[Structure and diversity of nirK-type denitrifying microbial community in marsh soils at different invasion stages of Spartina alterniflora in the Minjiang River estuary, China.] / é—½æ±Ÿæ²³å£äº’èŠ±ç±³è‰ä¸åŒå ¥ä¾µé˜¶æ®µæ¹¿åœ°åœŸå£¤nirKåž‹åç¡åŒ–å¾®ç”Ÿç‰©ç¾¤è½ç»“æž„åŠå¤šæ ·æ€§.

To explore the differences in structure and diversity of nirK-type denitrifying microbial community in marsh soils at different invasion stages of Spartina alterniflora, the mudflat (MF, before invasion) and the S. alterniflora marsh after seaward invasion for 1-2 years (SAN) and 6-7 years (SA) in Shanyutan of the Minjiang River estuary were investigated by high-through put sequencing method. Results showed that the seaward invasion of S. alterniflora reduced the richness and diversity of nirK-type denitrifying microbial community in marsh soils. The nirK-type denitrifying microbial community in soils at different invasion stages included Proteobacteria and Actinobacteria, with Proteobacteria as the dominant one. The seaward invasion of S. alterniflora greatly altered the composition of nirK-type denitrifying microbial community in marsh soils. The highest relative abundance of genus in soils from different invasion stages were Bradyrhizobium, Mesorhizobium and Alcaligenes, respectively. The seaward invasion of S. alterniflora increased the spatial heterogeneity of nirK-type denitrifying microbial community composition in marsh soils. In SAN plot, the enhancement of spatial heterogeneity was primarily due to higher environmental disturbances in plots and the increased spatial heterogeneity of environmental variables caused by the seaward invasion of S. alterniflora. The seaward invasion of S. alterniflora altered the physico-chemical properties (e.g., grain composition, pH and moisture) and N nutrient conditions (total N, NH4+-N and NO3--N) in marsh soils, which greatly altered the structure and diversity of nirK-type denitrifying microbial community. Our findings reveal the microbial mechanism of denitrification process in marsh soils during the seaward invasion of S. alterniflora.

Influence of Riverbed Incision and Hydrological Evolution on Water Quality and Water Age Based on Numerical Simulation: A Case Study of the Minjiang Estuary.

In recent years, problems such as water quality deterioration, saltwater invasion, and low oxygen have appeared in estuaries all over the world. The Minjiang River in Fujian, as a typical tidal estuary area, is facing these thorny problems. In this paper, the effects of topography and hydrologic evolution on the water age and water quality of the lower reaches of the Minjiang River were simulated by building a hydrodynamic and water quality model. The results show that: (1) It was found that the riverbed incision of the lower reaches of the Minjiang River led to the overall decline of river water level, the increase of river volume, and the increase of downstream water age, which eventually led to the decrease of dissolved oxygen (DO) and the deterioration of water quality in the downstream from Shuikou to Baiyantan. However, the decline of topography led to the increase of tidal volume in the estuary, the enhancement of the dilution effect of oxygen-rich water bodies in the open sea, and the increase of DO in the lower reaches of Baiyantan. (2) Under no tidal action, the concentration of pollutants in the water of the North Channel increased, the DO decreased, and the DO decreased from Baiyantan to the offshore water. After the enhancement of tidal action, the dilution of oxygen-enriched water from the offshore water increased, and the DO increased. (3) The hydrological and water quality characteristics of the upper part of the lower reaches of the Minjiang River were mainly controlled by topography, runoff, and pollutant discharge, which were more affected by the tidal current transport operation and pollutant discharge near the open sea. In recent decades, the deterioration of water quality and the aggravation of saltwater intrusion in the Minjiang River were closely related to the serious topographic downcutting. The results provide a scientific basis for revealing the deterioration of estuary water quality and long-term management of the estuary.

[Effects of spatial expansion of Phragmites australis and Cyperus malaccensis on distributions and stocks of phosphorus in marshes in the Minjiang River estuary, China.] / 闽江河口芦苇与短叶茳芏空间扩展对湿地系统磷赋存特征的影响.

To investigate the distributions and stocks of total phosphorus (TP) in plant-soil systems of marshes in Shanyutan of the Minjiang River estuary and explore its influencing factors, Phragmites australis (PA) marsh and Cyperus malaccensis (CM) marsh before spatial expansion and ecotonal marsh (EM, P. australis and C. malaccensis in EM were denoted by PA' and CM', respectively) during spatial expansion were studied. Results showed that, as affected by spatial expansion, the contents of TP in both plant and soil in different marshes showed great variations. Compared with PA and CM marshes, soil TP in EM increased by 20.0% and 7.1%, respectively. The variation of soil TP in EM might be attributed to the alteration of soil particle composition, plant bio-mass and root/shoot ratio during spatial expansion. Except for leaves, TP in organs of P. australis in P. australis-C. malaccensis community (PA') was lower than that in C. malaccensis in P. australis-C. malaccensis community (CM'), due to the differences in absorption, utilization and translocation way of P among organs between the two species. The competition effect caused by spatial expansion greatly changed plant P allocation ratio of the two species. Compared with PA and CM, the allocations of P in roots and leaves of PA' increased, while only that in roots of CM' rose. During spatial expansion, the two species might adopt different adaptation strategies for P absorption and utilization to maintain their competitiveness. The PA might compete primarily by strengthening the P accumulation capacities of its roots and promoting leaf photosynthesis, whereas the CM might resist the spatial expansion of PA by increasing its underground biomass to enhance P absorption.

[Effect of Increasing Tidewater Inundation on Porewater Geochemistries and CO2 and CH4 Effluxes in the Tidal Freshwater Marshes of the Minjiang River Estuary, Southeast China].

While the effect of increasing tidewater inundation caused by sea-level rise on carbon cycling had been well studied in saltmarshes, little is known about the effect of increasing tidewater inundation on CO2 and CH4 effluxes in the tidal freshwater marsh soils. Herein, the effects of tide inundation on porewater geochemistries (NH4+, NO3-, DOC, dissolved CH4, and DIC) and CH4 and CO2 effluxes were examined in the soils of tidal freshwater marshes in the Minjiang River Estuary, East China Sea. By applying "mesocosm" and a simulated tide pool, the tide inundation height increased by 15 cm and 30 cm over the control (CK). The CO2 effluxes decreased by 28.53% and 36.56%, and the dissolved CH4 concentrations increased by 47.83% and 73.91%, in treatments (CK+15 cm) and (CK+30 cm), respectively. The CH4 effluxes did not change significantly in the treatment (CK+15 cm), but increased by 29.27% in treatment (CK+30 cm). The increasing tidewater inundation had no significant impact on DOC concentrations, but increased NH4+ concentrations and decreased DIC and NO3- concentrations. Increasing tide inundation also reduced the temperature sensitivity of CH4 and CO2 effluxes. The study highlighted that the sea level rise-induced increase in tidewater inundation would decrease the annual global warming potential of tidal freshwater wetlands by 28% and 35% in the next 50 and 100 years, respectively.

[Effects of Spartina alterniflora invasion in a seaward direction on variations of inorganic sulfur forms in marsh soils of the Minjiang River estuary, China]. / é—½æ±Ÿæ²³å£äº’èŠ±ç±³è‰æµ·å‘å ¥ä¾µå¯¹æ¹¿åœ°åœŸå£¤æ— æœºç¡«èµ‹å­˜å½¢æ€çš„å½±å“.

To explore the effects of Spartina alterniflora invasion in a seaward direction on variations of inorganic sulfur forms in marsh soils, the levels of inorganic sulfur forms (H2O-S, Adsorbed-S, HCl-Soluble-S and HCl-Volatile-S) were determined in bare flat (BF, before invasion), S. alterniflora marsh after seaward invasion for one year (SA') and S. alterniflora marsh after seaward invasion for three years (SA) in Shanyutan of the Minjiang River estuary with the method of space-for-time substitution. Results showed that the seaward invasion of S. alterniflora altered the stocks and distribution of inorganic sulfur form in marsh soils. Compared with BF, the contents of H2O-S, Adsorbed-S and HCl-Volatile-S in soils of SA increased by 52.6%, 78.2% and 21.0%, respectively, while that of HCl-Soluble-S decreased by 3.4%. In contrast, the levels of H2O-S, Adsorbed-S and HCl-Soluble-S in soils of SA' increased by 43.9%, 70.6% and 29.6%, respectively, whereas that of HCl-Volatile-S decreased by 11.6%. The contents of total inorganic sulfur (TIS) in soils of SA and SA' increased by 40.7% and 37.8%, while the stocks of TIS increased by 26.8% and 31.4%, respectively. The key factors affecting different forms of inorganic sulfur in marsh soils had changed due to the seaward invasion of S. alterniflora. In particular, the key factors affecting the variations of H2O-S contents changed from soil grain composition and bulk density in BF to soil organic matter in SA' and SA. The seaward invasion of S. alterniflora significantly increased the content of TIS in marsh soils, which was mainly contributed by H2O-S and Adsorbed-S. Thus, it was concluded that the seaward invasion of S. alterniflora significantly increased the supply capacity of available sulfur in marsh soils, which, to some extent, accelerated its seaward invasion.

[Diffusive CO2 Flux Across the Water-air Interface of Reclaimed Shrimp Ponds in the Minjiang River Estuary Based on the TBL Model].

Freshwater aquatic ecosystems are important sources of greenhouse gases, such as CO2. However, few studies have presented data on the greenhouse gas flux from coastal aquaculture ponds. Diffusion models are important tools for estimating the CO2 exchange flux across the water-air interface of aquatic ecosystems. Several different parameterized means were selected to estimate the CO2 gas exchange rate (kx) and CO2 diffusive flux across the water-air interface of shrimp ponds in the Minjiang River Estuary. The results indicated that:① the CO2 gas exchange rate and diffusive flux over the culture period all presented significant temporal variation. This variation showed a dynamic trend:October > September > November > July > August and November > July > August > September > October. ② Wind speed, kx, CO2 concentration, pH, DOC concentration, and Chl-a concentration were important factors affecting the temporal variation of CO2 diffusive flux. ③ There were differences in the estimated value of CO2 diffusive flux across the water-air interface of the culture ponds in the Minjiang River Estuary among different parameterized approaches (P<0.01). This indicates that the model method has some uncertainties in estimating the CO2 diffusive flux in culture ponds. Our results suggest that the models RC01 and CW03 are more suitable methods for estimating the CO2 diffusive flux at the water-air interface of estuarine reclaimed aquaculture ponds in the Minjiang River Estuary, after comprehensive analysis of the water environment and the different estimation results.

Differential patterns of nitrogen and δ15N in soil and foliar along two urbanized rivers in a subtropical coastal city of southern China.

Urbanization usually pollutes the environment leading to alterations in key biogeochemical cycles. Therefore, understanding its effects on forest nitrogen (N) saturation is becoming increasingly important for addressing N pollution challenges in urban ecosystems. In this study, we compared soil (N availability, net N mineralization, net nitrification, and δ15N) and foliar (N concentrations and δ15N) variables in upstream, midstream and downstream forest stands of Bailongjiang River (BJR; more urbanized) and Wulongjiang River (WJR; less urbanized), the two branches of the Minjiang River Estuary. Total soil N, ammonium, nitrate, net N mineralization and nitrification rates, as well as soil δ15N were significantly higher in BJR compared with WJR forest stands. While no substantial difference in foliar N concentrations was noted between rivers, foliar δ15N was on average more than 2.5 times higher in BJR than WJR forest stands. Across the study area, foliar δ15N was positively related to soil δ15N, which also had positive linear relationships with soil nitrate concentrations, net N mineralization and net nitrification rates. Moreover, all variables except foliar δ15N and ammonium concentrations showed decreasing patterns in the order: upstream > midstream > downstream along the BJR forest stands. Soil ammonium and foliar values (N concentrations and δ15N) revealed clear patterns along the WJR, with the former increasing and the latter decreasing from the upstream to downstream forest stands. Our findings indicate an increase in urbanization-induced N inputs from the WJR to BJR and that forest stands along the BJR especially at the upstream have higher N availability and are shifting rapidly towards N saturation state. These results emphasize the need for effective N pollution control in urban environments through sustainable urban planning.

[The breadth and overlap of ecological niche of major fish species in the Minjiang River Estuary, China.] / é—½æ±Ÿå£ä¸»è¦æ¸”èŽ·é±¼ç±»çš„ç”Ÿæ€ä½å®½åº¦ä¸Žé‡å .

Based on the seasonal bottom trawl surveys in the Minjiang River Estuary in 2015, the breadth and overlap of ecological niche of major fish species were analyzed. Those fish species were identified based on the index of relative importance (IRI). A total of 137 species belonging to 37 families and 16 orders were collected. Fifteen major fish species were determined by the IRI, including six dominant species Polydactylus sextarius, Harpadon nehereus, Pennahia argentata, Secutor ruconius, Cynoglossus abbreviates, Coilia mystus, and nine important species Collichthys lucidus, Amblychaeturichthys hexanema, Upeneus japonicas, Lagocephalus spadiceus, Pampus argenteus, Larimichthys crocea, Thryssa kammalensis, Takifugu oblongus, Lepturacanthus savala. Seven species whose spatio-temporal niche breadth was higher than 1 in a declining order were C. abbreviates, C. lucidus, S. ruconius, A. hexanema, T. kammalensis, C. mystus, H. nehereus. The ecological niche of major fish species in the Minjiang River Estuary showed obvious seasonal dynamics. The percentage of species pairs with spatio-temporal niche overlap at the meaningful level was as high as 81.9%. Six species pairs reached significant ecological niche overlap, indicating that major fish species had similar distribution at the spatial and temporal scales and the existence of resource utilization competition. The species pairs of U. japonicus-L. savalawas had the highest spatio-temporal niche overlap value, whereas U. japonicus-C. lucidus had the lowest niche overlap value. The spatio-temporal niche overlap of major fish species in the Minjiang River Estuary had substantial seasonal variation.

[Effects of different salinity levels on nitrification processes in sediments of Minjiang River Estuary, China]. / 不同盐度对闽江河口沉积物硝化作用的影响.

Two estuary wetlands in Minjiang River, Shanyutan and Daoqingzhou, were selected as the research objects. Wetland sediments were collected to examine the effects of different salinity levels on nitrification processes in the wetland with a culture experiment. The results showed that the nitrification rate of sediment in Minjiang River estuary wetland was generally low. The highest nitrification rate of sediment in the Shanyutan wetland was 0.193 mg·kg-1·d-1, while that in the Daoqingzhou wetland did not exceed 0.050 mg·kg-1·d-1. In the low salinity level (5), the decrease of nitrification rate was attributed to the restraint of nitrifying bacteria activities. The nitrification rate slightly increased with the increases of salinity (10), but was still lower than the initial value. This would be owed to the fact that the inhibitory effect of salinity on the activities of aerobic bacteria was strengthened, which reduced the rate of NH4+-N production, and thus resulted in a decrease of the contribution of aerobic ammonification bacteria to the apparent nitrification rate. There were regional variations in the responses of sediment nitrifying activity to salinity. In saltwater wetland (Shanyutan wetland), the adaptability of microbes in sediment to salinity was stronger, so that the nitrification activity in high salinity conditions was still higher. While in the freshwater wetland (Daoqingzhou wetland), the adaptability of the sediment to the salinity change was relatively lower, with a lower nitrification activity of the sediment in high salinity than in middle salinity. Acidic condition was the main reason for the low nitrification in the sediments of Minjiang estuary wetland. The nitrification rate and nitrification activity of the two wetlands increased first and then decreased with the duration of the culture experiment, which was driven by combined effects of initial NH4+-N concentration, oxygen content and denitrifying.

[Short-term Effects of Nitrogen Deposition on CO2 and CH4 Fluxes from Wetlands in the Minjiang River Estuary].

In order to evaluate the effects of nitrogen deposition on CO2 and CH4 fluxes from a Cyperus malaccensis marsh in the Min River estuary at Daoqingzhou, Fujian, static chamber-gas chromatography (GC) techniques were used. CO2 and CH4 fluxes at a control (CK)[0 g·(m2·a)-1], N1[24 g·(m2·a)-1], N2[48 g·(m2·a)-1], and N3[96 g·(m2·a)-1] were measured and analyzed and the related environmental factors were recorded. The results show that,① compared to the control treatment, the effects of nitrogen deposition on the CO2 fluxes for N1 and N3 increased by 20.30% and 4.06%, respectively, whereas the CO2 fluxes for N2 reduced by 10.05%, furthermore, the CO2 fluxes under different treatments were not significantly different (P>0.05), except for the N2 and N3 treatments in December (P<0.05). ② Compared to the control treatment, the effects of nitrogen deposition on CH4 fluxes at N1, N2, and N3 were increased by 64.51%, 30.23%, and 80.57%, respectively, whereas the CH4 fluxes under different treatments were not significantly different (P>0.05). ③ There was significant positive correlation between CO2 and CH4 fluxes and soil temperature (P<0.05), however, the CO2 and CH4 fluxes were not significant with regards to soil pH and soil EC (P>0.05).

[Short-term Effects of Nitrogen and Sulfate Addition on CH4 and CO2 Emissions in the Tidal Marsh of Minjiang River Estuary].

In April 2015, using enclosed static opaque chamber-GC techniques, the short-term effects of nitrogen and sulfate addition on the CH4 and CO2 emissions were measured in the Cyperus malaccensis marsh in the high tidal flat of the Minjiang River estuary, and the key factors controlling the variation of CH4 and CO2 were examined. The influences of nitrogen and sulfate addition on the CH4 and CO2 emissions were different in different time scales. CH4 emission increased significantly under the NH4Cl (NH) and NH4NO3+K2SO4 (NS) additions (P<0.01), CO2emission increased significantly with NS addition (P<0.05), but CH4 and CO2 emissions demonstrated an obvious fluctuation pattern with KNO3 (NO) and K2SO4(S) additions. Compared with the control (CK), average CH4 emissions increased by 286.36% and 122.73%, respectively, in the NH and NS addition treatments, average CO2 emissions increased by 39.92% and 34.24%, respectively, with the NH and NS additions treatments. The nitrogen and sulfate addition changed the temporal variation of CH4 and CO2emissions from the C. malaccensis wetlands in growing season. Significant correlations were found among CO2, CH4 emissions, and soil temperature, electrical conductivity (EC), DOC (dissolved organic carbon) and NH4+-N (P<0.05 or P<0.01) in the treatments with NH and NS additions; and soil temperature, EC, DOC and NO3--N (P<0.05 or P<0.01) in the treatments with NO and NS additions. Temperature, EC and nitrogen availability were the dominant factors controlling the temporal variations of CH4 and CO2emissions in estuarine tidal marsh ecosystem.

Factors Contributing to Hypoxia in the Minjiang River Estuary, Southeast China.

Dissolved oxygen (DO) is not only a fundamental parameter of coastal water quality, but also an indication of organics decomposed in water and their degree of eutrophication. There has been a concern about the deterioration of dissolved oxygen conditions in the Minjiang River Estuary, the longest river in Fujian Province, Southeast China. In this study, the syntheses effects on DO was analyzed by using a four year time series of DO concentration and ancillary parameters (river discharge, water level, and temperature) from the Fuzhou Research Academy of Environmental Sciences, at three automated stations along the Minjiang River Estuary. Hypoxia occurred exclusively in the fluvial sections of the estuary during the high temperature and low river discharge period and was remarkably more serious in the river reach near the large urban area of Fuzhou. Enhancement of respiration by temperature and discharge of domestic sewage and industrial wastewater, versus regeneration of waters and dilution of pollutant concentration with increased river discharge, which regarded as the dominant antagonist processes that controlled the appearance of seasonal hypoxia. During the high temperature and the drought period, minimal mainstream flow above 700 m(3)Ÿs(-1), reduction of pollutants and forbidding sediment dredging in the South Channel should be guaranteed for strong supports on water quality management and drinking water source protection.

Distribution of trace metals and the benthic foraminiferal assemblage as a characterization of the environment in the north Minjiang River Estuary (Fujian, China).

A study of the total benthic foraminifera was carried out in 173 surficial sediment samples collected from the north Minjiang River Estuary and two bays. Foraminiferal assemblages are dominated by Ammonia tepida and subordinately by Elphidium advenum. Trace metal analyses reveal that the study area is unpolluted to moderately polluted with As, Cr, Cu, Ni, Pb, and Zn. The metal distribution has an affinity with fine-grained sediment. Five metal groups are recognized based on their distribution patterns: (1) As, Cr, Cu, Ga, Ni, V, and Zn, (2) Hg, Pb, and Sb, (3) Ba and Zr, (4) Rb and Y, and (5) Sr. The species-environment relationship showed that the species composition is adversely influenced by Cr, Cu, Ga, Pb, Rb, Zn, and Zr, whereas sand may exert a positive influence on Quinqueloculina. This study supports the adaptability of using benthic foraminifera as bio-monitors of trace metal pollution in marginal marine environments.

The source of natural and anthropogenic heavy metals in the sediments of the Minjiang River Estuary (SE China): implications for historical pollution.

Two sedimentary cores in the Minjiang River estuary (SE China) are documented for grain size, clay minerals, heavy metals, magnetic parameters and Pb isotopes to investigate the source and historical variation of heavy metals. The MJK9 core was collected outside of the Minjiang River estuary, and the core is composed of mixed sediments, of which ~70% from the Yangtze River and 30% from the Minjiang River. It is thus difficult to be used for tracing the human activity along the Minjiang River. In contrast, the sediments of MJK16 core which was collected in a nearshore area are primarily from the Minjiang River. The enrichment factors of the sediments were <1.5, indicating minor pollution. The results indicate that the sediments of the MJK16 core have Cu and Pb concentrations increasing since 1980, associated with the increase of magnetic mineral concentration and (206)Pb/(207)Pb and (206)Pb/(208)Pb of the sediments. We compared the Pb isotopic compositions between our results and those for the deposit mining in the Minjiang River basin, and aerosols and coal dust in south China, and considered that Pb in the sediments of the MJK16 core was derived primarily from weathered rocks as well as industrial emission (e.g. coal combustion). The sediments have anthropogenic Pb concentrations ranging from 6% in 1950 to 23.7% in 2010, consistent with the impact of rapid urban and industrial development in China.