Increased growth and distribution of Ephemerella aurivillii (Ephemeroptera) after hydropower regulation of the Aurland catchment in Western Norway

Abstract

The Aurland watershed has been regulated for hydropower since the establishment of a series of power plants during the period 1970-1983. This resulted in a strong reduction of the flow in the river Vassbygdelvi, the inlet river to lake Vassbygdvatn. In the downstream river Aurland, the flow has varied, but from 2000 the intention has been to simulate pre-regulation winter flow as far as possible. The temperature in the river Vassbygdelvi has increased from about 1500 degree-days per year before regulation to above 2000 degree-days after regulation. In the river Aurland the thermal regime, expressed as degree-days per year, was more or less unchanged, but a small reduction in the summer temperature and a corresponding increase during other periods was observed. The mayfly Ephemerella aurivillii (Bengtsson) was not recorded in Vassbygdelvi prior to regulation, but became abundant in the river after. Full-grown larvae were recorded 1-2 months earlier in the river Vassbygdelvi than in the river Aurland after regulation. E. aurivillii has a 1-year life cycle with imagos present in June-August. Young larvae occurred from June to early September. It is concluded that larvae of E. aurivillii could not complete their life cycle within 1 year before regulation in the river Vassbygdelvi, due to low temperature. The study demonstrates how temperature can regulate the distribution of a species with a strict 1-year life cycle.

Invertebrate response to impacts of water diversion and flow regulation in high‐altitude tropical streams

“…We found an opposite pattern in the stream with regulated flow (Sucus). Our results agreed with findings from Raddum, Fjellheim, and Velle () and Lytle and Poff (), who reported that flow regimes and temperatures influenced mayfly life cycles and phenology in regulated reservoirs releases. Flow alteration caused by regulation and diversions caused changes in the nymphal development of A. peruvianus , suggesting a potential cumulative effect on invertebrates phenology.…”

Using equilibrium temperature to assess thermal disturbances in rivers

“…Studies assessing thermal alterations in rivers and streams normally base their conclusions on the comparison of sections upstream and downstream from the alteration (e.g. Raddum et al, 2008;Prats et al, 2012). However, it is also possible to compare altered water temperatures with a reference value that is specific to the place and time of measurement.…”

Water temperature modeling in the Lower Ebro River (Spain): Heat fluxes, equilibrium temperature, and magnitude of alteration caused by reservoirs and thermal effluent

“…However, many studies regarding thermal alterations in streams and rivers [ Lessard and Hayes , 2003; Steel and Lange , 2007; Zolezzi et al , 2010] and regulations, such as the EU Directive 2006/44/CE, do not consider the longitudinal effects of water temperature alterations, and they assess thermal alterations by comparing two points: one upstream and the other downstream from the alteration point [e.g., Lessard and Hayes , 2003; Raddum et al , 2008; Prats et al , 2010]. This approach does not consider the length of the river affected by a thermal discharge or the possible existence of complex spatial patterns of water temperature variability.…”