Effects of aeration on the suspended matter from a tropical and eutrophic estuary

Does higher ratio of wheat straw addition decrease PAHs degradation in PAHs-contaminated paddy soils and PAHs concentrations in rice?

There are considerable studies focusing on impacts of straw returning on PAHs degradation and bioavailability in PAHs-contaminated upland soils, while similar research in paddy soils is limited. Incubation experiments and pot trials were conducted to study effects of straw returning on PAHs degradation in paddy soils and PAHs accumulation in rice, respectively. There are threshold effects of straw returning on PAHs degradation in PAHs-contaminated paddy soils. The inflection point of PAHs degrading was recorded under 0.8 % wheat straw treatment (conventional (CS) and pretreated wheat straw (PS)), which increased PAHs degradation by 18.13-32.36 %. The lowest PAHs concentrations in rice were recorded under 1 % straw (CS and PS) treatment, which was attributed to the highest PAHs degradation in rhizosphere soils. Compared to CS treatment, PS treatment significantly (p < 0.05) increased PAHs degradation by 7.93-10.28 % and PAHs concentrations in rice by 12.38-45.87 % due to that increasing dissolved organic carbon (DOC) enhanced PAHs concentrations in porewater of rhizosphere soils. Higher diversity enhanced the metabolic pathways and function genes to degrade PAHs by improving bacterial phenotypes and biochemical processes under 1 % wheat straw and PS treatment. The present study firstly demonstrated that the effects of straw returning on PAHs degradation in PAHs-contaminated paddy soils and PAHs concentrations in rice depended on amount and methods of straw returning.

Landsat observations of total suspended solids concentrations in the Pearl River Estuary, China, over the past 36 years

Information on long-term trends in total suspended solids (TSS) is critical for assessing aquatic ecosystems. However, the long-term patterns of TSS concentration (CTSS) and its latent drivers have not been well investigated. In this study, we developed and validated three semi-analysis algorithms for deriving CTSS using Landsat images. Subsequently, the long-term trends in CTSS in the Pearl River Estuary (PRE) from 1987 to 2022 and the driving factors were clarified. The developed algorithms yielded excellent performance in estimating CTSS, with mean absolute percentage errors <25% and root mean square errors of <13 mg/L. Long-term Landsat observations showed an overall decreasing trend and significant spatiotemporal dynamics of the CTSS in the PRE from 1987 to 2022. The analysis of driving factors suggested that industrial sewage, cropland, forests and grasslands, and built-up land were the four potential driving forces that explained 87.81% of the long-term variation in CTSS. This study not only provides 36-year recorded datasets of CTSS in estuary water, but also offers new insights into the complex mechanisms that regulate CTSS spatiotemporal dynamics for water resource management.

Traceability and Emission Reduction of Dissolved Inorganic Nitrogen in Minjiang Estuary, China

The accumulation of dissolved inorganic nitrogen (DIN) in estuaries has become a global environmental problem. A two-dimensional, hydrodynamic water quality model was constructed in this study to investigate the sources of DIN pollution in the Minjiang Estuary. The concentration response field between the stream input and DIN in the estuary was established by using the surveyed source data of the study area. A sharing coefficient method was used to calculate the contribution percentage of each outfall to derive and propose a reasonable nitrogen reduction plan. The results showed that the input of land-based nitrogen into the Minjiang River contributed more than half of the DIN in the near-shore sea; the middle and upper reaches of the Minjiang River largely influenced the estuary area (38.57%). Conversely, the estuary and the coastline accounted for a smaller proportion of only 5.24%, indicating that an integrated DIN reduction should be implemented in the estuary area of the whole river basin. The model calculations showed that the reduction results, after remediation according to the current national standards for wastewater discharge in rivers, were not satisfactory. Thus, a new scheme is proposed in this paper-the total nitrogen (TN) input from land-based sources into the Minjiang Estuary and from the Shuikou Dam to the Min'an section should be reduced to below 31.64%; simultaneously, the DIN concentration discharged from the Shuikou Dam should be controlled and maintained below 0.5 mg·L^-1 (TN = 0.8 mg·L^-1). These results will provide guidelines for developing strategies for the improvement of DIN and water quality in similar estuaries.