Sediment Total Phosphorus Research Articles

Nutrient and physicochemical properties as potential causes of stress in mangroves of the central Red Sea.

Mangrove ecosystems are some of the most productive and important sinks for sediment globally. Recently, there has been an increasing interest in possible causes of stress in mangroves, such as nutrient limitation, high salinity, solar radiation and temperature. We measured different factors casing stress and determined how they influenced oxidative stress and growth biomarkers in six study sites dominated by mangroves; Al Lith, South Jeddah, Dahban, Thuwal, Rabigh and Mastorah. Significant differences (P < 0.05) were recorded in water salinities and temperatures, nitrogen and phosphorus content in sediments, and antioxidant enzyme activities in different study sites. The highest salinity (40.75 ‰) and temperature (29.32°C) were recorded in the Rabigh mangrove stand, which corresponds to the lowest dissolved oxygen (5.21 mg/L). Total organic carbon, total nitrogen and total phosphorus in sediment across the study areas were in the order Rabigh>Thuwal>Dahban>Al Lith>South Jeddah>Mastorah. Total nitrogen in mangrove leaves at Rabigh was the highest and about 1.3 times higher than the total nitrogen in South Jeddah mangrove ecosystem, very different from the ratio of total nitrogen in the sediments at Rabigh and South Jeddah mangrove ecosystems. The average values of δ13C (-17.60‰) and δ15N (2.84‰) in the six mangrove ecosystems, and the highest δ13C (-13.62‰) and δ15N (4.39‰) at Rabigh in the sediments suggest that nutrient input differed among study sites. Higher nutrient levels at Rabigh mangrove ecosystem were attributed to restricted circulation, camel grazing and land runoff with agricultural waste during seasonal flooding events. However, N limitation and possibly salinity contributed to stress in Al Lith, South Jeddah, Dahban, Thuwal, Rabigh, and Mastorah mangrove ecosystems. Salinity (r = 0.9012) contribute more to stress at Rabigh.

Unveiling the role of sediments in phosphorus removal in pilot-scale constructed wetlands for swine wastewater treatment

The accumulation rate, fractions, and sorption capacity of phosphorus in sediments determine the removal efficiency and service life of constructed wetlands (CWs). Nine pilot-scale three-stage surface flow CWs were constructed to treat three loading rates of lagoon-pretreated swine wastewater, and surface sediment samples at initial and one-year treatment were collected to analyze the phosphorus fractions and sorption capacity. After one-year treatment, concentration of total phosphorus (TP) in sediments increased for high loading rates of wastewater, but remained stable for low loading rates. The annual accumulation rate of TP in sediments (Ma) was −43–445 mg kg−1 yr−1 at surface loading rate (SLR) of 36–355 g P m−2 yr−1. Their association could be described well using a sigmoid model, i.e., Ma = −23 + 538/(1 + exp.(−(SLR–262)/48)) (R2adj = 0.897, RMSE = 40.8, p < 0.01), indicating that the phosphorus accumulation rates in sediments were loading rate-dependent. The sum of inorganic phosphorus fractions contributed to 80–100% of the TP concentration, and accumulation of aluminum-bound phosphorus (AlP) and iron-bound phosphorus (FeP) was responsible for variability of TP concentration in sediments. Phosphorus sorption capacity of CW1 sediments increased by 1.3–1.8 times, attributed to increased pH, and concentrations of ammonium oxalate-extractable aluminum and iron in sediments due to the wastewater input. Selecting iron and aluminum-rich materials preferentially as substrates and regulating the ratio of metal ions to phosphorus in wastewater should be alternative enhancement strategies of CWs for phosphorus removal.

The response of sediment microbial communities to temporal and site-specific variations of pollution in interconnected aquaculture pond and ditch systems

Sediment microbial communities play critical roles in the health of fish and the biogeochemical cycling of elements in aquaculture ecosystems. However, the response of microbial communities to temporal and spatial variations in interconnected aquaculture pond and ditch systems remains unclear. In this study, 61 sediment bacterial samples were collected over one year from 11 sites (including five ponds and six ditches) in a 30-year-old fish aquaculture farm. The 16S rRNA approach was used to determine the relative abundances of microbial communities in the sediment samples. The relationships among nutrients, heavy metals, and abundant microorganisms were analyzed. Our results showed that Proteobacteria, Bacteroides and Chloroflexi were the predominant phyla in the sediments of aquaculture pond, with average abundances of 36.33%, 18.60%, and 14.58%, respectively. The microbial diversity in aquaculture sediments was negatively correlated (P < 0.05) with the concentrations of total nitrogen and total phosphorus in sediments, indicating that the microbial diversity is highly associated with the remediation of nutrients in sediments. The sediment samples with high similarities were discovered by the t-distributed stochastic neighbor embedding (t-SNE) method. The site-specific correlations between specific microorganisms and heavy metals were explored. The network analysis revealed that the microbial diversities in aquaculture ponds were more stable than that in aquaculture ditches. The network analysis also illustrated that the microbial genera with low relative abundances may become key groups of microbial communities in sediment ecosystems. Our work deepens the understanding of the relationships between microbial communities and the spatiotemporal characteristics of surface water and sediments in aquaculture farms.

Phosphorus Fractions and Quantitative Identification of Pollution Sources in Nanhai Wetland, Baotou

In this study, total phosphorus (TP) and the phosphorus (P) fractions in the water and surface sediments of the Baotou Nanhai wetland in China were determined using molybdenum blue/ascorbic acid spectrophotometry and continuous extraction methods. An APCS-MLR receptor model was combined with correlation analysis (CA) and principal component analysis (PCA) to identify and quantify the pollution sources. The results showed ① differences in the pollution level of phosphorus between the surface sediments and water. The contribution of dissolved inorganic phosphorus (DIP) to TP in the water (WTP) was the lowest, while the contribution of calcium-bound phosphorus (HCl-P) to TP in the surface sediments (STP) was the largest in the study area. The surface sediments of the Nanhai Lake (L area) and the wetland plant area (P area) exhibited high bioavailability and the potential for releasing phosphorus into the water, which could result in eutrophication and is therefore of concern. ② The APCS-MLR receptor model indicated that the main pollution sources of phosphorus were industrial wastewater and domestic sewage (29.07%), and pesticides and fertilizers (29.00%). In addition, the degradation of animal and plant residues (18.49%) also contributed to pollution in the study area.

Effects of algae and hydrophytes on the inorganic phosphorus pool of shallow hypereutrophic Lake Taihu

Abstract Sedimentary phosphorus is a crucial potential source of phosphorus in the eutrophic lake ecosystem. Different ecological types are supposed to affect the presence and variation of sediment phosphorus. On the basis of field investigations, the total sediment phosphorus load in Zhushan Bay was 1,457.48 mg/kg, nearly four times that of the hydrophyte-dominated area. Thereinto, 41.1% was in the form of iron and aluminum-bound phosphorus, which explicitly indicated the phosphorus contamination there. Analytical methods such as Pearson correlation, contamination assessment and principal component analysis were conducted to find out that ‘contamination’ was not equivalent to ‘release risk’. The contamination classification of East Lake Taihu was ‘clean’ in general. However, 63.3% of the total phosphorus could be mobilized under certain conditions. Therefore, light phosphorus loading does not equate to less release risk. In the long run, the implicit phosphorus release by the activation of organic phosphorus in hydrophytic areas needs close attention. This study provides a reference to understand the influence of hydrophytes and algae on the phosphorus cycle of sediment.

Dredging alleviates cyanobacterial blooms by weakening diversity maintenance of bacterioplankton community

Disentangling ecological mechanisms behind dredging is meaningful to implement environmental policy for improving water quality. However, environmental adaptation and community assembly processes of bacterioplankton in response to dredging disturbance are poorly understood. Based on Illumine MiSeq sequencing and multiple statistical analyses, we estimated interactions, functions, environmental breadths, phylogenetic signals, phylogenetic clustering, and ecological assembly processes of bacterioplankton community before and after dredging. We found distinct change in community composition, comparable decreases in diversity, functional redundancy and conflicting interaction, relatively low phylogenetic clustering, and relatively weak environmental adaptation after dredging. The bacterioplankton community assembly was affected by both stochastic and deterministic processes before dredging, but dominated by stochasticity after dredging. Sediment total phosphorus was a decisive factor in balancing determinism and stochasticity for bacterioplankton community assembly before and after dredging. Consequently, taxonomic and phylogenetic α-diversities of bacterioplankton exhibited higher contributions to the water trophic level represented by chlorophyl α before dredging than afterwards. Our results emphasized bacterioplankton in response to environmental changes caused by dredging, with nutrient loss and ecological drift playing important roles. These findings extend knowledge of contribution of bacterioplankton diversity to water trophic level and decipher mechanisms of bacterioplankton diversity maintenance in response to dredging, which is useful for guiding mitigation of cyanobacterial blooms.

Relationships between characteristics of macrobenthic assemblages and environmental variables in the Heihe River Basin, China

Abstract To clarify the characteristics of macrobenthic assemblages and their response to the aquatic environment in the upper and middle reaches of the Heihe River, water quality, sediments and macrobenthos measurements were conducted in the summers of 2018 and 2019. The results showed that 50 species of macrobenthos were identified, belonging to 3 phyla, 7 classes, 15 orders and 32 families, mainly arthropods (37 species) and mollusks (11 species). Argyroneta aquatica, Chlaznius sp., dragonfly nymphs, Palaemon modestus, Radix auricularia, Cyraulus albus and Suecinea sp. were the dominant species in the whole study region; most of these are pollution-tolerant and moderately pollution-tolerant species. The macrobenthos density and biomass ranged from 10 to 577 ind./m2 and from 0.0907 to 50.0562 g/m2, respectively, showing high spatial heterogeneity. Predators were the main functional feeding group. One-way analysis of variance clarified that Margalef's index and the Shannon–Wiener index differed significantly among the spatial areas (P &amp;lt; 0.05). Canonical correspondence analysis showed that the spatial heterogeneity of the macrobenthos was affected by the water temperature and the total nitrogen and total phosphorus in sediments (P &amp;lt; 0.05).

Riparian Forest Cover Modulates Phosphorus Storage and Nitrogen Cycling in Agricultural Stream Sediments.

Watershed land cover affects in-stream water quality and sediment nutrient dynamics. The presence of natural land cover in the riparian zone can reduce the negative effects of agricultural land use on water quality; however, literature evaluating the effects of natural riparian land cover on stream sediment nutrient dynamics is scarce. The objective of this study was to assess if stream sediment phosphorus retention and nitrogen removal varies with riparian forest cover in agricultural watersheds. Stream sediment nutrient dynamics from 28 sites with mixed land cover were sampled three times during the growing season. Phosphorus dynamics and nitrification rates did not change considerably throughout the study period. Sediment total phosphorus concentrations and nitrification rates decreased as riparian forest cover increased likely due to a decline in fine, organic material. Denitrification rates were strongly correlated to surface water nitrate concentrations. Denitrification rate and denitrification enzyme activity decreased with an increase in forest cover during the first sampling period only. The first sampling period coincided with the greatest connectivity between the watershed and in-stream processing, indicating that riparian forest cover indirectly decreased denitrification rates by reducing the concentrations of dissolved nutrients entering the stream. This reduction in load may allow the sediment to maintain greater nitrogen removal efficiency, because bacteria are not saturated with nitrogen. Riparian forest cover also appeared to lessen the effect of agriculture in the watershed by decreasing the amount of fine material in the stream, resulting in reduced phosphorus storage in the stream sediment.

Influence of sedimentary organic matter sources on the distribution characteristics and preservation status of organic carbon, nitrogen, phosphorus, and biogenic silica in the Daya Bay, northern South China Sea

Surface sediment samples were collected from Daya Bay in October 2018, and analyzed for total organic carbon (OC), total nitrogen (TN) and their stable isotopes (δ13C and δ15N), total phosphorus (TP), biogenic silica (BSi), sediment textures and specific surface area (SSA). The primary objective was to evaluate the influence of mariculture/aquaculture on the distribution characteristics of organic matter (OM), and preservation status of OC, TN, TP, and BSi in sediments. The average δ13C and δ15N values, and OC/TN ratios were −21.27‰, 6.74‰, and 8.90, respectively. Monte Carlo simulation results revealed that mariculture/aquaculture biodeposits accounted for >40% of the buried OM at sites where the breeding rafts and cages are located, whereas marine OM increased gradually to the open sea. Terrestrial OM was generally low accounting for 17% by average. The contents and distribution characteristics of biogenic elements were more influenced by mariculture/aquaculture and primary productivity than sediment textures. Lower OC/SSA (0.3–1.2 mg OC/m2), TN/SSA (~0.05–0.18 mg TN/m2), and TP/SSA (0.02–0.04 mg TP/m2) loadings indicated that increased sequestration of labile OM in a coastal bay could contribute to significant degradation of recalcitrant OM in sediments with significant loss of P relative to OC. Nitrogen contamination in surface sediments was due to increased injection of aquaculture biodeposits, and may pose a detrimental effect on the ecological sustainability of the bay. Higher BSi/SSA loadings (0.9–1.7 mg BSi/m2) revealed that BSi was more preserved, and that BSi-based proxy could be used for paleo-productivity studies. However, such preservation may induce adverse dissolved silicate limitation in a bay perturbed by eutrophication. Fine-grained sediments (clay and silt) accounted for >77% of the sediment texture types with higher SSA, and while controlling the contents of biogenic elements under given depositional conditions were not the main determining factors of OC, TN, TP, and BSi preservation.

Depositional time trends of phosphorous accumulation in a dated sediment core from the northwestern Arabian Gulf: Can phosphorous be used to support 210Pb chronologies in coastal aquatic sediments?

The use of 210Pb dating for the reconstruction of contaminant profiles in undisturbed sediments is the most widely acceptable technique historically. Due to the uncertainties associated with the technique, dating of sediments have often been supported by ancillary evidence such as an alternative historical marker in the catchment that is preserved in the sedimentary records. The most widely used verification marker is 137Cs, which is attributed to global fallout from past nuclear weapons testing, and the Chernobyl accident. In the southern hemisphere, and the mid-latitudes, the 137Cs signal from Chernobyl fallout is often absent from the sedimentary records making it very difficult to verify the 210Pb chronologies in these natural archives. This study reports the spatial and temporal variability of total phosphorus (TP) and its forms in sediments from Kuwait Bay and provides evidence of the possibility of using Phosphorous as a potential marker to support dates derived from 210Pb dating.In the current study we report the spatial and temporal variations in the concentrations of Phosphorus from near-shore sediments from Kuwait. The mean (and range) of TP concentration in surficial sediments is 19.4 (12.2 to 24) μmol-P g−1 dry weight. The highest concentrations were measured in the deepest portions of the Bay which is characterized by fine grained sediments. The vertical profile of TP in the sediments was characterized by a gradual increase in concentration from lower layers to a subsurface maximum (at approximately 4–5 cm) followed by an exponential decrease to the sediment-water interface. The sedimentary TP profile correlated remarkably well with changes in the population of Kuwait over the last three decades, suggesting that wastewater inputs into the Bay from treatment plants are an important source of phosphorus in the coastal waters. The decrease in concentration in sediment deposited over the last five years of the core is explained by the commissioning of an improved wastewater treatment plant with higher phosphorus removal efficiency. These fluctuations preserved in the sedimentary records linked to identifiable historical events provides powerful evidence that this nutrient associated with wastewater inputs in coastal aquatic environments can be used as ancillary information to support 210Pb dating.

Degradation of Nitrogen, Phosphorus, and Organic Matter in Urban River Sediments by Adding Microorganisms

Reducing and remediating endogenous sediment pollution in urban rivers using appropriate microbiological remediation technology is regarded as a safe, effective, and environmentally sustainable mechanism. In this study, the pollutant removal efficiency of three microorganism types at different dosages was studied in the laboratory. To optimize the microbial restoration scheme, a comprehensive analysis of their effectiveness in removing total nitrogen (TN), total phosphorus (TP), total organic matter (OM), and polycyclic aromatic hydrocarbons (PAHs) was conducted, and associated structural changes in the sediment bacteria were analyzed. The results showed that using nitrifying bacteria and Bacillus as microbial agents resulted in superior removal efficiencies of TN and TP in sediments, whereas yeast was not as effective. The removal rates of TN reached 27.65% and 20.88% when 5 mg nitrifying bacteria and 10 mg Bacillus respectively, were used. A comparative analysis showed that nitrifying bacteria exhibited a better TN removal effect; however, Bacillus exhibited a better TP removal effect. The results of high-throughput sequencing revealed no significant changes to the microbial community structures when optimal microorganisms or beneficial microorganisms that thrive using OM as a source of C and energy were added. This study provides insights into the processes and mechanisms involved in the microorganism degradation of black and odorous sediment, and the results can be used as a basis for developing endogenous pollution control policies and methods for urban rivers.

The impact of fish farming on the water column and marine sediments in three coastal regions from eastern Aegean coast.

The impacts of mariculture activities in the water and sediments were comprehensively evaluated for the first time in this study. Lower dissolved oxygen was detected near the cages during summer due to aquacultural activities and bacterial degradation of organic compounds. However, DO levels were not below the 5 mg L-1 limit recommended for aquatic growth, survival and metabolic processes. Different eutrophication assessment methods showed that Güllük Bay, where intensive aquaculture activities occurred, was characterized by poor status. Assessment of different eutrophication tools for Akköy and Ildır Bay indicated that water quality status was not similar to each other. The most noticeable effect of aquaculture activities is the sedimentation of faeces and uneaten food under the cages. Nutrients in the water indicated gradual decrease with distance from the cages. Comparison of total phosphorus in sediments showed that the most affected area is Güllük Bay owing to cumulative impact of aquaculture. The higher total organic carbon (TOC) in sediments was measured near and under the cages. TOC was a useful indicator to show benthic health, less than 10 mg g-1 corresponded to low risk deteriorations for all aquaculture sites. Sediment monitoring studies should be carried out to provide sustainable use of the aquaculture areas.

A dynamic flux model for analyses of phosphorus exchange between overlying water and sedimentary deposits of a reservoir in the cold area of north China

In this study, to clarify the quantitative relationship between the exchange flux of total phosphorus and water environment factors at the sediment-overlying water interface in reservoirs, and to reveal that the seasonal variation of total phosphorus exchange flux at the sediment-overlying water interface changes when the water environmental factors change in reservoirs located in cold regions, water environment factors including pH, DO, temperature, and others were analyzed. Specifically, in 2018, sediment samples of the Dahekou Reservoir from XilinGol League were collected, and via indoor orthogonal simulation experiments, a mathematical model of the total phosphorus exchange flux at the sediment–overlying water interface and environmental factors was established, i.e., R = 0.791 + 0.018[T] + 0.048[pH] - 0.180[DO] + 0.004[K]. This model was then combined with the input load of total phosphorus in the Luanhe and Tuligen rivers in the upper reaches of the reservoir in order to assess the contribution rate of the total phosphorus release load to the total phosphorus input from the reservoir. The results showed that the total phosphorus release pollutant load in the sediments of the Dahekou Reservoir was 0.297 t/a in 2018. The flux of total phosphorus at the sediment-overlying water interface showed seasonal changes: summer > spring > autumn > winter. The release load of total phosphorus in sediments in spring was 0.014–0.042 t/month, and the contribution rate to the total phosphorus input from the reservoir was 16.67%–26.44%. The contribution rate of total phosphorus release in summer from the sediments to the overlying water was 19.71%–33.56%. Although this was the highest value of the entire year, due to the role of water temperature stratification in the summer, its actual contribution to the total phosphorus input pollution in reservoirs may not be significant. The total phosphorus released from the sediments in autumn was 0.067–0.397 t/month, and the contribution rate to total phosphorus input pollution in the reservoir decreased to 5.28%–11.19%. In winter, the water temperature decreased, and the concentration of dissolved oxygen increased. These changes to the water environment increased the phosphorus release from water to sediment, with the exchange flux of total phosphorus between sediment and water changing from −0.004 to −0.011 t/month.

Environmental factors and microbial communities jointly regulate biological dephosphorization process in pond-ditch circulation systems (PDCSs) for rural wastewater treatment

Pond-ditch circulation systems (PDCSs) were proved to be an appropriate operation selection in rural wastewater remediation. However, the biological dephosphorization process has not been investigated and quantified in PDCSs. In this study, PDCSs exhibited higher total phosphorus (TP) removal efficiencies (77.8%–97.4%). The activities of polyphosphate kinase (PPK) and exopolyphosphatase (PPX) tightly associated with phosphorus biological removal ranged from 0.356 to 11.844 μmol hydroxamic acid min−1 mg−1 protein, and 0.008 to 0.446 μmol p-nitrophenol min−1 mg−1 protein, respectively. Both PPK and PPX in PDCSs increased with time, peaked at day 30, and then declined, and were negatively correlated with sediment total phosphorus (STP), sediment inorganic phosphorus (SIP), P bound to Al/Fe/Mn oxides and hydroxides (NaOH-P), P associated with Ca (HCl-P), and organic matter (OM) (p < 0.05). Results of high-throughput sequencing suggested that Bacillus (0.46%–19.77%) and Clostridium (0.40%–21.0%) genus might be the predominant groups in phosphorus aerobic biological absorption; while Geobacter (0.15%–4.74%) and Arthrobacter (0.03%–4.01%) genus dominated in anaerobic biological process. The RDA results showed that compared to the ditch, temperature (W-temp), TP, dissolved oxygen (DO), NaOH-P, and OM had stronger effects on microbial community structures in two ponds at day 30 than those at days 14 and 60. Path analysis further indicated that STP could impact PPK and PPX activities in PDCSs both directly and indirectly via altering the relative abundances of bacteria taxa. We found that the indirect effects of W-temp, DO, and OM on PPK and PPX activities mediated through modulating the relative abundances of bacteria taxa and STP. Our findings provide evidences that biological dephosphorization process in PDCSs are jointly modulated by environmental factors and microbial communities. The less-studied W-temp, DO, STP, and OM modulating the relative abundances of bacteria taxa was an existing but previously underestimated indirect pathway influencing on biological dephosphorization process in PDCSs.

Littoral eutrophication indicators are more closely related to nearshore land use than to water nutrient concentrations: A critical evaluation of stressor-response relationships

Biological assessment metrics and water chemistry measurements are used to quantify the link between stressors and their effects on lake ecosystems, for the Water Framework Directive. However, correlations between metrics and water chemistry are often poor. This is seen as major weaknesses of Water Framework Directive-related monitoring and assessment. We analyzed macrophytes, benthic algae, benthic macroinvertebrates, water chemistry and sediment total phosphorus content in the littoral of six lakes in the Western Balkans and used CORINE land use data to estimate nutrient enrichment via runoff from the adjacent land. Lakes with a higher estimated phosphorus runoff from the adjacent land did not have higher littoral water nutrient concentrations, but littoral diatom assemblages indicated more eutrophic conditions. These lakes also had higher abundances of littoral benthic primary producers, which in turn were associated with low concentrations of dissolved nutrients, but only in autumn, not in spring. This is consistent with primary producers taking up nutrients during the summer growth season. In lakes with high abundances of benthic primary producers, it is likely that the littoral vegetation plays a large role in the transfer of nutrients from the water to the benthos. This process impairs correlations between biological metrics and water nutrient concentrations. Our results suggest that CORINE land cover may be more useful to characterize littoral nutrient enrichment than lake water chemistry. Increased benthic primary producer biomasses and “eutrophic” diatom indices may indicate littoral nutrient enrichment even if water nutrient concentrations are low.

New insights into the role of lake sediments in understanding watershed non-point source phosphorus pollution

A deep understanding of the relationship between watershed non-point source (NPS) pollution and lake total phosphorus (TP) accumulation is the basis of watershed–lake environmental management and ecological reconstruction, in which the acquisition of long-term NPS P and lake TP data over corresponding temporal and spatial scales seems to be the key issue. In this study, three typical sub-basins within Hongze Lake were selected as study sites. The sediment TP concentrations were designated as the lake indicator to relate with the NPS P loads, and the role of sediment in representing watershed NPS pollution was quantitatively analyzed. The results showed that, first, a notable fluctuation tendency in NPS P loads, which was largely influenced by policy, was found for all three sub-basins. Second, the deposition rate for three sediment cores was approximately 0.40 cm per year, with 13 cm cores reflecting the period since 1990. Third, the sediment is a faithful recorder of watershed NPS P pollution and lake nutrient enrichment. The correlation coefficient (r) between watershed NPS P loads and lake sediment TP concentrations showed notable differences when each watershed was considered separately. In particular, an ideal relationship was found in Basins 1 and 2, especially in the bottom 7 and 8 cm of the sediment cores, in which r exceeded 0.8. This showed that sediment can be an effective indicator of NPS P pollution during certain periods, such as 1990 – 2002, and diverse roles can be attributed to land-use/cover change and lake resuspension conditions. In addition, the weakest relationship existed in the No. 3 watershed, largely due to higher rainfall amounts compared with other two watersheds. For all the watersheds, lake sediment is a suitable indicator of watershed NPS P pollution over certain temporal and spatial scales.

Dynamics of ecological risks associated with heavy metals in sediments during the construction process of the Yangtze River deepwater channel

The Yangtze River deepwater channel in the downstream of Nanjing China is the largest water transport project. It necessitates an effective ecological risk assessment of sediment–bound heavy metals driven by construction of the Yangtze River ship channel. We conducted a three–year field studies to investigate levels of heavy metals (Hg, Cd, Pb, Cu, and Zn), pH, and total phosphorus in sediments, as well as diversity of zoobenthos, phytoplankton, and zooplankton along the Taichang–Nantong reaches of the Yangtze River. Results showed that high–concentrations of Pb is at 130.62 mg/kg and of Hg is at 0.88 mg/kg in the sediments, which mainly emitted from the power electronics, power systems, and the hydrocarbon–based fuel combustion via principal component analysis. Based on optimized contamination indices for metals, we should consider their ecological risks when the potential ecological risk factor (Eri) of Hg is up to 210 in the basin. The channel construction resulted in significantly increasing concentrations and ecological risks of heavy metals at the lower reaches. Meanwhile, the community structure of aquatic organisms changed and the investigated species richness decreased significantly from 78 to 47 during the project. Through redundancy analysis, more significant variances of the plankton species richness (55% and 22%) were attributed to Eri of heavy metals and their combined risk index as compared with both planktonic and benthic organisms (52% and 17%). Moreover, the species density of both Melosira granulata and Navicula sp., major phytoplankton species in the basin, were significantly negatively correlated to Pb and Hg in sediments. Plankton was more sensitive indicators than zoobenthos due to the ability of plankton to reactivate and bioaccumulate sediment–bound heavy metals. This study innovatively warned management to control river engineering–induced ecological risks of metals in sediments and revealed their potential risk pathway of ingestion by sensitive plankton.

Characteristics and Driving Factors of the Aerobic Denitrifying Microbial Community in Baiyangdian Lake, Xiong'an New Area.

Here, the ion-exchangeable form of nitrogen (IEF-N), weak-acid extractable form of nitrogen (WAEF-N), strong-alkali extractable form of nitrogen (SAEF-N), strong-oxidant extractable form of nitrogen (SOEF-N), residue nitrogen (Res-N), and total nitrogen (TN) showed spatial differences, and most of the sediment nitrogen fractions exhibited positive correlations in Baiyangdian Lake. High-throughput sequencing analysis revealed that the aerobic denitrification microbial community was composed of proteobacteria (42.04%–99.08%) and unclassified_bacteria (0.92%–57.92%). Moreover, the microbial community exhibited significant differences (R2 = 0.4422, P < 0.05) on the basis of the adonis analysis. T(temperature), Moisture content (MC), sediment total phosphorus (STP), ion-exchangeable form of ammonia (IEF-NH4+-N), weak-acid extractable form of ammonia (WAEF-NH4+-N), weak-acid extractable form of nitrate (WAEF-NO3−-N), and strong-alkali extractable form of ammonia (SAEF-NH4+-N) were the dominant environmental factors and explained 11.1%, 8.2%, 10.7%, 6.9%, 9.3%, 8.1%, 10.5%, 7.5%, and 7% variation, respectively, of the total variation in the microbial community. Furthermore, the network analysis showed that symbiotic relationships accounted for a major percentage of the microbial networks. The keystone aerobic denitrifying bacteria belonged to Comamonas, Rhodobacter, Achromobacter, Aeromonas, Azoarcus, Leptothrix_Burkholderiales, Pseudomonas, Thauera, unclassified_Burkholderiales, and unclassified_bacteria. The composition of the keystone aerobic denitrifying microbial community also exhibited significant differences (R2 = 0.4534, P < 0.05) on the basis of the adonis analysis. T, STP, IEF-NH4+-N, ion-exchangeable form of nitrate (IEF-NO3−-N), WAEF-NO3−-N, SAEF-NH4+-N, and TN were the dominant environmental factors that explained 8.4%, 6.2%, 4.6%, 5.9%, 5.9%, 4.5%, and 9.4% variation, respectively, of the total variation in the keystone aerobic denitrifying microbial community. The systematic investigation could provide a theoretical foundation for the evolution mechanism of the aerobic denitrifying microbial community in Baiyangdian Lake.

Long-term sediment accretion and nutrient deposition in a tidal marsh of the Delaware Bay

Long-term sediment accretion and nutrient concentrations were investigated in tidal marsh sediments of the Murderkill River, Delaware. Radionuclides (210Pb and 137Cs), stable isotopes (13C and 15N), organic matter concentrations and nutrient concentrations were measured. Tidal marsh sediment accumulation rates ranged from 0.10 to 0.20 g cm-2 yr-1, and accretion rates ranged from 0.31 to 0.74 cm yr-1. The Carbon (C) to nitrogen (N) ratio (∼24) was higher in the downcore of upstream sites, and a similar C/N ratio was identified in surface sediment cores at the downstream sites. The sediment N concentration in the surface sediments was highest at the upstream sites (mostly ≥1% of N) and decreased downstream. Total nitrogen concentrations were highest from 1910 to 1920 (∼1.5% N), decreased to approximately 0.6% N by 1940, and then remained constant to present. The dominance of the C4 plant Spartina (cordgrass) over C3 plants after the 1940s may be due to an upward movement of saline water associated with hydrologic changes and a rise in relative sea level. Surface sediments in all of the cores have more total phosphorus (TP) than below ground. The downstream site closest to the estuary had an abrupt increase in surface TP (i.e., 0–10 cm). Sediment TP increased slightly from 2003 to present time (i.e., from 0.07 to 0.11% P). Sediment accumulation and accretion rates in the Murderkill River marshes are similar to the accretion rates determined by previous studies in the region.

Suitability of hyperspectral data for monitoring nitrogen and phosphorus content in constructed wetlands

ABSTRACTThe nitrogen and phosphorus content in water and sediment is an important index for evaluating the nutritional status of wetland ecosystems. This study used an inversion model to assess the total nitrogen (TN) and total phosphorus (TP) content of constructed wetland using the canopy spectral reflectance data of four wetland plants. And then determine their relative suitability as a remotely sensed environmental monitoring tool. For water, the coefficient of determination (R2) of floating plants (up to 0.92) was higher than that of emergent plants (up to 0.82). For sediment, the R2 of TN inversion for S. natans was 0.59 and that of TP inversion for L. minor was 0.52, suggesting that floating plant canopy spectral reflectance data are more useful for assessing water directly, while indicators for the sedimentary environment can be assessed using emergent plants. Overall, the results clearly show that it is feasible to estimate water and sediment TN and TP content using plant canopy spectral reflectance data, providing the basis for widespread, rapid, and reliable monitoring of wetland ecosystem health via hyperspectral remote sensing. This study provides a reference for the timely development of further wetland restoration and protection measures.