New insights into the impacts of suspended particulate matter on phytoplankton density in a tributary of the Three Gorges Reservoir, China

The role of green finance in mitigating climate change risks: a quantitative analysis of sustainable investments

The dire problem of climate change has garnered more attention in recent years and, with it, the necessity of reducing its damaging effects on the environment. Nevertheless, despite the green finance index's (GFI) potential advantages in combating climate change, empirical studies on the subject's consequences have been few, mostly because of the index's restricted data availability. This study's primary goal is to close this gap by employing panel data analysis to investigate the environmental effects of GFI in China between 2004 and 2021. Econometric methods like the Driscoll-Kraay standard error and other robustness test models are used to look into the links between political risk, green finance, the ecological footprint, and the economic complexity index. According to the research findings, there is a 0.31% and 0.81% decrease in ecological footprint resulting from the implementation of GFI and rises in GDP (gross domestic product). These results suggest that these strategies could play a major role in establishing a sustainable environment. However, in the chosen countries, the ecological footprint increases by 0.81% and 0.80%, respectively, due to the presence of political risk and economic complexity. This study suggests that government involvement is necessary to reduce carbon footprints and protect the ecosystem, based on these empirical findings. Implementing green financing initiatives, fostering technological development, economic diversification, and fostering a stable political environment are all ways to achieve sustainable investments.

Effects of suspended particles in the Jinjiang River Estuary on the physiological and biochemical characteristics of Microcystis flos-aquae

The effects of different concentrations (100, 150, 200, 250 mg/L) and different particle sizes (0-75 μm, 75-120 μm, 120-150 μm, 150-500 μm) on the soluble protein content, superoxide dismutase (SOD) and catalase (CAT) activity, malondialdehyde (MDA) content, chlorophyll a (Chla) content, and photosynthetic parameters of Microcystis flos-aquae were studied, and the mechanism of the effect of suspended particulate matter on the physiology and biochemistry of Microcystis flos-aquae was discussed. The results showed that the soluble protein content of Microcystis flos-aquae did not change noticeably after being stressed by suspended particles of different concentrations/diameters. The SOD activity of Microcystis flos-aquae first increased and then decreased with increasing suspended particulate matter concentrations. The SOD activity of Microcystis flos-aquae reached 28.03 U/mL when the concentration of suspended particulate matter was 100 mg/L. The CAT activity of Microcystis flos-aquae increased with increasing concentrations of suspended particles and reached a maximum value of 12.45 U/mg prot in the 250 mg/L concentration group, showing a certain dose effect. Small particles had a more significant effect on SOD, CAT, and MDA in Microcystis flos-aquae than large particles. The larger the concentration was and the smaller the particle size was, the stronger the attenuation of light and the lower the content of Chla. Both the maximum quantum yield of PSII (Fv/Fm) and the potential photosynthetic activity of PSII (Fv/F₀) of Microcystis flos-aquae increased at first and then decreased under different concentrations/sizes of suspended particles. The relative electron transfer rate gradually returned to a normal level over time. There was no significant difference in the initial slope (α) value between the treatment group and the control group, and the maximum photo synthetic rate (ETRmax) and the semilight saturation (I_k) decreased.

MODIS-Landsat fusion-based single-band algorithms for TSS and turbidity estimation in an urban-waste-dominated river reach

Riverine ecosystem management along an urban stretch mostly depends on high-frequent (daily-scale) monitoring of water quality at finer spatial resolutions. However, with the decrease in the number of in-situ monitoring stations owing to their expensive maintenance cost, there is a need to develop the next-generation remote sensing (RS) tools as an alternate approach with better synoptic coverage of river water quality assessment. This study advocates three novel model variants to estimate the total suspended solids (TSS) concentration at daily-scale using the public-domain MODIS and Landsat satellite datasets. The MOD_T model variant uses the 1-day×250 m MODIS public domain datasets, and the FUS_T model is based on the 1-day×30 m MODIS-Landsat fusion datasets, whereas the CFUS_T model integrates the Frank Copula with the FUS_T model. These hierarchical model variants are assessed in the urban-waste-dominated lower Ganges, namely the Hooghly River and the Brahmani River, in eastern India using the measured in-situ TSS datasets at multiple monitoring stations from 2016 to 2019. The results reveal that the CFUS_T is the best TSS estimation model variant that performs with the average coefficient of determination of 0.88-0.93, mean absolute error of 0.17-0.19, and normal root mean square error of 0.05-0.09. Conclusively, the proposed CFUS_T and CFUS_TU stochastic models can be used as potential tools for TSS and turbidity assessment along the dynamic river systems, respectively.

Freshwater suspended particulate matter-Key components and processes in floc formation and dynamics

Freshwater suspended particulate matter (SPM) plays an important role in many biogeochemical cycles and serves multiple ecosystem functions. Most SPM is present as complex floc-like aggregate structures composed of various minerals and organic matter from the molecular to the organism level. Flocs provide habitat for microbes and feed for larger organisms. They constitute microbial bioreactors, with prominent roles in carbon and inorganic nutrient cycles, and transport nutrients as well as pollutants, affecting sediments, inundation zones, and the ocean. Composition, structure, size, and concentration of SPM flocs are subject to high spatiotemporal variability. Floc formation processes and compositional or morphological dynamics can be established around three functional components: phyllosilicates, iron oxides/(oxy)hydroxides (FeOx), and microbial extracellular polymeric substances (EPS). These components and their interactions increase heterogeneity in surface properties, enhancing flocculation. Phyllosilicates exhibit intrinsic heterogeneities in surface charge and hydrophobicity. They are preferential substrates for precipitation or attachment of reactive FeOx. FeOx form patchy coatings on minerals, especially on phyllosilicates, which increase surface charge heterogeneities. Both, phyllosilicates and FeOx strongly adsorb natural organic matter (NOM), preferentially certain EPS. EPS comprise various substances with heterogeneous properties that make them a sticky mixture, enhancing flocculation. Microbial metabolism, and thus EPS release, is supported by the high adsorption capacity and favorable nutrient composition of phyllosilicates, and FeOx supply essential Fe.

Effects of flood discharge on the water quality of a drinking water reservoir in China - Characteristics and management strategies

Stormflow runoff is an important non-point source of pollution in drinking water reservoirs. Rationally managed flood discharge processes at estuaries can reduce the high concentration of pollutants carried by runoff, and thus their impacts on water plant operations. In this study, the physical and chemical water quality parameters upstream from a dam were measured for a flood discharge process in the Jinpen Reservoir of Northwest China. The results showed that the time needed for the flood to reach the reservoir was ∼9 h after flooding began, and this lag effect meant that water in the metalimnion and hypolimnion were vented in advance. Consequently, the undercurrent intruded into the hypolimnion. The water temperature increased by 1.83 °C, and the Schmidt stability index decreased from 3291.37 J m^-2 to 2496.32 J m^-2. Flood discharge can effectively reduce the volume of pollutants; however, it cannot completely prevent the deterioration of water quality in the main reservoir. The turbidity of the reservoir still exceeded 300 NTU after the flood discharge. When the outflow discharge decreased, the critical height of aspiration also decreased, and dissolved pollutants could neither be vented nor precipitated quickly, not allowing their concentration within the reservoir to decrease further. A three-dimensional hydrodynamic model was successfully used to simulate flood processes and determine an optimal flood discharge plan. We found that the elevations of the outlet and undercurrent layer are essential to determine the efficiency of flood discharge, while appropriate timing and outflow discharge volumes may further enhance the results. Therefore, using a hydrodynamic model to predict the position of an undercurrent layer, and opening spillways near the elevation of the undercurrent layer can improve the efficacy of flood discharge. Our findings provide novel insights that may be used to improve the operation and management of source water reservoirs.

Suspended particulate matter (SPM)-bound polycyclic aromatic hydrocarbons (PAHs) in lakes and reservoirs across a large geographical scale

Suspended particulate matter (SPM) plays a key role in the environmental fate of polycyclic aromatic hydrocarbons (PAHs) in lake environment. However, less is known about the occurrence, compositions and sources of SPM-bound PAHs as well as the correlations between SPM-bound PAHs and different suspended particulate organic matter (SPOM) on large geographical scale. In this study, we focused on the SPM-bound PAHs in 46 lakes and reservoirs across China to fill this gap. Our results showed that the concentrations of Σ₂₀ PAHs ranged from 334 to 38427 ng·g^-1 with a geometric mean (GM) of 3915 ng·g^-1. The occurrence of SPM-bound PAHs in this study was at a moderate level with large variations, which was associated with location and water depth according to linear discriminant analysis (LDA). Phenanthrene (Phe) was investigated as the overwhelming species with a GM of 1777 ng·g^-1, and was followed by fluoranthene (Fla), fluorene (Flu) and pyrene (Pyr) with GMs of 499 ng·g^-1, 276 ng·g^-1 and 184 ng·g^-1, respectively. The profiles of SPM-bound PAHs were primarily dominated by low-ring PAHs ranging from 56.0% to 97.1% (85.5% ± 7.7%, mean ± standard deviation). Four diagnostic ratios were applied for preliminary diagnoses, but inconsistent results were obtained in most samples. Ridge regression was applied to ascertain the potential influences of different SPOM on SPM-bound PAHs. The results revealed that the presence of SPM-bound PAHs was not only influenced by anthropogenic emissions, but also associated with biogenic organic matter. Our results provided a higher explanation than those just preliminarily estimated by total organic carbon (TOC). Nevertheless, there still exist over 50% of variance unexplained for most PAHs, and further study could focus more on the information of SPOM structures and potential local effects.

Implications of Nutrient Enrichment and Related Environmental Impacts in the Pearl River Estuary, China: Characterizing the Seasonal Influence of Riverine Input

The Pearl River estuary is an ecologically dynamic region located in southern China that experiences strong gradients in its biogeochemical properties. This study examined the seasonality of nutrient dynamics, identified related environmental responses, and evaluated how river discharge regulated nutrient sink and source. The field investigation showed significant differences of dissolved nutrients with seasons and three zones of the estuary regarding the estuarine characteristics. Spatially, nutrients exhibited a clear decreasing trend along the salinity gradient; temporally, their levels were obviously higher in summer than other seasons. The aquatic environment was overall eutrophic, as a result of increased fluxes of nitrogen and silicate. This estuary was thus highly sensitive to nutrient enrichment and related pollution of eutrophication. River discharge, oceanic current, and atmospheric deposition distinctly influenced the nutrient status. These factors accordingly may influence phytoplankton that are of importance in coastal ecosystems. Phytoplankton (in terms of chlorophyll) was potentially phosphate limited, which then more frequently resulted in nutrient pollution and blooms. Additionally, the nutrient sources were implied according to the cause–effect chains between nutrients, hydrology, and chlorophyll, identified by the PCA-generated quantification. Nitrogen was constrained by marine-riverine waters and their mutual increase-decline trend, and a new source was supplemented along the transport from river to sea, while a different source of terrestrial emission from coastal cities contributed to phosphate greatly.

Spatial and seasonal distribution of multi-elements in suspended particulate matter (SPM) in tidally dominated Hooghly river estuary and their ecotoxicological relevance

The present work represented first study of the spatio-seasonal distribution of the multi-elements in the suspended particulate matter (SPM) of the tropical Hooghly river estuary (HRE), eastern part of India. The high load of SPM (20-3460 mg/l) might have induced negative impact on the phytoplankton density. The relative abundance of the studied elements exhibited the following decreasing trend (concentration in μg/g and %): Si(26.44 ± 3.75%) > Al(7.94 ± 1.52%) > Fe(6.17 ± 1.9%) > K(3.05 ± 1.5%) > Ca(1.97 ± 1.11%) > Mg(1.57 ± 1.71%) > Na(1.45 ± 8.40%) > Mn(1273 ± 2003) > Zn(178.43 ± 130.95) > V(151.54 ± 27.13) > Cr(147.08 ± 32.21) > Cu(62.06 ± 14.03) > Ni(49.64 ± 12.09) > Pb(21.5 ± 10.45). The accumulation of Ni, Cr, Pb, and Cu is mainly controlled by the formation of Fe hydroxides along with particulate organic carbon (POC) and salinity. The average geo-accumulation index (I_geo) and enrichment factor (EF) endorsed the substantial input of Cr (I_geo = 0.037; EF = 1.61) and Zn (I_geo = 0.123; EF = 2.07) from diffused pollution sources. From ecotoxicological point of view, the quality guidelines (QGs) suggested that Cr and Ni might possess frequent adverse biological effects. However, the mean probable effect level (PEL) quotient values revealed 49% probability of toxicity to the aquatic biota for five toxic elements (Cr, Ni, Cu, Zn, and Pb). The geochemical approaches, pollution indices, and statistical evaluation together revealed low to moderate contamination in the estuary. This baseline data would be beneficial in adopting proper management strategies for sustainable utilization and restoration of the water resources. The authors strongly recommend continuous systematic monitoring and installation of treatment plants for management of this stressed estuary.

Impacts of phytoplankton blooms on trace metal recycling and bioavailability during dredging events in the Sado estuary (Portugal)

This work evaluates the impact of phytoplankton blooms on metal availability driven by dredging, in an area of the Sado estuary (Portugal), subject to ongoing dredging operations during the entire sampling period. In situ changes of chlorophyll a concentration, bioavailable trace metals (Cr, Mn, Co, Ni, Cu, Zn, Cd and Pb) in the water column, metal content in particulate matter, and particulate metal to bioavailable metal ratios were investigated during pre-bloom, bloom and post-bloom conditions to evaluate the potential of the phytoplankton-mediated metal removal. Metals in particulate matter significantly enhanced concomitantly with the decline of metals (mostly Mn, Co, Cu, Zn, and Pb) in the water column during the bloom, in comparison with pre- and post-bloom periods. During the peak of the phytoplankton bloom, bioavailable Cr, Mn, Co, Ni, Cu, Zn, Cd and Pb were reduced to 30, 99, 100, 87, 98, 72, 84 and 88% of their original levels (pre-bloom values). Copper and Pb, and to a lesser extent, Zn and Mn, were ranked as more particle reactive. Volume particulate matter concentrations of Mn, Ni, Cu and Pb much higher than the bioavailable concentrations, indicated that phytoplankton is likely to be a dominant sink of these metals during the bloom period. Thus, Mn, Ni, Cu and Pb are prone to be transferred and biomagnified into the marine food web. These results highlight phytoplankton blooms as important biological sinks of trace metals during dredging, which should be taken into consideration in planning and management of dredging, to minimise environmental impacts and protect estuarine and coastal ecosystems.