Search

The catchment phosphorus buffering capacity (PBF) determines the pressure-state-response relationship between anthropogenic P inputs and aquatic ecosystems at a catchment scale, and is affected by biogeochemical, hydrological, and ecological catchment characteristics. However, the complex relationship between these catchment characteristic factors and their impact pathways on PBF remains ambiguous, leading to large uncertainty in balancing agricultural productivity and water conservation via improving BF through management practices. In this study, the short-term buffering index, calculated from net anthropogenic P input and riverine P exports, was used to quantify the spatiotemporal variations in PBF in source agricultural catchments in the Dongting Lake basin. Partial least squares structural equation modeling was used to investigate the relationship between the PBF and the catchment characteristics. The results indicate that catchment PBF was directly determined by soil properties and hydrological conditions, while landscape patterns significantly mediated the effects of topography on soil and hydrology. Considering the pathway preferences of the model, landscape patterns could be the priority for characterizing and regulating PBF. According to a change-point analysis, the probability of PBF weakening increases dramatically when the proportion of farmland (Farm%) > 24.6%, degree of patch interspersion (Contagion index) < 64.5%, and Perimeter-Area Ratio Distribution (PARA) > 348.7. These findings provide new insights into catchment buffering mechanisms and can be used to promote the simultaneous achievement of agricultural production and environmental conservation goals., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Landscape composition and configuration determine the exchange of matter and energy among different landscape patches and may affect riverine phosphorus (P) exports derived from watershed legacy sources. However, a lack of understanding of landscape pattern effects on legacy P releases has yielded large uncertainties in mitigating watershed water quality using management practices or landscape planning. This study revealed the significance of legacy effect in the headwater catchments through the time-lag response of the long-term trend of river P exports to the change of net anthropogenic P input (NAPI). By constructing empirical statistical models that incorporated NAPI, hydroclimatic, terrain factors, soil chemical properties, and land use variables, the sources of annual riverine total phosphorus (TP) and dissolved inorganic phosphorus (DIP) exports were divided into current annual NAPI input and legacy sources inputs. The model estimations indicated that the contribution of legacy sources to riverine TP exports was 0.33-1.12 kg ha -1  yr -1 (50.7-82.8%), which was significantly higher than the contribution to DIP exports (0.18-0.49 kg ha -1  yr -1 , 42.4-81.4%) in 2012-2017. Redundancy analysis (RDA) and variance partitioning analysis (VPA) methods were used to quantify the relative contribution of landscape patterns, soil P content, and terrain factors to legacy P releases. Results revealed that the relative contribution of the landscape composition and configuration to the total variations of legacy P releases was greater than that of the soil P and terrain factors. For different land use patches, a large area of woodland with a high aggregation degree and a large area of ponds with multiple net structures may significantly alleviate legacy P releases. In contrast, the legacy P releases were significantly positively associated with highly aggregated agricultural, tea plantation, and residential patches. This study provides theoretical support for strategies aiming to control legacy P from the perspective of landscape planning., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Exploring the relationship between net anthropogenic phosphorus input (NAPI) and soil available P (SAP) content could inform applied issues related to environmental quality and agronomic productivity and increase our knowledge of element biogeochemical cycles. Here, the NAPI was estimated and the SAP content determined in eight counties in subtropical China from 1980 to 2010. It is suggested that the NAPI ranging 318-924 km -2  yr -1 in 1980 had increased substantially to 865-3601 km -2  yr -1 in 2010 across the eight counties, in which the P fertilizer application was estimated to represent the largest individual source of NAPI, accounting for an average of 36.1-74.6% of the NAPI. The NAPI in agricultural land (NAPI a ) was the largest component of the NAPI, and 60.7-77.1% of the NAPI a accumulated in the upper 20 cm layer of agricultural soils, which significantly increased soil total-P (TP) and SAP contents. The increases in SAP, resulting from 10,000 kg P km -2 of the NAPI a (IOP NAPI ), were estimated to be 1.61-4.36 mg P kg -1 in the counties. Both the correlation and variation partitioning analyses (VPAs) suggested that the soil pH and organic matter content (SOM) were the most important factors influencing the variations of IOP NAPI (determination coefficient: 72.5%). Therefore, the contribution of soil pH and SOM should be considered in enriching soil SAP levels and implementing optimal P management strategies to improving the agronomic effectiveness of P fertilization and further reduce the environmental risk of P loss in subtropical region., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Water eutrophication, particularly that caused by phosphorus runoff, is of major concern in China due to the serious threats it poses to watershed environments. We investigated one forested and nine agricultural watersheds with areas of 9-5212 ha in a hilly region of Hunan Province in a subtropical region of southern China from 2010 to 2012 to study total phosphorus (TP) loads and contributing factors. The annual TP loads varied from 35.7 to 222.1 kg P km(-2) year(-1) among the different watersheds, with the rainy season of spring and summer accounting for 56.3-82.0% of TP loss. The highest total maximum daily load (TMDL, 0.5 kg P km(-2) day(-1)) and existing exported daily TP loads (DTPL, 1.8 kg P km(-2) day(-1)) were observed under high flow and moist flow conditions in the ten watersheds. However, the target daily reduction ratios for the DTPLs to reach the water quality standard of 0.05 mg P L(-1) varied little with flow condition in the stream but depended on the type of watershed, i.e., <50, <80, and 80-90% for forested, agricultural, and livestock-dominated watersheds, respectively. Gray relational analysis (GRA) suggested that livestock density was the most important factor for watershed TP load under various hydrologic conditions, while livestock density (LD), soil available phosphorous (SAP), cropland percentage, and mean shape index (SHMN) were notable factors for daily reduction rate (DRR) under high and moist flow conditions. Therefore, to protect the local watershed environments, watershed management approaches that include the regulation of livestock production are recommended as the most effective means of reducing P loads at the watershed scale in subtropical areas of southern China.

Water eutrophication in subtropical regions of southern China threatens watershed health and is of major concern. However, annual phosphorus (P) loading and its dominant causes are still unclear, especially at the watershed scale. In this study, we investigated dynamic P loadings and associated factors (e.g., land use, livestock production, and runoff depth) in ten watersheds that varied in area from 9 to 5,212 ha in a hilly area of Hunan Province, China. A flowmeter was installed at the outlet of each watershed, and total P (TP) and soluble P (SP) concentrations were monitored periodically from June 2010 to October 2012. The results showed that annual P loadings (APLs) in the ten watersheds ranged from 22.8 to 247.8 kg P/km(2) and that P loss primarily occurred from April to June of each year during the main rainfall season in the study area. In addition, the average eutrophication (>0.05 mg P/L) ratio for stream waters was 86.7 % during the study period, which was indicative of a potentially serious condition for the local water environments. Annual P loadings were linearly related to livestock density (LD; R = 0.92, p < 0.01), whereas the eutrophication ratio of stream water was significantly (p < 0.05) correlated with LD (R = 0.61), percentage cropland (R = 0.71), and percentage forest cover (R = -0.68). Thus, it is concluded that the control of livestock production has the greatest potential for reducing P loadings in watersheds in this subtropical area. This will be beneficial to the amelioration and protection of local environment.

Intensive soil erosion and nutrient loss from slope land not only resulted in the serious degradation of soil quality, but also threatened the water environment of the lower area. In this paper, a simulated rainfall experiment with loessial soil was conducted to study the characteristics of the loss of different phosphorus forms under the conditions of tillage and compaction (no-tillage). The results showed that in comparing with compaction, tillage increased the loss of dissolved P(DP), sediment extractable P(SEP) and sediment total P(STP) by 10 times due to the increase of runoff and sediment amount. The forms of the lost P were mainly sediment-combined P, and the ratios of DP/BAP and BAP/TP in the lost runoff were 12% and 2.6% under compaction, and 15% and 2.4% under tillage, respectively. The application of no-tillage or mulch-keeping fallow in Summer was effective to decrease soil and nutrient loss from slope land, which would be effective and significant both to soil degradation prevention and water environment protection in the lower area of Loess Plateau.

A simulated rainfall experiment was conducted to study the effects of three phosphorus application methods on phosphorus loss and its forms in loss process. The results showed that the bio-available P (BAP) loss in runoff was positively correlated to the mixed intensity of P applied into soil. Under mixed application (MA), the dissolved phosphorus (DP) concentration, BAP concentration, DP/BAP and BAP/TP ratio in runoff were all the highest, and those under point application (PA) were the second. Under line application (LA), DP and BAP concentrations were low, DP/BAP and BAP/TP ratio were also relatively low, and the difference compared with control was insignificant. According to the reduction of P loss, the order of the three P application methods was LA > PA > MA.

Land use has obvious influence on surface water quality; thus, it is important to understand the effects of land use patterns on surface water quality. This study explored the relationships between land use patterns and stream nutrient levels, including ammonium-N (NH-N), nitrate-N (NO-N), total N (TN), dissolved P (DP), and total P (TP) concentrations, in one forest and 12 agricultural catchments in subtropical central China. The results indicated that the TN concentrations ranged between 0.90 and 6.50 mg L and the TP concentrations ranged between 0.08 and 0.53 mg L, showing that moderate nutrient pollution occurred in the catchments. The proportional areal coverages of forests, paddy fields, tea fields, residential areas, and water had distinct effects on stream nutrient levels. Except for the forest, all studied land use types had a potential to increase stream nutrient levels in the catchments. The land use pattern indices at the landscape level were significantly correlated to N nutrients but rarely correlated to P nutrients in stream water, whereas the influence of the land use pattern indices at the class level on stream water quality differentiated among the land use types and nutrient species. Multiple regression analysis suggested that land use pattern indices at the class level, including patch density (PD), largest patch index (LPI), mean shape index (SHMN), and mean Euclidian nearest neighbor distance (ENNMN), played an intrinsic role in influencing stream nutrient quality, and these four indices explained 35.08 % of the variability of stream nutrient levels in the catchments ( p<0.001). Therefore, this research provides useful ideas and insights for land use planners and managers interested in controlling stream nutrient pollution in subtropical central China. [ABSTRACT FROM AUTHOR]

Highlights: [•] Rice agriculture affects nutrient chemical composition in stream water [•] Rice agriculture has a potential to degrade stream water quality [•] Influence of rice agriculture on nutrients in stream water is nonlinear [•] Influence is detectable when areal proportion of rice agriculture is >12–29% [Copyright &y& Elsevier]