Organic vs. minerogenic acidity in headwater streams in Finland

This study provides an assessment of the transport of organic carbon and organic acids from typical Finnish forested catchments since the 1960's. The 21 study catchments (0.69–56 km²) are located over Finland excluding the northernmost regions. The mean annual total organic carbon (TOC) load from the catchments ranges from 2 600 to 8 800 kg/km²/a. Using a total acidity of 9.7 eq/mg DOC this would represent organic acid load of about 25–85 keq/km²/a which is higher than the mean annual deposition of strong acids in the highest deposition areas in southern Finland. The study demonstrates that organic acids dominate stream water acidity over large regions in Finland. In southern Finland minerogenic acidity is, however, more important. Organic acids exceeded mineral acids not only in autumn but also during spring snowmelt in 18 catchments. Moreover, the lowest pH values (25th percentile) were dominated by organic acids in 20 catchments. In most catchments TOC better explained pH than non-marine sulphate. In stepwise multiple regression base cations and TOC explained 67–83 % of the variation in pH for catchments divided into six groups according to season, deposition and peatland percentage; non-marine sulphate had minor contribution.     

A role for sediments in retarding the acidification of headwater lakes

Experiments conducted on selected minerals and headwater lake sediments showed that major acid neutralization reactions above pH 4.5 were reactions releasing Ca²⁺ and Mg²⁺ from the sediments. Analysis of the sediments and water from 97 headwater lakes in northern Ontario showed a predictable decrease in the exchangeable Ca⁺ Mg²⁺ of the sediments with decreasing lakewater pH. Estimates of the total potential buffering capacity for the sediments above PH 4.5 and for water in these headwater lakes were made, and it was found that, even when only the top 1 cm of sediment is considered, a substantial sediment buffering reserve is available.     

The benthic fauna of 41 acid sensitive headwater lakes in North Central Ontario

The benthic fauna of 41 nonhumic, soft water lakes situated north of lakes Superior and Huron were sampled during 1980. The pH range of the lakes sampled was 4.6 to 7.7. The benthic infauna displayed regional differences in abundance and composition, with large variation within each district. Total abundance, biomass, and number of taxa were not correlated with lake pH or alkalinity. The Chironomidae displayed a slight change in percent composition of the major species (p < 0.2) with lower pH. The Tanytarsini andChironomus salinarius group decreased, whileC. anthracinus group increased in relative abundance in those lakes with lower pH. Other factors appear to control the distribution of the various invertebrate orders, with depth and sediment nature being important variables.     

Effects of introduced fish on macroinvertebrate communities in historically fishless headwater and kettle lakes

Widespread fish introductions have led to a worldwide decline in the number of fishless lakes and their associated communities. Studies assessing effects of fish stocking on native communities in historically fishless lakes have been limited to high-elevation headwater lakes stocked with non-native trout. Little is known about the effect of fish stocking in historically fishless and hydrologically isolated lowland kettle lakes. We compared the effects of introduced fish on macroinvertebrate communities in kettle lakes stocked with centrarchids, salmonids, and cyprinids, and headwater lakes stocked with brook trout (Salvelinus fontinalis) in Maine, USA. Fish had significant effects on macroinvertebrate community structure in both lake types, with reduced species richness and abundances of taxa characteristic of fishless lakes. The effects of introduced fish were more pronounced in headwater lakes despite a less diverse fish assemblage than in kettle lakes. We attribute this to abundant submerged vegetation providing refuge from fish predation and reduced stocking frequency in kettle lakes. We assessed effects of stocking duration on macroinvertebrates in a subset of headwater lakes with known dates of trout introduction. Species richness and abundance of most taxa declined within 3 years following trout introduction; however, richness and abundance were least in lakes with long stocking histories (?40 years). Macroinvertebrates previously identified as fishless bioindicators were absent from all stocked lakes, indicating that trout rapidly eliminate these sensitive taxa. Conservation of this historically undervalued ecosystem requires protecting remaining fishless lakes and recovering those that have been stocked.     

Chemistry of soft-water seepage lakes in the upper midwest: Lacustrine alkalinity production in summer

A total of 26 soft-water, seepage lakes in the Northern Highlands (NH) of Wisconsin (N =16) and the Upper Peninsula (UP) of Michigan (N=10) were sampled four times between early May and mid October 1984 as part of the ‘PIRLA’ Project (Paleolimnological Investigations of Recent Lake Acidification). Because of low antecedent recharge of the local water-table, this ‘summer’ interval likely featured minimal groundwater inputs (<2 cm over lake surface) to most of these seepage lakes. Based on this hydrogeologic relationship, and on regional deposition data, I evaluated short-term net epilimnetic (June–August) and whole-lake (May–October) sediment-water exchange of ANC, base cations, acid oxy-anions, Al, DOC and silicic acid in these lakes using a simplified mass balance algorithm. Silica, nitrate and ammonium were all efficiently retained in these seepage lakes. The assimilation of NO₃ ^? (19±4 meq m^?2) slightly exceeded assimilation of NH₄ ⁺ (16±4), resulting in a net internal ANC production of only +3 meq m^?2 over 161 d between early May and mid October 1984. Over this same interval ANC production resulting from lacustrine S retention averaged +35±8 meq m^?2 in the NH, but was too variable to be statistically significant (+21±21 meq m^?2) in the UP. Epilimnetic S retentions in mid summer were more comparable (21±4 in NH; 14±5 meq m^?2 in UP). McNearney Lake (UP) illustrates how high sulfate, linked to low alkalinity, high Al, low P, and low productivity, can become a negative correlate of lacustrine S retention. Temporal changes in base cations in the 26 lakes were generally small and erratic compared with uncertainties in deposition inputs and analytical errors, rendering estimates of related ANC production inconclusive. Even small analytical biases can be critical when designing and interpreting lake monitoring studies.     

Trace metal speciation in natural waters: Computational vs. analytical

Improvements in the field sampling, preservation, and determination of trace metals in natural waters have made many analyses more reliable and less affected by contamination. The speciation of trace metals, however, remains controversial. Chemical model speciation calculations do not necessarily agree with voltammetric, ion exchange, potentiometric, or other analytical speciation techniques. When metal-organic complexes are important, model calculations are not usually helpful and on-site analytical separations are essential. Many analytical speciation techniques have serious interferences and only work well for a limited subset of water types and compositions. A combined approach to the evaluation of speciation could greatly reduce these uncertainties. The approach proposed would be to (1) compare and contrast different analytical techniques with each other and with computed speciation, (2) compare computed trace metal speciation with reliable measurements of solubility, potentiometry, and mean activity coefficients, and (3) compare different model calculations with each other for the same set of water analyses, especially where supplementary data on speciation already exist. A comparison and critique of analytical with chemical model speciation for a range of water samples would delineate the useful range and limitations of these different approaches to speciation. Both model calculations and analytical determinations have useful and different constraints on the range of possible speciation such that they can provide much better insight into speciation when used together. Major discrepancies in the thermodynamic databases of speciation models can be evaluated with the aid of analytical speciation, and when the thermodynamic models are highly consistent and reliable, the sources of error in the analytical speciation can be evaluated. Major thermodynamic discrepancies also can be evaluated by simulating solubility and activity coefficient data and testing various chemical models for their range of applicability. Until a comparative approach such as this is taken, trace metal speciation will remain highly uncertain and controversial.     

Terrestrial field dissipation of diclosulam at four sites in the United States.

The soil dissipation of diclosulam was studied using 14C-labeled and nonradiolabeled material in Mississippi, North Carolina, Georgia, and Illinois between 1994 and 1997. The test substance was preemergence broadcast applied at target rates of 35 and 37 g ai x ha(-1) for the 14C-labeled and the nonradiolabeled studies, respectively. The degradation of diclosulam was rapid with half-lives ranging from 13 to 43 days at the four sites. Rapid degradation rates and the increasing sorption to soil over time resulted in low persistence and mobility of this compound. Metabolite formation and dissipation in the field reflected observations of photolysis, hydrolysis, and aerobic soil metabolism studies in the laboratory. The rapid field dissipation rates, metabolite formation patterns, and sorption characteristics obtained in these field studies were consistent with the laboratory data generated for diclosulam, and reflect the multiple concurrent degradation mechanisms occurring in the field.     

Effects of Grafting on Alkali Stress in Tomato Plants: Datura Rootstock Improve Alkalinity Tolerance of Tomato Plants

Plant growth, nutritional status, and proline content were investigated in non-grafted and grafted greenhouse tomato plants onto five rootstocks of eggplant, datura, orange nightshade, local Iranian tobacco, and field tomato, exposed to 0, 5, and 10 mM sodium bicarbonate (NaHCO₃) to determine whether grafting could improve alkalinity tolerance of tomato. The leaf fresh mass of ungrafted and grafted tomato plants decreased significantly as NaHCO₃ levels increased. Despite other rootstocks and ungrafted plants, alkalinity had no significant effect on stem and root fresh mass and shoot phosphorus (P), potassium (K) and magnesium (Mg) concentrations of datura grafted plants. The lowest solution pH and electrical conductivity (EC) values and the highest leaf proline content were observed in the plants grafted onto datura rootstock. Moreover, sodium (Na) concentration in shoots was lower in plants grafted onto datura rootstock than in other plants especially under high NaHCO₃ levels. Overall, using datura rootstock improved alkalinity tolerance of tomato plants under NaHCO₃ stress.     

Aluminium chemistry in two contrasted acid forest soils and headwater streams impacted by acid deposition,Vosges mountains,N.E. France

Al chemistry was studied in two acidic watersheds, one with a podzol, the other with an acid brown soil, in the Vosges mountains (N.E. France), by analysing both leaching and centrifugation soil solutions and spring waters over 3 yr. In the podzol, Al was mobilized in the eluvial horizons under the predominant influence of organic acidity, then leached down the profile as organic and F-bound Al. Strong undersaturation with respect to proto-imogolite and imogolite showed that the proto-imogolite theory of podzolization could not apply. Al was transferred from the soil to spring water mostly as Al³⁺ and Al-F. Al³⁺, as well as additional minor species (AlOH²⁺, AlSO₄ ⁺), originated from the redissolution of the top of the spodic horizons under the influence of both soil solution acidity and the occurrence of mobile anions derived from atmospheric deposition. Conversely, in the acid brown soil, Al mobilization was regulated by nitrate and occurred mainly as Al³⁺. Most of Al was retained in the deep soil and only traces of monomeric Al reached spring water. In the podzol eluvial horizons, soil solutions were undersaturated with respect to all relevant mineral phases and their chemical composition agree with the concept of a mobilization of Al from the solid soil organic Al and a control of Al³⁺ activity by complexation reaction with the solid and soluble soil organic matter and F. In the acid brown soil, soil solutions were found to be in equilibrium with natural alunite, and the formation of this mineral, if confirmed, would account for the occurrence of 'open' vermiculites instead of the expected hydroxy-Al interlayered vermiculites. Al solubility control in surface water of both watersheds remains unclear. The Al-F species in both watersheds and the likely control of Al solubility by alunite in the acid brown soil emphasize the influence of acid deposition on Al chemistry in acid watersheds.     

Saltation vs. soil stabilization: Two processes determining the character of surfaces in arid regions

In satellite images of sandy areas in arid regions disturbed (crumbled) surfaces appear much brighter than stabilized soil. From observations of Landsat satellite images that show directional surface features along the dominant wind direction, two theses are inferred concerning eolian erosion and transport: (1) transport is dominantly a near-surface phenomenon of saltation rather than of aerodynamic entrainment and later deposition; (2) both the disturbed surface characteristics in the saltating regions (saltation formations in our terminology) and the stability of the crusted soil in the quiescent regions are locally self-perpetuating.Thesis (1) is suggested by the appearance of the zones in the lee of protrusions from the surface, or even a river, that constitute obstacles (across the dominant wind directon) to particle flow. In the lee of a ridge between two “streaks” or in the lee of a protruding outcropping within a “sheet”, one finds darker zones, in contrast to the adjacent bright saltation formation. These darker zones are laterally uniform, and have to be interpreted as stable, quiescent areas of non-deposition and non-erosion.Thesis (2) is inferred from (i) the sharpness of the transition in the reflectivity at the boundaries (parallel to the dominant wind direction) between the bright “streaks” or “sheets” and the darker stable surface, and (ii) the constant width of some long quiescent areas in the wind-shadow of an isolated obstacle. Variability of wind direction, in any season of any strength, should have produced a gradual boundary. The disturbed and the stable surfaces are therefore interpreted as locally a bi-stable situation: an occasional wind will produce no effect over a stable surface, which tends to be “immune” to the oelian influences, whereas the surface in a saltation formation is prone to be disturbed anew by a comparable wind. The bistable situation is linked to positive feedback mechanisms; the most important mechanism appears to be the cohesion of the crusted surface. Such a surface can be broken only by high energy impact. The feedback mechanisms have implications for designing measures to reduce the danger of dust storms.     

Potential contributions of smectite clays and organic matter to pesticide retention in soils.

Soil organic matter (SOM) is often considered the dominant sorptive phase for organic contaminants and pesticides in soil-water systems. This is evidenced by the widespread use of organic-matter-normalized sorption coefficients (K(OM)) to predict soil-water distribution of pesticides, an approach that ignores the potential contribution of soil minerals to sorption. To gain additional perspective on the potential contributions of clays and SOM to pesticide retention in soils, we measured sorption of seven pesticides by a K-saturated reference smectite clay (SWy-2) and SOM (represented by a muck soil). In addition, we measured the adsorption of atrazine by five different K-saturated smectites and Ca-saturated SWy-2. On a unit mass basis, the K-SWy-2 clay was a more effective sorbent than SOM for 4,6-dinitro-o-cresol (DNOC), dichlobenil, and carbaryl of the seven pesticides evaluated, of which, DNOC was sorbed to the greatest extent. Atrazine was sorbed to a similar extent by K-SWy-2 and SOM. Parathion, diuron, and biphenyl were sorbed to a greater extent by SOM than by K-SWy-2. Atrazine was adsorbed by Ca-SWy-2 to a much lesser extent than by K-SWy-2. This appears to be related to the larger hydration sphere of Ca(2+) (compared to that of K(+)) which shrinks the effective size of the adsorption domains between exchangeable cations, and which expands the clay layers beyond the apparently optimal spacing of approximately 12.2 A for sorption of aromatic pesticide structures. Although a simple relation between atrazine adsorption by different K-smectites and charge properties of clay was not observed, the highest charge clay was the least effective sorbent; a higher charge density would result in a loss of adsorption domains. These results indicate that for certain pesticides, expandable soil clays have the potential to be an equal or dominant sorptive phase when compared to SOM for pesticide retention in soil.     

Season vs. Nutrition-Dependent Fruit Loading: Effects on Pigment Dynamics of Tomato Leaves

ABSTRACT

The effect of season on fruit load is drastic when tomato (Lycopersicum esculentum, cv. Dombito) plants are grown hydroponically during winter or summer. In this paper, we report the effect of high (HT) vs. low (LT) temperatures on chlorophyll a and b, pheophytin a and b, carotene a and b, and zeaxanthin, lutein, antheraxanthin, neoxanthin, lutein-5,6-epoxide, and violaxanthin dynamics of tomato leaves. Furthermore, based on the assumption that season may prevail over nutrition, we report the effect of normal vs. quarter-normal Hoagland nutrient solution on these pigments' profiles. Chlorophyll concentration was three to four times higher during HT. Chlorophyll loss during LT was more intense for chlorophyll b (chl-b) than for chlorophyll a (chl-a), and the chl-a/chl-b ratio was higher during LT. Chlorophyll concentration was less affected by nutrition and more by season. Nutrition affected chlorophyll concentration more at HT. Pheophytin a (pheo-a) increased intensely with increase of temperature and total solar radiation (SR), while the opposite was observed for pheophytin b (pheo-b). Especially during LT, pheo-b presented an impressive increase opposite to that of chl-a, chl-b and pheo-a. Carotenoid concentration was less affected by nutrition and more by season. Nutrition affected the concentration of carotenes more than that of the other carotenoids, especially at HT. Carotenes a (car-a) and b (car-a) were significantly higher during HT, and the same was true for the concentrations of epoxide-free xanthophylls, zeaxanthin (Z), and lutein. Epoxide-free xanthophylls, car-a, car-b, and pheo-a presented the same pattern of changes during both seasons, and all these pigments were affected positively by the increase of SR and temperature. Concentrations of the mono-epoxides antheraxanthin (A), neoxanthin, and lutein-5,6-epoxide, and of the di-epoxide violaxanthin (V) presented a second group with the same pattern of changes. As opposed to epoxide-free xanthophylls, they were negatively affected by the increase of temperature and SR. In winter, the xanthophyll ratio A+Z/V (i.e, xanthophylls involved in the violaxanthin cycle, as a photoprotective mechanism) showed an impressive increase at the last five weeks (when temperature and SR were increased), when they were two times higher than during the remainder of the period (when temperature and SR were low). In summer, A+Z/V was high during the period of particularly high temperature and SR (weeks 7–11, with an average temperature of 33°C–35°C and SR of 29–32 MJ m^?2) and lower at the last five weeks, when temperature and SR decreased (< 28°C and SR 27 MJ m^?2 respectively).     

Sulfur vs. silica retention in oligotrophic lake sediments: Test of a simple residence time model

Limnologists have modeled solute retention (% of input) in lake sediments using the parameter: 100 k _s {(z:t _w +k _s}^?1, wherek _s is an empirical mass transfer coefficient or ‘sedimentation velocity’ (m yr^?1), z is lake mean depth (m), andt _w is lake hydraulic residence time (yr). This flushing or residence time model was tested against sulfate and silica concentrations in lakes of the northeastern and northcentral U.S.A., using data collected during the U.S. EPA's Eastern Lake Survey. This parameter failed to predict intra-regional variations in lake sulfate at fall turnover, but was consistently negatively correlated with silica in each of the regional lake populations. However, except in the western section of the Upper Peninsula of Michigan, lake sulfate was everywhere inversely dependent on DOC [mean slope=?0.020(SE=0.03) meq mM^?1]. Sulfur retention in aquatic environments appears more closely coupled to organic carbon and trophic state, than to variations in hydraulic residence time.     

Rare earth elements: a potential proxy for identifying the lacustrine sediment source and soil erosion intensity in karst areas

Purpose

The geochemistry of rare earth elements (REEs) taken from the sediments of a karst lake was analyzed to track the provenance of the sediments and the history of soil erosion in the Jiuzhaigou Nature Reserve (JNR) in Sichuan Province in southwest China.

Materials and methods

The REE concentrations of 177 samples including 150 lake sediments, 13 soils, 8 loess, 3 carbonate rocks, and 3 water were determined using a quadruple inductively coupled plasma mass spectrometer (Q-ICP-MS). The grain size distributions of 139 sediment samples were measured using a Malvern Master Size 2000 laser particle size analyzer. The carbonate contents of 159 sediment samples were determined using a gasometric method. The dried remains after reaction with HCl were defined as acid-insoluble residues. The mineral composition of the sediments was measured using a Philips X'Pert Pro X-ray diffractometer.

Results and discussion

The lake sediments in the JNR exhibit features similar to those of the neighboring soils, i.e., enriched REE content, a greater ratio of light REEs to heavy REEs, greater δCe values, and lower δEu values relative to those in the carbonate rocks. The REE signatures in the silt and sand fractions of the sediments are similar to those in the soils and carbonate rocks, respectively. The REE content, LREE/HREE, and δCe values in the sediments strongly negatively correlate with the carbonate content, indicating an intense carbonate effect on the REE geochemistry. The content of acid-insoluble residues is obviously positively correlated with ∑REEs in the sediments, and a negative relationship is observed between ∑REEs and the ratio of calcite to quartz in the sediments.

Conclusions

The sediments in the JNR originate from eroded soils and authigenic travertine deposits in the lakes. It is proposed that the increased ∑REEs in the sediments resulted from the elevated proportion of soil particles in lacustrine deposits was due to increasing soil erosion intensity. This hypothesis is evidenced by the coupling of ∑REEs with the intensity of soil erosion and anthropogenic activities in the JNR. In karst drainage, the total REE concentration might be a potentially powerful indicator for reconstructing the history of soil erosion.     

Structure and productivity of epiphytic algal communities onLobelia dortmanna L. in acidified and limed lakes

The epiphytic algal community growing onLobelia dortmanna L. was studied in two acidified lakes in southwestern Sweden from May through October 1980; Lake Gårdsjön (pH 4.3 to 4.7) and L. Högsjön (pH 6.3 to 6.7 after liming in 1978/79). In both lakes a layer of firmly attached diatoms,Eunotia veneris andE. rhomboidea, covered theLobelia leaves. Scanning electron microscope study revealed a mucoid matrix, and in L. Gårdsjön, heavy cover of detritus. The spring period in L. Gårdsjön was characterized by red algaBatrachospermum sp., which was followed by the appearance ofBinuclearia sp., andMougeotia spp. Blue-green algae appeared during the warmer period of the year. The spring period in L. Högsjön was characterized by the development of desmids. Diatoms dominated the community in the summer while green algae appeared in autumn. The biomass in L. Gårdsjön showed spring and late summer maxima, while in L. Högsjön it increased gradually reaching a maximum in autumn. Chlorophylla concentration was highest in L. Gårdsjön in late summer. Primary productivity rates calculated per unit substrate surface area at 1.0 m depth were highest in early summer and decreased in late summer. The results suggest that the liming of L. Högsjön caused significant structural changes in the epiphytic community, favoring diatoms and green algae, especially desmids. Blue-green algae were characteristic for L. Gårdsjön despite that lake's low pH. Productivity rates at 1.0 m depth show similar trends in both lakes.     

Acidification of Nova Scotia lakes I: Response of diatom assemblages in the Halifax area

A comparison is made of diatom remains in surficial lake sediments collected in 1971 and 1980. Changes of similar magnitude towards more acid tolerant assemblages are observed in four lakes studied in detail despite widely differing aquatic environments. No attempt is made to reconstruct past chemistry, the significant point being that at the most fundamental level, local lacustrine biological systems are being stressed to the point of alteration. The pattern of that alteration with emphasis on ‘simplification’ is discussed with the suggestion that rates of acidification may be as important as net changes.     

Diatom-based pH reconstruction studies of acid lakes in Europe and North America: A synthesis

The analysis of diatom assemblages in lake sediments is being increasingly used to reconstruct past trends in the pH of acid lakes. This paper briefly reviews the data that are now available for Europe and North America and concludes that the evidence is consistent with the acid deposition hypothesis for recent lake acidification.