Improved prediction of vegetation composition in NW European softwater lakes by combining location,water and sediment chemistry

Isoetids, as indicators of near-pristine softwater lakes, have a high priority in national and international (European Water Directive Framework) assessments of ecological lake quality. Our main goal was to identify the most important environmental factors that influence the composition of plant communities and specifically determine the presence and abundance of the isoetid Lobelia dortmanna in NW European softwater lakes. Geographical position and composition of surface water, porewater, sediment and plant communities were examined in 39 lakes in four regions (The Netherlands, Denmark, West Norway and East Norway) distributed over a 1,200-km long distance. We confirmed that lake location was accompanied by significant changes in environmental variables between NW European lakes. Lake location was the single most important determinant of vegetation composition and it had significant individual contributions independent of the coupling to environmental variables. This influence of location was supported by a significant decline of community similarity with geographical distance between pairs of lakes at regional, inter-regional and international scales. Combining the geographical position with environmental variables for surface water, porewater and sediment significantly improved prediction of vegetation composition. Specifically, the combination of latitude, surface water alkalinity, porewater phosphate and redox potential offered the highest correlation (BIO ENV correlation 0.66) to vegetation composition. This complex analysis can also account for high sediment variability in the littoral zone of individual lakes, by using site-specific physico-chemical sediment factors, and offer better predictions of vegetation composition when lake water chemistry is relatively homogeneous among lakes within regions.     

A systems approach for analyzing vegetative and soil degradation in Arnigad micro-watershed of Indian Himalayan region

This study analyzes the vegetative and soil degradation, measured as biomass and soil loss, for Arnigad micro-watershed located in Indian Himalayan state of Uttarakhand, in systems framework by using dynamic linear programming bio-economic model. The focus is at investigating the effects of alternate policy regimes, i.e., introduction of improved energy sources for cooking along with substitution of existing local livestock breeds with improved breed, reduction in human population growth and introduction of high yielding varieties of main crops including paddy, maize and wheat. The model horizon extended over a period of 25 years, i.e., from 2006 to 2030. It was found that the model scenario incorporating increased use of improved energy sources along with substitution of local cows by improved cows could be the most effective policy option in reducing vegetative and soil degradation. The vegetative biomass density declined to 19.76% compared to 35.24% in the BASE scenario and soil erosion loss was also lowered by 29.13%. Also, the reduction of population growth rate to half of the BASE scenario led to minor improvements in degradation. Introduction of high yielding varieties of main crops slightly increased vegetative degradation but reduced soil loss (8.35%) with respect to the BASE scenario. Such a phenomenon could be explained in terms of changed crop mix resulting in reduced amount of crop by-products requiring increased lopping of tree branches for animal fodder. The policy option of the increased use of improved energy sources along with substitution of improved breed of cows resulted in 9.58% higher income. Introduction of high yielding varieties of crops led to 1.92% increase in income, but the income decreased by 1.25 % when population growth was reduced to half. The usefulness of the model lies in analyzing the systems behavior in its entirety where the results can predict the possible direction of change as a result of manipulation in alternate economic regimes.     

Sustainable land use in Tikopia: Food production and consumption in an isolated agricultural system

The land use system on Tikopia – a Polynesian outlier in Solomon Islands – is analyzed to determine how it has developed since it was first described in the 1930s and again in the 1970s. Fieldwork included a household questionnaire survey, in-depth interviews on farming practices and decision making, and the collection of soil samples from the major soil and garden types. The Tikopian land use system has not undergone significant changes since the 1970s; indeed the focus on self-sufficiency in food crops may have been strengthened over the past 30 years as ship arrivals have become increasingly unreliable. Local agricultural production and exploitation of marine resources are essential to sustain the population, and with few exceptions farming and fishing techniques remain unchanged. Most of the island is still farmed permanently and the intensive agricultural system has not suffered long-term setbacks, not even from extreme events such as Cyclone Zoe in 2002. The high fertility of Tikopian soils reported in the 1960s was found to be unchanged. It is concluded that the land use system is highly resilient to shocks and that there are no indications that Tikopian villagers would not be able to support their subsistence in the future, provided there is no substantial increase in the resident ( de facto ) population.     

Depth colonization of eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis>) and macroalgae as determined by water transparency in Danish coastal waters

We present a comparative analysis of lower depth limits for growth of eelgrass, large brown algae and other macroalgae measured by SCUBA-diving along 162 transects in 27 Danish fjords and coastal waters, coupled to 1,400 data series of water chemistry (especially nitrogen) and Secchi depth transparency collected between March and October. Danish coastal waters are heavily eutrophied and characterized by high particle concentrations, turbid water and lack of macrophyte growth in deep water. Median values are 3.6 m for Secchi depth and median lower-depth limits are 4.0 m for eelgrass, 5.3 m for brown algae and 5.0 m for other macroalgae. Depth limits for growth of eelgrass and macroalgae increase linearly with transparency in the coastal waters. The relationships are highly significant (p<10⁻⁶) and transparency accounts for about 60% of the variability of depth limits. Eelgrass extends approximately to half the maximum depth of macroalgae, presumably because of greater respiratory costs to maintain the below-ground rhizomes and roots of eelgrass, which often constitutes half the plant weight. As a reflection of the importance of total nitrogen (TN) in controlling phytoplankton biomass and thus Secchi depth in coastal marine waters, we found that TN could explain 48–73% of the variation in depth limits of eelgrass and macroalgae, according to a multiplicative model (Y=aX^b). As with Secchi depth, the relationship to eelgrass showed a lower slope, reflecting the higher respiratory costs of eelgrass. The models show great sensitivity and a profound quantitative response with proportional effects on Secchi depth and depth limits when total-N concentrations are reduced.     

The dogma of matters neutrino-transparency

In this paper the observed underrepresentation of solar neutrinos in the various detector experiments performed is tentatively interpreted as a result of a substantial and often variable obsorption of neutrinos by various layers of the Sun, contrary to the dogma of neutrino-transparency by matter.     

The reactivity of iron oxides towards reductive dissolution with ascorbic acid in a shallow sandy aquifer (Rømø, Denmark)

The pool of iron oxides, available in sediments for reductive dissolution, is usually estimated by wet chemical extraction methods. Such methods are basically empirically defined and calibrated against various synthetic iron oxides. However, in natural sediments, iron oxides are present as part of a complex mixture of iron oxides with variable crystallinity, clays and organics etc. Such a mixture is more accurately described by a reactive continuum covering a range from highly reactive iron oxides to non-reactive iron oxide. The reactivity of the pool of iron oxides in sediment can be determined by reductive dissolution in 10 mM ascorbic acid at pH 3. Parallel dissolution experiments in HCl at pH 3 reveal the release of Fe(II) by proton assisted dissolution. The difference in Fe(II)-release between the two experiments is attributed to reductive dissolution of iron oxides and can be quantified using the rate equation J/m₀ = k′(m/m₀)^γ, where J is the overall rate of dissolution (mol s⁻¹), m₀ the initial amount of iron oxide, k′ a rate constant (s⁻¹), m/m₀ the proportion of undissolved mineral and γ a parameter describing the change in reaction rate over time. In the Rømø aquifer, Denmark, the reduction of iron oxides is an important electron accepting process for organic matter degradation and is reflected by the steep increase in aqueous Fe²⁺ over depth. Sediment from the Rømø aquifer was used for reductive dissolution experiments with ascorbic acid. The rate parameters describing the reactivity of iron oxides in the sediment are in the range k′ = 7·10⁻⁶ to 1·10⁻³ s⁻¹ and γ = 1 to 2.4. These values are intermediate between a synthetic 2-line ferrihydrite and a goethite. The rate constant increases by two orders of magnitude over depth suggesting an increase in iron oxide reactivity with depth. This increase was not captured by traditional oxalate and dithionite extractions.     

A summary of the PRUDENCE model projections of changes in European climate by the end of this century

An overview of the PRUDENCE fine resolution climate model experiments for Europe is presented in terms of their climate change signals, in particular 2-meter temperature and precipitation. A comparison is made with regard to the seasonal variation in climate change response of the different models participating in the project. In particular, it will be possible to check how representative a particular PRUDENCE regional experiment is of the overall set in terms of seasonal values of temperature and precipitation. This is of relevance for such further studies and impact models that for practical reasons cannot use all the PRUDENCE regional experiments. This paper also provides some guidelines for how to select subsets of the PRUDENCE regional experiments according to such main sources of uncertainty in regional climate simulations as the choice of the emission scenario and of the driving global climate model.