title: Export of dissolved organic carbon and nitrate from grassland in winter using high temporal resolution, in situ UV sensing.
abstract: 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.
authors.affiliation: Biogeochemistry Research Centre, School of Geography, Earth, and Environmental Sciences, University of Plymouth, Plymouth, PL4 8AA, England, UK. rsandford@plymouth.ac.uk
authors.forename: Richard C
authors.initials: RC
authors.lastname: Sandford
authors.forename: Jane M B
authors.initials: JM
authors.lastname: Hawkins
authors.forename: Roland
authors.initials: R
authors.lastname: Bol
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Worsfold
mesh_terms: D057486:Carbon Cycle; D057231:Climate Change; D004739:England; D004784:Environmental Monitoring / Q000295:instrumentation / Q000379:methods*; D006812:Humic Substances / Q000032:analysis*; D009566:Nitrates / Q000032:analysis*; D058458:Nitrogen Cycle; D011891:Rain / Q000737:chemistry; D012621:Seasons; D012914:Snow / Q000737:chemistry; D012987:Soil / Q000737:chemistry*; D013997:Time Factors; D014466:Ultraviolet Rays; D058438:Water Cycle
chemical_list: D006812:Humic Substances; D009566:Nitrates; D012987:Soil