Regulating effects of climate,net primary productivity,and nitrogen on carbon sequestration rates in temperate wetlands,Northeast China

Temperate wetlands in the Northern Hemisphere have high long-term carbon sequestration rates, and play critical roles in mitigating regional and global atmospheric CO₂ increases at the century timescale. We measured soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) from 11 typical freshwater wetlands (Heilongjiang Province) and one saline wetland (Jilin Province) in Northeast China, and estimated carbon sequestration rates using ²¹⁰Pb and ¹³⁷Cs dating technology. Effects of climate, net primary productivity, and nutrient availability on carbon sequestration rates (R_carbon) were also evaluated. Chronological results showed that surface soil within the 0–40 cm depth formed during the past 70–205 years. Soil accretion rates ranged from 2.20 to 5.83 mm yr⁻¹, with an average of 3.84 ± 1.25 mm yr⁻¹ (mean ± SD). R_carbon ranged from 61.60 to 318.5 gC m⁻² yr⁻¹ and was significantly different among wetland types. Average R_carbon was 202.7 gC m⁻² yr⁻¹ in the freshwater wetlands and 61.6 gC m⁻² yr⁻¹ in the saline marsh. About 1.04 × 10⁸ tons of carbon was estimated to be captured by temperate wetland soils annually in Heilongjiang Province (in the scope of 45.381–51.085°N, 125.132–132.324°E). Correlation analysis showed little impact of net primary productivity (NPP) and soil nutrient contents on R_carbon, whereas climate, specifically the combined dynamics of temperature and precipitation, was the predominant factor affecting R_carbon. The negative relationship observed between R_carbon and annual mean temperature (T) indicates that warming in Northeast China could reduce R_carbon. Significant positive relationships were observed between annual precipitation (P), the hydrothermal coefficient (defined as P/AT, where AT was accumulative temperature ≥10 °C), and R_carbon, indicating that a cold, humid climate would enhance R_carbon. Current climate change in Northeast China, characterized by warming and drought, may form positive feedbacks with R_carbon in temperate wetlands and accelerate carbon loss from wetland soils.     

Nitrate removal processes in a constructed wetland treating drainage from dairy pasture

¹⁵N-labelled NO₃^? was used in a surface-flow constructed wetland in spring to examine the relative importance of competing NO₃^? removal processes. In situ mesocosms (0.25 m²) were dosed with 2 l of ¹⁵NO₃^? (NaNO₃, 300 mg N l^?1, 99 atom% ¹⁵N) and bromide (Br^?) solution (LiBr, 4.3 g l^?1, as a conservative tracer). Concentrations of NO₃^?, Br^?, dissolved oxygen and ¹⁵N₂ were monitored periodically and replicate mesocosms were destructively sampled prior to and 6 days after ¹⁵N addition. Denitrification, immobilisation, plant uptake and dissimilatory NO₃^? reduction to NH₄⁺ (DNRA) accounted for 77, 11, 9 and 2% of ¹⁵NO₃^? transformed during the experiment. Only 6% of denitrification gases were directly measured as atmospheric or dissolved ¹⁵N₂; the remainder (71%) was determined via ¹⁵N mass balance. This indicated that a large proportion of the denitrification gases were entrapped within the soil matrix and/or plant aerenchyma. The floating plant Lemna minor exhibited a significantly higher NO₃^? uptake rate (221 mg kg^?1 d^?1) than Typha orientalis (10 mg kg^?1 d^?1), but periodic harvest of plants would remove <3% of annual NO₃^? inputs. Our results suggest that this 6-year-old constructed wetland functions effectively as a sink for NO₃^? during the growing season with less than one-quarter of the NO₃^? processed sequestered into wetland plant, algal and microbial N pools and the balance permanently removed by denitrification.     

Removal of nutrients from wastewater with Canna indica L. under different vertical-flow constructed wetland conditions

Constructed wetlands are becoming increasingly popular worldwide for removing contaminants from domestic wastewater. This study investigated the removal efficiency of nitrogen (N) and phosphorus (P) from wastewater with the simulated vertical-flow constructed wetlands (VFCWs) under three different substrates (i.e., BFAS or blast furnace artificial slag, CBAS or coal burn artificial slag, and MSAS or midsized sand artificial slag), hydraulic loading rates (i.e., 7, 14, and 21 cm d^?1), and wetland operational periods (0.5, 1, and 2 years) as well as with and without planting Canna indica L. The wastewater was collected from the campus of South China Agricultural University, Guangzhou, China. Results show that the percent removal of total P (TP) and ammonium N (NH₄⁺-N) by the substrates was BFAS > CBAS > MSAS due to the high contents of Ca and Al in substrate BFAS. In contrast, the percent removal of total N (TN) by the substrates was CBAS > MSAS > BFAS due to the complicated nitrification/denitrification processes. The percent removal of nutrients by all of the substrates was TP > NH₄⁺-N > TN. About 10% more TN was removed from the wastewater after planting Canna indica L. A lower hydraulic loading rate or longer hydraulic retention time (HRT) resulted in a higher removal of TP, NH₄⁺-N, and TN because of more contacts and interactions among nutrients, substrates, and roots under the longer HRT. Removal of NO₃^?N from the simulated VFCWs is a complex process. A high concentration of NO₃^?N in the effluent was observed under the high hydraulic loading rate because more NH₄⁺-N and oxygen were available for nitrification and a shorter HRT was unfavorable for denitrification. In general, a longer operational period had a highest removal rate for nutrients in the VFCWs.     

Nutrient retention function of a stream wetland complex—A high-frequency monitoring approach

The ability of riverine ecosystems to retain nutrients depends on different hydrological, chemical and biological conditions including exchange processes between streams and wetlands. We investigated nutrient retention in a stream wetland complex on the time scale of daily hydrological exchange between both systems. Daily mass balances of NO₃-N, NH₄-N, TP and SRP were calculated with data obtained by two automated measurement stations in a stream reach upstream and downstream of a wetland. The pattern of hydrological exchange between stream and wetland was used to classify characteristic hydrological periods like floods, base and low flows. The nutrient retention function of the stream wetland complex varied considerably during phases of similar hydrologic conditions. Despite re-wetting measures in the wetland, an overall net export of all nutrients except for NH₄-N characterised the whole growing season. Nitrate retention occurred during summer flood (retention in the wetland, 23 kg NO₃-N d^?1, 17% of the input load) and low flow (retention in the stream, 1 kg NO₃-N d^?1, 2% of the input load). TP retention during summer could be assigned to sedimentation (0.7 kg TP d^?1, 7% during flooding in the wetland, 0.2 kg TP d^?1, 4% during low flow in the stream). SRP retention was only intermittent. We concluded that the nutrient retention of streams and wetlands can only be optimised by restoration measures that regard both systems as one functional unit in terms of nutrient retention.     

Effect of different macrophytes in abating nitrogen from a synthetic wastewater

An experiment conducted in an unheated glasshouse from October 2006 to March 2008 studied the efficiency of different macrophytes in reducing NO₃-N and NH₄-N concentrations and loads in synthetic wastewaters. The experimental setup consisted of plastic tanks, filled with gravel and vegetated with Carex elata All., Juncus effusus L., Phragmites australis (Cav.) Trin., Typhoides arundinacea L. Moench (syn Phalaris arundinacea L.) var. picta and Typha latifolia L. There was also a control without vegetation. From January to July, a solution of 50–60 ppm of NH₄-N and NO₃-N was applied monthly; then the input concentration was doubled. The total load at the end of the experimental period was 70.4 g/m² of NO₃-N and 67.3 of NH₄-N. At the end of each month, water was discharged from the tanks and analysed to determine the two nitrogen forms. At the end of the experiment, 33 g/m² of total N (almost 24% of applied N) had disappeared in the control. Among species, the highest abatement was detected in T. latifolia (72 g/m², almost 52% of applied N) and the lowest in J. effusus (35%).A weekly chemical analysis in July showed that a large amount of NH₄-N quickly disappeared in all treatments, while NO₃-N only decreased in the vegetated tanks. In December, NH₄-N had similar dynamics, while NO₃-N increased.All water volumes entering and exiting the tanks were measured in order to evaluate evapotranspiration. T. latifolia showed the highest water consumption, reaching a cumulative value of above 1000 mm.At the end of the experiment, J. effusus presented the highest amount of nitrogen stored in the aerial parts (5.63 g/m²) and T. latifolia the lowest (1.92 g/m²).     

The role of plants in the removal of nutrients at a constructed wetland treating agricultural (dairy) wastewater,Ontario, Canada

The South Nation River Watershed, in eastern Ontario, Canada, is an agricultural watershed impacted by excess nutrient loading primarily from agricultural activities. A constructed wetland for the treatment of agricultural wastewater from a 150-cow dairy operation in this watershed was monitored in its eighth operating season to evaluate the proportion of total nitrogen (TN) (approximated by total Kjeldahl nitrogen (TKN) due to low NO₃⁻) and total phosphorus (TP) removal that could be attributed to storage in Typha latifolia L. and Typha angustifolia L., which dominate this system. Nutrient loading rates were high, with 16.2 kg ha⁻¹ d⁻¹ N and 3.4 kg ha⁻¹ d⁻¹ P entering the wetland and loading the first wetland cell. Plant uptake accounted for 0.7% of TKN removal when the vegetated free water surface cells were considered together. However, separately, in the second wetland cell with lower N and P loading rates, plants accounted for 9% of TKN, 21% of NH₄⁺ and 5% of TP removal. Plant uptake was significant to overall removal given wetland age and nutrient loading. Nutrient storage during the growing season at this constructed wetland helped reduce the nutrient load entering the watershed, already stressed by intensive local agriculture.     

Comparison of the treatment performances of blast furnace slag-based and gravel-based vertical flow wetlands operated identically for domestic wastewater treatment in Turkey

In 2001, to foster the practical development of constructed wetlands (CWs) used for domestic wastewater treatment in Turkey, vertical subsurface flow constructed wetlands (30 m² of each) were implemented on the campus of the METU, Ankara, Turkey. The main objective of the research was to quantify the effect of different filter media on the treatment performance of vertical flow wetlands in the prevailing climate of Ankara. Thus, a gravel-filled wetland and a blast furnace granulated iron slag-filled wetland were operated identically with primarily treated domestic wastewater (3 m³ d⁻¹) at a hydraulic loading rate of 0.100 m d⁻¹, intermittently. Both of the wetland cells were planted with Phragmites australis. According to the first year results, average removal efficiencies for the slag and gravel wetland cells were as follows: total suspended solids (TSS) (63% and 59%), chemical oxygen demand (COD) (47% and 44%), NH₄⁺–N (88% and 53%), total nitrogen (TN) (44% and 39%), PO₄³⁻-P (44% and 1%) and total phosphorus (TP) (45% and 4%). The treatment performances of the slag-filled wetland were better than that of the gravel-filled wetland in terms of removal of phosphorus and production of nitrate. Since this study was a pioneer for implementation of subsurface constructed wetlands in Turkey using local sources, it has proved that this eco-technology could also be used effectively for water quality enhancement in Turkey.     

Soil nitrate accumulation explains the nonlinear responses of soil CO2 and CH4 fluxes to nitrogen addition in a temperate needle-broadleaved mixed forest

The responses of soil-atmosphere carbon (C) exchange fluxes to growing atmospheric nitrogen (N) deposition are controversial, leading to large uncertainty in the estimated C sink of global forest ecosystems experiencing substantial N inputs. However, it is challenging to quantify critical load of N input for the alteration of the soil C fluxes, and what factors controlled the changes in soil CO₂ and CH₄ fluxes under N enrichment. Nine levels of urea addition experiment (0, 10, 20, 40, 60, 80, 100, 120, 140 kg N ha⁻¹ yr⁻¹) were conducted in the needle-broadleaved mixed forest in Changbai Mountain, Northeast China. Soil CO₂ and CH₄ fluxes were monitored weekly using the static chamber and gas chromatograph technique. Environmental variables (soil temperature and moisture in the 0–10 cm depth) and dissolved N (NH₄⁺-N, NO₃⁻-N, total dissolved N (TDN), and dissolved organic N (DON)) in the organic layer and the 0–10 cm mineral soil layer were simultaneously measured. High rates of N addition (≥60 kg N ha⁻¹ yr⁻¹) significantly increased soil NO₃⁻-N contents in the organic layer and the mineral layer by 120%-180% and 56.4%-84.6%, respectively. However, N application did not lead to a significant accumulation of soil NH₄⁺-N contents in the two soil layers except for a few treatments. N addition at a low rate of 10 kg N ha⁻¹ yr⁻¹ significantly stimulated, whereas high rate of N addition (140 kg N ha⁻¹ yr⁻¹) significantly inhibited soil CO₂ emission and CH₄ uptake. Significant negative relationships were observed between changes in soil CO₂ emission and CH₄ uptake and changes in soil NO₃⁻-N and moisture contents under N enrichment. These results suggest that soil nitrification and NO₃⁻-N accumulation could be important regulators of soil CO₂ emission and CH₄ uptake in the temperate needle-broadleaved mixed forest. The nonlinear responses to exogenous N inputs and the critical level of N in terms of soil C fluxes should be considered in the ecological process models and ecosystem management.     

Two-decade wetland cultivation and its effects on soil properties in salt marshes in the Yellow River Delta,China

Wetland cultivation and its effects on soil properties in salt marshes in the Yellow River Delta, China were examined by using a combination of the satellite imageries and field experiments. Results showed that the conversions mainly occurred between dry lands and Phragmites australis–Suaeda salsa–Tamarix chinensis marshes (PSTMs). The total area of marsh wetland was reduced by 65.09 km² during the period from 1986 to 2005, and these conversions might be attributed to a combination of farming, oil exploration and water extraction, as well as soil salinization. Significant differences were observed in bulk density, pH, salinity and NO₃⁻-N between different land-use types (P < 0.05). After the conversions from marsh wetlands to dry lands, bulk density, pH, salinity and NH₄⁺-N decreased slightly, while a significant increase in NO₃⁻-N, TN (total nitrogen), and AP (available phosphorus) (P < 0.05) was observed. The more loss of soil nutrient storage also occurred after the maximal area conversion from PSTMs to dry lands compared to other conversions during the study period. The storages of soil organic matter, NH₄⁺-N and total phosphorus decreased greatly under the conversion from three types of marshes to dry lands, while those of NO₃⁻-N, AP and TN showed an obvious increase during the whole study period.     

Kinetics of pollutant removal from domestic wastewater in a tropical horizontal subsurface flow constructed wetland system: Effects of hydraulic loading rate

The treatment capacity of constructed wetlands is expected to be high in tropical areas because of the warm temperatures and the associated higher rates of microbial activity. A pilot scale horizontal subsurface flow constructed wetland system filled with river sand and planted with Phragmites vallatoria (L.) Veldkamp was set up in the southern part of Vietnam to assess the treatment capacity and the removal rate kinetics under tropical conditions. The system received municipal wastewater at four hydraulic loading rates (HLRs) of 31, 62, 104 and 146 mm day^?1. Removals of TSS, BOD₅ and COD were efficient at all HLRs with mean removal rates of 86–95%, 65–83% and 57–84%, respectively. Removals of N and P decreased with HLRs and were: NH₄-N 0–91%; TN 16–84% and TP 72–99%. First-order area-based removal rate constants (k, m year^?1) estimated from sampling along the length of the wetland from inlet to outlet at the four HLRs were in the range of 25–95 (BOD₅), 22–30 (COD), 31–115 (TSS), 5–24 (TN and TKN) and 41–84 (TP) at background concentrations (C*) of 5, 10, 0, 1.5 and 0 mg L^?1, respectively. The estimated k-values should not be used for design purposes, as site-specific differences and stochastic variability can be high. However, the study shows that domestic wastewater can be treated in horizontal subsurface flow constructed wetland systems to meet even the most stringent Vietnamese standards for discharge into surface waters.     

Effect of hydraulic retention time on the treatment of secondary effluent in a subsurface flow constructed wetland

This study evaluates the potential of subsurface flow (SSF) constructed wetlands (CWs) for tertiary treatment of wastewater at four shorter HRTs (1–4 days). The CWs were planted with Typha angustata, which was observed in our earlier study to be more efficient than Phragmites karka and Scirpus littoralis. The CWs comprised four rectangular treatment cells (2.14 m × 0.76 m × 0.61 m) filled with layers of gravel of two different sizes (approximately 2.5 cm and 1.5 cm diameter) to a depth of 0.61 m. The inflow rates of the secondary effluent in the four cells were accordingly fixed at 300 L d^?1, 150 L d^?1, 100 L d^?1 and 75 L d^?1, respectively, for 1, 2, 3 and 4 days HRT. The hydraulic loads ranged between 59.05 mm d^?1 and 236.22 mm d^?1.The wastewater inflow into the CW system as well as the treated effluent were analyzed, using standard methods, at regular intervals for various forms of nitrogen (NH₄-N, NO₃-N and TKN), orthophosphate-P and organic matter (BOD and COD) concentrations over a period of five weeks after the development of a dense stand.The higher HRT of 4 days not only helped maximum removal of all the pollutants but also maintained the stability of the treatment efficiency throughout the monitoring period. For the nutrients (NH₄-N, NO₃-N and TKN), HRT played a more significant role in their removal than in case of organic matter (BOD₃ and COD). More than 90% of NO₃-N and TKN and 100% of NH₄-N were removed from the wastewater at 4 days HRT.At lower HRTs, the mass loading rate was higher with greater fluctuation. However mass reduction efficiency of the T. angustata CW for all forms of nitrogen was >80% with the HRTs of 2, 3 and 4 days.     

Kinetics of biodegradation of free gossypol by Candida tropicalis in solid-state fermentation

In the present work experiments were carried out to study the effect of free gossypol on the growth of Candida tropicalis ZAU-1, evaluate its ability in biodegrading free gossypol, analyze the time course of solid-state fermentation, and model the microbial growth by determining the kinetics of dry matter weight loss, total carbohydrate concentration and the free gossypol content during solid-state fermentation. Results showed that the biomass in inorganic salts glucose medium were unaffected by free gossypol at 500 and 1000 mg/l levels, compared with the control group (p > 0.05); degradation of free gossypol reached 95.12% and 94.12%, respectively. A logistic equation (R² = 0.9922), describing the growth model of C. tropicalis ZAU-1 was obtained, with the maximum values of u_m and X_m at 0.0970 h⁻¹ and 21.8631% of dry matter weight loss, respectively. A good-fit curvilinear regression model was achieved to describe the change pattern of total carbohydrate concentration (R² = 0.9910), and the biodegradation pattern of free gossypol (R² = 0.9825). These models could be used to predict the fermentation course by C. tropicalis ZAU-1 under solid-state fermentation.     

The effects of NH4+ and NO3− on growth,resource allocation and nitrogen uptake kinetics of Phragmites australis and Glyceria maxima

The effects of NH₄⁺ or NO₃⁻ on growth, resource allocation and nitrogen (N) uptake kinetics of two common helophytes Phragmites australis (Cav.) Trin. ex Steudel and Glyceria maxima (Hartm.) Holmb. were studied in semi steady-state hydroponic cultures. At a steady-state nitrogen availability of 34 μM the growth rate of Phragmites was not affected by the N form (mean RGR = 35.4 mg g⁻¹ d⁻¹), whereas the growth rate of Glyceria was 16% higher in NH₄⁺-N cultures than in NO₃⁻-N cultures (mean = 66.7 and 57.4 mg g⁻¹ d⁻¹ of NH₄⁺ and NO₃⁻ treated plants, respectively). Phragmites and Glyceria had higher S/R ratio in NH₄⁺ cultures than in NO₃⁻ cultures, 123.5 and 129.7%, respectively.Species differed in the nitrogen utilisation. In Glyceria, the relative tissue N content was higher than in Phragmites and was increased in NH₄⁺ treated plants by 16%. The tissue NH₄⁺ concentration (mean = 1.6 μmol g fresh wt⁻¹) was not affected by N treatment, whereas NO₃⁻ contents were higher in NO₃⁻ (mean = 1.5 μmol g fresh wt⁻¹) than in NH₄⁺ (mean = 0.4 μmol g fresh wt⁻¹) treated plants. In Phragmites, NH₄⁺ (mean = 1.6 μmol g fresh wt⁻¹) and NO₃⁻ (mean = 0.2 μmol g fresh wt⁻¹) contents were not affected by the N regime. Species did not differ in NH₄⁺ (mean = 56.5 μmol g⁻¹ root dry wt h⁻¹) and NO₃⁻ (mean = 34.5 μmol g⁻¹ root dry wt h⁻¹) maximum uptake rates (V_max), and V_max for NH₄⁺ uptake was not affected by N treatment. The uptake rate of NO₃⁻ was low in NH₄⁺ treated plants, and an induction phase for NO₃⁻ was observed in NH₄⁺ treated Phragmites but not in Glyceria. Phragmites had low K_m (mean = 4.5 μM) and high affinity (10.3 l g⁻¹ root dry wt h⁻¹) for both ions compared to Glyceria (K_m = 6.3 μM, affinity = 8.0 l g⁻¹ root dry wt h⁻¹). The results showed different plasticity of Phragmites and Glyceria toward N source. The positive response to NH₄⁺-N source may participates in the observed success of Glyceria at NH₄⁺ rich sites, although other factors have to be considered. Higher plasticity of Phragmites toward low nutrient availability may favour this species at oligotrophic sites.     

Soil quality assessment of coastal wetlands in the Yellow River Delta of China based on the minimum data set

Little information is available to assess the dynamic changes in wetland soil quality in coastal regions, though it is essential for wetland conservation and management. Soil samples were collected in Suaeda salsa wetlands (SWs), Tamarix chinensis wetlands (TWs), Suaeda salsa–Tamarix chinensis wetlands (STWs), freshwater Phragmites australis wetlands (FPWs) and saltwater Phragmites australis wetlands (SPWs) in three sampling periods (i.e., summer and autumn of 2007 and spring of 2008). According to the flooding characteristics of these wetlands, the study area could be grouped into three sub-regions: short-term flooding region (STFR), seasonal flooding region (SFR) and tidal flooding region (TFR). Soil quality was evaluated using the soil quality index (SQI), which was calculated using the selected minimum data set (MDS) based on principal components analysis (PCA). Our results showed that soil salt content (SSC), total carbon (TC), magnesium (Mg), nitrate nitrogen (NO₃⁻-N) and total sulfur (TS) consisted of a MDS among 13 soil properties. The SQI values varied from 0.18 to 0.66 for all soil samples, of which the highest and lowest SQI values were observed in TFR. The average SQI values were significantly higher in summer (0.50 ± 0.13) than in spring (0.37 ± 0.13) and autumn (0.36 ± 0.11) in the whole study area (p < 0.05). The average SQI values followed the order STFR (0.44 ± 0.12) > TFR (0.41 ± 0.15) > SFR (0.35 ± 0.09) although no significant differences were observed among the three regions (p > 0.05). SPWs and SWs soils showed higher SQI values (0.50 ± 0.10 and 0.47 ± 0.15, respectively) than TWs (0.30 ± 0.08) soils (p < 0.05). The SSC was the dominant factor of soil quality with its proportion of 34.1% contributing to the SQI values, followed by TC (24.5%) and Mg (24.1%). Correlation analysis also showed that SQI values were significantly negatively correlated with SSC. SSC might be a characteristic indicator of wetland soil quality assessment in coastal regions. The findings of this study showed that the SQI based on MDS is a powerful tool for wetland soil quality assessment.     

Effects of wetland construction on water quality in a semi-arid catchment degraded by intensive agricultural use

Many factors can influence the improvement of water quality in surface-flow constructed wetlands (SFW). To test if water quality was improved, especially in nutrient and salt content, after passage through SFW, 11 wetland plots of various sizes (50, 200, 800 and 5000 m²) were established within constructed wetlands on agricultural soils in the Ebro River basin (NE Spain) that had been affected by salinization. A set of 15 water quality parameters (e.g., nutrients, salts, sediments, and alkalinity) was obtained from samples collected at the inflow and outflow of the wetlands during the first 4 years after the wetlands were constructed. NO₃-N retention rates were as high as 99% in the largest (5000 m²) wetlands. After 4 years, total phosphorus was still being released from the wetlands but not salts. Over the same period, in small wetlands (50, 200, and 800 m²), retention rate relative to the input of NO₃-N increased from 40% to almost 60%. Retention of NO₃-N amounted to up to 500 g N m^?2 per year, for an average load concentration at inflow of ～20 mg l^?1. Release of Na⁺ declined from 16% to 0–2% by volume, for an average load concentration at inflow of ～70 mg l^?1. At the current retention rate of NO₃-N (76–227 g m^?2 per year), 1.5–4% of the catchment should be converted into wetlands to optimize the elimination of NO₃-N.     

Investigating CH4 and N2O emissions from eco-engineering wastewater treatment processes using constructed wetland microcosms

Methane (CH₄) and nitrous oxide (N₂O) are important greenhouse gases, because of their contribution to the global greenhouse effect. The present study assessed emissions of N₂O and CH₄ from constructed wetland microcosms, planted with Phragmites australis and Zizania latifolia, when treating wastewater under different biological oxygen demand (BOD) concentration conditions. The removal rate was 95% for BOD and more than 80% for COD in all three pollutant concentrations, both plants’ removal rates of pollutants were at almost the same level, and both were found to resist BOD concentrations as high as 200 mg L⁻¹. When BOD concentrations fell below 200 mg L⁻¹, the soil plant units reached an average of 80–92% T-N and T-P removal rates; however, as the concentrations increased to 200 mg mg L⁻¹ or when during the initial phases of winter, the removal rates for T-N and T-P decreased to less than 70%. With NH₃-N removal, the influences of BOD concentrations and air temperature were more obvious. When BOD concentrations increased to 100 mg L⁻¹ after October, an obvious decrease in NH₃-N removal was detected; almost no nitrification occurred beginning in December at BOD concentrations of 200 mg mg L⁻¹. N₂O and CH₄ emissions showed obvious seasonal changes; higher emissions were observed with higher BOD concentrations, especially among Z. latifolia units. The enumeration of methane-oxidizing bacteria and methane-producing bacteria was also conducted to investigate their roles in impacting methane emissions and their relationships with plant species. The pollutant purification potentials of P. australis and Z. latifolia plant units during wastewater treatment of different pollutant concentrations occurred at almost the same levels. The nutrient outflow and methane flux were consistently higher with Z. latifolia units and higher concentrations of BOD. The more reductive status and higher biomass of methanogens may be the reason for the lower nitrification and higher CH₄ emissions observed with Z. latifolia units and higher concentration systems. The Z. latifolia root system is shallow, and the activity of methanotrophs is primarily confined to the upper portion of the soil. However, the root system of P. australis is deeper and can oxidize methane to a greater depth. This latter structure is more favorable as it is better for reducing methane emissions from P. australis soil plant systems.     

Trispyrazolylmethane piano stool complexes of iron(II) and cobalt(II)

A series of cationic trispyrazolylmethane complexes of the general form [Tm^RM(CH₃CN)₃]²⁺ (Tm = tris(pyrazolyl)methane, 1, R = 3,5-Me₂, M = Fe(II); 2, R = 3-Ph, M = Fe(II); 3, R = 3,5-Me₂, M = Co(II); 4, R = 3-Ph, M = Co(II)) with ‘piano-stool’ structures was prepared by the reaction of the N₃tripodal ligands (Tm^R)with [(CH₃CN)₆M](BF₄)₂ in a 1:1 stoichiometric ratio. Magnetic susceptibility measurements indicate that all four complexes with BF₄⁻ counter anions are paramagnetic, high-spin systems in the solid state with μ_eff at high temperatures of 5.2 (1, S = 2), 5.4 (2, S = 2), 4.9 (3, S = 3/2) and 4.6 (4, S = 3/2) BM, respectively. Comparisons of bond lengths from the metal centre to the Tm^R nitrogen donors, and from the metal centre to the acetonitrile nitrogen donors indicate that the neutral tripodal ligands appear to be more weakly coordinated to the metal centre than are the acetonitrile ligands. Reactions of these tripodal complexes with bidentate phosphine ligands, such as 1,2-diphosphinoethane or 1,2-bis(diallylphosphino)ethane leads to displacement of the tripodal ligand, or to the formation of more thermally stable bis-ligand complexes M(Tm^R)₂ (R = 3,5-dimethyl).     

An integrated constructed wetland to treat contaminants and nutrients from dairy farmyard dirty water

Water pollution by agriculture can include inappropriately managed dairy farmyard dirty water. In Ireland, dairy farmyard dirty water includes farmyard runoff, parlour washings, and silage/farmyard manure effluents. The objectives of this study were to determine (i) the quality and quantity of dirty water generated at a farm-scale and (ii) the seasonal effectiveness of a constructed wetland to treat farmyard dirty water. The wetland system was 4800 m² in area and treated dirty water from a 42-cow organic dairy unit with an open yard area of 2031 m². Monthly dirty water inflow rate to the wetland ranged between 3.6 and 18.5 m³ d⁻¹. Farmyard dirty water accounted for 27% of hydrological inputs to the wetland, whereas rainfall on wetland, along with wetland bank inflows accounted for 45 and 28%, respectively. Farmyard dirty water quality and quantity did not vary with season. Yearly mass loads discharged to the wetland were 47 ± 10 kg yr⁻¹ of soluble reactive phosphorus (SRP), 128 ± 35 kg yr⁻¹ of NH₄⁺, 5484 ± 1433 kg yr⁻¹ of organic material as measured by five-day biological oxygen demand (BOD₅), and 1570 ± 465 kg yr⁻¹ of total suspended solids (TSS). Phosphorus retention by the wetland varied with season (5–84%) with least amounts being retained during winter.     

Light thresholds derived from seagrass loss in the coastal zone of the northern Great Barrier Reef,Australia

There is a world-wide trend for deteriorating water quality and light levels in the coastal zone, and this has been linked to declines in seagrass abundance. Localized management of seagrass meadow health requires that water quality guidelines for meeting seagrass growth requirements are available. Tropical seagrass meadows are diverse and can be highly dynamic and we have used this dynamism to identify light thresholds in multi-specific meadows dominated by Halodule uninervis in the northern Great Barrier Reef, Australia. Seagrass cover was measured at ∼3 month intervals from 2008 to 2011 at three sites: Magnetic Island (MI) Dunk Island (DI) and Green Island (GI). Photosynthetically active radiation was continuously measured within the seagrass canopy, and three light metrics were derived. Complete seagrass loss occurred at MI and DI and at these sites changes in seagrass cover were correlated with the three light metrics. Mean daily irradiance (I_d) above 5 and 8.4 mol m⁻² d⁻¹ was associated with gains in seagrass at MI and DI, however a significant correlation (R = 0.649, p < 0.05) only occurred at MI. The second metric, percent of days below 3 mol m⁻² d⁻¹, correlated the most strongly (MI, R = −0.714, p < 0.01 and DI, R = −0.859, p = <0.001) with change in seagrass cover with 16–18% of days below 3 mol m⁻² d⁻¹ being associated with more than 50% seagrass loss. The third metric, the number of hours of light saturated irradiance (H_sat) was calculated using literature-derived data on saturating irradiance (E_k). H_sat correlated well (R = 0.686, p < 0.01; and DI, R = 0.704, p < 0.05) with change in seagrass abundance, and was very consistent between the two sites as 4 H_sat was associated with increases in seagrass abundance at both sites, and less than 4 H_sat with more than 50% loss. At the third site (GI), small seasonal losses of seagrass quickly recovered during the growth season and the light metrics did not correlate (p > 0.05) with change in percent cover, except for I_d which was always high, but correlated with change in seagrass cover. Although distinct light thresholds were observed, the departure from threshold values was also important. For example, light levels that are well below the thresholds resulted in more severe loss of seagrass than those just below the threshold. Environmental managers aiming to achieve optimal seagrass growth conditions can use these threshold light metrics as guidelines; however, other environmental conditions, including seasonally varying temperature and nutrient availability, will influence seagrass responses above and below these thresholds.     

Soil and tree ring chemistry of Pinus banksiana and Populus tremuloides stands as indicators of changes in atmospheric environments in the oil sands region of Alberta,Canada

The impact of chronic air pollution such as increased CO₂ and NO_x emissions on forest ecosystems in the Athabasca oil sands region in Alberta, Canada, was investigated in Pinus banksiana (jack pine) and Populus tremuloides (trembling aspen, aspen) stands in two watersheds (NE7 and SM8) located at different distances from the main emission sources of oil sands mining and upgrading facilities, using δ¹³C, δ¹⁵N, and Ca/Al of soil and tree ring samples as indicators. Watershed NE7 was exposed to greater amounts of acid deposition due to its closeness to the mining and upgrading area. The δ¹⁵N in the forest floor was lower (p < 0.05) in NE7 (ranged from −1.42 to −0.87‰) than in SM8 (−0.54 to 1.43‰), implying a greater amount of recent deposition of ¹⁵N-depleted N in NE7. Tree ring δ¹³C gradually decreased over time for both tree species/watersheds, indicating the influence of ¹³C-depleted CO₂ emitted from industrial sources. Tree ring N concentration and δ¹⁵N were not different between watersheds and did not significantly change with time. Interestingly, however, the difference between watersheds (NE7–SM8) that is expressed as Diff_N (for N) increased with concomitant decreases in Diff_δ¹⁵N over time, implying greater increases in ¹⁵N-depleted N input in NE7 than in SM8. Such trends were stronger in aspen stands (R² = 0.64 and p < 0.001 for Diff_N and R² = 0.44 and p < 0.01 for Diff_δ¹⁵N between 1964 and 2009) than in jack pine stands. We conclude that δ¹⁵N in the forest floor and differences in N and δ¹⁵N of tree rings between watersheds are useful indicators reflecting the impact of spatial variations of air pollution on forest stands in the Athabasca oil sands region in western Canada.