The effects of minimal tillage, contour cultivation and in-field vegetative barriers on soil erosion and phosphorus loss.

Runoff, sediment, total phosphorus and total dissolved phosphorus losses in overland flow were measured for two years on unbounded plots cropped with wheat and oats. Half of the field was cultivated with minimum tillage (shallow tillage with a tine cultivator) and half was conventionally ploughed. Within each cultivation treatment there were different treatment areas (TA). In the first year of the experiment, one TA was cultivated up and down the slope, one TA was cultivated on the contour, with a beetle bank acting as a vegetative barrier partway up the slope, and one had a mixed direction cultivation treatment, with cultivation and drilling conducted up and down the slope and all subsequent operations conducted on the contour. In the second year, this mixed treatment was replaced with contour cultivation. Results showed no significant reduction in runoff, sediment losses or total phosphorus losses from minimum tillage when compared to the conventional plough treatment, but there were increased losses of total dissolved phosphorus with minimum tillage. The mixed direction cultivation treatment increased surface runoff and losses of sediment and phosphorus. Increasing surface roughness with contour cultivation reduced surface runoff compared to up and down slope cultivation in both the plough and minimum tillage treatment areas, but this trend was not significant. Sediment and phosphorus losses in the contour cultivation treatment followed a very similar pattern to runoff. Combining contour cultivation with a vegetative barrier in the form of a beetle bank to reduce slope length resulted in a non-significant reduction in surface runoff, sediment and total phosphorus when compared to up and down-slope cultivation, but there was a clear trend towards reduced losses. However, the addition of a beetle bank did not provide a significant reduction in runoff, sediment losses or total phosphorus losses when compared to contour cultivation, suggesting only a marginal additional benefit. The economic implications for farmers of the different treatment options are investigated in order to assess their suitability for implementation at a field scale

Measurement of flood peak effects as a result of soil and land management, with focus on experimental issues and scale

As a result of several serious flood events which have occurred since 2000, flooding across Europe is now receiving considerable public and media attention. The impact of land use on hydrology and flood response is significantly under-researched, and the links between land use change and flooding are still unclear. This study considers runoff data available from studies of arable in-field land use management options, applied with the aim of reducing diffuse pollution from arable land, in order to investigate whether these treatments also have potential to reduce downstream flooding. Intensive monitoring of 17 hillslope treatment areas produced a record of flood peak data covering different mitigation treatments for runoff which occurred in the winter of 2007–2008. We investigated event total runoff responses to rainfall, peak runoff, and timing of the runoff peaks from replicates of different treatments, in order to assess whether there is a significant difference in flood peak response between different mitigation options which could be used to mitigate downstream flood risk. A mixed-modelling approach was adopted in order to determine whether differences observed in runoff response were significant. The results of this study suggest that changes in land use management using arable in-field mitigation treatments can affect local-scale runoff generation, with differences observed in the size, duration and timing of flood peaks as a result of different management practices, but the study was unable to allow significant treatment effects to be determined. We suggest that further field studies of the effects of changes in land use and land use management need to upscale towards farm and catchment scale experiments which consider high quality before-and-after data over longer temporal timescales. This type of data collection is essential in order to allow appropriate land use management decisions to be made

Assessing the potential for using constructed wetlands as mitigation options for phosphorus and sediment within UK agriculture

vokMTT, Viestintä ja informaatiopalvelut, 31600 Jokioine

Improving water quality in agricultural catchments: sediment and nutrient retention in field wetlands

A recent update of Water Framework Directive classifications in the UK indicates that only 28% of water bodies currently achieve good ecological status and that agriculture is one of the main sectors responsible for the pressures contributed by sediment and nutrients. The use of edge-of-field features, such as field wetlands - small sediment and pollutant trapping features (<500 m2) constructed along runoff pathways, is one set of mitigation options available to farmers. Before reaching the waterways, polluted runoff is slowed down by passage through the field wetland, allowing some sediment and nutrients to settle out. Although the principle of field wetlands is well accepted, and they are widely used in Scandinavia for diffuse pollution mitigation, there is little quantitative evidence of their capability for water quality improvement in the UK. Ten field wetlands have been constructed in the UK agricultural landscape in order to quantify the potential for sediment and nutrient retention and to provide guidelines on their likely effectiveness under various conditions. The ten sites covered different combinations of soil type, field wetland design, wetland size relative to catchment area and runoff source. Sediment and nutrient retention was measured by annual sediment surveys at each field wetland. Sediment trapping rates of 0.5 – 6 t ha-1 yr-1 were recorded on a sandy soil site, compared to 0.02 – 0.4 t ha-1 yr-1 on a silty soil site and 0.01 – 0.07 t ha-1 yr-1 on a clay soil site, although rainfall was a confounding factor, with much lower rainfall at the clay site during the monitoring period. Concentrations of total phosphorus, total nitrogen and total carbon in the sediments trapped were highest at the sandy site, where there was a wastewater input in addition to the agricultural runoff. The importance of land use, and ground cover in particular, was highlighted by a ten-fold increase in the sediment trapped in one field wetland from one year to the next when pasture was ploughed up for an arable crop. These multi-functional edge-of-field features have shown good potential for reduction of sediment and nutrient input to the waterways. In addition, field wetlands provide biodiversity benefits and in some circumstances may also contribute to flood attenuation, and should be considered alongside in-field measures as part of an integrated solution for catchment management

Nutrient reduction in field wetlands: do they work for dissolved nutrients?

Pollution of natural waters arises from both point sources (direct inputs) and diffuse inputs (many small sources entering the waterways by numerous pathways). Legislation has ensured that pollution from point sources has been reduced, thus increasing the significance of diffuse sources, and the contribution from agriculture in particular. Field wetlands (small sediment and nutrient trapping features, < 500 m2), constructed along runoff pathways, are one set of options for diffuse pollution mitigation. Polluted surface runoff as well as subsurface drainage is slowed down by passage through the field wetland, allowing more opportunity for sediment and associated nutrients to settle out. However, the nutrients transported from soil to water are not only attached to the sediment but also in soluble form, and field drains have been identified as a fast pathway for dissolved nutrients to reach the waterways. The soluble form is critical in the short term because it is readily available for aquatic organisms. On the other hand, the particulate form (associated with sediment) is a reservoir for growth and development of aquatic organisms and represents a problem in the long term. The ability of field wetlands to reduce both the particulate and dissolved nutrient loads is being tested in the UK as part of a project on Mitigation Options for Phosphorus and Sediment. Ten field wetlands have been built on farms in the UK, capturing surface runoff and subsurface field drainage, to quantify the sediment and nutrient retention under a range of different conditions. At Whinton Hill in Cumbria (sandy soil), samples from the inlet and outlet of a field wetland system showed an average decrease in the concentration of total solids of 11%. Total phosphorus (TP) was reduced by an average of 43%. However, soluble reactive phosphorus, which accounted for approximately 50% of the TP at the inlet, was reduced by an average of 74%, showing that this wetland made a significant difference to both the particulate and dissolved fractions of phosphorus. For nitrogen, at least 80% of the total nitrogen was in dissolved form at the inlet, with most of this being in the form of ammonium. Concentrations of ammonium were reduced by an average of 72% between the inlet and outlet. We conclude that the long hydraulic residence times in this field wetland, due to very limited flow at the outlet of the wetland, maximise the opportunity for biological activity and uptake of soluble nutrients

Reducing diffuse pollution in agricultural catchments: retention of sediment and nutrients in field wetlands

Diffuse water pollution continues to be an important environmental concern, with only 28% of surface waters in the UK currently classified as ‘good ecological status’ in a recent update of Water Framework Directive classifications. Agriculture has been identified as the largest sector associated with diffuse sources of nutrients and sediment. Field wetlands have been used for mitigation of diffuse pollution in Scandinavia but there is currently little quantitative evidence of their effectiveness in the UK. Ten field wetlands have been built at four sites in the UK, covering a range of soil types, runoff sources, wetland sizes and wetland designs. The wetlands, small (< 350 m2), unlined ponds constructed along runoff pathways, slow the connection between the pollution source and the waterways, and provide more opportunity for sediment and nutrients to settle out or be taken up by aquatic organisms. This paper describes sediment retention in all ten wetlands and nutrient retention at one highly polluted site. Sediment retention was estimated from annual surveys of the sediment build-up in each wetland. Sediment trapping rates were highest on a sandy soil site (0.5 – 6 t ha-1 yr-1), compared to a silty soil site (0.02 – 0.4 t ha-1 yr-1) and a clay soil site (0.01 – 0.07 t ha-1 yr-1). Nutrient retention was estimated from samples collected at the inlet and outlet of each wetland. At Whinton Hill, Cumbria, a wetland system with a long hydraulic residence time, concentrations of both particulate and dissolved nutrients were observed to decrease between the inlet and outlet of the wetland system. The average concentration of some nutrients was observed to reduce by up to 80%. Overall, small field wetlands have shown good potential for mitigation of diffuse pollution and should be considered alongside in-field measures as part of an integrated solution for catchment management

Keeping agricultural soil out of rivers:evidence of sediment and nutrient accumulation within field wetlands in the UK

Intensification of agriculture has resulted in increased soil degradation and erosion, with associated pollution of surface waters. Small field wetlands, constructed along runoff pathways, offer one option for slowing down and storing runoff in order to allow more time for sedimentation and for nutrients to be taken up by plants or micro-organisms. This paper describes research to provide quantitative evidence for the effectiveness of small field wetlands in the UK landscape. Ten wetlands were built on four farms in Cumbria and Leicestershire, UK. Annual surveys of sediment and nutrient accumulation in 2010, 2011 and 2012 indicated that most sediment was trapped at a sandy site (70 tonnes over 3 years), compared to a silty site (40 tonnes over 3 years) and a clay site (2 tonnes over 3 years). The timing of rainfall was more important than total annual rainfall for sediment accumulation, with most sediment transported in a few intense rainfall events, especially when these coincided with bare soil or poor crop cover. Nutrient concentration within sediments was inversely related to median particle size, but the total mass of nutrients trapped was dependent on the total mass of sediment trapped. Ratios of nutrient elements in the wetland sediments were consistent between sites, despite different catchment characteristics across the individual wetlands. The nutrient value of sediment collected from the wetlands was similar to that of soil in the surrounding fields; dredged sediment was considered to have value as soil replacement but not as fertiliser. Overall, small field wetlands can make a valuable contribution to keeping soil out of rivers

Sediment and nutrient trapping in field wetlands.

Agriculture has been identified as the largest sector contributing to diffuse water pollution. Field drains have been identified as a fast pathway for dissolved nutrients to reach the waterways, potentially bypassing conventional buffer zones. Field wetlands, (small, unlined ponds (< 500 m2) constructed in unproductive agricultural areas and designed to intercept runoff), are a simple and effective option for diffuse pollution mitigation, addressing both sediment-associated and dissolved pollutants. This paper describes the results of sediment and nutrient trapping from ten field wetlands built at four sites in the UK, covering a range of soil types and runoff sources. Sediment and nutrient retention in the wetlands was estimated from samples collected at the inlet and outlet of each wetland, as well as from an annual survey of the sediment retained in each wetland. Sediment masses trapped within the wetlands ranged from 0.3 – 1 t yr-1 at a clay soil site to 25 – 40 t yr-1 at a sandy soil site. At the sandy site, 30 – 70 kg yr-1 total phosphorus (TP) and 60 – 200 kg yr-1 total nitrogen (TN) was trapped with the sediment. Rainfall was a confounding factor, with much lower rainfall at the clay site during the monitoring period. Concentrations of both particulate and dissolved nutrients were observed to decrease between the inlet and outlet of wetland systems. At a sandy soil site, the average concentration of some nutrients was reduced by up to 80% in a wetland system with a long hydraulic residence time. Overall, these multi-functional edge-of-field features have shown good potential for reduction of sediment and nutrient input to the waterways and should be considered alongside in-field measures as part of an integrated solution for catchment management