Unique Microbial Communities Inhabiting Underground Seawater in an Intertidal Area Utilized for Industrialized Aquaculture,as Compared with the Coastal Water

In recent decades, the decline of coastal water quality has promoted the birth of a new industrialized aquaculture mode in China, which involves the cultivation of organisms using underground seawater extracted from various depths below the intertidal zone. In view of the special physicochemical characteristics of underground seawater, the microbial community in this environment has attracted interest. In this study, the microbial community in the underground seawater of an intertidal area of the Qingdao coast of China was investigated. Compared with the upper coastal water, the underground seawater displayed lower numbers of microorganisms (2.7?±?0.3?×?10⁵ cells mL^?1 in underground seawater vs. 5.3?±?0.4?×?10⁵ cells mL^?1 in upper coastal seawater) but displayed much higher microbial diversity. At the phyla level, Proteobacteria, Bacteroidetes, Cyanobacteria, and Actinobacteria inhabited both environments, whereas bacteria in the phyla Planctomycetes, Deferribacteres, and Nitrospirae were recovered only from the underground seawater. Eighty-nine percent of the OTUs in the underground seawater were environmental specific. Furthermore, compared with coastal water, underground seawater displayed significant lower (p?<?0.05) concentration of NH₃-N, NO₂-N, PO₄-P, and DOC-C, and contained fewer potentially harmful pathogens (e.g., Verrucomicrobia/Opitutae) and more denitrifying bacteria (e.g., Shewanella denitrificans), thus making it more suitable for aquaculture.     

Optimization of biodrying pretreatment of municipal solid waste and microbial fuel cell treatment of leachate

The biodrying pretreatment of municipal solid waste (MSW) and the treatment of leachate were investigated. The biological oxygen demand (BOD) and NH₄ ⁺-N concentration of leachate from MSW biodrying pretreatment were measured, and the optimal conditions for MSW biodrying pretreatment and microbial fuel cell (MFC) performance were established. The results show that the optimal temperature and time for biodrying pretreatment of MSW were 40°C and 6 day, resulting in 30% weight loss of MSW, 20,800 mg/L leachate BOD, and 1,410 mg/L leachate NH₄ ⁺-N. Effects of leachate properties on MFC performance were then studied. The optimal conditions for electricity generation of the MFC were neutral pH, 5,093 mg/L leachate BOD, and 341 mg/L leachate NH₄ ⁺-N. The stable voltage of MFC generated using diluted leachate was 0.32 V, and the removal efficiencies of BOD and NH₄ ⁺-N by the MFC were 86.0 and 88.8% after 7 day of treatment, respectively. These findings provide guidelines for the pretreatment of MSW and the treatment of leachate, and for further research and actual engineering application.     

Effects of different nitrogen forms and combination with foliar spraying with 6-benzylaminopurine on growth,transpiration, and water and potassium uptake and flow in tobacco

NH₄ ⁺-N can have inhibitory effects on plant growth. However, the mechanisms of these inhibitory effects are still poorly understood. In this study, effects of different N forms and a combination of ammonium + 6-benzylaminopurine (6-BA, a synthetic cytokinin) on growth, transpiration, uptake and flow of water and potassium in 88-days-old tobacco (Nicotiana tabacum L. K 326) plants were studied over a period of 12 days. Plants were supplied with equal amounts of N in different forms: NO₃ ^–, NH₄NO₃, NH₄ ⁺ or NH₄ ⁺+6-BA (foliar spraying every 2 days after onset of the treatments). For determining flows and partitioning upper, middle and lower strata of three leaves each were analysed. During the 12 days study period, 50% replacement of NO₃ ^–-N by NH₄ ⁺-N (NH₄NO₃) did not change growth, transpiration, uptake and flow of water and K⁺ compared with the NO₃ ^–-N treatment. However, NH₄ ⁺-N as the sole N-source caused: (i) a substantial decrease in dry weight gain to 42% and 46% of the NO₃ ^–-N and NH₄NO₃ treatments, respectively; (ii) a marked reduction in transpiration rate, due to reduced stomatal conductance, illustrated by more negative leaf carbon-isotope discrimination (¹³C) compared with the NO₃ ^– treatment, especially in upper leaves; (iii) a strong reduction both in total water uptake, and in the rate of water uptake by roots, likely due to a decrease in root hydraulic conductivity; (iv) a marked reduction of K⁺ uptake to 10%. Under NH₄ ⁺ nutrition the middle leaves accumulated 143%, and together with upper leaves 206% and the stem 227% of the K⁺ currently taken up, indicating massive mobilisation of K⁺ from lower leaves and even the roots. Phloem retranslocation of K⁺ from the shoot and cycling through the root contributed 67% to the xylem transport of K⁺, and this was 2.2 times more than concurrent uptake. Foliar 6-BA application could not suppress or reverse the inhibitory effects on growth, transpiration, uptake and flow of water and ions (K⁺) caused by NH₄ ⁺-N treatment, although positive effects by 6-BA application were observed, even when 6-BA (10^–8 M) was supplied in nutrient solution daily with watering. Possible roles of cytokinin to regulate growth and development of NH₄ ⁺-fed plants are discussed.     

Effect of influent substrate ratio on anammox granular sludge: performance and kinetics

Effect of influent substrate ratio on anammox process was studied in sequencing batch reactor. Operating temperature was fixed at 35 ± 1 °C. Influent pH and hydraulic retention time were 7.5 and 6 h, respectively. When influent NO₂ ^?-N/NH₄ ⁺-N was no more than 2.0, total nitrogen removal rate (TNRR) increased whereas NH₄ ⁺-N removal rate stabilized at 0.32 kg/(m³ d). ΔNO₂ ^?-N/ΔNH₄ ⁺-N increased with enhancing NO₂ ^?-N/NH₄ ⁺-N. When NO₂ ^?-N/NH₄ ⁺-N was 4.5, ΔNO₂ ^?-N/ΔNH₄ ⁺-N was 1.98, which was much higher than theoretical value (1.32). The IC₅₀ of NO₂ ^?-N was 289 mg/L and anammox activity was inhibited at high NO₂ ^?-N/NH₄ ⁺-N ratio. With regard to influent NH₄ ⁺-N/NO₂ ^?-N, the maximum NH₄ ⁺-N removal rate was 0.36 kg/(m³ d), which occurred at the ratio of 4.0. Anammox activity was inhibited when influent NH₄ ⁺-N/NO₂ ^?-N was higher than 5.0. With influent NO₃ ^?-N/NH₄ ⁺-N of 2.5–6.5, NH₄ ⁺-N removal rate and NRR were stabilized at 0.33 and 0.40 kg/(m³ d), respectively. When the ratio was higher than 6.5, nitrogen removal would be worsened. The inhibitory threshold concentration of NO₂ ^?-N was lower than NH₄ ⁺-N and NO₃ ^?-N. Anammox bacteria were more sensitive to NO₂ ^?-N than NH₄ ⁺-N and NO₃ ^?-N. TNRR would be enhanced with increasing nitrogen loading rate, but sludge floatation occurred at high nitrogen loading shock. The Han-Levenspiel could be applied to simulate nitrogen removal resulting from NO₂ ^?-N inhibition.     

Impact of loads,season, and plant species on the performance of a tropical constructed wetland polishing effluent from sugar factory stabilization ponds

The effects of wastewater loading rates and two macrophyte species on treatment of sugar factory stabilization pond effluent were investigated in a pilot-scale free water surface constructed wetland (FWS CW) system in western Kenya. For 12 months, four CWs were operated at a hydraulic loading rate of 75 mm day⁻¹ and four at 225 mm day⁻¹. Half the CWs were planted with Cyperus papyrus and half with Echinochloa pyramidalis. Water samples were taken at the inlets and outlets and analyzed for TP, TDP, NH₄-N, and TSS. Mass removal rates of the selected water quality parameters were compared during three periods designated the short rain (period 1), dry (period 2), and long rain (period 3) seasons. There was a significant linear relationship between the mass removal rate of TP, NH₄-N, and TSS and the mass load, and season had a significant effect on the mass removal rate of TSS, NH₄-N, and TDP. Mass loading rates for TDP were about 78% of those for TP, whereas TDP comprised 78–99% of TP mass outflow rates, indicating a release of dissolved P within the CWs. The only significant difference between the two macrophyte species was associated with mass removal of NH₄-N, with more efficient removal in CWs planted with C. papyrus than those with E. pyramidalis. TP mass removal rates were 50–80% higher when a mean water loss for CWs 6–8 during periods 1 and 2 was assumed to represent evapotranspiration for all CWs in period 3 instead of pan evaporation data. This illustrated the importance of accurate estimations of evapotranspiration for pollutant mass removal rates in CWs in tropical climates.     

Influence of Agapanthus africanus on nitrification in a vertical subsurface flow constructed wetland

The aim of this study is to evaluate the influence of Agapanthus africanus (A. africanus) on nitrification in a vertical subsurface flow constructed wetlands (VSSFs) system. Two lab-scale VSSFs were operated: a) one was planted with A. africanus (vertical flow planted, VFP), and b) the other was unplanted (vertical flow control, VFC). The operation strategy was divided into three phases and consisted of increasing the ammoniacal nitrogen loading rate (ALR) (Phase I: 1.4; Phase II: 2.4; Phase III: 4.4 g NH₄⁺-N·m^?2·d^?1). Nitrification was evaluated in the system at two different depths in the VSSFs (30.5 cm and 60.3 cm, from the top of the system).

The removal efficiencies of COD, BOD₅, TP, and PO₄^?3-P were above 40% in the VFP and VFC during all operation. The mean removal efficiencies of NH₄⁺-N were above 70%. Nitrification was the principal NH₄⁺-N removal mechanism in both systems and transformed more than 50% of the NH₄⁺-N to NO₃^?-N. In terms of the effect of A. africanus on NH₄⁺-N removal during the three operational phases, nonsignificant differences between the two VSSFs were noted (p > 0.05). Thus, A. africanus did not influence nitrification. Finally, the analysis at different depths showed that nitrification occurred in the upper 30.5 cm.     

Nitrogen removal from secondary effluent by using integrated constructed wetland system

The treatment capacity of an integrated constructed wetland system (CWS) that was designed to reduce nitrogen (N) from secondary effluent was explored. The integrated CWS consisted of vertical-flow constructed wetland, floating bed and sand filter. The vertical-flow wetland was filled with gravel, steel slag and peat from the bottom to the top. Vetiver zizanioides was selected to grow in the vertical-flow constructed wetland and Coix lacrymajobi L. was grown in the floating bed. The results showed that the integrated CWS displayed superior removal efficiency for nitrate nitrogen (NO₃⁻-N), ammonia nitrogen (NH₄⁺-N), nitrite nitrogen (NO₂⁻-N), and total nitrogen (TN). The average NO₃⁻-N, NO₂⁻-N, NH₄⁺-N and TN removal efficiencies of the integrated CWS were 98.83%, 95.60%, 98.05% and 92.41%, respectively, during the whole experimental operation. The integrated CWS may have a good potential for removing N from secondary effluent.     

Induction of metamorphosis of pediveliger larvae of the mussel Mytilus galloprovincialis Lamarck, 1819 using neuroactive compounds,KCl, NH4Cl and organic solvents

Pediveliger larvae of Mytilus galloprovincialis were subjected to a series of bioassays to investigate the induction of metamorphosis using neuroactive compounds, K⁺, NH₄ ⁺ and organic solvents. Growth and survival of post-larvae obtained using ethanol and methanol were also observed. Epinephrine, phenylephrine, clonidine and metanephrine induced larval metamorphosis at 10^?6 to 10^?4 M in both 24-h and continuous exposure assays. In 24-h exposure assays, α-methyldopa at 5×10^?5 M and methoxyphenamine at 5×10^?5?10^?4 M induced 55?94% metamorphosis. Similarly, excess K⁺ at 3×10^?2 M induced 39% metamorphosis and NH₄ ⁺ at 1?5×10^?2 M induced 63–78% metamorphosis. The EC50s of seven organic solvents ranged from 0.04 to 0.82 M. Post-larvae that metamorphosed using ethanol and methanol survived as juveniles and grew at the same rate as those from microbial biofilm. Thus, the above compounds can be useful inducers of metamorphosis for antifouling studies using larvae and juveniles of M. galloprovincialis.     

The impacts of re-introducing Mississippi River water on the hydrologic budget and nutrient inputs of a deltaic estuary

Most wetlands of the Mississippi deltaic plain are isolated from riverine input due to flood control levees along the Mississippi River. These levees have altered hydrology and ecology and are a primary cause of massive wetland loss in the delta. River water is being re-introduced into coastal basins as part of a large-scale ecological engineering effort to restore the delta. We quantified freshwater, nitrogen, and phosphorus inputs to the Breton Sound Estuary for three climatically different years (2000, 2001, and 2002). Water budgets included precipitation, potential evapotranspiration, the diversion, stormwater pumps, and groundwater. Precipitation contributed 48–57% of freshwater input, while the diversion accounted for 33–48%. Net groundwater input accounted for less than 0.05% of freshwater inputs. Inputs of ammonium (NH₄-N), nitrate (NO₃-N), total nitrogen (TN), and total phosphorus (TP) were determined for each of the water sources. Atmospheric deposition was the most important input of NH₄-N (57–62% or 1.44 × 10⁵–2.32 × 10⁵ kg yr⁻¹) followed by the diversion. The diversion was the greatest source of NO₃-N (67–83%, 7.78 × 10⁵–1.64 × 10⁶ kg yr⁻¹) and TN (60–71%). The diversion contributed 41–60% of TP input (1.17 × 10⁵–2.32 × 10⁵ kg yr⁻¹). Annual loading rates of NH₄-N and NO₃-N were 0.17–0.27 and 1.2–2.3 g N m⁻² yr⁻¹, respectively, for the total basin indicating strong retention of nitrogen in the basin. Nitrogen retention through denitrification and burial was estimated for the upper basin.     

Biodiversity and water quality variations in constructed wetland of Yongding River system

This research was carried on in constructed wetlands of Guan-Ting Reservoir, Beijing, China, from 2004 to 2005. The phytoplankon community was composed of 8 divisions (94 species, including genus and varieties) and the average cell density was 980.93× 10⁴ cells per liter. The dominant divisions were Chlorophyta (36.8%), Bacillariophyta (31.0%) and Cyanophyta (23.4%). The removal rate of phytoplankton density was 72.7%. There was a positive linear correlation between phytoplankon density and total phosphorus. Here, 7 families (13 species) of aquatic vasular plants were found, which constituted emerging and submerging macrophyte communities. In the wetland system, the zooplankton community consisted of Protozoa, Rotifera, Cladocera and Copepoda (70 species). The average density was 4883 individuals per liter. Protozoan and Rotifera were the dominant groups and the removal rate of their density was 81.9%. The correlation between zooplankton and phytoplankton presented a quadratic curve. Also, the zoobenthos community contained Olisochaeta, Uniramia, Crustacea and Mollusca (15 species). The average density was 5670 individuals per m² (62.3% was Uniramia) and the removal rate of their density was 92.4 %. The wetland system reduced COD_Mn, BOD₅, TN, NH_3-N, NO_3-N, TP (total phosphor), PO_4-P and SS in the water of Yong Ding River at 52.9%–99.1%.     

Ecological indicators of nutrient enrichment, freshwater wetlands, Midwestern United States (U.S.)

Vegetation and soil indicators of nutrient condition were evaluated in 30 wetlands, 10 each in 3 Nutrient Ecoregions (NE) (VI-Corn Belt and Northern Great Plains, VII-Mostly Glaciated Dairy Region, IX-Temperate Forested Plains and Hills) of the Midwestern United States (U.S.) to identify robust indicators for assessment of wetland nutrient enrichment and eutrophication. Nutrient condition was characterized by surface water inorganic N (NH₄-N, NO₃-N) and P (PO₄-P) concentrations measured seasonally for 1 year, plant available and total soil N and P, and aboveground biomass, leaf N and P and species composition of emergent vegetation measured at the end of the growing season. Aboveground biomass, nutrient uptake and species composition were positively related to surface water NH₄-N (N) but not to PO₄-P or NO₃-N. Aboveground biomass and biomass of aggressive species, Typha spp. plus Phalaris arundinacea, increased asymptotically with surface water N whereas leaf P, senesced leaf N and senesced leaf P increased linearly with N. And, species richness declined with surface water N. Soil total P was positively related to surface water PO₄-P but it was the only soil indicator related to wetland nutrient condition. Individual regressions for each NE generally were superior to a single regression for all NEs. In NE VI (Corn Belt), few indicators were related to surface water N because of the high degree of anthropogenic disturbance (85% of the landscape is cleared) as compared to NEs VII and IX (24–53% cleared). Of the indicators evaluated, stem height (r² = 0.42 for all NEs, r² = 0.56 for NE VII + IX) and percent biomass of aggressive species, Typha spp. plus Phalaris, (r² = 0.46 for all NEs, r² = 0.54 for NE VII + IX), were the best predictors of wetland nutrient enrichment. Vegetation-based indicators are a promising tool for assessment of wetland nutrient condition but they may not be effective in NEs where landscape disturbance is intense and widespread.     

The effect of nutrient concentrations,nutrient ratios and temperature on photosynthesis and nutrient uptake by Ulva prolifera: implications for the explosion in green tides

The green-tide macroalga, Ulva prolifera, was tested in the laboratory to determine its nutrient uptake and photosynthesis under different conditions. In the nutrient concentration experiments U. prolifera showed a saturated uptake for nitrate but an escalating uptake in the tested range for phosphorus. Both N/P and NO₃ ^?/NH₄ ⁺ ratios influenced nutrient uptake significantly (p?<?0.05) while the PSII quantum yield [Y(II)] (p?>?0.05) remained unaffected. The maximum N uptake rate (33.9?±?0.8 μmol g^?1 DW h^?1) and P uptake rate (11.1?±?4.7) was detected at N/P ratios of 7.5 and 2.2, respectively. U. prolifera preferred NH₄ ⁺-N to NO₃ ^?-N when the NO₃ ^?-N/NH₄ ⁺-N ratio was less than 2.2 (p?<?0.05). But between ratios of 2.2 and 12.9, the uptake of NO₃ ^?-N surpassed that of NH₄ ⁺-N. In the temperature experiments, the highest N uptake rate and [Y(II)] were observed at 20 °C, while the lowest rates were detected at 5 °C. P uptake rates were correlated with increasing temperature.     

Transformation and Transport of Nitrogen Forms in a Sandy Entisol Following a Heavy Loading of Ammonium Nitrate Solution: Field Measurements and Model Simulations

Understanding the factors influencing water and nutrient transport through soil profile is important for the efficient management of nutrient and irrigation to minimize nutrient leaching below the rootzone. Transport of NO₃-N and NH₄-N was studied in a Candler fine sand following a heavy loading of a liquid fertilizer containing ammonium nitrate. Both NO₃-N and NH₄-N transported quite rapidly (within 3?d) and accumulated above the clay layer at about depth of 2.7?m. The concentrations of NH₄-N and NO₃-N approached background levels throughout the soil profile by 184?d. More than 50% of ammonium and nitrate contained in the spilled solution leached from the entire depth of soil profile sampled during the first 95?d. The cumulative amount of rainfall during this period was 329?mm, which accounted for 65% of the total rainfall for the entire study period. The concentrations of NH₄-N and NO₃-N at various depths within the entire soil profile reasonably predicted by the Leaching Estimation and Chemistry Model (LEACHM) and compared favorably with the measured concentrations, however, there are few places with high concentrations. The cumulative amount of leachate at the bottom of the soil profile predicted by LEACHM represented 90% of total rainfall that occurred during the study period. This demonstrated a substantial potential for leaching of soluble nutrients through the sandy soil profile.     

Powdered activated carbon added biological treatment of pre-treated landfill leachate in a fed-batch reactor

Biological treatment of landfill leachate usually results in low treatment efficiencies because of high chemical oxygen demand (COD), high ammonium-N content and also presence of toxic compounds such as heavy metals. A landfill leachate with high COD content was pre-treated by coagulation-flocculation followed by air stripping of ammonia at pH = 12. Pre-treated leachate was biologically treated in an aeration tank operated in fed-batch mode with and without addition of powdered activated carbon (PAC). PAC at 2 g l^–1 improved COD and ammonium-N removals resulting in nearly 86% COD and 26% NH₄-N removal.     

Nitrogen dynamics in a eutrophic lake sediment

Nitrogen flux from sediment of a shallow lake and subsequent utilization by water hyacinth (Eichhornia crassipes [Mart] Solms) present in the water column were evaluated using an outdoor microcosm sediment-water column. Sediment N was enriched with ¹⁵N to quantitatively determine the movement of NH₄-N from the sediment to the overlying water column. During the first 30 days. 48% of the total N uptake by water hyacinth was derived from sediment ¹⁵NH₄-N. This had decreased to 14% after 183 days. Mass balance of N indicates that about 25% sediment NH₄-N was released into the overlying water, but only 17% was assimilated by water hyacinth. NH₄-N levels in the water column were very low, with very little or no concentration gradients. NH₄-N levels in the interstitial water of the sediment were in the range of 30–35 mg L^–1 for the lower depths (> 35 cm), while in the surface 5 cm of depth NH₄-N levels decreased to 3.2 mg L^–1. Simulated results also showed similar trends for the interstitial NH₄-N concentration of the sediment. The overall estimated NH₄-N flux from the sediment to the overlying water was 4.8 µg cm^–2 day^–1, and the soluble organic N flux was 5.8 µg N cm^–2 day^–1. Total N flux was 10.6 µg N cm^–2 day^–1.     

Partial nitritation at elevated loading rates: design curves and biofilm characteristics

There is a need to develop low operational intensity, cost-effective, and small-footprint systems to treat wastewater. Partial nitritation has been studied using a variety of control strategies, however, a gap in passive operation is evident. This research investigates the use of elevated loading rates as a strategy for achieving low operational intensity partial nitritation in a moving bed biofilm reactor (MBBR) system. The effects of loading rates on nitrification kinetics and biofilm characteristics were determined at elevated, steady dissolved oxygen concentrations between 5.5 and 7.0 mg O₂/L and ambient temperatures between 19 and 21 °C. Four elevated loading rates (3, 4, 5 and 6.5 g NH₄⁺-N/m² days) were tested with a distinct shift in kinetics being observed towards nitritation at elevated loadings. Complete partial nitritation (100% nitrite production) was achieved at 6.5 g NH₄⁺-N/m² days, likely due to thick biofilm (572 µm) and elevated NH₄⁺-N load, which resulted in suppression of nitrite oxidation.

     

Three years of soil respiration in a mature eucalypt woodland exposed to atmospheric CO<Subscript>2</Subscript> enrichment

Large amounts of atmospheric N deposition cause negative effects on ecosystems. Effective mitigation strategies require the sources of N deposition to be identified and the contributions from individual sources to be quantified. Determination of the isotopic composition represents a useful approach in source apportionment. In this study, the δ¹⁵N-NH_x of wet and dry atmospheric deposition and the main NH₃ emission sources were analyzed at an urban, a suburban and a rural site in the Taihu Lake region of China. The 2-year average δ¹⁵N-\( {\text{NH}}_{4}^{ + } \) of precipitation was ? 3.0 ± 2.3, ? 3.1 ± 2.8 and ? 0.5 ± 2.8‰ for the urban, suburban and rural sites, respectively. These values were much lower than the corresponding values for particulate \( {\text{NH}}_{4}^{ + } \) (15.9, 15.2 and 14.3‰ at the urban, suburban and rural sites, respectively), and much higher than those of gaseous δ¹⁵N-NH₃ (? 16.7, ? 18.2 and ? 17.4‰ at the urban, suburban and rural sites, respectively). The δ¹⁵N-NH₃ of NH₃ from the main emission sources ranged from ? 30.8 to ? 3.3‰ for volatilized fertilizer, from ? 35.1 to ? 10.5‰ for emissions from a pig farm, and ? 24.7 to ? 11.3‰ for emissions from a dairy farm. Temporal variations of deposition δ¹⁵N-NH_x indicated that δ¹⁵N-NH_x values were lower in summer and autumn, but higher in winter and spring for both precipitation \( {\text{NH}}_{4}^{ + } \)-N and gaseous NH₃-N. Weather conditions such as temperature and precipitation significantly influenced the spatial and temporal distribution of isotope values of the deposition. Analysis of δ¹⁵N-NH_x in deposition and emission sources identified volatilized fertilizer and livestock wastes as the origins of both gaseous NH₃-N and precipitation \( {\text{NH}}_{4}^{ + } \)-N over the region. A stable isotope mixing model estimated that volatilized fertilizer and animal excreta contributed more than 65% to precipitation \( {\text{NH}}_{4}^{ + } \)-N, more than 60% to particulate \( {\text{NH}}_{4}^{ + } \)-N, and more than 75% to gaseous NH₃-N.     

Nutrient and faecal contamination and retention in wetland enclosures (gei wais) in the Mai Po Marshes,Hong Kong

Nutrient and faecal contamination is an increasing problem to the shrimp productivity and wildlife conservation at the internationally important wetland ecosystems of the Mai Po Marshes (Hong Kong, P.R. China). The present study examined the nutrient status and faecal bacteria loading and potential retention capacity of contaminants of two wetland enclosures. Water in the wetland enclosures was eutrophicated with high concentrations of dissolved inorganic nitrogen (inorg–N_diss= 15.0 mg l^–1) and orthophosphate phosphorus (o-P = 1.89 mg l^–1) and was loaded with high levels of faecal coliforms (172 ×10³ cfu in 100 ml) and faecal streptococci (1.94 ×10³ cfu in 100 ml). The pattern of nutrient enrichment of two wetland enclosures is related to a north-to-south pollution gradient from the Shenzhen River to the wetlands. By retaining tidal water in the wetland for an 8-day period, water quality was greatly improved; NH₄–N was removed by 83%, o-P by 45% and faecal bacteria by 100%. This implies a self-purification capability of the wetland enclosures and a potentiality of using them as an alternative sewage treatment.     

Urban pollutant removal by a constructed riparian wetland before typhoon damage and after reconstruction

Flood damage as a result of an extreme weather event is always a potential threat to constructed riparian wetlands in subtropical regions, and such damage can significantly impair the pollutant-removing performance of these wetlands The present study compares the pollutant-removal performance of the Hsin-Hai Bridge constructed wetland in the Tan-shui River basin of metropolitan Taipei in September 2000 (before the system was inundated by flood as a result of Typhoon Aere’) and in mid-October 2004 (after reconstruction of the wetland). The study analyses biochemical oxygen demand (BOD), ammonia nitrogen (NH₄-N), and total phosphorus (TP) of influents and effluents in each of several compartments and for the system as a whole before the typhoon and after reconstruction. The study finds that performance with respect to BOD and NH₄-N was marginally reduced (with no statistical significance) after reconstruction, but that performance with respect to TP was markedly improved (with statistical significance) after reconstruction. The study provides possible explanations for these findings and concludes that wetlands can be successfully reconstructed after extreme flood damage.