Påverkar jordbruk flödet av akvatiska insekter till land?
Effekter av jordbruk på akvatiskt tillflöde till land vid norrländska bäckar
Streams and riparian zone are closely linked by reciprocal flows of energy and nutrients. A large part of the transportation from water to land is in form of emerged aquatic insects. Conversion of land from forest to agriculture can greatly affect aquatic ecosystems, and due to the close link, also affect the adjacent terrestral zone. Investigating how the presence of agriculture in the surrounding area affects amounts of emergent aquatic insects gives an indication on how agriculture, in turn, may affect the terrestral enviroment. The study was preformed alongside ten streams in northern Sweden; five in landscape transformed by agriculture and five in undisturbed forest areas. Further two types of traps, deposition traps and window traps, were used and aquatic prey subsidy was calculated from the deposition traps. The results show that more insects emerge from agricultural streams than from undisturbed streams. This was, however, not reflected in the biomass. The most abundant group was Nematocera, followed by Plecoptera and Trichoptera. While Nematocera showed a preference for agricultural sites, Trichoptera did the opposite, and Plecoptera did not show any preference. The deposition trap was more efficient in catching emerged aquatic insects than the window trap. A great deviation in biomass/unit area between sites suggests there is a big variation in productivity within agriculture streams and forest streams, respectively. Nematocera alone can potentially supply more nitrogen in a month than background deposition provides per year. The effect of agriculture on emerging aquatic insects, and in extension on riparian zone, is evident.