Metal Deposition Chronologies in Boreal Shield Lakes: Distinguishing Anthropogenic Signals from Diagenetic Effects

Accurate metal deposition records in lake sediments are necessary to assess their present human health and ecological risk and to evaluate the effects of current or eventual measures to control metal emissions. Sediment cores and porewaters were collected in lakes located in uninhabited watersheds exposed to various levels of atmospheric metals. The interpretation of sedimentary metal profiles as historical records may be complex, however, as these profiles may be influenced by a variety of chemical, physical, and biological processes occurring naturally near the sediment-water interface. We used several independent approaches to distinguish the anthropogenic from the natural contributions in sediment metal profiles. A first approach compares metal profiles obtained in chemically similar lakes exposed to high and low metal loads from the atmosphere. A second approach uses geochemical and diagenetic modelling to evaluate the importance of metal diffusion as an internal remobilization process. Lastly, stable Pb isotopes are used to fingerprint possible sources of Pb to lake sediments and to evaluate their relative importance. Our preliminary results indicate that dated sediment profiles collected near large point sources essentially reflect chronological deposition trends. As shown for Cu, however, concentration profiles from remote sites can be slightly influenced by chemical changes occurring in surficial sediments.     

Exchange of phosphorus across the sediment-water interface

In this article, principles of phosphorus retention and phosphorus release at the sediment-water interface in lakes are reviewed. New results and hypotheses are discussed in relation to older models of phosphorus exchange between sediments and water. The fractional composition of sedimentary phosphorus is discussed as a tool for interpretation of different retention mechanisms. Special emphasis is given to the impact of biological, particularly microbial, processes on phosphorus exchange across the sediment-water interface and to the significance of biologically induced CaCO₃ precipitation to phosphorus retention in calcareous lakes.     

Considerations in modeling the sediment-water exchange of phosphorus

The potential to release accumulated phosphorus from sediments has been the major motive to study and to model the fate of this nutrient in sediments. For the dynamics of the sediment-water interaction the sizes of the pools involved and the rates of conversion/transport from one pool to another are of primary interest. As the sediment pools for phosphate are generally much larger than the pools in the water column, a rather slow adjustment of the sediment to management measures will occur. For the analysis of management measures it is obvious that the gradual change in sediment composition must be taken into account. Only for rather short periods the sediment composition can be assumed to be constant; this may be appropriate for studies of e.g. the annual cycle. The sediment-water interaction is a complex resultant of physical, chemical and biological processes, including:

physical processes: advection due to seepage or consolidation, pore-water diffusion, transport and mixing of solids by resuspension, sedimentation and bioturbation.

chemical processes: adsorption and desorption, dissolution and (co)precipitation, inclusion.

biological processes: mineralization of a wide range of organic compounds by various (micro)organisms, each with their own nutrient requirements and electron acceptors.

Aspects which are discussed and need to be considered in application of a model in research or management are the level of aggregation and detail that is required and may still be practical, the spatial and temporal scales which are applicable for the processes mentioned and their influence upon the numerical dispersion and model stability, the availability of data for calibration/validation and the resolution of the analytical techniques. These aspects are not independent however. Frequently models are not functional because they contain details which are either unnecessary or suggest a feigned accuracy which is not justified by analytical and experimental resolution of system characteristics.     

Uptake of radionuclides by some aquatic macrophytes of Ismailia Canal,Egypt

1. Uptake of the radionuclides Co-60, Cs-134, Sr-89 and P-32 by different aquatic plants present in Ismailia Canal was found to increase at increasing initial concentrations of the radionuclides in the water.
2. Maximum uptake was reached by most of the aquatic plants after different periods of contamination, ranging from 1 to 4 days.
3. Ceratophyllum was found to be the most favourable biological indicator for strontium radioisotopes in concentrations ranging from 0.5 to 10 µCi/1 and for contamination periods up to 16 days.
4. Elodea was found to serve as a biological indicator for either strontium or phosphorus radioisotopes for limited contamination periods of 2 to 16 days for Sr and to 2 days for P isotopes.
5. Potamogeton was also found to serve as a biological indicator for limited contamination periods for strontium, phosphorus and cesium radioisotopes: 0 to 2 days for Sr, 2 to 16 days for P. and 0 to 2 days for Cs isotopes.

     

Metal accumulation by fungi: Applications in environmental biotechnology

Summary Fungi can accumulate metal and radionuclide species by physico-chemical and biological mechanisms including extracellular binding by metabolites and biopolymers, binding to specific polypeptides and metabolism-dependent accumulation. Biosorptive processes appear to have the most potential for environmental biotechnology. Biosorption consists of accumulation by predominatly metabolism-independent interactions, such as adsorptive or ion-exchange processes: the biosorptive capacity of the biomass can be manipulated by a range of physical and chemical treatments. Immobilized biomass retains biosorptive properties and possesses a number of advantages for process applications. Native or immobilized biomass can be used in fixed-bed, air-lift or fluidized bed bioreactors; biosorbed metal/radionuclide species can be removed for reclamation and the biomass regenerated by simple chemical treatments.     

Variability of entrainment of cohesive sediments in freshwater

Estimates of sediment entrainment are required for models of particle transport in lakes and estuaries but are difficult to make because of the multiplicity of factors affecting cohesiveness of surficial sediments. We present results of sediment resuspension studies performed in an annular flume calibrated with laser-Doppler velocimetry. In our experiments, using sediments collected from two sites in the R. Raisin which flows into L. Erie and from one site in the western basin of L. Erie near the mouth of the R. Raisin, we applied shear stresses at the sediment-water interface in steps from 2 to 12 dyne/cm². Percent water content at the surface of the sediments was either 77 or 74%, and trials were run with and without oxygenating the water overlying the sediments. Entrainment rates as a function of shear stress at the sediment-water interface were best described by a power-law relationship. All but 14% of the variability in the power law expression was due to shear stress and percent water content; the variability not accounted for was due to differences in particle size distributions, chemical properties, and biological activity in the sediments.     

The measure of biological age in plant modular systems

Phytomorphology — if concerned with development — often concentrates on correlative changes of form and neglects the aspects of age, time and clock, although the plant's spatial and temporal organisation are intimately interconnected. Common age as measured in physical time by a physical process is compared to biological age as measured by a biological clock based on a biological process. A typical example for a biological clock on the organ level is, for example, a shoot. Its biological age is measured by the biological time unit of a plastochron, which itself is defined by the cyclic-periodic initiation of the leaves. In a controlled environment biological age may replace physical age. However, biological and physical age are not necessarily linearly convertible into each other. In stationary or steady state conditions the repetitive initiation of any organ, unit or module of an articulate plant or plant modular system may define the biological time unit. A linear — monotonous biological process, e.g. axis elongation, may also define a biological time unit as a certain amount of additional growth, e.g. of length. One may speak of periodical and of continuous plastochron or, perhaps, of plastochron and rheochron. A precise measure of biological age is the generalized plastochron index applying to any modular system and module respectively. However, one should be aware that it is based on two clocks, one of them referring to the periodic process of module initiation for counting the integer plastochrons and the other to the continuous plastochron of module growth for the determination of the fraction of one plastochron. The application of the concepts is restricted to phases of stationary or steady state growth and development. In certain cases of non-stationary or non-steady state conditions a normalized-age concept may apply.     

Ace Lake: three decades of research on a meromictic,Antarctic lake

Ace Lake (Vestfold Hills, Antarctica) has been investigated since the 1970s. Its close proximity to Davis Station has allowed year-long, as well as summer only, investigations. Ace Lake is a saline meromictic (permanently stratified) lake with strong physical and chemical gradients. The lake is one of the most studied lakes in continental Antarctica. Here, we review the current knowledge of the history, the physical and chemical environment, community structure and functional dynamics of the mixolimnion, littoral benthic algal mats, the lower anoxic monimolimnion and the sediment within the monimolimnion. In common with other continental meromictic Antarctic lakes, Ace Lake possesses a truncated food web dominated by prokaryote and eukaryote microorganisms in the upper aerobic mixolimnion and an anaerobic prokaryote community in the monimolimnion, where methanogenic Archaea, sulphate-reducing and sulphur-oxidizing bacteria occur. These communities are functional in winter at subzero temperatures, when mixotrophy plays an important role in survival in dominant photosynthetic eukaryotic microorganisms in the mixolimnion. The productivity of Ace Lake is comparable to other saline lakes in the Vestfold Hills, but higher than that seen in the more southerly McMurdo Dry Valley lakes. Finally, we identify gaps in the current knowledge and avenues that demand further investigation, including comparisons with analogous lakes in the north polar region.     

Time series analysis of water quality data from Lake Ontario: implications for the measurement of water quality in large and small lakes

SUMMARY 1. The normal strategy of monitoring water quality is to sample such parameters as chlorophyll no more than weekly. A preferable strategy is to first define the natural periodicities in the water body and then to set up a sampling scheme that takes into account the natural scales of variance in physical, chemical and biological parameters. Failure to do so leads to aliased and biased estimates of means and variances and an inability to interpret the underlying physical and biological mechanisms.
2. The natural scales of variance vary with basin size. In lakes, physical and biological processes overlap at scales of from 1 to 15 days. Time series analysis of daily data from Lake Ontario and other lakes showed how the means and variances of the data sets were determined by the physical and biological processes in the water columns and displayed the fundamental lags in the systems. Even in small lakes and reservoirs, advective processes were of great importance. Advection became the dominant process in Lake Ontario. Time lags and advection made simple correlations of physical and biological parameters meaningless.
3. Decimation of the daily data sets revealed the statistical dangers of less frequent sampling. The desirable frequency of sampling was shown to be a function of the physics of the mixed layer, the turnover times of the nutrient pools, and the biological activity. Data from the three lakes graphically demonstrated the inadequacy of normal sampling frequencies.     

An opto-electronic sediment detector and its use in the chemical micro-profiling of lakes

SUMMARY. A device for detecting (with minimum disturbance) the sediment-water interface in lakes is described. It is based on a commercially available slotted 'opto-switch' incorporating a light emitting diode and a phototransistor. The design of an audible and visual indicator is given. Possible uses are discussed and an example of chemical micro-profiling near to the sediment with the aid of the device is reported.     

Australian salt lakes: their history,chemistry, and biota — a review

A vast number of large lakes ( 100 km²) are typically very old features of the Australian landscape; they occupy areas which have changed little tectonically (e.g., they occupy ancient drainage systems in Western Australia or lie in deep depressions such as the Great Artesian Basin: Lake Eyre) and have not been transgressed by the sea since at least the Palaeogene. Other salt lakes, most of which are small ( 50 km²), have been affected morphologically during recurring glacial-interglacial cycles (e.g., lakes associated with gypsum or clay lunettes, sabkhas, pans, lakes near the coast behind barrier dunes as a result of sea-level changes) and their sedimentary records represent comparatively much shorter periods of time. There are also a number of unusually young (< 30 000 years) crater lakes, some of which are the best studied lakes in Australia.The major ions encountered today in Australian salt lakes consist of sodium and chloride although some lakes are also calcium sulphate rich. The origin of these ions is briefly discussed. Sodium carbonate lakes are rare in Australia today. Under past climatic/hydrological conditions the chemistry of a number of lakes was apparently different.The biota of Australian salt lakes is mostly endemic; it is highly diversified as witnessed by the crustacean fauna and is well adapted to the harsh conditions prevailing in saline water. This is the result of a long history of aridity in Australia. The characteristics of this biota are presented together with data on its distribution which is primarily related to climatic conditions.     

生物扰动对沉积物中污染物环境行为的影响研究进展

生物扰动由于显著改变沉积物结构和性质,进而影响沉积物中污染物的环境行为。综述生物扰动对沉积物中氮、磷、重金属和疏水性有机污染物环境行为的影响。生物扰动促进这些污染物从沉积物向水体释放。生物扰动还对不同的污染物产生其它不同的影响。对于氮,生物扰动还影响其硝化与反硝化作用;对于磷,生物扰动不仅改变其化学形态,还提高有机磷降解。对于重金属,生物扰动还能改变其在沉积物中的分布及化学形态。对于疏水性有机污染物,生物扰动主要增强生物富集和代谢,以及提高生物降解。     

How can increased use of biological N2 fixation in agriculture benefit the environment?

Caesium (Cs) is an alkali metal with chemical properties similar to potassium (K). It has no known role in plant nutrition and it is not toxic to plants at the micromolar concentrations occurring naturally in soil solutions. However, two radioisotopes of Cs (¹³⁴Cs and ¹³⁷Cs) are of environmental concern due to their relatively long half-lives, emissions of and radiation during decay, and rapid incorporation into biological systems. There is considerable interest in remediating sites contaminated by these isotopes using phytoextraction and, since the produce from radiocaesium-contaminated areas may enter the food chain, the introduction of `safe' crops that do not accumulate Cs. This article reviews the molecular mechanisms of Cs uptake by plants, and provides a perspective on strategies to develop: (1) plants that extract Cs efficiently from soils (for the phytoremediation of land), or (2) `safe' crops that minimise the entry of radiocaesium directly into the human food chain.     

Factors related to variance of residuals in chlorophyll — total phosphorus regressions in lakes and reservoirs of Argentina

Data from an extensive mid-summer survey of Argentinian lakes and reservoirs were used to study the effects of variability in internal processes on the residual variance in chlorophyll — total phosphorus (CHL-TP) regression models. These effects were compared with those related to the external characteristics of lakes, e.g. climate, morphometry and nutrient status. Zooplanktivorous fish biomass, mean macrozooplankton size, dissolved oxygen at the sediment-water interface, and submersed macrophyte development, were shown to be significant in explaining residual variance in CHL-TP for Argentinian lakes and reservoirs. The results suggest that those variables have discontinuous or threshold effects on CHL-TP residuals among lakes. Significant differences were also shown between CHL-TP regressions for lakes with and without zooplanktivorous fish and for lakes with small or large macrozooplankton. Lakes with zooplanktivorous fish, small body size macrozooplankton, and very low hypolimnetic oxygen also have higher chlorophyll levels than predicted from CHL-TP regression models.     

Chemical limnology of soft water lakes in the Upper Midwest

Water samples from 36 lakes in northern Minnesota, Wisconsin, and Michigan were collected and analyzed during 1983–1984. All study lakes were dilute and had total alkalinities of less than 150 eq · L^–1. Minnesota lakes have hydrologic inputs from the watershed and inputs of base cations derived from the watershed. Study lakes in Minnesota had higher total alkalinities, dissolved organic carbon, and noncarbonate alkalinity as a result of watershed inputs. Lakes in Michigan and Wisconsin were precipitation-dominated seepage lakes that have lower concentrations of base cations than lakes in Minnesota. All of the study lakes have lower sulfate concentrations than expected, based on atmospheric wet deposition and evapotranspiration.Pore water samples collected from one of the study lakes—Little Rock Lake—in Wisconsin were used to calculate diffusive fluxes between the sediment and water column. According to these calculations, the sediments were a source of total alkalinity and Ca²⁺ and a sink for SO₄ ^2–. The sediment-water exchange of total alkalinity, Ca²⁺, and SO₄ ^2– appears to be important in the whole-lake budgets of these ions for Little Rock Lake.     

NUTRIENTS IN AFRICAN LAKE ECOSYSTEMS: DO WE KNOW ALL?

SUMMARY

It is nearly sixty years since the first studies were undertaken on the nutrient chemistry of African lakes. There have been numerous studies on the chemical composition of African waters in the intervening years. Yet as recently as five years ago it was stated that little was known about nutrient cycling in lakes. Nutrient ‘species’ simply formed an additional list compiled along with lists of species of algae, zooplankton, aquatic plants and fish. A spate of monographs, papers and reports in recent years, however, has begun to fill some of the gaps in our knowledge of nutrient cycling in African lake ecosystems. This paper reviews the recent literature of nutrients in African lakes from the point of view of nutrient sources, in-lake nutrient kinetics and nutrient sinks, with particular reference to nitrogen and phosphorus, and their cycling rates into and out of various biotic and abiotic compartments. The principle conclusions that can be drawn from the review are as follows:

1. Allochthonous inputs, particularly in terms of external nutrient loading, have been relatively well-studied in recent years, but little is known of autochthonous nutrient inputs, despite numerous observations that nutrient regeneration is likely to be substantial in African lakes.

2. The rôle of microbial processes in nutrient cycling in African lakes is almost totally unknown, except in relation to nitrification and denitrification.

3. Recent studies have begun to examine the kinetics of the uptake of phosphorus by algae in African lakes; nitrogen uptake, other than nitrification, and nutrient release have only rarely been examined.

4. Nutrient uptake and release by aquatic macrophytes is reasonably well known, especially in the ‘nuisance’ weed species.

5. The role of zooplankton, zoobenthos and fish in nutrient cycling in African lakes has largely been ignored.

6. A great deal of study has been devoted to the rôle of abiotic process, particularly at the sediment-water interface, in the nutrient dynamics of African lakes.

As yet, little emphasis has been placed on inter-compartmental exchanges in studies on nutrient cycles but it would appear that these processes are now beginning to receive attention and, as nutrient cycling in African lake ecosystems becomes better known, research will tend toward a more numerical approach.     

Chemical and optical changes in freshwater dissolved organic matter exposed to solar radiation

We studied the chemical and optical changes inthe dissolved organic matter (DOM) from twofreshwater lakes and a Sphagnum bog afterexposure to solar radiation. Stable carbonisotopes and solid-state ¹³C-NMR spectraof DOM were used together with optical andchemical data to interpret results fromexperimental exposures of DOM to sunlight andfrom seasonal observations of two lakes innortheastern Pennsylvania. Solar photochemicaloxidation of humic-rich bog DOM to smaller LMWcompounds and to DIC was inferred from lossesof UV absorbance, optical indices of molecularweight and changes in DOM chemistry. Experimentally, we observed a 1.2 enrichment in ¹³$C and a 47% loss in aromaticC functionality in bog DOM samples exposed tosolar UVR. Similar results were observed inthe surface waters of both lakes. In latesummer hypolimnetic water in humic LakeLacawac, we observed 3 to 4.5enrichments in ¹³C and a 30% increase inaromatic C relative to early spring valuesduring spring mixing. These changes coincidedwith increases in molecular weight and UVabsorbance. Anaerobic conditions of thehypolimnion in Lake Lacawac suggest thatmicrobial metabolism may be turning overallochthonous C introduced during springmixing, as well as autochthonous C. Thismetabolic activity produces HMW DOM during thesummer, which is photochemically labile andisotopically distinct from allochthonous DOM orautochthonous DOM. These results suggest bothphotooxidation of allochthonous DOM in theepilimnion and autotrophic production of DOM bybacteria in the hypolimnion cause seasonaltrends in the UV absorbance of lakes.     

The origin and recycling of sedimented biogenic debris in a subalphine eutrophic lake (Lake Bled, Slovenia)

The areal distribution of organic C contents, ¹³C values, total N and P and biogenic Si contents in surficial sediments were used to study the distribution, origin and diagenetic transformations of sedimented biogenic debris in the eutrophic subalpine Lake Bled (Slovenia), which for most of the yearhas an anoxic hypolimnion. The influence of an allochthonous input, restricted to the western basin, was clearly traced by higher organic C and total N and P contents, higher ¹³C values, and higher sedimentation rate in comparison to the eastern basin. The low ¹³C values of sedimentary organic matter in the major part of the lake, lower than the ¹³C values of different types of organic matter, suggest that this sedimentary organic matter is most probably the product of a microbial community and not a residue of primary production.The temporal variation of benthic diffusive fluxes of NH₄, Si and PO₄, derived from modelling the pore water profiles, was related to sedimentation of phytoplanktonic blooms, while the PO₄ fluxes were also dependent on changing redox conditions at the sediment-water interface in the period of the winter-spring overtum. The removal of PO₄ in pore waters is probably due to the adsorption of phosphate and precipitation of apatite and vivianite. The budget of C, N and P at the sediment-water interface revealed a high recycling efficiency (>70%), also confirmed by the rather uniform (or only slightly decreasing) vertical profiles of organic C, total N and P in sediment cores and C/N and C/P ratios. The percentage of biogenic Si recycling is low (<10%), suggesting its removal in sediments.     

长江中下游四大淡水湖生态系统完整性评价

长江中下游地区是我国淡水湖泊集中分布区域,研究该区域湖泊生态系统完整性对于湖泊生态系统保护和恢复具有重要意义。物理、化学和生物完整性指标已经广泛应用于河湖生态系统健康评价,但是缺少物理、化学和生物完整性的综合评价方法。以历史调查状况为主要参照系统,构建了基于物理、化学和生物完整性的多参数湖泊完整性综合评价指标体系,结合近年来长江中下游四大淡水湖(洞庭湖、鄱阳湖、巢湖、太湖)生态系统调查数据,对四大淡水湖生态系统完整性进行了评价。结果表明,洞庭湖、鄱阳湖、巢湖和太湖的综合得分分别为66、71、57和57。根据评价等级划分标准,洞庭湖和鄱阳湖生态系统完整性状况都达到"好"的等级,而巢湖和太湖则处于"一般"等级;结果显示,该指标能够表征人类活动对于湖泊生态系统完整性不同方面的干扰,且能够反映四大淡水湖生态系统完整性历史变化状况。因此,该方法可以作为长江中下游淡水湖泊生态系统完整性综合评价的工具并能够为湖泊生态系统的保护和恢复提供科学支撑。     

Joint Russian—Finnish study of radioactive contamination in the NW part of Lake Ladoga

In August 1992 a joint Russian-Finnish expedition was arranged to the NW part of Lake Ladoga to study radioactive contamination in the region. Special attention was paid to the area surrounding the Heinämaa Islands, where the wreck of the former mine carrier ship Kit had been lying about 30 years before it was moved to Novaya Zemlya in 1991. During this period the wreck had been used as a store for radioactive waste containing principally ⁹⁰Sr, ¹³⁷Cs and ^239,24OPu. Lake water, bottom sediment and some biological samples were collected for strontium, plutonium and gammaspectrometric analyses. In all the samples the radioactivity concentrations were very low, indicating radioactive contamination of about the same level as caused by global fallout in the 1960's and the Chernobyl fallout in the area. Only in two water samples taken close to the former site of the wreck slightly elevated ^239,240Pu concentrations were detected. The great water volume of Lake Ladoga and effective water exchange at the wreck site may explain the very low levels of radioactive wastes detected in the aquatic environment.