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High terrestrial carbon load via groundwater to a boreal lake dominated by surface water inflow
Author(s) -
Einarsdottir Karolina,
Wallin Marcus B.,
Sobek Sebastian
Publication year - 2017
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2016jg003495
Subject(s) - groundwater , dissolved organic carbon , surface water , hydrology (agriculture) , groundwater discharge , environmental science , streams , shore , submarine groundwater discharge , groundwater flow , geology , oceanography , aquifer , environmental engineering , computer network , geotechnical engineering , computer science
Abstract The input of dissolved organic and inorganic carbon (DOC and DIC) via direct groundwater seepage to boreal lakes is often assumed to be small in noncarbonaceous areas. However, measurements are rare. We estimated the terrestrial load of DOC, DIC, and methane (CH 4 ) to a small boreal lake for the open water period, on the basis of measured concentrations of carbon species in near‐shore groundwater wells and inlet streams, and measured area‐specific discharge. The subcatchment directly draining into the lake via groundwater seepage contributed 18% to the total water input during the open water season. Compared to stream and lake water, near‐shore groundwater concentrations of DOC were slightly elevated, and groundwater DIC and CH 4 concentrations were highly elevated. Consequently, direct groundwater seepage contributed 27% to the total DOC load, 64% to the total DIC load, and 96% to the total CH 4 load from the catchment to the lake. Groundwater DIC import corresponded only to 5–8% of lake carbon dioxide (CO 2 ) emission. In incubation experiments, we observed higher photochemical DOC loss rates in stream and groundwater samples (18–55% DOC loss upon 72 h UV‐A exposure) than in lake water (15% DOC loss) and detected significant DOC flocculation in groundwater samples in both light and dark incubations (2–24% DOC loss). We conclude that even in regions where lake hydrology is dominated by surface water inflow via inlet streams, direct groundwater seepage can represent an important carbon source to boreal lakes, and groundwater DOC may be susceptible to in‐lake removal via degradation and flocculation.