An investigation of the impact of afforestation on stream-water chemistry in the Loch Dee catchment, SW Scotland

The impact of conifer afforestation on stream-water chemistry was investigated in the acidified catchment of Loch Dee, SW Scotland. Long-term trends in stream-water chemistry were evaluated during a period of forest growth from age 6 to 17 years. A significant increase was observed for pH (0.2 units) and a significant decline for aluminium (0.05 mg litre(-1)), sulphate (1.2 mg litre(-1)) and nitrate (0.02 mg litre(-1)) concentrations. The long-term decrease in stream-water acidity was ascribed to the marked reductions in sulphur depositions during the 1970s and early 1980s. There was no evidence that this response had been attenuated by afforestation, the improvements in stream-water chemistry being of a similar magnitude to those recorded in nearby moorland lochs and exceeding that in an adjacent moorland-catchment stream. The lack of a clear forest acidification effect is consistent with deposition-model estimates which show the increased scavenging of occult and dry deposition by the growing forest to be small at this site (相似文献   

Adsorption of aluminium by stream particulates

An experimental study was made of the adsorption of aluminium by fine particulates from Whitray Beck, a hill stream in NW England. Adsorption increased with Al(3) activity, pH and concentration of particles, and could be quantitatively described by the empirical equation: [Formula: see text] [particles] where square brackets indicate concentrations, curly brackets, activities, and alpha, beta and gamma are constants with values of 5.14x10(-10) (mol litre(-1))(2.015) (g particles litre(-1))(-1), 0.457, and 1.472, respectively. For the experimental data, the equation gave a correlation ratio of 0.99. The equation accounts reasonably well for the adsorption of Al by particulates from seven other streams. In applying the equation, it must be borne in mind that the desorption kinetics of Al depend on pH, and rapid reversibility (<15min) can only be assumed for pHor=10%) of total monomeric Al.     

Chemical and biological effects of acid, aluminium and lime additions to a Welsh Hill-stream

Chemical and biological responses to simultaneous additions of acid, aluminium and lime were investigated in contiguous 250m-reaches of a chronically acidic stream in Wales. Treatments were applied for 24 h, and from the upstream end were as follows: zone A-untreated, pH 5.0, 0.37 mg litre(-1) filterable Al; zone B-acidified to pH 4.5, 0.40 mg Al litre(-1) (47% of Al attributed to release from the stream bed due to acid additions); zone C-acidified to pH 4.5 and Al dosed to 0.67 mg litre(-1); zone D-dosed with limestone slurry, resulting in pH 7.2, 0.13 mg Al litre(-1). In all reaches, the chemistry of the interstitial water at depths of 0.15 and 0.3 m never fell below pH 5.5, with corresponding decreases in Al and increases in base cation concentrations. Brown trout, Salmo trutta, and crayfish, Austropotamobius pallipes, held in the stream showed decreases in plasma [Na(+)] and haemolymph [Na(+)], respectively, in all acidic zones (A, B, C): these responses were mitigated by liming (zone D). Thus both chronic and simulated episodic levels of pH and dissolved Al were sub-lethally toxic to test species of aquatic fauna. This experiment also demonstrates a stream bed source/sink of Al, and the availability of a possible refuge from acidic surface waters within the substratum.     

Land use influences macroinvertebrate community composition in boreal headwaters through altered stream conditions

Land use is known to alter the nature of land–water interactions, but the potential effects of widespread forest management on headwaters in boreal regions remain poorly understood. We evaluated the importance of catchment land use, land cover, and local stream variables for macroinvertebrate community and functional trait diversity in 18 boreal headwater streams. Variation in macroinvertebrate metrics was often best explained by in-stream variables, primarily water chemistry (e.g. pH). However, variation in stream variables was, in turn, significantly associated with catchment-scale forestry land use. More specifically, streams running through catchments that were dominated by young (11–50 years) forests had higher pH, greater organic matter standing stock, higher abundance of aquatic moss, and the highest macroinvertebrate diversity, compared to streams running through recently clear-cut and old forests. This indicates that catchment-scale forest management can modify in-stream habitat conditions with effects on stream macroinvertebrate communities and that characteristics of younger forests may promote conditions that benefit headwater biodiversity.     

Benthic macroinvertebrate community structure in 20 streams of varying pH and humic content

The structure of stream benthic macroinvertebrate communities in relation to pH and humic content was studied in 20 second and third-order forest streams in southern Sweden. Streams varied in pH from 4.2 to 8.0, and in humic content from a colour of 5 to 1200 mg Pt litre(-1). There was a positive relationship between pH and species richness, with a discontinuity occurring at pH approximately 5.7. At pH > 5.7, species richness decreased with increasing colour. At pH < 5.7 there was a positive correlation between species richness and humic concentration up to a colour of about 200-300 mg Pt litre(-1). this may be explained by high concentrations, 0.4-0.9 mg litre(-1), of labile monomeric Al occurring in the low coloured acid streams. In streams with a colour > 200 mg Pt litre(-1) labile monomeric Al was less than 0.2 mg litre(-1). There was no significant change in species richness above this threshold, but a shift in species composition towards a dominance of Plecoptera and Chironomidae. This threshold model seems to explain the observed differences in stream benthic community structure better than a simple linear relationship with pH or humic content.     

Artificial acidification of a non-acidic and an acidic headwater stream in Maine, USA

Two headwater streams with low DOC and different pHs (4.5-4.8 and 5-6.5) were acidified with H2SO4 to pH 4.1 and 4.5, respectively, for 24-h periods. Neutralization of the added acid occurred by protonation of ANC (HCO3-dominated in the higher pH stream), desorption of Ca (< 15 microeq litre(-1)) and Mg (<6 microeq litre(-1)), and desorption and dissolution of AL (<250 microg litre(-1)) from the stream bed. The concentrations of dissolved organic carbon (DOC) remained constant within the experimental reaches. The concentrations of Na, K an H4SiO4 also remained constant, indicating no detectable increase in the rate of chemical weathering in the stream bed. After acid addition was stopped, concentrations of Ca, Mg and Al decreased to below background, indicating reversible ion exchange as the principal mechanism for the mobility of Ca and Mg and to a lesser extent for Al. Repeated acidifications indicated that significant regeneration of cations on the exchange surfaces of the stream substrate occurs rapidly.     

Abundance and population structure of perch (Perca fluviatilis L.) in some acidic Norwegian lakes

Abundance (catch per unit effort, n=3752) and population structure of perch Perca fluviatilis were studied in 30 acidic Norwegian lakes with relation to pH (4.3-5.9), calcium (0.41-2.44 mg litre(-1)), labile aluminium (24-255 microg litre(-1)) and total organic carbon (TOC, 1.7-13.8 mg C litre(-1)). Standard series of bottom gill-nets were used to sample fish populations. A multiple regression analysis showed that abundance was significantly correlated to TOC (P<0.05) and, to a smaller extent, to the Ca in lakes with concentrations between 0.41 and 1.70 mg litre(-1) (P=0.07). The lakes which were inhabited by pike were excluded from the analysis. Recruitment failure seems to be the main cause of reductions in perch numbers in the lakes studied. However, high mortality among adult individuals was also evident, and an episode of fish kill was observed in one of the lakes.     

Water chemistry and fish community responses to episodic stream acidification in Pennsylvania, USA

Five streams were studied on the Northern Appalachian Plateau of Pennsylvania from October 1988 through June 1989 to determine chemical changes that occur during episodic storm run-off and the responses of fish to these events. These second-order streams flowed through undisturbed, wooded, sandstone bedrock catchments with surface areas ranging from 500 to 1000 hectares. Median pH of precipitations was about 4.2, and among streams it ranged from 5.0 to 6.2. During storm events, pH declined by as much as 1.2 units and peak concentrations of total monomeric Al ranged from < 0.01 to 0.75 mg litre(-1). Organically bound A1 was generally a minor component of total monomeric A1. Wild brook trout (Salvelinus fontinalis) were found in all streams, although only a remnant population existed in the most acidic stream. Sculpins (Cottus bairdi or C. cognatus) were collected only in the two streams with the least severe episodes. Mortality of brook trout and sculpins in in situ bioassays ranged from 0 to about 80% among streams during acidic episodes and was positively related to concentrations of total dissolved Al. Radio-tagged brook trout moved downstream during episodes when Al reached toxic concentrations. Some displaced trout were found near groundwater seeps, where pH was higher and dissolved Al was lower than in the main channel.     

Trout farm effluents: characterization and impact on the receiving streams

Effluents from three rainbow trout (Oncorhynchus mykiss) farms located in Northern Portugal were characterized and their impact on the receiving streams was evaluated. Mean fish productions in the studied fish farms were 15, 55 and 500 t of trout per year, respectively. The feeding water was abstracted from Fornelo, Inha and Coura Rivers, at flow rates ranging from 1.2 (15 t year(-1) fish farm) to 4.8 litre s(-1) per ton annual fish production (500 t year(-1) fish farm). As the water flows through the farms, net variations in the chemical characteristics were observed: a mean reduction in the dissolved oxygen (DO) concentration between 0.7 and 2.4 mg litre(-1); mean increases between 1.9 and 3.2 mg CaCO3 litre(-1) for total alkalinity, between 0.9 and 14 mg litre(-1) for BOD5, between 0.27 and 1.46 mg litre(-1) for ammonia nitrogen (NH4-N), between 0.060 and 0.579 mg litre(-1) for soluble phosphorus (PO4-P) and less than 16 mg litre(-1) for suspended solids; variations in the pH value and nitrate nitrogen concentration were not statistically significant (p<0.05). At the 500 t year(-1) fish farm it was also possible to detect net increases of total hardness (3.2 mg CaCO3 litre(-1)), electric conductivity (19 mS cm(-1)) and permanganate value (3.6 mgO2 litre(-1)). At the other farms net variations in these parameters were not significant. Net mass flow variations reported to the annual fish production are presented. The DO mass flow decreased, on average, between 255 and 549 g t(-1) of fish per day. The mean daily BOD5 increase ranged from 353 to 1510 g t(-1) of fish. The corresponding ranges for the other parameters were 105-157 g t(-1) for NH4-N, 24-62 g t(-1) for PO4-P, 348-1035 g CaCO3 t(-1) for total alkalinity and 224 x 10(6)-506 x 10(6) t(-1) for mesophilic bacteria. Daily net variations of suspended solids, total hardness, electric conductivity and permanganate value were below 1753 g t(-1), 342 g CaCO3 t(-1), 2081 mS cm t(-1) and 392 gO2 t(-1), respectively. Longitudinal concentration profiles for the most relevant parameters show the impact of the effluent discharges on the physico-chemical and bacteriological river water quality downstream from the trout farms. Analyzing the situations from a purely chemical point of view, the polluted stretches were 3, 5 and 12 km long downstream from the effluent discharges, respectively. The microbiological contamination extended over longer distances.     

The mixing zone between limed and acidic river waters: complex aluminium chemistry and extreme toxicity for salmonids

When liming running waters, dosers must compensate for different flow and water qualities and for the downstream inflow from acid tributaries which creates mixing zones. At a certain point in the mixing zone, a constant or fluctuating chemical disequilibrium will appear due to transformation processes. In laboratory assays, over-saturated solutions of aluminium with ongoing active precipitation of aluminium have been found to be especially toxic to fish. Recent experiments in a mixing zone in the limed River Audna, Norway, have confirmed this phenomenon. Atlantic salmon (Salmo salar L.) and sea trout (Salmo trutta L.) smolts were exposed to acid and limed waters and mixtures of the two waters downstream from the point of connection. In the acid tributary (mean values: pH=4.8, Ca=1.3 mg litre (-1)), Ali 236 microg litre(-1)=), LT5) was 22 and 40 h for Atlantic salmon and sea trout, respectively. In the mixing zone (pH=4.8-6.5, Ca=1.2-3.2 mg litre(-1), Ali=50-240 microg litre(-1)), LT50 was 7 h for both species, masking the normal species difference in tolerance. Osmoregulatory failure and rapid gill lesions occurred in the mixing zone as an effect of the transformation of Al into high molecular weight precipitating species. This is the first documentation of the existence of such highly toxic mixing zones in nature, and the results clearly show that the mixing zone is even more toxic to fish than acid aluminium-rich waters.     

The MAGIC simulation of surface water acidification at, and first year results from, the Bear Brook Watershed Manipulation, Maine, USA

The catchments of East and West Bear Brooks, Maine, USA, have been hydrologically and chemically monitored for 3.5 years. Stream chemistries and hydrographs are similar. These clear water streams are low in ANC (0-70 microeq litre(-1)), with variations caused by changing concentrations of base cations, SO4, NO3 and Cl. The latter range between 90-120, 0-40 and 65-75 microeq litre(-1), respectively. The West Bear catchment is being treated with six applications per year of dry (NH4)2SO4 at 1800 eq ha(-1) year(-1). After one year of treatment, the response of the stream chemistry and the response modelled by MAGIC are similar. Retentions of NH4 and SO4 are nearly 100% and greater than 80%, respectively. The additional flux of SO4 is compensated principally by an increased Ca concentration. Episodes of high discharge in the treated catchment are now characterized by lower ANC and pH, and higher Al than prior to the manipulation. Concentrations of NO3 have increased about 10 microeq litre(-1) during the dormant season, presumably due to additional nitrification of N from NH4. Discharge-chemistry relationships indicate that changes in stream chemistry, except for NO3, are dominated by ion exchange reactions in the upper part of the soil profile.     

Spatial patterns concentrations in upland Wales in relation to catchment forest cover and forest age

Data on nitrate nitrogen were collected weekly during 1984 from 136 sites on streams in upland Wales. Mean nitrate concentrations in summer (0.02 to 1.5 mg litre(-1)) were significantly lower (P<0.001) than in winter (0.02 to 1.26 mg litre(-1)), particularly at sites with mature conifers (>30 years old). Mean concentrations increased significantly with the average age of conifers on each catchment (P<0.001), and with increasing areal cover by trees over 30 years old (P<0.001). Nitrate concentrations increased significantly with stream total hardness (P<0.001), possibly reflecting nitrogen mineralisation in soils of higher base status. Concentrations also increased with stream chloride (P<0.001), which is predominantly atmospherically derived, implying that increased nitrate occurred where general atmospheric inputs of solutes were increased. After accounting for variation in hardness, residual nitrate concentrations still increased with the average age of the conifers (P<0.001), and with catchment cover by mature trees (P<0.001). We infer that some additional nitrate under older conifers is thus independent of catchment sources associated with increasing hardness. Two possibilities are increased inputs and decreased retention of nitrogen within the ecosystem of maturing conifer forest. Residual nitrate after accounting for variations in chloride also increased significantly with conifer age (P<0.01) and cover (P<0.01), a pattern implying that some sources of nitrate may also be independent of increased sea-salt deposition. We allude to the possibility that additional nitrogen deposition adds to nitrogen throughputs from maturing forests, and we discuss the potential ecological role of additional nitrogen in runoff.     

Egg mass and shell thickness in dippers Cinclus cinclus in relation to stream acidity in Wales and Scotland

The shell thickness and mass of eggs of the dipper (Cinclus cinclus) collected on streams of different pH in Wales and Scotland were measured. The aluminium, phosphorus and calcium content of their invertebrate prey were also measured. In a regression analysis, significant at p<0.05, stream pH accounted for up to 7% of the variance in shell thickness, with shells decreasing by 2.5% of the overall mean with each unit of pH decline. In the Welsh sample, differences in shell thickness due to pH were small compared with differences between years across all sites. In data pooled between Scotland and Wales, pH accounted for 17% of the variance in egg mass, but a greater proportion (25%) in Scottish eggs alone. Aluminium concentrations in invertebrates showed no relationship with stream pH, but calcium levels in two insect orders increased significantly with pH. Calcium rich prey, such as Gammarus, were found only in circumneutral streams. The importance of calcium in the diet of dippers before and during egg formation is discussed. No evidence that aluminium in prey adversely affected dipper eggs was found.     

Toxicity of acid-sulphate soil leachate and aluminium to the embryos and larvae of Australian bass (Macquaria novemaculeata) in estuarine water

The toxicity of leachate water from acid-sulphate soil to the early life stages of Australian bass, Macquaria novemaculeata, incubated in seawater was evaluated. Acid-sulphate soil leachate water (pH> or =6.8) delayed the hatching of fertilised eggs, but after 48 h the per cent hatching was normal. In comparison, acidic saline water (25 per thousand salinity) at pH 4.0 or less prevented embryos from hatching. The survival of yolk-sac larvae exposed to acid-sulphate soil leachate water at a concentration of 32% in seawater and an initial pH of 7.2, was significantly different to controls after 96 hours. In corresponding tests with only acidified saline water (20 per thousand salinity), pH levels equal to or below 5.0 killed yolk-sac larvae after 96 h exposure. Aluminum showed a pH dependent toxicity to yolk-sac larvae, with added aluminium as low as 200 microg litre(-1) having a significant effect on larval survival at pH 5.5, and concentrations of 600-800 microg litre(-1) having a significant effect on larval survival at an initial pH range of 6.0 < pH < 6.8. It was concluded that significant mortality of the early life stages of Australian bass would occur if they are exposed to acid-sulphate soil leachate that results in a pH in the receiving estuarine water below 5.5, or when the pH is below 6.8 and aluminium is present at a total concentration of 800 microg litre(-1) or greater.     

The impact of aluminium on green algae isolated from two hydrochemically different headwater streams, Bavaria, Germany

Two strains of green algae (Scenedesmus sp. and Chlorella sp.) have been isolated from two headwater streams differing in stream chemistry (Eger river: acidic, low alkalinity; Püttlach river: slightly alkaline, high alkalinity). In this study the growth response of these indigenous algae to increased concentrations of aluminium (Al) is investigated. A semi-continuous culture technique was used for Al-toxicity studies. Algal response was determined by calculating growth rates from turbidity and cell counts. Those Al-species which are well known to be toxic were estimated by equilibrium calculations using the WATEQ computer program (Truesdall & Jones, 1973). The pH-value of the culture media was usually pH=5, except for one of the test series. Tested concentrations ranged from c=4 to 220 micromol litre(-1). The isolated strains of green algae were highly sensitive to increased Al-concentrations. The strain isolated from the Püttlach river was more sensitive than the Eger river algae. A total growth inhibition occurs at Al-concentrations of c=4 micromol litre(-1) if the whole Al was added at once. If Al was added gradually into the growth media the response of the algae was delayed. This is due to Al-enrichment in cells. In our long term toxicity studies, growth inhibition occurs even at nearly neutral pH-conditions (pH=6.5) although Al toxicity is expected at pH-values less than pH=5.5. This new result confirms the need of long-term studies in continuous cultures under simulated natural conditions. This might be the only way to achieve valid conclusions about the fate and the toxicity of environmental pollutants.     

Changes in gill morphology of Atlantic salmon (Salmo salar) smolts due to addition of acid and aluminum to stream water

One-year-old Atlantic salmon smolts were held in three artificial channels adjacent to a softwater (mean sp. cond. 30 microS cm(-1), circumneutral stream. Water in one channel was untreated (mean pH 6.25); the others received additions of acid (to mean pH 5.6), or acid plus aluminum (to mean pH 5.5; mean exchangeable Al 158 microg litre(-1)). Gills were sampled after 16 and 23 days of exposure for morphometric examination. On primary lamellae, chloride cells were more numerous in both experimental treatments than in controls. In contrast, numbers of chloride cells on secondary lamellae were elevated only in fish exposed to acid without added Al. Chloride cell size and shape also varied with time and treatment. Fewer gill mucous cells were found in fish exposed to acid plus Al than in controls. Chloride cell proliferation and structural changes may represent an attempt to compensate for increased ionic effluxes with low pH stress by increasing uptake. However, if Al concentrations are high, chloride cells do not proliferate along the secondary lamellae, or proliferating cells are damaged and lost. This may limit the potential to increase ionic uptake.     

Effects of ammonia on periphytic communities

Laboratory tests were conducted to evaluate the chronic effects of ammonia on periphytic communities. Species richness of the protozoan component of these communities was affected at un-ionized ammonia concentrations of 相似文献   

Impacts of afforestation on water quality trends in two catchments in mid-Wales

The impact of afforestation on stream-water chemistry for two catchments in central Wales is investigated. Trends in water chemistry are evaluated with forest age progressing at 8-15 years and 20-27 years. To assess the possible exacerbating effect of afforestation on surface-water acidification two moorland catchments are used as controls. Absolute differences in inter-catchment streamwater chemistry are evident. Differences in acidity between the moorland and the young forest site reflect site preparation and modifications to water pathways. Differences in the observed present day chemistry between the young and old forest result from past interactions between deposition changes during forest development. An estimate of the future impact of forest growth was attained from model predictions. The model was calibrated to present day stream-water chemistry and incorporates, cation uptake, evapotranspiration/ concentration effect and increased scavenging of occult and dry deposition. Predictions suggest the pH will decline to 5.3 when the young forest progresses to 20 years of age, which is still much higher than the pH recorded at the older forest site at the age of 20 years.     

Aluminium speciation in surface waters from a Welsh upland area

The complete aluminium speciation of surface waters from an acidified catchment, during dry weather and during storm episodes, is obtained. For the first time, estimates of adsorbed aluminium (Al(ad)) are reported together with other aluminium species. Al(ad) is calculated from the difference between monomeric aluminium content before and after separation of suspended solids by filtration (0.015 microm pore diameter). This fraction was very significant (Al(ad) >; 40 microg litre(-1)) for samples with high suspended solids content (ss >; 20 mg litre(-1)) collected during storm episodes. Plots of pAl(3+) versus pH for samples collected during dry weather are approximated by a straight line, close to the solubility line of synthetic gibbsite, and have a slope of 2.5, which suggests that these samples were saturated with respect to gibbsite. The cloud of pAl(3+) versus pH points for samples from storm episodes has a near zero slope, and shows a significant degree of undersaturation with respect to synthetic gibbsite. Various mechanisms of aluminium mobilisation are discussed.     

Evaluating common drivers for color,iron and organic carbon in Swedish watercourses

The recent browning (increase in color) of surface waters across much of the northern hemisphere has important implications for light climate, ecosystem functioning, and drinking water treatability. Using log-linear regressions and long-term (6–21 years) data from 112 Swedish watercourses, we identified temporal and spatial patterns in browning-related parameters [iron, absorbance, and total organic carbon (TOC)]. Flow variability and lakes in the catchment were major influences on all parameters. Co-variation between seasonal, discharge-related, and trend effects on iron, TOC, and absorbance were dependent on pH, landscape position, catchment size, latitude, and dominant land cover. Large agriculture-dominated catchments had significantly larger trends in iron, TOC, and water color than small forest catchments. Our results suggest that while similarities exist, no single mechanism can explain the observed browning but show that multiple mechanisms related to land cover, climate, and acidification history are responsible for the ongoing browning of surface waters.