Biological soil crusts are microbial communities of bacteria, algae, bryophytes, lichens, and fungi. They are most commonly found in arid and semi-arid desert environments where they colonize soil surfaces in the spaces between vegetation patches, but are also found patchily distributed in some temperate ecosystems. Crusts are an important component of the soil environment because they can augment nutrient cycling, affect runoff and infiltration, promote seed germination, and reduce erosion from wind and water. Biological soil crusts comprised primarily of filamentous green algae have been documented and described across a wide area spanning hundreds of hectares of sand dunes in the Province Lands region at the northern tip of Cape Cod National Seashore. However, the effect of biological soil crusts on soil properties, hydrology, erosion, and plant communities has never been addressed in this unique ecosystem. To investigate the role biological soil crusts have on the hydrodynamics of the dunes and their influence on the seasonally flooded interdunal wetlands, we conducted a greenhouse study in which we constructed soil crust mesocosms and subjected them to simulated rainfall over one growing season. Each mesocosm received different treatments of crust development (crusted versus uncrusted), slope (2% slope versus 30% slope), and rain intensity (convective versus frontal rainfall). The volume of runoff and infiltration from the soil mesocosms was measured after each rain event and summed over the entire growing season.

Results/Conclusions

Non-parametric permutational multiple analysis of variance indicated that infiltration was significantly affected by the interaction of all three treatment variables and the interactions between crust and slope, and between crust and rainfall. However, the presence of crust alone did not have a significant effect on water infiltration. Runoff was significantly affected by all three treatment variables and their interactions. Pairwise comparisons indicated that crust and slope treatments were primarily responsible for differences in runoff, whereas the rainfall intensity treatment did not contribute significantly to the model. Our results suggest that under certain conditions, dunes with biological soil crusts may influence water inputs to seasonal wetlands in the Province Lands by resisting immediate infiltration at the dune surface, increasing runoff over the dune surface, and possibly redirecting rainfall to low-lying areas. In doing so, these biological soil crusts may contribute to the water supply of interdunal wetlands that are critical habitat for many species, including the state endangered eastern spadefoot toad and several rare plant species.