Reporting negative results to stimulate experimental hydrology: discussion of “The role of experimental work in hydrological sciences – insights from a community survey”*

Experimental work in hydrology is in decline. Based on a community survey, Blume et al. showed that the hydrological community associates experimental work with greater risks. One of the main issues with experimental work is the higher chance of negative results (defined here as when the expected or wanted result was not observed despite careful experimental design, planning and execution), resulting in a longer and more difficult publishing process. Reporting on negative results would avoid putting time and resources into repeating experiments that lead to negative results, and give experimental hydrologists the scientific recognition they deserve. With this commentary, we propose four potential solutions to encourage reporting on negative results, which might contribute to a stimulation of experimental hydrology.     

Grain-size normalization as a tool to assess contamination in marine sediments: is the <63 micron fraction fine enough?

A common method for compensating for grain-size differences in suites of sediment samples is to normalize potential contaminants by regression with a particular grain-size fraction, the <63 microm fraction being most often selected. However, this fraction is unlikely to represent accurately the clay content, which represents a major factor in the ability of sediments to adsorb contaminants. Moreover, no reliable estimation of clay content can be made from a coarser grain-size fraction. As a result, regression with coarser-grained fractions can produce spurious interpretations of background values and contamination. Normalization with the clay content or by an alternative grain-size proxy is recommended.     

Can channel banks be the dominant source of fine sediment in a UK river?: an example using 137Cs to interpret sediment yield and sediment source

Cultivated fields have been shown to be the dominant sources of sediment in almost all investigated UK catchments, typically contributing 85 to 95% of sediment inputs. As a result, most catchment management strategies are directed towards mitigating these sediment inputs. However, in many regions of the UK such as the Nene basin there is a paucity of sediment provenance data. This study used the caesium‐137 (¹³⁷Cs) inventories of lake and floodplain cores as well as the ¹³⁷Cs activities of present day sediment to determine sediment provenance. Sediment yields were also reconstructed in a small lake catchment. Low ¹³⁷Cs inventories were present in the lake and floodplain cores in comparison to the reference inventory and inventories in cores from other UK catchments. Caesium‐137 activities in the present day sediments were low; falling close to those found in the channel bank catchment samples. It was estimated that 60 to 100% of the sediment in the Nene originated from channel banks. Pre‐1963 sediment yields were approximately 11.2 t km^?2 yr^?1 and post‐1963 was approximately 11.9 t km^?2 yr^?1. The lack of increased sediment yield post‐1963 and low sediment yield is unusual for a UK catchment (where a yield of 28 to 51 t km^?2 yr^?1 is typical for a lowland agricultural catchment), but is explained by the low predicted contribution of sediment from agricultural topsoils. The high channel bank contribution is likely caused by the river being starved of sediment from topsoils, increasing its capacity to entrain bank material. The good agreement between the results derived using cores and recently transported sediments, highlight the reliability of ¹³⁷Cs when tracing sediment sources. However, care should be taken to assess the potential impacts of sediment particle size, sediment focusing in lakes and the possible remobilization of ¹³⁷Cs from sedimentary deposits. Copyright © 2016 John Wiley & Sons, Ltd.