The Effect of Land Use on Isotope Signatures of the Detritus Pathway in an Urban Wetland System

Abstract

Land use may be the anthropogenic alteration with the greatest effect on ecosystem dynamics. In aquatic systems, food web pathways are highly influenced by the land use of surrounding areas, leading to different responses to the role of detritus in aquatic food web pathways. We studied the influence of land use on benthic isotopic signatures in Xochimilco, a shallow, tropical high-elevation wetland impacted by a mix of rural and urban activities, such as agriculture, housing, tourism and mixed zones. We obtained carbon (δ13C) and nitrogen (δ15N) isotope signatures in benthic organic matter (BOM), suspended organic matter (SOM) and Chironomus sp. The results for δ15N values split Xochimilco into two regions, dominated by urban or rural activities. The values of the δ13C signatures showed several differences among the zones, but without a clear pattern related to any land use. Spatial analyses showed high heterogeneity within the canals for SOM and chironomid isotope signatures, whereas the sediment values were more homogenous. This can be explained by the contribution of SOM to chironomid signatures (>96 %) calculated using mixing models. These findings suggest that land uses have different influences on carbon and nitrogen isotope signatures, affecting benthic food web pathways.