Mammalian bioturbation amplifies rates of both, hillslope sediment erosion and accumulation, in coastal Chile
Abstract. Soil bioturbation activity affects soil texture, bulk density, soil water content and redistribution of nutrients. All of these parameters influences sediment redistribution, which shapes the earth surface. Hence it is important to include bioturbation into erosion models. However, up to present, the inclusion of bioturbation into erosion models was limited. This is because to realistically include bioturbation into the modelling, the interplay between bioturbation, sediment redistribution and environmental parameters is not understood.
Here, we included bioturbation into a soil erosion model and interpreted the impacts of bioturbation on sediment redistribution. To do this, we measured the needed soil properties and location of burrows created by bioturbating animals in four research sites located along the Chilean climate gradient. Then, we parametrized a semi-empirical erosion model by applying machine learning algorithms to upscale soil properties and burrow distribution. We ran the model for a time period of 6 years under two conditions: With and without bioturbation. We validated the model using several sediment fences in the field. We estimated the modelled sediment redistribution and surface runoff in all climate zones. Lastly, we identified environmental parameters determining the positive or negative impact of bioturbation on sediment redistribution.
We found that the model with integrated bioturbation performed much better (R2 = 0.71, RMSE = 0.63) than the model without integrated bioturbation (R2 = 0.17, RMSE = 1.18), meaning that model runs which considered bioturbation predicted the sediment redistribution more realistically. Furthermore, bioturbation increased sediment redistribution in all but the humid climate zone, especially in the Mediterranean zone. The quantity of sediment redistributed due to bioturbation was reliant on an interplay between elevation, slope, surface roughness and sink connectivity. Overall, bioturbation enhances sediment erosion in areas where more erosion is expected, and enhances sediment accumulation in areas which are more prone to accumulate sediment. In other words, considering bioturbation when studying earth surface evolution means an amplification of existing tendencies in sediment redistribution, and leads to a faster hillslope relief equalisation.
Paulina Grigusova et al.
Status: final response (author comments only)
- RC1: 'Comment on egusphere-2023-84', Emmanuel Gabet, 02 Mar 2023
- RC2: 'Comment on egusphere-2023-84', Anonymous Referee #2, 08 Mar 2023
Paulina Grigusova et al.
Paulina Grigusova et al.
Viewed (geographical distribution)
The authors clearly did a lot of work both in terms of field measurements and modeling. The results and the framing of the manuscript of the manuscript, however, left me feeling a bit underwhelmed. The main conclusions seem to be that (1) bioturbation increases rates of sediment redistribution, (2) that the rate of sediment transport by bioturbation increases with slope, and (3) models that incorporate bioturbation will yield better results than models that don't when applied to landscapes where bioturbation is an important process. First, conclusions (1) and (2) are not novel - both of these have been know for a long time and have already been demonstrated in previous studies. Second, conclusion (3) seems trivial - of course models that incorporate the main sediment transport processes will be more accurate than those that don't. I would encourage the authors, therefore, to identify what is truly new and unique about their study.
Also, the framing of the project felt a bit misleading. In the introduction, the authors argue that few models have accounted for bioturbation and that, when they have, the effects of bioturbation are 'hard-coded' into them. First of all, this is not accurate, and I provide examples of models where the effects of bioturbation are emergent properties. Second, the model presented by the authors has several instances where processes related to bioturbation are hard-coded into the model and do not arise naturally from more fundamental processes like competition, access to resources, compaction, etc. Therefore, I would recommend that the authors become more familiar with other models that have incorporated bioturbation and, also, not oversell their own model.
Not enough information was provided regarding the model. I understand that the model is described elsewhere, but individual manuscripts must stand on their own. For example, the authors report that, at some sites, including bioturbation in the model increases runoff rates but decreases in others; however, no explanation was provided describing why bioturbation would affect runoff rates and, without a description of how the model works, it's impossible for a reader to evaluate or even understand this result. I think that the most interesting result of this study is how well the modeled sediment flux matches the measured sediment flux, but without a good description of the model, that result was difficult to evaluate. Also, given the importance of that comparison, I would recommend putting Figure A3 into the main text.
Finally, I would recommend cutting down on the number of figures. There were figures presented as results that were just a simple function of how the model was parameterized (eg., Fig. A5) or figures that didn't seem to be relevant (eg, Fig. A6).