Coexistence of Lobelia dortmanna and Cladium mariscus, an ecological and paleobotanical study

Lobelia dortmanna L. (Lobeliaceae family) is an indicator species that is predominantly found in oligotrophic and acidic lakes. They are mainly distributed in northwestern Europe. Their occurrence in Poland is highly threatened by the increasing grade of human activity and environmental eutrophication; however, new sites of Lobelia were discovered in the last few decades, for example, in Lake Krzywce Wielkie situated in Bory Tucholskie National Park (BTNP), Poland. The existence of Lobelia in this lake was unexpected because Cladium mariscus was also found in the lake. Cladium has different ecological demands and is regarded as a species typical of calcareous habitats where calcium is found in abundance in the substrate. To explain the coexistence of both species in Krzywce Wielkie, pollen analysis of organic sediments was performed for four short cores collected from the littoral zone of the lake and for one long deep-water core. Additionally, macrofossil analysis was done for all the short cores. Pollen analysis revealed the existence of Cladium from the early Holocene period up to the present time. Pollen and seeds of Lobelia were found to be present since the beginning of the 20th century. Development of L. dortmanna and Myriophyllum alterniflorum populations and a decrease in the number of aquatic macrophytes in the eutrophic water indicate oligotrophication of water. This process started following the construction of drainage canal and the consequent water level decrease. This situation can be attributed to the abandonment of the agricultural areas adjoining the lake, which causes a decrease in the inflow of nutrients into the lake. Development of pine forest and establishment of BTNP enabled the protection and conservation of the surrounding catchment areas, thus restricting the potential eutrophication of the habitats.

Hydrogeochemical Evolution of an Aquifer Regulated by Pyrite Oxidation and Organic Sediments

Detailed full-scale groundwater monitoring was carried out over a period of nine years, sampling at selected points along the groundwater flow direction in its final stretch. This established the hydrogeochemical evolution along the flow of a natural system formed by a calcareous aquifer which discharges and then passes through a quaternary aquifer of lake origin which is rich in organic matter. This evolution is highly conditioned by the oxidation of pyrites that are abundant in both aquifers. In the first aquifer, one kilometre before the discharge location, oxidizing groundwater crosses a pyrite mineralization zone whose oxidation produces an important increase in sulphates and water denitrification over a short period of time. In the quaternary aquifer with peat sediments and pyrites, water experiences, over a small 500 m passage and residence time of between three and nine years, a complete reduction by way of pyrite oxidation, and a consequent increase in sulphates and the generation of hydrogen sulphuric acid. This is an example of an exceptional natural hydrogeological environment which provides guidance on hydrogeochemical processes such as denitrification.

A Tree-Ring chronology from Allerød–YD transition from Koźmin (Central Poland)

Subfossil trunks of pine (Pinus sylvestris L.) from the Late Weichselian were discovered in the site Koźmin in the Koło Basin, central Poland (Dzieduszyńska et al., 2014a). Another part of organic sediments with trunks was excavated in the frame of the research project. Altogether 224 samples from Koźmin were analysed dendrochronologically; they represented generally young trees, 40 to 70 years old. Based on the most convergent sequences, the chronology 2KOL_A1 was produced, 210 years in length. With the wiggle-matching method, it was dated to ca. 13065–12855 cal BP. Dendrochronological dating of trunks buried in organic sediments, most of which occurred in situ, revealed that tree deaths occurred successively, over more than 100 years. That could have been due to unfavourable climatic conditions, as well as extreme events, e.g. strong winds.

Toward a standardized procedure for charcoal analysis

Sedimentary charcoal records are used for understanding fire as an earth system process; however, no standardized laboratory methodology exists. Varying sample volumes and chemical treatments (i.e., type of chemical for length of time) are used for the deflocculation and extraction of charcoal from sediment samples. Here, we present the first systematic assessment of the effect of commonly used chemicals on charcoal area and number of fragments. In modern charcoal the area of fragments was significantly different depending on the chemical treatment. We subsequently applied H2O2 (33%), NaClO (12.5%), and HNO3 (50%) to a late-glacial–early Holocene paleorecord and tested different sample volumes. The effects of the treatments were consistent between modern and fossil experiments, which demonstrates the validity of applying results from the modern experiment to the fossil records. Based on our experiments we suggest (1) H2O2 33%, especially for highly organic sediments; (2) avoidance of high concentrations of NaClO for prolonged periods of time, and of HNO3; and (3) samples of 1 cm3 provided typically consistent profiles. Our results indicate that charcoal properties can be influenced by treatment type and sample volume, thus emphasizing the need for a common protocol to enable reliable multi-study comparisons or composite fire histories.

Thresholds of mangrove survival under rapid sea level rise

The response of mangroves to high rates of relative sea level rise (RSLR) is poorly understood. We explore the limits of mangrove vertical accretion to sustained periods of RSLR in the final stages of deglaciation. The timing of initiation and rate of mangrove vertical accretion were compared with independently modeled rates of RSLR for 78 locations. Mangrove forests expanded between 9800 and 7500 years ago, vertically accreting thick sequences of organic sediments at a rate principally driven by the rate of RSLR, representing an important carbon sink. We found it very likely (>90% probability) that mangroves were unable to initiate sustained accretion when RSLR rates exceeded 6.1 millimeters per year. This threshold is likely to be surpassed on tropical coastlines within 30 years under high-emissions scenarios.

Macrofauna and roots reduce methane production and attenuate nutrient recycling in organic-rich fluvial sediments

<p>Organic-rich freshwater sediments display millimetric oxygen and nitrate penetration and are sources of methane to the water column and to the atmosphere via diffusion and ebullition. Radial oxygen loss by submersed aquatic plants and burrow irrigation with O<sub>2</sub> and NO<sub>3</sub><sup>-</sup> enriched water by macrofauna can significantly alter the subsurface sediment volume where respiration processes alternative to methanogenesis occur. We tested this hypothesis in perifluvial organic sediments colonized by the submerged phanerogam <em>Vallisneria spiralis</em> and the oligochaete <em>Sparganophilus tamesis</em>. Gas ebullition and diffusive fluxes were measured in microcosms maintained under controlled laboratory conditions over a period of two weeks. Four conditions were reproduced: sediments alone, sediment with oligochaetes, sediment with plants and sediment with plants and oligochaetes. Microcosms with sediments alone released the largest methane volume whereas sediments with plants and macrofauna released the lowest amount. The presence of the oligochaete had comparatively a stronger effect than that of the macrophyte. Simultaneously, the bioturbation activity of the oligochaete enhanced the production of N<sub>2</sub> and the consumption of oxygen and nitrate, suggesting increased rates of aerobic respiration and of denitrification. The presence of plants attenuated net N<sub>2</sub> losses from the benthic system likely due to the competition between assimilative and dissimilative N-related processes.</p>