title: Changes in carbon and nitrogen stocks following conversion of plantation forest to dairy pasture on pumice soils, in the Central North Island

authors: Lewis, Riki Windsor

subjects: Carbon

abstract: Since 1990 approximately 36,000 ha of land in the Waikato has been converted from pine plantation to dairy farms. By changing land use from plantation forest to pasture there is potential to change soil properties. The property of interest, due to international discussion (Kyoto Protocol), is the potential for soils to store carbon. My main objective was to determine the rate and magnitude of change in soil carbon, soil nitrogen, and C:N ratio following land conversion from pine plantation to pasture. My study examined three areas (Atiamuri, Tokoroa and Wairakei) in the Central North Island of New Zealand. At each study area sites ranging from pine plantation, through 2, 3, 4, 5 and 11 years since conversion, to long-term (>40 years) dairy or sheep/beef pasture, were identified. Three transects were established at each site and 7 soil core samples each to a depth of 60 cm, were taken at random intervals along each transect. Soil cores were split into horizons with samples from each horizon bulked together for each transect. At the midpoint of each transect a pit was dug and soil dry bulk density samples were taken from each horizon. At one pit from each site a sample of each soil horizon was taken. In the laboratory all soil samples were passed through a 2 mm sieve and air dried. Air dried samples were crushed and analysed for total carbon and total nitrogen with a TruSpec CN Carbon/Nitrogen Determinator. Soil dry bulk density was lower (P<0.05) in the pine sites Ap horizons (0.47 to 0.54 g cm-3) than the Ap horizon for all other sites (0.59 to 0.76 g cm-3) at the Atiamuri, Tokoroa and Wairakei areas. There was no significant difference in Ap horizon depths between pine forest, recent conversion and long-term pasture sites at any of the study areas. Carbon concentration in the Ap horizon (5.5 to 9 %) showed few significant differences between land-use sites. The total soil carbon at Atiamuri and Wairakei was higher (P<0.05) in the long-term pastures (88 to 100 t/ha) than in the pine (42 to 54 t/ha), however there was no significant difference between pine and long-term pasture at Tokoroa and data from recently converted sites were variable with no apparent significant differences. Total soil nitrogen at all three study areas was higher (P<0.05) in the long-term pasture sites (5 to 8 t/ha) than in the pine sites (9 to 12 t/ha). The C:N ratio in the Ap horizon was higher (P<0.05) in pine sites (mean of 16) than in the long-term pasture sites (mean of 10). The variability in the recently converted sites meant that generally no short-term changes in carbon, nitrogen or C:N ratio, following conversion from pine forest to dairy pasture were discernable.

text: Changes in carbon and nitrogen stocks following conversion of plantation forest to dairy pasture on pumice soils, in the Central North Island Since 1990 approximately 36,000 ha of land in the Waikato has been converted from pine plantation to dairy farms. By changing land use from plantation forest to pasture there is potential to change soil properties. The property of interest, due to international discussion (Kyoto Protocol), is the potential for soils to store carbon. My main objective was to determine the rate and magnitude of change in soil carbon, soil nitrogen, and C:N ratio following land conversion from pine plantation to pasture. My study examined three areas (Atiamuri, Tokoroa and Wairakei) in the Central North Island of New Zealand. At each study area sites ranging from pine plantation, through 2, 3, 4, 5 and 11 years since conversion, to long-term (>40 years) dairy or sheep/beef pasture, were identified. Three transects were established at each site and 7 soil core samples each to a depth of 60 cm, were taken at random intervals along each transect. Soil cores were split into horizons with samples from each horizon bulked together for each transect. At the midpoint of each transect a pit was dug and soil dry bulk density samples were taken from each horizon. At one pit from each site a sample of each soil horizon was taken. In the laboratory all soil samples were passed through a 2 mm sieve and air dried. Air dried samples were crushed and analysed for total carbon and total nitrogen with a TruSpec CN Carbon/Nitrogen Determinator. Soil dry bulk density was lower (P<0.05) in the pine sites Ap horizons (0.47 to 0.54 g cm-3) than the Ap horizon for all other sites (0.59 to 0.76 g cm-3) at the Atiamuri, Tokoroa and Wairakei areas. There was no significant difference in Ap horizon depths between pine forest, recent conversion and long-term pasture sites at any of the study areas. Carbon concentration in the Ap horizon (5.5 to 9 %) showed few significant differences between land-use sites. The total soil carbon at Atiamuri and Wairakei was higher (P<0.05) in the long-term pastures (88 to 100 t/ha) than in the pine (42 to 54 t/ha), however there was no significant difference between pine and long-term pasture at Tokoroa and data from recently converted sites were variable with no apparent significant differences. Total soil nitrogen at all three study areas was higher (P<0.05) in the long-term pasture sites (5 to 8 t/ha) than in the pine sites (9 to 12 t/ha). The C:N ratio in the Ap horizon was higher (P<0.05) in pine sites (mean of 16) than in the long-term pasture sites (mean of 10). The variability in the recently converted sites meant that generally no short-term changes in carbon, nitrogen or C:N ratio, following conversion from pine forest to dairy pasture were discernable.

year: 2011

title: Utuhina Stream monitoring 2014: Effects of continuous alum dosing on fish and aquatic invertebrates

authors: Ling, Nicholas

abstract: This report presents the results of an ongoing assessment of the fish and aquatic macroinvertebrate communities of the Utuhina Stream from 2006 to 2014, and an assessment of the bioavailability of aluminium in fish and koura to satisfy annual resource consent conditions 9.6, 9.8 and 9.7, respectively, for the discharge of alum. Macroinvertebrates, fish and koura were sampled from one control and two treatment reaches of the Utuhina Stream in August 2014. Catch rates for common bully, juvenile trout and koura have fluctuated across all sites since monitoring began in 2006. Common bully, koura and juvenile trout were present at all sites. Differences in species abundance compared with previous years is most likely due to flood related disturbances to stream bank morphology and vegetative cover. No obvious effects of alum dosing on stream fish or macroinvertebrate communities were observed.

text: Utuhina Stream monitoring 2014: Effects of continuous alum dosing on fish and aquatic invertebrates This report presents the results of an ongoing assessment of the fish and aquatic macroinvertebrate communities of the Utuhina Stream from 2006 to 2014, and an assessment of the bioavailability of aluminium in fish and koura to satisfy annual resource consent conditions 9.6, 9.8 and 9.7, respectively, for the discharge of alum. Macroinvertebrates, fish and koura were sampled from one control and two treatment reaches of the Utuhina Stream in August 2014. Catch rates for common bully, juvenile trout and koura have fluctuated across all sites since monitoring began in 2006. Common bully, koura and juvenile trout were present at all sites. Differences in species abundance compared with previous years is most likely due to flood related disturbances to stream bank morphology and vegetative cover. No obvious effects of alum dosing on stream fish or macroinvertebrate communities were observed.

year: 2015

title: Assessment of effects of proposed treated wastewater discharge to the Te Arikiroa Thermal Channel and Sulphur Bay (Lake Rotorua)

authors: Dada, Ayokunle Christopher

abstract: After 2019, irrigation operations at the Land Treatment System (LTS) in the Whakarewarewa Forest are scheduled to cease. A number of options and locations have been considered for the discharge of the treated wastewater when the current discharge consent ceases. Following consultations and technical assessments, the preferred option of Rotorua Lakes Council is to upgrade the existing plant to a full Membrane Bioreactor Plant with the addition of an Ultraviolet Disinfection System (or alternative treatment to achieve an equivalent performance in terms of treated wastewater quality). Under this arrangement, wastewater would be subjected to biological, chemical and physical treatment processes, and the treated wastewater discharged through Te Arikiroa Thermal Channel to Sulphur Bay. Rotorua Lakes Council is thus undertaking an environmental impact assessment study to determine the effects of discharging treated wastewater to the thermal channel and Puarenga Bay (Lake Rotorua), with particular reference to aesthetic, water quality and ecological considerations. These considerations include potential effects related to faecal indicator bacteria, nutrient concentrations, metals, dissolved oxygen, and taonga species (native species of cultural significance).
The assessment focused on:
(i)	The projected treated wastewater characteristics;

(ii)	Existing conditions of the receiving water;

(iii)	The sensitivity of the receiving water and the impact of the proposed discharge on water quality and taonga species (native species of cultural significance) in Te Arikiroa Thermal Channel and Sulphur Bay.

The main techniques used to inform the assessment in this study were:
1) Analysis of historical water quality data, 2011-2014;
2) Collection of additional water quality data at Te Arikiroa Thermal Channel and Sulphur Bay and along a transect to quantify spatial variability (sampling in 2016 and 2017);
3) Mass balance dilution modelling to predict water quality in the Te Arikiroa Thermal Channel and Sulphur Bay (Lake Rotorua), at a site outside of the assumed mixing zone;
4) Lake ecosystem modelling conducted by Abell et al. (2015) to assess effects related to eutrophication;
5) Background review of biological information and field investigations for taonga species at Sulphur Bay and Te Arikiroa Thermal Channel (2017).

text: Assessment of effects of proposed treated wastewater discharge to the Te Arikiroa Thermal Channel and Sulphur Bay (Lake Rotorua) After 2019, irrigation operations at the Land Treatment System (LTS) in the Whakarewarewa Forest are scheduled to cease. A number of options and locations have been considered for the discharge of the treated wastewater when the current discharge consent ceases. Following consultations and technical assessments, the preferred option of Rotorua Lakes Council is to upgrade the existing plant to a full Membrane Bioreactor Plant with the addition of an Ultraviolet Disinfection System (or alternative treatment to achieve an equivalent performance in terms of treated wastewater quality). Under this arrangement, wastewater would be subjected to biological, chemical and physical treatment processes, and the treated wastewater discharged through Te Arikiroa Thermal Channel to Sulphur Bay. Rotorua Lakes Council is thus undertaking an environmental impact assessment study to determine the effects of discharging treated wastewater to the thermal channel and Puarenga Bay (Lake Rotorua), with particular reference to aesthetic, water quality and ecological considerations. These considerations include potential effects related to faecal indicator bacteria, nutrient concentrations, metals, dissolved oxygen, and taonga species (native species of cultural significance).
The assessment focused on:
(i)	The projected treated wastewater characteristics;

(ii)	Existing conditions of the receiving water;

(iii)	The sensitivity of the receiving water and the impact of the proposed discharge on water quality and taonga species (native species of cultural significance) in Te Arikiroa Thermal Channel and Sulphur Bay.

The main techniques used to inform the assessment in this study were:
1) Analysis of historical water quality data, 2011-2014;
2) Collection of additional water quality data at Te Arikiroa Thermal Channel and Sulphur Bay and along a transect to quantify spatial variability (sampling in 2016 and 2017);
3) Mass balance dilution modelling to predict water quality in the Te Arikiroa Thermal Channel and Sulphur Bay (Lake Rotorua), at a site outside of the assumed mixing zone;
4) Lake ecosystem modelling conducted by Abell et al. (2015) to assess effects related to eutrophication;
5) Background review of biological information and field investigations for taonga species at Sulphur Bay and Te Arikiroa Thermal Channel (2017).

year: 2018