Paleohydraulic reconstruction of a 40 kyr-old terrace sequence implies that water discharge was larger than today

The evolution of landscapes crucially depends on the climate history. This is particularly evident in South America where landscape responses to orbital climate shifts have been well documented. However, while most studies have focused on inferring temperature variations from paleoclimate proxy data, estimates of water budget changes have been complicated because of a lack of adequate physical information. Here, we present a methodology and related results, which allowed us to extract water discharge values from the sedimentary record of the 40 Ka-old fluvial terrace deposits in the Pisco valley, western Peru. In particular, this valley hosts a Quaternary cut-and-fill succession that we used, in combination with beryllium-10 (10Be)-based sediment flux, gauging records, channel geometries and grain size measurements, to quantitatively assess sediment and water discharge values c. 40 Ka ago in relation to present-day conditions. We compare these discharge estimates to the discharge regime of the modern Pisco River and find that the water discharge of the paleo-Pisco River, during the Minchin pluvial period c. 40 Ka ago, was c. 7–8 times greater than the modern Pisco River if considering the mean and the maximum water discharge. In addition, the calculations show that inferred water discharge estimates are mainly dependent on channel gradients and grain size values, and to a lesser extent on channel width measures. Finally, we found that the c. 40 Ka-old Minchin terrace material was poorer sorted than the modern deposits, which might reflect that sediment transport during the past period was characterized by a larger divergence from equal mobility compared to the modern situation. In summary, the differences in grain size distribution and inferred water discharge estimates between the modern and the paleo-Pisco River suggests that the 40 Ka-old Minchin period was characterized by a wetter climate and more powerful flood events.

Spatial distribution and impact of the gill-parasitic Mazocraes alosae (Monogenea Polyopisthocotylea) on Alosa alosa and A. fallax (Actinopterygii, Clupeidae)

Are the distribution of Mazocraes alosae and its impact on the host similar between Alosa alosa and A. fallax according to their resemblances? Parasites were numbered on each gill of shads sampled in North-East Atlantic coastal waters and connected rivers. Their impact on host condition was measured using girth, gonado-somatic ratio, C/N ratio, and Fulton’s K. Prevalence and mean intensity of M. alosae were significantly higher for A. alosa than for A. fallax, including in sympatric conditions. The mean intensity varied among sites whatever fish species; it was higher in coastal–estuarine versus fresh waters only for A. fallax. The distribution of M. alosae was aggregated in the host population whatever species. At the host individual level, some gills (second and third for A. alosa, second for A. fallax) were significantly more inhabited than others, probably in relation with larger water volumes flowing on these gills and mazocraeid sedentary lifestyle. Despite high prevalence and intensity, no negative impact of M. alosae was demonstrated on the host condition whatever the index considered. Our study underlines the major occurrence of M. alosae on shads and the potential use of such benign parasite as biological tag to discriminate closely related host species. © 2015, Springer International Publishing Switzerland.