TY - JOUR

T1 - Downstream changes in DOC

T2 - inferring contributions in the face of model uncertainties

AU - Tiwari, Tejshree

AU - Laudon, Hjalmar

AU - Beven, Keith

AU - Agren, Anneli M.

N1 - ©2014. American Geophysical Union. All Rights Reserved.

PY - 2014/1

Y1 - 2014/1

N2 - Dissolved organic carbon (DOC) is a central constituent of surface waters which control its characteristic color and chemistry. While the sources and controls of headwater stream DOC can be mechanistically linked to the dominant landscape types being drained, much remains unknown about the downstream controls at larger spatial scales. As DOC is transported from the headwaters to catchment outlets, the fate of stream DOC is largely dependent on the interaction of varying catchment processes. In this study, we investigated the main mechanisms regulating stream DOC in a mesoscale catchment. A landscape-mixing model was used to test the role of landscapes in determining stream concentrations. The quantity of DOC lost to in-stream processes was calculated using bacterial respiration and photooxidation rates. We investigated whether there was a change in water pathways using a mass balance model and comparison of hydrology between a headwater catchment and the entire catchment. A Monte Carlo approach was used to test robustness of the model assumptions and results to uncertainty in the process parameterizations. The results indicated that during high- and intermediate-flow conditions, DOC concentrations were regulated by the contributing upstream landscape types. During base flow, the connectivity between the mesoscale river and the upstream landscape reduced resulting in large residuals in the landscape model which could not be explained by the in-stream processes. Both the mass balance model and a specific runoff comparison between upstream/downstream sites independently indicated large input of deep groundwater during base flow. Deep groundwater was important for diluting stream DOC concentrations during base flow.Key Points Landscape types determine stream chemistry during high and intermediate flows Deep groundwater has large influences on stream chemistry during baseflow DOC lost to instream processes were small

AB - Dissolved organic carbon (DOC) is a central constituent of surface waters which control its characteristic color and chemistry. While the sources and controls of headwater stream DOC can be mechanistically linked to the dominant landscape types being drained, much remains unknown about the downstream controls at larger spatial scales. As DOC is transported from the headwaters to catchment outlets, the fate of stream DOC is largely dependent on the interaction of varying catchment processes. In this study, we investigated the main mechanisms regulating stream DOC in a mesoscale catchment. A landscape-mixing model was used to test the role of landscapes in determining stream concentrations. The quantity of DOC lost to in-stream processes was calculated using bacterial respiration and photooxidation rates. We investigated whether there was a change in water pathways using a mass balance model and comparison of hydrology between a headwater catchment and the entire catchment. A Monte Carlo approach was used to test robustness of the model assumptions and results to uncertainty in the process parameterizations. The results indicated that during high- and intermediate-flow conditions, DOC concentrations were regulated by the contributing upstream landscape types. During base flow, the connectivity between the mesoscale river and the upstream landscape reduced resulting in large residuals in the landscape model which could not be explained by the in-stream processes. Both the mass balance model and a specific runoff comparison between upstream/downstream sites independently indicated large input of deep groundwater during base flow. Deep groundwater was important for diluting stream DOC concentrations during base flow.Key Points Landscape types determine stream chemistry during high and intermediate flows Deep groundwater has large influences on stream chemistry during baseflow DOC lost to instream processes were small

KW - biogeochemistry

KW - boreal catchments

KW - modeling

KW - hydrology

KW - dissolved organic carbon

KW - uncertainty analysis

KW - DISSOLVED ORGANIC-MATTER

KW - SURFACE-WATER INTERACTIONS

KW - BOREAL STREAM NETWORK

KW - HYDROGRAPH SEPARATIONS

KW - MICROBIAL COMMUNITIES

KW - HEADWATER CATCHMENTS

KW - BACTERIAL-GROWTH

KW - NORTHERN SWEDEN

KW - TRANSIT-TIME

KW - CARBON DOC

U2 - 10.1002/2013WR014275

DO - 10.1002/2013WR014275

M3 - Journal article

VL - 50

SP - 514

EP - 525

JO - Water Resources Research

JF - Water Resources Research

SN - 0043-1397

IS - 1

ER -