Ecological impacts of dam removals on macro-invertebrates

BLETTLER MARTIN

Chinon

Workshop; Ecohydraulics and dam removal, 2nd meeting; 2018

LE STUDIUM, Institute for advanced studies, Loire Valley

Is the scientific knowledge of dam removal and its effect on invertebrates enough for reliable predictions? Are the studied cases diverse enough to stablish ecological patterns? What kind of dams, rivers and taxa have been predominantly studied? So, can we detect trends and biases in this knowledge? Is dam removal always the best option for river restoration? These and other ecological question have encouraged the present review. Many lotic ecosystems have been fragmented by dams worldwide, causing a reduction in natural levels of environmental variation and consequently a reduction of biodiversity in downstream communities (Rader et al. 2007). This is particularly true in countries such as US, since 28% of the total dams are located there (ICOLD World Register of Dams 2018). While some countries are removing the dams, others are on a dam-building spree. A key challenge is that the boom is concentrated in areas of South America, Southeast Asia and Africa, that are also bastions of relatively untouched freshwater ecosystems. Dams can be removed for many reasons, commonly because their age and loss of function have rendered them unsafe, obsolete or economically nonviable (Heinz Center 2002; Pohl 2002). Another key motivation is to rehabilitate rivers by restoring physical and ecological attributes and functions (Pohl 2002). The removal of a dam typically causes an immediately but often temporary pulse disturbance given by sediment exposure, erosion, sediment redistribution (Tullos et al. 2016), discharge increase and changes in temperature (Bednarek 2001), and the potential release of pollutants associated with sediments (Colas et al. 2013). Community structure are likely to respond to such dramatic changes in either a categorical (effect vs no effect) or a continuous (gradational) manner, depending on the type of organism or process examined and the relationship between sizes of the dam and river (Casper et al. 2006). Although dam removal is generally welcomed by most scientists, some call for more research into potential ill effects (Zarfl et al. 2015). The present study aims to detect trends and biases in the current scientific literature of dam removal and its effect on invertebrates, related to i) geographic area of the case study, ii) river and dam sizes, iii) sampling design and involved scales, iv) sediment pollution, and v) main effects on fauna. Knowledge of ecological and physical responses to dam removal, can inform dam emplacement decisions about where and how dams are built to avoid or minimize environmental disturbance and future economic liabilities.