Sediment deposition from eroding peatlands alters headwater invertebrate biodiversity

Freshwater invertebrate responses to fine sediment stress: A multi-continent perspective

Excessive fine sediment (particles <2 mm) deposition in freshwater systems is a pervasive stressor worldwide. However, understanding of ecological response to excess fine sediment in river systems at the global scale is limited. Here, we aim to address whether there is a consistent response to increasing levels of deposited fine sediment by freshwater invertebrates across multiple geographic regions (Australia, Brazil, New Zealand and the UK). Results indicate ecological responses are not globally consistent and are instead dependent on both the region and the facet of invertebrate diversity considered, that is, taxonomic or functional trait structure. Invertebrate communities of Australia were most sensitive to deposited fine sediment, with the greatest rate of change in communities occurring when fine sediment cover was low (below 25% of the reach). Communities in the UK displayed a greater tolerance with most compositional change occurring between 30% and 60% cover. In both New Zealand and Brazil, which included the most heavily sedimented sampled streams, the communities were more tolerant or demonstrated ambiguous responses, likely due to historic environmental filtering of invertebrate communities. We conclude that ecological responses to fine sediment are not generalisable globally and are dependent on landscape filters with regional context and historic land management playing important roles.

Land use/land cover change effect on soil erosion and sediment delivery in the Winike watershed, Omo Gibe Basin, Ethiopia

Information on soil loss and sediment export is essential to identify hotspots of soil erosion to inform conservation interventions in a given watershed. This study investigates the dynamics of soil loss and sediment export associated with land-use/land cover changes and identifying soil loss hotspot areas in the Winike watershed of the Omo-Gibe Basin of Ethiopia. Spatial data collected from satellite images, topographic maps, meteorological and soil data were analyzed. The land-use types in the study area were categorized into six: cultivated land, woodland, forest, grazing, shrubland, and bare land. The Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) of the sediment delivery ratio (SDR) model was used based on the analysis of land use/land cover and RUSLE factors. The results show that total soil loss increased from 774.86 thousand tons in 1988 to 951.21 thousand tons in 2018 while the corresponding sediment export increased by 3.85 thousand tons for the same period. These were subsequently investigated in each land-use type. Cultivated fields generated the highest soil erosion rate, increasing from 10.02 t/ha/year in 1988 to 43.48 t/ha/year in 2018 when compared with the grazing, shrub, forest, wood land and bare land-use types. This corresponds with the expansion of the cultivated area. This is logical as the correlation between soil loss and sediment delivery and expansion of cultivated area is highly significant (p < 0.001). Sub-watershed six (SW-6) showed the highest soil loss (23.17 t/ha/year) while sub-watershed two (SW- 2) has the lowest soil loss (5.54 t/ha/year). This is because SW-2 is situated in the lower reaches of the watershed under dense vegetation cover experiencing less erosion. The findings on the erosion hotspots presented in this study allow prioritizing the segments of the watershed that need immediate application of improved management interventions and informed decision-making processes.

Agricultural impacts on streams near Nitrate Vulnerable Zones: A case study in the Ebro basin, Northern Spain

Agricultural intensification during the last century has caused river degradation across Europe. From the wide range of stressors derived from agricultural activities that impact rivers, diffuse agricultural pollution has received most of the attention from managers and scientists. The aim of this study was to determine the main stressors exerted by intensive agriculture on streams around Nitrate Vulnerable Zones (NVZs), which are areas of land that drain into waters polluted by nitrates according to the European Nitrate Directive (91/676/EEC). The study area was located in the NW of La Rioja (Northern Spain), which has some of the highest nitrate concentrations within the Ebro basin. The relationships between 40 environmental variables and the taxonomic and functional characteristics of the macroinvertebrate assemblages (which are useful indicators of water quality) were analyzed in 11 stream reaches differentially affected by upstream agricultural activity. The streams affected by a greater percentage of agricultural land cover in the surrounding catchment had significantly higher nitrate concentrations than the remaining sites. However, hydromorphological alteration (i.e. channel simplification, riparian forest and habitat degradation), which is closely linked to agricultural practices, was the main factor affecting macroinvertebrate assemblages. We suggest that “good agricultural practices” should be implemented in streams affected by NVZs to reverse stream degradation, in concordance with the European Water Framework Directive (WFD).