Soil Organic Carbon Contents and Stocks in Coastal Salt Marshes with <Emphasis Type="Italic">Spartina alterniflora</Emphasis> Following an Invasion Chronosequence in the Yellow River Delta,China

Plant invasion alters the fundamental structure and function of native ecosystems by affecting the biogeochemical pools and fluxes of materials and energy. Native (Suaeda salsa) and invasive (Spartina alterniflora) salt marshes were selected to study the effects of Spartina alterniflora invasion on soil organic carbon (SOC) contents and stocks in the Yellow River Delta. Results showed that the SOC contents (g/kg) and stocks (kg/m²) were significantly increased (P < 0.05) after Spartina alterniflora invasion of seven years, especially for the surface soil layer (0–20 cm). The SOC contents exhibited an even distribution along the soil profiles in native salt marshes, while the SOC contents were gradually decreased with depth after Spartina alterniflora invasion of seven years. The natural ln response ratios (LnRR) were applied to identify the effects of short-term Spartina alterniflora invasion on the SOC stocks. We also found that Spartina alterniflora invasion might cause soil organic carbon losses in a short-term phase (2–4 years in this study) due to the negative LnRR values, especially for 20–60 cm depth. And the SOCD in surface layer (0–20 cm) do not increase linearly with the invasive age. Spearman correlation analysis revealed that silt + clay content was exponentially related with SOC in surface layer (Adjusted R2 = 0.43, P < 0.001), suggesting that soil texture could play a key role in SOC sequestration of coastal salt marshes.     

Emissions of biogenic sulfur gases (H<Subscript>2</Subscript>S,COS) from <Emphasis Type="Italic">Phragmites australis</Emphasis> coastal marsh in the Yellow River estuary of China

Emissions of biogenic sulfur gases (hydrogen sulfide (H₂S) and carbonyl sulfide (COS)) from Phragmites australis coastal marsh in the Yellow River estuary of China were determined during April to December in 2014 using static chamber-gas chromatography technique with monthly sampling. The results showed that the fluxes of H₂S and COS both had distinct seasonal and diurnal variations. The H₂S fluxes ranged from 0.09 μg/(m²·h) to 7.65 μg/(m²·h), and the COS fluxes ranged from–1.10 μg/(m²·h) to 3.32 μg/(m²·h). The mean fluxes of H₂S and COS from the P. australis coastal marsh were 2.28 μg/(m²·h), and 1.05 μg/(m²·h), respectively. The P. australis coastal marsh was the emission source of both H₂S and COS over the whole year. Fluxes of H₂S and COS were both higher in plant growing season than in the non-growing season. Temperature had a dramatic effect on the H₂S emission flux, while the correlations between COS flux and the environmental factors were not found during sampling periods. More in-depth and comprehensive research on other related factors, such as vegetation, sediment substrates, and tidal action is needed to discover and further understand the key factors and the release mechanism of sulfur gases.     

The impact of geomorphology of marsh creeks on fish assemblage in Changjiang River estuary

Tidal marshes are an important habitat and nursery area for fish. In the past few decades, rapid economic development in the coastal areas of China has led to the interruption and destruction of an increasing number of tidal marshes. The growing interest in tidal marsh restoration has increased the need to understand the relationship between geomorphological features and fish assemblages in the design of marsh restoration projects. We studied temporal variations in, and the effects of creek geomorphological features on, the estuarine tidal creek fish community. Using modified channel nets, we sampled fish monthly from March 2007 to February 2008 from seven tidal creeks along an intertidal channel system in Chongming Dongtan National Nature Reserve. Fourteen creek geomorphological variables were measured or derived to characterize intertidal creek geomorphological features. The Gobiidae, with 10 species, was the most species- rich family. The most abundant fish species were Liza affinis, Chelon haematocheilus, and Lateolabrax maculatus. The fish community was dominated by juvenile marine transients, which comprised about 80% of the total catch. The highest abundance offish occurred in June and July, and the highest biomass occurred in December. Canonical redundancy analyses demonstrated that depth, steepness, cross-sectional area, and volume significantly affected the fish species assemblage. L. affinis favored small creeks with high elevations. Synechogobius ommaturus, Acanthogobius luridus, and Carassius auratus preferred deep, steep creeks with a large cross-sectional area and volume. These findings indicate that the geomorphological features of tidal creeks should be considered in the conservation and sustainable management of fish species and in the restoration of salt marshes.     

Study on fluxes of CH4 emission from paddy fields in Changchun area

Little has been done in measurement and research of the flux of CH₄ emission from paddy fields in Changchun area, Jilin Province, China before 1994. So the purpose of the study is to offer available regional data of CH₄ emission flux and to discuss the factors which affect CH₄ emission from paddy fields. Experimental paddy fields are chosen using TM pictures respectively in Xinlicheng (43°49′N, 125°20′E) of the Yitong River’s and in Wanchang (43°44′10″N, 125°53′11″E) of the Yinma River’s alluvial plain. The fluxes of CH₄ emission from paddy fields are measured by the method of static chamber in Changchun area in 3 consecutive years. The research results show that the peak of CH₄ emission from paddy fields occurs during the booting stage. The mean fluxes of CH₄ emission are 7.056 mg/m(² · h) and 0.489 mg/(m² · h) in the paddy fields of flood and discontinuous irrigation respectively. The contrastive study holds that climate condition, the way of water management and fertilizer variation have significant influence on fluxes of CH₄ emission from paddy fields. The difference of climatic conditions causes the interannual change of the flux of CH₄ emission from paddy fields. In general, the flux of CH₄ emission from paddy fields of flood irrigation is greater than that from paddy fields of discontinuous irrigation. To change the way of water management perhaps in an available way to reduce CH₄ emission flux from paddy fields. Foundation item: Under the auspices of Jilin Commttee of Science and Technology (grant 963416 - 1), and Changchun Jingyuetan Remote Sensing Test Site of the Chinese Academy of Sciences (grant 9504). Biography: YAN Min-hua (1964 -), female, a native of Liaoning Province, master, associate professor. Her research interests include climate change, greenhouse gases and wetland climate.     

Regularity and estimation of methane emission from marshland in the Sanjiang Plain

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Distribution and accumulation of soil carbon in temperate wetland,northeast China

Estimating carbon sequestration and nutrient accumulation rates in Northeast China are important to assess wetlands function as carbon sink buffering greenhouse gas increasing in North Asia. The objectives of this study were to estimate accreting rates of carbon and nutrients in typical temperate wetlands. Results indicated that average soil organic carbon(SOC), total nitrogen(TN) and total phosphorus(TP) contents were 37.81%, 1.59% and 0.08% in peatlands, 5.33%, 0.25% and 0.05% in marshes, 2.92%, 0.27% and 0.10% in marshy meadows, respectively. Chronologies reconstructed by 210 Pb in the present work were acceptable and reliable, and the average time to yield 0–40 cm depth sediment cores was 150 years. Average carbon sequestration rate(Carbonsq), nitrogen and phosphorus accumulation rates were 219.4 g C/(m~2·yr), 9.16 g N/(m~2·yr) and 0.46 g P/(m~2·yr) for peatland; 57.13 g C/(m~2·yr), 5.42 g N/(m~2·yr) and 2.16 g P/(m~2·yr) for marshy meadow; 78.35 g C/(m~2·yr), 8.70 g N/(m~2·yr) and 0.71 g P/(m2·yr) for marshy; respectively. Positive relations existed between Carbonsq with nitrogen and precipitations, indicating that Carbonsq might be strengthened in future climate scenarios.     

Effects of Reclamation on Soil Carbon and Nitrogen in Coastal Wetlands of Liaohe River Delta,China

To evaluate the influence of wetland reclamation on vertical distribution of carbon and nitrogen in coastal wetland soils, we measured the soil organic carbon(SOC), soil total nitrogen(STN) and selected soil properties at five sampling plots(reed marsh, paddy field, corn field, forest land and oil-polluted wetland) in the Liaohe River estuary in September 2013. The results showed that reclamation significantly changed the contents of SOC and STN in the Liaohe River estuary(P 0.001). The SOC concentrations were in the order: oil-polluted wetland corn field paddy field forest land reed marsh, with mean values of 52.17, 13.14, 11.46, 6.44 and 6.16 g/kg, respectively. STN followed a similar order as SOC, with mean values of 1351.14, 741.04, 632.32, 496.17 and 390.90 mg/kg, respectively. Interaction of reclamation types and soil depth had significant effects on SOC and STN, while soil depth had significant effects on SOC, but not on STN. The contents of SOC and STN were negatively correlated with pH and redox potential(Eh) in reed marsh and corn field, while the SOC and STN in paddy field had positive correlations with electrical conductivity(EC). Dissolved organic carbon(DOC), ammonium nitrogen(NH_4~+-N) and nitrate nitrogen(NO_3~–-N) were also significantly changed by human activities. NH_4~+-N and NO_3~–-N increased to different degrees, and forest land had the highest NO_3~–-N concentration and lowest DOC concentration, which could have been caused by differences in soil aeration and fertilization. Overall, the results indicate that reed harvest increased soil carbon and nitrogen release in the Liaohe River Estuary, while oil pollution significantly increased the SOC and STN; however, these cannot be used as indicators of soil fertility and quality because of the serious oil pollution.     

Coatal salt marshes and mangrove swamps in China

Based on plant specimen data, sediment samples, photos, and sketches from 45 coastal crosssections, and materials from two recent countrywide comprehensive investigations on Chinese coasts and islands, this paper deals with China’s vegetative tidal-flats: salt marshes and mangrove swamps. There are now 141700 acres of salt marshes and 51000 acres of mangrove swamps which together cover about 30% of the mud-coast area of the country and distribute between 18°N (Southern Hainan Island) and 41 °N (Liaodong Bay). Over the past 45 years, about 1750000 acres of salt marshes and 49400 acres of mangrove swamps have been reclaimed. The 2.0×10⁹ tons of fine sediments input by rivers into the Chinese seas form extensive tidal flats, the soil basis of coastal helophytes. Different climates result in the diversity of vegetation. The 3∼8 m tidal range favors intertidal zone development. Of over 20 plant species in the salt marshes, nativeSuaeda salsa, Phragmites australis, Aeluropus littoralis, Zoysia maerostachys, Imperata cylindrica and introducedSpartina anglica are the most extensive in distribution. Of the 41 mangrove swamps species,Kandelia candel, Bruguiera gymnorrhiza, Excoecaria agallocha andAvicennia marina are much wider in latitudinal distribution than the others. Developing stages of marshes originally relevant to the evolution of tidal flats are given out. The roles of pioneer plants in decreasing flood water energy and increasing accretion rate in the Changjiang River delta are discussed. The project was supported by the NSFC (No. 49476281).     

Effects of vegetation type on surface elevation change in Liaohe River Delta wetlands facing accelerated sea level rise

Rising sea levels threaten the sustainability of coastal wetlands around the globe. The ability of coastal marshes to maintain their position in the intertidal zone depends on the accumulation of both organic and inorganic materials, and vegetation is important in these processes. To study the effects of vegetation type on surface elevation change, we measured surface accretion and elevation change from 2011 to 2016 using rod surface elevation table and feldspar marker horizon method(RSET-MH) in two Phragmites and two Suaeda marshes in the Liaohe River Delta. The Phragmites marshes exhibited higher rates of surface accretion and elevation change than the Suaeda marshes. The two Phragmites marsh sites had average surface elevation change rates at 8.78 mm/yr and 9.26 mm/yr and surface accretion rates at 17.56 mm/yr and 17.88 mm/yr, respectively. At the same time, the two Suaeda marsh sites had average surface elevation change rates at 5.77 mm/yr and 5.91 mm/yr and surface accretion rates at 13.42 mm/yr and 14.38 mm/yr, respectively. The elevation change rates in both the Phragmites marshes and the Suaeda marshes in the Liaohe River Delta could keep pace and even continue to gain elevation relative to averaged sea level rise in the Bohai Sea reported by the 2016 State Oceanic Administration, People's Republic of China projection(2.4–5.5 mm/yr) in current situations. Our data suggest that vegetation is important in the accretionary processes and vegetation type could regulate the wetland surface elevation. However, the vulnerability of coastal wetlands in the Liaohe River Delta need further assessment considering the accelerated sea level rise, the high rate of subsidence, and the declining sediment delivery, especially for the Suaeda marshes.     

CARBON CYCLE OF MARSH IN THE SANJIANG PLAIN

Peat~hisaprocessofbeinghelpfulfordecreasingtheincrementofopcontentintheair,whichiscausedbycombustionofdineralfuelsandhumanactivitiesinterrestrialecosystem.But,exploitingrnaxsh,eSPeCiallyPeatedtObefuels,impliesthatorgbocsubstanceaccUInulatedfroma~hereduringthepastthousandsofyearsisrapidlyOxidized.aamthemarShplaysanimPOrtantroleinthecycleofbiogaxhdristry.TheSanjiangPlainisalowplainformedbythecommonreactionoftheHeilongRiver,SonghuaherandWUSuliabover.Thetotalareais10.89X104klnZandmarsharea…     

Regularity and estimation of methane emission from marshland in the Sanjiang Plain

The regularity of CH₄ emission from marshland in the Sanjiang Plain was studied by sampling in the open field and analyzing under laboratory condition, the annual emission amount is also estimated. By Grey Relatively Analysis we know that the soil temperature in the 10-cm depth of grass-root layer is close related with CH₄ emission. CH₄ emission has different kinds of diurnal emission modes:before-dawn maximum mode, night maximum mode and irregular fluctuation mode. The seasonal variation trend of CH₄ emission rates is going up steadily from May to August and dropping down from September, the maximum lies behind the maximum of temperature. CH₄ emission rates of different marshland types are different, the CH₄ emission rate of Glyceriaspiculosa — Carex marshland is always higher than that of Carex lasiocarpa marshland. The paper also studies the difference of CH₄ emission rates in different managing modes and analyzes the emission rates between China and U. S. A. The result shows: the average value of CH₄ emission rate is 17.26mg/(m²·h), the annual amount of CH₄ emission is about 0.75Tg. Supported by National Natural Sciences Foundation of China, and thank the Ecological Test Station of Mires and Wetlands in the Sanjiang Plain, the Chinese Academy of Sciences.     

BIOGEOCHEMICAL BEHAVIOR OF NUTRIENTS AND THEIR FLUXES IN THE MINJIANG RIVER ESTUARY

IMRODUcTlONThe577km1ongMinjiangRiver,thelongestriverinFujianProvinceofChina,hasa6O992km2drainagebasin.Thewaterdischargeislarge(meaninyearsis198Om/s).TheannualrunofffromtheMinjiangRiveris5.84xlOlom,WhichismorethanthatoftheHuangheRiver,andranksthirdintheannualrunoffofmaorChineseriversWhang,l994).SimdentnutrientSfromtheMinjiangRivertotheseaisanarisa-ryconditionforthefonnationandcontinuingexistenceoftheMindongFisheryGroundandtheMihahongFisheryGround.Inthendingareaofriverwaterwithseaw…     

WETLANDS IN CHINA: FEATURE, VALUE AND PROTECTION

The estimated total area of wetland in China is more than 25.9 million hectares including about 11.9 million hectares of marshes and bogs, 9.1 million hectares of lake and about 2.2 million hectares of coastal salt marshes and mudflats. The area of wetland is equivalent to 2.7% of the land surface. China also has 2.7 million hectares of shallow sea water (less 5m in depth at low tide). Marshes and bogs are equivalent 1.3% of the land surface. Only three provinces (regions)—Qinghai, Xizang (Tibet) and Heilongjiang — have a larger total area of marsh and bog. According to the structure, type and development of wetland in different river basins, wetland can be classified nine main regions. The experiments indicate that the coefficient of the marsh to regulate flood is similar to that of lakes. Wetlands occupy 17.8% of the Sanjiang Plain area, the annual carbon contribution is 0.78 × 10⁴t. Carbon released from marsh soil return into atmosphere is 3.95 × 10⁶t/a. At present there is a sharp contradiction between population growth and natural resources shortage, causing wetland to be exerted with huge pressures and serious threats. Foundation item: Under the auspices of the Key B Item of the Chinese Academy of Sciences (KZ951-B1-201-02). Biography: LU Xian-guo (1957 —), male, a native of Changchun City, Jilin Provice, professor. His research interests include wetland process and environmental effect.     

Crop residue incorporation and nitrogen fertilizer effects on greenhouse gas emissions from a subtropical rice system in Southwest China

Crop residue incorporation has been widely accepted as a way to increase soil carbon (C) sequestration and sustain soil fertility in agroecosystems. However, effect of crop residue incorporation on greenhouse gas (GHG) emissions in rice paddy soils remains uncertain. A field experiment was conducted to quantify emissions of CH₄ and N₂O and soil heterotrophic respiration (R_H) from a paddy rice field under five different crop residue treatments (i.e., 150 kg N ha^-1 of synthetic N fertilizer application only [NF], 150 kg N ha^-1 of synthetic N fertilizer plus 5.3 Mg ha^-1 wheat residue [NF-WR1], 150 kg N ha^-1 of synthetic N fertilizer plus 10.6 Mg ha^-1 wheat residue [NF-WR2], 75 kg N ha^-1 of synthetic N fertilizer plus 10.6 Mg ha^-1 wheat residue [50%NF-WR2] and 150 kg N ha^-1 of synthetic N fertilizer plus 21.2 Mg ha^-1 wheat residue [NF-WR3]) in southwest China. Our results showed that crop residue incorporation treatments (NF-WR1, NF-WR2, 50%NF-WR2, NF-WR3) significantly increased CH₄ emissions by at least 60%, but N₂O emissions were not enhanced and even suppressed by 25% in the NF-WR3 treatment as compared to the NF treatment. Soil R_H emissions were comparable among experimental treatments, while crop residue incorporation treatments significantly increased soil carbon sequestrations relative to the NF treatment. Overall, CH₄ emissions dominated total global warming potentials (GWP) across all experimental treatments. The average yieldscaled GWPs for the NF and NF-WR1 treatments were significantly lower than for the NF-WR2, 50%NFWR2 and NF-WR3 treatments. Given the comparable yield-scaled GWPs between the NF and NF-WR1 treatments, the NF-WR1 treatment could gain net carbon sequestration as compared with the NF treatment with net soil carbon loss. Our findings suggest that the NF-WR1 treatment should be an effective option to sustain rice production while mitigating GHG emissions from the rice field in China.     

Effects of crude oil contamination on soil physical and chemical properties in Momoge wetland of China

Large oilfields are often coincidentally located in major river deltas and wetlands, and potentially damage the structure, function and ecosystem service values of wetlands during oil exploration. In the present study, the effects of crude oil contamination during oil exploration on soil physical and chemical properties were investigated in marshes of the Momoge National Nature Reserve in Jilin Province, China. The concentrations of total petroleum hydrocarbons in the marsh soil near the oil wells are significantly higher than those in the adjacent control marsh. Soil water contents in oil-contaminated marshes are negatively correlated with soil temperature and are significantly lower than those in the control area, especially in fall. Crude oil contamination significantly increases the soil pH up to 8.0, and reduces available phosphorus concentrations in the soil. The concentrations of total organic carbon are significantly different among sampling sites. Therefore, crude oil contamination could potentially alkalinize marsh soils, adversely affect soil fertility and physical properties, and cause deterioration of the marshes in the Momoge National Nature Reserve. Phyto-remediation by planting Calamagrostis angustifolia has the potential to simultaneously restore and remediate the petroleum hydrocarbon-contaminated wetlands. Crude oil contamination affects the soil physical and chemical properties, so developing an effective restoration program in the Momoge wetland is neccesary.     

Diurnal and seasonal dynamics of soil respiration at temperate Leymus chinensis meadow steppes in western Songnen Plain,China

To evaluate the diurnal and seasonal variations in soil respiration(Rs) and understand the controlling factors, we measured carbon dioxide(CO2) fluxes and their environmental variables using a LI-6400 soil CO2 flux system at a temperate Leymus chinensis meadow steppe in the western Songnen Plain of China in the growing season(May–October) in 2011 and 2012. The diurnal patterns of soil respiration could be expressed as single peak curves, reaching to the maximum at 11:00–15:00 and falling to the minimum at 21:00–23:00(or before dawn). The time-window between 7:00 and 9:00 could be used as the optimal measuring time to represent the daily mean soil CO2 efflux. In the growing season, the daily value of soil CO2 efflux was moderate in late spring(1.06–2.51 μmol/(m2·s) in May), increased sharply and presented a peak in summer(2.95–3.94 μmol/(m2·s) in July), and then decreased in autumn(0.74–0.97 μmol/(m2·s) in October). Soil temperature(Ts) exerted dominant control on the diurnal and seasonal variations of soil respiration. The temperature sensitivity of soil respiration(Q10) exhibited a large seasonal variation, ranging from 1.35 to 3.32, and decreased with an increasing soil temperature. Rs gradually increased with increasing soil water content(Ws) and tended to decrease when Ws exceeded the optimum water content(27%) of Rs. The Ts and Ws had a confounding effect on Rs, and the two-variable equations could account for 72% of the variation in soil respiration(p 0.01).     

The inhibitory degree between Skeletonema costatum and dinoflagllate Prorocentrum donghaiense at different concentrations of phosphate and nitrate/phosphate ratios

Interactions between Skeletonema costatum (S. costatum) and Prorocentrum donghaiense (P. donghaiiense) were inves-tigated using bi-algal cultures at different concentrations of phosphate (PO4-P) and nitrate/phosphate (N/P) ratios. Experiments were conducted under P-limited conditions and the Lotka-Volterra mathematical model was used to simulate the growth of S. costatum and P. donghaiense in the bi-algal cultures. Both of these two species were inhibited significantly in bi-algal culture. The results of the simulation showed that the inhibitory degree of S. costaum by P. donghaiense was high when the concentration of PO4-P was low (0.1μmolL-1/2 d), but that of P. donghaiense by S. costaum was high with increased PO4-P supply (0.6μmolL-1/2 d). At low concen-tration of PO4-P (0.1μmolL-1/2 d), or high concentration of PO4-P (0.6μmolL-1/2 d) with high N/P ratio (160), the interactions be-tween S. costatum and P. donghaiense were dependent on the initial cell densities of both species. At high concentration of PO4-P (0.6μmolL-1/2 d) with low N/P ratio (25 or 80), S. costatum exhibited a survival strategy superior to that of P. donghaiense. The de-gree of inhibition of P. donghaiense by S. costaum increased with elevated N/P ratio when the medium was supplemented with con-centration 0.1μmolL-1/2 d of PO4-P. The degree of inhibition to P. donghaiense by S. costaum increased with elevated N/P ratio at low concentration of PO4-P (0.1 μmolL-1/2 d). This trend was conversed at high concentration of PO4-P (0.6μmolL-1/2 d). However, the degree of inhibition of S. costaum by P. donghaiense increased with the increased N/P ratio at different PO4-P concentrations (0.1μmolL-1/2 d and 0.6μmolL-1/2 d). These results suggested that both phosphate concentration and N/P ratio affected the competition between S. costaum and P. donghaiense: P. donghaiense is more competitive in environments with low phosphate or high N/P ratio and the influence of N/P ratio on the competition was more significant with lower phosphate concentration.     

Tide and current observations in the central Chukchi Sea during the summer of 2012

Current data from a moored Acoustic Doppler Current Profiler(ADCP) deployed at 69?30.155′N,169?00.654′W in the central Chukchi Sea during 2012 summertime is analyzed in the present paper.Characteristics of tidal and residual currents are ob-tained with Cosine-Lanczos filter and cross-spectral analyses.The main achievements are as follows:1) Along with the local inertial frequency of 12.8 h,two other peaks at ~12-h and ~10-d dominate the time series of raw velocity;2) The M_2 dominates the 6 resolved tide constituents with significant amplitude variations over depth and the ratios of current speed of this constituent to that of the total tidal current are 54% and 47% for u and v components,respectively.All the resolved tidal constituents rotate clockwise at depth with the exception of MM and O1.The constituents of M_2 and S_2 with the largest major semi-axes are similar in eccentricity and orientation at deeper levels;3) The maximum of residual currents varies in a range of 20–30 cms~(-1) over depth and the current with lower velocities flow more true north with smaller magnitudes compared to the current in surface layer.The ~10 d fluctuation of residual current is found throughout the water column and attributed to the response of current to the local wind forcing,with an approximate 1.4 d lag-time at the surface level and occurring several hours later in the lower layer;4) Mean residual currents flow toward the north with the magnitudes smaller than 7 cms~(-1) in a general agreement with previous studies,which suggests a relatively weaker but stable northward flow indeed exists in the central Chukchi Sea.     

Seasonal changes in Porteresia coarctata (Tateoka) beds along a subtropical coast

Shoot density, standing crop (above- and below-ground biomass) and habitat of salt marsh grass Porteresia coarctata were investigated along the coast of Bakkhali estuary, Cox’s Bazar, Bangladesh from January to December 2006. Shoot density of P. coarctata was influenced by season and was found to be higher (>2 500 shoots/m 2 ) in post-monsoon and minimal in monsoon season; plants were particularly active in vegetative propagation during pre-monsoon. Above-ground biomass was greater along the protected coast compared with the exposed one in this estuary. Below-ground biomass was higher (7.75-269.53 g DW/m 2 ) than that above ground (2.20-114.75 g DW/m 2 ). Standing crops of P. coarctata showed a negative relationship (R=-0.77; P<0.05) with sedimentation rate, while seasonal activity influenced sedimentation. The recorded sedimentation rate was lower (6.09 mg/(cm 2 ·d)) in pre-monsoon and highest (14.55 mg/(cm 2 ·d)) in monsoon season. The mean value of pore water salinity was higher (34.25±5.05) during post-monsoon and lowest (18.0±3.71) in monsoon season. The soil was sandy clay in this P. coarctata bed; it consisted of 86% sand, 13% clay and 1% silt. Soil organic matter dropped during the monsoon season (0.78%-0.67%) and was highest ((2.17±1.42)%-(2.3±1.47)%) during post-monsoon, probably owing to accumulation of decomposed peat on the marsh surface. The mean pore water NH 4 -N concentration ranged from 2.44±1.65 to 3.33±1.82 μg/L, with a minimum air temperature of 22.09°C in post-monsoon and a maximum of 31.16°C in pre-monsoon. Variations of physico-chemical parameters in the soil, water, and climate governed biological parameters of P. coarctata in the Bakkhali estuary, and were comparable with estuarine environments elsewhere.     

CO2 concentration and flux near ground in marsh of the Sanjiang plain of Northeast China

There is limited information available on CO₂ concentration and flux over marsh. The objective of this work was to characterize CO₂ concentration and flux within and above marsh plant (Carex lasiocarpa Ehrh. and C. pseudocuraica F. Schm) canopy at heights 0.5, 1.0 and 1.5 m. CO₂ concentration was measured sequentially every 3 hours by using an infrared gas analyzer. Soil and air temperature, wind speed, net radiation and soil heat flux were also measured simultaneously. Extremely daily minimum and maximum CO₂ concentration ranged from 250 to 754 μmd/mol for the 4-year work. The typical minimum and maximum values ranged from 314 to 464 μmol/mol at the height of marsh plant (about 0.5 m) during the fruiting period and mature date. The seasonal changes in CO₂ concentration show that the minimum CO₂ concentration occurred in the fruiting period and mature date, and both of their minimum values were 314 μmol/mol. This illustrates that CO₂ consumed by photosynthesis was stable during the period. The flux of CO₂ can be thought as a turbulent diffusion phenomenon. By micrometeorological methods, the diurnal CO₂ fluxes were measured in the flowering period, fruiting period, early mature date, late mature date and yellow-ripe stage. Their values were −0.18, 38.15,24.13,10.9 and 4.91 μmol/mol respectively.