title: Variation in nitrate sources and delivery in space and time within the 389 ha Lake Okaro catchment

authors: Eyberg, Claire Elizabeth

subjects: Nitrate

abstract: The eutrophication of surface water is a global issue, with excessive nitrate 
concentrations reducing water quality and affecting water supplies, 
ecosystem health and its recreational use. In New Zealand, the degradation 
of freshwater quality has largely been attributed to nitrate leaching from 
intensive landuse, in particular from intensively grazed pastoral systems.   
As agricultural activity in catchments can contribute a large proportion of the 
nutrient pollution in surface waters, an understanding of nitrogen dynamics 
is therefore vital in managing the downstream effects of diffuse nitrogen 
inputs. Nitrate isotopes (δ¹⁵N, δ¹⁸O) have been increasingly used for 
determining nitrate cycling and source identification. Together with water 
isotopes (δ²H, δ¹⁸O), these conservative tracers can provide the necessary 
tools for determining the transport mechanisms of nitrate.   
    
Lake Okaro has suffered from water quality degradation for several decades, 
and has been the focus of intense lake restoration projects focused on 
nutrient management. The 389 ha agriculture-dominated catchment 
exemplifies New Zealand’s complex physiographic landscape.   

Results from high-resolution monitoring of streamflow during storm events 
demonstrates the potential to capture dynamic shifts in distinct water 
sources, but can be limited by insufficient monitoring of ancillary parameters, 
or a lack of pre-event characterisation of streamflow. Spatial sampling 
indicated characteristic fractionation processes for sites of similar 
environments, likely due to enhanced plant and microbial processing of 
carbon and nitrogen. This spatial sampling demonstrates that even in small 
catchments, there may be a significant degree of heterogeneity in water and 
nitrate flows, in both space and time.   
    
Nitrate contributions were much lower in summer relative to autumn and 
winter during baseflow or non-storm flow. Storm events contributed a 
disproportionate amount of nitrate, but the effect was most notable in winter.   

During baseflow, or non-stormflow, in the main inflow stream in the Lake 
Okaro catchment, nitrate had δ¹⁵N and δ¹⁸O values indicative of a soil 
nitrogen origin (+5.8 ‰ to +7.3 ‰, and -0.5 ‰ to +1.7 ‰, respectively).    

The dominant nitrate sources shifted during rain events, with streamflow in 
the winter event having δ¹⁵N and δ¹⁸O values indicative of urine, whereas 
the summer event observed δ¹⁸O-enriched baseflow signatures. Water 
isotope ratios indicated the winter event was dominated by event water. The 
differing seasonal responses to rainfall suggest nitrate inputs during storms 
in this catchment are strongly linked to seasonal nitrate availability in water 
flow paths.    

Patterns observed in temporal and spatial data collected require more 
investigation around potential reasons or mechanisms of fractionation. 
Further refinement of the Okaro catchment flows and cycling of nitrogen will 
help create more catered management techniques.

text: Variation in nitrate sources and delivery in space and time within the 389 ha Lake Okaro catchment The eutrophication of surface water is a global issue, with excessive nitrate 
concentrations reducing water quality and affecting water supplies, 
ecosystem health and its recreational use. In New Zealand, the degradation 
of freshwater quality has largely been attributed to nitrate leaching from 
intensive landuse, in particular from intensively grazed pastoral systems.   
As agricultural activity in catchments can contribute a large proportion of the 
nutrient pollution in surface waters, an understanding of nitrogen dynamics 
is therefore vital in managing the downstream effects of diffuse nitrogen 
inputs. Nitrate isotopes (δ¹⁵N, δ¹⁸O) have been increasingly used for 
determining nitrate cycling and source identification. Together with water 
isotopes (δ²H, δ¹⁸O), these conservative tracers can provide the necessary 
tools for determining the transport mechanisms of nitrate.   
    
Lake Okaro has suffered from water quality degradation for several decades, 
and has been the focus of intense lake restoration projects focused on 
nutrient management. The 389 ha agriculture-dominated catchment 
exemplifies New Zealand’s complex physiographic landscape.   

Results from high-resolution monitoring of streamflow during storm events 
demonstrates the potential to capture dynamic shifts in distinct water 
sources, but can be limited by insufficient monitoring of ancillary parameters, 
or a lack of pre-event characterisation of streamflow. Spatial sampling 
indicated characteristic fractionation processes for sites of similar 
environments, likely due to enhanced plant and microbial processing of 
carbon and nitrogen. This spatial sampling demonstrates that even in small 
catchments, there may be a significant degree of heterogeneity in water and 
nitrate flows, in both space and time.   
    
Nitrate contributions were much lower in summer relative to autumn and 
winter during baseflow or non-storm flow. Storm events contributed a 
disproportionate amount of nitrate, but the effect was most notable in winter.   

During baseflow, or non-stormflow, in the main inflow stream in the Lake 
Okaro catchment, nitrate had δ¹⁵N and δ¹⁸O values indicative of a soil 
nitrogen origin (+5.8 ‰ to +7.3 ‰, and -0.5 ‰ to +1.7 ‰, respectively).    

The dominant nitrate sources shifted during rain events, with streamflow in 
the winter event having δ¹⁵N and δ¹⁸O values indicative of urine, whereas 
the summer event observed δ¹⁸O-enriched baseflow signatures. Water 
isotope ratios indicated the winter event was dominated by event water. The 
differing seasonal responses to rainfall suggest nitrate inputs during storms 
in this catchment are strongly linked to seasonal nitrate availability in water 
flow paths.    

Patterns observed in temporal and spatial data collected require more 
investigation around potential reasons or mechanisms of fractionation. 
Further refinement of the Okaro catchment flows and cycling of nitrogen will 
help create more catered management techniques.

year: 2020

title: The Origins of Syrian Nationhood; Histories, Pioneers and Identity [Book Review]

authors: Drury, Abdullah

abstract: This article reviews the book 'The Origins of Syrian Nationhood; Histories, Pioneers and Identity', edited by Adel Beshara,

text: The Origins of Syrian Nationhood; Histories, Pioneers and Identity [Book Review] This article reviews the book 'The Origins of Syrian Nationhood; Histories, Pioneers and Identity', edited by Adel Beshara,

year: 2013-11

title: Life in a clinical diploma course

authors: Paterson, Keriata

subjects: Maori

abstract: This paper focuses on the author’s experience of a Clinical Diploma programme. The author is a Maori woman who is in her second year of a three year post-graduate Clinical Diploma programme. The paper includes comment on the cultural focus of content, culture conflicts and areas where the programme might be improved for Maori students.

text: Life in a clinical diploma course This paper focuses on the author’s experience of a Clinical Diploma programme. The author is a Maori woman who is in her second year of a three year post-graduate Clinical Diploma programme. The paper includes comment on the cultural focus of content, culture conflicts and areas where the programme might be improved for Maori students.

year: 1993