Effects of alpine hydropower operations on primary production in a downstream lake

Abstract

Abstract. During the past century, the construction of hydropower dams in the watershed of Lake Brienz has significantly altered the dynamics of turbidity, which has important implications for lake productivity. To assess these effects, we measured in situ carbon assimilation rates and ambient light intensities over 18 months. Based on experimental data, a numerical model was developed to assess gross primary production under present light conditions and those under a hypothetical case without upstream dams. Light conditions for the hypothetical no-dam situation were estimated from pre-dam Secchi depths and simulated no-dam particle concentrations.Current gross primary production is low (~66 gC m -2 yr -1 ), and could increase~44 % if the lake was less turbid. Disregarding nutrient retention in reservoirs, we estimate gross primary production would be~35 % lower in summer and~23 % higher in winter in the absence of reservoirs. The annual primary production (~58 gC m -2 yr -1 ) would decrease~12 % compared to the current primary production with dams. According to model calculations, hydropower operations have significantly altered the seasonal dynamics, but have little effect on annual primary production in Lake Brienz.

Bacterial Chitin Hydrolysis in Two Lakes with Contrasting Trophic Statuses

“…Both, the hydrological regime and the suspended particle load of the river Aare are influenced by hydropower operations. The continuous supply of suspended glacial particles, causing reduced light penetration, together with the scarcity of nutrients has led to an unusually low phytoplankton biomass (on average, Ͻ10 g m Ϫ2 ) (15,21).…”

“…In LB, it was as high as the zooplankton chitin biomass in May 2009, but it was only one-sixth of the zooplankton chitin biomass in September 2009. This discrepancy could be caused by the higher inorganic glacial particle load from the inflows in the second half of the year (15,16), which caused higher turbidity in the surface waters (1). As a consequence, the primary production maximum was shifted to a lower water depth of 2.5 m compared to May 2009, when it was observed at a water depth of 5 m (D. Carstens, K.E.…”

Lake Brienz Project: An interdisciplinary catchment-to-lake study

“…A low primary productivity of less than 70 gC/(m 2 yr) is reported by Finger et al (2007) based on in situ measurements. These data and the reconstructed light regime allows them to estimatethrough a comparison of different models -the impact of the upstream reservoirs on the productivity in Lake Brienz .…”

Wave-induced variability of the underwater light climate in the littoral zone

“…Thus, the variability of the light field is maximal at shallow depths (DERA & GORDON 1968, RØRSLETT et al 1997, SCHUBERT et al 2001). Light intensity is important for the growth of phytoplankton (FINGER et al 2007), biofilms, and macrophytes (SCHEFFER et al 1993) and affects habitat choice, food uptake, and predation pressure of fishes (UTNE-PALM 2004, SCHLEUTER & ECKMANN 2006. The biological relevance of fluctuating light is not only determined by the intensity of the fluctuations, but also by temporal scales (WALSH & LEGENDRE 1983, PAHL-WOSTL 1992.…”