Lake Water pH Research Articles

Diatoms as quantitative indicators of pH and water temperature in subarctic Fennoscandian lakes

Weighted averaging (WA) regression and calibrationbased optima and tolerances of lakewater pH andtemperature are presented for diatoms in ecologicallysensitive, subarctic Fennoscandian lakes. The studysites are mostly small, simple, oligotrophic,low-conductivity lakes with a pH range from 5.0 to7.7 and a temperature range (after data screening)from 9.3 to 15.0 °C. Experiments with inverse andclassical deshrinking, with or without tolerancedownweighting, were used to identify the bestcalibration functions. The model estimates wereadjusted by jackknifing procedures. WA by inversedeshrinking and with tolerance downweighting performedbest for pH prediction, whereas simple WA wasmarginally superior for predicting water temperature.The established pH model is accurate to within± 0.39 H units, and the temperature model towithin ± 0.88 degrees Celcius. Fifteen diatom taxawere identified as potential indicator species for pHand three for temperature.

Setting Restoration Goals for an Acid and Metal-Contaminated Lake: A Paleolimnological Study of Daisy Lake (Sudbury, Canada)

ABSTRACT Many lakes in the Sudbury region of Ontario have been affected by acidic and metal inputs as a result of local smelting operations. Several initiatives are now underway to restore some of these systems. Long-term limnological data are rarely available, therefore lake managers must use proxy methods to set reasonable targets for lakes undergoing mitigation. Daisy Lake is presently an acidic (pH 4.7), metal-contaminated lake (Ni=370 μg L−1; Al=350 μg L−1), that has been selected for mitigation efforts. We used fossil pollen analysis to reconstruct past changes in terrestrial vegetation, and paleolimnological techniques (primarily diatoms and chrysophytes) to identify pre-disturbance conditions and to reconstruct past changes in water quality variables in Daisy Lake. Our data indicate that, if Daisy Lake and its watershed are limed to restore the lake to a state that approximates the pre-disturbance natural pH, the lake water pH has to be about 1.5 pH units higher than its present level.

Influence of organic acids on model projections of lake acidification

We employed three mathematical models to make quantitative estimates of the pH of 33 statistically-selected lakes in the Adirondack mountains, New York (USA) prior to the Industrial Revolution (1840). The models included 1) the MAGIC watershed acidification model, 2) a paleolimnological model of diatom-inferred pH, and 3) the MAGIC model modified to incorporate an empirically-based model of natural organic acidity. Application of approaches 2) and 3) yielded consistent estimates of pre-industrial Adirondack lakewater pH. However, when the organic acid model was not included, MAGIC calculations and diatom-inferred values showed poor agreement. MAGIC projections of lakewater pH 50 years into the future, under differing atmospheric deposition scenarios, were also sensitive to inclusion of the organic acid model. MAGIC predicted greater recovery in response to reduced deposition when organic acids were not considered. These results suggest that failure to consider the pH buffering of naturally-occurring organic acidity will often result in biased projections which overemphasize the response of lakewater pH to changes in atmospheric inputs of strong acid.

Long-term trends in limnological characteristics in the Aurora trout lakes, Sudbury, Canada

Paleolimnological techniques were employed to document the limnological histories of the aurora trout lakes, located in the Sudbury region of Ontario. Two of these lakes are of special interest to fisheries managers, as they represent the only known native habitats of a rare strain of brook trout: the aurora trout. These lakes were limed as part of restoration efforts. Stratigraphic changes in diatom and chrysophyte assemblages from dated lake sediment cores indicate that all the lakes have been impacted by anthropogenic acidification, although the timing and the magnitude of acidification were different amongst the lakes. For example, Whirligig Lake was likely the most naturally acidic lake in the past, but it had further acidified since about 1960. This lake was limed in 1989 and then again in 1993. In Whitepine Lake, acidification started 1940; however, in the most recent sediments (∼1992), some recovery in lakewater acidity has occurred. In Little Whitepine Lake (a reference lake), acidification started earlier (∼1920) and the lakewater pH continued to decline until about 1990. This lake was limed in 1989. The chrysophyte paleoindicators suggest a recent recovery in this lake. The successful re-introduction of aurora trout in Whirligig and Whitepine lakes is undoubtedly related to the improved water quality through liming but, based on our paleolimnological indicators, the lakes' limnological characteristics (e.g. pH and metal concentrations) are still different from those present before atmospheric deposition of strong acids from the Sudbury smelters.

A high-resolution late-glacial and early Holocene diatom record from Baffin Island, eastern Canadian Arctic

An interval of late-glacial to early Holocene sedimentation, spanning the period 12.9–8.4 ka BP (14C dated by accelerator mass spectrometry), is contained within 15 cm of gyttja in a core from a small lake on southwestern Cumberland Peninsula, Baffin Island. This sediment was subsampled in continuous 2.5 mm increments for diatom analysis. Extremely low sediment accumulation rates (~1.8 cm ka−1) are characteristic of the initial phase of organic sedimentation, but they increase rapidly (to 14.2 cm ka−1) after 9 ka BP. The first 0.5 cm of gyttja contained an acidophilous diatom flora resembling that of underlying mineral sediments. Thereafter, and throughout the late glacial and earliest Holocene, diatom floras were dominated by alkaliphilous and circumneutral species of Fragilaria. Around 9 ka BP, shifts to acidophilous floras dominated by Brachysira brebissonii, and, later, Eunotia rhomboidea and Frustulia rhomboides vars. saxonica and crassinervia, suggest a period of natural lake acidification. High diatom production accompanied the lowered lake-water pH, which reflects, respectively, the paleolimnological response to an early Holocene climatic optimum, and progressive depletion of lake alkalinity sources. There is no evidence of diatom or sediment responses attributable to the Younger Dryas oscillation, implying that deglacial reorganizations of the North Atlantic Ocean did not necessarily affect paleoclimatic conditions in the southern Cumberland Sound region.

The environmental history of a mountain lake (Lago Paione Superiore, Central Alps, Italy) for the last c. 100 years: a multidisciplinary, palaeolimnological study

A palaeoecological study of an oligotrophic alpine lake, Paione Superiore (Italy), provided a record of historical changes in water quality. Historical trends in lake acidification were reconstructed by means of calibration and regression equations from diatoms, chrysophycean scales and pigment ratios. The historical pH was inferred by using two different diatom calibration data sets, one specific to the alpine region. These pH trends, together with the record of sedimentary carbonaceous particles and chironomid remains, indicate a recent acidification of this low alkalinity lake. Concentration of total organic matter, organic carbon, nitrogen, biogenic silica (BSiO2), chlorophyll derivatives (CD), fucoxanthin, diatom cell concentration and number of chironomid head capsules increased during the last 2–3 decades. When expressed as accumulation rates, most of these parameters tended to decrease from the past century to c. 1950, then all except P increased to the present day. A marked increase in sedimentary nitrogen may be related to atmospheric pollution and to the general increases in output of N in Europe. High C/N ratios indicate a prevailing allochthonous source of organic matter. Finally, the increase in measured air temperature from the mid-1800's appeared to be related to lake water pH before industrialization: cold periods generally led to lower pH and vice-versa. The more recent phenomenon of anthropogenic acidification has apparently decoupled this climatic-water chemistry relationship.

Diatom-based water chemistry reconstructions from northern Sweden: a comparison of reconstruction techniques

The diatom composition in surface sediments from 119 northern Swedish lakes was studied to examine the relationship with lake-water pH, alkalinity, and colour. Diatom-based predictive models, using weighted-averaging (WA) regression and calibration, partial least squares (PLS) regression and calibration, and weighted-averaging partial least squares (WA-PLS) regression and calibration, were developed for inferences of water chemistry conditions. The non-linear response between the diatom assemblages and pH and alkalinity was best modelled by weighted-averaging methods. The lowest prediction error for pH was obtained using weighted averaging, with or without tolerance downweighting. For alkalinity there was still some information in the residual structure after extracting the first weighted-averaging component, which resulted in a slight improvement of predictions when using a two component WA-PLS model. The best colour predictions were obtained using a two component PLS model. Principal component analysis (PCA) of the prediction errors, with some characteristics of the training set included as passive variables, was performed to compare the results for the different alkalinity predictive models. The results indicate that calibration techniques utilizing more than one component (PLS and WA-PLS) can improve the predictions for lakes with diatom taxa that have broad tolerances. Furthermore, we show that WA-PLS performs best compared with the other techniques for those lakes that have a high relative abundance of the most dominant taxa and a corresponding low sample heterogeneity.

Paleolimnological assessment of long-term water-quality changes in south-central Ontario lakes affected by cottage development and acidification

Sediment diatom assemblages were used to evaluate water-quality changes since preindustrial times in south-central Ontario lakes receiving acidic deposition and moderate shoreline (mainly cottage) development. Canonical correspondence analysis identified significant relationships between surface sediment diatoms and environmental factors. Relationships were sufficiently strong to develop weighted-averaging regression-calibration models for inferring lake water pH and total phosphorus concentration ((TP)) from diatoms. These models were accurate to within ±0.21 pH units and ±4.2 µg TP·L -1 . Postindustrial pH and (TP) changes were inferred from surface and pre-1850 sediment diatom assemblages. Results suggest that presently acid lakes (pH 7) has increased, as observed in other regions receiving elevated acidic deposition. Diatom-inferred (TP) suggests that cultural eutrophication has not been widespread. In almost all lakes, present-day (TP) is not higher than before European settlement. In many mesotrophic lakes, preindustrial (TP) was higher than at present. Several factors could account for declining lake water (TP), including (i) lake and (or) watershed acidification processes that reduce P loading, or increase P loss rates; and (ii) reductions in nutrient loading from watersheds as a result of reforestation. Resume : Nous nous sommes servis des assemblages de diatomees dans les sediments pour evaluer les changements de la qualite de l'eau, depuis la periode preindustrielle, dans des lacs du centre-sud de l'Ontario qui ont connu des depots acides et un developpement du littoral modere (principalement construction de chalets). L'analyse de correspondance canonique a releve des relations significatives entre la presence des diatomees dans les sediments superficiels et les facteurs environnementaux. Les relations etaient suffisamment fortes pour que nous elaborions des modeles de regression-calibration a moyenne ponderee permettant de calculer le pH de l'eau du lac et la concentration de phosphore total ((PT)) a partir des diatomees. Ces modeles etaient exacts jusqu'a ±0,21 unite de pH et ±4,2 µg PT·L -1 . Nous avons

The late Quaternary development of three ancient tarns on southwestern Cumberland Peninsula, Baffin Island, Arctic Canada: paleolimnological evidence from diatoms and sediment chemistry

Sediment diatom and chemical analyses of cores from three poorly buffered extra-glacial lakes on the northeastern margin of the Canadian Shield (Cumberland Peninsula, Baffin Island) record interactions between aquatic and terrestrial spheres that were influenced by late Quaternary climatic conditions. Although differences exist between each of the lakes, notably with regards to the intensity of pre-Holocene catchment erosion and the timing of the onset of organic sedimentation, an underlying pattern of lake ontogeny, common to all three lakes, is identified. Although intensified watershed erosion characterized the Late Wisconsinan and Neoglacial cold periods, the lakes nonetheless remained viable ecosystems at these times. Sudden catchment stabilization during the late-glacial to earliest Holocene is associated with incipient organic sedimentation. Lake-water pH increased at this time, likely in response both longer base cation residence times as lake flushing rates decreased, and enhanced alkalinity production from sediment biogeochemical reactions. Subsequently, as the catchments remained stable during the productive early Holocene (c.9–7 ka BP), then gradually received a renewed increase of minerogenic sedimentation, the breakdown of sources of lake alkalinity resulted in natural acidification. Burial of cation-rich mineral sediments and the loss of permanent sedimentary sinks for the products of microbial reduction likely impeded within-lake alkalinity production, and catchment-derived base cations appeared ineffective in curtailing pH declines. The general nature of the Holocene development of these lakes is similar to that observed elsewhere on crystalline terrains, following deglaciation. Our data therefore suggest that catchment glaciation is not a necessary precursor for models of lake development characterized by initial base cation enrichment and subsequent gradual acidification.

Controlled reversal of lake acidification by treatment with phosphate fertilizer

LAKES that have become acidified by airborne pollutants typically have low biological productivity and support an impoverished flora and fauna1. In their natural state, these lakes were poorly buffered, and had a pre-industrial pH on the acid side of neutral2. Although they can be neutralized by adding base, the resulting calcium-rich water supports plant and animal communities that are unlike those found in natural softwater lakes1. It is known, however, that the long-term buffering of soft waters can be appreciably influenced by their biological productivity3a¤-5. Here we report field-study results that show that by adding phosphate fertilizer to stimulate primary productivity, it is possible to generate sufficient base by the assimilation of nitrate to raise the pH of acid lake waters without drastically altering their community structure. Owing to the high efficiency of base production, only modest additions of phosphate are required, phytoplankton growth is not excessive and there is a marked increase in biological productivity at all trophic levels. In the longer term, additional quantities of base should be generated by the anoxic decomposition of organic material accumulating on the lake bed.

The representation of diatom communities by fossil assemblages in a small acid lake

The representative quality of fossil diatom assemblages in the recent sediment of a lake is compared with its contemporary diatom flora. In April 1986 experimental liming of the catchment of a small acidified lake, Loch Fleet (Galloway, U.K.), produced immediate changes in water quality. Lakewater pH rose from a mean of approximately 4.5 to 6.5, and in the two year period following liming a consistently higher pH was maintained. The marked response of diatom species to changing water quality provided a means of tracing events from living communities to the fossil assemblages. Diatom periphyton and plankton were sampled during a 20 month period and archived material was used to characterise earlier diatom communities. A comparison is made between living diatom communities and diatom assemblages collected by sediment traps and from sediment cores taken during the same period.

DIATOM EVIDENCE OF PAST WATER QUALITY CHANGES IN ADIRONDACK SEEPAGE LAKES (NEW YORK, U.S.A.)

Diatom assemblages were studied from the surface sediments of 20 seepage lakes in Adirondack Park, New York (U.S.A.). Diatom species composition was similar to that recorded in nearby drainage lakes, but the relative proportions of the taxa were different. Canonical correspondence analysis indicated that lakewater pH, watershed area, and elevation were important environmental variables correlated with the distribution of diatom taxa. Weighted-averaging regression and calibration were used to develop a lakewater inference model using the relative abundance of diatom taxa in the surface sediments of seepage lakes. This transfer function was then applied to infer pre-industrial lakewater pH from diatoms preserved in pre-industrial sediments of 13 seepage lakes. Our data indicate that, similar to Adirondack drainage lakes, recent acidification has occurred in seepage lakes; however, the magnitude of acidification has been less in the seepage lakes.

Recovery from acidification in Lake �rvattnet, Sweden

Lake Orvattnet has been monitored extensively for both chemical and biological variables since 1967. The lake acidified during the 1960's and pH was mostly below 5 throughout the 1970's. Due to the acidification, peat moss (Sphagnum spp.) expanded over the lake bottom and the only surviving fish species was perch (Perca fluviatilis), but it experienced reproduction problems. In the mid 1980's, the Sphagnum cover collapsed, and by 1989 it had almost disappeared. There has been a clear recovery of the perch population. Recovery of the lake is also recorded by diatom assemblages in the lake sediment. Diatom-inferred pH increased from 4.7 to 4.9. The development of measured lake-water pH is unclear, but acid episodes in spring have become less severe. By 1993, atmospheric sulphate deposition had decreased by 30–40% in this area of Sweden compared to the late 1960's. Lake-water sulphate concentrations have decreased by ∼30% since the 1960's. Nitrogen deposition has increased over the last decades, but is not yet contributing to lake acidification. No major land-use changes have occurred and changes in hydrology cannot explain the observed changes in chemistry and biology. We ascribe the recent recovery in the lake to reduced deposition of sulphate. In conclusion, Lake Orvattnet has begun to recover from acidification.

Abiotic and Seasonal Factors Influencing Trace Metal Levels (Cd, Cu, Ni, Pb, and Zn) in the Freshwater AmphipodGammarus fasciatusin Two Fluvial Lakes of the St. Lawrence River

The potential use of the freshwater amphipod Gammarus fasciatus as a biomonitor of metal pollution has been assessed in two fluvial lakes of the St. Lawrence River. Metal (Cd, Cu, Fe, Mn, Ni, Pb, and Zn) concentrations were measured twice at 22 sites in Lakes St. Pierre and St. Louis, both in oxic sediments and in amphipods. Concentrations of free-metal ions at the sediment–water interface were estimated from lake water pH and sediment/water sorption equilibria. Multiple linear regression models forecasting trace metal (Cd, Cu, Ni, Pb, and Zn) levels in amphipods were developed, using abiotic variables (sediment-bound metals, sediment organic carbon, free-metal ions, hydrogen ions, dissolved calcium, and dissolved organic carbon) and biotic (size class) variables. These models explained 73–81% of the observed variation, except in the case of Zn (68%) and Cu (61%), indicating that G. fasciatus is a promising biomonitor for Cd, Ni, and Pb in littoral environments. Seasonal patterns of amphipod contamination were identified for Fe, Ni, and Pb, summer concentrations being higher than those measured during the fall. Size-dependent variation in amphipod metal levels was found, smaller organisms being more contaminated than larger ones.

When Did Acid-Sensitive Adirondack Lakes (New York, USA) Begin to Acidify and Are They Still Acidifying?

A transfer function was used to reconstruct pH values of 20 low-alkalinity Adirondack Park lakes based on the species composition of scaled chrysophytes (Chrysophyceae, Synurophyceae) in stratigraphie intervals from210Pb-dated sediment cores. Approximately 80% of the lakes acidified since preindustrial times. Four categories of lake response to acidic deposition were identified: (i) lakes that showed little or no evidence of acidification since preindustrial times, (ii) lakes with preindustrial pH values between 5 and 6 that began to acidify ca. 1900, (iii) "naturally" acidic lakes that acidified even further ca. 1900, and (iv) lakes with preindustrial pH values around 6 that acidified ca. 1930–50. Lakes that acidified ca. 1900 were generally smaller, higher elevation lakes with lower preindustrial pH values than lakes in category i or iv. These patterns are consistent with the acidic deposition hypothesis of recent lake acidification. Our results indicated that "critical" sulfate deposition loads for Adirondack lakes that started to acidify ca. 1900 and ca. 1950 are between 5–10 and 20–25 kg∙ha−1∙yr−1, respectively. Post-1970 trends in lake water pH have been small and variable, suggesting that low-alkalinity Adirondack lakes have been relatively unresponsive to the post-1970 declines in sulfate deposition.

Volatile fluxes integrated over four decades at Grímsvötn volcano, Iceland

Samples of the subglacial lake in the crater of the tholeiitic basaltic caldera Grímsvötn in Iceland were obtained by using a hot‐water drill to sink two boreholes through the 250‐m‐thick ice shelf covering the lake. The lake generally shows an increase in solutes with increased depth, as solutes are added from the lake's bottom and dilute glacial meltwater is added continuously from above. The crater lake temperature ranges from 0°C in the upper part to temperatures of 1°C to 4°C near the bottom of the lake. The lake water pH ranges between 7.0 and 5.7. The crater lake is assumed to be closed, with respect to volatile components released from subsurface magma, except for periodic draining by jökulhlaups. From the periodicity and water chemistry of the jökulhlaups, we have estimated the volcano's average release rates of carbon, sulfur, chlorine and fluorine between 1954 and 1991 and corrected these rates for dissolution of bedrock into the lake water and seepage of solutes to groundwater. The corrected mean release rates are 5.3×107 kg C yr−1, 5.3×106 kg S yr−1, 6.6×105 kg Cl yr−1, and 1.5×105 kg F yr−1. The emission rate estimates for Grímsvötn, one of the most active volcanoes in Iceland, are the longest integrated estimates obtained for an active volcano and are equal to or lower than those of other major active volcanoes worldwide. This difference may imply that published release rates for other volcanoes are overestimated, because they are usually not integrated over time. The values of the S/Cl and F/Cl ratios for noneruptive periods are 0.53±0.20 and 0.013±0.003, and for the two eruptive events are 0.69 and 2.14, and 0.034 and 0.041, respectively. The response of the elemental ratios to eruptive events, followed by the return to lower ratios, supports the assumption of steady state, because no long‐term accumulation of volatiles occurs. The energy output from the volcano, estimated from the amount of ice melted by hydrothermal heat, is 4250 MW over the last four decades. Using the energy output to calculate magma solidification rates and maximum possible volatile release rates, we observe that emissions of F and S are strongly suppressed at Grímsvötn, while a significant portion of available Cl and C are released. These calculations also reveal that coverage of a volcano by a glacier, and subsequent raising of the water table, may cause significant scrubbing of magmatic gases so that these gases do not reach the atmosphere.

UREA PRODUCTION, ACID-BASE REGULATION AND THEIR INTERACTIONS IN THE LAKE MAGADI TILAPIA, A UNIQUE TELEOST ADAPTED TO A HIGHLY ALKALINE ENVIRONMENT

The Lake Magadi tilapia, Oreochromis alcalicus grahami, thrives in highly alkaline geothermal springs and pools surrounding Lake Magadi, Kenya (control pH=9.9, CCO2=173 mmol l-1), has a functional hepatic ornithine­urea cycle (OUC) and excretes all nitrogenous waste as urea-N at variable rates (JUrea) related to O2 consumption (M·O2). The mean value of JUrea/M·O2 (N/O2=0.183) was high for fish but below the theoretical maximum (approximately 0.27) for 100 % aerobic respiration of protein, so an exogenous source of substrates is not required to explain the observed JUrea. JUrea was insensitive to thiourea. Urea excretion occurred largely (80 %) through the gills, but urea-N was also present in bile and urine. Control blood pHe, pHi and [HCO3-] (approximately 8.1, 7.6 and 15 mmol l-1, respectively, at approximately 32°C) were extremely high. When fish were exposed to lake water titrated with HCl and aerated to remove CO2, N/O2 progressively declined. At a lake water pH of 7.05 and CCO2 of 0 mmol l-1, N/O2 was reduced by 80 % and an intense metabolic acidosis occurred (pHe=7.04, [HCO3-]=1.5 mmol l-1). Restoration of control water pH 9.9 at a CCO2 of 0 mmol l-1 resulted in intermediate levels of N/O2 and internal acid­base status. Additional experiments confirmed that urea production was inhibited by low pHe, was dependent on blood [HCO3-] with a Km of 3.06 mmol l-1 and was insensitive to acetazolamide. While metabolic acidosis clearly inhibited OUC ureagenesis, the system appeared to be saturated with HCO3- under control conditions so that additional basic equivalent loading would not stimulate ureagenesis. Urea production in the Lake Magadi tilapia does not appear to remove exogenous HCO3- or to play a role in normal acid­base regulation.

Modeling the acid‐base chemistry of organic solutes in Adirondack, New York, lakes

Data from the large and diverse Adirondack Lake Survey were used to calibrate four simple organic acid analog models in an effort to quantify the influence of naturally occurring organic acids on lake water pH and acid‐neutralizing capacity (ANC). The organic acid analog models were calibrated to observations of pH, dissolved organic carbon (DOC), and organic anion (An−) concentrations from a reduced data set representing 1128 individual lake samples, expressed as 41 observations of mean pH, in intervals of 0.1 pH units from pH 3.9 to 7.0. Of the four organic analog approaches examined, including the Oliver et al. (1983) model, as well as monoprotic, diprotic, and triprotic representations, the triprotic analog model yielded the best fit (r2 = 0.92) to the observed data. Moreover, the triprotic model was qualitatively consistent with observed patterns of change in organic solute charge density as a function of pH. A low calibrated value for the first H+ dissociation constant (pKal = 2.62) and the observation that organic anion concentrations were significant even at very low pH (<4) indicate that naturally occurring organic solutes in these waters have strongly acidic functional groups. Inclusion of organic acidity in model calculations resulted in good agreement between measured and predicted values of lake water pH and ANC. Assessments to project the response of surface waters to future changes in atmospheric deposition, through the use of acidification models, will need to include representations of organic acids in model structure to make accurate predictions of pH and ANC.

Nucleation of Celestite and Strontianite on a Cyanobacterial S-Layer

Synechococcus strain GL24 is a unicellular cyanobacterium that was isolated from Fayetteville Green Lake, New York, a meromictic lake which has high Ca and SO(4) concentrations. Epicellular mineralization of Synechococcus cells in the lake is the mechanism by which extensive calcitic bioherms (or microbial reefs) have been formed on the lake's shore and a marl sediment has been built on the lake bottom. Previous studies have shown that calcium carbonate (calcite) formation on the Synechococcus surface is dependent upon an alkaline pH, which is produced in the cellular microenvironment by the cells as their activity increases with seasonal warming of the lake water. At the circumneutral pH of bulk lake water, calcium sulfate (gypsum) is formed. In this study, we show that Synechococcus mediates a similar sulfate-to-carbonate transformation when Sr is the major divalent cation present, forming celestite and strontianite. In experimental systems to which equimolar amounts of Ca and Sr, Ca or Sr and Mg, or all three ions together were added to artificial lake water, Ca and Sr were incorporated equally into mineral formation to form CaSr(CO(3))(2). No Mg -containing carbonates were formed when either or both of the other two ions were present. Mineral formation takes place on a hexagonally arranged proteinaceous template (an S-layer) which forms the outermost surface of the Synechococcus cell. Our results provide evidence that the S-layer exhibits selectivity with respect to the ions bound and subsequently incorporated into carbonate minerals and that celestite and strontianite, previously thought to be purely evaporitic minerals, can be biogenically formed.

Metal concentration in the gill, gastrointestinal tract, and carcass of white suckers (Catostomus commersoni) in relation to lake acidity

Adult white suckers were collected from four lakes in Maine that ranged in pH from 7.0 to 5.4. The gastrointestinal tract and remainder of the carcass of fishes of similar age and size from each lake, and gills from additional fishes of similar size, were analyzed for Al, Cd, Pb, and Zn. Carcasses were also analyzed for Hg. Concentrations of Al, Cd, and Pb were highest in the gastrointestinal tract and lowest in the carcass; Zn concentration was highest in the gill. For carcass, all metals except Al differed significantly among lakes, for gill tissue Cd and Pb differed, and for gastrointestinal tract, only Cd differed among lakes. Where differences were significant, patterns among lakes were similar in each tissue analyzed. Concentrations of Cd, Hg, and Pb were negatively correlated with lake water pH, acid neutralizing capacity (ANC), Ca, and lake:watershed area, and positively correlated with lake water SO4, indicating that concentrations were higher in fish from more acidic lakes. Zinc concentrations in gills were unrelated to lake acidity, and carcass concentrations were higher in the less acidic lakes, which is the opposite of the pattern for the other metals studied. Zinc in gastrointestinal tract did not differ among lakes. Although the lakes we studied were located in undisturbed watersheds and did not receive any point source discharges, fish metal concentrations were comparable to or higher than those reported from waters receiving industrial discharges.