A modern isotope record of changes in water and carbon budgets in a groundwater‐fed lake: Blue Lake, South Australia

Abstract

Groundwater is often a major component of lake water and chemical balances. Alteration in catchment subsurface water balances through land-use change and pumping can affect lake biogeochemical cycles through changes in groundwater flow rates. We present a modern (ϳ200 yr) sediment isotope record (␦ 18 O carb , ␦ 13 C carb , and ␦ 13 C org ) of changes to the water and carbon budget of Blue Lake, which is situated in karstic limestone in South Australia and is mostly fed by groundwater. The 3.5‰ decrease in ␦ 18 O carb and ␦ 13 C carb deposited in lake sediments since ϳ1850 reflects higher rates of groundwater through-flow due to rainfall variability, land-use change, and increased rates of pumping over the past 40 yr. Calculated water residence times, based on the isotopic data, were 23 Ϯ 2 yr before 1850 and decreased by the late twentieth century to 8 Ϯ 2 yr. Concomitant dissolved inorganic carbon (DIC) residence times were 3.8 and 2.2 yr, respectively. Although burial rates of CaCO 3 have increased by about threefold over the past 40 yr, there is no evidence that substantial changes in organic carbon deposition has occurred. The shorter DIC residence time is largely due to increased input and higher CO 2 evasion rates. About 88% of C carb and ϳ96% of C org generated within the water column is remineralized, but the isotopic composition is essentially unaltered in the sediments. The measured variations in ␦ 13 C carb and ␦ 13 C org of sediments are thought to reflect changes to DIC residence time and increased CO 2 (aq) concentrations rather than changes in lake productivity.

Seasonal water-column dynamics of dissolved inorganic carbon stable isotopic compositions (δ13CDIC) in small hardwater lakes in Minnesota and Montana

“…The decoupling of algal productivity and d 13 C DIC values (e.g., Teranes et al, 1999;Hollander and Smith, 2001;Herczeg et al, 2003;Bade et al, 2004) is evident in the example of the three Minnesota lakes: McCarrons and Green lakes are eutrophic and Spectacle Lake is mesotrophic, but Spectacle Lake has the highest epilimnetic d 13 C DIC values, routinely exceeding 0& while the other lakes reach 0& only occasionally. Calcite precipitated in equilibrium with this DIC pool in the early summer would, in the standard interpretation, indicate that Spectacle Lake was the most eutrophic of the three.…”

“…Evasion of CO 2 to the atmosphere has been invoked to explain extreme enrichments in d 13 C DIC values (Schwalb et al, 1999;Valero-Garcés et al, 1999), as fractionation across the airwater interface removes 13 C-depleted CO 2 (Herczeg et al, 2003). In lakes with large external CO 2 influxes (e.g., volcanic or hydrothermal degassing through the lake floor) and long hydraulic residence times this process could produce lake water d 13 C DIC values of several per mil above atmospheric equilibrium.…”

Application of a risk management framework to a drinking water supply augmented by stormwater recharge

“…While considerable variation in groundwater travel time is expected in the karstic aquifer, natural (Cl") and applied tracers (SFß) have been used to determine a range in minimum aquifer residence time of 2 to 20 years (Vanderzalm et al 2009). The Blue Lake residence time has been reported as 6-10 years based on the 5^*0 and ô^-'C of carbonate in the lake sediments (Herczeg et al 2003).…”

“…These advances include the Water Resources Act 1976 (SA Government 1976), the Environment Protection Act 1993 (SA Government 1993). the National Water Quality Management Strategy (various documents including ANZECC and ARMCANZ 2000;NHMRC-NRMMC 2004a, b); the Blue Lake Management Plan (BLMC 2001(BLMC , 2006; and more recently the Australian Guidelines for Water Recycling: Managing Health and Environmental Risks (NRMMC-EPHC-AHMC 2006) including specific guidelines for Augmentation of Drinking Water Supplies (NRMMC-EPHC-NHMRC 2008), water recycling via Managed Aquifer Recharge (NRMMC-EPHC-NHMRC 2009a) and Stormwater Harvesting and Reuse (NRMMC-EPHC-NHMRC 2009&), Previous research on the Blue Lake has focused on the age and residence time of water (Leaney et al 1995;Herczeg et al 2003) and the annual colour change process in the lake (Telfer 2000;Turoczy 2002) but the treatment steps within the stormwater recycling system and their management for safe drinking water supply have not been assessed. This paper extends a recent assessment of Blue Lake quality doi: 10.2166/wst.2011.294 …”

Lake and Reservoir Management

“…Carbonate, organic C, and N contents and their respective ¶ 13 C were measured in four cores from Lake Kinneret, Israel in an attempt to reconstruct the lake s productivity and regional climatic conditions during the late Holocene (Dubowski et al, 2003). Modern (~200 yr) sediment isotope record ( ¶ 18 O carb , ¶ 13 C carb , and ¶ 13 C org ) of changes to the water and carbon budget of Blue Lake showed that the variations in ¶ 13 C carb and ¶ 13 C org of sediments reflected changes to DIC residence time and increased CO 2 (aq) concentrations rather than changes in lake productivity (Herczeg et al, 2003). A study analyzed how dissolved organic carbon (DOC) concentration in lakes of the North American temperate forest (Upper Great Lakes region) was related to nine catchment characteristics (lake area, lake perimeter, drainage area, ratio of drainage area to lake area, proportion of watershed occupied by wetlands, proportion of lake perimeter in wetlands, shoreline development, elevation, and watershed slope) and compared selected relationships to those from other regions across the globe (Marguerite et al, 2003).…”