Effects of chronic chlorine exposure on litter processing in outdoor experimental streams

SUMMARY 1. The effects of chlorine on litter ( Potamogeton crispus L.) processing were examined using six outdoor experimental streams. Downstream portions of two streams were dosed at c . 10 μg l⁻¹ Total Residual Chlorine (TRC), one stream at 64 μgl¹, and one stream at 230μg l⁻¹. Two control streams were not dosed; upstream riffles of each stream served as instream controls.
2. Two 35 day litter breakdown (per cent AFDW remaining) experiments indicated significantly lower decay rates in the high dose riffle. No other concentration of chlorine significantly affected decay rate.
3. A third experiment, conducted in medium and high dose streams, indicated that high dose chlorine exposure reduced litter decomposition rates significantly, and reduced microbial colonization, microbial electron transport system activity, and microbial litter decomposition after 4 days but not after 11 days of exposure. The number of amphipod shredders colonizing litter bags was also reduced significantly with high chlorine dose.
4. A fourth experiment, after dosing was terminated, provided direct evidence that amphipod shredders were important in facilitating litter decomposition: litter bags stocked with amphipods had significantly higher decomposition rates than bags which excluded shredders.
5. Overall results indicate that the high dose (c. 230 μgl⁻¹ TRC) of chlorine reduced litter processing rates partly by reducing initial microbial conditioning, but primarily by reducing the colonization of amphipod shredders.     

The influence of data characteristics on detecting wetland/stream surface-water connections in the Delmarva Peninsula,Maryland and Delaware

The dependence of downstream waters on upstream ecosystems necessitates an improved understanding of watershed-scale hydrological interactions including connections between wetlands and streams. An evaluation of such connections is challenging when, (1) accurate and complete datasets of wetland and stream locations are often not available and (2) natural variability in surface-water extent influences the frequency and duration of wetland/stream connectivity. The Upper Choptank River watershed on the Delmarva Peninsula in eastern Maryland and Delaware is dominated by a high density of small, forested wetlands. In this analysis, wetland/stream surface water connections were quantified using multiple wetland and stream datasets, including headwater streams and depressions mapped from a lidar-derived digital elevation model. Surface-water extent was mapped across the watershed for spring 2015 using Landsat-8, Radarsat-2 and Worldview-3 imagery. The frequency of wetland/stream connections increased as a more complete and accurate stream dataset was used and surface-water extent was included, in particular when the spatial resolution of the imagery was finer (i.e., <10 m). Depending on the datasets used, 12–60% of wetlands by count (21–93% of wetlands by area) experienced surface-water interactions with streams during spring 2015. This translated into a range of 50–94% of the watershed contributing direct surface water runoff to streamflow. This finding suggests that our interpretation of the frequency and duration of wetland/stream connections will be influenced not only by the spatial and temporal characteristics of wetlands, streams and potential flowpaths, but also by the completeness, accuracy and resolution of input datasets.     

Seasonal changes in the distribution and abundance of benthic invertebrates in six headwater streams in central Florida

Seasonal variations in invertebrate assemblages at two sites (upstream and downstream) on six central Florida headwater streams were compared by sampling at quarterly intervals with core and dip net samplers. Two of the streams were reclaimed following phosphate mining (～6 yr prior to this study), two received runoff from mined lands, and two were disturbed by agriculture and/or residential developments. Physical and chemical characteristics of the reclaimed streams differed markedly from those of the non-reclaimed streams; principal differences between the streams were in current velocity, percent organic matter (POM), Mn, conductivity and alkalinity. Annual mean densities of meiofauna and smaller macrofauna for the 12 stream sites ranged from 20?896 to 175?212 m^?2 and the mean for all sites was 56?492 m^?2. The reclaimed streams and one of the streams influenced by agriculture had annual means of less than 40?000 m^?2, 3- to 5-fold lower than the other streams. Fall and winter core densities were ～2.4-fold greater than those for spring or summer when drought and low dissolved oxygen prevailed. Meiofauna comprised 68–91% of the core sample invertebrates in reclaimed streams but only 43–62% in the non-reclaimed streams; principal functional groups were: gathering collectors – 61.5%, predators – 19.3% and filtering collectors – 15%. The taxonomic composition of the reclaimed streams was predominated by crustaceans (60–71%) while chironomids and annelids were more abundant (71–92%) in the non-reclaimed streams. Dip net sampling added 21 larger macrofauna species (Odonata, Hemiptera and Coleoptera) to our list of taxa, producing a total of 209 species. Species richness and diversity (H′ and N ₂) indices were lower in the reclaimed streams, but evenness was more variable. The Czekanowski–Dice–Sørensen similarity index showed that the reclaimed stream sites were quite similar to each other, but differed markedly from the other stream types; there was large variation both within and between seasons. For central Florida headwater streams, drought appears to have a larger influence on invertebrates than the type of land use, however this relationship should be confirmed using streams of similar hydrology.     

Small dams decrease leaf litter breakdown rates in Mediterranean mountain streams

The damming of rivers and streams alters downstream habitat characteristics and biotic assemblages, and might thus alter stream functioning, although there is not much direct evidence of this impact. In this study we compared breakdown of alder leaves upstream and downstream from 4 small (<1 hm³) dams in 4 Mediterranean mountain streams with no appreciable impact on water temperature and nutrient concentrations. Despite no effect on water characteristics, dams decreased leaf litter breakdown rates. Abundance and biomass of invertebrates and shredders and hyphomycete sporulation rates did not differ between upstream and downstream bags. However, the structure of invertebrate and hyphomycete assemblages did. Especially evident was a drop in limnephilids, which might explain the slower breakdown of leaf litter below dams. These results may help to explain some of the variability found in the literature on the effects of dams on decomposition rates. If dams increase water temperature and nutrient concentrations they may promote faster decomposition, but if dams do not change water characteristics, their impact on detritivore communities may cause slower decomposition rates.     

Stable isotopes identify dispersal patterns of stonefly populations living along stream corridors

1. Populations in different locations can exchange individuals depending on the distribution and connectivity of suitable habitat, and the dispersal capabilities and behaviour of the organisms. We used an isotopic tracer, ¹⁵N, to label stoneflies (Leuctra ferruginea) to determine the extent of adult flight along stream corridors and between streams where their larvae live. 2. In four mass, mark‐capture experiments we added ¹⁵NH₄Cl continuously for several weeks to label specific regions of streams within the Hubbard Brook Experimental Forest, NH, U.S.A. We collected adult stoneflies along the labelled streams (up to 1.5 km of stream length), on transects through the forest away from labelled sections (up to 500 m), and along an 800‐m reach of adjacent tributary that flows into a labelled stream. 3. Of 966 individual adult stoneflies collected and analysed for ¹⁵N, 20% were labelled. Most labelled stoneflies were captured along stream corridors and had flown upstream a mean distance of 211 m; the net movement of the population (upstream + downstream) estimated from the midpoint of the labelled sections was 126 m upstream. The furthest male and female travelled approximately 730 m and approximately 663 m upstream, respectively. We also captured labelled mature females along an unlabelled tributary and along a forest transect 500 m from the labelled stream, thus demonstrating cross‐watershed dispersal. 4. We conclude that the adjacent forest was not a barrier to dispersal between catchments, and adult dispersal linked stonefly populations among streams across a landscape within one generation. Our data on the extent of adult dispersal provide a basis for a conceptual model identifying the boundaries of these populations, whose larvae are restricted to stream channels, and whose females must return to streams to oviposit.     

Influence of marine-derived nutrients from spawning salmon on aquatic insect communities in southeast Alaskan streams

The objective of this study was to evaluate the influence of the nutrient transfer system between anadromous salmon and aquatic insect communities across multiple, natural stream systems. Between 2000 and 2002, we sampled seven streams in southeast Alaska, seasonally. Of the seven study streams, four received large annual salmon runs (high-run streams), and three were no-run streams. All the streams selected had a natural waterfall barrier to salmon, providing an upstream control reach for each study stream. Insect density, biomass, richness, diversity and functional feeding groups were analyzed before, during and after the fall salmon run in each stream section (i.e. above and below the barrier) of the seven study streams between 2001 and 2002. Results showed that diversity and richness were similar across stream sections and run size within each period, except for during the run when both were significantly lower in downstream sections of high-run streams. Functional feeding group patterns showed higher abundance and biomass of collector–gatherers and shredders during the post spawning, carcass decomposition period. High-run streams had upstream sections with greater abundance and biomass of mayflies (dominated by Baetidae, Heptageniidae and Ephemerellidae) during the run, and downstream sections with greater abundance and biomass of dipterans (dominated by Chironomidae). This study suggests that the often published positive relationship between MDN and stream insect abundance and biomass may only exist for certain taxa, primarily chironomid midges.     

Differences in temperature, organic carbon and oxygen consumption among lowland streams

1. Temperature, organic carbon and oxygen consumption were measured over a year at 13 sites in four lowlands streams within the same region in North Zealand, Denmark with the objectives of determining: (i) spatial and seasonal differences between open streams, forest streams and streams with or without lakes, (ii) factors influencing the temperature dependence of oxygen consumption rate, (iii) consequences of higher temperature and organic content in lake outlets on oxygen consumption rate, and (iv) possible consequences of forecasted global warming on degradation of organic matter. 2. High concentrations of easily degradable dissolved (DOC) and particulate organic carbon (POC) were found in open streams downstream of plankton‐rich lakes, while high concentrations of recalcitrant DOC were found in a forest brook draining a forest swamp. Concentrations of predominantly recalcitrant POC and DOC were low in a groundwater‐fed forest spring. Overall, DOC concentration was two to 18 times higher than POC concentrations. 3. Oxygen consumption rate at 20 °C was higher during summer than winter, higher in open than shaded streams and higher in lake outlets than inlets. Rate was closely related to concentrations of chlorophyll and POC but not to DOC. The ratio of oxygen consumption rate to total organic concentrations (DOC + POC), serving as a measure of organic degradability, was highest downstream of lakes, intermediate in open streams and lowest in forest streams. 4. Temperature coefficients describing the exponential increase of oxygen consumption rate between 4 and 20 °C averaged 0.121 °C^?1 (Q₁₀ of 3.35) in 70 measurements and showed no significant variations between seasons and stream sites or correlations with ambient temperature and organic content. 5. Oxygen consumption rate was enhanced downstream of lakes during summer because of higher temperature and, more significantly, greater concentrations of degradable organic carbon. Oxygen consumption rates were up to seven times higher in the stream with three impoundments than in a neighbouring unshaded stream and 21 times higher than in the groundwater‐fed forest spring. 6. A regional climate model has calculated a dramatic 4–5 °C rise in air temperature over Denmark by 2070–2100. If this is realised, unshaded streams are estimated to become 2–3 °C warmer in summer and winter and 5–7 °C warmer in spring and, thereby, increase oxygen consumption rates at ambient temperature by 30–40% and 80–130%, respectively. Faster consumption of organic matter and dissolved oxygen downstream of point sources should increase the likelihood of oxygen stress of the stream biota and lead to the export of less organic matter but more mineralised nutrients to the coastal waters.     

Leaf litter identity alters the timing of lotic nutrient dynamics

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Invertebrate responses to short-term water abstraction in small New Zealand streams

1. Small permanent streams are coming under increasing pressure for water abstraction. Although these abstractions might only be required on a short‐term basis (e.g. summer time irrigation), the highest demand for water often coincides with seasonal low flows. 2. We constructed weirs and diversions that reduced discharge in three small streams (<4 m width) to test the hypotheses that short‐term water abstractions would decrease habitat availability and suitability for invertebrates, resulting in increased invertebrate drift, reduced taxonomic richness and decreased benthic invertebrate densities. 3. We sampled benthic invertebrates, invertebrate drift and periphyton at control (upstream) and impact (downstream) sites on each stream before and during 1 month of discharge reduction. 4. Discharge decreased by an average of 89–98% at impact sites and wetted width decreased by 24–30%. Water depth decreased by 28–64% while velocity decreased by 50–62%. Water conductivity, temperature and dissolved oxygen showed varying responses to flow reduction among the three streams, whereas algal biomass and pH were unaffected in all streams. 5. The densities of invertebrate taxa tended to increase in the impact reaches of these streams, even though invertebrate drift increased at impact sites in the first few days following discharge reduction. There were a higher proportion of mayflies, stoneflies and caddisflies at the impact site on one stream after flow reduction. There were no changes to the number of taxa or species evenness at impact sites. 6. Our results suggest that for these small streams, the response of invertebrates to short‐term discharge reduction was to accumulate in the decreased available area, increasing local invertebrate density.     

Movement patterns of invertebrates in temporary and permanent streams

Summary Although it has been shown that invertebrates recolonize reflooded temporary streams from permanent refuges, e.g., the hyporheic zone, it has not been shown that they actively move into these refuges as streams dry. Substrate filled cages and drift nets were used to monitor invertebrate movement in two temporary streams and a permanent stream prior to and during drying to determine whether invertebrates leave drying riffles and enter flooded riffles. Invertebrate movement was essentially unidirectional in the permanent stream with downstream drift and with-in-substrate downstream movement dominating. In the temporary stream, movement vertically downward toward the hyporheic zone and upstream movement substantially contributed to a departure from a unidirectional pattern. In addition, prior to stream drying the relative colonization rate was higher and drift rate was lower in the temporary streams than in the permanent stream. During drying of the temporary stream, upstream movement continued to dominate but hyporheic movement was unimportant. Further, the upstream movement did not occur at the end of the riffle where it would lead to migration into non-drying riffles. Thus, even though movement patterns were different in permanent and temporary streams the pattern observed during stream drying would result in the concentration and subsequent death of invertebrates in drying riffles. This observation demonstrates that movement patterns of stream invertebrates do not necessarily result in behavioral avoidance of a dry period of temporary fiffles.     

Stimulation of leaf litter decomposition and associated fungi and invertebrates by moderate eutrophication: implications for stream assessment

1. We investigated the effect of moderate eutrophication on leaf litter decomposition and associated invertebrates in five reference and five eutrophied streams in central Portugal. Fungal parameters and litter N and P dynamics were followed in one pair of streams. Benthic invertebrate parameters that are considered useful in bioassessment were estimated in all streams. Finally, we evaluated the utility of decomposition as a tool to assess stream ecosystem functional integrity. 2. Decomposition of alder and oak leaves in coarse mesh bags was on average 2.3–2.7× faster in eutrophied than in reference streams. This was attributed to stimulation of fungal activity (fungal biomass accrual and sporulation of aquatic hyphomycetes) by dissolved nutrients. These effects were more pronounced for oak litter (lower quality substrate) than alder. N content of leaf litter did not differ between stream types, while P accrual was higher in the eutrophied than in the reference stream. Total invertebrate abundances and richness associated with oak litter, but not with alder, were higher in eutrophied streams. 3. We found only positive correlations between stream nutrients (DIN and SRP) and leaf litter decomposition rates in both fine and coarse mesh bags, associated sporulation rates of aquatic hyphomycetes and, in some cases, total invertebrate abundances and richness. 4. Some metrics based on benthic invertebrate community data (e.g. % shredders, % shredder taxa) were significantly lower in eutrophied than in reference streams, whereas the IBMWP index that is specifically designed for the Iberian peninsula classified all 10 streams in the highest possible class as having ‘very good’ ecological conditions. 5. Leaf litter decomposition was sufficiently sensitive to respond to low levels of eutrophication and could be a useful functional measure to complement assessment programmes based on structural parameters.     

Stream isotherm shifts from climate change and implications for distributions of ectothermic organisms

Stream ecosystems are especially vulnerable to climate warming because most aquatic organisms are ectothermic and live in dendritic networks that are easily fragmented. Many bioclimatic models predict significant range contractions in stream biotas, but subsequent biological assessments have rarely been done to determine the accuracy of these predictions. Assessments are difficult because model predictions are either untestable or so imprecise that definitive answers may not be obtained within timespans relevant for effective conservation. Here, we develop the equations for calculating isotherm shift rates (ISRs) in streams that can be used to represent historic or future warming scenarios and be calibrated to individual streams using local measurements of stream temperature and slope. A set of reference equations and formulas are provided for application to most streams. Example calculations for streams with lapse rates of 0.8 °C/100 m and long‐term warming rates of 0.1–0.2 °C decade^?1 indicate that isotherms shift upstream at 0.13–1.3 km decade^?1 in steep streams (2–10% slope) and 1.3–25 km decade^?1 in flat streams (0.1–1% slope). Used more generally with global scenarios, the equations predict isotherms shifted 1.5–43 km in many streams during the 20th Century as air temperatures increased by 0.6 °C and would shift another 5–143 km in the first half of the 21st Century if midrange projections of a 2 °C air temperature increase occur. Variability analysis suggests that short‐term variation associated with interannual stream temperature changes will mask long‐term isotherm shifts for several decades in most locations, so extended biological monitoring efforts are required to document anticipated distribution shifts. Resampling of historical sites could yield estimates of biological responses in the short term and should be prioritized to validate bioclimatic models and develop a better understanding about the effects of temperature increases on stream biotas.     

Longitudinal trends in concentration and composition of dissolved organic nitrogen (DON) in a largely unregulated river system

Dissolved organic nitrogen (DON) can comprise up to 80% of the dissolved N pool in riverine ecosystems, but concentration and compositional responses to catchment conditions has received limited attention. We examined the suite of nitrogenous nutrients along the length of the Ovens River, Victoria, Australia, a river with identifiable regions of native vegetation, agricultural activity and floodplain forest connection, carrying out longitudinal surveys in winter during a period of high flow and in summer during a period of stable base flow. We examined: the concentrations of DON, the proportion of DON that occurs as dissolved combined amino acids (DCAAs), whether concentration and DCAA composition varied between flow and whether land-use and tributaries have an impact upon nutrient concentration and DON composition. DON concentrations were greater than dissolved inorganic nitrogen under both base flow and high flow conditions. Under base flow DON exhibited a continuous increase in concentration downstream (ranging from 50 to 300 μg/L), compared to a much larger increase under high flow (150–600 μg/L) coupled with a major discrete increase of ~?350 μg/L at a tributary input (King River). Concentrations of NO_x (oxides of nitrogen) species were much higher under high flow conditions (range 50–250 μg/L) compared to 0–50 µg/L at base flow, and showed a significant increase in concentration with distance downstream. A discrete change in NO_x concentrations was also observed at the King River confluence under high flow, although in this case causing a decrease in concentration of ~100 µg/L. DCAA concentrations varied little along the length of the river at base flow but increased with distance downstream at high flow. The DCAA concentrations were of the same order of magnitude as ammonium at both base and high flows and nitrate concentrations at base flow. The proportion of DON that was in the form of DCAA was reasonably uniform during high flow (3–6%), but highly variable at base flow (5–44%). The amino acid (AA) composition of the DCAA varied along the river and differed between flow regimes (except below the confluence with the King River where AA composition under the two flow conditions converged) suggesting a strong influence of land use. We show that DON is potentially a large component (4–81%) of the total N budget and given that 5–23% is in the form of peptide/protein, represents an important source of N. DON and more specifically DCAAs should therefore be considered both when constructing N budgets and monitoring levels of in-stream nitrogen.     

Forest streams are important sources for nitrous oxide emissions

Streams and river networks are increasingly recognized as significant sources for the greenhouse gas nitrous oxide (N₂O). N₂O is a transformation product of nitrogenous compounds in soil, sediment and water. Agricultural areas are considered a particular hotspot for emissions because of the large input of nitrogen (N) fertilizers applied on arable land. However, there is little information on N₂O emissions from forest streams although they constitute a major part of the total stream network globally. Here, we compiled N₂O concentration data from low‐order streams (~1,000 observations from 172 stream sites) covering a large geographical gradient in Sweden from the temperate to the boreal zone and representing catchments with various degrees of agriculture and forest coverage. Our results showed that agricultural and forest streams had comparable N₂O concentrations of 1.6 ± 2.1 and 1.3 ± 1.8 µg N/L, respectively (mean ± SD) despite higher total N (TN) concentrations in agricultural streams (1,520 ± 1,640 vs. 780 ± 600 µg N/L). Although clear patterns linking N₂O concentrations and environmental variables were difficult to discern, the percent saturation of N₂O in the streams was positively correlated with stream concentration of TN and negatively correlated with pH. We speculate that the apparent contradiction between lower TN concentration but similar N₂O concentrations in forest streams than in agricultural streams is due to the low pH (<6) in forest soils and streams which affects denitrification and yields higher N₂O emissions. An estimate of the N₂O emission from low‐order streams at the national scale revealed that ~1.8 × 10⁹ g N₂O‐N are emitted annually in Sweden, with forest streams contributing about 80% of the total stream emission. Hence, our results provide evidence that forest streams can act as substantial N₂O sources in the landscape with 800 × 10⁹ g CO₂‐eq emitted annually in Sweden, equivalent to 25% of the total N₂O emissions from the Swedish agricultural sector.     

Longitudinal patterns in carbon and nitrogen fluxes and stream metabolism along an urban watershed continuum

An urban watershed continuum framework hypothesizes that there are coupled changes in (1) carbon and nitrogen cycling, (2) groundwater-surface water interactions, and (3) ecosystem metabolism along broader hydrologic flowpaths. It expands our understanding of urban streams beyond a reach scale. We evaluated this framework by analyzing longitudinal patterns in: C and N concentrations and mass balances, groundwater-surface interactions, and stream metabolism and carbon quality from headwaters to larger order streams. 52 monitoring sites were sampled seasonally and monthly along the Gwynns Falls watershed, which drains 170 km² of the Baltimore Long-Term Ecological Research site. Regarding our first hypothesis of coupled C and N cycles, there were significant inverse linear relationships between nitrate and dissolved organic carbon (DOC) and nitrogen longitudinally (P < 0.05). Regarding our second hypothesis of coupled groundwater-surface water interactions, groundwater seepage and leaky piped infrastructure contributed significant inputs of water and N to stream reaches based on mass balance and chloride/fluoride tracer data. Regarding our third hypothesis of coupled ecosystem metabolism and carbon quality, stream metabolism increased downstream and showed potential to enhance DOC lability (e.g., ~4 times higher mean monthly primary production in urban streams than forest streams). DOC lability also increased with distance downstream and watershed urbanization based on protein and humic-like fractions, with major implications for ecosystem metabolism, biological oxygen demand, and CO₂ production and alkalinity. Overall, our results showed significant in-stream retention and release (0–100 %) of watershed C and N loads over the scale of kilometers, seldom considered when evaluating monitoring, management, and restoration effectiveness. Given dynamic transport and retention across evolving spatial scales, there is a strong need to longitudinally and synoptically expand studies of hydrologic and biogeochemical processes beyond a stream reach scale along the urban watershed continuum.     

Relative influence of shredders and fungi on leaf litter decomposition along a river altitudinal gradient

We compared autumn decomposition rates of European alder leaves at four sites along the Lasset–Hers River system, southern France, to test whether changes in litter decomposition rates from upstream (1,300 m elevation) to downstream (690 m) could be attributed to temperature-driven differences in microbial growth, shredder activity, or composition of the shredder community. Alder leaves lost 75–87% of original mass in 57 days, of which 46–67% could be attributed to microbial metabolism and 8–29% to shredder activity, with no trend along the river. Mass loss rates in both fine-mesh (excluding shredders) and coarse-mesh (including shredders) bags were faster at warm, downstream sites (mean daily temperature 7–8°C) than upstream (mean 1–2°C), but the difference disappeared when rates were expressed in heat units to remove the temperature effect. Mycelial biomass did not correlate with mass loss rates. Faster mass loss rates upstream, after temperature correction, evidently arise from more efficient shredding by Nemourid stoneflies than by the Leuctra-dominated assemblage downstream. The influence of water temperature on decomposition rate is therefore expressed both directly, through microbial metabolism, and indirectly, through the structure of shredder communities. These influences are evident even in cold water where temperature variation is small.     

Assessment of Stream Restoration: Sources of Variation in Macroinvertebrate Recovery throughout an 11‐Year Study of Coal Mine Drainage Treatment

Stream restoration researchers have a complex array of alternative assessment methodologies using macroinvertebrates. We examined sources of variation among three field sampling methods and five metrics in three networked streams impacted by a circumneutral coal mine discharge treated midway through an 11‐year study. Constructed wetlands captured the primary stressor, 700 kg iron/day. Before pollution abatement, copious iron hydroxide smothered downstream sites for decades. Two second‐order streams and one fourth‐order receiving stream, each with matching locations upstream and downstream, were monitored midsummer from 1994 to 2004. We compared taxa density (TD) (number/sample), abundance, expected taxa richness (ETR), U.S. regional pollution tolerance values (RTV), and community similarity (CS) indices from 3 to 11 replicate samples/site using grab samples (i.e. D‐nets, rock washes) and incubated leaf packs. Variation due to sampling method, metric, location, and year significantly influenced outcomes when analyzed using regression and analysis of variance. TD, RTV, and CS indicated biological recovery lagged 6 years behind chemical improvement; ETR and abundance showed more severe, persistent impairment in the two, highly impacted second‐order streams compared to the fourth‐order stream. Incubated leaf packs offered a preview of stream recovery in downstream sites, providing clean food (leaves) and substrate (mesh) and attracted more taxa and abundance than grab samples. In light of the worldwide distribution of coal mining often accompanied by metal hydroxide deposits into streams, we suggest restoration project managers use a variety of sampling methods, metrics, and models to evaluate remediation of physical as well as chemical impairment from mining.     

Occupancy dynamics in small-stream habitats: niches define the responses to floods by two neotropical fishes

We modeled the occupancy dynamics of the benthic chum-chum (Pimelodella cf. gracilis) and the midwater threespot leporinus (Leporinus friderici) to determine how these fish species respond to disturbances caused by stream flooding. Fieldwork was conducted in two neotropical streams in central Brazil. Both species occupied fewer sites during floods than during periods with stable hydrology. The percentage of sites occupied by threespot leporinus increased from 57 to 75 %, and the percentage occupied by chum-chum increased from 27 to 87 %. Threespot leporinus moved upstream after floods, first recolonizing the sites farthest downstream and then recolonizing those farthest upstream. In contrast, chum-chum remained in several scattered sites along the stream during floods and recolonized nearby sites from these sources (i.e., colonization was not spatially concentrated). During wet hydroperiods, chum-chum used sites with water velocities ranging from 0.35 to 0.75 m/s. During the dry period, this range increased to 0.20–0.90 m/s (in sites that were colonized after the floods ended). Our results also showed that both species were more easily detected by snorkeling during the dry hydroperiod and that characteristics such as the substrate type and water velocity had different effects on the detectability of the two species. Overall, our study indicated that the annual persistence of threespot leporinus depends largely on seasonal upstream-biased movement, whereas the chum-chum population depends on the seasonal scattered colonization of temporary sites.     

Dissolved organic carbon and nitrogen in urban and rural watersheds of south-central Texas: land use and land management influences

Dissolved organic carbon (DOC) and nitrogen (DON) concentrations were quantified in urban and rural watersheds located in central Texas, USA between 2007 and 2008. The proportion of urban land use ranged from 6 to 100% in our 12 study watersheds which included nine watersheds without waste water treatment plants (WWTP) and three watersheds sampled downstream of a WWTP. Annual mean DOC concentrations ranged 20.4–52.5 mg L^?1. Annual mean DON concentrations ranged 0.6–1.9 mg L^?1. Only the rural watersheds without a WWTP had significantly lower DOC concentrations compared to those watersheds with a WWTP but all the streams except two had significantly reduced DON compared to those with a WWTP. Analysis of the nine watersheds without a WWTP indicated that 68% of the variability in mean annual DOC concentration was explained by urban open areas such as golf courses, sports fields and neighborhood parks under turf grass. There was no relationship between annual mean DON concentration and any land use. Urban open area also explained a significant amount of the variance in stream sodium and stream sodium adsorption ratio (SAR). Ninety-four percent of the variance in annual mean DOC concentration was explained by SAR. Irrigation of urban turf grass with domestic tap water high in sodium (>181 mg Na⁺ L^?1) may be inducing sodic soil conditions in watershed soils in this region resulting in elevated mean annual DOC concentrations in our streams.     

Success and failure in a lotic crayfish invasion: the roles of hydrologic variability and habitat alteration

1. This paper examines the distribution, habitat relationships, and potential for spread of non‐native signal crayfish (Pacifastacus leniusculus) in streams of the Truckee River catchment, California, U.S.A. Crayfish associations with natural features and with impoundments and flow alteration were examined in a survey of 33 streams. Abundance changes were followed over 5 years, which included some of the highest and lowest flows on record, in three streams, two unregulated and one regulated. Movement of marked crayfish was studied in one 0.5 km stream reach just upstream from a reservoir. 2. Signal crayfish were most abundant in low‐gradient streams and were positively associated with proximity to reservoirs (both upstream and downstream). Crayfish were more likely to be found in regulated than unregulated sites, and did not occur in sites upstream of barriers, such as culverts, that separated them from reservoirs or lakes. 3. Crayfish declined in abundance in years following particularly intense and prolonged wet‐season spates, leading to a negative association between crayfish abundance and both peak discharge and duration of bankfull flows. 4. Crayfish moved distances of up to 277 m, and at rates of up to 120 m day^?1, suggesting significant dispersal ability. Larger crayfish moved greater distances and were more likely to move downstream. Female crayfish showed a pattern of upstream movement in early summer and downstream movement late in the summer, opposite the pattern found in two other studies. 5. These results suggest that natural or artificial gradient barriers and, in regulated systems, management of flow regimes to include bankfull or greater flows may help to control invasive crayfish in streams.