Riverine flux of dissolved phosphorus to the coastal sea may be overestimated, especially in estuaries of gated rivers: Implications of phosphorus adsorption/desorption on suspended sediments

New insights into estimation of bioavailable inorganic phosphorus in natural coastal seawater

Considering the impact of the high salinity and high turbidity of coastal seawater on phosphorus forms, a new method was proposed to determine bioavailable inorganic phosphorus (BIP). The phosphorus most relevant to eutrophication is BIP, and traditional analysis methods may underestimate the degree of eutrophication. In this study, a microelectrode of multigold (AuμE) was fabricated for direct voltammetric determination of BIP without filtration, and BIP environmental characteristics including distribution and correlation relationships with environmental factors in typical coastal seawater of Northern China were analyzed. The proposed AuμE showed a low detection limit of 0.03 μM. The surface and bottom BIP concentrations ranged from 1.00 to 2.13 and from 0.88 to 2.05 μM, respectively. BIP dominated the total P (TP) accounting for 48.5-67.5 % in the surface layer samples, and 32.6-92.7 % in the bottom layer samples, respectively. The concentrations of BIP were obviously higher than those of DIP, indicating that DIP may underestimate the probability of eutrophication occurring. And BIP was positively correlated with dissolved oxygen (DO) (P < 0.05). BIP may be a promising indicator of eutrophication potential in coastal areas with high salinity and high turbidity. The proposed reliable voltammetry method provides a new indicator for environmental assessment and represents a significant step in the comprehensive analysis of P species.

Weekly variations of nutrients and their associations with phytoplankton blooms in the urban coastal waters of Andaman Sea coast: A case study in Patong Bay, Phuket, Thailand

Nutrient inputs to coastal waters are among the main contributors to phytoplankton blooms that can damage coastal ecosystems. To understand the main causal factors and timing of phytoplankton blooms in Patong Bay, where phytoplankton blooms have frequent occurred for the last decade, variations in phytoplankton abundance and the dissolved inorganic nutrients (nitrogen (DIN), phosphorus (DIP), and dissolved silica (DSi)) were monitored weekly from December 2021 to December 2022. The results revealed that ratios of DIP and DSi to DIN in seawater had increased rapidly in approximately 1-7 days prior to the blooms of Chaetoceros and Eunotogramma. This suggests that the diatom blooms in this area are significantly controlled by an excess of DIP and DSi, in otherwise appropriate environmental conditions. Our findings provide a thorough understanding of the role of excess nutrients on phytoplankton blooms in urban coastal waters, supporting informed coastal management actions.

Distribution of geochemical forms and bioavailability of phosphorus in the surface sediments of Beypore Estuary, southwestern coast of India

Nutrient management in shallow transitional aquatic systems is very complex due to the sediment-water exchange, especially for phosphorus. The present study tries to get an in-depth understanding of the distribution of geochemical forms of phosphorus in the surface sediments of Beypore Estuary, a tropical estuarine system in southwest India, which has been subjected to immense climate change in recent times. Total phosphorus in the sediments was found to be abysmally lower (76.8 to 889.12 µg/g) than those reported for other tropical estuaries. Organic-bound phosphorus constituted the majority of the total phosphorus in the sediments, and unlike other tropical estuaries, iron-bound and calcium-bound phosphorus were minor fractions in the study region. However, the bioavailable phosphorus was consistent throughout the study period and varied from 16.5 to 51.0% of total phosphorus. This reveals the active phosphorus buffering in the Beypore Estuary even in the absence of an external source. Statistical evaluation of two contrasting seasons (low and high runoff periods) could illustrate the major biogeochemical pathways for phosphorus in the Beypore Estuary. This study highlights the significant role of hydrographical parameters in regulating phosphorus bioavailability in this estuary; therefore, any modifications to the same by climate change could make nutrient management even more challenging.

Role of Mine Tailings in the Spatio-Temporal Distribution of Phosphorus in River Water: The Case of B1 Dam Break in Brumadinho

Human actions in the drainage network of hydrographic basins interfere with the functioning of ecosystems, causing negative impacts on the environment. Among these impacts, mass loads with a high concentration of phosphorus (P) have a significant potential for point and diffuse pollution of freshwater. The objective of this work was to model P spatially in the Paraopeba River basin, namely in the main water course and 67 sub-basins, and temporally in the years of 2019, 2020, and 2021, after the rupture of B1 tailings dam of Vale, SA company in Brumadinho (Minas Gerais Brazil). The distribution of total phosphorus concentrations (Pt) in relation to environmental attributes (terrain slope, soil class, and land use) and stream flow was assessed with the help of SWAT, the well-known Soil and Water Assessment Tool, coupled with box-plot and cluster analyses. The Pt were obtained from 33 sampling points monitored on a weekly basis. Mean values varied from 0.02 to 1.1 mg/L and maximum from 0.2 to 15.9 mg/L across the basin. The modeling results exposed an impact on the quality of Paraopeba River water in a stretch extending 8.8–155.3 km from the B1 dam, related with the rupture. In this sector, if the contribution from the rupture could be isolated from the other sources, the average Pt would be 0.1 mg/L. The highest Pt (15.9 mg/L) was directly proportional to the urban area of a sub-basin intersecting the limits of Betim town and Belo Horizonte Metropolitan Region. In general, urban sprawl as well as forest-agriculture and forest-mining conversions showed a close relationship with increased Pt, as did sub-basins with a predominance of argisols and an accentuated slope (>20%). There were various moments presenting Pt above legal thresholds (e.g., >0.15 mg/L), mainly in the rainy season.

Phosphorus in soils and fluvial sediments from a Cerrado biome watershed under agricultural expansion

Over the past decades, lands alongside Gurguéia River have witnessed rapid expansion of soybean agriculture which has increased soil degradation and affected nutrient concentration in sediment, especially phosphorus (P). The present study aimed to quantify the P concentration in soils under different land uses (i.e., croplands, grasslands, and cerrado) and fluvial sediments (suspended sediment, channel bank, and riverbed sediments), assessing pollution over the main watercourse in cerrado biome Gurguéia watershed, located in Piauí State, Brazil. In total, 136 composite soil samples at a depth of 0-5 cm, under different land uses, as well as 51 composite fluvial sediment samples were collected over the watershed. The land use change from native cerrado had resulted in an increase of total phosphorus (TP) whose concentration was higher in cropland areas, followed by suspended sediment, channel bank, and riverbed sediments. This high concentration in cropland areas resulted from phosphate fertilizer inputs. The transfer of phosphorus to water bodies was evidenced, since an increase of TP was observed in suspended sediment, channel bank and riverbed  sediments. Mineralogical signatures in sediments were identified by X-ray diffraction analysis which showed the occurrence of kaolinite, illite, smectite, iron oxides, and other minerals in lesser proportions. The presence of 1:1 minerals was higher in riverbed sediments and downstream sampling points, while 2:1 minerals were present in higher proportions in suspended sediment and channel bank sediment, as well as at the upstream and middle sampling points. This finding shows that land use change from cerrado to cropland due to soybean agriculture expansion might increase P discharges from terrestrial to aquatic environments, with sediments being the major carrier of this element.