Rivers In Semi-arid Regions Research Articles

Confluence simulations based on dynamic channel parameters in the grasslands lacking historical measurements

Technology has greatly promoted ecohydrological model development, but runoff generation and confluence simulations have fallen behind in ecohydrological model development due to limited innovations. To fully understand ecohydrological processes and accurately describe the coupling between ecological and hydrological processes, a distributed ecohydrological model was constructed by integrating multisource information into distributed dynamic process model (DDPM). We mainly describe runoff generation and convergence modules. Based on the improved HBV model and degree-3 h factor method, runoff generation and snow routines were constructed for semiarid grassland basins. In view of meandering and variable steppe river channels and steep hydrological relief characteristics, a confluence module was constructed; the 1-km bend radius equivalent concept was innovatively proposed to unify river channel bend degrees. The daily runoff simulation validation results obtained using two datasets were R2 = 0.947 and 0.932, NSE = 0.945 and 0.905, KGE = 0.971 and 0.680. In the 3-hour flood simulations, the DDPM could better restore small long-distance water flows than the confluence method that did not consider actual river lengths or bend energy losses; the DDPM more accurately simulated the flood peak arrival time than the confluence method that did not consider overflow. The simulated mainstream overflow frequency increased by 0.84/10 years, and significant interaction periods of 10 to 13 years occurred with local precipitation, ecological status, and global climate change. An approximately 2-year lag occurred in the global climate change response. This study helps us further understand and reveal the ecohydrological processes of steppe rivers in semiarid regions.

Smallholder perceptions and communication gaps shape East African riparian ecosystems

Human livelihood needs and nature conservation often contradict. Yet, healthy ecosystems are crucial for human livelihood quality. The semi-arid regions of East Africa suffer under demographic pressure and soil depletion. Ecosystem degradation becomes particularly visible along rivers in semiarid regions of south-east Kenya, where former pristine riparian forests have been transformed into agricultural fields and settlements with negative effects on ecosystem services. In this study, we aim to understand how local smallholders perceive the challenges for the riparian ecosystems and what factors affect their engagement in environmental conservation. We surveyed about 200 farmers and performed expert interviews with representatives from governmental institutions from the field of land- and resource management along Nzeeu River in south-east Kenya. We assessed the level of education, land use practices, environmental knowledge, attitudes and the willingness to contribute to nature conservation. We tested for spatial bias to understand smallholders’ perceptions on environmental challenges. Our data show that land division due to inheritance is not perceived as a problem by the farmers. However, owners holding < 1 ha of land property are less willing to spare some of their land for conservation, as opposed to those holding land plots above this size. Despite a high level of general willingness to conserve ecosystems, our data underline that local people hardly actively engage in conservation action. Furthermore, our data indicate a communication gap between local smallholders and regional governmental officers as well as overconfidence in mass media through the radio which can contradict successful adoption of pro-environment behavior. Sustainable land management in our study area is not a matter of education, but depends from the size of land property. There is an urgent need to bridge this communication gap, as a prerequisite to improve sustainable land management.

Do NH3 and chemical oxygen demand induce continuous release of phosphorus from sediment in heavily polluted rivers?

While phosphorus (P) is a vital element in freshwater systems, excessive P loads will induce eutrophication. Large inputs of various pollutants, including P, to rivers in semi-arid regions result in complex environmental problems. In this study, we investigate dissolved oxygen (DO), ammoniacal nitrogen (NH3), chemical oxygen demand (CODcr), soluble reactive P (SRP) in surface water and pore water, and sediment P in the Niuwei River, within the Hai River Basin. From our results we developed and tested a theory for P release in semi-arid regions driven by DO. The results show that NH3 and CODcr can cause variations in DO in surface water. The presence of pollutants at high concentrations caused seasonal hypoxia. Hypoxic river water induced adsorption and hydrolysis of NaOH-Pi and labile organic P (L-Po), which then resulted in increased SRP concentrations in pore water and surface water. Overall, our results illustrate that NH3 and CODcr may be important for P adsorption and desorption and for management of water quality problems in rivers in semi-arid regions.

Decision support system (DSS) for site selection floodwater spreading schemes using remote sensing (RS) and geographical information systems (GIS)

Most aquifers of semi-arid regions in Iran suffer from over-exploitation of groundwater for irrigation purposes. It is therefore important to augment the groundwater resource by artificial recharge, using floodwaters. Generally, the recharge schemes consist of diverting part of the flood discharges of ephemeral rivers in small to medium-size catchments into infiltration basins. Apart from recharging groundwater, and supporting food production and drinking water supplies, the schemes have other benefits, such as the mitigation of flood damage. The complexity of floodwater spreading schemes using flash floods of ephemeral rivers in semi-arid regions became evident during the task of selecting, defining and structuring criteria for the selection of suitable areas and sites for a scheme. Complexity is due to a large number of factors that play a role in the selection of the most suitable sites for deciding on investment in a scheme. These factors pertain to earth science (geology, geomorphology, soils), to hydrology (runoff and sediment yield, infiltration and groundwater conditions) and to socio-economic aspects (irrigated agriculture, flood damage mitigation, environment and so on). This paper deals with developing a DSS to assist decisions as to where suitable catchments and associated infiltration areas are located. The DSS developed relies on the combined use of remotely sensed information and GIS techniques. For implementation of the related phase of the DSS, a region (Bandar Abbas) was selected as the case study for suitable zone(s) selection. The DSS shows the great ability for selection of potential zones for floodwater spreading. It can be concluded that the interpretation results could be regarded as being more than the sum of separate ‘interpretation’ layers: i.e. geology, geomorphology and land use. The interpreter has to have a firm footing in earth science.

VARIABILITY IN THE INVERTEBRATE FAUNA OF AN INTERMITTENT STREAM OVER THREE CONSECUTIVE MIDSUMMER PERIODS

Summary Non-perennial rivers in semi-arid regions are exposed to unpredictable and highly variable rainfall and hydrology which can have considerable effects on faunal organisation at different scales. Spatial and temporal dynamics in the aquatic invertebrate fauna of an aseasonal intermittent river in the Eastern Cape, South Africa, were studied over three consecutive midsummer periods. Taxonomic composition varied widely from month to month and between years. Faunal abundances were generally low, and spatial distribution was highly heterogenous. Most of the abiotic variables measured remained within a narrow range over the study period, and only current speed in individual biotopes could be linked to biotic organisation. Faunal similarities were greatest between samples collected during similar hydrological conditions (rather than during similar times of the year). These findings suggest that rainfall and hydrology are major determinants of biotic organisation in this section of the river. The erratic n...

Limnological imbalances: an antipodean viewpoint

SUMMARY. 1. It is argued that modern limnology is excessively concerned with the study of fresh waters in the northern temperate region. Limnology has been and is unbalanced in its interests and emphases and, as a result, many widely held limnological concepts need revision.2. The genesis of the argument is outlined. It involved the initial assumption that Australia was limnologically distinctive. Later, it was realized that since most of the world is arid, semi‐arid, tropical or semi‐tropical, Australia was much less distinctive than originally thought.3. Other limnological assumptions considered in the paper concern saline lakes and salinization, the importance and nature of temporary bodies of standing fresh water, biological diversity in tropical fresh waters, the evolutionary importance of permanent freshwater lakes, and the global applicability of the River Continuum Concept. Consideration suggests that some widely‐held views on these matters are erroneous.4. Thus, saline lakes are more important (scientifically, commercially), widespread and numerous environments than is generally thought. Salinization is a significant environmental hazard for many rivers in semiarid regions. Temporary bodies of standing fresh water are geographically widespread and abundant aquatic environments with high species diversity, and in which many species have restricted distributions and low dispersal abilities. Biological diversity appears to be low in tropical fresh waters. Permanent freshwater lakes are perhaps less important loci for the evolution of the freshwater biota than generally thought, temporary fresh waters more so. Finally, the River Continuum does not seem to be applicable to many running waters outside the north temperate region.5. A number of suggestions are made of how a better balance in limnology may be arrived at: how a more globally comprehensive intellectual framework may be built. Suggestions include: an increased awareness of the frequently different natures of waters within and beyond the northern temperate region; recognition of the potential benefits to be gained from the study of waters outside the northern temperate region;