Impact of acidification on diatoms and chemistry of Dutch moorland pools

Old (ca 1920) and recent (1978) diatom assemblages from sixteen pristine moorland pools are compared by analysis of pH-spectra, diversity (Hill's index), (dis)similarity (number of species in common, Dyer dissimilarity) and principal component analysis. The pH-spectra of clear water pools indicate that the formerly wide range of pH (4–6) is very narrow now (3.7–4.6). No significant change of pH (ca 4.5) is observed in brown water moorland pools. Diversity significantly declines in clear water pools and has a tendency to rise in brown water pools. The number of species in common does not change. The Dyer dissimilarity significantly decreases in clear water lakes, no change is found in brown water lakes. The first principal component (PC 1) explains 61% of total variance between samples and is nearly completely determined byEunotia exigua. PC 1 has a strong positive correlation with both the absolute and relative sulfate concentration and other factors related to acidification (Ca²⁺, Al³⁺, Mg²⁺, electrical conductivity). PC1 has a negative correlation with factors characterizing humic acid waters (K MnO₄-consumption, Fe, (Na⁺ + K⁺)/ (Ca²⁺+Mg²⁺) etc.). Old samples have low scores on PC 1. Recent samples from clear waters have high scores on PC 1. The original variation, caused by regional factors, is replaced by a sulfate controled variation. The factors which are responsible for the recent differences in sulfate concentrations between pools are discussed (sulfate reduction, accumulation by dry deposition in adjacent pine forests and drought). Some observations contribute to the opinion that acidification may be considered as eutrophication and not as oligotrophication.     

Partial recovery of moorland pools from acidification: Indications by chemistry and diatoms

In 1994 the atmospheric deposition on three moorland pools in The Netherlands was only one third of its value in 1980. The effects of this reduction on these moorland pool ecosystems were examined by regular sampling of surface water chemistry and diatoms between 1979 and 1994. Moreover, diatom samples taken at irregular intervals between 1916 and 1978 were studied. In the pools Gerritsfles and Achterste Goorven, the median sulphate concentrations in 1994 were only one third of recorded values in 1980. Peak concentrations of sulphate were found after extremely dry summers. In the pool Kliplo, with an initially low concentration of sulphate, there was 16% increase of the concentration over the same period. Ammonium increased significantly in Kliplo and showed large variations in the other pools. Redundancy analysis showed that sulphate was the most important variable for the distribution of diatoms. As a consequence, the abundance of the acidification indicatorEunotia exigua in 1994 was only 25% of its value in 1980 in Achterste Goorven and 14% in Gerritsfles. Peaks ofE. exigua were found after drought periods. In Kliplo no clear change was observed. In 1994 the diatom assemblages of Achterste Goorven were much more similar to those of 1916–1925 than they were in 1980. In Gerritsfles a new situation, without historical analogue, developed. Overall, the large reduction of SO_x-deposition had very positive consequences for the diatom assemblages.     

Ecology and management of moorland pools: balancing acidification and eutrophication

Moorland pools originally are shallow, often hydrologically isolated, soft-water bodies, with a low productivity. Some thousands of moorland pools originated from the late Pleistocene onwards in the heathland landscape in The Netherlands and adjacent areas, where soils have a poor buffering capacity. As the pools are largely fed by atmospheric precipitation, they are very vulnerable to changes in the environment, e.g. eutrophication and acidification. Moorland pools are exposed to very high rates of wet atmospheric deposition: 44–50 mmol m⁻² yr⁻¹ sulphate and 84–103 mmol m ⁻² yr⁻¹ ammonium. Mass budgets indicate that 20–70% of the input of sulphate by precipitation is reduced, 40–100% of the ammonium input escapes to the air or sediments, apparently due to nitrification, and 90–100% of incoming nitrate disappears. The production of alkalinity ranges from 12 to 52 meq m⁻² yr⁻¹. The efficiency of these processes augments with pH-values of surface water increasing from 4.1 to 5.4. The accumulation of reduced sulphur compounds in the sediments is a threat in extremely dry summers, when desiccation causes oxydation of these compounds, resulting in very low pH-values (≤ 3.7). Acidification by acid atmospheric deposition and eutrophication by agricultural acidification are the main threats to the moorland pool ecosystems and affect the species composition of assemblages of aquatic macrophytes, desmids, diatoms, macrofauna, fishes and amphibians, as has been shown by comparison of old and recent records on their distribution and paleolimnological methods. Afforestation exacerbates acidification and also reduces wind dynamics. Particularly the decrease of isoetids and desmids by both processes indicate the biological impoverishment of the pools. Reductions of (potential) acid atmospheric deposition to less than 40 mmol m⁻² yr and of ammonia to less than 30 mmol m⁻² yr are necessary for recovery of the moorland pools. Methods for the addition of buffering material to a number of moorland pools, to counteract acidification until these deposition rates have lowered sufficiently, are given, as well as other methods for restoring the biological quality of moorland pools.     

Effects of decreased atmospheric deposition on the sulfur budgets of two Dutch moorland pools

The chemical composition of surface waters of two Dutch moorland pools and of incident precipitation, was monitored from 1982 to 1990. For this period, sulfur and water budgets were calculated using a hydrochemical model developed for well-mixed non-stratifying lakes. Total atmospheric deposition of S decreased significantly after 1986 at both locations. A model describing the sulfur budget in terms of input, output and reduction/oxidation processes predicted a fast decrease of pool water SO₄ ²⁻ concentrations after a decrease of atmospheric input. However, SO₄ ²⁻ concentrations in the surface water was lowered only slightly or remained constant. Apparently a source within the lake caused the unexpectedly high SO₄ ²⁻ concentrations. The possible supply of SO₄ ²⁻ from the sediment through regulation by (K-)Al-SO₄ containing minerals or desorption of SO₄ ²⁻ from positively charged surfaces in the sediment was evaluated. Solubility calculations of pore water with respect to alunite, basaluminite and jurbanite indicated that SO₄ ²⁻ concentration was not regulated by these minerals. It is suggested here (1) that desorption of SO₄ ²⁻ from peaty sediments may account for the estimated SO₄ ²⁻ supply provided that the adsorption complex is periodically recharged by partial oxidation of the upper bottom sediments and (2) that because of exposure of a part of the pool bottom to the atmosphere during dry summers and subsequent oxidation of reduced S, the amount of SO₄ ²⁻ may be provided which complements the decreasing depositional SO₄ ²⁻ input. In future research these two mechanisms need to be investigated.     

Changes in the moorland pools near Oisterwijk between 1840 and 1975

Summary The moorland pools (vennen) near Oisterwijk are originally oligotrophic, because the soil consists of nutrient poor cover sands. The original vegetation of most pools belongs to theIsoeto-Lobelietum and the consociation ofCarex rostrata andSphagnum.     

Acidification of three moorland pools in The Netherlands by acid precipitation and extreme drought periods over seven decades

SUMMARY. 1. Relations between acidification by atmospheric deposition, water depth and the occurrence of dry summers in this century, as well as their effects on chemistry, macrophytes and diatoms in three moorland pools, are described.
2. Direct observations and biological data indicate a decrease of pH by c. 0.5 unit over a period of seven decades in a pool where 20% of the bottom desiccates in extremely dry years, and 2 pH units over the same period in a pool where 70% of the bottom is exposed to the atmosphere in such years.
3. Acidification promotes the growth of Juncus bulbosus L., Sphagnum and the acidobiontic diatom Eunotia exigua (Bréb.) Rabenh. and suppresses the growth of isoetids (e.g. Lobelia dortmanna L.) and of acidophilus and circumneutral diatoms. Also the acidobiontic Frustulia rhomboides var. saxonica (Rabenh.) Toni and Navicula subtilissima Cleve, characteristic of humic waters, decline by acidification.
4. In two pools where more than half of the bottom desiccated in 1976, observed concentrations of sulphate were highest in 1977–78 and decreased later on. Juncus bulbosus had a maximum in 1977–80. Eunotia exigua became the dominant diatom after 1976 and decreased after 1981 in the pool with the shortest residence time (3 years).
5. In desiccating pools the long-term decrease of pH is apparently much larger than in softwater lakes in Scandinavia and North America. During the last 50 years, pH dropped rapidly after dry summers, probably due to oxidation of sulphur and nitrogen compounds which were originally derived from the atmosphere, reduced and stored in the sediments. Rapid falls in pH were followed by an increase, presumably due to alkalinity production during sulphate reduction and denitrification.     

Oligotrophication and eutrophication tendencies in some dutch moorland pools,as reflected in their desmid flora

An inventory of the desmid flora in a number of forest and moorland pools, carried out in 1975, revealed that an appreciable impoverishment has occurred since the turn of the century. In those pools which are immediately surrounded by arable land and pastures or are connected with cultivated areas by small streams, the deterioration is caused by eutrophication and pollution of the aquatic environment. In hydrologically isolated pools, situated within nature reserves, the decline must be attributed to an acidification and oligotrophication of the site. The latter phenomenon may be associated with a much increased acid deposition in the atmospheric precipitation owing to air pollution, as recorded in the Netherlands especially in the last decennia.     

The physiological response of marine diatoms to ocean acidification: differential roles of seawater pCO2 and pH

Although increasing the pCO₂ for diatoms will presumably down‐regulate the CO₂‐concentrating mechanism (CCM) to save energy for growth, different species have been reported to respond differently to ocean acidification (OA). To better understand their growth responses to OA, we acclimated the diatoms Thalassiosira pseudonana, Phaeodactylum tricornutum, and Chaetoceros muelleri to ambient (pCO₂ 400 μatm, pH 8.1), carbonated (pCO₂ 800 μatm, pH 8.1), acidified (pCO₂ 400 μatm, pH 7.8), and OA (pCO₂ 800 μatm, pH 7.8) conditions and investigated how seawater pCO₂ and pH affect their CCMs, photosynthesis, and respiration both individually and jointly. In all three diatoms, carbonation down‐regulated the CCMs, while acidification increased both the photosynthetic carbon fixation rate and the fraction of CO₂ as the inorganic carbon source. The positive OA effect on photosynthetic carbon fixation was more pronounced in C. muelleri, which had a relatively lower photosynthetic affinity for CO₂, than in either T. pseudonana or P. tricornutum. In response to OA, T. pseudonana increased respiration for active disposal of H⁺ to maintain its intracellular pH, whereas P. tricornutum and C. muelleri retained their respiration rate but lowered the intracellular pH to maintain the cross‐membrane electrochemical gradient for H⁺ efflux. As the net result of changes in photosynthesis and respiration, growth enhancement to OA of the three diatoms followed the order of C. muelleri > P. tricornutum > T. pseudonana. This study demonstrates that elucidating the separate and joint impacts of increased pCO₂ and decreased pH aids the mechanistic understanding of OA effects on diatoms in the future, acidified oceans.     

Multivariate analysis of diatoms and water chemistry in Bolivian saline lakes

Diatom assemblages are described from surface sediments in thirteen salt lakes located in the southern Bolivian Altiplano. Factor analysis of correspondences and cluster analysis are used to classify the diatom assemblages. New methods are proposed to establish the qualitative and quantitative relationships between diatom floras and ecological parameters. Diatom assemblages are linked more to the ionic elements than to the salinity, pH, depth, temperature or elevation. Environmental variables are divided into three modalities which allow considerations of many different variables not under the same units.     

The oceans are changing: impact of ocean warming and acidification on biofouling communities

Climate change (CC) is driving modification of the chemical and physical properties of estuaries and oceans with profound consequences for species and ecosystems. Numerous studies investigate CC effects from species to ecosystem levels, but little is known of the impacts on biofilm communities and on bioactive molecules such as cues, adhesives and enzymes. CC is induced by anthropogenic activity increasing greenhouse emissions leading to rises in air and water temperatures, ocean acidification, sea level rise and changes in ocean gyres and rainfall patterns. These environmental changes are resulting in alterations within marine communities and changes in species ranges and composition. This review provides insights and synthesis of knowledge about the effect of elevated temperature and ocean acidification on microfouling communities and bioactive molecules. The existing studies suggest that CC will impact production of bioactive compounds as well as the growth and composition of biofouling communities. Undoubtedly, with CC fouling management will became an even greater challenge.     

Associations of diatoms in the surficial sediments of lakes and peat pools in Atlantic Canada

The distribution of diatom frustules in the surficial sediments of lakes and ombrotrophic peat pools in Atlantic Canada are examined especially in relation to pH and bog lake succession. Sedimentary diatom associations for peat pools, strongly acidic lakes, and weakly acidic lakes are characterized. These associations and the derived diatom-pH calibration functions will facilitate improved paleoecological interpretation of natural ontogenetic pathways and assessments of recent anthropogenic impacts.     

The impact of drought and acidification on the chemical exports from a minerotrophic conifer swamp

A seven year chemical budget of a minerotrophic conifer swamp located on the PreCambrian Shield, Ontario, Canada and subjected to anthropogenically acidified deposition is presented. Contrary to other published studies, this swamp retains sulphate during wet years and exports it during dry years. Alkalinity is always retained (acidity is exported) and base cations are almost always exported. It is predicted that if this pattern continues, the cation exchange sites of the swamp will become increasingly saturated with protons and aluminum ions, and the waters passing through the swamp will be increasingly acidified.     

The impact of acidification on Chironomidae (Diptera) as indicated by subfossil stratification

The impact of acidification on the chironomid profundal fauna was studied by comparing chironomid head capsule deposits from different sediment layers. The 14–15 cm level was regarded as relatively unaffected by acid precipitation and therefore used as a control. The total number of capsules decreased, especially the number of Tanytarsinii capsules, from deeper to more superficial layers. Phaenopsectra and Psectrocladius showed a relative increase towards the surface level of the sediment. Probable causes for these changes are discussed.     

The impact of long-term elevated CO2 on C and N retention in stable SOM pools

Elevated atmospheric CO₂ frequently increases plant production and concomitant soil C inputs, which may cause additional soil C sequestration. However, whether the increase in plant production and additional soil C sequestration under elevated CO₂ can be sustained in the long-term is unclear. One approach to study C–N interactions under elevated CO₂ is provided by a theoretical framework that centers on the concept of progressive nitrogen limitation (PNL). The PNL concept hinges on the idea that N becomes less available with time under elevated CO₂. One possible mechanism underlying this reduction in N availability is that N is retained in long-lived soil organic matter (SOM), thereby limiting plant production and the potential for soil C sequestration. The long-term nature of the PNL concept necessitates the testing of mechanisms in field experiments exposed to elevated CO₂ over long periods of time. The impact of elevated CO₂ and ¹⁵N fertilization on L. perenne and T. repens monocultures has been studied in the Swiss FACE experiment for ten consecutive years. We applied a biological fractionation technique using long-term incubations with repetitive leaching to determine how elevated CO₂ affects the accumulation of N and C into more stable SOM pools. Elevated CO₂ significantly stimulated retention of fertilizer-N in the stable pools of the soils covered with L. perenne receiving low and high N fertilization rates by 18 and 22%, respectively, and by 45% in the soils covered by T. repens receiving the low N fertilization rate. However, elevated CO₂ did not significantly increase stable soil C formation. The increase in N retention under elevated CO₂ provides direct evidence that elevated CO₂ increases stable N formation as proposed by the PNL concept. In the Swiss FACE experiment, however, plant production increased under elevated CO₂, indicating that the additional N supply through fertilization prohibited PNL for plant production at this site. Therefore, it remains unresolved why elevated CO₂ did not increase labile and stable C accumulation in these systems.     

The impact of land degradation on the C pools in alpine grasslands of the Qinghai-Tibet Plateau

Aims

To determine the effect of grassland degradation on the soil carbon pool in alpine grassland.

Methods

In this study, we calculated the carbon pool in the above-and below-ground biomass, the soil microbial biomass carbon pool, the total organic carbon pool and the soil total carbon.

Results

Grassland degradation has resulted in decreases in biomass and carbon content and has changed the ratio of roots to shoots. However, there was less influence of degradation on dead root biomass. There was most likely a lag effect of changes in dead root biomass following grassland degradation. In the alpine grassland ecosystem, the carbon pool in soil accounts for more than 92 % of the total carbon both in vegetation and soil. The carbon in alpine grassland is stored primarily in the form of total organic carbon below-ground. As organic carbon decreases, the ratio of the microbial biomass carbon pool to the total organic carbon pool increases and then declines with increasing degradation level. Along the grassland degradation gradient, the total vegetation biomass (above-and below-ground) and the soil carbon pool (microbial biomass C, total organic C and total C) all decreased.