SFS Annual Meeting

5/24/2018  |   11:00 - 11:15   |  310 A

RIPARIAN ZONES: WHY BOTHER? Investigating the effect of land use on water quality at the catchment scale goes back decades. Recent land cover and land use changes with increasing anthropogenic pressure on water resources have occurred at a planetary scale, leading to water quality degradation. From a landscape perspective, riparian zones have long been considered buffer zones, acting as biogeochemical hot spots of nitrogen removal. However, riparian corridors are also zones of incredible spatiotemporal variability, which has been a major obstacle to scaling measured processes beyond the reach level. Yet, there is a pressing need to translate reach-small-scale process understanding to larger-scale catchment units of ca few km2, particularly for inter-catchments comparison, but this requires quantifying the effects of different spatial configurations of landscape units, including riparian zones, but also other landscape structures (e.g. hyporheic zone, aquifer, soils, floodplain) and physical characteristics on catchment water quality. In this context, we develop a conceptual framework that combines landscape-level topographic analysis, process based field investigations using biogeochemical proxies, and water retention time distributions to characterise landscape nitrogen removal capacity.

Gilles Pinay (Primary Presenter/Author), CNRS, gilles.pinay@ens-lyon.fr;


Benjamin Abbott (Co-Presenter/Co-Author), Department of Earth and Environmental Sciences, Michigan State University, USA, benabbo@gmail.com;


Florentina Moatar (Co-Presenter/Co-Author), INRAE, florentina.moatar@inrae.fr;


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5/24/2018  |   11:15 - 11:30   |  310 A

RIPARIAN ZONES: WHY BOTHER? Investigating the effect of land use on water quality at the catchment scale goes back decades. Recent land cover and land use changes with increasing anthropogenic pressure on water resources have occurred at a planetary scale, leading to water quality degradation. From a landscape perspective, riparian zones have long been considered buffer zones, acting as biogeochemical hot spots of nitrogen removal. However, riparian corridors are also zones of incredible spatiotemporal variability, which has been a major obstacle to scaling measured processes beyond the reach level. Yet, there is a pressing need to translate reach-small-scale process understanding to larger-scale catchment units of ca few km2, particularly for inter-catchments comparison, but this requires quantifying the effects of different spatial configurations of landscape units, including riparian zones, but also other landscape structures (e.g. hyporheic zone, aquifer, soils, floodplain) and physical characteristics on catchment water quality. In this context, we develop a conceptual framework that combines landscape-level topographic analysis, process based field investigations using biogeochemical proxies, and water retention time distributions to characterise landscape nitrogen removal capacity.

Gilles Pinay (Primary Presenter/Author), CNRS, gilles.pinay@ens-lyon.fr;


Benjamin Abbott (Co-Presenter/Co-Author), Department of Earth and Environmental Sciences, Michigan State University, USA, benabbo@gmail.com;


Florentina Moatar (Co-Presenter/Co-Author), INRAE, florentina.moatar@inrae.fr;


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5/24/2018  |   11:30 - 11:45   |  310 A

HOW DO WE MEASURE BIOGEOCHEMICAL HOT SPOTS AND MOMENTS? MOVING TOWARD A UNIFYING EMPIRICAL FRAMEWORK We have long recognized that rare locations and events can contribute disproportionately to biogeochemical cycling of nutrients (i.e. hot spots and hot moments concept, HSHM). However, our inability to accurately identify, predict, and incorporate HSHM into global models has limited the concept’s utility. This is due, in part, to a lack of comparison among diverse empirical methods used to identify and quantify biogeochemical HSHM. Using data from a high-frequency soil-monitoring network in a restored wetland (SW Ohio), we compared existing methods (e.g. comparison of means, proportions, outliers, Lorenz curve, and Gini coefficient) to quantify HSHM. By using a single dataset, of methane and nitrous oxide emissions from the aquatic-terrestrial interface, with one experimental design, our work highlights the advantages and disadvantages of differing empirical methods. We aim to recommend more consistent criteria for quantifying HSHM, with the hopes that unifying the empirical framework underlying the concept will increase the testability, reproducibility, and thus utility of the HSHM concept.

Laura Podzikowski (Primary Presenter/Author), University of Kansas, lpodziko@ku.edu;


Terrance D. Loecke (Co-Presenter/Co-Author), University of Kansas, loeckete@gmail.com;


Amy J. Burgin (Co-Presenter/Co-Author), University of Kansas, burginam@ku.edu;


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5/24/2018  |   11:45 - 12:00   |  310 A

THE ROLE OF VEGETATION IN THE NITROGEN REMOVAL CAPACITY FROM A MEDITERRANEAN RIPARIAN FOREST: INTERACTIONS BETWEEN WATER AND NITROGEN FLUXES Riparian zones can reduce part of the nitrogen (N) received from adjacent ecosystems, mainly via denitrification and vegetation uptake. However, in semiarid regions, where shallow organic soil layers are disconnected from groundwater, changes on these biogeochemical controls may arise. Here, we summarize results from different studies in order to examine the efficiency of plant uptake and denitrification on removing N exports from Mediterranean catchments. We found a remarkable spatial heterogeneity on water availability, with groundwater levels increasing from the near-stream zone (~0.6m deep) to the hillslope edge (~2.2m deep). Riparian trees obtained >80% of the water transpired from the vadose zone. Shallow groundwater tables enhanced the connectivity between vadose zone and groundwater at the near-stream zone, allowing greater transpiration and N uptake rates compared to the hillslope edge. Conversely, denitrification rates were generally low across all the riparian plot due to water limitation. Finally, simulation based on climate change projections suggested an increase in soil N concentrations as well as a reduction of the effective N-removal area. Overall, our findings highlight the spatial heterogeneity of Mediterranean riparian zones and challenge its well-accepted capacity to reduce N loads reaching the stream.

Anna Lupon (Co-Presenter/Co-Author), Swedish University of Agricultural Sciences, anna.lupon@slu.se;


Zahra Thomas (Co-Presenter/Co-Author), UMR SAS, AGROCAMPUS OUEST, INRA, 35000 Rennes, France, zahra.Thomas@agrocampus-ouest.fr;


Santiago Sabaté (Co-Presenter/Co-Author), Departament de Biologia Evolutiva, Ecologia i Ciències Ambientals, Universitat de Barcelona. Av. Diagonal 643, 08028 Barcelona, Spain./Centre for Ecological Research and Forestry Applications (CREAF). Campus de Bellaterra Edifici C, 08193, Cerdanyola del Vallès, Spain., santi.sabate@ub.edu;


Francesc Sabater (Co-Presenter/Co-Author), Universitat de Barcelona, fsabater@ub.edu;


Sílvia Poblador (Primary Presenter/Author), Research Group of Plants and Ecosystems, Department of Biology, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium, spoblador@gmail.com;


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5/24/2018  |   12:00 - 12:15   |  310 A

LINKING RIPARIAN AND STEAM NITROGEN DYNAMICS IN A MEDITERRANEAN HEADWATER CATCHMENT Riparian areas are recognized to be natural filters of nitrogen, yet their role at catchment scale still remains poorly understood. This is mostly because stream water chemistry integrates processes co-occurring within upland, riparian, and fluvial ecosystems. Here, we summarize results from different studies in order to examine some of the processes by which Mediterranean riparian zones can regulate stream nitrogen dynamics. First, riparian soils may be important sources of nitrate to streams because they exhibit higher net nitrification rates than upland soils. In addition, riparian evapotranspiration can influence the temporal pattern of stream flow and promote the stream hydrological retention during the vegetative period. Nonetheless, such stream hydrological retention is not always accompanied by a decrease in catchment nitrogen exports, likely because low flows, warm conditions, and large stocks of nitrogen-rich leaf litter enhance in-stream nitrification. Finally, riparian tree phenology can regulate in-stream photoautotrophic activity and thus reduce catchment nitrate exports in spring. Overall, our findings question the well-established idea that Mediterranean riparian zones are efficient nitrogen buffers, and stress that an integrated view of different landscape units is needed to advance in catchment biogeochemistry.

Anna Lupon (Primary Presenter/Author), Swedish University of Agricultural Sciences, anna.lupon@slu.se;


Francesc Sabater (Co-Presenter/Co-Author), Universitat de Barcelona, fsabater@ub.edu;


Sílvia Poblador (Co-Presenter/Co-Author), University of Barcelona, spoblador@ub.edu;


Eugènia Martí (Co-Presenter/Co-Author), Center for Advanced Studies of Blanes (CEAB-CSIC), eugenia@ceab.csic.es;


Susana Bernal (Co-Presenter/Co-Author), Center for Advanced Studies of Blanes (CEAB-CSIC), Spain, sbernal@ceab.csic.es;


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5/24/2018  |   12:15 - 12:30   |  310 A

HYDROLOGICAL CONTROLS OVER ORGANIC MATTER SUPPLY AND METABOLIC ACTIVITY IN BOREAL STREAMS The supply of dissolved organic matter (DOM) is an important driver of biogeochemical processes in streams. In boreal landscapes, DOM inputs often derive from organic rich, riparian soils connected to streams through lateral, near-surface flowpaths. Temporal changes in the riparian water table activate/deactivate these flowpaths, with higher flows typically leading to increased DOM quantity and quality in streams. These connections also vary in space, reflecting the influence of catchment topography on the size and arrangement of lateral flowpaths entering streams. Here we use estimates of ecosystem metabolism and additions of a metabolically active dye (resazurin) to explore how the processes regulating DOM inputs shape patterns of heterotrophic activity in boreal streams. Consistent with the predicted effects of activating surficial flowpaths, variation in discharge throughout the summer and autumn in a headwater stream was associated with large (5-fold) differences in ecosystem respiration. Furthermore, additions of resazurin revealed consistent increases in metabolic activity coinciding with the location of groundwater input zones. Together, these results illustrate how the physical processes governing the activation and spatial arrangement of riparian flowpaths influence patterns of boreal stream metabolism through effects on DOM delivery.

Ryan Sponseller (Primary Presenter/Author), Department of Ecology and Environmental Science, Umeå University, 901 87 Umeå, Sweden, ryan.sponseller@umu.se;


Anna Lupon (Co-Presenter/Co-Author), Swedish University of Agricultural Sciences, anna.lupon@slu.se;


Lluís Gómez-Gener (Co-Presenter/Co-Author), Centre for Research on Ecology and Forestry Application (CREAF), gomez.gener87@gmail.com;


Hjalmar Laudon (Co-Presenter/Co-Author), Swedish University of Agricultural Sciences, hjalmar.laudon@slu.se;


Erin Hotchkiss (Co-Presenter/Co-Author), Virginia Polytechnic Institute and State University (Virginia Tech), ehotchkiss@vt.edu;


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