Southern Ontario Streams Research Articles

Morphological and Habitat Quality of Salmonid Streams and their Relationship with Fish-Based Indices in Aotearoa New Zealand and Ontario (Canada).

Habitat degradation is one of the major reasons for freshwater species decline. Hydrogeomorphological processes (such as sediment transport, bank erosion, and flooding) operate at the catchment scale and determine habitat features in river reaches. However, habitat quality indices and restoration for freshwater fish species are often implemented at small spatial scales of a few hundred metres. The Morphological Quality Index (MQI) considers fluvial processes at larger scales as well as channel forms, human impacts, and historical changes, but few studies have assessed its relevance for ecosystem health. We investigated relationships between the MQI, habitat quality (using the Qualitative Habitat Evaluation Index, QHEI), land cover, and fish metrics (number of fish species, index of biotic integrity (IBI), and trout biomass) in 26 salmonid streams in Aotearoa New Zealand and Southern Ontario, Canada. We found a significant correlation between the MQI and QHEI, and both metrics were correlated with urban and native forest proportion in the catchment. However, we found no relation between the MQI and the proportion of agricultural land in the catchment, while the QHEI was correlated with agricultural land in the riparian zone, highlighting the importance of vegetated riparian buffers in providing fish habitat. Establishing a strong correlation with fish metrics remains challenging. Nevertheless, a modified MQI targeting ecological health could be used as an effective management tool for aquatic conservation.

Improving the representation of stream water sources in surrogate nutrient models with water isotope data

An important part of meeting nutrient reduction goals in the lower Great Lakes basin and assessing the success of different land management strategies is modeling nutrient losses from agricultural land. This study aimed to improve the representation of water source contributions to streamflow in generalized additive models for predicting nutrient fluxes from three headwater agricultural streams in southern Ontario monitored during the Multi-Watershed Nutrient Study (MWNS). The previous development of these models represented baseflow contributions to streamflow using the baseflow proportion derived using an uncalibrated recursive digital filter. Recursive digital filters are commonly used to partition stream discharge into separate components from slower and faster pathways. In this study, we calibrated the recursive digital filter using stream water source information from stable isotopes of oxygen in water. Across sites, optimization of the filter parameters reduced bias in baseflow estimates by as much as 68 %. In most cases, calibrating the filter also improved agreement between filter-derived baseflow and baseflow calculated from isotope and streamflow data: the average Kling-Gupta Efficiencies using default and calibrated parameters were 0.44 and 0.82, respectively. When incorporated into the generalized additive models, the revised baseflow proportion predictor was more often statistically significant, improved model parsimony, and reduced prediction uncertainty. Moreover, this information allowed for a more rigorous interpretation of how different stream water sources influence nutrient losses from the agricultural MWNS watersheds.

Hidden diversity: DNA metabarcoding reveals hyper-diverse benthic invertebrate communities

BackgroundFreshwater ecosystems, such as streams, are facing increasing pressures from agricultural land use and recent literature stresses the importance of robust biomonitoring to detect trends in insect decline globally. Aquatic insects and other macroinvertebrates are often used as indicators of ecological condition in freshwater biomonitoring programs; however, these diverse groups can present challenges to morphological identification and coarse-level taxonomic resolution can mask patterns in community composition. Here, we incorporate molecular identification (DNA metabarcoding) into a stream biomonitoring sampling design to explore the diversity and variability of aquatic macroinvertebrate communities at small spatial scales. While individual stream reaches can be very heterogenous, most community ecology studies focus on larger, landscape-level patterns of community composition. A high degree of community variability at the local scale has important implications for both biomonitoring and ecological research, and the incorporation of DNA metabarcoding into local biodiversity assessments will inform future sampling protocols.ResultsWe sampled twenty streams in southern Ontario, Canada, for aquatic macroinvertebrates across multiple time points and assessed local community variability by comparing field replicates taken ten meters apart within the same stream. Using bulk-tissue DNA metabarcoding, we revealed that aquatic macroinvertebrate communities are highly diverse at small spatial scales with unprecedented levels of local taxonomic turnover. We detected over 1600 Operational Taxonomic Units (OTUs) from 149 families, and a single insect family, the Chironomidae, contained over one third of the total number of OTUs detected in our study. Benthic communities were largely comprised of rare taxa detected only once per stream despite multiple biological replicates (24–94% rare taxa per site). In addition to numerous rare taxa, our species pool estimates indicated that there was a large proportion of taxa that remained undetected by our sampling regime (14–94% per site). Our sites were located across a gradient of agricultural activity, and while we predicted that increased land use would homogenize benthic communities, this was not supported as within-stream dissimilarity was unrelated to land use. Within-stream dissimilarity estimates were consistently high for all levels of taxonomic resolution (invertebrate families, invertebrate OTUs, chironomid OTUs), indicating stream communities are very dissimilar at small spatial scales.

English

Abstract An intensive, long-term study of the life history of O. rusticus was conducted in Fleetwood Creek, a small stream in Southern Ontario, Canada. The reproductive biology as well as molting cycle were investigated and the larval development and morphology was documented in detail for the first time in this important invasive species. Despite recent climate change effects, such as higher maximum temperatures as well as significant short term temperature fluctuations, the overall life cycle does not appear significantly different from previous studies conducted in the 1980s and 1990s but the crayfish activity appeared to be affected by temperature fluctuations associated with climate change. Mating and spawning occurred in the first week of April. The onset of mating and spawning occurred at temperatures of 9-10°C which was somewhat higher than previously reported for this species in this region of Ontario. Abdominal eggs were carried for approximately 7-weeks and larval stages remain attached to their mothers between 12 and 15 days. Free-living young were first observed in early June. Maturity is attained within the first summer, at 19-20 mm carapace length, in at least 30% of the young-of-the-year and most individuals of both sexes are mature at 25 mm carapace length. Monitoring was conducted weekly and daily during molting and spawning periods in spring 2021 and 2022, which makes this study unique with respect to most other life history field studies.

Traffic-related sources may dominate urban water contamination for many organic contaminants

Urban runoff and wastewater/sewage input are majorly responsible for the contamination of urban streams. In streams where wastewater input is not a considerable input, the importance of urban runoff as a mechanism of contaminant transport and delivery from urban surfaces to receiving waters is even more apparent. Extensive studies on two such streams in Southern Ontario, Canada yielded data on the occurrence and levels of multiple contaminant groups (polycyclic aromatic hydrocarbons and quinones, benzotriazoles (BTs), BT ultraviolet stabilizers, organophosphate esters, herbicides) and the influence of factors such as temperature, rainfall characteristics, and land use. Here, we collectively examined the data from these studies to identify any trends and further insights. Using concentration-discharge relationships, we found that the transport dynamics of many particle-bound compounds are strikingly similar to each other, and to that of suspended solids in which they were quantified, suggesting a single, predominant source. Similar urban to rural ratios across compound groups and strong correlations with road density further support the existence of a dominant source and point to traffic as this source, respectively. Although road traffic had not previously been implicated as a major source of many of the investigated compound groups, their uses suggest that traffic-related sources are very plausible. Overall, this work highlights that traffic is a major source of a surprisingly wide array of organic contaminants to urban surfaces, and subsequently to nearby streams.

Characterizing the exposure of streams in southern Ontario to agricultural pesticides

Aquatic communities can be exposed to pesticides transported from land. Characterizing this exposure is key to predicting potential toxic effects. In this study, samples of streamwater from 21 sites were used to characterize pesticide exposure to aquatic communities. Sites were in agricultural areas of southwestern Ontario, Canada and were sampled monthly from 2012 to 2019 from April to November. Samples were analyzed for a suite of hundreds of pesticides and pesticide degradation products and other water quality indicators (e.g., nutrients). Frequently detected pesticides included herbicides (2,4-D; bentazon; MCPP; metolachlor) and neonicotinoid insecticides (NNIs) (clothianidin; thiamethoxam) which were detected in >50% of samples collected between 2015 and 2019. Non-metric multidimensional scaling (NMDS) was used to explore connections between pesticide concentrations and upstream land use and crop type. Detectable concentrations of the NNI clothianidin and many herbicides were related to corn, soybean, and grain/cereal crops while concentrations of the NNI imidacloprid, insecticide flonicamid, and fungicide boscalid were related to greenhouse/nursery land use. Potential toxicity to aquatic communities was assessed by comparing pesticide concentrations to Pesticide Toxicity Index (PTI) values. Few samples exceeded levels where acute (1% of samples) or chronic toxicity (10.5%) would be expected. The diamide insecticide chlorantraniliprole was detected in several streamwater samples at levels that may cause toxicity to aquatic invertebrates, highlighting the need for continued toxicity research into this pesticide class. The number of pesticides detected was positively correlated with nutrient and total suspended solids levels, underscoring the multiple stressors aquatic communities are exposed to in these habitats.

Periphytic algal biomass as a bioindicator of phosphorus concentrations in agricultural headwater streams of southern Ontario

Algal blooms in Lake Erie have worsened in recent decades and are driven by diffuse export of phosphorus (P) from a large stream network that drains predominately agricultural land. Given the diffuse nature of nonpoint source pollution, best management practices (BMPs) must target areas where P levels are high. This requires long-term watershed-wide monitoring programs that do not currently exist in many jurisdictions. Instead of conventional nutrient analyses that can be costly and time-consuming, we propose the use of periphyton biomass as a bioindicator of trophic status in low-order streams, where agricultural runoff first enters watercourses. We carried out 2-week in-stream bioassays to measure periphytic algal biomass (CHLperi) in 19 low-order streams in southern Ontario across an agricultural gradient (8 % to 89 %). CHLperi was significantly related to total P (TP) concentration (r2 = 0.46; p = 0.0015) but was not significantly related to soluble reactive P (SRP). A relationship between TP and turbidity (r2 = 0.52; p = 0.0007) is consistent with previous observations of increasing SRP uptake in streams draining agriculturally-dominated landscapes. Stream temperature (°C) was correlated with the proportion of agricultural land (R = 0.55; p = 0.019) and may reflect the warming effects of the sun in unshaded agricultural streams. This method involving substrate rods (Peristix) is cost-effective, requires very little training, and yielded data that were significantly related to TP concentrations in agricultural streams. We recommend that environmental agencies and landowners use this bioassay to identify areas for implementing BMPs to reduce P export from the Lake Erie watershed.

Nutrient enrichment effects are conditional on upstream nutrient concentrations: Implications for bioassessment in multi-use catchments

Human impacts on stream ecosystems are expected to intensify with population growth and climate change. Decisive information on how stream communities respond to cumulative human impacts is therefore integral for protecting streams draining multi-use catchments. To determine cumulative influences of nutrient enrichment and assess more nuanced approaches for the evaluation of human impacts, we present results from one factorial and two gradient assessment designs applied to benthic algae and macroinvertebrate data from 14 mid-order streams in southern Ontario, Canada with pre-existing human impacts (i.e., sewage effluent and agriculture). We found that among stream variability in ecological indicators measured downstream of sewage effluent outfalls confounded our generalized factorial assessment and provided inconclusive information on a known human impact. Despite our gradient assessment also not having strong statistical support, accounting for the extent of nutrient enrichment associated with differences in sewage effluent and agricultural inputs revealed that larger longitudinal changes in stream communities were associated with increased nutrient enrichment. However, re-weighting our nutrient enrichment gradient based on upstream nutrient concentrations to account for nonlinearities in the response of stream communities to nutrient enrichment produced more robust assessment results that were consistent with predicted effects of nutrients on stream ecosystems. Thus, while our factorial assessment suggests that the communities are resistant to nutrients from cumulative human impacts, our targeted gradient assessment demonstrates that the effects of nutrient enrichment are highly conditional on upstream ecosystem conditions. Future assessments may need to go beyond traditional approaches (i.e., impact presence/absence) and more explicitly consider the environmental stressors and their associated complexities related to the impact under investigation.

Synchronous Biodegradability and Production of Dissolved Organic Matter in Two Streams of Varying Land Use.

In aquatic ecosystems, dissolved organic matter (DOM) composition is driven by land use, microbial activity, and seasonal variation in hydrology and water temperature, and, in turn, its microbial bioavailability is expected to vary due to differences in its composition. It is commonly assumed that DOM of terrestrial origin is resistant to microbial activity because it is composed of more complex aromatic compounds. However, the effect of DOM sources on the microbial reworking and degradation of the DOM pool remains debated. We performed laboratory incubation experiments to examine how temporal changes in DOM composition influence its microbial biodegradability in two contrasting streams (agricultural and forested) in southern Ontario, Canada. Despite a more allochthonous-like DOM signature in the forest stream and a more autochthonous-like DOM signature in the agriculture stream, we found that biodegradation and production of DOC were the same in both streams and synchronous throughout the sampling period. However, the initial DOM composition impacted how the DOM pool changed upon degradation. During the incubations, both autochthonous-like and allochthonous-like fractions of the DOM pool increased. We also found that a greater change in DOM composition during the incubations induced higher degradation of carbon. Finally, temporal variation in DOC biodegradation and production over time or across streams was not related to DOM composition, although there was a significant relationship between BDOC and nutrient concentrations in the agriculture stream. This observation potentially challenges the notion that DOM origin predicts its bioavailability and suggests that broad environmental factors shape DOC consumption and production in aquatic ecosystems. More research is needed to better understand the drivers of microbial biodegradability in streams, as this ultimately determines the fate of DOM in aquatic ecosystems.

Assessment of stream macroinvertebrate communities with eDNA is not congruent with tissue-based metabarcoding.

Freshwater biomonitoring programmes routinely sample aquatic macroinvertebrates. These samples are time-consuming to collect, as well as challenging and costly to identify reliably genus or species. Environmental DNA (eDNA) metabarcoding has emerged as a surrogate to traditional collection techniques and has been used in whole-community approaches across several taxa and ecosystems. However, the usefulness of eDNA-based detection of freshwater macroinvertebrates has not been extensively explored. Few studies have directly compared bulk sample and eDNA metabarcoding at a local scale to assess how effective each method is at characterizing aquatic macroinvertebrate communities. Here, we collected both eDNA and kicknet samples at the same sample transect locations across nine different streams in southern Ontario, Canada. We observed minimal overlap in community composition between these paired samples. Bulk tissue metabarcoding resulted in a greater proportion of sequences belonging to metazoan taxa (over 99%) than eDNA (12%) and had higher OTU richness for macroinvertebrate taxa. We suggest that degenerate primers are not effective for eDNA metabarcoding due to the high degree of nontarget amplification and subsequently low yield of target DNA. While both bulk sample and eDNA metabarcoding had the power to detect differences between stream communities, eDNA did not represent local communities. Bulk tissue metabarcoding thus provides a more accurate representation of local stream macroinvertebrate communities and is the preferred method if smaller-scale spatial resolution is an important factor in data analyses.

Metabolic regimes of three mid-order streams in southern Ontario, Canada exposed to contrasting sources of nutrients

Light, temperature, and discharge control stream metabolism, but the response of gross primary production (GPP) and ecosystem respiration (ER) to seasonal variation in these physical drivers may differ in accordance with the types of human activities present in the catchment. Our study examined three mid-order streams in southern Ontario, Canada that differed in anthropogenic nutrient sources (i.e., sewage treatment plant effluent, sewage lagoon effluent, and agriculture), but had comparable light, temperature, and discharge regimes. For each stream, GPP and ER were estimated daily from June through November. Comparisons of paired daily metabolic rates revealed pairwise differences among all streams, with streams receiving sewage effluent having greater rates and variability of GPP and ER than the stream draining agricultural land. The two sewage influenced streams differed only in ER. Temporal patterns of GPP and ER were correlated for all streams throughout the study period and were most affected by seasonal variation in temperature, whereby effluent receiving streams responded more rapidly to increases in temperature. Our findings suggest that managers may need to balance effects of human activities with regional environmental constraints on stream metabolism to maintain and enhance the ecological condition and services of stream ecosystems.

Glacially-streamlined hard and soft beds of the paleo- Ontario ice stream in Southern Ontario and New York state

An extensive tract of glacially-streamlined terrain across a large part of Southern Ontario, Canada, is recognized as the footprint of the paleo-Ontario Ice Stream (OIS) within the easternmost Great Lakes sector of the last Laurentide Ice Sheet. The upstream part is a drumlinized and megagrooved ‘hard bed’ underlain by Cambro-Ordovician carbonates and sandstones. Subglacial plucking of jointed limestone on the lateral margins of drumlinized escarpment interfluves and rock drumlins generated a large flux of coarse debris within the ice base, recorded by sporadic spreads of hummocky rubble moraine. Downstream, the hard bed passes underneath a streamlined ‘soft’ bed of till-cored (‘drift’) drumlins and megaridges of the classic Peterborough and New York State drumlin fields. The boundary between the two bed types is a~10km wide ‘mixed bed’ of isolated drift drumlins resting on drumlinized rock suggesting a common erosional origin. Spatial variation in the geomorphology of ~2500 drift drumlins, indicates that megaridges are clones resulting from the erosion and dissection of larger parent drumlins. A large moraine system may mark the final collapse and melt of the ice stream, accompanying abrupt flow switching of its margin.

Impacts of a tertiary treated municipal wastewater effluent on the carbon and nitrogen stable isotope signatures of two darter species (Etheostoma blennioides and E. caeruleum) in a small receiving environment

This study contrasted the influence of tertiary treated municipal wastewater effluent (MWWE) exposure on the abundance, food selection (stomach contents), and carbon (δ13C) and nitrogen (δ15N) stable isotope signatures of Rainbow Darter (Etheostoma caeruleum) and Greenside Darter (Etheostoma blennioides) in a small receiving stream in southern Ontario, Canada. Despite tertiary treatment resulting in relatively high effluent quality, there is continued concern for environmental degradation downstream of the effluent outfall because of the relatively small size of the receiving environment and recent studies that have indicated changes occurring in relative fish abundance and stable isotope signatures. In July and August of 2009 fish and benthic invertebrate communities were examined along with analysis of δ13C and δ15N of the most common species to determine the effects of effluent exposure on the food web. Rainbow Darter increased in abundance and their δ15N values were enriched immediately downstream of the effluent outfall throughout the summer (July and August). In contrast, while δ15N of Greenside Darter followed a similar pattern in July, they were not enriched in August. The benthic community was changed immediately downstream of the outfall and the δ15N of invertebrates was enriched, similar to that observed in Rainbow Darter. Stomach contents of the two darter species diverged the most in the summer possibly explaining some of the changes in δ13C and δ15N among sites. It is possible that Greenside Darter fed on less enriched food downstream of the outfall, or fed outside of the effluent plume during the summer. Rainbow Darter may be able to exploit the changes in habitat and prey composition, resulting in differences in relative abundance of darters immediately downstream of the effluent outfall.

The influence of watershed land use cover on stream fish diversity and size-at-age of a generalist fish

Changes in land use have manifold effects on stream ecosystems. Consequently, the degradation of watersheds can cause extreme responses if the resilience of the stream is exceeded, triggering changes in fish communities and a reorganization of the ecosystem. Fish community surveys are frequently used to evaluate the impact of anthropogenic pressures on freshwater streams. Dynamic indices such as individual growth are also interesting because they integrate the effects of environmental conditions through time, providing an assessment in the long term. In this study we have investigated the ecological implications of watershed land use cover on fish diversity and growth of the generalist species Umbra limi (central mudminnow) in six streams in Southern Ontario (Canada). In detail, the growth of U. limi has been explored using a Dynamic Energy Budget (DEB) model, which pursues a mechanistic explanation of the bioenergetics of an individual under different environmental conditions. Given the mechanistic approach, the outcomes of the DEB model can provide a solid foundation for extrapolating the conclusions of this study to a broader spatial scale. The results of this study reveal that the proportion of modified land use of the watershed (agricultural and urban land) can reach a tipping point beyond which the functioning of the stream abruptly changes. Consequently, land use cover may be used as a precautionary indicator for watershed management. The results also demonstrate that U. limi could be used as a sentinel species to identify potential impacts on fish diversity and size-at-age as a cost-effective indicator for stream monitoring programs.

Effects of golf course facilities on stream function in anthropogenically impacted streams

Abstract We sampled six streams in southern Ontario, Canada near 18-hole golf courses to determine how they affect stream function in the context of land use, land cover, and human activities in the upstream watershed. Water quality, optical dissolved organic matter (DOM), and benthic characteristics (e.g., leaf decomposition, ergosterol content, and N2 and O2 flux) were followed up and downstream of the golf courses over a three-week period in summer. Comparisons of univariate paired samples revealed lower dissolved organic carbon concentrations and higher total dissolved phosphorus concentrations, with relative losses in humic-like and gains in protein-like DOM downstream of golf courses. Total dissolved nitrogen and bacterial production were similar up and downstream of golf courses. Multivariate analysis indicated that streams did not significantly differ up and downstream of golf courses for landscape, water quality, and DOM groups, but significantly differed among streams. A significant multivariate benthic group interaction between stream and sampling location indicated, however, that the magnitude and the direction of change exerted by the golf course differed across streams. Streams did not change, lose, or recover benthic functionality after passing through a golf course. This response depended on the percent anthropogenic land use in the watershed's riparian zone and was not simply a uniform environmental response to golf course facilities. These findings show promise that in moderately human impacted streams golf course facilities could be managed to improve stream function. In severely human impacted streams, however, landscape management strategies that use golf courses as green spaces will unlikely improve stream function.

Optimal Effort Intensity in Backpack Electrofishing Surveys

We evaluated the effect of backpack electrofishing effort intensity on the precision of estimates of fish density in a southern Ontario stream. Single-pass electrofishing was conducted on 30 sites at three electrofishing effort intensities (5, 10 and 15 s/m2). We found that an effort of 5 s/m2 yielded an average catch that was 78% of the 15-s/m2 effort. An asymptotic model effectively described the catch–effort relationship for most fish taxa in the stream (i.e., Rainbow Trout Oncorhynchus mykiss, Brown Trout Salmo trutta, sculpin Cottus sp., dace Rhinichthys sp., and darter Etheostoma sp.). Using the catchability parameters of this model, we evaluated the trade-off between sampling many sites at low intensity or fewer sites at higher intensity. The survey design that maximizes precision of fish-density estimates depends on the average time spent traveling between sites and the average area of sites. For southern Ontario streams, where sample sites were approximately 300 m2 and travel time between sites was 75 min, the optimum electrofishing effort intensity was approximately 5 s/m2. The applicability of these results to other systems was demonstrated by showing how this optimum intensity was affected by differences in catchability rates of fish and travel distances. These findings will be used to standardize single pass electrofishing catches in nonshield areas of Ontario, and the approach may prove useful in other areas where this fishing technique is effective. Received January 5, 2012; accepted December 7, 2012

Nutrient recycling by fish in streams along a gradient of agricultural land use

Nutrient recycling is an essential ecosystem process provided by animals. In many aquatic systems, fish have been identified as important in ecosystem nutrient recycling; however, this importance can vary widely between systems. The factors controlling intersystem variation in animal-mediated nutrient cycling have rarely been examined and as such it remains unclear what impact human landscape changes will have upon these processes. Here we examined rates of nutrient recycling for temperate stream fish assemblages along a gradient of agricultural land use (proportion cropland in the watershed: 1–59%). We quantified nutrient excretion rates of both ammonium–N (NH4+–N) and phosphate (as soluble reactive phosphate: SRP) for fish assemblages at eight streams in southern Ontario, Canada with species-specific excretion measurements and quantitative assemblage sampling. For both nutrients, total assemblage excretion exhibited a strong positive relationship with riparian cropland. The distance required for fish assemblages to turn over ambient nutrient pools was shorter for cropland systems, indicating that the relative importance of excreted nutrients was higher in these systems. Based on measured uptake rates of NH4+–N in two streams (one higher cropland and one low cropland) and on modeled uptake rates for all streams, the proportion of ecosystem demand that can be satisfied by excretion is generally higher in the more agricultural streams. These patterns appear to be driven largely by disproportionate increases in fish assemblage biomass with increasing stream nutrient concentrations.

Sources and seasonal patterns of dissolved organic matter (DOM) in the hyporheic zone

The hyporheic zone is a region underneath streambeds that integrates surface and groundwater. Although its location is central to biogeochemical linkages between the riparian zone, dissolved nutrients, and benthic biota, the seasonal quality and likely sources of dissolved organic matter (DOM) in the hyporheic zone are not well understood. To investigate DOM characteristics in the hyporheic zone, water from the surface and subsurface (at depths 20, 60, and 100 cm below the streambed) was sampled every 4 weeks from 2007 to 2008 in a third-order stream in southern Ontario. Using UV spectroscopy, measures of spectral slopes, aromaticity, and A 254/A 365 ratios (molecular weight) were obtained. Temporal changes in these measures were consistent with watershed processes such as shedding of leaf litter in the fall, and photochemical and biofilm influence in the spring and summer. The fluorescence index (a measure of relative DOM source) suggested that at the surface and in the downwelling zone, DOM microbial sources increased with depth in the sediment, regardless of the season. Excitation–emission matrices (EEMs) showed seasonally distinct, protein-like DOM components of bacterial origin that were stronger in the fall. Leachates from specific allochthonous DOM sources—leaf litter from Betula papyrifera (white birch) and Thuja occidentalis (white cedar)—and an autochthonous source, biofilm, were isolated and incubated with unfiltered surface water. EEMs from these leachates indicated that these sources could indeed help explain observed patterns of DOM in surface and subsurface waters. These results suggest that although DOM sources were relatively constant, biogeochemical processing within the hyporheic zone resulted a DOM pool that was temporally dynamic and altered the nature of organic matter transported downstream into lakes and rivers.

Characterizing seasonal changes in physicochemistry and bacterial community composition in hyporheic sediments

The hyporheic zone of stream ecosystems is a critical habitat for microbial communities. However, the factors influencing hyporheic bacterial communities along spatial and seasonal gradients remain poorly understood. We sought to characterize patterns in bacterial community composition among the sediments of a small stream in southern Ontario, Canada. We used sampling cores to collect monthly hyporheic water and sediment microbial communities in 2006 and 2007. We described bacterial communities terminal-restriction fragment length polymorphism (TRFLP) and tested for spatial and seasonal relationships with physicochemical parameters using multivariate statistics. Overall, the hyporheic zone appears to be a DOC, oxygen, and nitrogen sink. Microbial communities were distinct from those at the streambed surface and from soil collected in the adjacent watershed. In the sediments, microbial communities were distinct between the fall, spring, and summer seasons, and bacterial communities were more diverse at streambed surface and near-surface sites compared with deeper sites. Moreover, bacterial communities were similar between consecutive fall seasons despite shifting throughout the year, suggesting recurring community assemblages associated with season and location in the hyporheic zone. Using canonical correspondence analysis, seasonal patterns in microbial community composition and environmental parameters were correlated in the following way: temperature was related to summer communities; DOC (likely from biofilm and allochthonous inputs) influenced most fall communities; and nitrogen associated strongly with winter and spring communities. Our results also suggest that labile DOC entering the hyporheic zone occurred in concert with shifts in the bacterial community. Generally, seasonal patterns in hyporheic physicochemistry and microbial biodiversity remain largely unexplored. Therefore, we highlight the importance of seasonal and spatial resolution when assessing surface- and groundwater interactions in stream ecosystems.

Relative Importance of Hydrological and Sediment-Transport Characteristics Affecting Effective Discharge of Small Urban Streams in Southern Ontario

Effective discharge (Qe) is an important design variable used in stream restoration design. Qe of a stream reach is affected by both the hydrological characteristics of the upstream watershed and the sediment-transport characteristics of the stream reach. This study identified the most critical hydrological and sediment-transport characteristics affecting Qe of small urban streams in southern Ontario. Continuous simulation of hypothetical watersheds was conducted to generate hourly streamflow data. Qe and other related variables of interest were determined based on simulated streamflow series and randomly generated sediment-transport rating curve parameters. Global sensitivity analysis using samples of input and output data indicated that Qe is highly sensitive to, first, the exponent of the sediment rating curve (β); second, the watershed storage coefficient reflecting the storage characteristics of a watershed; and third, the time of concentration of a watershed. Further, this study showed that only when β values are within a specific range, Qe and the discharge corresponding to a particular return period are close to each other.