Hydrological heterogeneity in agricultural riparian buffer strips

Abstract

Riparian buffer strips (RBS) may protect surface water and groundwater in agricultural settings, although their effectiveness, observed in field-scale studies, may not extend to a watershed scale. Hydrologically-controlled leaching plots have often shown RBS to be effective at buffering nutrients and pesticides, but uncontrolled field studies have sometimes suggested limited effectiveness. The limited RBS effectiveness may be explained by the spatiotemporal hydrological heterogeneity near non-irrigated fields. This hypothesis was tested in conventional corn and soy fields in the St. Lawrence Lowlands of southern Quebec (Canada), where spring melt brings heavy and rapid runoff, while summer months are hot and dry. One field with a mineral soil (Saint-Rochde-l'Achigan) and another with an organic-rich soil (Boisbriand) were equipped with passive runoff collectors, suction cup lysimeters, and piezometers placed before and after a 3 m-wide RBS, and monitored from 2011 to 2014. Soil topography of the RBS was mapped to a 1 cm vertical precision and a 50 cm sampling grid. On average, surface runoff intersects the RBS perpendicularly, but is subject to substantial local heterogeneity. Groundwater saturates the root zones, but flows little at the time of snowmelt. Groundwater flow is not consistently perpendicular to the RBS, and may reverse, flowing from stream to field under low water flow regimes with stream-aquifer connectivity, thus affecting RBS effectiveness calculations. Groundwater flow direction can be influenced by stratigraphy, local soil hydraulic properties, and historical modification of the agricultural stream beds. Understanding the spatiotemporal heterogeneity of surface and groundwater flows is essential to correctly assess the effectiveness of RBS in intercepting agro-chemical pollution. The implicit assumption that water flows across vegetated RBS, from the field to the stream, should always be verified.

A Regression Model of Stream Water Quality Based on Interactions between Landscape Composition and Riparian Buffer Width in Small Catchments

“…This is a crucial control on hydrological processes at the interface between the ground surface and soil, including the distribution of flowing water by overland flow and shallow underground flow. The continuity of overland flow or alternation with subsurface flow depends on the intensity of rainfall and the locations of relatively high infiltration patches isolated on hillslopes [69][70][71]. In this context, it is expected that high F/A catchments comprise a larger number of infiltration patches, and that subsurface flow dominates in these catchments.…”

Modelling impacts of agricultural practice on flood peaks in upland catchments: An application of the distributed TOPMODEL

“…However, for the Coverdale case, because bare areas were restricted to relatively insensitive parts of the catchment, there would be limited impacts on flood peaks by revegetating those zones. Instead, encouraging vegetation change towards rougher conditions in riparian zones, which is considered to be one of the best regions for management practices of surface water protection in catchments (Henault‐Ethier, Larocque, Perron, Wiseman, & Labrecque, ; Lyons, Trimble, & Paine, ), will yield greater benefits on reducing flood peaks from the catchment. This is because riparian zones are more efficient areas impacting overland flow delivery due to the converging shape of river catchments and the accompanying overland flow concentration (Gao et al, ).…”

Relationships between Soil Nutrients and Plant Diversity in Riparian Woodlands Along the Middle and Lower Reaches of the Yellow River, China

“…In riparian ecosystems, different riparian subzones may control the distribution of riparian plant species diversity. This may arise via differences in groundwater table, groundwater salinity, river discharge, and periodic flooding, among others [4,10,11]. We found that plant species diversity in riparian woodlands along the middle and lower reaches of the Yellow River in China varied with distance from the river.…”

“…On one hand, this suggests that distance from the river may either have no significant impact on the distribution of species inhabiting the riparian zone, or that they have a significant influence on species composition alone [42]. On the other hand, there might be other environmental gradients [9,11,43] or anthropogenic disturbances [14,17,18] that control the characteristics of species evenness or diversity in this ecosystem that were not included in the present study.…”

“…These environmental factors include both natural factors and anthropogenic activities. The natural factors influencing plant species diversity include hydrological characteristics (e.g., river discharge and periodic flooding) [10,11], topographic and geomorphic features [12,13], soil nutrients, and biogeochemistry [9,14]. Furthermore, altitudinal climate shifts, global climate change [6,15], and outbreaks of plant diseases and pests [14] are important as well.…”