RELATIONSHIP BETWEEN SEMI-AQUATIC MAMMAL OCCUPANCY AND PARTICULATE CARBON, NITROGEN, AND PHOSPHORUS DYNAMICS IN FRESHWATER ECOSYSTEMS

Author

Madison H. Stokoski, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2025

Degree Name

Master of Science

Department

Zoology

First Advisor

Narr, Charlotte

Abstract

Semi-aquatic mammals such as beavers (Castor canadensis) and muskrats (Ondatra zibethicus) can influence carbon (C), nitrogen (N) and phosphorus (P) dynamics in freshwater systems. While the effect of beavers, in particular, are typically attributed to their dam and lodge building behaviors, these animals do not always build these structures. It’s possible that other, non-damming behaviors (e.g. foraging and burrowing) may influence the availability of nutrients as well. To assess this possibility, we surveyed 54 lentic and lotic waterbodies across Southern Illinois and investigated the possibility that beaver and muskrat occupancy improved our ability to explain variation in nutrient availability across these sites. We created occupancy models based on repeated sign surveys and camera trap data, and we used these to relate mammal presence, land cover and physicochemical gradients to log-transformed particulate C, N, P and their molar ratios (C:N, C:P, N:P). We found that wetland cover was correlated with an increase in particulate concentrations of C and N, whereas forest cover was correlated with a decrease of particulate concentrations of C, N, and P. Lentic sites consistently contain higher(include specific nutrients) than lotic sites. After accounting for these landscape controls, increasing beaver occupancy probability was significantly associated with lower particulate C:N, while C:P and N:P were unaffected by either mammal and only negatively impacted by site type. Our results demonstrate that even subtle beaver activity can affect particulate stoichiometry by enriching N relative to C, potentially enhancing downstream food quality and partially offsetting nutrient signals of landcover. Semi-aquatic mammal occupancy may be valuable predictors of nutrient cycling and their under-appreciated roles as biogeochemical engineers.