{"id":{"repo_id":"whiterose","oai_identifier":"oai:etheses.whiterose.ac.uk:1078"},"canonical_url":"https://search.dev.ndltd.org/etd/whiterose/oai:etheses.whiterose.ac.uk:1078","repository":{"repo_id":"whiterose","name":"White Rose University Consortium","base_url":"https://etheses.whiterose.ac.uk/cgi/oai2"},"display":{"title":"Causes of temporal variations in N species transformations and mobility under acid grassland in York: The multi-functional role of plant litter","abstract":"Nitrogen cycling has been studied in soils from Hob Moor, an unimproved, unfertilized and N-impacted acid grassland near York, UK. Preliminary assessment of 7 soil profiles sampled to 60 cm depth indicated considerable N mineralization and nitrification in sub-soils. Later soils from a freely draining area of the grassland were sampled from 2 superficially similar profiles to 1 m depth to explore interactions between N species transformations and soils properties. The spatial heterogeneity of the 2 soil profiles was not anticipated, and was attributed to different fates of litter inputs to the soils. When N mineralization was expressed on a soil C basis, both profiles followed similar trends. These freely drained acidic profiles showed incredible potential for N mineralization and mobility well below the root zone which potentially could contaminate surface and/or ground-waters. This was confirmed using intact core microcosms with vegetation and litter layers. Episodic drainage water analysis revealed considerable and sustained NH4+-N and NO3--N concentrations from 3 freely draining soil profiles. One profile apparently had litter incorporated into sub-soils and behaved differently compared to the other two with more surficial litter presence. This led to design of a microcosm study to assess the litter effects on drainage water inorganic nitrogen (DIN), organic nitrogen (DON) and organic carbon (DOC) concentrations and fluxes over a natural seasonal temperature gradient over 7 months from early winter to mid summer. Litter mineralization resulted in substantial NH4+ production. Temperature apparently showed strong effects on NH4+ production. Mobile NH4+ from litter layers raised the extractable NH4+ concentrations in underlying subsoils. When litter was incorporated within subsoils, it greatly reduced NO3- concentrations in the drainage water, especially in winter when NO3- is many fold more mobile due to lower biological uptake. Extractable NH4+ concentrations correlated positively with water-soluble DOC, suggesting a role of DOC in NH4+ dynamics. In contrast, extractable NO3- concentrations were correlated negatively with DOC, indicating a role for DOC in NO3- immobilization by acting as substrate for microorganisms. Litter manipulations significantly altered concentrations and fluxes of DIN, DON and DOC in the drainage water. Concentrations of NH4+ increased substantially after freeze-thaw events, which facilitated NH4+ mobilization. Litter layers produced sustainable DOC and DON in the drainage water. In summer, increase in temperature significantly enhanced DOC and DON concentrations for the control and surface litter treatments; however, the reverse behaviour was observed for the subsurface litter treatment. Cumulative fluxes indicated that DON formed a significant component of total dissolved nitrogen (TDN), 42, 46 and 62% for the control, surface litter and subsurface litter treatments respectively. Cumulative fluxes showed net NH4+ retention in each treatment and significant reduction in NO3- flux associated with subsurface litter placement.","abstract_html":"Nitrogen cycling has been studied in soils from Hob Moor, an unimproved, unfertilized and N-impacted acid grassland near York, UK. Preliminary assessment of 7 soil profiles sampled to 60 cm depth indicated considerable N mineralization and nitrification in sub-soils. Later soils from a freely draining area of the grassland were sampled from 2 superficially similar profiles to 1 m depth to explore interactions between N species transformations and soils properties. The spatial heterogeneity of the 2 soil profiles was not anticipated, and was attributed to different fates of litter inputs to the soils. When N mineralization was expressed on a soil C basis, both profiles followed similar trends. These freely drained acidic profiles showed incredible potential for N mineralization and mobility well below the root zone which potentially could contaminate surface and/or ground-waters. This was confirmed using intact core microcosms with vegetation and litter layers. Episodic drainage water analysis revealed considerable and sustained NH4+-N and NO3--N concentrations from 3 freely draining soil profiles. One profile apparently had litter incorporated into sub-soils and behaved differently compared to the other two with more surficial litter presence. This led to design of a microcosm study to assess the litter effects on drainage water inorganic nitrogen (DIN), organic nitrogen (DON) and organic carbon (DOC) concentrations and fluxes over a natural seasonal temperature gradient over 7 months from early winter to mid summer. Litter mineralization resulted in substantial NH4+ production. Temperature apparently showed strong effects on NH4+ production. Mobile NH4+ from litter layers raised the extractable NH4+ concentrations in underlying subsoils. When litter was incorporated within subsoils, it greatly reduced NO3- concentrations in the drainage water, especially in winter when NO3- is many fold more mobile due to lower biological uptake. Extractable NH4+ concentrations correlated positively with water-soluble DOC, suggesting a role of DOC in NH4+ dynamics. In contrast, extractable NO3- concentrations were correlated negatively with DOC, indicating a role for DOC in NO3- immobilization by acting as substrate for microorganisms. Litter manipulations significantly altered concentrations and fluxes of DIN, DON and DOC in the drainage water. Concentrations of NH4+ increased substantially after freeze-thaw events, which facilitated NH4+ mobilization. Litter layers produced sustainable DOC and DON in the drainage water. In summer, increase in temperature significantly enhanced DOC and DON concentrations for the control and surface litter treatments; however, the reverse behaviour was observed for the subsurface litter treatment. Cumulative fluxes indicated that DON formed a significant component of total dissolved nitrogen (TDN), 42, 46 and 62% for the control, surface litter and subsurface litter treatments respectively. Cumulative fluxes showed net NH4+ retention in each treatment and significant reduction in NO3- flux associated with subsurface litter placement.","abstract_has_math":false,"creators":["Riaz, Muhammad"],"institution":"University of York","degree_name":"Ph.D","degree_level":"doctoral","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Cresser , Malcolm"],"committee_chairs":[],"committee_members":[],"year":2010,"date_issued":"2010","date_published":"2010","updated_at":"2026-07-24T06:04:07Z","subjects":[],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["uk.bl.ethos.535025"],"render_values":[{"text":"uk.bl.ethos.535025","href":null,"code":true}]}]},"links":{"outbound_url":null,"outbound_label":null,"outbound_source":null},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Cresser , Malcolm"]},{"key":"dc:creator","label":"Author","values":["Riaz, Muhammad"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2010"]},{"key":"dc:date.issued","label":"Date","values":["2010"]},{"key":"dc:publisher.commercial","label":"Dc Publisher Commercial","values":["University of York"]},{"key":"dc:publisher.department","label":"Dc Publisher Department","values":["Environment and Geography (York)","Environment"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of York"]},{"key":"dc:relation.isreferencedby","label":"Dc Relation Isreferencedby","values":["https://etheses.whiterose.ac.uk/id/eprint/1078/"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["doctoral"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["Ph.D"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["uk.bl.ethos.535025"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://etheses.whiterose.ac.uk/id/eprint/1078/1/Thesis_M.Riaz.doc"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Nitrogen cycling has been studied in soils from Hob Moor, an unimproved, unfertilized and N-impacted acid grassland near York, UK. Preliminary assessment of 7 soil profiles sampled to 60 cm depth indicated considerable N mineralization and nitrification in sub-soils. Later soils from a freely draining area of the grassland were sampled from 2 superficially similar profiles to 1 m depth to explore interactions between N species transformations and soils properties. The spatial heterogeneity of the 2 soil profiles was not anticipated, and was attributed to different fates of litter inputs to the soils. When N mineralization was expressed on a soil C basis, both profiles followed similar trends. These freely drained acidic profiles showed incredible potential for N mineralization and mobility well below the root zone which potentially could contaminate surface and/or ground-waters. This was confirmed using intact core microcosms with vegetation and litter layers. Episodic drainage water analysis revealed considerable and sustained NH4+-N and NO3--N concentrations from 3 freely draining soil profiles. One profile apparently had litter incorporated into sub-soils and behaved differently compared to the other two with more surficial litter presence. This led to design of a microcosm study to assess the litter effects on drainage water inorganic nitrogen (DIN), organic nitrogen (DON) and organic carbon (DOC) concentrations and fluxes over a natural seasonal temperature gradient over 7 months from early winter to mid summer. Litter mineralization resulted in substantial NH4+ production. Temperature apparently showed strong effects on NH4+ production. Mobile NH4+ from litter layers raised the extractable NH4+ concentrations in underlying subsoils. When litter was incorporated within subsoils, it greatly reduced NO3- concentrations in the drainage water, especially in winter when NO3- is many fold more mobile due to lower biological uptake. Extractable NH4+ concentrations correlated positively with water-soluble DOC, suggesting a role of DOC in NH4+ dynamics. In contrast, extractable NO3- concentrations were correlated negatively with DOC, indicating a role for DOC in NO3- immobilization by acting as substrate for microorganisms. Litter manipulations significantly altered concentrations and fluxes of DIN, DON and DOC in the drainage water. Concentrations of NH4+ increased substantially after freeze-thaw events, which facilitated NH4+ mobilization. Litter layers produced sustainable DOC and DON in the drainage water. In summer, increase in temperature significantly enhanced DOC and DON concentrations for the control and surface litter treatments; however, the reverse behaviour was observed for the subsurface litter treatment. Cumulative fluxes indicated that DON formed a significant component of total dissolved nitrogen (TDN), 42, 46 and 62% for the control, surface litter and subsurface litter treatments respectively. Cumulative fluxes showed net NH4+ retention in each treatment and significant reduction in NO3- flux associated with subsurface litter placement."]},{"key":"dc:format","label":"Dc Format","values":["text"]},{"key":"dc:title","label":"Title","values":["Causes of temporal variations in N species transformations and mobility under acid grassland in York: The multi-functional role of plant litter"]}]}],"canonical_facts":{"dc:contributor.advisor":["Cresser , Malcolm"],"dc:creator":["Riaz, Muhammad"],"dc:date":["2010"],"dc:date.issued":["2010"],"dc:description.abstract":["Nitrogen cycling has been studied in soils from Hob Moor, an unimproved, unfertilized and N-impacted acid grassland near York, UK. Preliminary assessment of 7 soil profiles sampled to 60 cm depth indicated considerable N mineralization and nitrification in sub-soils. Later soils from a freely draining area of the grassland were sampled from 2 superficially similar profiles to 1 m depth to explore interactions between N species transformations and soils properties. The spatial heterogeneity of the 2 soil profiles was not anticipated, and was attributed to different fates of litter inputs to the soils. When N mineralization was expressed on a soil C basis, both profiles followed similar trends. These freely drained acidic profiles showed incredible potential for N mineralization and mobility well below the root zone which potentially could contaminate surface and/or ground-waters. This was confirmed using intact core microcosms with vegetation and litter layers. Episodic drainage water analysis revealed considerable and sustained NH4+-N and NO3--N concentrations from 3 freely draining soil profiles. One profile apparently had litter incorporated into sub-soils and behaved differently compared to the other two with more surficial litter presence. This led to design of a microcosm study to assess the litter effects on drainage water inorganic nitrogen (DIN), organic nitrogen (DON) and organic carbon (DOC) concentrations and fluxes over a natural seasonal temperature gradient over 7 months from early winter to mid summer. Litter mineralization resulted in substantial NH4+ production. Temperature apparently showed strong effects on NH4+ production. Mobile NH4+ from litter layers raised the extractable NH4+ concentrations in underlying subsoils. When litter was incorporated within subsoils, it greatly reduced NO3- concentrations in the drainage water, especially in winter when NO3- is many fold more mobile due to lower biological uptake. Extractable NH4+ concentrations correlated positively with water-soluble DOC, suggesting a role of DOC in NH4+ dynamics. In contrast, extractable NO3- concentrations were correlated negatively with DOC, indicating a role for DOC in NO3- immobilization by acting as substrate for microorganisms. Litter manipulations significantly altered concentrations and fluxes of DIN, DON and DOC in the drainage water. Concentrations of NH4+ increased substantially after freeze-thaw events, which facilitated NH4+ mobilization. Litter layers produced sustainable DOC and DON in the drainage water. In summer, increase in temperature significantly enhanced DOC and DON concentrations for the control and surface litter treatments; however, the reverse behaviour was observed for the subsurface litter treatment. Cumulative fluxes indicated that DON formed a significant component of total dissolved nitrogen (TDN), 42, 46 and 62% for the control, surface litter and subsurface litter treatments respectively. Cumulative fluxes showed net NH4+ retention in each treatment and significant reduction in NO3- flux associated with subsurface litter placement."],"dc:format":["text"],"dc:identifier":["uk.bl.ethos.535025"],"dc:identifier.uri":["https://etheses.whiterose.ac.uk/id/eprint/1078/1/Thesis_M.Riaz.doc"],"dc:publisher.commercial":["University of York"],"dc:publisher.department":["Environment and Geography (York)","Environment"],"dc:publisher.institution":["University of York"],"dc:relation.isreferencedby":["https://etheses.whiterose.ac.uk/id/eprint/1078/"],"dc:title":["Causes of temporal variations in N species transformations and mobility under acid grassland in York: The multi-functional role of plant litter"],"dc:type":["Thesis"],"dc:type.qualificationlevel":["doctoral"],"dc:type.qualificationname":["Ph.D"]},"updated_at":"2026-07-24T06:04:07Z"}