A simple approach to the evaluation of the actual water renewal time of natural stratified lakes

Abstract

In natural lakes, where thermal stratification hinders complete mixing, the theoretical value T 0 of the water renewal time provides a low-order approximation to the time T 37 when 37% of the original water is still present within the lake; this time could be operatively regarded as the actual value of the water renewal time. In this paper, we present a simple nonparametric model to estimate the age distribution of water within stratified natural lakes, taking into account fundamental aspects of its mass exchange and thermal evolution. This distribution provides a straightforward way to compute T 37 . The model is presented as a system of ordinary differential equations along with a MATLAB script for its numerical solution, so that it can be easily applied to lakes where a minimum of limnological data are available, without the need of extensive meteorological data set and modeling expertise that an hydrodynamic model would require to the same purpose. The case of a deep oligomictic Italian prealpine lake (Lake Iseo) is considered: after a positive comparison with the results obtained using a 1-D lake hydrodynamic model, the reiterated application to the available time series allows to approximate the water age probability distribution. This distribution is used to compute the actual value of the water renewal time, that resulted T 37 5 1.6T 0 .

Spatiotemporal Dynamics of Submerged Aquatic Vegetation in a Deep Lake from Sentinel-2 Data

“…It is interesting to observe that the investigated area is located just in front of an active combined sewer weir (CSW) whose overflows significantly contribute to the nutrient pollution of this littoral area [60]. The future comparative analysis of the CSW overflows and of the SAV extension will certainly provide important insights to the comprehension of the SAV dynamics.…”

A modeling approach to identify the effective forcing exerted by wind on a prealpine lake surrounded by a complex topography

“…The main tributary of the lake is the river Oglio, whose waters enter the northern part of the lake mainly as interflow [Hogg et al, 2013;Pilotti et al, 2014a], with a temperature and discharge regime that affects both the thermal structure of the lake [Valerio et al, 2015] and its water renewal time [Pilotti et al, 2014a[Pilotti et al, , 2014b. Considering a volume of the lake of about 7.9 3 10 9 m 3 and the average inflow of 55 m 3 /s, the theoretical renewal time of the lake is about 4.5 years.…”

On the Use of StorAge Selection Functions to Assess Time‐Variant Travel Times in Lakes

“…Limited vertical mixing in vegetation‐affected lakes (e.g., Figure b) may result in older water near the surface for evaporation and more uniform selection of evaporation age. However, a stratified lake (e.g., Figure c) may depict younger evaporated water since the younger epilimnion water may not mix well with the older hypolimnion water (Castellano et al, ; Pilotti et al, ). Furthermore, if stratification was substantial then the actual lake residence time should be longer than the HRT (Ambrosetti et al, ).…”