Lakes In South-central Ontario Research Articles

Community science to the rescue: capturing water quality data during the COVID-19 pandemic

In 2020, the COVID-19 pandemic interrupted all aspects of human activity, including environmental research and monitoring. Despite a lack of laboratory access and other restrictive measures, we adapted an existing community science monitoring program to continue through the summer of 2020. We worked with local community groups to recruit 58 volunteers who collected lake water samples from 60 sites on 16 lakes in south-central Ontario from June to September 2020. We organized drop-off depots and had volunteers freeze samples to monitor nearshore nutrients (phosphorus and nitrogen) and chlorophyll-a. A survey was distributed to volunteers to analyze lake-front property owners’ activities during the pandemic. We found spatial patterns in nearshore water quality across the lakes, with sub-watershed development being a significant predictor of nutrients and chlorophyll-a. Additionally, pre-pandemic (2019) and pandemic (2020 and 2021) nutrient concentrations were compared, but there was no clear impact of the pandemic on nearshore nutrient concentrations, despite changes in lake-front property owners activities. Overall, this study demonstrated the ability of community science to provide water quality data on a large spatial scale despite a major societal disruption, providing insight into regional nutrient trends during the first year of the pandemic.

Effects of road-salt application on Cladocera assemblages in shallow Precambrian Shield lakes in south-central Ontario, Canada

Road-salt application is an integral part of winter road maintenance and safety in many cold regions. However, chloride (Cl−) runoff from salting activities may have adverse ecological effects. Lakes affected by road salt, particularly in urban areas, may have Cl− concentrations up to 300% higher than natural conditions. Zooplankton are sensitive to changes in water chemistry; however, little research has been conducted thus far into the biological effects of elevated Cl− concentrations from road-salt runoff. Using paleolimnological analyses, we studied the long-term effects of Cl− from road salt runoff on shallow, soft-water lakes within the southern Canadian Shield. Specifically, we examined Cladocera subfossils in dated sediment cores from 6 lakes within the Muskoka River Watershed of south-central Ontario, Canada. We compared long-term changes in cladoceran assemblages in the 5 lakes with the highest regional Cl− concentrations (32.8–90.9 mg/L) with a reference lake (0.91 mg/L). Prior to salting (ca. 1950), all of the lakes were dominated by Bosmina spp., and cladoceran assemblages showed little variation over time. After salting began, species assemblages in the 5 impacted lakes showed distinct taxonomic shifts, including increases in relative abundances of Chydorus brevilabris (Frey, 1980), Eurycercus spp., and the Daphnia pulex complex, and decreases in the relative abundance of Bosmina spp. and Alona spp. In 2 of the lakes, these changes were distinct and coincided with the onset of salting activities. In contrast to the species changes observed in the affected lakes, we recorded minimal directional changes in cladoceran assemblages in the nearby reference site. Overall, biological changes in the impacted lakes were best explained by changing Cl− concentrations associated with road-salt application. Among lakes, the severity of impact may have been indirectly mediated by differences in food quantity through its effect on Cl− toxicity.

Contrasting long-term trends of chloride levels in remote and human-disturbed lakes in south-central Ontario, Canada

Yao H, Paterson AM, James AL, McConnell C, Field T, Ingram R, Zhang D, Arnott SE, Higgins SN. 2020. Contrasting long-term trends of chloride levels in remote and human-disturbed lakes in south-central Ontrario, Canada. Lake Reserv Manage. XX:XXX–XXX. We examined a 41 yr data record from 4 monitored lakes in south-central Ontario, Canada, to demonstrate and explain long-term changes in chloride (Cl) loading and in-lake concentrations in relation to the degree of watershed disturbance. A mass balance calculation for each lake was used to determine ungauged shoreline loads. Correlations of lake Cl concentrations with each of 3 major contributing sources (inputs from inflowing streams, atmospheric deposition, and ungauged shoreline areas) revealed the contribution of each source to Cl trends at each lake. Areal loads (Cl load per year per unit area) showed the relative intensity of the contributions. Two lakes (Red Chalk, Plastic) with relatively undisturbed watersheds showed declining trends in atmospheric deposition, stream loads, lake export, and lake Cl concentrations, whereas 2 lakes (Harp, Dickie) with disturbed watersheds showed increased stream loads, lake export, and lake concentrations, despite long-term declines in atmospheric deposition. This contrasting trend was related to increased Cl concentrations in inflowing streams, which were caused by increased residential development and road salt applications. The ungauged shoreline loads in the disturbed watersheds made a contribution as high as 80% to total Cl loads. As increasing Cl concentrations have implications for aquatic biota, even at the relatively low concentrations observed in the study lakes, these findings highlight the need for improved management of road salt applications. Our results confirm that even relatively remote lakes within the Canadian Shield are potentially at risk from watershed disturbances that are disrupting the natural loading of Cl to inland waters.

Long-term trends in hypolimnetic volumes and dissolved oxygen concentrations in Boreal Shield lakes of south-central Ontario, Canada

Temperature–oxygen profiles, collected biweekly to monthly for ∼40 years, were used to calculate end-of-summer volume-weighted hypolimnetic oxygen (VWHO) concentrations in six small lakes located in south-central Ontario, Canada. Coherent decreases in thermocline depth and increases in hypolimnetic volume, mean hypolimnetic dissolved oxygen (DO) concentration, and VWHO were observed in five of the six study lakes. All lakes underwent an abrupt increase in VWHO and mean hypolimnetic DO after 2010. In four of the six study lakes, the highest hypolimnetic DO concentrations were observed in years where chlorophyll a concentrations were low, whereas at five of the six study lakes the highest hypolimnetic volumes were observed when dissolved organic carbon concentrations were relatively high. Warmer spring or winter air temperatures were associated with higher hypolimnetic DO concentrations at two sites, and longer ice-free periods were associated with smaller hypolimnetic volumes at two sites. These results suggest that the recent VWHO increases in the studied south-central Ontario lakes may be a function of multiple drivers that include changes in primary production, lake water transparency, and regional climatic factors.

Calcium decline reduces population growth rates of zooplankton in field mesocosms

Regional calcium (Ca) decline, a legacy of acid deposition and logging, is a potential threat to aquatic organisms. Lake surveys and laboratory studies indicate that Ca-rich daphniids are likely most susceptible, allowing for competitive release of other taxa with low Ca demand. Indeed, dramatic shifts in zooplankton community structure have been documented in lakes where Ca has declined, amid multiple other stressors. Given the perceived threat of this large-scale stressor, manipulative studies are needed to evaluate causal relationships between Ca decline and zooplankton community structure. We analysed per capita growth rates of zooplankton from three independent mesocosm experiments where we manipulated aqueous Ca concentrations to reflect current and future Ca concentrations. In two experiments where Ca concentration was reduced to 0.6 or 0.9 mg/L, we observed reduced growth rates for several taxa, including daphniids, bosminids, and copepods. No effect of Ca was detected in the experiment where Ca concentrations ranged from 1.2 to 2.5 mg/L, a gradient representing 68% of lakes in south-central Ontario. These results suggest that future Ca decline in soft-water Canadian Shield lakes may be accompanied by shifts in community structure and overall declines in zooplankton production.

Temporal changes in cladoceran assemblages subjected to a low calcium environment: combining the sediment record with long-term monitoring data

Lakewater calcium (Ca) decline affects softwater lakes across the Canadian Shield. Ca decline is one consequence of acid deposition, and has impeded biological recovery in formerly acidified lakes. Reduced Ca availability may advantage taxa better adapted to low Ca waters. Crosson Lake in south-central Ontario (Canada) has an extensive monitoring record and has experienced strong Ca decline since the late 1970s, recently falling below 1.5 mg L−1, a threshold value for some large Daphnia O.F. Muller, 1785 taxa. Paleolimnological analysis of the sedimentary cladoceran assemblages revealed that changes associated with the Ca decline began in the early 1970s. Relative abundances of the jelly-clad Holopedium glacialis Rowe, 2007 and the Daphnia pulex complex increased while Ca-sensitive members of the Daphnia longispina complex decreased. Zooplankton net hauls (1981–2010) corroborate the paleolimnological analysis, revealing that increases in the D. pulex complex were due to Daphnia catawba Coker, 1926 (a taxon tolerant of low Ca). Lakewater Ca, dissolved organic carbon and total phosphorus explain a significant amount of variation within the cladoceran community; however, the relationship between Ca concentration and the daphniid community was most apparent. The Crosson Lake paleolimnological and direct monitoring data may describe ecological changes that are also occurring in many other softwater lakes across the Canadian Shield and elsewhere.

Impediments to recovery from acid deposition

In response to large reductions in sulphur (S) emissions over the past 30 years, sulphate (SO42−) concentrations in precipitation at Plastic Lake in south-central Ontario, Canada, have declined by more than 70%. More recent decreases in NOx emissions have similarly led to a reduction in nitrate deposition (NO3−) and consequently the pH of bulk precipitation has increased by approximately 0.8 pH units since 1980. Despite the large decrease in acidic deposition, chemical recovery of the streams, as measured by an increase in pH and decrease in aluminum (Al), has been much less than expected, primarily due to losses of base cations from the shallow, base-poor soils. While nitrogen (N) is almost totally retained within the terrestrial catchment, S export continues to exceed inputs measured in bulk deposition and during the early part of the record approximately 70% of the anions in streams were buffered by calcium (Ca2+) and magnesium (Mg2+) compared with only 60% in 2011/12. In the wetland-draining stream (PC1), peak depressions in stream pH and peaks in SO42− and Al concentration in the fall are significantly positively correlated with annual drought days defined as the number of days when stream flow ceases. Even though reductions in SO2 and NOx emissions in Canada have resulted in large improvements in precipitation chemistry, the combined influence of soil acidification and climate-mediated biogeochemical processes occurring in wetlands cause acidification-related issues to persist. Forecasting the longer-term response of soils and surface waters in light of these observations is required to fully assess the need for further emission reductions.

SWAT-CSenm: Enhancing SWAT nitrate module for a Canadian Shield catchment

Nonpoint source modeling using hydrological models has been extensively studied at agriculture and urban watersheds; however, this has not been well addressed in forested ones where agricultural sources are comparatively minimal and nitrogen deposition exerts remarkable impacts on the nutrient cycles of a catchment. Thus it is critically important for hydrological models to incorporate the dynamics of nitrogen deposition and its transport processes, for reasonable nitrogen modeling. This is especially so for the Canadian Shield, which is characterized by a cold climate and special physiographic features. A revision of Soil and Water Assessment Tool for Canadian Shield (SWAT-CS) was proposed by Fu et al. (2014) to better characterize the hydrological features. In this study, more revisions were added to better simulate processes of nitrate by: 1) incorporating the dynamics of nitrogen deposition; and 2) allowing the deposition to distribute along with rapid-moving macropore flows. The newly revised model, SWAT-CSenm (SWAT-CS with an Enhanced Nitrate Module), and SWAT-CS were calibrated and tested with data of a subbasin of Harp Lake in south-central Ontario for 1990 to 2007. Modeling performance of nitrate flux rate in the stream for SWAT-CSenm was nearly acceptable with maximum daily Nash–Sutcliffe efficiencies (ENSs) for calibration and validation periods of 0.66 and 0.43, respectively; whereas the result of SWAT-CS was generally unsatisfied with maximum daily ENSs of 0.16 and 0.07, respectively. An uncertainty analysis using GLUE (generalized likelihood uncertainty estimation) showed a modest performance as about 50% of observations can be incorporated by the 95% prediction range deriving from the behavioral solutions (ENS≥0.5) for both daily and monthly simulations. It is concluded that the enhanced nitrate module improved the model performance of SWAT-CS on nitrate modeling, since the previous SWAT-CS failed to consider the effect of dynamics of nitrogen deposition and its sequential processes at the investigated site.

Relative contributions of stream concentration, stream discharge and shoreline load to base cation trends in Red Chalk and Harp lakes, south-central Ontario, Canada

We evaluated the importance and contributions of changes in stream base cation concentration, stream discharge and lake shoreline load to changes in base cation concentrations in two small inland lakes in south-central Ontario. The shoreline load from ungauged drainage areas was calculated with a mass balance equation. An evaluation method based on the partial Mann–Kendall test quantified the relative contributions of these three explanatory drivers to the observed trends in lake concentration of Ca, K, Mg and Na. Over a 29-year period (1978–2006) at Red Chalk and Harp lakes, declines in stream concentration and discharge were correlated with the declines in lake concentrations of all base cations (except for Na in Harp Lake), with contributions of 21–81% from stream concentration and 12–58% from discharge, whereas the shoreline load had little contribution to observed trends. The observed unusual increase in Na concentration at Harp Lake was correlated with the increase in stream Na concentration and additional load from road salts, with the shoreline load contributing a substantial 37%. These results may be applicable to numerous inland lakes with similar site conditions, including lakes found on the Canadian Shield. Copyright © 2015 John Wiley & Sons, Ltd.

A case against acidifying freshwater macrophytes prior to C and N stable isotope analysis

Acidifying organic samples prior to stable isotope analysis is a common practice to eliminate inorganic carbonates; however, it is still unclear what impact this has on δ 13C and δ 15N values. Here we present the first extensive study to test the effects of acidification on freshwater macrophyte carbon and nitrogen isotopic ratios. Focusing on the more productive and ecologically relevant seasons, we collected eleven common macrophyte species (both submerged and emergent), from four lakes in south-central Ontario, Canada. These lakes vary considerably in chemistry, particularly in the inorganic carbon and calcium concentrations. All individual plant samples were equally separated, prepared into acidified and un-acidified treatments, and analyzed for their carbon and nitrogen stable isotope ratios. No significant differences in macrophyte δ 13C or δ 15N were detected between the treatments. Additionally, we found that within-species δ 13C variability was greater in acidified samples. Finally, in assessing the isotopic values of different macrophytes across a chemical gradient at different times throughout the season, it became evident that natural variability exists in both the δ 13C and δ 15N of un-acidified samples within and between species. Based on these results, we assert that pre-analysis acidification of freshwater macrophytes from temperate lakes is unnecessary and not recommended. Additionally, we implore ecologists to acknowledge the macrophyte δ 13C and δ 15N variability in future food web studies.

Composition of native crayfish assemblages in southern Ontario rivers affected by rusty crayfish (Orconectes rusticus Girard, 1852) invasions – implications for endangered queensnake recovery

Orconectes rusticus (rusty crayfish) is an aggressive and prolific aquatic invader. Where introduced, it has caused dramatic ecosystem changes, including the replacement of native crayfishes. In Canada, it was first reported in Lake of the Woods in northwestern Ontario and a small number of south-central Ontario lakes during the 1960s. It has subsequently spread to other regions of the province. Its current expansion into southwestern Ontario rivers presents an unknown risk to the endangered queensnake (Regina septemvittata), an obligate feeder on freshly molted crayfish. We sampled 99 river sites across southern Ontario to: (i) describe crayfish assemblages within river reaches currently occupied by Queensnake; and, (ii) characterize the impact of O. rusticus on native crayfish assemblages. O. rusticus was caught at 41% of sites sampled, and was the only species at 24% of sites. The abundance, richness, and within-site distribution of native crayfishes were all significantly lower at sites with O. rusticus. Within the distribution of queensnake, crayfish assemblages were almost entirely dominated by O. propinquus, with O. rusticus being absent. However, O. rusticus was found along the lower Speed River, where only one dam separates it from Grand River queensnake populations. Given its past spread, O. rusticus will likely be introduced into areas used by queensnake and replace O. propinquus (the primary prey of queensnake). The adaptability of queensnake to prey upon non-native crayfish is unknown and requires investigation.

Forecasting cyanobacteria dominance in Canadian temperate lakes

Predictive models based on broad scale, spatial surveys typically identify nutrients and climate as the most important predictors of cyanobacteria abundance; however these models generally have low predictive power because at smaller geographic scales numerous other factors may be equally or more important. At the lake level, for example, the ability to forecast cyanobacteria dominance is of tremendous value to lake managers as they can use such models to communicate exposure risks associated with recreational and drinking water use, and possible exposure to algal toxins, in advance of bloom occurrence. We used detailed algal, limnological and meteorological data from two temperate lakes in south-central Ontario, Canada to determine the factors that are closely linked to cyanobacteria dominance, and to develop easy to use models to forecast cyanobacteria biovolume. For Brandy Lake (BL), the strongest and most parsimonious model for forecasting % cyanobacteria biovolume (% CB) included water column stability, hypolimnetic TP, and % cyanobacteria biovolume two weeks prior. For Three Mile Lake (TML), the best model for forecasting % CB included water column stability, hypolimnetic TP concentration, and 7-d mean wind speed. The models for forecasting % CB in BL and TML are fundamentally different in their lag periods (BL = lag 1 model and TML = lag 2 model) and in some predictor variables despite the close proximity of the study lakes. We speculate that three main factors (nutrient concentrations, water transparency and lake morphometry) may have contributed to differences in the models developed, and may account for variation observed in models derived from large spatial surveys. Our results illustrate that while forecast models can be developed to determine when cyanobacteria will dominate within two temperate lakes, the models require detailed, lake-specific calibration to be effective as risk-management tools.

Impact of wetland disturbance on phosphorus loadings to lakes

Total phosphorus (TP) concentrations have declined in many lakes and streams across south-central Ontario, Canada, over the past three decades, and changes have been most pronounced in wetland-dominated catchments. In this study, long-term (1980–2007) patterns in TP concentrations in streams were assessed at four wetland-dominated catchments that drain into Dickie Lake (DE) in south-central Ontario. Two of the subcatchments (DE5 and DE6) have particularly large wetland components (31%–34% of catchment area), and these wetlands are characterized by numerous standing dead trees and many young live trees (18–27 years old). These two streams exhibited large peaks in TP and potassium (K) export in the early 1980s. In contrast, TP and K export from DE8 and DE10 (wetland cover 19%–20%) were relatively flat over the entire record (1980–2007), and field surveys indicated negligible standing dead biomass in these wetlands and a relatively healthy, mixed-age tree community. The coincidence of high TP and K concentrations in the DE5 and DE6 streams as well as evidence of a disturbance event in their wetlands during the early 1980s suggest that disturbance events (e.g., flooding) that lead to wetland tree mortality may contribute to patterns in surface water TP observed in this region.

Potential factors leading to the formation of cyanobacterial scums in a mesotrophic softwater lake in Ontario, Canada

While the factors linked to the incidence of cyanobacterial blooms are well studied, the specific conditions that facilitate transition of blooms to surface scums are less understood. Three Mile Lake (TML), a mesotrophic, softwater lake in south-central Ontario, Canada, experienced cyanobacterial blooms in 2005, 2006, and 2007, but a surface scum event only occurred in 2005. Our objectives were therefore to (1) determine how phytoplankton change seasonally in relation to water quality and other environmental factors; (2) examine modern and historical water quality and meteorological data to explore possible causative factors of the 2005 surface scum; and (3) examine regional predictions of future climate (temperature and precipitation) from present to 2100 to assess the risk of future cyanobacterial scums. Our evaluation suggests that while high phosphorus concentration is a predisposition for the occurrence of cyanobacterial blooms, meteorological and hydrological conditions play an instrumental role in the actual development of surface scums. The 2005 scum event occurred during the fall period when air temperature was unusually high and wind speed and precipitation were low. Consequently, runoff from the surrounding catchment, and thus flushing, was minimal. We believe all these factors interacted to prolong thermal stratification and increase residence time, thereby promoting the proliferation of cyanobacteria and formation of surface scums. Our modeled climate data indicate that the frequency of scum occurrence will change over time as climatic change paves the way for the meteorological conditions that promote scum development.

Climate change drives coherent trends in physics and oxygen content in North American lakes

Using a 25-year record of monitoring data, we show that recent climate change has affected the thermal properties and oxygen content of seven lakes in south-central Ontario, Canada, and five lakes in north-central Wisconsin, USA. Coherent patterns in autumnal lake warming were driven by increased autumn air temperature in both lake districts. Temperature increases were restricted to the epilimnion and metalimnion of the lakes, resulting in increased thermal stability of the water column. Mixing depths also decreased over the study period. Shallower mixing depths in the Ontario lakes were due to climate-driven increases in lake-water dissolved organic carbon concentrations. Collectively, changes in the thermal regime of the lakes suggest autumn mixing of the water column may be delayed. Metalimnetic oxygen also increased in the Wisconsin lakes, perhaps in response to increased algal production as lake thermal regimes changed. The response of individual lakes to climate change was modified by lake chemistry in the Ontario lake district and by lake chemistry and morphometry in the Wisconsin lake district. Our results demonstrate coherent lake response to climate change and highlight the importance of both regional and local factors in regulating individual lake response to global climate change.

Linking temporal changes in crayfish communities to environmental changes in boreal Shield lakes in south-central Ontario

When aquatic ecosystems are among those most intensely affected by local and regional environmental change, it is crucial that stressors are identified to set priorities for future research and mitigation. Studies relating changes in important or sensitive assemblages to environmental changes provide a means to quantify potential stress on aquatic biota. Crayfish are ideal taxa for this type of study because they influence ecosystem structure and function and are sensitive to biotic and abiotic changes. We used historical and contemporary crayfish abundance and select environmental data for 100 inland lakes in central Ontario, to identify factors that are correlated with community membership and species distributions at each time and to elucidate environmental factors that can be directly linked to changes in relative abundance between the two time periods. Our results show that declines in lake calcium, invasions of warm-water centrarchids, and anthropogenic shoreline development have increased in their relative influence over time. These stressors may be affecting other freshwater biota directly, or indirectly through food web changes or altered abiotic interactions among the environmental changes.

Effects of multiple stressors on lakes in south-central Ontario: 15 years of change in lakewater chemistry and sedimentary diatom assemblages

Freshwater ecosystems are increasingly affected by human influences. Since the pre-industrial era, lakes of the Muskoka–Haliburton region of south-central Ontario have had increases in shoreline residential development and acid deposition. Previous research on 54 of these lakes, using sediment cores and diatom-based transfer functions, showed changes in lakewater pH and total phosphorus concentration between the preindustrial era and 1992. Since 1992, there has been further change, which we have documented for the same set of lakes, using similar methods. For example, dissolved organic carbon has increased and there have been significant increases in planktonic diatoms (e.g. Cyclotella stelligera) commonly associated with climate warming. More striking diatom changes have occurred in the past 15 years than between pre-industrial times and 1992. Significant changes observed in both chemical (e.g. pH, Ca, DOC) and biological data suggest that novel stressors, such as declines in lake calcium concentrations, acting in conjunction with climate and land-use change, have created ecosystems for which there are no historical analogs.

Changes since the onset of acid deposition among calcium-sensitive cladoceran taxa within softwater lakes of Ontario, Canada

Aqueous calcium (Ca) concentrations are currently decreasing in many softwater lakes on the Boreal Shield. As the onset of these declines often pre-date direct monitoring programs, indirect techniques are required to examine the impacts of reduced Ca availability on aquatic communities with relatively high Ca demands such as the Cladocera (Class: Branchiopoda). Among the Cladocera, the family Daphniidae has been identified as a taxonomic group potentially useful for inferring past Ca concentrations due to their high Ca demands and preservation in lake sediments. Here, we use a “top/bottom” paleolimnological analysis to compare present-day cladoceran communities preserved in the surface sediments of 36 softwater lakes in south-central Ontario, Canada, which are potentially vulnerable to Ca decline (i.e. small headwater systems with present-day lakewater [Ca] < 3 mg L−1), with the communities present in lake sediments deposited prior to the onset of regional acid deposition. To distinguish the potential impacts of lake acidification from those of Ca availability (as Ca and pH trends are strongly correlated in this region), the study lakes were chosen to be evenly distributed about a present-day lakewater pH of 6 and Ca concentration of 1.5 mg L−1 (threshold values). Despite the importance of pH as an explanatory variable for the present-day assemblages, a comparison of the sedimentary remains from the two time periods indicate there have been large declines since pre-industrial times in the relative abundances of Ca-rich Daphnia spp. (particularly of the Daphnia longispina species complex), regardless of present-day pH, accompanied by increases in the Ca-poor species Holopedium glacialis. These observations suggest that recent declines in Ca concentration may have already fallen below baseline conditions, with marked implications for ecosystem function due to the differential responses among cladoceran taxa.

Assessment of benthic algal biomonitoring protocols to evaluate effects of shoreline development on the nearshore zone of Precambrian Shield lakes in Ontario

We assessed the ability of benthic algal biomonitoring protocols to detect effects of differences in shoreline development in the littoral zone of oligo- to mesotrophic Precambrian Shield lakes in south-central Ontario. The study sites (n = 28 in Aug 2006, n = 29 in Aug 2007) spanned a broad gradient of shoreline development (e.g., intact forest, cottages, marinas) but a modest gradient of nutrient concentration (3–22 μg/L total phosphorus). Each site was sampled for water chemistry (nutrients, ions, metals, pH) and 5 levels of benthic algal bioassessment, which differed in the amount of time, resources and expertise required. Level 1 involved visual descriptions of algal cover; Level 2 involved biomass measurements (chlorophyll a, ash-free dry mass); Level 3 involved enumeration of algae to a coarse taxonomic level (i.e., the major algal classes); Level 4 involved quantification of photosynthetic pigments by high-performance liquid chromatography; and Level 5 involved high taxonomic resolution enumeration of diatom communities. Multi- and univariate numerical analyses (e.g., PCA, ANOSIM, ANOVA) were used to assess relationships between measurements of shoreline development, water chemistry, and benthic algal metrics. Results identified that Level 5 was the most sensitive to track differences in the shoreline development among sites. For lakes on the Precambrian Shield, we suggest that benthic algal biomonitoring programs focus on Level 5, despite the higher requirements of time, technical skill, and training. We further recommend that the other levels of bioassessment be explored further in other regions where broader gradients of shoreline development and lake trophic status exist. [Supplemental materials are available for this article. Go to the publisher's online edition of Lake and Reservoir Management to view the supplemental file.]

Modeling the establishment of invasive species: habitat and biotic interactions influencing the establishment of Bythotrephes longimanus

Bythotrephes longimanus is an invasive pelagic crustacean, which first arrived in North America from Europe in early 1980s and can now be found throughout the Great Lakes and in many inland lakes and waterways. Determining the suitability of lakes to Bythotrephes establishment is an important step in quantifying its potential habitat range and environmental risk. Lake environmental conditions, planktivorous fishes, sport fishes and Bythotrephes occurrence data from 179 south-central Ontario lakes were used in this study to model lake characteristics suitable for its establishment. The performance of principal component analysis and different predictive models was used to determine the habitats that are suitable for the survival of Bythotrephes and the factors that may regulate its spread. Four modeling approaches were employed: linear discriminant analysis; multiple logistic regression; random forests; and, artificial neural networks. Ensemble prediction based on the four modeling approaches was also used as an indicator for predicting Bythotrephes occurrence. Bythotrephes appears to establish more readily in larger, deeper lakes with lower elevation, that have more sport fishes. Bythotrephes occurrence can be best predicted by artificial neural networks when including the measures of fish data, in addition to lake environmental data. Lake elevation, surface area and sport fish occurrence were ranked as the most important predictors of Bythotrephes invasion. The inclusion of biotic variables (occurrence or diversity of sport or planktivorous fishes) enhanced cross-validated models relative to analyses based on environmental data alone.