Recent carbon sequestration dynamics in four temperate SE European peatlands using 210Pb dating

The last two centuries' anthropogenically-accelerated climatic changes and elevated atmospheric levels of CO₂ are influencing the recent carbon sequestration dynamics of peatlands, resulting in high variations of growth rates, and a general ascending trend in apparent carbon accumulation rates. In the present work, ²¹⁰Pb high-resolution chronologies and ¹³⁷Cs alternative markers were employed to study the recent carbon-related peat properties and their evolution throughout the last two centuries in four Sphagnum-dominated bogs in SE Europe (Romania). The results revealed a recent apparent carbon accumulation rate ranging from 9.5 to 437.5 g C m^-2 yr^-1, with a mean value of 144 ± 90.1 g C m^-2 yr^-1, that yielded an average increase of 18.25% of the rate from 1950 to the present period, suggesting an enhanced contemporaneous C uptake and storage in the peatlands. The mean C storage per unit area was 17.6 ± 7.6 kg C m^-2. The periods of decreased peat growth rates were identified and attributed to significant drought events at the regional scale. The results found in the present study confirm the observations and trends remarked by other researchers in the literature, and further reinforce the relevance of studying recent carbon dynamics in peatland ecosystems. The obtained ²¹⁰Pb chronologies were validated by ¹³⁷Cs markers, highlighting the suitability of this technique for peat profile dating.

Investigation of sedimentation rates and sediment dynamics in Danube Delta lake system (Romania) by 210Pb dating method

Being a dynamic environment associated with complex costal, fluvial and marine processes, only a few studies regarding the evolution of the Danube Delta and the human impacts on its ecosystem have been carried out. Being a sensible to all processes occurring in its catchment area, information is stored in the deposited sediments, which can be used as tracers for natural and anthropogenic processes. The aim of this study is to determine a detailed reconstruction of the sedimentation rates in the last century by applying the ²¹⁰Pb dating method validated by ¹³⁷Cs profiles. Additionally, the impacts of the construction of river-regulating structures (mainly the Iron Gates Hydro-Energetic Power Plants) are investigated, along with the assessment of natural phenomena (floods, storms etc.). To achieve this, 26 sediment cores from seven lakes were collected. ²¹⁰Pb_sup and ¹³⁷Cs were determined using gamma spectrometry, while ²¹⁰Pb_tot was measured via alpha spectrometry (²¹⁰Po), using the CRS model for age determination. From the assessed lakes, the most affected was the Matița Lake with a maximum sedimentation rate of 10.93 g cm^-2 yr^-1 and the least affected was the Isac Lake. Average sedimentation rates are: 0.95 g cm^-2 yr^-1 for Cruhlig Lake, 0.70 g cm^-2 yr^-1 for Uzlina Lake, 0.44 g cm^-2 yr^-1 for Isac Lake, 0.47 g cm^-2 yr^-1 for Cuibida Lake, 0.51 g cm^-2 yr^-1 for Iacob Lake, 1.00 g cm^-2 yr^-1 for Matița Lake and 0.76 g cm^-2 yr^-1 for Merhei Lake. Physical parameters (water content, porosity and bulk density) and LOI (organic matter and inorganic carbon content) were determined for each core to differentiate organic and non-organic sedimentation. Beside the natural influences, it is difficult to track the effects of the Iron Gates and not all analysed lakes were suitable for this task. The 1940-1970 period and the following ten years were compared in means of sedimentation: a decrease in sedimentation can be observed in four of the lakes: 59% in Cruhlig Lake, 16% in Uzlina Lake, 10% in Iacob Lake and 42% in Isac Lake, leading to an average 32% for the four lakes. The other three lakes show increasing tendencies of 39% in this period: 87% in Matița Lake, 6% in Merhei Lake and 24% in Cuibida Lake. Sedimentation rates show growths of 3 times after 1989, the most affected being the two northern lakes (3 times increase in both Matița Lake and Merhei Lake) and the four central lakes (2 times in case of Cuibida Lake, 3 times in Iacob Lake, 3 times in Isac Lake and 4 times in Uzlina Lake) with an average increase of 3 times, while the southern one (Cruhlig Lake) 2 times.