Diatom assemblages from herbarium macrophytes and old samples: potential for historical limnology and studies from Flanders (Belgium)

Herbarium material of aquatic macrophytes and old limnological samples provide the opportunity to obtain precisely dated samples of epiphytic, planktonic or sedimentary diatom assemblages from the more recent past. These allow an accurate assessment of former limnological conditions at specific sites, in particular types of surface waters or associated to certain macrophytes, and even in entire regions. Inferences made from diatom assemblage composition may range from species abundance and diversity estimates to a reliable reconstruction of important parameters (e.g. pH, nutrient concentrations, salinity) by the use of indicator values or calibration techniques. Such information can be used to determine appropriate goals for management and restoration (pre-deterioration conditions), to track temporal changes by comparison with more recent data and relate these to possible external influences (e.g. various forms of pollution), or to evaluate monitoring data in a broader time perspective. In many cases, the use of old samples may not allow to generate time series of similar length and resolution as the more commonly applied diatom analysis of sediment cores. This technique, however, does provide access to the history of waters that do not have a suitable sediment record (e.g. because of dredging or sediment disturbance), avoids the problems often encountered in dating core levels accurately, and - with comparable or less effort -can be applied to a score of waters from a certain area. Also, it may be used to corroborate conclusions derived from sediment core analyses. Furthermore, the shorter time averaging of environmental conditions by epiphyton or plankton compared to sediment assemblages can be used advantageously to study short-lived or abruptly occurring phenomena. Limitations are, of course, related to the availability of suitable samples, the fact that most samples post-date c. 1850, and the reliability or detail of the information on place and date of collection. Moreover, variability caused by substrate and small-scale spatial differences in ecological conditions may be difficult to account for. For these reasons, it is recommendable to examine multiple samples of different nature (epiphyton of different plant species, sediment from between the roots, ...) from a given site. So far, old samples and herbarium material of aquatic plants have been used for a number of diatom investigations on lentic waters in Flanders. These include a number of case studies on specific water bodies, e.g. the Blankaart reservoir (Woumen), pools in the "Fonteintjes" (Zeebrugge), a survey of pools in the region of Kalmthout prior to 1945, and a 'typological' study of standing waters throughout the entire Flemish region. In order to facilitate the selection of suitable material for such studies, an inventory was made of some of the most important herbarium and sample collections held by Belgian universities and research institutes (including the herbaria BR, GENT, LV, BRVU, ANTW and that of UCL, and the collections of Van Oye at RUG and RUCA, and of Adam & Goossens at KBIN)

Photoelectron spectra in strong-field ionization by a high frequency field

We analyze atomic photoelectron momentum distributions induced by bichromatic and monochromatic laser fields within the strong field approximation (SFA), separable Coulomb-Volkov approximation (SCVA), and ab initio treatment. We focus on the high frequency regime -- the smallest frequency used is larger than the ionization potential of the atom. We observe a remarkable agreement between the ab initio and velocity gauge SFA results while the velocity gauge SCVA fails to agree. Reasons of such a failure are discussed.Comment: Completely rewritten paper. Ionization by a two-color field is adde

A diatom and radiocarbon perspective of the palaeoenvironmental history and stratigraphy of Holocene deposits between Oostende and Nieuwpoort (western coastal plain, Belgium)

Diatom and radiocarbon data of two cores from the north-eastern part of the western Belgian coastal plain are discussed. The palaeoenvironmental reconstruction of these sites and additional stratigraphic and geochronological information, allow an assessment of the general development of this region throughout the Holocene. Prior to c. 7500 yrs cal. BP a rapidly transgressing coast exists. Basal peat development may have been fairly wide­spread. Extensive erosion channels form towards the interior once the volume of the developing tidal basin has in­creased sufficiently. In spite of very high rates of sediment accumulation, high-intertidal environments remain poorly developed due to the high rate of RSL rise and the relatively steep slope of the transgressed terrain. Diatom taphocoenoses of this period consist primarily of coastal tychoplankton (mainly Cymatosira belgica), deposited in association with flood transported sediment, and some epipsammon. Hereafter, the incidence of negative tendencies in marine influence increases, culminating between c. 6300 to 5600 yrs cal. BP. Diatom assemblages are now more varied with an improved representation of tidal flat and salt marsh communities. The marine species Paralia sulcata and Pseudopodosira westii become abundant in high intertidal deposits, which may involve selective transport, sedi­mentation and preservation mechanisms. In general, the environmental changes reflect the development of a broad intertidal sedimentation zone in which sediment supply remained high, combined with a gradual slowing down of the RSL rise. Coastal progradation finally leads to sufficiently sheltered conditions for long-lasting peat growth in the intracoastal area up to perhaps c. 2100 yrs cal. BP Presumably a coastal barrier, which remains intersected by some inlets, also develops during this period. At places, peat growth is interrupted at about 4200 yrs cal. BP by a marked but short-lived period of marine sedimentation. Within the general framework of a return to a transgressive setting and a déstabilisation of the barrier system due to a decreasing sediment supply, climatic conditions and human interference may have played a role in the final termination of peat growth and the resumption of tidal activity. So far, the exact chronology of the return of tidal sedimentation in the study area remains unclear. No general sedimentation cycles, or so-called Dunkerque transgressions, are identified during the deposition of the upper tidal deposits, which are again characterized by a high representation of Cymatosira, reflecting a more open coastal setting. A tentative chronology of regional tendencies in the marine influence is derived from both bio- and lithostratigraphical indications and compared with the assumed chronology of transgressive and regressive phases in the northern Netherlands. Points of agreement are discussed in terms of possible supra-regional processes

Diatom analysis of coastal deposits: methodological aspects

In the frame of a general introduction to diatom analysis, especially of Quaternary coastal deposits, the possibilities, problems and methods of this discipline are briefly discussed

Environmental Protection on the Example of Agricultural Lands

Agricultural land is the most valuable resource of today because the issue of food security in the world community now comes first. Unfortunately, the ecological condition of lands suitable for agricultural use in Ukraine and the situation in the field of their use is constantly deteriorating. The quality of land resources is declining and approaching catastrophic levels. In this regard, the purpose of the study is to explore the main aspects of legal and environmental regulation of fertile land protection and to suggest ways to improve the protection and preservation of agricultural land. The main research method is the method of analysis, thanks to which the world experience in the field of environmental protection in general and the protection of agricultural lands was comprehensively analysed. The normative-legal acts of Ukraine, which regulate the issues of land use, as well as protection and preservation of agricultural lands, were analysed. The proposed mechanisms of environmental protection on the example of agricultural lands can be used to form targeted government programs

Cryoablation and Immunotherapy: An Enthralling Synergy to Confront the Tumors.

Treatment of solid tumors by ablation techniques has gained momentum in the recent years due to their technical simplicity and reduced morbidity as juxtaposed to surgery. Cryoablation is one of such techniques, known for its uniqueness to destroy the tumors by freezing to lethal temperatures. Freezing the tumor locally and allowing it to remain in situ unleashes an array of tumor antigens to be exposed to the immune system, paving the way for the generation of anti-tumor immune responses. However, the immune responses triggered in most cases are insufficient to eradicate the tumors with systemic spread. Therefore, combination of cryoablation and immunotherapy is a new treatment strategy currently being evaluated for its efficacy, notably in patients with metastatic disease. This article examines the mechanistic fabric of cryoablation for the generation of an effective immune response against the tumors, and various possibilities of its combination with different immunotherapies that are capable of inducing exceptional therapeutic responses. The combinatorial treatment avenues discussed in this article if explored in sufficient profundity, could reach the pinnacle of future cancer medicine