Hydrochemical evaluation of surface water quality and pollution source apportionment in the Luan River basin, China

In the context of rapid economic growth in China, hydrochemical characteristics of stream water quality are being influenced by a variety of natural and anthropogenic inputs. We determined 10 hydrochemical parameters of the surface water at 29 monitoring sites in the Luan River basin of northern China during 2007-2009. Water quality hydrochemistry was evaluated using fuzzy comprehensive analysis based on the National Surface Water Environmental Quality Standards of China. Our results showed that 14 sites were classified as 'meeting standard (MS)' while the other 15 sites were classified 'non-meeting standard (NS)'. According to principal component analysis, four potential pollution sources were identified that explained 80.6% of the total variance among these MS sites, and three potential pollution sources that explained 78.3% of the total variance among these NS sites. Furthermore, multi-linear regression of the absolute principal component scores was used to estimate contributions from identified pollution sources. Most water pollution variables were influenced primarily by municipal sewage and non-point pollution in MS sites. In NS sites, chemical industry wastewater pollution dominated. Pollution in the main stream was more serious than that in the small tributaries. Our findings provide useful information for developing better pollution control strategies for the Luan River.     

Nitrogen loading on groundwater from the discharge of on-site domestic wastewater effluent into different subsoils in Ireland.

The performance of six separate percolation areas has been intensively monitored to ascertain the attenuation effects of the unsaturated subsoil with respect to on-site wastewater effluent. Septic tank effluent on three sites and secondary treated effluent on the other three sites was discharged into subsoils of varying percolation values. Samples of the percolating effluent were taken using suction lysimeters installed to nominal depths of 0.3, 0.6 and 1.0 m below the invert of the percolation trenches. The results clearly showed that the development of a biomat across the percolation areas receiving secondary treated effluent was muted on these sites compared to the sites receiving septic tank effluent. Significant differences were found between the sites receiving septic tank and secondary treated effluent in terms of the potential nitrogen loading to groundwater. The average nitrogen loading after 1.0 m depth of unsaturated subsoil per capita equated to 5.5, 3.3 and 3.2 gTotal-N/d for the sites receiving secondary treated effluent compared to 4.2, 1.7 and 0.3 gTotal-N/d for the sites receiving septic tank effluent. The noticeably higher nitrogen loading on one of the septic tank sites corresponded to the effluent percolating through highly permeable subsoil that counteracted any significant denitrification.     

Modelling Optimum Sites for Locating Reservoirs in Tropical Environments

A team of specialists normally carries out the task of locating reservoir sites based on general guidelines, technical knowledge and experience. Consequently, the procedures used are not based on a defined criteria in addition to being time consuming and expensive. Furthermore, the failure of a number of dams and the increase in environmental awareness will require the inclusion ofenvironmental and social factors in the processes besides economy. In this study, a criteria was developed and implementedto locate potential sites for reservoirs in the Langkawi Island, Malaysia based on all relevant factors including: topography, geology, hydrology, land use/cover types and settlements. A satellite imagery and digitized geological and elevation maps were utilized to generate the necessary data layers for the developed criteria. Then IDRISI, a raster based GIS was employed to implement the criteria using the Boolean and the Weighted Linear Combination (WLC) methods. The Boolean method produced five reservoir sites with the 70 Mld water capacity, two of which corresponded well with a field-based study. Whilst theproposed site with the 90 Mld water capacity did not correspond with the field based study. The WLC method produced five sites with the 70 Mld water capacity, three of which matched those of the field study. Whilst for the 90 Mld water requirement, two potential sites were produced and both have matched those of thefield study. The outcomes indicated that the developed criteria were sensitive to physical, environmental and economical settingson the Langkawi Island. Furthermore, GIS and remote sensing can be useful tools for generating, manipulating and handling relevant data layers and ultimately providing management optionsfor decision makers.     

Robust Decision-Making Technique for Strategic Environment Assessment with Deficient Information

This study developed a framework for an evaluative decision–making system that compensates for information deficiencies by considering the sensitivity of weight factor criteria. The developed decision–making system was applied to the strategic environmental assessment (SEA) for dam planning in South Korea. The SEA investigation included ten potential dam sites (four sites in the Han River, four in the Nakdong River, and two in the Geum River), performing an evaluative comparison of dam construction effects using environmental adequacy criteria and ranking the ten potential sites appropriately. Six different deficient information filling methods were applied: the normal and uniform distribution generations, Maximax, Maximin, Hurwicz, and the equal likelihood criterion. Results indicated sites GM2, HN3, ND4, and GM2 demonstrated the highest environmental adequacies across the combined effected rivers, the Han River, the Nakdong River, and the Geum Rivers, respectively. The probabilistic distribution generations, Hurwicz and the equal likelihood criterion methods produced similar priority scores and rankings based on different river conditions; however, the Maximax and Maximin methods calculated different priority scores and rankings, indicating users should be careful when applying the latter two methods for use in a decision support system (DSS) with deficient information. In future works, it will be necessary to apply other deficient data conditions or SEA examples to perform a more robust verification of the proposed framework.     

Application of multi-criteria decision-making methods to identification of soil moisture monitoring sites in an urban catchment in South Australia

When choosing sites for monitoring of soil moisture for hydrological purposes, a suitable process that considers the factors influencing soil moisture level should be followed. In this study, two multi-criteria decision-making (MCDM) methods, the multi-influencing factor (MIF) method and the analytical hierarchy process (AHP) method, were used to identify the optimal soil moisture monitoring (SMM) sites in the Dry Creek Catchment in South Australia. The most representative areas for nine SMM sites were obtained using the MIF method, considering the factors of rainfall, soil type, land use, catchment slope, elevation, and upslope accumulated area (UAA). The AHP method was used to select the optimal sites using the site-specific criteria. 30.3% of the catchment area in the Australian Water Resources Assessment Landscape (AWRA-L) Grid_DC2 can be considered acceptable as representative area with the MIF method. Four potential sites were evaluated for each AWRA-L grid using the relative weights of the site-specific criteria with the AHP method. The Grid_DC2 required two sites that had the highest overall weight chosen with the AHP analysis. The procedure was repeated for the remaining four AWRA-L grids within the study area to select the required SMM sites.     

Spatial patterns in dry weight of nearshore Lake Michigan prey fishes

The ability for individuals to adapt to local food sources likely allows for regional persistence of aquatic populations. In the Laurentian Great Lakes, invasive species and changing physical conditions have vastly altered local and regional food webs, leading to the potential for variation in energy flow up to large predators. To assess the potential that prey fish condition varies spatially, we examined patterns in proportion dry weight of prey fishes collected from Lake Michigan nearshore areas (<16 m) in 2010 and 2011. Absolute pairwise differences in dry weight of fishes were as high as 9% between some of our sampling sites, but sites exhibiting relatively high or low values were patchily spread across the lake. The range of proportion dry weight values observed in our study do encompass previously-reported mean values; however, the values reported in our study are slightly lower than those previously reported for Lake Michigan. In contrast to previous studies, our analyses do not suggest that variation in prey fish condition exhibits a consistent spatial pattern around nearshore Lake Michigan, and high within-site variation of prey fish condition prevents strong conclusions about specific sites providing generally more (or less) energy-rich prey to predators.     

Bioassessment of Benthic Macroinvertebrates in Wetland Habitats of Lake Saint-Pierre (St. Lawrence River)

We evaluated the potential of vegetation and sediment habitats in wetlands of the St. Lawrence River for developing a macroinvertebrate bioassessment program with reference conditions. During September 2004, we collected macroinvertebrates in emergent vegetation and sediment in both fluvial sites (reference) and tributary-plume sites (impacted) in waters of the north and south shores of Lake Saint-Pierre (St. Lawrence River). In each habitat, we compared taxa richness, abundance, and community structure of macroinvertebrates between reference and impacted sites, and used multivariate models to relate macroinvertebrate community to environmental conditions. Each habitat was suitable for discriminating reference fluvial sites from impacted tributary-plume sites based on macroinvertebrate communities. In emergent vegetation, macroinvertebrates were dominated by epibenthic fauna such as crustaceans (Gammaridae, Asellidae) and molluscs (Valvatidae) at fluvial sites, and insect larvae (Chironomidae, Caenidae) at tributary-plume sites. In sediment, macroinvertebrates comprised a greater proportion of endobenthic fauna such as Oligochaeta and Sphaeridae. Crustaceans and molluscs were still dominant at fluvial sites and Oligocheata and Chironomidae at tributary-plume sites. No strong difference was depicted in macroinvertebrate composition between north and south shore water masses. Environmental variables explained a higher proportion of variance in macroinvertebrate community composition in emergent vegetation than in sediment (68% versus 44%). Macroinvertebrate composition in sediment was more related to metal contamination, whereas macroinvertebrate composition in emergent vegetation was related primarily to vegetation type and water quality. Relevance of the study for bioassessment of macroinvertebrates in the St. Lawrence River using the reference condition approach is discussed.     

Benefits to 0+ fishes of connecting man‐made waterbodies to the lower River Trent,England

Floodplain waterbodies are reputed to enhance recruitment of riverine fish populations via provision of spawning and nursery habitat, refuge from floods, and increased availability of planktonic food resources compared with main river channels. Notwithstanding, there have been few parallel studies of fishes and their food resources at both main river and floodplain sites. Thus, this study investigated the 0+ fishes, zooplankton and phytoplankton (chlorophyll a) at four main river and four (man‐made) floodplain sites on the lower River Trent, England, between May 1999 and October 2004 inclusive. All sites shared the same key fish species, and there were no consistent differences in the densities, growth or condition of 0+ fishes from main river and floodplain sites. Similarly, all sites shared the same key zooplankton taxa. However, zooplankton densities, notably of large‐bodied cladocerans, and chlorophyll a concentrations, were significantly higher at floodplain sites than at main river sites. Thus, connection of man‐made waterbodies has the potential to enhance recruitment of riverine fish populations via provision of important spawning and nursery habitat, and superior feeding opportunities for 0+ fishes compared with main river channels. Copyright © 2007 John Wiley & Sons, Ltd.     

An evaluation of fish spawning on degraded and remnant reefs in Saginaw Bay,Lake Huron

Saginaw Bay is a shallow, nutrient-rich embayment in Lake Huron that historically had a complex network of natural rocky reefs. These reef habitats were used as spawning and nursery areas for a variety of fish species, but decades of land-use related sedimentation caused many of these reefs to be degraded. Our study objectives were to analyze abiotic and biotic conditions on degraded and remnant reefs and describe spawning patterns of walleye (Sander vitreus) and lake whitefish (Coregonus clupeaformis) at these sites to determine the potential for increased utilization following reef restoration. During fall and spring 2014–2016, we evaluated water quality and egg predation at four sites with varying levels of reef degradation. Further, we documented reproductive utilization through capture of spawning adults and quantification of egg deposition. Walleye and lake whitefish utilized multiple sites for reproduction; however, densities of spawners and deposited eggs were low, suggesting that they were not utilizing study sites as major spawning locations. Walleye and lake whitefish eggs were eaten by multiple fish species, including larger fish such as channel catfish (Ictalurus punctatus). Dissolved oxygen levels were adequate (i.e., >7 mg 0₂ L^?1) during spring walleye egg incubation; however, bottom dissolved oxygen levels became very low at some sites during winter ice cover, coinciding with lake whitefish egg incubation. As restoration of rocky reefs proceeds in the Bay, evidence of remnant reef spawning fish bodes well for long-term success, though potential limiting factors such as low dissolved oxygen, sedimentation, and egg predation require continued monitoring.     

Seasonal and spatial variation in algal growth potential and growth-limiting nutrients in a shallow endorheic lake: Lake Pátzcuaro (Mexico)

The present research focused on the functional role of the phytoplankton of an economically important endorheic tropical lake from the perspective of algal growth bioassays. The algal growth potential of the lake water was compared for littoral and pelagic sites during the wet and dry seasons. Algal growth potentials at open waters reached minimum and maximum values following the seasonal alternation of dilution (by rain) and concentration (by evaporation) respectively. Conversely, at southern littoral stations high algal growth responses related to the availability of nutrients from point contamination sites. There was no such effect at nearby offshore sites or elsewhere in the lake which suggests filtration and competitive interactions for these nutrients between phytoplankton and littoral macrophytes. Nitrogen and phosphorus both acted consistently as limiting nutrients at open waters by colimitation. Nitrogen to phosphorus ratios seemed to approach equilibrium where limitation easily shifted to one element or the other temporally and spatially.     

Two decades since first invasion: Revisiting round goby impacts on nearshore aquatic communities in the Upper St. Lawrence River

Time Since Invasion (TSI) at invaded sites is an important factor that can moderate invasive species abundances and their ecological impacts on resident communities, and yet it remains rarely addressed by invasion studies. We revisit the ecological impacts of round goby invasion in the Upper St. Lawrence River (Canada) on macroinvertebrate and fish communities, by taking into consideration the effects of TSI since initial invasion 20 years ago. Our objectives were to: 1) test the effect of TSI and invasion status on round goby abundance, and 2) investigate the effects of TSI, invasion status, and round goby abundance on macroinvertebrate and fish communities. Round goby abundance displayed a strong positive relationship with TSI. Environmental conditions, especially substrate and water conductivity were found to reduce round goby TSI and characterize uninvaded sites and >12 years TSI sites. However, we detected first potential signals of a reduction in round goby abundance at sites with TSI of 17–19 years compared with sites having 13–16 years TSI which had similar environmental conditions. Nonetheless, round gobies continued to have enduring impacts on total macroinvertebrate diversity, even at sites with TSI of 17–19 years, likely as a result of ongoing predation. This observation was supported by a negative association of round goby TSI on the abundance of dominant macroinvertebrate taxa at sampling sites in the Upper St Lawrence River, as well as dietary stomach content data. The fish community was less sensitive to round goby TSI than macroinvertebrate communities.     

Energy stores and mercury concentrations in a common minnow (spottail shiner,Notropis hudsonius) associated with a peaking hydroelectric dam

Peaking hydroelectric facilities release water from dams to match energy production with demand, often on a daily cycle. These fluctuating flows downstream can exert several potential stressors on organisms that may inhibit their growth, indirectly causing higher contaminant concentrations through reduced growth dilution. We collected spottail shiner (Notropis hudsonius) at two sites upstream and two sites downstream of a peaking hydroelectric dam in east‐central Saskatchewan, Canada, and compared their body condition, triglyceride concentrations, and mercury concentrations. Condition decline was observed in one of two downstream sites from August to September, and the lowest triglyceride concentrations were consistently found downstream of the dam where hydropeaking had the most perceptible effects on the shoreline. Mercury concentrations were significantly greater at both downstream sites relative to upstream. Despite these results, inconsistencies in response parameters across sites and time limited our ability to isolate the effects of hydropeaking as a causative agent and suggest indirect effects such as shifts in algal and macroinvertebrate communities may be responsible for our observations. These results suggest that hydroelectric power generation may indirectly increase mercury concentrations in downstream fish, but more research will be required to determine the specific mechanisms by which this occurs. The results and data also provide useful insights into the physiology of wild spottail shiner populations, which can help to inform the development of these fish as a North American sentinel species.     

Linking the thermal regimes of streams in the Great Lakes Basin,Ontario, to landscape and climate variables

The lack of geographically broad‐scale temperature data has limited our ability to classify stream temperatures and assess the processes affecting them. Continuous data (1 July 2005–30 June 2006) from 90 sites throughout the Great Lakes Basin (GLB) were used to classify and model the thermal regimes of streams in Ontario. Existing and newly developed temperature metrics were used to characterize the data for each site. The 90 sites clustered into three thermal regimes based on maximum weekly maximum temperature (°C) and spring rate of change (°C · d^?1). The centroids of regime 1, 2 and 3 had temperatures of 26.4, 28.4, 23.5°C and warming rates of 0.20, 0.12 and 0.10°C · d^?1, respectively. There was a regional pattern in the thermal regimes; most sites in the north were regime 1 and most sites in the south were regime 2 but neither regime was limited to those areas. Regime 3 sites were found throughout the study area. Discriminant function analysis indicated that per cent riparian forest, mean annual air temperature, per cent surface water and groundwater discharge potential influenced the thermal regimes at the sites, and demonstrated how variables at three spatial scales influence stream temperatures. This study provides a framework for thermal assessments elsewhere and demonstrates how anthropogenic activities such as riparian deforestation, groundwater withdrawal, stream regulation and climate change will all affect the main drivers of thermal regimes in streams. Copyright © 2009 John Wiley & Sons, Ltd.     

Fish living near two wastewater treatment plants have unaltered thermal tolerance but show changes in organ and tissue traits

Municipal wastewater treatment plants (WWTPs) are a significant source of anthropogenic pollutants and are a serious environmental stressor in Laurentian Great Lakes ecosystems. In this study, we examined whether three freshwater fish species (bluegill sunfish Lepomis macrochirus, green sunfish Lepomis cyanellus, and round goby Neogobius melanostomus) collected near two wastewater effluent outflows in Lake Ontario showed altered measures of somatic investment and thermal tolerance. Fish of all three species collected near the WWTPs were larger with 50–60% heavier body masses compared to those collected at reference sites. Green sunfish had higher body condition and increased haematocrit at wastewater-contaminated sites, and both round goby and bluegill sunfish had larger livers (controlling for body mass) at wastewater-contaminated sites. Thermal tolerance (critical thermal maximum, CT_max) differed between species (green sunfish > bluegill sunfish > round goby), but was similar in fish collected at wastewater-contaminated sites compared to cleaner reference sites. Wastewater-contaminated sites had poorer water quality, higher nutrient loadings, and higher concentrations of anthropogenic contaminants (measured via polar organic chemical integrative samplers, POCIS) than reference sites. Our results suggest that fish in the wild may have some capacity to cope with WWTP effluent and avoid any potential impairments in thermal tolerance. Our findings also suggest that treated wastewater is changing water quality locally in Great Lakes watersheds, and that many fish species may be able to access extra nutrients provided by such effluent outflows. However, if outflow areas become preferred foraging areas this will inadvertently increase exposure to anthropogenic stressors and pollutants.     

Crustacean zooplankton available for larval walleyes in a Lake Michigan embayment

Adequate densities of zooplankton prey are critical for growth and survival of larvae of many fish species. Little information exists on the density of zooplankton in Great Lakes inshore areas during early spring, when larvae of important fishes rely on zooplankton. Reduced age-0 walleye recruitment and the absence of data on zooplankton availability for larval walleyes in northern Green Bay, Lake Michigan, led us to assess zooplankton densities during this critical spring period. We conducted biweekly vertical plankton tows in 2014–2016 near reefs and river plumes used by spawning walleyes for periods when larval walleyes were expected to be relying on zooplankton prey. Densities of zooplankton were well below literature values identified for good growth and survival of larval walleyes, averaging 1.5 individuals L⁻¹ for all taxa and 0.12 individuals L⁻¹ for large-bodied taxa across all sites and sampling dates. Various factors could contribute to the low density of zooplankton observed. We found low but significantly higher densities of cyclopoid copepods, nauplii, Bosmina, and total zooplankton at river mouth sites compared to open water sites. These results suggest that food availability for larval walleye in our study area was severely limiting which is consistent with the paucity of strong year classes observed since 2000. We suspect northern Green Bay has limited potential for producing strong year classes of walleyes under such conditions. Fishery managers working in unproductive waters should consider assessing the zooplankton community during critical periods to identify potential bottlenecks to reproductive success and larval fish survival.     

Potential Impacts of Nesting Double-crested Cormorants on Great Blue Herons and Black-crowned Night-herons in the U.S. Great Lakes Region

With recovery of double-crested cormorants (Phalacrocorax auritus) in the Great Lakes region, their numbers have increased significantly leading to concern about potential impacts on other species. Cormorants are thought to affect co-occurring colonial waterbirds by usurping limited habitat and destroying vegetation used as nest sites by these species. This paper summarizes initial results from a study to assess potential impacts of double-crested cormorants on great blue herons (Ardea herodius) and black-crowned night-herons (Nycticorax nycticorax) in the Great Lakes. The study examined population trends, interspecific interactions, and cormorant impacts on vegetation. Despite a steady increase in breeding cormorants in the U.S. Great Lakes over the past two decades, population trends of great blue herons and black-crowned night-herons do not indicate cormorants have negatively influenced breeding distribution or productivity of either species at a regional scale. Cormorants have caused total or partial loss of forest cover at a number of islands in the U.S. Great Lakes and these initial data suggest soil chemistry at cormorant colony sites will affect normal plant growth and survival. However, site use data and field observations indicate double-crested cormorant presence has not caused black-crowned nightheron or great blue heron declines or abandonment except under special circumstances. Although preliminary, these results suggest cormorant control policy should not be justified by assumption of potential impacts on other waterbird species without careful documentation.     

Vegetation development and restoration potential of drained reservoirs following dam removal in Wisconsin

Dam removal is potentially a powerful tool for river and riparian restoration. However, long‐term studies on the fate of former reservoirs do not exist, limiting assessment of the utility of dam removal as a means of riparian restoration. We took advantage of the decades‐long legacy of dam removals in Wisconsin to determine human uses of drained reservoirs and to evaluate vegetation establishment and species replacement at these sites. More than half of the 30 dam removal sites in southern Wisconsin over the past 47 years were used as commercial areas, parks and agricultural land, and active riparian restoration occurred on only two sites. For the 13 sites that were allowed to revegetate on their own, plants established in the first growing season and cover was very high at all sites in 2001. Species diversity and frequency (defined as percentage of sampled quadrats where a species is present) of trees were positively correlated with time since removal. No relationship existed between site age and frequencies of other growth forms, nor were there significant relationships between site age and the number or frequency of introduced species. However, mean frequency of introduced species was 75% per site and several sites were dominated by the introduced grass Phalaris arundinacea. Frequency of P. arundinacea was negatively correlated with number of native forbs, and lowest species diversity occurred on sites dominated by P. arundinacea. Ordination analyses revealed substantial site‐to‐site variation in vegetation that was weakly associated with gradients of site location, age, area, and soil phosphorus. Thus, temporal vegetation dynamics following dam removal were site‐specific. Rapid revegetation demonstrates the potential of these sites for riparian restoration. However, if dam removal is used as a means of restoring native riparian communities, then approaches must be tailored to individual sites and will need to focus on techniques to minimize establishment of aggressive invading species. Copyright © 2006 John Wiley & Sons, Ltd.     

Evaluation and Quality Control of Environmental Analytical Data from the Niagara River Using Multiple Chemometric Methods

The use of artificial neural networks (ANN), principal component analysis (PCA) and universal process modelling (UPM) to identify the source of water samples based on the variation of chemical data from these samples has been investigated. Chromatographic data sets generated from three locations on the Niagara River were used in this research. The concentrations of target organic compounds were chromatographically determined and used as classification features. Chromatographic variation between three sampling sites was determined over a one-year period and included 149 separate samples. Variation within sampling sites was evaluated over a seven-year period. ANN and UPM techniques correctly identified the source of 95% of the water samples based on minor differences in the chromatographic data. PCA and UPM gave direct visualization of differences within chemical data sets. PCA and UPM were also found to be useful tools for the detection of chromatographic outliers from within sampling sites. The correlation between target compounds and surrogates are discussed. The results show that these methods are useful for the determination of the variation of target organic compounds over time both within and between sampling sites. The potential of these systems for monitoring analytical quality control based on entire data sets is also presented.     

Comparative Simulation of GIS-Based Rainwater Management Solutions

Rain Water Harvesting (RWH) as a solution for sustainable rainwater management is the focus of this research. To locate the potential sites for RWH, multi-criteria analysis following analytical hierarchy process using land-use/landcover, slope, drainage density, and runoff depth has been performed. By introducing continuous soil moisture accounting procedure in the globally used SCS-CN method, discrepancies in computed runoff values have been assessed. To appraise the usefulness of revised Soil Moisture Accounting (SMA) -enhanced SCS-CN models, a number of modifications have been compared. The models’ performance has been evaluated using R², Root Mean Square Error (RMSE), Nash Sutcliffe Efficiency (NSE), Percent BIAS (PBIAS) statistical indicators, and Rank Grading System (RGS) and the best has been selected to calculate the runoff depth for RWH potential zones. The resultant suitability map classifies Gurriala catchment into three suitability zones. 33.8% of the total area has been found as least suitable, comprised mainly of forest, residential land, and water bodies, while 46.8% and 19.4% of the area is recognized as moderately suitable and high suitable respectively. Selected suitable sites have been further classified into suitability zones for enhanced RWH structures and runoff volume contributed by each RWH structure has been computed. The total runoff potential of the area is 22.47 MCM that is enough to fulfill the water demands of suburban areas as a most inexpensive solution.

     

Robust Parameter Set Selection for a Hydrodynamic Model Based on Multi-Site Calibration Using Multi-Objective Optimization and Minimax Regret Approach

A robust parameter set (ROPS) selection method for a hydrodynamic flow model was proposed based on the multi-site calibration by combining multi-objective optimization with the minimax regret approach (MRA). The multi-site calibration was defined by a multi-objective optimization problem for which individual objective functions were used to measure errors at each site. In the hydrodynamic model, coefficients of power functions that show the changing relationships between Manning’s roughness and discharge in each sub-reach were optimized by minimizing the residuals of multiple sites. Different combinations of weights were assigned to sites in the application of an aggregation approach to solve the multi-objective function, and the corresponding Pareto optimal parameter sets were assumed as the ROPS candidates. All performance measures to individual Pareto optimal parameter sets were calculated and the ROPS was determined using MRA. The set which has the lowest maximum regret obtained by averaging the results from calibration and validation was determined as the only ROPS. It was found that the estimated variable roughness and the corresponding computed water levels varied considerably depending on the weights assigned to sites. Using the proposed method, the task to assign proper weights on multiple sites can be easily achieved for multi-site calibration problems. This study provides a multi-criteria decision making method to choose a ROPS that has the lowest potential regret among various alternatives for hydrologic and hydraulic models.