Annual runoff is 24% less for 100% forested than 100% grassland catchment  Land use affects moderate flood peaks but effect is constrained by soil moisture  Drainage ditches support larger flood peaks in forested than grassland catchment  Peat grassland storage enhances spring monthly runoff ratios, reaching 100%  Integrated catchment runoff shown to be derivable from proportional land cover

Groups of Romney Marsh ewes (n = 24) were injected with exogenous melatonin or subjected to extended darkness or a combination of both at dusk from the winter to the summer solstice before being re-exposed to the natural photoperiod at 35 degrees S. The animals were at all times exposed to natural dawn. The onset of subsequent oestrus was delayed when compared with controls subjected to the natural photoperiod. Either melatonin or darkness or a combination were equally effective at delaying oestrus. The results are consistent with a hypothesis based on an external coincidence model of seasonal breeding involving the coincidence of a light-sensitive phase set close to dusk that, when exposed to light in spring and summer, prepares the reproductive axis to respond correctly to the direct effects of the inductive photoperoid in autumn. The offset of the time of oestrus was not affected by the experimental treatments nor was the timing of the subsequent reproductive season. Since melatonin was as effective as darkness at influencing the assumed photosensitive signal, even in the presence of natural light, melatonin may act through the light reception system.

Two experiments, using Romney Marsh ewes, tested for the existence and role of a critical interval of the circadian pacemaker located near dusk that may be integrally involved in the precise timing of the breeding season. Groups of Romney Marsh ewes (n = 6) were provided with exogenous melatonin by injection at dusk (Experiment 1) or by infusion at dawn or subjected to extended darkness at dawn (Experiment 2) from the winter to the summer solstice before being exposed to natural photoperiod at latitude 35 degrees S. Other than the experimental protocols, all animals were held in natural photoperiod. The onset of the breeding season (defined as cyclic ovarian activity as indicated by plasma progesterone monitoring) was normal in those animals treated with morning melatonin but was delayed in those animals treated with melatonin at dusk or extended darkness at dawn compared to controls in natural photoperiod (p < .01). Exogenous melatonin at dusk was associated with a phase advance of the onset of the circadian pacemaker (as measured by endogenous melatonin in acutely extended darkness); additional darkness at dawn was associated with a phase delay of both the onset and the offset of the circadian pacemaker. Exogenous morning melatonin did not change the phase of the circadian pacemaker relative to the controls. The results are consistent with an external coincidence model of seasonal breeding in which a critical interval of the circadian pacemaker requires exposure to light during spring/summer to time estrus correctly. The proposed critical interval appears to be located near dusk in this model and is phase locked to the circadian pacemaker. The effect of the exogenous melatonin on the timing of the breeding season is similar to darkness when administered at dusk but is not equivalent to darkness at dawn. The timing of anestrus was not affected by any of the experimental treatments and may reflect a common response to an environmental influence.

Azimi-Ghomi et al. This is an open access article distributed under the terms of the Creative Commons Attribution License CC-BY 4.0., which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.