title: Long term nitrate removal in a denitrification wall

authors: Long, Lauren M.

subjects: bioreactor

abstract: Nitrogen (N) inputs to groundwater are one of the most widespread environmental problems globally. However, as N is important for crop production to support the current global population, it is difficult to limit N input to an extent where groundwater contamination is completely avoided. Researchers have been testing new ways to remove N (in the form of nitrate (NO3-)) from groundwater, primarily through enhancing microbial denitrification. One technology utilizing this microbial process is a denitrification wall, which is an inexpensive, low-maintenance technology compared to other options to treat NO3--contaminated groundwater. Denitrification walls have been shown to be effective for removing NO3- from groundwater through denitrification for seven years in New Zealand, nine years in Iowa, and 15 years in Canada; however, long-term data on the efficacy of denitrification walls remain limited. In order to understand how these systems function in the long term, the performance of a New Zealand denitrification wall installed in 1996 was examined. Field sampling was carried out during the winter of 2010 at the denitrification wall at Bardowie Farm in Cambridge, New Zealand. This farm had received relatively high N inputs from spray-irrigation of effluent from the nearby Hautapu Dairy Factory for over 30 years. The denitrification wall was originally constructed by mixing 40 m3 Pinus radiata sawdust with soil down to a depth of 1.5 m where it intercepted groundwater flow. Groundwater samples were collected from wells installed upslope and within the wall and samples were analyzed for NO3- concentrations on five occasions. Soil samples were collected on four occasions from below the water table and analyzed for denitrifying enzyme activity (DEA), total carbon (C), available C, and microbial biomass C. Results were compared to previous measurements. Groundwater NO3- concentrations entering the wall averaged 2.6 mg N L-1, which was a decrease from 2002 where NO3- entered the wall at an average of 9 mg N L-1. Despite this decrease, NO3- concentrations within the wall averaged 0.2 mg N L-1, which corresponded to 92% NO3- removal. DEA rates in the wall were nearly as high as the first year of construction. In contrast, total C and microbial biomass C had decreased by half, while available C remained the same as measured two years after construction. Denitrification in the wall remained NO3- limited suggesting that C was still sufficiently available to the denitrifiers. These data indicated that the denitrification wall was still effective after 14 years. To predict denitrification wall longevity, a first-order decay curve was fitted to the total C data through time (R2 = 0.92; p < 0.05). The decay curve was used to predict the time until total C reached 0.1%, although it is unclear at what %C denitrification will become C limited. Using this decay curve, it was estimated that C in the wall would not be depleted for 66 years, although it is possible that C will become limiting to denitrifiers before that time. This long-term study suggested that denitrification walls are cost-effective solutions to removing NO3- from groundwater as they can be effective for a number of years without any maintenance.

text: Long term nitrate removal in a denitrification wall Nitrogen (N) inputs to groundwater are one of the most widespread environmental problems globally. However, as N is important for crop production to support the current global population, it is difficult to limit N input to an extent where groundwater contamination is completely avoided. Researchers have been testing new ways to remove N (in the form of nitrate (NO3-)) from groundwater, primarily through enhancing microbial denitrification. One technology utilizing this microbial process is a denitrification wall, which is an inexpensive, low-maintenance technology compared to other options to treat NO3--contaminated groundwater. Denitrification walls have been shown to be effective for removing NO3- from groundwater through denitrification for seven years in New Zealand, nine years in Iowa, and 15 years in Canada; however, long-term data on the efficacy of denitrification walls remain limited. In order to understand how these systems function in the long term, the performance of a New Zealand denitrification wall installed in 1996 was examined. Field sampling was carried out during the winter of 2010 at the denitrification wall at Bardowie Farm in Cambridge, New Zealand. This farm had received relatively high N inputs from spray-irrigation of effluent from the nearby Hautapu Dairy Factory for over 30 years. The denitrification wall was originally constructed by mixing 40 m3 Pinus radiata sawdust with soil down to a depth of 1.5 m where it intercepted groundwater flow. Groundwater samples were collected from wells installed upslope and within the wall and samples were analyzed for NO3- concentrations on five occasions. Soil samples were collected on four occasions from below the water table and analyzed for denitrifying enzyme activity (DEA), total carbon (C), available C, and microbial biomass C. Results were compared to previous measurements. Groundwater NO3- concentrations entering the wall averaged 2.6 mg N L-1, which was a decrease from 2002 where NO3- entered the wall at an average of 9 mg N L-1. Despite this decrease, NO3- concentrations within the wall averaged 0.2 mg N L-1, which corresponded to 92% NO3- removal. DEA rates in the wall were nearly as high as the first year of construction. In contrast, total C and microbial biomass C had decreased by half, while available C remained the same as measured two years after construction. Denitrification in the wall remained NO3- limited suggesting that C was still sufficiently available to the denitrifiers. These data indicated that the denitrification wall was still effective after 14 years. To predict denitrification wall longevity, a first-order decay curve was fitted to the total C data through time (R2 = 0.92; p < 0.05). The decay curve was used to predict the time until total C reached 0.1%, although it is unclear at what %C denitrification will become C limited. Using this decay curve, it was estimated that C in the wall would not be depleted for 66 years, although it is possible that C will become limiting to denitrifiers before that time. This long-term study suggested that denitrification walls are cost-effective solutions to removing NO3- from groundwater as they can be effective for a number of years without any maintenance.

year: 2011

title: Comment

authors: Carr, Margaret

abstract: Introduction to this special issue of the Early Childhood Folio on key learning competencies across place and time. Publication of these working papers (adapted and edited for the Early Childhood Folio) from a Teaching and Learning Research Initiative (TLRI) project means they will now be widely available for teachers. These are articles by teachers for teachers.

text: Comment Introduction to this special issue of the Early Childhood Folio on key learning competencies across place and time. Publication of these working papers (adapted and edited for the Early Childhood Folio) from a Teaching and Learning Research Initiative (TLRI) project means they will now be widely available for teachers. These are articles by teachers for teachers.

year: 2011

title: My journey with te reo Māori: From primary schooling in the mid 20th century to retirement from full-time academic service in the early years of the 21st Century

authors: Houia-Roberts, Ngaere

subjects: New Zealand

abstract: This is not an academic article in the traditional sense. It is a personal account of my experiences, as a first language speaker of te reo Māori, of New Zealand's educational system from the middle of the 20th century to the early years of the 21st century, from the early days of my primary schooling, through my service as a teacher, teacher trainer and academic researcher until my retirement from full-time academic service in 2005. A great deal has been written about the ways in which attitudes and approaches to te reo Māori have changed over that period of time but very little has been written about how it felt to be part of these changes. Our society is based on facts and feelings. If our mokopuna are to understand the fabric of our society, they need to have access to feelings as well as to facts. In this paper, weft and warp, facts and feelings, are woven together. This personal account is dedicated to our mokopuna, to all of our mokopuna, whatever their origin and whatever their colour. The future of our society depends upon their understanding.

text: My journey with te reo Māori: From primary schooling in the mid 20th century to retirement from full-time academic service in the early years of the 21st Century This is not an academic article in the traditional sense. It is a personal account of my experiences, as a first language speaker of te reo Māori, of New Zealand's educational system from the middle of the 20th century to the early years of the 21st century, from the early days of my primary schooling, through my service as a teacher, teacher trainer and academic researcher until my retirement from full-time academic service in 2005. A great deal has been written about the ways in which attitudes and approaches to te reo Māori have changed over that period of time but very little has been written about how it felt to be part of these changes. Our society is based on facts and feelings. If our mokopuna are to understand the fabric of our society, they need to have access to feelings as well as to facts. In this paper, weft and warp, facts and feelings, are woven together. This personal account is dedicated to our mokopuna, to all of our mokopuna, whatever their origin and whatever their colour. The future of our society depends upon their understanding.

year: 2006-02