Peat properties and mercury methylation in drained and restored boreal peatlands

Jacob Smeds

doi:10.54612/a.2dd04kk3ti

Peat properties and mercury methylation in drained and restored boreal peatlands

Bidragets översatta titel: Torvegenskaper och kvicksilvermetylering i dränerade och restaurerade boreala myrar

Jacob Smeds

Institutionen för skogens ekologi och skötsel

Publikation: Avhandling › Doktorsavhandling

16 Nedladdningar

Sammanfattning

Trots efterfrågan att restaurera dränerade myrar saknas fortfarande en gedigen förståelse för effekterna på de biogeokemiska processerna i torven. Utöver de avsedda ekosystemtjänsterna kan återvätning även leda till skadliga effekter och potentiella miljöhot, till exempel kvicksilvermetylering. Åtskilliga årtionden av dränerade förhållanden har också förändrat torvens egenskaper, vilket gör effekterna av restaurering på de biogeokemiska processerna svåra att förutspå. Denna avhandling utvärderar effekterna av dränering och restaurering på torvens fysikaliska och kemiska egenskaper, samt hur återvätning påverkar kvicksilvermetylering. För varje dränerad och restaurerad myr som undersöktes provtogs en närliggande opåverkad referensmyr. Varje myr provtogs ner till 50 cm djup och analyserades för kol (C), kväve (N), δ13C, δ15N, innehållet av organiskt material (OM), och bulkdensiteten (BD). Mätningar och analyser på de restaurerade myrarna, med tillhörande referensmyrar, inkluderade också svavel (S) XANES, oorganiskt kvicksilver (IHg), metylkvicksilver (MeHg), samt grundvattennivån. Dränering av myrar ledde till en signifikant påverkan på torvens fysikaliska och kemiska egenskaper. I de dränerade och restaurerade myrarna ökade BD samt innehållet av C och N, medan innehållet av OM, C:N kvot och δ13C minskade relativt de naturliga referensmyrarna. Trots restaureringsinsatserna var grundvattennivån fortfarande fem centimeter lägre i de restaurerade myrarna än i de naturliga myrarna. Förekomsten av reducerade former av S relativt de oxiderade formerna var högre i naturliga myrar, vilket är i linje med en lägre grundvattennivå. Även om restaurering misslyckades med att återskapa hydrologin och redoxförhållanden relativt referensytorna så ökade nettoformeringen av metylkvicksilver i de restaurerade myrarna. Den kumulativa massan av MeHg och IHg i torvens översta 50 cm ökade också efter dränering och restaurering, vilket ökar risken för MeHg- och IHg-export från de restaurerade myrarna till närliggande bäckar och sjöar.

Bidragets översatta titel	Torvegenskaper och kvicksilvermetylering i dränerade och restaurerade boreala myrar
Originalspråk	Engelska
Kvalifikation	Doktor i filosofi
Förlag	Swedish University of Agricultural Sciences
Tryckta ISBN	978-91-8046-462-8
Elektroniska ISBN	978-91-8046-512-0
DOI	https://doi.org/10.54612/a.2dd04kk3ti
Status	Publicerad - 2025

Nyckelord

boreal peatlands
carbon cycle
mercury methylation
nitrogen cycle
peat decomposition
peat properties
peatland restoration

SLU-serie

Acta Universitatis Agriculturae Sueciae

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10.54612/a.2dd04kk3ti

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@phdthesis{b2dc91698f7041d38780b9cd5c137252,

title = "Peat properties and mercury methylation in drained and restored boreal peatlands",

abstract = "Despite the societal demand for restoring drained boreal peatlands, a firm understanding of how drainage and restoration (through rewetting) affect the biogeochemistry of these ecosystems is missing. In addition to the intended ecosystem services, restoration may result in undesired effects and potential environmental threats, such as mercury (Hg) methylation. It is important to note that prolonged drainage can alter the peat properties, which makes the effects of restoration difficult to predict.This thesis evaluates how drainage and restoration impact physical and chemical peat properties and net methylmercury (MeHg) formation. For each drained and restored peatland, a corresponding undisturbed natural reference peatland was sampled. Each peatland was sampled to a depth of 50 cm and analysed for carbon (C), nitrogen (N), δ13C, δ15N, organic matter content (OM), and dry bulk density (BD). The restored peatlands (and the natural peatlands) involved additional measurements of sulphur (S) XANES, along with the groundwater level and concentrations of inorganic mercury (IHg) and MeHg.Peatland drainage was found to significantly alter the physical and chemical peat properties. The drained and restored peatlands, when compared with natural reference peatlands, were characterised by increased BD and C and N contents in OM, along with decreased OM contents, C:N ratios, and δ13C. Despite restoration efforts, the groundwater level of the restored peatlands remained five centimetres deeper than what was observed for natural reference peatlands. Although restoration failed to replicate the water table levels and redox conditions in natural peatland sites, the drainage and subsequent restoration increased concentrations of IHg and MeHg, as well as \%MeHg of total Hg. The cumulative mass of MeHg and IHg in the top 50 cm of peat also increased after drainage and restoration. Thus, increasing the risk of MeHg and IHg export from peatlands to adjacent streams and lakes.",

keywords = "boreal peatlands, carbon cycle, mercury methylation, nitrogen cycle, peat decomposition, peat properties, peatland restoration, boreal peatlands, carbon cycle, mercury methylation, nitrogen cycle, peat decomposition, peat properties, peatland restoration",

author = "Jacob Smeds",

year = "2025",

doi = "10.54612/a.2dd04kk3ti",

language = "English",

isbn = "978-91-8046-462-8",

series = "Acta Universitatis Agriculturae Sueciae",

publisher = "Swedish University of Agricultural Sciences",

number = "2025:27",

address = "Sweden",

}

TY - BOOK

T1 - Peat properties and mercury methylation in drained and restored boreal peatlands

AU - Smeds, Jacob

PY - 2025

Y1 - 2025

N2 - Despite the societal demand for restoring drained boreal peatlands, a firm understanding of how drainage and restoration (through rewetting) affect the biogeochemistry of these ecosystems is missing. In addition to the intended ecosystem services, restoration may result in undesired effects and potential environmental threats, such as mercury (Hg) methylation. It is important to note that prolonged drainage can alter the peat properties, which makes the effects of restoration difficult to predict.This thesis evaluates how drainage and restoration impact physical and chemical peat properties and net methylmercury (MeHg) formation. For each drained and restored peatland, a corresponding undisturbed natural reference peatland was sampled. Each peatland was sampled to a depth of 50 cm and analysed for carbon (C), nitrogen (N), δ13C, δ15N, organic matter content (OM), and dry bulk density (BD). The restored peatlands (and the natural peatlands) involved additional measurements of sulphur (S) XANES, along with the groundwater level and concentrations of inorganic mercury (IHg) and MeHg.Peatland drainage was found to significantly alter the physical and chemical peat properties. The drained and restored peatlands, when compared with natural reference peatlands, were characterised by increased BD and C and N contents in OM, along with decreased OM contents, C:N ratios, and δ13C. Despite restoration efforts, the groundwater level of the restored peatlands remained five centimetres deeper than what was observed for natural reference peatlands. Although restoration failed to replicate the water table levels and redox conditions in natural peatland sites, the drainage and subsequent restoration increased concentrations of IHg and MeHg, as well as %MeHg of total Hg. The cumulative mass of MeHg and IHg in the top 50 cm of peat also increased after drainage and restoration. Thus, increasing the risk of MeHg and IHg export from peatlands to adjacent streams and lakes.

AB - Despite the societal demand for restoring drained boreal peatlands, a firm understanding of how drainage and restoration (through rewetting) affect the biogeochemistry of these ecosystems is missing. In addition to the intended ecosystem services, restoration may result in undesired effects and potential environmental threats, such as mercury (Hg) methylation. It is important to note that prolonged drainage can alter the peat properties, which makes the effects of restoration difficult to predict.This thesis evaluates how drainage and restoration impact physical and chemical peat properties and net methylmercury (MeHg) formation. For each drained and restored peatland, a corresponding undisturbed natural reference peatland was sampled. Each peatland was sampled to a depth of 50 cm and analysed for carbon (C), nitrogen (N), δ13C, δ15N, organic matter content (OM), and dry bulk density (BD). The restored peatlands (and the natural peatlands) involved additional measurements of sulphur (S) XANES, along with the groundwater level and concentrations of inorganic mercury (IHg) and MeHg.Peatland drainage was found to significantly alter the physical and chemical peat properties. The drained and restored peatlands, when compared with natural reference peatlands, were characterised by increased BD and C and N contents in OM, along with decreased OM contents, C:N ratios, and δ13C. Despite restoration efforts, the groundwater level of the restored peatlands remained five centimetres deeper than what was observed for natural reference peatlands. Although restoration failed to replicate the water table levels and redox conditions in natural peatland sites, the drainage and subsequent restoration increased concentrations of IHg and MeHg, as well as %MeHg of total Hg. The cumulative mass of MeHg and IHg in the top 50 cm of peat also increased after drainage and restoration. Thus, increasing the risk of MeHg and IHg export from peatlands to adjacent streams and lakes.

KW - boreal peatlands

KW - carbon cycle

KW - mercury methylation

KW - nitrogen cycle

KW - peat decomposition

KW - peat properties

KW - peatland restoration

KW - boreal peatlands

KW - carbon cycle

KW - mercury methylation

KW - nitrogen cycle

KW - peat decomposition

KW - peat properties

KW - peatland restoration

UR - https://res.slu.se/id/publ/132967

U2 - 10.54612/a.2dd04kk3ti

DO - 10.54612/a.2dd04kk3ti

M3 - Doctoral thesis

SN - 978-91-8046-462-8

T3 - Acta Universitatis Agriculturae Sueciae

PB - Swedish University of Agricultural Sciences

ER -