Linking soil- and stream-water chemistry based on a Riparian Flow-Concentration Integration Model

J Seibert,T Grabs,K Bishop,H Laudon,M Winterdahl,S Köhler

doi:10.5194/hess-13-2287-2009

Abstract

Abstract. The riparian zone, the last few metres of soil through which water flows before entering a gaining stream, has been identified as a first order control on key aspects of stream water chemistry dynamics. We propose that the distribution of lateral flow of water across the vertical profile of soil water chemistry in the riparian zone provides a conceptual explanation of how this control functions in catchments where matrix flow predominates. This paper presents a mathematical implementation of this concept as well as the model assumptions. We also present an analytical solution, which provides a physical basis for the commonly used power-law flow-load equation. This approach quantifies the concept of riparian control on stream-water chemistry providing a basis for testing the concept of riparian control. By backward calculation of soil-water-chemistry profiles, and comparing those with observed profiles we demonstrate that the simple juxtaposition of the vertical profiles of water flux and soil water chemistry provides a plausible explanation for observed variations in stream water chemistry of several major stream components such as Total Organic Carbon (TOC), magnesium, calcium and chloride. The "static" implementation of the model structure presented here provides a basis for further development to account for seasonal influences and hydrological hysteresis in the representation of hyporheic, riparian, and hillslope processes.

Highlights

In the effort to understand how stream water is influenced by catchment inputs, the riparian zone (RZ) has been identified as a key part of the catchment, especially when considering the short term dynamics of water chemistry which are of great ecological importance (Buffam et al, 2001; Fiebig et al, 1990; Gregory et al, 1991; Hill, 2000; Smart et al, 2001)
We propose that the distribution of lateral flow of water across the vertical profile of soil water chemistry in the riparian zone provides a conceptual explanation of how this control functions in catchments where matrix flow predominates
By backward calculation of soil-water-chemistry profiles, and comparing those with observed profiles we demonstrate that the simple juxtaposition of the vertical profiles of water flux and soil water chemistry provides a plausible explanation for observed variations in stream water chemistry of several major stream components such as Total Organic Carbon (TOC), magnesium, calcium and chloride

Summary

Introduction

In the effort to understand how stream water is influenced by catchment inputs, the riparian zone (RZ) has been identified as a key part of the catchment, especially when considering the short term dynamics of water chemistry which are of great ecological importance (Buffam et al, 2001; Fiebig et al, 1990; Gregory et al, 1991; Hill, 2000; Smart et al, 2001). The temporal variation of flow pathways through the riparian zone associated with changing groundwater levels connects different combinations of these solute sources in the RZ soil profile to the stream. The dynamics of stream water chemistry reflect the chemical “fingerprint” of the combination of chemostatlike soil solute sources in the RZ that connect to the stream at a given flow rate. The RZ is a dominant control in first order catchments, which in turn are crucial for our understanding of water chemistry dynamics in larger aquatic systems (Bishop et al, 2008)

Methods

Results

Discussion

Conclusion