The semi-arid regions of the eastern Eurasian Steppe and the Altai Region are highly sensitive towards climate change and are expected to increasingly experience drought conditions by rising temperatures during the next decades (Batima et al., 2005;Dai, 2011). This sensitivity is mostly due to its continentality and complex climate forcing by the interplay of several large-scale atmospheric circulation patterns affecting moisture advection and precipitation variability (Aizen et al., 2001;D'Arrigo et al., 2000). While the cold and dry winter climate is controlled by the Siberian High, moisture and precipitation is mainly brought by the mid-latitude Westerlies and in the past to some extent by the low-latitude East Asian Summer Monsoon (EASM; Hoerling et al., 2001;Visbeck, 2002). However, the past evolution of those atmospheric circulation systems remains controversial, and little is known about their interactions and how they have affected climate variability in the region. Currently, paleoclimate information from the Altai Region is mainly derived from pollen-based vegetation reconstructions that mostly show more extensive forests and boreal woodlands before ∼4 ka, and the dominance of steppe vegetation thereafter. This is generally interpreted to indicate warmer conditions with increased precipitation before ∼4 ka, followed by colder conditions with decreased precipitation (Blyakharchuk et al., 2007;Brugger et al., 2018;Rudaya et al., 2009). However, the expansion of grasslands and steppes after ∼4 ka BP could also be driven by intensified anthropogenic land-use, which is assumed to start with the introduction of mobile pastoralism from the Western Eurasian
A multiproxy-workflow was used to assess > plant protection products (PPP) in sediment samples from a Swiss lake under heavy agricultural pressure. The results show the appearance of PPP for the first time in the early 1960s with an overall detection of 34 PPP and with herbicides and fungicides found in equal proportions. Paleolimnological data (e.g., chronology, hyperspectral imaging of sedimentary green pigments and semi-quantitative elemental composition (µXRF scans)) suggest that PPP concentrations and fluxes to the sediment over time are not related to land surface processes such as soil erosion or lake biogeochemistry but are attributed mainly to PPP application (inferred from sales) or regulatory measures (bans).Additional compounds with similar sources of contamination as the target PPP captured by nontarget trend analysis (≥ 2000 unknown profiles), reveal significant inputs of contaminants to the lake starting in the 1970s, followed by a decrease of contamination at the beginning of the 1990s and a constant increase by ~28% of the unknown compounds since the year 2000.An ecological risk assessment conducted on detected PPP indicates that since the 1980s the sediment quality is insufficient with risk quotients values displaying maximum levels in the most recent sediments (~2010), despite bans of specific PPP and environmental regulations.
Submarine fresh groundwater discharging from discrete zones such as conduits overlain by thick sediment remains poorly documented and understood despite common anecdotal accounts of it. We analyzed this phenomenon by a suite of variable‐density, variably saturated groundwater flow simulations guided by field studies. The field observations included point flux and salinity measurements using seepage meters spread across the intertidal and the subtidal zones. The discretely measured seepage fluxes in the subtidal region were as high and the salinity was as fresh as those from the intertidal zone. Both fluxes and salinities varied with tides. Two‐dimensional simulations of the idealized beach‐ocean vertical section with discrete freshwater springs at the base showed the development of seawater recirculation cells along the edge of freshwater discharge plumes emanating from the outlets, causing mixing. Brackish water discharges at the sediment‐water interface above where the plume mixes with the recirculating seawater. Sensitivity analyses showed that stronger terrestrial fresh groundwater flow increases the freshwater plume size but does not affect the mixing zone width. Tidal oscillations and a dynamic fresh groundwater flow widened the mixing zones and increased pore water flux across the sediment‐water interface. Sediment thickness had a minor effect on the width of both the freshwater plume and its surrounding mixing zone. The subtidal freshwater plume and mixing zone likely represent a unique but potentially ubiquitous setting which hosts dramatic ecological and chemical gradients. Their local biogeochemical niche and coastal scale ecosystem impacts will need to be considered in investigations of coastlines.
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