## 1 Introduction  
Lake sediments are archives of past variations in biological communities which respond to environmental and climate change and vary in time and space [1, 2, 3, 4, 5]. These changes result from a complex interaction between climate, anthropogenic activities and the characteristic of aquatic systems that imply its study and recording [6, 7, 5]. Such records are particularly lacking for the Southern Hemisphere [6, 7, 8]. The Mediterranean coast of Chile corresponds to a climatic and vegetational transition zone and is considered as an area sensitive to environmental changes due to anthropogenic impacts and climate alternations [6; 9; 10; 11; 12]. Indeed, historical records have emphasised the influence of anthropogenic activities on lakes in the region over the last 500 years [13; 14]. In particular, intensive periods of land use, clear-cutting of native forest and the replacement by exotic plantation forestry (_Pinus radiata_ and _Eucalyptus_ spp. ), wheat growing, urbanisation and industrialisation processes have caused changes in the trophic status, chemical composition and water quality of the lakes [13; 14; 15; 16]. Regional studies in the Chilean Mediterranean Zone revealed that prehispanic native cultures had no significant impact on land use [17]. However, since the mid-sixteenth century, Spanish colonisation induced disturbances on the natural landscape. The introduction of the Mediterranean Hispanic Model of agriculture-livestock resulted in pronounced land-use changes [18; 19]. In addition, the urbanisation of the coastal zone has intensified over the last decades and generated a significant increase in nutrient inputs to watersheds, leading to gradual environmental degradation and an increase in phytoplankton productivity [13; 16; 20; 21; 22; 23]. For example, diatom studies in Laguna Grande and Laguna Chica (San Pedro de la Paz, Biobio region, south-central Chile) revealed that trophic state changes occurred after the Spanish arrival [13; 20; 22]. Moreover, cyanobacterial blooms have been detected in Laguna Grande in the last decades [24], which is likely related to the recent increase in temperature due to global warming and increased nutrient concentrations [25; 26; 27]. However, few studies focused on long-term changes in the entire phytoplankton community have been considered in Chilean coastal lakes to explain their response to environmental conditions [6; 9; 28; 29; 30]. Sedimentological and biological proxies such as (sub)fossil remains, total organic carbon concentration, C and N stable isotopes and phytoplankton pigments can provide valuable information on past changes in primary production and the phytoplankton community structure [6; 7; 31; 32; 33; 34; 35; 36; 37; 38; 39]. Phytoplankton pigments have the advantages that they also allow for the study of soft-bodied organisms which do not readily fossilise. A disadvantage is that pigments are relatively sensitive to degradation in response to high irradiance, oxygen concentrations, bacterial activity, grazing and high temperatures [34; 36; 40; 41; 42; 43; 44]. Nevertheless, once buried in suitable conditions (anoxic sediments), pigments can be preserved for thousands of years [42; 45; 46; 47]. Stable isotope ratios of carbon and nitrogen and the atomic C/N ratios can provide insights into the origin of organic matter in aquatic ecosystems, vegetation sources, aquatic algae proportions or terrestrial organic matter. Moreover, they are used to interpret paleoenvironmental changes in lakes and their watersheds [48; 49; 50; 51; 4]. The tracking of environmental changes allows historical trajectories, local and regional patterns to be revealed [11; 52; 53]. This paper is aimed at reconstructing primary production during the late Holocene to the present-day based on a multiproxy approach, which includes the sedimentological description, biogenic silica, carbon and nitrogen isotopic composition and fossil pigments in two Mediterranean coastal lakes in Chile, namely Laguna Grande and Chica de San Pedro.