Lake responses to long‐term disturbances and management practices

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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.     

Catchment Liming to Restore Degraded, Acidified Heathlands and Moorland Pools

Current restoration measures of degraded, acidified heathland ecosystems have not always been successful in the Netherlands. Positive effects of a restored hydrology are often counteracted by acidification of the soil and the local groundwater system. Liming of the heathlands in the catchment of moorland pools might contribute to the restoration of both habitats. Experimental catchment liming was carried out in two degraded Dutch heathlands, with doses varying between 2 and 6 tons/ha. Catchment liming resulted in increased pH and base cation concentrations in the highest elevated limed parts, as well as in the lower situated, nonlimed heath areas and moorland pools. Generally, catchment liming created suitable conditions for the return of heathland target species, and the positive effects lasted for at least 6 years. The response of the heathland vegetation to the liming has, however, been slow because only a small number of endangered plant species increased in abundance. In contrast, four Red List soft‐water macrophytes strongly increased in abundance in the moorland pool. Our results show that, even with the slow return of Red List plant species, catchment liming can be a successful management tool for the restoration of the acidified heathland landscape.     

Short-term effects of liming on perch Perca fluviatilis populations in acidified lakes in South-West Sweden

Gill net catches of perch Perca fluviatilis in eight acidified lakes immediately before liming are compared] with catches in the same lakes two years after liming. Simultaneously, six control lakes, not limed, were investigated with the same procedures. A significant increase in the average catches of perch was found in the limed lakes, but not in the control lakes. This result confirms earlier reports, although seldom supported with data from controls, on successful recovery after liming.     

Odonates as Indicators of Shallow Lake Restoration by Liming: Comparing Adult and Larval Responses

Odonate assemblages were compared between replicate sets of shallow lakes that had been created and acidified by open‐cast mining across a large area (2,451 ha) of southwest France (Arjuzanx, Landes); one set of lakes (n = 5) was experimentally restored by liming with calcium carbonate, whereas another group (n = 5) was left as untreated reference lakes. Both odonate adults and exuviae were sampled bimonthly during May–August 1998. Elevated turbidity and conductivity in limed lakes were the only physicochemical measures differing between restored and reference lakes, because deacidification occurred naturally, even in reference lakes during the 17 years after the onset of restoration. Restoration by liming can apparently lead to effects on lake turbidity that might be considered adverse. Twenty‐four and 19 odonate species occurred among adults and exuviae, respectively, but there were no significant differences in richness between restored and reference sites. However, significantly, more exuviae were collected from the reference sites (588 vs. 180), where exuvial diversity and rank abundance indicated more evenly structured assemblages than those in restored lakes. Ordination showed that adult assemblages differed significantly between restored and reference lakes, and varied highly significantly with lake turbidity. This effect occurred because a small group of generally scarce adults were characteristic of reference sites (Chalcolestes viridis, Lestes virens, Cordulia aenae, Leucorrhinia albifrons, and Sympetrum sanguineum). Exuviae of these same species were less abundant at restored sites, but exuvial assemblages overall did not discriminate between restored and reference lakes. We conclude that lake restoration by liming can reduce diversity and larval numbers among odonates and subtly affects adult assemblages. In this case study, adult assemblages discriminated best between the lake types involved in the experiment, but important additional information arose from exuvial abundance and structure. This study indicates that natural recovery processes after acidification in formerly open‐cast areas––rather than chemical intervention through liming––might lead to preferable conservation outcomes.     

Phytoplankton in 63 limed lakes in comparison with the distribution in 500 untreated lakes with varying pH

As a result of the different weathering of lime in soils and varying acid deposition, the pH of Swedish oligotrophic lake waters has a broad range from ca. 4 to 8.5. Phytoplankton species occur in all lakes, but the composition and species richness varies in relation to pH. The maximum number of taxa was recorded within the pH-range 7.0–7.6, while the number decreased at higher pH and especially at pH below 5.6. During 1975–1985, thousands of lakes in Sweden were limed with the intention to restore biotic diversity and production. In order to find out whether there are differences in quality between limed and unacidified waters, the distribution of 57 selected phytoplankton taxa in 63 limed lakes was compared with that in 500 unlimed lakes with varying pH. The study shows that most common species in unacidified lakes also occur in the limed ones. However, several species of Cyanophyceae and Conjugatophyceae were missing especially in lakes that were strongly acidified before liming. On the other hand, some taxa were more frequent in the limed lakes.     

Effects of acidic pH and phytoplankton on survival and condition of Bosmina longirostris and Daphnia pulex

The effects of pH, algal composition and algal biomass on abundance, size, reproduction and condition of Daphnia pulex and Bosmina longirostris were tested in a field experiment using water and natural phytoplankton assemblages from a circumneutral (pH 6.43) and a moderately acidic (pH 5.75) lake in south-central Ontario. Both species were affected by pH and phytoplankton composition, with decreased egg production, lipid reserves, body size or abundance in treatments containing algae and/or water from the more acidic lake compared to treatments containing water and phytoplankton from the circumneutral lake. This result was unexpected for Bosmina, which often increases in relative and/or absolute abundance in acidified lakes. The negative effect of acidic conditions on Bosmina suggests that the population increase observed in most acidified lakes is not due to a positive response to low pH or ambient phytoplankton, but to altered biotic interactions possibly involving reduced competition.     

Contrasts between dystrophic and clearwater lakes in the long‐term effects of acidification on cladoceran assemblages

1. Most studies on zooplankton responses to acidification have focused on clearwater lakes with a dramatic acidification history. The role of dissolved organic carbon (DOC) in moderating zooplankton responses to acidification in naturally acidic, dystrophic lakes is less well understood and is partially impeded by a lack of baseline data. 2. Cladocera leave identifiable remains preserved in lake sediments that can be used to provide information on pre‐industrial species assemblages and their responses to environmental stressors such as acidification. Therefore, we used palaeolimnological approaches to track cladoceran assemblage responses to acidification since c.1850 (inferred from sedimentary diatom assemblages) in three acidified lakes in Kejimkujik National Park (Nova Scotia, Canada) that differ markedly in DOC content. These include two highly dystrophic lakes (Kejimkujik and Pebbleogittch lakes), and one clearwater lake (Beaverskin Lake). 3. In dystrophic Pebbleogittch Lake, an increase in the acid‐tolerant, jelly‐clad, pelagic taxon Holopedium glacialis occurred coincident with diatom‐inferred pH (DI‐pH) declines, but no other notable cladoceran assemblage shifts occurred. Similarly, Cladocera assemblages did not appear to respond to lakewater acidification in dystrophic Kejimkujik Lake. 4. In contrast, in the clearwater Beaverskin Lake, several observed shifts in cladoceran assemblage corresponded to DI‐pH declines, including an increase in the proportion of littoral taxa and an increase in Hill’s N2 species diversity. This may indicate increased water clarity as a result of acidification‐related decreases in DOC, which may have enhanced growth of emergent aquatic macrophytes and improved visibility for planktivorous fish, leading to increased predation on pelagic taxa. Species shifts within the littoral assemblage of Beaverskin Lake may reflect the differing tolerances of littoral taxa to low pH and aluminium toxicity. 5. Overall, our results suggest that cladoceran assemblages in naturally acidic, dystrophic lakes may be resilient against additional pH declines related to industrial emissions of acidifying agents, as dystrophic lakes are less vulnerable to increased aluminium toxicity and acidification‐induced increases in water clarity and often have a pre‐industrial cladoceran assemblage already adapted to acidic conditions.     

Long-term trends in limnological characteristics in the Aurora trout lakes, Sudbury, Canada

Paleolimnological techniques were employed to document the limnological histories of the aurora trout lakes, located in the Sudbury region of Ontario. Two of these lakes are of special interest to fisheries managers, as they represent the only known native habitats of a rare strain of brook trout: the aurora trout. These lakes were limed as part of restoration efforts. Stratigraphic changes in diatom and chrysophyte assemblages from dated lake sediment cores indicate that all the lakes have been impacted by anthropogenic acidification, although the timing and the magnitude of acidification were different amongst the lakes. For example, Whirligig Lake was likely the most naturally acidic lake in the past, but it had further acidified since about 1960. This lake was limed in 1989 and then again in 1993. In Whitepine Lake, acidification started 1940; however, in the most recent sediments (1992), some recovery in lakewater acidity has occurred. In Little Whitepine Lake (a reference lake), acidification started earlier (1920) and the lakewater pH continued to decline until about 1990. This lake was limed in 1989. The chrysophyte paleoindicators suggest a recent recovery in this lake. The successful re-introduction of aurora trout in Whirligig and Whitepine lakes is undoubtedly related to the improved water quality through liming but, based on our paleolimnological indicators, the lakes' limnological characteristics (e.g. pH and metal concentrations) are still different from those present before atmospheric deposition of strong acids from the Sudbury smelters.     

The effects of low pH and palliative liming on beech litter decomposition in acid-sensitive streams

The decomposition of allochthonous leaf litter is retarded by stream acidification, but few studies have evaluated whether this effect can be offset by liming – the palliative addition of calcium carbonate either to streams or their catchments. We assessed the response of litter decomposition to pH and experimental liming in Welsh upland streams. Small-mesh (<335 μm) litter-bags containing common beech (Fagus sylvatica L.) were submerged in main river sites along the River Wye, and in replicate acid, circumneutral and experimentally limed tributaries (all n = 3) for 20 days. Beech decomposition was inhibited in acid tributaries and main river sites compared to circumneutral tributaries. Despite having only moderately increased pH relative to acid streams, limed sites had increased decomposition rates that were indistinguishable from naturally circumneutral streams. Decomposition rates increased highly significantly with pH across all 12 sites studied, and values were near identical to those in more prolonged experiments elsewhere. There were no significant variations in shredder numbers with decomposition rate, and no evidence that sites with faster decomposition had smaller shredder proportions. Although based on short-term observations and leaves from just one tree species, these results are consistent with the well-known retardation at low pH of some aspect microbial decomposition (e.g. by hyphomycete fungi). They are among the first to suggest that stream liming to combat acidification might reverse such impacts of low pH. Further data are required on the microbiological causes and ecological consequences of altered detrital processing in acid-sensitive and limed streams.     

Studies on zooplankton in two acidified high mountain lakes in the Alps

Being located in remote areas, alpine lakes are good indicators of regional and global pollution, and are particularly sensitive to atmospheric depositions. When situated in areas where acidic rocks dominate, they are sensitive to acidification. In the framework of an international project partially funded by the EU, a two-year study on zooplankton was carried out on two lakes, Lake Paione Inferiore (LPI) and Lake Paione Superiore (LPS), selected because of their susceptibility to acidification. In particular, LPS is permanently acidified, with pH ranging between 5.3 and 6.2, and LPI is acidified during the ice melt, when pH drops to 6.1 units. In addition, LPI is subjected to further anthropogenic interference, since fish (Onchorynchus mykiss) have been repeatedly introduced into the lake during the last thirty years. Literature information is available on the species composition and the seasonal dynamics of the zooplankton communities of the two lakes before these anthropogenic disturbances took place. Previously, the two lakes had a similar species composition and abundant zooplankton. An analysis of the present-day situation reveals significant changes compared to the past. Both acidification and the introduction of fish are responsible for the marked alterations observed. By reconstructing of the past cladocera assemblages and by analysing the literature on lakes with different impacts of the two factors (pH and fish), we can estimate the relative importance of the two different anthropogenic disturbances on species composition and abundance of the zooplankton communities of the two lakes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Trophic Dependence of Ecosystem Resistance and Species Compensation in Experimentally Acidified Lake 302S (Canada)

Ecosystem resistance to the impacts of diverse human insults depends on the replacement of sensitive species by ones more tolerant of the stressor. Here we present evidence from a whole-lake acidification experiment (Lake 302S, Experimental Lakes Area, Canada) that resistance and species compensation decline with increasing trophic level. Diverse and fast-growing algal and rotifer assemblages with high dispersal potentials showed significant compensatory species dynamics, resulting in the maintenance of total biomass despite 30%–80% declines in species richness. Canonical correspondence analysis showed that significant compensatory algal and rotifer dynamics were best explained by differential species tolerances of acidified chemical conditions coupled with release from resource limitation and predation. However, less diverse cladoceran, copepod, and fish assemblages showed significant declines in total biomass and weak species compensation with loss of species during acidification. In comparison, algal and zooplankton species dynamics remained relatively synchronized in a nearby unperturbed reference lake (Lake 239) during the experiment. As a result, Lake 302S showed limited ecosystem resistance to anthropogenic acidification. Therefore, we hypothesize that lost species will increase the susceptibility of acidified lakes to the adverse impacts of other environmental stressors (for example, climate warming, stratospheric ozone depletion, invasive species). Consequently, the ecosystem stability of boreal lakes is expected to decline as global change proceeds. Received 2 January 2001; accepted 12 July 2002.     

Benthic macroinvertebrate fauna of two alpine lakes over the last century: The value of historical data for interpreting environmental changes

Data on benthic macroinvertebrate assemblages of two alpine lakes in the Tatra Mts (Slovakia) collected in 1914, 1933, 1979–1982, 1993–1997, and 2000 were collated and analysed in an attempt to define their relationship to major environmental events affecting these alpine lakes over the last century. The oldest data were considered an important background before the onset of acidification in one of the lakes in the 1950s, while the most current contain possible information on biological recovery. Results show that data from the 1910s are insufficient to characterize the macroinvertebrate fauna. Deep zone assemblages of both studied lakes have remained stable since the 1930s. Changes in the density of dominant species over time were found in the acidified lake, suggesting a connection between an increase in phosphorus and chlorophyll-a concentration. The composition of the littoral assemblages in the acidified lake in the 1930s indicates that the lake was not strongly acidified at that time. A stable composition since the 1980s reflects the ongoing acid stress. Incomplete species data on the non-acidified lake did not allow us to detect possible changes in the littoral fauna related to acidification. Single findings of species indicating a recovery process need longer-term data to confirm such a trend. Results from this study suggest that historical datasets consist of valuable information that can supplement palaeolimnological analyses in the reconstruction of lake ontogeny.     

Effects of liming on the occurrence and abundance of fish populations in acidified Swedish lakes

Test fishing with multimesh gillnets was performed in 103 acidified Swedish lakes before and 2–4 years after liming. In a subset of 39 lakes additional test fishing was carried out 5–9 years after liming. Taking into account the sampling biases due to differences between water temperature and number of nets used on different sampling occasions, an increase of the total CPUE, the number of species caught and recruitment of dominating species was evident after liming. Decreased recruitment was found for perch (Perca fluviatilis) at a pH below 5.2 and for roach (Rutilus rutilus) at a pH below 6.1. During the acidification phase and 2–4 years after liming acid-tolerant perch dominated the lakes, but when a longer time had elapsed after liming species dominance shifted and acid-sensitive planktivorous species increased in CPUE while perch decreased.     

Littoral microcrustaceans (Cladocera and Copepoda) as indices of recovery of a limed water system

A 7 year study (1992–1998) of littoral microcrustaceans (Cladocera and Copepoda) in the watercourse of the River Rore, South Norway, illustrates that qualitative data on cladocerans and copepods are well suited to indicate the recovery of lakes following liming. Eight limed, two acid and two circum neutral reference lakes, were sampled twice a year (June/July and September/October). In the limed lakes, species associated with neutral lakes have become more common, whereas apparently acid-tolerant species have become rarer. In Lake Rore and Lake Syndle, the two largest limed lakes which exhibited a gradual increase in pH, the changes in species composition indicated that these lakes were about to recover. Species composition in Lake Røynelandsvatn, which has reacidified after liming, first reflected improved water quality, then reverted to dominance by acid-tolerant species. In the remaining lakes, the species composition reflects a fauna which has recovered compared with the preliming situation. There is strong evidence, however, that temporary fluctuations in pH have a negative influence on the speed of recovery, confirming the importance of keeping pH stable.     

Effects of liming on forage availability and nutrient content in a forest impacted by acid rain

Acidic deposition and subsequent forest soil acidification and nutrient depletion can affect negatively the growth, health and nutrient content of vegetation, potentially limiting the availability and nutrient content of forage for white-tailed deer (Odocoileus virginianus) and other forest herbivores. Liming is a mitigation technique that can be used to restore forest health in acidified areas, but little is known about how it affects the growth or nutrient content of deer forage. We examined the effects of dolomitic limestone application on the growth and chemical composition of understory plants in an acidified forest in central Pennsylvania, with a focus on vegetative groups included as white-tailed deer forage. We used a Before-After-Control-Impact study design with observations 1 year before liming and up to 5 years post-liming on 2 treated and 2 untreated 100-ha sites. Before liming, forage availability and several nutrients were below levels considered optimal for white-tailed deer, and many vegetative characteristics were related to soil chemistry. We observed a positive effect of liming on forb biomass, with a 2.7 fold increase on limed sites, but no biomass response in other vegetation groups. We observed positive effects of liming on calcium and magnesium content and negative effects on aluminum and manganese content of several plant groups. Responses to liming by forbs and plant nutrients show promise for improving vegetation health and forage quality and quantity for deer.     

Responses of phytoplankton and epilithon during acidification and early recovery of a lake

1. Lake 302S in the Experimental Lakes Area of Canada was acidified from pH 6.7 (1981) to 5.1 (1986). The pH was further reduced to 4.5 in 1987 and held at that level until 1991. From 1992 to 1995, the pH was allowed to increase to a target value of 5.8.
2. The response of the phytoplankton community to decreasing pH from 6.0 to 5.1 was similar to that observed in another experimentally acidified lake (223) and in other atmospherically acidified lakes. Acidification affected species diversity of both the phytoplankton and epilithon. Phytoplankton diversity was positively correlated with pH. Epilithic algal diversity was more variable and did not correlate with pH.
3. Phytoplankton biomass was enhanced by acidification as the assemblage shifted from a dominance of chrysophytes to large dinoflagellates ( Gymnodinium sp. and Peridinium inconspicuum ). Epilithon biomass was unaffected, but dominance shifted from filamentous cyanophytes ( Lyngbya ) to acidophilic diatoms ( Tabellaria quadriseptata and Anomoeonis brachysira ).
4. The only taxon to be similarly affected in both the phytoplankton and epilithon was the cyanobacteria, being significantly reduced below pH 5.1. During early recovery (pH 5.5–5.8), cyanobacteria increased and species present prior to acidification recolonized both habitats.
5. In the early stages of recovery, planktonic and benthic assemblages remained more similar to acidified than natural assemblages, but more profound change began at pH > 5.5.     

浅水湖泊鱼类群落结构评估: 复合网目刺网与网簖的比较

准确评估鱼类群落结构是渔业管理和鱼类资源养护的必要前提, 而不同渔具采样结果往往会产生较大差异。研究同时采用欧洲标准采样网具-复合网目刺网(Multi-mesh gillnet)和中国传统网具-网簖对长江中游典型浅水湖泊扁担塘的鱼类群落结构进行了评估。2种网具共采集到27种鱼类, 并发现黄尾鲴(Xenocypris daviai)和湖鲚(Coilia nasus taihuensis)2种新记录种, 扁担塘的鱼类群落结构较1999年和2003年均发生了较明显的改变。2种渔具捕获的鱼类组成、相对丰度和生物量以及鱼类体长分布频率均存在显著性差异。基于鱼类的相对生物量和相对丰度的NMDS排序表明2种网具捕获到的鱼类群落结构也存在显著差异。另外还比较了复合网目刺网与其他定量采样网具间的差异, 作者认为复合网目刺网比较适合长江中下游浅水湖泊鱼类群落研究的定量取样, 但仅凭单一网具评估鱼类群落结构具有局限性。     

The effects of catchment liming on the chemistry and biology of upland Welsh streams: testing model predictions

1. The catchments of three acidified streams in mid Wales were limed in 1987/88. Here we assess their chemical and biological response in comparison with unmanipulated reference streams over a period of 5 years post-liming. 2. Stream chemistry was measured weekly/fortnightly between 1985 and 1992, while macroinvertebrates were sampled annually. Colonization by acid-sensitive taxa was assessed and trends in community structure were monitored by TWINSPAN. Real biological responses were compared with those predicted by an empirical model constructed using chemical data. 3. There were marked changes in stream chemistry following liming: calcium concentrations and pH values increased, while aluminium concentrations decreased to levels similar to those in naturally circumneutral streams. These conditions have persisted since liming. 4. Empirical models predicted that stream invertebrates would respond to the altered stream chemistry, with the establishment of communities typical of circumneutral conditions. 5. Following liming, the taxon richness and abundance of acid-sensitive taxa was significantly higher in limed compared with reference streams. Colonization by, and persistence of acid-sensitive taxa was patchy, however, and richness was still substantially lower than in naturally circumneutral streams. Moreover, contrary to the model predictions, there were no wholesale changes in the structure of macroinvertebrate communities. 6. We conclude that liming has created and maintained chemical conditions suitable for macroinvertebrate communities typical of circumneutral streams, but these chemical changes have not been matched by sustained responses among the biota. The views expressed in this article are those of the authors and do not necessarily reflect those of the NRA.     

Major changes in pelagic rotifers during natural and forced recovery from acidification

Pelagic rotifers were studied in lakes with contrasting acidification histories situated in an acid-stressed region of southern Norway. Life histories and spatial distribution varied considerably between the investigated species, and influenced the recovery processes. Most headwater lakes have experienced strongly acidified environments during the last five decades, whereas lakes close to the Skagerrak coast have been stable within the same period. Rotifer diversity and abundance were reduced in the most acidic sites and increased towards the coast. Most surveyed species are known to possess sediment egg-banks, and after chemical recovery most rotifers dispersed into the plankton from these egg-banks and produced viable populations. Some species of the genera Polyarthra and Collotheca, and the species Kellicotta longispina and Keratella serrulata showed a striking ability to tolerate acidification, and were the dominant taxa in the acidmost environments. K. serrulata characterised, but did not numerically dominate, acid rotifer communities especially in the most coloured sites, and decreased following liming. The predominantly bacteriophageous genus Conochilus exploded in numbers shortly after liming, most probably because bacteria increased strongly during this transition phase. Planktivorous fish influenced indirectly rotifer abundance by consuming invertebrate predators and important rotifer competitors such as filter feeding cladocerans. Invertebrate predators, such as larvae of Chaoborus spp. and Heterocope saliens probably influenced rotifer distributional patterns in a complex top-down manner, both during chronic acidification and liming in environments with low fish predation. Important rotifer predators such as pelagic cyclopoid copepods, Bythotrephes longimanus and Leptodora kindti, were absent from the most acidic fishless lakes. Considerable populations of large-sized Daphnia longispina probably suppressed several rotifer species in sites with low fish predation, as did large populations of Bosmina longispina and Ceriodaphina quadrangula in lakes with intense fish predation.