Stream Salinity Research Articles

Management Of Saline Groundwater Discharge By Long-term Windmill Pumping In The Wheatbelt, Western Australia

Land and stream salinization in the Western Australian wheatbelt developed as a result of clearing of native vegetation. This caused a shift in the hydrological balance and a 10- to 30-fold increase in recharge. Rising water levels rejuvenated groundwater flow through paleao channels and increased baseflow to drainage lines. An increase in saline groundwater ascension (TDS 5000–30 000 mgl−1) to the near-surface, induced by rising pressure heads in the deeper semi-confined aquifer system, advanced land and stream salinization. Areas in a catchment where groundwater flow is channelled upwards by subsurface geological strctures are especially susceptible to salinization and water logging.

Ground‐Water Contribution to Stream Salinity in a Shale Catchment, R.S.A.

AbstractThe salinity in the Breede River in the Robertson area (S. W. Cape, South Africa) has increased at an alarming rate over the past two decades. Water analyses have shown that a few tributary streams which drain Bokkeveld Shale catchments are responsible for the high salinity in this agriculturally important river. Research carried out to investigate the sources of salinity in one such catchment, the Poesjesnels River Valley, found that heavy salt loads were contributed by return flow seepages after irrigation of deeply ripped, thin soils which overlie decomposed shale. A smaller contribution was coming from ground water which had leached out some salt from these shales while moving through bedrock fractures under pressure from the head in the encircling mountains, and eventually seeped into the river; evidence for this was provided by comparison of the oxygen isotope ratios of the various water bodies in the valley with that of the river water. A salt balance model drawn up to differentiate between the sources of salinity gave an indication of the systems which need management in future hydrological and agricultural development in this and similar valleys.

Modeling Transport of Subsurface Salinity from a Mancos Shale Hillslope

AbstractIn the Upper Colorado River Basin, irrigated agriculture is associated with increasing stream salinity. In areas targeted for control of salinity transport to streams, as much as 90% of stream salinity has been estimated to originate from ground water flowing through salt‐bearing stratum. Primary salt sources are the marine shales and the shale residuum that underlie the soils throughout much of the basin. Shallow subsurface flow systems, created by seepage from canals and deep percolation of irrigation water, are believed to be the primary agents leaching the salts from underlying shale deposits and carrying them to streams. This study attempts to determine the relative importance of advective, dispersive, and diffusive salt transport processes from the alluvium covered, shale hillslopes of the region. The results of various irrigation management schemes for appraising the possibility of controlling salt loading to streams are presented.

Salinity trends in the wheatbelt of Western Australia: results of water and salt balance studies from Cuballing catchment

A study of water and salt balances within a first-order catchment in the Western Australian wheatbelt has shown that the salt load in the main surface drainage comes largely from groundwater discharging upstream from the basement highs and dykes that extend across the surface drainage and conductive channels within the regolith. Although salt fall from rainfall is about 2.0 g m −2 year −1 (Cl −), the stream load ranges from 180 to 850 g m −2 year −1 with an out/input ratio of 100–425. Salt storage in the catchment varies from 900–4000 g m −2 in the top 3 m, to 27 000–71 000 g m −2 in the 3–15 m depth range and 5000–21 000 g m −2 below 15 m. Groundwater discharge calculated using Br and Cl as tracers for the groundwater component fluctuates between 20 and 40% of streamflow. Stream salinity during the last 3 years was below the long-term average. This is attributed to a reduction in groundwater discharge caused by low rainfall during this period. The downward displacement and leaching of salt stored in the regolith indicates that if groundwater levels continue to rise, the quantity and salinity of groundwater discharge will continue to increase causing further rises in stream salinity.

The chemical evolution of groundwater in a first-order catchment and the process of salt accumulation in the soil profile

The chemical characteristics of surface water, base flow and groundwater in a first-order catchment in the wheatbelt of Western Australia were used to study the weathering process and its relationship to the development of groundwater and stream salinity. Meteoric water infiltrates through the unsaturated zone to the water table aquifer and through the aquifer outcrop in the case of a confined aquifer. The groundwater composition changes in space and time, becoming more saline with depth and distance away from the recharge zone. The concentration of salt in the system can be explained by four main mechanisms: withdrawal of water through uptake by plant roots for transpiration; loss of water during the weathering process and the formation of new minerals; leakage between aquifers; evaporation upstream of geological structures and near discharge zones. The groundwater is mainly of Na-Cl type, and is at saturation with respect to most of the carbonate minerals, chalcedony, talc and tremolite. The water changes in its chemical composition as rock-water interaction takes place. The weathering products are gibbsite and kaolinite, with the release of Na +, K +, Mg 2+, Ca 2+, HCO − 3 and H 4SiO 4. The preclearing weathering products are produced in a system open to CO 2 (through the plant roots), with groundwater under this system having excess Na +. After clearing the system becomes depleted in CO 2 and the groundwater becomes depleted in Na + through exchange with Mg 2+ from the rock surface. Geochemical modelling showed that most of the constituents in groundwater can be accounted for by taking into consideration the constituents of rainfall, with minor additions from the weathering process.

Ecohydrological Changes in the Murray-Darling Basin. I. The Number of Trees Cleared Over Two Centuries

The Murray-Darling Basin occupies over 1 million km 2 of south-eastern Australia. Since European settlement 200 years ago, massive tree clearing and disturbance to other native vegetation types has resulted in increases in dryland and stream salinity. An attempt is made to estimate the number of trees cleared from the Basin. This information is useful for making decisions on broad policy and revegetation prescriptions. Structural classes for pre-European and present-day vegetation were previously mapped at the 1:5 million scale. Digital versions of these maps were used to quantify the original and present-day areas for each class. The number of trees per class was established by field sampling. Information on areal extent and number of trees per class was then used to estimate total number of trees per class (...)

Lowering of a shallow, saline water table by extensive eucalypt reforestation

Land and stream salinisation in Western Australia has occurred as a result of the clearing of native vegetation for agricultural development. One approach to controlling the salinisation, extensive reforestation, has been tested on a site which was 35% cleared and converted to pasture in the 1950s. By 1979 saline ground water was discharging in the valley where the clearing had taken place. At that time 63 Eucalyptus and two Pinus species were planted in 0.5 ha blocks across the site, covering some 70% of the cleared land. The reforestation has been succesful in substantially lowering the saline groundwater table across the site. Over the 1980–1989 period, the average minimum groundwater levels beneath reforestation declined by 5.5 m relative to the ground level and by 7.3 m relative to a nearby pasture control site. After the first 3 years the rate of decline was near-uniform with time. The average salinity of the ground water beneath reforestation decreased by 11%.

Spatial modelling of dryland salinization potential in Victoria, Australia

The goal of the project discussed in this paper is to produce small-scale maps of dryland salinization potential for Victoria, Australia; maps which putatively identify areas where salinization effects might be expected to worsen or where effects have yet to become evident. This paper assumes: (a) that current stream salinity levels can be modelled empirically using a relationship reported by Greig and Devonshire (1981), and (b) that a subset of these levels are indicative at an early stage of the maximum long-term severity (meaning extensiveness) of proximate dryland salinization should water-tables rise. This paper uses computer induction to relate modelled stream salinity to observed salinization and hence to dryland salinization potential.

Effects of partial deforestation on hydrology and salinity in high salt storage landscapes. I. Extensive block clearing

A small (344ha) experimental catchment in southwest Western Australia was partially deforested (western 53% of the catchment) in 1976 to study the effects of agricultural development on water quantity and quality. The impact on the groundwater system in the cleared area was dramatic. Initial rates of rise were only 0.11 m year −1 but this increased after 10 years to average 2.3 m year −1. Groundwater rises of 15 m in the valley and 20–25 m on the lower sideslopes were observed over 13 years. A small seep (groundwater discharge area) appeared for the first time in 1988 and by 1989 it covered an area of 1 ha. Streamflow initially increased by 30 mm year −1 (4.0% rainfall) compared with a native forest average streamflow of 8 mm year −1 (1.0% rainfall). However, since the seep area developed, the increase in streamflow has been 50 mm year −1 (6.6% rainfall). Stream salinity was low prior to clearing (30 mgl −1Cl −) and remained low for 9 years after clearing. However, since 1987, stream salinity increased dramatically as the ground water approached the ground surface, and by 1989 reached an annual average of 290 mgl −1Cl −. The daily maximum in 1989 was 2200 mgl −1Cl − compared with 92 mgl −Cl − from 1976 to 1986. The catchment changed from net salt accumulation pre-clearing to net salt export after 1987. Thirteen years after clearing, the groundwater level, stream yield, stream salt load and stream salinity had not reached equilibrium but were all still increasing.

Effects of partial deforestation on hydrology and salinity in high salt storage landscapes. II. Strip, soils and parkland clearing

A small (300 ha) experimental catchment in a high salt storage landscape in southwest Western Australia was subject to several different clearing treatments to determine their respective impacts on groundwater levels. Within subcatchments that were 60–70% cleared, groundwater level rises were observed of 7.8–10.2 m compared with a 5.8 m rise with 32% clearing and a 2.3 m fall in a native forest control, from 1977 to 1989. Under parkland clearing (leaving wide-spaced trees), the rate of groundwater level rise has declined in recent years in response to increasing crown leaf areas, and in contrast to other treatments (strips and block clearing) where groundwater rise has accelerated. The presence of a bedrock high at the valley invert within one subcatchment has led to substantial groundwater rises in recent years which could intercept the surface in the next 5 years if the current rates of rise are maintained. The combination of clearing treatments affecting 38% of the catchment has resulted in a modest (13 mm) increase in catchment streamflow. This was over double the average forested streamflow. Stream salinity has remained low. Stream yield, stream salt load and stream salinity appear to be at an equilibrium. However, as a result of considerable expanses of clearing located close to or on the streamline or valley invert, there is a significant risk of salt discharge to the stream in the future.

Effects of agroforestry-pasture associations on groundwater level and salinity

Stream and land salinisation brought about by rising groundwater levels due to the clearing of native forest for agricultural development is a major environmental and resource problem in Western Australia and several other semi-arid regions of the world. One potential approach to reclamation with simultaneous economic benefits is agroforestry. To determine the effects of agroforestry on groundwater level and salinity, two experiments were carried out in Western Australia. In Experiment I a pinius-pasture agroforestry covering 58% of the cleared area with final stem densities of 75–225 stems ha−1 was successful in lowering a saline groundwater table. Over the period 1979–1989, groundwater levels decliend by 1.0 m relative to groundwater levels beneath a nearby pasture site. In Experiment II the eucalyptus-pasture agroforestry covering 57% of farmland at a final density of 150–625 stems ha−1 was found to successfully lower the yearly minimum groundwater level by 2.0 m relative to a pasture site over seven years. The salinity of the groundwater beneath agroforestry decreased by 9% and 6% for Experiments I and II respectively, which was contrary to some early expectations. The design of agroforestry for controlling saline groundwater tables needs further evaluation with respect to species, stem densities and proportion of cleared area planted.

Regional analysis of stream salinisation in southwest Western Australia

Stream salinities in southwest Western Australia are strongly influenced by land use, soil salt storage and rainfall. The salinities of forest catchments are fresh and have declined over the last two decades due to decreasing groundwater solute discharge under lower than average rainfall conditions. Catchments extending to or lying in lower rainfall areas ( < 900 mm yr −1) where agricultural clearing has taken place have stream salinities ranging from marginal to saline. Over the last 20 years stream salinities have increased rapidly on these catchments. Higher stream salinities are associated with higher catchment salt storage (lower rainfall) and a higher proportion of catchment cleared. Annual salinities of salt-affected catchments vary inversely with annual rainfall. A projected trend of decreasing rainfall is likely to exacerbate the stream salinity problem.

Ground‐Water Modeling for Salinity Management: An Australian Case Study

ABSTRACTRecognition of the severity of land and stream salinity problems in Australia over the past few decades has resulted in the application of a range of mitigation strategies. In terms of stream salinity management, ground‐ water interception has proved the most cost‐effective strategy, and a number of ground‐water interception schemes have now been implemented. In all cases, the scheme design and assessment of feasibility were based on hydrogeological investigations only. This paper presents an analysis of ground‐water behavior associated with the Mildura interception scheme, illustrating the development and use of mathematical models of ground‐water flow in simulating a range of management options for the mitigation of river salinity. The study found that: over the period of simulation, the interception scheme had been operating below its achievable operational effectiveness, 48 compared to 72 percent; effectiveness could be further enhanced to 80 percent by judicious placement of three additional well fields; and improved irrigation practices in the area would significantly reduce the flow of salt to the river. The modeling approach applies to similar river salinity problems elsewhere.

Streamflow and stream salinity in a small water supply catchment in southwest Western Australia after reforestation

In the mid-1970s high salinities developed in the Padbury reservoir in southwest Western Australia due to the conversion of 80% of its catchment from native forest to farmland in previous decades. Between 1977 and 1983 some 70% of this farmland was planted with pines and eucalypts. Most of the slopes were reforested, but only some of the valleys. In 1978 a gauging station was established in the catchment to monitor the effect of reforestation on streamflow and stream salinity. Results obtained by the end of 1986 are presented here. Reforestation led to a substantial and continuous reduction in streamflow. There was also a steady reduction in salt discharge from the catchment. In most years the reduction in streamflow outweighed the reduction in salt discharge. Stream salinity was therefore generally higher than it would have been without reforestation. Since 1978, when hydrologic monitoring began, the annual rainfall was generally below the long-term mean of 880 mm, and often below 800 mm. While these dry conditions were at least partly responsible for the increases in stream salinity, it is not known whether salinity would have decreased in all years if the rainfall had been normal. It is argued that completely replanting the valleys would have resulted in lower stream salinities. If rainfall had been normal, or if the valleys had been planted, and particularly with a combination of the two, reforestation may have resulted in a general decrease in stream salinity. Yet, any salinity benefit due to reforestation must be balanced against the concurrent reduction in streamflow. For a small water supply catchment like the one described here, reforestation may therefore not be an appropriate strategy to alleviate salinity problems. However, it is shown that reforestation is useful in large salt-affected catchments in the region where the areas which contribute most of the salt generate only little of the streamflow.

The effect of logging and regeneration on groundwater, streamflow and stream salinity in the southern forest of Western Australia

In the late 1960s the Forests Department of Western Australia decided to change its logging strategy in the southern forest from light selection cutting to heavy selection cutting and clear-felling. This raised some concern about the effect on the water resources in the region. Four small catchments (Crowea, Poole, Iffley and Mooralup) were therefore selected in 1975 to study the effect of heavy selection cutting and clear-felling followed by regeneration on streamflow, stream salinity and groundwater levels. The catchments were logged between November 1976 and March 1978. Regeneration began within eighteen months after the completion of logging. During the study (1976–1985) the annual rainfall in the region was generally below the long-term mean. This probably influenced the magnitude and duration of the hydrologic response to logging and regeneration, but not the general trends. Groundwater levels rose for two–four years after logging and then started to fall again. They can be expected to reach the values they would have been at without logging within fifteen years after the beginning of regeneration. In the relatively dry Mooralup catchment, logging had little effect on the groundwater level. As a result of logging streamflow increased for two years (1977 and 1978) and then gradually declined again as the vegetation regenerated. Streamflow is also likely to be back to pre-logging values within fifteen years after the beginning of regeneration. In the Mooralup catchment, where streamflow volumes are naturally small, this may have happened after six years of regeneration. Flow-weighted mean annual stream salinities rose for one–three years after logging but have declined since. Even at their highest level they remained below the upper limit for high-quality drinking water. Stream salinites are likely to return to the level they would be at without logging at the same time as streamflow and groundwater levels.

Predicting the effects of land disturbances on stream salinity in southwest Western Australia

A model developed by A. J. Peck to predict the effects of land disturbances on stream salinity has been extended to take account of increased stream runoff, and applied to the jarrah forest region with improved parameter estimates. Validation on Wights experimental catchment suggests that the model is capable of reliable predictions in the case of agricultural clearing. However, the extended model did not provide discernibly better predictions than the original model. When applied to rainfall zones of the northern jarrah forest of W.A., the model predicted that agricultural clearing would result in average stream salinity increases of -70 mg 1 for the high rainfall zone (&gt; 1100 mm yr-1), of -270 mg L-1 for the intermediate rainfall zone (900-1100 mm yr-1), and of ~3400 mg L-1 for the low rainfall zone (&lt;900 mm yr-1). In the case of bauxite mining followed by reforestation, the model was limited to consideration of long-term effects, and neglected transient effects. Predicted stream salinity increases were considerably smaller than for agricultural clearing, primarily because mining involves clearing smaller areas, and these areas are reforested. The model is sensitive to variations in parameter values which implies that a wide range of stream salinity increases could occur within any one rainfall zone, due to the variation of local conditions.

Effect of Salinity on Leaf Ionic Content and Photosynthesis of Taxodium distichum L.

Bald cypress (Taxodium distichum L.) seedlings were subjected to flooding with salinity levels ranging from 0-140 moles m-3 NaCl. Imposition of salinity was designed to simulate the increase in salinity level which some of Louisiana's extensive cypress forests are currently experiencing due to rapid subsidence in the Mississippi River Deltaic Plain. The effect of salt water on leaf tissue ion concentrations and subsequent changes in net photosynthesis were measured. Leaf concentrations of Na, K, Ca and Mg increased substantially as salinity of floodwater increased. Net photosynthesis declined from 7.6 ,umol.m-2s-1 to 0.9 ,umol.m-2s-1 when salinity increased from 0-140 moles m-3 NaCl. Despite the parallel reduction in both stomatal conductance and net photosynthesis, the leaf internal CO2 concentrations remained relatively constant over the entire range of salt concentrations. These results suggest that elevated floodwater salinity causes excess accumulation of several ions in the bald cypress leaf tissue. Consequently, increase in leaf ionic content is primarily the cause of reductions in photosynthesis which is accompanied by simultaneous diffusional limitations caused by stomatal closure. INTRODUCTION Significant parts of coastal forests including bald cypress (Taxodium distichum L.) stands are currently being subjected to saltwater intrusion caused by rapid subsidence and compaction of recent Mississippi River alluvial sediment. Salinity in streams flowing through the extensive cypress forests bordering Lake Pontchartrain has been reported as high as 50 moles m-3 NaCl (Salinas et al., 1986). The continuous land subsidence in wetland coastal areas and the projection indicating faster sea level rises in the future (Hoffman et al., 1983) may result in elimination of many salt-sensitive, but otherwise flood-tolerant species by exposing them to high salinity. Despite the potential impact of saltwater intrusion on survival, productivity and species composition of coastal vegetation, there is little information on the extent of salt tolerance and the physiological characteristics of these species. Assessment of physiological response of bald cypress seedlings to salt stress is important in order to identify the level of tolerance and possible adaptation/acclimation to salinity conditions. Salt stress reduces growth through several effects including water stress, excess ion and biochemical relations (Greenway and Munns, 1980). Presumably, plants can survive sublethal salt stress as long as they are able to photosynthesize positively. The photosynthetic rates of glycophytes, however, declines in response to salinity. Such response has been attributed to stomatal closure as well as direct effect of excess ion content on photosynthetic processes (Seemann and Critchley, 1985). Reports of photosynthetic response of bald cypress to salinity is limited to those of Pezeshki et al., (1986) and Pezeshki et al., (1987). The former studied the photosynthetic response of different leaf age group under salinity and the latter reported photosynthetic responses to a wide range of floodwater salinity. Generally, significant declines in net photosynthesis have been observed as a result of both flood and salt stresses in bald cypress. In our continuous efforts to further investigate the response of this key wetland tree species to increased inundation and salinity, this study was conducted to examine the effects of floodwater salinity on leaf ionic contents and the subsequent effects on photosynthesis.

Stream salinity in the Indian arid zone

Streamwater quality was determined in the Indian desert for a period of three years, 1979–1981. Total dissolved salts (TDS) varied from 161 to 12,495 mg l −1 in various streams, depending upon the geology, landscape and volume of runoff. Highest concentrations of TDS were recorded at the onset of runoff in the initial flow event, followed by a rapid decrease in concentrations during the rising and recession flow stages. Sodium concentrations decreased with increasing discharge whereas calcium concentrations increased with discharge. Magnesium and potassium concentrations remained relatively uniform throughout the flow. TDS and individual ion concentrations displayed an annual fluctuation. Maximum concentration values were recorded following a flood year whereas minimum concentrations occur during the flood year.

Measurement and prediction of evaporation from forested and agricultural catchments

The workshop on Land and Stream Salinity held in Perth, Western Australia in November 1980 recommended that remedies to the salinity problems of south-western Australia should be sought in the recharge areas, as opposed to the treatment of the saline discharge areas. In the climate of that area, vegetation could evaporate at much higher rates than occurs at present, either from the agricultural crops or from the native forests; introduction of such vegetation could therefore lower the water table and reduce saline seepages. Calculations show that to achieve a significant decrease in the height of the water table would require that either the replacement vegetation had a very high rate of evaporation or a large proportion of the agricultural area had to be converted to the new vegetation. The major differences in meteorological and biological characteristics between forests and agricultural crops are highlighted. Methods of measuring evaportation are briefly reviewed and compared. It is emphasised that methods of measuring evaporation from large areas and over periods of years can only be used to determine the total evaporation. Whereas physically based methods used for smaller areas and shorter periods can measure the individual evaporation components and provide a sound basis for prediction of evaporation. It is concluded that the Monteith-Penman equation is most suitable for predicting the effects of changes in land use management. The necessary data collection and analysis for use with this equation are discussed.

Land and Stream Salinity

Soil salinity and salinity in water supplies are two major problems facing agricultural production in many arid and semi‐arid regions of the world. Salt, in varying concentrations, occurs naturally in both soils and aquifers. However, salinity problems usually result from man's interference with natural processes and disturbance of the hydrologic balance. For example, the clearing of trees in southwestern Australia and the breaking of native sod on the Great Plains of North America for wheat cropping have reduced evapotranspiration. At the same time, over irrigation in dry regions concentrates dissolved salts in the soil profile, while irrigation return flows add to downstream salinity problems. These problems are of great economic significance, and opportunities are being sought for improved drainage and for interception and disposal of saline groundwater. However, these structural solutions are capital‐intensive and quite expensive to say the least. The most cost‐effective measures, but also the most challenging, are in the areas of improved on‐farm water management to reduce losses, modified cropping patterns, selected retirement of marginally productive lands, and basin‐wide water resource management with regard to both quantity and quality objectives.