title: Relationship between soil δ¹⁵N, C/N and N losses across land uses in New Zealand

authors: Stevenson, Bryan A.

subjects: nitrogen isotopes

abstract: Several of the major processes that result in N loss from soil (nitrification, ammonia volatilization, and denitrification) discriminate against ¹⁵N and fractionate the stable N isotopes, thus δ¹⁵N of ecosystem components has been suggested as an indicator of ecosystem N leakiness. This concept has been applied more successfully to native systems (primarily forest) than to managed systems where N inputs are greater and N cycling processes have potentially been modified. We analysed 210 New Zealand soils (0–100 mm depth) from different land-use systems (increasing in intensity of land use management from indigenous, to plantation forestry, pasture under drystock, pasture under dairy, and cropping) for δ¹⁵N and measures of N availability (total N, C/N, and N mineralization) to determine whether increasing intensity of land use management would lead to increased soil δ¹⁵N values. Mean soil δ¹⁵N differed between land uses with intensively managed cropping having the highest mean soil δ¹⁵N (6.2‰) followed by dairy (5.4‰), drystock (3.8‰), forestry (2.8‰) and indigenous forests (2.1‰). Over all land uses there was a negative correlation between δ¹⁵N and the soil C/N ratio (ρ = −0.73) and regression analysis indicated a relatively strong linear relationship between δ¹⁵N and C/N (r² = 0.56, P < 0.001) when cropping sites (where significant loss of soil C had occurred), and sites with C/N ratio >18 were excluded. Typical N balances for each land use showed that total N loss (and in particular fractionating N losses from ammonia volatilization and nitrate leaching) also increased with increasing land-use intensity. Our results indicate that soil δ¹⁵N may be a useful tool in assessing potential N losses in different soils.

text: Relationship between soil δ¹⁵N, C/N and N losses across land uses in New Zealand Several of the major processes that result in N loss from soil (nitrification, ammonia volatilization, and denitrification) discriminate against ¹⁵N and fractionate the stable N isotopes, thus δ¹⁵N of ecosystem components has been suggested as an indicator of ecosystem N leakiness. This concept has been applied more successfully to native systems (primarily forest) than to managed systems where N inputs are greater and N cycling processes have potentially been modified. We analysed 210 New Zealand soils (0–100 mm depth) from different land-use systems (increasing in intensity of land use management from indigenous, to plantation forestry, pasture under drystock, pasture under dairy, and cropping) for δ¹⁵N and measures of N availability (total N, C/N, and N mineralization) to determine whether increasing intensity of land use management would lead to increased soil δ¹⁵N values. Mean soil δ¹⁵N differed between land uses with intensively managed cropping having the highest mean soil δ¹⁵N (6.2‰) followed by dairy (5.4‰), drystock (3.8‰), forestry (2.8‰) and indigenous forests (2.1‰). Over all land uses there was a negative correlation between δ¹⁵N and the soil C/N ratio (ρ = −0.73) and regression analysis indicated a relatively strong linear relationship between δ¹⁵N and C/N (r² = 0.56, P < 0.001) when cropping sites (where significant loss of soil C had occurred), and sites with C/N ratio >18 were excluded. Typical N balances for each land use showed that total N loss (and in particular fractionating N losses from ammonia volatilization and nitrate leaching) also increased with increasing land-use intensity. Our results indicate that soil δ¹⁵N may be a useful tool in assessing potential N losses in different soils.

year: 2010

title: Detection and distribution of Craspedacusta sowerbii: Observations of medusae are not enough

authors: Duggan, Ian C.

subjects: Constructed waters

abstract: The freshwater cnidarian Craspedacusta sowerbii, native to the Yangtze valley, has invaded lakes and ponds throughout the world. Most distribution records have to date been based on observations of the medusa (jellyfish) stage, including numerous recent publications. We aimed to determine whether polyps are widespread in lakes, and geographical areas, outside of where medusae have been observed, and whether constructed waters are more easily invaded than natural waters. Our results show that C. sowerbii is more common and widespread than is apparent from observations of medusae. We argue that observed occurrences of medusae provide little useful information regarding the distribution of this species, and that published records of new jellyfish occurrences provide unreliable estimates of the timing of introduction, establishment or spread of C. sowerbii in new regions. We found no evidence that constructed waters were more readily invaded than natural waters. Overall, accurate determination of Craspedacusta occurrence and distribution requires systematic surveys of the polyp stages.

text: Detection and distribution of Craspedacusta sowerbii: Observations of medusae are not enough The freshwater cnidarian Craspedacusta sowerbii, native to the Yangtze valley, has invaded lakes and ponds throughout the world. Most distribution records have to date been based on observations of the medusa (jellyfish) stage, including numerous recent publications. We aimed to determine whether polyps are widespread in lakes, and geographical areas, outside of where medusae have been observed, and whether constructed waters are more easily invaded than natural waters. Our results show that C. sowerbii is more common and widespread than is apparent from observations of medusae. We argue that observed occurrences of medusae provide little useful information regarding the distribution of this species, and that published records of new jellyfish occurrences provide unreliable estimates of the timing of introduction, establishment or spread of C. sowerbii in new regions. We found no evidence that constructed waters were more readily invaded than natural waters. Overall, accurate determination of Craspedacusta occurrence and distribution requires systematic surveys of the polyp stages.

year: 2012

title: Te tātari i te kaupapa

authors: Ka'ai, Tānia M.

abstract: The primary objective of this thesis focuses on the linking of the National Qualifications Framework and standards-based assessment as an emancipatory mechanism for Māori in Kaupapa Māori schooling and the wider Māori community in New Zealand.

Argued from an eclectic theoretical approach incorporating Kaupapa Māori theory, it espouses a position which rejects structural inequalities that perpetuate the subordinate positioning of Māori people through the development of culturally responsive assessment theories and practices in written language for teachers and children in Kura Kaupapa Māori which purport a culturally responsive pedagogy.

The thesis also links curriculum, assessment and pedagogy using Kaupapa Māori theory which provides insights into Māori views of emancipation in education.

text: Te tātari i te kaupapa The primary objective of this thesis focuses on the linking of the National Qualifications Framework and standards-based assessment as an emancipatory mechanism for Māori in Kaupapa Māori schooling and the wider Māori community in New Zealand.

Argued from an eclectic theoretical approach incorporating Kaupapa Māori theory, it espouses a position which rejects structural inequalities that perpetuate the subordinate positioning of Māori people through the development of culturally responsive assessment theories and practices in written language for teachers and children in Kura Kaupapa Māori which purport a culturally responsive pedagogy.

The thesis also links curriculum, assessment and pedagogy using Kaupapa Māori theory which provides insights into Māori views of emancipation in education.

year: 1995