Riverine fluxes of different species of phosphorus in the Pearl River estuary

Phosphorus is the most limiting nutrient in coastal waters of China, particularly in the Pearl River (PR) estuary. Rivers have different P forms including dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP), particulate inorganic phosphorus (PIP), and particulate organic phosphorus (POP). Their input to coastal seas has been overlooked. We hypothesize that DIP is a small fraction of total phosphorus (TP). We investigated these P forms and estimated their fluxes in PR eight outlets during 2015-2019. DIP on average is only a 30.90 % fraction of TP with PIP, POP and DOP accounting for 22.43, 31.56 and 15.37 %, respectively. The average annual fluxes of TP, DIP, DOP, PIP and POP were 12.58×, 3.34×, 1.68×, 3.19× and 4.26 × 106 mol/month, respectively, which are regulated by runoff and suspended particulate matter (SPM). The finding reveals the importance of other P forms for phytoplankton in the Pearl River estuary and their bio-availability deserves further study.

Multi-isotopes revealing the coastal river anthropogenic pollutants and natural material flux to ocean: Sr, C, N, S, and O isotope study

Coastal river exports massive terrestrial materials to the adjacent marine environment with information about chemical weathering, providing critical insights on riverine flux and the potential impact on marine ecosystem. In this study, the preliminary data of dissolved strontium (Sr) and ⁸⁷Sr/⁸⁶Sr in a typical coastal river in southeastern China were collected along with hydrochemistry and C, N, S, and O isotopes to discriminate the source of terrestrial weathering and the riverine flux. Sr concentrations exhibited a range of 0.084 ~ 1.307 μmol L^-1, and ⁸⁷Sr/⁸⁶Sr values ranged 0.7089 ~ 0.7164. The total cationic charge (TZ⁺) ranged 0.2 ~ 11.7 meq L^-1 with the predominant Ca²⁺ which accounted for > 50% of TZ⁺, while the anions were dominated by HCO₃^-. The extremely high Na⁺ and Cl^- near the estuary indicated seawater mixing in such a coastal river. δ¹³C-DIC, δ¹⁵N-NO₃^-, δ¹⁸O-NO₃^-, and δ³⁴S-SO₄^2- of river water ranged - 24.1‰ ~  - 9.2‰, 0.3‰ ~ 22.7‰, - 2.1‰ ~ 21.4‰, and - 9.3‰ ~ 18.0‰, respectively. δ¹³C enhanced correspondingly to decreased δ³⁴S, confirming the attendance of H₂SO₄ in carbonate weathering. Most δ¹⁸O values exhibited within ± 10‰, indicating the dominant nitrification process. δ¹⁵N presented slightly negative relationship with δ¹³C and no obvious correlation with δ³⁴S, indicating relatively limited impact of denitrification. The depleted δ¹³C and δ¹⁵N may be attributed to carbonate dissolution with nitric acids and the oxidation of organic matters into C and N pools. Quantitative analysis revealed that silicate weathering accounts for 79% of total dissolved Sr, indicating the dominant weathering process. The estimated monthly flux of dissolved Sr to the East China Sea was 138.1 tons, demonstrating an potential impact on seawater Sr isotope evolution. Overall, the investigations of multi-isotopes revealed the enhancement of weathering rates and the consequently depleted CO₂ consumption, which further proved the involvement of strong acids (H₂SO₄ and HNO₃). This study provides scientific insight in terrestrial weathering and anthropogenic impact of a typical coastal watershed and may orient the management of environmental issues related to coastal ecosystems.

Pollution characterization of pharmaceutically active compounds (PhACs) in the northwest of Tai Lake Basin, China: Occurrence, temporal changes, riverine flux and risk assessment

PhACs have attracted great attentions of researchers because of their potential ecological and healthy risks. However, their long-term pollution tendency study is very scarce. In this study, 32 target PhACs from surface water, wastewater treatment plants, fishponds and livestock farms were investigated in Wujin, a city located in the northeast of Tai Lake, using grab sampling. The occurrence, spatiotemporal distribution characteristics, potential sources, riverine flux and risk assessment were systematically analyzed. It was found that non-antibiotics were the mainly PhACs category in Wujin and CF, SMX were the predominant non-antibiotics and antibiotics, respectively. Besides, the average concentrations of total PhACs were 586.6 ng L^-1 and 273.2 ng L^-1 in 2018 and 2019, respectively. This improvement could be mainly attributed to the closure of fishponds and livestock farms. Moreover, CF/CBZ ratios which was considered as an indicator to trace untreated wastewater decrease significantly in 2019, and this was also a main reason for the improvement. Riverine flux could be calculated through arranging control sampling sites in the boundary and the net riverine inflow flux of PhACs in Wujin was 264.3 kg/a. Finally, CF, SMX, EM were evaluated as the high risk contaminants based on a comprehensive risk assessment method.

A quarter-century of nutrient load reduction leads to halving river nutrient fluxes and increasing nutrient limitation in coastal waters of central Japan

Nutrient load reduction is widely used to improve coastal water quality, but it can lead to oligotrophication. This paper evaluates the current status of river water origin and the water recharge system based on isotope values and dissolved compositions recorded in 2018, and it also assesses the impact of nutrient load reduction efforts on river nutrient fluxes and coastal water quality using 25 years of monitoring data. This study focuses on the coast of Toyama Bay as a model area because (1) up to 20% of terrestrially derived nutrient support the growth of coastal primary productivity, and (2) the adjacent land is a typical city in a population-dense area (~ 500 persons/km²), a demographic characteristic that exists in 88% of Japan's total land area and 96% of the total length of the country's coastline. Since the government adopted new wastewater treatment systems in 1993, river nutrient supplies in the study area have been halved, while the total river flow and annual precipitation have remained almost unchanged. The reduction in riverine nutrient supply has increased phosphorus deficiencies in the coastal waters. Most notably, the decline in nutrient concentrations in coastal surface waters and the enlarged nutrient-restricted areas are facing most parts of Japan, suggesting a resulting 25-50% decrease in CO₂ uptake by primary production. This study is in agreement with previous studies from various countries in emphasizing the importance of setting appropriate nutrient-management goals for maintaining a sustainable marine environment. This paper recommends the need to accumulate various case studies of different areas and to share in a timely manner scientific evidence on a regional and global scale.

The contribution of 137Cs export flux from the Tone River Japan to the marine environment

The contribution of ¹³⁷Cs transport to the marine environment via the Tone River, Japan was investigated. This river has the largest discharge among rivers on the North Pacific side of eastern Japan. The sampling site was located upstream near the river mouth and dissolved and particulate ¹³⁷Cs in the river water was measured during 2014-2015, three years after the Tokyo Electric Power Corporation Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. Annual fluxes of total (dissolved and particulate) ¹³⁷Cs with considering desorption of ¹³⁷Cs from riverine particles by change of salinity from the Tone River were similar in both years (78-107 × 10⁹ Bq/y), indicating that about 0.03-0.06% of the estimated total amount of ¹³⁷Cs deposited in the catchment (1.9-2.8 × 10¹⁴ Bq) was transported to the marine environment each year. Although the annual flux was about one order of magnitude lower than the daily direct discharge into the ocean from the FDNPP (800 × 10⁹ Bq/y) during the corresponding period, continuous monitoring of rivers in the southern coastal area of east Japan on the North Pacific side are needed for the effect of ¹³⁷Cs release via the rivers in the Kanto area over the long-term.

Seasonal variations and spatial distributions of perfluoroalkyl substances in the rivers Elbe and lower Weser and the North Sea

The spatial distributions and seasonal variations of perfluoroalkyl substances (PFASs) in surface waters were investigated for the German rivers Elbe and lower Weser, and the North Sea. ∑PFAS concentrations ranged from 4.1 to 250ngL(-1) in the River Elbe, from 3.8 to 16ngL(-1) in the lower Weser, and from 0.13 to 10ngL(-1) in the North Sea. The most abundant compound was perfluorobutanesulfonate (PFBS) with a proportion of 24% in river water and 31% in seawater samples. The concentrations of perfluorohexanoic acid (PFHxA) and perfluorooctanoic acid (PFOA) in Elbe River water showed significant seasonal variation in 2011. The seasonal variations might be related to the variations of water discharge. The highest concentrations of PFOA and PFHxA were detected in August. Pearson correlations showed that perfluorobutanoic acid (PFBA) and PFBS had different sources from other PFASs, and the current manufacturing and use of C4-based products could explain the distinction. The estimated fluxes of individual substances and ∑PFASs in the River Elbe showed no significant seasonal variation. The annual fluxes of PFASs to the North Sea were estimated to be 335±100kgyear(-1) from the River Elbe and 102±22kgyear(-1) from the River Weser.

Occurrence and spatial distribution of organophosphate ester flame retardants and plasticizers in 40 rivers draining into the Bohai Sea, north China

Organophosphate esters (OPEs) are alternatives to polybrominated diphenyl ethers, often used as flame-retardants and plasticizers. There are few reports of OPEs in river water. This study focused on the occurrence and spatial distribution of 11 OPE congeners and one synthetic intermediate triphenylphosphine oxide (TPPO) in 40 major rivers entering into the Bohai Sea. Total OPEs ranged from 9.6 to 1549 ng L(-1), with an average of 300 ng L(-1). Tris(1-chloro-2-propyl) phosphate (TCPP) (4.6-921 ng L(-1), mean: 186 ng L(-1)) and tris(2-choroethyl) phosphate (TCEP) (1.3-268 ng L(-1), mean: 80.2 ng L(-1)) were the most abundant OPEs and their distribution patterns are similar, indicating the same source (r = 0.61, P < 0.05) and the influence of large production and consumption of chlorinated OPEs in the region. Priority should be given to TCPP, PCEP and TPPO due to their high concentrations in the rivers and potential threat to aquatic organisms.