Towards Mechanistic Hydrological Limits: A Literature Synthesis to Improve the Study of Direct Linkages between Sediment Transport and Periphyton Accrual in Gravel-Bed Rivers

Abstract

Altered hydrological, sediment, and nutrient regimes can lead to dramatic increases in periphyton abundance in rivers below impoundments. Flushing flows are a commonly adopted strategy to manage the excess periphyton that can accumulate, but in practice they often prove ineffective. Designing hydrological regimes that include flushing flows may be overlooking key processes in periphyton removal, particularly the role of abrasion and molar action induced by substrate movement. Setting flow targets which aim to initiate substrate movement are likely to improve periphyton removal, but an understanding of the site-specific thresholds for substrate entrainment and periphyton removal is required. Despite decades of entrainment studies accurate and consistent measurement and prediction of substrate entrainment remains elusive, making it challenging to study the relationship between substrate movement and periphyton removal, and to set flow targets. This paper makes a case for using substrate entrainment and transport thresholds as the target metric for flushing flows to manage excess periphyton accrual. This paper critically reviews the determinants of periphyton accrual and associated management methods. This paper also aims to provide a reference for interdisciplinary research on periphyton removal by summarising the geomorphic and hydraulic literature on methods for estimating and measuring substrate entrainment and transport. This will provide a basis for ecologists to identify tools for quantifying entrainment and transport thresholds so they are better placed to explore the direct linkages between phases of sediment transport and periphyton accrual. These linkages need to be identified in order for river managers to set effective flushing flow targets.

A simplified stochastic optimization model for logistic dynamics with control-dependent carrying capacity

“…From a management view point of river environment, increasing the magnitude and frequency of flood events, if their costs are small, may be an effective way for more cost-effective algae population management. This would especially apply to the river environment in a dam downstream where the magnitude and frequency of floods are artificially decreased from natural conditions where ρ is very small [34,41]. In addition, if such an environment has been established, the population can be managed subject to small deviation q * −q.…”

Stochastic control of single-species population dynamics model subject to jump ambiguity

“…In this context, the decision-maker is a manager of the river environment. The jump ambiguity in this case comes from the lack of knowledge of the decision-maker on the flood frequency such that a large part of the algae population would be flushed out [30,54].…”

Changes of Periphyton Abundance and Biomass Driven by Factors Specific to Flooding Inflow in a River Inlet Area in Erhai Lake, China

“…Processes occurring in the river inlet area have been poorly studied. Previous studies found that periphyton biomass, taxonomic diversity, and function are heavily dependent on hydrological regime (Biggs et al, 1999;Bondar-Kunze et al, 2015;Neverman et al, 2018). Especially, when a flooding event happens in the rainy season, the scouring effect of flooding and consequently high current velocity and suspended matter concentrations can act as a major reset mechanism to initiate new cycle metabolism and structural succession for the periphyton community and even the whole river ecosystem (Tett et al, 1978;Fisher et al, 1982;Lindström and Traaen, 1984;Reiter and Carlson, 1986;Townsend et al, 2012).…”