Comparative kinetic study between moving bed biofilm reactor-membrane bioreactor and membrane bioreactor systems and their influence on organic matter and nutrients removal

New technologies regarding wastewater treatment have been developed. Among these technologies, the moving bed biofilm reactor combined with membrane bioreactor (MBBR-MBR) is a recent solution alternative to conventional processes. This paper presents the results obtained from three wastewater treatment plants working in parallel. The first wastewater treatment plant consisted of a membrane bioreactor (MBR), the second one was a MBBR-MBR system containing carriers both in anoxic and aerobic zones, and the last one consisted of a MBBR-MBR system which contained carriers only in the aerobic zone. The reactors operated with a hydraulic retention time of 26.47 h. During the study, the difference between the experimental plants was not statistically significant concerning organic matter and nutrients removal. However, different tendencies regarding nutrients removal are shown by the three wastewater treatment plants. In this sense, the performances in terms of nitrogen and phosphorus removal of the MBBR-MBR system which contained carriers only in the aerobic zone (67.34 ± 11.22% and 50.65 ± 11.13%, respectively) were slightly better than those obtained from another experimental plants. As a whole, the pilot plant which consisted of a MBR showed better performance from the point of view of the kinetics of the heterotrophic and autotrophic biomass with values of μ_m,H = 0.00858 h⁻¹, μ_m,A = 0.07646 h⁻¹, K_M = 2.37 mg O₂ L⁻¹ and K_NH = 1.31 mg N L⁻¹.     

Microbial community in conventional and extended aeration activated sludge plants in India

This study was conducted to determine the relationship between the ciliated protozoan population density and the effluent quality at two different modes of activated sludge plants (ASP) operating in India. A wide variety of ciliated protozoa (26 sp.) in higher density were identified at the conventional ASP, Haridwar, that delivered high quality effluent in terms of low biochemical oxygen demand (BOD = 15 mg/L), suspended solids (SS = 17 mg/L), turbidity (2.7 NTU), ammoniacal nitrogen (NH₃–N = 3 mg/L), chemical oxygen demand (COD = 37 mg/L), total coliforms (TC = log 5.2), fecal coliforms (FC = log 4.7) and fecal Streptococci (FS = log 3.7). Whereas, a few protozoan species (15 sp.) in lower density were reported in extended aeration plant (EAP) Delhi, that delivered turbid and lower quality effluent in terms of high BOD (23 mg/L), SS (80 mg/L), turbidity (12 NTU), NH₃–N (55 mg/L) and COD (68 mg/L). However, in spite of relatively poor effluent quality, lower concentration of TC (log 4.2), FC (log 3.9) and FS (log 3.2) was observed in EAP, Delhi. The constant presence of two filamentous bacterial species (Beggiatoa and Spirillum) in extended aeration process can be considered as the probable reason of high coliforms removal, since filamentous bacteria are capable of removing organic as well as microbial pollutants from wastewater.     

Simultaneous removal of chlorpyrifos and dissolved organic carbon using horizontal sub-surface flow pilot wetlands

Rural areas of developing countries require low-cost treatment systems to purify wastewater which is contaminated with pesticides and organic matter. This work evaluated for six months the simultaneous removal of chlorpyrifos and dissolved organic matter in water using four horizontal sub-surface flow constructed wetlands (SSFCW) at a pilot scale, that were planted with Phragmites australis at 20 ± 2 °C water temperature. In each wetland, three concentrations of chlorpyrifos and three of dissolved organic carbon (DOC) were tested by liquid chromatography and an organic carbon analyzer respectively. The pesticide and DOC were added to the wetlands in synthetic wastewater. For the experiments, four wetlands of equal dimensions were used, with granular material of igneous rocks, 3.9–6.4 mm in diameter and at a depth of 0.3 m with a layer of water 0.2 m deep. For each treatment, regular sampling was carried out for the influent and effluents. As a supporting feature NH₄⁺, NO₃^? and PO₄^3? were quantified and in situ measurements of dissolved oxygen (DO), pH, electrical conductivity, water temperature and redox potential were taken. The overall removal of the chlorpyrifos (92.6%) and DOC (93.2%) was high, as was DOC removal as a function of pesticide concentration in the influent. The minimum magnitude (92.0%) was reached with 425.6 μg L^?1 of chlorpyrifos and, with the highest pesticide removal (96.8%). At lower concentrations of the agrochemical, DOC removal increased. The removals were possibly due to mineralization processes, biological decomposition and sorption in plants. These findings demonstrate that SSFCW are capable of simultaneously removing dissolved organic matter and organophosphate pesticides such as chlorpyrifos, which indicate that chlorpyrifos did not interfere with the removal of organic material.     

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.     

Anaerobic treatment of saline wastewater by Halanaerobium lacusrosei

An upflow anaerobic packed bed reactor was operated continuously with synthetic saline wastewater at different initial COD concentrations (COD₀ = 1900–6300 mg/L), salt concentrations (0–5%, w/v) and hydraulic retention times (θ_H = 11–30 h) to investigate the effect of those operating parameters on COD removal from saline synthetic wastewater. Anaerobic salt tolerant bacteria, Halanaerobium lacusrosei, were used as dominant microbial culture in the process. The percent COD removal reached up to 94% at COD₀ = 1900 mg/L, 19 h hydraulic retention time and 3% salt concentration. No substrate inhibition effect was observed at high feed CODs. Increasing hydraulic retention time from 11 h to 30 h resulted in a substantial improvement in the COD removal from 60% to 84% at around COD₀ = 3400 mg/L and 3% salt concentration. Salt inhibition effect on COD utilization was observed at above 3% salt concentration. Modified Stover–Kincannon model was applied to the experimental data to determine the biokinetic coefficients. Saturation value constant, and maximum utilization rate constant of Stover–Kincannon model for COD were determined as K_B = 5.3 g/L day, U_max = 7.05 g/L day, respectively.     

Performance evaluation of various bioreactors for the removal of Cr(VI) and organic matter from industrial effluent

Performances of various bioreactors under different operating conditions were evaluated with respect to hexavalent chromium (Cr(VI)) reduction and COD removal. Continuous reactor studies were carried out with (i) aerobic suspended growth system, (ii) aerobic attached growth system, and (iii) anoxic attached growth system, using both synthetic and actual industrial wastewater. Arthrobacter rhombi-RE (MTCC7048), a Cr(VI) reducing strain enriched and isolated from chromium contaminated soil, was used in all the bioreactors for Cr(VI) biotransformation and COD removal. Aerobic and anoxic batch experiments were conducted to evaluate the bio-kinetic parameters. The bio-kinetic parameters for aerobic system were: μ_max = 2.34/d, K_s = 190 mg/L (as COD), K_i = 3.8 mg/L of Cr(VI), and Y_T = 0.377. These parameters for anoxic conditions were: μ_max = 0.57/d, K_s = 710 mg/L (as COD), K_i = 8.77 mg/L of Cr(VI), and Y_T = 0.13. Aerobic attached growth system, operated at a hydraulic retention time (HRT) of 24 h and an organic loading rate (OLR) of 3 kg/m³/d, performed better than aerobic suspended and the anoxic attached growth systems operated under identical conditions, while treating synthetic wastewater as well as industrial effluent.     

Application of anaerobic–aerobic sequential treatment system to real textile wastewater for color and COD removal

A sequential anaerobic packed column reactor and an activated sludge unit was operated continuously for treatment of a textile industry wastewater, in Izmir, Turkey. Metal sponges were used as support material in anaerobic unit and pre-activated textile dyestuff biodegrading PDW facultative anaerobic bacterial culture was immobilized on the support particles. Effects of hydraulic retention times in anaerobic unit (θ_H anaerobic = 12–72 h) and initial COD concentration (COD₀ = 3000 ± 200 mg/L and 800 ± 100 mg/L) at θ_H anaerobic = 24 h on color and COD removal performance of the system were investigated. The results indicated that over 85% decolorization and about 90% COD removal efficiency can be obtained up to θ_H anaerobic = 48 h but higher retention times causes decreasing in decolorization efficiency. Operating the system with real wastewater without adding any nutrients at θ_H anaerobic = 24 h resulted in over 60% improvement in color removal in studied wastewater compared to existing treatment plant.     

Asociación de la fuerza muscular con marcadores tempranos de riesgo cardiovascular en adultos sedentarios

ObjectiveTo assess the association between muscle strength and early cardiovascular risk (CVR) markers in sedentary adults.Materials and methodsA total of 176 sedentary subjects aged 18-30 years were enrolled. Body mass index and fat percentage were calculated, and waist circumference, grip strength by dynamometry, systolic blood pressure, diastolic blood pressure, mean arterial pressure, and maximal oxygen uptake by VO_2max were measured as CVR markers. A multivariate logistic regression analysis was used to assess associations between muscle strength and CVR markers.ResultsInverse correlations were found between muscle strength and adiposity (r = -.317; P = .001), waist circumference (r = -.309; P = .001), systolic blood pressure (r = -.401; P = .001), and mean arterial pressure (r = -.256; P = .001). Subjects with lower levels of muscle strength had a 5.79-fold (95% CI 1.57 to 9.34; P = .008) risk of having higher adiposity levels (≥ 25%) and a 9.67-fold (95% CI = 3.86 to 19.22; P < .001) risk of having lower physical capacity values for VO_2max (≤ 31.5 mL/kg/min^-1).ConclusionsIn sedentary adults, muscle strength is associated to early manifestations of CVR. It is suggested that muscle strength testing is added to routine measurement of VO_2max and traditional risk factors for prevention and treatment of cardiovascular risk.     

2-, 3-, and 4-(1-Oxo-1H-2,3-dihydroisoindol-2-yl)benzoic acids and their corresponding organotin carboxylates: Synthesis,characterization, fluorescent,and biological activities

Three novel organotin complexes with general formula Sn(OH)(bz)₂L (bz = benzyl, HL = 2-, 3-, or 4-(1-oxo-1H-2,3-dihydroisoindol-2-yl)benzoic acid) and one of their ligands were prepared and characterized. In vitro antifungal and antibacterial activities of these complexes and ligands were investigated with the representative strains of Candida albicans, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. Their fluorescence properties have also been discussed.     

STK15 rs2273535 polymorphism and cancer risk: A meta-analysis of 74,896 subjects

Background: It has been suggested that the serine/threonine kinase 15 (STK15) T91A rs2273535 polymorphism is associated with susceptibility to cancer. However, the results are conflicting. We performed this meta-analysis to derive a more precise estimation of the relationship. Methods: PubMed was searched to select studies. Case–control studies containing available genotype frequencies of the STK15 rs2273535 polymorphism were chosen, and the odds ratio (OR) with its 95% confidence interval (CI) was utilized to assess the strength of association. Results: 52 studies – including 34,057 cases and 40,839 controls – were identified. A significant effect of the STK15 rs2273535 polymorphism on cancer risk was found (AA vs. TT: OR = 1.13, 95%CI = 1.01–1.26, P_{heterogeneity} < 0.001; AA vs. TA/TT: OR = 1.12, 95%CI = 1.02–1.22, P_{heterogeneity} < 0.001; TA/AA vs. TT: OR = 1.06, 95%CI = 1.01–1.12, P_{heterogeneity} < 0.001). Stratified analysis by cancer type revealed that the STK rs2273535 polymorphism may contribute to the risk of breast cancer (AA vs. TT: OR = 1.21, 95%CI = 1.01–1.44, P_{heterogeneity} = 0.002), colorectal cancer (AA vs. TA/TT: OR = 1.24, 95%CI = 1.05–1.47, P_{heterogeneity} = 0.124), and esophageal cancer (AA vs. TA/TT: OR = 1.19, 95%CI = 1.02–1.39, P_{heterogeneity} = 0.148). Further subgroup analysis by ethnicity indicated that there was a statistically increased cancer risk in Asians (AA vs. TA/TT: OR = 1.20, 95%CI = 1.05–1.37, P_{heterogeneity} = 0.004). Conclusion: This meta-analysis suggests that the STK15 rs2273535 polymorphism is a candidate gene polymorphism for cancer susceptibility, especially in Asian populations.     

Mathematical modeling of Microcystis aeruginosa growth and [D-Leu1] microcystin-LR production in culture media at different temperatures

The effect of temperature (26 °C, 28 °C, 30 °C and 35 °C) on the growth of native CAAT-3-2005 Microcystis aeruginosa and the production of Chlorophyll-a (Chl-a) and Microcystin-LR (MC-LR) were examined through laboratory studies. Kinetic parameters such as specific growth rate (μ), lag phase duration (LPD) and maximum population density (MPD) were determined by fitting the modified Gompertz equation to the M. aeruginosa strain cell count (cells mL⁻¹). A 4.8-fold increase in μ values and a 10.8-fold decrease in the LPD values were found for M. aeruginosa growth when the temperature changed from 15 °C to 35 °C. The activation energy of the specific growth rate (Eμ) and of the adaptation rate (E₁/LPD) were significantly correlated (R² = 0.86). The cardinal temperatures estimated by the modified Ratkowsky model were minimum temperature = 8.58 ± 2.34 °C, maximum temperature = 45.04 ± 1.35 °C and optimum temperature = 33.39 ± 0.55 °C.Maximum MC-LR production decreased 9.5-fold when the temperature was increased from 26 °C to 35 °C. The maximum production values were obtained at 26° C and the maximum depletion rate of intracellular MC-LR was observed at 30–35 °C. The MC-LR cell quota was higher at 26 and 28 °C (83 and 80 fg cell⁻¹, respectively) and the MC-LR Chl-a quota was similar at all the different temperatures (0.5–1.5 fg ng⁻¹).The Gompertz equation and dynamic model were found to be the most appropriate approaches to calculate M. aeruginosa growth and production of MC-LR, respectively. Given that toxin production decreased with increasing temperatures but growth increased, this study demonstrates that growth and toxin production processes are uncoupled in M. aeruginosa. These data and models may be useful to predict M. aeruginosa bloom formation in the environment.     

Removal of total nitrogen by Cyperus alternifolius from wastewaters in simulated vertical-flow constructed wetlands

The vertical-flow constructed wetland (VFCW) is a promising engineering technique for removal of excess nutrients and certain pollutants from wastewaters. This study investigated the uptake and removal of total nitrogen (TN) by Cyperus alternifolius from domestic wastewaters in simulated VFCWs. A total of eight simulated VFCW treatments, including two different substrates, two different wet-to-dry ratios, and with and without C. alternifolius species (2 × 2 × 2 = 8), were employed for an operation period of 2 years in this study. Results show that more TN was removed from the influent with the presence of C. alternifolius compared to without this plant species. A linear correlation existed between the aboveground biomass and its TN content. An increase in total biomass by 100 g resulted in an increase in TN accumulation in the aboveground biomass by 2.4 g. Large amounts of TN were removed by the aboveground biomass compared to those by substrate adsorption. Results suggest that C. alternifolius played a discernable role in removal of TN from wastewaters in the simulated VFCWs.     

Structure and magnetic properties of a trinuclear nickel(II) complex with benzenetricarboxylate bridge

Novel trinuclear Ni(II) complex [Ni₃(pmdien)₃(btc)(H₂O)₃](ClO₄)₃ · 4H₂O, 1 where pmdien = N,N,N′,N′,N″-pentamethyldiethylenetriamine, H₃btc = 1,3,5-benzenetricarboxylic (trimesic) acid, has been prepared and structurally characterized. Three nickel atoms are bridged by btc trianion and their coordination sphere is completed by three N atoms of pmdien and O atom of the water molecule. The three nickel(II) magnetic centers are equivalent and their coordination spheres are completed to deformed octahedrons. Magnetic susceptibility was measured over the temperature range 1.8–300 K and zJ′ = ?0.19 cm^?1, D = 3.79 cm^?1, g = 2.18 parameters were calculated.     

The eccentric,concentric strength relationship of the hamstring muscles in chronic low back pain

ObjectiveThe objective of this study was to measure hamstring muscle eccentric and concentric strength in individuals with and without low back pain (LBP). Two composite scores for the relative balance of eccentric to concentric strength at the different movement velocities were calculated (the DEC and SEC), to determine whether or not self perceived pain, disability, or fear avoidance measures were associated with hamstring strength characteristics.DesignCross-sectional repeated measures design.SettingUniversity laboratory.ParticipantsFifteen individuals with chronic LBP and 15 matched controls.Main outcome measuresIsokinetic eccentric and concentric strength at 30° s^?1 and 120° s^?1_. Composite scores (DEC and SEC) based on peak torque were calculated to evaluate the relationship between the different muscle actions across the test velocities. Self report measures included the Oswestry disability index, general health and well being, fear avoidance, and pain.ResultsEccentric/concentric strength ratio at 30° s^?1 was higher for the LBP group (F(1,58) = 4.81, p = 0.032). The SEC was also higher for the LBP (F(1,58) = 5.97, p = 0.018). Fear avoidance beliefs and mental well-being were significantly associated with the SEC only in the LBP group (adjusted r² = 0.26, (F(2,27) = 5.8, p = .008). For the control group both the DEC and SEC were associated with self report measures. Matched differences between groups’ for the SEC were best explained by fear avoidance beliefs about work (adjusted r² = 0.12, F(1,28) = 5.1, p = 0.03).ConclusionReduced concentric relative to eccentric strength is best identified by the SEC. The SEC was significantly associated with impaired self report measures of fear avoidance and mental well being in individuals with LBP. Differences between groups for the SEC were best explained by fear avoidance beliefs about work.     

Two ways to achieve an anammox influent from real reject water treatment at lab-scale: Partial SBR nitrification and SHARON process

A comparative study to produce the correct influent for Anammox process from anaerobic sludge reject water (700–800 mg NH₄⁺-N L⁻¹) was considered here. The influent for the Anammox process must be composed of NH₄⁺-N and NO₂⁻-N in a ratio 1:1 and therefore only a partial nitrification of ammonium to nitrite is required. The modifications of parameters (temperature, ammonium concentration, pH and solid retention time) allows to achieve this partial nitrification with a final effluent only composed by NH₄⁺-N and NO₂⁻-N at the right stoichiometric ratio. The equal ratio of HCO₃⁻/NH₄⁺ in reject water results in a natural pH decrease when approximately 50% of NH₄⁺ is oxidised. A Sequencing batch reactor (SBR) and a chemostat type of reactor (single-reactor high activity ammonia removal over nitrite (SHARON) process) were studied to obtain the required Anammox influent. At steady state conditions, both systems had a specific conversion rate around 40 mg NH₄⁺-N g⁻¹ volatile suspended solids (VSS) h⁻¹, but in terms of absolute nitrogen removal the SBR conversion was 1.1 kg N day⁻¹ m⁻³, whereas in the SHARON chemostat was 0.35 kg N day⁻¹ m⁻³ due to the different hydraulic retention time (HRT) used. Both systems are compared from operational (including starvation experiments) and kinetic point of view and their advantages/disadvantages are discussed.     

Phosphorus removal from agricultural runoff by constructed wetland

A free-water surface wetland covering an area of 2800 m² was operated from March 2002 to June 2004 for agricultural runoff treatment in the Dianchi Valley in China. In the wetland were grown Zizania Caduciflora Turez Hand-mazt and Phragmites australis (Cav.) Trin.ex Steud. The instantaneous inflow rate was measured and the integrated flux was recorded by an ultrasonic flow instrument all year round. The average inflow rate, hydraulic loading rate (HLR) and hydraulic retention time (HRT) were kept at 242 m³ d^?1, 12.7 cm d^?1 and 2.0 d, respectively. The annual average total phosphorus (TP) in the inflow was 0.87 mg L^?1, and the corresponding removal efficiency was calculated to be 59.0%. Biannual plant uptake and removal by harvesting and seed transport was the main pathway for TP removal, while the influent TP load was 12.9 g m^?2 year^?1. Hydraulic retention time had a significant positive correlation with the removal of P (r² = 0.88). Water temperature, inflow phosphorus load, inflow and hydraulic load rates were positively correlated with the removal of P. Inflow phosphorus concentrations were negatively correlated with the removal of P. It is shown that the free-water surface wetland was an effective and economical system for agricultural runoff treatment in lake regions.     

Application of chemical precipitation and membrane bioreactor hybrid process for piggery wastewater treatment

This study was conducted to investigate the chemical precipitation (CP) and membrane bioreactor (MBR) hybrid process for the treatment of piggery wastewater. Average removal efficiencies for BOD, COD and turbidity in CP process were 64.3%, 77.3% and 96.4%, respectively. CP process had a moderate effect on NH₃–N removal (40.4%) which improved up to 98.2% mainly due to nitrification and filtration processes in MBR. The average removal efficiencies of BOD, COD and turbidity in MBR were 99.5%, 99.4% and 99.8%, respectively. Monod equation was used to explain the microbial activities in terms of specific growth rate. The specific growth rate of bacteria in aeration tank (N-batch) and anoxic tank (D-batch) were 0.013 and 0.005 d^?1 with a biomass yield of 0.78 and 0.43 mg MLSS produced/mg COD utilized, respectively. Microorganisms from the N-batch and D-batch showed a low-level of nitrifying and moderate-level of denitrifying capabilities which were 1.08 mg NH₃–N/(g MLVSS.h) and 2.82 mg NO₃–N/(g MLVSS.h), respectively. Carbohydrates were the main component in extracellular polymeric substance (EPS) compounds that could be attached to the membrane surface easily and led to membrane biofouling. The increase of MLSS, EPS and sludge viscosity concentration, decrease of sludge floc size and incomplete chemical cleaning procedure resulted in the increase of membrane resistance. Total membrane resistance increased from 3.19 × 10¹² m^?1 to 5.43 × 10¹⁴ m^?1.     

Nutrient concentrations in tidal creeks as indicators of the water quality role of mangrove wetlands in Southwest Florida

Coastal mangroves have the potential to improve the water quality of urban and rural runoff before it is discharged into adjacent coastal bays and oceans; but they also can be impaired by excessive pollutants from upstream. Nutrients (phosphorus and nitrogen), salinity, and other water quality parameters were measured in five mangrove tidal creeks in different hydrogeomorphic and urbanization settings during high and low tides over a calendar year of wet (June and August 2015) and dry (February and April 2016) seasons in the Greater Naples Bay area in Southwest Florida, USA. Nutrient concentrations (ave. ± std error) in the tidal creeks were 0.055 ± 0.008 mg-P/L for total phosphorus (TP) and 0.610 ± 0.020 mg-N/L for total nitrogen (TN), with an average N:P ratio of 11.4:1. Average wet season TP (0.075 ± 0.010 mg-P/L) was significantly higher than the dry season TP (0.033 ± 0.003 mg-P/L; p < 0.01, f = 15.17, f_crit = 3.89) and the average wet season TN (0.75 ± 0.03 mg-N/L) was significantly higher than dry season TN (0.52 ± 0.02 mg/L; p < 0.01, f = 64.14, f_crit = 3.89), suggesting that urban stormwater runoff is directly or indirectly affecting the nutrient conditions in these mangroves. Significant differences in nutrient concentrations between low tide and high tide were not found for either TP (p = 0.43, f = .63, f_crit = 3.88) or TN (p = 0.20, f = 1.66, f_crit = 3.89). These differences were confirmed by a PCA and cluster analyses, which found differences to be seasonal. We could not conclude from these results whether these five mangrove wetlands were sources nor sinks of nutrients based simply on the measurement of nutrient concentrations. But we illustrated that nutrient concentrations were indicators of the mangroves’ hydrogeomorphic settings, their tidal fluxes from Naples Bay, and the Bay's upstream watersheds, and less by direct urban runoff.     

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.     

Use of tolerance values to diagnose water-quality stressors to aquatic biota in New England streams

Identification of stressors related to biological impairment is critical to biological assessments. We applied nationally derived tolerance indicator values for four water-quality variables to fish and benthic macroinvertebrate assemblages at 29 sites along an urban gradient in New England. Tolerance indicator values (TIVs), as biologically based predictors of water-quality variables, were determined for dissolved oxygen, nitrite plus nitrate (nitrate), total phosphorus, and water temperature for each site based on observed biological assemblages (TIV_O), and for expected assemblages (TIV_E). The quotient method, based on a ratio of the TIVs for observed and expected assemblages (tolerance units), was used to diagnose potential water-quality stressors. In addition, the ratio of measured water-quality values to water-quality criteria (water-quality units) was calculated for each water-quality variable to assess measured water-quality stressors. Results from a RIVPACS predictive model for benthic macroinvertebrates and Bray-Curtis dissimilarity for fish were used to classify sites into categories of good or impaired ecological condition. Significant differences were detected between good and impaired sites for all biological tolerance units (fish and benthic macroinvertebrate assemblages averaged) except for nitrate (P = 0.480), and for all water-quality units except for nitrate (P = 0.183). Diagnosis of water-quality stressors at selected sites was, in general, consistent with State-reported causes of impairment. Tolerance units for benthic macroinvertebrate and fish assemblages were significantly correlated for water temperature (P = 0.001, r = 0.63), dissolved oxygen (P = 0.001, r = 0.61), and total phosphorus (P = 0.001, r = 0.61), but not for nitrate (P = 0.059, r = −0.35). Differences between the two assemblages in site-specific diagnosis of water-quality stressors may be the result of differences in nitrate tolerance.