Presentations 2016

The Netherlands hosts a well-developed agricultural sector that largely relies on an almost guaranteed availability of fresh water from surface water or ground water sources. This business strategy is at risk of failure, however, because socio-economic developments and climate change will lead to prolonged periods of water scarcity due to increasing water demand and decreasing water availability. In order to secure sufficient agricultural water supply to maintain current crop yields in future, water managers seek for measures to mitigate water scarcity. In search for these measures, particular interest is exhibited to the implementation of measures for improving regional self-sufficiency in water demand by re-using waste water as a source for agricultural crop irrigation. Major challenge for implementation of this strategy is the development of a cost-effective infrastructure for equal distribution and supply of waste water across agricultural fields. In this study, we investigated whether such infrastructure can be provided by sub-irrigation systems. Sub-irrigation is a parcel-scale, subsurface technique for water distribution and supply across agricultural fields. It consists of a network of subsurface drains, interconnected through a collector tube, and connected to an inlet control pit for supply water to enter the drainage system. Sub-irrigation may be more efficient compared to classical, above ground irrigation techniques, as evaporation losses are prevented and vast agricultural fields can be irrigated in equal or manageable amounts. Moreover, when irrigating from waste water, sub-irrigation prevents crop leaves from being exposed to the waste water, and its solutes, which can be harmful for the crop itself or lead to public health risks. A possible disadvantage of sub-irrigation with waste water is that sub-optimal water quality may speed up clogging of drain tubes used to distribute and supply irrigation water equally over the parcel. This would require more regular and intense maintenance, causing additional costs. To foresee and prevent costs associated with clogging of the drain tubes, we employed experimental research on two soil columns that were supplied with waste water from the Bavaria Beer Brewery. To this purpose, two undisturbed soil columns (1.0 x 0.5 x0.5 m) were collected from an agricultural field by gently pressing a perforated casing made of stainless steel into the soil. After installing perforated bottom plates, a drain, 6 cm in diameter, was installed along the longitudinal axis of each soil column. The soil columns, cased in perforated stainless steel, were installed in containers filled with course-grained sand, and attached to inflow and outflow containers with adjustable water levels. Head differences over and within the soil column and outflow fluxes were measured hourly using pressure sensors. Based on these experimental data and supporting Hydrus 2D simulations we quantify irrigation and clogging rates and translate the results to field scale application. With this poster, we present the method and results of a series of column experiments and seek for discussion about additional experimental research on measures to prevent clogging of sub-irrigation systems when using waste water.

Anthropogenic groundwater nitrate contamination in the Central Valley aquifer system, California, is widespread, with over 40% of domestic wells in some counties exceeding drinking water standards. Sources of groundwater nitrate include leaky municipal wastewater systems, municipal wastewater recharge, onsite wastewater treatment (septic) systems, atmospheric nitrogen deposition, animal farming, application of organic waste materials (sludge, biosolids, animal manure) to agricultural lands, and synthetic fertilizer. At the site or field scale, nitrogen inputs to the landscape are balanced by plant nitrogen uptake and harvest, atmospheric nitrogen losses, surface runoff of nitrogen, soil nitrogen storage changes, and leaching to groundwater. Irrigated agriculture is a dominant player in the Central Valley nitrogen cycle: The largest nitrogen fluxes are synthetic fertilizer and animal manure applications to cropland, crop nitrogen uptake, and groundwater nitrogen losses. We construct a historic field/parcel scale groundwater nitrogen loading model distinguishing urban and residential areas, individual animal farming areas, leaky wastewater lagoons, and approximately 50 different categories of agricultural crops. For non-agricultural landuses, groundwater nitrate loading is based on reported leaching values, animal population, and human population. For cropland, groundwater nitrate loading is computed from mass balance, taking into account diverse and historically changing management practices between different crops. Groundwater nitrate loading is estimated for 1945 to current. Significant increases in groundwater nitrate loading are associated with the expansion of synthetic fertilizer use in the 1950s to 1970s. Nitrate loading from synthetic fertilizer use has stagnated over the past 20 years due to improvements in nutrient use efficiency. However, an unbroken 60 year exponential increase in dairy production until the late 2000s has significantly impacted the nitrogen imbalance and is a significant threat to future groundwater quality in the Central Valley system. The model provides the basis for evaluating future planning scenarios to develop and assess long-term solutions for sustainable groundwater quality management.