Chaos arising from the hydrological behaviour of a floodplain river during the last century

The hydrological regime is the main factor governing the functioning of floodplain rivers. A full comprehension of its dynamic leads to a better understanding of the system’s behaviour and of the proper methods that must be used. We analysed the daily water level of the Paraná River during the last century at three gauge stations using linear and non-linear tools to characterise the hydrological dynamic and to analyse to what extent chaotic behaviour prevails. The three water level time series were characterised as non-linear and non-stationary by power spectrum, autocorrelation function, and surrogate test analyses. A strange attractor was developed when the phase space was reconstructed, having a low dimensional chaos supported by correlation dimension, positive maximum Lyapunov exponents, and recurrence quantification analysis. In line with this, the system resulted unpredictable with a threshold by sample entropy, and with an intermediate hydrological complexity, while Hurst exponent characterised the system as persistent and with sensitive dependence on initial conditions. In a general overview, all the evidence obtained indicates that the Paraná River’s behaviour is at the edge of chaos. A latitudinal gradient of decreasing chaoticity was observed as the floodplain extent increased, whereas complexity was highest at the intermediate river station due to the inflow of tributaries with different hydrology. This paper attempts to offer some additional insights for understanding the hydrological behaviour of floodplain rivers and the proper methods to understand their complexity.

What evidence exists on the impacts of flow variability on fish and macroinvertebrates of temperate floodplain rivers in Central and Western Europe? A systematic map protocol

Background Flow variability is considered a fundamental factor affecting riverine biota. Any alterations to flow regime can influence freshwater organisms, and this process is expected to change with the projected climate change. This systematic map, therefore, aims at investigating the impacts of natural (resulting from climatic variability), anthropogenic (resulting from direct human pressure), and climate change-induced flow variability on fish and macroinvertebrates of temperate floodplain rivers in Central and Western Europe. Particular focus will be placed on the effects of extreme low and high discharges. These rare events are known to regulate population size and taxonomic diversity. Methods All studies investigating the effects of flow variability on metrics concerning freshwater fish and macroinvertebrates will be considered in the map, particularly metrics such as: abundance, density, diversity, growth, migration, recruitment, reproduction, survival, or their substitutes, such as biomonitoring indices. Relevant flow variability will reflect (1) anthropogenic causes: dams, reservoirs, hydroelectric facilities, locks, levees, water abstraction, water diversion, land-use changes, road culverts; (2) natural causes: floods, droughts, seasonal changes; or (3) climate change. Geographically, the map will cover the ecoregion of Central and Western Europe, focusing on its major habitat type, namely “temperate floodplain rivers and wetlands”. The review will employ search engines and specialist websites, and cover primary and grey literature. No date, language, or document type restrictions will be applied in the search strategy. We expect the results to be primarily in English, although evidence (meeting all eligibility criteria) from other languages within the study area will also be included. We will also contact relevant stakeholders and announce an open call for additional information. Eligibility screening will be conducted at two levels: title and abstract, and full text. From eligible studies the following information will be extracted: the cause of flow variability, location, type of study, outcomes, etc. A searchable database containing extracted data will be developed and provided as supplementary material to the map report. The final narrative will describe the quantity and key characteristics of the available evidence, and identify knowledge gaps and knowledge clusters, i.e. subtopics sufficiently covered by existing studies allowing full systematic review and meta-analysis.

On the discretization of river networks for large scale hydrologic-hydrodynamic models

ABSTRACT The discretization of river networks is a critical step for computing flow routing in hydrological models. However, when it comes to more complex hydrologic-hydrodynamic models, adaptations in the spatial representation of model calculation units are further required to allow cost-effective simulations, especially for large scale applications. The objective of this paper is to assess the impacts of river discretization on simulated discharge, water levels and numerical stability of a catchment-based hydrologic-hydrodynamic model, using a fixed river length (Δx) segmentation method. The case study was the Purus river basin, a sub-basin of the Amazon, which covers an area that accounts for rapid response upstream reaches to downstream floodplain rivers. Results indicate that the maximum and minimum discharges are less affected by the adopted Δx (reach-length), whereas water levels are more influenced by this selection. It is showed that for the explicit local inertial one-dimensional routing, Δx and the α parameter of CFL (Courant-Friedrichs-Lewy) condition must be carefully chosen to avoid mass balance errors. Additionally, a simple Froude number-based flow limiter to avoid numerical issues is proposed and tested.

Effects of intermittent starvation on the survival, growth, and nutritional status of the freshwater prawn Macrobrachium borellii Nobili, 1896 (Decapoda: Caridea: Palaemonidae)

We examined the effect of the double restriction-recovery cycle on survival, growth, and nutritional status of the freshwater prawn Macrobrachium borellii (Nobili, 1896), native to floodplain rivers of Argentina. The restriction period consisted of intermittent starvation (alternating four-day feeding with no feeding for four days) and a recovery period of continuous feeding following the restriction period. Survival was high over a 20-week trial with cycles of food scarcity. Prawns showed a slight impact on their growth throughout the entire first cycle of restriction-recovery; however, compensatory growth was not triggered. The reduction of growth was markedly more drastic after the second restriction period, but compensatory growth was not exhibited when the second recovery period was reestablished. Any possible impact of the double cycle of intermittent starvation on energy reserves and structure of the hepatopancreas was compensated by a posterior cycle of continuous feeding. The results demonstrated that M. borelli can successfully support long-term food scarcity throughout the juvenile and adult phases, at least intermittently and followed by a recovery period. The high nutritional flexibility is an adaptation to fluctuations in food availability and an advantage for successful ornamental aquaculture.

Alien Fish Species in the Mbô Floodplain Rivers in Cameroon

The aim of this study was to identify different alien fish species introduced in the Mbô Floodplain (MF) Rivers in Cameroon and to study their life-history traits. For this purpose, a total number of 237 fishes with a total length (TL) of 24.50 ± 5.97 cm and total weight of 199.50 ± 106.78 g collected by traditional fishing gears were used for taxonomic identification. Four species grouped into three families were identified: Clariidae (Clarias gariepinus), Cichlidae (Oreochromis niloticus and Tilapia cameronensis), and Channidae (Parachanna obscura). There are two types of fish introduction: accidental introduction and intentional transfer. All fish species collected and examined were of large sizes (TL > 25 cm). The regression coefficient b of the length-weight relationship ranged from 3.00 (C. gariepinus) to 3.37 (T. cameronensis) (3.18 ± 0.17). Fish species showed a monthly and seasonal fluctuation in abundance in number of individuals. Alien fish species in the Mbô Floodplain showed two types of somatic growth: isometric and positive allometric. 75% of overall alien fish species were established and they recorded a mean K factor of 0.70 ± 0.40. Only 25.00% of the sampled species had more females than males.