Dilute Lakes Research Articles

The hydrologic classification of dilute lakes

Dilute lakes, herein defined as having an electrical conductivity ≤25 µS cm−1, are considered valuable culturally, as water and recreational resources; biologically, as unique ecosystems; and scientifically, as sentinels of climate change. However, research and interest has been spread over many disciplines focusing on various issues, making hydrologic comparisons somewhat difficult. Here, 15 dilute lakes are subdivided into lake subtypes based on the dominant hydrologic input and output using annual water balance data. Dilute conditions occur in lakes dominated by all hydrologic inputs (precipitation, surface inflow, and groundwater) and outputs (evaporation, surface outflow, and groundwater), though not all possible input/output combinations produce dilute conditions. Of the nine possible hydrologic lake subtypes (three input by three output fluxes), dilute conditions have been reported in six lake subtypes, not just the traditional seepage and drainage lakes typically suggested in the literature. When annual water balance data are plotted on a “Piper‐type” graph, these six hydrologic lake subtypes are grouped into three hydrologic clusters emphasizing specific hydrologic landscape characteristics and limiting conditions hydrology may impose on naturally dilute lakes. Implications of such a classification system and possible future research questions are discussed.

Temperature Dependence of Freshwater Phytoplankton Growth Rates and Zooplankton Grazing Rates

Phytoplankton growth rates and zooplankton grazing rates were estimated on 16 occasions over a period of 17 months in University Lake, a highly eutrophic lake on the campus of Louisiana State University. Phytoplankton growth rates and chlorophyll a concentrations averaged 1.0 ± 0.2 d−1 and 240 ± 120 mg m−3, respectively. Chlorophyll a concentrations were at or above the inflection point of the Holling type I curve that described the relationship between zooplankton grazing rates and chlorophyll a concentrations. In most cases, it was necessary to dilute lake water by more than a factor of 4 before zooplankton grazing rates became sensitive to chlorophyll a concentrations. Chlorophyll a concentrations were positively correlated with temperature and were roughly fourfold higher at 30 °C than at 15 °C. An analysis of the temperature dependence of the growth rates and grazing rates in this study and 87 other paired estimates of limnetic phytoplankton growth rates and zooplankton grazing rates revealed virtually identical temperature dependences of growth rates and grazing rates that were very similar to the temperature dependence predicted by the metabolic theory of ecology. Phytoplankton growth rates exceeded zooplankton grazing rates by 0.13 ± 0.05 d−1 at all temperatures over a temperature range of 8.5–31.5 °C. The Q10 for both phytoplankton growth rates and zooplankton grazing rates was 1.5 over that temperature range.

The Hot Spring Hypothesis for an Origin of Life.

We present a testable hypothesis related to an origin of life on land in which fluctuating volcanic hot spring pools play a central role. The hypothesis is based on experimental evidence that lipid-encapsulated polymers can be synthesized by cycles of hydration and dehydration to form protocells. Drawing on metaphors from the bootstrapping of a simple computer operating system, we show how protocells cycling through wet, dry, and moist phases will subject polymers to combinatorial selection and draw structural and catalytic functions out of initially random sequences, including structural stabilization, pore formation, and primitive metabolic activity. We propose that protocells aggregating into a hydrogel in the intermediate moist phase of wet-dry cycles represent a primitive progenote system. Progenote populations can undergo selection and distribution, construct niches in new environments, and enable a sharing network effect that can collectively evolve them into the first microbial communities. Laboratory and field experiments testing the first steps of the scenario are summarized. The scenario is then placed in a geological setting on the early Earth to suggest a plausible pathway from life's origin in chemically optimal freshwater hot spring pools to the emergence of microbial communities tolerant to more extreme conditions in dilute lakes and salty conditions in marine environments. A continuity is observed for biogenesis beginning with simple protocell aggregates, through the transitional form of the progenote, to robust microbial mats that leave the fossil imprints of stromatolites so representative in the rock record. A roadmap to future testing of the hypothesis is presented. We compare the oceanic vent with land-based pool scenarios for an origin of life and explore their implications for subsequent evolution to multicellular life such as plants. We conclude by utilizing the hypothesis to posit where life might also have emerged in habitats such as Mars or Saturn's icy moon Enceladus.“To postulate one fortuitously catalyzed reaction, perhaps catalyzed by a metal ion, might be reasonable, but to postulate a suite of them is to appeal to magic.”—Leslie Orgel

Field Evaluation and in Situ Stress Testing of the Organic-Diffusive Gradients in Thin-Films Passive Sampler.

The organic-diffusive gradients in thin-films (o-DGT) technique has emerged as a promising aquatic passive sampler that addresses many of the challenges associated with current sampling tools used for measurement of polar organic contaminants. This study represents the first comprehensive field evaluation of the o-DGT in natural surface waters, across a wide suite of polar pharmaceuticals and pesticides. We explore the utility and limitations of o-DGT as a quantitative measurement tool compared to grab sampling and the polar organic chemical integrative sampler (POCIS) across four connected agricultural and wastewater-influenced freshwater systems spanning 600 km from the U.S. border to northern Manitoba, Canada. Overall, the suite of analytes detected with o-DGT and POCIS was similar. Concentrations in water estimated using o-DGT were greater than concentrations estimated from POCIS in 71 of 80 paired observations, and on average, the estimates from o-DGT were 2.3-fold greater than estimates from POCIS. Grab sample concentrations suggested that the systematic underestimation with POCIS were largely a result of sampling rate variation related to flow rate and boundary-layer effects, an issue reported consistently in the POCIS literature. These comprehensive measurements in an agriculturally influenced fast-flowing river, long-term sampling (>40 days) in a large dilute lake system, deployments in wastewaters, and under ice at near-freezing temperatures represent effective stress testing of o-DGT under representative and challenging conditions. Overall, its strong performance and improved accuracy over POCIS supports its use as a robust, quantitative, and sensitive measurement tool for polar organic chemicals in aquatic systems.

Climate drivers of diatom distribution in shallow subarctic lakes

Abstract Global warming can induce profound changes to the functioning of northern freshwater ecosystems. Diatom (Bacillariophyceae) communities often provide early warning signs of associated ecological regime shifts, responding sensitively to alterations in underwater light climate, nutrient regimes, habitat availability and lake water acid–base balance. The underlying mechanisms are manifold and may be mediated via direct climate impact on the physical and chemical properties of lakes or via changes in the terrestrial environment and catchment‐lake coupling. To address catchment‐mediated climate effects on diatom community composition, spatial diatom distribution in the surface sediments of 31 subarctic treeline lakes displaying a broad gradient in terrestrial dissolved organic matter (tDOM) was contrasted with limnological indices of light climate, nutrient availability and lake water pH. To evaluate direct and indirect climate impacts on the long‐term development of benthic phototrophic communities at the subarctic treeline, fossil diatom assemblages in the sediments of a shallow oligotrophic lake were examined against established temperature variability and inferences of terrestrial influence over the past 600 years. The regional lake set was used to test local calibration models for reconstructing dissolved organic carbon as well as lake water pH that is a fundamental environmental determinant for diatom distribution and may echo temperature variability in dilute lakes. Across the treeline, lake water pH imposed primary control over the benthic‐dominated surface sediment diatom communities. The pH influence was connected to catchment geomorphology, soils and vegetation cover and, together with habitat controls, largely superseded tDOM impact on underwater light attenuation and nutrient levels. Similarly, temporal changes in diatom distribution in the sediment core appeared to be relatively little affected by tDOM variability. The species shifts were subtle yet occurred in distinct synchrony with centennial temperature fluctuations, attributed to changing length of the ice cover period and associated effects on lake water chemistry, nutrient regimes and physical habitats. Our results suggest that diatom flora in shallow lakes at the subarctic Fennoscandian treeline may be comparatively resilient towards climate‐driven changes in terrestrial carbon and nutrient fluxes. Diatom communities in poorly buffered lakes may, however, be susceptible to catchment greening and changes in hydrology through effects on lake water acid–base balance. While diatom responses in the sediment sequence were subtle, the palaeolimnological record indicates that periphytic diatom communities in shallow oligotrophic subarctic lakes may be sensitive to the effects of global warming.

Isotope and hydrochemistry reveal evolutionary processes of lake water in Qinghai Lake

Abstract Qinghai Lake is the largest lake in China and is one of more than 500 brackish lakes on the Tibet Plateau. This study investigated stable isotopes (δ 18 O and δ 2 H) and hydrochemistry of lake water in Qinghai Lake and surrounding lakes to understand the lakes' evolutionary processes. These processes help explain the formation and evolution of the brackish and salt lakes on the Tibetan Plateau. The original isotopic and chemical compositions of lake water were controlled by a mixture of water from river water, groundwater, and precipitation. The values of δ 18 O and δ 2 H of most of the lake water samples were greater than zero due to continuous strong evaporation. The cations were in the order Na + > Mg 2 + > K + > Ca 2 + , and anions were in the order Cl − > SO 4 2 − > HCO 3 − . The hydrochemical types of Qinghai Lake and surrounding lakes were Na + -Cl − . The lake water, excluding Erhai Lake, was saturated with CaCO 3 . There was significant aragonite precipitation, and the Ca 2 + concentration was relatively low. Haiyanwan Lake and Gahai Lake, which have no surface water inputs, had experienced stronger evaporation than Qinghai Lake since the lakes were isolated from Qinghai Lake due to the dropping lake level and the arid climate. Erhai Lake water had relatively low salinity due to the fresh water coming in from the Daotang River. With the continued strong evaporation of lake water, Qinghai Lake and surrounding lakes should become increasingly saline. However, the salinity of lakes on the Tibetan Plateau is likely to slowly decrease in future decades due to the increasing precipitation and runoff, which will dilute lake water. In the longer term, however, Qinghai Lake and the brackish lakes will likely still become more saline, given the continued contribution of chemical ions from river water and groundwater and strong evaporation from the lake surface.

Decrease in CO2 efflux from northern hardwater lakes with increasing atmospheric warming.

Boreal lakes are biogeochemical hotspots that alter carbon fluxes by sequestering particulate organic carbon in sediments and by oxidizing terrestrial dissolved organic matter to carbon dioxide (CO2) or methane through microbial processes. At present, such dilute lakes release ∼1.4petagrams of carbon annually to the atmosphere, and this carbon efflux may increase in the future in response to elevated temperatures and increased hydrological delivery of mineralizable dissolved organic matter to lakes. Much less is known about the potential effects of climate changes on carbon fluxes from carbonate-rich hardwater and saline lakes that account for about 20 per cent of inland water surface area. Here we show that atmospheric warming may reduce CO2 emissions from hardwater lakes. We analyse decadal records of meteorological variability, CO2 fluxes and water chemistry to investigate the processes affecting variations in pH and carbon exchange in hydrologically diverse lakes of central North America. We find that the lakes have shifted progressively from being substantial CO2 sources in the mid-1990s to sequestering CO2 by 2010, with a steady increase in annual mean pH. We attribute the observed changes in pH and CO2 uptake to an atmospheric-warming-induced decline in ice cover in spring that decreases CO2 accumulation under ice, increases spring and summer pH, and enhances the chemical uptake of CO2 in hardwater lakes. Our study suggests that rising temperatures do not invariably increase CO2 emissions from aquatic ecosystems.

Environmental impacts of desalination on the ecology of Lake Urmia

Lake Urmia, the second largest hypersaline lake by area in the world, has fluctuated in salinity over time, but in recent years, it has reached a maximum of 340 g/L. The lake is the main habitat for the endemic Iranian brine shrimp, Artemia urmiana, and is a protected aquatic environment. Efforts have been made by the Iranian government to enhance the diversity of its wildlife. One approach has been to look for a method to reduce the salt content of the lake. We investigate the feasibility of this by first considering the water chemistry of Lake Urmia and then the various technologies used to extract salt from marine and brackish waters. Average concentrations of Na, Mg, K, Ca, Cl, SO 4, and HCO 3 were 125 g/L, 11.3 g/L, 2.63 g/L, 0.55 g/L, 216 g/L, 22.4 g/L, and 1.38 g/L, respectively, and cations and anions were balanced, However, Lake Urmia waters have a ‘very high’ salinity hazard and a high sodium adsorption ratio (SAR). Moreover, the saturation index (SI) for each of the major cations was greater than zero, indicating that the water in Lake Urmia is supersaturated, and precipitation is likely. The extraction of available salts from the lake for the use in petrochemical industries is economically feasible. However, technologies based on removing salts by distillation or reverse osmosis and then using this fresh water to dilute lake salinity are problematic. A better strategy would be better to allow more fresh water to reach the lake rather than creating fresh water through reverse osmosis and distillations processes. While concerns have been raised about the salinity tolerance of A . urmiana, it has successfully tolerated various salinity ranges from 166 to 340 g/L, and so the species is not threatened, unless the lake desiccates. Because the lake is saturated with salts, it seems unlikely that salinity could increase much higher.

Watershed-scale reconstruction of middle and late Holocene paleoenvironmental changes on Melville Peninsula, Nunavut, Canada

Arctic regions have heightened sensitivity to climatic changes, however regional scale differences exist in the magnitude and timing of biotic responses. Melville Peninsula in the east-central Canadian Arctic is a transitional area with respect to modern climate, with a continental climate to the west, and more maritime influences to the east. This, and the presence of Thule archaeological sites, make the Peninsula an area of high importance for paleoclimate reconstructions. Lake sediment cores from two adjacent ultra-oligotrophic and very dilute lakes (SP02 and SP04) from interior Melville Peninsula (68°33′N and 83°17′W, 220 m a.s.l.) were analyzed for diatom assemblages (microscopic algae) to track paleoclimatic changes. High magnetic susceptibility, coarse-grained sediments, low organic matter, and lack of diatoms in sediments older than 6000 years BP confirm earlier suggestions of a persistent ice cap on the Peninsula. Peak diatom concentration and biogenic silica, and maximum values for sediment organic matter, between 4400 and 2900 years BP may indicate the Holocene Thermal Maximum (HTM). The timing of the HTM is similar to that of the Baffin region to the east. Decreases in these proxies, as well as small shifts in diatom assemblages following 2900 years BP indicate the advancement of Neoglacial cooling. The changes of the pre-industrial portion of the last millennium were of smaller magnitude than those of the HTM, but subtle changes in diatom assemblages after 750 years BP may be indicative of the Little Ice Age, the timing of which agrees well with that of Boothia Peninsula to the west. The Anthropocene is well marked in these records, with increases in diatom species richness from a pre-industrial maximum of 28–51 diatom species in the modern assemblage at Lake SP02. Planktonic diatoms appear in the 20th century, signalling profound ecological changes associated with longer ice-free seasons.

Relationships between freshwater sedimentary diatoms and environmental variables in Subarctic Icelandic lakes

The distribution patterns of surface sediment diatom assemblages from 49 lakes were used to explore the relationship between limnological variables and diatom assemblages as well as to assess an ecological classifi ca- tion system as a tool for the management and conservation of Icelandic freshwaters. Lakes were limnologically diverse ranging from deep, oligotrophic, ionically dilute lakes, to shallow lakes with a wide range of nutrient and ionic contents. Physical conditions (depth, surface area, surface water temperature) and nutrient and ion concentra- tions differed signifi cantly among ecological lake categories (i.e., plateau, spring-fed, direct-runoff, valley, glacial, and coastal lakes) (ANOVA, p 20 % in all but 4 of the lakes, most likely due to the generally cold lake water conditions in this subarctic region. Variation in diatom distributions was best explained by the combination of mean depth (infl uencing littoral versus planktonic habitats), surface water temperature, specifi c conductivity, alkalinity, total organic carbon, total nitrogen and SiO2 in a canonical correspondence analysis (CCA). However, these variables did not explain distribution patterns amongst small benthic Fragilaria taxa, although some weak relationships between some taxa and these variables were evident. Distinct diatom assemblages and limnological properties among ecological lake categories support the classifi cation of Icelandic freshwaters based on major topographic, geological and hydrological characteristics. More detailed inclusion of lake depth along with lake basin form, as well as more refi ned categories of lake water origin and topographical positioning to better approximate regional climatic conditions, may improve the ecological classifi cation of Icelandic freshwaters for conservation and management practices.

A palaeolimnological record of diatom-community dynamics and late-Holocene climatic changes from Prescott Island, Nunavut, central Canadian Arctic

Palaeolimnological analyses from Lake PW03, a small, dilute lake on crystalline bedrock on Prescott Island, Nunavut, Canada (73°07′ N, 96°41′ W, 243 m a.s.l.), provide a sensitive record of the impacts of Holocene climatic change on diatom communities. A high-resolution sequence from 3500 cal. BP to present indicates that a significant change in diatom assemblages takes place at 2300 cal. BP, when alkaliphilous fragilarioids and planktonic taxa are replaced by benthic, epiphytic and acidophilous diatoms. These changes coincide with the onset of neoglacial cooling and likely reflect more persistent ice-cover and associated acidification of lake water. Maximum diatom species richness occurs during this period of transition. Dense bryophyte communities in the littoral zone provide habitats to sustain diatom production even under the cooler conditions following 2300 cal. BP. The concentration of diatom valves declines at 500 cal. BP, coincident with cooling at the time of the `Little Ice Age', and minor changes in species composition take place at that time. The sediments deposited over the past 150 years show modest increases in fragilarioids and planktonic diatoms, in response to a longer ice-free season under a warmer climate. Diatom valve production increases significantly in these recent sediments but increases in diversity are relatively small. Diatom diversity, production and the species composition of diatom communities do not change simultaneously in response to climatic changes.

Paleolimnological reconstructions of Rouyn-Noranda lakes within the zone of influence of the Horne Smelter, Québec, Canada

Diatoms were identified and enumerated from a surface sediment calibration set of 50 lakes in northwestern Quebec. The relationship between species composition and environmental variables was examined using canonical correspondence analysis (CCA). Forward selection and Monte Carlo permutation tests in CCA indicated that diatom species distributions in the data set are most strongly correlated to lakewater pH. A strong (r 2 boot = 0.83) weighted averaging calibration model, that includes bootstrapped error estimates, was developed for inferring past lakewater pH. Using this model, temporal changes in pH were reconstructed for two kettle lakes, Lac de la Pepiniere and Lac Perron. Based on limnological data, both the study lakes were expected to have recently acidified due to increased acidic precipitation and increases in anthropogenic metal loading. However, our long-term pH inference data indicate that these lakes were naturally acidic during pre-industrial times. Nonetheless, the rate of acidification, particularly in Lac de la Pepiniere, has accelerated in the last ∼75 years. These long-term pH records developed for the dilute lakes in northwestern Quebec suggest that the region has received increased atmospheric pollutants from the nearby Horne smelter in Rouyn-Noranda. The pH inference profiles are markedly different from many other paleolimnological studies in acid-sensitive regions of Canada that have become acidic primarily as a result of industrial activities.

Authigenic calcium carbonate flux in groundwater-controlled lakes: Implications for lacustrine paleoclimate records

Groundwater dominated lakes are an important feature of many landscapes. Their sediments are a particularly valuable source of paleoenvironmental information in semiarid regions where perennial lakes may otherwise be scarce. Where groundwater and lake composition are favorable, carbonate mineral precipitation, evaporative concentration of lake water, and microbial processes can combine to strongly deplete dissolved Ca relative to influent groundwaters. The authigenic carbonate flux (ACF) can then become limited by water column cation availability and thereby be coupled to groundwater inflow rates and aquifer recharge. Here we analyze sedimentary records from two marl-producing, groundwater-controlled lakes and demonstrate a link between one-dimensional ACF and the Palmer Drought Severity Index (PDSI), a measure of land surface wetness. In a restricted outflow lake with high-carbonate alkalinity, ACF is enhanced during historically wet climatic periods in response to increased aquifer recharge rates. ACF in this lake declines during droughts. A neighboring dilute lake with a high rate of groundwater outflow shows comparatively weak coupling between ACF and PDSI history. Ionic chemistry, carbonate mineral equilibria, and δ 13C patterns of dissolved inorganic carbon show that the sensitivity of the ACF signal depends on the degree of evaporative evolution of lake water and the mineral saturation state of the water column under conditions of stratification and ice cover.

Application of a Hypolimnetic Oxygen Profile Model to Lakes in Ontario

ABSTRACT We tested a previously published empirical multivariate regression model that predicts end-of-summer oxygen concentrations in the hypolimnia of small, dilute lakes in the Boreal ecozone. The model inputs include only lake morphometry and total phosphorus concentration at spring-overturn. In this study, we tested the validity of the model using information for lakes that are larger or deeper, and have higher phosphorus concentrations than the lakes that were the basis for the original regression model. Data from 32 lakes in the Gull River watershed in central Ontario and 10 lakes in eastern Ontario were used to evaluate the model's ability to predict end-of-summer oxygen profiles. Results indicated that the original model was satisfactory for most of the 42 study lakes, but had more limited success in the deeper and larger lakes within the data set. For the eastern Ontario lake set, the original model's ability to predict oxygen in the hypolimnia was better than for the Gull River watershed lakes. It is suggested that the most useful application of the model would be to predict the change in hypolimnetic oxygen concentrations at given depths that would result from increases or decreases in total phosphorus concentrations in the lake. This would allow resource managers concerned with sportfish habitat, to estimate and assess the impact that changes in lake trophic status might have on oxygen concentrations.

Climate modulates the acidity of Arctic lakes on millennial time scales

High-resolution diatom stratigraphies from two lakes on eastern Baffin Island (Nunavut, Canadian Arctic) are used to reconstruct lake-water pH over the past 5 k.y. Despite contrasting geomorphic histories and markedly different diatom floras, the inferred pH of both lakes declined in concert with Neoglacial cooling. This result confirms that climate exerts a first-order influence on the acidity of these poorly buffered oligotrophic lakes, through links between lake ice cover, primary productivity, and dissolved inorganic carbon dynamics. Diatom-based pH inferences from dilute lakes can therefore assist paleoclimatic interpretations from lake sediments.

Mercury Loading and Methylmercury Production and Cycling in High-Altitude Lakes from the Western United States

Studies worldwide have shown that mercury (Hg) is a ubiquitouscontaminant, reaching even the most remote environments such ashigh-altitude lakes via atmospheric pathways. However, very fewstudies have been conducted to assess Hg contamination levels ofthese systems. We sampled 90 mid-latitude, high-altitude lakes from seven national parks in the western United States during afour-week period in September 1999. In addition to the synoptic survey, routine monitoring and experimental studies were conducted at one of the lakes (Mills Lake) to quantify MeHg fluxrates and important process rates such as photo-demethylation. Results show that overall, high-altitude lakes have low total mercury (HgT) and methylmercury (MeHg) levels (1.07 and 0.05 ng L-1, respectively), but a very good correlation of Hg to MeHg (r2= 0.82) suggests inorganic Hg(II) loading is a primary controlling factor of MeHg levels in dilute mountain lakes. Positive correlations were also observed for dissolved organic carbon (DOC) and both Hg and MeHg, although to a much lesser degree. Levels of MeHg were similar among the seven national parks, with the exception of Glacier National Park where lowerconcentrations were observed (0.02 ng L-1), and appear to berelated to naturally elevated pH values there. Measured rates ofMeHg photo-degradation at Mills Lake were quite fast, and thisprocess was of equal importance to sedimentation and stream flowfor removing MeHg. Enhanced rates of photo-demethylation are likely an important reason why high-altitude lakes, with typically high water clarity and sunlight exposure, are low in MeHg.

Top‐down biological controls on tropical lake productivity

Although productivity is primarily controlled by bottom-up factors (nutrient levels), there are secondary effects caused by biological factors such as zooplankton grazing and algal self-shading. The measurement of grazing effects and determination of the contributions of different nutrient pools should elucidate the roles of nutrient levels and biotic effects and also infer the relative importance of classical and microbial food webs. To produce a series of grazing intensity, after initial screening to remove macrozooplankton, lake water was filtered to remove remaining zooplankton. This was used to dilute whole lake water in a filtered : unfiltered ratios from 0:1 to 1:0, which was then incubated with nutrient enrichment. Results show an increase of up to 20% in productivity for surface midlake waters. To investigate grazing by nutrient dilution/deletion, grazing dilutions were again prepared; however, nutrients were added to produce three different conditions,+N +P (all nutrients), –N (nitrogen omitted) and –P (phosphorus omitted). From productivity measurements, the contributions of internal, external and recycled nitrogen and phosphorus nutrient pools were calculated. Sites at Hippo Point (HP) (midlake) and Malewa River inflow (MR) (near the mouth of the River Malewa) show little difference in the contribution of external nutrients, but remaining productivity is mostly fuelled by recycled nutrients at the MR site. Little difference was found between nitrogen and phosphorus-limited conditions.

Waldo Lake, Oregon Chemical Composition: Major Ions, Buffering Capacity, and Nutrient Loading

Previous limnological investigations have identified Waldo Lake as one of the most pristine and chemically dilute lakes in the world. This study focusing on the major ion chemistry of Waldo Lake has confirmed this status. Situated at a topographical divide in the central Oregon Cascades, with a very small watershed (watershed area to lake area ratio = 2) and shallow, porous soils, Waldo Lake chemistry is dominated by precipitation input with relatively less influence from watershed processes. Based on median values, conductivity for Waldo Lake is 3.4 μS·cm−1, while the cation and anion sums are 39 and 29 μeq·L−1, respectively. Acid neutralizing capacity (ANC, also total alkalinity) is 17 μeq·L−1 (0.85 mg·L−1 as CaCO3), indicating that Waldo Lake is very weakly buffered and highly susceptible to acidification from acidic deposition, although there is no evidence that this has occurred. Chloride (14 μeq·L−1) and sulfate (2.1 μeq·L−1) are derived mainly from precipitation (wet and dry deposition), ANC is derived mainly from weathering of watershed base minerals, and base cations (Ca+Mg+Na+K) are derived from both precipitation (two-thirds) and weathering reactions (one-third). Waldo Lake has been classified as ultraoligotrophic based on the extraordinarily low values of primary productivity and nutrient concentrations. Reported nutrient concentrations vary widely due to the extremely low concentrations and insensitivity of methods employed. However, phosphorus has been identified as the limiting nutrient based on algal bioassay methods. Best estimates based on literature data are total P < 3 ug·L−1, about 50% as inorganic P, and total N < 100 to 200 ug·L−1, more than 90% as organic N. There is a net removal of most inorganic N and P from precipitation in the watershed and lake, but watershed and internal lake processes affecting N and P are not well understood. Estimated total phosphorus loading to the lake is 620 kg y−1 and estimated total phosphorus loss from the lake is 81 kg y−1, with about 85% of P retained in the sediments. Waste disposal facilities installed within the last 30 years could substantially increase phosphorus loading and thus alter the ecology of the lake, although remediation measures are now under consideration.

Preliminary investigations on the distribution of scaled chrysophytes in Vermont and New Hampshire (USA) lakes and their utility to infer lake water chemistry

A total of 38 taxa of scaled chrysophytes, representing seven genera, were observed in the surface sediments of eleven lakes in Vermont and New Hampshire, USA. The number of taxa found per lake ranged from 10 to 23, with greater diversity and abundances of scales in the New Hampshire localities. The flora was similar to those described from other temperate regions of North America and Europe. The flora described from the New Hampshire waterbodies was typical of those observed in slightly acidic, dilute lakes situated in primarily forested watersheds. The flora observed in the Vermont lakes was more typical of ones previously described from regions rich in waterbodies with both high pH and concentrations of dissolved salts. The occurrences of several rarely reported species in North America, including Mallomonas alata, M. parvulu, M. retrorsu. and Synura lapponica, are documented. It was also determined that paleolimnological inference models developed in Connecticut for pH, specific conductivity and trophic score worked well using the scale remains from the study lakes.

Volcanic lake systematics II. Chemical constraints

A database of 373 lake water analyses from the published literature was compiled and used to explore the geochemical systematics of volcanic lakes. Binary correlations and principal component analysis indicate strong internal coherence among most chemical parameters. Compositional variations are influenced by the flux of magmatic volatiles and/or deep hydrothermal fluids. The chemistry of the fluid entering a lake may be dominated by a high-temperature volcanic gas component or by a lower-temperature fluid that has interacted extensively with volcanic rocks. Precipitation of minerals like gypsum and silica can strongly affect the concentrations of Ca and Si in some lakes. A much less concentrated geothermal input fluid provides the mineralized components of some more dilute lakes. Temporal variations in dilution and evaporation rates ultimately control absolute concentrations of dissolved constituents, but not conservative element ratios.Most volcanic lake waters, and presumably their deep hydrothermal fluid inputs, classify as immature acid fluids that have not equilibrated with common secondary silicates such as clays or zeolites. Many such fluids may have equilibrated with secondary minerals earlier in their history but were re-acidified by mixing with fresh volcanic fluids. We use the concept of ‘degree of neutralization’ as a new parameter to characterize these acid fluids. This leads to a classification of gas-dominated versus rock-dominated lake waters. A further classification is based on a cluster analysis and a hydrothermal speedometer concept which uses the degree of silica equilibration of a fluid during cooling and dilution to evaluate the rate of fluid equilibration in volcano-hydrothermal systems.