The relative importance of Lemna gibba L., bacteria and algae for the nitrogen and phosphorus removal in duckweed-covered domestic wastewater

To arrive at detailed nutrient balances for duckweed-covered wastewater treatment systems, five laboratory-scale experiments were carried out in shallow (3.3 cm), 1 l batch systems to assess separately the contributions of duckweed itself, attached and suspended bacteria as well as algae to N- and P-removal in domestic wastewater. Depending on the initial concentrations, our duckweed-covered systems removed 120–590 mg N m⁻² d⁻¹ (73–97% of the initial Kjeldahl-nitrogen) and 14–74 mg P m⁻² d⁻¹ (63–99% of the initial total phosphorus) in 3 days. Duckweed (Lemna gibba L.) itself was directly responsible for 30–47% of the total N-loss by uptake of ammonium and, probably dependent on the initial P-concentrations, for up to 52% of the total P-loss. The indirect contribution of duckweed to the total nutrient removal was also considerable and included the uptake (and adsorption) of ammonium and ortho-phosphate by algae and bacteria in the attached biofilm and the removal of N through nitrification/denitrification by bacteria attached to the duckweed. Together these accounted for 35–46 and 31–71% of the total N- and P-loss, respectively. Therefore, approximately of the total N- and P-loss could be attributed to the duckweed mat. The remaining quarter is due to non-duckweed related components: uptake and nitrification/denitrification by algae and bacteria attached to the walls and the sediment of the system (including sedimentation). Other processes, like NH₃-volatilisation, N-fixation and nutrient uptake as well as nitrification/denitrification by suspended microorganisms did not influence the N- and P-balance of our systems, but could become important with increasing water depths and retention times.     

Effect of organic solvents on growth of freshwater algae

The impact of acetone, methanol, ethanol and dimethyl sulfoxide (DMSO) as carrier solvents on two species of algae was investigated. Scenedesmus quadricauda of green algae and Anabaena flos‐aquae of blue green algae were subjected to different concentrations of the studied solvents which ranged from 0.01 to 7.29 mL/L for 10 days in batch studies. The data recommended the use of acetone, ethanol and methanol than dimethyl sulfoxide in this order as a carrier solvent for chemical toxicity tests using a maximum concentration of 7.29 mL/L which represents 0.729% (volume/volume) in the algal bioassay test.     

K2FeO4预氧化对颤藻和腐殖酸复合絮凝相互作用的研究

采用K2FeO4预氧化复合高岭土和聚合氯化铝(PAC)混凝处理含藻和腐殖酸的混合水.结果表明,当藻浓度不变时,在一定范围内,随着腐殖酸浓度的升高,浊度、腐殖酸及藻去除率均逐渐下降.当腐殖酸浓度固定时,随着藻液浓度的升高,腐殖酸和藻去除率逐渐上升,而浊度去除率基本不变.同时考察了矿物高岭土投加量及目数、K2FeO4预氧化时间、不同污染物浓度比例对K2FeO4预氧化处理混合水效果的影响,当高岭土投加量为8 mg/L、粒径为140目时,浊度和腐殖酸、藻类的去除率分别为91.0%,80.9%和88.2%,投加量过大或目数过大,沉降性能变差,起不到良好的助凝作用.     

密云水库水质变化规律初探

在对2001年-2003年密云水库的藻类及相关水质指标进行对比分析的基础上,探讨了水库水质的变化规律及水质参数对藻类产生的影响.研究发现藻类生长出现两个峰值,3月-4月为其第一个生长峰期,以硅藻为优势藻;9月-10月为第二个生长峰期,优势藻种为硅藻和蓝藻等;第二峰期的藻浓度明显高于第一峰期.2001年-2003年的水温变化趋势与藻类浓度变化趋势非常吻合,说明水温可能是诱发蓝藻水华的关键因子.     

Modification, calibration and verification of the IWA River Water Quality Model to simulate a pilot-scale high rate algal pond

We implemented the IWA River Water Quality Model No. 1 (Reichert et al., 2001. River Water Quality Model No. 1, IWA Scientific & Technical Report No. 12) to simulate water-quality characteristics in two pilot-scale High Rate Algal Ponds. Simulation results were compared with two years' of data from the ponds. The first year's data from one pond were used for model calibration; the remaining data were used for validation. As originally formulated and parameterized, the model consistently yielded summer-time algal biomass concentrations which were too low - with consequent failures in its reproduction of dissolved oxygen, pH and nutrient dynamics. We experimented with various structural/parametric changes to improve the model's performance. The most effective strategy was to greatly increase the respiratory losses suffered by the heterotrophic osmotrophs (thereby giving the algae access to a larger fraction of the incoming dissolved organic carbon and nitrogen). This suggests that CO₂-bubbling alone cannot entirely preclude resource-limitation of algal production. We doubt that our parameterization of heterotrophic osmotrophs is correct and infer that the algae derive a large fraction of their nutrition by direct osmotrophic uptake of dissolved organic matter. This inference is supported by the literature concerning the physiology of the dominant algal species in our ponds.     

A mathematical model of a shallow and eutrophic lake (the Keszthely Basin, Lake Balaton) and simulation of restorative manipulations

Concern about the overall management of lakes has been growing, and a lake ecological model provides the guidelines necessary for such management. In this study, an ecological model describing the ecosystem of the Keszthely Basin, Lake Balaton, Hungary, one of the typical shallow and eutrophic lakes, was proposed. This model includes three types of zooplankton and two types of fish as well as two types of algae and nutrients. Parameters concerning the algae and fish were estimated based on observations in the basin between 1991 and 1995. The other parameters and the structure of the model were determined by our previous study. The parameters of the model were calibrated with the Monte Carlo technique, and its predictability was confirmed. The effects on the basin's ecosystem of three restorative manipulations, namely a biomanipulation, reduction of loading phosphorus, and dredging the sediment, were assessed by simulation studies using the proposed model. The simulation results indicated that a biomanipulation that removed 90% of the bream should suppress the growth of algae temporarily through bottom-up regulation; however, this effect seemed to not be perpetuated in this basin. The reduction of loading phosphorus seemed to be the most effective means to suppress algal growth, while dredging of sediment seemed to be the most desirable restoration method from the standpoint of the overall management of the lake, because it was expected to accelerate the growth of fish population as well as to suppress algal growth. Furthermore, the algal growth suppression mechanism of the dredging was discussed on the basis of the model calculations.     

饮用水供水过程中藻类及其代谢产物的去除与再生长控制

饮用水源富营养化导致的藻类大量繁殖及藻类代谢物分泌对饮用水质安全造成严重影响,本文以水质安全多级屏障控制与保障的角度,系统总结了饮用水处理、输配与二次供水过程去除与控制藻细胞及其代谢产物的工艺方法。其中,藻细胞灭活、凝聚与絮凝、固液分离（沉淀或气浮）及过滤分离等工艺过程是去除饮用水中藻细胞的主要单元;吸附、氧化等是控制藻细胞代谢产物（藻毒素、geosmin与2-MIB等致嗅微量有机物等）的关键工艺;对于输配与二次供水过程中,对供水系统进行优化设计并提高科学管理水平,这是最为可行的避免藻类生长的途径。在饮用水处理与输配过程以及建筑给水工程中应尽可能去除藻及其代谢产物,并控制由此产生的水质安全风险,从根本上保障饮用水质安全。     

Revue des reactions des algues aux micropolluants mineraux et organiques; consequences ecologiques et possibilites d'applications industriellesAlgae reactions to mineral and organic micropollutants, ecological consequences and possibilities for industrial-scale application: a review

An aquatic ecosystem may react to pollution in different ways, some of which combat the pollution actively; in particular, algae participate therein by developing various substances capable of complexing or degrading numerous organic or mineral pollutants.When heavy metals are not directly accumulated in algae, they can often be complexed by their extracellular metabolites (Hart, 1981), e.g. hydroxamates (McKnight and Morel, 1980; Jardim and Pearson, 1984), to form organo-metallic compounds; the ecological consequences of these phenomena, most often due to the presence of Cyanophyceae (Walsby, 1974), are varied:Useful effects: greater assimilability of certain indispensable trace elements (Provasoli et al., 1957; Johnston, 1964; Allen, 1976; Murphy et al., 1976; Gaechter et al., 1978), reduced toxicity of heavy metals brought in by pollution (Barber, 1973), etc.;Harmful effects: among others, antagonistic action against copper-based algaecidal treatments (Gaechter et al., 1978; Gnassia-Barelli et al., 1978; Van den Berg et al., 1979; McKnight and Morel, 1980).Organic micropollutants are often metabolized or even assimilated by algae, for instance:Hydrocarbons: assimilation by marine algae such as the diatom Chaetoceros calcitrans (Boutry et al., 1977a, b), or by fresh water algae (Krauss et al., 1973; Schroeder and Rehm, 1981a, b);Phenols: metabolization which can go as far as to completely remove them (Werner and Pawlitz, 1978; Stom et al., 1978), through the action of phenoloxidases which induce the formation of transient degradation products, in particular quinones (Stom et al., 1978);Pesticides: these more stable compounds are most often accumulated in algae (Soedergren, 1968; Vance and Drummond, 1969); however, certain algae are capable of causing their partial degradation (Miyazaki and Thorsteinson, 1972; Neudorf and Khan, 1975; Werner and Moerschel, 1978; Goulding and Ellis, 1981), but this may result in the temporary appearance of metabolites more toxic than the initial product (e.g. DDE from DDT);PCBs: these still more stable micropollutants are fixed, without being metabolized, by living algae (Keil et al., 1971; Veber, 1980), and even dead ones (Urey et al., 1976).The various reactions we have just seen above explain that in nature, certain algae prove specifically tolerant to various industrial wastes that contain mineral pollutants (Madgwick and Ralph, 1977; Say et al., 1977; Palmer, 1980; Strong et al., 1982), or organic pollutants (Palmer, 1980; Walsh et al., 1982).These observations, made both in the laboratory and in the field, could well lead to new applications in the biological treatment of industrial waste water; such possibilities have already been proved for vascular plants, for instance for the removal of heavy metals (Wolverton, 1975a, b and c; Tridech et al., 1981; Muramoto and Oki, 1983) or phenols (Seidel, 1965; Seidel and Kickut, 1967; Karaseva and Papchenkov, 1974; Kaminskii and Gvozdeva, 1976; Stom et al., 1978). The new generation of biological treatments of industrial effluents will be based on selected algae species acting in symbiosis with bacteria (Yurovskaya et al., 1968; Bagnyuk et al., 1975) in traditional lagooning or through more intensive processes, e.g. “activated algae” (McGriff and McKinney, 1971; McKinney et al., 1971) or cultures of algae immobilized in agar beads (Pore and Sorenson, 1981) or on rotating discs (Przytocka-Jusiak et al., 1984b), etc.Where the latter are still in the pilot plant stage, natural lagooning is now a tried-and-tested technique which has already been applied to certain industrial effluents (Lee et al., 1978; Palmer, 1980; Rebattu, 1981; Altona et al., 1983), but without previous selection of the species of algae to be used: they will be selected as a function of their ability to remove pollutants: either by bioaccumulation as for heavy metals (Filip et al., 1979; Shumate et al., 1980; Nakajima et al., 1981; Becker, 1983) or pesticides or else by metabolization and/or assimilation as for phenols (Stom et al., 1978), nitrogen-laden effluents (Matusiak et al., 1976, 1977; Przytocka-Jusiak et al., 1984a, b), hydrocarbons, etc.In addition, it should be pointed out that in its conventional applications, natural lagooning often suffered from the lack of additional clarification of the effluent; the latter may contain over 100 mg 1⁻¹ of residual algae (Shelef et al., 1972; Bratby and Marais, 1974; Harris et al., 1977; Russell et al., 1983; Przytocka-Jusiak et al., 1984a), which then bring in a high additional BOD₅, especially after their death (Varma and Digiano, 1968; King et al., 1970; Rance Bare et al., 1975; Friedman et al., 1977; McGimpsey, 1978). Therefore, it is always more advisable to remove the algae and possibly use them as a source of energy or food.In the cases studies here, this additional treatment would be absolutely essential to protect the receiving water not only from the algae themselves, but also from the micropollutants that they would have accumulated. The different processes available for harvesting algae are listed: filtration through sand (Harris et al., 1977; Filip et al., 1979; Russell et al., 1983), microstraining (Kormanik and Cravens, 1978 and 1979; Cravens and Lauritch, 1982; Harrelson and Cravens, 1982), dissolved air flotation (Van Vuuren et al., 1965; Funk et al., 1968; Bratby and Marais, 1974; Rance Bare et al., 1975; Stone et al., 1975; Shelef, 1982; Viviers and Briers, 1982), sedimentation (Friedman et al., 1977), separation through microfiltration or ultrafiltration membranes (Shelef et al., 1972; Castelas et al., 1984), etc.In fact, there is not one system which is universally applicable: this explains the wide-ranging opinions on the subject. Depending on the case, microstraining, direct filtration, accelerated settling with sludge contact, membrane technology and above all dissolved air flotation may well be usefully applied in this field. The performances of the various processes are examined, and several principles for the choice of a method of separation of algae as a function of local conditions are proposed.     

Algal growth in primary settled sewage: The effects of five key variables

Photoperiod, at 3240 lx (300 ft candle) light intensity, was found to be the primary limiting factor for algal biomass growth in a bench scale series of experiments using primary settled sewage. At a retention time of seven days, a total effective photoperiod of greater than 6 h a day was required to produce algae at concentration above 500 mg 1⁻¹.Increasing dissolved CO₂ concentration promoted green algae production and resulted in a higher yield than that obtained from the blue green algae which dominated at low levels of dissolved CO₂. Unfortunately, most of the green algae were unicellular, discrete, small particles, and would be expensive to harvest compared with blue-green algae which often grow in colonies possessing a gelatinous sheath or are of filamentous construction.Low temperature favoured algal biomass production because of its effect upon the solubility of CO₂. The addition of bicarbonate also increased algal biomass yield but an excess of ammonium nitrate inhibited algal production.The removal of nitrogen and phosphorus by algae varied with the quantity of algal biomass produced. Under the experimental conditions, nitrogen removal corresponded to about 3 mg per 100 mg of biomass produced and phosphorus removal to about 0.5 mg per 100 mg biomass produced.     

Biomonitoring of maritime pollution by heavy metals (Pb and Zn) in the coast of Jijel (Algeria)

This paper reports a study of pollution in the coastal waters of Jijel, Algeria, using algae Ulva lactuca and Corallina officinalis as bioindicators. Samples of seawater and algae were collected at four different stations from the coast of Jijel, during the period of April–June 2014. The heavy metal content (Pb and Zn) was determined in seawater and in the algae tissue by the technique of atomic absorption spectrophotometry. In seawater, the contents of heavy metals vary from 0.017 to 0.03 mg/l (Pb) and 0.235 to 0.873 mg/l. In the algae tissues, metals concentrations vary between 1.88 to 6.25 μg g^?1 dry weight (Pb), and from 92 to 178.9 μg g^?1 dry weight (Zn). These levels differ by site and species. The calculation of the bioconcentration factor (BCF) leads us to conclude that algae bioaccumulate significant levels of Pb and Zn metals in their tissues. Our results shows that the species of C. officinalis bioaccumulate the metals Pb and Zn more than U. lactuca, where, high biosorption of Zn was observed with BCF values between 203.21 and 238.40. Zn content in seawater and algae tissues appear higher than standards set by USEPA and guides values of Certified Reference Materials, but Pb levels appear lower than this standard.     

Organic nitrogen transformations in a 4-stage Bardenpho nitrogen removal plant and bioavailability/biodegradability of effluent DON

Nitrogen species, specifically, the fate and occurrence of organic nitrogen (ON) within a 4-stage Bardenpho process bioreactor producing low total nitrogen (TN) effluents were investigated in this study. The results showed release of ON in primary anoxic zone and no ON release in the first aerobic zone of the process. The research included investigation of biodegradability/bioavailability of wastewater-derived effluent dissolved ON (DON). The final-effluent DON utilization was evaluated by two different bioassay protocols in the presence and absence of nitrate. About 28–57% of the effluent DON was bioavailable/biodegradable. Bioavailable (to algae and bacteria) DON (ABDON) and biodegradable (to bacteria) DON (BDON) results did not show significant differences in terms of quantity, but DON utilization rates by ABDON (0.13 day⁻¹) protocol were higher than that of the BDON (0.04 day⁻¹) protocol in the nitrate-removal samples. As a result, ABDON requires a shorter time to exert the bioavailable fraction due to symbiotic relationship between algae and bacteria. In the nitrate-containing samples, it appears that nitrate competes with labile DON as a nitrogen source to microorganisms in both ABDON and BDON protocols. The first order decay rate of DON in the presence of nitrate was 0.11 day⁻¹ and 0.02 day⁻¹ for ABDON and BDON, respectively.     

The mechanisms of potassium permanganate on algae removal

The effect of potassium permanganate as preoxidant for algae-laden source water and the mechanism that it causes algae cells aggregation was investigated. Synthetic algae suspensions, prepared from lab-cultured Chodatella sp., were used for batch preoxidation and settling tests. In order to study the effect of water hardness on the function of permanganate, some algae suspensions were spiked with CaCl2 solution. Experiments with preformed MnO2 to look into its effect on algae cell aggregation were also conducted. The results show that preoxidation with potassium permanganate would promote the aggregation of algae cells, and this phenomenon was even more significant with the existence of hardness causing ion, calcium. In addition to incorporating its reducing product, MnO2, into algae floc, and increased its specific gravity, and therefore its settling velocity, permanganate may also induce the release of extracellular organic matters (EOM) from algae cell. Based on SEM observation, EOM probably enhanced the incorporation of MnO2 into algae floc. The role played by calcium ion in promoting the function of permanganate can be explained by charge neutralization and also bridging between negatively charged surfaces.     

Linking biokinetics and consumer-resource dynamics of zinc accumulation in pond abalone Haliotis diversicolor supertexta

A dynamic model that links biokinetics and consumer–resource dynamics for describing zinc (Zn) accumulation in abalone Haliotis diversicolor supertexta has been developed and then applied to Zn data from real abalone farms. The biokinetic parameters used in this study, uptake and depuration rate constants of abalone and their food source, red alga Gracilaria tenuistipitata var. liui, were obtained from a laboratory 14-d exposure experiment. We carried out a sensitivity analysis of the model by using the fractional factorial design technique, taking into account the influence of consumer–resource-related parameters such as growth and death rates and biomass and biokinetic parameters characterized by bioconcentration factor. Results indicate that the response time of biomagnification dynamics of Zn accumulation in abalone was influenced mainly by the growth rate of algae and biomass and the death rate of abalone and by interactions algae biomass and abalone death rate and abalone and algae biomass. New algae production results in substantially higher values of biomagnification factor. The linked model was then applied to field observations from a real-life situation of variable Zn concentrations occurring in abalone farms. Simulation results show that the predicted values are within a factor of 2 of the measured values (% errors range from 5.3±4% to 44.1±8%). Both model analysis and model application to the abalone farms suggest that the linking influences between biokinetics and consumer–resource dynamics support Zn accumulation in H. diversicolor supertexta and in G. tenuistipitata var. liui as functions of Zn concentration in water and abundance of food occurring in abalone farms.     

太湖芦苇根系中溶藻菌的分离鉴定及溶藻效果

富含氮、磷、钾等营养物质的污水排入河流、湖泊,造成蓝藻爆发,而溶藻菌可以有效降解水体中的蓝藻污染。从蓝藻污染严重的太湖百渎港岸边芦苇根系中筛选出1株溶藻菌(Bacillus sp),命名为G6,系统发育分析表明,G6菌株与芽孢杆菌同源性最高。将培养至对数期的G6菌液以菌藻比1∶10的比例,在温度28℃、光强2 500lx、光暗比12h∶12h的条件下经光照培养箱培养7d,对铜绿囊藻液Chla去除率可达82%。此外,G6菌株在无光照条件下也具有溶藻特性,这有利于其在缺少光照的深水域中增殖并发挥溶藻作用。G6通过分泌溶藻物质杀灭铜绿囊藻,属于间接溶藻,且溶藻物质具有热稳定性,能够在较高温度下发挥溶藻特性。     

TP浓度和季节变化对再生水水体中藻类生长的影响

藻类的过度生长是将再生水用于城市景观水体时面，临的难题之一。采用城市再生水，在南方某市开展了以再生水为补水的景观水体的藻类生长模拟试验，重点考察了春、夏、秋、冬四个不同季节以及不同总磷浓度下的藻类生长特征。结果表明，在春、夏、秋季，影响藻类生长的最主要因素是总磷浓度，而在冬季则是活跃的藻种。这一研究成果对于再生水景观水体的运行管理和藻类生长的控制具有一定的参考价值。     

Recovery of Giardia cysts from water: Centrifugation vs filtration

Methods for the recovery of Giardia cysts from large volume (1900 l.) water samples were experimentally examined in the laboratory and applied to 22 surface water supplies around Washington state. Orlon yarn-wound filters (7 and 1 μm porosity) were compared, with higher cyst recovery rates observed for 1 μm filters. For each experiment, half the recovered material was processed through a series of screens while the other half was processed through an algae (Foerst) centrifuge. Both methods recovered cysts from 1900 l. water samples containing as few as 6000 cysts, with higher recovery rates observed for the algae centrifuge. Cysts were recovered more often from surface water sources implicated in outbreaks (3 of 4) than from sources not implicated in known outbreaks (2 of 18).     

不同混凝剂强化除藻、除浊的研究

采用聚合氯化铝(PAC)、聚合氯化铝铁(PAFC)、聚合硫酸铁(PFS)、聚合硫酸铝(PAS)和硫酸铝(AS)五种混凝剂对某含藻湖水进行强化混凝除藻、除浊试验研究,考察了混凝剂种类及投量、原水pH、沉降时间等因素对强化混凝效果的影响。结果表明,五种混凝剂的综合除藻、除浊性能排序为:PACPAFCPFSPASAS;在原水pH值为5~9的范围内,含铁混凝剂PFS和PAFC对pH的适应性较强,且在pH值为5~7的弱酸性条件下,PFS的除藻、除浊性能最优,当其投量为4 mg/L时,除藻率近80%,除浊率可达80%以上;而在pH值为7~9的弱碱性条件下,PAC则表现出更好的除藻、除浊效果,当其投量为4 mg/L时,除藻率和除浊率可分别达到83%和90%;AS对pH的适应性最差,其除藻、除浊效果最差;另外,五种混凝剂的除藻率、除浊率均随沉降时间的延长而增大,最佳沉降时间为20 min。     

The impact of differing cell and algogenic organic matter (AOM) characteristics on the coagulation and flotation of algae

The aim of this study was to compare the coagulation and flotation of different algae species with varying morphology and algogenic organic matter (AOM) composition in order to link physical and chemical algae characteristics to treatment. Microcystis aeruginosa (cyanobacteria), Chlorella vulgaris (green algae), Asterionella formosa and Melosira sp. (diatoms) were treated by coagulation with aluminium sulphate and flotation. The AOM was extracted and treated separately. Analyses included cell counts, dissolved organic carbon, aluminium residual and zeta potential. Removal efficiencies in the range 94-99% were obtained for each species. Cells, AOM and aluminium were concurrently removed at a coagulant dose that was related on a log-log basis to both cell surface area and total charge density, although the relationship was much stronger for the latter. This was attributed to a significant proportion of the coagulant demand being generated by the AOM. The implications of such findings are that relatively simple charge measurements can be used to understand and control coagulation and flotation of algae.     

Future algal biofuels: implications of environmental temperature on production strain selection

Current and future economic mass production of microalgae or cyanobacteria will require suitable, preferably relatively high, levels of photosynthetically active radiation (PAR). Most large-scale productions sites, as well as those under development or under consideration, have been located between 40N and 40S raising the possible issue of the algae being periodically, or routinely, subjected to elevated temperatures (>30°C). The effects of environmental temperatures in the range 8–35°C on the marine, oleaginous model alga Nannochloropsis oculata were assessed. Active growth was observed at all temperatures except 35°C, where cells bleached and died. The implications of elevated temperature regimes were assessed for a variety of potential biofuel producing, biotechnologically relevant freshwater, marine and hyper-saline algae and the implications for their biotechnological exploitability discussed.     

Inorganic carbon limited growth kinetics of some freshwater algae

The inorganic carbon limited growth kinetics were determined for three green and three blue-green algae over a range of light and temperatures. Anabaena flos aquae was found to be the only algae to grow at 39°C. Selenastrum capricornutum and Scenedesmus quadricauda were favored at low temperatures with Selenastrum growing best at high light and carbon levels while Scenedesmus was the most rapidly growing algae under low light, carbon and temperature conditions.Chorella was the fastest growing alga at temperatures from 27 to 33°C under all light and inorganic carbon concentrations. Neither Oscillatoria nor Microcoleus were found to be the dominant algae under the conditions tested. However, under reduced light and temperature conditions, Oscillatoria grew well at high inorganic carbon concentrations.