Browsing by Author "Gomes, P. I. A"

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Open Access
Assessment of pollution sources, fate of pollutants, and potential instream interventions to mitigate pollution of earthen canals of urban to rural-urban fringe
(Springer International Publishing, 2019-11) Gomes, P. I. A; Fernando, B. A. V. W; Dehini, G. K
Three representative earthen canals from urban, peri-urban, and rural-urban fringe of Sri Lanka were studied for a 2-year period against different seasons to capture insights important in ecological rehabilitation. Only the canal from rural-urban fringe showed a better water quality in wet season; elucidating, the impact of contaminated catchment runoff in the other canals. At a given sampling session, one or two peaks (relative maxima) were observed in urban and peri-urban canals for pollution representative parameters such as nitrate nitrogen and soluble reactive phosphorus. Those peaks were highly localised, an indication of poor advection. In general, two-dimensional variations of electrical conductivity and turbidity in dry season were uniform in urban and peri-urban canals, an indication of dominant molecular diffusion. This was further evidenced via physical models for different flow stages (low, high, and bankfull). Therefore, fate of contaminants had to be mainly governed by assimilation via sediments. However, grey water footprint analyses showed urban and peri-urban canals have over utilised the natural assimilation capacity of many water quality parameters by several folds. This study proved the importance of inducing attenuation by instream physical heterogeneity similar to natural streams or naturalised canals such as the canal from the rural-urban fringe of this study.
Open Access
Comparison of Cell-In-Series and Meso-Scale Physical Habitat Sampling for the Interpretation of Spatiotemporal Variation of Stream Water Quality
(IAHR-HK Student Research Forum, 2012-11-17) Gomes, P. I. A; WAI, O. W. H
Although scale dependence of ecological patterns is conceptually recognised, the studies involving quantitative assessments are rare and rudimentary. Here we evaluate spatiotemporal variation of water quality using two sampling scales (approaches): cell-in-series (CIS) and meso-scale physical habitats (MPH). CIS has its origins in probabilistic sampling and relatively simple. It also reported to be suitable for streams with advective transport. MPH approach is relatively novel for water quality assessments and it considers medium scale morphological units such as pools, riffles, glides, etc. for sampling. Sampling was carried out in the short and steep Tseng Lan Shue stream, during Spring and Summer of 2012. The stream is subject to regulation and various anthropogenic inputs, but with irregular occurrence. For each season, observations were carried out during periods with no influence of severe weather events (typical state) as well as after a rainfall (flushed state). The response variables including water chlorophyll, turbidity, dissolved oxygen, nitrate, nitrite, ammoniacal nitrogen and soluble reactive phosphorous were checked against a set of hydro-environmental variables. These included: stream velocity, width, depth, and slope, bankfull dimensions, and substrate conditions. Relationships among variables were evidenced using redundancy analysis. In general, the water quality parameters showed an irregular variation in the longitudinal direction of the stream. Response and hydro-environmental variables based on two best axes showed a 41% of variance in spring response data in the MPH approach. For CIS it was around 44%. But in flashed floods these were observed to be 60% and 35 % for MPH and CIS, respectively. Similar trend was observed in summer where explanatory power based on CIS was higher for typical state but otherwise for the flashed state. Furthermore, significant environmental variable(s) for respective cases changed with the scales being used: substrate conditions for CIS and stream width and slope for MPS. This study shows that MPH approach is more suitable than CIS as a modelling tool when the stream has less anthropogenic loads. We conclude that the explanatory powers of the MPH and CIS scales (approaches) could be useful in providing a quantitative definition on identifying a “pristine stream”.
Open Access
Concrete lined urban streams and macroinvertebrates: a Hong Kong case study
(Springer US, 2020-02) Gomes, P. I. A; Wai, O. W. H
In this study an urban stream network with earthen and concreted sections were studied for different seasons (wet and dry) to investigate the macroinvertebrate composition and the governing factors. The factors considered were water quality (nitrogen species, soluble reactive phosphorus etc.) and stream eco-hydraulics (velocity, wetted depth and width, vegetative indicators, number of mesoscale physical habitats, etc.). In contrast to common perception, results showed that concrete lined sites are not ecologically dead. Even though low, concrete line section had viable populations of macroinvertebrates and importantly a few native species. Interestingly, some macroinvertebrate indices of the concrete lined sites did not show a significant difference with the earthen sites. About 60% of the macroinvertebrates were grazers and filterers, and these two group populations always showed an inverse relationship. Earthen and concrete lined sites had similar diversities, but for different reasons. In general earthen sites diversity and pollution tolerance index of macroinvertebrates (PTI) was positively correlated, but no uniform correlation was observed in concrete lined sites. Some concrete lined sites with high diversity showed low PTIs (i.e. high diversity as a result of many types of pollution tolerant species) whereas in some the high diversity associated with high PTIs. Macroinvertebrate composition and the influencing factors were to a greater degree section dependent and to a lesser extent were dependent on the season. Physical heterogeneity played an important role in the macroinvertebrate responses in earthen sites. Water quality and flow rate explained comprehensively, the variations in the concrete lined sites. Results proved that nutrient levels need to be limited and instream heterogeneity needs to be improved to enhance diversity and populations of pollution intolerant species. Also, controlled vegetation harvesting is recommended in contrast to the current practice of complete removal for flow conveyance.
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Condominium price dynamics in Sri Lanka: correlation with inflation and periods of concern
(Routledge, 2020-05-03) Gomes, P. I. A; Yathushan, V
This study conducted in Sri Lanka’s commercial capital – Colombo, investigated temporal variation of condominium prices from 1998 to 2018, to identify price – inflation relationships and periods of concern. The price increased non-linearly with time without abnormal trends. Unit root, cointegration and vector error correction method tests showed inflation can explain temporal variation of semi-luxury condominium’s price appreciation, and it showed a statistically significant (P < 0.01) positive impact in the long run. Price appreciation and inflation showed a weak negative, yet statistically significant impact for luxury condominiums. The impact of inflation on price appreciation in the short run was mostly a negative correlation and as per explanatory powers the impact was minor. It seemed that Sri Lankan condominium market would mostly be without any periods of concern considering the increasing presales and the decreasing price to rental ratios. However, there is a continuous increment of the ratio between the price and household annual income, and it was about 5.25 as at 2018 (price bubbles occurred when this ratio is over six). More studies are recommended specially on future periods of concern and studies that incorporate ultra-luxury apartments being developed by international developers.
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The deflectors influence on flow complexity, bed morphology, sediment transport and water quality of urban lotic waters - A laboratory study
(wiley, 2022-11-25) Sooriyaarachchi, D. T. A; Gomes, P. I. A
In this laboratory study different combinations of bed (sand, pebble gravel [gravel], and a mix of sand and gravel) and flow (typical and overtopping) were experimented with to investigate the impact of porous deflectors in flow diversity, water quality, and fish performance in prismatic open channels. Deflectors changed the gradually varied flow to a rapidly varied flow, as a sudden change in the water depth was observed at the deflectors, and this change was large for smooth beds. With the presence of gravel, the scouring near the downstream deflector was almost twice that of the sand bed, and with the scouring at its own upstream deflector, irrespective of whether the flow was typical or overtopping. This behavior was a result of sand mobilization due to shear stress and sand mobilization aided gravel transport. The mixed bed showed less gravel movement compared to the gravel-only bed. The percentage of sediment washed out was minor for all bed scenarios, indicating that sediment transport was local. Relative to the sand bed without deflectors (representing a typical urban canal), deflectors resulted in reduced and improved water quality (in terms of sediment load) for sand, and mixed bed, respectively. The fishes found refuge and were comfortable in the pool areas created by deflectors unlike in channels without deflectors where they showed exhaustion
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Deflectors to introduce heterogeneity to canals
(2017 6th National Conference on Technology and Management (NCTM, SLIIT, 2017-01-27) Randima, W. A. H; Wijethilaka, M. A. D. K; Kumara, G. H. V. S; Gomes, P. I. A
Canals are manmade lotic water systems constructed for flood control, navigation, irrigation, etc. In general, canals are eco-hydrologically homogeneous. As such, a canal might have the same prismatic cross section and an even bed profile along its course. Such characteristics do not support rich biota, something a sustainable society expects. Several past studies have attributed heterogeneity to be an important factor for a healthy stream. In this study the deflectors were used to introduce the heterogeneity in canals. In tandem studying flow complexity by deflectors, their role with respect to sediment (sand) and seed transport, and fisheries were also studied. The model canal's (laboratory flume) homogenous velocity of 0.4 m/s changed to a range of values from 0.1 to 0.7 m/s after placing deflectors. Similarly, water depth changed from a uniform 30 mm to a range from 20 mm to 70 mm. This resulted in formation of flow patches similar to flow patches formed by meso-scale physical habitats such as pools and riffles. Sediment deposition was patchy and seemed to be stable as only a minor bedload movement was observed for prolonged durations. This meant it is possible to achieve a quasi-equilibrium state in field canals where upstream brings sediments. Seed trapping was weak for floating type seeds, whereas non-floating seeds managed to get deposited with sediment. Fishes quickly migrated to the pool like areas that resulted from deflectors. The results suggested the role of deflectors in transforming a homogenous channel to heterogeneous channel that has the potential to have rich biota which is essential in ecological rehabilitation works.
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Deriving optimal hydraulic, water quality and habitat quality criteria against a predefined reference state of urban canals via an analytical method: Implications on ecological rehabilitation
(Elsevier, 2022-09) Gomes, P. I. A; Dehini, G. K
The aim of this study was to showcase derivation of numerical ranges of important environmental variables (hydraulics, water quality and habitat quality) for a predefined reference state of canals in an area where ecological rehabilitation is sought. The reference state was defined based on pollution tolerance index (PTI) of macroinvertebrates. From data collected for two years from three canals with varying levels of pollution for different seasons, detrended correspondence and redundancy analysis ordination plots revealed moderate to weak spatiotemporal gradients. Relationships were built via multiple linear regression (MLR) and by linear or quadratic bivariate models. MLR models managed to explain over 70% of the PTI variation and was significant at P < 0.1. Solving single parameter models with co-efficient of determination >0.3 and P < 0.1 with a targeted PTI of 11, gave season dependent feasible solutions and were mostly hydraulic and habitat quality variables. Out of 24 environmental variables, dry and wet seasons gave 15 and eight feasible solutions, respectively. This study validated the importance of certain environmental variables that are debatable in the context of a healthy stream (e.g., mesoscale physical habitats), showed instances where hydraulics became the defining factor of stream health, and also provided pros and cons of a widely discussed method in ecological rehabilitation.
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Do sediments of ephemeral and perennial streams show different impacts on water quality when subjected to the same drying conditions?
(Wiley Online Library, 2021) Gomes, P. I. A; Perera, M. D. D
Empirical evidence was studied to investigate whether ephemeral stream sediments have redeeming biological and physical attributes with respect to water quality, via a laboratory mesocosm study simulating stagnant pooled conditions in ephemeral and perennial streams. In addition to stream type, the effect of sediment quantity variation (sediment to water ratio) was also studied. From the water quality parameters tested (electrical conductivity, dissolved oxygen, pH, nitrogen species and phosphate), only electrical conductivity showed a significant difference between the two stream types irrespective of sediment to water ratio. However, the temporal water quality of a given stream type changed with sediment quantity in the mesocosm. Re-flooding of mesocosms after complete drying did not result in blackwater conditions, but a similar spike in nutrient concentration was observed in both stream types. The absence of blackwater was attributed to the lack of addition of new organic matter and litter, as well as the saturation of dissolved oxygen in mesocosms, therefore, indicating that aeration and litter control could be used as mitigation methods for blackwater events. It was evident that water quality variations in ephemeral streams are purely based on the flow regime (hydrological flow conditions) and organic loading. No evidence was found for any unique biological and physical properties of ephemeral sediment that redeem water quality.
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Eco‐hydraulic evaluation of herbaceous ecosystems below headwater dams without a base flow: Observing below dam reaches as new stream sources
(Wiley Online Library, 2017-01) Gomes, P. I. A; Wai, O. W. H; Yan, X. F
The roles of headwater streams are usually underestimated and inadequately managed compared with the larger downstream river systems. This two and half-year study covering several wet and dry seasons evaluated the impacts of small headwater dams without a base flow on downstream herbaceous dynamics. Results showed herb aerial cover and diversity below dams (new stream sources) are unique and different to original stream sources as well as to a comparable unregulated reach. The geomorphological habitats formed subsequent to damming did not show major influence on aerial cover of herbs; nevertheless, diversity showed a clear dependence. Downstream of dams were dominated by Acorus gramineus, which had >40% aerial cover, and this figure increased up to 60% within 2 years (in between a major flood event). Simultaneously, downstream herb diversity decreased by 33%. However, diversity and aerial cover of the unregulated reach and original sources remained more or less the same. Herb pulling tests (simulating an uprooting mechanism during a flood) showed A. gramineus can withstand an eightfold higher force than the other herbs, especially in concrete surfaces and rock/sand pools. The estimated shear force on bed during the major flood was several folds less than the observed. This suggests downstream of dams behave opposite to the conventional understanding that large floods are considered as an agent of restoration.
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Ecohydrologic structure and function of stream networks with earthen upstream and concrete-lined downstream
(Wiley Online Library, 2019-06) Gomes, P. I. A; Wai, O. W. H
Concrete-lined streams are one of the most extreme forms of river regulation. This study investigated an urban stream network with concrete-lined (C) and earthen (E) sections. The C sections were positioned downstream of the E sections. This abrupt change of stream type due to concrete lining was compared with the predictions of river continuum concept and process domain concept. River continuum concepts predictions on the macroinvertebrate functional feeding group fractions against stream order and energy sources showed disagreements in this study. Furthermore, other than abundance of pollution intolerant species variation, most of the species responses did not support the process domain concept predictions. Correlations between explanatory variables (stream hydraulics or water quality) and response variables (macroinvertebrate composition and vegetation) observed to be dependent on stream lining and seasons. Stream discharge showed positive correlations with the pollution representative species in both section types but was more obvious in C sections. Water budget estimations showed that wastewater accounted for at least 5% of stream discharge of the C sections in the dry season. pH was the most important and significant water quality parameter of the C sections. Against expectations, nitrogen species and soluble reactive phosphorus did not have a major impact on species variables. Hydraulic variables that represented stream heterogeneity were more useful in explaining species variables of the E sections. Similar explanatory powers by the hydraulics and water quality variables of the C sections demonstrated the importance and interdependency of stream hydraulics and water quality in rehabilitating of this unique ecosystem.
Open Access
A geo-spatial database about the eco-environment and its key issues in South Asia
(Taylor & Francis, 2018-07-03) Li, A; Deng, W; Zhao, W; Liu, B; Zhang, J; Kong, B; Nan, X; Bian, J; Koirala, H. L; Gilani, H; Sati, V. P; Gomes, P. I. A; Khanal, N. R
The South Asia has high variability ingeographical features, climate,and landscapes. With the rapid economic development and populationgrowth, the increased pressure on natural resources, land degradation,water crisis, and climate change become the common concerns for thecountries in the region. To get a deep and general idea about the landand water natural resources and environment in South Asia, a knowl-edge database was constructed based on the climatic condition, landuse/cover, water resources, water disasters, and geohazards. The resultspresented a scientific insight regarding the spatio-temporal changingpattern of the eco-environmental components in this region. Riskassessments were performed for thefloods, droughts, and geohazardswhich occurred with a high frequency. In general, the big knowledgedatabase established in this study would be helpful to aid the devel-opment of future policies and programs (like the Belt and RoadInitiative) for environmental issues adaptation in the region, includinginitiatives for regional cooperation and capacity building in naturalresources and environment management
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Impact of calcium and magnesium on growth and morphological acclimations of Nitella: implications for calcification and nutrient dynamics
(Taylor & Francis, 2010-12-01) Gomes, P. I. A; Asaeda, T
The impact of calcium (Ca) and magnesium (Mg) on the growth and morphology of a Charophyte, Nitella pseudoflabellata, and the influence of Mg on calcification and phosphorous (P) speciation were studied in laboratory experiments for variable concentrations (≤q120 mg · L−1) of Ca and Mg. It was clearly identified that Mg aided shoot elongation. An increase in Ca concentrations produced intensified shoot elongation also, but at a lesser rate than the equivalent levels of Mg. Depending on the availability of Ca and Mg, the morphological appearance differed significantly, suggesting significant levels of ecoplasticity. Furthermore, Mg was observed to produce less calcite encrustation. Plant P-speciation suggested a higher Mg concentration corresponding to a more water-soluble and less carbonate-bound P fraction. This indicates that upon senescence and decomposition, a large fraction of P is supplied to the water column; ultimately behaving similar to a typical vascular plant.
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Impact of increased instream heterogeneity by deflectors on the removal of hydrogen sulfide of regulated urban waterways—A laboratory study
(Wiley Online Library, 2021-03) Gomes, P. I. A; Samararatne, S.; Wai, O. W. H; Perera, M. D. D
Laboratory experiments were conducted to test the hypothesis that increase in physical heterogeneity by deflectors would improve the water quality of urban regulated (straight and prismatic) waterways. Deflectors changed the near-uniform flow to a rapidly var-ied flow, as such the depth, velocity, and Froude number (Fr) variations were four, 10, and 14 times more than the without deflector scenario, respectively. Removal of hydro-gen sulfide (H2S), the main focus of the study, was significantly high when deflectors were placed in the laboratory urban waterway. Introduction of a sediment bed further improved H2S removal; however, in this case turbidity and color were significantly high too. These observations endorse the fact that attenuation induced by deflectors and assimilation promoted by the sediment bed aids the H2S removal. These facts were fur-ther strengthened by the significant strong negative correlations H2S made with DO and pH for all experiments. Further studies are recommended for different deflector orientations and modified sediment beds (e.g., mixture of sediment and gravel), identi-fication of localized water quality hot spots to capture spatial variation of water quality, and impact of increased heterogeneity on flood safety
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In‐stream physical heterogeneity, rainfall aided flushing, and discharge on stream water quality
(Water Environment Federation, 2015-08) Gomes, P. I. A; Wai, O. W. H
Implications of instream physical heterogeneity, rainfall-aided flushing, and stream discharge on water quality control have been investigated in a headwater stream of a climatic region that has contrasting dry and wet seasons. Dry (low flow) season's physical heterogeneity showed a positive correlation with good water quality. However, in the wet season, physical heterogeneity showed minor or no significance on water quality variations. Furthermore, physical heterogeneity appeared to be more complementary with good water quality subsequent to rainfall events. In many cases stream discharge was a reason for poor water quality. For the dry season, graywater inputs to the stream could be held responsible. In the wet season, it was probably the result of catchment level disturbances (e.g., regulation of ephemeral freshwater paths). Overall, this study revealed the importance of catchment-based approaches on water quality improvement in tandem with in-stream approaches framed on a temporal scale.
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Integrating vegetation indices and geo-environmental factors in GIS-based landslide-susceptibility mapping: using logistic regression
(Springer, Cham, 2022-02) Abeysiriwardana, H. D; Gomes, P. I. A
This study aimed to assess the potential of in-situ measured soil and vegetation characteristics in landslide susceptibility analyses. First, data for eight independent variables, i.e., soil moisture content, soil organic content, compaction of soil (soil toughness), plant root strength, crop biomass, tree diameter at knee height, Shannon Wiener Index (SWI) for trees and herbs was assembled from field tests at two historic landslide locations: Aranayaka and Kurukudegama, Sri Lanka. An economical, finer resolution database was obtained as the field tests were not cost-prohibitive. The logistic regression (LR) analysis showed that soil moisture content, compaction of soil, SWI for trees and herbs were statistically significant at P < 0.05. The variance inflation factors (VIFs) were computed to test for multicollinearity. VIF values (< 2) confirmed the absence of multicollinearity between four independent variables in the LR model. Receiver Operating Characteristics (ROC) curve and Confusion Metrix (CM) methods were used to validate the model. In ROC analysis, areas under the curve of Success Rate Curve and Prediction Rate Curve were 84.5% and 96.6%, respectively, demonstrating the model’s excellent compatibility and predictability. According to the CM, the model demonstrated a 79.6% accuracy, 63.6% precision, 100% recall, and a F-measure of 77.8%. The model coefficients revealed that the vegetation cover has a more significant contribution to landslide susceptibility than soil characteristics. Finally, the susceptibility map, which was then classified as low, medium, and highly susceptible areas based on the natural breaks (Jenks) method, was generated using geographical information systems (GIS) techniques. All the historic landslide locations fell into the high susceptibility areas. Thus, validation of the model and inspection of the susceptibility map indicated that the in-situ soil and vegetation characteristics used in the model could be employed to demarcate historical landslide patches and identify landslide susceptible locations with high confidence.
Open Access
Investigation of Long-Term River Water Quality Trends in Hong Kong to Identify Role of Urbanization, Seasons and Pollution Sources
(Springer International Publishing, 2020-07) Gomes, P. I. A; Wai, O. W. H
This study investigated the long-term stream water quality trends of nine catchments in Hong Kong with different levels of urbanization using monthly water quality data for a 30-year period at annual and seasonal (wet and dry) scales. Raw data were modeled using redundancy analysis and Mann–Kendall test. Only one river showed a clear difference of water quality responses between the upstream and downstream monitoring stations. Nevertheless, in general, water quality of monitoring stations that had built areas less than 40% showed improving trends, whereas their downstream counterparts with built areas more than 70% showed deterioration trends for some parameters. Majority of water quality trends were season-independent. Out of the variables that were indicative of a long-term deterioration trend, total solids, total suspended solids, turbidity and electrical conductivity (all surrogates of sediment load of the river) were prominent. Nitrate concentration demonstrated an increasing trend for most streams, whereas phosphates a decreasing trend. This study concluded that the main source of pollution could be the surface runoff (nonpoint sources), not the wastewater inputs (point sources). Stream discharge was increasing and decreasing in the downstream and upstream stations, respectively. This could be attributed to the increase in imperviousness in the downstream and water extraction in the upstream. The downstream discharge increment with time would also support the fact that contamination was due to surface runoff. This study provides evidence that the Hong Kong legislative control actions on point source pollution work well, but not on nonpoint source pollution.
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Investigation of long-term river water quality variations using different urbanization indices and assessment of common scientific perspectives of urbanization on water quality
(wiley, 2023-03) Karunatilaka, P. D.; Gomes, P. I. A
This study investigated the water quality variation spanning 30 years (1986–2017) in 16 catchments of Hong Kong against different urbanization indices, namely, built area fraction; population; and product of population and built area fraction. Pearson correlations of three different periods of time (1988–1990, 1998–2000, and 2015–2017) indicated that water quality trends were dependent on the urbanization index. Total solids, nitrite-nitrogen, total phosphorus, electrical conductivity, dissolved oxygen, and flow rate had significant deteriorative trends (Pearson r > 0.5 and p < 0.05) with population and product of built area and population. Results also interpreted that built area fraction and product of built area and population were the worst and best indices that represented urbanization and/or its impacts, respectively. Mann-Kendall test for the entire 30 year period showed that water quality had improved with time with respect to certain water quality parameters (e.g., dissolved oxygen, ammoniacal nitrogen and total suspended solids). The results portrayed that although the urbanization of catchments had increased with time, the river water quality with respect to many parameters showed signs of improvement and the legislative measures implemented seemed to be effective in controlling pollution.
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Iron and manganese removal from textile effluents in anaerobic attached-growth bioreactor filled with coirfibres
(IWA Publishing, 2007) Jayaweera, M. W; Gomes, P. I. A; Wijeyekoon, S. L
t A laboratory scale study on Fe and Mn removal in upflow anaerobic bioreactor of a working volume of 20 L with coir fibre as the filter medium was investigated for a period of 312 days. The maximum Fe and Mn levels considered were 10 and 5 mg/L respectively, which are the typical average values of textile effluents subsequent to the primary and secondary treatments. Ten sub-experimental runs were conducted with varying HRTs (5 days to 1 day), ratios of COD:SO22 4 (20 to 3.5), Fe levels (0.005 to 10 mg/L) and Mn levels (0 to 5 mg/L). COD:SO22 4 of 3.5 was identified as the optimum point at which sulphate reducing bacteria (SRBs) out competed methane producing bacteria (MPBs) and further reduction of this ratio caused total and/or significant inhibition of MPBs, thus building sulphate reducing conditions. The effluent contained Fe and Mn below the permissible levels (1.6 and 1.1 mg/L for Fe and Mn, respectively) stipulated by US National Pollution Discharge Elimination System (NPDES) for inland surface waters at HRTs higher than 3 days. Results of the mass balance showed more Fe accumulation (60%) in sediments whereas 27% in the filter media. An opposite observation was noticed for Mn
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Phycoremediation of Chromium (VI) by Nitella and impact of calcium encrustation
(Elsevier, 2009-07-30) Gomes, P. I. A; Asaeda, T
This article discusses the applicability of the Charophyte, Nitella pseudoflabellata in the remediation of Cr (VI) contaminated waters at different calcifying potentials. Its growth was found to be positively correlated with Ca in water (CaW), but marginally significant in the presence of Cr (VI) in water (CrW). High CaW resulted in calcite encrustation on the plant cell wall. CaW was found to be aiding Cr (VI) fixation in the long run, as this correlated positively with both CaW and CrW. However, Ca interfered with passive Cr (VI) accumulation in live plant matter at low CrW concentrations (≤0.2 mg/L). Biosorption by dead plant matter seemed to be the major mechanism as the dead plant organs contained >1 mg/g Cr dry weight of plant. Cr (VI) concentrations greater than 0.4 mg/L were too toxic, showing maximum quantum efficiency of PSII photochemistry (Fv/Fm) values < 0.63. The opposite was noticed (Fv/Fm > 0.76) when Cr (VI) was less than 0.2 mg/L. Elongation curve patterns based on shoot lengths showed similar scenarios. In all cases high CaW units with calcite encrustation found to be least affected by Cr (VI) toxicity. Optimum remediation was obtained using a combination of high Ca and Cr (VI) in the case of passive (short-term) operation and low Ca and Cr (VI) for active (long-term) operation. Under the passive scenario, plants accumulated above 1.2 mg/g Cr dry weight whereas in the active case, accumulation was 0.8 mg/g Cr dry weight. We conclude that Nitella-mediated Cr (VI) remediation is a promising technique within the range and conditions investigated.
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Phytoremediation of heavy metals by calcifying macro-algae (Nitella pseudoflabellata): implications of redox insensitive end products
(Pergamon, 2013-08-01) Gomes, P. I. A; Asaeda, T
To evaluate the phytoremediation of heavy metals in water and understand the biochemistry of end products of calcifying macro algae (charophytes), an 84-wk laboratory experiment was conducted. Eighteen microcosms were maintained with and without plants. These were given different heavy metal treatments: no heavy metals, 0.2 mg L−1 Cr6+ and 0.01 mg L−1 Cd. Accumulation observed to be 0.06% Cr by dry weight and for Cd it was 0.02%. The bioconcentration factors were 3000 and 25 000 for Cr and Cd, respectively. Ratios of heavy metal accumulation in alkaline (i.e., calcified areas) to acidic areas of plants were 6 to 4 (for Cr) and 1 to 1 (for Cd). This elucidated an association between heavy metal accumulation and calcification. This was validated by sequential extraction of sediments. It was shown that in microcosms with plants, the heavy metals were mainly in redox insensitive and less bioavailable carbonate bound form (39–47%). This was followed by organic-bound form (23–34%). Carbonate bound end products will ensure long term storage of heavy metals and after plant senescence these will not re-enter the water column.