Responses of epibenthic algal assemblages to water abstraction in Hong Kong streams

Abstract

We studied the effects of flow reduction on epibenthic algal assemblages by comparing up-and down-stream reaches of ten Hong Kong streams subject to different degrees of water abstraction during [2007][2008]. Downstream discharge declined by 71 and 54% during the wet and dry seasons, respectively. Algal responses varied seasonally and according to morphological guild and reflecting reductions in discharge and current velocity, or changes in total nitrogen and phosphate, or their combined effects. Significant inter-reach assemblage differences were observed during the both seasons, but wet-season assemblage structure was not directly influenced by any flow-related variable. During the dry season, scouring-tolerant prostrate/adnate diatoms (especially Achnanthes, Cocconeis) were relatively abundant upstream, whereas intolerant stalked (Eunotia, Gomphonema) and mobile diatoms were more numerous downstream. Both low-and high-profile (erect diatoms, Chamaesiphon, Calothrix) guilds were sensitive to changes in nutrients. Low-flow conditions downstream, surprisingly, enhanced algal diversity, and richness. Based on the linear response of Cocconeis (mainly C. placentula) to discharge reduction, we recommend that[65% of dry-season discharge should be maintained in downstream reaches in order to sustain near-natural algal assemblages; 32% of discharge is required to avoid substantial alterations in assemblage structure.

Multi-scale temporal dynamics of epilithic algal assemblages: evidence from a Chinese subtropical mountain river network

“…Second, several likely important environmental variables have been omitted due to procedural limitations. For example, climatic and water flow fluctuations may affect temporal patterns of algae (Hering et al, 2010;Tang et al, 2013a). However, such variables are difficult to characterize for each site in this remote mountain river network with only one gauge station and one meteorological station.…”

Altitudinal pattern of stream periphyton biomass in tributaries of the Lancang–Mekong River: An indicator of anthropogenic impact?

“…Hydropower stations were built in Lingquan Stream and Maoshi Stream. Both water abstraction and hydropower stations change stream flow regimes greatly (Wu et al, 2010b;Tang et al, 2013), complicating the response of periphyton to nutrients.…”

The impact of flow regulation by hydropower dams on the periphyton community in the Soča River, Slovenia

“…Several studies have examined the effects of river flow regulation on periphyton (Lowe 1979, Biggs 1987, Valentin et al 1995, Bergey et al 2010, Tang et al 2013. Flow regulation can influence periphyton species composition and the abundance of individual species (Biggs 1996), causing their numbers to increase or decrease depending on site-specific characteristics and the exact nature of hydrological change.…”

“…The effects of reduced flow caused by water intake for selected HPPs in Slovenia during periods of drought showed changes in the periphytic species composition in alpine (Smolar-Žvanut 2001, Smolar et al 2005, Smolar-Žvanut and Krivograd-Klemenčič 2011, lowland and karst rivers (Smolar et al 1998), respectively. Many studies that have examined the impact of river regulation due to dam operation have focused specifically on diatom communities (e.g. Wu et al 2010, Tang et al 2013), but not on whole periphytic communities and their biomass. Most work has also focused on rivers where the discharges have been reduced across the whole flow regime, including reduced flood occurrence.…”