Biogeochemical fluxes in landscapes

Authors: Ülo Mander Xiuzhen Li Martin J Wassen

Publish Date: 2013/03/17

Volume: 28, Issue: 4, Pages: 577-581

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Abstract

The relationship between landscape pattern and material cycling in landscapes and its functional units—watersheds catchments—is a classic area in landscape research Bormann and Likens 1979 Peterjohn and Correll 1984 Wassen and Barendregt 1992 Arheimer and Brand 2000 Pionke et al 2000 Burt and Pinay 2005 Laudon et al 2007 Naiman and Decamps 2007 Pärn et al 2012 Together with metapopulation dynamics in mosaic landscapes landuse dynamics and landscape structure analysis these fields cover the majority of all investigations in landscape ecology Wu and Hobbs 2002 Li and Mander 2009 Of biogeochemical fluxes cycles of carbon and nitrogen—those that are most altered by human activities Vitousek et al 1997—as well as their hotspots in landscapes have been under examination Peterson et al 2001 McClain et al 2003 Seitzinger et al 2006 Likewise phosphorus cycling which is significant for the ecological status of freshwater bodies and terrestrial ecosystems is among the most frequently studied material cycles in landscapes and catchments Sharpley et al 1994 Carpenter et al 1998The alteration of biogeochemical cycles influences all landscape processes including those related to biodiversity issues Tilman et al 1996 Wassen et al 2005 Naeem et al 2012 In recent decades due to growing interest in phenomena caused by global warming the quantity of studies on greenhouse gas emissions at watershed scale Vilain et al 2012 and local to regional landscape scale Le Mer and Roger 2001 Sozanska et al 2002 Lilly et al 2003 Sommer et al 2004 Mander et al 2010 Wolf et al 2010 Nol et al 2012 Schelde et al 2012 has increased significantlyTo help improve our understanding of “landscape biogeochemistry” we organized a symposium entitled “Biogeochemical Fluxes in Landscapes” during the 8th World Congress on Landscape Ecology in Beijing in August 2011 This special issue is based on the Beijing symposiumThe special issue consists of eight research articles In the first one Mitsch et al 2013 consider the role of wetlands in climate warming Wetland ecosystems provide an optimum natural environment for the sequestration and longterm storage of carbon dioxide CO2 from the atmosphere yet are natural sources of greenhouse gas emissions especially methane CH4 It is shown that most wetlands do not have 25 times more CO2 sequestration than CH4 emissions when carbon C sequestration is compared to methane emissions therefore most wetlands would be considered by many landscape managers and non specialists to be sources of climate warming or net radiative forcing The dynamic modeling of carbon flux results from 21 detailed wetland studies has shown that CH4 emissions become unimportant within 300 years compared to C sequestration in wetlands Within that time frame or less most wetlands become both net carbon and radiative sinks It has also been estimated that the world’s wetlands despite being only about 5–8  of the terrestrial landscape may currently act as net carbon sinks of about 830 Tg/year of carbon with an average of 118 gC/m2/year of net carbon retention Most of that carbon retention occurs in tropical/subtropical wetlands The authors demonstrate that almost all wetlands are net radiative sinks when balancing C sequestration and CH4 emissions and conclude that wetlands can be created and restored to provide C sequestration and other ecosystem services without great concern for creating net radiative sources in the climate due to CH4 emissionsIn their perspective paper Wassen et al 2013 integrate a number of recent research findings into known relationships that together reveal interactions between different elemental cycles and the water cycle through vegetation and could potentially have unexpected effects on landscapes and largerscale continental global systems These interactions include processes on very distinct temporal and spatial scales in which plants and vegetation play a key role This implies that vegetation is not only affected by global change but also drives global change by influencing fluxes of these elements and the link between them The authors propose that it is necessary to account for plant processes and how these interfere with elemental cycles in order to achieve a better understanding of the effects of changes in land cover and land use for biogeochemical and biogeophysical fluxes Directions for further research to fill the current knowledge gaps are suggestedHaas et al 2013 present a new model system for the simulation of biosphere–atmosphere–hydrosphere exchange processes at landscape scale The new framework LandscapeDNDC—partly based on the biogeochemical sitescale model DNDC—facilitates scaling of ecosystem processes from the site to regional simulation domains and inherits a series of new features with regard to process descriptions model structure and data functionality LandscapeDNDC incorporates different vegetation types and management systems for the simulation of C nitrogen N and waterrelated biosphere–atmosphere–hydrosphere fluxes in forest arable and grassland ecosystems and allows the dynamic simulation of land use changes The modeling concept divides ecosystems into six substrates and provides alternative modules for those substrates The model can be applied on the site scale and also for threedimensional regional simulations For regional applications LandscapeDNDC integrates all grid cells synchronously forward in time This allows for easy coupling to other spatiallydistributed models eg for hydrology or atmospheric chemistry and efficient twoway exchange of states Two of these are presented The first sample application demonstrated that calculated nitrous oxide N2O emissions for the State of Saxony Germany with LandscapeDNDC 2693 t N2O–N/year were 24 times higher than those calculated according to the IPCC Tier I methodology and 28  higher than the results of the German National Inventory Report IPCC Tier II The second example illustrates the capabilities of LandscapeDNDC for the building of a fullycoupled threedimensional model system on the landscape scale The model combines biogeochemical and plant growth calculations into a hydrological transport model and demonstrates N transport along a virtual hill slope and the associated formation of indirect N2O emissionsHansen et al 2013 studied greenhouse gas fluxes in a freeair humidity manipulation FAHM facility established in 2006 in Estonia in order to investigate the effect of humidity on the performance of forest ecosystems The trial is located on former arable land and offers the opportunity to change relative air humidity through controlled artificial misting and drying Measurements were carried out once a month from July 2009 to October 2010 on three humidification plots and in three control plots using closed chamber and gaschromatograph techniques The dry summer in 2010 interacted stronger with the humidification than the rainy vegetation period in 2009 In this summer the CO2 flux decreased when the air moisture was higher than in the control plots The soil Endogleyic Planosol always acted as a sink for methane although less CH4 was oxidized in the soil with increased humidity There was a smaller N2O flux during the increased humidity period As expected CO2 emission and CH4 consumption demonstrated strong positive correlations with soil temperatureGall et al 2013 examined timeseries of hydrological and biogeochemical responses of managed catchments in terms of the degree of stochastic nonlinear filtering of hydroclimatic and anthropogenic drivers Two metrics of catchment filtering were applied to three case studies to examine the degree of synchronicity between catchment signals eg drivers and responses The first filtering metric evaluates the relative inequality of the two signals whereas the second metric is based on spectral analysis and evaluates the relative memory of the two signals These metrics were used to evaluate the filtering of precipitation inputs to discharge outputs from four stations in different moisture regimes and to identify the human impact on catchment hydrology The analyses suggest that an increasing human impact on landscapes 1 causes hydrological and biogeochemical processes to exhibit increasing functional homogeneity 2 contributes to shifts in nitrate NO3 − memory between catchment drivers and responses and 3 decreases the temporal inequality of nutrient export dynamics

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