An increasing number of streams are becoming intermittent due to global warming and water abstraction. An important ecosystem service likely affected by this increasing intermittency is the export of resources rich in omega-3 polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA), from aquatic to terrestrial systems. Here, we investigated how flow intermittency affected EPA transfer to riparian spiders along 9 headwater streams of an alpine catchment (Val Roseg, Switzerland) with different degrees of intermittency. We used fatty acid analysis to test if there were differences in fatty acid content in spiders sampled along streams varying in degree of intermittency. In addition, we used compound-specific isotope analysis (²H-CSIA) to determine the origin of different fatty acids present in spiders. We found a higher content of the omega-3 fatty acids EPA, stearidonic acid (SDA) and docosahexaenoic acid (DHA), but a lower α-linolenic acid (ALA) content in spiders collected along perennial streams compared to periodically intermittent streams. However, spiders from seasonally drying streams showed similar fatty acid mass fractions as spiders from perennial streams. d²H values indicated that fatty acid sources also differed between streams varying in intermittency. Our results suggest that stream intermittency likely affects subsidy transfers from aquatic to riparian ecosystems, indicating far-reaching consequences for riparian communities especially in resource poor alpine environments, but also lower elevation fluvial networks.

Primary Presenter: Carmen Kowarik, eawag (carmen.kowarik@eawag.ch)

Authors:

Carmen Kowarik, eawag  (carmen.kowarik@eawag.ch)

Pierre Chanut, eawag  (pierre.chanut@eawag.ch)

Matthias Pilecky, Wasser Cluster Lunz  (Matthias.Pilecky@donau-uni.ac.at)

Christopher Robinson, eawag  (christopher.robinson@eawag.ch)