Acidification Stage Research Articles

Effect of Prior Acid Exposure on Physiological Responses of Juvenile Rainbow Trout (Salmo gairdneri) to Acute Handling Stress

Acid-stressed fish appear to be more sensitive to additional stressors than unstressed fish. When juvenile rainbow trout, Salmo gairdneri, were exposed to acid conditions (pH 5.7–4.7) for 5 d, plasma cortisol was affected only slightly during the initial hours of exposure, but plasma glucose and hematocrit increased, and plasma sodium decreased. However, when fish held at pH 4.7 were subsequently subjected to a 30-s handling stress, poststress plasma cortisol rose to a peak level of more than twice that in handled fish held at ambient pH (6.6). Effects of handling on plasma glucose or sodium were not apparent against levels already altered by the chronic acid exposure, judging by the corticosteroid response, we conclude that the acid-stressed fish were more sensitive to additional handling, even though they appeared to be physiologically normal after 5 d. Thus, as a management consideration, when fish are stocked in acidified waters, care should be taken to avoid situations where the fish may encounter additional disturbances in the new environment. Plasma glucose and sodium were better indicators of chronic acid stress alone than plasma cortisol, but the greater cortisol response to handling at low pH may be a useful method of detecting increased interrenal activity during early stages of environmental acidification.

Identification of organic compounds in leachate from a waste tip

Two different types of leachate from a municipal waste tip have been analyzed. The first type of leachate was collected from a waste tip in the acidification stage. The organic load of this leachate was high and consisted mainly of free volatile acids (over 95% of the TOC). Volatile amines and ethanol were also present (0.8 and 0.7% of the TOC respectively). The leachate was extracted with hexane and the extract was analyzed with infrared and nuclear magnetic resonance spectroscopy and a gas chromatograph-mass spectrometer combination. In the extract alcohols, hydrocarbons, esters, terpenes and phthalates have been identified. High molecular weight compounds were present only in a low concentration. The second type of leachate was collected from a waste tip in the methane fermentation stage. The organic load was relatively low. An important part of the organics was identified as high molecular weight compounds. About 32% of the organic carbon consisted of compounds with a molecular weight over 1000. Acids, amines and alcohols could not be detected. This means that the organic compounds present were end products of degradation processes. Furthermore there was a remarkable difference in heavy metal content between the two types of leachate.

Anaerobic digestion of free volatile fatty acids in soils below waste tips

Leachate from a waste tip in the acidification stage contains a lot of volatile fatty acids. Soil column experiments showed that the removal of these acids in soil by CH4-fermentation can be quite effective, especially in soils with a high buffering capacity. In sandy loam soil columns, where the retention time was only 17 days, the fatty acids were removed completely, even at a high concentration level of 6500 mg l−1 acetic acid equivalents. In sandy soils with a low buffering capacity the CH4-fermentation was already limited at rather low acid concentrations.

A simple approach for identifying and measuring acidification of freshwater

ACIDIFICATION of lakes and rivers accompanied by the loss of fish populations is a problem in Scandinavia1–4, northeastern USA5,6, and southeastern Ontario, Canada7,8. These areas have granitic or other siliceous bedrock types, thin and patchy podsolic soils, and extremely soft and poorly buffered surface waters, and receive precipitation which is decidedly acidic (volume-weighted average pH 4.0–4.6). Sulphate, whose principal source is precipitation, is usually the major anion in these acidified waters. In similar areas such as northern Scandinavia and northwestern Ontario, in which precipitation is not acidic (pH>5.0) such oligotrophic pristine softwaters generally have pH levels >5.5, and bicarbonate is the major anion9–11. Acidification of such waters entails a decrease in the bicarbonate buffer (alkalinity) with only minor decreases in pH, and then after exhaustion of the bicarbonate an increase in acidity to pH levels well below 5.0. Because of the severe damage to fish populations, and other biological consequences, the decreases in pH that characterise the later stages of the acidification process are of major concern. We need, therefore, a simple ‘early warning’ indicator that identifies lakes and rivers which are undergoing the first stage of acidification, the loss of alkalinity, but which have not yet reached the stage of marked pH decreases. Furthermore, we need quantitative estimates of the degree of acidification. We show here that excess sulphate concentrations, or current calcium concentrations and alkalinities can provide such an estimate.

Thermally stratified acid water in late winter ? a key factor inducing self-accelerating processes which increase acidification

Ion separation of acid air pollutants out of snow causes sudden, deep pH-drops in lakes and running waters at an early stage of snowmelting. These pH-drops have drastic effects on fish populations and are suggested to be the main cause of Sphagnum invasion and changes in the microflora already at an early stage of acidification, i.e. when summer pH-values are about 6. These effects in turn reduce the nutrient recycling and accelerate the acidification process.

Dialysis Separation of Sewage Sludge Digestion

The purpose was to study both stages of high-rate anaerobic digestion separately. Raw sludge fed into the acid fermentation tank provided substrate for the bacterial production of volatile acids. The acids could then be transferred by diffusion, through the plastic membrane in the dialysis unit, into the methane fermentation tank for conversion to gaseous end products. The process of sludge digestion can be performed using a dialysis-fermentation tank system. The dialysis-fermentation tank apparatus permits the pseudo-enrichment culturing of the acidification and gasification stages in sludge digestion in separate fermentation tanks. The acid fermentation stage is the rate limiting process in anaerobic digestion of sewage sludge. The acid fermenters operate at below optimum to satisfy the optimum conditions necessary for the methane fermentation of the volatile acids.

Mikromorphologische und chemische untersuchungen eines entbasten parabraunerdeprofils des schweizerischen mittellandes und deutung seiner entwicklungstendenz

The soils of the Swiss Plateau are exposed to a marked acidification. Among the brown earth of low base content, saturated and even calcareous soils are formed. This pattern is the result of various local factors influencing or stopping the acidification process. A close relation exists between the acidification stage of the soil profile and the extent of clay migration. In neutral or weak alkaline soils the clay minerals remain at the place of formation. Clay migration in the brown-earth profile only takes place in weak acidic conditions. But the clay skins are attacked or removed if pH falls below a value of 5. During extreme acidification also a great part of the clay minerals may be disintegrated.In thin sections these facts can be observed by morphological investigation of the profile horizons. The clay minerals move downwards from the A horizon and are coagulated only in lower horizons of higher base saturation. In this way the B horizon of gray brown podzolic soils grows larger and penetrates into the C horizon. Therefore the depth of the B horizon is in relation to the genetic evolution of the profile. Simultaneously the A horizon also becomes thicker, and the organic matter content increases. Consequently the soil fabric remains porous and stable.The factors promoting further acidification and regeneration seem to be in equilibrium in the acidic gray brown podzolic soils of the lower parts of the Swiss Plateau. But in the adjacent hilly region, with somewhat higher rainfall, all clay skins are removed by the leaching of she soil profile under slightly higher acidic conditions. The acidic brown earth without argillic horizon is most likely formed in this way.