Lentic wetlands are usually regarded as the most important natural freshwater sources of methane (CH₄) and nitrous oxide (N₂O) to the atmosphere, and very few studies have quantified the importance of lowland streams in trace gas emissions. In this study, we estimated fluxes of CH₄ and N₂O in three macrophyte-rich, lowland agricultural streams in New Zealand, to place their trace gas emissions in context with other sources and investigate the value of minimising their emissions from agricultural land. All three streams were net sources of both gases, with emission of CH₄ ranging from <1 to 500 μmol m-² h-¹ and of N₂O ranging from <1 to 100 μmol m-² h-¹ during mid-summer. For CH₄, both turbulent diffusion across the surface and ebullition of sediment gas bubbles were important transport processes, with ebullition accounting for 20-60% of the emissions at different sites. The emissions were similar on a per area basis to other major global sources of CH₄ and N₂O. Although small on a catchment scale compared to emissions from intensively grazed pastures, they were significant relative to low-intensity pastures and other agricultural land uses. Because hydraulic variables (viz. depth, velocity and slope) strongly influence turbulent diffusion, complete denitrification can best proceed to N₂ as the dominant end-product (rather than N₂O) in riparian wetlands, rather than in open stream channels where N₂O fluxes are sometimes very large.

To assess possible adverse effects of residual chlorines from hypochlorite-treated seawater to non-target marine organisms, bioassays were carried out on marine amphipod Hyale barbicornis and estuarine fish Oryzias javanicus. Acute toxicity tests were first conducted using various concentrations of sodium hypochlorite (NaOCl) followed by a long-term exposure to residual chlorines from a test water treated with 1 mg L⁻¹ NaOCl. Results showed that NaOCl was acutely toxic to both organisms. However, long-term exposure to residual chlorines from NaOCl-treated waters caused no major adverse effects to both organisms under laboratory conditions since free chlorines in the treated water was reduced to about 10% by 23-h holding and 1-h aeration. No H. barbicornis died but residual chlorine-exposed juveniles had significantly shorter body lengths at the end of exposure. Residual chlorine-exposed O. javanicus also showed no significant differences to that of the control in all measured endpoints except for hatching time. The results suggest that using 1 mg L⁻¹ NaOCl for disinfection of ballast waters will produce residual chlorines that is far below the LC50 and EC50 of H. barbicornis and O. javanicus even on a long-term basis.

Predicting the environmental effects of de-icing salt requires knowledge of the pathways taken by salt from on-road application through spread to the surroundings to deposition and fate in the roadside environment. This study described differences in chloride deposition and distribution in soil with increasing distance from the road by means of field observations and modelling. The dynamic modelling approach successfully represented the spread of de-icing salt from road to surroundings, deposition in the roadside environment and the subsequent infiltration into roadside soil. The general decrease in soil chloride content with distance from the road was described by differences in salt deposition, soil physical properties, vegetation properties and snow characteristics. The uncertainty in model predictions was highest in areas close to the road due to a complex combination of high salt deposition, snow-ploughed masses and road runoff. The exponential decline in salt deposition with distance from the road could not be justified close to the road. Different types of field investigations were applied in a calibration procedure to establish reasonable ranges for the most influential model parameters. Measured electrical resistivity reflected well the changes in simulated chloride content in soil during winter and spring when chloride concentrations were high. However, during summer or periods with low chloride concentrations the measured resistivity was substantially lower than simulated values, as it reflected the total contamination level in soil.

A coagulation treatment study was conducted using both natural (sago and potato flour) and commercial (poly aluminum chloride and aluminum sulfate) coagulants in semiconductor wastewater. The effects for settling time and dosage of the coagulants as well as their interactions on the reduction of chemical oxygen demand (COD) and turbidity were investigated using a three level factorial design, Response Surface Methodology (RSM). Sago concentration showed more influence on the COD and turbidity reduction than settling time, with concentrations lower than 1.5 g L⁻¹ giving the better reduction. The interaction of settling time and concentration on the COD and turbidity were observed when using potato starch. Concentrations higher than 1.5 g L⁻¹ potato starch reduced the COD and turbidity better. The polyaluminium chloride and ammonium sulphate revealed that lower concentrations (0.02-1.0 g L⁻¹) and longer settling time (30-60 min) gave the greatest reduction in COD and turbidity.

A study on perchlorate distribution was conducted in male adult prairie voles (Microtus ochrogaster). Excretion via urine was the major pathway for perchlorate fate in the body, with the highest concentrations of perchlorate detected in urine after exposure to perchlorate through drinking water [250 μg/ml Mg(ClO₄)₂], and an average of 34% and 88% of perchlorate intake recovered in urine in the 4- and 8-h exposure groups, respectively. Perchlorate mass in kidney, thyroid, blood, and urine were related to perchlorate intake (254.5-2687.7 μg). Perchlorate excretion and depuration patterns via urine were tested further using male adult deer mice (Peromyscus maniculatus). Animals were exposed to perchlorate through dosed drinking water (0, 17, 165, and 1600 ng/ml). Perchlorate concentrations in urine showed a significant difference among the three dosed groups during a 28-day exposure period. However, no difference was found in urine among the three dosages in terms of mass percentage of perchlorate intake from water at each sampling time over the 28-day exposure period. Both concentrations of perchlorate and mass percentage in urine reached a steady state after 1 day in all treatments. On average 46%, 46%, and 61% of perchlorate intake from water was recovered in urine over the exposure period in high, medium, and low dose groups, respectively. Including perchlorate consumption from rodent chow (1.44 ng/g), less than 46% of perchlorate intake was recovered in urine in the high and medium dose groups, and <61% in the low dose group. Three parameter first-order decay models fit the depuration curve very well, with r > 0.99 in both the low and high dose groups; half-lives of perchlorate in deer mice were estimated as 9.12 and 7.25 h in the low and high dose groups, respectively. Endogenous generation of perchlorate and/or some degree of retention or metabolism of perchlorate may occur in deer mice, based in part on the uncompleted mass balance in the excretion and depuration experiments. The data reported herein should provide additional insight for perchlorate fate determination in animals and humans and valuable information for perchlorate risk assessment in the environment, especially wildlife.

Water resources are threatened globally and declining water quality is primarily due to stormwater, agricultural, urban, and mining runoffs. Steamboat Creek in Nevada is the largest non point source (NPS) of pollution to the Truckee River. Treatment wetlands are a cost-effective and reliable technique to control NPS pollution, therefore, a large-scale wetland along Steamboat Creek has been proposed as a component of a regional watershed restoration plan. This study used ten parallel pilot-scale wetland mesocosms, and tested the effects of drying and rewetting, hydraulic retention time (HRT), and high nitrogen loading on the efficiency of nutrient and total suspended solids (TSS) removal. Drying and rewetting produced noticeable effects on nutrient retention, but the effect was short-lived. During longer HRT period nutrient removal in manipulated mesocosms with an 8 h HRT were higher than controls with a 4 h HRT. Reducing the HRT from 4 h to 30 min further decreased nutrient interception. During increased influent nitrogen loading (9.5 ± 2.4 mg l⁻¹), manipulated mesocosms functioned as sinks for total nitrogen (TN) with removal efficiency increasing from 45 ± 13% to 87 ± 9%. The average change in TN concentration was 9.1 ± 2.2 mg l⁻¹. Drying/rewetting and varying HRT influenced total phosphorus (TP) and TSS similarly, and TP removal was associated with TSS removal. Results can help make decisions regarding wetland construction, management, and operation more effective in order to reduce nutrient loads to the Truckee River.

An investigation was made into a novel system aimed at reducing the impact of highly polluting wastewaters, and based on the combined action of catalytic oxidation and microbial biotechnology. The experimental part incorporated the following three schemes: chemical treatment using Fenton's reaction for a single process (stage 1); biological treatment only (stage 2); and chemical oxidation followed by biological treatment (stage 3). Wastewaters with 2-mercaptobenzothiazole (MBT; 7,200-7,400 mg O₂ l⁻¹) were oxidized by stoichiometric amounts of dilute hydrogen peroxide (35%) in the presence of water soluble iron catalysts, either Fe (II) or Fe (III), at concentrations up to 1% w/w and above. As a result, transformation by chemical means of recalcitrant organics to more easily attackable end-products occurs, that can subsequently undergo conventional or advanced (microflora and biomass dispersed or adhered) biological treatments, with 90% of chemical oxygen demand abatement and 95% of MBT.

The effect of aeration rate on nutrient removal from slaughterhouse wastewater was examined in two 10-L laboratory-scale sequencing batch reactors (SBRs--SBR1 and SBR2) operated at ambient temperature. The contaminants in the slaughterhouse wastewater had average concentrations of 4,000 mg chemical oxygen demand (COD) L⁻¹, 350 mg total nitrogen (TN) L⁻¹ and 26 mg total phosphorus (TP) L⁻¹. The duration of a complete SBR operation cycle was 8 h and comprised four operational phases: fill (7 min), react (393 min), settle (30 min) and draw/idle (50 min). During the react phase, the reactors were intermittently aerated four times at 50-min intervals, 50 min each time. DO, pH and oxidation-reduction potential (ORP) in the reactors were real-time monitored. Four aeration rates--0.2 L air min⁻¹ in SBR1 for 70 days, 0.4 L air min⁻¹ in SBR1 for 50 days, 0.8 L air min⁻¹ in SBR2 for 120 days and 1.2 L air min⁻¹ in SBR1 for 110 days--were tested. When the aeration rate was 0.2 L air min⁻¹, the SBR was continuously anaerobic. When the aeration rate was 0.4 L air min⁻¹, COD and TP removals were 90% but TN removal was only 34%. When the aeration rates were 0.8 and 1.2 L air min⁻¹, average effluent concentrations were 115 mg COD L⁻¹, 19 mg TN L⁻¹ and 0.7 mg TP L⁻¹, giving COD, TN and TP removals of 97%, 95% and 97%, respectively. It was found that partial nitrification followed by denitrification occurred in the intermittently aerated SBR systems.

The direct spectrophotometric analysis of aqueous nitrates is a simple analytical procedure but prone to interferences. A twelve-month study of the Preakness Brook in Wayne Township, New Jersey demonstrated that two wavelength, three wavelength, and second derivative calculation methods provide very different results from the same ultraviolet absorption spectrum. On average, the two wavelength and second derivative methods yielded the same concentration at each sample point over the entire study period. These methods provided concentration results closest to those obtained by ion chromatography and significantly lower than the three wavelength computation method. The degree of variation between the different computation methods was not consistent as it rose with increasing absorbances at wavelengths associated with interfering compounds. This variation was especially pronounced between May and August.

This paper presents an improved version of a general, process-based mass-balance model (LakeMab/LEEDS) for phosphorus in entire lakes (the ecosystem scale). The focus in this work is set on the boundary conditions, i.e., the domain of the model, and critical tests to reveal those boundary conditions using data from a wide limnological range. The basic structure of the model, and many key equations have been presented and motivated before, but this work presents several new developments. The LakeMab-model is based on ordinary differential equations regulating inflow, outflow and internal fluxes and the temporal resolution is one month to reflect seasonal variations. The model consists of four compartments: surface water, deep water, sediment on accumulation areas and sediment on areas of erosion and transportation. The separation between the surface-water layer and the deep-water layer is not done from water temperature data, but from sedimentological criteria (from the theoretical wave base, which regulates where wind/wave-induced resuspension of fine sediments occurs). There are algorithms for processes regulating internal fluxes and internal loading, e.g., sedimentation, resuspension, diffusion, mixing and burial. Critical model tests were made using data from 41 lakes of very different character and the results show that the model could predict mean monthly TP-concentrations in water very well (generally within the uncertainty bands given by the empirical data). The model is even easier to apply than the well-known OECD and Vollenweider models due to more easily accessed driving variables.