Estimation of lacustrine groundwater discharge using heat as a tracer and vertical hydraulic gradients – a comparison

S Rudnick,J Lewandowski,G Nützmann

doi:10.5194/piahs-365-79-2015

Abstract

Abstract. Lacustrine groundwater discharge (LGD) can play a major role in water and nutrient balances of lakes. Unfortunately, studies often neglect this input path due to methodological difficulties in the determination. In a previous study we described a method which allows the estimation of LGD and groundwater recharge using hydraulic head data and groundwater net balances based on meteorological data. The aim of this study is to compare these results with discharge rates estimated by inverse modelling of heat transport using temperature profiles measured in lake bed sediments. We were able to show a correlation between the fluxes obtained with the different methods, although the time scales of the methods differ substantially. As a consequence, we conclude that the use of hydraulic head data and meteorologically-based groundwater net balances to estimate LGD is limited to time scales similar to the calibration period.

Highlights

Lakes are an important part of terrestrial ecosystems and provide essential ecosystem services
Studies focusing on nutrient balances of lakes often neglect input via groundwater, which can hardly be quantified, some studies showed that lacustrine groundwater discharge (LGD) can play a significant role in the nutrient balance of lakes (e.g. Hayashi and Rosenberry 2002, Nakayama and Watanabe 2008)
As we could not find any quantitative description of the degree of dependency of clogging on the gradients we introduced a clogging factor as a logistic growth function of the vertical hydraulic gradients (VHGs)

Summary

Introduction

Lakes are an important part of terrestrial ecosystems and provide essential ecosystem services. One challenge in terms of adequate management is the identification and quantification of the nutrient input paths. Sacks et al (1992) used hydraulic head data to divide the shoreline of the studied lake into areas of exfiltration and infiltration, and used this for numerical modelling. Ommen et al (2012) used a combination of hydraulic gradients between piezometers and a lake, in combination with seepage meters (Rosenberry and LaBaugh 2008), to assess the nutrient budget of the lake. The use of natural tracers is widely spread and has been successfully applied in many studies. Chemical gradients of natural solutes such as chloride can be used to estimate fluxes (Hurwitz et al 2000), as well as temperature profiles in the sediment (Schmidt et al 2006, Meinikmann et al 2013)

Objectives

Results

Conclusion