| 1. |
- Hladyz, Sally, et al.
(författare)
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Stream ecosystem functioning in an agricultural landscape : the importance of terrestrial-aquatic linkages
- 2011
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Ingår i: Ecosystems in a human-modified landscape. - San Diego : Academic Press. - 9780123747945 ; 44, s. 211-276
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Bokkapitel (refereegranskat)abstract
- The loss of native riparian vegetation and its replacement with non-native species or grazing land for agriculture is a worldwide phenomenon, but one that is prevalent in Europe, reflecting the heavily-modified nature of the continent's landscape. The consequences of these riparian alterations for freshwater ecosystems remain largely unknown, largely because bioassessment has traditionally focused on the impacts of organic pollution on community structure. We addressed the need for a broader perspective, which encompasses changes at the catchment scale, by comparing ecosystem processes in woodland reference sites with those with altered riparian zones. We assessed a range of riparian modifications, including clearance for pasture and replacement of woodland with a range of low diversity plantations, in 100 streams to obtain a continental-scale perspective of the major types of alterations across Europe. Subsequently, we focused on pasture streams, as an especially prevalent widespread riparian alteration, by characterising their structural (e.g. invertebrate and fish communities) and functional (e.g. litter decomposition, algal production, herbivory) attributes in a country (Ireland) dominated by this type of landscape modification, via field and laboratory experiments. We found that microbes became increasingly important as agents of decomposition relative to macrofauna (invertebrates) in impacted sites in general and in pasture streams in particular. Resource quality of grass litter (e.g., carbon : nutrient ratios, lignin and cellulose content) was a key driver of decomposition rates in pasture streams. These systems also relied more heavily on autochthonous algal production than was the case in woodland streams, which were more detrital based. These findings suggest that these pasture streams might be fundamentally different from their native, ancestral woodland state, with a shift towards greater reliance on autochthonous-based processes. This could have a destabilizing effect on the dynamics of the food web relative to the slower, detrital-based pathways that dominate in woodland streams.
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| 2. |
- Chauvet, Eric, et al.
(författare)
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Litter decomposition as an indicator of stream ecosystem functioning at local-to-continental scales : insights from the European RivFunction project
- 2016
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Ingår i: Large-scale ecology. - London : Academic Press. - 9780081009352 ; 55, s. 99-182
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Bokkapitel (refereegranskat)abstract
- RivFunction is a pan-European initiative that started in 2002 and was aimed at establishing a novel functional-based approach to assessing the ecological status of rivers. Litter decomposition was chosen as the focal process because it plays a central role in stream ecosystems and is easy to study in the field. Impacts of two stressors that occur across the continent, nutrient pollution and modified riparian vegetation, were examined at > 200 paired sites in nine European ecoregions. In response to the former, decomposition was dramatically slowed at both extremes of a 1000-fold nutrient gradient, indicating nutrient limitation in unpolluted sites, highly variable responses across Europe in moderately impacted streams, and inhibition via associated toxic and additional stressors in highly polluted streams. Riparian forest modification by clear cutting or replacement of natural vegetation by plantations (e.g. conifers, eucalyptus) or pasture produced similarly complex responses. Clear effects caused by specific riparian disturbances were observed in regionally focused studies, but general trends across different types of riparian modifications were not apparent, in part possibly because of important indirect effects. Complementary field and laboratory experiments were undertaken to tease apart the mechanistic drivers of the continental scale field bioassays by addressing the influence of litter, fungal and detritivore diversity. These revealed generally weak and context-dependent effects on decomposition, suggesting high levels of redundancy (and hence potential insurance mechanisms that can mitigate a degree of species loss) within the food web. Reduced species richness consistently increased decomposition variability, if not the absolute rate. Further field studies were aimed at identifying important sources of this variability (e.g. litter quality, temporal variability) to help constrain ranges of predicted decomposition rates in different field situations. Thus, although many details still need to be resolved, litter decomposition holds considerable potential in some circumstances to capture impairment of stream ecosystem functioning. For instance, species traits associated with the body size and metabolic capacity of the consumers were often the main driver at local scales, and these were often translated into important determinants of otherwise apparently contingent effects at larger scales. Key insights gained from conducting continental scale studies included resolving the apparent paradox of inconsistent relationships between nutrients and decomposition rates, as the full complex multidimensional picture emerged from the large-scale dataset, of which only seemingly contradictory fragments had been seen previously.
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| 3. |
- Mark, O., et al.
(författare)
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Application of hydroinformatics tools for water quality modeling and management : case study of Vientiane, Lao PDR
- 2010
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Ingår i: Journal of Hydroinformatics. - 1464-7141 .- 1465-1734. ; 12:2, s. 161-171
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Tidskriftsartikel (refereegranskat)abstract
- The application of hydroinformatics tools is restricted in developing countries due to the non-availability of the required data and information under local conditions. This paper presents the state of water quality of the city of Vientiane (capital of Lao PDR) before the extensive rectification of its drainage network and describes an approach and methodology for water quality modeling. This is done with respect to the application of a combined hydrodynamic/water quality model based on minimal input data and observations for model verification. It further evaluates options to improve the deteriorating water quality observed in the rectified channels associated with the absence of suitable wastewater treatment. Two pollutants associated with the enrichment of receiving water bodies by wastewaters, total-P and NH4-N, are modeled. The modelling study is carried out in three steps: dry weather flow simulation, wet weather flow simulation and nutrient modeling using MOUSE. The dry weather flow simulations are carried out to calibrate the model for hydraulic roughness coefficient, dispersion coefficient and travel time. The wet weather flow simulations analyze the effect on flooding of two channel states, namely unvegetated and vegetated conditions. Nutrient modeling therefore evaluates removal efficiency by the vegetation. Model results are compared with the observed data and recommendations are made with respect to the predicted effects of the water quality improvement schemes studied. In conclusion, the modeling approach herein presented can be applied for performance analyses of urban channels in the developing part of the world, where data are often limited.
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| 4. |
- Back, C, et al.
(författare)
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High-dosage treatment of a Quebec stream with Bacillus thuringiensis serovar. israelensis : efficacy against black fly larvae (Diptera, Simuliidae) and impact on nontarget insects
- 1985
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Ingår i: Canadian Entomologist. - 0008-347X .- 1918-3240. ; 117:12, s. 1523-1534
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Tidskriftsartikel (refereegranskat)abstract
- A typical lake outlet of the Canadian Shield was treated for 15 min with a high dose (5.28 g/L s−1 of discharge) of Teknar®, a commercial formulation of Bacillus thuringiensis serovar. israelensis. Efficacy on Simuliidae larvae and impact on non-target aquatic insects of this stream were monitored using drift nets, counting plates, and artificial turf substrates along a 1000-m section downstream of the site of application. Compared with a 4-day pre-treatment average for 12-h sampling periods, drift of Simuliidae increased from 64 to 92 ×, with shorter peaks of 133–184 ×, 2–6 h after treatment. There was no evident drift increase in larvae of Ephemeroptera, Plecoptera, Trichoptera, Chironomidae, or dipterous pupae, but larvae of Blephariceridae (Diptera) were severely affected as their drift was increased by up to 50 × and remained high for 3 days. After 30 h the mortality of Simuliidae on counting plates ranged from 95 to 82% in the first 300 m, with detachment rates of 78.5–46.5%. Densities of non-target insect larvae were not reduced on the artificial substrates, except for 2 genera of Chironomidae (Eukiefferella and Polypedilum) which were reduced 26 to 39% of their original density. Drifting larvae of 1 chironomid genus (Phaenopsectra) also showed symptoms of toxemia by B.t.i. The main impact of the treatment was thus seen in 2 Nematocera families (Chironomidae and Blephariceridae) which were mainly exposed to B.t.i. sedimented on the bottom of the stream or attached to periphyton growing on rocks.
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| 5. |
- Hart, J.R., et al.
(författare)
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The effects of vegetation on the hydraulic residence time of stormwater ponds
- 2014
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Ingår i: Proceedings of the 19th IAHR-APD Congress 2014, Hanoi, Vietnam.
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Konferensbidrag (refereegranskat)abstract
- Storm water ponds treat polluted run-off from urban areas, highways and agricultural land. Vegetation plays a key role in water treatment, but further understanding is required to identify how vegetation density and spatial distribution within a pond affect the residence time, an important parameter with respect to water treatment. This paper presents results from a preliminary study where the residence time distribution and discharge of a water treatment pond were measured at two stages within the vegetation’s seasonal growth cycle, representing the minimum and maximum states of the vegetation’s density. The results show clear and significant differences between the residence time distribution for the two cases, and highlight the need for further work on the topic.
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| 6. |
- Islam, Kamal Ziaul, et al.
(författare)
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Low cost rainwater harvesting : an alternate solution to salinity affected coastal region of Bangladesh
- 2014
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Ingår i: American Journal of Water Resources. - 2333-4819. ; 2:6, s. 141-148
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Tidskriftsartikel (refereegranskat)abstract
- This study investigated the prospect of rainwater harvesting as a low cost alternative potable water supply option along the coastal region of Bangladesh, which is considered as one of the most vulnerable countries in the world due to climate change and resulting sea level rise. Because of increasing salinity intrusion, potable water scarcity become severe at the south-western coastal region of the country. The study area for this investigation was Patkelghata in Satkhira district of Bangladesh located in the same zone. The Satkhira district averages nearly 1,710 mm rainfall per year. Based on rural housing pattern of the region, a rainwater harvesting system is proposed, which consists of roof catchment, gutters, down pipes, first flush devices, filter chamber and storage tank. The minimum catchment area was assumed to be 6 m2 and storage tank of 2000 liter capacity. Data was collected on the present state of freshwater supply, sources and quality, average rainfall in the region, dry spell period, family size, water use nature, rain water quality and material to be used for storage, etc. Rainwater quality was also tested and the parameters were found to be within Bangladesh’s standard limit. After a detail calculation, an approximate cost was assumed to be $171 for building and operation of the whole system. A questionnaire survey was also conducted on views and opinion of local people to understand the problems, prospects and the popularity of rainwater harvesting in Bangladesh.
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| 7. |
- Lacoursière, Jean O., 1958-
(författare)
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A laboratory study of fluid flow and microhabitat selection by larvae of Simulium vittatum (Diptera: Simuliidae)
- 1992
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Ingår i: Canadian Journal of Zoology. - 0008-4301 .- 1480-3283. ; 70:3, s. 582-596
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Tidskriftsartikel (refereegranskat)abstract
- Microhabitat selection by Simulium vittatum Zetterstedt larvae in a flume was studied at different mainstream velocities on two substrates; a thin flat plate parallel to the flow and a cylinder in cross flow. The results do not support the generally accepted assumptions that simuliid larvae keep within the boundary layer to avoid the direct influence of mainstream current and that they select the fastest velocity available when offered a longitudinal velocity gradient within their tolerance range. Instead, larvae gathered along the zone of boundary layer separation and remained along the stagnation line at the leading point of the cylinder when artificially positioned there. Further, under most conditions, larvae avoided zones of maximum surface shear stress. Larval reaction to hydraulic changes was immediate. It is hypothesized that S. vittatum larvae first scan the velocity profile at the substrate, initially moving toward increasing flow velocity (or water acceleration). They than cue on a steep velocity gradient along the body as part of the processes involved in choosing a location for suspension feeding.
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| 8. |
- Lacoursière, Jean O., 1958-, et al.
(författare)
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A small flume for studying the influence of hydrodynamic factors on benthic invertebrate behaviour
- 1990
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Ingår i: Journal of The North American Benthological Society. - 0887-3593 .- 1937-237X. ; 9:4, s. 358-367
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Tidskriftsartikel (refereegranskat)abstract
- A compact, versatile flume for studying the influence of hydrodynamic factors on the behaviour of benthic invertebrates is described. A range of lotic micro-environments can be simulated under controlled and replicable conditions by tailoring the velocity profile at the entrance of the test section. A specially designed diffuser composed of an array of adjustable horizontal rods allows tailored flow (e.g., zone of high shear stress, adjustable velocity gradient and turbulence level) to which organisms can be exposed. Water velocities of up to a maximum of 81.5 plus or minus 0.6 cm/s, with a turbulence intensity of 0.8% can be achieved. Simultaneous observations of flow and organism behaviours can be done by means of standard flow visualization techniques. Compact (72 cm long x 22 cm high x 10 cm wide; volume 10 L) and easily transportable, this flume is an inexpensive "desk-top" version of larger, more bulky systems, without sacrifice of performance and versatility.
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| 9. |
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| 10. |
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| 11. |
- Lacoursière, Jean O., 1958-, et al.
(författare)
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Fluid transmission and filtration efficiency of the labral fans of black fly larvae (Diptera: Simuliidae) : Hydrodynamic, morphological, and behavioural aspects
- 1993
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Ingår i: Canadian Journal of Zoology. - 0008-4301 .- 1480-3283. ; 71:1, s. 148-162
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Tidskriftsartikel (refereegranskat)abstract
- Body stance and water flow through the labral fans of suspension-feeding Simulium vittatum Zetterstedt larvae were examined using dead and live larvae. Transmission of flowing water through the fans were determined by means of dye injections. Feeding stance is the outcome of an active feedback process between flow forces and behavioural reactions that maintains the fans in an optimal filtering position. Fans responded to velocity increases through structural reconfiguration, which resulted in an increase in aperture size. As the velocity decreased, an increased fraction of the water directly approaching the fan aperture flowed around its perimeter, with no flow through the fans below 2.5 cm/s. Fluid transmission never exceeded 30-35%, even at velocities up to 50 cm/s. Calculations of suspension-feeding efficiency are reformulated to reflect labral fan transmission and behavioural components of the feeding process. Simulium vittatum larvae are consequently showed to be 4-26 times more efficient in filter feeding than has been previously assessed. The effect of flow on labral fan transmission is discussed in relation to known habitat choices and feeding behaviours of simuliid larvae.
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| 12. |
- Lacoursière, Jean O., 1958-, et al.
(författare)
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Laboratory study of the influence of water temperature and pH on Bacillus thuringiensis var. israelensis efficacy against black fly larvae (Diptera: Simuliidae)
- 1988
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Ingår i: Journal of the American Mosquito Control Association. - 8756-971X .- 1943-6270. ; 4:1, s. 64-72
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Tidskriftsartikel (refereegranskat)abstract
- An experimental formulation of Bacillus thuringiensis var. israelensis was used in the laboratory to assess the influence of water temperature and pH on the relationship between concentration, duration of exposure, and mortality of the northern black fly species Simulium decorum and Prosimulium mixtum/fuscum group. Mortality increases in both species with increases in duration of exposure, concentration, temperature and pH. Onset of death is shortened by increase in concentration and temperature. As temperature rises, the concentration of B. t. i required to induce mortality decreases; the sharpest decline occurring between 12 and 18 degree C for S. decorum , and between 4 and 8 degree C for P. mixtum/fuscum larvae. Lower pH induces a loss of efficacy of the B. t. i. formulation on S. decorum larvae at 4 and 12 degree C.
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| 13. |
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| 14. |
- Lacoursière, Jean O., 1958-, et al.
(författare)
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Short-term Maintenance System for Black Fly Larvae (Diptera: Simuliidae)
- 1987
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Ingår i: Journal of medical entomology. - 0022-2585 .- 1938-2928. ; 24:4, s. 463-466
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Tidskriftsartikel (refereegranskat)abstract
- A simple, readily transportable apparatus for maintenance of black fly larvae in the laboratory is proposed as an alternative to a full-scale rearing system. This compact apparatus of the compressed-air type can maintain dense populations of black fly larvae without time-consuming manipulation. Large numbers of Simulium venustum Say complex, Simulium decorum Walker, and Prosimulium mixtum Syme & Davies group larvae (> 1,200 larvae per liter) were maintained successfully at low temperature in our laboratories for 3 – 5 mo. Mortality rates for mid- to late instars of each of the three species were <5%. Large areas of removable substrate allow easy access to larvae. This system can be used in the field to transport larvae to the laboratory, where they can be maintained or reared to the adult stage.
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| 15. |
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| 16. |
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| 17. |
- Lacoursière, Jean O., 1958-, et al.
(författare)
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Use of the continuity principle to evaluate water processing rate of suspension-feeding mosquito larvae
- 1999
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Ingår i: Journal of the American Mosquito Control Association. - 8756-971X .- 1943-6270. ; 15:2, s. 228-237
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Tidskriftsartikel (refereegranskat)abstract
- Water processing rates of active suspension-feeding larvae of Culiseta morsitans and Cities quinquefasciatus 2nd and 4th instars were estimated through video image analysis of the conical jet flow driving the large recirculation patterns surrounding the organisms. In accordance with the principle of continuity, individual processing rates (PRs) were assessed by averaging a series of consecutive flow rates (Q(x)) defined as the product of the water velocity (U-x) and the associated cross-sectional area (A(x)) along a transect passing through the center of the delineated jet flow. Results clearly show very tight adherence to the principle of continuity. They also demonstrate that, although extreme care must be taken when streamtube delineation is performed, the methodology used can generate reliable assessment of individual processing rates regardless of the instars or species studied. The small coefficient of variation observed in assessing PR at the larval level further underlines the consistency of the method. Significant differences in water processing rates were observed for different species and instars. These could partially be related to body size, head width, and the length of the lateral palatal brushes (LPBs, which are the structures involved in the production of the water jet. Assessment of the jet velocity at the feeding groove level suggests the keg role of LPB beating frequency in the jet intensity, and consequently the magnitude of the processing rate. Analysis of data further indicates that obligate suspension feeders such as Cs. morsitans must sustain a larger flow pattern around the larvae to ensure sufficient particle entrapment than facultative suspension feeders (or even brushers) such as Cs. quinquefasciatus.
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| 18. |
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| 19. |
- Minh Tran, Thao, et al.
(författare)
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Capacity of Vitiver grass in treatment of a mixture of labaratory and domestic wastewaters
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this study, laboratory wastewater containing organic matters, heavy metals and aromatic compounds, was treated by vetiver grass (Vetiveria zizanioides) as a phytoremediation method to remove the above three groups of pollutants. Sewage effluent, as a source of nutrient supply for plant growth, was firstly fed to two wetland systems: mini horizontal subsurface flow (HSSF) and floating raft (FR) wetlands. Next, laboratory wastewater was added gradually to mix with sewage. Nominal hydraulic retention time in both wetlands are 12 hours. Pollutants removal efficiencies were monitored. Microbial community change corresponding with each stages of sewage only and mixture with laboratory wastewater was also examined. The examined microbial community includes Nitrogen-fixing (N-fixing) bacteria, Phosphate-solubilizing (P-solubilizing) microorganism, Pseudomonas sp., and Zoogloea sp. In HSSF wetland, base materials (gravel and sand), algae, and vetiver root were in turn investigated for pollutant removal efficiencies. The results reveal that even with the presences of heavy metals and aromatic compounds, vetiver presented reasonable removal efficiencies of about 62%, 68.6%, and 58.3% for BOD, TN, and TP removal, respectively. Base materials showed almost no effect on pollutant removal. Algae was slightly responsible for approximate 6.3%, 16.6%, and 19.7% of BOD, TN, and TP removals, respectively. On the other hand vetiver roots, in term of heavy metals, had an impressive removal efficiencies of 99.2, 95.8, 96.2, and 96.7% of Cr+6 (in K2Cr2O7), Mn (MnSO4), Fe (FeSO4), and Cu (CuSO4), respectively. For aromatic compounds, the wetland is responsible for 96.8 and almost 100% of correspondingly phenol and benzene removal efficiencies. For microbial aspect, N-fixing microorganisms (e.g. Azospirillum sp., Azotobacter sp.) and Phosphate-solubilizing bacteria (Bacillus sp.) increased gradually in population during domestic wastewater feeding stage. When laboratory wastewater was added, N-fixing and P-solubilizing bacteria were quantitatively decreased slightly while population of Pseudomonas sp. increased. Besides, Zoogloea sp. was also found increasing through out the experiment and keeping a stable growth even during laboratory wastewater adding. In FR wetland, both algae and vetiver root were also investigated for BOD and aromatic compounds and heavy metals. The outcomes show similar tendencies in treatment and microbial behaviours as in HSSF wetland. Vetiver grass, mainly responsible for organic matters and nutrients removal, presented slightly lower removal efficiencies than those in HSSF wetland. The average values of removal efficiencies are 59%, 63.5%, and 53.0% for BOD, TN, and TP removal, respectively. Algae, also, took minor responsibility for approximate 3.3%, 9.1%, and 8.9% of BOD, TN, and TP removals, respectively. Heavy metals of Cr+6 (in K2Cr2O7), Mn (MnSO4), Fe (FeSO4), and Cu (CuSO4) were found removing less than in HSSF wetland with average removal efficiencies values of 92.4, 85.1, 91.8, and 91.5%, respectively, by vetiver root. Algae show almost no effect on heavy metals and aromatic removals. The vetiver root likewise plays important role in phenol and benzene removals with values of 91.5 and 96% in efficiency, respectively. N-fixing and P-solubilizing microorganisms, Pseudomonas sp., and Zoogloea sp. presented similar responses tendencies to different living condition when domestic and laboratory wastewaters, in turn, were fed.
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| 20. |
- Tessier, Louis, et al.
(författare)
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Characterization of Hydropsyche slossonae (Trichoptera: Hydropsychidae) capture net polypeptides
- 2000
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Ingår i: Canadian Entomologist. - 0008-347X .- 1918-3240. ; 132:1, s. 59-68
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Tidskriftsartikel (refereegranskat)abstract
- A laboratory study on the sublethal effects of malathion on the net-spinning behavior of the caddisfly larvae Hydropsycheslossonae was conducted in order to assess the potential of net anomalies as an indicator of chronic exposure to organophosphorus insecticides. Two anomalies were identified after chronic exposure to 0.01, 0.05, 0.1, 0.5 and 1.0 μg l−1 malathion. The first was a distortion of the midline meshes where the normal diamond shape structure was disrupted and the meshes were separated by extra strands (called ‘midline’ anomaly). The second aberration observed was a significant decrease in net symmetry. Both anomalies were highly correlated to the toxic action of malathion, i.e. inhibition of the acetylcholinesterase enzyme (AChE). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses of capture nets did not show any modification of silk polypeptides after exposure to malathion, indicating that net distortions were not related to silk composition. Both anomalies seem to represent the symptoms of the specific toxic action of malathion; nevertheless, they can serve as an index of the physiological condition of the larvae, especially the midline anomaly. The symmetry of the nets decreased significantly after exposure to 0.5 and 1.0 μg l−1. However, the toxicity curves (EC50) showed that the sensitivity threshold for the midline anomaly ranged from 0.11 to 0.28 μg l−1, which reflect more realistic exposure to concentrations expected to occur in the field. Hence, the use of capture net anomalies of hydropsychid larvae could represent a valuable indicator of sublethal toxicity induced by malathion and other organophosphorus insecticides in running waters.
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| 21. |
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| 22. |
- Vought, Lena B. M., et al.
(författare)
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Nutrient retention in riparian ecotones
- 1994
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Ingår i: Ambio. - 0044-7447 .- 1654-7209. ; 23:6, s. 342-348
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Tidskriftsartikel (refereegranskat)abstract
- Nutrient retention mechanisms in riparian buffer strips are reviewed with emphasis on surface runoff and subsurface flows, the main pathways of exchanges between the stream and its surroundings. Unique physical and biogeochemical properties prevailing in these riparian ecotones dictate the flux of water, nutrients and other exogenous substances between the upland areas and the stream. Removal of nutrients from surface inflows is induced by deposition of sediment bound nutrients and exchange of dissolved nutrients with the soil/litter surface. Removal of nitrogen in subsurface flows can partly be explained by vegetation uptake, but the main mechanism for removal is usually denitrification. In channelized streams, the subsurface inflows have, in most cases, been altered to discharges via drainage tiles, with the exchange flows (water leaving and re-entering the open-channel via the stream bed and banks) being greatly decreased. Consequently, to improve nitrogen removal in these systems, these flows have to be intercepted or reestablished either through restoration of the old stream valley or through managed structures in the buffer strips.
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| 23. |
- Whelan, M. J., et al.
(författare)
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The behaviour of linear alkyl benzene sulphonate under direct discharge conditions in Vientiane, Lao PDR
- 2007
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Ingår i: Water Research. - 0043-1354 .- 1879-2448. ; 41:20, s. 4730-4740
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Tidskriftsartikel (refereegranskat)abstract
- Direct discharge of untreated sewage to surface waters is a common practice in many parts of the world. However, relatively little is known about the behaviour of synthetic organic pollutants under these conditions. This paper describes a sampling campaign designed to track changes in water quality in a surface water system in Vientiane (Lao PDR) receiving significant quantities of untreated waste water. The study was based on following in-channel transport using a fluorescent tracer injected as a pulse, with a focus on the anionic surfactant linear alkylbenzene sulphonate (LAS) and ammonia. Water samples were collected at a number of stations with sampling times estimated to coincide with solute time-of-travel. The reduction in LAS concentration with flow-time could be approximated by first-order kinetics with a half life of about 7 h. Free ammonia concentrations decreased more slowly than LAS and remained above the level believed to be toxic for sensitive aquatic species along the entire channel. Changes in the ratios of LAS alkyl chain homologues to total LAS concentrations suggest a preferential removal of longer chain lengths. The role of biodegradation in the removal of LAS was confirmed by the presence of LAS metabolites (sulphophenylcarboxylates, SPCs) which increased systematically (as a fraction of LAS remaining) with flow-time.
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