Survival estimates across five life stages of redfin (Perca fluviatilis) exposed to simulated pumped-storage hydropower stressors.

The global prevalence of pumped-storage hydropower (PSH) is expected to grow exponentially as countries transition to renewable energy sources. Compared to conventional hydropower, little is currently known regarding PSH impacts on aquatic biota. This study estimated the survival of five life stages (egg, two larval stages, juvenile and adult) of redfin (European) perch (Perca fluviatilis) following passage through a PSH facility during the pumping phase. This was achieved by simulating the individual stressors expected to occur during passage through a 2000-MW PSH facility using laboratory-simulated (shear strain and extreme compression) and modelling (blade strike, BS) approaches. Our results indicate that redfin could survive the shear, pressure and BS stressors expected within the PSH facility, but impacts varied among life stages. Juvenile survival was >70% across all shear strain rates, while the survival of eggs and larvae declined markedly as strain rate increased. All life stages had high survival when exposed to rapid compression and BS. The high survival of redfin to the stressors tested suggests the PSH facility could facilitate the passage of redfin during the pumping phase from the lower to the higher elevation reservoir. This outcome would be welcomed in situations where the species is native, but could have adverse implications for the conservation of native biota where the species is considered a pest.

Managed floodplain inundation maintains ecological function in lowland rivers.

Managed environmental flows are one mechanism by which managers may restore carbon dynamics, diversity and ecological function of rivers affected by anthropogenic activities. Empirical studies that quantify such interactions in detail are few, so we measured the amounts of dissolved organic carbon, nutrients, algae and invertebrates in the main river channel following a managed environmental flow that inundated an adjacent floodplain forest. Dissolved organic carbon (DOC), seston carbon, total nitrogen (TN), and chlorophyll-a (chl-a) concentrations were greatly increased downstream. The net yield of DOC, seston carbon, TN and chl-a from the floodplain peaked at approximately 100, 50, 5 and 0.1 t d-1, respectively during the major flow event. Total phosphorus mobilisation peaked at approximately 0.4 t d-1. Stable isotope analysis showed that allochthonously-derived carbon was rapidly incorporated into biofilm and grazing macroinvertebrates, persisting in riverine food webs for up to four months following the flood. During a subsequent smaller flow event, the floodplain either generated no further carbon or nutrients, or was a sink for carbon and nutrients. Our results provide empirical support for the River Wave Concept and show that allowing floodplain water to return to the river downstream of forests is important for maintaining ecological function within the river channel.

Flexible and non-invasive passive integrated transponder (PIT) tagging protocols for tropical freshwater fish species.

Passive integrated transponder (PIT) tagging has proven to be an effective mark-recapture technique for many temperate freshwater and marine fish species, but its adaptability to tropical freshwater species remains largely unknown. Nevertheless, many tropical river systems, such as the Mekong in South East Asia, are currently being developed at an unprecedented rate for their relatively abundant water resources. Consequently, there is an urgent need for efficient mark-recapture technologies to understand and assess the impacts of human developments on the movement ecology of tropical freshwater fish species. This paper discusses the development of an optimal protocol for PIT tagging tropical freshwater fishes, using two Mekong River species - Striped catfish (Pangasianodon hypophthalmus) and Goldfin tinfoil barb (Hypsibarbus malcolmi) - as model species. •The PIT tagging protocol is flexible in that it allows the transponders to be placed in a variety of body locations.•The protocol has high tag retention rates (>90%) and is non-invasive, since it does not affect fish growth or mortality rates.•The application of PIT tags can be used to evaluate the success of fishways and other remedial works for supporting crucial life-cycle processes potentially requiring fish passage, such as spawning.

Assessing the potential for using wetlands as intermediary storages to conjunctively maintain ecological values and support agricultural demands.

Water sharing to meet both agricultural and environmental demands is a critical issue affecting the health of many floodplain river systems around the world. This study explored the potential for using wetlands as temporary off-river storages to conjunctively maintain ecological values and support agricultural demands by assessing the effects of artificial drawdown on wetland aquatic plant communities. An initial experiment was undertaken in outdoor mesocosms in which four different treatments were compared over a 131 day duration: (1) natural drawdown where the water was left to drawdown naturally via evaporation; (2) partial drawdown where approximately half of the volume of water was pumped out after 42 days; (3) stepped drawdown where approximately half of the volume of water pumped out after 42 days, and then the remaining volume of water was pumped out after 117 days; and (4) total drawdown where all of the of water was pumped out after 117 days. A complementary field study was subsequently undertaken where two wetlands were left to drawdown naturally and two were partially drawn down artificially (i.e. had approximately half of their volume removed by pumping). Results from both of these studies indicated that neither aquatic plant abundance nor taxon richness were adversely affected by partial drawdown. Rather, both studies showed that aquatic plant communities subjected to a partial drawdown treatment became more species rich and diverse than communities subjected to a natural drawdown treatment. This suggests that it may be possible to use wetlands as intermediary storages for the dual purposes of maintaining ecological values and supporting agricultural demands.