Natural and anthropogenic factors controlling the hydrological regime of the Wairau Plain Aquifer, New Zealand

The Wairau River is situated in the Marlborough Region in the North of New Zealand’s South Island. Near its mouth into the Pacific Ocean, the river is recharging a regionally important aquifer which is managed for drinking water production in the Blenheim region and for irrigation of New Zealand’s largest wine growing area. The Wairau Plain Aquifer is almost exclusively recharged by the Wairau River and closely related to its hydrological regime. The groundwater levels and spring flows at the Wairau Plain Aquifer have shown progressive decline in the past decades. This study analyses potential factors to explain this trend and a change in the hydrological regime using a combination of field investigations and a detailed numerical flow model. Results indicate that the driving forces of the system, rainfall and runoff, exhibit not only a strong interannual variability but seem to be also correlated with longer climate oscillations. The groundwater storage is also affected by strong seasonal variations and is particularly vulnerable to the frequency and duration of low-flow periods in summer. Climate variability alone, however, does not explain the log-term trends in storage. Another factor is the erosion of the Wairau River bed which can lead to a permanent loss of storage capacity and is caused by the effects of river training but also by extreme flood events. Another factor that should be taken into consideration is groundwater abstraction for irrigation, which accounts only for 1% of the total estimated storage, but up to 20% of the “live” manageable storage. The better understanding of the mechanisms and factors controlling the Wairau Plain Aquifer contributes to the identification of adaptation strategies for a sustainable management of the groundwater resources

Modeling of Nonequilibrium Bromide Transport through Alluvial Gravel Vadose Zones

Understanding solute transport and flux through the vadose zone is important for predicting potential contaminant loading to groundwater systems. Two dual-permeability models: mixing cell (MC) and HYDRUS 1D (H1DDP) were used to simulate long-term nonequilibrium Br- leaching using data derived from suction cup samples at two field sites (sampled to 7- and 4-m depths) on the Canterbury Plains, New Zealand. Effective model parameters were derived by inverse methods to represent average transport processes through the heterogeneous profiles. Suction cup samples indicated rapid initial movement of solute through the profiles followed by a long tail. The "management type" MC model results were comparable to the more complex HYDRUS model, providing similar overall fits to the observed data (similar RMSE ~ 0.05-0.1). Modeling indicated that macropore flux was significant in transporting solute through the profile (MC range 5-59%; H1DDP range 15-54% of total fluxes) and simulations of cumulative fluxes from both models were similar. The MC model results indicated macropore transporting water contents of ~0.003 (v/v) and matrix domain transporting water contents of around 0.1 to 0.15 (v/v) for the two field sites. These estimates suggest that only 3 mm of bulk drainage is required to transport solutes 1 m through the macropore domain, whereas approximately 100 to 150 mm of drainage is required to transport solutes the same distance through the matrix domain. More accurate representation of boundary conditions, texture spatial distributions, and hydraulic interactions is important for obtaining a better understanding of flux dynamics in future studies

Modeling of irrigation and related processes with HYDRUS

Future agriculture calls for increased input (e.g., water, nutrients, pesticides) use efficiency while maintaining or improving productivity, minimizing environmental impacts, and increasing profitability. Complete understanding of complex irrigation systems requires laborious, time-consuming, and expensive field investigations, which invariably involve only a limited number of treatments. On the other hand, fully calibrated process-based models, such as HYDRUS, can quickly evaluate different irrigation management strategies without the need for labor-intensive fieldwork and have become valuable research tools for predicting complex and interactive water flow and solute transport processes in and below the root zone. HYDRUS codes have been used worldwide in several hundreds of studies evaluating various types of irrigation (e.g., sprinkler, furrow, basin, and surface and subsurface drip), their scheduling (e.g., the timing of irrigation and its amount), and solute-related factors (e.g., fertigation, chemigation, salinization, and sodification). The objective of this manuscript is to review the current modeling capabilities of HYDRUS to evaluate various irrigation methods and related processes. The manuscript starts with a section describing governing flow and transport equations solved numerically by the HYDRUS codes, the corresponding initial and boundary conditions, and related factors such as soil hydraulic properties and root water and nutrient uptake. Modeling of different irrigation techniques is described in subsequent sections, followed by sections dealing with solute-related topics such as fertigation, chemigation, and salinization/sodification. Topics, including the effects of spatial variability, optimization of irrigation systems, and special irrigation methods, are covered in the later sections. The manuscript emphasizes the advantages and opportunities of HYDRUS in describing various processes in the root zone of irrigated plants that support sustainable irrigated agriculture. All the project files of the discussed examples and their descriptions are available for download at https://www.pc-progress.com/en/Default.aspx?hyd5-AdvancesInAgronomy

Residence times of groundwater along a flow path in the Great Artesian Basin determined by 81Kr, 36Cl and 4He: Implications for palaeo hydrogeology.

Understanding the age distribution of groundwater can provide information on both the recharge history as well as the geochemical evolution of groundwater flow systems. Of the few candidates available that can be used to date old groundwater, 81Kr shows the most promise because its input function is constant through time and there are less sources and sinks to complicate the dating procedure in comparison to traditional tracers such as 36Cl and 4He. In this paper we use 81Kr in a large groundwater basin to obtain a better understanding of the residence time distribution of an unconfined-confined aquifer system. A suite of environmental tracers along a groundwater flow path in the south-west Great Artesian Basin of Australia have been sampled. All age tracers (85Kr, 39Ar 14C, 81Kr, 36Cl and 4He) display a consistent increase in groundwater age with distance from the recharge area indicating the presence of a connected flow path. Assuming that 81Kr is the most accurate dating technique the 36Cl/Cl systematics was unravelled to reveal information on recharge mechanism and chloride concentration at the time of recharge. Current-day recharge occurs via ephemeral river recharge beneath the Finke River, while diffuse recharge is minor in the young groundwaters. Towards the end of the transect the influence of ephemeral recharge is less while diffuse recharge and the initial chloride concentration at recharge were higher

Modeling Soil Processes: Review, Key Challenges, and New Perspectives

The remarkable complexity of soil and its importance to a wide range of ecosystem services presents major challenges to the modeling of soil processes. Although major progress in soil models has occurred in the last decades, models of soil processes remain disjointed between disciplines or ecosystem services, with considerable uncertainty remaining in the quality of predictions and several challenges that remain yet to be addressed. First, there is a need to improve exchange of knowledge and experience among the different disciplines in soil science and to reach out to other Earth science communities. Second, the community needs to develop a new generation of soil models based on a systemic approach comprising relevant physical, chemical, and biological processes to address critical knowledge gaps in our understanding of soil processes and their interactions. Overcoming these challenges will facilitate exchanges between soil modeling and climate, plant, and social science modeling communities. It will allow us to contribute to preserve and improve our assessment of ecosystem services and advance our understanding of climate-change feedback mechanisms, among others, thereby facilitating and strengthening communication among scientific disciplines and society. We review the role of modeling soil processes in quantifying key soil processes that shape ecosystem services, with a focus on provisioning and regulating services. We then identify key challenges in modeling soil processes, including the systematic incorporation of heterogeneity and uncertainty, the integration of data and models, and strategies for effective integration of knowledge on physical, chemical, and biological soil processes. We discuss how the soil modeling community could best interface with modern modeling activities in other disciplines, such as climate, ecology, and plant research, and how to weave novel observation and measurement techniques into soil models. We propose the establishment of an international soil modeling consortium to coherently advance soil modeling activities and foster communication with other Earth science disciplines. Such a consortium should promote soil modeling platforms and data repository for model development, calibration and intercomparison essential for addressing contemporary challenges