Suspended sediments in the Kharaa River catchment (Mongolia) and its impact on hyporheic zone functions

Abstract

A previous study investigating the ecological status of the Kharaa River in Northern Mongolia reported fine-grained sediments as being a major stress factor causing adverse impacts on the benthic ecology. However, the source of these sediments within the catchment as well as the specific impact on hyporheic zone functions in the Kharaa River remained unclear. Therefore, the objective of the current study was to investigate the underlying sourcereceptor system and implement an integrated monitoring approach. Suspended sediment sources within the Kharaa catchment were identified by using extensive spatially distributed sediment sampling and geochemical and isotope fingerprinting methods. On the receptor side, the ecological implications across a gradient of fine-grained sediment influx were analyzed using a distinct hyporheic zone monitoring scheme at three representative river reaches along the Kharaa River. Results of suspended sediment source monitoring show that during snowmelt runoff, riverbank and gully erosion were the dominant sources. During the summer period, upland erosion contributed a substantial share of suspended sediment. Finegrained sediment influx proved to be the cause of habitat loss in the hyporheic zone and benthic oxygen production limitation. This combined catchment and in-stream monitoring approach will allow for a better understanding and spatially explicit analysis of the interactions of suspended sediment transport and hyporheic zone functioning. This information has built the basis for a coupled modeling framework that will help to develop efficient management measures within the Kharaa River basin with special emphasis on rapidly changing land-use and climatic conditions.

Science-Based IWRM Implementation in a Data-Scarce Central Asian Region: Experiences from a Research and Development Project in the Kharaa River Basin, Mongolia

“…Agriculture contributes 35% of total nitrogen and 32% of total phosphorus emissions [41][42][43][44], mostly through erosion from cultivated land and fallows. Sediment input caused by river bank erosion is a significant emission pathway for phosphorus [47][48][49]. This process is triggered by an increasing degradation of riparian vegetation due to high livestock densities with free access to the running waters.…”

“…Furthermore, high fine sediment loads constitute a major problem themselves since sediment-induced clogging inhibits essential habitat functions of the hyporheic zone [47,50]. As a consequence, functional shifts of the macroinvertebrate community and fish fauna have already been observed [44,51].…”

“…As a consequence, functional shifts of the macroinvertebrate community and fish fauna have already been observed [44,51]. Isotope-based sediment source fingerprinting techniques identified riverbank erosion (74.5%) and surface upland erosion (21.7%) as the main contributors to the suspended fine sediment load in the catchment [47,48]. Using erosion risk scenarios, Priess et al [52] showed that erosion could increase more than twofold in the steppe regions of the lower KRB and up to sevenfold in the forested and mountainous upper KRB due to the combined impacts of land use and climate changes.…”

“…Sediment sources were identified using geochemical and isotope-based fingerprinting techniques. River-bank erosion was identified as the predominant fine sediment source [47,48]. For the period 2007 to 2013, the transport loads of sediments, nutrients, heavy metals, and sediments were calculated based on water quality and hydrological data [37,[44][45][46].…”

Integrated Water Resources Management under different hydrological, climatic and socio-economic conditions

“…The foci are (1) regional hydrological processes (Vetter et al 2011), (2) land use impacts on the ecological quality of surface waters (Hartwig et al 2011), (3) innovative decentralized wastewater management strategies backed with an integrated analysis (Sigel et al 2011) and (4) institutional settings as a prerequisite for effective implementation (Horlemann and Dombrowsky 2011).…”