Seasonal nutrient export dynamics in a mixed land use subwatershed of the Grand River,Ontario, Canada

Algal blooms in the Great Lakes are a concern due to excess nutrient loading from non-point sources; however, there is uncertainty over the relative contributions of various non-point sources under different types of land use in rural watersheds, particularly over annual time scales. Four nested subwatersheds in Southern Ontario, Canada (one natural woodlot, two agricultural and one mixed agricultural and urban) were monitored over one year to identify peak periods (‘hot moments’) and areas (‘hot spots’) of nutrient (dissolved reactive phosphorus, DRP; total phosphorus, TP; and nitrate, NO₃⁻) export and discharge. Annual nutrient export was small at the natural site (0.001 kg DRP ha⁻¹; 0.004 kg TP ha⁻¹; 0.04 kg NO₃^—N ha⁻¹) compared to the agricultural and mixed-use sites (0.10–0.15 kg DRP ha⁻¹; 0.70–0.94 kg TP ha⁻¹; 9.15–11.55 kg NO₃^—N ha⁻¹). Temporal patterns in P concentrations were similar throughout the sites, where spring was the dominant season for P export, irrespective of land use. Within the Hopewell Creek watershed, P and N hot spots existed that were consistently hot spots across all events with the location of these hot spots driven by local land use patterns, where there was elevated P export from a dairy-dominated sub-watershed and elevated N export from both of the two agricultural sub-watersheds. These estimates of seasonal- and event-based nutrient loads and discharge across nested sub-watersheds contribute to the growing body of evidence demonstrating the importance of identifying critical areas and periods in which to emphasize management efforts.     

Towards the development of an ecosystem model for the Hamilton Harbour,Ontario, Canada

Our main objective is to undertake a synthesis of the Hamilton Harbour ecosystem and to elucidate the relative importance of the underlying trophic relationships using the mass-balance modeling software Ecopath with Ecosim (EwE). We present a conceptual model comprising all the essential food web components of the system, which was parameterized using both local and literature-based information. Among the trophic relationships considered by the Hamilton Harbour ecosystem model, our analysis highlights the central role of round goby demonstrating a wide range of effects on a number of functional groups at both higher and lower trophic levels. Several ecosystem attributes (e.g., primary production/biomass, biomass/total throughput, system omnivory index, amount of recycled throughput, and Finn's cycling index) provide evidence that the Hamilton Harbour is an immature and fairly simple system with linear food chain structure, although the internal redundancy and the system overhead estimates indicate that the Harbour possesses substantial reserves to overcome external perturbations. The aggregation of the ecosystem into discrete trophic levels suggests that most of the trophic flows are concentrated within the first two trophic levels, while flows were practically insignificant at the higher trophic levels of the food web. The fairly low ecotrophic efficiency values for both carnivorous and herbivorous cladocerans are indicative of low zooplanktivory levels in the system. Finally, our study identifies knowledge gaps and critical next steps to rigorously assess the credibility of the model and to consolidate its use for predictive purposes.     

Volume Visualization of Temperature in Hamilton Harbour,Lake Ontario

The inner structures of lakes can be revealed using volume visualization algorithms since lakes are three-dimensional objects that are explored by taking samples at various stations and at different depths. These algorithms did not exist 20 years ago, they could only be run on supercomputers 10 years ago, on workstations 3 years ago, and now they can be run on personal computers. Using computer graphics it is now possible to combine data, their three-dimensional location, and lake topography to create images of water quality patterns which supersede conventional surface, two-dimensional, graphics. Through solid modeling, temperature data collected on 28 May 1990 and 8 August 1990 in Hamilton Harbour, Lake Ontario, are mapped into voxels and projected onto two-dimensional screens. Various three-dimensional representations of temperature data are displayed including water masses with temperatures of less than 12°C, 13 to 14°C, 16°C to 17°C, and greater than 23°C. The calculation of the 3D representations allows the computation of volumetric properties, e.g., masses, since each voxel has water quality values associated with it and these values can be summed or elaborated numerically as needs arise. For example the harbor has a volume of 254 × 10⁶ m³, and the water mass on 28 May 1990 at 12–13°C had a complex three-dimensional shape with a volume of 61 × 10⁶ m³. A third benefit of visualization is that the data can be viewed interactively from different viewpoints thus increasing the interaction between scientist and the data. These methods should also be able to be used in other limnological applications such as visualization of sediments, algal blooms, and other biological and chemical data.     

Organochlorine Contaminant Levels in Waterbird Species from Hamilton Harbour,Lake Ontario: an IJC Area of Concern

The levels of organochlorine (OC) contaminants in eggs and tissues of waterbird species nesting in Hamilton Harbour, Ontario, an International Joint Commission Area of Concern, were monitored between 1981 and 1992. PCBs, DDE, and mirex were present at the highest concentrations of the 29 organochlorines and one trace metal measured. Most contaminants in the various species tested showed a declining temporal pattern during that period. Double-crested cormorant eggs generally had higher concentrations of contaminants than those in herring gull eggs which in turn were higher than those in eggs of black-crowned night-herons, Caspian terns and common terns. The levels of contaminants in the eggs reflect the dietary preferences of the species with the fish-eating birds containing consistently higher accumulations of contaminants when compared to the herbivorous Canada goose for which the levels were consistently much lower for all compounds. The concentrations of contaminants detected are among some of the highest in the Great Lakes but when compared to other sites on Lake Ontario, the levels in Hamilton Harbour are generally equal or lower. Elevated levels of contaminants such as PCBs, mirex, and DDE were also detected in liver and muscle tissues of migrant waterfowl species from the harbor. Despite habitat degradation and continued presence of contaminants, the harbor supports a large number and wide variety of waterbird species. Except for black-crowned night-herons, the nesting populations of colonial waterbirds have increased between 21 and 1061 % since the last survey in 1987.     

Eutrophication risk assessment in Hamilton Harbour: System analysis and evaluation of nutrient loading scenarios

Environmental modeling has been an indispensable tool of the Hamilton Harbour restoration efforts, where a variety of data-oriented and process-based models have been used for linking management actions with potential ecosystem responses. In this study, our objective is to develop a biogeochemical model that can effectively describe the interplay among the different ecological mechanisms modulating the eutrophication problems in Hamilton Harbour, Ontario, Canada. First, we provide the rationale for the model structure adopted, the simplifications included, and the formulations used during the development phase of the model. We then present the results of a calibration exercise and examine the ability of the model to sufficiently reproduce the average observed patterns along with the major cause–effect relationships underlying the Harbour water quality conditions. The present modeling study also undertakes an estimation of the critical nutrient loads in the Harbour based on acceptable probabilities of compliance with different water quality criteria (e.g., chlorophyll a, total phosphorus). Our model suggests that the water quality goals for TP (17 μg L⁻¹) and chlorophyll a concentrations (5–10 μg L⁻¹) will likely be met, if the Hamilton Harbour RAP phosphorus loading target at the level of 142 kg day⁻¹ is achieved. We also provide evidence that the anticipated structural shifts of the zooplankton community will determine the restoration rate as well as the stability of the new trophic state in the Harbour.     

Phthalate Esters in Sediments Near a Sewage Treatment Plant Outflow in Hamilton Harbour,Ontario: SFE Extraction and Environmental Distribution

Esters of phthalic acid are ubiquitous environmental contaminants as a result of their use as plasticizers and as constituents in many other commercial products. Although the acute toxicity of phthalates is low, recent concerns over their potential to disrupt the gonadal development of vertebrates has prompted interest in determining the distribution of these compounds in the environment. However, trace analysis of phthalates in environmental samples has been hampered by their presence as ubiquitous laboratory contaminants. In this study, the problem of high background contamination was addressed by developing an analytical method using supercritical fluid extraction (SFE), which was used to extract phthalates from sediment samples collected near the outflow of a sewage treatment plant (STP) in Hamilton Harbour at the western end of Lake Ontario. GC-MS-SIM analysis of sediment samples indicated that di(2-ethylhexyl) phthalate (DEHP)was present at very high concentrations; ranging from a mean of 29.7 μg/g dry weight at a site near the STP outflow to a mean of 6.5 μg/g dry weight at a site 300 m away. Di-n-butyl phthalate (DBP), and benzylbutyl phthalate (BBP) were judged to be present in some sediment samples but at concentrations below the Method Detection Limits (< 0.3 μg/g). Di-isononyl phthalate (DINP) and diethyl phthalate (DEP) were not detected in any of the sediment samples. This study indicates that SFE can be an efficient extraction method for phthalates in sediments, which avoids the extensive use of glassware and organic solvents that may contaminate environmental samples. In addition, STP effluents are sources of phthalates in the aquatic environment; in particular, DEHP.     

Long-term and seasonal nitrate trends illustrate potential prevention of large cyanobacterial biomass by sediment oxidation in Hamilton Harbour,Lake Ontario

Several studies have shown that large, experimental additions of nitrate (NO₃) to eutrophic systems can mitigate large populations of nuisance cyanobacteria and that high NO₃ concentrations can oxidize anoxic sediments. These studies are consistent with observations from numerous aquatic systems across a broad trophic range showing development of reduced surficial sediments precedes the formation of large cyanobacteria populations. We use 50+ years of data to explore whether high NO₃ concentrations may have been instrumental both in the absence of large populations of cyanobacteria in eutrophic Hamilton Harbour, Lake Ontario in the 1970s when total phosphorus (TP) and total nitrogen (TN) concentrations were high, and in delaying large populations until August and September in recent decades despite much lower TP and TN. Our results indicate that large cyanobacteria population events do not occur at the central station in July-September when epilimnetic NO₃ > 2.2 mg N L^?1. The results further suggest that remedial improvements to wastewater treatment plant oxidation capacity may have been inadvertently responsible for high NO₃ concentrations > 2.2 mg N L^?1 and thus for mitigating large cyanobacteria populations. This also implies that large cyanobacteria populations may form earlier in the summer if NO₃ concentrations are lowered.     

Influence of the land use pattern on the concentrations and fluxes of priority pollutants in urban stormwater

This paper presents the results of the concentrations (μg/L) and fluxes (g/ha) of priority substances in stormwater from three watersheds with different land use patterns (namely, residential, urban dense, high urban density). Samples were collected at the outlet of these watersheds. Thirteen chemical groups were investigated corresponding to 88 individual substances before treatment. Results showed that stormwater discharges contained 55 substances, among them some metals, organotins, PAHs, PCBs, alkylphenols, pesticides, phthalates, cholorophenols and volatile organic compounds. Therefore, stormwater was highly contaminated. However, this contamination was often comparable from site to site, since no significant difference of the pollutant load was observed between the land use patterns.     

加拿大雨水管理保障措施与典型城市雨水排放费制度研究

为保证我国城市雨水管理工作高效健康地进行和推动雨水排放费制度在我国施行,通过对加拿大雨水管理保障措施和雨水排放费实施进展进行调研,得出了加拿大采用的组织保障、法律保障、技术保障、经费保障、激励机制保障和公众参与保障等六个方面的雨水管理保障措施,以及目前加拿大所采用的统一费率制度、分类费率制度、不透水面积统一费率制度、住宅等效单元费率制度、径流系数与开发强度费率制度和独立住宅等效单元费率制度等六种主要雨水收费制度类型。对米西索加等典型城市雨水排放费的收费方式以及不同用地性质和建筑类型的收费方法进行了分析,并分析了不同类型的雨水排放费的补贴方法。在对加拿大典型城市雨水排放费和补贴制度实行效果分析的基础上,结合我国雨水管理工作实际情况,建议我国加强雨水排放费与补贴制度的计算方法与制度设计的研究工作,做好宣传与公众教育工作,并在部分海绵城市建设试点城市开展雨水排放费与补贴制度的试点探索工作。     

Application of a numerical model for circulation,temperature and pollutant distribution in Hamilton Harbour

The restoration of Hamilton Harbour, from an environmental standpoint, is a current concern for the agencies involved with remediation efforts in the harbour. Estimates of circulation and mixing are needed to assess the fate and transport of water quality constituents in the harbour. A three-dimensional hydrodynamic modeling system (ELCOM) is used to study the circulation and thermal structure in the harbour. The model results were compared with profiles of temperature at several moorings and currents and water levels in the harbour. The model showed considerable skill in reproducing the thermal structure, surface currents and water levels. Mean summer circulation in the harbour showed two counter-rotating gyres occupying the harbour. The model produced harbour-lake exchange characteristics are in agreement with previous studies. Simulations using passive tracers qualitatively agreed with chemical tracer studies conducted near a sewage treatment plant outfall. The accuracy of these simulations suggests that the model is capable of describing flow and transport of material required for detailed water quality simulations.     

Impact of land use land cover change on a sand dune ecosystem in Northwest Beach,Point Pelee National Park,Canada

This paper analyses Land use land cover (LULC) change in the Northwest (NW) Beach, Point Pelee National Park (PPNP) to understand its effect on sediment transport dynamics for sand dune restoration. Due to development of infrastructure, beginning in the 1960s, sand dunes were completely removed from parts of NW beach. Spatial-temporal changes for LULC were assessed using aerial photos and images for 1959, 1977, 2006 and 2015. Based on the Ecological Land Classification System (Southern Ontario), object based image analysis and feature extraction methods were used to generate classified maps. The photos were the highest quality available in the Parks Canada, PPNP archive. LULC classes included Shoreline Vegetation, Deciduous Thicket, Sand Barren and Dune Type, and Infrastructure. Aerial photographs of LULC change for 1959–1977 and South Western Ontario Orthoimagery Project (SWOOP) images for 2006–2015 were analysed. A large gap exists between 1977 and 2006 as no images were available for that time period. Results indicated a significant increase in the Deciduous Thicket in 2015, acting as a barrier for sand movement to the parking lots. Decrease in the Shoreline Vegetation Type along with an increase in the lake level indicate a decrease in beach width and supply area for sediment transport. Based on the analysis, active management through the removal of cottonwood trees, and policy changes are recommended for dune restoration in Point Pelee. Accuracy assessment of the 2015 classification using an error matrix resulted in an overall accuracy for the LULC classification of 88%.     

Analyzing the influence of changes in land use and management practices on the lag time of peak flows for tropical watersheds of Ethiopia

Changes in peak flow response time governed by rainfall and physical configurations of watersheds have been the topic of many studies, but other factors are also important. We aimed to analyze the dynamics in the lag time (T_L) of peak flow for a tropical watershed (Kecha) and its sub-watersheds (Dokmit, Zenjero Maderia, and Wotit Minch) in Ethiopia, as influenced by land-use changes from 1982 to 2017 and the implementation of soil and water conservation (SWC) practices since 2011. Layered maps of land use, soil type, and SWC practices were used to determine the curve number, and the Natural Resource Conservation Service hydrologic model was used to estimate T_L. We compared the estimated values against measured median values of T_L for 30 rainfall–runoff events. The estimated T_L of 1982, 2005, and 2017 varied from 9 to 19 min, 8 to 18 min, and 10 to 22 min, respectively, in the Dokmit, Zenjero Maderia, and Wotit Minch sub-watersheds. The smallest (8 min) and greatest (22 min) values of T_L were observed during 2005 and 2017, respectively. These results are likely attributable to the increased amount of cultivated area at the expense of bushland and forest in 2005 as compared to 1982, and the implementation of SWC practices in 2011–2017. Dokmit had the lowest T_L values of the three sub-watersheds, most likely because of its greater coverage of grazing and cultivated lands and degraded Nitic Luvisol. The variation in T_L values among the sub-watersheds was related to changes in both land use and SWC practices but also to the presence of degraded areas inherited from past human activities. Overall, such spatiotemporal flow response time analysis can provide useful information for the proper design of sustainable development strategies for particular niches in tropical regions of Ethiopia and elsewhere.     

Dissolved and particulate organic carbon concentrations in stream water and relationships with land use in multiple-use watersheds of the Han River (Korea)

This study examines temporal variation in dissolved organic carbon (DOC) and particulate organic carbon (POC) concentrations in streams in the Han River watershed, Korea. On days without significant antecedent rain, DOC and POC concentrations ranged from 0.87 to 3.23 mg C/L and 0.24 to 2.92 mg C/L, respectively. Following rain events, both DOC and POC concentrations were higher. Soil and compost had δ¹³C values similar to stream δ¹³C-DOC and δ¹³C-POC. These results demonstrate the importance of studies using tracer approaches and the value of research on sources of organic carbon transported in streams in multiple use monsoonal watersheds.     

Spatial Analysis of Seasonal and Annual Temperature and Precipitation Normals in Southern Ontario,Canada

This study presents some univariate and multivariate low-pass filtering methodologies (ordinary kriging, ordinary cokriging, modified residual kriging, inverse distance weighting) to spatially model seasonal temperature and precipitation normals in an environment where climate patterns are variably modified by regional water bodies and physiography. Cross-validation and maps of modeled climate patterns are used as a criteria to assess particular climate realizations. The results of the exercise show how an agro-climatologist might use these methods to assess spatial representations of the modeled phenomena, the relevance of covariates, and the shortcomings and strengths of different techniques to characterize lake-physiography-climate interactions on a seasonal basis. The methods are also useful for evaluating station networks for capturing important Great Lakes climate patterns.     

Influence of Topography,Peak Demand,and Topology on Energy Use Patterns in four Small to Medium-Sized Systems in Ontario,Canada

The aim of this paper is to characterize the relationship between system characteristics of topography, peak demand, and topology and the energy dynamics of four small to medium-sized water distribution systems in Ontario, Canada. First, previously developed energy indicators were used to evaluate and compare the energy efficiency, energy lost to friction, energy lost to leakage, and the surplus energy of the four systems. The systems had a high energy efficiency ranging from 75 to 94% (leak-free) and 58–70% (leaky). Friction losses comprised 3–22% of the total energy input to the systems. Energy lost to leakage comprised 23–26% of total energy input to the systems. Second, hypothesis testing was used to identify statistically significant correlations between system characteristics and energy use patterns in the system. No statistically significant correlation was found between the standard deviation of node elevation and energy use in the four systems. Hydraulic redundancy and energy use did not have a statistically significant correlation. This is because during a ‘typical’ day of service, the most efficient flow paths are concentrated through the trunk mains rather than in the smaller distribution mains that account for most of the looping and hydraulic redundancy of a system. Correlations between peak hour factor and the energy indicators were near the cut-off p-value level (p < 0.05) so it was not clear if the correlations are statistically significant. Despite this, moderate to high Spearman rank correlation coefficients (?0.6 to +0.8) were calculated for the leaky and leak-free systems.     

Dynamics of wet‐season turbidity in relation to precipitation,discharge, and land cover in three urbanizing watersheds,Oregon

Frequent intense precipitation events can mobilize and carry sediment and pollutants into rivers, degrading water quality. However, how seasonal rainfall and land cover affect the complex relationship between discharge and turbidity in urban watersheds is still under investigation. Using hourly discharge, rainfall, and turbidity data collected from six stations in three adjacent watersheds between 2008 and 2017, we examined the temporal variability of the discharge–turbidity relationship along an urban–rural gradient. We quantified hysteresis between normalized discharge and turbidity by a hysteresis index and classified hysteresis loops during 377 storm events in early, mid, and late wet season. Hysteresis loop index and direction varied by site land cover type and season. Turbidity values peaked quicker in the watersheds with higher degrees of urban development than in a less urbanized watershed. The positive relation between discharge and turbidity was highest in two downstream stations in the mid wet season, whereas it was highest in two upstream stations in the early wet season. Correlation and regression analysis showed that maximum turbidity was best explained by discharge range, and the sensitivity of turbidity to discharge change was higher in the larger downstream watershed than in the small upstream watersheds. A flashiness index was negatively associated with the slope of turbidity versus discharge, suggesting that turbidity is difficult to predict solely on the basis of discharge in flashy urban streams. This paper contributes to a deeper understanding of the spatial and temporal variation of discharge–concentration relationship in urbanizing watersheds, which can help water managers increase the resiliency of water‐related ecosystem services to impacts of climate change.     

Vegetation,river management and land use in the dutch rhine floodplains

The floodplains of the lower Rhine are situated in a densely populated area of the Netherlands. Although they are used intensively the floodplains still fulfill important ecological functions. The lower Rhine is the downstream sedimentation zone of the River Rhine and its floodplains are characterized by river-transported vascular flora originating from southern and eastern Europe. Using multivariate methods data from previously published work and field data on grasslands and former river beds have been analysed to determine trends in ecological changes. The consequence of continued sedimentation and decreased erosion is an increased drying out of the floodplains. Excavation and recultivation of formerly excavated land does not reverse the losses in flora and vegetation. Statistically there is a negative relationship between the characteristic flora and recultivated land. The natural transversal river gradient also disappears, together with its characteristic ecological diversity. Aquatic environments in the floodplains have been changed completely since regulation work started in the 19th century. Most former river beds have disappeared due to silting up. Data on short-term vegetation succession confirm the long term analysis of map data.     

Modelling the influence of seiche-events on phosphorous-loading dynamics in three Lake Ontario coastal wetlands

Coastal Wetlands (CWs) provide critical ecosystem services that maintain biogeochemical processes and habitats in the coastal zone of the Great Lakes. When nutrient-laden surface waters flow into CWs from their watersheds, internal physical, chemical, and biological processes can alter the final nutrient loadings to the lake. However, CWs can periodically be inundated with lake water from seiche events, and little is known about the impacts of seiches on nutrient processing and loadings from CWs. To evaluate the influence of lake seiches on CW phosphorous-loading dynamics, we built a multi group structural equation model (SEM) using climatic and wave data, and interannual (2009–2018) estimated sediment and phosphorous loadings from three CWs on the north-shore of central Lake Ontario (Rouge Marsh, Duffin’s Marsh, and Carruthers Marsh). Wind speeds, lake levels, and an increased peak period of wave spectra were significant explanatory variables of seiche events (p-value < 0.001). We identified that seiche events caused significant sediment resuspension (p-value < 0.001) in CWs, which contributed to a significant increase of phosphorous loading to the coastal zone of Lake Ontario (p-value < 0.001). Our results indicate that lake-seiche events can influence CW phosphorous-loadings to Lake Ontario, and should be considered when modelling water quality in the nearshore zone.