Eutrophic Areas Research Articles

Aerobic anoxygenic phototrophic bacteria correlate with picophytoplankton across the Atlantic Ocean but show unique vertical bioenergetics

AbstractAerobic anoxygenic phototrophic (AAP) bacteria are a common part of microbial communities in the sunlit ocean. They contain bacteriochlorophyll a (BChl a)‐based photosystems that harvest solar energy for their metabolism. Across different oceanic regions, AAP bacteria seem to be more abundant in eutrophic areas, associated with high chlorophyll concentrations. While most previous studies focused on surface samplings, there is limited information regarding their vertical distribution in euphotic zones of the major ocean basins. Here, we hypothesized that AAP bacteria will follow a similar structure to the chlorophyll depth profile across areas with different degrees of stratification. To test this hypothesis, we enumerated AAP cells and determined bulk water BChl a concentrations along the photic zone of a latitudinal transect in the South and Central Atlantic Ocean. Overall, the distribution of AAP bacteria was highly correlated to that of chlorophyll a and to the abundance of picophytoplankton across both vertical and horizontal gradients. Furthermore, estimated light energy captured across the water column showed that, while AAP bacteria share a common latitudinal pattern of light absorption with picophytoplankton, they display a unique vertical arrangement with highest photoheterotrophic activity in the top 50 m of the surface ocean.

Impacts of eutrophication on microbial community structure in sediment, seawater, and phyllosphere of seagrass ecosystems.

Seagrass-associated microbial communities play a crucial role in the growth and health of seagrasses. However, like seagrass meadows, seagrass-associated microbial communities are often affected by eutrophication. It remains unclear how eutrophication influences the composition and function of microbial communities associated with different parts of seagrass. We employed prokaryotic 16S rRNA gene high-throughput sequencing combining microbial community structure analysis and co-occurrence network analysis to investigate variances in microbial community compositions, potential functions and complexities across sediment, seagrass leaves, and seawater within different eutrophic areas of two adjacent seagrass meadows on Hainan Island, China. Our results indicated that microbial diversity on seagrass leaves was significantly lower than in sediment but significantly higher than in seawater. Both sediment and phyllosphere microbial diversity showed no significant difference between the highly eutrophic and less eutrophic sites in each lagoon. However, sediment microbial diversity was higher in the more eutrophic lagoon, while phyllosphere microbial diversity was higher in the less eutrophic lagoon. Heavy eutrophication increased the relative abundance of phyllosphere microorganisms potentially involved in anaerobic metabolic processes, while reducing those responsible for beneficial functions like denitrification. The main factor affecting microbial diversity was organic carbon in seawater and sediment, with high organic carbon levels leading to decreased microbial diversity. The co-occurrence network analysis revealed that heavy eutrophication notably reduced the complexity and internal connections of the phyllosphere microbial community in comparison to the sediment and seawater microbial communities. Furthermore, ternary analysis demonstrated that heavy eutrophication diminished the external connections of the phyllosphere microbial community with the sediment and seawater microbial communities. The pronounced decrease in biodiversity and complexity of the phyllosphere microbial community under eutrophic conditions can lead to greater microbial functional loss, exacerbating seagrass decline. This study emphasizes the significance of phyllosphere microbial communities compared to sediment microbial communities in the conservation and restoration of seagrass meadows under eutrophic conditions.

Community science approach reveals temporal and eutrophication-related spatial patterns in bladderwrack-associated invertebrate fauna

Coastal zones are affected by a variety of anthropogenic drivers. While scientific assessments of the large-scale impacts are often insufficient due to limited resources, community science approaches (i.e. engaging voluntary participation by the general public in scientific research) may allow studying processes on larger geographic and/or temporal scales. In this study, a community science campaign was launched to assess geographic and temporal patterns in subtidal bladderwrack (Fucus vesiculosus) -associated invertebrate fauna along the coastal eutrophication gradient of the Finnish Baltic Sea coast in 2020–2021. The data collected by the community scientists were quality-controlled and generally similar to scientist-collected data. However, most taxa had somewhat lower abundances than data collected with another, more established sampling method. The community composition of fauna differed between areas with varying eutrophication status, and the total abundances of fauna were highest in the areas with the lowest eutrophication impacts. The data also revealed spatial and temporal patterns of individual taxa. For example, the abundance of blue mussel (Mytilus edulis) was highest in less eutrophied areas, while the abundance of non-indigenous Harris mud crab (Rhithropanopeus harrisii) was highest in the areas with moderate eutrophication impacts. A two-fold increase in the abundance of isopods that graze on bladderwrack was observed between the study years, indicating a sizeable temporal variation in bladderwrack grazing pressure. The study provides novel information on bladderwrack-associated invertebrate fauna and the applicability of using community science in marine subtidal research. The results suggest that community science is an effective approach to assessing subtidal community-level patterns, and its continued use is recommended to complement data collection across large spatial and temporal scales in marine key habitats.

Floristic classification of opportunistic green macroalgae communities of the European myxomesohaline seas

Shallow-water communities of opportunistic green marine macroalgae in eutrophicated areas are currently gaining an advantage over communities dominated by other groups of macrophytes. Therefore, their classification, study of composition and observation of structural changes are of particular importance. One class (Ulvae intestinalis–Ulvetea linzae), one order (Ulvae intestinalis–Ulvetalia linzae), three alliances (Ulvae intestinalis–Ulvion linzae, Ulvae intestinalis– Ceramion virgati, Ulvae rigidae–Gelidion spinosi) and three new associations of macroalgal communities of meso- and polysaprobic sublittoral vegetation within the shelf of the Black, Azov and Baltic Seas are described for the first time, using the Braun-Blanquet approach. Principal components analysis revealed two main factors influencing the floristic composition of the investigated communities: salinity and nutrient enrichment with associated turbidity. The proposed classification of opportunistic communities of green algae should be used in assessing the dynamics of the state of vegetation during eutrophication of the aquatic environment.

Provenance analyses of silted sediments in Shenzhen Bay: Insights based on rare earth elements and stable isotopes

Shenzhen Bay (SZB) in southern China is a typical eutrophic area, with internal pollution from its sediments representing an important nutrient source. However, the transport paths and sources of sediments in SZB remain unclear, making it difficult to analyze the nutritional budget and propose effective sediment management strategies. To address this, we linked a sediment fingerprinting technique to a Bayesian mixing model (MixSIAR) and conducted provenance analyses. We collected particle samples from SZB sediment and surrounding areas, including the Shenzhen River (SZR), Pearl River Estuary (PRE), and the northern South China Sea (SCS). Two groups of natural tracers were measured to trace different phases of sediments: (1) C and N parameters for the fates of the organic phase of sediments, and (2) rare earth element (REE) patterns for the provenance of mineral fragments. The results showed that the concentrations of total organic C and total N were 0.89–1.44 % and 0.05–0.13 %, respectively. MixSIAR suggested that fluvial inputs from SZR and PRE contributed 46.6 % and 30.3 % of organic matter, respectively. The organic matter in the PRE mainly originated from sewage and the upper reaches of the Pearl River. The concentration range of REEs in SZB sediments was 153.12–480.09 mg/kg with clear enrichment for light REE. MixSIAR results showed that the mineral fragments mainly originated from the outer bay (SCS and PRE, which contributed 57.2 % and 32.7 %, respectively). These results indicate that organic pollution follows a different path from the inorganic base, which is mainly related to anthropogenic input from land. This study highlights that complex sediment transport processes and pollution intrusions from the Pearl River are the issues that must be considered for eutrophication restoration in SZB.

Microbial interaction patterns and nitrogen cycling regularities in lake sediments under different trophic conditions

Exploring how nitrogen (N) cycling microbes interact in eutrophic lake sediments and how biogenic elements influence the nitrogen cycle is crucial for understanding biogeochemical cycles and nitrogen accumulation mechanisms. In this study, sediment samples were collected from various areas of Taihu Lake with different trophic conditions in all four seasons from 2015 to 2017. Using high-throughput sequencing and molecular ecological network analysis, we investigated the microbial interaction patterns and the role of nitrogen cycling in sediments from lakes with different trophic conditions. The results showed distinct structures of sediment microbial networks between lake areas with different trophic conditions. In the more eutrophic region, network indices indicate higher transfer efficiency of energy, material, and information, more significant competition, and weaker niche differentiation of the microbial community. The sedimentary environment in the moderately eutrophic area exhibited greater potential for denitrification, nitrification, and anammox compared to the mesotrophic area, but the inhibition between N functional microbes and limitations in N removal processes were also more likely to occur. The topological structure of the networks showed that the carbon (C), sulfur (S), and iron (Fe) cycles had a strong influence on the nitrogen cycle in both lake areas. In the moderately eutrophic lake area, C- and S-cycling functional bacteria facilitated a closed cycle of the coupled N fixation–nitrification–DNRA (dissimilatory nitrate reduction to ammonium) process and reduced N removal. In the mesotrophic lake area, C- and S-cycling functional bacteria promoted both N fixation and mineralization, and Fe-cycling functional bacteria coupled with denitrifiers enhanced the nitrogen removal process of products from nitrogen fixation and mineralization. This study improved the understanding of the nitrogen cycling mechanism in lake sediments under different trophic conditions.

A simulation-optimization approach based on the compound eutrophication index to identify multi-nutrient allocated load

Eutrophication with nutrient enrichment is a global marine ecosystem concern that threatens human health, economic activities, and ecosystem functions. Therefore, a nutrient load optimization method is required to help control marine eutrophication. However, eutrophication-based nutrient allocated load optimization is a multi-objective project due to a series of eutrophication pressures, such as cross-regional land-based nutrient loads and multi-nutrient regimes and ratios. In this study, a synergistic multi-nutrient control method was developed for the Bohai Sea (BS), China, which links multi-nutrient pressures with eutrophication states. Based on the eutrophication control standard, which is the second level of compound eutrophication index (CEI), the total maximum allocated loads (CEI-based TMALs) of total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and the chemical oxygen demand (COD) were calculated by a simulation-optimization approach. Using the end year of China's 13th Five-Year Plan (2020) as the reference year, 154 high load pressure jurisdictions (HLPJs) that contribute to eutrophication response segments in the BS were identified. Accordingly, practiced the optimized annual reduction rates of TDN, TDP, and COD in the HLPJs at 15 %, 11 %, and 2 % according to CEIII, respectively, the proportion of eutrophicated areas gradually decreased from 32 % in 2020 to 15 % in 2025 and might be 0 % in 2035 with ecosystem resilience in 2035. In particular, under the annual reduction rates of TDN and TDP optimized based on CEIII, the DIN/DIP molar ratio in the BS decreased to 16:1 by 2035. The simulation–optimization approach associated with the CEI-based TMALs for multi-nutrient control in this study might make implementing land-sea coordination more efficiency and marine nutrient regime stably. This can provide scientific and technological support for improving the health of coastal ecosystems.

A Physical Perspective of Recurrent Water Quality Degradation: A Case Study in the Jiangsu Coastal Waters, China

AbstractEstuarine‐coastal systems receive pollutants from various sources at an alarming rate. Some systems are extremely susceptible to terrestrial input, as a relatively small amount of pollutant loading induces lasting water quality degradation. The Jiangsu coastal waters (JCWs), located in the southwestern Yellow Sea, are such areas that lack large river discharge but suffer from recurrent eutrophication recently. We hypothesize that the low flushing efficiency in the JCWs largely accounted for the susceptibility to coastal pollution. To test it, transit time (TT) and pollutant flushing rates in the JCWs were estimated under various scenarios using a validated three‐dimensional hydrodynamic model. Results show that TT in many inshore waters of the JCWs and the northern radial sand ridges is >240 days, which are consistent with the observed frequently eutrophic areas. The JCWs are better flushed and thus less eutrophic in summer, as a consequence of the stronger tidal residual coastal circulation. The baroclinic pressure gradient, modulated by the formation and destruction of thermal stratification in offshore waters, poses a dominant control on the seasonal variations of the coastal circulation and flushing rates, while wind effects are secondary. River‐borne pollutants from the Yangtze and Jiangsu local rivers are shown to primarily affect regions south and north of 32.5°N, respectively. Our study interprets the vulnerability of the JCWs to pollutant enrichment from a physical perspective and finds the flushing efficiency to be a good indicator of eutrophication, providing references for environmental managers of local and global estuarine‐coastal systems with recurrent pollution.

Alien Macroalgal Rearrangement in the Soft Substrata of the Venice Lagoon (Italy): Impacts, Threats, Time and Future Trends

Non-native species are a concern for aquatic environments both for the ecosystem biodiversity and from the economical point of view. The Venice Lagoon is a Mediterranean hotspot of alien introductions and macroalgae are probably the most represented systematic category. For this reason, alien macroalgal distribution and variation were monitored in late spring-autumn surveys, carried out in 2011, 2014, 2018 and 2021 in the soft bottoms of the entire lagoon (87 common stations). Overall, 21 taxa were recorded; three of them (i.e., Acanthosiphonia echinata, Caulacanthus okamurae, Osmundea oederi) are well-established recent introductions for the lagoon, which has increased the total number of non-native species to 33. Ulva australis, previously reported as Ulva laetevirens, is the most abundant species and it is replacing Ulva rigida, especially in the less eutrophic areas. The invasive Gracilariopsis vermiculophylla, an engineering species colonizing the eutrophic choked areas especially in the central lagoon, is instead decreasing. Other abundant established taxa are now dominant components of the lagoon biomass, whereas many others are rare or have small sizes that make their biomass negligible. Overall, these species do not represent serious threats to the environment, but they rather increase biodiversity, with some of them having positive effects on ecosystem services.

The Effect of Eutrophication on Drinking Water

The effects of eutrophication on the environment may have deteriorate consequences of health of exposed animal and human populations through various path way’s. when fresh water, extracted from eutrophic areas, is used for the production of drinking water severe impacts can also occur during watering in eutrophic waters. eutrophication is complex processes which occurs both in fresh and marine waters, where certain types of algae disturbs the aquatic ecosystem and become a threat for animals and human health the primary cause of eutrophication is an excessive concentration of plant nutrient’s originating from agriculture of sewage treatment. The main cause of eutrophication is the large input of nutrient mixed to water body and the main effect is imbalance in the food web that results in the high levels of phytoplankton, zooplankton, algae biomass in stratified water bodies. This can lead algal blooms. The direct consequences is in an excess of oxygen consumption near bottom of the water body. eutrophication processes can be divided in to two categories depending on weather they are linked to the nutrients dispersion and phytoplankaton growth to oxygen cycle near the bottom of the water body. Various effects can be observed depending upon the severity of the eutrophication. Treatment of eutrophic water for producing drinking water. algae disturbs the aquatic ecosystems a threat for animal and human health..eutrophication concern the availability of oxygens. Some species of algae may also contain toxins but incidents where fresh water algae or the origin of cause human or animal illness. Some cynobacteria have capacity to produces toxins dangerous to human beings. A variety of symptoms depending on toxins implicated our observed such as fatigues, headache, diarrhoea, vomiting, and some throat fever skin irritations. Good practices to inform people about risks of bathing or sporting activity in normally colored or turbid waters. Allergic bathers of people walking along shore of water body affected by algae blooms. Any allergies releasing not only toxin but also allergic compounds. In some specific case; local authorities must rely on eutrophic water for producing drinking water.

Drift macroalgae positively influence seagrass-associated nekton communities of the northern Gulf of Mexico

Drift macroalgae, often found in clumps or mats adjacent to or within seagrass beds, can provide additional food resources and habitat complexity, leading to increased animal abundance, but large concentrations can also inhibit faunal movements, smother benthic communities, and contribute to hypoxia, reducing nekton abundance. Despite its ubiquity, few studies have quantified drift macroalgal prevalence over large spatial scales or its effects on seagrass-associated nekton, hindering our understanding of the functional role of drift macroalgae in ecosystems. We quantified the relationship between drift macroalgal biomass and the seagrass-associated nekton community within five estuaries spanning 2000 km across the northern Gulf of Mexico. Overall, increases in macroalgal biomass within seagrass meadows significantly influenced community structure, increasing shrimp, crab, and fish abundances, but the effect varied by region. Relationships between species richness, diversity, organism size, and macroalgal biomass were not observed, suggesting that drift macroalgae provide additional habitat but not necessarily new niche space. Small nekton play a vital role in many local fisheries, providing valuable food resources for fish and invertebrates. Increased recruitment into macroalgae can benefit local fisheries by providing shelter and increased food resources, which may increase the survival, growth, and population size of recreationally and economically important species. While excess levels of drift macroalgae can negatively impact benthic plant and animal communities, particularly in eutrophic areas, the moderate levels observed during this survey were associated with positive effects on organismal abundance, suggesting that drift algal dynamics should be considered in habitat-based management strategies for coastal estuaries.

Why do red tides occur frequently in some oligotrophic waters? Analysis of red tide evolution history in Mirs Bay, China and its implications

The process and management of red tide in oligotrophic waters are poorly understood as most studies on red tide were focused on eutrophic areas. In this study, 404 red tide events together with the historical water quality dynamics during 1991–2020 were investigated in an anthropogenically influenced bay in China - Mirs Bay, whose most region is oligotrophic except small inshore areas. Red tides of oligotrophic offshore accounted for 20 % of all. With the effective governmental management on inshore areas, concentration of PO4 and DIN has been decreased to a low level (PO4 <0.01 mg/L while DIN <0.1 mg/L) in the bay since about 2000. However, the reduction of nutrients was still accompanied by the frequent outbreaks of red tides, as well as a shift of dominant algae from diatoms to dinoflagellates, which might be due to the unbalanced nutrient reduction, such as N:P ratio fluctuation and organic nutrient increase. This shift might trigger more red tide events and even some super ones (long-duration or large-scale) in oligotrophic areas. Detailed analysis on red tide events combined with model simulation proved that the outbreak of red tide in Mirs Bay was caused by the joint contribution of nutrients and hydrodynamics. Nutrients of inshore area supported the red tides there, and with the help of physical conditions, red tides inshore could be transferred to offshore areas and then were likely to bloom again or be preyed to support blooms of other organisms. This study acknowledged that the reduction of both N and P either inorganic or organic nutrients was essential to control red tides, even in oligotrophic waters, but a balanced strategy considering the dual reduction of both nitrogen and phosphorus was of pivotal role to restore the health of coastal water systems disturbed by human.

Organic Enrichment Induces Shifts in the Trophic Position of Infauna in a Subtropical Benthic Food Web, Hong Kong

Anthropogenic nutrient input to coastal waters is one of the most common disturbances within inshore marine benthic communities. Organic enrichment in sediments leads to the reduction or disappearance of sensitive organisms, and influences the quality and quantity of primary producers which serve as food sources for the benthic fauna. Such changes, in turn, affect the energy flow and food-web interactions in benthic communities. To examine how organic enrichment may alter marine benthic trophic relationship, a stable isotope (δ13C and δ15N) analysis of the potential food sources and a range of meiofauna and polychaetes from an organically polluted and a relatively unpolluted site was compared in subtropical waters of Hong Kong. Results indicated that some omnivorous infauna shifted from a mainly carnivorous diet at the unpolluted site to a largely herbivorous diet at the organically polluted site. This dietary shift is likely to be related to the oxygen stress, prey limitation and increased abundance and nutritional quality of primary producers in the eutrophic area, resulting in an increase in utilization of plant materials as the major food source. The present findings suggest that such changes in trophic position induced by organic enrichment can provide further insights into the structure and function of coastal benthic communities under pollution stress.

Satellite observations estimating the effects of river discharge and wind-driven upwelling on phytoplankton dynamics in the Chesapeake Bay.

Phytoplankton growth in estuaries is regulated by a complex combination of physical factors with freshwater discharge usually playing a dominating role controlling nutrient and light availability. The role of other factors, including upwelling-generating winds, is still unclear because most estuaries are too small for upwelling to emerge. In this study, we used remotely sensed proxies of phytoplankton biomass and concentration of suspended mineral particles to compare the effect of river discharge with the effect of upwelling events associated with persistent along-channel southerly winds in the Chesapeake Bay, a large estuary where upwelling and its effects on biogeochemical dynamics have been previously reported. The surface chlorophyll-a concentrations (Chl-a) were estimated from Visible Infrared Imaging Radiometer Suite (VIIRS) satellite data using the Generalized Stacked-Constraints Model (GSCM) corrected for seasonal effects by comparing remotely sensed and field-measured data. Light limitation of phytoplankton growth was assessed from the concentration of suspended mineral particles estimated from the remotely sensed backscattering at blue (443 nm) wavelength bbp (443). The nine-year time series (2012-2020) of Chl-a and bbp (443) confirmed that a primary factor regulating phytoplankton growth in this nearshore eutrophic area is discharge from the Susquehanna River, and presumably the nutrients it delivers, with a time lag up to four months. Persistent southerly wind events (2-3 days with wind speed >4 m/s) affected the water column stratification in the central part of the bay but did not result in significant increases in remotely sensed Chl-a. Analysis of model simulations of selected upwelling-favorable wind events revealed that strong southerly winds resulted in well-defined lateral (East-West) responses but were insufficient to deliver high-nutrient water to the surface layer to support phytoplankton bloom. We conclude that, in the Chesapeake Bay, which is a large, eutrophic estuary, wind-driven upwelling of deep water plays a limited role in driving phytoplankton growth under most conditions compared with river discharge. Integr Environ Assess Manag 2022;18:921-938. © 2022 SETAC.

Physiological Response of the Freshwater Mussel Unio douglasiae in Microcystis aeruginosa Bloom Waters

In the present study, we evaluated the effects of different environments on the filtering rate (FR), mortality, and biodeposition (BD) of the freshwater mussel Unio douglasiae in bloom waters containing the toxic cyanobacterium Microcystis aeruginosa. The mean FR of 19 selected individuals (shell length, 5.0–9.8 cm) was 0.30 ± 0.03 L g−1 h−1 (range = 0.24–0.35 L g−1 h−1). Shell length was strongly correlated with both net and gross BD of mussels (P < 0.0001). The mean FR was higher in river water (0.405 ± 0.052 L g−1 h−1) than in lake water (0.304 ± 0.051 L g−1 h−1). In contrast, the BD of mussels was higher in RW (0.671 ± 0.609 mg g−1 h−1) than in LW (0.275 ± 0.027 mg g−1 h−1). For algal species, the FR of mussels ranged from 0.114 ± 0.024 to 0.553 ± 0.019 L g−1 h−1. The FR of U. douglasiae was higher in river water (mainly diatoms), whereas BD was higher in lake water (mainly Microcystis). U. douglasiae did not prefer toxic M. aeruginosa, which was significantly accumulated in pseudofaeces and faeces. The maximum FR of U. douglasiae in algal bloom water was recorded at a water temperature of 25°C and water depth of 50 cm. Moreover, the in situ mortality of U. douglasiae was strongly affected by water temperature and nitrogen concentration. Overall, U. douglasiae can enhance water quality in eutrophic areas by removing dominant cyanobacteria, although its removal efficiency depends on environmental parameters and site of introduction.

Bacterial community assembly in surface sediments of a eutrophic shallow lake in northern China

Anthropogenic perturbations make negative effects on wetland ecosystems, such as increasing levels of eutrophication. Under variable environmental conditions, studying the processes and mechanisms underlying their spatial distribution is critical to biogeochemical significance of microorganisms. In order to understand the changes in sediment bacterial community and their assembly with long-term eutrophication of the Baiyangdian Lake of China, we explored the microbial communities for 24 surface sediment samples using high throughput sequencing of V3-V4 region of 16S rRNA gene, meanwhile we employed Neutral community model (NCM) to characterize the community assembly processes. Then, the β-nearest taxon index (βNTI) based on a null model was used to provide a quantitative description of the assembly processes of the bacterial community. Dispersal limitation, quantified by βNTI, accounted for ∼64.6% of all assembly processes. As the increasing levels of eutrophication, deterministic processes of bacterial community assembly may be enhanced. Moreover, the significant correlation between the βNTI and change in water NO3− or sediment pH might lead to deterministic processes. There was some selection pressure acting within the Baiyangdian lake sediments. The neutral community model properly explained bacterial community assembly. The NO3−, NH4+, pH and EC were main influencing factors on the composition of the bacterial community. The overlying water NO3−, surface water NO3− and sediment pH were the three most crucial environmental factors to drive bacterial assembly. The findings revealed that Group 4 with relatively stronger deterministic processes as a more eutrophic area should be monitored as an indicator for eutrophication governance.

New insights into identifying sediment phosphorus sources in river-lake coupled system: A framework for optimizing microbial community fingerprints

Identifying sediment phosphorus sources in river-lake coupled system is a question in developing preferential control strategies for phosphorus. As sediments adsorbed phosphorus and microbes would be transported with changing hydrodynamic, the phosphorus source-specific microbial community fingerprints shed light on determining the major sediment phosphorus sources. However, the identification of microbial community fingerprints is a challenge because both microbial succession and hydrological characteristics of river-lake systems would affect the stability of fingerprints. Therefore, this study provided a framework for optimizing phosphorus source-specific microbial community fingerprints, and attempted to identify the major sources of sediment phosphorus in river-lake coupled ecosystem. Meiliang Lake is one of the highly eutrophic area in Taihu Lake, where the sediments, bacterial communities, and phosphorus had a close relationship. Through analyzing the connectivity of microbes along water continuum, a microbial fingerprints candidate database was constructed. The phosphorus-related bacterial communities were screened and optimized by comparing the difference of predicted results between upstream and downstream, forming the stable microbial community fingerprints which consisted of Bacteroidia, Bacilli, Clostridia, and other species at the class level. SourceTracker results that based on the optimized phosphorus source-specific microbial community fingerprints indicated that the major sediment phosphorus sources to Meiliang Lake were Liangxi River, Wujingang River, and Donghuandi River, with the relative standard deviations ranging from 2.59% to 27.56%. The accuracy of phosphorus source apportionments was further confirmed based on the composite pollution index and hydrodynamic condition. This study put forward suggestions on how to improve the stability of microbial community fingerprints, and would help to improve the understanding of applying microbial source tracking method to identify the sources of abiotic pollution like sediment phosphorus.

Variation in sediment and seagrass characteristics reflect multiple stressors along a nitrogen‐enrichment gradient in a New England lagoon

AbstractWe examined concentrations of organic carbon, dissolved sulfides, total sediment sulfur, and stable sulfur isotope ratios in seagrass leaf tissues across a nitrogen‐enrichment gradient in a coastal marine ecosystem (Cape Cod, Massachusetts) in 2007–2010 and 2017–2019. We also measured seagrass aboveground and belowground biomass, epibiota biomass, and leaf chlorophyll content. Seagrasses were present at all sites in the former period but were lost at our most nitrogen‐impacted site (Snug Harbor) by 2011. In 2007–2010, sediment organic carbon and dissolved sulfides were highest in Snug Harbor and decreased along the gradient; leaf tissues depleted in 34S also indicated higher sulfide intrusion into seagrass tissues in more eutrophic areas. By 2017–2019, sediment organic carbon and pore‐water soluble sulfides had decreased in Snug Harbor, but had increased at the intermediate site, to levels found at the most impacted site prior to the seagrass die‐off. Again, leaf tissue 34S depletion reflected this pattern, indicating seagrasses were exposed to the highest sulfides at the intermediate site. The decreases in sediment organic carbon and soluble sulfides in Snug Harbor years after the loss of the seagrasses illustrate a feedback between high organic matter in seagrass beds and increasing stressors like elevated soluble sulfides in nutrient‐enriched systems. We found significant relationships between sediment conditions and seagrass responses, including greater aboveground to belowground biomass ratios, epibiota biomass, and 34S‐depleted leaves at sites with high pore‐water sulfide and highly organic sediments. Our research suggests that the reduction of anthropogenic nitrogen entering the harbor is necessary for improving sediment quality and preventing seagrass mortality.

Hydrodynamics-based modeling of phosphorus balance and dynamics in a large tropical floodplain

The development of a multidimensional phosphorus dynamic model for lake–floodplain systems is still limited due to its complex hydrodynamics and environmental processes, which constrains our understanding and environmental management on eutrophication. Therefore, we developed a horizontal two-dimensional hydrodynamics-based phosphorus model and applied it to understand the phosphorus dynamics in the Tonle Sap Lake, a large tropical lake–floodplain system in Cambodia. This phosphorus dynamic model is based on a hydrodynamic model (local inertial model) and integrates the major phosphorus processes in the lake and the phosphorus inputs from tributaries and floating villages. The phosphorus dynamic model was applied to the period from September 1999 to December 2003 for elucidating the total phosphorus balance and the spatiotemporal distribution of its concentration. The model reproduced the seasonality of total phosphorus concentration with its root mean square error of 12 and 16 µg/L for the calibration and validation periods, respectively. During 1999–2003, the lake was in a mesotrophic to eutrophic state, whereas the average eutrophic area expanded from 8.0% in October to 45.3% in May, when the inundated area was reduced, due to a relatively high internal loading and the high concentration of tributary inputs. In addition, the model estimated that most of the external total phosphorus loading was settled down and the internal processes play an important role in phosphorus dynamics in the Tonle Sap Lake. As presented, the model analysis integrating hydrodynamics and internal processes substantially helps us understand the spatiotemporal dynamics of phosphorus in the lake–floodplain systems.

Sources of terrestrial nitrogen and phosphorus mobilization in South and South East Asian coastal ecosystems

South and Southeast Asia (SSEA) is a socially, economically and ecologically diverse region, with a rapidly growing population and accelerating industrial development, agricultural intensification using manufactured fertilizers, terrestrial landscape change, expansion of water engineering, sewage production and land conversions. Nitrogen and phosphorus are major nutrients that play an essential role in the eutrophication of inland and coastal water bodies. Eutrophic areas, when combined with appropriate coastal ocean physical conditions, can develop into hypoxic zones that result in long-term ecosystem disruption. This study addressed changes in terrestrial nitrogen and phosphorus mobilization associated with land-use transitions, fertilizer use and sewage from 2002 to 2016 in the SSEA region, with a focus on the Mekong and Krishna-Godavari watersheds. Terrestrial mobilization results from the internal production or addition of reactive, soluble and/or plant available forms of nitrogen and phosphorus. To estimate terrestrial mobilization associated with land conversion, published data were mined for estimates of land cover change effects on soil carbon, nitrogen and phosphorus pools. Data on exogenous fertilizer and sewage effluents were also compiled from the literature. From the analysis, it showed that fertilizer input was the largest source of nitrogen and phosphorus in both case study watersheds. Sewage and land conversion were not a significant source of terrestrial phosphorus mobilization in either watershed. All land conversions resulted in declines in soil carbon, ranging from 11% to 38%. Nitrogen increased, on average by 15%, in conversions of agricultural to urban land, but decreased in all other conversions. Phosphorus increased by 89% in wetland to agriculture conversions, but decreased between 2% and 24% for other land conversions. Expansion of agriculture at the expense of forest was the dominant land conversion in the Mekong watershed. Urbanization, at the expense of agriculture and forest, was the dominant land conversion in the Krishna/Godavari watershed. These results suggest that management of nutrient pollution (N and P) in SSEA will need to focus on reducing the use and/or improving the efficiency of fertilizer use along with regular consolidated monitoring in both watersheds.