TY - JOUR
T1 - Are herbarium mosses reliable indicators of historical nitrogen deposition?
AU - Nielsen, Tora Finderup
AU - Larsen, Jesper Ruf
AU - Michelsen, Anders
AU - Bruun, Hans Henrik
PY - 2017/12
Y1 - 2017/12
N2 - Mosses collected decades ago and stored in herbaria are often used to assess historical nitrogen deposition. This method is effectively based on the assumption that tissue N concentration remains constant during storage. The present study raises serious doubt about the generality of that assumption. We measured tissue N and C concentrations as well as δ15N, δ13C, Pb and Mg in herbarium and present day samples of seven bryophyte species from six sites across Denmark. While an increase in nitrogen deposition during the last century is well-documented for the study site, we surprisingly found foliar N concentration to be higher in historical samples than in modern samples. Based on δ15N values and Pb concentration, we find nitrogen contamination of herbarium specimens during storage to be the most likely cause, possibly in combination with dilution though growth and/or decomposition during storage. We suggest ways to assess contamination and recommend caution to be taken when using herbarium specimens to assess historical pollution if exposure during storage cannot be ruled out. Analyses of moss tissue stored in a herbarium for a century raises serious concern about the reliability of this data source to past levels of nitrogen deposition.
AB - Mosses collected decades ago and stored in herbaria are often used to assess historical nitrogen deposition. This method is effectively based on the assumption that tissue N concentration remains constant during storage. The present study raises serious doubt about the generality of that assumption. We measured tissue N and C concentrations as well as δ15N, δ13C, Pb and Mg in herbarium and present day samples of seven bryophyte species from six sites across Denmark. While an increase in nitrogen deposition during the last century is well-documented for the study site, we surprisingly found foliar N concentration to be higher in historical samples than in modern samples. Based on δ15N values and Pb concentration, we find nitrogen contamination of herbarium specimens during storage to be the most likely cause, possibly in combination with dilution though growth and/or decomposition during storage. We suggest ways to assess contamination and recommend caution to be taken when using herbarium specimens to assess historical pollution if exposure during storage cannot be ruled out. Analyses of moss tissue stored in a herbarium for a century raises serious concern about the reliability of this data source to past levels of nitrogen deposition.
UR - http://www.scopus.com/inward/record.url?scp=85017462742&partnerID=8YFLogxK
U2 - 10.1016/j.envpol.2017.04.020
DO - 10.1016/j.envpol.2017.04.020
M3 - Journal article
C2 - 28420490
AN - SCOPUS:85017462742
SN - 0269-7491
VL - 231
SP - 1201
EP - 1207
JO - Environmental Pollution
JF - Environmental Pollution
IS - Part 1
ER -