Integrated stream and wetland restoration: A watershed approach to improved water quality on the landscape

Water quality in Upper Sandy Creek, a headwater stream for the Cape Fear River in the North Carolina Piedmont, is impaired due to high N and P concentrations, sediment load, and coliform bacteria. The creek and floodplain ecosystem had become dysfunctional due to the effects of altered storm water delivery following urban watershed development where the impervious surface reached nearly 30% in some sub-watersheds. At Duke University, an 8-ha Stream and Wetland Assessment Management Park (SWAMP) was created in the lower portion of the watershed to assess the cumulative effect of restoring multiple portions of stream and former adjacent wetlands, with specific goals of quantifying water quality improvements. To accomplish these goals, a three-phase stream/riparian floodplain restoration (600 m), storm water reservoir/wetland complex (1.6 ha) along with a surface flow treatment wetland (0.5 ha) was ecologically designed to increase the stream wetland connection, and restore groundwater wetland hydrology. The multi-phased restoration of Sandy Creek and adjacent wetlands resulted in functioning riparian hydrology, which reduced downstream water pulses, nutrients, coliform bacteria, sediment, and stream erosion. Storm water event nutrient budgets indicated a substantial attenuation of N and P within the SWAMP project. Most notably, (NO₂⁻ + NO₃⁻)-N loads were reduced by 64% and P loads were reduced by 28%. Sediment retention in the stormwater reservoir and riparian wetlands showed accretion rates of 1.8 cm year⁻¹ and 1.1 cm year⁻¹, respectively. Sediment retention totaled nearly 500 MT year⁻¹.     

Phosphorus release from sediments in a treatment wetland: Contrast between DET and EPC0 methodologies

Wetlands are capable of reducing nutrient loadings to receiving water bodies, and hence many artificial wetlands have been constructed for wastewater nutrient removal. In this study, diffusive equilibrium in thin films (DETs) and equilibrium phosphorus concentration (EPC₀) analysis were used to examine the role of sediment as a nutrient source or sink in a constructed treatment wetland in summer. The effect of dredging on sediment-water nutrient exchange was also studied. Soluble reactive phosphorus (SRP), ammonium (NH₄⁺) and sulphate (SO₄²⁻) concentration profiles were measured by DET across the sediment-water interface (SWI) in both a settling pond and iris reed bed within the wetland. The SRP concentrations in the sediment pore-waters of the settling pond were extremely high (up to 29,500 μg l⁻¹) near the SWI. This is over an order of magnitude higher than the levels found in the water column, which in turn are over an order of magnitude higher than environmental levels proposed to limit eutrophication in rivers. The profiles demonstrated an average net release of SRP and NH₄⁺ from the settling pond sediment to the overlying water of 58 mg m⁻² d⁻¹ (±32 mg m⁻² d⁻¹ (1 sd)) and 16 mg m⁻² d⁻¹ (±25 mg m⁻² d⁻¹ (1 sd)), respectively. The DET SO₄²⁻ concentration profiles revealed that the sediment was anoxic within 2 cm of the SWI. Dredging of the reed bed made no significant difference to the P release characteristics across the SWI. The EPC₀s were much lower than the SRP concentration of the overlying water, indicating that the sediment had the potential to act as a phosphate sink. The apparent contradiction of the DET and EPC₀ results is attributed to the fact that DET measurements are made in situ, where as EPC₀ measurements are ex situ. These results show that substantial releases of P can occur from wetland sediments, and also highlight the need for caution when interpreting ex situ EPC₀ analytical results.     

Internal eutrophication of restored peatland stream: The role of bed sediments

The improvement of site hydrology is a major determinant of the success or failure of wetland restoration. Unfortunately, the influence of new hydrological conditions on wetland chemistry and nutrient cycling is often ignored or simply not monitored. This study assessed how changes in the composition of stream sediments that occurred after peatland stream restoration affected the pool and bioavailability of phosphorus (P) stored on the stream floor. The studied watercourses were located in the Narew River valley, NE Poland. They were restored in 2002 by excavating channels about 4-6 m wide and 1-1.5 m deep. Channels were cut through a peat layer to basal sands that underlay the organic deposits. Due to fallacious assumption about the high stability of peat stream banks, the banks were not modelled or protected by any technical measures to eliminate potential slump and erosion.Within a few years of the completion of the restoration project, peat bank failures led to the substantial deposition of organic material onto the floor of the newly created water-bodies. This resulted in an increase in the mean total phosphorus (TP) concentration in the sediment from 19 μmol g⁻¹ to more than 35 μmol g⁻¹ as well as an increase in both the concentration and pool of potentially mobile P fractions. A potential for the release of P was confirmed by the change in the concentration of P fractions that has been recorded over the summer period. Between June and October 2008 their content in the top 1-cm layer diminished from 134.1 mmol m⁻² to 100.6 mmol m⁻², implying an average net release of P of about 0.3 mmol m⁻² day⁻¹.This suggests that examined sediments primarily act as a highly dynamic transformer system, being the sink for particulate organic and mineral forms of P and serving as the net source of bioavailable (soluble reactive phosphorus) SRP.     

Benthic transfer and speciation of mercury in wetland sediments downstream from a sewage outfall

In order to evaluate the role of hypoxic conditions of overlying water in the benthic flux and speciation of Hg, we analyzed sediment cores from hypoxic or oxic sites downstream from a sewage outfall in the Damyang Riverine Wetland, Korea. Each core was analyzed for total Hg (THg), monomethylmercury (MMHg), and elemental Hg (Hg⁰) from sediment, and for THg and MMHg from pore water. Hypoxic conditions of the overlying water near the sewage outfall were associated with a peak production of Hg⁰, but the lowest production of MMHg, in the upper 2 cm sediments. The benthic fluxes of THg and MMHg were estimated at 130-2109 ng m⁻² day⁻¹ and −12 to 260 ng m⁻² day⁻¹, respectively. The order of MMHg flux from sediment to overlying water at each site did not follow the order of MMHg concentration in sediment, but was highest in hypoxic water conditions. The results suggest that maintaining oxic conditions in wetland water is important for decreasing the transfer of MMHg from sediment into overlying water.     

Methane emissions from freshwater riverine wetlands

To better understand methane emissions from freshwater riverine wetlands, seasonal and spatial patterns of methane emissions were measured over a 1-year period from created freshwater marshes and a river division oxbow, and at a river-floodplain edge (riverside) in central Ohio, USA. Plots were distributed from inflow to outflow and from shallow transition edges to deep water zones in the marshes and oxbow. Median values of CH₄ emissions ranged from 0.33 to 85.7 mg-CH₄-C m⁻² h⁻¹, at the riverside sites and 0.02-20.5 mg CH₄-C m⁻² h⁻¹ in the created marshes. The naturally colonizing marsh had more methane emissions (p = 0.047) than did the planted marsh, probably due to a history of higher net primary productivity in the former. A significant dry period and lower productivity in the oxbow may explain its low range of methane emissions of −0.04 to 0.09 mg CH₄-C m⁻² h⁻¹. There were significantly higher rates of methane emissions in deep water zones compared to transition zones in the created marshes. Overall CH₄ emissions had significant relationships with organic carbon and soil temperature and appear to depend on the hydroperiod and vegetation development. Riparian wetlands can be designed to minimize greenhouse gas emissions while providing other ecosystem services.     

A comparison of irradiance and phosphorus effects on the growth of three submerged macrophytes

A fully factorial pond experiment was designed using two irradiance levels and two phosphorus concentrations to investigate irradiance and phosphorus effects on the growth of three submerged macrophytes: common waterweed (Elodea canadensis), Eurasian water milfoil (Myriophyllum spicatum), and water stargrass (Zosterella dubia). Results revealed that higher irradiance (230 μmol s⁻¹ m⁻² vs. 113 μmol s⁻¹ m⁻² at 2 m depth) had significant positive effects on submerged macrophyte growth: increasing the number of individuals (seven-fold), the number of species surviving (two-fold), aboveground biomass (11-fold), belowground biomass (10-fold), and total biomass (11-fold), whereas elevated sediment phosphorus (2.1–3.3 mg g⁻¹ vs. 0.7 mg g⁻¹ dry sediment) did not have any significant impact. However, responses to irradiance differ among macrophyte species due to their morphology and physiology. Waterweed increased in numbers of individuals and total biomass under high irradiance while biomass per individual remained the same (∼0.02 g). The other species increased both in numbers and biomass per individual. These results suggest that increased irradiance rather than decreased phosphorus loading is the main driver of changes in submerged macrophytes in North American temperate lake ecosystems.     

Overyielding and the role of complementary use of nitrogen in wetland plant communities

Biodiversity and ecosystem functioning experiments have demonstrated that plant biomass of species grown in mixtures is often greater than plant biomass of monocultures (i.e., mixtures over yield). While we understand that plant species utilize resources differently, how a combination of species increases resource use and productivity is not well known, especially in wetland ecosystems. Here, we used a mesocosm experiment to explore diversity effects on plant biomass production and to examine the role of N partitioning as a mechanism for overyielding in wetland ecosystems. Plant functional groups (FGs) represented the unit of diversity, and we included five levels of diversity (0-4 FGs). To test for N partitioning, we used a stable isotope technique to determine niche breadth and proportion similarity of inorganic N use (NO₃⁻ and NH₄⁺) for individual FGs as well as mixtures containing 3 and 4 FGs. We found that total plant biomass increased in the first season from an average of 290 ± 60 SE g ash-free dry mass (AFDM) m⁻² at the 1 FG level to 490 ± 70 g AFDM m⁻² at the 4 FG level and in the second season from an average of 560 ± 80 g AFDM m⁻² at the 1 FG level to 1000 ± 90 g AFDM m⁻² at the 4 FG level indicating overyielding. Plant species comprising the majority of mesocosm biomass demonstrated preferential uptake of ¹⁵NO₃⁻, while species with relatively less biomass (e.g., Acorus calamus and Carex crinita) preferred ¹⁵NH₄⁺. Concentrations of ¹⁵N in biomass increased with FG richness, but only in the ¹⁵NO₃⁻ treatment. Niche breadth did not vary among levels of FG richness. We observed a greater niche overlap with an increase of FGs, with species taking up greater proportion of ¹⁵NO₃⁻ than ¹⁵NH₄⁺. Our results indicate that plant overyielding in wetland mesocosms is not the result of niche partitioning of N chemical forms, but is associated with greater uptake of NO₃.     

The 1994 experimental opening of the Bonnet Carre Spillway to divert Mississippi River water into Lake Pontchartrain, Louisiana

A diversion of Mississippi River water into Lake Pontchartrain, Louisiana, USA by way of the Bonnet Carre Spillway has been proposed as a restoration technique to help offset regional wetland loss. An experimental diversion of Mississippi River water into Lake Pontchartrain was carried out in April 1994 to monitor the fate of nutrients and sediments in the spillway and Lake Pontchartrain. Approximately 6.4×10⁸ m³ of Mississippi River water was diverted into Lake Pontchartrain over 42 days. As water passed through the Bonnet Carre Spillway, there were reductions in total suspended sediment concentrations of 82–83%, nitrite+nitrate (NO_x) of 28–42%, in total nitrogen (TN) of 26–30%, and in total phosphorus (TP) of 50–59%. 3.9±1.1 cm of accretion was measured in the spillway. Nutrient concentrations at the freshwater plume edge in Lake Pontchartrain compared to the Mississippi River were lower for NO_x (44–81%), TN (37–57%), and TP (40–70%), and generally higher for organic nitrogen (−7–57%). The Si:N ratio generally increased and the N:P ratio decreased from the river to the plume edge. Nutrient stoichiometric ratios indicate water at the plume edge was not silicate limited, suggesting conditions favoring diatomic phytoplankton.     

Seasonal and storm event nutrient removal by a created wetland in an agricultural watershed

This study examines the effectiveness of a 1.2-ha created/restored emergent marsh at reducing nutrients from a 17.0 ha agricultural and forested watershed in the Ohio River Basin in west central Ohio, USA, during base flow and storm flow conditions. The primary source of water to the wetland was surface inflow, estimated in water year 2000 (October 1999–September 2000) to be 646 cm/year. The wetland also received a significant amount of groundwater discharge at multiple locations within the site that was almost the same in quantity as the surface flow. The surface inflow had 2-year averages concentrations of 0.79, 0.033, and 0.16 mg L⁻¹ for nitrate + nitrite (as N), soluble reactive phosphorus (SRP), and total phosphorus (TP), respectively. Concentrations of nitrate–nitrite, SRP, and TP were 40, 56, and 59% lower, respectively, at the outflow than at the inflow to the wetland over the 2 years of the study. Concentrations of SRP and TP exported from the wetland increased significantly (α = 0.05) during precipitation events in 2000 compared to dry weather flows, but concentrations of nitrate–nitrite did not increase significantly. During these precipitation events the wetland retained 41% of the nitrate–nitrite, 74% of the SRP, and 28% of the TP (by mass). The wetland received an average of 50 g N m⁻² per year of nitrate–nitrite and 7.1 g m⁻² per year of TP in 2000. Retention rates for the wetland were 39 g N m⁻² per year of nitrates and 6.2 g P m⁻² per year. These are close to rates suggested in the literature for sustainable non-point source retention by wetlands. The design of this wetland appears to be suitable as it retained a significant portion of the influent nutrient load and did not lose much of its retention capacity during heavy precipitation events. Some suggestions are given for further design improvements.     

Evaluation of a lab-scale tidal flow constructed wetland performance: Oxygen transfer capacity, organic matter and ammonium removal

Oxygen transfer capacity and removal of ammonium and organic matter were investigated in this study to evaluate the performance of a lab-scale tidal flow constructed wetland. Average oxygen supply under tidal operation (350 g m⁻² d⁻¹) was much higher than in conventional constructed wetlands (<100 g m⁻² d⁻¹), resulting in enhanced removal of BOD₅ and NH₄⁺. Theoretical oxygen demand from BOD₅ removal and nitrification was approximately matched by the measured oxygen supply, which indicated aerobic consumption of BOD₅ and NH₄⁺ under tidal operation. When BOD₅ removal increased from 148 g m⁻² d⁻¹ to 294 g m⁻² d⁻¹, neither exhausted oxygen from the aggregate matrix during feeding period (111 g m⁻² d⁻¹) nor effluent dissolved oxygen (DO) concentration (2.8 mg/L) changed significantly, demonstrating that the oxygen transfer potential of the treatment system had not been exceeded. However, even though DO had not been exhausted, inhibition of nitrification was observed under high BOD loading. The loss of nitrification was attributed to excessive heterotrophic biofilm growth believed to induce oxygen transfer limitations or oxygen competition in thickened biofilms.     

Understanding the potential effects of water regime and salinity on recruitment of Melaleuca ericifolia Sm.

Although many emergent wetland plants may readily tolerate rapid changes in flooding and drying under freshwater conditions, their tolerance to dynamic water regimes may be compromised by salinity. Melaleuca-dominated woodlands occur naturally in Australia, south-east Asia and New Caledonia. Coastal wetlands dominated by Swamp paperbark (Melaleuca ericifolia) (Myrtaceae), native to south-east Australia, are commonly degraded as a consequence of altered water regime and salinity. This study simulates the release of M. ericifolia seeds from the aerial canopy under a range of water regime and salinity scenarios to determine conditions limiting sexual recruitment. Plant growth and survival were examined following seed release under two static water regimes (moist and flooded sediment) and two dynamic water regimes (simulated drawdown—“flooded-moist” and simulated re-flooding—“moist-flooded”). All water regimes, excluding the continuously flooded regime, were examined at three salinities: 0.1 dS m⁻¹ (fresh), 8 dS m⁻¹ and 16 dS m⁻¹, over a 50-day period commencing 44 days after the seeds were sown. The flooded treatment was examined at 0.1 dS m⁻¹ only, to confirm that flooding prohibits establishment of M. ericifolia. Seed and seedlings were positively buoyant and establishment was limited to moist soil. Flotation of seedlings in the flooded-moist treatment, however, did not inhibit subsequent establishment upon moist soil, even at the highest salinity of 16 dS m⁻¹. Growth, but not survival, was reduced by salinities of 8 dS m⁻¹ and 16 dS m⁻¹ in the moist treatment. Flotation of seedlings in saline water in the flooded-moist treatment did not reduce growth or survival compared with fresh water. Survival of seedlings in the moist-flooded treatment was lower in the freshwater and 16 dS m⁻¹ treatment compared with the moist treatment, but not at 8 dS m⁻¹. These findings suggest that water regime influences establishment of young M. ericifolia plants more strongly than does salinity, at least up to ∼1/3 seawater and in the short term (<2 months). Seedlings are likely to establish during a drawdown where the soil is exposed at salinities of ≤16 dS m⁻¹. In contrast, premature re-flooding of seedlings, even with fresh water, will compromise survival.     

Mountain cheese factory wastewater treatment with the use of a hybrid constructed wetland

This paper describes the activity period of an experimental hybrid wetland system placed in a cold climate region. The aim is to determine the efficiency of the system in reducing TSS, BOD₅, COD and other pollutants. The constructed wetland consists of a fat-removal unit and a basin for the storage and the distribution of the wastewater which precedes three phytoremediation beds: the first two are parallel and they work as submerged vertical flow wetland with gravel medium for an area of 180 m²; the last is a submerged horizontal flow wetland with sand medium and an area of 360 m². The CW was designed to process a total estimated BOD₅ loading rate of about 24 g m⁻² d⁻¹, which was less than half of the average actual loading rate. The wastewater treatment did not meet the required Italian law outflow limits, most likely due to BOD₅ overloading.     

Assessing constructed wetland functional success using diel changes in dissolved oxygen, pH, and temperature in submerged, emergent, and open-water habitats in the Beaver Creek Wetlands Complex, Kentucky (USA)

We assessed the functional success of restored wetlands by determining if the patterns in dissolved oxygen (DO), temperature, and pH were similar to those conditions observed in natural wetlands. The Beaver Creek Wetlands Complex consists of dozens of marshes and ponds built in a former Licking River floodplain, in the hills of east Kentucky, USA. In natural wetland ecosystems, aquatic primary production is highest in emergent and submerged vegetations zones; where daybreak dissolved oxygen (DO) is often near zero, and DO may rise to well over 100% saturation past mid-day. Open-water areas, dominated by phytoplankton, have less dramatic diel DO fluctuations—often without pre-dawn anoxia. Compared to open water, temperatures fluctuate less dramatically in vascular vegetation, due to shading and suppression of wind and waves. Measurements of ecosystem metabolism (diel changes in DO and pH) in three aquatic habitats of the constructed wetlands (emergent vegetation, submerged vegetation, open water) were compared to these natural ideals. In Beaver Creek Wetlands, water temperature patterns were not as dramatic as in natural habitats, nor did they did follow a similar trend. Waters in emergent vegetation (29.5 °C) were warmest; submerged vegetation coolest (26.5 °C); open-water intermediate (27.4 °C). Diel DO and pH patterns were not similar to natural habitats. Highest net primary production (NPP) and gross primary production (GPP) were measured in emergent vegetation waters (mean GPP = 7.58 g m⁻² d⁻¹); lowest in submerged vegetation (mean GPP = 5.48 g m⁻² d⁻¹); and intermediate in open-water (mean GPP = 6.95 g m⁻²d⁻¹). Diel pH changes were greatest in the highly productive emergent waters (median maximum daily difference of 0.36), and not as pronounced in submerged vegetation and open-water (median maximum change = 0.16 and 0.22, respectively). Water-column respiration was generally about double NPP. Like natural ecosystems, near anoxic DO concentrations were consistently measured in emergent and submerged plants before dawn; whereas open-water zones were generally >4 mg l⁻¹. These restored wetland systems may need more time to be functionally equivalent to natural marshes.     

Community metabolism and buffering capacity of nitrogen in a ruppia cirrhosa meadow

Fluxes of oxygen, inorganic nitrogen (DIN) and denitrification (isotope pairing) were measured from January 1997 to February 1998 via intact cores incubation in a shallow brackish area within the eutrophic Valli di Comacchio (northern Adriatic coast, Italy). Rates were measured in the light and in the dark in sediments colonized by the rooted macrophyte Ruppia cirrhosa and in adjacent sediments with benthic microalgae. Ruppia biomass (25-414 g DW m^− 2) exhibited a seasonal evolution whilst that of microphytobenthos (12-66 mg chl a m^− 2) was more erratic. Net (NP) and gross (GP) primary productivity was 1.15 and 6.89 mol C m^− 2y^− 1 for bare and 25.4 and 51.7 mol C m^− 2y^− 1 for Ruppia vegetated sediments. Nitrogen pools in Ruppia standing stock varied from 43.6 to 631.4 (annual average 201.2) mmol N m^− 2; the macrophyte N content was correlated with DIN concentration in the water column. Estimated N pool in microphytobenthos was one order of magnitude lower (from 2.4 to 14.5 mmol N m^− 2, annual average 7.2). Theoretical DIN assimilation calculated from NP was 127.8 and 1112.6 mmol N m^− 2y^− 1 whilst that calculated from GP was 765 and 2282 mmol N m^− 2y^− 1 for microphytobenthos and Ruppia respectively. Measured annual fluxes of DIN were 974.6 and − 577 mmol N m^− 2y^− 1 in bare and Ruppia vegetated sediments meaning that the two sites were a source and sink for DIN and that from 25 to 50% of Ruppia annual DIN requirements came from the water column. During the period of this study total denitrification was lower in the macrophyte colonized (92.3 mmol N m^− 2y^− 1) compared to bare sediments (163.3 mmol N m^− 2y^− 1) as a probable consequence of higher competition between denitrifiers and phanerogams. At both sites the ratio between denitrification of water column nitrate (D_W) and denitrification coupled to nitrification (D_N) was >1.6 due to little oxygen penetration in reducing sediments (< 1.2 mm) and scarce nitrification activity. D_W (0-35 µmol N m^− 2h^− 1) was significantly correlated with water column NO₃⁻  (2-16 µM). Theoretical DIN assimilation to denitrification ratio varied from 12.0 to 24.8 for Ruppia vegetated and from 0.8 to 4.7 for unvegetated sediments.At Valle Smarlacca, Ruppia may influence nitrogen cycling by incorporating large DIN pools in biomass which is scattered in surrounding areas and fuels intense bacterial activity. With increasing anthropogenic nutrient input and insignificant organic matter export in the open sea the already severe eutrophic conditions are enhanced and may accelerate the decline of the macrophyte meadow.     

Components of floating emergent macrophyte treatment wetlands influencing removal of stormwater pollutants

Floating treatment wetlands planted with emergent macrophytes (FTWs) provide an innovative option for treating urban stormwaters. Emergent plants grow on a mat floating on the water surface, rather than rooted in the bottom sediments. They are therefore able to tolerate the wide fluctuations in water depths that are typical of stormwater ponds. To better understand the treatment capabilities of FTWs, a series of replicated (n = 3) mesocosm experiments (12 × 0.7 m³ tanks using 0.36 m² floating mats) were conducted over seven day periods to examine the influence of constituent components of FTWs (floating mat, soil media, and four different emergent macrophyte species) for removal of copper, zinc, phosphorus and fine suspended solids (FSS) from synthetic stormwater. The presence of a planted floating mat significantly (P < 0.05) improved removal of copper (>6-fold), fine suspended particles (∼3-fold reduction in turbidity) and dissolved reactive P (in the presence of FSS) compared to the control. Living plants provided a large submerged root surface-area (4.6-9.3 m² of primary roots m⁻² mat) for biofilm development and played a key role in the removal of Cu, P and FSS. Uptake of Cu and P into plant tissues during the trials could only account for a small fraction of the additional removal found in the planted FTWs, and non-planted floating mats with artificial roots providing similar surface area generally did not provide equivalent benefits. These responses suggest that release of bioactive compounds from the plant roots, or changes in physico-chemical conditions in the water column and/or soils in the planted FTWs indirectly enhanced removal processes by modifying metal speciation (e.g. stimulating complexation or flocculation of dissolved fractions) and/or the sorption characteristics of biofilms. The removal of dissolved zinc was enhanced by the inclusion of a floating mat containing organic soil media, with reduced removal when vegetated with all except one of the test species. The results indicate that planted FTWs are capable of achieving dissolved Cu and Zn mass removal rates in the order of 5.6-7.7 mg m⁻² d⁻¹ and 25-104 mg m⁻² d⁻¹, respectively, which compare favourably to removal rates reported for conventional surface flow constructed wetlands treating urban stormwaters. Although not directly measured in the present study, the removal of particulate-bound metals is also likely to be high given that the FTWs removed approximately 34-42% of the turbidity associated with very fine suspended particulates within three days. This study illustrates the promise of FTWs for stormwater treatment, and supports the need for larger-scale, longer-term studies to evaluate their sustainable treatment performance.     

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.     

Performance evaluation and prediction for a pilot two-stage on-site constructed wetland system employing dewatered alum sludge as main substrate

Dewatered alum sludge, a widely generated by-product of drinking water treatment plants using aluminium salts as coagulants was used as main substrate in a pilot on-site constructed wetland system treating agricultural wastewater for 11 months. Treatment performance was evaluated and spreadsheet analysis was used to establish correlations between water quality variables. Results showed that removal rates (in g/m² d) of 4.6-249.2 for 5 day biochemical oxygen demand (BOD₅), 35.6-502.0 for chemical oxygen demand (COD), 2.5-14.3 for total phosphorus (TP) and 2.7-14.6 for phosphate (PO₄P) were achieved. Multiple regression analysis showed that effluent BOD₅ and COD can be predicted to a reasonable accuracy (R² = 0.665 and 0.588, respectively) by using input variables which can be easily monitored in real time as sole predictor variables. This could provide a rapid and cheap alternative to such laborious and time consuming analyses and also serve as management tools for day-to-day process control.     

Performance of a composite membrane bioreactor for the removal of ethyl acetate from waste air

Ethyl acetate removal from an air stream was carried out by using a flat composite membrane bioreactor. The composite membrane consisted of a dense polydimethylsiloxane top layer with an average thickness of 0.3 μm supported in a porous polyacrylonitrile layer (50 μm). The membrane bioreactor (MBR) was operated during 3 months, and a maximum elimination capacity of 225 g m⁻³ h⁻¹ at an empty bed residence time of 60 s was observed. Removal efficiencies higher than 95% were obtained for inlet loads lower than 200 g m⁻³ h⁻¹ and empty bed residence times as short as 15 s. The estimated yield coefficient, determined from the carbon dioxide production, resulted in 0.82 g dry biomass synthesized per gram of ethyl acetate degraded. No data of ethyl acetate treatment in MBR have been found in the literature, but the results illustrate that membrane bioreactors can potentially be a good option for its treatment.     

Stimulating denitrification in a stream mesocosm with elemental sulfur as an electron donor

The heavy use of fertilizers in agricultural lands can result in significant nitrate (NO₃⁻) loadings to the aquatic environment. We hypothesized that biological denitrification in agricultural ditches and streams could be enhanced by adding elemental sulfur (S^o) to the sediment layer, where it could act as a biofilm support and electron donor. Using a bench-scale stream mesocosm with a bed of S^o granules, we explored NO₃⁻ removal fluxes as a function of the effluent NO₃⁻ concentrations. With effluent NO₃⁻ ranging from 0.5 mg N L⁻¹ to 4.1 mg N L⁻¹, NO₃⁻ removal fluxes ranged from 228 mg N m⁻² d⁻¹ to 708 mg N m⁻² d⁻¹. This is as much as 100 times higher than for agricultural drainage streams. Sulfate (SO₄²⁻) production was high due to aerobic sulfur oxidation. Molecular studies demonstrated that the S^o amendment selected for Thiobacillus species, and that no special inoculum was required for establishing a S^o-based autotrophic denitrifying community. Modeling studies suggested that denitrification was diffusion limited, and advective flow through the bed would greatly enhance NO₃⁻ removal fluxes. Our results indicate that amendment with S^o is an effective means to stimulate denitrification in a stream environment. To minimize SO₄²⁻ production, it may be better to place S^o deeper in the sediment layer.