Chemical and isotopic composition of karstic lakes in Jamaica, West Indies

Abstract

Lakes in the limestone region of Jamaica exhibit a range of chemical characteristics that reflect varying inputs from precipitation, surface runoff and groundwater, together with the subsequent evolution of the water within the limnic environment . Detailed spatial and temporal sampling was conducted on one lake, Wallywash Great Pond . Chemical data, together with D/H, 180/160 13C/12C and 87 Sr/86 Sr ratios confirm that the karstic spring waters entering the lake evolve chemically through degassing, mixing with rainfall and runoff, biogenic decalcification (resulting mainly from bicarbonate assimilation by the high biomass of submerged macrophytes), and evaporation . Modern carbonate sedimentation in Wallywash Great Pond is largely of high-Mg calcite . This is consistent with Mg/Ca molar ratios >2 within much of the lake . However, aragonite forms on the adaxial leaf surfaces of Potamogeton spp . This may be explained either as a result of locally elevated Mg concentrations or a high degree of supersaturation favouring very rapid carbonate precipitation . Two small lakes to the north of Wallywash Great Pond show minor influence of the Na-Cl dominated coastal aquifer, suggesting that coastal lakes are sensitive to variations in the boundary between fresh and brackish groundwater caused by changes in climate or sea level . Their 13 C/ 12C ratios are strongly influenced by biogenic CO2 derived from plant respiration or decay .

Sample-size implications of the trace-element variability of ostracod shells

“…Diurnal and seasonal temperature ranges are both $3°C, which is sufficient to have influenced Mg partitioning in the ostracod population. The fact that Sr/Ca ratios show limited spatial variability in the lake water (Holmes et al, 1995a) and that Sr partitioning into ostracod shells is not significantly affected by temperature, explain the limited variability in Sr/Ca ratios within the living ostracods. For the core sediments, each analysed level integrates between several decades (late Holocene levels) to centuries (late Pleistocene levels).…”

The relationship between suspended sediment settling velocity and water table sinking rates in intermittent lakes in karstic depressions

“…The sediment of lakes can be of chemical origin (Holmes et al, 1995;Valero Garcé s et al, 2014) or can be transported into the lake. The transported sediment is most often of fluvial origin (Li et al, 2010;Oliveira et al, 2008;Develle et al, 2011), but it can also be of subaerial (Develle et al, 2011) or mass movement origin (Denizman et al, 2010;Morello et al, 2009).…”

“…However, the origin of lakes of two types is also different. The water of karstic lakes of permanent waters can originate from karstic springs (Develle et al, 2011), ground water (Holmes et al, 1995), rainwater (Valero Garcé s et al, 2014) and karst water (Sweeting, 1973;Zhang, 1980), while the water of intermittent karstic lakes mainly originates from rainwater (Veress, 1987a(Veress, , 2000 or karstwater (Sweeting, 1973).…”

“…Thus, climate change (Holmes et al, 1995;Oliveira et al, 2008; BarreiroLostres et al, 2013), the composition of the rocks of the catchment area (Oliveira et al, 2008;Develle et al, 2011), the sediment sources of various origins such as aeolian origin (Develle et al, 2011), the anthropogenic effects on the catchment area (BarreiroLostres et al, 2013;Schmidt et al, 2000), changes of the vegetation (Develle et al, 2011;Schmidt et al, 2000), changes of water level (Holmes et al, 1995), the intensity of sediment transportation (Barreiro-Lostres et al, 2013) and the relationship between denudation and accumulation (Li et al, 2010). However, they also reflect the change of state of the lake thus, the change of water level and water depth (Schmidt et al, 2000), that of water quality (Holmes et al, 1995;Develle et al, 2011), eutrophication (Obelič et al, 2005 or the changes of flora and fauna (Wantzen et al, 2008).The sedimentation of karstic lakes with permanent water does not differ significantly from the non-karstic lakes with permanent water while that of intermittent karstic lakes is different to some extent because lake sediment can be transported into the karst. Thus, not the depression, but the karstic passage is the sediment trap.…”

Modern stable isotopic (δ18O, δ2H, δ13C) variation in terrestrial, fluvial, estuarine and marine waters from north‐central Sarawak, Malaysian Borneo

“…The local Subis Limestone has an average δ 13 C value of 0·36‰ (Stephens, 2004) and is similar to other marine limestones from around the world due to their formation in similar environments and an average value of c. 0‰ (Craig, 1953;Hitchon and Krouse, 1972;Holmes et al, 1995).…”