Zoobenthos community turnover in a 1650‐yr lake‐sediment record of climate‐driven hydrological change

Abstract

In fluctuating lake ecosystems, the severity of anthropogenic disturbance is often difficult to assess because the magnitude of natural dynamics rivals or surpasses that of ecosystem alteration due to human impact. Consequently, it is also difficult to evaluate the resilience of these ecosystems' plant and animal communities to that impact. Unfortunately, lake ecosystem response to natural cycles of lake-level and salinity fluctuation at multi-annual time scales is poorly understood, due to complex relationships between hydrological dynamics and the local availability or distribution of ecological niches. We present a 1650-yr-long paleoecological record from Lake Naivasha in Kenya (East Africa) which traces community assembly and turnover in two prominent groups of benthic invertebrates (chironomids and ostracods) in response to a climate-driven sequence of 10 major lake-level fluctuations. Over this time period, lake depth (inferred from sedimentology) fluctuated between~3 and >35 m, and salinity (inferred from fossil diatom assemblages) varied between~100 and~23,500 µS/cm. Prior to~780 yr ago, the unique community response to salinity was stronger than to lake depth. Around that time the lake transitioned to a more open hydrology, relatively stable freshwater conditions and greater prevalence of macrophyte-associated benthic habitat, so that community response to variations in lake depth (and surface area) became stronger. Notably, major community restructuring in the course of this transition was not synchronous between the two groups, because it depended on the proliferation of key freshwater species in each group. Our results imply that (1) climate-sensitive lake ecosystems are more likely controlled by salinity change if both its amplitude and frequency are large enough to induce ecological species sorting; (2) community response to such salinity changes may be predictable, and likely to show coherence across different groups of aquatic biota; and (3) the timing of major community restructuring strongly depends on the ecology of key species, and whether the species sorting is driven by salinity change itself or indirectly by the salinity-dependent availability of ecological niches.

Simulating evaporative wet and dry cycles in Gale crater, Mars using thermochemical modeling techniques.

“…Lakes in terrestrial settings vary in their characteristics based on climatic variations. There are broadly three types of lakes based on the ratio of lake inflow and discharge Moknatian & Piasecki, 2020;Van der Meeren & Verschuren, 2021): perennial lakes (high water content: water never fully evaporates even in drought periods and the system takes a relatively long time to form evaporites), ephemeral lakes (lower water content compared to perennial lakes with significantly low water levels during water periods enabling evaporite formation faster than in perennial lakes), and dry lakes (predominantly dry with sporadic water content which enables fastest evaporite formation compared to other closed lake systems).…”

“…In terrestrial settings the average wet-dry cycling time (i.e., the amount of time required for a closed lake system to complete a cycle comprising of highest water content in a wet period to lowest water content in a dry period) is approximately 1.5 years for dry lakes with sporadic water presence, 9 years for ephemeral lakes, and 65 years for perennial lakes. Figure 3 shows an illustration of relative water amounts varying over time with the average cycling time for dry lakes with sporadic water presence, ephemeral lakes, and perennial lakes (compiled from Moknatian and Piasecki, 2020;Van der Meeren and Verschuren, 2021). associated with deltaic deposits.…”

Checklist of the diatoms (Bacillariophyta) from Lake Naivasha, Kenya, with some historical notes

“…Lake Sonachi is normally a strongly saline-alkaline (‘soda’) lake, but substantial changes in salinity during past episodes of wetter and drier climate conditions have also been reported in historical times ( Verschuren et al 1999a ). This implies that freshwater as as well as inland saline communities of aquatic biota, among others of diatoms, can be found in the lakes of this aquatic system, making Lake Naivasha and its satellite lakes ideal for paleolimnological research involving both climate reconstruction and long-term ecological dynamics ( Verschuren et al 1999a , b , 2000a , 2000b ; Mergeay et al 2011 ; Van der Meeren et al 2019 ; Van der Meeren and Verschuren 2021 ).…”