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Flooding is a major disturbance that impacts aquatic ecosystems and the ecosystem services that they provide. Predicted increases in global flood risk due to land use change and water cycle intensification will likely only increase the frequency and severity of these impacts. Extreme flooding events can cause loss of life and significant destruction to property and infrastructure, effects that are easily recognized and frequently reported in the media. However, flooding also has many other effects on people through freshwater aquatic ecosystem services, which often go unrecognized because they are less evident and can be difficult to evaluate. Here, we identify the effects that small magnitude frequently occurring floods (< 10-year recurrence interval) and extreme floods (> 100-year recurrence interval) have on ten aquatic ecosystem services through a systematic literature review. We focused on ecosystem services considered by the Millennium Ecosystem Assessment including: (1) supporting services (primary production, soil formation), (2) regulating services (water regulation, water quality, disease regulation, climate regulation), (3) provisioning services (drinking water, food supply), and (4) cultural services (aesthetic value, recreation and tourism). The literature search resulted in 117 studies and each of the ten ecosystem services was represented by an average of 12 ± 4 studies. Extreme floods resulted in losses in almost every ecosystem service considered in this study. However, small floods had neutral or positive effects on half of the ecosystem services we considered. For example, small floods led to increases in primary production, water regulation, and recreation and tourism. Decision-making that preserves small floods while reducing the impacts of extreme floods can increase ecosystem service provision and minimize losses. [ABSTRACT FROM AUTHOR]

The aim of our study was; (i) to characterize the composition of DOM in stream water and their potential sources (groundwater, overland flow, subsurface flow and rain water) and (ii) to analyze changes in DOM concentration and composition under different hydrological conditions (baseflow and high flow) in a third-order Pampean stream (Argentina). Pampean streams are mainly fed by the shallow aquifer under baseflow conditions and they lack of riparian forest. In addition, water velocity is low due to the gentle slope of the region and nutrient levels are high, favoring the development of rich macrophyte communities. DOM optical properties in the stream and end members were determined by combining absorbance-fluorescence spectroscopy techniques. Our results indicated that DOM chemical characteristics in the stream were mainly modulated by a differential contribution of end members to stream water depending on hydrological conditions. We observed that DOM in groundwater showed a microbial origin while DOM in runoff was terrestrially-derived. DOC concentration and inputs of humic substances from the riparian zone increased with discharge at high flow conditions. Due to the strong link between DOC properties and the riparian environment, structural alterations in the stream channel and changes in riparian vegetation (forestation) may result in changes in DOM composition and dynamics. [ABSTRACT FROM AUTHOR]

Abstract: A survey was conducted to examine river bedforms using side-scan sonar, sub-bottom profiler and an Acoustic Doppler Profiler in the middle–lower (mid-lower) Changjiang (Yangtze) River (downstream of Wuhan), China, during August 14–20, 2003 when the discharge was 27,000–36,000m3s−1. The results show bedforms of a range of sizes occur in the channel and their heights and lengths follow an exponential correlation below Flemming''s maximum line. Not all bedforms were formed under the flow conditions experienced during the survey, as shown by comparison to three existing models in the literature. Small-scale bedforms with a length <60m, defined as flat bed, mega-ripple and small dune in the present study, are mostly in equilibrium and are probably formed under the existing flow conditions. The large dunes with a length of >60m are not in equilibrium and are believed to be the relicts of previous large discharges now undergoing adjustment. Different bedform types occur in the five river reaches in this section of the Changjiang (Wuhan–Tianjiazhen, Tianjiazhen–Anqing, Anqing–Maanshan, Maanshan–Jiangyin and Jiangyin–estuary downstream). In the narrow and single channel reaches above Anqing, large/small dunes are limited to the channel with higher water surface slope where stream power is strong enough for riverbed sediments to be moved frequently. In the downstream reaches between Anqing and Jiangyin, characterized by anabranching channels, small-scale bedforms superimposed on large dunes occur widely due to intensive riverbed sediment transport from frequent diverging/converging flow during both floods and low-flow periods. Mega-ripples and flat beds prevail in the lowermost channel below Jiangyin where wider cross-sections result in dispersed stream power. [Copyright &y& Elsevier]

A unique data set of suspended sediment transport from the Breelva, which drains the Werenskioldbreen (Southwestern Spitsbergen), is reported for the period 2007–2012. This basin is thoroughly described hydrologically, glaciologically, and chemically. However, until now there was a lack of full recognition of mechanical denudation. This study extends the information on quantitative suspended sediment load (SSL), amounting to 37.30–130.94 kt per year, and also underlines the importance of its modification by high discharge events, triggered by intense snowmelt or heavy rainfall. The large floods during the hydrologically active season transported even 83% of the total SSL. The variability of the SSL is controlled by glacial storage and release mechanisms. Particularly interesting is the second half of the hydrologically active season when intense rainfall events plays a key role in shaping the sediment supply pattern. The main source of fine mineral matter is the basal moraine, drained by subglacial outflows. Their higher mobilization occurs when the hydrostatic pressure increases, often as a result of rainwater supply to the glacier system. An increasing precipitation trend for Hornsund fjord region determines a positive trend predicted for sediment flux. [ABSTRACT FROM AUTHOR]