Diatom-inferred Total Phosphorus Research Articles

Rates of palaeoecological change can inform ecosystem restoration

Abstract. Accelerations of ecosystem transformation raise concerns, to the extent that high rates of ecological change may be regarded amongst the most important ongoing imbalances in the Earth system. Here, we used high-resolution pollen and diatom assemblages and associated ecological indicators (the sum of tree and shrub pollen and diatom-inferred total phosphorus concentrations as proxies for tree cover and lake-water eutrophication, respectively) spanning the past 150 years to emphasize that rate-of-change records based on compositional data may document transformations having substantially different causes and outcomes. To characterize rates of change also in terms of other key ecosystem features, we quantified for both ecological indicators: (i) the percentage of change per unit time, (ii) the percentage of change relative to a reference level, and (iii) the rate of percentage change per unit time relative to a reference period, taking into account the irregular spacing of palaeoecological data. These measures document how quickly specific facets of nature changed, their trajectory, as well as their status in terms of palaeoecological indicators. Ultimately, some past accelerations of community transformation may document the potential of ecosystems to rapidly recover important ecological attributes and functions. In this context, insights from palaeoecological records may be useful to accelerate ecosystem restoration.

Influence of cultural eutrophication, climate, and landscape connectivity on 3 Kawartha lakes (Ontario, Canada) since the early 1800s

Laird KR, Li S, Gushulak CAC, Moir KE, Wang Y, Leavitt PR, Cumming BF. 2023. Influence of cultural eutrophication, climate, and landscape connectivity on 3 Kawartha lakes (Ontario, Canada) since the early 1800s . Lake Reserv Manage. 39:120–140. Paleolimnological analyses of 3 lakes within the Trent-Severn Waterway (TSW) were examined to evaluate the role of regional land-use practices (forestry and agriculture), climate change, and landscape position on cultural eutrophication and lake response over the past ∼200 yr. The lakes were selected to represent lake position along the chain of lakes of the TSW; these 3 lakes vary in lake-water conditions from a lower nutrient headwater lake (Cameron Lake) to more nutrient-rich sites (Pigeon and Stony lakes) downstream. Diatom-inferred total phosphorus (TP) concentrations estimate that all lakes had TP levels of ∼15 µg/L in the 1700s, which increased to ∼20–30 µg/L in the 1800s and 1900s. Significant changes in diatom and Cladocera assemblages circa the 1830s are consistent with increased water levels and elevated phosphorus conditions associated with the intensification of forest harvest, agriculture, and development of the TSW. Diatom-inferred TP levels varied among lakes since the early 1900s, declining in Cameron Lake, increasing in Pigeon Lake, and stabilizing in Stony Lake, reflective of landscape position, degree of water inflow from the northern forested regions, and responsiveness of basins to point-source nutrient reductions and climate change. Timing of changes in TP, and changes in planktonic community composition varied among lakes. Lake production (as pigments) increased coherently in 2 lakes over the past ∼20 yr, and modern algal composition (diatoms and pigments) are lake specific and unique in comparison to the last ∼200 yr, likely reflecting combined effects of climate change and changes in nutrient loading.

Climatic and hydrological variability as a driver of the Lake Gościąż biota during the Younger Dryas

The Younger Dryas (YD) is a roughly 1,100-year cold period marking the end of the last glaciation. Climate modelling for northern Europe indicates high summer temperatures and strong continentality. In eastern Europe, the scale of temperature variation and its influence on ecosystems is weakly recognised. Here, we present a multi-proxy reconstruction of YD conditions from Lake Gościąż (central Poland). The decadal-resolution analysis of its annually varved sediments indicates an initial decrease in Chironomidae-inferred mean July air temperature followed by steady warming. The pollen-inferred winter-to-summer temperature amplitude and annual precipitation is highest at the Allerød/YD transition and the early YD (ca. 12.7–12.4 ky cal BP) and YD/Holocene (11.7–11.4 ka cal BP) transition. Temperature and precipitation were the main reasons for lake level fluctuations as reflected in the planktonic/littoral Cladocera ratio. The lake’s diatom-inferred total phosphorus decreased with increasing summer temperature from about mid YD. Windy conditions in the early YD until ∼12.3 ka cal BP caused water mixing and a short-lived/temporary increase in nutrient availability for phytoplankton. The Chironomidae-inferred summer temperature and pollen inferred summer temperature, winter temperature and annual precipitation herein are one of only a few in eastern Europe conducted with such high resolution.

Assessing the ecological responses of a shallow mesotrophic lake to multiple environmental stressors using paleolimnological techniques

Murphy MJJ, Sivarajah B, Grégoire DC, Vermaire JC. 2022. Assessing the ecological responses of a shallow mesotrophic lake to multiple environmental stressors using paleolimnological techniques. Lake Reserv Manage. 38:67–79. White Lake, located in southeastern Ontario, Canada is a long, shallow, multibasin lake that supports recreational activities year-round and has 1538 private and commercial dwelling units. The construction of a dam at Waba Creek in 1845 resulted in the minimum water level at White Lake increasing by ∼1.5 m, and several water-level management strategies have been implemented since the mid 20th century. The lake has also been impacted by land-clearance activities and shoreline development along the eastern shores and is presently mesotrophic. More recently, White Lake was colonized by zebra mussels (Dreissena polymorpha) in 2015, and annual algal blooms have also been observed. In this paleolimnological study, diatom-based approaches and loss on ignition were used to track past changes in water quality and sediment characteristics, respectively, to inform the White Lake Property Owners Association’s ongoing lake monitoring program. The diatom-inferred total phosphorus (DI-TP) reconstruction suggests that White Lake has been mesotrophic (DI-TP range 11.5 − 17 µg/L) over the past ∼200 years. Notable changes in the diatom assemblages and declines in sedimentary organic content were recorded around the 1890s in the sediment core retrieved near Hardwood Island. The decrease in sedimentary organic content was likely a response to early land-clearance activities around the lake as erosion often leads to greater inorganic export from the catchment to the lake. The switch among benthic fragilarioid diatom taxa suggests that the light conditions at this shallow lake may have changed in response to higher allochthonous inputs. Continuous monitoring of White Lake is needed to ensure that the cumulative impacts from emerging environmental stressors (e.g., climate-mediated changes, invasion by dreissenids) are considered when making management decisions.

Towards a history of Holocene P dynamics for the Northern Hemisphere using lake sediment geochemical records

Abstract. Present-day lake water phosphorus (P) enrichment and accelerated P cycling are changes superimposed on a dynamic Holocene history of landscape development following glaciation, changes in climate, and long-term low-intensity human activity. Knowledge of the history of long-term P dynamics is essential for understanding present-day landscape P export and for managing both terrestrial and aquatic environments. This study is the first attempt to constrain the timing and magnitude of terrestrial changes in Holocene P dynamics across the Northern Hemisphere using lake sediment records. Here we reconstruct trajectories in terrestrial Holocene P dynamics for the Northern Hemisphere. We apply a simple process model to published lake sediment geochemical P records from 24 sites, producing records of landscape P yield and reconstructing lake water total phosphorus (TP) concentrations. Individual site trajectories of landscape P yield and lake water TP vary systematically, with differences attributable to local landscape development history. Three distinct traits are apparent. Mountain sites with minimal direct human impact show falling P supply and conform to conceptual models of natural soil development (Trait 1). Lowland sites where substantial (pre-)historic agriculture was present show progressively increasing P supply (Trait 2). Lowland sites may also show a rapid acceleration in P supply over the last few centuries, where high-intensity land use, including settlements and farming, is present (Trait 3). Where data availability permitted comparison, our reconstructed TP records agree well with monitored lake water TP data, and our sediment-inferred P yields are comparable to reported catchment export coefficients. Comparison with diatom-inferred TP reveals good agreement for recent records. Our reconstructions form the first systematic assessment of average terrestrial P export for the Northern Hemisphere over the Holocene and provide the empirical data needed for constraining long-term landscape P cycling models and values for terrestrial P export that could be used for ocean P cycling models. The long-term perspective provided by our sediment-inferred TP can be used to identify pre-disturbance baselines for lake water quality, information essential to target-driven lake management. We find the first detectable anthropogenic impacts on P cycling ca. 6000 BP, with more substantial impacts as early as 3000 BP. Consequently, to characterize pre-disturbance lake P conditions at Trait 2 and Trait 3 sites, it is necessary to consider time periods before the arrival of early farmers. Our use of trait classifications has a predictive power for sites without sediment records, allowing prediction of TP baselines and P trajectories based on regional landscape development history.

Cultural eutrophication of a Central European lowland lake from the Bronze Age to the present recorded in diatom and Cladocera remains

Diatom and Cladocera (Crustacea) remains in the sediment of a lowland lake located in an area with a long history of human settlement, covering a period of at least 5,000 yrs, were analyzed and used as proxies to reconstruct past changes in the lake’s trophic state. The changes in trophic state were quantified with the diatom inferred total phosphorus model. The first signs of human impact on the lake’s ecosystem were recorded in the Neolithic (~4,500–4,000 cal. BP) followed by the Bronze ages (3,300–2,800 cal. BP), but they intensified during the Iron age (2,500–1,300 yrs ago) and especially during the Medieval age (after 1,000 yrs ago). Then, the diatom-inferred total phosphorus indicated hypertrophic conditions (DI-TP > 100 µg L-1), and substantial changes in the zooplankton assemblage structure were recorded, namely increase in species related to turbid water and a muddy bottom, pointing toward intensive eutrophication and fishing. The pulses of eutrophication were generally correlated with human settlement phases but inferred increases in the trophic state near 2.8 ka cal. BP and 1.3 ka cal. BP were related to minima of total solar irradiance and were driven by climatic factors and erosion in the lake catchment rather than by human activity. The strongest influence on the lake’s ecosystem was attributed to people of the Bogaczewo culture (dated to the late Iron Age), an early-Medieval Galindia tribe, and economic activity over the last 200 yrs.

Lake restoration time of Lake Taibai (China): a case study based on paleolimnology and ecosystem modeling

Reducing excessive external nutrient loading is in principle the first adaptive management against eutrophication, whereas little is known about the recovery time of such intervention, especially in the context of global warming. Here, we use an ensemble approach of paleolimnological records and modeling PCLake to evaluate the recovery time of Lake Taibai, China under diverse combinations of nutrient reduction and climate change scenarios. The model was calibrated for seven sensitive parameters and further validated using the total phosphorus (TP) concentrations in sediment cores reconstructed using a diatom-TP transfer function. The paleolimnological records show that species indicative of eutrophic conditions and the diatom-inferred TP (DI-TP) were low before the 1980s and slightly increased thereafter. The calibrated model not only captures the dynamics of TP concentrations but also performs well in identifying the regime shift between the 2 alternative stable states of the lake: macrophyte-dominated (clear) and algae-dominated (turbid) states. The scenarios results suggest that lake restoration (from turbid to clear state) would take 10–20 years with an annual nutrient loading (both N and P) reduction rate of 15–25% from 2019. Meanwhile, global warming would impede the effectiveness of nutrient reduction by not only increasing the restoration time but also decreasing the vegetation restoration level (as indicated by vegetation dry weight in lake water) and critical nutrient loading for re-oligotrophication. Our results imply that in the long run, nutrient loading reduction measurement for sustainable lake restoration should be adjusted following temperature changes. The present study highlights the feasibility and relevance of a novel methodology using paleolimnological records for model calibration and projections. The modeling approach presented here may provide a better understanding and critical implications of the long-term dynamics and future restoration of Lake Taibai and other similar shallow lake ecosystems.

Paleolimnological assessment of long-term changes in a boreal recreational lake of the Fermont mining region (subarctic Quebec, Canada)

Jacques O, Pienitz R, Ibrahim G. 2020. Paleolimnological assessment of long-term changes in a boreal recreational lake of the Fermont mining region (subarctic Quebec, Canada). Lake Reserv Manage. 36:314–334.Lac Carheil is a boreal recreational lake located near Fermont, a remote town of subarctic Quebec built in the 1970s to support iron ore mining activities. Harmful cyanobacterial blooms were recently observed at its surface, suggesting that it suffered from eutrophication. However, long-term water quality data were lacking to properly understand its current condition. We therefore undertook a paleolimnological study to investigate past limnological changes in the lake based on the multiproxy analysis of sediment cores. The cores retrieved from Lac Carheil were marked by numerous distinct laminae representing past episodes of high-energy events in the lake catchment. Furthermore, diatom assemblages of the sediments revealed that the limnological conditions of the lake had been relatively stable for more than a thousand years before beginning to change around 1840 AD. This was mainly evidenced by the emergence of species indicative of nutrient enrichment (e.g., Aulacoseira subarctica, Fragilaria crotonensis), which suggested an early eutrophication potentially attributable to climate change. The period of modern settlement (1971–2015) was characterized by a decrease in the carbon to nitrogen ratio (C/N) of the sediments, and marked increases in their organic matter content, diatom total abundance, and diatom-inferred total phosphorus concentrations, which indicated an enhanced primary production. Nevertheless, our results suggested that the disturbance level of the lake was weak and that its prospect for recovery is good. Our study provides valuable reference data to assist the management of Lac Carheil, and reveals first insights into the sedimentological and limnological history of the Fermont mining region.

Changes in the ratio of benthic to planktonic diatoms to eutrophication status of Muskegon Lake through time: Implications for a valuable indicator on water quality

Ratio of benthic to planktonic diatoms has been used to indicate lake changes related to light availability reaching the bottom of the lake, such as changes in water clarity with eutrophication and changes in water depth. To explore using of the ratio to track long-term changes of eutrophication status of Muskegon Lake, we analyzed relationships between the ratio and land use change information, inferred TP based on diatoms from different habitats a good history of spatially and temporally isolated changes in the watershed and geochemistry indices of a long sediment core retrieved from the lake. We found the ratio related well with diatom-inferred TP (DI-TP) and geochemistry proxies at different temporal and spatial scales. From European settlement to around 1920, the ratios are relatively stable and indicates a relatively high natural nutrient status of the lake. When manufacturing and population boomed in the Muskegon River Watershed, the ratios greatly decreased with the increase of DI-TP and measured geochemistry proxies. Our results showed the decrease of the ratio was most possibly due to the increase of urban land use throughout watershed during this period. Both the ratio and the water clarity sharply increased in around 1973, which was probably caused by the great decrease of the nutrients input from the watershed. Low nutrient concentrations resulted in the collapse of eutrophic planktonic diatom community. Dreissenid mussel invasion might not have a great influence on the ratios because either quagga or zebra mussel did not increase to sufficiently high abundances in the 1990s in Muskegon Lake. On the other hand, the substrate of Muskegon Lake is not suitable for dreissenid mussel colonization. Performance of the ratio on indicating trophic status of the complex case of Muskegon Lake suggested the ratio would be a promising indicator for evaluating eutrophication status in lakes.

Reconstructing the Trophic History of an Alpine Lake (High Tatra Mts.) Using Subfossil Diatoms: Disentangling the Effects of Climate and Human Influence

Diatom analysis was undertaken on a 200-year sediment record in an alpine lake (Popradské pleso, Tatra Mountains, Central Europe). Due to its remote character and well-documented human influence since the mid-nineteenth century, it allows a study of the relationship between anthropogenic pressures and diatom assemblages. Altogether, 122 diatom taxa of 40 genera were identified, and two major taxonomic shifts were revealed in the stratigraphic record. The timing of the first significant shift in ~ 1850 precludes the possibility of being caused by direct human activities, since according to historic documents there was neither continuous human presence nor grazing in the valley before that time. In addition, the direct effect of organic pollution early in the 1960s connected with the operation of a tourist hotel was not clearly reflected in the diatom signal. The diatom-inferred total phosphorus (DI-TP) reconstruction indicated the highest TP content well before the most direct wastewater pollution from a newly built hotel. There was a considerable effect of climate to diatom assemblage structure as well as diatom life forms. Our results suggest that direct organic pollution influenced the diatom communities less than expected, and the main driver of change was climate warming. We hypothesize that it is because of the short residence time of the lake, since it has both strong inlet and outlet, and it has been showed that the inlet had significant effect on benthic communities in the past. At the same time, fish manipulation could have been the reason for some fluctuation in DI-TP unrelated to climate and organic pollution.

Quantifying the effects of hydrological changes on long-term water quality trends in temperate reservoirs: insights from a multi-scale, paleolimnological study

Declining water quality in reservoirs is of growing concern in many regions, yet there is still little understanding of long-term water quality trends in these systems. Across the landscape, reservoirs have diverse origins, functions, and operational strategies. In temperate environments, winter water-level drawdown is a common operational practice in reservoirs but the long-term impacts of this hydrological modification has not been extensively studied. We paired a comparative, pre-dam-to-contemporary study (i.e. a top–bottom design) of 12 reservoirs with a detailed paleolimnological study of a focal lake to generate quantitative insights into the relative effect of hydrological changes vs. landscape and climatic drivers on water quality. The focal reservoir, Grand Lac Saint-Francois, is of relatively similar morphometry, geography, and limnology to our other sites, and has experienced annual winter water-level drawdown of ~ 5 m since it was dammed approximately 100 years ago. Based on our top–bottom analysis, we did not find strong correlations between long-term changes in water quality (i.e. diatom-inferred TP estimates) and winter water-level drawdown amplitudes. Instead, reservoir morphometry and watershed characteristics (i.e. geography, maximum depth, and cropland areas) appeared to be stronger drivers of trends across the region. From the detailed paleolimnological analysis, we found that sedimentary pigments and DI-TP concentrations significantly increased over the last century based on Mann–Kendall trend analyses. Breakpoint analyses showed that changes in biological-proxy trends, as well as the sedimentology (i.e. lithology and accumulations rates), coincided with dam construction and the onset of water level regulation. However, given the high variability in metrics and the extent of water level monitoring records, we were unable to quantitatively associate the impacts of drawdown with water quality trends at Grand Lac Saint-Francois. Conversely, we did find that watershed nutrient surpluses from livestock farming, and warming temperatures were significant explanatory variables of water quality metrics.

Eutrophication and recovery of a Lake inferred from sedimentary diatoms originating from different habitats

Eutrophication and recovery of Muskegon Lake resulted from a complex set of interacting factors according to diatom-inferred total phosphorus (TP), geochemical proxies, detailed modeling of land use land cover change in the watershed, and accounts of past point source management and non-native species invasions. Benthic and planktonic diatoms responded to phosphorus environments differently in this lake that receives 95% of its input from one river and has only a 23days average retention time. Planktonic diatoms reflected river conditions more than benthic diatoms, and benthos reflected lake conditions more than plankton. Inferred TP from planktonic diatoms indicated the Muskegon River was relatively nutrient rich compared to inferred TP for Muskegon Lake based on benthic diatoms before Europeans settled the watershed. Early European settlement and logging caused no changes in phosphorus condition in the Muskegon River, but modest increases in phosphorus were indicated in Muskegon Lake during the middle and late thirds of the 19th century. Extensive watershed-scale agricultural activity in the early 20th century apparently had little effect on trophic status of the lake, perhaps because it preceded high fertilizer use on farms. During the industrial and population boom in the watershed during the early half of the 20th century, river conditions changed little, but eutrophication of Muskegon Lake increased greatly. Reduction in river phosphorus by dams occurred during the first half of the 20th century. Phosphorus reduction in the lake was indicated after advanced wastewater treatment for Muskegon Township was implemented in 1973. Current diatom inferred phosphorus concentration in the lake is the same as before European settlement, however many attributes of the lake still differ because other stressors persist.

Lake Erie's ecological history reconstructed from the sedimentary record

We evaluated the recent ecological history of Lake Erie from diatoms and geochemistry in sediment cores. Two major transition points in the ecology of the western basin (WB; 1985 and 2008) and central basin (CB; 1935 and 1982) were defined. Changes in abundance of diatom eutrophic indicators and geochemical markers were interpreted as a degradation in water quality after 1935 due to the effects of increased population, agriculture, and industrialization until abatement measures were enacted in the 1970s and 1980s. Diatom indicators suggested modest recovery from eutrophic conditions in Lake Erie, however diatom-inferred total phosphorus suggested that despite abatement efforts total phosphorus was not reduced below pre-impact levels. The effects on diatoms of increased temperature and dissolved silica also became apparent in the 1980s, and in the WB recent shifts were likely caused by increased pollution and recent climatic warming. Based on stratigraphic changes since 1985, the diatom trajectory suggests the phytoplankton of Lake Erie will likely remain in a state of flux for the near future due to a variety of countervailing impacts including unknown effects of mitigation efforts, legacy pollution, climate change, and changing upstream conditions.

Climate as a driver of increasing algal production in Lake of the Woods, Ontario, Canada

ABSTRACTPaterson AM, Rühland KM, Anstey CV, Smol JP. 2017. Climate as a driver of increasing algal production in Lake of the Woods, Ontario, Canada. Lake Reserv Manag. 33:403–414.Lake of the Woods (LOW) is a large, transboundary lake that straddles the provinces of Ontario and Manitoba, and the state of Minnesota. Although algal blooms have been reported in the lake since the early 1800s, monitoring data and anecdotal evidence suggest that toxic, cyanobacterial blooms have increased in frequency and intensity in recent years. However, total phosphorus inputs from the lake's primary tributary, the Rainy River, have declined significantly since the late 1960s. We explore this disconnect by examining spectrally-inferred determinations of chlorophyll a (Chl-a) in lake sediment cores, as a measure of past changes in aquatic primary production. Beginning in the late 1970s to early 1980s, inferred Chl-a increased at 5 impact sites in the north end of LOW that currently experience cyanobacterial blooms in late summer and autumn. In contrast, no change in Chl-a was observed at an oligotrophic reference site with much lower cyanobacteria biomass. At the impact sites, Chl-a generally showed no significant relationship to long-term trends in diatom-inferred total phosphorus concentrations, but was significantly and positively correlated to climatic variables, including mean annual air temperature at all sites and total annual precipitation at 4 sites. These data suggest that climate change may exacerbate algal blooms in this moderately-enriched lake. The results also show that the effects of climate change on aquatic production may be enhanced at sites with higher nutrient concentrations, likely because of positive feedbacks between cyanobacteria biomass, water temperature and nutrient availability. The impact of climate change should be considered carefully in future management initiatives.

Evolution of Lake Ailike (northern Xinjiang of China) during past 130 years inferred from diatom data

We have studied diatom assemblages of a 42-cm-long sediment core obtained from Lake Ailike in northern Xinjiang of China to reconstruct the hydrological and ecological variations of the past 130 years. Three environmental parameters of lake water (i.e., diatom-inferred pH, diatom-inferred total phosphorus and diatom-inferred conductivity) were estimated by comparing the fossil diatom assemblages from the Lake Ailike core with the modern diatom assemblages in the European Diatom Database. The reconstruction exhibited two major stages: stage A (1884–1960) was a “natural” stage and stage B (1960–2013) was a “human” stage. The “natural” stage can be further divided into two sub-stages: A-1 (1884–1920) was characterized by an averagely low lake area and A-2 (1920–1960) was a stably high lake-area period. The comparison between the reconstructed lake-area variations from Lake Ailike with the treering-recorded Palmer Drought Severity Index (PDSI) variations from nearby Hutubi shows that the low lake area from 1884 to 1920 was correspondent with a dry period and that the high lake area from 1920 to 1960 with a wet period. The similarity between PDSI from Hutubi and the Atlantic Multidecadal Oscillation (AMO) implies a climatic linkage. The linkage is revealed by the tight in-phase relationship between AMO and SWP (Siberian warm-season precipitation), that is, the AMO-promoted SWP might have extended its influence to northern Xinjiang. The “human” stage can also be divided into two sub-stages: B-1 (1960–2000) was a regressing stage and B-2 (2000–2013) was a transgressing stage. The man-made regression led to dramatic increases in TP of the lake water, TOC and TN of the sediments and also in the resulted decrease in lake water pH. Fortunately, the Irtysh-Karamay Canal started to inject water into the lake in 2001, resulting in a constant expansion of lake-covered area and also in a constant improvement of ecological conditions.

Managing lake trout lakes in a warming world: a paleolimnological assessment of nutrients and lake production at three Ontario sites

ABSTRACTNelligan C, Jeziorski A, Rühland KM, Paterson AM, Smol JP. 2016. Managing lake trout lakes in a warming world: A paleolimnological assessment of nutrients and lake production at three Ontario sites. Lake Reserve Manage. 32:315−328.Recent declines in hypolimnetic dissolved oxygen (DO) concentrations in many lakes throughout Ontario have prompted concern regarding the health of lake trout (Salvelinus namaycush) populations. We used diatom assemblages and spectrally inferred chlorophyll a from the dated sediments of 3 lake trout lakes to track trends in total phosphorus (TP) and whole-lake production over the past ∼150 years. Eagle Lake is considered a sensitive lake trout lake because DO concentrations have been lower than the provincial standard (>7 mg/L) since the early-2000s; however, a lack of monitoring data impedes the evaluation of current conditions within a historical context. For a regional perspective, we compared trends in Eagle Lake with those of 2 additional lake trout lakes ∼200 km away. The diatom assemblages of Eagle Lake underwent a shift in the early-1980s, marked by a decline in the relative abundance of Stephanodiscus minutulus and an increase in small Cyclotella (sensu lato) taxa. This change is indicative of nutrient reductions and is consistent with a decline in both monitored and diatom-inferred TP. Sedimentary chlorophyll a peaked after the 1980s, suggesting whole-lake production has increased independent of nutrient loading, likely due to regional warming and a longer growing season. Diatom compositional changes at the 2 other sites are indicative of climate warming, with increases in the relative abundance of Discostella stelligera and spectrally inferred chlorophyll a. Our data suggest climate is likely the dominant driver of the observed algal changes, highlighting that the effects of warming on habitat quality should be considered in lake management strategies.

Developing a lake management strategy by dovetailing lake monitoring with paleolimnological techniques: a case study from a kettle lake on the Oak Ridges Moraine (Ontario, Canada)

Moos MT, Ginn BK. 2016. Developing a lake management strategy by dovetailing lake monitoring with paleolimnological techniques: a case study from a kettle lake on the Oak Ridges Moraine (Ontario, Canada). Lake Reserv Manage. 32: 234–245.In response to concerns about declining water quality, increased aquatic plant biomass, and harmful algal blooms, a lake monitoring program was undertaken on a suburban kettle lake near Toronto, Canada. We identified environmental conditions consistent with eutrophication, and the largest source of phosphorus (P) loading was from sediment release during an extended period of low dissolved oxygen during thermal stratification of the water column. To put these current environmental conditions in perspective, account for long-term limnological trends, and develop a sustainable lake management strategy, we also undertook paleolimnological analysis of a sediment core. Using diatoms as proxy indicators, historic limnological conditions were reconstructed. Although pre-European settlement conditions were typical of lakes with forested catchments in this region, the lake was mesotrophic (total phosphorus [TP] ∼17.5 µg/L), likely from P bound to dissolved organic carbon. P concentrations increased with the use of chemical fertilizers and establishment of seasonal lakeside cottages and resorts starting in the 1920s (the beginning of the diatom-inferred (DI-) TP upward trend). With the conversion of these cottages into year-round homes (since 1960) and further urbanization of the catchment, including servicing with municipal water supply but continued reliance on septic tanks, P has increased further (TP ∼26.1 µg/L). For restoration to a sustainable state, methods of preventing sediment P release (capping the sediment surface or oxygenation of the hypolimnion) should be considered, along with installation of municipal wasterwater servicing and stewardship projects to prevent further P loading from septic systems and surface runoff.

Using sedimentary diatoms to identify reference conditions and historical variability in shallow lake ecosystems in the Yangtze floodplain

The reference condition and historical variability of aquatic ecosystems are key ecological characters for understanding the dynamic and ecological assessment of wetland systems. Based on high-resolution chronological sequences of diatom records from 10 lakes in the Yangtze floodplain, this study aims to determine their ecological and chemical reference conditions, the historical variability and its controlling factors. Mesotrophic species Aulacoseria granulata, along with non-planktonic species Fragilaria spp., Navicula spp., Cocconeis placentula, Achnanthidium minutissimum, Cymbella spp. etc, were most abundant in the reference samples (1800–50). Accordingly, a relatively high chemical reference (50 µg L–1 in diatom-inferred total phosphorus concentration) was defined. The degree of floristic change comparing present with reference samples reveals that six of the 10 lakes have undergone significant ecological changes. The historical variability in those lakes was found to be regulated by the distance from the Yangtze River (negatively) and the lake catchment area (positively). This reflects the mechanism driving ecological change in floodplain lakes: the ecological conditions were sensitive to the nutrient input from the catchment and disturbance by the Yangtze River. This study demonstrates the robustness of palaeolimnological techniques in reconstructing the historical ecological characters of lake ecosystems, which may provide essential information for the management of wider types of wetland.

Establishing realistic management objectives for urban lakes using paleolimnological techniques: an example from Halifax Region (Nova Scotia, Canada)

To determine pre-disturbance limnological conditions, evaluate the impact of environmental stressors (surface water acidification, nutrient inputs, climate change, and winter deicing salt), and set realistic recovery targets for lake management strategies, a rapid assessment paleolimnological approach was used to determine the amount (and likely causes) of environmental changes over the past ∼100–150 years in 51 urban lakes from Halifax, Nova Scotia (Canada). Diatom assemblages from lake sediment cores were used with “top” (recently deposited, surface) samples being matched to measured limnological conditions, and “bottom” (generally from >15 cm deep) samples used to infer pre-disturbance limnological conditions such as pH, total phosphorus (TP), specific conductance, and shifts due to changing climatic conditions. Environmental change was assessed by calculating the metric of change in species composition between present-day and pre-disturbance diatom assemblages, and inferences from quantitative estimates of diatom-inferred pH, specific conductance, and TP. All 51 study lakes have experienced floristic changes in diatom species composition since pre-disturbance times, but different environmental stressors were implicated: 8 of the 51 lakes underwent significant (i.e., >2 times the root mean-squared error [2X RMSE] of the inference model) decreases in diatom-inferred pH; 8 lakes had significant increases in diatom-inferred TP; and 19 otherwise relatively pristine lakes had increases in planktonic taxa consistent with observations linked to changes in lake seasonality and limnological changes most closely linked to climate warming in Nova Scotia and other regions. The remaining 16 lakes did not have large and consistent changes in diatom flora or changes in diatom-inferred TP or pH >2X RMSE of the prediction of the models. Lake-specific factors were related to these inferences, and the lakes that acidified were mainly the currently most acidic sites, whereas those that experienced issues related to eutrophication were generally among the most alkaline sites. Of our 51 lakes, 22 (including some experiencing pH, TP, or showing floristic changes linked to climate changes) had increases in measured conductivity (1980–2002) and, correspondingly, increased relative abundances of halophilic diatom taxa. These lakes, often with catchments containing high surface areas of impervious surfaces, are examples of a trend of increasing salinity in northeastern North American lakes likely related to winter application of deicing (road) salt. The application of this paleolimnological approach enabled us to identify which lakes have undergone significant changes in diatom assemblages, as well as which environmental stressor(s) were most probable. This information can help lake managers develop more targeted and effective management strategies.

Reconstructing long-term trophic histories for lakes using two independent approaches: Application of dynamic computer modelling and palaeolimnology to Lough Mask, Ireland

An understanding of the extent to which natural variability has been and is being exceeded by the effects of human activity can make an important contribution to the effective management of impacted water bodies, including their restoration. Frequently, however, the required monitoring data are not available, particularly for the period prior to human impact, or are of insufficient quality. Two methodological solutions to this problem are often proposed, both of which involve the reconstruction of past variations in water quality and associated ecological conditions through indirect means: computer (hindcast) modelling and sedimentary (palaeolimnological) analyses. Both proposed solutions are not without their own challenges, however. Here a series of dynamic computer models (a catchment model and an in-lake ecological response model) and palaeolimnological techniques (including sediment-based diatom-inferred total phosphorus, DI-TP), were used to reconstruct total phosphorus (TP) concentrations and measures of primary productivity in Lough Mask, Co. Mayo, for the period ad 1905–2006. Although results from both approaches indicated similar patterns of nutrient enrichment in the lake during the twentieth century, sediment-based DI-TP values were consistently higher than hindcast-modelled in-lake TP concentrations. Both approaches indicated oligotrophic to mesotrophic conditions in Lough Mask prior to c. ad 1950. Elevated trophic conditions (in the range mesotrophic–eutrophic) were evident from c. ad 1970. Modelling results indicated that increased diffuse phosphorus loading from agricultural sources was the main driver of nutrient enrichment from c. ad 1970. Eutrophication was also concurrent with climatic warming, which was manifested in strengthened thermal stratification in model simulations. Results generated by the two approaches suggest that pre-ad 1950 trophic conditions could be used as a reference baseline, representing conditions prior to major impacts from agricultural intensification, for defining current water quality management targets.