About me

New paper is out: R. Ladwig, L. Rock, and H. Dugan, Impact of salinization on lake stratification and spring mixing, Limnology & Oceanography Letters (2021). Check it out here.

Welcome, my name is Robert. I am a limnologist with a keen interest in aquatic ecosystem modeling, physical limnology, aquatic ecology and theory-guided data science.

I am a Postdoctoral Research Fellow at the Center for Limnology at the University of Wisconsin-Madison advised by Hilary Dugan and Paul Hanson working on simulating aquatic ecosystems using GLM-AED2. My research focuses on how physical and biogeochemical process can influence an aquatic ecosystem’s biology and ecosystem function by taking advantage of cutting-edge data-intensive and computationally demanding techniques. My current research focuses on three main aspects: understanding the impact of drivers on long-term aquatic ecosystem dynamics, developing open-access scientific software and tools, and improving ecological modeling code and algorithms built on state-of-the-art Biological theory.

Do physical interactions (mixing, morphology) govern water quality, and, if so, are biological drivers only important over specific time scales or can they become the main causal drivers after the occurrence of disturbances? Then, how can physical, biological, and physiological disturbances alter aquatic ecosystem phenology, biodiversity and functioning?

To find (some) answers to these broad questions, I’m applying aquatic ecosystem models to long-term monitoring data with the intention to identify causal relationships. My current research interests in a nutshell:

  • lake phenology (i.e., stratification and ice dynamics, lake metabolism, phytoplankton succession):
    • long-term dissolved oxygen depletion and metabolism dynamics in lakes (anoxia in Lake Mendota, metalimnetic oxygen minimum)
    • investigating the impact of climate change on future lake mixing dynamics (Lake Tegel, Global ensemble analysis)
    • integrating stochastic processes into deterministic models, e.g. to improve simulations of phytoplankton bloom dynamics
  • sustainable water resources management:
  • aquatic ecosystem modeling:

I aim to make tools that enable transparency into scientific design, analysis, and reporting, such that future researchers – and curious individuals in general – can access and reproduce others’ work. Here, I’m advocating for open access and open science paradigms and ideas in general! Science is and has always been international, interdisciplinary and collaborative. To collaborate more efficiently and ensure reproducibility, it’s paramount to implement the principles of open data and open science. After all, sharing data is fun, right? Of course, no one can learn all tools to be a good open scientist, but through collaboration we all might be able to round out our open science toolbox. It’s also important to actively communicate results to the public and stakeholders, because - of course - we do science for the benefit of all. In the end, we want people from all over the world to use our data, work with our code and apply our models to their systems. In the best case, together. To achieve this, I am especially commited to provide open-source lake modeling code in R that (a) can be adapted and modified for other research questions and (b) highlights how mathematical models work. Below you see the visualization of Lake Mendota’s (Wisconsin, USA) simulated vertical water temperature profiles over the course of one year. This simulation was done in four steps: (i) calculate vertical eddy diffusivities for vertical exchange, (ii) simulate vertical diffusion using a central difference scheme and heat exchange between atmosphere and surface water layer, (iii) estimate mixing depth at which (internal) potential energy is higher than (external) kinetic energy by wind and mix water column up to that depth, and (iv) solve vertical density instabilities by averaging. All code and driver data can be accessed here.

I did my PhD work at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB) in Berlin, Germany, supervised by Michael Hupfer and Reinhard Hinkelmann. Here, I studied the impact of multiple stressors on urban lakes using field sampling, monitoring and numerical modeling (e.g. vertical 1D GLM-AED2, vertical 1D FLake, depth-averaged 2D open TELEMAC-MASCARET).

Here is an overview of some of my software projects:

Fresh modeling Paradigms for Freshwater Phytoplankton (FP-FP): Interested in working together on lake modeling tools? I’m currently in the process of writing routines in phyton for vertical transport and couled reactive processes. If you’d like to collaborate on that, please take a look at the pythonLakeModeling repository and contact me (or feel free to submit a pull request with improvements!). The goal for this project is to build simple models for numerical experiments. Most often scientists have awesome ideas but the prospect of changing source code in Fortran kills most curiosity. Therefore, providing example python and R scripts for lake modeling can kick-start a wave of novel research projects. Hopefully.


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