Differential resilience of ancient sister lakes Ohrid and Prespa to environmental disturbances during the Late Pleistocene

Abstract

Abstract. Ancient lakes, like lakes Ohrid and Prespa on the Balkan Peninsula, have become model systems for studying the link between geological and biotic evolution. Recently the scientific deep drilling program "Scientific Collaboration on Past Speciation Conditions in Lake Ohrid" (SCOPSCO) has been launched to better understand the environmental, climatic and limnological evolution of the lake. It revealed that Lake Ohrid experienced a number of environmental disturbances during its ca. 2.0 million year long history. They comprise disturbances that lasted over longer periods of times ("press events") such as Heinrich events as well as sudden and short disturbances ("pulse events") like the deposition of volcanic ashes. The latter include one of the most severe volcanic episodes during the Late Pleistocene, the eruption of the Campanian Ignimbrite (known as Y-5 marine tephra layer) from the Campi Flegrei caldera, dated at 39.6 ± 0.1 ka ago. The event is recorded by the deposition of a ca. 15 cm thick Y-5 tephra layer in sediment cores of lakes Ohrid (DEEP-5045-1) and Prespa (Co1204). This pulse event is overlain by the Heinrich event 4 (H4), 40.0–38.0 ka ago. In the current paper, diatoms were used as proxies to compare the responses of these lakes to the Y-5 (pulse) and the H4 (press) disturbances. Based on stratigraphically constrained incremental sum of squares cluster (CONISS) and unconstrained Partitioning Around Medoids (PAM) analyses, we found only little evidence that the diatom community compositions in either lake responded to the H4 event. However, the Y-5 influx caused clear and rapid diatom community changes. After the initial response, community composition in Lake Ohrid and, to a lesser extent, in Lake Prespa slowly returned to their quasi pre-disturbance state. Moreover, there is no evidence for disturbance-related extinction events. The combined evidence from these findings suggests that lakes Ohrid and Prespa likely did not experience regime shifts. It is therefore concluded that both lakes show resilience to environmental disturbance. However, it seems that Lake Ohrid is more resilient than Lake Prespa as the recovery of diatom communities is more pronounced and as its estimated recovery time is only ca. 1400 years vs. ca. 3600 years in Lake Prespa. The reasons for the differential responses remain largely unknown, but differences in geology, lake age, limnology, and intrinsic parameters of the diatom proxies may play a role. Given the relative robust results obtained, this study provides important new insights into the response of lakes to (multiple) environmental disturbances. Moreover, it contributes to one of the major goals of the SCOPSCO project – to evaluate the influence of major geological events onto the evolution of endemic taxa in Lake Ohrid.

Constant diversification rates of endemic gastropods in ancient Lake Ohrid: ecosystem resilience likely buffers environmental fluctuations

“…The second scenario is supported by the mollusk and diatom fossil records (Cvetkovska et al, 2015;Jovanovska et al, 2015) for the past ∼ 100 ky. For instance, the Campanian Ignimbrite Y5 tephra influx 39.6 ky ago (see Leicher et al, 2015) altered the water chemistry of Lake Ohrid and increased the content of silica, which in turn amplified diatom growth rates. However, it did not cause severe changes in diatom community structures or even extinction events .…”

Diatoms do radiate: evidence for a freshwater species flock

“…2 kyr) between 446.65 and 406.96 mcd, because of an increased appearance of endemic species (Table S2). Cleaned diatom samples were studied on 1 000× magnification using a Carl Zeiss Axioplan 2 microscope and identified based on recent taxonomic literature (see Jovanovska et al ., for details). For the upper 247.8 mcd ( c .…”

Sedimentological processes and environmental variability at Lake Ohrid (Macedonia, Albania) between 637 ka and the present

“…Grain flows that enter the deep parts of the Lake Ohrid basin via the steep slopes might transform into a mesopycnal flow at the boundary of the hypolimmion (cf. also Mulder and Alexander, 2001;Juschus et al, 2009), which would have prevented erosion of the underlying sediments.…”