Agricultural intensification vs. climate change: what drives long-term changes in sediment load?

Abstract

Abstract. Climate change and agricultural intensification are expected to increase soil erosion and sediment production from arable land in many regions. However, to date, most studies have been based on short-term monitoring and/or modeling, making it difficult to assess their reliability in terms of estimating long-term changes. We present the results of a unique data set consisting of measurements of sediment loads from a 60 ha catchment – the Hydrological Open Air Laboratory (HOAL) – in Petzenkirchen, Austria, which was observed periodically over a time period spanning 72 years. Specifically, we compare Period I (1946–1954) and Period II (2002–2017) by fitting sediment rating curves (SRCs) for the growth and dormant seasons for each of the periods. The results suggest a significant increase in sediment loads from Period I to Period II, with an average of 5.8 ± 3.8 to 60.0 ± 140.0 t yr−1. The sediment flux changed mainly due to a shift in the SRCs, given that the mean daily discharge significantly decreased from 5.0 ± 14.5 L s−1 for Period I to 3.8 ± 6.6 L s−1 for Period II. The slopes of the SRCs for the growing season and the dormant season of Period I were 0.3 and 0.8, respectively, whereas they were 1.6 and 1.7 for Period II, respectively. Climate change, considered in terms of rainfall erosivity, was not responsible for this shift, because erosivity decreased by 30.4 % from the dormant season of Period I to that of Period II, and no significant difference was found between the growing seasons of periods I and II. However, the change in sediment flux can be explained by land use and land cover change (LUCC) and the change in land structure (i.e., the organization of land parcels). Under low- and median-streamflow conditions, the land structure in Period II (i.e., the parcel effect) had no apparent influence on sediment yield. With increasing streamflow, it became more important in controlling sediment yield, as a result of an enhanced sediment connectivity in the landscape, leading to a dominant role under high-flow conditions. The increase in crops that make the landscape prone to erosion and the change in land uses between periods I and II led to an increase in sediment flux, although its relevance was surpassed by the effect of parcel structure change under high-flow conditions. We conclude that LUCC and land structure change should be accounted for when assessing sediment flux changes. Especially under high-flow conditions, land structure change substantially altered sediment fluxes, which is most relevant for long-term sediment loads and land degradation. Therefore, increased attention to improving land structure is needed in climate adaptation and agricultural catchment management.

Testing CASE: A new event‐based Morgan‐Morgan‐Finney‐type erosion model for different rainfall experimental scenarios

“…When surface runoff, sediment and structural connectivities are to be investigated, and event‐based soil loss is of interest, models from the (R)USLE family are therefore not the obvious choice among available erosion models. The total sediment yield of a catchment area is frequently dominated by only a few extreme events, as lined out by Edwards and Owens (1991), Boardman (2006), González‐Hidalgo et al (2009), Gonzalez‐Hidalgo et al (2012) or Wang et al (2022), so we assume that concentrating modelling efforts on these events is a feasible approach. For example, the main cropping regions in Austria, these events mainly occur when the soil is not covered and therefore most prone to soil loss, right after seedbed preparation in spring and early summer (Klik & Eitzinger, 2010; Strauss et al, 1995; Strohmeier et al, 2016).…”

Citizens Science Perspectives on Drivers of Sedimentation in the Lusitu River Catchment in Chirundu District, Zambia

“…Local factors which include topography, river control structures, soil and water conservation measures, tree cover, landuse or land disturbance such as agriculture and mining influence sediment loads in rivers [21]. Further, climate change is influencing sediment loads of rivers around the world due to changes in sediment yields as a result of climate change and associated changes in rainfall and runoff [22]. Effects of climate change in sediment yield may also interact with other anthropogenic causes of sedimentation in rivers, such as agricultural production [23,24,25].…”

Detection and attribution of changes in river flow and sediment loads in the Nile basin

“…Wang et al (2022) shows how Land Use Land Cover (LULC) and land structure changes are responsible for explaining the long term changes in soil erosion and sediment loads rather than climate change in the Hydrological Open Air Laboratory (HOAL) catchment, Austria. Li et al (2019) also found out that livestock grazing accelerated soil erosion more than climate change on the Qinghai-Tibet Plateau leading to increased sediment deposition.…”