Export of dissolved organic carbon and nitrate from grassland in winter using high temporal resolution, in situ UV sensing.

Co-deployment of two reagentless UV sensors for high temporal resolution (15 min) real time determination of wintertime DOC and nitrate-N export from a grassland lysimeter plot (North Wyke, Devon, UK) is reported. They showed rapid, transient but high impact perturbations of DOC (5.3-23 mg CL(-1)) and nitrate-N export after storm/snow melt which discontinuous sampling would not have observed. During a winter freeze/thaw cycle, DOC export (1.25 kg Cha(-1)d(-1)) was significantly higher than typical UK catchment values (maximum 0.25 kg Chad(-1)) and historical North Wyke data (0.7 kg Cha(-1)d(-1)). DOC concentrations were inversely correlated with the key DOC physico-chemical drivers of pH (January r=-0.65), and conductivity (January r=-0.64). Nitrate-N export (0.8-1.5 mg NL(-1)) was strongly correlated with DOC export (r ≥ 0.8). The DOC:NO3-N molar ratios showed that soil microbial N assimilation was not C limited and therefore high N accrual was not promoted in the River Taw, which is classified as a nitrate vulnerable zone (NVZ). The sensor was shown to be an effective sentinel device for identifying critical periods when rapid ecosystem N accumulation could be triggered by a shift in resource stoichiometry. It is therefore a useful tool to help evaluate land management strategies and impacts from climate change and intensive agriculture.

[1]  D. J. Dowrick,et al.  Export of dissolved organic carbon from peatlands under elevated carbon dioxide levels , 2004, Nature.

[2]  M. Billett,et al.  A review of the export of carbon in river water: fluxes and processes. , 1994, Environmental pollution.

[3]  E. Bååth,et al.  Bioavailability of DOC in leachates, soil matrix solutions and soil water extracts from beech forest floors , 2009 .

[4]  E. A. Garwood,et al.  Hydrological consequences of artificial drainage of grassland , 1991 .

[5]  R. Sandford,et al.  In situ determination of dissolved organic carbon in freshwaters using a reagentless UV sensor. , 2010, Journal of environmental monitoring : JEM.

[6]  C. Neal,et al.  Soil water in the riparian zone as a source of carbon for a headwater stream , 1990 .

[7]  P. Hobbs,et al.  Seasonal changes in soil microbial communities along a fertility gradient of temperate grasslands , 1999 .

[8]  M. Futter,et al.  Testing seasonal and long-term controls of streamwater DOC using empirical and process-based models. , 2008, The Science of the total environment.

[9]  M. Hayes,et al.  Dissolved organic carbon losses from grazed grasslands under different management regimes. , 2001, Water research.

[10]  R. Milne,et al.  EXPORTS OF ORGANIC CARBON IN BRITISH RIVERS , 1997 .

[11]  Pete Smith,et al.  UK land use and soil carbon sequestration. , 2009 .

[12]  David L. Jones,et al.  Fast turnover of low molecular weight components of the dissolved organic carbon pool of temperate grassland field soils , 2007 .

[13]  W. Oechel,et al.  Microbial activity in soils frozen to below −39 °C , 2006 .

[14]  S. Jarvis,et al.  Potential for denitrification at depth below long-term grass swards , 1994 .

[15]  Kimberley M. Driscoll,et al.  Chemical response of lakes in the Adirondack Region of New York to declines in acidic deposition. , 2003, Environmental science & technology.

[16]  J. Szatyłowicz,et al.  Water‐table management in lowland UK peat soils and its potential impact on CO2 emission , 2007 .

[17]  G. Asner,et al.  Dissolved Organic Carbon in Terrestrial Ecosystems: Synthesis and a Model , 2001, Ecosystems.

[18]  Hao Zhang,et al.  In situ speciation measurements of trace metals in headwater streams. , 2009, Environmental science & technology.

[19]  John Hamilton-Taylor,et al.  Quantification of natural DOM from UV absorption at two wavelengths , 2009 .

[20]  H. Mooney,et al.  Human Domination of Earth’s Ecosystems , 1997, Renewable Energy.

[21]  Don Monteith,et al.  Alternative explanations for rising dissolved organic carbon export from organic soils , 2006 .

[22]  P. Groffman,et al.  Soil freezing alters fine root dynamics in a northern hardwood forest , 2001 .

[23]  J. Galloway,et al.  Transformation of the Nitrogen Cycle: Recent Trends, Questions, and Potential Solutions , 2008, Science.

[24]  W. Chardon,et al.  Speciation of Water-Extractable Organic Nutrients in Grassland Soils , 2010 .

[25]  Pete Smith,et al.  Carbon losses from soil and its consequences for land-use management. , 2007, The Science of the total environment.

[26]  Andreas Richter,et al.  Production of dissolved organic carbon and low-molecular weight organic acids in soil solution driven by recent tree photosynthate , 2007 .

[27]  Ji‐Hyung Park,et al.  Controls on the dynamics of dissolved organic matter in soils: a review. , 2000 .

[28]  R. Comans,et al.  Partitioning of organic matter and heavy metals in a sandy soil: Effects of extracting solution, solid to liquid ratio and pH , 2008 .

[29]  The hydrological response of heavy clay grassland soils to rainfall in south-west England using delta2H. , 2010, Rapid communications in mass spectrometry : RCM.

[30]  Paul J Worsfold,et al.  Nitrogen cycling in natural waters using in situ, reagentless UV spectrophotometry with simultaneous determination of nitrate and nitrite. , 2007, Environmental science & technology.

[31]  H. Laudon,et al.  Cold winter soils enhance dissolved organic carbon concentrations in soil and stream water , 2010 .

[32]  H. Govers,et al.  Influence of temperature and origin of dissolved organic matter on the partitioning behavior of polycyclic aromatic hydrocarbons , 2010, Environmental science and pollution research international.

[33]  J. Feyen,et al.  Dissolved organic carbon fluxes under bare soil. , 2007, Journal of environmental quality.

[34]  H. Harmens,et al.  Interactions between elevated CO2 and warming could amplify DOC exports from peatland catchments. , 2007, Environmental science & technology.

[35]  H. Laudon,et al.  Regulation of stream water dissolved organic carbon (DOC) concentrations during snowmelt : the role of discharge, winter climate and memory effects , 2010 .

[36]  P. Chapman,et al.  The importance of the relationship between scale and process in understanding long-term DOC dynamics. , 2010, The Science of the total environment.

[37]  A. Townsend,et al.  Stoichiometric control of organic carbon–nitrate relationships from soils to the sea , 2010, Nature.