Landscape configuration alters spatial arrangement of terrestrial-aquatic subsidies in headwater streams
Freshwater ecosystems depend on surrounding terrestrial landscape for resources. Most important are terrestrial leaf litter subsidies, which differ depending on land use. We lack a good understanding of the variation of these inputs across spatial scales.
We sought to determine: (1) the relative importance of local versus catchment-level forestation for benthic leaf litter biomass in streams, (2) how landscape configuration alters these relationships, and (3) how land use affects the quality and diversity of leaf litter subsidies.
We measured biomass and identity of benthic leaf litter in 121 reaches in 10 independent catchments seasonally over the course of a year. We assessed direct and indirect effects of forestation, reach position, and seasonality on leaf litter biomass using structural equation models, and assessed how leaf litter diversity varied with land use.
In catchments with forested headwaters, the degree of forestation and reach position in the catchment influenced benthic leaf litter biomass indirectly through local reach-scale forestation. In catchments where forest was only located downstream, or with minimal forest, none of these factors influenced reach-level benthic leaf litter. Leaf litter diversity peaked in fall in all land use types, but was generally lowest in forested reaches.
Not only habitat amount, but its location relative to other habitats is important for ecosystem function in the context of cross-ecosystem material flows. Here, lack of upstream forest altered spatial patterns of leaf litter storage. Studies with high spatiotemporal resolution may further reveal effects of landscape configuration on other ecosystems.
KeywordsLand use Leaf litter Meta-ecosystem Resource subsidies River network Terrestrial-aquatic linkages
The authors sincerely thank the Kanton Thurgau Office of the Environment facilitating access to sampling sites, and all landowners whose property we crossed. We are also grateful to Pravin Ganesanandamoorthy, Elvira Mächler, and Simon Flückiger for help with fieldwork and laboratory work, and Katharina Kaelin and Rosi Sieber for assistance with parts of the GIS analysis. We thank two anonymous reviewers for their helpful comments. This project was funded by Swiss National Science Foundation Grants PP00P3_150698 and PP00P3_179089.
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