Kretzschmaria deusta

The decline in Ulmus pollen frequencies that occurred ca. 5000 14C years ago before present (BP) is a key biostratigraphic marker horizon in northwest European pollen diagrams, although its causes are still a subject of debate. To investigate this event further, fungal spore analyses were carried out across the Ulmus decline at Moel y Gerddi, north Wales, United Kingdom. The Ulmus decline was in three phases, with a primary decline with low cereal and Rumex pollen records as the only agricultural indicators. This was followed by a more significant decline, with general forest opening and the grassland/pasture indicator Plantago lanceolata. A third, less significant, decline was again accompanied by cereal-type pollen. Tree pollen frequencies subsequently recovered, with cereal-type pollen remaining well represented. The fungal data recorded woodland taxa and a background level of the obligate dung fungus Sporormiella, a proxy for local herbivore abundance. Sporormiella frequencies increased greatly after the main Ulmus decline, around which there were high percentages of the ascospores of the wood rot fungus Kretzschmaria deusta. The neoecology of Kretzschmaria deusta, and the behavior of its spore curve suggests the colonisation of local populations of already severely wounded trees. At this site Ulmus, and perhaps Tilia were infected at a time of markedly increased inferred herbivore concentrations. Neolithic farming techniques could have provided mortally wounded trees while enhancing livestock grazing, although the role of disease must also be considered. Elevated Kretzschmaria deusta values may be of ecological significance in the interpretation of the causes and nature of the Ulmus decline and similar forest disturbance events, and the indicator role of this fungus in forest paleoecology requires further study.</p

Varve formation since 1885 and high-resolution varve analyses in hypertrophic Baldeggersee (Switzerland)

According to their microstratigraphical composition the laminated sediments of Baldeggersee are true varves. Two varve time-series from freeze cores taken in the deepest part (66 m) of Baldeggersee have been analysed for annual and seasonal layers. The varve time-series covers the period of 1885 to 1993. The two freeze-cores from Baldeggersee can be accurately correlated by means of distinct layers (e.g. marker varves, turbidites), lithological units, and varve measurements. The Baldeggersee varve chronology has been checked by independent high-resolution 137Cs dating. Mobility of cesium has not been detected in Baldeggersee. A highly positive correlation between phosphorus concentration in the lake water and median grain size of calcite crystals has been observed and allows, together with the results of geochemical analyses, to hindcast the trophic state in Baldeggersee for periods where no limnological data are available. The main features of the Baldeggersee varve time-series can be summarized as follows: before 1885 there are packets of 5 – 10 varves interrupted by massive, homogeneous marl beds, indicating oscillating hypolimnetic oxygen levels until the lake ultimately became anoxic in 1885. Between 1885 and 1905 varves are thin, with a high carbonate content. Between 1905 and 1910 the thickness of varves increased steadily, and an increase in calcite grain size suggests a major step in eutrophication. Median grain size values increase again at the end of the 1940s, whereas the thickness of the seasonal layers decreased between the early 1940s and the early 1960s. At the onset of the 1960s, during the time of highest epilimnetic phosphorus concentrations in Baldeggersee, the total phosphorus concentrations in the sediments as well as the varve thickness and the total accumulation rates all increased. At the beginning of the 1980s the median grain size decreased substantially as a result of lower phosphorus concentrations in Baldeggersee