Extreme hydrological events and the ecological restoration of flowing waters

Abstract

1. Extreme hydrological events (floods, droughts) in flowing waters can alter habitat availability and structure and produce significant shifts in biodiversity, species assemblages and ecosystem processes. 2. Extreme floods and droughts occur over large spatial extents and can greatly alter links between streams and their catchments. The nature and strengths of these links differ between degraded and intact streams and their catchments, strongly influencing the responses to and recovery from extreme events. It is essential that these catchment-stream linkages be identified and considered when planning stream restoration. 3. Despite the scarcity of comprehensive, long-term monitoring of most stream restoration projects, our understanding of the influence of extreme events on running waters suggests both positive and negative impacts on restoration efforts. Extreme hydrological events can impair stream restoration efforts giving rise to delays or complete failures in achieving restoration objectives. Alternatively, extreme floods may facilitate progress towards restoration goals by engendering key ecological processes. 4. Understanding the impacts and the temporal-spatial scales over which extreme events alter the ecological structure and function of streams (in both natural and damaged systems), as well as their underlying mechanisms, is a challenge for stream restorers that will only progress with the accumulation of long-term data. Restorers should recognise and plan for hydrological extreme events and their interactions with other disturbances (e.g. fire, urban development). Increasing connectivity of restoration efforts along with their spatial extent can lessen the negative effects of extreme hydrological events on stream restoration. 5. Successful ecological stream restoration requires long time spans and thus with a changing climate the prediction of more frequent and intense extreme events only strengthens the need to incorporate their likelihood into restoration planning and implementation.

Ecological effects of extreme climatic events on riverine ecosystems: insights from Australia

“…As the resilience of aquatic organisms is lessened by a range of anthropogenic stressors, the effects of extreme events on riverine ecosystems must be considered alongside those of human activities (e.g. Balcombe et al ., ; Leigh et al ., ; Reich & Lake, ). As extreme events also occur against a backdrop of gradual climate change, outcomes of future events must be considered in the light of these longer term trends in climate, especially progressive warming.…”

Drought intensification alters the composition, body size, and trophic structure of invertebrate assemblages in a stream mesocosm experiment

“…Many regions of the world are expected to experience more intense and prolonged droughts over the coming century (Trenberth et al, 2014). In running waters, the ecological impacts of droughts have been less well studied than those of floods (Boulton & Lake, 2008;Reich & Lake, 2015) or changes in average conditions (Ledger & Milner, 2015), yet they can have more profound and immediate impacts on stream communities (Thornton, Ericksen, Herrero, & Challinor, 2014;Woodward et al, 2016). Much of our understanding of stream drought comes from studies of intermittent systems that experience predictable, seasonal drying events.…”

Biodiversity in perennial and intermittent rivers: a meta‐analysis

“…Floods enhance connectivity among aquatic habitats, whereas drying fragments them (Stanley et al , Boulton ). Although it is widely known that floods and drying events affect the structure and function of rivers (Bonada et al , Reich and Lake ) and that research on drying events has significantly increased during the last decade (Leigh et al ), the effects of floods have been more frequently reported that those of drying events (Datry et al , Lake et al ). This may be because floods occur in all river types, whereas drying events are particular to intermittent rivers (IRs), in which surface flow ceases at some point in time and space (Acuña et al , Datry et al , Leigh et al ).…”