertainties for non-point source pollution (NPSP). This research centers on orchard-influenced planting areas (OIPA) in the Wulong River Watershed of Shandong Province, China, which are known for their heightened nitrogen (N) and phosphorus (P) pollution. Leveraging meteorological data from both historical (1989–2018) and projected future periods (2041–2100), this research identified five extreme rainfall indices (ERI): R10 (moderate rain), R20 (heavy rain), R50 (rainstorm), R95p (Daily rainfall between the 95th and 99th percentile of the rainfall), and R99p (>99th percentile). Utilizing an advanced watershed hydrological model, SWAT-CO2, this study carried out a comparison between ERI and average conditions and evaluated the effects of ERI on the hydrology and nutrient losses in this coastal watershed. The findings revealed that the growth multiples of precipitation in the OIPA for five ERI varied between 16 and 59 times for the historical period and 14 to 65 times for future climate scenarios compared to the average conditions. The most pronounced increases in surface runoff and total phosphorus (TP) loss were observed with R50, R95p, and R99p, showing growth multiples as high as 352 and 330 times, and total nitrogen (TN) growth multiples varied between 4.6 and 30.3 times. The contribution rates of R50 and R99p for surface runoff and TP loss in the OIPA during all periods exceeded 55%, however, TN exhibited the opposite trend, primarily due to the dominated NO3-N leaching in the sandy soil. This research revealed how the OIPA reacts to different ERI and pinpointed essential elements influencing water and nutrient losses.

Response of runoff N and P concentrations, losses, and stoichiometry to rainfall amount category, multisource fertilization, and straw return in sloping croplands

Nitrogen (N) and phosphorus (P) losses via runoff from sloping croplands are a major threat to the degradations of soil fertility and water quality worldwide. Rainfall amount category and agricultural practices, such as multisource fertilization and straw return, are key factors regulating nutrient loss via runoff in sloping croplands. Yet, the impacts of these factors on N and P losses via runoff remain elusive. This study investigated the responses of N and P in runoff to rainfall amount category, multisource fertilization, and the combination of multisource fertilization and straw return in sloping cropland with a radish and maize rotation during multiple natural rainfall events between 2019 and 2021. Three agricultural treatments (three replications for each), i.e., local traditional fertilization (CK), multisource fertilization (T1), and a combination of T1 and straw return (T2), were applied on nine 8 m × 3 m plots. The concentrations and losses of total nitrogen (TN), total phosphorus (TP), dissolved nitrogen (DN), dissolved phosphorus (DP), particulate nitrogen (PN) and particulate phosphorus (PP) and their paired stoichiometries in runoff were determined. The runoff depth during rainstorms was similar to that in large rainstorms and was 191.1 % and 178.7 % higher than in moderate and heavy rains, respectively (p < 0.05). The PN concentration was the highest during moderate rain, and the highest concentrations of TP and DP were observed during large rainstorms (p < 0.05). Rainstorms and large rainstorms produced higher runoff losses for PN, TP, DP, and PP than for other rainfall amount categories (p < 0.05). Compared to CK, the runoff depth was marginally reduced by 4.2 % and 12.7 % in T1 and T2, respectively, and the concentrations and losses of N and P in runoff also slightly increased in T1 and T2. The DN and DP losses accounted for 70.5 % and 59.8 % of the TN and TP losses across all treatments, respectively, indicating that the dissolved forms played a dominant role in nutrient loss via runoff. TN:TP (77:1) in runoff was higher than the Redfield ratio (16:1) across all treatments, implying a stoichiometric potential for P depletion in the runoff. Our results highlight the potential risk of N and P losses in dissolved form via runoff regulated by rainfall, multisource fertilization and straw return in sloping croplands.

Application of improved risk assessment methods to best management practices research for non-point source pollution: From a hilly mountainous-dominated region of Southern China

Non-point source pollution (NPSP) significantly affects regional water environments worldwide. Identifying critical source areas (CSAs) and implementing best management practices (BMPs) are essential to prevent and control NPSP. This study used the Soil and Water Assessment Tool model to simulate and evaluate the characteristics of NPSP in the Gongjiang Watershed, a typical, hilly mountainous area in Southern China. The study identified CSAs of NPSP using total nitrogen (TN), total phosphorus (TP), water quality level, and population density factors. The reduction effect of different BMPs on the NPSP load was evaluated, and the cost-effectiveness (CE) of various BMPs was evaluated for the control of NPSP in the watershed. The interannual variation in NPSP load was high from 2013 to 2018, with the largest pollution load in 2016 (wet year) and the smallest in 2018 (dry year). The pollution load fluctuated throughout the year and was related to fertilization and precipitation runoff. The spatial heterogeneity of NPSP was large, with TN and TP losses showing a spatial pattern of high in the south, low in the north, and highest in the center. The CSAs of the NPSP covered 1566.66 km2, representing 9.77 % of the total watershed area. However, TN and TP loads accounted for 19.39 % and 23.53 % of total watershed production. The order of effectiveness of individual management measures in reducing TN was stubble coverage (SC) > vegetative buffer strips (VBS) > terrace engineering (TE) > grassed waterways (GW) > 20 % fertilizer reduction (FR20) > 10 % fertilizer reduction (FR10). The order of effectiveness of TP reduction was SC > VBS > TE > FR20 > GW > FR10. Combined management measures were much more effective in reducing TN and TP than individual measures, with an average increase in TN and TP reduction of 20.59 % and 25.23 %, respectively. Based on the results of the CE evaluation of BMPs, a combination of FR20, GW, and VBS was more effective than individual measures. We suggest a combination of FR20, GW, and VBS measures for effective NPSP prevention and control in Southern China’s typical, hilly mountainous areas.

Optimized ridge-furrow technology with biochar amendment for alfalfa yield enhancement and soil erosion reduction based on a structural equation model on sloping land

Water scarcity and water-related soil erosion are severely exacerbated by inappropriate human activities and global climate change. Hence, to find a suitable technology to mitigate drought and soil erosion, three consecutive field experiments were conducted to explore the impact of ridge-furrow cropping with biochar amendment on soil water storage, runoff, sediment yield, soil nutrient losses, alfalfa (Medicago sativa L) fodder yield, crop water productivity (WPc), and economic benefit from 2019 to 2021. This experiment was conducted in a split-plot design, taking biochar amendment patterns (no biochar amendment and biochar amendment at a rate of 3× 104 kg ha−1) as a main plot and ridge-furrow technologies (traditional planting, open-ridging, and tied-ridging) as a split-plot. The combination of biochar amendment with ridge-furrow technology, especially tied-ridging technology, increased soil water storage, and captured runoff, sediment, and related soil nutrient losses, consequently increasing alfalfa fodder yield, WPc, and income. During this study, compared to traditional planting, open-ridging depicted an increase in soil water storage by a range of 9.8–39.6 mm, an alfalfa fodder yield boost ranging from 9.8% to 38.6%, and a WPc increase ranging from 0.1 to 16.5 kg ha−1 mm−1. On the other hand, tied-ridging showed greater improvements with soil water storage increasing by 29.1–65.1 mm, alfalfa fodder yield growing by 11.6–44.4%, and WPc advancing by 0.9–17.5 kg ha−1 mm−1. The mean decrease in runoff, sediment, and nutrients (total nitrogen, total phosphorus, and organic matter) loss for open-ridging was 17.9%-37.7%, 46.4%-75.5%, and 40.4%-75.3%, respectively, while for tied-ridging, it was 22.3%-55.5%, 62.1%-87.6%, and 49.0%-87.3%, respectively. Compared to no biochar amendment, soil water storage, alfalfa fodder yield, and WPc for biochar amendment increased by 9.1%-20.4%, 5.8%-52.7%, and 4.6–7.8 kg ha−1 mm−1, respectively, while runoff, sediment, and nutrients loss for biochar amendment decreased by 32.2%-40.9%, 25.5%-55.5%, and 35.9%-53.3%, respectively. Structural equation modeling analysis indicated that the significant direct effect of biochar amendment and ridge-furrow technology on WPc was 0.20 and 0.62, respectively, whereas the significant direct effect of runoff and actual crop evapotranspiration on alfalfa fodder yield was −0.40 and 0.94, respectively. Tied-ridge cropping combined with biochar addition was a highly suggested approach for addressing soil erosion and enhancing alfalfa fodder yields in the Loess Plateau in China. This technology could mitigate soil water scarcity and soil erosion, and give farmers the confidence to invest in this technology in dryland regions.

Study of Steroid Estrogen Loss in Soil after the Application of Composted Manure as a Fertilizer

Steroid estrogens (SEs) play a significant role as endocrine-disrupting substances, and one of their major sources is animal manure. However, there is limited information available regarding the loss of SEs in farmland soil after the application of commercial composted animal manure or fertilizers. To address this gap, our study aimed to simulate rainfall and flood irrigation scenarios and investigate the loss characteristics of SEs, as well as Chemical Oxygen Demand (COD), Total Nitrogen (TN), and Total Phosphorus (TP) in runoff from soil–manure mixtures. The results demonstrated that the loss concentrations of SEs (73.1 ng/L of the mean E2β active equivalent factor) presented a potential environmental risk. Additionally, substituting composted manure with commercial organic fertilizers lead to a significant reduction in TP (maximum 56%) and TN (maximum 24%) loss. Consequently, the application of commercial organic fertilizers offers considerable advantages in maintaining nitrogen and phosphorus fertilization efficiency while controlling SEs loss. Furthermore, our study explored the synergistic pollution mechanism among these pollutants and observed significant correlations between SEs and TN, TP, and COD loss concentrations, indicating the simultaneous occurrence and migration of these pollutants in agricultural non-point source pollution. These results provide valuable insights into the environmental risk associated with SEs from agricultural non-point sources.

Evaluating the long-term effects of best management practices on pollution reduction and soil quality improvement in sloping farmland of the Three Gorges Reservoir area

Reducing nonpoint-source pollution and improving soil quality by applying best management practices (BMPs) on sloping farmland are essential for ensuring water environmental safety and sustainable agricultural development. However, little is known about the accumulative effect of the long-term application of BMPs on reducing pollution and improving soil quality in major land use types of sloping farmland in watersheds. We conducted a nine-year field experiment for citrus orchard and cropland of sloping farmland in the Three Gorges Reservoir area of China. The treatment settings for the citrus experimental plots were as follows: (1) citrus intercropped with white clover (WC), (2) citrus orchard soil mulched with straw (SM), (3) citrus intercropped with Hemerocallis flava contour hedgerows (HF) and (4) conventional citrus planting pattern (C-CK). The treatment settings for the crop experimental plots were as follows: (1) wheat-peanut rotation intercropped with Toona sinensis contour hedgerows (TS), (2) wheat-peanut rotation intercropped with alfalfa contour hedgerows (AF), (3) ryegrass-sesame rotation (RS) and (4) conventional wheat-peanut rotation (W-CK). We found that compared with C-CK and W-CK, (1) runoff, sediment, total nitrogen and total phosphorus losses were reduced by 18.0 %, 66.1 %, 35.6 % and 40.2 %, respectively, in WC; by 22.4 %, 61.2 %, 43.9 % and 52.4 %, respectively, in SM; by 25.4%, 69.5 %, 52.0 % and 58.1 %, respectively, in HF; by 45.1 %, 73.7 %, 64.6 % and 66.0 %, respectively, in TS; by 41.8 %, 67.4 %, 59.3 % and 60.8 %, respectively, in AF; and by 24.1 %, 42.9 %, 39.3 % and 40.3 %, respectively, in RS; (2) the soil quality index values of the BMP treatments increased; and (3) the application of these BMPs did not significantly affect yield or product value. We suggest the application of these BMPs on sloping farmland to (1) efficiently reduce total runoff, total sediment, and soil total nitrogen and total phosphorus losses; (2) improve soil quality; and (3) have no significant effect on output, of which the BMP HF applied to citrus orchard and the BMP TS applied to cropland are the most effective.

Impact of Intercropping on Nitrogen and Phosphorus Nutrient Loss in Camellia oleifera Forests on Entisol Soil

Soil and water loss represent a significant environmental challenge in purple soil cropland in China. However, the quantity and mechanism of nutrient loss from purple soil remain unclear. To understand water and soil conservation and address nitrogen (N) and phosphorus (P) mitigation in Camellia oleifera forest stands on purple soil slope farmland, this study aimed to explore the resistance control effect of forest stands on N and P loss in such agricultural landscapes. In the study, a runoff plot experiment was conducted in purple soil slope farmland. The experiment included three distinct treatments: intercropping of oil tea (Camellia oleifera) and ryegrass (Lolium perenne L.), Camellia oleifera monoculture, and barren land served as the control treatment (CK). Water samples were collected and analyzed from the soil surface runoff and the middle soil layer at a depth of 20 cm (interflow) in three treatment plots under natural rainfall conditions in 2023. Various nutrient components, including total nitrogen (TN), dissolved nitrogen (DN), nitrate nitrogen (NO3−-N), ammonium nitrogen (NH4+-N), particulate nitrogen (PN), total phosphorus (TP), dissolved phosphorus (DP), phosphate (PO4+-P), and particulate phosphorus (PP), were measured in the water samples. The results indicated that intercropping effectively mitigated the loss of various forms of N and P in both surface runoff and interflow within purple soil slope farmland. Compared to the CK, the ryegrass intercropping reduced TN and TP loss by 29.3%–37.3% and 25.7%–38.9%, respectively. The ryegrass intercropping led to a decrease in the average total loss of TN, DN, NO3—N, and NH4+-N by 63.0, 24.3, 4.5, and 6.8 g/ha, corresponding to reductions of 33.3%, 47.6%, 58.3%, and 49.1%, respectively, compared to the CK. The average total loss of TP, DP, and PP decreased by 4.4, 1.8, and 1.4 g/hm2 in the intercropping, reflecting reductions of 32.3%, 31.3%, and 31.1%, respectively. The most significant proportion was observed in PN and PP within the runoff water solution, accounting for 53.3%–74.8% and 56.9%–61.0% of the TN and TP, respectively. These findings establish a foundation for purple soil and water conservation. The research provides valuable insights for land management and policymakers in developing erosion prevention and control programs for sloping cultivated land with Camellia oleifera forests in purple soils. Additionally, it offers guidance for soil and water conservation and prevention of surface source pollution in purple soil regions.

Transport dynamics of watershed discharged diffuse phosphorus pollution load to the lake in middle of Yangtze River Basin

Diffuse pollution, including that in the lower and middle reaches of the Yangtze River, is the primary source of pollution in several agricultural watersheds globally. As the largest river basin in China, the Yangtze River Basin has suffered from total phosphorus (TP) pollution in the past decade owing to diffuse pollution and aquatic ecology destruction, especially in the midstream tributaries and mid-lower reaches of the lakes. However, the transport dynamics of diffuse pollutants, such as phosphorus (P) from land to water bodies have not been well evaluated, which is of great significance for quantifying nutrient loss and its impact on water bodies. In this study, diffuse pollution estimation with remote sensing (DPeRS) model coupled with Soil and Water Assessment Tools (SWAT) was utilized to simulate the transport dynamics of P, investigate the spatial heterogeneity and P sources in the Poyang Lake Basin. Additionally, the P transport mechanism from land to water and the migration process in water bodies were considered to investigate the impact of each loss unit on the water body and evaluate the load generated by diverse pollution types. The estimated diffuse TP loss was 6016 t P·yr−1, and the load to inflow rivers and to Poyang Lake were 11,619 and 9812 t P·yr−1, respectively. Gan River Basin (51.09%) contributed most TP to Poyang Lake among five inflow rivers, while waterfront area demonstrated the highest TP load per unit area with 0.057 t km−2·yr−1. Our study also identified P sources in the sub-basins and emphasized agricultural diffuse sources, especially planting, as the most significant factor contributing to TP pollution. Additionally, to improve the aquatic environment and water ecological conditions, further nutrient management should be applied using a comprehensive approach that encompasses the entire process, from source transportation to the water body.

Effects of “source-sink” landscape on spatiotemporal differentiation of phosphorus output in multiple watersheds in mountainous areas based on the modified location-weighted landscape index

Optimizing the landscape structure and spatial configuration of the basin is one of the most important ways to reduce the harm of non-point source pollution (NPSP) to water bodies. The coupling relationship between the “source-sink” landscape pattern and NPSP process had long been a research hotspot of “source-sink” landscape theory. However, the “source-sink” landscape index represented by the classic location-weighted landscape index (LWLI) is suitable only for watersheds with similar environmental backgrounds, and cannot reflect the spatiotemporal heterogeneity of phosphorus output between watersheds with large differences in environmental backgrounds. In this study, 15 tributary watersheds in the Poyang Lake Basin were selected as the case study. The characteristics of “source-sink” landscape structure in 2020 were described by using landscape area structure indices. Moreover, the classical LWLI was modified by adding the topographic wetness index, soil erodibility index and vegetation interception index, and by evaluating the spatiotemporal differences in the effect of “source-sink” landscape patterns on phosphorus export in three hydrological periods (normal, wet and dry) by pearson correlation analysis and redundancy analysis. We found that (1) the proportion of “sink” landscape (greater than 58%) was greater than that of “source” landscape (less than 40%) in all sub-watersheds. In addition, the results of Lorentz curves showed that when the elevation and slope increased, the proportion of “source” landscape decreased and the proportion of “sink” landscape increased. (2) the classical and modified LWLI values were less than 0.5, which indicated that the potential contribution of the “sink” landscape was greater than that of the “source” landscape. (3) The correlation between the classical LWLI and total phosphorus (TP) in the wet period and normal period was stronger than the correlation between all “source-sink” landscape area structure indices and TP, indicating that the LWLI was more effective in describing TP loss than were the “source-sink” landscape area structure indices. (4) the correlation of the modified LWLI with TP in the three periods were stronger than those of the classical LWLI with TP, which indicated that the modified LWLI could better indicate the coupling relationship between the “source-sink” landscape pattern and the phosphorus output by introducing the factors of terrain runoff, soil erodibility and vegetation interception. This study can help with the evaluation of the spatial and temporal heterogeneity of nutrient loss in different watersheds with various landscape patterns, and provide a basis for scientific prevention and control of NPSP.

Pressurized electro-osmotic dewatering treatment of sludge: focusing on the influences on nutrients for agricultural application

ABSTRACT Sewage sludge requires effective dewatering and high nutrients retention before disposal for agricultural application. Pressurized electro-osmotic dewatering (PEOD) process with low energy consumption can effectively remove water from sludge, but the influences of PEOD process on nutrients for agricultural application still lacks in-depth research. In this study, the influences of PEOD process on nutrients for agricultural application were investigated, including organic matter, nitrogen, phosphorus, potassium and silicon contents. Layered experiments were conducted to investigate the layered variation of nutrients in sludge and to understand the potential change mechanisms. The experimental results showed that PEOD process caused small losses (<10%) of organic matter and total phosphorus (TP) in sludge, but caused 11.2−18.4% loss of total nitrogen (TN). PEOD process also caused 18.6−27.0% loss of total potassium (TK) and over 80% loss of available potassium in sludge, and could weaken the potential salt damage during the agricultural application of sludge. Furthermore, the available phosphorus content of sludge in the anode area increased significantly after the PEOD process, indicating that PEOD process could enhance the phosphorus bioavailability of sludge in the anode area. Besides, PEOD process caused a slight loss of silicon components in sludge, but improved the long-term silicon dissolution and release ability of sludge. This work could expand the knowledge about the influences of PEOD process on sludge nutrients and provide scientific guidance for the agricultural application of PEOD sludge.

Runoff, sediment, organic carbon, and nutrient loads from a Canadian prairie micro-watershed under climate variability and land management practices

This study conducted a spatio-temporal analysis of runoff, total suspended sediment, suspended particulate carbon, nitrogen, and phosphorus loadings within the 2.06 km2 Steppler subwatershed in southern Manitoba of Canada based on 11 years of field monitoring data collected at nine stations. Results showed that the nutrient losses were very small because of the implementation of multiple BMPs in the study area. However, a high spatio-temporal variation of runoff and water quality parameters was found for the nine fields within the subwatershed. The average runoff coefficient was 0.19 at the subwatershed outlet with sediment, suspended particulate carbon, total nitrogen, and total phosphorus losses of 73.8, 6.10, 4.54, and 0.76 kg/ha respectively. Spring snowmelt runoff was about 74.5% of the annual runoff at the subwatershed outlet, while for sediment, suspended particulate carbon, total nitrogen, and total phosphorus, the proportions were 61.1%, 63.6%, 74.9%, and 81.2% respectively during the monitoring period, which suggests that BMPs designed for reducing nutrient loadings from snowmelt runoff would be more effective than BMPs designed for reducing pollutant loading from rainfall storms in the study area. Research findings from this study will benefit the enhancement of current BMPs and the development of new BMPs in the region to minimize soil and nutrient losses from agricultural fields and improve water quality in receiving water bodies.

Grazing management impacts on ecosystem services under contrasting climatic conditions in Texas and North Dakota

Grazing management is an important factor affecting the delivery of ecosystem services at the watershed scale. Moreover, characterizing the impacts of climate variation on water resources is essential in managing rangelands. In this study, the effects of alternative grazing management scenarios on provisioning, regulating, and supporting services were assessed in two watersheds with contrasting climates; the Lower Prairie Dog Town Fork Red River (LPDTFR) Watershed in North Texas and the Apple Watershed in South Dakota. The impacts of heavy stocking continuous grazing, light stocking continuous grazing, Adaptive Multi-Paddock (AMP) grazing, and an ungrazed exclosure were compared using the Soil and Water Assessment Tool (SWAT) model. Our results indicate that the quantity of snow and timing of snow melt substantially influenced grazing management effects on ecosystem services in the Apple Watershed. In contrast, precipitation was the main factor influencing these effects in the LPDTFR Watershed because it highly affected the variation in water cycling, streamflow, sediment, and nutrient controls. Simulated results indicated that AMP grazing was the optimal grazing management approach for enhancing water conservation and ecosystem services in both watersheds regardless of climatic conditions. The Apple Watershed, which is a snow-dominated watershed, exhibited greater ecosystem service improvements under AMP grazing (50.6%, 58.7%, 74.4%, 61.5% and 72.6% reduction in surface runoff, streamflow, and sediment, total nitrogen (TN) and total phosphorus (TP) losses, respectively as compared to HC grazing) than the LPDTFR Watershed (46.0%, 22.8%, 34.1%, 18.9% and 38.4% reduction in surface runoff, streamflow, and sediment, TN and TP losses, respectively). Our results suggest that improved grazing management practices enhance ecosystem services and water catchment functions in rangeland-dominated areas, especially in colder climates.

Loss and conservation of soil organic carbon and nutrients in arid and semiarid China during aeolian dust emissions

In this study, based on the application of the integrated wind erosion modeling system (IWEMS), we comprehensively simulated the loss and conservation of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and total potassium (TK) during aeolian dust emissions over 2001–2020 in the arid and semiarid areas of China (ASAC). It was found that the past two decades witnessed decreasing trends in nutrient losses over the central-eastern region of Inner Mongolia, most parts of Qinghai Province, the southern part of the Xinjiang Autonomous Region, and the northwestern part of the Tibet Autonomous Region. The results, being model-based estimates, showed that the ecosystems of the ASAC were crucial in preventing annual losses of SOC, TN, TP and TK: approximately 27318.25 Gg, 2311.18 Gg, 1077.28 Gg and 35780.10 Gg, respectively. Both the losses and conservation of SOC, TN, TP and TK were consistently greater in spring and winter than in summer and autumn. The losses of SOC and nutrients during aeolian dust emissions were more serious in the west of the ASAC than in the east, both in the actual situation and the potential degenerative status. The prevention rates of SOC, TN, TP and TK for different land cover types were all greater than 92%. Comparatively speaking, the prevention rates of SOC, TN, TP and TK were the lowest for barren or sparsely vegetated land (∼92.85%−93.12%), open shrublands (∼95.65%−96.10%) and grasslands (∼98.44%−98.50%). For other land cover types, the prevention rates of SOC, TN, TP and TK were all over 99.62%.

Analysis of nitrogen and phosphorus loss of typical economic forests in Zhejiang Province

The quantitative relationship between accumulated rainfall and accumulated total nitrogen and total phosphorus loss was analyzed by setting up economic forest experimental sites in typical regions of Zhejiang Province, and the response efficiency of accumulated total phosphorus and total nitrogen loss in different economic forests to rainfall was compared The results showed that there was a significant linear relationship between accumulated rainfall and accumulated total nitrogen and total phosphorus loss. The total nitrogen and total phosphorus loss rate of Castanea mollissima Blum economic forest was higher than that of Phyllostachys edulis forest and nursery &gt; Morella rubra &gt; Camellia sinensis &gt; Phyllostachys edulis. Man-made disturbance of economic forest will accelerate the loss of total nitrogen and total phosphorus, and its loss rate is 1.5~4 times that of natural economic forest. The total nitrogen loss rate of 28% and total phosphorus loss rate of 47% can be reduced by planting shrubs or herbs under the in the Phyllostachys edulis forest. The purification efficiency of total phosphorus and total nitrogen of different economic forests is affected by economic forest types, ecological restoration, rainfall, and the purification efficiency varies between 30% and 70%.

Monitoring, Modeling and Planning Best Management Practices (BMPs) in the Atwood and Tappan Lake Watersheds with Stakeholders Engagements

This study was conducted in the Atwood and Tappan Lakes watersheds of the Tuscarawas basin of Ohio. The flow, total nitrogen (TN), and total phosphorus (TP) loadings were monitored with the help of local stakeholders for a few years at various locations of the watershed to develop the Soil and Water Assessment Tool (SWAT). The multi-site SWAT model calibration and validation were accomplished with a reasonable model performance. In the next step, the scenario analysis was conducted in the SWAT model using various BMPs, including vegetative filter strips, grass waterways, fertilizer reduction, crop rotation, and cover crops to evaluate their performance in reducing TN and TP from the watershed. While BMPS in many studies are decided based on researchers’ intuition, these BMPs were selected based on active consultation with the local stakeholders, who were engaged in the reduction of TN and TP loadings from the watersheds. Since the SWAT model calibration for TN and TP was not as good as the hydrologic model calibration, various scenarios of TN and TP reduction using BMPs were investigated for several years using both calibrated and uncalibrated SWAT models. We examined all the BMPs in 12 sub-watersheds of the Atwood and 10 sub-watersheds of the Tappan Lake watershed. The analysis indicated that the management practices of cover crops (rye) in combination with grass waterways with a 10% fertilizer reduction could minimize the TN and TP loading by as much as 88%, without significantly compromising the agricultural yield. However, a 10% fertilizer reduction without any BMPs could reduce TN and TP by just 9%. The cover crop (rye) including 10% fertilizer reduction with grass waterways seemed to be the most effective in reducing TN and TP, whereas the implementation of a filter strip led to a 70% reduction and was the next effective BMPs in reducing TN and TP loadings. In general, TN losses were reduced by 8% to 53%, while TP losses were reduced by 7% to 88%, depending on the BMPs used. By and large, the TN and TP reduction achieved through the calibrated model was not significantly different from the uncalibrated model, even though the reduction using the calibrated model was slightly higher for all scenarios than that of the uncalibrated model. The TN and TP loadings were highly sensitive to cattle grazing. When just 50% of the cattle were permitted to graze, the model predicted that there would be a 40% increase in total nitrogen and a 70% increase in total phosphorus in both watersheds. Our investigation revealed that monitoring the watershed at a small sub-watershed scale and calibrating the SWAT model for nitrogen and phosphorus is delicate.

Biochar or Straw Substituting Chemical Fertilizer Increase the Risk of Phosphorus Loss in Subsurface Runoff in Sloping Farmland

The purple soil slope farmland is an important agricultural land in southwest China but is also one of the main sources of agricultural non-point source pollution in the Three Gorges Reservoir area. Taking reasonable measures to control the loss of soil nutrients is of great significance to the treatment of non-point source pollution in the region. Here, a three-year (2018-2020) field runoff experiment was conducted to monitor and evaluate the phosphorus (P) loss in sloping farmland via surface runoff (i.e., surface flow, 0-20 cm) and subsurface runoff (i.e., subsurface flow, 20-60 cm), with five treatments including no fertilization (CK), conventional fertilization (CF), optimal fertilization (OF), biochar combined with 85% of OF (BF), and straw combined with 85% of OF (SF). The results showed that fertilization application reduced the sediment yields and surface runoff flux but increased the subsurface runoff flux. The total loss flux of phosphate (PO3-4-P), total phosphorus (TP), and particulate phosphorus (PP) in surface flow were the highest in the BF treatment and the lowest in the SF treatment. All fertilization applications increased the P loss fluxes in subsurface flow relative to that in CK. The highest PO3-4-P and TP loss flux in subsurface flow was found in the BF (213.88 g·hm-2 and 694.54 g·hm-2, respectively) treatment, followed by that in the OF and SF treatments. Redundancy analysis (RDA) results showed that surface runoff flux and biochar application were the main factors contributing to increased P loss in surface flow, and subsurface runoff flux was the main factor contributing to increased P loss in subsurface flow. In summary, the SF treatment reduced the amount of sediment yield and surface runoff flux in sloping farmland of purple soil and was the most effective for controlling P loss, whereas the risk of subsurface runoff flux requires further attention.

Study on characteristics of soil and nutrient losses in Sunjiagou small watershed in cold black soil area.

Investigating the impact of different factors on soil and nutrient loss and suggesting viable control measures is currently a significant concern. This study aims to examine the variations in soil erosion, as well as nitrogen and phosphorus loss, in the core area of the typical hilly diffuse Blackland erosion control. To achieve this, runoff plots with slopes of 3° and 5° were set up in the Sunjiagou sub-basin, located in the upper reaches of the Feiketu River. These plots were subjected to various soil and water conservation measures, along with different levels of vegetation cover. This study aims to analyze the soil and nutrient loss patterns and characteristics in each runoff plot during the natural rainfall events occurring between 2020 and 2022. The results show that soil and nutrient losses are highly significantly and positively correlated with rainfall intensity. The RUSLE model demonstrates a better fit for both cross ridge tillage and bare ground. The loss of nitrogen was much more significant than that of phosphorus, and nitrate nitrogen is the main form of nitrogen loss. Nitrogen loss is mainly dominated by nitrate nitrogen (NN), which is easily soluble in water and constantly migrates with runoff due to the negatively charged NN (NN accounted for 45.2% ~ 81.8% of total nitrogen (TN)). In contrast, the positively charged ammonia nitrogen (AN) is more stable in combination with the soil; large losses only occur under severe sediment erosion. Phosphorus is easily attached to sediment, and the high sediment production leads to a more serious loss of total phosphorus (PP) in the particulate state (PP accounts for 72.7% ~ 96.2% of total phosphorus (TP)). Changing longitudinal ridge tillage to cross ridge tillage and planting vegetation with better water retention and sediment fixation as plant hedges can effectively prevent the loss of soil, runoff, nitrogen, and phosphorus.

Soil erosion and nutrient loss due to changes in rainfall intensity under different wind directions

AbstractIn nature, wind often occurs simultaneously with rainfall, causing nutrient loss in soil and water on slopes. However, the influence of different rainfall intensities combined with different wind directions on soil erosion and nutrient loss remains unclear. This study utilized wind‐driven rainfall laboratory flume experiments to analyse the influence of different wind directions (windward, leeward and crosswind) and rainfall intensities (30, 60 and 90 mm h−1) with constant wind speed (5 m s−1) on slope runoff, sediment yield and the associated losses of different forms of N ( , ) and P ( ‐P). The response of soil erosion, N and P loss to rainfall changes with different wind directions. When the rainfall intensity was constant, runoff, sediment yield and sediment‐associated total nitrogen (TN) and total phosphorus (TP) losses on slopes showed a trend of leeward &gt; crosswind &gt; windless &gt; windward, whereas runoff‐associated TN and TP losses showed a trend of windward &gt; crosswind &gt; windless &gt; leeward. Runoff, sediment yield and sediment‐associated TN and TP losses on leeward slopes were 1.09–1.17, 1.25–1.44, 1.33–1.62, and 1.40–1.66 times than windless slopes. Moreover, with constant wind direction, the runoff, sediment yield and associated N and P losses increased significantly with increasing rainfall intensity. When the rainfall intensity increased from 30 to 60 and 90 mm h−1, the runoff, sediment yield and associated TN and TP losses increased 2.02–2.28, 3.65–5.35, 3.96–34.39 and 4.28–8.45 times, respectively. The effects of rainfall on soil erosion and nutrient loss were significantly greater than those of wind. The loss of different forms of N and P associated with runoff and sediment was consistent with that of TN and TP losses. However, with an increase in rainfall intensity, the growth rates of runoff, sediment yield and associated N and P losses exhibited a gradually weakening trend for all wind directions. An increase in rainfall intensity enhanced the vertical vector force of wind‐driven rainfall, which increasingly decreased the angle between the rain incidence and the normal line of the horizon; therefore, the direction of the rain erosion force gradually approached that of windless conditions.