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Nutrient discharge into rivers and estuaries and the factors that control it need to be further understood to decrease the risk of harmful algae blooms on these ecosystems. Preliminary seasonal physicochemical parameters at six stations along the Negro River Estuary (Argentina) were studied during 2019 (Austral summer, winter, and spring) with high- and low-frequency data. Three of the stations were mainly estuarine-influenced and three were marine-influenced ones. The concentration of phosphate (P), river discharge, meteorological conditions, seasonality, and physicochemical variables were analyzed. Total phosphorus (TP) showed seasonal variations and was higher than previously reported for the upper watershed in all stations in the warmer months, except for the marine control one. Orthophosphate values were also high compared to previous watershed data and changed independently of TP fluctuations. Changing turbidity, water temperature, pH, and conductivity did not appear to have an essential role in phosphorus variations. An unexplained high TP spike in the late spring sample shows the need for further research in the area, while the seawater mixing with P-rich river water could be acting as a dilution agent at the mouth of the river. [ABSTRACT FROM AUTHOR]

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Over the past decades, wildfires have affected vast areas of Mediterranean ecosystems leading to a variety of negative on- and off-site environmental impacts. Research on fire-affected areas has given more attention to sediment losses by fire-enhanced overland flow than to nutrient exports, especially in the Mediterranean region. To address this knowledge gap for post-fire losses of phosphorus (P) by overland flow, a recently burnt forest area in north-central Portugal was selected and instrumented immediately after a wildfire. Three slopes were selected for their contrasting forest types (eucalypt vs. pine) and parent materials (granite vs. schist). The selected study sites were a eucalypt site on granite (BEG), a eucalypt site on schist (BES) and a maritime pine site on schist (BPS). Micro-plots were monitored over a period of six months, i.e. till the construction of terraces for reforestation obliged to the removal of the plots. During this 6-month period, overland flow samples were collected at 1- to 2-weekly intervals, depending on rainfall. Total P and PO 4 -P losses differed markedly between the two types of forests on schist, being lower at the pine site than at the eucalypt site, probably due to the presence of a protective layer of pine needle cast. Parent material did not play an important role in PO 4 -P losses by overland flow but it did in TP losses, with significantly lower values at the eucalypt site on granite than that on schist. These differences in TP losses can be attributed to the coarser texture of granite soils, typically promoting infiltration and decreasing runoff. The present findings provided further insights into the spatial and temporal patterns of post-fire soil nutrient losses in fire-prone forest types during the initial stages of the window-of-disturbance, which can be useful for defining post-fire emergency measures to reduce the risk of soil fertility losses. [ABSTRACT FROM AUTHOR]

Dissolved reactive phosphorus (DRP) export from agricultural areas is a leading cause of nutrient pollution in freshwater systems (e.g., the North American Great Lakes). A potential solution to mitigate the excessive release of DRP is the use of nutrient management. To evaluate the effectiveness of nutrient management for phosphorus (P) in the United States, we conducted a review to synthesize P management and DRP export data from peer-reviewed articles published between 2000 to 2022. We identified 15 publications and extracted 113 and 90 observations from plot- and field-scale studies, respectively. At the plot scale, mean DRP concentrations were approximately 60% lower when P application rates were below the maximum recommended rate. In addition to the lower mean value, more extreme DRP export events occurred when the P fertilization rate was greater than the maximum recommended rate. In terms of application method, subsurface placement reduced mean DRP concentrations during rainfall simulations by 88% relative to surface placement (i.e., broadcasting). For fertilizer sources, mean DRP concentrations were similar between inorganic and organic fertilizers. However, at high application rates, organic fertilizers had a greater potential to produce extreme DRP export events. At the field-scale, organic fertilizers applied at high rates had the potential to produce extreme DRP export events. However, field-scale results for the other nutrient management techniques were generally inconclusive due to a limited number of studies and confounding factors. Overall, these results displayed the potential adverse impacts of overfertilization and the surface application of P fertilizers and highlighted the need for further research into the influence of nutrient management on P losses.

• P export in mixed land use, subtropical catchment simulated using HYPE. • P export is mainly driven by surface runoff erosion and adsorption/desorption. • Point inputs led to elevated stream TP concentrations in low-flow conditions. • Storm events during March-August account for most of the annual TP export. Water quality degradation and eutrophication in surface water bodies caused by excessive phosphorus loads from agriculture and urbanisation are widespread problems. Although phosphorus (P) is often the limiting factor of aquatic ecosystems, only few studies have characterised the primary factors that influence P export in subtropical monsoon catchments. This study aims to assess the temporal and spatial variations in P fluxes, and to investigate the factors controlling P export in a subtropical catchment. Runoff and P export in the Le An River catchment, which flow to Poyang Lake (China) were evaluated using the HYPE model. Sensitivity analysis and calibration of hydrological and P transport parameters were undertaken using PEST. Results show that: (a) HYPE reproduced sufficiently well (NSE ≥ 0.73, | PBIAS | ≤ 14.5%) the stream flow dynamics for widely varying climatic conditions and across six sub-catchments of contrasting physiographic characteristics; (b) HYPE captured intra-annual patterns of total P (TP) loads, although with overestimation of annual TP loads by 8.5–47.0% across two monitoring sites; (c) TP loads had the ranges between 0.24 and 0.88 kg/ha/yr and 4.31–4.69 kg/ha/yr from forest-dominant upstream areas and the downstream plains region, respectively, with the latter being more urbanised and having higher percentage of agriculture; (d) Soil erosion from surface runoff and adsorption/desorption of soil P are the main factors controlled P export from the catchment; (e) most P export occurred during March-August when rainfall-runoff is highest and agricultural practices are most active; (f) stream TP concentrations were greatly affected by point source inputs, especially during low-flow conditions in downstream plains region. This study indicates that measures to reduce TP export to receiving water bodies in subtropical monsoon areas, like Poyang Lake, should focus on managing diffuse sources from soil erosion and surface runoff etc., whereas improvements to sewage management is more likely to reduce river TP concentrations during low-flow periods. [ABSTRACT FROM AUTHOR]