105 research outputs found
A neighborhood statistics model for predicting stream pathogen indicator levels
Because elevated levels of water-borne Escherichia coli in streams are a leading cause of water quality impairments in the U.S., water-quality managers need tools for predicting aqueous E. coli levels. Presently, E. coli levels may be predicted using complex mechanistic models that have a high degree of unchecked uncertainty or simpler statistical models. To assess spatio-temporal patterns of instream E. coli levels, herein we measured E. coli, a pathogen indicator, at 16 sites (at four different times) within the Squaw Creek watershed, Iowa, and subsequently, the Markov Random Field model was exploited to develop a neighborhood statistics model for predicting instream E. coli levels. Two observed covariates, local water temperature (degrees Celsius) and mean cross-sectional depth (meters), were used as inputs to the model. Predictions of E. coli levels in the water column were compared with independent observational data collected from 16 in-stream locations. The results revealed that spatio-temporal averages of predicted and observed E. coli levels were extremely close. Approximately 66 % of individual predicted E. coli concentrations were within a factor of 2 of the observed values. In only one event, the difference between prediction and observation was beyond one order of magnitude. The mean of all predicted values at 16 locations was approximately 1 % higher than the mean of the observed values. The approach presented here will be useful while assessing instream contaminations such as pathogen/pathogen indicator levels at the watershed scale
Recommended from our members
Do rearing salmonids predictably occupy physical microhabitat?
Microhabitat suitability models are commonly used to estimate salmonid habitat abundance and quality with unknown accuracy or reliability. When tested, the metrics used to evaluate these models are often limited by the methods used to develop them. More generalized bioverification strategies that transcend methodology are therefore needed in ecohydraulics. This study further developed and applied such a generalized bioverification framework to four approximately 1-m-resolution rearing salmonid microhabitat suitability models. Water depth and velocity habitat suitability criteria (HSC) functions were developed for two size classes of rearing Oncorhynchus tshawytscha and O. mykiss using snorkel survey data collected over three years at seven sites along the lower Yuba River in California, USA. An expert-based cover HSC function was modified from previous studies. HSC functions were applied to previously validated, approximately 1-m-resolution two-dimensional hydrodynamic models and cover maps of the river. Mann–Whitney U tests confirmed that suitability values were significantly higher at utilized locations compared to randomly generated, non-utilized locations for all four models. Bootstrapped forage ratios demonstrated that microhabitat suitability models accurately predicted both preferred and avoided habitat beyond the 95% confidence level. This generalized bioverification framework is recommended for evaluating and comparing the accuracy and reliability of ecohydraulic models used in habitat management worldwide
Recommended from our members
How alternative urban stream channel designs influence ecohydraulic conditions.
Streams draining urban catchments ubiquitously undergo negative physical and ecosystem changes, recognized to be primarily driven by frequent stormwater runoff input. The common management intervention is rehabilitation of channel morphology. Despite engineering design intentions, ecohydraulic benefits of urban channel rehabilitation are largely unknown and likely limited. This investigation uses an ecohydraulic modeling approach to investigate the performance of alternative channel design configurations intended to restore key ecosystem functioning in urban streams. Channel reconfiguration design scenarios, specified to emulate the range of channel topographic complexity often used in rehabilitation are compared against a reference 'natural' scenario using ecologically relevant hydraulic metrics. The results showed that the ecohydraulic conditions were incremental improved with the addition of natural oscillations to an increasing number of individual topographic variables in a degraded channel. Results showed that reconfiguration reduced excessive frequency of bed mobility, loss of habitat and hydraulic diversity particularly as more topographic variables were added. However, the results also showed that none of the design scenarios returned the ecohydraulics to their reference conditions. This indicate that channel-based restoration can offer some potential changes to hydraulic habitat conditions but are unlikely to completely mitigate the effects of hydrologic change. We suggest that while reach-scale channel modification may be beneficial to restore urban stream, addressing altered hydrology is critical to fully recover natural ecosystem processes
Recommended from our members
Particle size characterization of historic sediment deposition from a closed estuarine lagoon, Central California
Recent studies of estuarine sediment deposits have focused on grain size spectra as a tool to better understand depositional processes, in particular those associated with tidal inlet and basin dynamics. The key to accurate interpretation of lithostratigraphic sequences is establishing clear connections between morphodynamic changes and the resulting shifts in sediment texture. Here, we report on coupled analysis of shallow sediment profiles from a closed estuarine lagoon in concert with recent changes in lagoon morphology reconstructed from historic sources, with a specific emphasis on the ability of suite statistics to provide meaningful insights into changes in sediment transport agency. We found that a major reorganization in lagoon morphology, dating to the 1940s, was associated with a shift in sediment deposition patterns. The restricted inlet was associated with deposition of sediments that were finer, less negatively skewed, and less leptokurtic in distribution than sediments deposited while the lagoon had a more open structure. These shifts are associated with a change in transport process from fluvial (through-flow) to closed basin (trapping). We also found other chemostratigraphic changes accompanying this shift in sediment texture, reflecting changes in organic matter source, wetland species composition, and an increase in sediment organic content, as presumably coarse, well-ventilated floodplain sediments tend to result in mineralization rather than sequestration of organic matter. In conclusion, we found that grain size analysis, in concert with the suite statistics technique, reflected changes in coastal configuration supported by historic maps and photos, however, we also recognize that this analysis was more informative given further context through additional sedimentary analyses. These findings provide a basis for the interpretation of particle size distribution in lithostratigraphic sequences associated with bar-built estuaries, where understanding natural and anthropogenically-modified inlet dynamics may help shape conservation management where concerns exist with respect to fish passage, water quality, and sediment transport.KEYWORDS: Lagoon sedimentation, Granulometry, ICOLL, Sediment texture, Sediment sorting, Intermittently open estuarie
Recommended from our members
Effects of antecedent hydrologic conditions, time dependence, and climate cycles on the suspended sediment load of the Salinas River, California
See pdf for abstract.Keywords: Non-stationary Effective discharge, Suspended sediment, El Niño Southern Oscillation, Small mountainous rivers, Arid river
Recommended from our members
The effect of El Niño Southern Oscillation cycles on the decadal scale suspended sediment behavior of a coastal dry-summer subtropical catchment
Rivers display temporal dependence in suspended sediment–water discharge relationships. Although most work has focused on multi-decadal trends, river sediment behavior often displays sub-decadal scale fluctuations that have received little attention. The objectives of this study were to identify inter-annual to decadal scale fluctuations in the suspended sediment–discharge relationship of a dry-summer subtropical river, infer the mechanisms behind these fluctuations, and examine the role of El Niño Southern Oscillation climate cycles. The Salinas River (California) is a moderate sized (11,000 km²), coastal dry-summer subtropical catchment with a mean discharge (Q[subscript mean]) of 11.6 m³ s⁻¹. This watershed is located at the northern most extent of the Pacific coastal North America region that experiences increased storm frequency during El Niño years. Event to inter-annual scale suspended sediment behavior in this system was known to be influenced by antecedent hydrologic conditions, whereby previous hydrologic activity regulates the suspended sediment concentration–water discharge relationship. Fine and sand suspended sediment in the lower Salinas River exhibited persistent, decadal scale periods of positive and negative discharge corrected concentrations. The decadal scale variability in suspended sediment behavior was influenced by inter-annual to decadal scale fluctuations in hydrologic characteristics, including: elapsed time since small (~0.1 × Q[subscript mean]), and moderate (~10 × Q[subscript mean]) threshold discharge values, the number of preceding days that low/no flow occurred, and annual water yield. El Niño climatic activity was found to have little effect on decadal-scale fluctuations in the fine suspended sediment–discharge relationship due to low or no effect on the frequency of moderate to low discharge magnitudes, annual precipitation, and water yield. However, sand concentrations generally increased in El Niño years due to the increased frequency of moderate to high magnitude discharge events, which generally increase sand supply.Keywords: Non-stationarity, Suspended sediment, El Niño Southern Oscillation, Long-term memory, Arid river
A neighborhood statistics model for predicting stream pathogen indicator levels
Because elevated levels of water-borne Escherichia coli in streams are a leading cause of water quality impairments in the U.S., water-quality managers need tools for predicting aqueous E. coli levels. Presently, E. coli levels may be predicted using complex mechanistic models that have a high degree of unchecked uncertainty or simpler statistical models. To assess spatio-temporal patterns of instream E. coli levels, herein we measured E. coli, a pathogen indicator, at 16 sites (at four different times) within the Squaw Creek watershed, Iowa, and subsequently, the Markov Random Field model was exploited to develop a neighborhood statistics model for predicting instream E. coli levels. Two observed covariates, local water temperature (degrees Celsius) and mean cross-sectional depth (meters), were used as inputs to the model. Predictions of E. coli levels in the water column were compared with independent observational data collected from 16 in-stream locations. The results revealed that spatio-temporal averages of predicted and observed E. coli levels were extremely close. Approximately 66 % of individual predicted E. coli concentrations were within a factor of 2 of the observed values. In only one event, the difference between prediction and observation was beyond one order of magnitude. The mean of all predicted values at 16 locations was approximately 1 % higher than the mean of the observed values. The approach presented here will be useful while assessing instream contaminations such as pathogen/pathogen indicator levels at the watershed scale
- …