Acid Stream Water Remediation Using Limestone Sand on Bear Run in Southwestern Pennsylvania

Instream limestone sand application is used at many sites in Pennsylvania to neutralize acidic stream water resulting from acid deposition. However, questions remain about the effectiveness of limestone sand in the treatment of acid waters, such as reduced contact time at high flow, remobilization of aluminum, and adverse effects on macroinvertebrates. A 1‐year evaluation of limestone sand application to Bear Run, an acidic stream in southwestern Pennsylvania, was begun in 1999. Another nearby acid stream, Linn Run, served as a control. Water quality during baseflow and episodic acidification events, along with fish and macroinvertebrates, were monitored to evaluate impacts of the sand application. Hydrogen ion (H ⁺ ) concentration and total dissolved aluminum (TDA) were significantly reduced, and acid neutralizing capacity was significantly increased downstream of the limestone sand application compared with the upstream site on Bear Run. These parameters at the downstream sites were also different (∝ 0.10) from the comparable sites on the control stream. TDA and hydrogen ion concentrations were significantly decreased (∝ 0.10) compared with concentrations before the sand application to Bear Run but not on the control stream. No fish were present upstream of the sand application site, and only a few fish were found downstream at the mouth of Bear Run. Standing crop, number of taxa, and Shannon‐Weaver diversity index values indicated that macroinvertebrate populations were negatively impacted 300 m downstream from the sand application and improved at the site 1,600 m downstream. Although water quality was improved on Bear Run, benefits to macroinvertebrates depended on downstream location, and fish populations did not show improvement.     

Homing in juvenile salmon in response to imposed and spontaneous displacement: experiments in an artificial stream

Displacement of juvenile Atlantic salmon Salmo salar within an artificial stream was either spontaneous (fish left areas of shallow water in response to experimental reduction in water level) or imposed (fish were removed by the experimenter from areas of shallow water and placed at a distance from their home site). Prior to displacement, the fish showed a high degree of site fidelity in terms of preferential use of specific areas within the stream, but the extent to which this persisted once they had left/been removed from their preferred sites was variable. Direction of displacement was not a critical factor, but homing was significantly less likely to occur following spontaneous as opposed to imposed displacement. In the case of imposed displacement, fish that were more strongly site attached prior to displacement were more likely to return to their home site after this manipulation.     

Social status and growth rates as determinants of site attachment in juvenile Atlantic salmon

This paper describes an experimental study of the effects of food supply, growth rates and social interactions on homing by juvenile Atlantic salmon Salmo salar in response to displacement. Groups of five fish were housed in a section of an artificial stream and given either rations allowing maximum growth (the rich condition) or 0·1 of this amount (the poor condition); daily specific growth rates were significantly higher in the rich condition. After a 6-day settlement period, the fish were captured, displaced downstream and their movements recorded over the next 3 h. Prior to displacement, the fish showed a high degree of site fidelity and high levels of aggression. Dominant fish and those with stronger site attachment grew faster prior to displacement, these effects being independent. Following displacement, 24% of all fish returned to their previously favoured site and stayed there, 23% returned home initially, but subsequently moved on, 5% settled in a new site and 49% failed to move. The distribution of responses was identical for the rich and poor conditions, but fish that homed were dominant and had grown faster during the pre-displacement period.     

Downstream fish assemblage response to river impoundment varies with degree of hydrologic alteration

River impoundments can fundamentally restructure downstream fish assemblages by altering flow regimes. However, the degree of alteration and associated ecological change may depend on pre-existing hydrologic regimes. We used long-term datasets to compare downstream hydrological and fish assemblage responses to impoundment in two catchments classified as having intermittent and perennial-flashy natural hydrologic regimes. We observed significant shifts in fish assemblage structure at both sites after stream impoundment. The historically intermittent stream shifted to a stable perennial flow regime. Changes in fish assemblage structure covaried with changes in five different components of the flow regime; most species that increased in abundance require fluvial habitats and likely benefited from increased flows during historically low flow seasons. Shifts in fish assemblage structure were also observed in the perennial stream, despite minimal flow alteration after impoundment; however, most species shifts were associated with lentic environments, and were more likely related to proximity of reservoirs in the drainage system rather than changes in stream flow. Findings from this study confirm that downstream fish assemblage response to river impoundment can be associated with high levels of hydrologic alteration, but other factors including expansion of lentic species into lotic environments also influence shifts in assemblage structure.     

Homing behaviour of stream-dwelling brook charr following experimental displacement

Precise homing of 24 brook charr Salvelinus fontinalis (157–215 mm L_F), displaced from their site of capture in a natural stream, was rare both in fish displaced upstream and those displaced downstream. Most fish settled in preferred habitats (pool or glide) away from their home site and showed restricted movement up to the pre-spawning period. Partial return responses, however, were stronger in fish displaced downstream than in fish displaced upstream. Most fish displaced downstream showed directional upstream movement soon after displacement, whereas fish displaced upstream did not show directional upstream movement, suggesting that it is primarily olfactory cues from upstream locations, and not positive rheotaxis, which mediate the return response. Homing success was unrelated to distance of displacement, body size, or population density in the home site, but daily mobility increased with body size for fish displaced downstream. There was no evidence of switching between specific areas between night and day, nor of differences between daytime and night-time mobility, suggesting that diel movement cycles did not bias the evaluation of homing success. Site attachment in stream-dwelling brook charr may be characterized as persistent (undisturbed fish remain stationary over long periods), but readily disrupted by involuntary displacement.     

Migratory drift of larval freshwater shrimps in two tropical streams, Puerto Rico

1. Migratory shrimps are often major biotic components of tropical stream communities, yet spatial and temporal patterns of their migration have yet to be described. This information is of increasing importance given the continued fragmentation of tropical streams by damming and water abstraction/diversion, which can disrupt migratory life cycles. 2. Larval amphidromous shrimps are released by adult females in freshwater streams. They then drift passively to an estuarine habitat where they metamorphose before migrating back upstream. Drift of larval shrimps was sampled over two to five 24-h periods at each of three sites along two rivers that drain the Luquillo Experimental Forest in Puerto Rico: the Espíritu Santo (10, 135 and 335 m a.s.l.) and the Mameyes (10, 90 and 290 m a.s.l.). A total of seventeen diel samplings were conducted. 3. Shrimp drift increased in the downstream direction in both catchments, and had a significant positive exponential relationship with length of stream channel above each site. There was no significant difference between catchments with respect to mean daily drift rate per km of stream channel. Maximum observed larval shrimp density was 69 102 larvae 100 m^–3 (1.7 g dry mass 100 m^–3), which is high relative to published invertebrate drift studies. 4. The pattern of shrimp drift agreed with the ’risk of predation hypothesis‘. In stream reaches with predatory fish, drift of larval shrimps occurred at night and was slight during the day. A nocturnal peak in drift occurred between 19.00 and 22.00 h. At a high-altitude site, where predatory fish were absent, no diel pattern was discernible. 5. The present study provides information on the timing of migratory drift of larval shrimps, which can minimize the adverse effects of water abstraction from streams draining the Luquillo Experimental Forest. Elimination of water withdrawal during peak larval drift after dark will significantly reduce shrimp mortality.     

Effects of stream restoration and wastewater treatment plant effluent on fish communities in urban streams

1. Fish community characteristics, resource availability and resource use were assessed in three headwater urban streams in Piedmont North Carolina, U.S.A. Three site types were examined on each stream; two urban (restored and unrestored) and a forested site downstream of urbanisation, which was impacted by effluent from a wastewater treatment plant (WWTP). Stream basal resources, aquatic macroinvertebrates, terrestrial macroinvertebrates and fish were collected at each site. 2. The WWTPs affected isotope signatures in the biota. Basal resource, aquatic macroinvertebrate and fish δ¹⁵N showed significant enrichments in the downstream sites, although δ¹³C signatures were not greatly influenced by the WWTP. Fish were clearly deriving a significant part of their nutrition from sewage effluent‐derived sources. There was a trend towards lower richness and abundance of fish at sewage‐influenced sites compared with urban restored sites, although the difference was not significant. 3. Restored stream sites had significantly higher fish richness and a trend towards greater abundance compared with unrestored sites. Although significant differences did not exist between urban restored and unrestored areas for aquatic and terrestrial macroinvertebrate abundances and biotic indices of stream health, there appeared to be a trend towards improvements in restored sites for these parameters. Additional surveys of these sites on a regular basis, along with maintenance of restored features are vital to understanding and maximising restoration effectiveness. 4. A pattern of enriched δ¹³C in fish in restored and unrestored streams in conjunction with enriched δ¹³C of terrestrial invertebrates at these sites suggests that these terrestrial subsidies are important to the fish, a conclusion also supported by isotope cross plots. Furthermore, enriched δ¹³C observed for terrestrial invertebrates is consistent with some utilisation of the invasive C4 plants that occur in the urban riparian areas.     

Benthic invertebrate assemblage change following dam removal in a Wisconsin stream

Small dams (height <10 m) have transformed stream networks across the United States. Shopiere Dam was removed from Turtle Creek, a fourth order stream in Southeastern Wisconsin in the fall of 1999. We sampled three sites (upstream of the impoundment, immediately below the dam, and farther downstream) before and after dam removal to identify changes in the invertebrate assemblage following removal. Prior to removal, upstream and downstream sites had similar taxonomic composition. In contrast the dam site had more taxonomic variation. The upstream, dam and downstream sites responded differently to dam removal in analyses of diversity, functional feeding groups, and invertebrate composition. Upstream at the reference site, changes in functional feeding group composition appeared to be associated with a decrease in silt coverage. At the dam site, taxonomic composition changed following dam removal, however diversity and functional feeding groups remained similar. At the downstream site, the invertebrate assemblage remained similar in all analyses. Our observations indicate that the effects of dam removal were not uniform through the stream, rather each site responded in a different way.     

Dissolved organic carbon and its utilization in a riverine wetland ecosystem

Variations in dissolved organic carbon (DOC) concentrations of surface waters and subsurface interstitial groundwater of riparian and wetland soils to 1.2 m depth were evaluated in a riverine wetland ecosystem over one year. DOC was monitored at seven sites within the wetland pond, two sites on the inflow stream, and one site on the outflow stream. Surface concentrations in the inflow stream ranged from 0.74 to 11.6 mg C L^–1 and those of the outflow from 2.1 to 8.0 mg C L^–1 Average DOC from stream floodplain hydrosoils (3.1 to 32.1 mg C L^–1 was greater than DOC from the sediments below the stream channel (1.6 to 6.8 mg C L^–1 Surface DOC within the wetland varied seasonally, with greatest fluctuations in concentrations through the summer and autumn (range 4.8 to 32.6 mg C L^–1 ) during intensive macrophyte growth and bacterial production. DOC was less variable during the winter months (1.7 to 3.3 mg C L^–1 Within the wetland pond, average DOC concentrations (7.1 to 48.2 mg C L^–1) in the subsurface waters were significantly greater (p < 0.05) than average surface concentrations. The microbial availability of surface and subsurface DOC to bacteria was evaluated from losses of DOC by wetland bacteria grown on the DOC. Bacterial growth efficiencies ranged from 5 to 20% and were negatively correlated to the percentage of DOC removed by bacteria (r²=0.93). Throughout the ecosystem, DOC concentrations were greatest in the subsurface waters, but at most depths this DOC was a less suitable substrate than surface DOC for utilization by bacteria.     

The post‐spawning movements of migratory brown trout Salmo trutta L.

The post spawning behaviour of sea trout Salmo trutta was studied over a 2 year period in the river and estuary of the River Fowey, south‐west England. Forty‐five sea trout kelts were trapped immediately after spawning in December and intraperitoneally tagged with miniature acoustic transmitters. The subsequent emigration into coastal waters was monitored using acoustic receivers deployed throughout the river catchment. The levels of gill Na⁺K⁺ATPase activity in sea trout kelts sampled at the same time as the tagged fish were within the range of 2·5 to 4·5 μmol Pi per mg protein per h indicating that the post‐spawning fish were not physiologically adapted to salt water. The tagged kelts were resident in fresh water between 4 and 70 days before entering the estuary. Sixty two per cent of the tagged kelts subsequently migrated successfully into coastal waters, with a higher success rate for male fish (75%) than females (58%). There was a significant size related difference in the run‐timing of the kelts with the larger fish moving more quickly into coastal waters after spawning than smaller fish. Seaward migration within fresh water was predominantly nocturnal and generally occurred in conjunction with increasing river discharge and rising water temperature. Migration through the estuary continued to be predominantly nocturnal and occurred during an ebbing tide. Residency within the estuary varied amongst individuals although it was invariably short, with most fish moving out into coastal waters within one to two tidal cycles. Five tagged kelts returned from the coastal zone and re‐entered fresh water during April and June. Marine residence time varied between 89 and 145 days (mean 118 days) and the minimum estimated marine survival was c. 18%. One of these sea trout was subsequently recaptured after successfully spawning in the vicinity where it had been previously tagged demonstrating a degree of spawning site fidelity.     

Effects of floods on fish assemblages in an intermittent prairie stream

1. Floods are major disturbances to stream ecosystems that can kill or displace organisms and modify habitats. Many studies have reported changes in fish assemblages after a single flood, but few studies have evaluated the importance of timing and intensity of floods on long‐term fish assemblage dynamics. 2. We used a 10‐year dataset to evaluate the effects of floods on fishes in Kings Creek, an intermittent prairie stream in north‐eastern, Kansas, U.S.A. Samples were collected seasonally at two perennial headwater sites (1995–2005) and one perennial downstream flowing site (1997–2005) allowing us to evaluate the effects of floods at different locations within a watershed. In addition, four surveys during 2003 and 2004 sampled 3–5 km of stream between the long‐term study sites to evaluate the use of intermittent reaches of this stream. 3. Because of higher discharge and bed scouring at the downstream site, we predicted that the fish assemblage would have lowered species richness and abundance following floods. In contrast, we expected increased species richness and abundance at headwater sites because floods increase stream connectivity and create the potential for colonisation from downstream reaches. 4. Akaike Information Criteria (AIC) was used to select among candidate regression models that predicted species richness and abundance based on Julian date, time since floods, season and physical habitat at each site. At the downstream site, AIC weightings suggested Julian date was the best predictor of fish assemblage structure, but no model explained >16% of the variation in species richness or community structure. Variation explained by Julian date was primarily attributed to a long‐term pattern of declining abundance of common species. At the headwater sites, there was not a single candidate model selected to predict total species abundance and assemblage structure. AIC weightings suggested variation in assemblage structure was associated with either Julian date or local habitat characteristics. 5. Fishes rapidly colonised isolated or dry habitats following floods. This was evidenced by the occurrence of fishes in intermittent reaches and the positive association between maximum daily discharge and colonisation events at both headwater sites. 6. Our study suggests floods allow dispersal into intermittent habitats with little or no downstream displacement of fishes. Movement of fishes among habitats during flooding highlights the importance of maintaining connectivity of stream networks of low to medium order prairie streams.     

Contrasted impacts of climate change on stream fish assemblages along an environmental gradient

Aim To investigate the potential impacts of climate change on stream fish assemblages in terms of species and biological trait diversity, composition and similarity. Location One‐thousand one‐hundred and ten stream sections in France. Methods We predicted the future potential distribution of 35 common stream fish species facing changes in temperature and precipitation regime. Seven different species distribution models were applied and a consensus forecast was produced to limit uncertainty between single‐models. The potential impacts of climate change on fish assemblages were assessed using both species and biological trait approaches. We then addressed the spatial distribution of potential impacts along the upstream–downstream gradient. Results Overall, climate change was predicted to result in an increase in species and trait diversity. Species and trait composition of the fish assemblages were also projected to be highly modified. Changes in assemblages’ diversity and composition differed strongly along the upstream–downstream gradient, with upstream and midstream assemblages more modified than downstream assemblages. We also predicted a global increase in species and trait similarity between pairwise assemblages indicating a future species and trait homogenization of fish assemblages. Nevertheless, we found that upstream assemblages would differentiate, whereas midstream and downstream assemblages would homogenize. Our results suggested that colonization could be the main driver of the predicted homogenization, while local extinctions could result in assemblage differentiation. Main conclusions This study demonstrated that climate change could lead to contrasted impacts on fish assemblage structure and diversity depending on the position along the upstream–downstream gradient. These results could have important implications in terms of ecosystem monitoring as they could be useful in establishing areas that would need conservation prioritization.     

A Study on the Impact of Urban and Industrial Development in the Linggi River Basin,Malaysia. 2. Chemical Environment

An investigation of the chemical environment of the Linggi River Basin was carried out at 15 main and 27 supplementary stations between January 1983 and January 1984. Spatial and temporal changes in pH, specific conductivity, alkalinity, chloride, ammonia-nitrogen, nitrite-nitrogen, nitrate-nitrogen, orthophosphate, dissolved oxygen, BOD, and diurnal variations were studied in relation to influence of various kinds of pollutants. The chemical composition of natural water analysed at a few undisturbed forest stream stations in the basin can be considered very good. A drastic change in river water quality was noticed in downstream polluted stations. The pH in the basin varied from 4.05 to 10.5 units, conductivity from 23.0–1,500 umhos/cm, alkalinity from 6.0–1,388 mg/l, chloride from 0.9–160.9 mg/l, orthophosphate from 0.5–5.21 mg/l, ammonia-N from 0.001–53.75 mg/l, nitrite-N from 0.0–8.2 mg/l, nitrate-N from 0.03–6.77 mg/l and BOD₃, from 0.32–384.0 mg/l and COD from 0.02 to 79.2 unit. Among all the rivers, very high values were recorded at Kundor, Simin and Linggi (sensu stricto).     

Effects of location of food delivery and social status on foraging-site selection by juvenile Atlantic salmon

Synopsis Experiments were conducted to investigate the response of juvenile Atlantic salmon,Salmo salar, to changes in the location at which food entered a stream tank. Experience with the location of food input into the system significantly influenced foraging-site selection by the dominant fish. Dominant fish changed location of their foraging site in response to a change in the location of food input, and occupied, aggressively defending, sites just downstream of the location of food introduction. In contrast, subordinate fish occupied foraging sites at the downstream end of the stream tank, regardless of location of food input. As a result of both site selection and social status, dominant fish captured significantly more prey than subordinates. Our results support the contention that salmonids choose foraging sites to maximize foraging opportunities. Our results also provide a possible explanation for the use of atypical foraging sites by individual fish within their home range over the course of a single day, as observed in a number of salmonid species in the field.     

老爷岭多年冻土小流域春季冻融期径流溶解性有机碳变化特征

溶解性有机碳（DOC）的输移过程是流域碳循环中重要的组成部分,对全球碳循环产生重要影响。以大兴安岭多年冻土区的典型森林小流域-老爷岭流域为研究对象,获得2021年4月9日到6月30日冻融期降雨量、气温、土温等气象数据及逐日径流量、径流DOC浓度,计算了冻融循环期（4月9日-28日）和融化期（4月29日-6月30日）流域径流DOC的输出通量,揭示了径流DOC浓度及输出通量的影响因素。结果表明：（1）研究时段内,老爷岭流域径流DOC浓度变化范围为3.88-33.75 mg/L,流域上游的径流DOC浓度变化趋势与下游基本一致,DOC浓度随着温度的升高呈现下降趋势,4月份平均径流DOC浓度明显高于5、6月份。（2）研究时段内流域径流DOC总输出通量为3215.48 kg/km²,其中5月径流DOC输出通量高于4、6月份。径流量与径流DOC输出通量存在显著正相关关系（P<0.05）,是流域DOC输出通量的主导因素。（3）研究时段内流域DOC浓度与平均气温呈极显著负相关（R²=0.5048,P<0.001）;降水样品中的DOC浓度变化范围为1.06-9.42 mg/L,显著低于径流DOC浓度;土壤中DOC含量变化趋势与径流DOC变化趋势一致,0-10 cm、10-20 cm土壤平均DOC浓度范围为77.57-133.99 mg/L。（4）冻融循环期平均日径流DOC浓度（24.02 mg/L）显著（P<0.05）高于融化期（14.64 mg/L）,而融化期平均日DOC输出通量（48.02 kg/km²）是冻融循环期（9.52 kg/km²）的5倍。研究结果揭示了大兴安岭多年冻土小流域春季冻融期径流DOC的输移特征及其影响因素,对理解多年冻土区碳循环有重要意义。     

A survey of the macro-fauna of the River Cynon, a polluted tributary of the River Taff (South Wales)

(1) A survey of the macro-invertebrates and fish in the River Cynon, a trout stream in south-east Wales receiving industrial and domestic wastes, and nine of its tributaries, was carried out in the summer of 1970. Its principal purpose was to describe the structure of these communities before waste treatment facilities, in course of construction, reduce the degree of pollution. (2) The macro-invertebrate communities changed dramatically at station C4, there being a very varied fauna upstream and one dominated by chironomids and oligochaetes downstream, principally Nais barbata., Cricotopus bicinctus and Syncricotopus rufiventris. It seems likely that coal particles, influencing the substrate, are largely responsible for this change. Further downstream, and below substantial organic discharges, tubificids and the enchytraeid, Lumbricillus rivalis, became increasingly abundant. The total density of macro-invertebrates increased from about 2000/m2 in the headwaters to over 20,000/m2 in the lower reaches. (3) The fauna of the clean tributaries, Hir (C16) and Wenallt (C19) was similar to that ofthe unpolluted upper reaches ofthe Cynon (C1-C3) whereas that of tributaries affected by coal particles was similar to the fauna of the Cynon downstream of C4. (4) Six species of fish were recorded (bullhead, eel, minnow, trout, stickleback and stoneloach) of which tbree (bullhead, eel and trout) were confined to reaches upstream (C8 and above) of industrial eflluents at Abercwmboi. For 0–8 km downstream of these effluents the river was fishless and further downstream, to the confluence with the River Taff, fish density and biomass were reduced. (5) In the upper Cynon and its tributaries the density and biomass of trout were within the range recorded elsewhere in the British Isles. The growth rate of trout in the catchment is low. Diflerences in growth rate and shape of trout in the main river and tributaries suggest that there is little interchange between these areas, except perhaps with very young fish. 0 + * * The convention of referring to fish in their first year as 0+, in their second year as 1 + and so on is adopted here.
fish were only caught in abundance at two tributary stations and their numbers, even if widely distributed, could not permanently support the current density of older fish throughout the upper catchment. (6) Stone loach and minnow reached a very large size and individuals caught of the latter species approached the maximum recorded length for the British Isles.     

Seasonal dynamics of moss-dwelling chironomid communities

Chironomid communities of mosses in a small upland stream in central Germany were highly dynamic across the year with respect to their abundance, biomass and dominant taxa. During 1988 semi-submersed mosses near a main spring and those occurring some 700 m downstream were compared with permanently submersed mosses in immediate vicinity of the downstream site. All the chironomids sampled were conspicuously small, with nearly 98% being less than 5 mm in length. A total of 65 chironomid species from 26 genera were found, with a higher diversity occurring near the source and a change in dominant taxa along the upper stream section. The mean abundance in permanently submersed mosses (250 larvae/10 cm², n = 125) was about five times higher than in semi-submersed mosses. The maximum value of 830 larvae/10 cm² (n = 1) is the highest chironomid density ever reported, which is explained by the sampling method used. The mean standing crop was also highest in permanently submersed mosses (1.5 mg AFDW/10 cm² (n = 125)), even though the highest individual value was recorded in semi-submersed mosses near the spring (10.4 mg AFDW/10 cm²). The evidence suggested that the dominance of chironomid taxa depended mainly on the location of the moss along the stream, whereas abundance and biomass were determined mainly by constancy in the ambient discharge as well as the factors influenced by this (e.g. temperature, detritus deposition). A trend was seen towards a seasonal succession among the chironomid taxa colonizing lotic mosses.     

The consequences of flooding for the dispersal and fate of poeciliid fish in an intermittent tropical stream

Summary We studied the rainy season dispersal of the fish Poecilia gillii (Poeciliidae) from pools in a steepgradient, intermittent stream in Santa Rosa National Park, Costa Rica. The stream consisted of about 20 pools separated by dry streambed except during two floods and subsequent brief periods of flow. Individually recognizable tags permitted mark-recapture estimates of population size and information on individual movements. The first flood was very severe, with pools losing an average of 75% of their populations (range 12–99%). Most of the lost fish died by becoming trapped in desiccating pools. Males and juveniles were more likely to be lost than were females. Population loss was negatively related to pool volume and positively related to streambed slope. In addition, population loss was positively related to preflood population size when the effects of pool volume and slope were removed indicating that pools with higher densities lost more fish. Of the fish recaptured after the flood, the average proportion found in the pool in which they had been tagged varied from 16%–96%, depending on the area of the stream. Of fish that moved, 92% went downstream. The second flood was less severe though stream flow lasted as long, and there was little effect on the pool populations. Involuntary flushing during the flood and voluntary departure apparently interacted to produce the observed patterns.     

Effects of permethrin on aquatic organisms in a freshwater stream in south-central Alaska.

Permethrin (0.5%) was applied to individual Lutz spruce, Picea x lutzii Little, to protect them from attack by spruce beetles, Dendroctonus rufipennis (Kirby). Residue levels were monitored in a freshwater stream above, adjacent to, and below the treatment site at intervals before, during, and after treatment. Maximum residue levels in the stream within the treatment site ranged from 0.05 +/- 0.01 ppb 5 h after treatment to 0.14 +/- 0.03 ppb 8-11 h after treatment, with a decrease to 0.02 +/- 0.01 ppb 14 h after treatment. Levels of permethrin in standing pools near the stream within the treatment site were 0.01 +/- 0.01 ppb. Numbers of drifting aquatic invertebrates increased 2-fold during treatment and 4-fold 3 h after treatment and declined to before spray numbers within 9 h. Terrestrial insects did not appear to respond to treatments because none was found in stream drift samples. Trout fry (Dolly Varden), aquatic insect larvae, and periphyton (attached algae) within and below the treatment site during and after treatment did not show signs of mortality compared with an upstream untreated control site.     

Effect of flooding on fish assemblages in small streams in South Korea

The impact of Typhoon-Rusa-generated flood on fish assemblages was investigated in small streams in the northeastern part of South Korea. As a result of high precipitation (870 mm day⁻¹) during the typhoon, stream morphology and substrate composition changed. Stream depth and width decreased and slightly enlarged, respectively. Substantial amounts of mud and silt flowed into the streams and modified substrate composition to a simple state. Although the total number of individual fish significantly decreased after the flood, the dominant species remained the same relative to before the typhoon, and their relative abundance subsequently increased. However, the rank order of fish assemblages before and after the flood changed. Three years after the flood, fish assemblage recovered, but the number of individuals per site was still lower than prior to the flood. Flooding affects fish assemblages both directly and indirectly. Indirect impacts, such as habitat alteration, more critically affected the change in local fish assemblage and delayed recovery time. Nonetheless, fish assemblages persisted at sites where floods occurred.