A Holocene Sedimentary Record and the Impact of Sea-Level Rise in the Karst Lake Velo Blato and the Wetlands on Pag Island (Croatia)

Tamara Marković,Josip Terzić,Ivona Ivkić Filipović,Branko Petrinec,Martina Šparica Miko,Ozren Hasan,Slobodan Miko,Nikolina Ilijanić

doi:10.3390/w14030342

Tamara Marković, Josip Terzić + Show 6 more

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https://doi.org/10.3390/w14030342

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Abstract

Lakes in coastal lowland areas represent a critically vulnerable environment as a transitional space between freshwater and seawater environments. The paleoenvironmental reconstruction and anthropogenic impact are assessed through the lake sediment cores from Velo, Malo, and Kolanjsko Blato using multi-proxy analyses (sedimentological, mineralogical, geochemical, 137Cs and ostracod analyses, and AMS 14C radiocarbon dating). The freshwater lake Velo Blato was formed at 8100 cal yr BP due to rising groundwater levels as a consequence of sea-level rise. The brackish conditions in Lake Velo Blato started at 7100 cal yr BP, giving the index point for the sea-level curve of 7-m lower than present. Lead concentrations showed slightly increased values in the last 1800 cal yr BP, while the spike in Malo Blato lake sediments probably derived from bird hunting with lead bullets. Kolanjsko Blato sediment core archives the sediment record of the last 2050 years, which represents a shallow brackish coastal wetland under marine influence. Enrichment factors showed the accumulation of Cu, Hg, P, Pb, S, and Zn in the sediments from Kolanjsko Blato in the last 650 cal yr BP, which coincides with the high organic carbon content, and in sediments from Malo Blato after the lake’s formation (from the depth of 20 cm upwards). Anthropogenic Cu introduced into the Kolanjsko Blato sediments is the highest in the surface sample. Surficial sediments from Velo Blato are characterized by the high organic carbon, S, P, and N content, indicating high productivity and eutrophication which led to occasional anoxic conditions on the lake bottom in the last 200 years.

Highlights

The low-lying coastal areas in the Mediterranean, such as the eastern Adriatic coast (EAC), are under constant threat of marine influence during Holocene transgression, i.e., relative sea-level (RSL) rise
The overall objective of this study is to identify paleolimnological and paleo-hydrological processes controlling the Holocene evolution of karst lakes in the coastal karstic region of Croatia using multiproxy methods
Along the sediment core from Velo Blato (0–557 cm, +11 cm in core catcher), changes in the color of the sediment are visible from dark grey, almost black in the upper 21 cm, to the bright lake carbonate sediment with occasional layers of darker sediment

Summary

Introduction

The low-lying coastal areas in the Mediterranean, such as the eastern Adriatic coast (EAC), are under constant threat of marine influence during Holocene transgression, i.e., relative sea-level (RSL) rise. A fluctuating sea level generates changes in coastal areas due to the increase in salinity. Lake levels, and seawater impacts may greatly influence wetland biota. Coastal wetlands are defined as ecosystems found within an elevation gradient that ranges between subtidal depths, at which light penetrates to support photosynthesis of benthic plants, and the landward edge, where the sea passes its hydrologic influence to groundwater and atmospheric processes [6]. Coastal lakes and wetlands are transitional ecosystems between land, freshwater, and seawater. The Croatian karstic coast is scant in terms of permanent freshwater body occurrences; most of the basins drowned from the period of the

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