Before-after Control-impact Design Research Articles

Ground-Based Pyrethroid Adulticides Reduce Mosquitoes But Not Nontarget Insects in Central Florida.

As stewards of public and environmental health, mosquito control agencies are rightfully concerned about impacts on nontarget organisms. This study examined the impact of a modern, pyrethroid based ground adulticide program using ultra-low volume applications in a metropolitan county in central Florida. Nontarget insects and mosquitoes were collected in a before-after control-impact design at 21 sites over 1.5 years. While mosquitoes were reduced, we found no evidence for reduction of nontarget insects, regardless of taxon. Night-flying Lepidoptera may experience greater risk than other nontarget taxa, but overall effects of adulticide missions on this group were low and inconsistent. Instead, meteorology, habitat, and phenology dominate patterns of nontarget abundance. Mosquito reduction was more clearly observed and corrected post-mission reduction was consistent with results expected in complex urban and suburban treatment zones.

Subsurface phosphorus and nitrogen loss following liquid dairy manure and commercial fertilizer application on a clay soil in northwest Ohio.

Nutrient source has been the focus of much debate regarding the re-eutrophication of Lake Erie, despite that only 20% of nutrients applied to crops in the Western Lake Erie Basin (WLEB) originate from organic sources. However, limited data and assessments exist on the subsurface tile drainage water quality comparison between organic (liquid dairy manure) and commercial (mono-ammonium phosphate [MAP]) sources in crop production systems. Subsurface tile drainage, dissolved reactive phosphorus (DRP) and total phosphorus (TP) losses in tile drainage discharge following equal phosphorus (P) based applications of liquid dairy manure and MAP were assessed using a before-after control-impact design and four years of data from a paired field system located in northwest Ohio, USA. Nitrate-nitrogen (NO3--N) and total nitrogen (TN) losses were also examined to supplement the P findings; however, due to dissimilar nitrogen application rates, losses were assessed in a different context. No significant differences (p > 0.05) were detected in drainage discharge volumes or TP loads between the control and impact sites. However, statistically significant increases (p < 0.05) were measured for mean daily DRP, NO3--N, and TN loads from the dairy manure site. While significant, mean daily DRP differences between commercial (MAP) and liquid dairy manure treatments were only on the order of 0.01 g DRP/ha. Assuming current manure application extent and rates, when accumulated annually across the WLEB watershed, these losses are equivalent to less than 1% of target loads. These findings also help to inform nutrient management stewardship as it relates to nutrient source. Furthermore, additional research across a range of soil characteristics and cropping managements should be explored as well as the impacts of other livestock manure nutrients. This article is protected by copyright. All rights reserved.

Missing in action: Reference sites

White et al. (2023) measured land area with precision in coastal areas exposed to river diversions, but the absence of concurrent measurements in reference sites prohibits them from making conclusions, which they do, that river diversions have a beneficial or neutral consequences but not harmful effects. Their global conclusions about land gain are inappropriate for analyses of areas embedded in ecosystems when there are no reference areas included in the analysis. Their inferences about the temporal on-site changes are valid, but measurements in suitable reference sites are needed to separate out the environmental ‘noise’ common to both and to allow conclusions about putative causes. Environmental impacts are typically discerned within a Before-After-Control-Impact (BACI) analysis. White et al.'s study design is a’BA’, but not a BACI design. They are critical of one of two of Turner et al.'s (2019) photogrammetric methods, but neglect to realize that the different methods reveal different aspects of land loss and are used independently of each other within a BACI framework having multiple reference sites. They also neglect to account for 1) results from a BACI analysis of thirty-two sites from farther downstream, 2) a striking loss of land after a natural river diversion opened up in 1973, and 3) they omit important information placing sediment retention into context. The problem of omitting reference sites in evaluations of environmental impacts is commonly observed and deserves wider attention to improve the general ecological intelligence of responsible parties and lay communities. Treating environmental projects a priori as experiments with testable hypotheses with alternative outcomes and actionable exit strategies will reduce errors and bias in endeavors with many unexpected unknowns.

Does experimental seaweed cultivation affect benthic communities and shorebirds? Applications for extensive aquaculture.

Extensive seaweed aquaculture is a growing industry expected to expand globally due to its relatively low impact and benefits in the form of ecosystem services. However, seaweeds are ecosystem engineers that may alter coastal environments by creating complex habitats on previously bare mudflats. These changes may scale up to top-consumers, particularly migratory shorebirds, species of conservation concern that regulate trophic webs at these habitats. Understanding how habitats are transformed and how this affects different species is critical to direct ecological applications for commercial seaweed management. We experimentally assessed through a Before-After Control-Impact design the potential changes exerted by Gracilaria chilensis farming on bare mudflats on the abundance, biomass, and assemblage structure of benthic macroinvertebrates, and their scaled-up effects on shorebirds' habitat use and prey consumption. As predicted, experimental cultivation of G. chilensis significantly affects different components of biodiversity that scale-up from lower to upper trophic levels. The total biomass of benthic macroinvertebrates increased with seaweed cultivation and remained high for at least 2 months after harvest, boosted by an increase in the median size of polychaetes, particularly Nereids. Tactile-foraging shorebirds tracked these changes at the patch level increasing their abundance and spending more time foraging at seaweed cultivated plots. These results suggest that seaweed farming has the potential to impact shorebird populations by favoring tactile-foraging species which could lead to a competitive disadvantage to species that rely on visual cues. Therefore, the establishment of new seaweed farms in bare mudflats at key sites for shorebirds must be planned warranting habitat heterogeneity (i.e., cultivated and non-cultivated areas) at the landscape level and based on a previous experimental approach to account for local characteristics. Fostering properly designed extensive seaweed farming over other aquaculture industries with greater negative environmental impacts would provide benefits for human well-being and for ecosystem functions.

Short-term effects of macrophyte removal on aquatic biodiversity in rivers and lakes

Mass development of macrophytes is an increasing problem in many aquatic systems worldwide. Dense mats of macrophytes can negatively affect activities like boating, fishing or hydropower production and one of the management measures often applied is mechanical removal. In this study, we analyzed the effect of mechanical macrophyte removal on phytoplankton, zooplankton, and macroinvertebrate (pelagic and benthic samples) assemblages. Our study covered five sites in four countries in Europe and Africa with highly variable characteristics. In all sites, dense mats of different macrophyte species (Juncus bulbosus in a river in Norway; a mix of native macrophytes in a German river, Elodea nuttallii in a lake in Germany, Ludwigia spp. In a French lake and Pontederia crassipes in a South African lake) are problematic and mechanical removal was applied. In every country, we repeated the same BACI (Before-After-Control-Impact) design, including “before”, “one week after”, and “six weeks after” sampling in a control and an impact section. Repeating the same experimental design at all sites allowed us to disentangle common effects across all sites from site-specific effects. For each taxonomic group, we analyzed three structural and three functional parameters, which we combined in a scoring system. Overall, the removal of macrophytes negatively affected biodiversity, in particular of zooplankton and macroinvertebrate assemblages. In contrast, plant removal had positive effects on the phytoplankton assemblages. Effects were more pronounced one week after removal than six weeks after. Consequently, we suggest a stronger consideration of the effect of plant removal on biodiversity to arrive at more sustainable management practices in the future.

Using Satellite NDVI Time-Series to Monitor Grazing Effects on Vegetation Productivity and Phenology in Heterogeneous Mediterranean Forests

The reintroduction of livestock grazing to regulate biomass load is being tested for large-scale restoration in Mediterranean landscapes affected by rural abandonment. Concurrently, there is a need to develop cost-effective methods to monitor such interventions. Here, we investigate if satellite data can be used to monitor the response of vegetation phenology and productivity to grazing disturbance in a heterogenous forest mosaic with herbaceous, shrub, and tree cover. We identify which vegetation seasonal metrics respond most to grazing disturbances and are relevant to monitoring efforts. The study follows a BACI (Before-After-Control-Impact) design applied to a grazing intervention in a Pyrenean oak forest (Quercus pyrenaica) in central Portugal. Using NDVI time-series from Sentinel-2 imagery for the period between June 2016 and June 2021, we observed that each type of vegetation exhibited a distinct phenology curve. Herbaceous vegetation was the most responsive to moderate grazing disturbances with respect to changes in phenology and productivity metrics, namely an anticipation of seasonal events. Results for shrubs and trees suggest a decline in peak productivity in grazed areas but no changes in phenology patterns. The techniques demonstrated in this study are relevant to a broad range of use cases in the large-scale monitoring of fine-grained heterogeneous landscapes.

Assessing the short-term response of fish assemblages to damming of an Amazonian river

The enormous biodiversity of tropical freshwater combined with a considerable increase in the construction of reservoirs urges to understand the ecological effects caused by damming. Using rarely available data obtained before (one year) and after (four years) the filling of a hydroelectric plant on the Teles Pires River (Amazon River basin), the effects on abundance, biomass, and diversity of the fish assemblage were evaluated using two complementary approaches: a BACI (before-after-control-impact) design with mixed models and analyses of covariance. Significant Before-After × Control-Impact interactions in abundance, biomass, and species richness were observed, with decreases of abundance and species richness and more stable biomass after filling. Some abundant species, such as Jupiaba polylepis, Jupiaba acanthogaster, Knodus cf. heteresthes, and Moenkhausia lepidura among others, declined in abundance or disappeared from the impact sites. However, temporal and particularly spatial variation independent of damming explained more variation in all the response variables analyzed, including species composition, and analyses of covariance demonstrated general negative trends irrespective of damming. This study illustrates the usefulness of BACI designs to assess the effects of damming but also that other statistical approaches are complementary, given the difficulty of identifying control sites and the short length of most ecological time series. The results also suggest that preserving tributaries upstream of reservoirs and natural regimes of spatial and temporal environmental variation might help to mitigate the impacts of damming in tropical ecosystems.

Field scale discharge and water quality response, to drainage water management

Subsurface (tile) drainage, while necessary for viable agricultural crop production in the humid, poorly drained regions of the world, has been linked to offsite nutrient transport, culminating in harmful algal blooms and hypoxia in downstream waterbodies. Drainage water management (DWM), also known as controlled drainage, has been promoted as a method to reduce nitrogen (N) and phosphorus (P) loss from field scale tile drainage; however, subsequent changes in surface runoff and associated water quality have not been explored. Four years of surface and subsurface discharge, N, and P loss from two sets of paired field sites in northwest Ohio, USA were evaluated using a before-after control-impact (BACI) design to quantify the impact of DWM. Mean event surface runoff was greater (significant at one site) under DWM while tile drainage discharge was less at both sites but not significant. There was no significant difference in surface nitrate-N (NO3--N) loss; however, significant reductions in tile NO3--N loss under DWM were measured at both sites. Similar to discharge, dissolved reactive P (DRP) loss measured in surface runoff was greater under DWM (significant at one site), while no significant differences were noted in mean event tile drainage DRP loss. Total P (TP) surface runoff losses were significantly greater under DWM at the site with significantly greater surface runoff, while DWM reduced tile drainage TP loss at only one site. These findings suggest that DWM reduced tile NO3--N loss, while also highlighting that any benefit from DWM with respect to tile DRP or TP loss could be negated in part by increased surface losses. Furthermore, these findings emphasize the need to understand the natural resource concern to which the practice is targeted and also call for additional research on DWM implementation that includes surface runoff across a range of soil textures, cropping management, and climates.

Beyond BACI: Offsetting carcass numbers with flight intensity to improve risk assessments of bird collisions with power lines.

The continuing global expansion of electricity networks increases the risk of bird collisions with power lines. Several field studies have demonstrated that this risk can be reduced by marking lines with flight diverters. A before‐after control‐impact (BACI) design is currently the suggested approach for evaluating the effectiveness of these diverters and is generally assumed to give unbiased results.Using systematic flight survey data, we demonstrate that the assumptions underlying the BACI approach are frequently violated, leading to biased effectiveness estimates. We present an alternative field and statistical design in which the number of bird strike victims is directly related to bird flight intensity (“fusion design”), instead of estimating it indirectly using a control site. The presented design is validated based on simulations.We demonstrate that the presented method is unbiased and shows an approximately 3‐fold higher statistical power compared with BACI, even under ideal/unbiased data conditions, with similar field‐experimental effort. Moreover, this approach can provide a direct analysis of bird reactions/collisions, estimation of collision rates, and the possibility of conducting the required fieldwork within a single season.Our presented method can be used to standardize and improve future studies on diverter effectiveness, for example, by supporting the acquisition of a more detailed picture of species‐, diverter type‐, and habitat‐specific estimates.

Recent Invaders in Small Mediterranean Islands: Wild Boars Impact Snakes in Port-Cros National Park

Mediterranean islands host unique ecosystems that are particularly vulnerable to invasive species. However, knowledge regarding the precise impact of invasive species on local biodiversity remains limited for many of these systems. Here we report on the negative impacts of invasive wild boars (Sus scrofa) on native snakes on islands in the Mediterranean basin. Capture-mark-recapture was initiated in 2012 on two snake species (Montpellier snake, Malpolon monspessulanus and Ladder snake, Zamenis scalaris) across two islands of Port-Cros National Park. Several wild boars, an invasive species, reached the islands in 2007. They remained confined to small areas of the islands for several years. In Port-Cros, the numbers of wild boars suddenly increased in 2015, and rapidly colonized the whole island damaging vast land surfaces. In Porquerolles, wild boars did not proliferate. This offered an opportunity to examine the impact of wild boar outbreak with a Before-After Control-Impact design (BACI). Snake counts and mark-recapture modeling showed that demographic traits were stable before 2016 for both snake species on both islands. As well as abundance, recruitment, and population growth rate of Montpellier snakes significantly declined where wild boars proliferated but remained constant on the island where they did not. Wild boars probably impacted snake numbers through habitat destruction and direct killing. The rapid decline of snakes (apex predators) and intensive uprooting that strongly damage ground dwelling species (plants, animals) suggest that wild boars represent a serious threat to island biodiversity. As elsewhere around the world, these invasive ungulates proliferate in the Mediterranean basin, they are proficient swimmers and exhibit a remarkably high invasive potential. We recommend vigilance and fast eradication to prevent population outburst; even a few a localized non-proliferating individuals contain the latent potential for devastating outbreaks.

Effects of Livestock Exclusion on Stream Banks and Riparian Vegetation in Washington and Oregon

Livestock exclusion is a widespread restoration technique in the Pacific Northwest to protect and improve riparian and stream habitats. To assess stream restoration outcomes from excluding livestock, the Washington State Salmon Recovery Funding Board and the Oregon Watershed Enhancement Board evaluated 12 livestock exclusion projects from 2004 to 2017 using a before-after control-impact design. Paired treatment and control reaches were monitored once before restoration implementation (year 0) and several years after implementation (years 1, 3, 5, and 10) to assess bank erosion, bank canopy cover, riparian vegetation structure, pool tail fine sediment, and exclosure fencing function. Livestock exclusion significantly reduced bank erosion and bare ground. Bank erosion in treatment reaches decreased from 44% pre-project to 11% by year 10. In treatment reaches, bare ground was over 1.5 times lower in year 10 than pre-project. Most treatment reaches had intact fencing at the conclusion of the ten-year monitoring period, but there were instances where fencing did not fully function as intended, allowing livestock to access riparian areas inside the exclosure. Several metrics did not respond over time, which may be the result of several factors, including limitations of the sampling protocols, evidence of livestock grazing in treatment reaches, lack of site stratification, control reaches that were not well matched with treatment reaches, and short-duration of pre-project data collection. Despite these limitations, we still detected significant decreases in bank erosion and bare ground within treatment reaches. Future livestock exclusion monitoring should consider focus on ensuring fence maintenance, improved monitoring oversight, and the use of more quantitative monitoring protocols.

The implementation of irrigation leads to declines in farmland birds

Assessing the effects of agricultural intensification on biodiversity is critical for developing effective management plans for farmland conservation. Among other factors, the direct and indirect impacts of irrigation on wildlife have yet to be thoroughly studied despite significant increases in the surface area of irrigated farmlands since the mid-twentieth century (currently greater than 300 million hectares worldwide). Here, we evaluate the impact of irrigation on bird species occurrence patterns using a BACI (Before-After Control-Impact) design. Our study occurs in a 100 km2 area with rainfed agriculture in the Mediterranean region of northern Spain. We analysed a 13-year dataset comprised of the 47 most common bird species in the region using a multi-species hierarchical occurrence model. We examined how the implementation of irrigation in a rain-fed farmland area altered the local bird community, identifying which species were negatively or positively impacted by changes to the local ecosystem. The implementation of irrigation had an overall negative impact on the bird community, with occurrence rates of most species (55%) decreasing and only a small fraction (11%) increasing after the onset of irrigation, leading to an overall reduction in site-level species richness. Irrigation had the most detrimental impact on farmland birds (including steppe birds, which are of high conservation concern), but also had negative effects on forest, shrubland, and non-specialist bird species that occur frequently in rainfed agricultural environments. The observed negative impacts on bird occurrences are likely due to the loss of nesting and foraging habitat arising from shifts in crops and/or loss of fallow lands associated with irrigation. The fact that only a few species responded positively to the implementation of irrigation suggests that in the long-term irrigation may lead to substantial negative changes in local bird communities, with less diversity and a lack of ecologically-important farmland species. Irrigation schemes should thus be implemented carefully, avoiding areas with high species richness or high densities of endangered species. In cases where irrigation cannot be avoided, promoting diverse agrosystems, avoiding monocultures, and including interspersed rainfed crops and fallow lands may help to mitigate negative effects on local bird communities and their ecosystems.

Road-effect mitigation promotes connectivity and reduces mortality at the population-level

Roads are one of the most prevalent threats to wildlife because they fragment landscapes and increase mortality. In response to the threat of roads to population persistence, road-effect mitigation strategies are increasingly common, typically as a combination of exclusion fencing to reduce mortality and crossing structures to enhance connectivity. To evaluate the success of mitigation structures at reducing road mortality of amphibians and reptiles, we conducted a six year paired Before-After-Control-Impact (BACI) experiment. We used road surveys to estimate the effectiveness of exclusion fencing, and a combination of hoop trapping, passive integrated transponder tag scanners and camera traps to evaluate connectivity structure effectiveness. Exclusion fencing reduced the number of turtles and amphibians on the road but had no effect for snakes. Cameras recorded 54 turtles, 72 snakes, 615 frogs, and 271 salamanders using tunnels. PIT tag scanners detected similar usage by turtles (55 uses; 24 unique individuals) and snakes (69 uses; 15 unique individuals). Tunnel usage was neither spatially nor demographically biased, indicating that the tunnels were likely to be broadly used by the local species assemblage. Crossing rates of tagged individuals suggest ~5–15% of turtles and 44% of snakes are using crossing structures. We contextualized crossing rates with population size estimates for painted and snapping turtles in the surrounding habitats. Our study is one of the first of its kind to incorporate both a robust BACI design and the context of population-level effects to demonstrate the efficacy of road-effect mitigation for protecting wildlife, especially for reptiles and amphibians.

Far-Field Effects of Impulsive Noise on Coastal Bottlenose Dolphins

Increasing levels of anthropogenic underwater noise have caused concern over their potential impacts on marine life. Offshore renewable energy developments and seismic exploration can produce impulsive noise which is especially hazardous for marine mammals because it can induce auditory damage at shorter distances and behavioral disturbance at longer distances. However, far-field effects of impulsive noise remain poorly understood, causing a high level of uncertainty when predicting the impacts of offshore energy developments on marine mammal populations. Here we used a 10-year dataset on the occurrence of coastal bottlenose dolphins over the period 2009–2019 to investigate far-field effects of impulsive noise from offshore activities undertaken in three different years. Activities included a 2D seismic survey and the pile installation at two offshore wind farms, 20–75 km from coastal waters known to be frequented by dolphins. We collected passive acoustic data in key coastal areas and used a Before-After Control-Impact design to investigate variation in dolphin detections in areas exposed to different levels of impulsive noise from these offshore activities. We compared dolphin detections at two temporal scales, comparing years and days with and without impulsive noise. Passive acoustic data confirmed that dolphins continued to use the impact area throughout each offshore activity period, but also provided evidence of short-term behavioral responses in this area. Unexpectedly, and only at the smallest temporal scale, a consistent increase in dolphin detections was observed at the impact sites during activities generating impulsive noise. We suggest that this increase in dolphin detections could be explained by changes in vocalization behavior. Marine mammal protection policies focus on the near-field effects of impulsive noise; however, our results emphasize the importance of investigating the far-field effects of anthropogenic disturbances to better understand the impacts of human activities on marine mammal populations.

Broad-Scale Responses of Harbor Porpoises to Pile-Driving and Vessel Activities During Offshore Windfarm Construction

Offshore windfarm developments are expanding, requiring assessment and mitigation of impacts on protected species. Typically, assessments of impacts on marine mammals have focused on pile-driving, as intense impulsive noise elicits adverse behavioral responses. However, other construction activities such as jacket and turbine installation also change acoustic habitats through increased vessel activity. To date, the contribution of construction-related vessel activity in shaping marine mammal behavioral responses at windfarm construction sites has been overlooked and no guidelines or mitigation measures have been implemented. We compared broad-scale spatio-temporal variation in harbor porpoise occurrence and foraging activity between baseline periods and different construction phases at two Scottish offshore windfarms. Following a Before-After Control-Impact design, arrays of echolocation click detectors (CPODs) were deployed in 25 km by 25 km impact and reference blocks throughout the 2017–2019 construction. Echolocation clicks and buzzes were used to investigate porpoise occurrence and foraging activity, respectively. In parallel, we characterized broadband noise levels using calibrated noise recorders (SoundTraps and SM2Ms) and vessel activities using AIS data integrated with engineering records. Following an impact gradient design, we then quantified the magnitude of porpoise responses in relation to changes in the acoustic environment and vessel activity. Compared to baseline, an 8–17% decline in porpoise occurrence was observed in the impact block during pile-driving and other construction activities. The probability of detecting porpoises and buzzing activity was positively related to the distance from vessel and construction activities, and negatively related to levels of vessel intensity and background noise. Porpoise displacement was observed at up to 12 km from pile-driving activities and up to 4 km from construction vessels. This evidence of broad-scale behavioral responses of harbor porpoises to these different construction activities highlights the importance of assessing and managing all vessel activities at offshore windfarm sites to minimize potential impacts of anthropogenic noise.

Improving the ability of a BACI design to detect impacts within a kelp-forest community.

Distinguishing between human impacts and natural variation in abundance remains difficult because most species exhibit complex patterns of variation in space and time. When ecological monitoring data are available, a before-after-control-impact (BACI) analysis can control natural spatial and temporal variation to better identify an impact and estimate its magnitude. However, populations with limited distributions and confounding spatial-temporal dynamics can violate core assumptions of BACI-type designs. In this study, we assessed how such properties affect the potential to identify impacts. Specifically, we quantified the conditions under which BACI analyses correctly (or incorrectly) identified simulated anthropogenic impacts in a spatially and temporally replicated data set of fish, macroalgal, and invertebrate species found on nearshore subtidal reefs in southern California, USA. We found BACIfailed to assess very localized impacts, and had low power but high precision when assessing region-wide impacts. Power was highest for severe impacts of moderate spatial scale, and impacts were most easily detected in species with stable, widely distributed populations. Serial autocorrelation in the data greatly inflated false impact detection rates, and could be partly controlled for statistically, while spatial synchrony in dynamics had no consistent effect on power or false detection rates. Unfortunately, species that offer high power to detect real impacts were also more likely to detect impacts where none had occurred. However, considering power and false detection rates together can identify promising indicator species, and collectively analyzing data for similar species improved the net ability to assess impacts. These insights set expectations for the sizes and severities of impacts that BACI analyses can detect in real systems, point to the importance of serial autocorrelation (but not of spatial synchrony), and indicate how to choose the species, and groups of species, that can best identify impacts.

The influence of a high-density sludge acid mine drainage (AMD) chemical treatment plant on water quality along the Blesbokspruit Wetland, South Africa

The Eastern Basin chemical acid mine drainage (AMD) treatment plant is one of the world’s largest high-density sludge (HDS) plants, and came into operation in August 2016. The plant is situated near the inoperative Grootvlei Mine in Springs, South Africa, and upstream of the Blesbokspruit Wetland, a former Ramsar Wetland of International Importance, now on the Montreux Record. Since being in operation it has had a major influence on surface water quality along the wetland area. The plant was constructed to mitigate the anticipated decant of AMD water from the abandoned Grootvlei Mine into the Blesbokspruit Wetland. Making use of the BACI (Before-After-Control-Impact) design, this study compares surface water quality of the Blesbokspruit upstream (control site) and downstream (impact site) of the treatment plant for 3-year periods before and after it came into operation. Quarterly water quality data (aluminium, ammonia, chloride, conductivity, dissolved oxygen, fluoride, iron, magnesium, manganese, nitrate, pH, phosphate, sodium and sulphate) from 2013–2019 were used for 5 historical Rand Water monitoring sites along the Blesbokspruit. The current HDS treatment process has negatively influenced conductivity, chloride, magnesium, sodium and sulphate levels downstream. Since the commissioning of the treatment plant, the levels of these parameters have increased significantly. Notably, conductivity and sulphate have reached the management range defined as ‘unacceptable’ within the framework set out by the Blesbokspruit Forum (which is less stringent than the national guidelines for aquatic ecosystems), with potential impacts on salinization of the Vaal Barrage downstream. However, the significant reduction of iron, ammonia and phosphate concentrations downstream of the plant may be a combined beneficial effect of dilution by increased discharge from the plant and the wetland removing these contaminants. These results highlight the need for further research into possible secondary treatment and desalinisation mechanisms and the potential ecological and downstream water supply implications of increasing salinity within the area.

Comparison of staircase and asymmetrical before–after, control–impact (aBACI) experimental designs to test the effectiveness of stream restoration at increasing juvenile steelhead density

Before–after, control–impact (BACI) experimental designs are commonly used in large-scale environmental experiments, but these designs can be confounded by location and time interactions. Staircase designs, where replicate treatments are staggered temporally, have been suggested as an alternative to BACI designs. We performed a simulation study based on data from an ongoing watershed-scale restoration experiment within three streams to test the effectiveness of adding large wood to increase habitat complexity and abundance and productivity of juvenile steelhead (Oncorhynchus mykiss). We compared the power of two asymmetric BACI (aBACI) designs with two staircase designs for detecting changes in the density of steelhead (fish·m–2). A staircase design where treatments were temporally staggered in one treatment section in each stream had the highest power and best precision, especially when the innate spatial and temporal variances of steelhead density were large. A traditional BACI performed the worst, and a variation on another BACI and staircase design had intermediate performance. Multistream staircase designs are also more logistically and economically feasible and can maximize learning by replicating experiments across different stream types.

Continuous riverine biodiversity changes in a 10‐years‐post‐restoration‐study—Impacts and pitfalls

AbstractEvaluating river restoration effects over several years is the exception rather than the rule. The benthic invertebrate fauna of three small mountain streams was investigated yearly from 2010 to 2019 following remeandering measures. Additionally, upstream near‐natural reaches were studied following a Before‐After‐Control‐Impact (BACI) design. Species richness and Ephemeroptera, Plecoptera and Trichoptera richness decreased strongly immediately after restoration but had positive effect sizes in the following 6 years. Abundances increased in all sites after restoration. These patterns were consistent also in the upstream near‐natural reaches, except for the decrease in richness in the second year, indicating that other factors beside the restoration affected the sites. A large flood event coincided with the implementation of the restoration measures depleting also the near‐natural sites. The similarity between paired reaches showed a sharp decline in the first year after restoration, followed by a direct increase, which indicates fast recolonization from the upstream reaches. Community composition analysis showed a shift of all communities with the time axis, underlining a substantial effect of external factors. Generalized linear mixed effects models exhibited that the percentage of tree cover and riparian vegetation had significant effects on changes in richness and abundance. Clear‐cut logging in the floodplains to restore natural floodplain forest supposedly increased water temperatures because many cold‐adapted upstream species were replaced by species naturally inhabiting more downstream reaches. The results emphasize that multiannual samples and a BACI design are necessary to understand restored systems. Furthermore, floodplain restoration and natural hydrology often shape benthic invertebrate communities more than pure instream restoration measures.

Conditioned odor aversion as a tool for reducing post‐release predation during animal translocations

AbstractPredation is a key factor in prey population dynamics and could impact population recovery. One common means employed to recover prey populations is that of translocations, but most fail owing to high predation during the early stages. We tested whether conditioned odor aversion can reduce predation during animal translocations by using the predation of the European rabbit Oryctolagus cuniculus by the red fox Vulpes vulpes as a case study. Following a before‐after control‐impact design (BACI), we deployed bait stations monitored using camera‐traps in two zones to which rabbits were translocated. One week before the rabbits were released, microencapsulated levamisole was added to rabbit baits located in the treatment zones, along with vanilla essence as an odor cue. A total of 148 rabbits were distributed in artificial warrens with the odor cue and 68 of them were fitted with radio collars in order to determine their survival rates. The response to the treatment and translocation as regards subsequent rabbit abundance was evaluated using N‐mixture models, while rabbit establishment was evaluated using a warren use index (WUI). The treatment decreased the proportion of baits consumed by foxes, but this decrease was partially compensated by other predators. WUI and rabbit population growth increased significantly more after translocations in the treatment zones than in the control zones. The short‐term survival of translocated rabbits was also higher in the treatment zones than in the control zones. Our study showed that conditioned odor aversion reduced rabbit predation by foxes, and had a positive effect on rabbit population growth after translocation, since there was an increase in rabbit survival and warren establishment. This method could be used as a non‐lethal tool for the recovery of a key prey when carrying out programs concerning the reintroduction of endangered predators or for other vulnerable species requiring translocations.