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Pools are common in northern peatlands but studies have seldom focused on their nutrient biogeochemistry, especially in relation to their morphological characteristics and through seasons. We determined the environmental characteristics controlling carbon (C), nitrogen (N) and phosphorus (P) biogeochemistry in pools and assessed their evolution over the course of the 2016 growing season in a subboreal ombrotrophic peatland of eastern Canada. We showed that water chemistry variations in 62 pools were significantly explained by depth (81.9%) and the surrounding vegetation type (14.8%), but not by pool area or shape. Shallow pools had larger dissolved organic carbon (DOC) and total nitrogen (TN) concentrations and lower pH than deep pools, while pools surrounded by coniferous trees had more recalcitrant DOC than pools where vegetation was dominated by mosses. The influence of depth on pool biogeochemistry was confirmed by the seasonal survey of pools of different sizes with 47.1% of the variation in pool water chemistry over time significantly explained. Of this, 67.3% was explained by the interaction between time and pool size and 32.7% by pool size alone. P concentrations were small in all pools all summer long and combined with high N:P ratios, are indicative of P-limitation. Our results show that pool biogeochemistry is influenced by internal processes and highlight the spatial and temporal heterogeneity of nutrient biogeochemistry in ombrotrophic peatlands. [ABSTRACT FROM AUTHOR]

Abstract: In large regions of Europe and North America, peatlands have been exposed to elevated rates of atmospheric nitrogen (N) deposition. We investigated the fate of experimentally added N (NH4 15NO3) at two different N loads (1.2 and 4.7 g N m−2 yr−1) and water tables (1 and 32 cm) in intact cores from two peatlands, located in Central and Eastern Canada. The sites receive an estimated total N load of 0.6 g m−2 a−1 and 1.5 g m−2 yr−1, excluding nitrogen fixation. In all treatments, experimentally added nitrate (NO3 −) was fully (96–99%) and ammonium (NH4 +) mostly (81–97%) retained by the plant cover, mainly consisting of Sphagnum mosses, or in the unsaturated zone below. However, on average only 48% of the 15N were recovered from the plant cover, and substantial amounts were found in depth layers of 2–6 cm (21–46%) and 8–12 cm (1.4–10.8%) below the moss surface. The amount of 15N retained also significantly decreased with a lower water table from 56± 9% to 40±10%. These findings document a substantial mobility of N, particularly during water table drawdown. Analysis of 15N by a sequential diffusion procedure revealed a transfer of 15N from NO3 − into NH4 + and dissolved organic N (DON), but the contents of 15N in these pools accounted for less than 1% of the total N, natural background subtracted. The mass flux of dissolved 15N into the peat was small compared to the total mass flux of 15N. The accumulation of 15N in the bulk peat must have been caused by a mechanism that was not investigated, possibly by transport of particulate organic N. [Copyright &y& Elsevier]