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Multispectral modelling of 114 tropical Andean lakes in Southern Ecuador was implemented using observations of the maximum depth (Zmax). Five machine learning methods (MLMs), namely the multiple linear regression model (MLRM), generalised additive model (GAM), generalised linear model (GLM), multivariate adaptive regression splines (MARS), and random forest (RF), were applied on a LANDSAT 8 mosaic. Within the scope of a split-sample (SS) evaluation test, for each of the MLMs, a single model was developed for 70% (i.e., 80) of the studied lakes. Statistical measures and graphical inspection were used in the evaluation tests. An analysis of the absolute value of the model residuals (|res|) revealed that the MARS method outperformed the other MLMs. Nevertheless, a |res| > 10 m was observed for approximately 10% of the lakes. The worst predictions were produced by the GLM. These findings were confirmed in the model validation phase (SS test). With the exception of the GLM, the MLMs correctly predicted whether a lake was shallow or deep in more than 80% of the cases. In a more stringent multi-site (MS) test, the performance of the five Zmax models was assessed in predicting the bathymetry of 11,636 pixels that were not considered when fitting the models. Once more, MARS outperformed the other MLMs. However, a |res| > 10 m for 20% of the pixels was observed. Nevertheless, the quality of the predictions may still be regarded as acceptable for management purposes. Promising multispectral bathymetric predictions could be obtained, even with only a limited number of observations. The evaluation tests used in this pioneering study could be easily replicated elsewhere. [ABSTRACT FROM AUTHOR]

In this study, we explore the utility of stable isotopes of water (δ2H and δ18O) as integrative proxies for evaporative condition in high-mountain tropical lakes using a set of small Ecuadorian lakes in the Cajas National Park. Specifically, we (1) characterize the variability of stable water isotopic composition across several lakes of varying size and depth and (2) determine the evaporation as a fraction of inflow using stable isotopes of water for these lakes. We have used the Hydrocalculator tool for estimation of the evaporation to inflow (E/I) ratio. Results indicated that larger lakes have lower seasonal variability in isotopic composition across their depth compared with the smaller lakes. Further, there was clear seasonal variation across the monthly E/I ratios estimated in several lakes, indicating that evaporation likely plays some (albeit limited) role in the water level variability experienced within a year. [ABSTRACT FROM AUTHOR]

Very little is known on high mountain tropical lakes of South America. Thus, the main motivation of this research was obtaining base bathymetric data of 119 tropical lakes of the Cajas National Park (CNP), Ecuador, that could be used in future geomorphological studies. Eleven interpolation methods were applied with the intention of selecting the best one for processing the scattered observations that were collected with a low-cost fishing echo-sounder. A split-sample (SS) test was used and repeated several times considering different proportions of available observations, selected randomly, for training of the interpolation methods and accuracy evaluation of the respective products. This accuracy was assessed through the use of empirical exceedance probability distributions of the mean absolute error (MAE). A single best interpolation method could not be identified. Instead, the study suggested six better-performing methods, including the complex methods Kriging (ordinary), minimum curvature (spline), multiquadric, and TIN with linear interpolation but also the much simpler methods natural neighbour and nearest neighbour. A sensitivity analysis (SA), considering several data error magnitudes, confirmed this. This advocated that sophisticated interpolation methods do not always produce the best products as geomorphological characteristics of the study site(s) together with observation data characteristics are likely to play important roles in their performance. As such, this type of assessment should be carried out in any terrestrial mapping of bathymetry that is based on the interpolation of scattered observations. Upon the analysis of the relative hypsometric curves of the 119 study lakes, they were classified into three average form categories: convex, concave, and mixed. The separated accuracy analysis of these three groups of lakes did not help in identifying a single best method. Finally, the interpolated bathymetries of 114 of the study lakes were incorporated into the best DEM of the study site by equalising their elevation reference systems. It is believed that the resulting enhanced DEM could be a very useful tool for a more appropriate management of these very beautiful but fragile high mountain tropical lakes. [ABSTRACT FROM AUTHOR]