Humic Water Research Articles

Postglacial shifts in lake trophic status based on a multiproxy study of a humic lake

The long-term development of a humic lake ecosystem in Poland was investigated via palaeoecological analyses of age-dated sediment cores. Peat and lacustrine deposit records spanning approximately 12,000 years of lake history were analysed with regard to palynomorphs, plant macrofossils, degree of peat decomposition, Cladocera and geochemistry. Our study demonstrated the difficulty of classifying sediments deposited in humic lakes. We considered it inadequate to classify dy sediment exclusively using macroscopic criteria in the absence of geochemical parameters. Our study of the palaeoecology of the humic lake suggested three primary shifts in its trophic status: from oligotrophy to mesotrophy (Allerød-Boreal), to eutrophy (Atlantic), and to humotrophy (from the Sub-Boreal to the present). The results indicated that shifts in the trophic status occurred in response to climatic changes and factors linked to the catchment. The transformation from a clearwater lake of high trophic status to a humic lake was possible, such that the latter may originate not only from an oligotrophic lake. As a result of our pioneering study, we determined that a humic water body may even develop because of transformation of a eutrophic lake.

Variations of soil water isotopes and effective contribution times of precipitation and throughfall to alpine soil water, in Wolong Nature Reserve, China

Alpine shrubs and soils in catchments of the headwaters of the Yangtze River in west China are very important for reducing flooding and sustaining base flow during the summer. However, the contributions of precipitation, throughfall, and interflow to soil water and their effective contribution times in alpine shrub soil are not fully understood. In this study, we investigated a time series of stable isotopes in soil water, precipitation, canopy throughfall, interflow, litter, and humus water in a hillslope area. In addition, the spatial variation of water isotopes in soil profile in the Wolong Valley, located in the upper watershed of the Yangtze River, Sichuan, China, was considered. We found that (1) precipitation and throughfall significantly affected water isotopes in litter, humus, and shallow soil (0cm to 50cm deep) by affecting preferential flows. (2) Rainwater from a small precipitation event (about 4.0mm d−1) also penetrated soil to depths of 40cm to 50cm. (3) Interflow could comprise as much as 96% of water in soil columns during non-rainy days, but the proportion would decrease quickly after the precipitation amount reached more than 3mm d−1. (4) Mean effective contribution times of recharge in soil (0cm to 50cm deep) occurred 3 to 5days despite the occurrence of large precipitation events (15.0mm and 18.9mm). Therefore, preferential flows composed of precipitation/throughfall and interflow were dominant in hillslope hydrology in the southeast edge of Tibet, which caused runoff to increase during the rainy season.

Should a water colour parameter be included in lake total phosphorus prediction models used for the Water Framework Directive?

Under the Water Framework Directive (WFD) lakes are classified according to a variety of criteria. This classification facilitates state of the environment assessments and helps identify work needed to achieve the objectives of the WFD, which are broadly to maintain and/or restore water quality and ecological status at a level recognised as good or high. To achieve high or good status, lakes must meet a criterion for total phosphorus (TP) that is linked to a predicted reference condition value that is derived by various models. Lakes which fail to meet good status may require expensive remedial actions to be undertaken, thus accurate identification of the reference condition TP concentration is vital for effective environmental management. However, the models currently employed could be improved for some regions, particularly those with carbon rich soils. By examining 19 reference condition lakes (i.e. lakes essentially non-impacted by humans) in peaty areas of Scotland, we found that a simple parameter linked to water colour and humic substances was a better predictor of TP than the currently employed models (R2 0.585 vs R2 < 0.01). Therefore, for Scotland and elsewhere, in regions with carbon rich soils and lakes with humic waters the TP predictive models could be improved by development and incorporation of a parameter related to water colour and humic components.

The trophic status of Suwałki Landscape Park lakes based on selected parameters (NE Poland)

This study describes changes in the trophic status of 12 lakes within Suwałki Landscape Park (SLP). All of the trophic classifications of the lakes were based on the trophic continuum division. Trophic status was determined by means of multiparameter indices using several diverse criteria. In this study, the assessment of the trophic status of lakes included water quality; abundance and biomass of bacterioplankton, phytoplankton, and zooplankton; and primary production of phytoplankton. The Carlson trophic state index (TSI) describes the level of water fertility and indicated the dominance of moderately eutrophic waters. Lakes Perty, Jeglówek, and Hańcza have a trophic status that indicates mesotrophy (TSI <50). The trophic status of the studied lakes was determined based on the bacterial abundance and clearly showed a lack of oligotrophic lakes in SLP. Based on the number of bacteria, only Lake Szurpiły can be classified as β-mesotrophic, whereas Lake Linówek can be characterized as hypertrophic with some features typical for humic waters. The greatest value of gross primary production was observed in Lake Linówek (126.4 mg C/m3/h). The phytoplankton trophy index varied from 1.59 to 2.28, and its highest value, which indicated eutrophy, was determined for Lake Udziejek. In the case of Lakes Hańcza, Szurpiły, Perty, Jeglówek, and Kojle, the index ranged from 1.25 to 1.74, which indicated mesotrophy. The majority of the lakes were classified as mesoeutrophic (1.75–2.24). The highest trophic status was assessed for lakes with a marked dominance of cyanobacteria (Lake Przechodnie, Lake Krajwelek, Lake Udziejek, and Lake Pogorzałek), which is commonly recognized as an indicator of high trophic status. Considering all of the indices of trophic status, the analysis of rotifer community structure indicates that the studied group of lakes is mesoeutrophic or eutrophic. The values of crustacean zooplankton indices indicated that the trophic status of the studied lakes was close to that determined using a TSI. The parameters of zooplankton abundance and species structure allowed for the observance of changes in the tropic levels of lakes, which are difficult to detect by a chemical assay alone.

Plasticity of source‐water acquisition in epiphytic, transitional and terrestrial growth phases of Ficus tinctoria

ABSTRACTDespite continued studies on the ecology and physiology of strangling hemiepiphytes, there is little quantitative information about the variations in source‐water uptake by these species under different growth phases. In this study, the water acquisition patterns of a hemiepiphyte, Ficus tinctoria, is investigated in relation to growth phase (epiphytic, transitional and terrestrial) and season (foggy, hot‐dry and rainy). Stable isotope compositions of water in xylem, soil, canopy humus, fog and rainfall were sampled on seasonally distinct dates, and soil water content and leaf carbon isotope composition were measured in order to determine the proportion of different water sources. Results indicated that F. tinctoria displayed a high degree of plasticity in source‐water acquisition associated with the growth‐phase transition from purely canopy‐rooted epiphyte to transitional plant to terrestrial tree. During the foggy season and the hot‐dry season, epiphytes utilized a combination of recently received rainwater (82–89%) and fog water (11–18%) present in canopy humus soil, whereas terrestrial trees exclusively depended on shallow and deep terrestrial soil water and exhibited marked flexibility in depth of soil water uptake. Transitional‐phase plants relied predominantly on shallow soil water (79–86%) and extracted only a small fraction of canopy humus water (14–21%). During the rainy season, epiphytes relied almost exclusively on recent rainwater (96%) and had a negligible water uptake from fog, whereas trees extracted their water primarily from the shallow soil and less from the deep soil. Plants in transitional‐phase drew a considerable fraction of water from canopy humus soil. This plasticity of source‐water uptake to cope with radical changes in rooting environment is likely the key feature enabling hemiepiphytic species to thrive and successfully establish in the tropical rainforests. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Seasonal variations of NOM composition and their reactivity in a low humic water

Natural organic matter (NOM) and its potential to form disinfection by‐products (DBPs) during water treatment are of great public health concern. Understanding the seasonal changes in NOM composition and their reactivity in DBP formation could lead to a better treatment of drinking water and a more consistent water quality. NOM from the Terkos Lake was fractionated and characterized by XAD resin adsorption and ultrafiltration (UF) techniques during four different seasons within a year. XAD fraction analysis indicates that the HPI (38%) and the TPI (21%) were the dominant chemical fractions as DOC masses across the sampling period. Moreover, the fractions contributing to the most UV254 absorbance were HPO, which accounted for more than 72% of total UV254. It was found that the percentages of UV254 of HPI and TPI showed significant amount of variation with coefficients of variation of 48% (HPI) and 35% (TPI), respectively. Moreover, it was concluded that the HPO fraction was the primary THM precursor, which contributed more than 48%, and while the primary fraction of HAA precursors was found to be TPI, accounting for more than 47% of total HAAFP with exceptions in January 2011. As obviously seen in this study, the hydrophobic constituents in Terkos Lake water are on the low end of the spectrum in terms of their reactivity to form HAAs. In the context of THM reactivity, the physical properties (i.e., moleculer size) of Terkos Lake NOM are more important than their chemical properties (i.e., aromaticity). On the other hand, the predominant fraction as the source of HAAs precursors was found to be with the TPI and HPI chemical fractions. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 962–971, 2014

Humic Acids Degradation and Membrane Fouling in Photocatalytic MF Systems for Drinking Water Treatment

Humic acids (HA) that are one of the major organic components in natural water play an important role in water treatment because they can interact with metals, trace organics, and chlorine while generating toxic complexes and by-products. In this work, photocatalytic degradation of HA and its kinetic behavior were investigated in a photocatalytic microfiltration (MF) system, along with evaluation of membrane permeability at different fluxes. The mechanisms of adsorption and desorption of HA on TiO2 surfaces were elucidated with adsorption isotherm tests of HA before and after photocatalysis of humic water. The kinetic parameters for humic acids, k (rate constant) and K (equilibrium adsorption coefficient) of the Langmuir-Hinshelwood equation, were obtained based on mass balances in continuous stirred tank reactor (CSTR) operations. Regarding membrane fouling, it was assumed that the rate of degree of fouling is disproportional to the fouling resistance. It was found that the fouling rate constant started increasing substantially when the flux increased to a level of greater than 50 L/m2-h. This indicated that the photocatalytic MF system should be operated at a flux below the critical value to prevent serious membrane fouling.

Origin, concentration, availability and fate of dissolved organic carbon in coastal lagoons of the Rio de Janeiro State

The coastal lagoons in the northern Rio de Janeiro State (Brazil) present a wide gradient of dissolved organic carbon (DOC) and water color, with the highest DOC concentrations reported in the literature for aquatic ecosystems. Thus, they represent a peculiar set of ecosystems for the study of the origin, processing and fate of DOC in inland waters. We reviewed data from 2 decades of studies on the carbon cycle in these coastal lagoons and discussed the fluctuations in the concentration and quality of DOC, factors affecting DOC microbial and photochemical degradation, CO2 emission, as well as the role of humic and non-humic carbon to the energy flow through the trophic chains. We show that DOC quality, not its quantity, determines the rates of photochemical and microbial degradation both seasonally (within system) and spatially (among systems), with the exception of DOC photo-oxidation among lagoons, which is partially explained by DOC concentration at regional scale. In humic lagoons, there is a fairly predictable pattern of seasonal variation in DOC concentration associated to rainfall-induced inputs of allochthonous C. However, little is known about the exact timing of these allochthonous inputs and how they relate to the seasonal variation of DOC chemical properties (i.e. its quality). Depth-integrated photo-oxidation rates were less representative in highly humic lagoons, due to strong light attenuation in the water column. Nevertheless, the potential contribution of photo-oxidation and bacterial respiration to total CO2 efflux (~11%) did not differ significantly when all lagoons were pooled together. Contrary to prevailing paradigms for humic waters, microalgae seem to be the main C source in humic lagoons, sustaining pelagic food webs through zooplankton, in spite of some contribution of allochthonous C. Thus, the predominant role of the microbial loop in the DOC recovery to food webs in such systems is to be questioned.

Occurrence of Cu and Cr in the sedimentary humic substances and pore water from a typical sugar cane cultivation area in São Paulo, Brazil

Purpose The purpose of this paper is to study the interactions of sedimentary humic substances (SHS) from a sugarcane cultivation area with Cu(II) and Cr(III) and to evaluate the occurrence of these metals in the pore water and SHS.

Contrasting responses of two Sitka spruce forest plots in Ireland to reductions in sulphur emissions: results of 20 years of monitoring

Long-term trends in ion concentrations of bulk precipitation, throughfall, forest floor leachate (humus water) and shallow and deep soil water were assessed at two Sitka spruce (Picea sitchensis) stands—one on an Atlantic peat bog in the west of Ireland (Cloosh), the other on the east coast on a peaty podzol (Roundwood). Deposition at Cloosh was dominated by marine ions (sodium, [Na+], chloride [Cl−], and magnesium [Mg2+]), whereas bulk precipitation and throughfall at Roundwood was characterized by inputs of non-marine sulphate (nmSO42−), acidity and inorganic nitrogen (NH4+, NO3−). Significant declines in concentrations of nmSO42− and acidity in bulk precipitation and throughfall were observed at both sites. The decline in throughfall nmSO42− was significantly related to reductions in European sulphur dioxide (SO2) emissions. At Roundwood, SO42− declined significantly in humus, shallow and deep soil water. In deep soil water this was accompanied by a long-term increase in pH and a reduction in total aluminum (Altot). The recovery from acidification was delayed by high concentrations of NO3−, which strongly influenced acidity and Altot concentrations. At Cloosh, there was a significant decline in SO42− in humus water but long-term trends were not evident in shallow or deep soil water; SO42− concentrations at these depths fluctuated in response to drought-events. Marine ions strongly influenced soil water chemistry at both sites; at Cloosh soil water acidity was strongly related to Na+ and Cl−, while at Roundwood, Na+, Cl− and Mg2+ influenced Altot concentrations. Dissolved organic carbon increased significantly in humus and soil water at Roundwood, where it was associated with declining acidity. Soil water at both sites was influenced by a combination of anthropogenic sulphur (S) and nitrogen (N) deposition, drought and sea-salt events. The study highlights the value of long-term monitoring in assessing the response of forest soils to S and N deposition against a background of climate influences on soil water through drought and sea-salt events.

Developmental Changes in the Historical and Present-Day Trophic Status of Brown Water Lakes. Are Humic Water Bodies a Uniform Aquatic Ecosystem?

The long-term development of three humic lake ecosystems in Poland was investigated through palaeoecological analyses of sediment cores. These wetland records spanning the Holocene were analyzed for plant macroremains, degree of peat decomposition, sediment geochemistry along with radiocarbon dating. Morphological characteristics of the catchments and data on contemporary water quality and management approaches were integrated. Our research on the palaeoecology of humic lakes suggests two main states: humic and eutrophic-humic. Of the lakes studied, only one consistently presented features typical of the humic type. The other two showed various states, and dynamic patterns of transformation. The results indicate that these systems can change from humic to eutrophic-humic, and back again, in response to catchment-linked factors, climatic change and human impact. Thus determination of uniform pattern in the development of humic lakes is questionable. This suggests that a reassessment of brown water lakes is necessary.

A comparison of photosynthetic and respiration rates in six aquatic carnivorous Utricularia species differing in morphology

The rootless carnivorous plant genus Utricularia includes about 50 submerged aquatic or amphibious species. They usually grow in standing humic waters rich in CO2 and are known to be strict photosynthetic CO2 users. In this study, oxygen-based net photosynthetic (PN) and dark respiration (RD) rates were measured in trap-free leaves of shoot segments from different aged sections of Utricularia australis and U. vulgaris and the photosynthetic CO2 affinity was estimated in adult shoot segments. PN and RD were compared in adult trap-free leaves in three species with linear shoots (U. australis, U. vulgaris, U. purpurea) and four populations of three rhizomatous/rosette species (U. dichotoma, U. resupinata, U. volubilis) under standard conditions (25°C, 400μmolm−2s−1 PAR, 0.25mM CO2). In U. australis and U. vulgaris shoots, dry-weight based RD was highest in the youngest segments (174–184mmolkg−1h−1) and gradually declined down to the progressively senescent segments (43–58mmolkg−1h−1). In U. vulgaris, PN increased from the shoot apex up to the 25th leaf nodes, while it was highest in the 3rd leaf nodes and decreased significantly down to the shoot bases in U. australis. Chlorophyll-based PN rates along the shoots in both species were almost constant. Dry-weight based PNmax in U. australis was significantly greater than that in U. vulgaris (1634±69 vs. 1077±56mmolkg−1h−1), while the CO2 affinity (Km) was opposite – 48±10 vs. 21±2μM. Although the mean photosynthetic parameters for individual species usually differed considerably from each other between both subgroups and supported the view that the linear-shoot species have higher PN rates than the other subgroup (732–1592 vs. 155–687mmolkg−1DWh−1), statistically significant difference between both subgroups was only found for chlorophyll a-based PN. The differences in photosynthetic characteristics found between both morphological subgroups of Utricularia presumably reflect the differences in growth rates: the linear-shoot species with high PN rates are known to grow very rapidly while those from the other subgroup with lower PN grow slowly. The high PN rates of the linear-shoot Utricularia species approach the upper limit of PN reported for other aquatic non-carnivorous plants and are a prerequisite for their very rapid growth. Therefore, to attain such high PN rates and rapid growth, these species demand high [CO2] >0.15mM in their habitats.

Towards Universal Wavelength-Specific Photodegradation Rate Constants for Methyl Mercury in Humic Waters, Exemplified by a Boreal Lake-Wetland Gradient

We report experimentally determined first-order rate constants of MeHg photolysis in three waters along a Boreal lake-wetland gradient covering a range of pH (3.8-6.6), concentrations of total organic carbon (TOC 17.5-81 mg L(-1)), total Fe (0.8-2.1 mg L(-1)), specific UV254 nm absorption (3.3-4.2 L mg(-1) m(-1)) and TOC/TON ratios (24-67 g g(-1)). Rate constants determined as a function of incident sunlight (measured as cumulative photon flux of photosynthetically active radiation, PAR) decreased in the order dystrophic lake > dystrophic lake/wetland > riparian wetland. After correction for light attenuation by dissolved natural organic matter (DOM), wavelength-specific (PAR: 400-700 nm, UVA: 320-400 nm and UVB: 280-320 nm) first-order photodegradation rate constants (kpd) determined at the three sites were indistinguishable, with average values (± SE) of 0.0023 ± 0.0002, 0.10 ± 0.024 and 7.2 ± 1.3 m(2) E(-1) for kpdPAR, kpdUVA, and kpdUVB, respectively. The relative ratio of kpdPAR, kpdUVA, and kpdUVB was 1:43:3100. Experiments conducted at varying MeHg/TOC ratios confirm previous suggestions that complex formation with organic thiol groups enhances the rate of MeHg photodegradation, as compared to when O and N functional groups are involved in the speciation of MeHg. We suggest that if the photon fluxes of PAR, UVA, and UVB radiation are separately determined and the wavelength-specific light attenuation is corrected for, the first-order rate constants kpdPAR, kpdUVA, and kpdUVB will be universal to waters in which DOM (possibly in concert with Fe) controls the formation of ROS, and the chemical speciation of MeHg is controlled by the complexation with DOM associated thiols.

Can Humic Water Discharge Counteract Eutrophication in Coastal Waters?

A common and established view is that increased inputs of nutrients to the sea, for example via river flooding, will cause eutrophication and phytoplankton blooms in coastal areas. We here show that this concept may be questioned in certain scenarios. Climate change has been predicted to cause increased inflow of freshwater to coastal areas in northern Europe. River waters in these areas are often brown from the presence of high concentrations of allochthonous dissolved organic carbon (humic carbon), in addition to nitrogen and phosphorus. In this study we investigated whether increased inputs of humic carbon can change the structure and production of the pelagic food web in the recipient seawater. In a mesocosm experiment unfiltered seawater from the northern Baltic Sea was fertilized with inorganic nutrients and humic carbon (CNP), and only with inorganic nutrients (NP). The system responded differently to the humic carbon addition. In NP treatments bacterial, phytoplankton and zooplankton production increased and the systems turned net autotrophic, whereas the CNP-treatment only bacterial and zooplankton production increased driving the system to net heterotrophy. The size-structure of the food web showed large variations in the different treatments. In the enriched NP treatments the phytoplankton community was dominated by filamentous >20 µm algae, while in the CNP treatments the phytoplankton was dominated by picocyanobacteria <5 µm. Our results suggest that climate change scenarios, resulting in increased humic-rich river inflow, may counteract eutrophication in coastal waters, leading to a promotion of the microbial food web and other heterotrophic organisms, driving the recipient coastal waters to net-heterotrophy.

Influence of coagulant/lime dosing sequence on treatment of soft humic waters

The influence of dosing sequence of lime and alum as a coagulant in the treatment of soft humic waters (requiring pre-alkalinisation of raw water) was studied. The experiments show that the traditional dosing order, i.e. pre-alkalinisation first and coagulant second, might give worse results in comparison with the reversed order, i.e. coagulant dosing followed by pre-alkalinisation. The influence of aggregation time on residual coagulant and UV absorbance was also studied.

Foraging efficiency and prey selectivity in a visual predator: differential effects of turbid and humic water

Predators exert strong regulating forces on lower trophic levels through predation. As most fish are visual foragers, visual conditions in the water may alter the strength of this regulation. We evaluated effects of turbidity and humic water on foraging efficiency and prey-size selectivity in Northern pike (Esox lucius) feeding on roach (Rutilus rutilus). Encounter rates decreased in both turbid and humic water but were not counteracted by increased searching activity. Capture success was unaffected by turbidity but was nonlinearly affected by humic water by being high in clear and highly humic water but low in less humic water. In highly humic water, the visual range approached pike’s strike distance and, together with its cryptic colours, pike may have initiated its attack before the prey detected it, limiting the possibility for prey evasive manoeuvres. Prey-size selectivity towards small prey in clear water disappeared in turbid water but was maintained in humic water. Owing to its optical properties, turbidity degrades the quality of the visual information more through scattering than humic water does through absorption. We show that the effect of visual degradation on foraging depends on the cause of visual degradation, which has not previously been acknowledged in the visual foraging literature.

News in ecophysiological research on aquatic Utricularia traps

Aquatic carnivorous plants comprise the species Aldrovanda vesiculosa L. (Droseraceae) and about 50 species of the genus Utricularia L. (Lentibulariaceae). Aquatic Utricularia species usually grow in shallow, standing humic waters which are usually poor in N and P, but occasionally also in K. Although they take up all necessary nutrients either directly from the water by their rootless shoots or from animal prey by traps, under favorable conditions, they exhibit very rapid apical shoot growth of 3-4 leaf nodes d-1, while their shoot bases decay at this same high rate.

Effects of brown and turbid water on piscivore–prey fish interactions along a visibility gradient

Summary1. Environmental changes such as eutrophication and increasing inputs of humic matter (brownification) may have strong effects on predator–prey interactions in lakes through a reduction in the visual conditions affecting foraging behaviour of visually oriented predators.2. In this experiment, we studied the effects of visual range (25–200 cm) in combination with optically deteriorating treatments (algae, clay or brown humic water) on predator–prey interactions between pike (Esox lucius) and roach (Rutilus rutilus). We measured effects on reaction distance and strike distance for pike and escape distance for roach, when pike individuals were exposed to free‐swimming roach as well as to roach held in a glass cylinder.3. We found that reaction distance decreased with decreasing visual range caused by increasing levels of algae, clay or humic matter. The effect of reaction distance was stronger in turbid water (clay, algae) than in the brown water treatment.4. Strike distance was neither affected by visual range nor by optical treatment, but we found shorter strike distances when pike attacked roach using visual cues only (roach held in a cylinder) compared to when pike could use multiple senses (free‐swimming roach). Escape distance for roach was longer in turbid than in brown water treatments.5. Changes in environmental drivers, such as eutrophication and brownification, affecting the optical climate should thus have consequences for the strength of predator–prey interactions through changes in piscivore foraging efficiency and prey escape behaviour. This in turn may affect lake ecosystems through higher‐order interactions.

Effects of Degraded Optical Conditions on Behavioural Responses to Alarm Cues in a Freshwater Fish

Prey organisms often use multiple sensory cues to gain reliable information about imminent predation threat. In this study we test if a freshwater fish increases the reliance on supplementary cues when the reliability of the primary cue is reduced. Fish commonly use vision to evaluate predation threat, but may also use chemical cues from predators or injured conspecifics. Environmental changes, such as increasing turbidity or water colour, may compromise the use of vision through changes in the optical properties of water. In an experiment we tested if changes in optical conditions have any effects on how crucian carp respond to chemical predator cues. In turbidity treatments we added either clay or algae, and in a brown water colour treatment we added water with a high humic content. We found that carp reduced activity in response to predator cues, but only in the turbidity treatments (clay, algae), whereas the response in the brown water treatment was intermediate, and not significantly different from, clear and turbid water treatments. The increased reliance on chemical cues indicates that crucian carp can compensate for the reduced information content from vision in waters where optical conditions are degraded. The lower effect in brown water may be due to the reduction in light intensity, changes in the spectral composition (reduction of UV light) or to a change in chemical properties of the cue in humic waters.

Photodegradation of pyribenzoxim in water

Photolysis of pyribenzoxim was assessed in various aqueous solutions under sunlight. In direct photolysis, half-lives of pyribenzoxim were 26.9 and 9.2 days for deaerated and nondeaerated distilled water, respectively. Five photoproducts, bispyribac, benzophenone oxime, 2-hydroxy-6-(4,6-dimethoxypyrimidin-2-yloxy)benzoic acid, benzophenone, and 2-hydroxy-6-(4-hydroxy-6-methoxy-pyrimidin-2-yloxy)benzoic acid, were identified after irradiation under a xenon lamp for 4 h. In indirect photolysis, halflives of pyribenzoxim were 6.0, 3.6, 4.8, 2.2, 11.4, and 9.8 days for humic water, paddy water, rose bengal, Fenton’s reagent, furfuryl alcohol, and mixture of furfuryl alcohol and rose bengal. The photolysis rate of pyribenzoxim in Fenton’s reagent aqueous solution was faster than other sensitizers. Furfuryl alcohol, a singlet oxygen quencher, inhibited the photodegradation of pyribenzoxim to some extent.