Phosphorus mobilization in rewetted fens: the effect of altered peat properties and implications for their restoration

Abstract

Rewetting of drained fens is necessary to stop further soil degradation and to reestablish important ecological functions. However, substantial changes of peat characteristics in the upper soil layers, due to drainage and land use, could counteract their recovery as nutrient-poor systems for an unknown period. We assessed the importance of altered peat properties, such as the degree of peat decomposition and the amount of redox-sensitive phosphorus (P) compounds, for P mobilization in different degraded fens. An experimental design involving 63 intact peat cores from fens with varying drainage and land-use histories was developed to quantify the mobilization of P, as well as that of iron (Fe), ammonium, carbon dioxide, and methane, all indicators of organic-matter decomposition and/or P-releasing processes. We found that net P release rates in peat cores with highly decomposed peat (range: 0.1-52.3 mg P x m(-2) x d(-1)) were significantly correlated to the amount of P bound to redox-sensitive compounds and the molar Fe:P as well as Al:P ratios of peat. We conclude that the following general rules apply for P mobilization in rewetted fens: (1) elevated levels of P release rates and P concentrations in pore water up to three orders of magnitude larger than under natural reference conditions can only be expected for rewetted fens whose surface soil layers consist of highly decomposed peat; (2) peat characteristics, such as the amount of P bound to redox-sensitive Fe(III) compounds (positive correlation) and molar ratios of Fe:P or Al:P (negative correlations), explain the high range of P release rates; and (3) a critical P export to adjacent lakes or rivers can only be expected if molar Fe:P ratios of highly decomposed peat are less than 10.

Long-term fire effects of the drained open fen on organic soils

“…Post-fi re lowering of the fen surface caused longer and deeper spring fl oodings, and prolonged reductive conditions, resulting in P release. Molar ratio of Fe:P in the surface layer of the soil is about 11.4, which is close to the value considered by Zak et al (2010) as promoting P release after fl ooding. As stated in Zak et al (2014), the effects of increased availability of phosphorous can be long lasting.…”

Water and nutrient discharge to a high‐value terrace–floodplain fen: resilience and risk

“…Phosphorus will be released under hypoxic or anoxic conditions in the fen as a result of microbial Fe reduction process, which are known to have a dominant influence on P-dynamics (Sharpley, 1995). As reduced Fe compounds are less able to bind P, stagnation of anoxic water in P-rich materials will increase P mobilization (Zak et al, 2010;Lamers et al, 2014). We observed P concentrations nearly 20 times higher in fen groundwater than in ponded fen surface water, and note that the redox status of the subsurface was hypoxic (low DO, low ORP and high NH 4 -N concentrations) indicate conditions consistent with release of P via iron-reduction.…”

Do Water Management and Climate-Adapted Management of Wetlands Interfere in Practice? Lessons from the Biebrza Valley, Poland

“…Frequent saturation of the decomposed peat, either in response to natural phenomena (increasing groundwater level, flooding) or human-related issues (fen rewetting and management of land reclamation systems) interrupts nutrient balance by favoring soluble fractions of phosphorus to be released from organic soils to pore water, groundwater and-finally, in certain geochemical conditions-to surface waters (Zak et al 2010). In result, the eutrophication of aquatic and wetland ecosystems should be expected and mitigated.…”