Acidification Stage Research Articles

Correlating microbial diversity patterns with geochemistry in an extreme and heterogeneous environment of mine tailings.

Recent molecular surveys have advanced our understanding of the forces shaping the large-scale ecological distribution of microbes in Earth's extreme habitats, such as hot springs and acid mine drainage. However, few investigations have attempted dense spatial analyses of specific sites to resolve the local diversity of these extraordinary organisms and how communities are shaped by the harsh environmental conditions found there. We have applied a 16S rRNA gene-targeted 454 pyrosequencing approach to explore the phylogenetic differentiation among 90 microbial communities from a massive copper tailing impoundment generating acidic drainage and coupled these variations in community composition with geochemical parameters to reveal ecological interactions in this extreme environment. Our data showed that the overall microbial diversity estimates and relative abundances of most of the dominant lineages were significantly correlated with pH, with the simplest assemblages occurring under extremely acidic conditions and more diverse assemblages associated with neutral pHs. The consistent shifts in community composition along the pH gradient indicated that different taxa were involved in the different acidification stages of the mine tailings. Moreover, the effect of pH in shaping phylogenetic structure within specific lineages was also clearly evident, although the phylogenetic differentiations within the Alphaproteobacteria, Deltaproteobacteria, and Firmicutes were attributed to variations in ferric and ferrous iron concentrations. Application of the microbial assemblage prediction model further supported pH as the major factor driving community structure and demonstrated that several of the major lineages are readily predictable. Together, these results suggest that pH is primarily responsible for structuring whole communities in the extreme and heterogeneous mine tailings, although the diverse microbial taxa may respond differently to various environmental conditions.

Simulation analysis of producing xylitol from hemicelluloses of pre-hydrolysis liquor

The pre-hydrolysis liquor (PHL) of the kraft-based dissolving pulp production process is currently sent to the recovery boiler and incinerated. However, PHL contains about 5–8% lignocelluloses that can be utilized in the production of value-added chemicals. In this study, a process for producing xylitol from hemicelluloses in PHL is developed. This process involves several acidification, neutralization, adsorption (along with reactivation) and evaporation stages. The mass balance indicates that 533kg/h xylitol (with 99% purity), 187kg/h lignin, 806kg/h basic ferric acetate, and 1600kg/h gypsum can be produced from 41,670kg/h PHL. The energy balance shows that the evaporators are the largest consumers of energy, while the reactivation kiln, acidification, neutralization, and precipitation processes generate some heat. Overall, 41% conversion of xylose to xylitol is achieved.

HIGH RATE BIO METHANATION OF MUNICIPAL SOLID WASTE

Growing urbanization and industrialization have led to the generation of large quantities of solidwastes, which can be broadly classified as MSW (Municipal Solid Waste) and ISW (Industrial SolidWaste). Among the options available for solid waste management, biomethanation appears to be themost desirable because it is a technology with triple benefits: yields biogas which can replaceconventional fuels, provides digested sludge which can be used as a soil conditioner and manages theenvironment.This work involved the development of a three-stage leachate based bioreactor system for solid wastemanagement. The first stage involves extraction of high organic strength (high in chemical oxygendemand - COD) liquid called leachate from the solids. This stage is known as the hydrolysing stage.Acid formation takes place in the second or the acidification stage in a separate reactor known as theacidification reactor. Biogas is generated by treating the acidified leachate in an upflow anaerobicfilter (AF) reactor in the third (or the methanation) stage.Three stage anaerobic systems arc increasingly finding its place in biogas generation. Two kineticallydissimilar groups of bacteria, acetogenes and methogencs arc physically separated in acetogenicreactor and methanogenic reactor. This separation allows optimization of both acetogenesis andmethanogenesis stages making the process control easier.In this method, the organic solid waste is cut into small pieces, fed into the hydrolysing reactor withwater and circulated at a fixed rate to wash off organic acids formed until high organic strength isobtained. This is then fed in to the acidification reactor. The acidification phase has retention time ofG days. Anaerobic conditions prevail inside the reactor during the whole process. The residue leftinside from the first reactor is subjected to drying for manure preparation.The final concentrated leachate obtained after 6 days is fed in to the AF reactor for methanation. Thisphase has retention time of 5 days. The microbial consortia present in the AF sludge destroys highamount of COD, forming biogas comprising of 65% - 75% methane. This system is economicallyviable, the total space and the time required for the process is low compared to conventional singlephaseprocesses that takes 30-40 days. The system has low water consumption because of the reuse ofthe AF reactor overflow to the acidification reactor.

Evaluation of single vs. staged mesophilic anaerobic digestion of kitchen waste with and without microwave pretreatment

Effects of single and dual stage (acidogenic–methanogenic) mesophilic anaerobic digestion (AD) of kitchen waste (KW) was evaluated at hydraulic retention times (HRTs) of 20, 15, 12 and 9 d with and without thermal microwave (MW) pretreatment (145 °C). Anaerobic acidification in terms of acid accumulation was superior compared to microaerophilic acidification. Maximum anaerobic acidification of KW was determined to occur with an HRT of 2 d which was then selected for the acidification stage. The dual stage AD system fed with untreated KW produced the maximum biogas and volatile solids (VS) stabilization efficiencies at the shortest HRT of 9 d. Conversely, for free liquid resulting from MW pretreatment of KW the two stage reactor at 20 d HRT produced three fold more methane compared with the untreated free liquid control. However, MW pretreatment and AD of the free liquid fraction only, was not a sustainable treatment option. For KW, staging of the AD process had a greater positive impact on waste stabilization and methane yield compared to single stage reactors or MW pretreatment. KW can be characterized as being a readily biodegradable solid waste; concomitantly it is recommended that digester staging without MW pretreatment be employed to maximize methane yield and production.

Impacts of simulated acid rain on recalcitrance of two different soils

Laboratory experiments were conducted to estimate the impacts of simulated acid rain (SAR) on recalcitrance in a Plinthudult and a Paleudalfs soil in south China, which were a variable and a permanent charge soil, respectively. Simulated acid rains were prepared at pH 2.0, 3.5, 5.0, and 6.0, by additions of different volumes of H2SO4 plus HNO3 at a ratio of 6 to 1. The leaching period was designed to represent 5 years of local annual rainfall (1,200 mm) with a 33 % surface runoff loss. Both soils underwent both acidification stages of (1) cation exchange and (2) mineral weathering at SAR pH 2.0, whereas only cation exchange occurred above SAR pH 3.5, i.e., weathering did not commence. The cation exchange stage was more easily changed into that of mineral weathering in the Plinthudult than in the Paleudalfs soil, and there were some K(+) and Mg(2+) ions released on the stages of mineral weathering in the Paleudalfs soil. During the leaching, the release of exchangeable base cations followed the order Ca(2+) >K(+) >Mg(2+) >Na(+) for the Plinthudult and Ca(2+) >Mg(2+) >Na(+) >K(+) for the Paleudalfs soil. The SARs above pH 3.5 did not decrease soil pH or pH buffering capacity, while the SAR at pH 2.0 decreased soil pH and the buffering capacity significantly. We conclude that acid rain, which always has a pH from 3.5 to 5.6, only makes a small contribution to the acidification of agricultural soils of south China in the short term of 5 years. Also, Paleudalfs soils are more resistant to acid rain than Plinthudult soils. The different abilities to prevent leaching by acid rain depend upon the parent materials, types of clay minerals, and soil development degrees.

Comparative assessment of single-stage and two-stage anaerobic digestion for the treatment of thin stillage

A comparative evaluation of single-stage and two-stage anaerobic digestion processes for biomethane and biohydrogen production using thin stillage was performed to assess the impact of separating the acidogenic and methanogenic stages on anaerobic digestion. Thin stillage, the main by-product from ethanol production, was characterized by high total chemical oxygen demand (TCOD) of 122g/L and total volatile fatty acids (TVFAs) of 12g/L. A maximum methane yield of 0.33L CH4/gCODadded (STP) was achieved in the two-stage process while a single-stage process achieved a maximum yield of only 0.26L CH4/gCODadded (STP). The separation of acidification stage increased the TVFAs to TCOD ratio from 10% in the raw thin stillage to 54% due to the conversion of carbohydrates into hydrogen and VFAs. Comparison of the two processes based on energy outcome revealed that an increase of 18.5% in the total energy yield was achieved using two-stage anaerobic digestion.

Influence of Temperature on Hydrolysis Acidification of Food Waste

For two-phase anaerobic digestion process of food waste, degree of hydrolysis and products by acidification during hydrolysis and acidification phase directly affect the performance of methanogenesis phase. Temperature has great impact on hydrolysis and acidification of food waste. This paper monitored the dynamic change of biogas production, biogas composition, pH, soluble chemical oxygen demand (SCOD) and volatile fatty acids (VFAs) during hydrolysis and acidification stage so as to investigate specific influence of temperature on food waste. With the same inoculum and 9 days’ fermentation, three different temperatures (35, 55 and 70 °C) were taken into consideration. The results showed that cumulative gas production was 4860 mL at 70 °C, which was 129.79% and 37.87% higher than that at 35 and 55 °C. Besides, hydrogen content at 70 °C was 45.34%, which was the highest among the three temperatures. Hydrolysis rate was proportional to the increase of temperature. Meanwhile, total VFAs yield and composition widely differed at three different temperatures. The hydrolysis and acidification products at 35 °C were mainly ethanol and acetic acids and the highest concentrations of ethanol at 35 °C were 3.28 and 3.65 times of that at 55 and 70 °C, but more acetic, isobutyric and butyric acids were generated at 55 and 70 °C. Among three temperatures, 70 °C had the highest acetic acids concentration while 55 °C had the highest isobutyric and butyric acids concentration.

Combined effect of sodium dodecyl sulfate and enzyme on waste activated sludge hydrolysis and acidification

The combined effect of sodium dodecyl sulfate (SDS) and enzyme system on hydrolysis and acidification of waste activated sludge (WAS) was investigated. The results showed that the combined system was more effective in the promotion of sludge hydrolysis than sole SDS and sole enzyme, and the SDS+mixed-enzymes (ME) system had better hydrolysis performance than SDS+single enzyme system. Compared with SDS+protease and SDS+amylase systems, the soluble protein concentration in SDS+ME system increased respectively by 20.0% and 44.4%, and the soluble carbohydrate concentration increased by 78.3% and 37.0%, respectively. During the WAS acidification stage, the SDS, ME and SDS+ME system could make the maximum short-chain fatty acids (SCFAs) concentration increased by 1.82 (6th day), 2.04 (5th day), 2.32 (7th day) times, respectively. The composition analysis of SCFAs produced in SDS+ME system indicated that acetic acid was the most prevalent product and propionic acid was the second one.

Proton and cation transport activity of the M2 proton channel from influenza A virus

The M2 protein is a small, single-span transmembrane (TM) protein from the influenza A virus. This virus enters cells via endosomes; as the endosomes mature and become more acidic M2 facilitates proton transport into the viral interior, thereby disrupting matrix protein/RNA interactions required for infectivity. A mystery has been how protons can accumulate in the viral interior without developing a large electrical potential that impedes further inward proton translocation. Progress in addressing this question has been limited by the availability of robust methods of unidirectional insertion of the protein into virus-like vesicles. Using an optimized procedure for reconstitution, we show that M2 has antiporter-like activity, facilitating K(+) or Na(+) efflux when protons flow down a concentration gradient into the vesicles. Cation efflux is very small except under conditions mimicking those encountered by the endosomally entrapped virus, in which protons are flowing through the channel. This proton/cation exchange function is consistent with the known high proton selectivity of the channel. Thus, M2 acts as a proton uniporter that occasionally allows K(+) to flow to maintain electrical neutrality. Remarkably, as the pH inside M2-containing vesicles (pH(in)) decreases, the proton channel activity of M2 is inhibited, but its cation transport activity is activated. This reciprocal inhibition of proton flux and activation of cation flux with decreasing pH(in) first allows accumulation of protons in the early stages of acidification, then trapping of protons within the virus when low pH(in) is achieved.

Simulation of surface water chemistry change resulting from soil acidification: a strontium isotope approach

Soil monoliths were treated with artificial acid rain (pH 3.71). The acidity load was 40 times higher than the present acidity load. Surface water chemistry was modelled on the basis of atmospheric deposition and organic and mineral soil horizon contributions to drainage water. Contributions were calculated using 87Sr/86Sr ratios measured in Sr sources and drainage water. In the early stages of acidification the contribution of organic horizons to surface water chemistry increased by up to 70%. This increase was accompanied by increases in Ca2+, Mg2+, K+, Na+, and dissolved organic carbon (DOC) concentrations. The amount of DOC washed out from mineral horizons was higher than from organic horizons, in contrast to base cations. In the range of acidity loads from 1.4 to 2.1 keq/ha, organic anions were predominant in solution. Further acidification resulted in a reduction of all solute concentrations and an increase in the contributions by deposition and mineral horizons.

Architecture of a nascent viral fusion pore

Enveloped viruses use specialized protein machinery to fuse the viral membrane with that of the host cell during cell invasion. In influenza virus, hundreds of copies of the haemagglutinin (HA) fusion glycoprotein project from the virus surface. Despite intensive study of HA and its fusion activity, the protein's modus operandi in manipulating viral and target membranes to catalyse their fusion is poorly understood. Here, the three-dimensional architecture of influenza virus–liposome complexes at pH 5.5 was investigated by electron cryo-tomography. Tomographic reconstructions show that early stages of membrane remodeling take place in a target membrane-centric manner, progressing from punctate dimples, to the formation of a pinched liposomal funnel that may impinge on the apparently unperturbed viral envelope. The results suggest that the M1 matrix layer serves as an endoskeleton for the virus and a foundation for HA during membrane fusion. Fluorescence spectroscopy monitoring fusion between liposomes and virions shows that leakage of liposome contents takes place more rapidly than lipid mixing at pH 5.5. The relation of ‘leaky' fusion to the observed prefusion structures is discussed.

Contrasting chemical response to artificial acidification of three acid-sensitive streams in Maine, USA

We experimentally acidified three low alkalinity first-order streams in forested catchments in Maine, USA. We evaluated water samples from a reference site above the point of hydrochloric acid addition and from two or three sites located 16 to 94 m downstream. Neutralization included protonation of weak acids, adsorption of sulfate, and ion exchange of base cations and aluminum (Al) for protons (H +). Protonation of bicarbonate was significant in the relatively high pH Hadlock Brook. Protonation of weak organic acids dominated in the high dissolved organic carbon (DOC) Mud Pond Inlet. The response in low DOC, low pH East Bear Brook was dominated by stream substrate release of cations. East Bear Brook had the strongest acid neutralization response per unit catchment area. In all streams, exchangeable calcium (Ca) and magnesium (Mg) were mobilized, with Ca > Mg. Al was also mobilized. During initial stages of acidification, Ca desorbed preferentially, whereas Al mobilization dominated later. Early in the recovery, adsorption of Ca to the streambed sediments was kinetically favored over adsorption of Al. Though pH increased downstream of acid addition, the streams remained undersaturated with respect to amorphous Al(OH) 3, so Al did not precipitate. In East Bear Brook, however, Al left solution further downstream through adsorption. This process was likely kinetically controlled, because it occurred in East Bear Brook (3–4 L/s) but did not occur in Hadlock Brook (ca. 40 L/s) or Mud Pond Inlet (ca. 60 L/s). During experimental acidification, the initial Al:Ca ratio of a stream's response may indicate the acidification status of the catchment. Short-term stream acidification experiments illuminate processes characteristic of episodic stream acidification and of long-term catchment acidification. East Bear Brook and Hadlock Brook catchments are in early to intermediate stages of acidification. The Mud Pond Inlet catchment (high Al:Ca ratio) is in a later stage of acidification.

Cystic Fibrosis Transmembrane Conductance Regulator-independent Phagosomal Acidification in Macrophages

It was reported recently that the cystic fibrosis transmembrane conductance regulator (CFTR) is required for acidification of phagosomes in alveolar macrophages (Di, A., Brown, M. E., Deriy, L. V., Li, C., Szeto, F. L., Chen, Y., Huang, P., Tong, J., Naren, A. P., Bindokas, V., Palfrey, H. C., and Nelson, D. J. (2006) Nat. Cell Biol. 8, 933-944). Here we determined whether the CFTR chloride channel is a generalized pathway for chloride entry into phagosomes in macrophages and whether mutations in CFTR could contribute to alveolar macrophage dysfunction. The pH of mature phagolysosomes in macrophages was measured by fluorescence ratio imaging using a zymosan conjugate containing Oregon Green(R) 488 and tetramethylrhodamine. Acidification of phagolysosomes in J774A.1 macrophages (pH approximately 5.1 at 45 min), murine alveolar macrophages (pH approximately 5.3), and human alveolar macrophages (pH approximately 5.3) was insensitive to CFTR inhibition by the thiazolidinone CFTR(inh)-172. Acidification of phagolysosomes in alveolar macrophages isolated from mice homozygous for DeltaF508-CFTR, the most common mutation in cystic fibrosis, was not different compared with that in alveolar macrophages isolated from wild-type mice. We also measured the kinetics of phagosomal acidification in J774A.1 and murine alveolar macrophages using a zymosan conjugate containing fluorescein and tetramethylrhodamine. Phagosomal acidification began within 3 min of zymosan binding and was complete within approximately 15 min of internalization. The rate of phagosomal acidification in J774A.1 cells was not slowed by CFTR(inh)-172 and was not different in alveolar macrophages from wild-type versus DeltaF508-CFTR mice. Our data indicate that phagolysosomal acidification in macrophages is not dependent on CFTR channel activity and do not support a proposed mechanism for cystic fibrosis lung disease involving defective phagosomal acidification and bacterial killing in alveolar macrophages.

Measured and computed neutralization potentials from static tests of diverse rock types

Static tests typically are used in the initial stage of environmental assessments to predict the potential for acid mine drainage, and also are used to monitor waste disposal at active mining operations. The neutralization potential (NP) of 19 sedimentary, metamorphic, and igneous extrusive rocks was measured by the Sobek method to compare the results with those computed by using the quantitative mineralogy of the rocks and the NP values that were deemed to be appropriate for the individual minerals. Most of the computed NP values of the rocks are lower than the measured values, but a close relationship is evident. If the contents of carbonate minerals are low, the NP in non-ultramafic igneous rocks typically is controlled by the amount of Ca substitution in plagioclase, whereas in ultramafic rocks the NP contribution is dominated by the amount of olivine and serpentine. Compositional and NP analyses of plagioclase concentrates indicate that the NP systematically varies from <1 for the Na end-member to about 14 for compositions near that of the Ca end-member. Among several variables that can affect the Sobek NP values, the volume and normality of the acid added to the sample are well-known to influence the results; however, the temperature and duration of the acidification stage can also have a pronounced effect on the measured NP of some rocks, depending on their mineralogy. Fizz tests to estimate the carbonate content and the consequent acid addition are highly subjective, and the ‘no fizz’ rating is not to be taken literally. The NP results themselves provide a clear indication of whether a sample has been over-acidified or under-acidified in the test procedure.

Subfossil chironomids (Diptera, Chironomidae) in three Tatra Mountain lakes (Slovakia) on an acidification gradient

Three lakes were studied in the High Tatra Mountains at altitudes from 2000 to 2157 m a.s.l., which represent three categories of acidity status recognised in the Tatra lakes in the 1980s: non-acidified, acidified, and strongly acidified. Subfossil chironomid remains from dated sediment cores covering ca. throughout 200 years were analysed. The chironomid thanatocoenoses of all cores layers reflected ultra-oligotrophic non-acidified conditions in L’adove pleso. Nevertheless, the finding of the acid-tolerant species Zalutschia tatrica in littoral samples in 1980s indicates that the littoral zone was more influenced by acidification than deeper areas of the lake. Three stages of lake developmental history can be distinguished in the acidified lake Vysne Wahlenbergovo pleso based on the chironomid subfossil record: the pre-acidification stage before the 1920s, the anthropogenic acidification stage between the 1920–1980s, and the recovery of the lake from the end of the 1980s. The period of acidification was accompanied by a decline in chironomid numbers, while chironomid fauna composition was unchanged during the whole investigated history of the lake. None of the chironomid taxa present prior to the acidification period disappeared during the peak of acidification. The most apparent change in the sediment record taken from the strongly acidified lake Starolesnianske pleso was recognised in the layers corresponding to the period 1960–1980. It is characterised by the disappearance of the dominant acid-sensitive Tanytarsus lugens group and the dominance of acidtolerant Tanytarsus gregarius group. The most recent chironomid assemblage probably benefits from the amount of food resources as a result of increased lake productivity induced by acidification.

Diversity of epilithic diatoms in high mountain lakes under the stress of acidification (Tatra Mts, Poland)

Using the epilithic diatoms as indicators of environmental conditions, 10 lakes in the High Tatra Mountains were characterised with regard to their stage of acidification. The diatom communities were diverse; 210 taxa were found, including 27 species of north and alpine preference. On the basis of cluster analysis, two groups of lakes were distinguished. The first group included shallow, moderately acidified lakes (Dlugi and Zmarzly Gasienicowy lakes), where acidophilous organisms prevailed, with Achnanthes marginulata being the most numerous. The structure of the diatom community in Dlugi lake was stable over 4 years of observations and did not show any progress in acidification. The second group included mostly very deep, non-acidified lakes where circumneutral organisms prevailed, and among them Achnanthes minutissima was dominant in most cases. The diatom community structures mostly confirmed the status of the lakes studied as judged from their water chemistry.

Effects of Gamma Irradiation on the Fermentative Microorganisms and Lactate Dehydrogenase Activity in Kimchi at Different Fermentation Stages

Gamma irradiation treatment was performed at the early and mid-fermentation stages of Kimchi preparation. Changes in fermentative microorganisms and lactate dehydrogenase activity during the fermentation periods were investigated to determine proper irradiation point for extending the shelf life of Kimchi. Initial levels of acid producing bacteria and yeast in Kimchi were 10⁴ CFU g^(-1) and 10¹ CFU g^(-1), and reached up to 10^9 CFU g^(-1) after 15 days and 10^7 CFU g^(-1) after fermentation for 30 days at 10℃, respectively. The radiation resistance of acid producing bacteria in the earlier stage (D_10 value was 0.87 kGy) was higher than at the midfermentation stage (after 10 days at 10℃, D_(10) value was 0.69 kGy). Microbial growth and lactate dehydrogenase activity were inhibited significantly by gamma irradiation at the early fermentation stage of Kimchi and acidification was effectively delayed during the subsequent storage period. Although the growth of fermentative microorganisms was inhibited by gamma irradiation at the mid-fermentation stage of Kimchi, lactate dehydrogenase activity was maintained and acidification continued during the storage period.

Treatment of winery wastewater by an anaerobic sequencing batch reactor

Treatment of winery wastewater was investigated using an anaerobic sequencing batch reactor (ASBR). Biogas production rate was monitored and permitted the automation of the bioreactor by a simple control system. The reactor was operated at an organic loading rate (ORL) around 8.6 gCOD/L.d with soluble chemical oxygen demand (COD) removal efficiency greater than 98%, hydraulic retention time (HRT) of 2.2 d and a specific organic loading rate (SOLR) of 0.96 gCOD/gVSS.d. The kinetics of COD and VFA removal were investigated for winery wastewater and for simple compounds such as ethanol, which is a major component of winery effluent, and acetate, which is the main volatile fatty acid (VFA) produced. The comparison of the profiles obtained with the 3 substrates shows that, overall, the acidification of the organic matter and the methanisation of the VFA follow zero order reactions, in the operating conditions of our study. The effect on the gas production rate resulted in two level periods separated by a sharp break when the acidification stage was finished and only the breaking down of the VFA continued.

Life history characteristics of brown trout in lakes at different stages of acidification

In 66 Norwegian lakes with allopatric populations of brown trout Salmo trutta that ranged from highly acidified to non-acid (pH 4·7–6·6) there was a significant inverse correlation between mean age and relative abundance (CPUE). As mean annual survival rates were not significantly related to CPUE, this population response may indicate that recruitment was lower in low-density lakes. Age-specific masses were significantly higher in populations that had declined in abundance than in unaffected populations. Mean body mass at sexual maturity in both males and females was inversely correlated with CPUE. Between populations, high age at maturity was associated with high survival rates in both sexes. Age at maturity correlated positively with specific growth rate between the ages of 1 and 2 years in females only.

Life history characteristics of brown trout in lakes at different stages of acidification

In 66 Norwegian lakes with allopatric populations of brown trout Salmo trutta that ranged from highly acidified to non‐acid (pH 4·7–6·6) there was a significant inverse correlation between mean age and relative abundance (CPUE). As mean annual survival rates were not significantly related to CPUE, this population response may indicate that recruitment was lower in low‐density lakes. Age‐specific masses were significantly higher in populations that had declined in abundance than in unaffected populations. Mean body mass at sexual maturity in both males and females was inversely correlated with CPUE. Between populations, high age at maturity was associated with high survival rates in both sexes. Age at maturity correlated positively with specific growth rate between the ages of 1 and 2 years in females only.