Chemical composition of water-bodies in the English Lake District: relationships between chloride and other major ions related to solid geology, and a tentative budget for Windermere

SUMMARY.

• 1 Mean tarnwater concentrations of CI^- and other ions (Na ⁺, K⁺, Ca²⁺, Mg²⁺, SO₄^2-+ NO₃^-) decrease with increasing distance from the sea and altitude but are also related to solid geology. Lowest concentrations occur on slow-weathering igneous rocks (Borrow-dale Volcanics); minima of c. 100 μequiv. CI^-I^-1 are similar to the volume-weighted mean for bulk precipitation. At least 10–20% of Na⁺ is leached from upland catchments, giving Na⁺/CI^- ratios greater than the equivalent ratio (0.86) in seawater and precipitation. Evapotranspiration at 20–30% annual rainfall accounts for CI^- concentrations in many tarns on igneous rocks but not all; some CI^- may be leached from the rocks in upland catchments and come from groundwaters at low altitudes near the sea. Sea-spray has little influence on tarnwaters near the coast.
• 2 On sedimentary rocks overall mean CI^- concentrations are 27–73% higher than equivalent means on Borrowdale Volcanics; concentrations of other ions are also higher. A 5-fold to 10-fold range of CI^-concentrations is not simply due to increased evapotranspiration. Na⁺/CI^- ratios are < 0.86, especially on Skiddaw Slates where tarnwaters contain 10% or more excess CI^- balanced by Ca²⁺, apparently derived from groundwaters rich in CaCI₂. On other sedimentary rocks (Silurian Slates and Carboniferous, Triassic and Permian series) tarn waters display a similar but less pronounced excess of CI^- and Ca^2-+ relative to Na⁺. Some extra CI^- may be captured by dry deposition on vegetation but a portion, perhaps 15–30% of the total, apparently comes from the rocks or from groundwaters via deep aquifers in contact with seawater or connate water.
• 3 Anthropogenic sources on the catchments are also considered: deicing salt used on highways in winter accounts for a 27% increase of CI^- in Windermere South Basin over a 20-year period.

     

Long-term and seasonal changes in the chemical composition of precipitation and surface waters of lakes and tarns in the English Lake District

SUMMARY. The composition of bulk (wet and dry) precipitation in 1975 and 1976 was similar to that found 22 years previously. In 1975, mean values for nine precipitation samplers at one site (Wraymires) ranged from pH 4.3 to 4.5; similar values were obtained in 1976. Samplers covered with fine-mesh plastic gauze caught substantially more Ca²⁺ and K⁺ than open samplers, but pH and SO^2-₄+ NO₃^- concentrations were similar in open and covered samplers. In precipitation, c. 50% of H⁺ was balanced by NO₃^- and c. 50% by SOi; 80% of the SO^2-₄ was balanced by Ca²⁺ and Mg²⁺. Conccntrations of major cations (H⁺, Na⁺, K⁺,Ca²⁺, Mg²⁺) and anions (CI^-, NO₃^- SO^2-₄ and alkalinity [Alk—largely HCO₃^-]) in upland water- bodies were similar to those found in precipitation, but pH levels were generally higher and above 6.0 m some tarns. At lower altitudes, on base-rich roeks and soils, Ca²⁺ and Alk become dominant. Results of a survey of lakes and tarns in 1974–78 are compared with a survey in 1953–56 and published data (chiefly for pH and Alk) for 1947–50, 1932 and 1928. Comparisons are also made with other measurements of Alk in three productive lakes (Blelham Tarn, Esthwaite Water and Windermere) for 1936–39 and 1945–80. Winter levels of NO₃-N, PO₄-P and Si are given for these lakes; although the first two have increased during the late 1960s and the 1970s there has been no significant change in the last. NO₃^- and probably some SO^2-₄. In productive lakes a substantial (c. 50%) rise in mean Alk occurred during the late 1960s and the 1970s, possibly related to increased winter levels of NO₃-N and PO₄-P derived from sewage and fertilizers. In this period the maximum pH levels reached in summer were notably high, sometimes exceeding pH 10. The rise in Alk, conductivity and pH of surface waters is influenced by climatic factors (a decade of drier years), sewage input and biological productivity within the lakes. Considerable seasonal fluctuations in the concentrations of major ions, a characteristic feature of surface waters in the English Lake District, are illustrated and some implications for cation-anion balance briefly discussed. Mid-winter concentrations are usually high forNa⁺, K⁺, Cl^-. NO₃^-and low for Ca²⁺, Mg²⁺, Alk. SO^2-₄. Alkalinity. pH and conductivity of Lake District tarns and lakes show no signs of acidification during the period 1928–80. On the contrary, productive lakes have become more alkaline and some unproductive low-alkalinity (< 100 μ-equiv. 1^-1) lakes also show signs of alkalization, with increased mean concentrations of Na⁺. Ca²⁺ and Mg²⁺, balanced by Alk.     

Relationships between chloride and major cations in precipitation and streamwaters in the Windermere catchment (English Lake District)

SUMMARY. 1. The ranges of concentrations for pH, CV. Na⁺. K⁺Ca²⁺, Mg²⁺ are given for streams draining igneous rocks (Borrowdale Volcanics) and sedimentary muds, silts and shales (Silurian Slates) in the catchment of Windermere (230 km²). Impacts on the biota are briefly discussed. Relative contributions of inputs from various sources are examined: precipitation, rocks and soils, sewage, deicing salt used on highways./ 2. In bulk precipitation, ratios of Na⁺/CV (as μequiv. I^?1) ranged from 0.41 to 1.83 over a 2-year period. The overall volume-weighted mean ratio was 0.86, as in seawater, hut 2′4%(1975) and 5.7% (1976) of Cl^? was non-marine in origin, being balanced by H ⁺ (in winter), K and Ca²⁺ (in summer). In moorland headwater streams, CI^? is largely derived from precipitation: there is a pronounced annual cycle of midwinter high and midsummer low concentrations unrelated to stream discharge. Na* and K⁺ display similar cycles but Na⁺, Ca2⁺ and Mg²⁺ (and pH) are discharge-related due to leaching from rocks and soils: 10–20% Na+, 15–17% Mg²⁺ and 65–75% Ca²⁺ are so-derived whereas K+ comes from precipitation. Na⁺/Cl⁺ ratios in streams on Borrowdale Volcanics alter seasonally, with midsummer values >1. Lower values occur in streams on Silurian Slates where some CI^? is apparently derived from rocks. 3. Seasonal changes in streamwater concentrations of Cl, Na⁴ andK⁺are exponentially related to time. Instantaneous rates of change i day-1¹) are compared in relation to position in the catchment and inputs from anthropogenic sources. Deicing salt has raised (10–100-fold) the concentrations of Na^* and Cl^? in streams on mountain passes; the effects persist throughout the year.     

Persistent surface water acidification in an organic soil-dominated upland region subject to high atmospheric deposition: The North York Moors,UK

The North York Moors National Park, in Northeast England, is one of the few upland areas of the United Kingdom located immediately downwind of major sulphur and nitrogen emission sources. Despite this, few studies of air pollution impacts have been undertaken, and there is no formal long-term upland water quality monitoring site. We examined the condition of surface waters in the National Park based on (1) a unique 20 year stream pH record from three locations; and (2) a snapshot survey of 51 surface waters draining moorland and conifer plantations. Interpretation was supported by sulphur isotope analysis of a subset of water samples, and a diatom survey of one of the monitoring streams. Long-term pH data for a stream draining the peat plateau demonstrate extreme, year-round acidification, with recovery only evident in the last few years. Lower-elevation sites are less acidic, but show similar temporal trends, and are characterised by frequent and severe acid episodes. The snapshot survey confirmed that acidification of the moorland area is widespread, to a degree observed in few other areas globally; out of 37 moorland streams sampled, 32 had an acid neutralising capacity (ANC) below −50 μequiv. l⁻¹. Sulphate was found to be (by far) the dominant cause of acidification, and sulphur isotope analysis confirmed that this derives primarily from atmospheric deposition. Nitrate concentrations remain low, indicating that the organic moorland soils continue to retain most incoming nitrogen. It appears that conifer planting has exacerbated acidification, leading to fivefold higher nitrate and threefold higher aluminium concentrations compared to the moorland sites. Available biological data suggest that waters in the region have been impoverished by acidification. We speculate that the slow recovery of surface waters in the North York Moors is due to the release of a legacy of stored sulphur from the peats, released during droughts. We conclude that: (1) acidification is far from being a solved problem in this sensitive near-source upland region, despite reductions in sulphur deposition; (2) plantation forestry has exacerbated the effects of atmospheric pollution, and triggered nitrogen saturation; (3) the lack of any formal long-term monitoring in the North York Moors represents a major gap in the current evidence base for the effects of long-range air pollutants on UK upland ecosystems.     

Effects of spring acid episodes on macroinvertebrates revealed by population data and in situ toxicity tests

1. While streams in Europe and North America are now recovering chemically from chronic acidification, severe episodic acidification continues to threaten sensitive biota. To appraise further the biological importance of episodic acidification, we surveyed the distribution of the mayfly Baetis alpinus in streams in the Southern Alps (Canton Ticino, Switzerland) in relation to runoff acidity during spring floods. Moreover, to improve mechanistic understanding, in situ toxicity assays were carried out on nymphal B. alpinus during low flows and spring floods, both in streams prone to acid episodes and in well‐buffered controls. 2. Streams surveyed for invertebrates represented three groups which contrasted in susceptibility to episodic acidity. Group one included streams that were acid (alkalinity <0) in spring; group two streams were susceptible to acid episodes because of low base‐flow alkalinity (<200 μeq L^?1); and group three streams were well‐buffered and unlikely ever to be acid. The abundance of B. alpinus was similar among groups during stable flows in winter and summer, but was significantly lower in groups one and two following spring snowmelt. 3. During the bioassays, control streams remained circumneutral to alkaline (pH >6.4). By contrast, episodic streams were circumneutral at low flows, but became acid (pH 4.5–5.6 and total dissolved aluminium to 276 μg L^?1) during intense spring snowmelt. After 15‐day exposures, nymphal B. alpinus survival in the circumneutral control streams exceeded 92% irrespective of flow. In the episodic streams, survival matched the controls during low flows, but declined significantly to 10–20% during acid episodes in spring. Shorter exposure (2–4 days) to pH 5.5–5.7 did not cause significant mortality either during the exposure or over the following 7 days, indicating that B. alpinus might recover from short acid episodes. 4. Our data suggest that the spring distribution of B. alpinus in acid sensitive parts of the Alps directly reflects the toxicity of acid runoff during snowmelt. Our study illustrates that even mild episodic acidification can have significant consequences in Alpine streams for one of the most important invertebrate indicators of acidity.     

Regional and temporal variation in pH, alkalinity and carbon dioxide in Danish streams, related to soil type and land use

SUMMARY 1. The Weichsel glaciation has divided Denmark into two regions with different susceptibility to acidification. East of the Weichselian terminal moraine, soils are usually clayey and calcareous, and the streams are alkaline (mean alkalinity 2.24 mmol 1-^-1) and resistant to inputs of acidifying substances. 2. Trend analysis of pH and alkalinity of water samples taken over 15 years in two streams with alkalinities above 1.5 mmol 1^?1 in eastern Jutland, showed no trends of acidification. 3. West of the terminal moraine the soils are sandy and leached and alkalinity is lower (mean 0.59 mmol 1^?1). Although such streams with medium alkalinity are believed not to be vulnerable to acidification, we have documented significant decreases in their pH and alkalinity over 12 years. 4. Trends of pH and alkalinity in four western streams with mean alkalinities between 0.05 and 0.79 mmol 1^?1 showed annual decreases of 0.027 pH units and 4.7 nmol 1^?1 in alkalinity. 5. Overall, Danish streams contain about 7.9 times more calculated free CO₂ (pCO₂=10^?2.⁶ atm) than water in equilibrium with air (pCO₂= 10^?3.⁵ atm). The calculated free CO₂ content has increased significantly in western Danish streams over the study period (6.9 μmol 1^?1 yr^-1). This increase cannot be explained by the prevailing global increase in atmospheric pCO₂ which only can account for 0.54 pmol 1^?1 yr^?1 at maximum. 6. Reasons for the ongoing stream acidification in the western part of Denmark are discussed. We suggest that atmospheric deposition causes stream acidification in a heath-covered catchment without agriculture. In heavily cultivated regions the main acidification factor is argued to be proton production in the soil through nitrification of ammonium-containing fertilizers.     

CO2 dynamics along Danish lowland streams: water–air gradients, piston velocities and evasion rates

We measured CO₂ concentration and determined evasion rate and piston velocity across the water–air interface in flow-through chambers at eight stations along two 20 km long streams in agricultural landscapes in Zealand, Denmark. Both streams were 9–18-fold supersaturated in CO₂ with daily means of 240 and 340 μM in January–March and 130 and 180 μM in June–August. Annual CO₂ medians were 212 μM in six other streams and 460 μM in four groundwater wells, while seven lakes were weakly supersaturated (29 μM). Air concentrations immediately above stream surfaces were close to mean atmospheric conditions except during calm summer nights. Piston velocity from 0.4 to 21.6 cm h^?1 was closely related to current velocity permitting calculation of evasion rates for entire streams. CO₂ evasion rates were highest in midstream reaches (170–1,200 mmol m^?2 day^?1) where CO₂-rich soil water entered fast stream flow, while rates were tenfold lower (25–100 mmol m^?2 day^?1) in slow-flowing lower reaches. CO₂ evasion mainly derived from the input of CO₂ in soil water. The variability of CO₂ evasion along the two lowland streams covered much of the range in sub-Arctic and temperate streams reported previously. In budgets for the two stream catchments, loss of carbon from soils via the hydrological cycle was substantial (3.2–5.7 mmol m^?2 day^?1) and dominated by CO₂ consumed to form HCO₃ ^? by mineral dissolution (69–76%) and export of organic carbon (15–23%) relative to dissolved CO₂ export (7–9%).     

Inter-Annual Precipitation Variability Decreases Switchgrass Productivity from Arid to Mesic Environments

Cellulosic biofuels are an important source of renewable biomass within the alternative energy portfolio. Switchgrass (Panicum virgatum L.), a perennial C₄ grass native to North America, is widely studied as a biofuel feedstock for its consistently high yields and minimal input requirements. The influences of precipitation amount and temporal variability on the fertilizer response of switchgrass productivity are not fully understood. Moreover, global climate models predict changes in rainfall patterns towards lower and increasingly variable soil water availability in several productive areas worldwide, which may impact net primary production of biofuel crops. We conducted a meta-analysis of aboveground net primary production of switchgrass from 48 publications encompassing 82 different locations, 11 soil types, 52 switchgrass cultivars, fertilizer inputs between 0 to 896 kg N ha^?1 year^?1, and 1 to 6 years of annual productivity measures repeated on the same stand. Productivity of the lowland ecotype doubled with N rates >?131 kg N ha^?1 year^?1, but upland ecotype productivity increased only by 50%. Results showed an optimum N rate of 30 to 60 kg N ha^?1 year^?1 for both ecotypes, after which biomass gain per unit of N added decreased. Growing season precipitation (GSPPT) and inter-annual precipitation variability (inter-PPTvar) affected both ecotypes similarly. Long-term mean annual precipitation (MAP) differentially affected lowland and upland productivity, depending on the N level. Productivity responses to MAP and GSPPT were similar for both upland and lowland ecotypes at none or low N rates. When N increased beyond 60 kg N ha^?1 year^?1, lowland cultivars had a greater growth response to MAP than uplands. Productivity increased with increasing GSPPT and MAP and had a positive linear response to MAP ranging from 600 to 1200 mm year^?1. One third of the variability in switchgrass production was accounted for by inter-PPTvar. After accounting for MAP, sites with higher inter-PPTvar had lower switchgrass productivity than sites with lower inter-PPTvar. Increased inter-annual variation in precipitation reduced production of both ecotypes. Predicted changes in the amount and timing of precipitation thus likely will exert greater influence on production of upland than lowland ecotypes of switchgrass.     

Effects of episodic acidification on macroinvertebrate assemblages in Swiss Alpine streams

1. Despite long‐standing ecotoxicological evidence that episodes of acidification in streams are important biologically, there is still uncertainty about their effects on invertebrate communities. We surveyed 20 streams in an acid sensitive Alpine area (Canton Ticino, Switzerland), where episodes are driven by snowmelt in spring and by rainstorms at other times of the year. Samples of water and macroinvertebrates were collected in pre‐event conditions (winter and summer) and during periods of high flow (spring and autumn). 2. Using pH, [Ca²⁺] and [Alⁿ⁺], streams were clustered into six acid–base groups that were either well buffered (groups 4–6), soft‐water with stable pH (group 3), or poorly buffered with low pH at high flow (groups 1 and 2). 3. Severe episodes occurred during snowmelt, when the group 1 streams became acidic with pH down to 5.0 and [Alⁿ⁺] up to 140 μg L^?1. pH declined to 6.2 in streams of group 2, but remained > 6.6 in groups 3–6. 4. Detrended canonical correspondence analysis showed that the streams sensitive to episodes (groups 1 and 2) had different invertebrate assemblages from well‐buffered sites (groups 4 and 5) or soft‐water stable streams (group 3), with faunal differences largest following spring snowmelt. Empididae, Isoperla rivulorum, Rhithrogena spp. and Baetis spp. were scarce in streams sensitive to episodes (groups 1 and 2). By contrast, Amphinemura sulcicollis was scarcer in hard‐water streams (groups 4–6). Taxonomic richness was lower in the episodic streams of group 1 than in other streams. 5. Together, these results indicate clear biological differences between acid‐sensitive streams with similar low‐flow chemistry but contrasting episode chemistry. Severe episodes of acidification appear to affect macroinvertebrate assemblages in streams in the southern Swiss Alps.     

Stream acidification increases nitrogen uptake by leaf biofilms: implications at the ecosystem scale

1. While anthropogenic stream acidification is known to lower species diversity and impair decomposition, its effects on nutrient cycling remain unclear. The influence of acid‐stress on microbial physiology can have implications for carbon (C) and nitrogen (N) cycles, linking environmental conditions to ecosystem processes. 2. We collected leaf biofilms from streams spanning a gradient of pH (5.1–6.7), related to chronic acidification, to investigate the relationship between qCO₂ (biomass‐specific respiration; mg CO₂‐C g^?1 fungal C h^?1), a known indicator of stress, and biomass‐specific N uptake (μg NH₄‐N mg^?1 fungal biomass h^?1) at two levels of N availability (25 and 100 μg NH₄‐N L^?1) in experimental microcosms. 3. Strong patterns of increasing qCO₂ (i.e. increasing stress) and increasing microbial N uptake were observed with a decrease in ambient (i.e. chronic) stream pH at both levels of N availability. However, fungal biomass was lower on leaves from more acidic streams, resulting in lower overall respiration and N uptake when rates were standardized by leaf biomass. 4. Results suggest that chronic acidification decreases fungal metabolic efficiency because, under acid conditions, these organisms allocate more resources to maintenance and survival and increase their removal of N, possibly via increased exoenzyme production. At the same time, greater N availability enhanced N uptake without influencing CO₂ production, implying increased growth efficiency. 5. At the ecosystem level, reductions in growth because of chronic acidification reduce microbial biomass and may impair decomposition and N uptake; however, in systems where N is initially scarce, increased N availability may alleviate these effects. Ecosystem response to chronic stressors may be better understood by a greater focus on microbial physiology, coupled elemental cycling, and responses across several scales of investigation.     

Carbon dynamics in successional and afforested spruce stands in Thuringia and the Alps

Changes in the carbon stocks of stem biomass, organic layers and the upper 50 cm of the mineral soil during succession and afforestation of spruce (Picea abies) on former grassland were examined along six chronosequences in Thuringia and the Alps. Three chronosequences were established on calcareous and three on acidic bedrocks. Stand elevation and mean annual precipitation of the chronosequences were different. Maximum stand age was 93 years on acid and 112 years on calcareous bedrocks. Stem biomass increased with stand age and reached values of 250–400 t C ha^?1 in the oldest successional stands. On acidic bedrocks, the organic layers accumulated linearly during forest succession at a rate of 0.34 t C ha^?1 yr^?1. On calcareous bedrocks, a maximum carbon stock in the humus layers was reached at an age of 60 years. Total carbon stocks in stem biomass, organic layers and the mineral soil increased during forest development from 75 t C ha^?1 in the meadows to 350 t C ha^?1 in the oldest successional forest stands (2.75 t C ha^?1 yr^?1). Carbon sequestration occurred in stem biomass and in the organic layers (0.34 t C ha^?1 yr^?1on acid bedrock), while mineral soil carbon stocks declined. Mineral soil carbon stocks were larger in areas with higher precipitation. During forest succession, mineral soil carbon stocks of the upper 50 cm decreased until they reached approximately 80% of the meadow level and increased slightly thereafter. Carbon dynamics in soil layers were examined by a process model. Results showed that sustained input of meadow fine roots is the factor, which most likely reduces carbon losses in the upper 10 cm. Carbon losses in 10–20 cm depth were lower on acidic than on calcareous bedrocks. In this depth, continuous dissolved organic carbon inputs and low soil respiration rates could promote carbon sequestration following initial carbon loss. At least 80 years are necessary to regain former stock levels in the mineral soil. Despite the comparatively larger amount of carbon stored in the regrowing vegetation, afforestation projects under the Kyoto protocol should also aim at the preservation or increase of carbon in the mineral soil regarding its greater stability of compared with stocks in biomass and humus layers. If grassland afforestation is planned, suitable management options and a sufficient rotation length should be chosen to achieve these objectives. Maintenance of grass cover reduces the initial loss.     

Faunal and chemical dynamics of some acid and alkaline New Zealand streams

SUMMARY 1. Water from acid (pH 4.3–5.7), brown water streams was low in alkalinity (0–2.3 g m^?3 CaCO₃) and conductivity (2.5–4.1 mS m^?1) but contained relatively high concentrations of dissolved organic carbon (6.6–16.3 gm^?3). In contrast, alkaline (pH 6.6–8.0), clearwater streams had high CaCO₃ (12.6–57.6 g m^?3) and conductivity (3.7–22.3 mS m^?1) but low dissolved organic carbon concentrations (0.3–4.7 g m^?3). 2. Total reactive aluminium (Al) concentrations were high in acid streams (123–363 mg m?³) but never exceeded 84 mg m?³ in alkaline streams. Acid-soluble and organic monomeric Al were the major Al species in the acid streams (31–168 and 84–178mg m?³, respectively). Concentrations of toxic inorganic monomeric Al were low in all streams (<50mg m?³). 3. Sixty-four invertebrate taxa were collected from the alkaline streams compared to forty-seven from the acid sites. Numbers of taxa in specific insect orders were similar at all sites, however. Benthic faunas at most sites were dominated by the mayfly Deleatidium sp. and chironomids. 4. Overall, mean densities of benthic invertebrates were 2.4–4.8 times higher in alkaline streams than acid streams. No seasonal patterns of abundance were evident at any site. 5. Temporal variability of invertebrate densities was correlated with stream channel stability such that fluctuations in densities declined as stability increased. 6. Sources of dissolved organic carbon and aluminium in acid, brown water streams are discussed. We suggest that changes in the food supply available in acid streams account for the depauperate faunas found there.     

Structure and Spatial‐Temporal Dynamics of Chironomidae Fauna (Diptera) in Upland and Lowland Fluvial Habitats of the Chocancharava River Basin (Argentina)

Structure of benthic Chironomidae assemblages and their spatial‐temporal dynamic were analyzed in upland and lowland habitats from the Chocancharava River basin (Córdoba, Argentina). Sampling was performed in three tributary streams and in three lowland reaches of the river during high and low rainfall periods. Characteristic taxa of upland and lowland reaches and of the different habitats in these reaches were identified using the IndVal method. Chironomidae assemblages were different between upland and lowland reaches and among habitats in each reach, as assessed by Multiresponse Permutation Procedure and Canonical Correspondence Analyses. Substrate type and current velocity were the major explanatory variables structuring the assemblages in upland reaches whereas in lowland reaches current velocity and aquatic vegetation were the most important variables. The highest richness was found in the most complex habitat units in both upland and lowland stretches as assessed by Analyses of Variance. Chironomidae larvae responded to longitudinal changes of hydraulic variables and to local variations of fluvial habitats at different reaches. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Concentration,Distribution, Source,and Risk Assessment of PAHs and Heavy Metals in Surface Water from the Three Gorges Reservoir,China

Fifteen polycyclic aromatic hydrocarbons (PAHs) and heavy metals (Cr, Ni, As, Cd, Pb, and Hg) were quantified in 19 surface water sites of the Three Gorges Reservoir, China. The total concentrations of 15 PAHs and six heavy metals in the 19 sample sites ranged from 130.8 ng L^?1 to 227.5 ng L^?1 and 3.2 μg L^?1 to 6.0 μg L^?1, respectively. The mean concentration of As was the highest among the six heavy metals (2.1 ± 0.3 μg L^?1), followed by Cr (0.5 ± 0.3 μg L^?1), Ni (1.3 ± 0.1 μg L^?1), Cd (0.2 ± 0.01 μg L^?1), Pb (0.07 ± 0.08 μ g L^?1) and Hg (0.05 ± 0.08 μg L^?1). The isomer ratio results suggest that PAHs at most sites were mainly from petroleum combustion, while coal and biomass combustion was the main source at sites 1, 2, 6, 7, 9, 14, and 17. Based on principal component analysis, the main source of heavy metals was anthropogenic activities and weathering of bedrocks. Depending on characteristic of RQ_(NCs) ≥ 1 and RQ_(MPCs) < 1, BaA showed higher potential ecological risk than other PAHs, therefore, all sampling site needed to be paid much more attention, included some remedial actions. Meanwhile, after assessing human health risk of heavy metal, it was unlikely to experience adverse health effects, even exposing through more pathways and six kinds of heavy metals simultaneously.     

Chemical character and origin of organic acids in streams and seepage lakes of central Maine

Organic acids and inorganic chemistry were examined in seventeen seepage lakes, seven streams, and one seep in central Maine. The objectives of this analysis were to determine the quantity and quality of dissolved organic carbon (DOC), and to assess the relationship between organic and inorganic surface water chemistry. Lakes and streams sampled were dilute (average conductivity of 20.3 μS cm^?1) with a wide range of DOC (125–2593 μmol C L^?1). Organic acids in DOC were evaluated by:

DOC fractionation (hydrophobic acids and neutrals, and hydrophilic acids, bases, and neutrals);

DOC isolation followed by FT-IR, base titration, and chemical analyses;

adsorption on solid phase extraction columns; and charge balance studies.

All lakes and streams were dominated by hydrophobic and hydrophilic acids (60 to 92% of DOC). Lakes and streams with low DOC had low hydrophobic to hydrophilic acid ratios (ca 1.2–1.3), regardless of pH and acid neutralizing capacities (ANC), compared to lakes and streams with moderate to high DOC concentrations (ca 1.9–2.4). Based on FT-IR spectroscopy and chemical analysis, organic acids were found to be dominated by a strong carboxylic character. Titration data of isolated DOC allowed accurate prediction of organic anions, which were strongly pH dependent (organic anions ranged from 14 to 198 μeq L^?1). Exchange acidity averaged 11.3, 13.6, and 8.7 μeq mg C^?1 for lake hydrophobic acids, lake hydrophilic acids, and stream hydrophobic acids, respectively. Overall evidence suggested that DOC and organic acid characteristics were related to their carboxylic functional group content and that the nature of these constituents was similar despite the source of origin (upland soils, wetlands, or Sphagnum deposits). Also, contact of soil leachates with B horizons seemed to be a controlling factor in DOC quantity and quality in the lakes and streams studied.     

Long-term effects of catchment liming on invertebrates in upland streams

1. Catchment liming to mitigate acidification causes major chemical change in freshwaters but longer‐term effects are poorly understood. Using a replicated basin‐scale experiment with a multiple BACI design (= before‐after‐control‐impact), we assessed chemical and biological effects for 10 years after the catchments of three acidified Welsh streams at Llyn Brianne were limed in 1987/88. 2. Stream chemistry was measured weekly to monthly, and macroinvertebrates monitored annually, between 1985 and 1998. Biological change through time was assessed from the abundance and taxon richness of invertebrates. We paid particular attention to 18 species known to be acid‐sensitive. The effects of liming were assessed by comparing chemical and biological trends among the three replicate limed streams, three acid reference streams and two naturally circumneutral streams. 3. Following single lime applications, acid‐base chemistry in treated streams changed significantly. High mean pH (> 6), increased calcium (> 2.5 mg L^?1) and low aluminium (< 0.1 mg L^?1) persisted throughout the 10 years following liming. 4. The effects of liming on invertebrates were modest. Acid sensitive taxa increased significantly in abundance in limed streams, but only during 2 years following treatment. Significant effects on richness were more sustained, but on average added only 2–3 acid‐sensitive species to the treated streams, roughly one‐third of their average richness in adjacent circumneutral streams. Only the mayfly Baetis rhodani and the stonefly Brachyptera risi occurred significantly more often in limed streams after treatment than before it. 5. Despite these modest long‐term effects on invertebrates, nearly 80% of the total pool of acid‐sensitive species has occurred at least once in the limed streams in the 10 years since treatment. This pattern of occurrence suggests that the colonization of limed streams by acid‐sensitive taxa reflects limited persistence rather than restricted dispersal. We present evidence to show that episodes of low pH continued to affect acid‐sensitive taxa even after liming. We highlight the importance of extending the time‐periods over which the effects of large‐scale ecological experiments are assessed.     

Land-use influence on stream water quality and diatom communities in Victoria, Australia: a response to secondary salinization

Diatom communities were analyzed in 39 streams located in drainages with varied land-use practices throughout Victoria, Australia. Thirteen water quality parameters were also measured in each stream. Most streams had low HCO₃ ^1- concentrations (low buffering capacity) with >90% of the waters dominated by Na¹⁺ and Cl^1-. Phosphate concentrations ranged from 0.003 to 2.0 mg/L. Diatom communities (245 taxa) were strongly correlated with land-use practices, i.e. historic clear cutting, and secondary salinization. Streams influenced by heavy irrigation practices and dryland farming had reduced species diversity and richness compared to systems with low to moderate land use. A nonmetric multidimensional ordination of diatom communities in the 39 streams was conducted. An ANOSIM on the ordination showed that diatom communities in upland watersheds with native forest canopies and low salinization, lowland streams in watersheds with cleared forest canopies, moderate agricultural utilization and salinization, and lowland streams in areas with high irrigation and salinization were all significantly different (p<0.001) from one another. Community ordination techniques showed that both specific conductance (salinity) and phosphorus interacted to determine stream diatom community structure in drainages with high secondary salinization. Drainages with low to moderate agricultural activity and low nutrients, but with a wide range of salinities showed strong associations with the diatom taxa Amphora coffeaeformis, Cymbella pusilla and Entomoneis paludosa, whereas, streams in regions with heavy agricultural practices and high phosphorus had Bacillaria paradoxa, Nitzschia hungarica, N. frustulum and Aulacoseira granulata as numerically important diatoms. In contrast, Rhizosolenia eriensis, Frustulia rhomboides, Eunotia pectinatus and Tabellaria flocculosa were strongly associated with upland streams with fast current, relatively low O-PO₄ ^3- concentrations, low pH, low salinity, and low temperature. In general, the diatom communities in saline streams (3 mS) were similar to those previously reported in saline lakes in Victoria.     

Longitudinal changes in δ13C of riffle macroinvertebrates from mountain to lowland sections of a gravel‐bed river

Summary 1. To understand longitudinal changes in the trophic base of benthic macroinvertebrates from mountain to lowland river sections, we investigated carbon stable isotopic compositions (δ¹³C) of macroinvertebrates and their food resources in riffles for four seasons at 14 sites along the main stem of the Toyo River, Japan. 2. At each site, δ¹³C was usually highest or nearly highest for periphyton (epilithic biofilm) and was lowest for transported leaf materials. Among macroinvertebrate groups, grazers usually had higher δ¹³C values than filterers or predators. 3. During all seasons, δ¹³C of periphyton and all macroinvertebrate groups increased downstream from mountain to upland sections, but decreased downstream from upland to lowland sections. In addition, the difference between grazer δ¹³C and filterer δ¹³C decreased from mountain to upland sections, but increased from upland to lowland sections. 4. The observed changes in δ¹³C of periphyton and macroinvertebrates from mountain to upland sections agree with previous reports: the δ¹³C of periphyton and consumers increased with stream size and productivity. The decrease in δ¹³C of periphyton and macroinvertebrates from upland to lowland sections has not been reported previously, and this may have resulted from an increased importance of terrestrial detritus relative to periphyton production in the lowland section, where riffles were infrequent and pools dominated the reach. 5. A simple mixing model of δ¹³C showed that grazers rely mostly on periphyton at all sites, whereas the importance of periphyton for filterers changed longitudinally increasing from mountain to upland sections and decreasing from upland to lowland sections. This longitudinal trend for filterers is possibly associated with the changes in the availability or quality of terrestrial detritus in transported particulate organic matter. 6. Longitudinal changes in the relative importance of autochthonous production and allochthonous detritus appear to be reflected in δ¹³C of riffle benthic communities. The longitudinal changes were not monotonic, and specific reach characteristics may be responsible for the greater importance of allochthonous detritus in mountain and lowland sections.     

Coarse Woody Debris Quantity and Distribution in Central European Streams

Summarized here are ten investigations concerning the volume of coarse woody debris (CWD) in Central European streams. Altogether, 69 stream sections were examined ranging from Northern German lowland streams to brooks in alpine regions. Most of the study streams are according to Central European standards quasi‐natural and are bordered by deciduous forest. The geometric mean of CWD volume related to stream length is 1.44 m³ /100 meter reach. Related to stream bottom area, the geometric mean of CWD volume is 0.202 m³ /100 m² . The mean number of logs (≥10 cm diameter) is 12.5 logs/100 meter reach, and 3.01/100 m² bottom area (geometric means). Regarding only quasi‐natural stream sections (riparian forest currently unmanaged and no removal of CWD for at least 10 years), the geometric mean of CWD standing stock is 0.45 m³ /100 m² for lowland streams, 0.38 m³/100 m² for streams in lower mountainous areas and 0.02 m³ /100 m² for alpine floodplains. From the distribution of size classes and comparison with other studies it is likely, that the current CWD standing stock is considerably less than the potential amount of CWD. For centuries all of the streams have been influenced by man. Historic alterations of the stream, its floodplain and the riparian vegetation may still affect CWD supply and standing stock. We conclude that virtually all streams in Central Europe are highly altered with respect to the amount of CWD, and that the importance of CWD is under‐represented in recent assessment principles for streams in Germany.     

Spatial and temporal patterns of nitrogen concentrations in pristine and agriculturally-influenced prairie streams

Long-term data on nitrogen chemistry of streams draining Konza Prairie Biological Station (Konza), Kansas were analyzed to assess spatial and temporal patterns and examine the influence of agricultural activity on these patterns. Upland watersheds of Konza are predominantly tallgrass prairies, but agricultural fields and riparian forests border the lower reaches of the streams. We have up to 11 years of data in the relatively pristine upland reaches and 4 years of data on wells and downstream reaches influenced by fertilized croplands. Seasonal and spatial patterns in total nitrogen (TN) concentrations were driven largely by changes in the nitrate (NO₃ ^–) concentrations. A gradient of increasing NO₃ ^– concentrations occurred from pristine upland stream reaches to the more agriculturally-influenced lowland reaches. Nitrate concentrations varied seasonally and were negatively correlated with discharge in areas influenced by row-crop agriculture (p = 0.007). The NO₃ ^– concentrations of stream water in lowland reaches were lowest during times of high precipitation, when the relative influence of groundwater drainage is minimal and water in the channel is primarily derived from upland prairie reaches. The groundwater from cropland increased stream NO₃ ^– concentrations about four-fold during low-discharge periods, even though significant riparian forest corridors existed along most of the lower stream channel. The minimum NO₃ ^– concentrations in the agriculturally influenced reaches were greater than at any time in prairie reaches. Analysis of data before and after introduction of bison to four prairie watersheds revealed a 35% increase of TN concentrations (p < 0.05) in the stream water channels after the introduction of bison. These data suggest that natural processes such as bison grazing, variable discharge, and localized input of groundwater lead to variation in NO₃ ^– concentrations less than 100-fold in prairie streams. Row-crop agriculture can increase NO₃ ^– concentrations well over 100-fold relative to pristine systems, and the influence of this land use process over space and time overrides natural processes.