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

[摘要] Climate change and agricultural intensification areexpected to increase soil erosion and sediment production from arable landin many regions. However, to date, most studies have been based on short-termmonitoring and/or modeling, making it difficult to assess their reliabilityin terms of estimating long-term changes. We present the results of aunique data set consisting of measurements of sediment loads from a 60 hacatchment – the Hydrological Open Air Laboratory (HOAL) – in Petzenkirchen,Austria, which was observed periodically over a time period spanning 72years. Specifically, we compare Period I (1946–1954) and Period II(2002–2017) by fitting sediment rating curves (SRCs) for the growth and dormantseasons for each of the periods. The results suggest a significant increasein 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 sedimentflux 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 forPeriod II. The slopes of the SRCs for the growing season and the dormantseason of Period I were 0.3 and 0.8, respectively, whereas they were 1.6 and1.7 for Period II, respectively. Climate change, considered in terms ofrainfall erosivity, was not responsible for this shift, because erosivitydecreased 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 ofperiods I and II. However, the change in sediment flux can be explained byland use and land cover change (LUCC) and the change in landstructure (i.e., the organization of land parcels). Under low- and median-streamflowconditions, the land structure in Period II (i.e., the parcel effect) had noapparent influence on sediment yield. With increasing streamflow, it becamemore important in controlling sediment yield, as a result of an enhancedsediment connectivity in the landscape, leading to a dominant role under high-flow conditions. The increase in crops that make the landscape prone toerosion and the change in land uses between periods I and II led to anincrease in sediment flux, although its relevance was surpassed by theeffect of parcel structure change under high-flow conditions. We conclude that LUCC and land structure change should be accountedfor when assessing sediment flux changes. Especially under high-flowconditions, 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 inclimate adaptation and agricultural catchment management.

[学科分类] 妇产科学