Diatom taxa and assemblages for establishing nutrient criteria of lakes with anthropogenic hydrologic alteration

Stressor-response models offer guidance for concentration-based nutrient criteria in lakes under human intervention. Diatom-based statistics from biological responses were incorporated to derive taxon-specific and community-level change points (thresholds) of phosphorous and nitrogen in 77 Yangtze floodplain lakes. Diatom metrics relating with conductivity were adopted as response variables, since conductivity explained the maximum variation (38.1%) in diatom assemblages via Bootstrapped regression trees. Nonparametric change-point analysis and Threshold Indicator Taxa ANalysis showed threshold responses of diatom community structure at 0.05–0.08 mg TP/L in connected lakes and 0.02–0.04 mg TP/L in isolated lakes. Distinct community change points of sensitive diatoms occurred at 0.96–1.63 mg TN/L in connected lakes and 0.52–0.63 mg TN/L in isolated lakes. Diatom community structures of tolerant taxa were substantially altered beyond 0.22–0.23 mg/L in connected lakes and 0.52–0.69 mg NO_x/L in isolated lakes. Hydrological river-lake connectivity differed significantly in ecological nutrient criteria with more TN/TP criteria and less NO_x criteria in connected lakes. Given the ecological significance and biological integrity, diatom-based statistics can provide more reliable change points (thresholds) for nutrient criteria than Chl a-nutrient relationships.     

Effects of nutrients on arsenic accumulation by arsenic hyperaccumulator Pteris vittata L.

This research investigated the effects of various nutrients on arsenic (As) removal by arsenic hyperaccumulator Pteris vittata L. in a Hoagland nutrient solution (HNS). The treatments included different concentrations of Ca and K in 20% strength of HNS, different strengths of HNS (10, 20 and 30%), different strengths of HNS (10 and 20%) with and without CaCO₃, and different concentrations of Ca, K, NO₃, NH₄, and P in 20% strength of HNS. The plants were grown in nutrient solution containing 1 mg As L^?1 for 4 weeks except the Ca/K experiment where the plants were grown in nutrient solution containing 10 or 50 mg As L^?1 for 1 week. Adding up to 4 mM Ca or 3 mM K to 20% strength HNS significantly (P < 0.05) increased plant arsenic accumulation when the solution contained 10 mg As L^?1. Plant arsenic removal was reduced with increasing Ca and K concentrations at 50 mg As L^?1. Lower strength of HNS (10%) resulted in the greatest plant arsenic removal (79%) due to lower competition of P with As for plant uptake. Addition of CaCO₃ to 20% strength of HNS significantly increased arsenic removal by P. vittata. Among the nutrients tested, NO₃ and CaCO₃ were beneficial to plant arsenic removal while NH₄, P and Cl had adverse effects. This experiment demonstrated that it is possible to optimize plant arsenic removal by adjusting nutrients in the growth medium.     

Regional nutrient thresholds in wadeable streams of New York State protective of aquatic life

Human influence on the landscape has caused nutrients in surface waters to increase to the point where their presence has substantially altered biological communities. Because this is a nationally recognized problem, the United States Environmental Protection Agency (USEPA) tasked each state, tribe, and territory to adopt numeric nutrient criteria. Here we integrate the concept of ecological thresholds with the derivation of effects-based numeric nutrient criteria. Acceptable levels of risk exceeding predefined biocriteria were determined using conditional probability and nonparametric changepoint analysis. We show how certain community metrics exhibit threshold responses to nutrients. Using these thresholds, we suggest nutrient values protective of aquatic life and characterize community composition. Nutrient criteria were suggested for two aggregations of USEPA's nutrient ecoregions in New York State an upland pristine forested region (Ecoregions VIII and XI) and a nutrient-enriched lowland region (Ecoregions VII and XIV). Of 11 biological community metrics evaluated, 5 had a strong response to nutrients (NBI-P, NBI-N, HBI, TRI, and DMA). Maximum probabilities of exceeding the biological impairment thresholds established for these metrics ranged from 81% to 100%. Changepoint analysis conducted on probability outcomes of these metrics resulted in nutrient thresholds at or above USEPA nutrient guidance values, depending on ecoregion and nutrient variable (Ecoregion VIII/XI: 15 μg/L TP, 472 μg/L TN, 150 μg/L NO₃-N, Ecoregion VII/XIV: 17 μg/L TP, 1133 μg/L TN, 356 μg/L NO₃-N). Results of taxonomic similarity percentages (SIMPER) and species contributions indicate that several orders of macroinvertebrates and diatoms exhibit significant shifts in their percent of contributions to sample similarity in response to changes in nutrient concentrations.     

Ecological classification of lakes: Uncertainty and the influence of year-to-year variability

Regular monitoring of lakes is important to determine their ecological state and development and of key significance when deciding whether action should be taken to improve their quality, for instance by reducing the external loading of nutrients. Imprecise or inadequate knowledge of the ecological state increases the risk of misclassification and of wrong management decisions. Based on Danish lake data, we aimed to determine temporal variations, in particular natural year-to-year differences, and to describe the uncertainty in assessing the ecological state of lakes. We analysed environmental data from ca. 350 Danish lakes (1100 lake years), including three case studies, with long-term data series (up to 24 years), with no significant changes in external nutrient loading. We used summer means of selected water chemical variables, phytoplankton and submerged macrophytes as indicators of ecological state and found considerable variations in all indicators, which could not be ascribed alone to meteorological variation. In shallow lakes, chlorophyll a concentrations exhibited large year-to-year variations, especially at TP ranging between 0.05 and 0.15 mg L⁻¹ where the lakes may shift between a macrophyte- and a phytoplankton-dominated state. For example, chlorophyll a varied by a factor 5–10 between years and was particularly low when submerged macrophyte coverage exceeded 20% compared with lakes without macrophytes. Use of a multimetric index including four phytoplankton indicators reduced the coefficient of variation. Generally, the 95% confidence interval of ecological classification was approximately 50% lower when the assessment of ecological state was based on 4–5 years’ measurements than if based on only one year's measurements. Knowledge and awareness of the uncertainty of indicators used in ecological classification are highly relevant for lake managers and policy makers when defining efficient monitoring and restoration strategies.     

The effect of lake morphology on aquatic vegetation development and changes under the influence of eutrophication

Data on aquatic and emergent vegetation, morphology and water quality from 274 Polish lowland lakes surveyed in the years 1996–2009 were used to validate the preliminary typology of Polish lakes based on macrophytes and to indicate the environmental parameters which most significantly determine the vegetation patterns in lakes under various morphological conditions. In highly alkaline lowland lakes representing non-disturbed conditions the key determinants influencing the vegetation patterns were mean depth and the shape of the littoral. Three morphological lake types were distinguished: shallow (<3.5 m), deep, and additionally, within the latter, deep ribbon-shaped, with a clearly elongated base and steep bed slopes. The lake types varied in their vegetation patterns developed under non-disturbed conditions. In the shallow lakes, the share of the phytolittoral in the total lake area (%phytol) was the highest (40–100%, 72.3% on average) and the maximum colonisation depth (C_max) the lowest (3.2 m as the maximum) compared to the lakes from both deep types. In the ribbon-shaped deep lakes, %phytol and the plant coverage (%cover) were the lowest, the proportion of submerged vegetation was extraordinarily high (over 90%) and the emergent vegetation was extremely sparsely developed (<6%) compared to the lakes of the two other types.The alterations of aquatic vegetation resulting from the eutrophication process in distinguished morphological lake types were explored. Within the macrophyte variables tested, three groups of indicators were distinguished: (a) metrics performing best in selected lake types, i.e. the type-specific indicators (abundance metrics, %Pota), (b) metrics performing equally well in all the lake types, considered as the universal indicators (e.g. S_Chara, %Subm and %Emerg) and (c) metrics performing poorly in all the lake types, with generally limited applicability (most of the metrics on syntaxonomic richness). In the shallow lakes, %cover and %phytol performed notably better than in deep lakes, whereas C_max worked best in deep lakes and showed the strongest response in the deep regular-shaped lakes. Moreover, in deep regular-shaped lakes the number of communities of stoneworts and submerged plants (S_Chara and S_Subm), and in deep ribbon-shaped lakes the proportion of area inhabited by vascular plant communities (%Pota) performed exceptionally better than in the other two lake types. The most universal metrics, performing equally well in all the lake types, were the proportions of submerged (%Subm) and emergent (%Emerg) vegetation in the total phytolittoral area.     

Improved retrieval of Secchi depth for optically-complex waters using remote sensing data

Water transparency is one of the ecological indicators for describing water quality and the underwater light field which determines its productivity. In the European Water Framework Directive (WFD) as well as in the European Marine Strategy Framework Directive (MSFD) water transparency is used for ecological status classification of inland, coastal and open sea waters and it is regarded as an indicator for eutrophication in Baltic Sea management (HELCOM, 2007). We developed and compared different empirical and semi-analytical algorithms for lakes and coastal Nordic waters to retrieve Secchi depth (Z_SD) from remote sensing data (MERIS, 300 m resolution). The algorithms were developed in water bodies with high coloured dissolved organic matter absorption (a_CDOM(442) ranging 1.7–4.0 m⁻¹), Chl a concentration (0.5–73 mg m⁻³) and total suspended matter (0.7–37.5 g m⁻³) and validated against an independent data set over inland and coastal waters (0.6 m < Z_SD < 14.8 m). The results indicate that for empirical algorithms, using longer wavelengths in the visible spectrum as a reference band decreases the RMSE and increases the coefficient of determination (R²). The accuracy increased (R² = 0.75, RMSE = 1.33 m, n = 134) when Z_SD was retrieved via an empirical relationship between Z_SD and K_d(490). The best agreement with in situ data was attained when Z_SD was calculated via both the diffuse and the beam attenuation coefficient (R² = 0.89, RMSE = 0.77 m, n = 89). The results demonstrate that transparency can be retrieved with high accuracy over various optical water types by the means of ocean color remote sensing, improving both the spatial and temporal coverage. The satellite derived Z_SD product could be therefore used as an additional source of information for WFD and MSFD reporting purposes.     

A high pressure liquid chromatography-based assay for glutathione-S-transferase class distinction assay

In order to expedite the process of classification of the members of the family of glutathione-S-transferases (GSTs) high performance liquid chromatography with photodiode array detection (HPLC-PDA) was used as a means for measuring enzymatic activity. The GST chosen for the development of the HPLC-PDA technique was from equine liver (E-GST). The characterizing substrates, ethacrynic acid (EA) and bromosulfophthalein (BSP), along with previously gathered characterization data allowed for the distinction of α, μ or π-class enzymes. In an initial characterization of the previously unclassified E-GST it was determined that the enzyme was of the π-class with specific activities of 0.062, ± 0.0015 μmol min^− 1 mg^− 1 and 0.0019, ± 0.00064 μmol min^− 1 mg^− 1 for EA and BSP, respectively. Finally, the activity of the E-GST with the EA and BSP substrates, was measured by HPLC-PDA, and was found to be 0.027, ± 0.003 μmol min^− 1 mg^− 1 and 0.002, ± 0.0005 μmol min^− 1 mg^− 1, respectively. While the HPLC-PDA data do not mirror the spectrophotometric results quantitatively the overall response by the E-GST was the same. In general, the E-GSTs were shown to belong to the π-class when characterized by HPLC-PDA due to an EA specific activity greater than 0.01 μmol min^− 1 mg^− 1 and a negligible BSP activity (≤ 0.002 μmol min^− 1 mg^− 1).     

Protocorm culture of Dendrobium candidum in balloon type bubble bioreactors

Protocorm cultures of Dendrobium candidum were established in balloon type bubble bioreactors using Murashige and Skoog (MS) medium with 0.5 mg l⁻¹ α-naphthaleneacetic acid (NAA), 2.5% (w/v) sucrose, 5:25 mM NH₄:NO₃ and 1% (v/v) banana homogenate for the production of biomass and bioactive compounds. In 3 l bioreactor containing 2 l medium, a maximum protocorm biomass (21.0 g l⁻¹ dry biomass) and also optimum quantities of total polysaccharides (389.3 mg g⁻¹ DW), coumarins (18.0 mg g⁻¹ DW), polyphenolics (11.9 mg g⁻¹ DW), and flavonoids (4.5 mg g⁻¹ DW) were achieved after 7 weeks of culture. Based on these studies, 5 and 10 l bioreactor cultures were established to harvest 80 g and 160 g dry biomass. In 10 l bioreactors, the protocorms grown were accumulated with optimal levels of polysaccharides (424.1 mg g⁻¹ DW), coumarins (15.8 mg g⁻¹ DW), polyphenols (9.03 mg g⁻¹ DW) and flavonoids (4.7 mg g⁻¹ DW). The bioreactor technology developed here will be useful for the production of important bioactive compounds from D. candidum.     

Performance of the Phytoplankton Index for Lakes (IPLAC): A multimetric phytoplankton index to assess the ecological status of water bodies in France

A new phytoplankton-based index was designed to respond to the Water Framework Directive (WFD) requirements concerning the assessment of lake ecological status. The “Indice Phytoplancton Lacustre” (IPLAC) is a multimetric index, taking into account biomass, abundance and species composition of communities. The first metric is based on the total phytoplankton biomass (MBA), the second on the abundance and taxonomic composition (MCS) of 165 indicator taxa. The IPLAC was developed on 2 independent databases, one for the calibration and the second for the validation of the metrics. The calibration dataset was composed of 255 “lake-years” from 214 distinct lakes sampled between 2005 and 2012. The validation dataset included 173 lake-years in order to confirm the response of the index to the trophic gradient and anthropogenic pressure.The results show that the IPLAC correctly highlights chemical pressure (eutrophication). Especially high Pearson correlations are shown with total phosphorus (r = −0.71, p-value <0.001), chlorophyll-a (r = −0.83, p-value <0.001) and water transparency (r = 0.73, p-value <0.001) which are the main proxies for the trophic level. Corine land cover was used as an indication of the anthropogenic pressure and good correlations are also found with the watershed land use, negatively correlated with agricultural area (r = −0.60, p-value <0.001), population density (r = −0.36, p-value <0.001) and positively with forest area (r = 0.57, p-value <0.001).The index is WFD-compliant and is dedicated to natural lakes and artificial water bodies in metropolitan France, and will be routinely used by the French Ministry of the Environment to assess lake ecological status through the phytoplankton community. However, the results must be carefully interpreted in two cases: reservoirs with large water level fluctuations, and samples that include less than 5 indicator species.     

Quantile regression analysis as a predictive tool for lake macroinvertebrate biodiversity

The Water Framework Directive introduced in Europe major changes to improve the management of water resources. This study aims to highlight some of the potential implications of its implementation for lake water monitoring in Italy. A Life+ project was launched to plan the first monitoring of lake macroinvertebrates standardized at the national level.Quantile regression analysis was used to explain different metrics of diversity describing macroinvertebrate communities in response to twenty-one variables representing chemical, physical and morphological characteristics of the environment. Nine lakes located in two Italian regions (Piedmont and Sardinia) were analyzed covering a wide trophic spectrum, from oligotrophy to hyper-eutrophy. The lakes were sampled following the national standardized protocol with samples covering the three recognized lake zones: littoral, sublittoral, profundal.The studied lakes had high chemical variability with conductivity ranging between 53 and 561 μS/cm, pH between 6.5 and 9.1, and alkalinity between 14 and 398 mg/l. The bottom sediments were characterized by fine sand (range 51–99%), followed by silt (1–35%) and clay (0–28%). When the Lake Habitat Survey was also applied to these lakes, its synthetic indices (LHMS, Lake Habitat Modification Score and LHQA, Lake Habitat Quality Assessment) produced higher values in natural lakes (mean values ± SD: LHMS = 26 ± 7, LHQA = 57 ± 3) than in the reservoirs (LHMS = 22 ± 4, LHQA = 52 ± 6). In all lakes, macroinvertebrates mainly consisted of chironomids and oligochaetes characterized by relative abundances up to 80% and >90%, respectively.Using quantile regression to evaluate limiting responses, only two variables, namely sampling depth and oxygen percent saturation (oxygen content), resulted the ones that best explained all the analyzed metrics of diversity of the macroinvertebrate communities. Depth and oxygen were then used to suggest synthetic models describing the various metrics of potential community diversity. These models can help the environmental agencies responsible for monitoring at the national level in distinguishing entire lakes or part of them with high biodiversity from those in altered conditions and then address remediation efforts toward the water bodies with the most critical conditions. Such approach could also be used to optimize the sampling procedures for the application of the Benthic Quality Index for lakes currently adopted at national level.     

Phosphorus retention capacity of agricultural headwater ditch sediments under alkaline condition in purple soils area,China

Phosphorus (P) retention by headwater ditch sediments adsorption plays a pivotal ecological role in P buffering in freshwater ecosystems. Previous studies focused on headwater ditch sediment adsorption and its P retention capacity in acid conditions, but little information is available for headwater ditches under alkaline condition. In this study, adsorption behavior of phosphorus was investigated in headwater ditch sediments under alkaline condition using a batch equilibrium technique, thus determining phosphorus retention capacity of headwater ditch sediments collected at 11 sites at base-flow on 2 March 2006 in purple soils area of China. Results showed that headwater ditch sediments had elevated phosphorus sorption maximum (S_max) values (122.72–293.23 mg P kg^?1) and P binding energy (K) values (1.64–8.65 L mg^?1), while they had low equilibrium phosphorus concentration (EPC₀) (0.001–0.108 mg L^?1) and degree of phosphorus saturation (DSP) (1.93–10.19%). Analysis of EPC₀ and soluble P concentration indicated that sediments acted as a sink for P across all headwater ditches. Therefore, there were high intrinsic P retention capacities of headwater ditch sediments. Positive correlations of both K and S_max with oxalate-extractable Fe (r of 0.93 and 0.81, p < 0.05) and total carbon (TC) (r of 0.89 and 0.74, p < 0.05) were found, thus suggesting that organic matter and amorphous or poorly crystalline Fe would play dominant roles in P adsorption in the headwater ditch sediments under alkaline condition. Since neither S_max nor K were correlated with CCE (CaCO₃) (r of 0.15 and ?0.06, p > 0.05), the high-energy sorptive surfaces of Fe oxides were more important than CaCO₃ in P sorption of sediment under alkaline condition. At the same time, these poor correlations between CCE and K and S_max imply a non-linear relationship between P retention and the content of carbonate. The negative correlations of both K and S_max with pH (r of–0.73, and–0.58, p < 0.05) revealed that an increase in pH would not improve sediment retention capacity under alkaline conditions.     

Nitrate removal and greenhouse gas production in a stream-bed denitrifying bioreactor

Denitrifying bioreactors are currently being tested as an option for treating nitrate (NO₃^?) contamination in groundwater and surface waters. However, a possible side effect of this technology is the production of greenhouse gases (GHG) including nitrous oxide (N₂O) and methane (CH₄). This study examines NO₃^? removal and GHG production in a stream-bed denitrifying bioreactor currently operating in Southern Ontario, Canada. The reactor contains organic carbon material (pine woodchips) intended to promote denitrification. Over a 1 year period, monthly averaged removal of influent (stream water) NO₃^? ranged from 18 to 100% (0.3–2.5 mg N L^?1). Concomitantly, reactor dissolved N₂O and CH₄ production, averaged 6.4 μg N L^?1 (2.4 mg N m^?2 d^?1), and 974 μg C L^?1 (297 mg C m^?2 d^?1) respectively, where production is calculated as the difference between inflow and effluent concentrations. Gas bubbles entrapped in sediments overlying the reactor had a composition ranging from 19 to 64% CH₄, 1 to 6% CO₂, and 0.5 to 2 ppmv N₂O; however, gas bubble emission rates were not quantified in this study. Dissolved N₂O production rates from the bioreactor were similar to emission rates reported for some agricultural croplands (e.g. 0.1–15 mg N m^?2 d^?1) and remained less than the highest rates observed in some N-polluted streams and rivers (e.g. 110 mg N m^?2 d^?1, Grand R., ON). Dissolved N₂O production represented only a small fraction (0.6%) of the observed NO₃^? removal over the monitoring period. Dissolved CH₄ production during summer months (up to 1236 mg C m^?2 d^?1), was higher than reported for some rivers and reservoirs (e.g. 6–66 mg C m^?2 d^?1) but remained lower than rates reported for some wastewater treatment facilities (e.g. sewage treatment plants and constructed wetlands, 19,500–38,000 mg C m^?2 d^?1).     

Biomonitoring potential of a Caryophyllaeid tapeworm: Evaluation of Adenoscolex oreini infection level and health status in three fish species of the genus Schizothorax across eutrophication and pollution gradients

Endoparasitic infections vary significantly across altered aquatic ecosystems, making these organisms ideal for the biomonitoring of degraded environments. To assess the biomonitoring potential of the Caryophyllaeid tapeworm Adenoscolex oreini and the possible impact of water quality on fish species, a study was carried out in three lakes with marked eutrophication and pollution gradients. The A. oreini infection level in three host fish species of the genus Schizothorax and corresponding fish health status were determined. The pattern of cestode infection varied significantly in the three fish species across the pollution gradient. The prevalence of infection in two fish species (Schizothorax esocinus and S. curvifrons) was significantly greater (P < 0.05) in the eutrophic lake than in the reference lake, whereas in S. niger, the maximum was reached in the hypereutrophic lake. The estimated marginal mean intensity and other infection indices varied significantly (P < 0.05) across the inter- and intra-pollution gradients of lakes. Multivariate statistical analysis results revealed maximum cestode infection in the eutrophic lake. An altered seasonal pattern was observed in the highly stressed lake. The gonadosomatic index (GSI) and condition factor values were significantly greater in fish collected from the reference lake than in those collected from the other lakes. A significant negative relationship between GSI and cestode prevalence was observed in the hypereutrophic lake as compared to least eutrophic lake. These findings indicate that infection indices of the Caryophyllaeid tapeworm and health attributes of fish can act as surrogates for the environmental quality of deteriorated lentic water bodies of the north-western Himalayan region, which is currently undergoing environmental degradation.     

Response in root morphology and nutrient contents of Myriophyllum spicatum to sediment type

Sediment may play an important role during the submerged macrophyte decline in the eutrophication progress. In order to investigate the response in root morphology and nutrient contents of submerged macrophytes Myriophyllum spicatum to sediment, five sediment types were treated and used (five types of sediment were used in the experiment: treatment 1 was nature sediment + sand, a 50:50 (v/v) mixture, treatment 2 was the studied sediment only, treatment 3 was sediment + nitrogen (N, NH₄Cl 400 mg kg^?1), treatment 4 was sediment + phosphorus (P, NaH₂PO₄ 300 mg kg^?1); treatment 5 was sediment + phosphorus (P, NaH₂PO₄ 600 mg kg^?1)). The results show that the root N content was only significantly affected by adding N in sediments and P was elevated by adding N and P. The root mass and its percentage increased at first, the peak values were reached at 35 d, and then decreased. The root growth was restrained by adding sand and N in sediments, root senescence process was delayed at the later experimental time by adding P in sediments. The increase of root volume showed a similar trend to that of root growth, except for plant with P addition where root volume remained high after 35 d. The root volume decreased while the main root number increased significantly by adding sand in sediments. The mean root length and main root diameter were reduced by adding P in sediments. The compatible sediment nutrient condition is necessary to restore submerged macrophytes in a degraded shallow lake ecosystem, and the effect of sediment on the root morphology and nutrient content is one of the important aspects restricting the restoration of submerged macrophytes.     

Efficient nitrogen removal in a pilot system based on upflow multi-layer bioreactor for treatment of strong nitrogenous swine wastewater

In order to prevent the toxic effect caused by high strength ammonium in a swine wastewater treatment system, a patented upflow multi-layer bioreactor (UMBR) as a pre-anoxic tank was applied to a pilot-scale plant with a treatment capacity of 5 m³/d. This plant was operated for 4 months at a high IR ratio in the range of 10–17, in order to alleviate the toxic effects caused by high strength ammonium. A computational fluid dynamic (CFD) analysis was also conducted to design and configure the rotating distributors in the UMBR. At an IR ratio of about 17, the influent NH₄⁺-N (1169 mg N/L) was diluted to less than 80 mg N/L at the head of the UMBR, and then was completely nitrified (about 98.3%) in the aeration tank, without any inhibition caused by high strength ammonium. The nitrate at a concentration of about 58.2 mg N/L recycled from the aeration tank was completely denitrified in UMBR #1, which was operated at an actual hydraulic retention time (HRT) of 3.5 h.     

Assessment of Lemna gibba L. (duckweed) as a potential ecological indicator for contaminated aquatic ecosystem by boron mine effluent

Duckweeds, as a group, are important early warning indicators for the assessment of contaminated ecosystems due to their propensity to accumulate pollutants. In the present study, we investigated the potential use of Lemna gibba L. (Lemnaceae) as an ecological indicator for boron (B) mine effluent containing B concentration above 10 mg l⁻¹. For this purpose, L. gibba fronds were grown for 7 days in simulated water contaminated with B mine effluent. The important note is that this study was carried out in Kırka (Eskişehir, Turkey) B reserve area, which is the largest borax reserve in all over the world, under natural climatic conditions in the field. The results demonstrated that accumulations of B by L. gibba gradually increased based on the initial B concentrations (10, 25, 50, 100, and 150 mg l⁻¹) of the mine effluent. B concentration in the dry weight of the plant reached 639 mg kg⁻¹ when the minimum initial dosage (10 mg l⁻¹) was applied and 2711 mg kg⁻¹ when the maximum initial dosage (150 mg l⁻¹) was applied during the study. However, significant reductions in their relative growth rates occurred in 50, 100 and 150 mg l⁻¹ initial B concentrations. Results suggest that 25 mg l⁻¹ B concentration in water seemed to be a sensitive endpoint for L. gibba that could be used as a critical bioindicator level of B contaminated water. Following our data, we also constructed a simple growth model under the climatic conditions in this region of Turkey, but in instructive as a worldwide model. L. gibba is, therefore, suggested to be able to use as both an indicator and a phytoremediation tool because of its high accumulation capacity for B contaminated water.     

Spatiotemporal modeling of watershed nutrient transport dynamics: Implications for eutrophication abatement

The main objective of this study was to quantify nutrient transport dynamics of a previously ungauged, temperate watershed (145 km²) surrounding a shallow eutrophic lake and discern lake response to external nutrient loading, based on soil water assessment tool (SWAT) and the Organization of Economic Cooperation and Development (OECD) empirical lake models, respectively. A SWAT model was used to simulate baseline nutrient dynamics after its calibration and validation against daily tributary flow, total dissolved phosphorus (TDP), total phosphorus (TP), and nitrate (NO₃) loads. On the watershed scale, median annual TDP, TP, and NO₃ losses were 0.4, 1.1, and 2.0 kg ha^− 1, respectively. The highest median annual TP and NO₃ losses were estimated at 3.7 and 7.7 kg ha^− 1 for pastureland and 1.7 and 3.8 kg ha^− 1 for cropland and mixed forests, respectively. Baseflow was the major nutrient transport pathway over a wide range of precipitation events (450 to 900 mm yr^− 1). Erosion was the predominant surface process exporting P across the watershed. Critical source areas (CSAs) of TP and NO₃ comprised 17% and 4% of the watershed, respectively. Annual mean TP, and mean and maximum chlorophyll content indicated a hyper-eutrophication risk for the lake. An external P load reduction by excess of 80% could be necessary to restore mesotrophy in the lake. Our results suggested that subsurface P transport should not be overlooked a priori when groundwater-dependent and extensively farmed watersheds are managed for eutrophication abatement.     

Arsenic reduced scale-insect infestation on arsenic hyperaccumulator Pteris vittata L.

Arsenic hyperaccumulation by Pteris vittata L. (Chinese brake fern) may serve as a defense mechanism against herbivore attack. This study examined the effects of arsenic exposure (0, 5, 15 and 30 mg kg^?1) on scale insect (Saissetia neglecta) infestation of P. vittata. Scale insects were counted as a percentage fallen from the plant to the total number of insects after 1 week of As-treatment. The arsenic concentrations in the fronds ranged from 5.40 to 812 mg kg^?1. Greater arsenic concentrations resulted in higher percentage of fallen-scale insects (17.2–55.0%). Lower arsenic concentrations (≤5 mg kg^?1) showed significantly lower effect on the population compared to 15–30 mg kg^?1 (p < 0.05). Arsenic content in the fallen-scale insects was as high as 194 mg kg^?1, which indicated that arsenic has been ingested by the scale insects via plant sap. This study is consistent with the hypothesis that arsenic may help P. vittata defend against herbivore's attack.     

Evaluation of phosphorus distribution and bioavailability in sediments of a subtropical wetland reserve in southeast China

The phosphorus (P) fractions and bioavailable P in the sediments from the Quanzhou Bay Estuarine Wetland Nature Reserve were investigated using chemical extraction methods for the first time to study the distribution and bioavailability of P in the reserve sediments. A hypothesis was presented suggesting that the bioavailable P in the sediments could be evaluated using the P fractions. The total phosphorus (TP), inorganic phosphorus (IP), organic phosphorus (OP), non-apatite phosphorus (NAIP), and apatite phosphorus (AP) contents in the sediments were in the ranges of 303.87–761.59 mg kg⁻¹, 201.22–577.66 mg kg⁻¹, 75.83–179.16 mg kg⁻¹, 28.86–277.90 mg kg⁻¹, and 127.36–289.94 mg kg⁻¹, respectively. The water soluble phosphorus (WSP), readily desorbable phosphorus (RDP), algal available phosphorus (AAP), and NaHCO₃ extractable phosphorus (Olsen-P) contents in the sediments were in the ranges of 0.58–357.17 mg kg⁻¹, 80.77–586.75 mg kg⁻¹, 1.09–24.12 mg kg⁻¹, and 54.96–676.82 mg kg⁻¹, respectively. The correlation analysis results showed that the NAIP was the major component of the bioavailable P and that the impact of the AP on the bioavailable phosphorus may be minimal. Due to the low TP content in the sediments of the Quanzhou Bay Estuarine Wetland Nature Reserve, the potential pollution risks of P in the sediments may not be very high. The results also show that the bioavailable P concentrations in the sediments of the Quanzhou Bay Estuarine Wetland Nature Reserve could not be evaluated by measuring the P fractions and that the hypothesis was untenable.     

Growth of the fungus Paecilomyces lilacinus with n-hexadecane in submerged and solid-state cultures and recovery of hydrophobin proteins

The filamentous fungus Paecilomyces lilacinus was grown on n-hexadecane in submerged (SmC) and solid-state (SSC) cultures. The maximum CO₂ production rate in SmC (V_max = 11.7 mg CO₂ L_g⁻¹ day⁻¹) was three times lower than in SSC (V_max = 40.4 mg CO₂ L_g⁻¹ day⁻¹). The P. lilacinus hydrophobin (PLHYD) yield from the SSC was 1.3 mg PLHYD g protein⁻¹, but in SmC, this protein was not detected. The PLHYD showed a critical micelle concentration of 0.45 mg mL⁻¹. In addition, the PLHYD modified the hydrophobicity of Teflon from 130.1 ± 2° to 47 ± 2°, forming porous structures with some filaments <1 μm and globular aggregates <0.25 μm diameter. The interfacial studies of this PLHYD could be the basis for the use of the protein to modify surfaces and to stabilize compounds in emulsions.