• Energy Research

Chlorination is widely used to prevent biological fouling in power station cooling water systems. It may impact non-target organisms both within the cooling system and after discharge (primary and secondary entrainment). However, there is a lack of data on the impacts of the low chlorine concentrations that occur in the discharged plume on marine phytoplankton community structure and function. We examine the impacts on natural phytoplankton communities of single and multiple exposures to chlorination at concentrations between 0.02 and 0.1 mg/L total residual oxidants (TRO). Low-level chlorination causes limited changes in diversity and has no impact on total biomass. However, changes in size structure and functional diversity quantified using flow cytometry do show a reduction in smaller cells, particularly eukaryote picophytoplankton. These impacts are not detectable using chlorophyll a concentration alone, so flow cytometry provides important additional information over more standard ecotoxicological methods. The effects are likely to be localised in the vicinity of the discharges (mixing zone) where the environmental quality standard (EQS) of 10 μg/L for chlorine is exceeded, but impacts on coastal food webs and biogeochemical cycles should be further evaluated.

Chlorination is a widely used method to prevent biofouling in power station cooling water systems in coastal and estuarine environments. This study evaluated the impact of chlorination together with temperature increase to simulate primary entrainment of a phytoplankton community. Biomass, diversity, and photosynthetic activity were monitored over 72 hours to establish impacts on the phytoplankton community. Biomass was significantly reduced after treatment. The mean cell size of the population significantly increased immediately after treatment highlighting an impact on the smaller cell size species of the community (picophytoplankton). Changes in accessory pigments composition suggest an effect on groups such as Prasinophyceae, Cyanobacteria and Chlorophycea. Species composition, dominated by diatoms, was also affected with Skeletonema marinoi and Asterionellopsis glacialis amongst the most sensitive species. Photosynthetic activity was affected in the short term but recovered after 48 hours. This study shows that by using a combination of measurements (e.g biomass, diversity, and physiology) the effects of entrainment in power station cooling water systems, that may be of longer-term significance for specific functional groups of phytoplankton communities, can be discerned. These changes would not necessarily be seen using individual techniques alone such as cell number counts or biomass assessment which may indicate apparent community recovery.

Chlorination is a widely used antifouling method for freshwater and marine applications. Chlorine added to seawater reacts to form oxidants that are toxic to biofouling organisms. Further, the oxidants that result are short-lived, but may nevertheless affect non-target species in waterbodies receiving the antifouling effluent. This study evaluated the toxicity of chlorinated seawater (e.g. following sodium hypochlorite addition) on two different species of marine benthic diatoms (Achnanthes spp., and Navicula pelliculosa), which are representative of microphytobenthos communities - an important component in coastal habitats that may be exposed to chlorinated seawater. To evaluate the growth inhibition over a 72 h period, algae were immobilised in alginate beads and exposed to different levels of chlorination in a flow through system. Growth rates and physiological condition of the microalgae were evaluated using a Fast Repetition Rate fluorometer (FRRf). To determine whether alginate influenced the sensitivity of algal response, studies were also conducted in a static test system (without renewal of test solutions) using both free cells and immobilised cells with initial chlorine added to achieve a similar range of concentrations as those used in the flow-through study. Within the first hour of the exposure period there was an indication that, for both species, the free algal cells in the static system were more sensitive to exposure to chlorinated seawater than were alginate-immobilised cells in the flow through system. Immobilised cells in a static system with a single addition of chlorine were also less sensitive to chlorination than free algal cells. However, for periods of 24 h or more due to decay of TRO in the static system the exposure of immobilised algae in the flow through system had a greater impact and hence lower effect concentrations. For the flow-through studies Achnanthes spp. was the most sensitive after 72 h exposure with a potential no effect concentration EC10 value of 0.02 mg l-1 as Cl2 equivalents expressed as total residual oxidants (TRO) compared 0.04 mg l-1 TRO for N. pelliculosa. Immobilisation of algal cells in alginate was found to be an effective means of determining the impact of chlorination and is likely to be effective for other non-persistent substances. Based on the data produced, the extent and significance of ecological effects of chlorination upon algal species typical of microphytobenthos are likely to be limited providing discharges comply with a maximum allowable concentration of 0.01 mg l-1 TRO at the edge of an agreed mixing zone.

The Severn Estuary is a large macrotidal estuary which includes an extensive mudflat with microphytobenthos (MPB) playing a key role in the ecosystem. This study evaluated the impact of chlorination at two different dosing levels (0.05 and 0.5 mg/l as total residual oxidants, TRO, representative of potential concentrations in the mixing zone and within the cooling water systems of a power station) on a MPB community representative of the Severn Estuary. Biomass and diversity were not negatively impacted while physiology was partially affected at the beginning of the experiment, and it recovered towards the end of the experiment. Further investigations for diversity are needed to consolidate our findings. In conclusion our results show that MPB is resilient to chlorination up to a concentration of 0.5 mg/l which is much higher (>10 times) than what might be expected near the chlorinated discharges for most coastal power stations.