The key role of increased fine sediment loading in shaping macroinvertebrate communities in a Eurasian steppe river (Kharaa River, Mongolia) under multiple stressor

Aquatic communities across the Eurasian steppe belt are facing increased anthropogenic pressures that result from rapid population growth and catchment wide land-use changes. The particular variety, intensity, overlay and legacy of these impacts provide a unique setting to investigate ecological responses of multiple stressors. We studied macroinvertebrate communities along the Kharaa River in Mongolia, which displayed a distinct, downstream directed gradient of nutrient enrichment, disturbed bank morphology, reduced riparian vegetation, elevated turbidity and increased fine sediment intrusion into the hyporheic zone. Under these impacted conditions (TP 0.02 – 0.09 mgl-1, TN 0.33 – 0.96 mgl-1, FNU 0.62 - 5.43) population densities and biomass of macroinvertebrates were high (5293 ± 409 individuals m-2 and 2631 ± 153 mg dry weight m-2) and stable. In contrast, macroinvertebrate community structure showed significant negative linear relationships (Pearson’s r) for taxa richness (r = -0.79), Shannon Index of Diversity (r = -0.85), Evenness (r = -0.81), relative abundance of EPT individuals (r = -0.88) and relative biomass of hard substrate colonisers. At the same time, relative biomass of Chironomidae and Oligochaeta (r = 0.76) was positively correlated to mean turbidity values. Our results indicate a key impact of suspended fine sediment loads on macroinvertebrate community structure and to a lesser extent on habitat complexity at low rates of hyporheic fine sediment intrusion (mean values 0.9 - 1.6 g DW l-1d-1) in the Kharaa River. Hence, the implementation of effective regional management strategies aiming at to reduce erosion processes to ecologically tolerable levels deserves high priority.

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Зохиогч Michael Schäffer, Claudia Hellmann, Saulyegul Avlyush, Dietrich Borchardt
Сүүлийн шинэчлэл 2018 9-р сар 28, 02:10 (UTC)
Үүссэн 2018 9-р сар 28, 02:10 (UTC)