Determining sources of suspended sediment
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This document discusses methods for determining sources of suspended sediment in watersheds. It examines using sediment fingerprinting to distinguish sediments from different source areas, such as bank erosion or surface runoff from different land uses. The study specifically looks at a watershed in Atlantic Canada to identify whether sediments mainly come from bank or surface erosion and how contributions may differ between land use types. It outlines approaches for simple and complex watershed studies, including taking source and sediment samples at multiple locations to better understand spatial variability in sediment sources.
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Determining sources of suspended sediment
- 1. Determining Sources of Suspended Sediment in an Agricultural Watershed in Atlantic Canada Agriculture and Agri-Food Canada University of Manitoba Monica Boudreault, Sheng Li, David Lobb, Glenn Benoy and Kui Liu
- 2. Sediment leads to water quality concerns Sources of sediments vary in type and quantity Bank erosion Surface runoff erosion Different land uses Sediments transported by streams frequently embody a mixture of sediment derived from different source areas Sediments http://www.barrierreef.org/our-science/research-we-support/attributes/sediment-sourcing
- 3. Questions to be answered 3 Where are the sediments coming from Is the majority of suspended sediment coming from bank or surface erosion? If suspended sediment is coming from surface erosion can we distinguish between land use types to determine the contribution from each? Can we estimate the contributions from a specific source at a specific time?
- 4. Sediment fingerprinting It is based on the assumption that one or more properties of suspended sediment will reflect its origins and can be used as tracers/signatures to track the sediment back to its source. Sediment = mixture of S1 and S2 Source 1 Ts₁=10 Source 2 Ts₂=20 Tss=15: 50%=S₁ 50%=S₂ Tss=18: 80%=S2 20%=S1 Unmixing
- 5. Traditional experiments 5 Sampling Sediment samples: only one location --- watershed outlet Source samples: random locations in the watershed for all possible sources Assumptions Sources are uniform within the watershed High connectivity along the water path
- 6. Other experimental designs 6 What if Not enough samples (e.g., source difficult to sample) Watershed is heterogeneous in nature Blockages/storages along the water path Strategies Taking source samples outside the watershed Taking additional sediment samples Different ways to analyze the data b b b a a a
- 7. Simple versus complex watershed studies 7 Simple watershed study = not spatially defined Watershed source sampling / single sediment sampling Regional source sampling / single sediment sampling Watershed source sampling / multiple sediment sampling Complex watershed study = spatially defined Upstream source definition Reach source definition Traditional experiment
- 8. Simple versus complex watershed studies 8 Simple watershed study = not spatially defined Watershed source sampling / single sediment sampling Regional source sampling / single sediment sampling Watershed source sampling / multiple sediment sampling Complex watershed study = spatially defined Upstream source definition Reach source definition b b b a a a
- 9. Simple versus complex watershed studies 9 Simple watershed study = not spatially defined Watershed source sampling / single sediment sampling Regional source sampling / single sediment sampling Watershed source sampling / multiple sediment sampling Complex watershed study = spatially defined Upstream source definition Reach source definition
- 10. Simple versus complex watershed studies 10 Simple watershed study = not spatially defined Watershed source sampling / single sediment sampling Regional source sampling / single sediment sampling Watershed source sampling / multiple sediment sampling Complex watershed study = spatially defined Upstream source definition Reach source definition
- 11. Simple versus complex watershed studies 11 Simple watershed study = not spatially defined Watershed source sampling / single sediment sampling Regional source sampling / single sediment sampling Watershed source sampling / multiple sediment sampling Complex watershed study = spatially defined Upstream source definition Reach source definition
- 12. Study site 65% agricultural 21% forest 14% residential or wetland area Black Brook Watershed (BBW) Northwest New Brunswick, Canada Potato production systems
- 13. Source Samples: Field Soil transects extend from the top of the stream bank, through the riparian zone and into the field (3-7 samples/transect) Down-slope, mid-slope and upslope
- 14. Source Samples: Stream Bank Sampled actively eroding stream banks 3 profiles from each location 10 cm increments
- 15. Suspended Sediment 15 Modified version of the Phillips designed in- situ time-integrated suspended sediment sampler Collected seasonally, from 2008-2014
- 16. Measurements/tracers Tracers may include: *Colour properties *Radionuclide Geochemical Particle Size Stable Isotopes Organic constituents Mineralogy and Magnetism Distinct diagnostic signatures used to determine the proportion of each source contributing to suspended sediment (assortment of mixed signature sources) Selection of tracers based on the following criteria: 1. Conservative behaviour 2. Ability to distinguish between sources 3. Linearly additive behaviour
- 17. Tracer 1: Spectral-Reflectance/Color Spectral differences due to heterogeneous combination of: o Minerals o Water o Organic matter Quantified using diffuse reflectance spectrometry 350-2500 nm wavelength spectroradiometer ASD FieldSpecPro Reflected light collected with a fiber optic cable
- 18. Tracer 2: Radionuclide Cs-137 18 Man-made radionuclide Nuclear weapon testing Distributed back to Earth by precipitation Found only of surface soils Tracer used to distinguish between surface and subsurface soil
- 19. Un-mixing Model: MixSIAR 19 MixSIAR (R program) Originally developed for ecological studies Used to estimate the relative contribution of potential sediment sources at each sediment sampling site Bayesian isotopic mixing model Monte Carlo methods Statistical procedures Canonical Discriminant Analysis (sources) Shapiro Wilk test (normality) MixSIAR BIPLOT Analysis in R (signature conservative, major sources included) Kruskall-Wallis H-Test (signature different among sources) Stepwise Discriminate Function Analysis (DFA) (signature combination
- 20. Watershed source sampling / single sediment sampling
- 21. Regional source sampling / single sediment sampling
- 22. Watershed source sampling / multiple sediment sampling
- 23. Complex study --- upstream definition
- 24. Complex study --- reach definition
- 25. Summary 25 Both bank erosion and field erosion can contribute significantly into the sediments in streams of the BBW Switch in sources from headwaters to outlet (forest for upper reaches and cultivated field for lower reaches) can only be detected with nested spatial framework Strong local influences at some locations High uncertainties with small sample sizes
- 26. Funding Agriculture and Agri-Food Canada NSERC Strategic and Discovery Grants programs Environment Canada Field and lab work Serban Danielescu Rick Allaby Fangzhou Zheng Sylvie Lavoie Lionel Stevens Meagan Betts Tegan Smith Zisheng Xing Acknowledgement
- 27. Thank you for your attention! Questions?
Editor's Notes
- Sources of sediments vary in type and quantity depending on location and erosional process responsible Sediments transported by streams or rivers frequently embody a mixture of sediment derived from different source areas and source types within a catchment Identification of main sources (pinpoints polluters) Pinpointing the main causes of non-point source pollution is vital for the proper management of sediments entering water sources. Best management practices (BMPs) can be utilized to control/reduce water quality degradation by sediments however knowledge about where the sediments are coming from is necessary. For example, there may be many possible non-point source polluters in an area…
- BBW covers approximately 1450 ha at about 7.5 km long and 3.5 km wide It is a tributary of Little River Watershed (LRW) which accounts for 380 square-kilometres and discharges into the St. John River Valley 65% of land used for agriculture 21% forest 14% residential
- Surface soil samples were taken upstream of where the suspended sediment samplers were installed. Each sub-watershed within BBW was sampled for suspended sediment and had at least one soil sample transect completed. Soil transects extended from the top of the stream bank through the riparian zone and into the field. Each transect was sampled to represent each section of the slope including downslope, midslope and upslope. Surface soil sampling locations were selected based on the following criteria: 1) visible evidence of erosion or soil degradation 2) distance and potential connectivity to stream 3) access and safety Only surface soils that could potentially erode and contribute to suspended sediment were sampled. In agricultural fields, soil samples were taken to the same depth as the tillage layer because the tilling of soil often mixes many different soil horizons changing its natural vertical profile.
- The stream bank sampling procedure was based on the knowledge that over time banks will erode across the entire bank height either by instantaneous collapse or non-synchronous lower and upper bank retreat through a combination of erosion processes
- Cross-sectional difference between inlet tube and pipe reduces sediment/water velocity which collects the sample Low maintenance, installed and left for an entire season, checked every 2 weeks to ensure that stream flow and tree branches haven’t washed away samplers, Low cost as well and doesn’t require power (electrical) source like many other suspended sediment sampler types.
- Sediment fingerprinting is a technique used to develop a better understanding of sediment dynamics within watersheds Based on the assumption that one or more properties of the suspended sediment will reflect its origins and can be used as a tracer to track the sediment Distinct diagnostic signatures of potential sources are used to determine the proportion of each source contributing to the suspended sediment which represents an assortment of mixed signature sources Used to determine the proportion of sources in a mixture Determining the source of erosion is incredibly important for trying to manage for it Best Management Practices (BMPs) are used to control water pollution. They are particularly utilized and useful in agricultural landscapes that tend to have significant effects on surface water through pesticides, organic pollutants and suspended sediments. In order to implement the right BMP’s that will be the most useful in reducing erosion, the sources of erosion must be determined, this can be done using sediment fingerprinting Based on the assumption that one or more of the properties of the suspended sediment will reflect its origins and can be used as a tracer to track the sediment
- Quantified using diffuse reflectance spectrometry Relatively inexpensive means of characterising the physical, chemical and biological properties of soils Spectral differences due to the behaviour of the heterogeneous combination of: Minerals Water Organic matter Best used in small catchments Non-conservative Reflectance spectra of sediments and source materials were quantified using a diffuse reflectance spectrometry Martinez et al. (2010) tested the colour based fingerprinting approach on medium and large sized catchments and found that the level of source discrimination decreased as the catchment size increased. This is likely caused by heterogeneous pedology and geology, source overlap and intra-source variability (Martinez et al. 2010).
- Nuclear weapon testing in the late 1950’s Chernobyl 1986 (Northern hemisphere only)
- A type of mixing/unmixing model that can be applied to solve various environmental problems Mixing v.s. Unmixing depending on your objectives, typically for sediment fingerprinting (Un-Mixing), ecological (Mixing) MixSIAR is often used in research pertaining to: Diet composition, population structure and animal movements (Most common use) Carbon sources in soils Carbon sources for ecosystem respiration Pollutant sourcing Sediment fingerprinting Originally developed for ecological studies; however, it is a basic mixing model and can be used with any fingerprint property as long as the assumptions of linear mixing are met Used to estimate the relative contribution of the potential sediment sources at each sediment sampling site Bayesian isotopic mixing model **because it uses the underlying probability of distribution of each statistic rather than the fixed sample means or point estimates which other mixing models use. Because Bayesian uses variance instead of means and standard deviations the output will always differ if run multiple times Written in open source languages R and Jags (Just Another Gibbs Sampler) Created from the creators of MixSIR and SIAR Sediment grouped by sampling site and year Monte Carlo methods producing simulations of possible values of sediment source proportions using prior distributions consistent with data Monte Carlo specifies the number of iterations to run the model at, the longer it runs the more accurate it is. The data, data specification prior information/distributions, iterations can all be easily imputed using the easy to use GUI (graphical user interface) Current models (MixSIAR) have covariates, hierarchical variance structures, concentration dependencies, discrimination factors and include complex variability in isotopic signatures allowing them to be more accurate then previous models.
- Nuclear weapon testing in the late 1950’s Chernobyl 1986 (Northern hemisphere only)