{'fraction_non_alphanumeric': 0.020850367947669663, 'fraction_numerical': 0.034750613246116106, 'mean_word_length': 4.826190476190476, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
High net CO 2 and CH 4 release at a eutrophic shallow lake 1 on a formerly drained fen 2 3

11 Drained peatlands often act as carbon dioxide (CO2) hotspots. Raising the groundwater table is 12 expected to reduce their CO2 contribution to the atmosphere and revitalize their function as carbon 13 (C) sink in the long term. Without strict water management rewetting often results in partial flooding 14 and the formation of spatially heterogeneous, nutrient-rich shallow lakes. Uncertainties remain as to 15 when the intended effect of rewetting is achieved, as this specific ecosystem type has hardly been 16 investigated in terms of greenhouse gas (GHG) exchange. In most cases of rewetting, methane (CH4) 17 emissions increase under anoxic conditions due to a higher water table and in terms of global warming 18 potential (GWP) outperform the shift towards CO2 uptake, at least in the short-term. 19 Based on eddy covariance measurements we studied the ecosystem–atmosphere exchange of CH4 and 20 CO2 at a shallow lake situated on a former fen grassland in Northeast (NE) Germany. The lake evolved 21 shortly after flooding, 9 years previous to our investigation period. The ecosystem consists of two main 22 surface types: open water (inhabited by submerged and floating vegetation) and emergent vegetation 23 (particularly including the eulittoral zone of the lake, dominated by Typha latifolia). To determine the 24 individual contribution of the two main surface types to the net CO2 and CH4 exchange of the whole 25 lake ecosystem, we combined footprint analysis with CH4 modelling and net ecosystem exchange (NEE) 26 partitioning. 27 The CH4 and CO2 dynamics were strikingly different between open water and emergent vegetation. 28 Net CH4 emissions from the open water area were around 4-fold higher than from emergent vegetation 29 stands, accounting for 53 and 13 g CH4 m a, respectively. In addition, both surface types were net 30 CO2 sources with 158 and 750 g CO2 m a, respectively. Unusual meteorological conditions in terms 31 2 of a warm and dry summer and a mild winter might have facilitated high respiration rates. In sum, even 32 after 9 years of rewetting the lake ecosystem exhibited a considerable C loss and global warming 33 impact, the latter mainly driven by high CH4 emissions. We assume the eutrophic conditions in 34 combination with permanent high inundation as major reasons for the unfavourable GHG balance. 35