The summary which provides background information on the issues in this area highlights that sediment, nutrients and pesticides are potential pollutants of water-bodies. SOWAP measured sediment and nutrient levels and there are European regulatory standards for some nutrients. Under the EU Nitrates Directive surface waters are considered polluted if nitrate concentrations are greater than 50 mg/l (this is also the limit set by the Drinking Water Directive) whereas phosphate concentrations in rivers are described as ‘high' (by the UK's Environment Agency) if they are greater than 0.1 mg/l.

STREAM CHEMISTRY

Conservation tillage tends to lower nitrogen levels in UK streams but not in Hungary

• UK streams in conservation tillage catchments tended to have lower background nitrogen levels than mouldboard plough catchments
• The situation in Hungary was different, with streams draining mouldboard plough fields having better water quality rather than those in conservation tillage catchments
• In both countries, levels of stream nitrate were below the 50mg/l level
• Stream phosphate levels were ‘high’ in Hungary

• In the UK, the streams draining conservation tillage fields were significantly richer in invertebrate and plant species than mouldboard plough catchments
• For diatoms, there were no significant differences between the two tillage types in the UK, although diatom indices based on diversity suggested a tendency for conservation tillage streams to be of better quality than streams in mouldboard plough catchments.
In Hungary again, the situation was reversed with a tendency towards greater invertebrate diversity in streams draining mouldboard plough fields

In the UK , macro-invertebrate species richness, a fundamental measure of overall environmental quality, was significantly higher in conservation tillage streams than in those in mouldboard plough catchments (Figure 2). In Hungarian streams the relationships between macro-invertebrates and soil management practice were generally opposite to those seen in the UK , with conservation tillage streams having generally lower quality than mouldboard plough streams.

In the UK, there was a suggestion that the abundance of sensitive species like mayflies, stoneflies and caddis flies was higher in conservation tillage streams, although the difference was only significant between mouldboard plough and woodland streams. In Hungary , there were more mayflies, stoneflies and caddis flies in mouldboard plough streams

An assessment of the ‘SPecies At Risk' (SPEAR) pesticide impact showed that there were significantly more SPEAR pesticide sensitive species in the conservation tillage streams in the UK (Figure 3).

Macrophytes species richness in the UK was significantly higher in conservation tillage streams than in mouldboard plough streams although, numerically, the difference between treatments was small (Figure 4)

Diatoms

There were relatively few impacts of soil management on diatoms in UK streams. There were no significant differences in species richness or other indicators. However, for two measures of environmental quality - the Shannon (diversity) index (Figure 5) and the Evenness (more diverse assemblages tend to have higher evenness) index there was an indication that both increased in value in conservation tillage sites compared to conventional sites. There were also highly significant differences in these two indices between the mouldboard plough and woodland sites

SOWAP has demonstrated that the UK streams draining conservation tillage catchments were significantly richer in invertebrates and plants than mouldboard plough sites. Background chemical data from the sites showed that streams from conservation tillage catchments tended to have lower background nutrient levels than mouldboard plough streams, although the differences were not statistically significant. However, nitrogen and phosphorus levels in all catchments were below thresholds of concern.

A different pattern was seen in Hungary . Here both chemical and biological data pointed to better water quality, and a tendency towards greater invertebrate biodiversity in streams draining mouldboard plough rather than conservation tillage catchments.

There have been very few previous studies with which the current results can be compared. Two North American studies of stream invertebrates broadly agree with our UK results of better quality in streams draining conservation tillage rather than ploughed farmland. The findings from Hungarian steams are interesting in this respect because, contrary to expectation, streams draining conservation tillage catchments were of lower chemical and biological quality than streams in conventional mouldboard plough landscapes.

The intensity of the different farming systems is a likely explanation. Hungarian farmers using conservation tillage techniques typically have sufficient financial resources to invest both in modern machinery and fertilisers which, since the early 1990s, have been comparatively expensive in Hungary . In contrast farmers using mouldboard ploughing techniques typically lack financial resources, and for this reason, attempt to minimise their costs by minimising the use of fertilisers.

Based on these results, SOWAP suggests that conservation tillage can be beneficial as a mitigation option to improve stream quality when applied within landscapes already under intensive arable cultivation. Its practice would make a contribution to delivering the good chemical and ecological status of inland waters required by the EU's Water Framework Directive. However, in landscapes where cultivation is traditionally “low intensity” it is unlikely that conservation tillage use, alone, will mitigate against ecological degradation to streams caused by increasing agricultural intensity.

This report is based on the work of Miklos Bercsényi at the University of Pannonia in Hungary; Jeremy Biggs , Penny Williams and M.Whitfield at Pond Conservation and Silke Skytte Johanssen at the University of Bristol, all in the UK.