Effects of recent increases in salinity and nutrient concentrations on the microbialite community of Lake Clifton (Western Australia): are the thrombolites at risk?

Abstract

The Yalgorup lakes, a groundwater-fed system in south-western Australia recognized as a Ramsar wetland, hold significant scientific and conservation value due to the presence of a unique range of lake systems, resident waterfowl and, on the eastern shore of Lake Clifton, the presence of the only thrombolite reef in the southern hemisphere. Recent concern over changing physico-chemical conditions in the lakes, particularly an increase in salinity, prompted this study: the current status of the inherent thrombolite community is unknown. Salinity, total phosphorous (TP), phosphate, total nitrogen (TN), nitrate, chlorophyll-a and relative abundance of the thrombolite microflora were measured in Lake Clifton to analyse changing conditions in this lake and to determine the effect of these water parameters on the thrombolite community. Comparisons with historical data revealed a significant increase in salinity since 1985 and a possible increase in phosphorus concentrations in the lake in the recent decade, although historical nutrient data are rather sparse. The increased salinity may be due to concentration of lake water through a combination of high evaporation, long-term reduction in rainfall and increased groundwater abstraction. Comparison of the composition of the thrombolite community with historical data indicates a large reduction in relative abundance of Scytonema sp. and other filamentous cyanobacterial species, which are believed to be fundamental for the thrombolite structure. It is concluded the changing physico-chemical environment of the Yalgorup Lakes may have led to the decline in important genera in the thrombolite community; however, the mechanisms underlying this change remain unknown.

Biodiversity of Living, Non-marine, Thrombolites of Lake Clifton, Western Australia

“…Nonetheless, given the lake 401 conditions at the time, it is reasonable to assume that cyanobacteria were more numerous 402 some 20-30 years ago than currently recorded. The current study reinforces the suggestion 403 from the microscopy-based study of Smith et al (2010) that cyanobacteria are no longer the 404 dominant organisms at the lake. We can conclude that the changing physico-chemical 405 conditions at Lake Clifton may have contributed to a decline in the cyanobacterial 406 populations thought to be fundamental to thrombolite formation in this system; however 407 further work is required to elucidate the underlying mechanisms that will be impacted by 408 such changes.…”

“…In the current study we report a significant change in water chemistry -the salinity on the 313 day we collected our samples (Dec 2008) Smith et al 2010). This, along with other more comprehensive analyses of water 316 quality at Lake Clifton as measured by the UWA Centre for Water Research (per.…”

“…To determine whether 199 microbial community structure was significantly impacted by thrombolite sampled (T2 versus 200 T3), or depth (outer surface versus inner surface) multivariate statistical analyses were 201 performed in Primer 6 (Primer-E Ltd., United Kingdom). Analyses were performed on data 202 that had been generated using the QIIME pipeline as described above, with no transformation 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 were recently reported to have declined to <1% (Smith et al, 2010). 227 XRD analysis showed that thrombolite samples contain only two crystalline phases; 228 aragonite (CaCO 3 , a calcium carbonate mineral) and halite (NaCl, salt resulting from the 229 surrounding lake water).…”

The importance of groundwater flow to the formation of modern thrombolitic microbialites

“…The salinity increase has continued into the 2010s, with seasonal lows of 58.6–62.2 g/L TDS in 2012 and seasonal highs of 92.4–95.9 g/L TDS in 2014 (Warden, ; Warden, Breecker, & Bennett, ). Possible drivers of rising salinity include (a) decreasing rainfall and increasing evaporation in southwest Western Australia, and (b) reduction in inflows and/or decreases in the proportion of fresh to brackish water inflows caused by either groundwater pumping or construction of the Dawesville Channel (1994) connecting nearby Peel‐Harvey Estuary to the Indian Ocean (Bates, Hope, Ryan, Smith, & Charles, ; Knott et al., ; Moore et al., ; Smith et al., ; Warden, ), or a combination of these factors. The lake water salinity increase coincides with a shift in the microbial taxa inhabiting thrombolites, including a possible reduction in the abundance of Scytonema sp.…”

Stevensite in the modern thrombolites of Lake Clifton, Western Australia: A missing link in microbialite mineralization?

“…1B;Moore and Burne, 1994). We have comprehensively reexamined samples collected between 1985 and 1988, prior to the radical alteration of the lake salinity, chemistry, and biota by human activities (Smith et al, 2010).…”