Principles of environmental physics

Book Review

Principles of environmental physicsJ.L. Monteith and M.H. Unsworth Second edition. London: Edward Arnold, 1990. xii + 291 pages. £30.00 (hardback), £14.95 (paperback). ISBN 0-7131-2931-X     

A metabolomics approach exploring the function of the ESX-3 type VII secretion system of M. smegmatis

The genome of Mycobacterium, including Mycobacterium tuberculosis, contains five copies of a cluster of genes encoding a novel type VII secretion system, named the ESX gene cluster region. This ESX-3 gene cluster is essential for in vitro growth and is thought to play a role in iron and zinc homeostasis, however, its exact functionality remains an enigma. A metabolomics research approach was subsequently used to compare the metabolite profiles of a M. smegmatis ESX-3 knockout strain to that a wild type parental strain, in order to elucidate its functionality from a metabolic perspective. Statistical analysis of the GC–MS generated data showed a clear separation between the wild type and knockout sample groups, based on the analysed metabolite profiles of these organisms. Of all the metabolite markers identified, various amino acids and metabolite pathways related to these, appeared to be most affected by the ESX-3 knockout, especially those with enzymes regulated by iron and zinc, supporting previous genomics and proteomics generated hypotheses and findings. This study is the first to demonstrate the capacity of using metabolomics, in conjunction with previous genomics and proteomic findings, to identify underlying metabolic changes and confirm previous hypotheses related to the functionality of ESX-3 in Mycobacterium growth and survival.     

Using Satellite Remote Sensing to Estimate the Colored Dissolved Organic Matter Absorption Coefficient in Lakes

Given the importance of colored dissolved organic matter (CDOM) for the structure and function of lake ecosystems, a method that could estimate the amount of CDOM in lake waters over large geographic areas would be highly desirable. Satellite remote sensing has the potential to resolve this problem. We carried out model simulations to evaluate the suitability of different satellite sensors (Landsat, IKONOS, and the Advanced land Imager [ALI]) to map the amount of CDOM in concentration ranges that occur in boreal lakes of the Nordic countries. The results showed that the 8-bit radiometric resolution of Landsat 7 is not adequate when absorption by CDOM at 420 nm is higher than 3 m⁻¹. On the other hand, the 16-bit radiometric resolution of ALI, a prototype of the next generation of Landsat, is suitable for mapping CDOM in a wider range of concentrations. An ALI image of southern Finland was acquired on 14, July 2002 and in situ measurements were carried out in 15 lakes (18 stations). The results showed that there is a high correlation (R² = 0.84) between the 565 nm/660 nm ALI band ratio and the CDOM absorption coefficient in lakes. Analysis of 245 lakes in the acquired satellite image showed a normal distribution of CDOM concentration among the lakes. However, the size distribution of lakes was highly skewed toward small lakes, resulting in the CDOM concentration per unit lake area being skewed toward high values. We showed that remote sensing enables synoptic monitoring of the CDOM concentration in a large number of lakes and thus enables scaling up to the level of large ecosystems and biomes.     

Validation of the MERIS products on large European lakes: Peipsi,Vänern and Vättern

The Medium Resolution Imaging Spectrometer (MERIS/Envisat) was launched in March 2002 for coastal zone monitoring. Preliminary data from MERIS show that its imagery of large lakes is superior to that of other common ocean colour sensors. The main objective of the present study is to evaluate the MERIS data on large European lakes, Vänern and Vättern in Sweden and Peipsi in Estonia/Russia. In these lakes, coloured dissolved organic matter (CDOM) can be a major contributor to the optical properties of the water. Another characteristic of the waters under investigation is the large temporal and spatial variability in the concentrations of chlorophyll (C _Chl) and suspended sediments (C _TSS). Potentially toxic cyanobacterial blooms occur in Lake Peipsi in late summer. We have compared the MERIS products from the latest reprocessing (finished in March 2006) with available in situ data. There is a reasonably good correlation between the MERIS algal_2 product and the measured C _chl over all three lakes, but no correlation was found for other optically active substances. A significant portion of the pixels (up to 90%) are flagged as invalid results after atmospheric correction.     

Application of optical classifications to North European lakes

Two classifications (rough and fine) based on the optical properties of water were used to classify 42 Estonian, Finnish, and Swedish lakes. The rough classification was based on the amount of optically active substances (OAS: chlorophyll a, suspended matter, and colored dissolved organic matter) in the water. The basic variables of the fine classification were chlorophyll a concentration, beam attenuation coefficient of light in the photosynthetically active radiation (PAR) region in the water (or corresponding Secchi depth), and the beam attenuation coefficient for filtered water at 380 nm. All optical classes were represented in the studied lakes by both classifications, when they changed their class depending on the seasonal and biological conditions. In a large lake, different parts of the lake belonged to different optical classes. The results obtained by both classifications were in good agreement. There was a concurrence between optical classes and water transparency by Secchi depth. Often the bio-optical variations of water properties are described from the measurements of all three OAS and Secchi depth because these parameters belong to routine monitoring datasets and have been carefully recorded. The water classes provide a method to summarize the influences of the different factors.     

Effects of different types of low‐intensity management on plant‐pollinator interactions in Estonian grasslands

In the face of global pollinator decline, extensively managed grasslands play an important role in supporting stable pollinator communities. However, different types of extensive management may promote particular plant species and thus particular functional traits. As the functional traits of flowering plant species (e.g., flower size and shape) in a habitat help determine the identity and frequency of pollinator visitors, they can also influence the structures of plant−pollinator interaction networks (i.e., pollination networks). The aim of this study was to examine how the type of low‐intensity traditional management influences plant and pollinator composition, the structure of plant−pollinator interactions, and their mediation by floral and insect functional traits. Specifically, we compared mown wooded meadows to grazed alvar pastures in western Estonia. We found that both management types fostered equal diversity of plants and pollinators, and overlapping, though still distinct, plant and pollinator compositions. Wooded meadow pollination networks had significantly higher connectance and specialization, while alvar pasture networks achieved higher interaction diversity at a standardized sampling of interactions. Pollinators with small body sizes and short proboscis lengths were more specialized in their preference for particular plant species and the specialization of individual pollinators was higher in alvar pastures than in wooded meadows. All in all, the two management types promoted diverse plant and pollinator communities, which enabled the development of equally even and nested pollination networks. The same generalist plant and pollinator species were important for the pollination networks of both wooded meadows and alvar pastures; however, they were complemented by management‐specific species, which accounted for differences in network structure. Therefore, the implementation of both management types in the same landscape helps to maintain high species and interaction diversity.     

Stability of Capped Dredged Sediments in a Confined Disposal Facility at Malmøykalven,Oslofjord, SE Norway

Conventional sediment capping is a widely used technique where clean sediments are placed over contaminated sediments to reduce the migration of contaminants to the environment. A concern of the method is initial contaminant transport through the cap during the consolidation of the underlying disposed sediments. The current study was conducted to investigate the efficiency of the cap placed over the Malmøykalven confined disposal facility (CDF). The thickness of the soft disposed sediments reached 6 m in maximum, and was subject to extensive consolidation when the cap was placed. Vertical profiles of trace metals (Cd, Cu, Hg, Pb, Zn) and the structure of the cap layer were studied in six gravity cores. The cap material was clearly distinguishable in the sediment cores, both visually and chemically. The results provided evidence that consolidation-induced pore water advection was able to transport fine particles (<63 µm) and organic material into the cap layer. Metal transport in the particulate phase was suggested to be the main transport process into the cap layer. The study shows the importance of an appropriate cap layer design to prevent any particle transport and to minimize the effects of consolidation-induced advective transport.     

Highlights of large lake research and management in Europe

Lakes in Europe have a bipolar distribution by latitude with higher lake densities in the north (58–65° N) and south (38–48° N). By area, 95% of the large lakes (>100 km²) are located at altitudes lower than 100 m above sea level (ASL) and only 1% lie higher than 1,000 m ASL. Physically large lakes exhibit several similarities to seas and oceans in their thermal structure and circulation dynamics. From the chemical point of view, lakes are important accumulation sites for substances transported from the watershed or built up in the lake itself but they may contribute positively to global greenhouse gas emission. Fauna and flora of ancient large lakes such as the Caspian Sea and Lake Ohrid include large numbers of endemic species, which become endangered if conditions change because of direct human impact, alien species invasions or climate change. Large lakes offer a wide range of ecosystem services to society, the multiple use of which creates multiple pressures on these water bodies such as nutrient load and toxic pollution, modification of hydrology and shore line structure, and shifting of the food web balance by stocking or harvesting various species. Although large lakes are among the best-studied ecosystems in the world, the application to them of environmental regulations such as the European Water Framework Directive is a challenging task and requires that several natural and management aspects specific to these water bodies are adequately considered.     

Reconstruction of the Time Series of the Underwater Light Climate in a Shallow Turbid Lake

Lake ülemiste is a shallow, eutrophic lake which has served the city of Tallinn as a water reservoir for many centuries. Its light climate was studied by combining a routinely measured data set with a modelling approach. For 26 years (1978–2004), data was collected on such optically active substances (OAS) and water parameters as water colour, turbidity and phytoplankton biomass. Simple modelling enabled the quantification of long-term time-series data and the subsequent calculation of the diffuse attenuation coefficient, euphotic depth and average light of the mixed layer. Several changes in the hydrological cycle have taken place during the period under study, among which are an increase in the water level of about 0.5 m and a decrease in the external water load from 108 million m³ year⁻¹ to about 25 million m³ year⁻¹. At the same time euphotic depth has shown a distinct trend towards increasing since the early 1990s. The euphotic depth also showed an increase (from 1.1 to 1.4 m) due to an improvement in underwater light conditions – mainly in the spring (April and May) and autumn (October and November) because of the lower amount of dissolved organic matter in the lake. The average light availability in the mixed layer has increased, but this has not affected the phytoplankton biomass as the latter is not light-limited during the summer period.     

Variability of bio-optical parameters in two North-European large lakes

The bio-optical properties of some North-European large lakes were examined during 1995–2005 using field data and laboratory measurements. The key variables were optically active substances (OAS: chlorophyll, total suspended matter and dissolved organic matter), Secchi depth, and the “spectrometric” and diffuse light attenuation coefficients. Our main study sites were Lake Peipsi and Lake Võrtsjärv in Estonia, both eutrophic with mean Secchi depth below 3 m. The measured water parameters were compared with those obtained from two clear-water Swedish lakes, Lake Vänern and Lake Vättern. This comparison describes the bio-optical differences of the water in eutrophic and oligotrophic lakes. The variability of water parameters in the turbid Estonian lakes was rather high, e.g. the chlorophyll content varied from 1.8 to 102 mg m^?3 and the diffuse light attenuation coefficient from 0.92 to 6.5 m^?1. The change in water properties depends on the season and the biological activity of phytoplankton. We found no apparent long-time trend in water properties. Regression analysis showed that in the turbid Estonian lakes the optical properties were well correlated with chlorophyll and suspended matter, but not with dissolved organic matter. The highest determination coefficients (between 0.73 and 0.89) were obtained when the optical parameters were correlated with all three OAS together (multiple regressions). Our results concerning the variability and interconnections among bio-optical parameters in two Estonian large lakes illustrate the effect of OAS and light field on the ecological conditions of lakes in general.