Does the invasive plant, Impatiens glandulifera, promote soil erosion along the riparian zone? An investigation on a small watercourse in northwest Switzerland
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The invasive plant, Impatiens glandulifera (common English name: Himalayan Balsam), is now found in many river catchments in most European countries. Its preference for damp, nutrient-rich soils, along with its intolerance to cold weather and rapid dieback, has implicated it in promoting soil erosion along the riparian zone. Despite the implication, its influence on the sediment dynamics of river systems remains unconfirmed. This communication reports the preliminary findings of ongoing work to investigate a possible link between I. glandulifera and accelerated erosion rates in inland river systems.
Materials and methods
Erosion pins, a micro-profile bridge, and a digital caliper were employed to measure changes in the soil surface profile (SSP) at six separate locations, each contaminated with I. glandulifera, along the riparian zone of a small watercourse in northwest Switzerland. Changes in SSP were also measured at an identical number of nearby locations supporting natural vegetation, in order to establish baseline erosion conditions. Soil surface profiles at all 12 locations were re-measured on seven separate occasions, from October 2012 to May 2013. This covers the time before dieback occurred to the germination and seasonal regrowth of new plants.
Results and discussion
A total of 720 individual SSP measurements were recorded during the above monitoring period. Increasingly negative values relative to initial values were documented at most transects, indicating a net reduction in soil surface elevations. This is interpreted as evidence of the removal (i.e., erosion) of surface material. Paired samples statistical analysis of the data indicate that erosion from contaminated sites was significantly greater than erosion from topographically comparable reference sites (t =−5.758; P < 0.05; N = 359) supporting natural vegetation.
The results provide tentative yet compelling evidence that I. glandulifera promotes soil erosion along the riparian zone of the watercourse investigated. Given the unrelenting spread of this notoriously invasive plant throughout inland river systems in many countries, the likelihood of greater quantities of nutrient-rich sediment entering into aquatic environments may steadily reduce water quality in all affected catchments. An absence of effective control measures capable of halting or even slowing its rate of invasion may make it increasingly difficult for affected European Union member states to meet and then maintain key water quality standards set by the Water Framework Directive (WFD) when fully implemented in 2015.
KeywordsImpatiens glandulifera (Himalayan Balsam) Erosion pins Invasive plant Micro-profile bridge Riparian zone Soil surface profile
This investigation was funded by the Physical Geography and Environmental Change Research Group, Department of Environmental Sciences, University of Basel, Switzerland. We are grateful to the ‘Bürgergemeinde’ (Community Mayor of Common Lands) from the town of Brislach, in Canton Basel-Landschaft, for granting ongoing access to the study site. Thanks are also extended to Dr. W. Fister for his help and advice, to S. Kuonen for producing Fig. 2, to D. Hügli, S. Tresch, and R. Gisin, for their collective assistance in making the study possible, and to three anonymous reviewers for their extremely helpful comments and suggestions, all of which have served to strengthen the paper.
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