South-central Ontario Research Articles

Human shoreline development and the nutrient stoichiometry of aquatic plant communities in Canadian Shield lakes

Human activities associated with residential development potentially alter ecological processes in lake littoral zones. We determined how the nutrient stoichiometry of aquatic plant communities relates to residential density around lakes of south-central Ontario. We calculated the elemental composition of entire plant communities from multiple sites in 12 lakes using measurements of individual plant C:N:P ratios and their areal biomass. We found considerable variability in the C:N:P ratios of whole aquatic plant communities among sites and lakes, which was not accounted for by intraspecific variability in the elemental composition of aquatic plants. Instead, differences in community-level C:N:P ratios primarily resulted from high interspecific variability in the elemental composition among dominant plant taxa and variable taxonomic composition of sampled plant communities. Plant community composition differed among lakes with and without shoreline residences, and we found lower C:N and C:P ratios in communities from littoral zones in human-developed lakes. Our results thus demonstrate a link between the elemental and taxonomic composition of aquatic plant communities, which may mediate biogeochemical responses of littoral zones to development of lake shorelines.

Decreasing soil water Ca2+ reduces DOC adsorption in mineral soils: Implications for long-term DOC trends in an upland forested catchment in southern Ontario, Canada

Positive trends in dissolved organic carbon (DOC) concentration have been observed in surface waters throughout North America and northern Europe. Although adsorption in mineral soils is an important driver of DOC in upland streams, little is known about the potential for changes in DOC adsorption to contribute to these trends. We hypothesized that long-term declines in soil water Ca2+ levels, in response to declining acid deposition, might influence DOC adsorption and that this could contribute to long-term DOC trends in an upland forested catchment in south-central Ontario, Canada. Between 1987 and 2009, DOC concentrations increased significantly (p<0.05) in stream water and B horizon soil water (2 out of 3 sites). The null point DOC concentration (DOCnp), which is a measure of the soil water DOC concentration at equilibrium with the soil, ranged from 1.27 to 3.75mgL−1 in B horizon soils. This was similar to the mean DOC concentrations of B horizon soil water (2.04–6.30mgL−1) and stream water (2.20mgL−1), indicating that soil and stream water DOC concentrations are controlled by equilibrium processes at the soil–water interface. Adsorption experiments using variable Ca2+ concentrations demonstrated that as Ca2+ decreased the DOCnp increased (1.96 to 4.74mgL−1), which was consistent with the observed negative correlation between DOC and Ca2+ in B horizon soil water (p<0.05; r2=0.21). Additional adsorption experiments showed that Na+ had no effect on DOC adsorption (p>0.05), indicating that changes in DOC adsorption might be related to cation bridging. We conclude that declines in soil water Ca2+ concentration can contribute to increasing DOC trends in upland streams by reducing DOC adsorption in mineral soils.

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.

The life history of a gall-inducing mite: summer phenology, predation and influence of gall morphology in a sugar maple canopy

1 Eriophyoid mites are among the most ubiquitous gall-inducing arthropods, and are adapted species-specifically to a broad diversity of plants, although their life histories remain poorly studied outside agricultural systems. 2 We examined the seasonal phenology of a leaf-galling eriophyid mite, the maple spindle gall mite Vasates aceriscrumena (MSGM), in naturally occurring stands of sugar maple Acer saccharum in south-central Ontario in 2007 and 2008. 3 Galls were first induced in spring (mid-May) and were devoid of mites by late August. In the study region, MSGM appears to have at least two generations, with overwintering, deutogyne females that initiate galls in spring (mid-May) after leaf flush, giving rise to a generation of protogyne (primary) females and a few morphologically similar males (<1 for every 10 females) and, subsequently, to a new generation of deutogyne females in mid-July to early August. In July, some galls can be highly crowded, with 50–200 individuals per gall. 4 In addition, a tarsonemid mite, Tarsonemus acerbilis, was found in approximately 40% of MSGM galls examined. As much as 95.4% of galls in 2007 and 97.4% in 2008 that contained tarsonemid larvae did not contain MSGM eggs (by contrast, only 2.3% of tarsonemid-free galls contained no MSGM eggs), suggesting that these juveniles feed, at least opportunistically, on MSGM eggs. 5 Gall ostiole morphology appeared to influence both MSGM and Tarsonemus densities within galls, with ‘open’ ostioles (versus ‘closed’) being much more susceptible to invasion by the tarsonemid. The latter is likely to be an important regulator of MSGM populations. We hypothesize that the two ostiole types are the result of selection pressures on the gall inducer, favouring closed gall entrances for increased protection, and possibly also on the host tree, favouring open galls to increase predator access.

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.]

Nitrogen enrichment and the emission of nitrous oxide from streams

[1] Nitrous oxide (N2O) is a potent greenhouse gas produced during nitrogen cycling. Global nitrogen enrichment has resulted in increased atmospheric N2O concentrations due in large part to increased soil emissions. There is also a potentially important flux from streams, rivers and estuaries; although measurements of these emissions are sparse, and role of aquatic ecosystems in global N2O budgets remains highly uncertain. Using the longest-term measurements of N2O fluxes from streams to date, we found annual fluxes from 14 sites in five streams of south-central Ontario, Canada varied widely–from net uptake of 3.2 ± 0.2 (standard deviation)μmol N2O m−2 d−1 to net release of 776 ± 61 μmol N2O m−2 d−1. N2O consumption was associated with very low nitrate concentrations (<2.7 μM). Mean annual (log-transformed) N2O emissions from our study streams (across sites and years) were positively related to nitrate concentrations (r2= 0.59).This nitrate-N2O relationship can be generalized across all 20 streams (in Canada, Japan, Mexico, and the midwestern United States) for which published data now exist and could provide a new basis for the IPCC to calculate agricultural emissions from streams. In addition to predicting annual emissions, we present the first measurements of N2O concentrations under ice in streams. Nitrate was a strong predictor of N2O % saturation during periods of ice cover (r2 = 0.89), when gas exchange is negligible. Given the small surface area of streams within a catchment and the fact our measured areal fluxes are comparable to reported fluxes from agricultural soils, this suggests streams are a small regional N2O source.

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.

Increased abundance of the non-indigenous zooplanktivore, Bythotrephes longimanus, is strongly correlated with greater spring prey availability in Canadian Shield lakes

The non-indigenous zooplanktivore, Bythotrephes longimanus, is a large Palaearctic cladoceran that is spreading rapidly in the Great Lakes watershed in North America. As a voracious predator, Bythotrephes can reduce herbivorous cladoceran abundance and diversity; however, the variables that affect its abundance are not well understood. To determine what bottom-up factors are associated with the abundance and seasonal dynamics of established Bythotrephes populations, two Bythotrephes datasets from lakes in south-central Ontario, Canada, were analysed using multiple regression and multivariate analyses: a multi-lake dataset of nine lakes sampled in 2003 and a multi-year dataset of one of these lakes, Harp Lake, sampled from 1994–1998 and 2001–2004. Bottom-up variables tested were Secchi disk depth, epilimnetic temperature, cladoceran (prey) density, total phosphorus, dissolved organic carbon and Chlorophyll a, as well as maximum depth for the multi-lake dataset. In both analyses and datasets, springtime abundance of herbivorous cladocerans was consistently found to be a significant factor associated with Bythotrephes (June–September) abundance; Bythotrephes annual abundance was significantly and positively associated with mean May and June prey abundance, along with mean Secchi disk depth for the multi-lake dataset, and groups of lakes or years with similar Bythotrephes seasonal abundance patterns were predicted by June prey abundance. Additionally, prey availability was the dominant contributor towards changes in weekly Bythotrephes birth rates calculated for two of the study lakes. Our study suggests that prey availability influences Bythotrephes abundance, which provides evidence that Bythotrephes establishment success is affected by the abundance of its prey.

Effects of broad-scale geological changes on patterns in macroinvertebrate assemblages

Understanding the broad-scale factors that influence biological communities has long been a goal of community ecology. We used benthic macroinvertebrate data to identify broad geographical patterns in macroinvertebrate community composition and specifically to examine the influence of the Precambrian Shield on stream abiotic and biotic conditions. The Precambrian Shield is a geological feature that encompasses most of northern North America. Geology differs between Shield and off-Shield areas, creating distinctly different physical and chemical conditions in aquatic systems. We focused our regional-scale study on south-central Ontario, where both Shield and off-Shield conditions are found in adjacent areas. We used constrained and unconstrained multivariate analyses to examine patterns in biotic, abiotic, and spatial variables. Our results showed that, in low-order lotic systems, macroinvertebrate communities differ between Shield and off-Shield streams. Shield streams have higher dissolved O2, velocity, and discharge, larger amounts of woody debris, and greater canopy cover than off-Shield streams. In contrast, off-Shield streams have higher conductivity, alkalinity, pH, turbidity, and water temperature, and frequently are surrounded by meadow, cultivated, or pastured land. In general, macroinvertebrate communities at off-Shield sites had a greater proportion of taxa preferring pool or depositional habitats, whereas macroinvertebrate communities at Shield sites contained taxa typically associated with riffles or erosional habitats. Analysis of spatial location indicated that the Shield/off-Shield distinction probably is the result of a combination of intertwined abiotic and spatial factors.

Water quality changes in south-central Ontario lakes and the role of local factors in regulating lake response to regional stressors

The long-term monitoring of eight lakes near Dorset, Ontario, indicates that the water quality has changed significantly over the last 30 years. However, trends in the Dorset lakes may not be representative of changes in other south-central Ontario lakes, as the Dorset lakes are within a small area and span a limited gradient of lake and watershed characteristics. To determine the regional extent of water quality changes, we assessed the chemical changes in 36 diverse lakes that were first sampled between 1981 and 1990 and were resampled in 2004–2005. Similar to trends in the Dorset lakes, changes in the regional lakes included decreasing acidity, calcium, conductivity, metals, and phosphorus, and increasing dissolved organic carbon, nitrogen, sodium, and chloride. Water quality changes were driven by regional stressors, including acidic deposition, climate, and lakeshore residential development. However, stressor-induced responses differed among lakes. Increases in sodium and chloride were greater in developed lakes that were close to winter-maintained roads. Site-specific characteristics, such as lake and watershed morphometry, could not explain heterogeneous changes in the remaining water quality parameters. These results indicate that other factors play an important role in regulating individual lake response to regional stressors.

Stream Nitrate Responds Rapidly to Decreasing Nitrate Deposition

Ecosystem acidification and eutrophication resulting from increased deposition of dissolved inorganic nitrogen (DIN) are issues of increasing global concern. Consequently, costly policy decisions are being implemented to decrease nitrogen oxide (NOx) emissions. Although declining DIN deposition along with rapid declines of DIN in surface waters have been reported in parts of Europe, the same observation is just emerging in North America. Here we find a significant decline in bulk deposition NO3− during the later part of a 28-year record in southcentral Ontario, Canada. Despite high N retention and substantial inter-annual variability in the long-term record due to periods of drought, we find significant declines in annual NO3− concentrations and export at six out of 11 streams that drain upland-dominated catchments. In contrast, five streams draining primarily wetland-dominated catchments with lower levels of NO3− show no decreasing trend in NO3− concentration or export. The rapid response in stream NO3− to declining atmospheric inputs was observed at sites with historically moderate inputs of DIN (~870 mg m−2 y−1) in bulk deposition. Topographic features such as slope, and related catchment features including wetland cover, appear to influence which catchments will respond positively to declining DIN deposition. These findings force us to revise our original conceptualization of the N saturation status of these catchments.

Assessing the effects of multiple environmental stressors on zooplankton assemblages in Boreal Shield lakes since pre-industrial times

Zooplankton communities in Boreal Shield lakes of south-central Ontario, Canada, have become increasingly exposed to the effects of multiple anthropogenic stressors, such as declines in calcium (Ca) and total phosphorus (TP) concentrations, shifts in predation regimes, and climate warming. The paleolimnological approach provides an effective means of examining cladoceran zooplankton communities prior to the onset of these major environmental stressors and assessing how the increasing impacts of these stressors have affected zooplankton community composition. We examined the chitinized remains of cladocerans from recent and pre-industrial (pre- ~1850s) sediments in 42 oligotrophic lakes from south-central Ontario and compared these assemblages using ANOSIM and SIMPER. Differences in cladoceran assemblages since pre-industrial times were related to five environmental variables that significantly influence cladoceran community composition in surface sediments. These included measured physical (depth), chemical [Ca, pH, sulphate, dissolved organic carbon (DOC)], and biological (fish community biomass) limnological variables. Two changes were recorded in the cladoceran species assemblages of the study lakes. The first was a significant increase in the ratio of pelagic species compared to littoral species over time in most lakes which we cannot attribute to any measured environmental variable with certainty but it likely represents a multiple stressor effect. The second was changes in relative abundances of daphniid cladocerans in several lakes since pre-industrial times, which we attribute to the interactive effects of several environmental stressors, including: differences in Ca availability within our lakes, resulting in decreased abundances of daphniids over time in lakes with lower Ca levels; long-term increases in DOC concentrations, which may provide refuge for daphniids from visual predators; and long-term declines in TP concentrations which may contribute to the dominance of species that are more efficient grazers, such as daphniids. Overall, this study provides field-based evidence that the modern-day cladoceran communities in south-central Ontario lakes are different than they were prior to human settlement in the region, and therefore these paleolimnological data provide a long-term, historical component to contemporary cladoceran datasets and an extended perspective on how multiple environmental stressors have impacted aquatic organisms from Boreal Shield lakes.

Thermal habitat characteristics for warmwater fishes in coastal embayments of Lake Ontario

Along 40 km of the Lake Ontario shoreline near Toronto, Ontario, small coastal embayments (4.38–848 × 10 3 m 2) have been constructed or modified by lake-infilling to restore warmwater fish habitat. We describe how the thermal regimes of these embayments differ from those of small inland lakes, how embayment bathymetry alters the degree of exchange with Lake Ontario, and predict how embayment thermal regimes affect warmwater fish growth. The accumulated growing-degree days, calculated from a 14 °C baseline (∑ GDD 14), of seven South-Central Ontario inland lakes and an embayment disconnected from Lake Ontario ranged from 844 to 1157 GDD. Compared to the inland lakes and disconnected embayment, the coastal embayments connected to Lake Ontario achieved fewer ∑ GDD 14 and had a greater range, 390–1047, reflecting differences in their degree of exchange with and the cooling effect of Lake Ontario. The thermal regime of coastal embayments differs most from inland lakes during May–late-July. During early summer, mean embayment depth explains over 50% of the variability in ∑ GDD 14, with deeper embayments cooling more from lake exchange than shallow embayments. After mid-summer, the cooling embayments are warmed by exchanges with Lake Ontario. This late-summer warming is insufficient to compensate for the cooling effect of the Lake earlier in the summer. Bioenergetic simulations of bluegill, Lepomis macrochirus, growth indicate that most of these embayments are too cool for adequate summer growth of YOY sunfish. Nevertheless, small coastal embayments that are shallow with suitable controls on exchange with the Lake can provide acceptable warmwater fish habitat.

Effect of moisture and temperature variation on DOC release from a peatland: Conflicting results from laboratory, field and historical data analysis

Peatlands are large repositories of atmospheric carbon and concern has been raised over the stability of this carbon store because increasing dissolved organic carbon (DOC) concentrations have been observed in peatland drainage waters. A number of potential causes have been proposed in the literature, and conflicting results among studies conducted at different spatial and temporal scales suggest that the methodological approach may be an important confounding factor. The objective of this study was to determine the influence of moisture and temperature on DOC release from a south-central Ontario peatland during the fall (a major export period) following three commonly used approaches: laboratory microcosms, an intensive field study and analysis of long-term data (1980–2008). The effect of variations in temperature and moisture differed among microcosm, field study and analysis of the long-term record. Water content was important at the microcosm scale as DOC concentration and aromaticity increased with peat water-saturation. Drought caused a decrease in DOC concentration and pH, and an increase in sulphate and base cation concentrations. In contrast, the field study indicated that DOC concentration was strongly associated with temperature, and weakly correlated (negatively) with stream discharge. Average fall DOC concentration (but not export) increased over the 29 year record, and was correlated with fall discharge and precipitation (negative) and summer precipitation and fall stream pH (positive). As no common strong predictor of fall DOC was found at three scales of investigation at a single, well-studied site, it may be unreasonable to expect to identify a universal driver behind the widespread increase in DOC concentration.

MASS MORTALITY ASSOCIATED WITH KOI HERPESVIRUS IN WILD COMMON CARP IN CANADA

Koi herpesvirus (KHV) was identified as being associated with more than one mortality event affecting common carp in Canada. The first was an extensive mortality event that occurred in 2007 in the Kawartha Lakes region, Ontario, affecting Lakes Scugog and Pigeon. Fish had branchial necrosis and hepatic vasculitis with an equivocal interstitial nephritis. Several fish also had branchial columnaris. Subsequent mortality events occurred in 2008 in additional bodies of water in south-central Ontario, such as Lake Katchewanooka and outside of Ontario in Lake Manitoba, Manitoba. Koi herpesvirus was detected in fish submitted for examination from all of these lakes by polymerase chain reaction (PCR), and sequence of the PCR product revealed 100% homology to KHV strains U and I. Real-time PCR analysis of KHV-infected wild carp revealed viral loads ranging from 6.02×10(1) to 2.4×10(6) copies μg(-1) host DNA. This is the first report of KHV in Canada.

Moral distress experienced by health care professionals who provide home-based palliative care

Health care providers regularly encounter situations of moral conflict and distress in their practice. Moral distress may result in unfavorable outcomes for both health care providers and those in their care. The purpose of this study was to examine the experience of moral distress from a broad range of health care occupations that provide home-based palliative care as the initial step of addressing the issue. A critical incident approach was used in qualitative interviews to elicit the experiences on moral distress from 18 health care providers drawn from five home visiting organizations in south central Ontario, Canada. Most participants described at least two critical incidents in their interview generating a total of 47 critical incidents. Analyses of the critical incidents revealed 11 issues that triggered moral distress which clustered into three themes, (a) the role of informal caregivers, b) challenging clinical situations and (c) service delivery issues. The findings suggest that the training and practice environments for health care providers need to be designed to recognize the moral challenges related to day-to-day practice.

Shifting invertebrate zooplanktivores: watershed-level replacement of the native Leptodora by the non-indigenous Bythotrephes in Canadian Shield lakes

The abundance of the native, pelagic macroinvertebrate predator, Leptodora kindtii, is negatively correlated with the abundance of a new invasive competitor, Bythotrephes longimanus, in a small number of Canadian Shield lakes. However, we do not yet know if Bythotrephes is replacing Leptodora on a regional scale. We determined the distribution of both species in 166 lakes in the District of Muskoka, south-central Ontario, Canada—the watershed with the longest history and largest prevalence of Bythotrephes invasions in North America. The frequency of occurrence of Leptodora was substantially reduced (twofold) in the presence of Bythotrephes. We argue that Bythotrephes is responsible for this dramatic reduction in the frequency of occurrence of Leptodora. Lakes in which both species co-occurred could not be distinguished from invaded lakes without Leptodora, suggesting a pattern of species replacement at a watershed level. We believe this is the first account of the widespread replacement of a native, pelagic macroinvertebrate predator by Bythotrephes in North America, and it does not bode well for Leptodora given the rapid, ongoing spread of Bythotrephes.

Assessing pest control using changes in instantaneous rate of population increase: Treated targets and stable fly populations case study

The instantaneous rate of population increase was used to assess the ability of attractive targets coated with permethrin to control stable fly populations on 3 dairy farms in south central Ontario, Canada. Two attractive targets were deployed over 10 wk in 2001 at each of 6 dairy farms. Three farms were outfitted with 2 untreated targets and 3 were outfitted with 2 targets treated with permethrin [Ectiban-impregnated Coroplast (Ectiban: Schering-Plough Canada Inc., Pointe-Claire, Québec, Canada; Coroplast: Great Pacific Enterprises Inc., Granby, Québec, Canada)]. Population growth rate was measured in terms of degree-days above a 10°C developmental threshold (rDD10). The rDD10 at the 3 treated dairy farms were significantly lower than rDD10 at the 3 neighboring untreated dairy farms (mean rDD10: treated=0.0088, untreated=0.013), but not in the previous year when targets were not installed (mean rDD10: treated=0.012, untreated=0.015). This supports a long-term approach to management that lowers population growth rates in those regions where stable fly numbers increase exponentially from spring until winter, by shortening the period of economic impact of this pest.

Fluorescence Analysis of Natural Organic Matter Fractionated by Ultrafiltration: Contrasting Between Urban-Impacted Water, and Radio-Contaminated Water from a Near-Pristine Site

Aqueous natural organic matter (NOM) impacted by two contrasting human impacts was analyzed using by multiresponse fluorescence, decoupled with the resolution routine PARAFAC. The first site is Chalk River, Ontario, Canada, near a pit formerly used to dispose low-level wastes. The second site is the Grand River in Cambridge, south-central Ontario, which is impacted by urban activities and agriculture. Our analysis included raw water, plus fractions from ultrafiltration and solid-phase extraction (SPE). The fluorescence spectra of the NOM, resolved with PARAFAC, showed three common features: humic-like components, at excitation/emission wavelengths 325–350/450–475 nm, fulvic-like components at 325/380–420 nm and protein-like components, at 275/300 nm. Ultrafiltration revealed that most of the NOM comprised fine material below 5,000 Da cut-off (<4% of the total) in the urban-impacted sites and the clean site at Chalk River, but the colloidal fraction (larger than 5,000 Da) was substantially higher in the contaminated water, with ∼18–26% of the total. The protein-like components in the contaminated Chalk River water were affected by ultrafiltration, but less so in the clean Chalk River sample and the urban-impacted waters. SPE preferentially removed the protein-like component in the contaminated Chalk River water (typically 89–95% signal decrease), but had a limited effect on humic- and fulvic-like components elsewhere. In conclusion, multiresponse fluorescence provided new information on the NOM quality from two contrasting sites, aided by ultrafiltration and SPE. These results are consistent with the in situ production of NOM in the Chalk River contaminated site, and natural production at the other sites.

A comparison of pre-industrial and present-day changes in Bosmina and Daphnia size structure from soft-water Ontario lakes

Understanding the long-term controls on cladoceran size structure has important implications for aquatic ecosystems. Although there has been considerable interest in zooplankton size trends for Canadian Shield lakes, data are not available for zooplankton size structure prior to the period of anthropogenic disturbances. Here, we present pre- and post-impact size data for the common pelagic cladocerans Bosmina and Daphnia for 44 well-studied Shield lakes in south-central Ontario (Canada). We show that Daphnia were larger and that the length of Bosmina body appendages (mucrones and antennules) was longer in pre-industrial times than they are today. The reduction in Bosmina appendage length we observed may suggest a reduction in copepod predation pressure since pre-industrial times. Reduced maximum body size in Daphnia is a predicted response to a warming climate in north temperate lakes; however, we suggest that alternate explanations, specifically acidification and subsequent recovery following emission reductions, should also be explored as the primary drivers of Daphnia size changes in this lake set. Overall, our results highlight the importance of pre-impact data for understanding the long-term controls on cladoceran body size from pre-1850 to present.