Lake Kauhako-, Moloka'i, Hawai'i: biological and chemical aspects of a morpho-ectogenic meromictic lake

Abstract

We undertook the first combined microbiological and hydrochemical study of the 248 m deep meromichc Lake KauhakG. Situated at sea level 1.6 km from the sea in the crater of an extinct volcano on the island of Moloka'i, Hawai'i, USA, Lake KauhakB has the highest relative depth (ratio of depth to surface area, z, = 374 %) of any lake in the world. The upper 4.5 m were stratified (T= 23 to 26'C, salinity = 6 to 24.5), but below a pycnocline at -4.5 m temperature and salinity were uniform (T = -26.25"C; salinity = 32). Seawater hkely intrudes by horizontal hydraulic conductivity through rock separating the lake and the Pacific Ocean. Anoxia commenced below 2 m. Hydrogen sulfide was undetectable at 4 m. but averaged -130 PM between 5 and 28 m. Dissolved inorganic carbon concentrations ranged from -1.50 mM at the surface to -3.3 mM below 5 m. Total organic carbon peaked at 0.94 mM above the pycnocline hut rernaiced about 0.30 mM be!ow 5 m. Soluble reactive phosphorus and ammunium concentrations, nanomolar above the pycnocline, increased to -28 and l75 PM, respectively, at greater depth. Nitrate attained 3.7 PM in shallow water, but was -0.2 pM from the pycnocline to 100 m. Leucine aminopeptidase (LAPase) activity at the surface exceeded 1100 nmol of substrate hydrolyzed I-' h-' Activities of a-and P-glucosidase were lower, but showed depth distributions similar to that of LAPase. Surface waters hosted large and diverse picoplankton populations; chlorophyll a (chl a) exceeded 150 1-19 I-'. and heterotrophic bacteria and autofluorescent bacteria attained 2 X log and 9 X 109 1-l, respectively. Filamentous cyanobacteria and 'Proch1orococcus'-like autotrophs occurred only in the upper 2 m. Chl a was the dominant pigment above 2 m, but pigment diversity increased markedly in anoxic waters between 3 and 5 m. Lake Kauhako is a unique habitat for further studies, particularly of interactions among flora and fauna restricted to a shallow water column within a single basin.

Stratification of the microbial community inhabiting an anchialine sinkhole

“…Correspondence of H 2 S and NH 4 profiles have previously been observed in Bundera Sinkhole (Humphreys 1999), and while it has not been reported in other anchialine systems, this coupling is often observed within meromictic lake systems (e.g. Donachie et al 1999). As also previously observed at this site, the distributions of NH 4 and NO 3 exhibited inversely related profiles, which is indicative of nitrification (Ward 1986).…”

“…Consequently, anchialine habitats generally support diverse and often chemolithotrophic microbial assemblages (Pohlman et al 1997, Donachie et al 1999). However, very few studies have investigated the ecology and spatiotemporal dynamics of microbial communities with-ABSTRACT: Bundera Sinkhole in northwestern Australia is an anchialine ecosystem characterised by a highly stratified water column comprising a complex polymodal profile of several physico-chemical parameters.…”

Limnological Characterization of the Largest Freshwater Lake in Remote Oceania (Lake Letas, Gaua Island, Vanuatu)

“…However, even at 95 m depth traces of oxygen were confirmed with the electrode and the Winkler method, showing that this large lake is not meromictic throughout the year. In this respect it contrasts with several deep, meromictic volcanic crater lakes in Oceania whose sheltered position, smaller surface area, and inflow of saltwater lead to anoxic condi-tions in the monimolimnion (Maciolek and Yamada 1981, Donachie et al 1999, Sichrowsky et al 2014.…”

Hydrochemical properties, bacterioplankton abundance and biomass in the meromictic Lake Starodworskie in 2004

“…The key factor is that the surface area is small in comparison to depth, represented by a high index of relative depth (Donachie et al 1999). Additionally, this phenomenon is stimulated by increasing primary production and the accumulation of decomposition products in the near-bottom waters, saline springs leaking into lake bottoms, or sewage input into lakes.…”