title: Effects of solutions with high monovalent cation concentrations and high pH on soil properties

authors: Lieffering, Robert Ewout

abstract: The effects of solutions with high monovalent cation concentrations and high pH on selected soil physical and chemical properties were investigated using a range of New Zealand soil types.

Some industries produce liquid wastes which are characterized by high pH and high monovalent cation concentrations. However, land treatment of these liquid wastes have been observed to cause adverse effects on soil properties, especially structural deterioration of the 0-10 cm depth of soil. To establish the mechanisms which cause the observed adverse effects, laboratory experiments were conducted to investigate the processes which occur when high pH solutions which contain monovalent cations (NaOH and KOH) are applied to soil. To isolate pH and cation effects, NaCl and KCl solutions were also used as treatments throughout this study. In addition to laboratory experiments, a field trial was conducted to examine the short term (12 months) effects of a surface applied amendment (gypsum, applied at 5 t ha⁻¹) on selected properties of a soil which had been irrigated with high pH dairy factory liquid wastes. 

Single-step extraction experiments showed that hydroxide solutions dissolved organic carbon (OC) through the range of concentrations typically found in high pH liquid wastes (i.e. pH 10.5 - 13.5) and OC dissolution increased with increasing hydroxide concentration (i.e. increasing solution pH). Although NaOH dissolved more OC than KOH in the short term (after a single extraction), repeated treatment of soil with fresh hydroxide solution (using multi-step extractions) caused OC dissolution to increase though no cationic differences were measured in the longer term. In contrast to hydroxide solutions, chloride solutions dissolved minimal amounts of OC.

The saturated hydraulic conductivity (Kₛ) of the soils used in this study decreased over time when hydroxide solutions were used as influent solutions. Aggregate stability was also shown to decrease when soils were treated with hydroxide solutions. A two-stage process was proposed to explain the decrease in Kₛ when high pH solutions were applied to soil. First, OC is dissolved at the surface of the soil (i.e. 0-1 cm depth of soil) where the high pH solution is in contact with soil aggregates. The time required for dissolution to weaken aggregates being concentration dependent. Second, once a critical amount of OC had been removed, increased repulsion of soil particles (associated with increased negative charge on variable charge components in the soil due to increased pH) was thought to cause dispersion and deflocculation of clays and movement of the dislodged particles into pore spaces resulted in decreased Kₛ. In contrast to hydroxide solutions, aggregate stability was unaffected when soil was treated with chloride solutions and Kₛ was maintained or increased when chloride solutions were used as influent solutions. Decreasing the electrolyte concentration of the soil solution (by replacing the influent chloride solutions with distilled water) caused Kₛ to decrease, consistent with widely accepted diffuse double layer theory.

Cation exchange capacity (CEC) increased with increasing hydroxide concentration whereas chloride solutions had no effect on CEC. The increase in CEC in hydroxide-treated soil was attributed to negative sites being generated on components possessing variable charge characteristics. In general, higher exchangeable sodium percentage (ESP) and exchangeable potassium percentage (EPP) were found in hydroxide-treated soil compared to chloride-treated soil and were attributed to the new negative sites being counter-balanced by the monovalent cation present in the hydroxide solution (either Na⁺ or K⁺). Equations commonly used to predict ESP and EPP values from the composition of the soil solution (Richards, 1954) accurately predicted ESP and EPP in chloride-treated soil but did not accurately predict ESP or EPP in hydroxide-treated soil. These prediction equations do not take into account the increased total negative charge of the soil system and can therefore not be used to accurately predict ESP and EPP when high pH solutions are applied to soil.

The field trial showed that gypsum application increased infiltration rates in the irrigated soil by decreasing both the ESP and EPP of the soil and increasing the exchangeable Ca²⁺ concentration. Generally, gypsum did not affect any of the other measured properties (pH, OC, CEC, and bulk density) over the duration of the trial. In non-irrigated soil, the lack of effect of gypsum on any of measured soil properties was attributed to the high initial exchangeable Ca²⁺ concentration and low exchangeable Na⁺ and K⁺ concentrations compared to the irrigated soil.

It was concluded that for successful land treatment of liquid wastes with high monovalent cation concentrations and high pH, pH neutralisation of the liquid is essential to decrease the likelihood of OC dissolution and a build-up of negative charge on soil particles occurring. In addition, divalent cations should either be added to the liquid waste prior to disposal or should be applied to the soil in a relatively soluble form, in order to decrease the magnitude of problems associated with accumulation of monovalent cations on exchange sites. A conceptual model was proposed to describe the reactions that occur in soils when liquid wastes with high monovalent cation concentrations and high pH are applied using land treatment systems.

text: Effects of solutions with high monovalent cation concentrations and high pH on soil properties The effects of solutions with high monovalent cation concentrations and high pH on selected soil physical and chemical properties were investigated using a range of New Zealand soil types.

Some industries produce liquid wastes which are characterized by high pH and high monovalent cation concentrations. However, land treatment of these liquid wastes have been observed to cause adverse effects on soil properties, especially structural deterioration of the 0-10 cm depth of soil. To establish the mechanisms which cause the observed adverse effects, laboratory experiments were conducted to investigate the processes which occur when high pH solutions which contain monovalent cations (NaOH and KOH) are applied to soil. To isolate pH and cation effects, NaCl and KCl solutions were also used as treatments throughout this study. In addition to laboratory experiments, a field trial was conducted to examine the short term (12 months) effects of a surface applied amendment (gypsum, applied at 5 t ha⁻¹) on selected properties of a soil which had been irrigated with high pH dairy factory liquid wastes. 

Single-step extraction experiments showed that hydroxide solutions dissolved organic carbon (OC) through the range of concentrations typically found in high pH liquid wastes (i.e. pH 10.5 - 13.5) and OC dissolution increased with increasing hydroxide concentration (i.e. increasing solution pH). Although NaOH dissolved more OC than KOH in the short term (after a single extraction), repeated treatment of soil with fresh hydroxide solution (using multi-step extractions) caused OC dissolution to increase though no cationic differences were measured in the longer term. In contrast to hydroxide solutions, chloride solutions dissolved minimal amounts of OC.

The saturated hydraulic conductivity (Kₛ) of the soils used in this study decreased over time when hydroxide solutions were used as influent solutions. Aggregate stability was also shown to decrease when soils were treated with hydroxide solutions. A two-stage process was proposed to explain the decrease in Kₛ when high pH solutions were applied to soil. First, OC is dissolved at the surface of the soil (i.e. 0-1 cm depth of soil) where the high pH solution is in contact with soil aggregates. The time required for dissolution to weaken aggregates being concentration dependent. Second, once a critical amount of OC had been removed, increased repulsion of soil particles (associated with increased negative charge on variable charge components in the soil due to increased pH) was thought to cause dispersion and deflocculation of clays and movement of the dislodged particles into pore spaces resulted in decreased Kₛ. In contrast to hydroxide solutions, aggregate stability was unaffected when soil was treated with chloride solutions and Kₛ was maintained or increased when chloride solutions were used as influent solutions. Decreasing the electrolyte concentration of the soil solution (by replacing the influent chloride solutions with distilled water) caused Kₛ to decrease, consistent with widely accepted diffuse double layer theory.

Cation exchange capacity (CEC) increased with increasing hydroxide concentration whereas chloride solutions had no effect on CEC. The increase in CEC in hydroxide-treated soil was attributed to negative sites being generated on components possessing variable charge characteristics. In general, higher exchangeable sodium percentage (ESP) and exchangeable potassium percentage (EPP) were found in hydroxide-treated soil compared to chloride-treated soil and were attributed to the new negative sites being counter-balanced by the monovalent cation present in the hydroxide solution (either Na⁺ or K⁺). Equations commonly used to predict ESP and EPP values from the composition of the soil solution (Richards, 1954) accurately predicted ESP and EPP in chloride-treated soil but did not accurately predict ESP or EPP in hydroxide-treated soil. These prediction equations do not take into account the increased total negative charge of the soil system and can therefore not be used to accurately predict ESP and EPP when high pH solutions are applied to soil.

The field trial showed that gypsum application increased infiltration rates in the irrigated soil by decreasing both the ESP and EPP of the soil and increasing the exchangeable Ca²⁺ concentration. Generally, gypsum did not affect any of the other measured properties (pH, OC, CEC, and bulk density) over the duration of the trial. In non-irrigated soil, the lack of effect of gypsum on any of measured soil properties was attributed to the high initial exchangeable Ca²⁺ concentration and low exchangeable Na⁺ and K⁺ concentrations compared to the irrigated soil.

It was concluded that for successful land treatment of liquid wastes with high monovalent cation concentrations and high pH, pH neutralisation of the liquid is essential to decrease the likelihood of OC dissolution and a build-up of negative charge on soil particles occurring. In addition, divalent cations should either be added to the liquid waste prior to disposal or should be applied to the soil in a relatively soluble form, in order to decrease the magnitude of problems associated with accumulation of monovalent cations on exchange sites. A conceptual model was proposed to describe the reactions that occur in soils when liquid wastes with high monovalent cation concentrations and high pH are applied using land treatment systems.

year: 1995

title: Supporting interactive system testing with interaction sequences

authors: Turner, Jessica Dawn

subjects: interactive systems

abstract: Despite extensive research into the modelling and testing of interactive systems, existing strategies do not adequately cover all parts of an interactive system. These existing strategies model and test either the functional or interactive components of an interactive system separately, however, issues may arise where these components intersect. Therefore, further investigation into the modelling and testing of this intersection is required. 
Interaction sequences are a series of steps a user can take to complete a specific task or to arbitrarily explore an interactive system. In this research interaction sequences are used as an abstraction of the interactive system to inform a model-based testing approach using lightweight formal methods. Interaction sequences provide an abstract view of the point at which the functional and interactive components intersect, and as a result also provide a good starting point for investigation into the modelling and testing of this area. Interaction
sequences are applicable to all types of interactive systems irrespective of the type of interaction, therefore modelling and testing approaches using this abstraction are also applicable to all types of interactive systems.
In this thesis the findings of our investigation into modelling and testing using interaction sequences are presented. We describe formalisation of interaction sequences and modelling of these sequences using Finite State Automata (FSA). We introduce the self-containment property and show how this is used to control the size and state space of FSA. We demonstrate simulating interaction sequences and discuss how these models can be applied within both model checking and testing techniques. Lastly, we present a new approach for generating tests from interaction sequences and their associated models.

text: Supporting interactive system testing with interaction sequences Despite extensive research into the modelling and testing of interactive systems, existing strategies do not adequately cover all parts of an interactive system. These existing strategies model and test either the functional or interactive components of an interactive system separately, however, issues may arise where these components intersect. Therefore, further investigation into the modelling and testing of this intersection is required. 
Interaction sequences are a series of steps a user can take to complete a specific task or to arbitrarily explore an interactive system. In this research interaction sequences are used as an abstraction of the interactive system to inform a model-based testing approach using lightweight formal methods. Interaction sequences provide an abstract view of the point at which the functional and interactive components intersect, and as a result also provide a good starting point for investigation into the modelling and testing of this area. Interaction
sequences are applicable to all types of interactive systems irrespective of the type of interaction, therefore modelling and testing approaches using this abstraction are also applicable to all types of interactive systems.
In this thesis the findings of our investigation into modelling and testing using interaction sequences are presented. We describe formalisation of interaction sequences and modelling of these sequences using Finite State Automata (FSA). We introduce the self-containment property and show how this is used to control the size and state space of FSA. We demonstrate simulating interaction sequences and discuss how these models can be applied within both model checking and testing techniques. Lastly, we present a new approach for generating tests from interaction sequences and their associated models.

year: 2019

title: Two-step human−environmental impact history for northern New Zealand linked to late-Holocene climate change

authors: Newnham, Rewi M.

subjects: New Zealand

abstract: Following resolution of a long-standing debate over the timing of the initial settlement of New Zealand from Polynesia (late 13th century), a prevailing paradigm has developed that invokes rapid transformation of the landscape, principally by fire, within a few decades of the first arrivals. This model has been constructed from evidence mostly from southern and eastern regions of New Zealand, but a more complicated pattern may apply in the more humid western and northern regions where forests are more resilient to burning. We present a new pollen record from Lake Pupuke, Auckland, northern New Zealand, that charts the changing vegetation cover over the last 1000 years, before and after the arrival of people. Previous results from this site concurred with the rapid transformation model, although sampling resolution, chronology and sediment disturbance make that interpretation equivocal. Our new record is dated principally by tephrochronology together with radiocarbon dating, and includes a cryptotephra deposit identified as Kaharoa tephra, a key marker for first settlement in northern New Zealand. Its discovery and stratigraphic position below two Rangitoto-derived tephras enables a clearer picture of environmental change to be drawn. The new pollen record shows an early phase (step 1) of minor, localised forest clearance around the time of Kaharoa tephra (c. 1314 AD) followed by a later, more extensive deforestation phase (step 2) commencing at around the time of deposition of the Rangitoto tephras (c. 1400‒1450 AD). This pattern, which needs to be corroborated from other well-resolved records from northern New Zealand, concurs with an emerging hypothesis that the ‘Little Ice Age’ had a significant impact on pre-European Māori with the onset of harsher conditions causing a consolidation of populations and later environmental impact in northern New Zealand.

text: Two-step human−environmental impact history for northern New Zealand linked to late-Holocene climate change Following resolution of a long-standing debate over the timing of the initial settlement of New Zealand from Polynesia (late 13th century), a prevailing paradigm has developed that invokes rapid transformation of the landscape, principally by fire, within a few decades of the first arrivals. This model has been constructed from evidence mostly from southern and eastern regions of New Zealand, but a more complicated pattern may apply in the more humid western and northern regions where forests are more resilient to burning. We present a new pollen record from Lake Pupuke, Auckland, northern New Zealand, that charts the changing vegetation cover over the last 1000 years, before and after the arrival of people. Previous results from this site concurred with the rapid transformation model, although sampling resolution, chronology and sediment disturbance make that interpretation equivocal. Our new record is dated principally by tephrochronology together with radiocarbon dating, and includes a cryptotephra deposit identified as Kaharoa tephra, a key marker for first settlement in northern New Zealand. Its discovery and stratigraphic position below two Rangitoto-derived tephras enables a clearer picture of environmental change to be drawn. The new pollen record shows an early phase (step 1) of minor, localised forest clearance around the time of Kaharoa tephra (c. 1314 AD) followed by a later, more extensive deforestation phase (step 2) commencing at around the time of deposition of the Rangitoto tephras (c. 1400‒1450 AD). This pattern, which needs to be corroborated from other well-resolved records from northern New Zealand, concurs with an emerging hypothesis that the ‘Little Ice Age’ had a significant impact on pre-European Māori with the onset of harsher conditions causing a consolidation of populations and later environmental impact in northern New Zealand.

year: 2018