Responses of Protozoan Communities to Multiple Environmental Stresses (Warming, Eutrophication, and Pesticide Pollution).

To explore the impacts of multiple environmental stressors on animal communities in aquatic ecosystems, we selected protozoa-a highly sensitive group of organisms-to assess the effect of environmental change. To conduct this simulation we conducted a three-factor, outdoor, mesocosm experiment from March to November 2021. Changes in the community structure and functional group composition of protozoan communities under the separate and combined effects of these three environmental stressors were investigated by warming and the addition of nitrogen, phosphorus, and pesticides. The results were as follows: (1) Both eutrophication and pesticides had a considerable promotional effect on the abundance and biomass of protozoa; the effect of warming was not considerable. When warming was combined with eutrophication and pesticides, there was a synergistic effect and antagonistic effect, respectively. (2) Eutrophication promoted α diversity of protozoa and affected their species richness and dominant species composition; the combination of warming and pesticides remarkably reduced the α diversity of protozoa. (3) Warming, eutrophication, and pesticides were important factors affecting the functional groups of protozoa. Interaction among different environmental factors could complicate changes in the aquatic ecological environment and its protozoan communities. Indeed, in the context of climate change, it might be more difficult to predict future trends in the protozoan community. Therefore, our results provide a scientific basis for the protection and restoration of shallow lake ecosystems; they also offer valuable insights in predicting changes in shallow lakes.

Blue revolution turning green? A global concern of cyanobacteria and cyanotoxins in freshwater aquaculture: A literature review.

To enhance productivity, aquaculture is intensifying, with high-density fish ponds and increased feed input, contributing to nutrient load and eutrophication. Climate change further exacerbates cyanobacterial blooms and cyanotoxin production that affect aquatic organisms and consumers. A review was conducted to outline this issue from its inception - eutrophication, cyanobacterial blooms, their harmful metabolites and consequential effects (health and economic) in aquacultures. The strength of evidence regarding the relationship between cyanobacteria/cyanotoxins and potential consequences in freshwater aquacultures (fish production) globally were assessed as well, while identifying knowledge gaps and suggesting future research directions. With that aim several online databases were searched through June 2023 (from 2000), and accessible publications conducted in aquacultures with organisms for human consumption, reflecting cyanotoxin exposure, were selected. Data on cyanobacteria/cyanotoxins in aquacultures and its products worldwide were extracted and analyzed. Selected 63 papers from 22 countries were conducted in Asia (48%), Africa (22%), America (22%) and Europe (8%). Microcystis aeruginosa was most frequent, among over 150 cyanobacterial species. Cyanobacterial metabolites (mostly microcystins) were found in aquaculture water and fish from 18 countries (42 and 33 papers respectively). The most affected were small and shallow fish ponds, and omnivorous or carnivorous fish species. Cyanotoxins were detected in various fish organs, including muscles, with levels exceeding the tolerable daily intake in 60% of the studies. The majority of research was done in developing countries, employing less precise detection methods, making the obtained values estimates. To assess the risk of human exposure, the precise levels of all cyanotoxins, not just microcystins are needed, including monitoring their fate in aquatic food chains and during food processing. Epidemiological research on health consequences, setting guideline values, and continuous monitoring are necessary as well. Further efforts should focus on methods for elimination, prevention, and education.

Zooplankton functional diversity in subtropical reservoirs of distinct trophic states (São Paulo state, Brazil).

Studies on functional traits of aquatic communities are useful for understanding the ecosystem dynamics as well as the diversity of ecological niches. Here, we characterize zooplankton functional groups and which limnological factors are responsible to changes in traits. Water samples were collected to evaluate limnological parameters and vertical hauls with plankton net (68 µm) were performed to characterize the community in seven reservoirs (Itupararanga, Atibainha, Salto Grande, Rio Grande, Igaratá, Barra Bonita, and Broa, São Paulo state, Brazil). Each species identified was classified according to a trophic group, reproduction mode, body length, habitat, and feeding habitats. Our results showed a predominance of pelagic suspensory herbivores with cilia (31%) followed by pelagic herbivore suspension filter feeders (17%) and raptorial omnivores (15.38%). The other individuals were categorized as pelagic herbivore suspension with oral device (12.3%), littoral herbivores suspensive with cilia (12.3%), pelagic-sucking herbivores (9.2%), and littoral grazing herbivores (3%). The dominance of herbivores may be influenced by the availability of nutrients, influencing their food sources. The abundance of omnivores engaged in predatory behavior can be attributed to disponible prey, thereby exerting significant repercussions on the organization of biological communities.

Access to bedding and outdoor runs for growing-finishing pigs: is it possible to improve welfare without increasing environmental impacts?

Providing bedding or access to an outdoor run are husbandry aspects intended to improve pig welfare, which is currently financially supported through animal welfare schemes in several European countries. However, they may significantly affect the environment through changes in feed efficiency and manure management. Therefore, the aim of this paper was to compare farms differing in animal welfare relevant husbandry aspects regarding (1) the welfare of growing-finishing pigs and (2) environmental impact categories such as global warming (GW), acidification (AC), and freshwater (FE) and marine eutrophication (ME), by employing an attributional Life Cycle Assessment. We collected data on 50 farms with growing-finishing pigs in seven European countries. Ten animal-based welfare indicators were aggregated into three pig welfare indices using principal component analysis. Cluster analysis of farms based on husbandry aspects resulted in three clusters: NOBED (31 farms without bedding or outdoor run), BED (11 farms with bedding only) and BEDOUT (eight farms with bedding and outdoor run). Pigs on farms with bedding (BED and BEDOUT) manipulated enrichment more often (P < 0.001), pen fixtures less frequently (P = 0.003) and showed fewer oral stereotypies (P < 0.001) than pigs on NOBED farms. There were fewer pigs with a short(er) tail on farms with than without bedding (P < 0.001). Acidification of BEDOUT and BED farms was significantly higher (compared to NOBED farms P = 0.002) due to higher ammonia emissions related to farmyard manure. Also, BEDOUT farms had higher ME than NOBED farms (P = 0.035). There were no significant differences regarding GW and FE between husbandry clusters, due to the large variability within clusters regarding feed composition and conversion. Therefore, both husbandry aspects associated with improved animal welfare have a significant influence on some environmental impacts, such as acidification and marine eutrophication. Nevertheless, the large variation within clusters suggests that trade-offs may be minimised through e.g. AC and ME.

Physico-chemical characterisation of irrigation basin waters and inventory study of their algal communities.

To cope with the water shortage in Sous Massa region of Morocco, agricultural producers in the region have resorted to different types of water supply basins, known as "irrigation basins" but the phenomenon of eutrophication has hindered the continuity of agricultural productivity by altering the quality of the water used for irrigation on the one hand, and causing economic damage to agricultural producers due to the clogging of the water pumping network on the other. We began by characterising the physico-chemical quality of the water to determine the causes of its high nutrient content, then we determined the taxonomy of the algal species in the irrigation basins to which we had access. A qualitative study of the water in the irrigation basins in order to better explain the inventory obtained from the taxonomic identification of the algal biomass collected, which proved the existence of new species, not previously identified, characterising the freshwaters of the Moroccan region, is under the scope of this work. The species studied belong mainly to the following groups: green algae (11 genera of Chlorophyta and 7 genera of Charophyta), blue algae (7 genera of Cyanobacteria), brown algae (7 genera of Diatoms), and one genus of Euglenophyta.

Trade-offs between nitrogen and phosphorus removal with floodplain remediation in agricultural streams.

To improve water quality and reduce instream erosion, floodplain remediation along agricultural streams can provide multiple ecosystem services through biogeochemical and fluvial processes. During floodplain inundation, longer water residence time and periodic anoxic conditions can lead to increased nitrogen (N) removal through denitrification but also mobilization of phosphorus (P), impeding overall water quality improvements. To investigate the capacity for N and P processing in remediated streams, we measured potential denitrification and nitrous oxide production and yields together with potential P desorption and P fractions in floodplain and stream sediments in ten catchments in Sweden. Sediment P desorption was measured as equilibrium P concentration, using P isotherm incubations. Denitrification rates were measured with the acetylene inhibition method. Sediment nutrient process rates were combined with hydrochemical monitoring along remediated streams and their paired upstream control reaches of trapezoidal shape to determine the impact of floodplains on water quality. The correlation between floodplain denitrification rates and P desorption (r = 0.53, p = 0.02) revealed a trade-off between soluble reactive P (SRP) and nitrate removal, driven by stream water connectivity to floodplains. Nitrous oxide production was not affected by differences in P processing, but nitrous oxide yields decreased with higher denitrification and P desorption. The release of SRP from floodplains (0.03 ± 0.41 mg P kg-1 day-1) was significantly lower than from trapezoidal stream banks (0.38 ± 0.37 mg P kg-1 day-1), predicted by long-term SRP concentrations in stream water and floodplain inundation frequency. The overall impact of SRP release from floodplains on stream SRP concentrations in remediated reaches was limited. However, the remediated reaches showing increased stream SRP concentrations were also frequently inundated and had higher labile P content and coarse soil texture in floodplain sediments. To fully realize the potential for water quality improvements with constructed floodplains in agricultural streams, the promotion of denitrification through increased inundation should be balanced against the risk of P release from sediments, particularly in streams with high SRP inputs.

Nutrient concentration, loads and retention in a semiarid micro-estuary: The relative contribution of baseflow and flood events.

Estuaries are a significant source of nutrients to the marine environment. The magnitude of this source is a function of nutrients load reaching the estuary and removal (attenuation) within estuaries. Most estuarine research is conducted in large estuaries, which do not reflect the processes in small estuaries in urban and semi-arid regions where flood water is a substantial portion of the annual discharge and the estuarine baseflow is often low and dominated by wastewater. To improve the understanding of nutrient attenuation and load into the Mediterranean, we conducted high-resolution nutrient sampling in the eutrophic Alexander micro-estuary as a test case. We sampled once per month during baseflows (years 2014-2019) and hourly during floods (years 2016-2018). The concentrations of inorganic nutrients (phosphorous (P) and nitrogen (N)) were extremely high during baseflows. Dissolved ammonium and particulate P were the only nutrients that were in the estuary (by 55 % and 30 %, respectively). Floods were rare, occurring ~4 % of the time, but contributed 62 % of the annual water discharge of the Alexander micro-estuary (14.7 ± 3.8 106 m3 y-1). The concentration of all dissolved nutrients decreased during floods but was higher than expected (DIN 584 ± 50 µmol L-1, phosphate 21 ± 2 µmol L-1), accounting for 42 % and 55 % of the overall annual DIN (123.5 ± 44.9-ton yr-1) and P (6.7 ± 1.9 ton yr-1) loads to sea, respectively. The N:P ratios were 16 and 34 during baseflow and flood events, respectively. Previously, nutrient loads were calculated by multiplying baseflow-measured concentrations by the total water volume of baseflow and floods. Our calculations, based on high-resolution sampling, revealed lower annual loads of P and N to the sea that were 56 % and 89 % of previous estimates, which is a considerable difference in an oligotrophic system such as the eastern Mediterranean.

Chronic increasing nitrogen and endogenous phosphorus release from sediment threaten to the water quality in a semi-humid region reservoir.

The water quality in the drinking water reservoir directly affects people's quality of life and health. When external pollution input is effectively controlled, endogenous release is considered the main cause of water quality deterioration. As the major nitrogen (N) and phosphorus (P) sources in reservoirs, sediment plays a vital role in affecting the water quality. To understand the spatial and temporal variation of N and P in the sediment, this study analyzed the current characteristics and cumulative effects of a semi-humid reservoir, Yuqiao Reservoir, in North China. The N and P concentrations in the reservoir sediment were decreased along the flow direction, while the minimum values were recorded at the central sediment profile. External input and algal deposition were the main factors leading to higher sediment concentrations in the east (Re-E) and west (Re-W) areas of reservoir sediment profiles. According to the long-term datasets, the peaks of both sediment total nitrogen content and deposition rate were observed in the 2010s, which has increased about three times and six times than in the1990s, respectively. Therefore, the increase in phosphorus concentration may be the main reason for eutrophication in water in recent years. The mineralization of organic matter has a significant promoting effect on releasing N and P from sediments, which will intensify eutrophication in water dominated by P and bring huge challenges to water environment management. This study highlights that the current imbalance in N and P inputs into reservoirs and the endogenous P release from sediment will have a significant impact on water quality.

Phosphorus immobilization/release behavior of lanthanum-modified bentonite amended sediment under the dual effects of pH and dissolved organic carbon.

Lanthanum modified bentonite (LMB) is typical P-inactivating agent that has been applied in over 200 lakes. Dissolved organic carbon (DOC) and high pH restrict the phosphorus (P) immobilization performance of LMB. However, the P immobilization/release behaviors of LMB-amended sediment when suspended to overlying water with high pH and DOC have not yet been studied. In the present work, batch adsorption and long-term incubation experiments were performed to study the combined effects of pH and DOC on the P control by LMB. The results showed that the coexistence of low concentration of DOC or preloading with some DOC had a negligible effect on P binding by LMB. In the presence of DOC, the P adsorption was more pronounced at pH 7.5 and was measurably less at pH 9.5. Additionally, the pH value was the key factor that decided the P removal at low DOC concentration. The increase in pH and DOC could significantly promote the release of sediment P with a higher EPC0. Under such condition, a higher LMB dosage was needed to effectively control the P releasing from sediment. In sediment/water system with intermittent resuspension, the alkaline conditions greatly facilitated the release of sediment P and DOC, which increased from 0.087 to 0.581 mg/L, and from 11.05 to 26.56 mg/L, respectively. Under the dual effect of pH and DOC, the P-immobilization performance of LMB was weakened, and a tailor-made scheme became essential for determining the optimum dosage. The desorption experiments verified that the previously loaded phosphorus on LMB was hard to be released even under high pH and DOC conditions, with an accumulative desorption rate of less than 2%. Accordingly, to achieve the best P controlling efficiency, the application strategies depending on LMB should avoid the high DOC loading period such as the rainy season and algal blooms.

Indirect Impact of Eutrophication on Occurrence, Air-Water Exchange, and Vertical Sinking Fluxes of Antibiotics in a Subtropical River.

A significant challenge that warrants attention is the influence of eutrophication on the biogeochemical cycle of emerging contaminants (ECs) in aquatic environments. Antibiotics pollution in the eutrophic Pearl River in South China was examined to offer new insights into the effects of eutrophication on the occurrence, air-water exchange fluxes (Fair-water), and vertical sinking fluxes (Fsinking) of antibiotics. Antibiotics transferred to the atmosphere primarily through aerosolization controlled by phytoplankton biomass and significant spatiotemporal variations were observed in the Fair-water of individual antibiotics throughout all sites and seasons. The Fsinking of ∑AB14 (defined as a summary of 14 antibiotics) was 750.46 ± 283.19, 242.71 ± 122.87, and 346.74 ± 249.52 ng of m-2 d-1 in spring, summer, and winter seasons. Eutrophication indirectly led to an elevated pH, which reduced seasonal Fair-water of antibiotics, sediment aromaticity, and phytoplankton hydrophobicity, thereby decreasing antibiotic accumulation in sediments and phytoplankton. Negative correlations were further found between Fsinking and the water column daily loss of antibiotics with phytoplankton biomass. The novelty of this study is to provide new complementary knowledge for the regulation mechanisms of antibiotics by phytoplankton biological pump, offering novel perspectives and approaches to understanding the coupling between eutrophication and migration and fate of antibiotics in a subtropical eutrophic river.

The origins of odor (ß-cyclocitral) under different water nutrient conditions: Algae or submerged plants?

Among the problems caused by water eutrophication, the issue of odor compounds has attracted notable attention. ß-Cyclocitral, a widely distributed and versatile odor compound, is commonly derived from both algae and aquatic plants. Planting aquatic plants is a common method of water purification. However, there is limited study on their impact on ß-cyclocitral levels in water. Here, we conducted a study on the ß-cyclocitral levels in water and the submerged plant leaves under three nutrient levels and six plant density treatments. Our findings revealed the following: (1) Chlorophyll-a (Chla), ß-cyclocitral in the water (Wcyc), ß-cyclocitral in Potamogeton lucens leaves (Pcyc) and the biomass of the submerged plants increase with rising nutrient concentration, which increased about 83 %, 95 %, 450 %, 320 % from eutrophic treatment to oligotrophic treatment, respectively. (2) In water, ß-cyclocitral is influenced not only by algae but also by submerged plants, with primary influencing factors varying across different nutrient levels and plant densities. The main source of ß-cyclocitral in water becomes from plants to algae as the water eutrophication and plant density decrease. (3) As submerged plants have the capability to emit ß-cyclocitral, the release of ß-cyclocitral increases with the density of submerged plants. Hence, when considering planting submerged plants for water purification purposes, it is crucial to carefully manage submerged plant density to mitigate the risk of odor pollution emanating from aquatic plants. This study offers fresh insights into selecting optimal water density for submerged plants and their role in mitigating the release of ß-cyclocitral.

Enhanced nitrogen removal by an isolated aerobic denitrifying strain in a vertical-flow constructed wetland.

The addition of bacterial agents is an effective method for improving nitrogen removal from wetlands. Herein, an aerobic denitrifier, RC-15, was added to a vertical-flow constructed wetland (CW), and the presence of functional genes and microbial communities was investigated at different CW depths. For the RC-15-treated CW, the removal of NO3- and TN during the process was significantly greater than in the control. Quantitative PCR revealed that nirS is a dominant denitrifying gene for treating WWTP tailwater. Moreover, the presence of the RC-15 strain significantly enhanced the abundance of the napA gene and nirK gene in the CWs. The napA gene was concentrated in the upper layer of the CWs, and the nirK gene was concentrated in the middle and bottom layers. Compared to the control, the addition of the bacterial agent Trial resulted in a more diverse denitrification pathway, a greater abundance of 16Sr RNA, and a greater number of denitrifying strains. According to the microbial community analysis, Proteobacteria and Chloroflexi dominated denitrification in the CWs. Greater abundances of Thauera, Aeromonas and Ardenticatenales were found at the genus level, indicating that these genera have potential applications in future nitrogen removal projects.

Particulate and water-mobilizable phosphorus from a watershed with a plain river network contributes equal amounts of algal available phosphorus to its downstream lake.

This research was designed to estimate the contributions of phosphorus (P) in different factions from an upstream plain river network to algal growth in a downstream shallow eutrophic lake, Taihu Lake, in China. During three flow regimes, the P fractions in multiple phases (particulate, colloidal and dissolved phases) and their algal availabilities were assessed via bioassays with Dolichospermum flos-aquae as the test organism. The P partitioning patterns among multiple phases were strongly affected by the concentration of total suspended solids (TSS) that changed with the river flow regime, with stronger disturbance of sediments at lower water levels (low flow) and weaker disturbance of sediments at higher water levels (high flow) in the plain river network. The median TSS concentration across the river network decreased from 157.4 mg/L during low flow to 31.8 mg/L during high flow, and the median particulate P concentration decreased from 0.132 mg/L to 0.093 mg/L. The particulate P contributed equally to the amount of algal available P (AAP) as did the water-mobilizable P (colloidal plus dissolved phase) in the rivers flowing into Taihu Lake. The annual average concentrations of particulate algal available P (P-AAP), colloidal algal available P (C-AAP) and dissolved algal available P (D-AAP) were estimated to be 0.032 mg/L, 0.012 mg/L and 0.019 mg/L, respectively, during 2012-2018, accounting for 50.8 %, 19.0 % and 30.2 %, respectively, of the total AAP. At the watershed scale, controlling P drainage from downstream urbanized areas should be emphasized. Additionally, controlling sediment resuspension or reducing the TSS concentration in the inflowing rivers is important for decreasing the particulate P flux to downstream lakes.

Including Methane Emissions from Agricultural Ponds in National Greenhouse Gas Inventories.

Agricultural ponds are a significant source of greenhouse gases, contributing to the ongoing challenge of anthropogenic climate change. Nations are encouraged to account for these emissions in their national greenhouse gas inventory reports. We present a remote sensing approach using open-access satellite imagery to estimate total methane emissions from agricultural ponds that account for (1) monthly fluctuations in the surface area of individual ponds, (2) rates of historical accumulation of agricultural ponds, and (3) the temperature dependence of methane emissions. As a case study, we used this method to inform the 2024 National Greenhouse Gas Inventory reports submitted by the Australian government, in compliance with the Paris Agreement. Total annual methane emissions increased by 58% from 1990 (26 kilotons CH4 year-1) to 2022 (41 kilotons CH4 year-1). This increase is linked to the water surface of agricultural ponds growing by 51% between 1990 (115 kilo hectares; 1,150 km2) and 2022 (173 kilo hectares; 1,730 km2). In Australia, 16,000 new agricultural ponds are built annually, expanding methane-emitting water surfaces by 1,230 ha yearly (12.3 km2 year-1). On average, the methane flux of agricultural ponds in Australia is 0.238 t CH4 ha-1 year-1. These results offer policymakers insights into developing targeted mitigation strategies to curb these specific forms of anthropogenic emissions. For instance, financial incentives, such as carbon or biodiversity credits, can mobilize widespread investments toward reducing greenhouse gas emissions and enhancing the ecological and environmental values of agricultural ponds. Our data and modeling tools are available on a free cloud-based platform for other countries to adopt this approach.

Lanthanum-modified pyroaurite as a geoengineering tool to simultaneously sink Microcystis cyanobacteria and immobilize phosphorus in eutrophic water.

Excessive phosphorus (P) in eutrophic water induces cyanobacterial blooms that aggravate the burden of in-situ remediation measures. In order to ensure better ecological recovery, Flock & Lock technique has been developed to simultaneously sink cyanobacteria and immobilize P but requires a combination of flocculent and P inactivation agent. Here we synthesized a novel lanthanum-modified pyroaurite (LMP), as an alternative for Flock & Lock of cyanobacteria and phosphorus at the background of rich humic acid and suspended solids. LMP shows a P adsorption capacity of 36.0 mg/g and nearly 100 % removal of chlorophyll-a (Chl-a), turbidity, UV254 and P at a dosage (0.3 g/L) much lower than the commercial analogue (0.5 g/L). The resultant sediment (98.2 % as immobile P) exhibits sound stability without observable release of P or re-growth of cyanobacteria over a 50-day incubation period. The use of LMP also constrains the release of toxic microcystins to 1.4 µg/L from the sunk cyanobacterial cells, outperforming the commonly used polyaluminum chloride (PAC). Similar Flock & Lock efficiency could also be achieved in real eutrophic water. The outstanding Flock & Lock performance of LMP is attributable to the designed La modification. During LMP treatment, La acts as not only a P binder by formation of LaPO4, but also a coagulant to create a synergistic effect with pyroaurite. The controlled hydrolysis of surface La(III) over pyroaurite aided the possible formation of La(III)-pyroaurite networking structure, which significantly enhanced the Flock & Lock process through adsorption, charge neutralization, sweep flocculation and entrapment. In the end, the preliminary economic analysis is performed. The results demonstrate that LMP is a versatile and cost-effective agent for in-situ remediation of eutrophic waters.

Phosphorus accumulation during the ice-on season in macrophyte-dominated eutrophic lakes and its implications.

Macrophyte overgrowth in eutrophic lakes can hasten the decline of shallow water bodies, yet the impact of macrophyte deposition on sediment phosphorus (P) accumulation in the ice-on season remains unclear. Comparative analyses of P variations among 13 semi-connected sub-lakes in Wuliangsu Lake in China, a typical MDE lake, considered external flow and macrophyte decomposition as driving forces. Sediment P fractions and water total phosphorus (TP) were analyzed at 35 sampling points across three ice-on season stages, along with macrophyte TP content to assess debris contributions. Our findings reveal that phosphorus accumulation occurs during the ice-on season in the MDE lake, with an average TP content increase of 16 mg/kg. However, we observed a surprisingly small sediment nutrient accumulation ratio (ΔTP/ΔTN=0.006) compared to macrophyte nutrient levels before decomposition. Further analysis of the dominant species, Potamogeton pectinatus, indicates that a significant portion (55%) of macrophyte phosphorus is released before the ice-on season. This highlights the critical importance of timing macrophyte harvesting to precede the phosphorus leaching process, which has implications for lake management and ecosystem restoration efforts. Additionally, our research demonstrates similar transformations among different sediment fractions as previously reported. Macrophyte debris decomposition likely serves as the primary source of Residual P (Res-P) or TP accumulation. In addition, Ca-bound P (Ca-P) generally showed a decrease, which mainly caused by its transformation to Fe/Al-bound P (Fe/Al-P), Exchange-P (Ex-P), and sometimes to Res-P. However, we emphasize the significant impacts of flow dynamics on Ca-P transport and transformations. Its hydrodynamic action increases water dissolved oxygen, which accelerates the transformation of Ca-P to more easily released Fe/Al-P and Ex-P. Furthermore, hydrodynamic transport also leads to upstream Ca-P transport to downstream. This underscores the necessity of considering flow dynamics when estimating phosphorus variations and formulating phosphorus restoration strategies.

Seasonal hypoxia enhances sediment iron-bound phosphorus release in a subtropical river reservoir.

Dams worldwide commonly accelerate the eutrophication of reservoirs. While the seasonal hypoxia in deep reservoirs is widely acknowledged, there is limited research on its impact on benthic phosphorus (P) cycling and P fraction release from the reservoir sediments. Here we show that seasonal hypoxia enhances sediment P release and P fluxes at the sediment-water interface (SWI) which might alter P dynamics in deep reservoirs. We conducted a detailed measurement of sediment P fractions through the SEDEX approach, combined with a labile P gradient analysis using the diffusive gradients in thin films (DGT) technique to understand P cycling patterns in sediments during the transition period from spring (oxic) to late summer (hypoxic) conditions. The sediment P pool was predominantly composed of iron-bound phosphorus (FeP, 76-80 %), primarily due to the widespread occurrence of lateritic red soil (rich in Fe2O3/MnO2) in subtropical areas. More organic-P was observed in summer compared to spring. A significant increase in labile P occurred at the depth of 0-4 cm and 0-1 cm in spring and summer, respectively, where sediment P release was primarily governed by the reduction of FeP and the generation of S2-. A higher apparent fluxes of phosphate across the SWI were observed in summer characterized by higher temperature and lower oxygen levels. The current results suggest that seasonal hypoxia was a crucial factor affecting P cycling and diffusion in deep reservoirs. These findings present important implications for the ecology and management of the watershed-coast ecosystem.

Microalgal assemblages response to water quality remediation in coastal waters of Perth, Australia.

Nutrient reduction is an essential environmental policy for water quality remediation, but climate change can offset the ecological benefits of nutrient reduction and lead to the difficulty of environmental evaluation. Here, based on the records of three lipid microalgal biomarkers and stable isotopes of carbon and nitrogen in two sediment cores from the embayment of Perth, Australia, we reconstructed the microalgal biomasses (diatoms, dinoflagellates and coccolithophores) over the past century and evaluated the ecological effects of nutrient reduction on them, using Change Point Modeling (CPM) and redundancy analysis (RDA). The CPM result showed that total microalgal biomarkers increased by 25% and 51% in deep and shallow areas, respectively, due to nutrient enrichment caused by industrial wastewater in the 1950s and the causeway construction in the 1970s, and dinoflagellates were beneficiaries of eutrophication. The nutrient reduction policy since the 1980s had not decreased total microalgal biomass, and diatoms were beneficiaries of this period. RDA based on time series of sediment cores and water monitoring data revealed that the increase of sea-surface temperature and the decrease of rainfall since the 1980s may be important factors sustaining the high total microalgal biomass and increasing the degree of diatom dominance. The result also indicated that the variations of microalgal assemblages may better explain the effect of nutrient reduction rather than total microalgal biomass.

TP or Not TP? Successful Comparison of Two Independent Methods Validates Total Phosphorus Inference for Long-Term Eutrophication Studies.

Validating paleo total phosphorus (TP) inference methods over long time scales is essential for understanding historic changes in lake P supply and the processes leading up to the present-day global lake eutrophication crisis. Monitored lake water TP time series have enabled us to identify the drivers of eutrophication over recent decades. However, over longer time scales, the lack of reliable TP inference means our understanding of drivers is speculative. Validation of lake water TP reconstruction, therefore, remains the "ultimate aim" of eutrophication studies. Here, we present the first critical comparison of two fully independent paleo TP inference approaches: the well-established diatom method (DI-TP) and a recently developed sediment geochemical method (SI-TP). Using lake sediment records from a small eutrophic U.K. lake (Crose Mere), we find a statistically significant agreement between the two inferred TP records with greater than 60% shared variance. Both records show identical timings, with a 19th century acceleration in TP concentration and subsequent declines following a peak in 1930. This significant agreement establishes the validity of long-term paleo TP inference for the first time. With this, we can now test assumptions and paradigms that underpin understanding of catchment P sources and pathways over longer time scales.

Long-term study of phytoplankton dynamics in a supply reservoir reveals signs of trophic state shift linked to changes in hydrodynamics associated with flow management and extreme events.

This study analyses over a decade (2009-2022) of monitoring data to understand the impact of hydrological characteristics on water quality and phytoplankton dynamics in Prospect Reservoir, a critical water supply for Greater Sydney, Australia, known for its excellent water quality. Water quality and phytoplankton dynamics were related to hydrodynamics, linked to flow management and the water quality of inflows. Phytoplankton biovolume increased after a prolonged drawdown and subsequent refill event, mainly driven by dinoflagellates, and corresponded to increases in total phosphorus and water temperature. The hydrological period following the 2019/2020 summer bushfires (post-bushfire) that impacted connected reservoirs, was marked by increased flow activity and nutrient loading, leading to significant shifts in the phytoplankton community. Functional group classification and ordination analysis indicated a transition from taxa typically dominant in oligotrophic conditions to meso­eutrophic. This transition correlated with elevated nutrient levels and chlorophyll-a (Chl-a), and reduced Secchi depth and dissolved oxygen, providing evidence of eutrophication. Q index indicated good water quality post-bushfire, contrasting with a eutrophic status assessment using Chl-a. Our findings highlight the importance of analysing long-term datasets encompassing varied hydroclimatological conditions for a deeper understanding of reservoir behaviour. A comprehensive approach to water quality assessment is recommended, combining functional group classification, Q index and Chl-a measurements for effective reservoir health assessment. This research provides novel insights into the effects of disturbances such as bushfires, on water quality and phytoplankton dynamics in an underrepresented geographic region, offering valuable knowledge for managing water resources amidst growing climate variability.