Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo Investigating the impact of anthropogenic land use on a hemiboreal lake ecosystem using carbon/nitrogen ratios and coupled-optical emission spectroscopy N. Stivrins a,b,c, ⁎ , M. Liiv b , A. Brown d,e , R.Y. Banerjea d , A. Heinsalu b , S. Veski b a Department of Geography, Faculty of Geography and Earth Sciences, University of Latvia, Jelgavas street 1, Riga LV-1004, Latvia b Department of Geology, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia c Lake and Peatland Research Centre, Purvisi, Puikule, Alojas District, Latvia d Department of Archaeology, University of Reading, Whiteknights, PO Box 227, Reading RG6 6AB, United Kingdom e Wessex Archaeology, Portway House, Old Sarum Park, Salisbury SP4 6ED, United Kingdom ARTICLE INFO Keywords: Environmental change Chara Soil erosion EU H3140 Non-pollen palynomorphs Paleolimnology ABSTRACT Anthropogenic impacts on lake ecosystems have increased substantially towards the present. However, the strength and timing in most cases are not evaluated in detail, missing valuable information on the response and recovery of an aquatic system. In this study, we use the sediment total organic carbon/total nitrogen ratio (C/N) and inductively coupled-optical emission spectroscopy (ICP-OES) elements and the available information about the biological processes to explore anthropogenic land use impact on the lake ecosystem. As a case study we selected a hemiboreal lake Trikātas (Latvia, NE Europe). The Pearson correlation was used to statistically test the correlations of all variables. Our results show that the C/N ratio lowered immediately with the onset of crop cultivation at 500 BCE. Extensive forest clearance and an abrupt increase in land use are reflected through the associated chemical elements from ICP-OES and the increasing presence of herbivore dung spores since 1200 CE. These changes concur with the excess of fish remains suggesting a decrease in fish populations. Interestingly, anthropogenic land use driven erosion and accompanied calcium carbonate (CaCO 3 ) matter influx favoured the abundance of Chara spp. in Lake Trikātas since 500 CE, which currently forms the protected specific habitat-type (H3140) of the European Union. At present, specific submerged macrophyte Chara habitat-type diminished almost entirely due to increased nutrient input, phytoplankton blooming, hypertrophic conditions and reduced light availability. The continued land use practices led to a switch in organic matter source in the lake from macrophytes to solely algal origin. The current study underlines the need of additional methods used to detect the sensitivity of lake ecosystem to external disturbances such as minor anthropogenic land use that might not necessarily be apparent in more traditional analyses such as palynology. 1. Introduction Knowing the timing of first external disturbances on lake ecosystems provides valuable data on the response of an aquatic complex and provides essential insight into the legacy of human impacts on the contemporary aquatic system (Dubois et al., 2018). Historical baselines, in the relative absence of humans, are the conceptual benchmark for biodiversity assessment and management, but it is reasonable to ask whether past conditions remain relevant reference points for the re- storation and management of contemporary human-altered systems (Kopf et al., 2015; Dietze et al., 2018). Climate and anthropogenic activity are two of the most critical factors affecting freshwater lakes in the Northern Hemisphere (Douglas and Smol, 1999; Smol et al., 2005; Rantala et al., 2015). Climate change influences lake ecosystems both directly and indirectly (Fritz and Anderson, 2013; Smith et al., 2015; O'Reilly et al., 2015). Although climate change and lake ontogeny drive the development of lake eco- systems over the long-term, it was the impact of human activities that act as a trigger for noticeable aquatic changes. Bradshaw et al. (2005) demonstrated that human activities over thousands of years not only impacted and shaped the Danish terrestrial landscape but played a significant role in lake development. More recent studies showed that specific human activities such as flax retting, biomanipulation and catchment land use could lead to drastic changes in nutrient cycling in https://doi.org/10.1016/j.palaeo.2019.01.007 Received 29 August 2018; Received in revised form 3 January 2019; Accepted 3 January 2019 ⁎ Corresponding author at: Department of Geography, Faculty of Geography and Earth Sciences, University of Latvia, Jelgavas street 1, Riga LV-1004, Latvia. E-mail address: normunds.stivrins@lu.lv (N. Stivrins). Palaeogeography, Palaeoclimatology, Palaeoecology 518 (2019) 1–9 Available online 07 January 2019 0031-0182/ © 2019 Elsevier B.V. All rights reserved. T