No abstract

Abstract:Groundwater is often a critical source of water for municipal, industrial and agricultural uses, especially in arid and semi-arid environments. Songnen Plain, located in the central part of northeast China, is such a region, it being an important productive base of commodity grain in this country. In the past two decades, groundwater quality in the region, especially salinization, has deteriorated under natural changes and human activities, and has become a crucial factor restricting sustainable ecoenvironmental and socio-economic development. In this paper, The Taoer River catchment, situated in the middle of the region, was selected as the study area for the groundwater quality evolution study using hydrochemistry and stable isotopes to obtain a better understanding of the system. Fifty-two groundwater samples were collected with systematic design during the low-water and high-water periods in 2003. A series of comprehensive quality data interpretations, e.g. statistics, ratios of ions and Piper diagrams, together with stable isotope data, have been used to gain an insight into the spatial and temporal variations and evolution laws of groundwater hydrochemistry. The following main hydrochemical processes were identified as controlling the water quality of the groundwater system: weathering-dissolution, evaporation-condensation, ion-exchange reactions and groundwater salinization. This latter process, salinization, is the most important process and is caused by the leaching of superficial or near-surface salts from the saline-alkaline soil into shallow groundwater.

The heat-pulse method was used to estimate transpiration rates continuously for periods up to 2 years in mature trees oi Eucalyptus wandoo and Eucalyptus salmonophloia at two topographic locations in a remnant native woodland in the Western Australian wheatbelt. Annual transpiration per tree ranged from about 11 400 to 18 000 L per tree. Highest transpiration rates occurred in late spring or early summer, depending on rainfall distribution. The trees were able to rapidly utilize water following heavy rain outside the agricultural growing season. Extrapolating transpiration rates from single trees to an area of woodland showed that annual transpiration at the ridge site was 150 mm and 168 mm at a site alongside a drainage line. Scaling up transpiration from individual trees requires caution and should allow for variability in trees and soils. The role of trees in curtailing salinization is discussed.

No abstract

The paper presents the development and evaluation of methods that estimate recharge and discharge, water flow, and salt fluxes in rivers. The methods in combination provide an inferential framework to predict dryland salinity and the selection of the appropriate management scenarios. Hydrogeomorphic Analysis of Regional Spatial Data (HARSD) was used for delineating hydrogeologically homogenous units, and to translate limited hydrological data into hydraulic head surfaces and ultimately a steady state flow net representing recharge‐discharge relationships. A complex, physically based water, energy, and carbon model (WAVES) was developed and tested to provide recharge estimates required for the flow net simulations. Remote sensing imagery and analysis techniques involving airborne, advanced very high resolution reflectance (A VHRR) and LANDSAT‐Thematic Mapper (TM) data were used to infer the temporal and spatial patterns of leaf area index (LA1) and land‐cover type. The techniques were applied in 22 subcatchments in the Loddon and Campaspe and for the two major catchments. Modeled recharge was consistent with local estimates based on inverse methods and with subcatchment‐scale estimates based on stream salt loads under a steady‐state assumption. The calibrated flow nets for each of the subcatchment have been used to test the sensitivity of this system to changes in recharge resulting from land use change. It is shown, for example, that the Upper Campaspe subcatchment would require the reforestation of key recharge areas totaling 45% of the subcatchment to reduce salt loads from approximately 25 000 Mg yr−1 down to 18 000 Mg yr−1 under steady state assumption.