Whole-lake algal responses to a century of acidic industrial deposition on the Canadian Shield (original) (raw)
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Limnology and Oceanography, 1999
Fossil pigment analyses and 19 year-long historical records were used to quantify whole-lake algal response to changes in optical and chemical properties following experimental acidification of Lake 302 with H 2 SO 4 (south basin, 302S; 1981-1989) or HNO 3 (north basin, 302N; 1982-1986) and HCl (1987-1989). Undisturbed sediments were collected by freeze-coring, sectioned in approximately annual intervals, and analyzed for fossil carotenoids, chlorophylls, and derivatives by high performance liquid chromatography. Concentrations of fucoxanthin (diatoms, chrysophytes, some dinoflagellates) were correlated with algal standing crop (r 2 ϭ 0.67, P Ͻ 0.05; 1978-1989) and increased 6-fold following acidification of Lake 302S with H 2 SO 4 from pH 6.6 to 5.0, consistent with observed reductions in dissolved organic carbon (DOC) from 7 to 4.5 mg liter Ϫ1 , improved water clarity, and increased biomass of deep-water chrysophytes. However, fucoxanthin concentrations declined to baseline values in sediments from 1988 to 1990, concomitant with severe acidification to pH 4.5, continued DOC loss (Ͻ1.5 mg liter Ϫ1) and an estimated 8-fold increase in the penetration of UVb radiation (UVR-b). Increased penetration of ultraviolet radiation (UVR) was recorded also by increased relative abundance of pigments characteristic of UVR-transparent environments. In contrast, pigments from green algae (Chl b, pheophytin b, lutein-zeaxanthin) doubled during acidification with H 2 SO 4 , while those from cryptophytes (alloxanthin) were unaffected and diatoxanthin from diatoms declined. Patterns of ubiquitous -carotene, Chl a, and pheophytin a suggested that total algal biomass increased ϳ200-400% by the mid-1980s, but declined to near-baseline under severe acidification. Variance partitioning using redundancy analysis captured 80-83% of variation in fossil chlorophylls and carotenoids and suggested that the direct effects of pH were greater (ϳ50% of total variance) than those of irradiance (ϳ12%), but that ϳ20% of variance was attributable to factor interactions. Fossil concentrations of pigments from green algae and diatoms increased ϳ100% following acidification of Lake 302N to pH 6.1, but there were few signals of deep-water blooms, possibly because DOC remained 3.5-5.0 mg liter Ϫ1. Such complex interactions between pH, DOC, and light may help explain the high variability of algal biomass response to lake acidification.
PeerJ
Meromictic Crawford Lake, located in SW Ontario, Canada is characterized by varved sediments, making it suitable for high-resolution paleoecological studies. Freeze cores, the only coring method available that reliably preserves the fragile laminations representative of seasonal deposition in the lake, were used to document siliceous diatom and chrysophyte community structure at an annual resolution from 1930–1990CE. Stratigraphically constrained cluster analysis identified major assemblage changes that are believed to have been caused by local, regional and possibly global anthropogenic impacts. The assemblage changes within the siliceous algae are attributed to regional weather and increased industrial emissions and related effects of acid deposition on the lake’s catchment associated with the Great Acceleration –the massive economic, industrial, and demographic expansion beginning in the mid-20th century. Observed increases in spheroidal carbonaceous particles (SCPs) in varved la...
Ecosystems, 2013
In the region northeast of Wawa, Ontario (Canada), many circumneutral lakes downwind of a nearby iron-sintering plant were strongly acidified (pH 3-4) in response to the emissions of large amounts of sulfur dioxide from 1939-1998. Following closure of the plant in 1998, lakewater pH has returned to circumneutral conditions due to the high buffering capacity of the local geological substrate. Prior paleolimnological analyses of dated sediment cores have detected some biological recovery among algal communities (diatoms and chrysophytes), although they have not returned to their pre-impact assemblages. Here we take a broader ecosystem approach, and build upon the algal analyses by examining cladoceran sedimentary assemblages, and spectrally-inferred chlorophyll a and dissolved organic carbon (DOC) from the same dated sediment cores. Similar to the algal communities, recent cladoceran sedimentary assemblages from three impacted lakes remain in an altered state relative to the pre-impact period (for example, increased relative abundances of Chydorus brevilabris and reduced cladoceran density in sediments). However, trends in the spectrally-inferred chlorophyll a and DOC were mixed, with long-term decreases in the study lake closest to the plant and long-term increases within the other lakes. Collectively, the multi-proxy paleolimnological analyses of these markedly acidified lakes demonstrate the delayed biological recovery from acidification (and differences in timing) across multiple trophic levels, despite the near-elimination of acid deposition almost a decade previously, which led to a striking recovery in lakewater pH and increased food availability.
Canadian Journal of Fisheries and Aquatic Sciences, 2009
Chemical recovery is hypothesized to promote rapid recovery of benthic algal communities in formerly acidified lakes; this expectation needs modification. We evaluated the hypothesis in a small lake (L302S) in the boreal forest of northwestern Ontario, Canada, during a decade of pH recovery following a prior decade of experimental acidification from pH 6.7 to 4.5. To account for regional changes during the study, we also studied a nearby reference lake (L239). Taxonomic changes in the epilithon (biofilm on rock surfaces) included persistently lower cyanobacterial biomass following its acidification-related decline and increases in both diatoms and greens. Epilithic metabolic recovery was incomplete because the acidification-induced increase in respiration continued, although the prior decline in photosynthesis was reversed. Unexpectedly, blooms of metaphytic filamentous green algae occurred at higher pH during recovery than during acidification. Although several community attributes recovered fully, recovery of many aggregate functional and taxonomic properties lagged improvements in pH. Divergence was greater at the taxonomic than at the functional level. Despite pH recovery, potential causes of incomplete algal recovery include incomplete chemical recovery and the persistent absence of functionally important biota. Our findings counter the assumption that ecological recovery mirrors the pathway of damage caused by a human stressor.
Environmental Pollution, 1997
The effects of liming on the aquatic macrophyte vegetation have been investigated in S and SW Norway. In the western part of the study area, Juncus bulbosus was considerably more frequent in the limed than in the unlimed lakes, whilst in the eastern part there were no such differences, and the J. bulbosus populations were generally not so vital. In some southwestern areas a luxuriant and massiv nuisance growth ofJuncus bulbosus in the depth zone 0-4 m was recorded. The most vital plants produced up to I m long annual shoots, and developed extensive, dense and vital surface mats in shallow areas (depth zone 0-3 m) after 4-5 years. The original isoetid vegetation had disappeared in the areas of dense J. bulbosus populations, and this development seems to be more or less irreversible. The massive J. bulbosus expansion is seen mainly in directly limed lakes with a sometimes visible layer of calcium carbonate on the sediment surface, but enhanched growth has been observed also in lakes downstream liming. The massive expansion is believed to be due to an increase of CO 2 and ammonium in the sediment pore water, combined with a mild climate with a very high precipitation. In many areas the liming has led to an increase in species diversity, and a (re-)establishment of some acid-intolerant species such asMyriophyllum alterniflorum andPotamogeton spp.
Journal of Great Lakes Research, 2015
Narrow river-valley reservoirs are typically spatially heterogeneous. Little is known about how (a) water quality and algal community composition change longitudinally along a reservoir and (b) how algal composition and production change as a reservoir ages. To address these unknowns, multiple sediment cores were collected from mid-channel locations along the longitudinal axis of Lake Diefenbaker, Saskatchewan, Canada, a long, narrow river-valley reservoir on the Canadian Prairies. Profiles of concentrations of various pigments in sediment cores were measured to infer spatial and temporal trends in algal biomass and community composition. Diverse mixtures of pigments derived from filamentous and colonial cyanobacteria, diatoms, chlorophytes, and other phyla were observed. Spatial patterns of sedimentation of pigments (nmol m −2 yr −1) in surficial sediments suggest increases in algal biomass with distance down-reservoir, with maximum inferred biomass occurring in midreservoir. This is consistent with general knowledge of patterns of primary production in narrow, river-valley reservoirs. However, myxoxanthophyll, a biomarker of filamentous or colonial cyanobacteria, detected only at sites furthest down-reservoir, did not follow this general trend. Temporally, an increase in algal biomass occurred at down-reservoir locations after 1990, followed by a substantial increase after 2000 at the majority of sites. Profiles of concentrations of pigments exhibited no clear trends to support the prevailing paradigm that predicts an initial upsurge in trophic status upon formation of reservoirs. This pattern may result from limited penetration of light in the early years after reservoir formation. This study reinforces the need for paleolimnological analyses among hydrologic zones of large reservoirs.