Suspended-sediment responses after strip thinning in headwater catchments

We examined changes in suspended-sediment yields (SSY) after a 50 % strip thinning in headwater streams draining a Japanese cedar (Cryptomeria japonica) and cypress (Chamaecyparis obtusa) plantation forest. We applied a paired-catchment analysis to treated (K _T : 17.1 ha) and control (K _C : 8.9 ha) catchments. Annual suspended-sediment yield (SSY_an) in the prethinning period in the K _T and K _C catchments was 110.0 and 142.1 kg/ha per year. For the postthinning period, SSY_an in the K _T catchment became 5055.6 kg/ha per year, whereas that in the K _C catchment increased 893.2 kg/ha per year. The paired-catchment analysis revealed that SSY in the K _T catchment increased 17.0-fold compared with the prethinning period. However, the dominant hysteresis pattern remained clockwise in both pre- and postthinning periods. Sequences of large storm events in the postthinning period elevated SSY in both catchments. Increase in suspended sediment in the K _T catchment was associated with the combined impacts of thinning and sequences of storm events during the period of thinning operation.     

Human settlements in headwater catchments are associated with generalist stream food webs

Hydrobiologia - While a variety of anthropogenic impacts on lotic biodiversity have been documented, food-web responses to catchment development are poorly understood. We selected 27 stream food...     

Hydrological processes in small catchments of mountain headwater lakes: The Tatra Mountains

This study evaluates runoff and different methods for the estimation of water balance and runoff genesis in four small alpine catchments, which lie outside the standard network of hydrological and climate networks. These test catchments, whose size ranges between 2.3 and 110 ha, are located above the timberline at elevations between 1,784 and 2,380 m. Their land surfaces consist of lakes, rock formations, debris deposits, and alpine meadows. Hydrological data were collected for the water year 2001. The catchments were instrumented by three automatic weather stations recording global and net solar radiation, air temperature, humidity, precipitation, and soil temperature. Lake water levels were registered with staff gauges and runoff evaluated from water storage calculations. Runoff genesis was investigated by means of chemical tracers (Rhodamine WT and Lithium chloride). Hydrological process estimations were made using standard methods including: the input of precipitation and snowmelt, both potential and actual evaporation, which was estimated by the approaches of Hamon, Priestley-Taylor, Penman and Grindley, and runoff calculated from the lake storage, were compared with results of the conceptual hydrological Brook90 model. The empirical results show that hydrological processes are governed by the temperature-dependent regime of high mountain snowmelt. However, the major differences in water yield and runoff genesis between watersheds were due to differences in the morphologies of the lakes and their basins, the soilvegetation complex, and runoff routing. Evaluating approaches to estimation, Penman’s combination of both aerodynamic and energy balance method provides the best fit to observed data with observed evapotranspiration being 78 to 99% of the potential calculated. The deterministic Brook90 model is effective for precipitation-runoff genesis studies in small headwater catchments. In the L’adové pleso basin predicted and observed water yield show close correlation. The annual sum of actual evapotranspiration calculated by BROOK90 (352 mm) corresponds closely to that estimated by the approach of Penman (386 mm).     

Leaf litter decomposition and macroinvertebrate communities in headwater streams draining pine and hardwood catchments

Benthic invertebrates, litter decomposition, andlitterbag invertebrates were examined in streamsdraining pine monoculture and undisturbed hardwoodcatchments at the Coweeta Hydrologic Laboratory in thesouthern Appalachian Mountains, USA. Bimonthlybenthic samples were collected from a stream draininga pine catchment at Coweeta during 1992, and comparedto previously collected (1989–1990) benthic data froma stream draining an adjacent hardwood catchment. Litter decomposition and litterbag invertebrates wereexamined by placing litterbags filled with pine ormaple litter in streams draining pine catchments andhardwood catchments during 1992–1993 and 1993–1994. Total benthic invertebrate abundance and biomass inthe pine stream was ca. 57% and 74% that of thehardwood stream, respectively. Shredder biomass wasalso lower in the pine stream but, as a result ofhigher Leuctra spp. abundance, shredderabundance was higher in the pine stream than thehardwood stream. Decomposition rates of both pine andred maple litter were significantly faster in pinestreams than adjacent hardwood streams (p<0.05). Total shredder abundance, biomass, and production weresimilar in maple bags from pine and hardwood streams. However, trichopteran shredder abundance and biomass,and production of some trichopteran taxa such asLepidostoma spp., were significantly higher in maplelitterbags from pine streams than hardwood streams(p<0.05). In contrast, plecopteran shredders(mainly Tallaperla sp.) were more important inmaple litterbags from hardwood streams. Shredderswere well represented in pine litterbags from pinestreams, but low shredder values were obtained frompine litterbags in hardwood streams. Resultssuggest conversion of hardwood forest to pinemonoculture influences taxonomic composition of streaminvertebrates and litter decomposition dynamics. Although the impact of this landscape-leveldisturbance on invertebrate shredder communitiesappeared somewhat subtle, significant differences indecomposition dynamics indicate vital ecosystem-levelprocesses are altered in streams draining pinecatchments.     

Episodic sulphate export from wetlands in acidified headwater catchments: prediction at the landscape scale

Sulphate (SO ₄ ^–2 ) concentrations in 34 intensively measured Canadian Shield streams near the Dorset Research Centre, central Ontario, were used to test a hydrogeologic model that uses simple measures of wetland area and till depth to identify catchments that produce SO ₄ ^–2 pulses. Mean annual measured maximum SO ₄ ^–2 concentrations were significantly greater in shallow till (<1 m depth) catchments containing wetlands than catchments covered with deeper tills (>1 m depth) containing wetlands or catchments with no wetlands. Average maximum SO ₄ ^–2 concentrations in wetland catchments during years with dry summers were >20 mg/L in 19 of 20 catchments with average till depths of <1 m, whereas concentrations were <20 mg/L in 5 of 6 watersheds with average till depths of >1 m. Peaks in mean annual maximum SO ₄ ^–2 concentrations from wetland catchments with shallow till occurred during summers with rain fall 150–200 mm less than potential evaporation estimates. There were no significant differences in mean average annual SO ₄ ^–2 concentration among the different catchments during wet summers, with SO ₄ ^–2 concentrations ranging from 6 to 13 mg/L. These observations suggest that a large portion of the temporal and spatial variation in SO ₄ ^–2 chemistry and export can be predicted in headwater catchments of the Canadian Shield and perhaps in other landscapes where till depth influences upland-wetland hydrologic connections.     

Spawning and rearing behavior of bull trout in a headwater lake ecosystem

Environmental Biology of Fishes - Numerous life histories have been documented for bull trout Salvelinus confluentus. Lacustrine-adfluvial bull trout populations that occupy small, headwater lake...     

Benthic sediment influence on dissolved phosphorus concentrations in a headwater stream

Phosphate interacts with inorganic sediment particles through sorption reactions in streams. Collectively, this phosphorus (P) buffering mechanism can be an important determinant of soluble reactive P (SRP) concentrations. If sorption reactions control SRP concentrations in a stream, then differences in sediment characteristics may cause spatial differences in SRP concentrations. This prediction was tested by examining sediment-buffering characteristics and spatial variation in SRP among reaches with distinct sediment composition (i.e., fine versus coarse particles) in two tributaries of Boulder Creek, a headwater stream in central Wisconsin. SRP concentrations were significantly lower and algal available P and P sorption capacity were significantly higher in the reach dominated by fine sediments. Although fine particles such as sand had the greatest P sorption capacity, no retention could be attributed to biotic processes, whereas over 50% of P retention in coarse particles such as gravel could be linked to biotic uptake. Equilibrium P concentration (EPC₀) assays from different sediment fractions also indicate that biotic uptake is relatively unimportant in sand particles (EPC_live 10 μg/L: EPC_killed 10 μg/L) but very important in gravel or larger particles (EPC_live 10 μg/L: EPC_killed 80 μg/L). Thus, sediment influence on stream water P concentrations can shift predictably from abiotic sorption in reaches with fine particles to biotic retention in areas dominated by coarse sediments. Consequently, changes in sediment composition due to natural or anthropogenic disturbance have the potential to alter the type and strength of sediment-associated processes determining ambient stream P concentrations.     

Mercury inputs and outputs at a small lake in northern Minnesota

Storages and cycling of total mercury (Hg_T), methylmercury (MeHg), and Hg⁰ are described for Spring Lake, a small bog lake in the Marcell Experimental Forest in north-central Minnesota. We quantified photoredox transformations, MeHg photolysis, burial to the sediments, and internal and external loadings of Hg_T and MeHg. Atmospheric deposition was the main input of Hg_T; MeHg was supplied by a combination of atmospheric, near-shore wetland, and biotic (methylation) sources. Hg_T outputs were dominated by burial (67%), and Hg⁰ evasion accounted for 26% of Hg_T outputs. The watershed of Spring Lake is small (3.7× lake surface area), and accordingly, bog and upland runoff were minor contributors to both Hg_T and MeHg inputs. Wet deposition was ∼9% of total MeHg input, and other external inputs (runoff, sediment porewater) provided only an additional 7%, indicating that internal production of MeHg was occurring in the lake. Photolysis of MeHg, measured in the field and laboratory, removed ∼3× the lake mass of MeHg (20 mg) annually, and was the dominant sink for MeHg. Residence times of MeHg and Hg_T in the lake were 48 and 61 days, respectively, during the open-water season, compared with only 8 days for the residence time of MeHg on settling particles (seston). Photoreduction of Hg²⁺ to Hg⁰ was greater than the reverse reaction (Hg⁰ photooxidation), and the residence time of Hg⁰ in the photic zone was short (hours). Data from this study show active cycling of all the measured species of mercury (Hg_T, MeHg, and Hg⁰) and the importance of MeHg photolysis and photo-redox processes.     

Modelling suspended sediment lead concentrations in contaminated peatland catchments using digital terrain analysis

Upland peat soils in close proximity to urban and industrial areas can be contaminated with high concentrations of atmospherically deposited lead. The peat soils of the Peak District (UK) are characterised by extensive eroding gullies. Fine-resolution digital topographic data were used to map the extent and depth of these gullies. Peat samples from eroding gully walls and suspended sediments were collected and analysed for lead content. Variability in lead concentrations of gully wall material and suspended sediments can be explained by differences in mean upslope gully depth. The lead content of suspended sediment exported from catchments characterised by shallow peat gullies is higher than that exported from catchments with deep peat gullies. The empirical relationship between sediment-associated lead concentration and mean upslope gully depth was combined with the gully depth mapping to produce a predictive spatial model of suspended sediment lead concentrations across the Peak District. This model may be particularly useful for catchment managers who are currently involved in the restoration of eroding peat soils in the Peak District uplands.     

Mercury concentrations in hair exposed in vitro to mercury vapor

Hair is often used as an index of environmental and industrial exposure to different metals. The interpretation of metal levels in hair is difficult because of the risk of external contamination. The aim of this study was to define the degree of external contamination of hair exposed in vitro to mercury vapor. Specimens of hair were exposed to concentration: 0.026, 0.21, and 2.7 mg Hg/m³ for 2–28 d. Mercury levels in hair increased during 28 d of exposure 2, 3 and 13, times, respectively, when compared to initial values. Mercury levels in hair exposed to the first and second (but not third) concentration of mercury vapor attained a steady state on the 21st d of exposure. The contamination of hair with mercury could not be removed by washing with water, solvent, and detergent. Hair may be used as an index of internal uptake of mercury provided that it was not externally exposed to mercury vapor. In cases of occupational exposure to mercury vapor, hair could become a useful tool for monitoring exposures.     

Modelling faecal indicator concentrations in large rural catchments using land use and topographic data

AIMS: To characterize and model spatial variations in faecal-indicator organism concentrations in watercourses draining a large rural catchment during the bathing season. METHODS AND RESULTS: Presumptive coliform (PC), presumptive Eschericia coli (PE) and presumptive enterococci (PEnt) concentrations were determined under base- and high-flow conditions at 24 monitoring points in the Rheidol/Ystwyth catchment, Wales. Relationships with land use and topographic variables within their 'subcatchments' were investigated. Geometric mean (GM) concentrations typically increase more than 10-fold at high flow. The proportion of improved pasture within subcatchments explains 81.6, 73.0 and 85.8%, respectively, of the variance in high-flow GM PC, PE and PEnt concentrations. Distributed modelling suggests that organisms derived from more distant parts of subcatchments may be lost through die-off and sedimentation along watercourses at base flow, although not at high flow. Reductions in concentrations are also evident downstream of reservoir impoundments. CONCLUSIONS: Large rural catchments may contribute substantially to faecal indicator loadings in coastal waters. Indicator concentrations can be modelled successfully using land use and topographic data. SIGNIFICANCE AND IMPACT OF THE STUDY: Development of a modelling approach that provides valuable insight into faecal indicator sources and the transport and survival of these organisms within large catchments.     

Reproduction in an Irish lake population of the crayfish Austropotamobius pallipes (Lerehoullet)

SUMMARY. 1. Mature crayfish were collected in 1984 from an alkaline Irish lake before and after the mating season.
2. There was some correlation between frequency of mating and decrease in vasa deferentia weight in captive males, but in the field vasa deferentia weight losses were highly variable. The data indicate that one third of adult males may not have mated in the wild.
3. All females appear to have spawned, whether or not mated, with an average 85% reduction in ovary weights over the season.
4. Pleopodal egg counts directly after laboratory spawning were on average 81% of ovarian counts; in the field, an estimated 50 days after spawning, they were only 61% of estimated ovarian egg numbers.
5. Average ovarian egg size was positively correlated with female size. Also, larger crayfish had a wider range of egg sizes than smaller crayfish.
6. It is suggested that aggression and competition for shelter among brooding females may result in a progressive loss of eggs.     

Comparison of sulfur concentrations within lake sediment profiles

Sediment cores from lakes in four regions (Adirondacks, Northern New England, Northern Great Lakes States, and Northern Florida) were analyzed for total S concentration. In all regions S concentrations in pre-1900 (1820–1900) sediment were similar and pre-1900 net sediment accumulation rates of S were not significantly different. Sulfur enrichment was greatest in Adirondack lake sediment (Big Moose L., Upper Wallface P., Queer L., and Deep L.), which had total post-1900 S accumulation of 1.1 to 7.4 times pre-1900 S accumulation; post-1900 net sediment accumulation rates of S were significantly greater than the other regions. Sediment from Maine (Little Long P. and Haystack P.) and Vermont (Mud P.) generally had lower S concentration than Adirondack sediments. Sulfur enrichment factors in these lakes ranged from 1.2 to 2.1. There was a positive correlation between contemporary limnetic sulfate concentration and post-1900 net sediment accumulation rates for Adirondack and Northern New England study lakes. Sediment from the Northern Great Lakes States region (McNearney, Andrus, Hustler L. and Dunnigan L.) had similar S concentration and distribution with depth to Northern New England sediment. In two Northern Florida lakes (Mirrow and Fore) sediment showed little variation in S concentration with depth, but L. Mary and L. Barco had higher S in deeper layers (30–55 cm). These different patterns of S distribution among lakes were attributed to differences in limnetic sulfate concentration, organic and inorganic sedimentation, and S diagenesis.     

On the summer peak of nutrient concentrations in lake water

The nutrient concentrations of lake water are strongly influenced by both the combination of inflowing nutrients and those released from sediment in the lake. The former may be related to the nutrient concentration of the lake in winter, and the latter to the peak concentration in summer. This paper considers the problem of how the summer peak may be generated, using actual data from two lakes in Japan. By using a mathematical simulation it can be shown that the summer peak may be generated largely from nutrient materials released from sediment. Using this approach, release rates have been calculated for two lakes. The approach makes a prediction of water improvement due to sediment removal.     

A net ecosystem carbon budget for snow dominated forested headwater catchments: linking water and carbon fluxes to critical zone carbon storage

Climate-driven changes in carbon (C) cycling of forested ecosystems have the potential to alter long-term C sequestration and the global C balance. Prior studies have shown that C uptake and partitioning in response to hydrologic variation are system specific, suggesting that a comprehensive assessment is required for distinct ecosystems. Many sub-humid montane forest ecosystems in the US are projected to experience increased water limitation over the next decades and existing water-limited forests can be used as a model for how changes in the hydrologic cycle will impact such ecosystems more broadly. Toward that goal we monitored precipitation, net ecosystem exchange and lateral soil and stream C fluxes in three semi-arid to sub-humid montane forest catchments for several years (WY 2009–2013) to investigate how the amount and timing of water delivery affect C stores and fluxes. The key control on aqueous and gaseous C fluxes was the distribution of water between winter and summer precipitation, affecting ecosystem C uptake versus heterotrophic respiration. We furthermore assessed C stores in soil and above- and below-ground biomass to assess how spatial patterns in water availability influence C stores. Topographically-driven patterns in catchment wetness correlated with modeled soil C stores, reflecting both long-term trends in local C uptake as well as lateral redistribution of C leached from upslope organic soil horizons to convergent landscape positions. The results suggest that changes in the seasonality of precipitation from winter snow to summer rain will influence both the amount and the spatial distribution of soil C stores.     

Chemical properties of an acidified humic headwater lake with respect to reducing acidic depositions and expected climate change

During the hydrological years 1989 and 1990, water analyses of the dystrophic mountain cirque Lake Huzenbach and the precipitation within its watershed were performed. Periods of droughts which are supposed to be induced by climate change as well as acidic pulses modify the chemical composition of lake water. Snow melt and heavy rains cause flash floods in lake inflows which are controlled by subsurface-flow. One of the inflows exhibits extremely low pH values [pH_min = 3.66], high concentrations for aluminium [Al_max = 1.10 mg l^-1], dissolved organic carbon [DOC_max = 30.7 mg l^-1], and sulfate [SO_4max = 9.08 mg l^-1]. Organic and inorganic acids are both likely to contribute to the acidity of these surface waters. During baseflow conditions, groundwater springs still show slightly positive alkalinity values as well as increased pH values up to about 6.0. Since 1985 lake surface samples demonstrate an increasing tendency towards pH values higher than 5.0 during dry summer periods. Positive alkalinity values occur in the hypolimnion during anoxic conditions.     

Mercury and cadmium concentrations in the tissues of three species of southern albatrosses

Cadmium and mercury concentrations were measured in the tissues of 64 individual albatrosses [23 wandering albatrosses (Diomedea exulans), 9 royal albatrosses (Diomedea epomophora) and 32 shy albatrosses (Thalassarche cauta)] which were killed as by-catch in longline fishing activities between 1991 and 1994. Mercury concentrations were also determined for 33 shy albatross eggs (excluding shells). The birds were all sexed and assigned to one of two age classes (immature and adult). The three species exhibited differences both in overall concentrations of cadmium and mercury, and also in the pattern of accumulation of metals with age and sex. Wandering albatrosses exhibited the highest mercury concentrations with a mean concentration in adult liver samples of 920.0 ± 794.1 μg g⁻¹ dry weight. Shy albatrosses had the lowest mercury concentrations with mean concentrations in adult livers of 36.3 ± 21.4 mg g⁻¹ dry weight. The highest mercury concentration was 1800 μg g⁻¹ for an adult female wandering albatross. Cadmium concentrations were less variable, with adult royal albatrosses having the highest average concentrations (180.0 ± 165.0 in adult kidneys) and adult shy albatrosses the lowest (40.1 ± 20.0 in adult kidney). The highest individual cadmium concentration was 287 μg g⁻¹ for a juvenile wandering albatross. There was no evidence of increased accumulation of cadmium with age in any of the species, but wandering albatrosses showed higher mercury concentrations in adults than juveniles. Female wandering albatrosses also had significantly higher mercury concentrations than males. The mercury contents of the shy albatross eggs were very low, with a maximum concentration of 5.4 μg g⁻¹. The results of this study are consistent with the findings of previous work on albatrosses and support the notion that the life-history strategy of these species (i.e. long-lived with low reproductive output) may be an important determinant in the concentrations of some metals found in their tissues. Accepted: 15 February 1999     

Mercury concentrations in fish, plankton and water from three Western Atlantic estuaries

Total mercury concentrations were determined in the clupeid, Brevoortia tyrannus , from three estuaries of the Western Atlantic, and in the plankton on which they feed, as well as in the water sampled from the same localities. Although there was some indication that the food chain is a likely source of mercury contamination in these fish, as seen by the very much higher levels found in viscera compared with the rest of the fish, there was no evidence of strong food chain intensification. Fish mercury levels (0.3 to 0.5 part/10⁶ dry wt) were about twice that for plankton (0.1–0.2 part/10⁶ dry wt), with higher levels in phyto-than in zooplankton.     

Influence of temperature and high acetate concentrations on methanogenesis in lake sediment slurries

Methanogenesis from main methane precursors H(2)/CO(2) and acetate was investigated in a temperature range of 2-70 degrees C using sediments from Lake Baldegg, Switzerland. Psychrophilic, psychrotrophic, mesophilic, and thermophilic methanogenic microbial communities were enriched by incubations for 1-3 months of nonamended sediment slurries at 5, 15, 30, and 50 degrees C. Isotope experiments with slurries amended with (14)C-labeled bicarbonate and (14)C-2-acetate showed that in the psychrophilic community (enriched at 5 degrees C), about 95% of methane originated from acetate, in contrast to the thermophilic community (50 degrees C) where up to 98% of methane was formed from bicarbonate. In the mesophilic community (30 degrees C), acetate was the precursor of about 80% of the methane produced. When the hydrogen-carbon dioxide mixture (H(2)/CO(2)) was used as a substrate, it was directly converted to methane under thermophilic conditions (70 and 50 degrees C). Under mesophilic conditions (30 degrees C), both pathways, hydrogenotrophic and acetoclastic, were observed. At low temperatures (5 and 15 degrees C), H(2)/CO(2) was converted into methane by a two-step process; first acetate was formed, followed by methane production from acetate. When slurries were incubated at high partial pressures of H(2)/CO(2), the high concentrations of acetate produced of more than 20 mM inhibited acetoclastic methanogenesis at a temperature below 15 degrees C. However, slow adaptation of the psychrophilic microbial community to high acetate concentrations was observed.