Long-Term Suspended Sediment Concentrations and Loads from a Relatively Undisturbed Agroforested Catchment in the Northwest of the Iberian Peninsula

M Rodríguez-Blanco,M Taboada-Castro

doi:10.3390/w10101302

Abstract

The suspended sediment dynamics in small catchments are difficult to estimate accurately because they result from the coupling of complex processes occurring at different scales. In this study, the dynamics of suspended sediment concentrations (SSC) and loads were assessed in an agroforested humid catchment in NW Spain, based on a long-term rainfall, discharge and suspended sediment dataset (12 hydrological years) from high-frequency monitoring. The results highlight the episodic nature of sediment transport in the study area, given that about 78% of SS was exported over 10% of the study period. The SS transport was related to runoff generation and flooding, although sediment availability also played an important role in SS transport. The SS load was mainly driven by high-magnitude rainfall events, while intense rainfall episodes generated high SSC peaks. The mean annual suspended sediment yield was relatively low from a quantitative stand point (10 Mg km−2 y−1); however, during 11% of the monitoring, SS concentrations exceeding the threshold threatened surface water quality (Freshwater Fish Directive 78/659/EEC and Directive 75/440/EEC), mainly during runoff events, indicating the need to adopt management practices in order to reduce or mitigate sediment loss during such episodes.

Highlights

In recent decades, one of the main environmental problems is considered to be soil erosion and the subsequent sediment transfer to streams and oceans, and this is determined by a large number of complex natural processes strongly influenced by human activities, such as agriculture, urbanization, deforestation, etc. [1,2]
The soil erosion processes and the measures taken to reduce soil loss, the effect of land use on sediment yield, suspended sediment (SS) dynamics, reservoir sedimentation and the ecological aspect related to SS transport have been extensively studied in catchments [7,8,9], but determining the degree to which SS yield from catchments can be attributed to soil erosion in a specific area of the catchment is challenging
Given the importance to the preservation of aquatic ecosystems of headwater catchments as a water source for downstream reaches and ecological habitats, this study aims to contribute to a better understanding of fluvial transport of SS from headwater catchments under humid conditions by using a high-temporal scale rainfall, discharge and SS data from a small headwater catchment of the Mero basin, located in NW Spain

Summary

Introduction

One of the main environmental problems is considered to be soil erosion and the subsequent sediment transfer to streams and oceans, and this is determined by a large number of complex natural processes strongly influenced by human activities, such as agriculture, urbanization, deforestation, etc. [1,2]. Soil erosion can be the major factor increasing the SS yield, so in the last few decades, there has been a growing interest in understanding the main drivers of soil erosion and its impact on the degradation and productivity of land and water resources. The soil erosion processes and the measures taken to reduce soil loss, the effect of land use on sediment yield, SS dynamics, reservoir sedimentation and the ecological aspect related to SS transport have been extensively studied in catchments [7,8,9], but determining the degree to which SS yield from catchments can be attributed to soil erosion in a specific area of the catchment is challenging.

Objectives

Methods

Findings

Conclusion