Adverse environmental impact: 30-year search for a definition

Since passage of the Clean Water Act in 1972, there has been a long, unresolved struggle to define a key phrase in Section 316(b) of the act: "adverse environmental impact" (AEI). Section 316(b) requires that the best technology available be used in cooling-water intake structures to minimize AEI due to entrainment and impingement of aquatic organisms. Various attempts were made to evaluate and define AEI, including focused national conferences on impact assessment. Unresolved arguments regarding AEI were reinvigorated following the 1995 Consent Decree requiring EPA to propose new rules to implement Section 316(b). This article reviews and compares eight proposed definitions of AEI. Six of the definitions define AEI as impact expressed at the population or higher level of biological organization. The two remaining definitions are unrelated to populations: a 1% cropping of the near-field organisms and "one fish equals AEI". The latter definition is based on the desire of some stakeholders to define AEI as the loss of any public trust resources. Equating loss of public trust resources with AEI hampers consensus on a definition because a societal-based policy concept (public trust resources) is commingled with science-based definitions based on population effects. We recommend that a population-based definition of AEI be incorporated into Section 316(b) guidance and observe that this will not preclude a state from exercising its law and policy to protect public trust resources.     

Minimizing adverse environmental impact: how murky the waters

The withdrawal of water from the nation's waterways to cool industrial facilities kills billions of adult, juvenile, and larval fish each year. U.S. Environmental Protection Agency (EPA) promulgation of categorical rules defining the best technology available to minimize adverse environmental impact (AEI) could standardize and improve the control of such mortality. However, in an attempt to avoid compliance costs, industry has seized on the statutory phrase "adverse environmental impact" to propose significant procedural and substantive hurdles and layers of uncertainty in the permitting of cooling-water intakes under the Clean Water Act. These include, among other things, a requirement to prove that a particular facility threatens the sustainability of an aquatic population as a prerequisite to regulation. Such claims have no foundation in science, law, or the English language. Any nontrivial aquatic mortality constitutes AEI, as the EPA and several state and federal regulatory agencies have properly acknowledged. The focus of scientists, lawyers, regulators, permit applicants, and other interested parties should not be on defining AEI, but rather on minimizing AEI, which requires minimization of impingement and entrainment.     

Proposed methods and endpoints for defining and assessing adverse environmental impact (AEI) on fish communities/populations in Tennessee River reservoirs

Two multimetric indices have been developed to help address fish community (reservoir fish assemblage index [RFAI]) and individual population quality (sport fishing index [SFI]) in Tennessee River reservoirs. The RFAI, with characteristics similar to the index of biotic integrity (IBI) used in stream fish community determinations, was developed to monitor the existing condition of resident fish communities. The index, which incorporates standardized electrofishing of littoral areas and experimental gill netting for limnetic bottom-dwelling species, has been used to determine residential fish community response to various anthropogenic impacts in southeastern reservoirs. The SFI is a multimetric index designed to address the quality of the fishery for individual resident sport fish species in a particular lake or reservoir[4]. The SFI incorporates measures of fish population aspects and angler catch and pressure estimates. This paper proposes 70% of the maximum RFAI score and 10% above the average SFI score for individual species as "screening" endpoints for balanced indigenous populations (BIP) or adverse environmental impact (AEI). Endpoints for these indices indicate: (1) communities/populations are obviously balanced indigenous populations (BIP) indicating no adverse environmental impact (AEI), or are "screened out"; (2) communities/populations are considered to be potentially impacted; and (3) where the resident fish community/population should be considered adversely impacted. Suggestions are also made concerning how examination of individual metric scores can help determine the source or cause of the impact.     

Defining "adverse environmental impact" and making paragraph 316(b) decisions: a fisheries management approach

The electric utility industry has developed an approach for decisionmaking that includes a definition of Adverse Environmental Impact (AEI) and an implementation process. The definition of AEI is based on lessons from fishery management science and analysis of the statutory term "adverse environmental impact" and is consistent with current natural resource management policy. The industry has proposed a definition focusing on "unacceptable risk to the population"s ability to sustain itself, to support reasonably anticipated commercial or recreational harvests, or to perform its normal ecological function." This definition focuses not on counting individual fish or eggs cropped by the various uses of a water body, but on preserving populations of aquatic organisms and their functions in the aquatic community. The definition recognizes that assessment of AEI should be site-specific and requires both a biological decision and a balancing of diverse societal values. The industry believes that the definition of AEI should be implemented in a process that will maximize the overall societal benefit of the paragraph 316(b) decision by considering the facility"s physical location, design, and operation, as well as the local biology. The approach considers effects on affected fish and shellfish populations and the benefits of any necessary best technology available (BTA) alternatives. This is accomplished through consideration of population impacts, which conversely allows consideration of the benefits of any necessary BTA modifications. This in turn allows selection of BTAs that will protect potentially affected populations in a cost-effective manner. The process also employs risk assessment with stakeholder participation, in accordance with EPA's Guidelines for Ecological Risk Assessment. The information and tools are now available to make informed decisions about site-specific impacts that will ensure protection of aquatic ecosystems and best serve the public interest.     

Intermittent Pool Beds Are Permanent Cyclic Habitats with Distinct Wet,Moist and Dry Phases

Recognition that intermittent pools are a single habitat phase of an intermittent pool bed that cycles between aquatic and terrestrial habitat greatly enhances their usefulness for addressing general questions in ecology. The aquatic phase has served as a model system in many ecological studies, because it has distinct habitat boundaries in space and time and is an excellent experimental system, but the aquatic to terrestrial transition and terrestrial phase remain largely unstudied. We conducted a field experiment within six replicate natural intermittent pool beds to explore macroinvertebrate community dynamics during the transition from aquatic to terrestrial habitat and during the terrestrial phase. We monitored and compared macroinvertebrate communities within leaf packs that i) remained wet, ii) underwent drying (i.e., started wet and then dried), and iii) remained dry. Our results show that i) a diverse macroinvertebrate community inhabits all phases of intermittent pool beds, ii) pool drying involves colonization by an assemblage of macroinvertebrates not recorded in permanently terrestrial leaf packs, iii) the community within dried leaf packs remains distinct from that of permanently terrestrial leaf packs for an extended period following drying (possibly until subsequent refilling), and iv) there are likely to be strong spatial and temporal resource linkages between the aquatic and terrestrial communities. The unique environmental characteristics of intermittent pool beds, which repeatedly cycle from aquatic to terrestrial habitat, should continue to make them valuable study systems.     

Role of epibiotic diatoms isolated from the barnacle shell in the cyprid metamorphosis of <Emphasis Type="Italic">Balanus amphitrite</Emphasis>

The mechanisms structuring aquatic communities across environmental gradients are often difficult to distinguish from one another and can produce similar patterns of species distributions. In freshwater systems, the amount of canopy cover from surrounding trees is often associated with transitions in local community structure. These community changes could be driven by habitat selection prior to colonization of the aquatic habitat and/or species-sorting post-colonization. To assess the contributions of pre- versus post-colonization processes in structuring larval dragonfly assemblages, we tested the impact of artificial and natural canopy cover on the selection of experimental aquatic mesocosms by adult dragonflies, and monitored the performance (i.e. growth and survival) of larval dragonflies that were placed in mesocosms under a gradient of natural canopy cover. We found that greater levels of canopy cover resulted in fewer adult visits to mesocosms, and more natural canopy cover decreased the species richness of visitors. There were no effects of canopy cover on the growth and survival of larvae added to the mesocosms. Our results suggest that adult habitat selection plays a dominant role in structuring larval dragonfly assemblages across a canopy cover gradient, and that canopy cover can be an important environmental filter on species distributions.     

Indicators of AEI applied to the Delaware Estuary

We evaluated the impacts of entrainment and impingement at the Salem Generating Station on fish populations and communities in the Delaware Estuary. In the absence of an agreed-upon regulatory definition of "adverse environmental impact" (AEI), we developed three independent benchmarks of AEI based on observed or predicted changes that could threaten the sustainability of a population or the integrity of a community. Our benchmarks of AEI included: (1) disruption of the balanced indigenous community of fish in the vicinity of Salem (the "BIC" analysis); (2) a continued downward trend in the abundance of one or more susceptible fish species (the "Trends" analysis); and (3) occurrence of entrainment/impingement mortality sufficient, in combination with fishing mortality, to jeopardize the future sustainability of one or more populations (the "Stock Jeopardy" analysis). The BIC analysis utilized nearly 30 years of species presence/absence data collected in the immediate vicinity of Salem. The Trends analysis examined three independent data sets that document trends in the abundance of juvenile fish throughout the estuary over the past 20 years. The Stock Jeopardy analysis used two different assessment models to quantify potential long-term impacts of entrainment and impingement on susceptible fish populations. For one of these models, the compensatory capacities of the modeled species were quantified through meta-analysis of spawner-recruit data available for several hundred fish stocks. All three analyses indicated that the fish populations and communities of the Delaware Estuary are healthy and show no evidence of an adverse impact due to Salem. Although the specific models and analyses used at Salem are not applicable to every facility, we believe that a weight of evidence approach that evaluates multiple benchmarks of AEI using both retrospective and predictive methods is the best approach for assessing entrainment and impingement impacts at existing facilities.     

Biological Recover y from Lake Acidification: Zooplankton Communities as a Model of Patterns and Processes

Knowledge of the recovery of aquatic communities from lake acidification is limited. Data from studies of crustacean zooplankton communities, however, do reveal some of the major mechanisms important in the biological recovery process. Important influences on recovery include factors related to habitat quality and the ability of organisms to colonize. During recovery, existing species and colonists from internal and external sources interact to form a new community. The relative roles of internal and external influences remain poorly understood. Four general community types can be identified as possible outcomes of the recovery process: the original community, a normal alternate community, a community limited by dispersal, and a community limited by biological resistance. Empirical data indicate that, given suitable water quality, about a decade is sufficient to permit substantial recovery of zooplankton communities if there are no severe physical or biological barriers to restructuring.     

Impact of terrestrial protected areas on the fish diversity and habitat quality: Evidence from tropical river Pranhita,India

The conservation and management of inland fish and freshwater ecosystems immensely contribute to global sustainable development. The existing ‘Protected Area’ (PA) network does not represent freshwater resources well and seldom considers its fish communities, while designating PAs. A study was undertaken to quantitatively assess the role played by the three terrestrial PAs (IUCN category IV) in conserving fish diversity and preserving habitat quality in the river reaches bordering the three PAs of the river Pranhita. It is a unique river system in the Indian Deccan Plateau in terms of fish diversity and community structure. Field surveys were conducted during the non-monsoon and monsoon seasons in 2020–21, that recorded 53 species including endemic and threatened fishes from river Pranhita, which represent more than one-third the number of fish species of Telangana state. The higher diversity and lower dominance index value (p < 0.01) reported in PAs compared to Eco Sensitive Zones and unprotected areas during the non-monsoon season indicate the role of intact physical habitat in providing refuges to the fish species in monsoon dependent tropical rivers. The optimal water quality revealed no significant difference (p > 0.0001) between protected and unprotected river reaches, and healthy biotic integrity assessed on the basis of fish community structure was attributed to the contiguous flow and less anthropogenic disturbance. This study supports that it can be considered as a representative zone for the conservation and protection of indigenous and endemic fish species of the Godavari Basin. The results concluded that the scope of the terrestrial PA network in India could be potentially extended to their bordering aquatic ecosystems, especially rivers to maintain pristine habitat conditions and conserve the fish genetic resources to ensure the flow of ecosystem services.     

The effect of a large-scale irrigation scheme on the fish community structure and integrity of a subtropical river system in South Africa

Large scale irrigation schemes are vitally important for food security in developing countries. This is especially relevant in subtropical countries where there is pressure on their water resources. However, the potential impacts on the fish communities of the rivers associated with these irrigation systems are extensive and potentially devastating. Therefore, the aim of the study was to evaluate the impact of the Vaalharts Irrigation Scheme (VHIS) on the fish community of two rivers (Harts and Vaal rivers) in the subtropical region of South Africa. The fish community was assessed during a three year period from 2007 to 2009 together with environmental and habitat quality parameters. A multivariate approach together with a local biotic index was used to determine the present ecological state and the environmental drivers responsible for the fish community structure. The results indicated that the fish community was in a largely natural state at the start of the VHIS and increasingly became modified due to various environmental parameters being affected by the irrigation scheme. Annual variation in the fish community structures was high while nitrate, zinc and sulphates corresponded with changes in the fish community. The outcome of the study highlighted that a lack of long term monitoring of fish community structures together with environmental and habitat parameters are a major challenge in many developing countries that can potentially affect management of irrigation schemes and the fish communities associated with the aquatic ecosystems.     

Colonisation of Heliconia caribaea by aquatic invertebrates: resource and microsite characteristics

Abstract.  1. Colonisation of ephemeral aquatic habitats via oviposition by invertebrates may be influenced by a variety of factors, such as the quality of aquatic habitat and the characteristics of the surrounding terrestrial environment. The water-holding bracts of Heliconia caribaea , a subtropical herb that produces ephemeral aquatic habitats, are colonised by a variety of aquatic invertebrates. To date, no experiments have been conducted to identify the cues that affect colonisation patterns via oviposition selection in Heliconia .
2. Artificial bracts were used to assess the influence of two types of resources found in bracts (plant produced carbohydrates and terrestrial snail faeces) on oviposition site-selection by invertebrate taxa via a replicated factorial design at four locations in the Luquillo Experimental Forest of Puerto Rico, U.S.A. Eleven microsite characteristics thought to affect oviposition were measured for each experimental container.
3. Most taxa responded in a minor way to microsite characteristics, whereas site selection by the most numerically dominant groups (e.g. Syrphidae) were influenced principally by resources within artificial bracts. Overall, the greatest response by particular taxa was to the presence of snail faeces. At the community level, total abundance, richness, and evenness of invertebrates increased with increasing biomass of faeces. Variation in sugar produced a more complex response.
4. In general, the terrestrial matrix surrounding these aquatic habitats was only a secondary determinant of population and community attributes; the principal factor affecting site selection was the quality of the aquatic habitat.     

Communities at the extreme: Aquatic food webs in desert landscapes

Studying food webs across contrasting abiotic conditions is an important tool in understanding how environmental variability impacts community structure and ecosystem dynamics. The study of extreme environments provides insight into community‐wide level responses to environmental pressures with relevance to the future management of aquatic ecosystems. In the western Lake Eyre Basin of arid Australia, there are two characteristic and contrasting aquatic habitats: springs and rivers. Permanent isolated Great Artesian Basin springs represent hydrologically persistent environments in an arid desert landscape. In contrast, hydrologically variable river waterholes are ephemeral in space and time. We comprehensively sampled aquatic assemblages in contrasting ecosystem types to assess patterns in community composition and to quantify food web attributes with stable isotopes. Springs and rivers were found to have markedly different invertebrate communities, with rivers dominated by more dispersive species and springs associated with species that show high local endemism. Qualitative assessment of basal resources shows autochthonous carbon appears to be a key basal resource in both types of habitat, although the particular sources differed between habitats. Food‐web variables such as trophic length, trophic breadth, and community isotopic niche size were relatively similar in the two habitat types. The basis for the similarity in food‐web structure despite differences in community composition appears to be broader isotopic niches for predatory invertebrates and fish in springs as compared with rivers. In contrast to published theory, our findings suggest that the food webs of the hydrologically variable river sites may show less dietary generalization and more compact food‐web modules than in springs.     

Spatially explicit population responses of crayfish Procambarus alleni to potential shifts in vegetation distribution in the marl marshes of Everglades National Park,USA

Hydropattern disturbance has had wide-ranging impacts on wetland communities of the Florida Everglades, especially on the habitats and the aquatic biota of the seasonally flooded marl marshes. We used the Everglades crayfish Procambarus alleni as a model to study the associations among hydrology, vegetation distribution, and population dynamics to assess the potential impacts of hydrological changes on the aquatic faunal community in Everglades National Park. To classify benthic habitats as sources or sinks for the crayfish population, we quantified vegetation community structure using GIS maps in which dominant vegetation types were weighted by local hydroperiod (length of inundation). Regression analysis showed that this habitat classification was associated with crayfish density distribution. We then used a spatially explicit, stage-structured population model to describe crayfish population fluctuations under current environmental conditions and to simulate the potential population-level responses to habitat changes that might occur following hydrological restoration. In habitat that was initially saturated with crayfish, the crayfish population size declined under current environmental conditions and then stabilized at about 13% of the initial density over a 50-year period. A 4-month increase in hydroperiod was then simulated by converting shorter-hydroperiod Muhlenbergia-dominated marsh habitat to longer-hydroperiod Cladium-dominated marshes. The model predicted a rapid 7-fold increase in crayfish density following the simulated habitat restoration. This indicated that several functional effects may result from the restoration of historical hydropatterns in marl marshes: (1) the areal extent of habitat sinks will be reduced to isolated patches, whereas the spatial distribution of aquatic source habitats will expand; (2) crayfish population size will increase and persist over time; (3) the minimum threshold needed to increase secondary aquatic productivity may be a 7-month hydroperiod over 90% of the marl marsh landscape. Restoration of historical hydropatterns could thus have cascading positive effects throughout the Everglades aquatic food web.     

Comparing Clean Water Act Section 316(b) policy options

This paper develops a comparative framework for policy proposals involving fish protection and Section 316(b) of the Clean Water Act (CWA). Section 316(b) addresses the impingement and entrainment of fish by cooling-water intake structures used principally by steam electric power plants. The framework is motivated by examining the role of adverse environmental impacts (AEIs) in the context of Section 316(b) decision making. AEI is mentioned in Section 316(b), but not defined. While various AEI options have been proposed over the years, none has been formalized through environmental regulations nor universally accepted. Using a multiple values approach from decision analysis, AEIs are characterized as measurement criteria for ecological impacts. Criteria for evaluating AEI options are identified, including modeling and assessment issues, the characterization of ecological value, regulatory implementation, and the treatment of uncertainty. Motivated by the difficulties in defining AEI once and for all, a framework is introduced to compare options for 316(b) decision making. Three simplified policy options are considered, each with a different implicit or explicit AEI approach: (1) a technology-driven rule based on a strict reading of the 316(b) regulatory text, and for which any impingement and entrainment count as AEI, (2) a complementary, open-ended risk-assessment process for estimating population effects with AEI characterized on a site-specific basis, and (3) an intermediate position based on proxy measures such as specially constructed definitions of littoral zone, sensitive habitat, or water body type. The first two proposals correspond roughly to responses provided, respectively, by the Riverkeeper environmental organization and the Utility Water Act Group to the U.S. Environmental Protection Agency (EPA)'s proposed 316(b) new facilities rule of August 2000; the third example is a simplified form of the EPA's proposed August 2000 new facilities rule itself. The simplified policy positions are compared using the three dimensions of the comparative policy framework: (1) the role of CWA philosophy or vision, such as the use of technology-forcing rules, (2) regulatory policy implementation, and (3) the role for scientific information and the knowledge base. Strengths and weaknesses of all three 316(b) policy approaches are identified. The U.S. EPA's final new facilities rule of November 2001 is briefly characterized using the comparative policy framework and used to further illustrate the approach.     

Developing fish community based ecohydrological indicators for water resources management in Taiwan

With concerns about the maintenance of both aquatic communities and flow conditions, a number of hydrologic indicators have been developed. These indicators are generally based on the development of hydrologic statistics for flows that are important to the maintenance of aquatic ecosystems. Although the hydrologic basis for indicators is well defined by common techniques in stochastic hydrology, the basis for ecological integration is still being developed. A critical evaluation of hydrologic indicators intended to protect aquatic ecosystems finds that proposed indicators are based more on standard hydrologic statistics and measures of hydrologic alteration than the habitat needs and ecological requirements of local or desired aquatic communities. We argue that hydrologic indicators are not ecohydrological indicators unless direct connections between flow events and aquatic community habitat and ecological needs are the basis of the indicator development and selection. In this article, we identify ecohydrological indicators that are based on habitat and ecological needs of fish communities. The indicator identification process is initiated with the analysis of community needs using an autecology matrix. Hydrologic statistics are then selected that are appropriate to the target fish community. The resulting ecohydrological indicators provide a direct connection to fish community flow requirements and the physical habitat conditions and associated ecology and life history needs of fish species. Handling editor: J. A. Cambray     

Differential influence of a monotypic and diverse native aquatic plant bed on a macroinvertebrate assemblage; an experimental implication of exotic plant induced habitat

Aquatic plants mediate ecological processes in aquatic habitats, specifically predator–prey (bluegill sunfish (Lepomis macrochirus Rafinesque)-macroinvertebrate) interactions. Macroinvertebrate colonization is directly and indirectly influenced by substrate heterogeneity, interstitial space, and surface complexity. Exotic invasive plant species, such as Hydrilla verticillata L.F. Royle, may alter the available structure in aquatic habitat by creating a shift to a homogeneous habitat, thus affecting the macroinvertebrate community. Since macroinvertebrates provide a food base for young phytophilic fishes, changes in their density and abundance may alter food webs. We investigated the hypothesis that macroinvertebrate community structure is influenced by differences in habitat heterogeneity by measuring difference between a heterogeneous native aquatic plant bed, homogenous hydrilla plant bed, and habitat with no plants. Studies were conducted in the field (pond) and the experimental treatments were: (1) no plants, (2) monotypic bed of hydrilla, and (3) diverse native plants. Aquatic plants, regardless of species, supported greater macroinvertebrate abundance, richness, and biomass. Macroinvertebrate abundance, richness, and biomass in a hydrilla-dominated habitat did not differ significantly from a diverse plant habitat, except for richness in October. Indicator taxa did differ significantly between respective treatments, suggesting a change in species composition. However, no significant effect of fish predation on macroinvertebrate populations and/or community structure was documented. The data suggest that a shift from a natural mosaic of vegetated habitat to a highly complex monotypic habitat (e.g., exotic hydrilla) may reduce spatial heterogeneity important to structuring a macroinvertebrate assemblage. Handling editor: S. M. Thomaz     

The influence of habitat heterogeneity on freshwater bacterial community composition and dynamics

Multiple forces structure natural microbial communities, but the relative roles and interactions of these drivers are poorly understood. Gradients of physical and chemical parameters can be especially influential. In traditional ecological theory, variability in environmental conditions across space and time represents habitat heterogeneity, which may shape communities. Here we used aquatic microbial communities as a model to investigate the relationship between habitat heterogeneity and community composition and dynamics. We defined spatial habitat heterogeneity as vertical temperature and dissolved oxygen (DO) gradients in the water column, and temporal habitat heterogeneity as variation throughout the open-water season in these environmental parameters. Seasonal lake mixing events contribute to temporal habitat heterogeneity by destroying and re-creating these gradients. Because of this, we selected three lakes along a range of annual mixing frequency (polymictic, dimictic, meromictic) for our study. We found that bacterial community composition (BCC) was distinct between the epilimnion and hypolimnion within stratified lakes, and also more variable within the epilimnia through time. We found stark differences in patterns of epilimnion and hypolimnion dynamics over time and across lakes, suggesting that specific drivers have distinct relative importance for each community.     

Upper Mississippi River restoration: implementation,monitoring, and learning since 1986

Upper Mississippi River Restoration (UMRR) was implemented to monitor environmental status and trends and restore degraded habitat. There was little experience conducting restoration in large rivers, and engineering and ecological integration evolved through project implementation. Loss of depth in backwaters and side channels, excessive biological oxygen demand, increased currents, and low water temperatures were common symptoms of backwater eutrophication that were primary objectives for implementing UMRR. Biological outcome monitoring was initially funded for six projects using the most common methods to restore aquatic and wetland habitat. UMRR island construction occurred as four generations of learning. Current plans represent a comprehensive restoration approach including: physical process modeling (i.e. hydraulic and wind‐wave modeling) of existing conditions and alternative restoration measures. Habitat Rehabilitation and Enhancement Projects, fish response monitoring validated winter habitat suitability models. Long term fish population monitoring indicates sustainable recovery, and now population interaction among restored lakes is under investigation. Isolated wetland management in Illinois River backwater lakes can achieve bottom consolidation that promotes emergent wetland habitat response that migratory waterfowl exploit in large numbers. Adult fish movement between the river and management units is restricted to flood stage or through control structures and post‐project movements into the lake for overwintering were not apparent. The lack of Illinois River overwintering habitat is shown by an abundance of young fish and few older fish in status and trends monitoring. Upper Mississippi River System ecosystem restoration practitioners have implemented ecosystem restoration science and practice in a manner that exemplifies the best intent of adaptive management.     

Effects of flash flooding on mosquito and community dynamics in experimental pools

Pulsed disturbances of larval mosquito sites are likely to have a direct negative effect on mosquitoes but may also have indirect effects due to the alteration of community structure. These altered communities may become attractive to gravid mosquitoes searching for oviposition sites when the disturbances decrease the abundance of mosquito antagonists such as competitors, which often results in an increase in mosquito food resources. However, flash flood disturbances in intermittent riverbeds can also remove mosquito food resources such as algae, so that the net effect of flash floods could be either to increase or decrease mosquito abundance. We conducted an outdoor mesocosm experiment to assess the effects of flash floods on mosquito oviposition habitat selection and larval abundance during the post‐disturbance period of community recovery. Mesocosms were artificially flooded. Mosquito oviposition, immature abundance, invertebrate species diversity, chlorophyll a, and abiotic parameters were monitored. Our results showed that the flash flood negatively affected phytoplankton and zooplankton, leading to a decrease of mosquito oviposition in flooded mesocosms compared to non‐flooded mesocosms. More broadly, this study indicates how disturbances influence mosquito oviposition habitat selection due to the loss of food resources in ephemeral pools, and it highlights the importance of considering the effects of disturbances in management, habitat restoration, and biodiversity conservation in temporary aquatic habitats.