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Testing the efficacy of mitigation measures for reducing fine sediment and associated pollutant delivery to and through rivers in agricultural catchments of England.
Submitted for the Degree of Doctor of Philosophy at the University of Northampton
2016
Matilda Biddulph © Matilda Biddulph [November 2016] This thesis is copyright material and no quotation from it may be published without proper acknowledgement.
Abstract Agricultural intensification has contributed to the degradation of freshwaters in the UK, through enhanced delivery of fine sediment and associated contaminants, leading to sedimentation and eutrophication. European legislation (Water Framework Directive 2000/60/EC) and subsequent UK government initiatives such as Catchment Sensitive Farming (CSF) and Demonstration Test Catchments (DTC), aim to improve the quality of freshwaters. The DTC programme aims to find cost-effective ways to reduce agricultural diffuse water pollution. This study aimed to monitor rivers in the Hampshire Avon DTC with existing and planned mitigation measures, to measure the effectiveness of the mitigation measures, and to develop an experimental design for wider application for pollution mitigation. The methods used and tested in this study were a combination of affordable, replicable and sustainable methods (in-stream sediment collection and water quality monitoring), more complicated, expensive, analytical laboratory methods (particle size, loss-on-ignition, geochemistry, mineral magnetism, environmental radionuclides), and sediment source fingerprinting. The mitigation measures were: improvement to farm infrastructure, a wooded and a grassed riparian buffer, and a constructed wetland and in-stream pond treatment train. The improved farm infrastructure (resurfacing of a farm track, installation of a retention pond, improvements to a drainage ditch) effectively reduced inputs of sediment and associated contaminants to the river, however, this had little positive impact on the river due to greater importance of inputs from other sources. The riparian buffers were reducing fine sediment and associated contaminant inputs laterally and from upstream, however, the effectiveness of the riparian buffers was undermined by a lack of riparian buffers upstream and by sub-surface field drains. Combined analysis of the river from the farm infrastructure in the headwaters (farm scale) to the wooded riparian buffer downstream (sub-catchment scale) showed a change in the dominant source of sediment. This highlighted that an experimental design would require monitoring at varying spatial scales, as individual farm scale mitigation measures may have little impact on an entire sub-catchment due to the importance of other sources from a larger drainage area. The constructed wetland and instream pond were not effective at reducing longitudinal delivery of fine sediment and
associated contaminants due to issues related to maintenance and design, emphasising the importance of appropriate targeting, design, and maintenance of mitigation measures. The results from this study showed that the methods used would be suitable as part of an experimental design for wider application. Although complex and expensive, sediment source fingerprinting is essential for determining appropriate and cost-effective mitigation at farm and sub-catchment scales. Monitoring of the sediment and water quality using the affordable, replicable and sustainable methods could be managed by farmers and landowners across a dense spatial area, at a high temporal frequency, to ensure sustainable effectiveness of mitigation. There is a need for more co-working between policy makers and scientists to ensure appropriate funding and timescales for research are provided, and with farmers and landowners to improve understanding and vested interest in the contribution of agriculture to the degradation of water quality.
Acknowledgements I would first and foremost like to thank my supervisors, Ian Foster, Adie Collins and Naomi Holmes, I am extremely grateful, and lucky, to have been given their unwavering support, knowledge and advice. Thanks must go to the people of the Hampshire Avon DTC programme, including Chris Hodgson and Martin Blackwell. I am extremely grateful to the farmers and landowners in the DTC sub-catchments, who kindly granted me access to their land and offered their knowledge and advice; especially to Mr Rasch of Priors Farm, and to Mr Stiles and his family of Hays Farm. Thank you to Mr Stiles for also kindly lending me your ATV, which made fieldwork immeasurably easier when the alternative was an old hatchback. I would also like to thank the Environment Agency for providing me with rainfall and river stage data. Thank you to Simon Pulley for your advice and guidance throughout my PhD. Thank you to the laboratory technicians at the University of Northampton, Tina and Tanya, for letting me loose in the labs. Thank you to Kathryn Harrold, for your moral support and motivation in and out of the office. I would sincerely like to thank my fieldwork assistants, of which there were many; some had good weather and some had it bad. Thank you to: my supervisors, Simon Pulley, Harry Neal, Ben Cullen, Jennine Evans, Mum, Dad and my brother, Max. Thank you also to Rich Higgins for proof reading my work. Finally, thank you to my family and thank you to Harry.
Table of Contents 1. Study Context ............................................................................................................ 1 1.1.
Introduction ............................................................................................................. 1
1.2.
Legislation ............................................................................................................... 2
1.2.1.
European Legislation ....................................................................................... 2
1.2.2.
Water Management in England and Wales .................................................... 4
1.3.
Pollution .................................................................................................................. 5
1.3.1.
Sediment .......................................................................................................... 5
1.3.2.
Phosphorus ...................................................................................................... 8
1.3.3.
Nitrogen ......................................................................................................... 10
1.4.
Conceptualising Catchment Behaviour ................................................................. 11
1.4.1.
Connectivity ................................................................................................... 11
1.4.2.
Catchment Characteristics ............................................................................. 13
1.5.
Mitigation .............................................................................................................. 15
1.5.1.
Drivers for Mitigation .................................................................................... 15
1.5.2.
Monitoring Techniques .................................................................................. 16
1.5.3.
Land Management ........................................................................................ 17
1.5.4.
Mitigation Measures ..................................................................................... 18
1.5.5.
Implementation ............................................................................................. 20
1.6.
Summary ............................................................................................................... 21
1.7.
Research Aims and Objectives .............................................................................. 22
2. Methodology ........................................................................................................... 23 2.1.
Study Area ............................................................................................................. 23
2.2.
Experimental Approach ......................................................................................... 26
2.3.
Study Sites ............................................................................................................. 27
2.3.1.
Improving farm infrastructure: disconnecting point sources. ........................ 28
2.3.2.
Riparian buffers: reducing longitudinal connectivity. .................................... 36
2.3.3.
Wetlands and ponds: reducing longitudinal connectivity. ............................. 39
2.4.
Field Methods ........................................................................................................ 41
2.4.1.
In-stream sediment monitoring ..................................................................... 41
2.4.2.
Runoff sampling: dustpan sampler (DPS) ...................................................... 45
2.4.3.
Sediment retention ........................................................................................ 46
2.4.4.
Water quality monitoring .............................................................................. 47
2.4.5.
Sediment source sampling ............................................................................. 49
2.5.
Laboratory Methods .............................................................................................. 50
2.5.1.
Absolute particle size ..................................................................................... 51
2.5.2.
Organic matter content ................................................................................. 52
2.5.3.
Geochemistry ................................................................................................. 53
2.5.4.
Mineral magnetism ....................................................................................... 54
2.5.5.
Environmental radionuclides ......................................................................... 56
2.6.
Sediment Source Fingerprinting ............................................................................ 58
2.7.
Summary ............................................................................................................... 59
3. Improving farm infrastructure: disconnecting point sources. ................................... 61 3.1.
Introduction ........................................................................................................... 61
3.2.
Rainfall trends pre- and post-mitigation ............................................................... 63
3.3.
Sediment Mass ...................................................................................................... 65
3.4.
Sediment Properties .............................................................................................. 69
3.4.1.
Potential sediment source properties ............................................................ 70
3.4.2.
Total phosphorus (TP) .................................................................................... 72
3.4.3.
Copper (Cu) .................................................................................................... 75
3.4.4.
137
3.4.5.
Specific surface area (SSA) ............................................................................. 78
Cs ............................................................................................................... 76
3.5.
Effectiveness of Mitigation Measures on Water Quality ...................................... 78
3.6.
Sediment Source Fingerprinting ............................................................................ 82
3.7.
Summary ............................................................................................................... 89
3.8.
Interpretation ........................................................................................................ 93
3.8.1. Impact: has there been a change in the mass of fine sediment and concentrations of its associated contaminants in the River Sem from pre- to postmitigation? ..................................................................................................................... 93 3.8.2. Effectiveness: were the mitigation measures effectively retaining fine sediment and associated contaminants? ....................................................................... 97 3.8.3.
Summary ....................................................................................................... 98
4. Riparian buffers: reducing longitudinal connectivity, and sub-catchment scale mitigation. ..................................................................................................................... 99 4.1.
Introduction ........................................................................................................... 99
4.2.
Sediment Mass .................................................................................................... 101
4.3.
Sediment Properties ............................................................................................ 103
4.3.1.
Total phosphorus (TP) .................................................................................. 103
4.3.1.
Organic matter (OM) ................................................................................... 104
4.3.2.
137
4.3.3.
Specific surface area (SSA) ........................................................................... 108
4.4.
Cs ............................................................................................................. 107
Sediment Source Fingerprinting .......................................................................... 112
4.4.1.
Wooded Riparian Buffer .............................................................................. 113
4.4.1.
Sub-catchment scale: sediment source apportionment at d/s D and d/s T . 113
4.4.2.
Grassed Riparian Buffer ............................................................................... 116
4.5.
Summary ............................................................................................................. 118
4.6.
Interpretation ...................................................................................................... 119
4.6.1. Effectiveness: was the Wooded Riparian Buffer Strip effective as mitigation against excess fine sediment and associated contaminants?. ..................................... 119 4.6.2. Effectiveness: was the Grassed Riparian Buffer Strip effective as mitigation against excess fine sediment and associated contaminants?. ..................................... 123 4.6.3. Sub-catchment scale: were the mitigation measures on Hays Farm and Priors Farm effective at reducing the mass and improving the quality of the fine sediment in the Priors DTC sub-catchment? .................................................................................... 125 5. Wetlands and ponds: reducing longitudinal connectivity using in-stream mitigation. .. .............................................................................................................................. 129 5.1.
Introduction ......................................................................................................... 129
5.2.
River Ebble Stage Record ..................................................................................... 130
5.3.
Sediment Mass .................................................................................................... 131
5.4.
Sediment Properties ............................................................................................ 134
5.4.1.
Geochemistry ............................................................................................... 134
5.4.2.
Organic matter (OM) ................................................................................... 136
5.4.3.
137
5.4.4.
Specific surface area (SSA) ........................................................................... 138
Cs ............................................................................................................. 137
5.5.
Stored Pond Sediment ......................................................................................... 140
5.6.
Potential Sediment Source Properties ................................................................ 143
5.7.
Sediment Source Fingerprinting .......................................................................... 144
5.8.
Summary ............................................................................................................. 146
5.9.
Interpretation ...................................................................................................... 147
5.9.1.
Sources of fine sediment and associated contaminants to the River Ebble . 147
5.9.2. Effectiveness: was the constructed wetland effective at reducing the downstream mass of fine sediment and concentrations of its associated contaminants in the River Ebble? ........................................................................................................... 148 5.9.3. Effectiveness: was the in-stream pond effective at reducing the downstream mass of fine sediment and concentrations of its associated contaminants in the River Ebble? ..................................................................................................................... 151 6. Discussion ............................................................................................................. 154 6.1. Objective 1: To identify evidence and causes of fine sediment and associated contaminant pollution in the Hampshire Avon DTC sub-catchments. ............................ 154 6.1.1.
Published findings from UK rivers ................................................................ 154
6.1.2.
Priors DTC sub-catchment: River Sem (Chapters 3 and 4) ........................... 159
6.1.3.
Ebble sub-catchment: River Ebble (Chapter 5) ............................................ 166
6.2. Objective 2: To test the effectiveness of a range of mitigation options for reducing connectivity. .................................................................................................................... 168
6.2.1.
Improving farm infrastructure ..................................................................... 168
6.2.2.
Riparian buffers and sub-catchment scale mitigation ................................. 173
6.2.3.
Wetlands and ponds .................................................................................... 178
6.3. Objective 3: To develop an experimental design that can be transferred to other catchments to provide robust and fit-for-purpose evidence on the efficacy of on-farm mitigation measures. ....................................................................................................... 182 6.3.1.
In-stream sediment monitoring ................................................................... 183
6.3.2.
Water quality spot sampling ....................................................................... 186
6.3.3.
Sediment source fingerprinting ................................................................... 190
6.4.
Final remarks ....................................................................................................... 191
7. Conclusions ........................................................................................................... 193 7.1.
Main Conclusions ................................................................................................ 193
7.2.
Reflections: what could have been improved to provide more robust results? . 193
7.3.
Looking forward: national scale mitigation of agricultural pollution .................. 195
7.4.
Bigger picture: constraints for moving forward .................................................. 197
8. References ............................................................................................................ 199 9. Appendices ............................................................................................................ 234
List of Figures Figure 2.1
Location of the Hampshire Avon catchment Figure 2.2 The Hampshire Avon catchment and DTC sub-catchments. Red box: Priors DTC sub-catchment (River Sem). Orange box: Ebble sub-catchment (River Ebble). Figure 2.3 Before-After Control-Impact (BACI) experimental approach. BACI 1: comparing a control and manipulated or impacted subcatchment. BACI 2: comparing upstream and downstream of a manipulated or impacted area. Both include comparison before and after manipulation (mitigation) or impact. Figure 2.4 The layout of Hays Farm, the implemented mitigation measures, and the sampling locations. Not to scale. Figure 2.5 The upper farm track (FTU) at Hays Farm. Standing from the farmyard looking downslope (Figure 2.4). A) pre-mitigation, BD) post-mitigation. Figure 2.6 The lower farm track (FTL) at Hays Farm. Standing from the bridge crossing looking towards the bottom of FTU (Figure 2.4). Unconsolidated sediment and deep channels from machinery can be observed in wet weather. Figure 2.7 A) channel re-profiling in October 2012; unvegetated, steep channel banks, B) view upstream from d/s B, showing the pipe underneath the FTL bridge crossing, C) view downstream from d/s B showing a riffle-pool sequence, D) ditch entering the River Sem. Figure 2.8 The mitigation measures being implemented on Hays Farm. A) resurfaced FTU with swale along the side, B) bottom of FTU as it levels out, with end of swale connected underneath to retention pond, C) retention pond, D) newly dredged drainage ditch flowing towards the River Sem, E) v-notch weirs installed along the ditch. See Figure 2.4. Photographs: July 2013. Figure 2.9 Post-mitigation at Hays farm. Bottom left: view from the bottom of FTU looking towards the River Sem along FTL. Top images: retention pond. Bottom right: bottom of the swale trapping runoff behind a v-notch weir. Figure 2.10 The drainage ditch post-mitigation. Left: view from the retention pond looking towards the River Sem. Middle and right: v-notch weirs within the drainage ditch.
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Figure 2.11
Figure 2.12
Figure 2.13
Figure 2.14 Figure 2.15 Figure 2.16 Figure 2.17 Figure 2.18
Figure 3.1
The River Sem flowing east from Hays Farm to Priors Farm in the Priors DTC sub-catchment. On Hays Farm the farm track (FTU, FTL) and drainage ditch are labelled, with red arrows showing the direction of runoff from the farmyard (see Figure 2.4). On Priors Farm the wooded riparian buffer and grassed riparian buffer are labelled. d/s T is the furthest monitoring location downstream on the River Sem. Map taken from Google Maps (2017). The layout and mitigation measures on Priors Farm. A) young trees planted along the channel as part of wooded riparian buffer (Elder, Beech), B) heavily poached, but lower, channel banks upstream of the wooded riparian buffer, C) meandering gravel-bed channel with riffles and bars, D) managed grassed riparian buffer. Not to scale. The layout and mitigation measures in the River Ebble at Ebbesbourne Wake. A) undefined banks upstream of Ebbesbourne Wake, B) looking upstream from the start of the wetland, C) downstream of the wetland, D) looking upstream through the wetland from the bridge crossing, E) the in-stream pond from the bridge crossing, F) looking downstream of the instream pond. Not to scale. Time-integrated suspended sediment trap (TIS) based on design by Phillips et al. (2000). TIS in situ. A) in the River Sem at Hays Farm, B) in the River Ebble during Summer 2013 at the inlet of the in-stream pond. Bed disturbance experiments based on the method by Lambert and Walling (1988). Dustpan sampler (DPS) experiment. Locations of the nine pond samples (PS) collected from around the in-stream pond at Ebbesbourne Wake, labelled 1-9. Monitoring locations u/s pond and d/s are shown with black squares. Sediment was collected with an Eckmann grab sampler. Map taken from Edina Digimap (2016). Total monthly rainfall. Sampling Period (SP): from Environment Agency records at Tisbury (01/01/13 to 15/03/15). Long-term Average (LTA): from Met Office data between 1981- 2010 at Fontmell Magna (Met Office, 2016). Dotted lines mark the start and end of the active mitigation period. After April 2014, 2-
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Figure 3.2
Figure 3.3
Figure 3.4
Figure 3.5
Figure 3.6
Figure 3.7
Figure 3.8
month rainfall has been divided equally due to the reduction in sampling frequency (Section 2.4). A) Suspended sediment mass collected from TIS and B) Bed sediment mass calculated from disturbance sampling of the riverbed. Arrows separate pre-, active and post-mitigation periods. Dotted line marks the start and end of ‘active mitigation’. Shaded box represents the actual mitigation works (June-July 2013). Boxplots showing A) TP concentration, B) Cu concentration, C) 137 Cs activity, and D) SSA of each source group that had potential to deliver sediment and associated contaminants to the River Sem (see Section 2.4.5). The ditch pre- and postmitigation was not a potential source for u/s B as this was upstream of the ditch (Figure 2.4). TP concentration of the postmitigation ditch sediment has been shown on a separate scale in A) for easier visual analysis. A) TP concentration of the suspended sediment collected from TIS and B) TP concentration of the bed sediment calculated from disturbance sampling from the riverbed. Arrows separate pre-, active and post-mitigation periods. Dotted line marks the start and end of ‘active mitigation’. Shaded box represents the actual mitigation works (June-July 2013) A) Cu concentration of the suspended sediment collected from TIS and B) Cu concentration of the bed sediment calculated from disturbance sampling from the riverbed. Arrows separate pre-, active and post-mitigation periods. Dotted line marks the start and end of ‘active mitigation’. Shaded box represents the actual mitigation works (June-July 2013). Phosphate (PO4) concentration at points along the settling system on Hays Farm and in the River Sem (Figure 2.4), from colorimeter spot samples (Section 2.4.4). (Pond: retention pond, Ditch u/s: upstream end of the ditch, Ditch d/s: downstream end of the ditch, DPS: dustpan sampler). Mean and SD of A) TP concentration, B) Cu concentration, C) 137 Cs activity, and D) OM content in the grab samples from the drainage ditch pre- and post-mitigation, and the retention pond (Section 2.4.3). Mass of sediment collected in the DPS each month (Section 2.4.2). DPS was not present during mitigation work in June and July 2013. Dotted lines mark the start and end of the active mitigation period.
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Figure 3.9 Average median predicted contributions of sources to suspended sediment based on the mean of three un-mixing models. Predicted contributions from Hays farm track sources are not included at Road as these were not a potential source for this site. Dotted lines mark the start and end of the active mitigation period. Figure 3.10 Average median predicted contributions of sources to bed sediment based on the mean of three un-mixing models. Predicted contributions from Hays farm track sources are not included at Road as these were not a potential source for this site. Dotted lines mark the start and end of the active mitigation period. Figure 3.11 FTL crossing the River Sem A) view south from FTL across the bridge crossing to the pasture fields, B) bridge crossing in December 2012 before monitoring began, C) and D) view of bridge crossing from d/s B in-stream. Figure 4.1 The mass of sediment upstream and downstream of both riparian buffer strips on Priors Farm. A) suspended sediment (trees), B) bed sediment (trees), C) suspended sediment (grass), D) bed sediment (grass). Only months with data for both sites have been used for comparison. Figure 4.2 The TP concentration of sediment upstream and downstream of both riparian buffer strips on Priors Farm. A) suspended sediment (trees), B) bed sediment (trees), C) suspended sediment (grass), D) bed sediment (grass). Only months with data for both sites have been used for comparison. Figure 4.3 The OM of sediment upstream and downstream of both riparian buffer strips on Priors Farm. A) suspended sediment (trees), B) bed sediment (trees), C) suspended sediment (grass), D) bed sediment (grass). Only months with data for both sites have been used for comparison. Figure 4.4 The 137Cs activity of sediment upstream and downstream of both riparian buffer strips on Priors Farm. A) suspended sediment (trees), B) bed sediment (trees), C) suspended sediment (grass), D) bed sediment (grass). Counting errors are shown to ±1SD. Only months with data for both sites have been used for comparison. Figure 4.5 The SSA of sediment upstream and downstream of both riparian buffer strips on Priors Farm. A) suspended sediment (trees), B) bed sediment (trees), C) suspended sediment (grass), D) bed
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sediment (grass). Only months with data for both sites have been used for comparison. Figure 4.6 A) Average median predicted contribution of sources to suspended sediment at d/s T based on the mean of three unmixing models. Pre-, active and post-mitigation periods on Hays Farm (Chapter 3) are shown. Dotted lines mark the start and end of the active mitigation period. B) The probability density functions for the overall average median predicted contributions generated by the un-mixing model analyses. Figure 4.7 A) Average Median predicted contribution of sources to bed sediment at d/s T based on the mean of three un-mixing models. Pre-, active and post-mitigation periods on Hays Farm (Chapter 3) are shown. Dotted lines mark the start and end of the active mitigation period. B) The probability density functions for the overall average median predicted contributions generated by the un-mixing model analyses. Figure 4.8 A) Average median predicted contributions of sources to suspended sediment at u/s G based on the mean of three unmixing models. B) The probability density functions for the overall average median predicted contributions generated by the un-mixing model analyses. Figure 4.9 A) Average median predicted contributions of sources to the bed sediment samples at u/s G based on the mean of three unmixing models. B) The probability density functions for the overall average median predicted contributions generated by the un-mixing model analyses. Figure 4.10 The wooded riparian buffer along the River Sem on Priors Farm. A) and B) Young trees (Elder, Beech) and brambles, C) view of the old trees (Hazel, Beech, Oak) along the wooded riparian buffer from the River Sem. Photographs from February 2015 (Figure 2.12; Table 4.1). Figure 4.11 The grassed riparian buffer along the tributary leading into the River Sem at Priors Farm in October 2013, shortly after mowing (Figure 2.12; Table 4.1). Figure 4.12 Field immediately upstream of u/s T. An unfenced field where cattle were allowed to access the river. The wooded riparian buffer began directly downstream of this. Photograph from May 2013. Figure 5.1 River stage throughout the monitoring period. Stage taken from 15-minute EA data recorded from the gauging station located
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downstream of the pond at site d/s. Stage used due to incomplete records of discharge at the time of analyses. Figure 5.2 A) Suspended sediment mass and B) Bed sediment mass at the four sites at Ebbesbourne Wake throughout the monitoring period. Figure 5.3 TP concentration in A) suspended sediment and B) bed sediment. Note that the months with data vary for each and the difference in scale. Figure 5.4 Cu concentration in A) suspended sediment and B) bed sediment. Note that the months with data vary for each and the difference in scale. Figure 5.5 OM content in A) suspended sediment and B) bed sediment. Note that the months with data vary for each and the difference in scale. Figure 5.6 137Cs activity in A) suspended sediment and B) bed sediment. Counting errors are shown to ± 1SD. Note that the months with data vary for each and the difference in scale. Figure 5.7 SSA of A) suspended sediment and B) bed sediment. Note that the months with data vary for each and the difference in scale. Figure 5.8 A) TP concentration, B) Cu concentration, C) 137Cs activity, D) OM content, and E) SSA of the sediment collected from pond samples (PS). PS 1-9 are shown in Figure 2.18. Figure 5.9 A) TP concentration, B) Cu concentration, C) 137Cs activity, and D) SSA of each sediment source group that has the potential to deliver fine sediment and associated contaminants to the River Ebble (see Section 2.4.5). Figure 5.10 Average median predicted contributions of sources to the River Ebble at site u/s in A) suspended sediment and B) bed sediment, based on the mean of three un-mixing models. Potential sources are: channel banks (CB), topsoil sources (TS) and damaged road verges (DRV). The probability density functions are shown in C) for suspended sediment and D) for bed sediment, for the overall average median predicted contributions generated by the un-mixing model analyses. Figure 5.11 The River Ebble (March 2015) A) at site u/s, gravel river bed, and B) in the wetland, fine sedimentation on river bed.
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Figure 5.12 The constructed wetland looking upstream, standing on the bridge crossing between the wetland and in-stream pond. A) dense macrophyte vegetation and no water (June 2014) B) macrophytes remain underwater (February 2015). Figure 5.13 The in-stream pond of the River Ebble. A) Dry pond inlet (September 2013), B) water present in the in-stream pond (February 2015). Figure 6.1 Channel bank at d/s B in the River Sem at Hays Farm in A) December 2014, B) March 2015. Figure 6.2 Bridge crossing between the constructed wetland and in-stream pond of the River Ebble (site u/s pond) in Ebbesbourne Wake (Chapter 5). Figure 6.3 View of the drainage ditch on Hays Farm looking from the River Sem to the bottom of FTU (Figure 2.4). A) post-dredging in July 2013, B) dense vegetation and fencing in December 2015. Figure 6.4 FTL on Hays Farm A) pre-mitigation (January 2013), B) postmitigation (June 2014). Pre-mitigation there was no fencing, poached track verges, and many visible areas of weakness to the riparian buffer along the ditch. Figure 6.5 Runoff from the farmyard at Hays Farm in December 2014. View from the top of FTUN (Figure 2.4). Figure 6.6 Downstream end of the wooded riparian buffer (looking upstream from site d/s T) along the River Sem on Priors Farm, showing the lack of wooded vegetation to the right-hand side of the channel (October 2013) (Figure 2.12). Figure 6.7 The grassed riparian buffer along the tributary leading into the River Sem at Priors Farm (Figure 2.12). The A) December 2014 and B) October 2013 view downstream from u/s G to d/s G after the mowing of the vegetation, C) view upstream of the grassed riparian buffer (May 2013). Figure 6.8 Dense macrophyte vegetation in the constructed wetland in the River Ebble. View from bridge crossing looking upstream. A) no water in channel (July 2013), B) water in channel (June 2014). Figure 6.9 Bridge crossing between the constructed wetland and in-stream pond in the River Ebble, showing the pipes that the river flows through to enter the pond. View from bank of the in-stream pond looking upstream towards the wetland (Figure 2.13).
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List of Tables
Table 1.1
The 44 identified mitigation measures from Cuttle et al. (2007) Rivers Sem and Ebble sub-catchment characteristics for the study sites. Based on data from the DTC Phase 1 Report (DTC, 2015). Summary of the study sites, pollution problems and mitigation measures in place. Summary of the sampling methods used at each site Potential sources from which samples were obtained for sediment source fingerprinting at each site. See Figures 2.4, 2.12 and 2.13 for the in-stream monitoring locations. Number of samples collected from each potential source in both the Priors DTC and Ebble sub-catchment. Useable elements, wavelengths and mean contamination (and standard deviation) of blank samples (aqua regia and ultrapure water) Magnetic measurements used as by Foster et al. (2008), properties highlighted in blue were used as sediment source fingerprinting tracers (see Section 2.6). Characteristics of Hays Farm, monitoring methods and experimental approach. Rainfall characteristics for SP and LTA at Hays Farm. Regional annual average and LTA total monthly rainfall is from the Met Office between 1981-2010 (Met Office, 2016), collected from Fontmell Magna (12.8km south of Hays Farm). SP total monthly rainfall and total annual rainfall for 2013 and 2014 are from daily data from the Environment Agency between 01/01/13 to 15/03/15 collected at Tisbury. Periods for pre-, active and postmitigation are outlined in Table 3.1. The mean and SD in suspended and bed sediment mass at the monitoring locations in the pre- and post-mitigation periods. Kruskal-Wallis H-tests were used to test for statistically significant differences (p=
