Event controls on intermittent streamflow in a temperate climate

Intermittent streams represent a substantial part of the worldwide stream network and their occurrence is expected to increase due to climate change. Thus, it is of high relevance to provide detailed information of the temporal and spatial controls of streamflow intermittency to support management decisions. This study presents an event-based analysis of streamflow responses in intermittent streams in a meso-scale catchment with temperate climate. According to the streamflow responses, events were classified into flow or no-flow classes. Response controls like precipitation, soil moisture, and temperature were used as predictors in a random forest model to identify temporal controls of streamflow intermittency at the event-scale. Soil moisture was revealed as the most important predictor in the catchment. However, different patterns of predictor importance were found among the three dominant geologies in the catchment. Streamflow responses in the slate geology were controlled by soil moisture in the shallow and deep soil layers, while streamflow in the marl geology was primarily controlled by the soil moisture in the upper soil layer. Streamflow responses in catchments covering both marls and sandstone were dependent on soil moisture whereas streamflow in the only catchment with pure sandstone geology depended on precipitation characteristics. In both the slate and marl geology, streamflow intermittency also showed a relationship with seasonal fluctuations of soil temperature, probably as a proxy-variable of seasonal changes in evapotranspiration as well as an indicator of freezing conditions.

ECOLOGIA DE PEIXES DE RIACHOS INTERMITENTES

The ecology of fish from intermittent streams in the Brazilian semi-arid region is still little known. In the past twenty years, the number of researchers dedicated to this topic has increased considerably. However, significant gaps still exist when compared to the perennial streams of other regions of Brazil. Questions that address seasonal variations come up against the determination of capture methods and techniques that are efficient in the different phases of the hydrological cycle. In addition, techniques widely used in perennial systems, such as electrofishing, in most cases, have not been effective. Aspects related to biology, physiology, behavior, functional and taxonomic ecology of fish still need to be investigated taking into account seasonal and spatial scale variations. In view of the growing transformation imposed on the Brazilian semi-arid region by the extensive use of natural resources and by climate change, aquatic environments and their biodiversity are threatened by the transformation of riparian vegetation, the sewage release, the species introduction, the modification of its course and artificial perennialization. Thus, we will present and discuss, in this paper, the studies developed on the ecology of fish in the intermittent streams of the Brazilian semi-arid region and the gaps and challenges to be faced by future research.

Diversity of Adult Caddisfly (Trichoptera) in Two Intermittent Streams During Dry Season in Phayao Province, Thailand

The effect of anthropogenic activities on natural intermittent stream and diversity of adult caddisfly were studied at the University of Phayao, Thailand. The caddisfly adults were collected monthly from 2 intermittent streams (the Huai Thub Chang and Huai Luang streams) from February to May 2015 (cool-dry to hot-dry season) using a black-light trap. Huai Thub Chang stream received wastewater from the oxidation pond, while Huai Luang stream was affected by an agricultural field of the university. Both streams are located in a deciduous forest. The 14 species of 7 families were collected and identified. Cheumatopsyche lucida (Hydropsychidae) and Leptocerus dirghachuka (Leptoceridae) were found in both streams. C. lucida was the most abundant species. Micrasema turbo, Amphipsyche meridiana, C. globosa, Diplectrona lavinia, Macrostemum dohrni, Marilia sumatrana, and Wormaldia relicta were found only in Huai Thub Chang stream, whereas C. dhanikari, Lepidostoma doligung and Chimarra toga were found only in Huai Luang stream. A high number of C. lucida in both streams from February to April reflected a drought effect on the emergence of the caddisflies. Huai Thub Chang stream had a higher diversity of Trichoptera species than Huai Luang stream because of the variety of substrate types which were suited for the larval stage, especially hydropsychids.

Advances in the simulation of nutrient dynamics in cold climate agricultural basins: developing new N and P modules for the Cold Regions Hydrological Modelling Platform

Excess nutrients in aquatic ecosystems is a major water quality problem globally. Worsening eutrophication issues are notable in cold temperate areas, with pervasive problems in many agriculturally dominated catchments. Predicting nutrient export to rivers and lakes is particularly difficult in cold agricultural environments because of challenges in modelling snow, soil, frozen ground, climate, and anthropogenic controls. Previous research has shown that the use of many popular small basin nutrient models can be problematic in cold regions due to poor representation of cold region hydrology. In this study, the Cold Regions Hydrological Modelling Platform (CRHM), a modular modelling system, which has been widely deployed across Canada and cold regions worldwide, was used to address this problem. CRHM was extended to simulate biogeochemical and transport processes for nitrogen and phosphorus through a complex of new process-based modules that represent physicochemical processes in snow, soil and freshwater. Agricultural practices such as tillage and fertilizer application, which strongly impact the availability and release of soil nutrients, can be explicitly represented in the model. A test case in an agricultural basin draining towards Lake Winnipeg shows that the model can capture the extreme hydrology and nutrient load variability of small agricultural basins at hourly time steps. It was demonstrated that fine temporal resolutions are an essential modelling requisite to capture strong concentration changes in agricultural tributaries in cold agricultural environments. Within these ephemeral and intermittent streams, on average, 30%, 31%, 20%, and 16% of the total annual load of NO, NH, SRP and partP occurred during the episodic snowmelt freshet ~9 days, accounting for 21% of the annual flow), but shows extreme temporal variation. The new nutrient modules are critical tools for predicting nutrient export from small agricultural drainage basins in cold climates via better representation of key hydrological processes, and a temporal resolution more suited to capture dynamics of ephemeral and intermittent streams.