Influence of catchment land cover on stoichiometry and stable isotope compositions of basal resources and macroinvertebrate consumers in headwater streams

Anthropogenic land use affects aquatic landscapes. For example, landscape-level conversion to urban or agricultural land can heavily influence nutrient cycles in headwater streams via increased nutrient loading and altered hydrologic patterns. Recent studies in headwater streams have found that the stoichiometry and stable isotope compositions of basal resources and consumers can vary as a result of landscape-level change. To this end, we examined the stoichiometry and stable isotope compositions (C-13 and N-15) of headwater stream flora and fauna in 16 streams located within forested, agricultural, urban, and mixed (urban, forested, and agricultural) catchments. Our results suggest basal resource stoichiometry varied across streams, with leaf litter being the most variable basal resource. Macroinvertebrate consumers maintained stoichiometric homeostasis across stream groups, but consumer stoichiometry differed across families. Values of C-13 did not vary across stream groups for basal resources; however, consumer C-13 did. Although N-15 did not differ among basal resources across stream groups, macroinvertebrate consumer N-15 differed because of the interaction between stream group and family. Our results show catchment land cover did not predictably alter the stoichiometry or stable isotope compositions of basal resources or consumers in headwater streams. The quality of basal resources in headwater streams could differ across catchments with varying land cover, but it is evident that differences in stoichiometry of basal resources did not lead to differences in stoichiometry of consumers in our study. Given the variability of stable isotope compositions, additional effort should be made to improve our understanding of the landscape factors that might influence isotopic data.