Assessing the impact of changes in landuse and management practices on the diffuse pollution and retention of nitrate in a riparian floodplain.

Centre for Sustainable Water Management, Lancaster Environment Centre, Lancaster, United Kingdom.
Science of The Total Environment (Impact Factor: 3.16). 02/2008; 389(1):149-64. DOI: 10.1016/j.scitotenv.2007.08.057
Source: PubMed

ABSTRACT In many European lowland rivers and riparian floodplains diffuse nutrient pollution is causing a major risk for the surface waters and groundwater to not achieve a good status as demanded by the European Water Framework Directive. In order to delimit the impact of diffuse nutrient pollution substantial and often controversial changes in landuse and management are under discussion. In this study we investigate the impact of two complex scenarios considering changes in landuse and land management practices on the nitrate loads of a typical lowland stream and the riparian groundwater in the North German Plains. Therefore the impacts of both scenarios on the nitrate dynamics, the attenuation efficiency and the nitrate exchange between groundwater and surface water were investigated for a 998.1 km(2) riparian floodplain of the Lower and Central Havel River and compared with the current conditions. Both scenarios target a substantial improvement of the ecological conditions and the water quality in the research area but promote different typical riparian landscape functions and consider a different grade of economical and legal feasibility of the proposed measures. Scenario 1 focuses on the optimisation of conservation measures for all natural resources of the riparian floodplain, scenario 2 considers measures in order to restore a good status of the water bodies mainly. The IWAN model was setup for the simulation of water balance and nitrate dynamics of the floodplain for a perennial simulation period of the current landuse and management conditions and of the scenario assumptions. The proposed landuse and management changes result in reduced rates of nitrate leaching from the root zone into the riparian groundwater (85% for scenario 1, 43% for scenario 2). The net contributions of nitrate from the floodplain can be reduced substantially for both scenarios. In case of scenario 2 a decrease by 70% can be obtained. For scenario 1 the nitrate exfiltration rates to the river drop even below the infiltration rates from the river, the riparian floodplain in that scenario represents a net sink for river derived nitrate. As the nitrate contributions from the investigated riparian floodplain represent only a small proportion of the total nitrate loads within the river (1% p.a.) the overall impact of the scenario measures on the nitrate loads at the river outlet remains small. However, during the ecologically most sensitive summer periods under current conditions nitrate contributions from the riparian groundwater of the Lower and Central Havel River (which covers only 5% of the area of the Havel catchment) represent more than 20% of the river loads. By the implementation of the investigated landuse changes within the research area the groundwater derived nitrate contributions could be halved to only 10% during summer baseflow conditions.

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    ABSTRACT: The demand for foods in central Chile is increasing and arable land is expanding rapidly onto floodplain soils, which are being cleared for maize cultivation. After harvest, a significant amount of residual nitrogen (N) may be still present in the soil in autumn–winter, when a high risk of nitrate leaching (NL) is expected due to occasional flooding events. Determining nitrate (NO3−) movement through the vadose zone is essential for studying the impact of agricultural practices on surface water quality. This study focused on understanding the processes of NO3− leaching in a floodplain environment and compared the effectiveness of four different methods: soil coring (T0), an observation well (T1), ceramic suction cup lysimeters (T2) and a capillary lysimeter (FullStop™ wetting front detector) (T3) for monitoring NL using an infiltration cylinder to simulate the conditions generated during flush flooding events during autumn–winter season in a typical coarse-textured alluvial floodplain soil. The comparison showed that T0 and T3 can be used for monitoring NL during flush flooding events during autumn–winter season in stratified coarse-textured floodplain soils, whereas T1 and T2 are not appropriate for these site conditions. A correlation was found between NO3 and soluble salt (Cl− concentration and EC) only in the first measurements after the dry summer period. The results of this study suggest that most of the surplus N could be leached by excessive irrigation during the crop growing season (spring–summer), while a lower amount of residual N may still be present in the soil in autumn–winter available to be lost by NL during flush flooding events. Overall the two monitored flushing events could have leached around 6% of the total NO3–N load. There was no significant effect of sampler devices on saturated hydraulic conductivity.
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    ABSTRACT: With current trends of converting grasslands to row crop agriculture in vulnerable areas, there is a critical need to evaluate the effects of land use on groundwater quality in large river floodplain systems. In this study, groundwater hydrology and nutrient dynamics associated with three land cover types (grassland, floodplain forest and cropland) were assessed at the Cedar River floodplain in southeastern Iowa. The cropland site consisted of newly-converted grassland, done specifically for our study. Our objectives were to evaluate spatial and temporal variations in groundwater hydrology and quality, and quantify changes in groundwater quality following land conversion from grassland to row crop in a floodplain. We installed five shallow and one deep monitoring wells in each of the three land cover types and recorded water levels and quality over a three year period. Crop rotations included soybeans in year 1, corn in year 2 and fallow with cover crops during year 3 due to river flooding. Water table levels behaved nearly identically among the sites but during the second and third years of our study, NO3-N concentrations in shallow floodplain groundwater beneath the cropped site increased from 0.5 mg/l to more than 25 mg/l (maximum of 70 mg/l). The increase in concentration was primarily associated with application of liquid N during June of the second year (corn rotation), although site flooding may have exacerbated NO3-N leaching. Geophysical investigation revealed differences in ground conductivity among the land cover sites that related significantly to variations in groundwater quality. Study results provide much-needed information on the effects of different land covers on floodplain groundwater and point to challenges ahead for meeting nutrient reduction goals if row crop land use expands into floodplains. Copyright © 2015 Elsevier Ltd. All rights reserved.

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