Abstract:The influence of emergent and submerged macrophytes on flow velocity and turbulence production is demonstrated in a 140 m reach of the River Blackwater in Farnborough, Hampshire, UK. Macrophyte growth occurs in patches and is dominated by Sparganium erectum and Sparganium emersum. In May 2001, patches of S. erectum were already established and occupied 18% of the channel area. The flow adjusted to these (predominantly lateral) patches by being channelled through a narrower cross-section. The measured velocity profiles showed a logarithmic form, with deviations attributable to topographic control. The channel bed was the main source of turbulence. In September 2001, in-stream macrophytes occupied 27% of the channel, and overhanging bank vegetation affected 32% of the area. Overall flow resistance, described by Manning's n, showed a threefold increase that could be attributed to the growth of S. emersum in the middle of the channel. Velocity profiles showed different characteristic forms depending on their position relative to plant stems and leaves. The overall velocity field had a three-dimensional structure. Turbulence intensities were generally higher and turbulence profiles tended to mirror the velocity profiles. Evidence for the generation of coherent eddies was provided by ratios of the root mean square velocities. Spectral analysis identified deviations from the Kolmogorov 5/3 power law and provided statistical evidence for a spectral short-cut, indicative of additional turbulence production. This was most marked for the submerged vegetation and, in some instances, the overhanging bank vegetation. The long strap-like leaves of S. emersum being aligned approximately parallel to the flow and the highly variable velocity field created by the patch arrangement of macrophytes suggest that the dominant mechanism for turbulence production is vortex shedding along shear zones. Wake production around individual stems of S. emersum close to the bed may also be important locally.

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were monitored at a site on the River Lambourn (The CEH River Lambourn Observatory) and major instream and riparian impacts were observed. Measurements clearly demonstrated how weed cutting enhanced flood flow conveyance, reduced water levels (river and wetland), increased river velocities, and mobilised suspended sediment (with associated chemicals) and reduced the capacity for its retention within the river channel. Potential implications in relation to flood risk, water resources, downstream water quality, instream and riparian ecology, amenity value of the river, and wetland greenhouse gas emissions were considered. Provided the major influence of macrophytes on instream and riparian environments is fully understood then the manipulation of macrophytes represents an effective management tool that demonstrates the great potential of working with nature.

Article (refereed) -postprint Rameshwaran, Ponnambalam; Tepe, Akin; Yazar, Attila; Ragab, Ragab. 2016. Effects of drip-irrigation regimes with saline water on pepper productivity and soil salinity under greenhouse conditions. Contact CEH NORA team at noraceh@ceh.ac.ukThe NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. AbstractThe aim of this study was to investigate the response of sweet pepper (Capsicum annuum L.) to saline irrigation water and various irrigation regimes. The experiments were conducted in a greenhouse with two sweet pepper varieties (ONUR F1 and ADA F1) over two cropping seasons: Spring and Autumn on the Mediterranean coast at Antalya, Turkey. The irrigation regimes comprised four levels of Class A pan-evaporation and were applied using a drip irrigation system when evaporation reached a target value of around 10 mm. These four levels represented 0.50, 0.75, 1.00 and 1.25 of Class A panevaporation. In each irrigation regime the sweet pepper plants were exposed to four salinity treatments with electrical conductivities of 1.0, 2.5, 3.5 and 6.0 dS m -1 respectively. The study showed that both pepper varieties generally performed in a similar manner (except in terms of vegetative biomass production). The amount of salt accumulation within the root-zone was higher in Spring compared to Autumn; and therefore related to the total amount of irrigated water usage between seasons due to climatic variability. Increased salinity induced higher levels of salt accumulation within the pepper plant's root-zone, while an increased amount of saline irrigation water increased the size of the affected layer within the root-zone. Overall, an increased level of salinity alongside increased irrigation considerably depressed both vegetative growth and yield. Higher irrigation water productivities were attained with a regime comprising 0.50 of Class A pan-evaporation and which appeared to fulfil crop water requirements. It was found that sweet pepper varieties ONUR F1 and ADA F1 are moderately sensitive to salinity with a threshold value of 1.43 dS m -1 and a decreasing slope value of 11.1%.Although both seasons revealed a single salinity response function, there were considerable differences in the actual fresh pepper yield. This study demonstrates that for pepper crops irrigated with saline water (or grown on salt-affected soils), pepper growers must consider the salinity response function and seasonal productivity alongside an appropriate irrigation regime.Keywords: Capsicum annuum L.; class A pan-evaporation, modelling; sweet pepper varieties; salinity response function; salinity tolerance index, season; irrigation water productivity; yield. 2 IntroductionPepper (Capsicum annuum L.) is a high-value crop cultivated in many parts of the world (DeWitt and Bosland, 1993). In the Mediterranean basin, pepper crops are grown in greenhouses and often irrigated in salt-affect...