A patch use behaviour approach to model leaf litter breakdown in aquatic environment

We present a mechanistic model of reed leaves decomposition in a Mediterranean coastal lagoon (Lake Alimini Grande, Puglia, Italy). Our aim is to assess the importance of the heterogeneity of leaf detritus and of the different rules of patch colonization by macroinvertebrates on reed detritus processing. To this end, we propose two versions of the model (homogeneous and heterogeneous detritus model) where the microflora is supposed to complete all the life cycle on a leaf patch, while the macroinvertebrates move towards or left the patch according to patch attractiveness. The threshold of patch attractiveness and the number of colonizers are the behavioural sources of variation in the model. The effects of the behaviour of invertebrate consumers on detritus mass loss are tested by a multi-factorial ANOVA design. A field study on reed leaf decomposition in Lake Alimini Grande is used as reference to set a number of biological parameters. Simulated leaf detritus loses weight according to a negative exponential model. The comparison between simulated and experimental data selects the heterogeneous detritus model for describing reed leaf decomposition. Behaviourally–related characteristics of invertebrate consumers also affect decomposition rates, which are directly related to invertebrate abundance and inversely to resource attractiveness threshold. The model results suggest that reed leaf decomposition in Lake Alimini Grande is probably driven by microbial activity.