Thesis--Ph. D., University of Hong Kong. / Typewritten.

How much water can a crop abstract from below a saline water table and how does the salinity affect yield? These questions are important because shallow groundwater may represent a substantial resource in flat, low-lying areas, but may also represent a threat to sustainability where salinity is high. A series of experiments in a glasshouse aimed to elucidate irrigation management practice under salinity conditions and to develop a root uptake model under both osmotic and matric stresses. The extraction of soil water and groundwater by lettuce and perennial ryegrass crops were measured in three instrumented lysimeters. Water table depths were 0.6,0.9 and 1.2 rn below the soil surface. The lysimeters were initially saturated with saline water (electrical conductivity 4.5 dS m- 1 for lettuce, 9.4 dS m- I for the first crop of ryegrass and 0.4,7.5 & 15.0 dS m-1 for the second crop of ryegrass) and drained until an equilibrium soil water profile was attained. Water with the same electrical conductivity was then supplied by Marione siphons to maintain the constant water table. The water table contribution was recorded and water losses from the soil profile were estimated from daily readings of soil water potential using tensiometersa; nd gypsum blocks. Solute samples were extracted periodically for salinity measurement. The cropping period of lettuce was 90 days from sowing and the lst & 2nd cropping periods of ryegrass were 223 & 215 days respectively. The first ryegrass experiment showed that the water table depth (60,90 and 120 cm) did not have significant contribution (37,36 and 36 mm) on either total soil moisture use or groundwater contribution. Similar results were found for total soil moisture use for lettuce, though the groundwater contribution varied significantly. The second ryegrass experiment showed that salinity at the water table strongly influenced total soil moisture use, but the total groundwater contribution varied only slightly. The overall crop experiments show that the groundwater contribution was within the range of 25-30% of the total water use, except for the 15 dS m7l treatment where the contribution was greater than the soil moisture use. Groundwater contribution rate was higher when the plants were subjected to more osmotic and matric stresses. Yield component data show that increasing salinity leads to a reduction in total yield, but the drymatter proportion was higher. Higher salinities occurred in the upper 15 cm of the root zone, because of the greater soil moisture depletion. Below that depth the salinization rate was smaller, because of the greater groundwater contribution in the later part of the season. There is reasonable agreement between measured and estimated (based on convective transport theory) values soil salinity. Salinities increased in the root zone by about 3-fold of initial salinity for lettuce and around 4-fold for ryegrass in the top 5 cm depth, but below 15 cm depth it was less than 2 fold. Finally, a simplified model was developed to describe the interaction of root-zone salinity and water uptake, considering salinity and water stress as additive. The model shows that the higher the root-zone salinity stress, the higher the predicted water uptake while plant uptake considered -1.5 MPa. This variation is ranged from 4 to 17% for 0.4 to 9.4 dS m-1 and 30 % for 15 dS m-1. The model was developed in a climate with low atmospheric demand, but needs testing in a more severe environment.

The goal of this research was to study the effect of salinity on the waterflood of initially oil-wet clay-rich sand packs. Two one-foot long sand packs with 8% initial water saturation and 50% porosity were aged in crude oil for two weeks and flooded with either a low salinity (1000 ppm NaCl, pH 6.3) or a high salinity (20000 ppm CaCl, 20000 ppm MgCl, 20000 ppm NaCl, 20000 PPM KCl, pH 6.2) brine. 1D low salinity floods yield an incremental oil recovery of 15% and a significant change in the relative permeability. Initial breakthrough brine analysis showed that the low salinity flood results in more cation exchange activity compared to the high salinity case. A pH change of up to 1.4 point was witnessed for the high salinity case whereas the low salinity case had a 1.1 point pH change. The pH stayed below 7 in both low salinity and high salinity cases. The relative permeability of the low salinity case indicates a more water-wet state than that of the high salinity flood. The 2D study focused on capturing the movement of the water saturation fronts in transparent 2D sand packs via digital recordings. Two-dimensional sand packs of the oil-aged clay-rich sands were constructed in plastic quarter 5-spot models. Secondary water floods were performed. Low salinity flooding yielded higher oil recovery at breakthrough than the high salinity case. There was more areal bypassing in the case of low salinity flooding. It was difficult to pack the 2D cells uniformly which affected the water floods. / text

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Two factorial greenhouse experiments were performed to determine the effects of four arbuscular mycorrhizal fungi (AMF) species (Glomus arenarium, Funneliformis caledonius, F. mosseae, and Rhizophagus irregularis) and a root endophyte (Piriformospora indica) on four ‘day-neutral’ strawberry (Fragaria × ananassa Duch.) cultivars (‘Albion’, ‘Charlotte’, ‘Mara des Bois’, and ‘Seascape’), and mixed-AMF species (R. irregularis + F. mosseae) on cv. ‘Seascape’, under salt conditions (0-200 mM NaCl). In its biomass, ‘Seascape’ was more tolerant to salinity than the other cultivars. Cultivars responded differently to fungal inoculation as to salinity. G. arenarium had a negative effect on plant growth and ‘Mara des Bois’ responded negatively to inoculation. Among the remaining inoculants and cultivars, fungal-symbiosis was beneficial to growth. R. irregularis alleviated the symptoms of salt stress and improved fruit quality to a higher degree than the other AMF species and the root endophyte. Our results support the use of bio-inoculants in salty horticultural areas.

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Soil salinity is one of the major problems in and and semi-arid zones, affecting up to 50% of arable land in Syria. Salt-affected soils are usually desalinized by leaching the excess salts out of the soil profile. Some studies have shown that applying the leaching water intermittently instead of continuously may result in more efficient leaching. This thesis aims to investigate, theoretically and experimentally, the benefits and limitations of intermittent leaching and to develop mathematical models able to simulate solute transport through structured soils under such conditions. Laboratory leaching experiments were conducted on bi-continuum media, as an analogue of structured soils, created by packing porous aggregates (ceramic spheres or soil aggregates of uni- or multi- diameters) in glass columns. The columns were either leached continuously or intermittently and with different pore-water velocities. Intermittent leaching was undertaken either under saturated or drained conditions. Under "saturated conditions" the column remained saturated throughout the experiment, while under "drained conditions" the column was allowed to drain at the beginning of each rest period and remained like this until being saturated again for the next leaching period. The solute concentration in the leachate was monitored continuously (either using a flow-through conductivity cell, or by using ion-selective electrodes for Ký and Br' ) to produce breakthrough curves. These curves were used to investigate solute transport through such media and validate the developed models. The experiments showed that water savings of up to 22% under intermittent leaching from a soil aggregate column were possible under saturated conditions. Such saving increased with aggregate size, flow velocity and duration of rest period. Under drained conditions, for ceramic spheres, 12% more solute was leached with the same amount of water under intermittent leaching. Two models were developed, the SIL (Saturated Intermittent Leaching) and the DIL (Drained Intermittent Leaching) models, for saturated and drained conditions respectively. The SIL model simulated solute transport in structured soils under intermittent leaching. The governing equations during displacement period were the mobile-immobile convection-dispersione quations. During the rest period the flow is stopped, and the solute transfers only by diff-usion between immobile and mobile water regions. The DIL model simulated solute transport when the soil drained. Here, during the displacement period, the mobile water was drained. The model simulated this using the equations of the SIL model by assuming that air displaced the solution in a piston-type displacement. During the rest periods the solute difluses within the aggregates establishing a more uniform concentration in the immobile water across the aggregate. The models can be used with a wide range of column conditions and for both sorbed and non-sorbed solutes. Both models were verified against experimentarel sults.

Increased levels of total dissolved solids (TDS) in stream habitats are of concern due to salinity as well as the presence of potentially toxic ions. Natural gas drilling in the Marcellus shale could increase TDS in nearby streams. This thesis investigated the effects of water with elevated TDS on the locomotory activity and body weight of the streamside salamander Desmognathus ochrophaeus. Salamanders were exposed to water collected from streams in southwest Pennsylvania with elevated TDS as well as synthetic ion solutions that mimicked the ionic composition found in streams. Chronic, but not acute exposure to solutions of 1000 ppm TDS caused significant differences in weight loss and locomotory activity, although the effect depended on the exact ion composition of the dissolved solids. Finally, field surveys of salamander abundance were completed on two streams to provide baseline data with which to track population changes should the TDS in the streams increase. / Bayer School of Natural and Environmental Sciences / Biological Sciences / MS / Thesis

Research Doctorate - Doctor of Philosophy (PhD) / The Hunter Estuary Wetlands (NSW, Australia) are important locally, nationally and internationally. They contain significant breeding and nursery grounds for commercial fisheries and are essential shorebird foraging and roost sites. Originally a mosaic of fresh- and salt-marsh, these wetlands have become degraded due to the erection of flood mitigation structures. Reintroduction of a more natural tidal regime is proposed, which is expected to decrease freshwater macrophytes and increase saltmarsh distribution. An a priori approach was undertaken to assess the relative salinity tolerance of three macrophytes, prior to restoration commencing. Study species included a glycophyte, Phragmites australis (Cav) Trin. ex Steudel, and two closely related estuarine saltmarsh species, the invasive exotic Juncus acutus L. and native Juncus kraussii Hochst.. Short- and long-term effects of salinity at key life stages were assessed for each species. For P. australis, the reliability of physiological and morphological responses to salinity stress was assessed under both laboratory and field conditions as potential indicators for future monitoring of initial restoration progress. Competitive/facilitative interactions between the two Juncus species under various salinity regimes were also examined. Results showed salinity affected viability of P. australis but not Juncus species seeds. Irrespective of species, cooler temperatures enhanced germination capabilities under saline conditions. Juncus species displayed superior germination capabilities ≤ 10 ppt salinity; however, unexpectedly, above 10 ppt germination of P. australis was higher. All three species are highly salt tolerant, although salt adaptation mechanisms were found to differ among species. P. australis excluded sodium (Na+) where possible, only accumulating Na+ to toxic levels beyond particular salinity concentrations (~ 20 ppt) and temporal duration (four months). Juncus spp. accumulated Na+ in both root and shoot tissue without noticeable damage. Overtime, J. acutus regulated Na+ uptake at exposure concentrations above 5 ppt salinity, while J. kraussii did not commence regulation until concentrations exceed 10 ppt. A 50% reduction in photosynthesis, biomass, height and density of P. australis was apparent at 20 ppt salinity and mortality at 30 ppt. In P. australis, although height and density were indicative of salinity stress under laboratory conditions, only density showed potential as an indicator of reduced vigour under field scenarios, providing a valuable potential tool to track initial expected restoration trajectories. Although affected, neither Juncus species experienced a 50% reduction in measured endpoints at 40 ppt salinity. However, biomass allocation was asymmetrical. Under stressful conditions, J. acutus maintained shoot increase at the expense of root development. Conversely, as salinity rose J. kraussii preserved root development rather than shoot growth. J. acutus was facilitated by the presence of J. kraussii under freshwater conditions, but suffered a competitive response at 10 ppt salinity. Juncus kraussii was detrimentally affected by being grown with J. acutus at 5 ppt, but unaffected under non-saline and 10 ppt salinity conditions. All three species possess overlapping salinity tolerances. Creating conditions that favour a particular species is perhaps not realistic, given the limited resources of many restoration initiatives. Flooding duration, depth and waterlogging may modify these results. However, the most plausible scenario is that P. australis will continue to dominate marshes after tidal reinstatement. With time, where soil salinity rises above 30 ppt, distribution of Juncus species will increase. The relative salinity tolerances of J. acutus and J. kraussii are analogous. Under mild salinity regimes J. acutus is likely to out-compete J. kraussii. Juncus kraussii is expected to be restricted to areas of high salinity stress.