Environmental impact of a salmonid farm on a well flushed marine site: II. Biosedimentology

An environmental monitoring study was carried out between 1993, 1995 on the site of a marine trout farm located in the Bay of Cherbourg (English Channel), France. The study dealt with the sea bottom and solid waste from the farm, and concerns the deposition rate, sediment analysis and chemistry (fine fraction < 63 μm, organic matter, carbon, nitrogen and trace metals such as Cu and Zn), bottom oxygen demand, benthic macrofauna, and underwater video surveying. The observed impact was very moderate and localised, and showed no real abnormality. This was mainly due to the strong hydrodynamics characterising the site. A separate phase of the same study dealt with dissolved waste and the water mass (Part One: Current and water quality).     

Comparing habitat quality within and between environments using giving up densities: an example based on the winter habitat of white‐tailed deer Odocoileus virginianus

We previously developed a model, based on the precepts of optimal patch use, to compare habitat quality both within and between environments. Here we illustrate the use of this model in a study estimating quality of winter habitats (deer yards) of white‐tailed deer Odocoileus virginianus near the northern limit of their range by following their foraging behaviour. We compare giving up densities (GUDs), the amount of food remaining in a patch when a forager ceases foraging there, with and without the presence of supplemental food in order to draw inferences about the relative quality either of habitats within an environment or of distinct environments. We use our model to evaluate the impact of alterations to the winter habitat of deer at two distinct sites that differed in their level of predation risk and food availability. The first site, the Mont Rigaud deer yard, was surrounded by farm land and gradually‐expanding suburbs. Predators were rare and food was available in winter either in farm fields or around private homes but deer browsing in the past had left little food in the forest. At the second site, the Calumet deer yard, deer experienced a higher predation risk and did not have access to supplemental food from farm fields or private homes. However, past browsing by deer had not drastically reduced food in the forest. We offered food to deer in four habitats per site (forest, forest edge, clearing, clearing edge) with four to six replicates per site and measured the GUDs after 24 h. Analysis of these data, interpreted according to our model, suggests that deer are more sensitive to metabolic costs at Mont Rigaud and food availability at Calumet; predation risk does not alter deer behaviour between the two sites. Within habitats, deer at Mont Rigaud reacted to clearings as though they imposed higher metabolic costs than the forest. They also reacted to an interaction in which missed food costs influenced GUD only when metabolic costs were not too high. Thus our model appears to provide a convenient tool for comparing habitat quality both within and between environments.     

Influence of a Trout Farm on Water Quality and Macrozoobenthos Communities of the Receiving Stream (Trešnjica River,Serbia)

Trout farming is constantly increasing and poses a serious threat to water quality of clean highland streams. In the present work, we investigated the influence of the farm with the highest trout production in Serbia on water quality and macrozoobenthos communities of the receiving stream, the Trešnjica River. Our study revealed that changes of water chemistry parameters downstream from the trout farm were moderate and mainly confined to the part of the watercourse closest to the wastewater outlet. Moreover, use of food with 0.8% phosphorus content was sufficient to completely eliminate soluble phosphates from water samples of the Trešnjica River. However, the changes in water chemistry were sufficient to cause significant changes in the macrozoobenthos community. These changes remained statistically significant even 500 m downstream and were lost about 3.5 km from the trout farm wastewater effluent. The trout biomass on the farm is a parameter that adequately defines the magnitude of its impact, above all the intensity of its influence on the zoobenthos community structure. The most informative parameters for estimating that influence were the Baetidae/Ephemeroptera ratio, Margelef's index and the Modified biotic index. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High Diversity of Fungi may Mitigate the Impact of Pollution on Plant Litter Decomposition in Streams

We investigated how a community of microbial decomposers adapted to a reference site responds to a sudden decrease in the water quality. For that, we assessed the activity and diversity of fungi and bacteria on decomposing leaves that were transplanted from a reference (E1) to a polluted site (E2), and results were compared to those from decomposing leaves either at E1 or E2. The two sites had contrasting concentrations of organic and inorganic nutrients and heavy metals in the stream water. At E2, leaf decomposition rates, fungal biomass, and sporulation were reduced, while bacterial biomass was stimulated. Fungal diversity was four times lower at the polluted site. The structure of fungal community on leaves decomposing at E2 significantly differed from that decomposing at E1, as indicated by the principal response curves analysis. Articulospora tetracladia, Anguillospora filiformis, and Lunulospora curvula were dominant species on leaves decomposing at E1 and were the most negatively affected by the transfer to the polluted site. The transfer of leaves colonized at the reference site to the polluted site reduced fungal diversity and sporulation but not fungal biomass and leaf decomposition. Overall, results suggest that the high diversity on leaves from the upstream site might have mitigated the impact of anthropogenic stress on microbial decomposition of leaves transplanted to the polluted site.     

Nonphotosynthetic pigmented bacteria in a potable water treatment and distribution system

The occurrence of pigmented bacteria in potable water, from raw source water through treatment to distribution water, including dead-end locations, was compared at sample sites in a large municipal water system. Media used to enumerate heterotrophic bacteria and differentiate pigmented colonies were standard method plate count (SPC), m-SPC, and R2A agars, incubated up to 7 days at 35 degrees C. The predominant pigmented bacteria at most sample locations were yellow and orange, with a small incidence of pink organisms at the flowing distribution site. Seasonal variations were seen, with the yellow and orange organisms shifting in dominance. SPC agar was the least productive medium for both heterotroph counts and pigmented bacteria differentiation. At the flowing distribution site, percentages of pigmented bacteria on SPC medium ranged from 2.3 to 9.67 times less than on m-SPC and from 2.3 to 9.86 times less than on R2A. At the same site, seasonal trends in the percentage of pigmented bacteria were the same for m-SPC and R2A media, and the highest and lowest percentages occurred in the fall and winter, respectively. At site 6, there appeared to be an inverse relationship between the yellow and orange pigmented groups, but upon analysis, this did not hold and all correlations between yellow and orange pigmented bacteria were positive. The study results indicate that pigmented bacteria could readily be detected by using plate counting media developed for heterotroph enumeration in potable waters with incubation periods of 7 days. Pigmented bacteria can be used as an additional marker for monitoring changes in water quality. High numbers of heterotrophs, including pigmented forms, were found at dead-end locations, usually in the absence of a free chlorine residual and when the water temperature was greater than 16 degrees C. The association of some pigmented bacteria with nosocomial and other infections raises concern that the organisms may have originated from the potable water supply. High levels of pigmented bacteria could pose an increased health risk to immunologically compromised individuals. Therefore, the bacterial quality of the distribution water should be controlled to prevent the development of high concentrations of heterotrophic plate count bacteria, including the pigmented forms.     

Nonphotosynthetic pigmented bacteria in a potable water treatment and distribution system.

The occurrence of pigmented bacteria in potable water, from raw source water through treatment to distribution water, including dead-end locations, was compared at sample sites in a large municipal water system. Media used to enumerate heterotrophic bacteria and differentiate pigmented colonies were standard method plate count (SPC), m-SPC, and R2A agars, incubated up to 7 days at 35 degrees C. The predominant pigmented bacteria at most sample locations were yellow and orange, with a small incidence of pink organisms at the flowing distribution site. Seasonal variations were seen, with the yellow and orange organisms shifting in dominance. SPC agar was the least productive medium for both heterotroph counts and pigmented bacteria differentiation. At the flowing distribution site, percentages of pigmented bacteria on SPC medium ranged from 2.3 to 9.67 times less than on m-SPC and from 2.3 to 9.86 times less than on R2A. At the same site, seasonal trends in the percentage of pigmented bacteria were the same for m-SPC and R2A media, and the highest and lowest percentages occurred in the fall and winter, respectively. At site 6, there appeared to be an inverse relationship between the yellow and orange pigmented groups, but upon analysis, this did not hold and all correlations between yellow and orange pigmented bacteria were positive. The study results indicate that pigmented bacteria could readily be detected by using plate counting media developed for heterotroph enumeration in potable waters with incubation periods of 7 days. Pigmented bacteria can be used as an additional marker for monitoring changes in water quality. High numbers of heterotrophs, including pigmented forms, were found at dead-end locations, usually in the absence of a free chlorine residual and when the water temperature was greater than 16 degrees C. The association of some pigmented bacteria with nosocomial and other infections raises concern that the organisms may have originated from the potable water supply. High levels of pigmented bacteria could pose an increased health risk to immunologically compromised individuals. Therefore, the bacterial quality of the distribution water should be controlled to prevent the development of high concentrations of heterotrophic plate count bacteria, including the pigmented forms.     

Simulation models of finfish farms

A set of simulation models has been developed to aid in the understanding of environmental impacts of finfish mariculture. Because several different kinds of environmental impact are being investigated, it was decided to focus the modeling work on creating separate modules rather than a single monolithic programme. The overall structure of the model package is described and is available for test runs. At the heart of the package is a model (called FISH) which represents a single fish, specifically a salmon. This is a physiological model representing the specific kind of fish and using parameters such as the size and feeding regime, and environmental factors such as water temperature. She output of the FISH model is information on the growth and metabolism of the fish. The next level model is called POINT and represents the combination of fish present at a given site by age and size; it generates point source strengths for oxygen demand, nutrient excretion, and particulates. The output of the POINT model is used for input to three separate models dealing with effects on different space and time scales. One of these models is called FARM and deals with internal oxygen levels within a single farm site. The POINT model is used to calculate the oxygen demand within the farm, and this is combined with benthic and natural oxygen dynamics and a simple hydrodynamic model of flushing to calculate the net oxygen budget. A second model called SETTLE uses average currents and diffusion processes to calculate the benthic deposition of faeces and food particles, again using the point source strength for articulates computed from the POINT model. The third model is a large scale water quality model which uses a set of point sources corresponding to actual farm sites to look at predicted nutrient levels and biological oxygen demand throughout an entire estuary All models except for the water quality model were developed in Fortran using the BSIM simulation package and run on many different kinds of computers. Currently the mofels are being used for investigation of the environmental effects of salmon aquaculture in the L'Etang estuary on the South West coast of New Brunswick.     

Impact of a caged-trout farm on parasites of Galaxias maculatus in Lake Moreno, southern Argentina

The present study was conducted to determine the impact of a caged-trout farm on the helminth parasites of the wild fish puyen chico (Galaxias maculatus) in Lake Moreno, southern Argentina. Samples of water, fish (G. maculatus), and snails (Heleobia hatcheri) were taken at 4 sampling stations in January 2001. Wild fish were parasitized by 8 helminth species, all of which are endemic in the region; therefore, the farm did not introduce any helminth parasite to G. maculatus. Fish captured near the farm were not infected by the digenean Steganoderma szidati, whereas the abundance of the digenean Acanthostomoides apophalliformis in these fish was significantly lower than that in fish captured away from the farm. This lower abundance may be explained by the absence in this area of the snail H. hatcheri, the parasite's first intermediate host, because of the effect of sediments and ammonium produced by the farm. To our knowledge, this is the first study in the Americas linking fish-farm pollution to helminth parasites in wild fish.     

The relationships between hydrodynamics, the concentration of hydrogen sulphide produced by polluted sediments and fish health at several marine cage farms in Scotland and Ireland

Waste products from marine cage salmon farming can cause organic enrichment of the benthos in the immediate area of the farm with potentially deleterious consequences to fish health. The relationships between benthic enrichment and hydro-dynamic parameters - mean current speed, maximum current speed and incidence of low currents - were examined. Benthic impact was assessed on the basis of SCUBA diver observation and measurements of hydrogen sulphide in the water immediately (within 30 cm) overlying the sediment at slack water. Other factors such as maximum site biomass and the age of the site were also considered. At 7 of the 8 salmon farms studied there was a good correlation between mean current speed ( r =−0.877) and incidence of low currents ( r = 0.943) with log mean hydrogen sulphide concentration. The lack of correlation for the remaining site was thought to be due to a combination of high levels of terrigenous organic input to the site and overfeeding.
The relationship between fish growth and mortality with hydrogen sulphide concentration was also examined. Good correlation between both fish growth ( r =−0.819) and cumulative percentage mortality ( r = 0.941), and log mean hydrogen sulphide concentration were found when the data from one exceptional site were excluded.     

Prairie Wolf Slough Wetlands Demonstration Project: A Case Study Illustrating the Need for Incorporating Soil and Water Quality Assessment in Wetland Restoration Planning,Design and Monitoring

In northeastern Illinois, restored wetlands are used to improve water quality in streams degraded by agriculture and urban development. Using freshwater wetlands to reduce nitrogen loading to lakes and rivers is well documented; however, there are fewer studies addressing their use to remove phosphorous. In 1998, a systematic water quality monitoring project was begun at Prairie Wolf Slough Wetland Demonstration Project, a restored palustrine emergent marsh wetland located on an abandoned farm field north of Chicago. The wetland drains 98 ha of mixed land uses into the Chicago River. Our objectives were to assess spatial and temporal variations in total suspended solids, soluble reactive and total phosphorous concentrations, and mass loadings and compute a mass balance and retention efficiency for these constituents. Water sampling was conducted from 1998 to 2003. In 2004, soil samples were collected from the marsh and an adjacent abandoned farm site and analyzed for soil test (Bray) phosphorus. The marsh effectively traps suspended solids but acts as a source of soluble reactive and total phosphorous to the river both during the growing and nongrowing seasons. Net export of phosphorous from the wetland was likely due to mobilization of orthophosphate as a result of anoxic conditions produced during inundation events. Often little consideration is given to the link between soil and water quality when locating restoration sites. Our study adds to a growing body of literature that clearly demonstrates the need for both soil and water quality assessments in wetland restoration planning, design, and monitoring.     

Effects of a participatory approach,with systematic impact matrix analysis in herd health planning in organic dairy cattle herds

The animal health and welfare status in European organic dairy production does not in all aspects meet the organic principles and consumers’ expectations and needs to be improved. To achieve this, tailored herd health planning, targeted to the specific situation of individual farms could be of use. The aim of this study was to apply herd health planning in a structured participatory approach, with impact matrix analysis, not previously used in this context, in European organic dairy farms and to assess changes in animal health and welfare. Herd health planning farm visits were conducted on 122 organic dairy farms in France, Germany and Sweden. The farmer, the herd veterinarian and/or an advisor took part in the farm discussions. The researcher served as facilitator. Baseline data on the animal health status of the individual farm, collected from national milk recording schemes, were presented as an input for the discussion. Thereafter a systematic impact matrix analysis was performed. This was to capture the complexity of individual farms with the aim to identify the farm-specific factors that could have a strong impact on animal health. The participants (i.e. farmer, veterinarian and advisor) jointly identified areas in need of improvement, taking the health status and the interconnected farm system components into account, and appropriate actions were jointly identified. The researcher took minutes during the discussions, and these were shared with the participants. No intervention was made by the researcher, and further actions were left with the participants. The number of actions per farm ranged from 0 to 22. The change in mortality, metabolic diseases, reproductive performance and udder health was assessed at two time points, and potential determinators of the change were evaluated with linear regression models. A significant association was seen between change in udder health, as measured by the somatic cell count, and country. At the first follow-up, a significant association was also found between change in the proportion of prolonged calving interval and the farmers’ desire to improve reproductive health as well as with an increase in herd size, but this was not seen at the second follow-up. The degree of implementation of the actions was good (median 67%, lower quartile 40%, upper quartile 83%). To conclude, the degree of implementation was quite high, improvement of animal health could not be linked to the herd health planning approach. However, the approach was highly appreciated by the participants and deserves further study.     

The environmental impact of Mediterranean cage fish farms at semi-exposed locations: does it need a re-assessment?

During spring and summer 2003, we measured a variety of chemical and biological parameters in five medium-sized, Mediterranean cage farms that exploit semi-offshore conditions, and controlled the supply of fodder. The objective was to assess whether modern cage farms proliferating at semi-offshore sites exert environmental impact levels equivalent to the levels described from more traditional cage farms located in shallow, sheltered sites. In the water column, we examined the concentration of dissolved inorganic nutrients and heterotrophic bacteria in both surface and near-bottom water. At the bottom, we examined the concentrations of benthic chlorophyll a, phaeophytin and organic matter in sediments, the granulometric structure of the sediment, and the taxonomic (at the family level) abundance of benthic macroinvertebrates. For most parameters, we found no substantial differences between farm and control sites. Rather, most variation was explained as a function of depth (surface versus bottom water) or season (spring versus summer conditions). Deviations of farm values from control values, when they occurred, were small and did not indicate any significant impact on either bacterioplankton or benthic chlorophyll. Only one of the five farms studied exerted a detectable impact on the benthic macroinvertebrate community immediately under the cages. These results suggest that medium-sized fish farms located on semi-exposed western Mediterranean coasts have fewer environmental impacts than traditional fish farms located in shallow, sheltered sites. Impact characterization in these new farms may require refinement of the standard approach to deal with rapid dispersal of effluents and sub-lethal levels of environmental disturbance.     

Structural and trophic alterations in macrobenthic communities downstream from a fish farm outlet

The changes generated by a Spanish trout farm, located in the upper Río Tajuña (Central Spain), on benthic macroinvertebrates were studied by comparing biological characteristics of an upstream station (S-1) with those of three downstream sites placed 0.01 (S-2), 0.15 (S-3) and 1 (S-4) km below the fish farm outlet. In addition, a biological index is presented for estimating relative contributions (informative weights) of major macroinvertebrate groups to the macrobenthic community. Species richness and Shannon diversity were depressed downstream from the trout farm. However, density and biomass values were significantly higher at downstream stations during the summer, presumably due to an increase in water temperature and food supply. Amphipods, plecopterans and planarians were the macroinvertebrates most adversely affected by the fish farm effluent. Coleopterans, ephemeropterans and trichopterans were absent immediately below the outlet (S-2), but exhibited a partial downstream spatial recovery of their informative weights at S-3 and S-4. The abundance of tubificid worms, chironomids, simuliids and leeches increased below the trout farm, with dipterans predominating at all downstream sampling sites. The macrobenthic trophic structure was altered downstream from the trout farm by a significant increase in collectors (gathers and filter feeders) and predators, and a marked decrease in shredders and scrapers. The highest environmental impact was found just below the troutfarm outlet (S-2). It is concluded that the fish farm generates potamological effects on the functional structure of the macrobenthic community.     

Potential causes of habitat degradation and spawning time delay of the Chinese sturgeon (Acipenser sinensis)

In fish conservation, it is important to simulate fish habitat suitability and determine the potential impact on habitat quality and species behavior. This study analyzed the impact of several hydraulic projects on fish habitat quality and spawning time by numerical modeling. The case study involved the only Chinese sturgeon spawning site in the Yangtze River, China. Four habitat assessment indexes reflected both habitat quality and spatial characteristics, including fragmentation and connectivity. Previous studies did not simulate the water temperature impact on the fish habitat; spawning time delay was attributed to water temperature increases and discharge decreases. The results of the present study showed that the water temperature increase from the Three Gorges Reservoir (TGR) impoundment primarily caused the habitat degradation and spawning time delay. The effect of the water temperature increase on the degradation of average habitat suitability was eight times that of a decrease in discharge. A 25-day delay in the water temperature trend line was significantly correlated with a 26-day delay in the first spawning date. A decrease in discharge after TGR impoundment did not cause the spawning date delay. The Dike Project mainly impacted spawning site connectivity. Controlling the water temperature of the released water discharge is the most important means of conserving the wild Chinese sturgeon. This research can benefit other regions considering hydraulic projects by identifying potential factors impacting fish habitat quality and overall ecosystem health.     

Land-use proximity as a basis for assessing stream water quality in New York State (USA)

The influence of the proximity of urbanization and agriculture to stream water quality is often difficult to quantify. The objectives of this study were to (1) compare the influence of far-field land-use, encompassing a watershed drainage area, to a near-field, 200-m buffer on each side of the stream in an attempt to determine on which zone of influence land-use has the largest impact on water quality, and (2) incorporate the EPA's Rapid Habitat Assessment Protocol (Barbour et al., 1999) to characterize the riparian and channel characteristics of a stream that influence water quality, which can improve New York State's monitoring protocols. Impacts were assessed through biological, chemical, and physical-habitat data from 29 streams located within a variety of land-use categories. Land-use was identified through USGS National Land Cover Data (NLCD). Principal components analysis (PCA) indicated that land-use and water quality variables were associated with non-point source contaminants (e.g. nutrients and specific conductance). Using Spearman's rank correlation coefficient, significant relationships between all three land-use types and stream water quality were determined at the 200-m buffer zone of influence. At the watershed zone of influence, water quality indicators did not correlate significantly with land cover type. DO and BAP values within the 200-m buffer zone varied inversely with the percentage of urban-land cover. The stronger correlation between land cover and stream water quality at the 200-m proximity than that of the watershed suggests that the presence of a riparian buffer zone between streams and agricultural and urban areas is a significant factor in reducing contamination from non-point source loading.     

Evaluation of salmon farming effects on marine systems in the inner seas of southern Chile: a large-scale mensurative experiment

The impact of salmon farming on the environment has been widely studied; there is, however, no consensus on the magnitude and quality of these effects and little information on their extent over large salmon farming areas. Forty‐three salmon farm sites of which 29 are in full operation and grouped in nine locations in southern Chile were evaluated. Using statistical methods (two‐way anova ), no effects were found on water column variables such as nitrate, ammonia, orthophosphate and chlorophyll, whereas they were significant on sediment variables such as nitrogen (N), phosphorus (P) and organic carbon (OC), among others. Natural variability evaluation of some parameters revealed that P in sediments had the lowest coefficient of variation (23.2%) when compared with N (65.2%), particulate organic matter (POM) (139%) and OC (39%), and showed more marked salmon farming effects with no locality effects. Four of the nine locations showed stronger effects on sediments, with average P values ranging from 150 to 230 mmol that were six to nine times higher than in control sites (25 mmol). Nitrogen and carbon in sediments, while showing significant effects on salmon farming, also showed locality effects that revealed other biogenic processes influencing sediment composition. Thus, P in sediments was proposed as a promising indicator of impact on salmon farming, although the relationship with fauna in sediments was not linear and somewhat variable; more research is therefore needed to understand such connections. Considering entire geographical locations, no relationship was found between sediment conditions under salmon cages and the condition of the water column at a farm. This may indicate the possibility of high dilution rates and recycling processes, which so far preclude the detection of more global impacts beyond the cages shadow.     

The effect of habitat-specific sampling on biological assessment of water quality using a predictive model

1. Detection of impairment in macroinvertebrate communities using rapid biological assessment depends on the ability to compare sites, with confidence that differences obtained result from water quality. However, collections from more than one habitat type may introduce variation that can potentially mask water quality differences among sites. Data were collected from the riffle, edge, pool-rock and macrophyte habitats at reference (minimally disturbed) and test (disturbed) stream sites throughout the Australian Capital Territory. The effect of habitat-specific sampling on predictive models for detecting impairment in macroinvertebrate communities was determined. Four models were used: riffle only, edge only, each habitat as an individual object, and all habitats sampled at a site considered as a composite sample. 2. Macroinvertebrates from individual habitats generally clustered into separate groups because collections from the same habitat at different sites were more similar than collections from different habitats within a site. Thus, in the habitats as individual objects model, the taxa predicted to occur at a test site may be an indication of habitat type rather than water quality. The outputs of the composite habitats and riffle and edge models were similar. However, the variable number of habitats included at each site in the composite model may confound the detection of biological impairment because of unequal sampling effort. The riffle and edge models were the most robust because they were less confounded by inter-habitat variation and were based on comparisons made between equivalent environmental units. 3. Comparison of observed/expected taxa ratios for test sites showed that each model could detect biological impairment, indicating considerable data redundancy was introduced by sampling several habitats. In particular, the pool-rock and macrophyte habitats contributed no information with regard to macroinvertebrate taxon occurrence or detection of biological impairment that could not be obtained from either the riffle or edge habitats within the study area.     

Spatial variability in the response of lower trophic levels after carp exclusion from a freshwater marsh

Large common carp (Cyprinus carpio >30 cm) wereexcluded from a turbid, eutrophic coastal marsh of Lake Ontario with theconstruction of a fishway at the outlet. The marsh was sampledintensively for 2 seasons prior to (1993, 1994) and following (1997,1998) carp exclusion to study changes in water quality and shifts incommunity structure of phytoplankton and zooplankton. Samples werecollected from May to September in three habitats: open water, vegetated(cattail beds) and sewage lagoon. In the first year after carpexclusion, mean seasonal water turbidity decreased at all sites by49–80%; this was accompanied by growth of submergentplants in shallow, sheltered areas including the vicinity of cattails atthe vegetated site. This drop in turbidity was not significant in thesecond year after exclusion at the open water and lagoon sites, withturbidity levels declining by only 26–54% of1993–1994 values; only the vegetated site showed a sustaineddecrease in turbidity and persistent growth of submergent plants. At thevegetated site, increased clarity was concurrent with a significantreduction in edible algal biomass and an increased representation oflarge zooplankton grazers and substrate-associated cladocerans. At theopen water site, a spring clear-water phase was evident during the firstyear of exclusion and this coincided with the unusual appearance of alarge population of Daphnia. Compared to the other sites, thelagoon remained relatively turbid throughout the study. Results of thisstudy indicate that the response of lower trophic levels tobiomanipulation was variable from site-to-site and contributed to theco-existence of two alternative states in the marsh. In vegetated areas,water clarity was maintained by a positive feedback system betweenzooplankton and submergent macrophytes in the first 2 years followingexclusion. We suggest that both benthivore removal (to reducebioturbation) and planktivore reductions (to produce top down effects)were required to produce clear water and allow submersed macrophytegrowth. Although carp removal likely contributed to a 45%reduction in turbidity, an unusual climactic event in 1997, resulting indelayed fish spawning in the marsh, temporarily reduced zooplanktivoryand favoured zooplankton grazing-induced water clarity improvements.     

Responses of foraminifera communities to aquaculture‐derived organic enrichment as revealed by environmental DNA metabarcoding

Current monitoring methods to assess benthic impacts of marine finfish aquaculture are based on complex biological indices and/or geochemistry data. The former requires benthic macrofauna morpho‐taxonomic characterization that is time‐ and cost‐intensive, while the latter provides rapid assessment of the organic enrichment status of sediments but does not directly measure biotic impacts. In this study, sediment samples were collected from seven stations at six salmon farms in British Columbia, Canada, and analyzed for geochemical parameters and by eDNA metabarcoding to investigate linkages between geochemistry and foraminifera. Sediment texture across farm sites ranged from sand to silty loam, while the maximum sediment pore‐water sulphide concentration at each site ranged from 1,000 to 13,000 μM. Foraminifera alpha diversity generally increased with distance from cage edge. Adonis analyses revealed that farm site explained the most variation in foraminifera community, followed by sediment type, enrichment status, and distance from cage edge. Farm‐specific responses were observed in diversity analyses, taxonomic difference analyses, and correlation analyses. Results demonstrated that species diversity and composition of foraminifera characterized by eDNA metabarcoding generated signals consistent with benthic biodiversity being impacted by finfish farming activities. This substantiates the validity of eDNA metabarcoding for augmenting current approaches to benthic impact assessments by providing more cost‐effective and practicable biotic measures than traditional morpho‐taxonomy. To capitalize on this potential, further work is needed to design a new nomogram that combines eDNA metabarcoding data and geochemistry data to enable accurate monitoring of benthic impacts of fish farming in a time‐ and cost‐efficient way.     

Effects of land use on water quality and aquatic biota of three North Carolina Piedmont streams

Three streams in the Piedmont ecoregion of North Carolina were studied to evaluate the effect of land use (forested, agricultural, urban) on water quality and aquatic biota. In comparison with the forested stream, there were few changes in water quality at the agricultural and urban streams. Suspended-sediment yield was greatest for the urban catchment and least at the forested catchment. Suspended-sediment concentrations during storm events followed this same pattern, but at low-moderate flows suspended-sediment concentrations were greatest at the agricultural site. Most nutrient concentrations were highest at the agricultural site, and the amount of available dissolved nitrogen was elevated at both the urban and agricultural sites. High concentrations of metals (totals) in the water column were sometimes observed at all sites, but maximum average concentrations were recorded at the urban site (especially Cr, Cu, and Pb). Maximum sediment metal concentrations, however, were not found at the urban site, but were usually recorded at the forested site. Only minor differences were noted between fish communities of the forested and agricultural sites, although both abundance and average size of some species increased at the agricultural site. The fish community at the urban site was characterized by low species richness, low biomass, and the absence of intolerant species.Invertebrate taxa richness, a biotic index, and the number of unique invertebrate species (found at only one site) indicated moderate stress (Fair water quality) at the agricultural site and severe stress (Poor water quality) at the urban site. At the agricultural site, declines in taxa richness within intolerant groups were partially offset by increases within tolerant groups. The agricultural stream had the highest abundance values, indicating enrichment. The urban site, however, was characterized by low species richness for most groups and very low abundance values. Analysis of seasonal patterns suggested detritus was the most important food source for invertebrates in the forested stream, while periphyton was of greater importance in the agricultural stream. Dominant macroinvertebrate groups shifted from Ephemeroptera at the forested site, to Chironomidae at the agricultural site, and Oligochaeta at the urban site. There was little between-site overlap in dominant species (8–7%), indicating that land use strongly influenced the invertebrate community. Chemical and physical parameters measured at the three sites did not seem sufficient to account for all of the observed differences in the invertebrate communities, suggesting some unmeasured toxicity. Biological measurements, especially macroinvertebrates community structure, consistently indicated strong between-site differences in water and habitat quality.