Unaffected Streams Research Articles

Climatically promoted taxonomic homogenization of macroinvertebrates in unaffected streams varies along the river continuum

Biotic homogenization appears to be a global consequence of anthropogenic change. However, the underlying environmental factors contributing to homogenization are difficult to identify because their effects usually interact and confound each other. This can be the reason why there is very little evidence on the role of climate warming in homogenization. By analysing macroinvertebrate assemblages in 65 streams that were as close to natural conditions as possible, we avoided the confounding effects of common anthropogenic stressors. This approach resulted in revealing a significant effect of increased temperature (both summer and winter) on changes in macroinvertebrate compositional over the past two decades. However, homogenization was significant only at opposite ends of the river continuum (submontane brooks, low-altitude rivers). Surprisingly, species of native origin predominated overall, increasing in frequency and abundance (“winners”), while only a minority of species declined or disappeared (“losers”). We hypothesise that undisturbed conditions mitigate species declines and thus homogenization, and that the temperature increase has so far been beneficial to most native species. Although we may have only captured a transitional state due to extinction debt, this underscores the importance of maintaining ecological conditions in stream to prevent species loss due to climate change.

Robust change detection for large-scale data streams

Robust change point detection for large-scale data streams has many real-world applications in industrial quality control, signal detection, and biosurveillance. Unfortunately, it is highly nontrivial to develop efficient schemes due to three challenges: (1) the unknown sparse subset of affected data streams, (2) the unexpected outliers, and (3) computational scalability for real-time monitoring and detection. In this article, we develop a family of efficient real-time robust detection schemes for monitoring large-scale independent data streams. For each data stream, we propose to construct a new local robust detection statistic called the -CUSUM (cumulative sum) statistic that can reduce the effect of outliers by using the Box-Cox transformation of the likelihood function. Then the global scheme will raise an alarm based upon the sum of the shrinkage transformation of these local -CUSUM statistics to filter out unaffected data streams. In addition, we propose a new concept called false alarm breakdown point to measure the robustness of online monitoring schemes and propose a worst-case detection efficiency score to measure the detection efficiency when the data contain outliers. We then characterize the breakdown point and the efficiency score of our proposed schemes. Asymptotic analysis and numerical simulations are conducted to illustrate the robustness and efficiency of our proposed schemes.

Sustained effects of volcanic ash on biofilm stoichiometry, enzyme activity and community composition in North- Patagonia streams

Volcanic eruptions are extreme perturbations that affect ecosystems. These events can also produce persistent effects in the environment for several years after the eruption, with increased concentrations of suspended particles and the introduction of elements in the water column. On 4th June 2011, the Puyehue-Cordón Caulle Volcanic Complex (40.59°S-72.11°W, 2200m.a.s.l.) erupted explosively in southern Chile. The area affected by the volcano was devastated; a thick layer of volcanic ash (up to 30cm) was deposited in areas 50 km east of the volcano towards Argentina. The aim of the present study was to evaluate the effect of volcanic ash deposits on stream ecosystems four years after the eruption, comparing biofilm stoichiometry, alkaline phosphatase activity, and primary producer's assemblage in streams which were severely affected by the volcano with unaffected streams. We confirmed in the laboratory that ash deposited in the catchment of affected streams still leach phosphorus (P) into the water four years after eruption. Results indicate that affected streams still receive volcanic particles and that these particles release P, thus stream water exhibits high P concentration. Biofilm P content was higher and the C:P ratio lower in affected streams compared to unaffected streams. As a consequence of less P in unaffected streams, the alkaline phosphatase activity was higher compared to affected streams. Cyanobacteria increased their abundances (99.9% of total algal biovolume) in the affected streams suggesting that the increase in P may positively affect this group. On the contrary, unaffected streams contained a diatom dominant biofilm. In this way, local heterogeneity was created between sub-catchments located within 30 km of each other. These types of events should be seen as opportunities to gather valuable ecological information about how severe disturbances, like volcanic eruptions, shape landscapes and lotic systems for several years after the event.

Long-term studies of seasonal variability enable evaluation of macroinvertebrate response to an acute oil spill in an urban Mediterranean-climate stream

Benthic macroinvertebrates show seasonal fluctuations with variability in hydrologic conditions. Coastal northern California (USA) is located in a Mediterranean-climate area, which is characterized by predictable wet and dry seasons, and consequently stream flows. Monthly sampling over multiple years (2004–2005, 2010–2013) was used to examine seasonal variability in taxonomic composition and abundances of benthic macroinvertebrates at three sites in Strawberry Creek, an urban stream on the University of California, Berkeley campus. Although wet and dry seasons at all sites had similar taxa occurrences, seasonal variation in taxa abundances was evident at two sites. The effects of an accidental oil spill in winter 2011 were examined using a Before–After design. Three days post-spill, macroinvertebrate richness and abundances at the impacted site decreased dramatically compared with pre-spill levels; taxonomic composition recovered one year later. Resilience was likely from drift via an unaffected stream fork and the flushing effects of winter stream flows. The combination of monthly sampling over multiple years and the opportunistic evaluation of responses to an acute disturbance enabled us to identify five taxa that are common, abundant, and easily identified, which can be used as a framework for enhancing future volunteer-based biomonitoring research projects.

Hydrogeomorphic connectivity on roads crossing in rural headwaters and its effect on stream dynamics

Unpaved roads are ubiquitous features that have been transforming the landscape through human history. Unpaved roads affect the water and sediment pathways through a catchment and impacts the aquatic ecosystem. In this study, we describe the effect of unpaved road on the hydrogeomorphic connectivity at the rural headwater scale. Measurement was based on the stream crossing approach, i.e., road superimposing the drainage system. We installed a Parshall flume coupled with single-stage suspended sediment sampler at each stream crossing. In addition, we displayed our monitoring scheme with an upscaling perspective from second-order to third-order stream. We concluded that the road–stream coupling dramatically changed the stream dynamic. The increase of discharge caused by roads at the headwater was 50% larger compared to unaffected streams. Additionally, suspended sediment concentration enhancement at stream crossings ranged from to 413% at second-order streams to 145% at third-order streams. The landform characteristics associated with the road network produced an important hydrogeomorphic disruption in the landscape. As a result, the sediment filter function of the riparian zone was reduced dramatically. Therefore, we recommend that projects for aquatic system restoration or conservation in rural landscape consider the role of the road network on stream dynamics.

Geochemistry of Trace Metals and Rare Earth Elements in Stream Water, Stream Sediments and Acid Mine Drainage from Darrehzar Copper Mine, Kerman, Iran

Darrehzar porphyry copper mine is located 10 km south of the famous Sarcheshmeh porphyry copper mine in Kerman province, Iran. Water and sediment samples in the Darrehzar porphyry copper mine were collected and analyzed in order to characterize the environmental effects of regional geology and mining activity. Stream affected by acid mine drainage (AMD) are \({\hbox {Ca}}{-}{\hbox {SO}}_{4}^{2-}\) in type, while unaffected streams are \({\hbox {Ca}}{-}{\hbox {HCO}}_{3}^{- }\) type. Acid drainage, with pH values as low as 2.5, is quite rich in dissolved copper (mean 306.53 mg/L) \(>\) iron (77.83 mg/L) \(>\) aluminium (48.62 mg/L) \(>\) manganese (6.90 mg/L) \(>\) zinc (2810.42 \(\upmu \)g/L) \(>\) cobalt (831.55 \(\upmu \)g/L) \(>\) nickel (298.47 \(\upmu \)g/L). The high sulfate concentration makes sulfate the major controlling factor of electrical conductivity. The strong correlation among the majority of the elements indicates either similar geochemical behavior or a common origin, (mostly sulfides). Calculation of Acid Mine Drainage Index (AMDI) indicates that Darrehzar mine is classified as dangerous in view of AMD hazards. In Darrehzar porphyry copper mine, total rare earth element content (\(\Sigma \)REE) in AMD (5.54–417.76 \(\upmu \hbox {g L}^{-1})\) is higher than natural water (REE in upstream and downstream water is 0.87–1.40 and 0.83–1.71 \(\upmu \hbox {g L}^{-1}\)respectively). The North American Shale Composite (NASC) normalized REE patterns of AMDs revealed strong enrichment of middle REE (MREE), and heavy REE (HREE) compared with light REE (LREE). Speciation modeling indicates the predominance of aqueous species i.e., \(\hbox {LnSO}_{4}^{+}\), \(\hbox {Ln} (\hbox {SO}_{4})_{2}^{-}, \hbox {Ln}^{3+}, \hbox {LnCO}_{3}^{+}, \hbox {LnHCO}_{3}^{2+}\) and \(\hbox {Ln} (\hbox {CO}_{3})_{2}^{-}\) (Ln refers to any lanthanide element). In upstream, where pH is 7.2 \(\le \) pH, REEs primarily exist as \(\hbox {LnCO}_{3}^{+}\), and HREE bicarbonate complexes (Ln \((\hbox {CO}_{3})_{2}^{-})\) exceed those of LREEs. Based on mean geoaccumulation indices (\(I_\mathrm{{geo}}\)), Darrehzar river sediments at mine site display the following trend: \(\hbox {Cu}>\hbox {Mo}>\hbox {Pb}>\hbox {Sb}>\) Cd. Calculated potential ecological risk index (RI) indicates higher risk at mine site. The mean potential ecological risk factors \((\hbox {E}_{\mathrm{i}})\) for sediment metals display the following trend: \(\hbox {Mo}>\hbox {Cd}>\hbox {Cu}>\) As \(>hbox{Pb}>\hbox {Ni}>\hbox {Cr}> \hbox {Zn}\).

The response of epilithic diatom assemblages to sewage pollution in mountain streams of the Czech Republic

Background and aim – Mountain streams represent sensitive ecosystems of prime importance for biodiversity conservation. However, the knowledge of the impact of sewage pollution related to intensive recreational exploitation is still limited in these habitats. Our aim was to assess the response of stream diatom assemblages to sewage pollution in the Giant Mountains and the Bohemian Forest, and to find the main factors influencing the community structure. Methods – Epilithic samples from sixteen streams were collected, both in unaffected stream sections and at sites downstream of sewage outflows from mountain cottages or small villages. Basic physical and chemical parameters were measured and relative abundances of diatoms were determined using light microscopy. Key results – A total number of 153 diatom taxa belonging to 44 genera were identified. Based on species data, samples were divided into two groups: the first belonged mainly to sites influenced by pollution, whereas the second consisted of not or slightly affected sites. Both groups were further divided into several subgroups characterised by specific ecological conditions and assemblage composition. Canonical correspondence analysis (CCA) revealed five environmental parameters with significant influence on diatom species composition, some of which were related to sewage pollution (pH, water temperature, discharge volume and concentrations of nitrate nitrogen and organic nitrogen). Conclusions – As a consequence of sewage pollution, oligo- to mesotraphentic taxa were outcompeted by pollution tolerant taxa. However, pollution had no significant influence on diatom diversity, which was similar at sites both upstream and downstream of the outflows. In this study, diatom assemblages performed well as indicators of sewage pollution, and biomonitoring proved to be a useful tool in the detection of environmental stress in mountain streams. Overall, the response of diatom assemblages showed that an increase of recreational activities might significantly alter the ecological status of these ecosystems.

Thawing of massive ground ice in mega slumps drives increases in stream sediment and solute flux across a range of watershed scales

AbstractIce‐cored permafrost landscapes are highly sensitive to disturbance and have the potential to undergo dramatic geomorphic transformations in response to climate change. The acceleration of thermokarst activity in the lower Mackenzie and Peel River watersheds of northwestern Canada has led to the development of large permafrost thaw slumps and caused major impacts to fluvial systems. Individual “mega slumps” have thawed up to 106 m3of ice‐rich permafrost. The widespread development of these large thaw slumps (up to 40 ha area with headwalls of up to 25 m height) and associated debris flows drive distinct patterns of stream sediment and solute flux that are evident across a range of watershed scales. Suspended sediment and solute concentrations in impacted streams were several orders of magnitude greater than in unaffected streams. In summer, slump impacted streams displayed diurnal fluctuations in water levels and solute and sediment flux driven entirely by ground‐ice thaw. Turbidity in these streams varied diurnally by up to an order of magnitude and followed the patterns of net radiation and ground‐ice ablation in mega slumps. These diurnal patterns were discernible at the 103 km2 catchment scale, and regional disturbance inventories indicate that hundreds of watersheds are already influenced by slumping. The broad scale impacts of accelerated slumping are indicated by a significant increase in solute concentrations in the Peel River (70,000 km2). These observations illustrate the nature and magnitude of hydrogeomorphic changes that can be expected as glaciogenic landscapes underlain by massive ice adjust to a rapidly changing climate.

Response of Water Tower on Wind Induced Vibration Considering Interaction of Fluid and Structure

The paper deals with the numerical analysis of forced vibrations of a slender water tower structure. The computation model has been developed using finite elements in the ANSYS program environment. For CFD (Computational Fluid Dynamics) analysis the CFX module was used. The computation model includes the precisely modeled thin-walled steel structure and two variants of fluid domain. Elements FLUID30 formulated for direct description of the fluid pressure field has been applied and Lagrange description FLUID80. The Raleigh’s model of energy dissipation has been used. Similarity of normal modes of vibration has been applied as the criterion for defining the relations between computed natural frequencies of the empty tank and filled with water. To obtain accurate wind induced forces the CFD model of air surrounding was modeled. From this model the relation between velocity of unaffected stream and vortex separation frequency. Forced vibrations of the tower excited by vortex shedding harmonic pulsations have been computed.

Streamflow response in small upland catchments in the Chilean coastal range to the MW 8.8 Maule earthquake on 27 February 2010

Hydrological response to earthquakes has long been observed, yet the mechanisms responsible still remain unclear and likely vary in space and time. This study explores the base flow response in small upland catchments of the Coastal Range of south‐central Chile after the MW 8.8 Maule earthquake of 27 February 2010. An initial decline in streamflow followed by an increase of up to 400% of the discharge measured immediately before the earthquake occurred, and diurnal streamflow oscillations intensified after the earthquake. Neither response time, nor time to maximum streamflow discharge showed any relationship with catchment topography or size, suggesting non‐uniform release of water across the catchments. The fast response, unaffected stream water temperatures and a simple diffusion model point to the sandy saprolite as the source of the excess water. Base flow recession analysis reveals no evidence for substantial enhancement of lateral hydraulic conductivity in the saprolite after the earthquake. Seismic energy density reached ∼170 J/m3 for the main shock and ∼0.9 J/m3 for the aftershock, exceeding the threshold for liquefaction by undrained consolidation only during the main shock. Although increased hydraulic gradient due to ground acceleration‐triggered, undrained consolidation is consistent with empirical magnitude‐distance relationships for liquefaction, the lack of independent evidence for liquefaction means that enhanced vertical permeability (probably in combination with co‐seismic near‐surface dilatancy) cannot be excluded as a potential mechanism. Undrained consolidation may have released additional water from the saturated saprolite into the overlying soil, temporarily reducing water transfer to the creeks but enlarging the cross‐section of the saturated zone, which in turn enhanced streamflow after establishment of a new hydraulic equilibrium. The enlarged saturated zone facilitated water uptake by roots and intensified evapotranspiration.

Acid mine drainage affects the development and function of epilithic biofilms in streams

Acid mine drainage (AMD) is a legacy of historical coal mining that affects several thousand stream kilometers around the world by contributing high loads of acidity, SO42−, metals, and other cations. Most research has focused on how AMD affects diversity and structure of various biological assemblages, whereas considerably less has focused on functional processes in streams. We investigated how AMD from abandoned coal mines affects epilithic biofilm development and function. Algal biomass and accrual rates were significantly lower in AMD-affected stream reaches than in control streams. Biomass and accrual rates were lowest at intermediate AMD-affected sites (pH = 5.1–5.9), probably because copious amounts of AlOH3 precipitates smothered the benthic habitat. Ratios of β-glucosidase (GLU):β-xylosidase (XYLO) were significantly correlated with algal biomass (r = 0.60, p < 0.01), probably because algae are important sources of C that is readily broken down by bacterial GLU activity, whereas XYLO is mostly associated with C of allochthonous origin. Thus, reduced algal biomass could indirectly exacerbate AMD effects on bacterial function by providing less C needed for cellular functions. Ratios of phosphatase∶leucine aminopeptidase significantly increased as pH decreased (R2 = 0.88, p < 0.01). This increase indicated potential P limitation or stressful conditions for microbial communities because PO4-P readily adsorbs to metal hydroxides, rendering it biologically inaccessible. Ratios in 3 of 4 control streams indicated that N limitation may be more typical in unaffected streams of the region. Low algal biomass and potential P limitation of biofilms may indicate that AMD-affected streams have reduced capabilities to retain nutrients and energy needed to support healthy ecosystems. Considering the links between biofilm structure and function can provide a framework for developing management strategies to restore and conserve ecosystem processes, such as nutrient retention and spiraling, energy flow, food webs, and biodiversity.

Macrophyte species composition in streams of Latvia under different flow and substrate conditions

INTRODUCTION Streams are heterogeneous environments with differences in physical and chemical parameters. Different studies worldwide obviously indicate that the knowledge of the macrophyte species composition and abundance provides important information on the aquatic ecosystem (e.g., Best, 1995; Dawson & Szoszkiewicz, 1999; Baatrup-Pedersen et al., 2003). Macrophytes are a key component in the functioning of streams where they grow in relatively high abundance (Clarke, 2002). The physical stream environment has a major impact upon the development and growth of submersed macrophytes (Baatrup-Pedersen & Riis, 1999). In shallow, low-energy streams where macrophytes are able to grow abundantly, plants greatly influence the functioning of the ecosystem (Sand-Jensen et al., 1989). Substrate and flow velocity are the two most important factors influencing the distribution of macrophytes in streams. And vice versa, the growth of macrophytes has important impacts upon flow resistance, flow velocities, and sediment dynamics. Macrophytes grow abundatly under such current velocity and in sediments where they can be best rooted and withstand the erosive force of the water during periodic scour events (Chambers et al., 1991). Velocity is an important controlling factor of substrate stability and composition of macrophytes. Several researchers have argued that flow velocity is the main factor in controlling macrophyte composition and biomass in streams (Westlake, 1967; Nilsson, 1987; Chambers et al., 1991; Riis & Biggs, 2003; Haslam, 2006). Flow velocity has often been found to affect the distribution of macrophytes in streams (e.g., Riis et al., 2000; Demars & Harper, 2005). River surveys have indicated that many macrophyte species are associated with sediment of particular particle size (Holmes, 1983; Haslam, 2006). Substrate stability is a significant controlling factor because a stable substrate allows rooting and establishment of macrophyte communities. Mobile substrates prevent this, resulting in a limited potential for plant community development (Riis & Biggs, 2003; Haslam, 2006). Despite the apparent importance of water movement in regulating macrophyte communities in lowland rivers, the nature of the processes and the factors controlling their dynamics are not well understood (Franklin et al., 2008). For an assessment of the ecological status of a stream using macrophytes a certain minimum plant quantity is required. The variability of macrophyte richness is linked to physical factors in the environment, which make an important contribution to the pattern of macrophyte distribution (Abou-Hamdan et al., 2005). Since there are still numerous unaffected streams in Latvia, knowledge of the riverine vegetation in Latvia could be of regional importance on a European scale; for example, Baatrup-Pedersen et al. (2008) found a high similarity of species-based predictions in Denmark before intensive land use started there around 1900 with vegetation in Latvian and Lithuanian streams. The aim of the study was to examine the role of different environmental factors in the formation of macrophyte vegetation in middle-sized lowland streams in Latvia, focusing on the importance of flow velocity and substrate type of streams. The objectives were to investigate the macrophyte vegetation at 131 stream sites throughout the country, and to supplement each survey with a description of environmental factors (substrate type, flow velocity, shading, stream width, and water depth). MATERIAL AND METHODS Study area The study area covers the whole territory of Latvia. There is a dense network of streams in Latvia. The total number of streams is up to 12 500, of which only 17 exceed 100 km (Klavins et al., 1999). The streams are classified as lowland streams with averagely low flow velocities and modest hydrological variability. However, spring flow velocities may be high and summer velocities low. …

Hydrochemical characteristics and seasonal influence on the pollution by acid mine drainage in the Odiel river Basin (SW Spain)

The Odiel river Basin is heavily affected by acid mine drainage (AMD) from the sulphide mining areas in the Iberian Pyrite Belt (IPB). A thorough study has been conducted along this fluvial system, monitoring the seasonal influence on the pollution level and its hydrochemical characteristics. From 2002 to 2006, surface water samples were collected at 91 different points throughout the Odiel river Basin and analyzed by field and laboratory methods for dissolved metals and metalloids. Acid mine drainage affects 37% of the length of the drainage network, which shows a great diversity of geochemical conditions as well as significant variations through the hydrological year. Unaffected streams show different water types depending on the lithological substrate and the marine aerosol influence. Mean concentrations in the contaminated streams are very high: 231 mg/L of Fe, 135 mg/L of Al, 56 mg/L of Zn, 16 mg/L of Cu, etc. Four types of contaminated streams were recognized based on hydrochemical and physicochemical characteristics. There are important seasonal variations depending on the precipitation regimen, level of pollution and proximity to the AMD sources. In the more contaminated samples the M/Fe ratio (M = metals other than Fe) decreases during the summer season. Slightly contaminated samples show an inverse evolution as this ratio increases in spring and summer due to substantial Fe precipitation. A recomparison of contaminant loads suggests that the Odiel river Basin (including the Tinto river) accounts for 15% of the global gross flux of dissolved Zn and 3% of the global gross flux of dissolved Cu transported by rivers into the ocean.

Evaluation of a Stream System after Clearcut Logging Disturbance in the Gulf Coastal Plain

ABSTRACT We examined potential impacts of removal of timber, road construction, and military operations on a stream system at Fort Polk, Louisiana. In 1989, approximately 1,057 ha of upland pine and riparian hardwood timber were removed from the middle section of the Birds Creek watershed. In addition, roads were installed to facilitate vehicular passage during military exercises. Approximately 2.6-km of Birds Creek stream length occurred within the logged portion, which has been maintained as a cleared area since timber was harvested. During 2001–2005, we evaluated the assemblage structure of fishes and macroinvertebrates and the associated habitat at five sites in Birds Creek and five sites in an adjacent but unaffected stream, Whiskey Chitto Creek. Whatever the effects of timbering and construction, 12-yrs after the disturbance the affected sites on Birds Creek contained heterogeneous habitats that supported rich and diverse fish and macroinvertebrate assemblages, not unlike those of the other sites on Birds Creek and the adjacent control stream.

Processes affecting the chemical composition of Blue Lake, an alluvial gold-mine pit lake in New Zealand

Blue Lake is an abandoned, water-filled alluvial gold-mine pit in Central Otago, New Zealand. Alluvial gold mining is generally considered to be chemically benign, unless mercury is added to assist gold separation. The major element, trace metal and isotopic composition of the pit lake was compared to nearby, unaffected streams. Blue Lake was found to be enriched in the major cations, with levels that were 2–5 times higher than in unaffected streams. Furthermore, Cu, Ni and Zn concentrations exceeded 10 nmol L–1 in Blue Lake; these levels were 2–30 times higher than those in nearby, unaffected streams. Processes affecting the lake’s characteristics include evaporative concentration, and the oxidation and dissolution of locally derived sulfide and sulfate minerals. Localised acidification in surface and ground waters around the lake leads to the mobilisation of Zn and Ni, resulting in lake waters being strongly enriched in these trace metals (concentrations greater than 40 nmol L–1), whereas surrounding stream waters have much lower Ni and Zn concentrations (less than 5 nmol L–1). Ongoing evaporative concentration, and the continuing mobilisation of trace metals, implies that metal enrichment in lake waters will continue to occur. The present study demonstrated that the ‘benign’ process of alluvial gold mining can have significant chemical consequences in resulting water bodies.

Comparison of Hyporheic Organisms in Two Intermittent Streams to Assess a Local Disturbance

ABSTRACT Hyporheic pot samplers were used to assess the effects of a uranium contaminated site and its cleanup on the aquatic biota of an intermittent stream. The potentially affected stream was compared with an unaffected stream in an adjacent watershed. All of the sampling locations were dry when samplers were deployed; all but one were dry at retrieval. The communities at the two streams showed a high degree of similarity (0.84 with the Morisita-Horn index). Collembola and Hydracarina were the predominant organisms. The hyporheic zone was not being used as a refugium.

The intention to act improves unilateral left neglect

Unilateral neglect involves a spatial bias to one side of space, usually to the right. Perceptual and motor systems interact in the manifestation of this disorder, and there is also evidence that motor manipulative responses may have access to unique streams of information not available for non-motoric judgements. It is therefore predicted that the manifestation of neglect may be alterable by changing the purpose of otherwise very similar responses to spatially extended objects. In Experiment 1, neglect-based deviation to the right of centre was significantly less when subjects reached towards metal rods as if to pick them up in the centre, compared to when they pointed to their centres. In Experiment 2, subjects pointed to the centre of a rectangular box with a swivelled lid. They were then asked to place a coin at the centre of this lid, in a position sufficiently central to prevent the lid tilting and the coin falling into the box; in fact, the lid was fixed and subjects never received feedback. Responses were significantly more central with the balancing response than with the pointing one. These results suggest that prehensive movements towards objects allow 'leakage' of information about their spatial extent, via an unaffected stream of information available for motor-manipulative responses.

The intention to act improves unilateral left neglect: two demonstrations

Unilateral neglect involves a spatial bias to one side of space, usually to the right. Perceptual and motor systems interact in the manifestation of this disorder, and there is also evidence that motor manipulative responses may have access to unique streams of information not available for non-motoric judgements. It is therefore predicted that the manifestation of neglect may be alterable by changing the purpose of otherwise very similar responses to spatially extended objects. In Experiment 1, neglect-based deviation to the right of centre was significantly less when subjects reached towards metal rods as if to pick them up in the centre, compared to when they pointed to their centres. In Experiment 2, subjects pointed to the centre of a rectangular box with a swivelled lid. They were then asked to place a coin at the centre of this lid, in a position sufficiently central to prevent the lid tilting and the coin falling into the box; in fact, the lid was fixed and subjects never received feedback. Responses were significantly more central with the balancing response than with the pointing one. These results suggest that prehensive movements towards objects allow 'leakage' of information about their spatial extent, via an unaffected stream of information available for motor-manipulative responses.

Macroinvertebrate recolonization and water quality characteristics of a reconstructed stream after surface coal mining in northwestern Pennsylvania, USA

ABSTRACT Water quality and the size and composition of macro-invertebrate communities in a first order stream were compared prior to and after its relocation by surface mining. These parameters were also compared with those obtained from an unaffected stream in the adjacent watershed. Aside from the possibiblity of elevated stream temperatures in late summer, relocation did not adversely affect water quality. The number of taxa re-colonieing the relocated stream did not differ significantly from those present in the stream prior to raining. There was, however, a change in the composition of the taxa comprising invertebrate community. The morphology and the resultant channel morphology affected the type of organism that recolonized the stream. In the future, the channel morphology and the riparian vegetation should be duplicated as closely as possible during channel reconstruction.

Factors Affecting Aquatic Macroinvertebrates Below a Fly Ash Pond Discharge

ABSTRACT The effluent stream of the Cardinal Plant coal fly ash pond in eastern Ohio was characterized by less diverse habitat and food resources and a less complex substratum compared with an adjoining stream unaffected by the effluent, and supported a less diverse macroinvertebrate fauna dominated by physicochemically tolerant, fine particle-consumers. A sampling site in the unaffected stream contained large numbers of shredders and generally exhibited greater macroinvertebrate abundance than two sites in the effluent. Variation in numbers and taxa of macroinvertebrates among the three sampling sites was statistically associated primarily with differences in current velocity, substrate heterogeneity, and leafy detritus abundance, with fly ash pond water quality of lesser significance despite the presence of potentially toxic constituents.