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Examination of the potential relationship between droughts, sulphate and dissolved organic carbon at a wetland‐draining stream
Author(s) -
EIMERS M. CATHERINE,
WATMOUGH SHAUN A.,
BUTTLE JAMES M.,
DILLON PETER J.
Publication year - 2008
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/j.1365-2486.2007.01530.x
Subject(s) - dissolved organic carbon , environmental science , wetland , hydrology (agriculture) , deposition (geology) , total organic carbon , surface water , spring (device) , northern hemisphere , drainage basin , seasonality , environmental chemistry , ecology , chemistry , structural basin , atmospheric sciences , geology , biology , geography , mechanical engineering , paleontology , geotechnical engineering , cartography , environmental engineering , engineering
Rising dissolved organic carbon (DOC) concentrations observed at a number of sites in the northern hemisphere over recent decades are the subject of much debate, and recent reports suggest a link between DOC patterns in surface waters and changes in sulphate (SO 4 ) related to droughts or deposition. In order to investigate the potential influence of changes in SO 4 concentration on DOC patterns in south‐central Ontario, we used long‐term (1980–2001) stream monitoring data from a wetland‐dominated catchment (Plastic Lake‐1 subcatchment, PC1) that has been the focus of intensive investigations of both SO 4 and DOC dynamics. Annual average volume‐weighted DOC concentration increased significantly between 1980 and 2001, whereas SO 4 concentration declined, but the decrease was not significant due to large increases in SO 4 that occurred during drought years. There was no relationship between SO 4 and DOC in annual data series; however, seasonal analyses indicated significant negative correlations between SO 4 and DOC concentrations in spring (March–April–May), summer (June–July–August) and fall (September–October–November). In spring, DOC concentration was negatively correlated with flow whereas SO 4 concentrations increased with flow, and their opposing relationships with discharge explain the negative correlation between SO 4 and DOC in this season. In summer and fall, low SO 4 concentrations occur during periods of low flow as a result of microbial SO 4 reduction, whereas correspondingly high DOC concentrations in the summer and fall can be attributed to optimal conditions (i.e. stagnant flow, warm temperatures) for DOC production in the wetland. Increases in SO 4 (and acidity) following droughts were not associated with declines in DOC; instead the primary impact of droughts on DOC was to limit DOC export due to diminished stream flow. Rather than an acidification effect, we suggest that negative relationships between SO 4 and DOC were either directly (spring) or indirectly (summer/fall) caused by underlying relationships with hydrology.