Water Age Research Articles

Hydrodynamics and water renewal in the Pearl River Estuary, China: A numerical study from the perspective of water age

The time required for water renewal in an estuary is closely related to its self-purification ability and environment degree. A FVCOM-based water age (WA) model was conducted to investigate the renewal timescale in the Pearl River Estuary (PRE) under various hydrodynamic scenarios. Model sensitivities revealed the depth-averaged WA during the summer was significantly smaller than that during the winter; meanwhile, the region with vertically significant variations in the WA varied from almost the whole estuary to the downstream. It can be explained that the seaward residual currents became stronger and narrowed the region of vertical circulations by impeding salinity invasion and stratification. During typhoon Hagupit, the depth-averaged WA was apparently increased in the most of the estuary because the horizontal water circulations between the estuary and open sea were significantly decreased by the strong up-estuary surge-waves. Moreover, the vertical WA distribution almost became a single-layer structure with the severely weakened vertical circulations. After reclamations, the variable shorelines in the PRE significantly affected the hydrodynamic characteristics and water circulations, thus the depth-averaged WA complicatedly changed, and the vertical difference of the WA values slightly increased in narrowed waterways and their downstream due to the limited effects on the vertical circulations.

Retention time of lakes in the Larsemann Hills oasis, East Antarctica

Abstract. This study provides first estimates of the water transport timescale for five lakes located in the Larsemann Hills oasis (69∘23′ S, 76∘20′ E) in East Antarctica. We estimated lake retention time (LRT) as a ratio of lake volume to the inflow and outflow terms of a lake water balance equation. The LRT was evaluated for lakes of epiglacial and landlocked types, and it was assumed that these lakes are monomictic, with water exchange occurring during the warm season only. We used hydrological observations collected in four seasonal field campaigns to evaluate the LRT. For the epiglacial lakes Progress and Nella/Scandrett, the LRT was estimated at 12–13 and 4–5 years, respectively. For the landlocked lakes Stepped, Sarah Tarn and Reid, our results show a great difference in the LRT calculated from the outflow and inflow terms of the water balance equation. The LRTs for these lakes vary depending on the methods and errors inherent to them. We relied on the estimations from the outflow terms, since they are based on hydrological measurements with better quality. Lake Stepped exchanged water within 1.5 years. Sarah Tarn and Lake Reid are endorheic ponds, with water loss mainly through evaporation. Their LRTs were estimated as 21–22 and 8–9 years, respectively. To improve the LRT estimates, special hydrological observations are needed to monitor the lakes and streams during the warm season with a uniform observational programme.

The Fractal Scaling Relationship for River Inlets to Lakes

AbstractScaling relationships provide simple rules for understanding complex hydrographic patterns. Globally, river inlet abundance varies among lakes by about three orders of magnitude, but few scaling relationships describe this aspect of lake‐river connectivity. In this study, we describe a simple theoretical scaling relationship between lake surface area and river inlet abundance, and test this theory using data from Scandinavia. On average, the number of inlets increases by 67% for each doubling of lake area. However, lakes of vastly different areas can have the same number of inlets with relatively small variations of drainage density, lake shape, or junction angle ‐ characteristics that can often be linked to specific geological processes. Our approach bridges the gap between the detailed understanding of geomorphic processes and large‐scale statistical relationships, and engenders predictions about additional patterns including the relationship between lake area and water residence time.

New insights into eutrophication management: Importance of temperature and water residence time

Eutrophication and harmful cyanobacterial blooms threaten water resources all over the world. There is a great controversy about controlling only phosphorus or controlling both nitrogen and phosphorus in the management of lake eutrophication. The primary argument against the dual nutrients control of eutrophication is that nitrogen fixation can compensate the nitrogen deficits. Thus, it is of great necessary to study the factors that can significantly affect the nitrogen fixation. Due to the difference of climate and human influence, the water quality of different lakes (such as water temperature, N:P ratio and water residence time) is also quite different. Numerous studies have reported that the low N:P ratio can intensify the nitrogen fixation capacities. However, the effects of temperature and water residence time on the nitrogen fixation remain unclear. Thus, 30 shallows freshwater lakes in the eastern plain of China were selected to measure dissolved N2 and Ar concentrations through N2: Ar method using a membrane inlet mass spectrometer to quantify the nitrogen fixation capacities and investigate whether the temperature and water residence time have a great impact on nitrogen fixation. The results have shown that the short lake water residence time can severely inhibit the nitrogen fixation capacities through inhibiting the growth of nitrogen-fixing cyanobacteria, changing the N:P ratio and resuspending the solids from sediments. Similarly, lakes with low water temperature also have a low nitrogen fixation capacity, suggesting that controlling nitrogen in such lakes is feasible if the growth of cyanobacteria is limited by nitrogen.

Late glacial and Holocene paleoenvironments in the midcontinent United States, inferred from Geneva Lake leaf wax, ostracode valve, and bulk sediment chemistry

Geneva Lake in Wisconsin, USA, is > 20,000 years old and contains a 30-m thick lacustrine sediment record of mid-continent North American climate and environmental change. Here we describe a sediment record from Geneva Lake spanning the past 14,500 years. From scanning X-ray fluorescence, organic C and N concentrations and isotopes, X-ray diffraction, magnetic susceptibility, and grain size of bulk sediments, we infer changes in sediment sources over time including: abrupt decline in inputs of remobilized loess ∼13,400 cal yr BP followed by a gradual transition to organic-rich marl deposition by ∼10,400 cal yr BP as the landscape stabilized following a period of permafrost thaw and vegetation development; deposition of a minerogenic unit at ∼8,200 cal yr BP that may record enhanced eolian activity during the widespread “8.2 ka event; ” and elevated zinc, lead, and arsenic from human activities following regional industrialization. Within the Holocene marl, we also use isotopic (δ18O and δ13C) and trace metal ratio (Sr/Ca and Mg/Ca) analyses of ostracode valves paired with concentrations and hydrogen isotopic composition (δ2H) of leaf wax n-alkanes to infer climate and hydrological change. Groundwater had a large but declining influence on lake water chemistry from 11,800 to 9,700 cal yr BP, precluding inferences of regional climate from our lacustrine proxies during this period. δ2H values of terrestrial n-C29 alkanes show little variability from 9,700 to present, indicating the average isotopic composition of local precipitation was relatively stable, reflecting stable condensation temperatures and source. In contrast, a gradual trend towards more δ18O- and δ2H-depleted lake water and lower lake water Sr/Ca from 9700 cal yr BP to present suggest decreasing evaporation of lake water and increasing precipitation amounts throughout the Holocene and resulting shorter lake water residence times. Lake water Mg/Ca variations over the past 9,700 years broadly parallel regional pollen-based reconstructions of summer temperatures. Neither Mg/Ca nor terrestrial leaf wax δ2H suggest long-term directional shifts in temperature at this site through the middle to late Holocene, as climate became wetter. It appears that precipitation isotopes did not track local temperatures on millennial timescales in this part of mid-continent North America through the Holocene, and instead may have covaried with changes in Northern Hemisphere latitudinal temperature gradients driven by large Arctic temperature changes.

Quantifying the dependence of cyanobacterial growth to nutrient for the eutrophication management of temperate-subtropical shallow lakes

The increasing global occurrence of cyanobacterial blooms, attributed primarily to human-induced nutrient enrichment, significantly degrades freshwater ecosystems and poses serious risks to human health. The current study examined environmental variables and cyanobacterial biovolume (BCyano) of 28 shallow lakes in the eastern China plains during the spring and summer of 2018. We used a 95% quantile regression model to explore season-specific response of BCyano to total nitrogen (TN), or total phosphorus (TP), and robust linear relationships were observed between log(BCyano+0.001) and log(TN), or log(TP) in both spring and summer periods. Based on these regressions, regional-scale and season-specific TN and TP thresholds are proposed for these lakes to ensure the safety for recreational waters and drinking water source. However, actual BCyano for a given concentration of TN (or TP) for many observations were considerably lower than the results of the 95% regression model predict, indicating that other factors significantly modulated nutrient limitation of BCyano. Generalized additive model and quantile regression model were used together to explore potentially significant modulating factors, of which lake retention time, macrophytes cover and N: P ratio were identified as most important. Thus, it is necessary to develop type-specific nutrient thresholds with the consideration of these significant modulating factors. Furthermore, nutrient-BCyano relationships of our studied lakes with lake retention time>100 days and no macrophyte were further explored and nutrient thresholds of this lake type were proposed. Nutrient thresholds proposed in this study may play an essential role in achieving a cost-effective eutrophication management for shallow lakes both in the eastern China plains and elsewhere with similar climatic background. On a broader scale, the approaches and findings of this study may provide valuable reference to formulate reasonable nutrient reduction targets for other ecoregions with different climatic conditions.

Variable responses of dissolved organic carbon to precipitation events in boreal drinking water lakes

In boreal regions, increased concentrations of dissolved organic carbon (DOC) have been linked to extreme wet years; however, less is known about the extent to which precipitation events are altering DOC concentration and quality. We assessed the effects of rain events on a suite of six lakes in Maine, U.S.A., to better understand how events alter DOC quantity and quality. DOC concentrations and DOC quality (measured as DOC-specific absorption coefficients (Specific Ultraviolet Absorbance (SUVA254 (also a*254), a*320, and a*380)) were quantified 24 h before, and at three time points (24–48 h, 5–7 days, and 3 weeks) after five different precipitation events. Our results revealed three types of responses across the lakes: (1) an initial spike in DOC concentrations of 30–133% and in the three quality metrics of 20–86% compared to pre-storm levels, followed by return to pre-storm concentrations; (2) a sustained increase in DOC concentrations (by 4–23%) and an increase in the three DOC quality metrics (by 1–43%) through the second post-storm sampling, with concentrations falling by the third post-storm sampling compared to pre-storm levels; and (3) no change during all sampling periods. Lake residence time was a key driver of changes in DOC concentration and DOC quality in response to storm events. Our research provides evidence that precipitation events contribute to short-term abrupt changes in DOC quantity and quality that are largely driven by key landscape and lake characteristics. These changes in DOC may have important implications for management of water utilities, including alteration or implementation of treatment strategies.

Characterization of Chromophoric Dissolved Organic Matter in the Littoral Zones of Eutrophic Lakes Taihu and Hongze during the Algal Bloom Season

Chromophoric dissolved organic matter (CDOM) is a key component with a critical role in the littoral zones of eutrophic shallow lakes; yet the characteristics of CDOM in these zones remain seldom systematically reported. In this study, the differences in sources, biogeochemical characteristics, and fates of CDOM between the littoral zones of eutrophic lakes Taihu (LLT; frequently occurring algal blooms and longer lake residence time) and Hongze (LLH; no obvious algal blooms and shorter residence time) were compared during the algal bloom season using ultraviolet-visible spectra and excitation and emission matrix spectroscopy combined with parallel factor analysis. Three humic-like fluorescent dissolved organic matter (FDOM) components (C1, C3, and C4) and one protein-like component (C2) were identified. Results showed that FDOM components were dominated by protein-like fluorescent substances in LLT, and humic-like materials in LLH, respectively. The CDOM in LLT had a lower relative aromaticity and molecular weight, humification degree and a higher autotrophic productivity because of algal blooms. Furthermore, CDOM depletion rates in LLT were higher than those in LLH due to a longer lake residence time in LLT. In addition, CDOM shifted from high molecular weight to low molecular weight as the humification degree decreased during the CDOM depletion process. This comparative study showed that algal blooms and lake residence time were the significant factors for distinguishing characteristics of CDOM between littoral zones of shallow lakes on a similar trophic level. This study provides field-based knowledge for remote sensing CDOM measurement and serves as a reference for lakeshore aquatic environmental management.

Groundwater contribution keeps trophic status low in Sylvan Lake, Alberta, Canada

Water well drilling records combined with geologic observation around Sylvan Lake suggest a permeable, fractured groundwater-bearing channel sandstone extends along the northeast margin of the lake, and is surrounded by a matrix of shale with small sandy interbeds. Chloride and water isotope mass-balance approaches found groundwater fluxes were 37 to 43% of total annual lake water inputs, and were consistent with Darcy flux estimates for the channel sandstone. The groundwater contribution to the lake water budget contributes to an estimated lake-water residence time ranging from 22 to 30 years, which is much lower than other lakes in the region and lakes of similar size. Groundwater through-flow in the hydraulically connected channel sandstone unit of the Paskapoo Formation appears to play a critical role in maintaining the relatively low total dissolved solids (and trophic status) of Sylvan Lake, as compared to other lakes in south-central Alberta. Due to the hydraulic connection of the sandstone channel with Sylvan Lake, land use along the north side of the lake (above the sandstone channel unit) should be carefully considered to mitigate groundwater (and consequently lake water) quality impacts.

Widespread Atmospheric Tellurium Contamination in Industrial and Remote Regions of Canada.

High tech applications, primarily photovoltaics, have greatly increased demand for the rare and versatile but toxic element tellurium (Te). Here we examine dated lake sediment Te concentration profiles collected near potential point sources (metal smelters, coal mining/combustion facilities, oil sands operations) and from rural regions and remote natural areas of Canada. Te contamination was most prevalent near a Cu/Zn smelter where observed deposition infers 21 g Te released per metric ton (t) of Cu processed. Globally, 9,500 t is predicted to have been atmospherically deposited near Cu smelters post-1900. In a remote area of central Canada (Experimental Lakes Area; ELA), preindustrial Te deposition rates were equivalent to the estimated average global mass flux supplied from natural sources; however more surprisingly, modern Te deposition rates were 6-fold higher and comparable with Te measurements in precipitation. We therefore suggest that sediment cores reliably record atmospheric Te deposition and that anthropogenic activities have significantly augmented atmospheric Te levels, making it an emerging contaminant of potential concern. Lake water residence time was found to influence lake sediment Te inventories among lakes within a region. The apparent settling rate for Te was comparable to macronutrients (C, N, P), likely indicative of significant biological processing of Te.

Temperature, salinity and water-age variations in a tidal creek network, Bushehr Port, Iran

The spatio-temporal variability of temperature and salinity was studied for a creek network and its adjacent coastal waters along the northwestern coast of the Persian Gulf during warm and cold months. Salinity variations and tidal fluctuations were found to be out of phase throughout the creek. Temperature variations at the creek were exhibit a direct correlation with tidal fluctuations during cold months and were inversely related during warm months. The creek water was colder (warmer) than offshore water during the cold (warm) season. The salinity values observed inside this inverse estuary were higher during the warm season than the corresponding values during the cold season due to a change in evaporation rates; while the open water salinity had an opposite pattern. Using salinity as a tracer, the water-age (WA) was calculated, which shows almost linear increase from the mouth to the head. The maximum WA increases from ~10 days in winter to ~30 days in summer due to the corresponding increase in longitudinal salinity gradient. Based on the calculated non-dimensional Peclet number, the diffusion process is more rapid than the advection process in this water body, especially during the cold season.

The world\u2019s largest High Arctic lake responds rapidly to climate warming

Using a whole-watershed approach and a combination of historical, contemporary, modeled and paleolimnological datasets, we show that the High Arctic’s largest lake by volume (Lake Hazen) has succumbed to climate warming with only a ~1 °C relative increase in summer air temperatures. This warming deepened the soil active layer and triggered large mass losses from the watershed’s glaciers, resulting in a ~10 times increase in delivery of glacial meltwaters, sediment, organic carbon and legacy contaminants to Lake Hazen, a >70% decrease in lake water residence time, and near certainty of summer ice-free conditions. Concomitantly, the community assemblage of diatom primary producers in the lake shifted dramatically with declining ice cover, from shoreline benthic to open-water planktonic species, and the physiological condition of the only fish species in the lake, Arctic Char, declined significantly. Collectively, these changes place Lake Hazen in a biogeochemical, limnological and ecological regime unprecedented within the past ~300 years.

Comparison of the Chemical Composition of Dissolved Organic Matter in Three Lakes in Minnesota.

New information on the chemical composition of dissolved organic matter (DOM) in three lakes in Minnesota has been gained from spectral editing and two-dimensional nuclear magnetic resonance (NMR) methods, indicating the effects of lake hydrological settings on DOM composition. Williams Lake (WL), Shingobee Lake (SL), and Manganika Lake (ML) had different source inputs, and the lake water residence time (WRT) of WL was markedly longer than that of SL and ML. The hydrophobic organic acid (HPOA) and transphilic organic acid (TPIA) fractions combined comprised >50% of total DOM in these lakes, and contained carboxyl-rich alicyclic molecules (CRAM), aromatics, carbohydrates, and N-containing compounds. The previously understudied TPIA fractions contained fewer aromatics, more oxygen-rich CRAM, and more N-containing compounds compared to the corresponding HPOA. CRAM represented the predominant component in DOM from all lakes studied, and more so in WL than in SL and ML. Aromatics including lignin residues and phenols decreased in relative abundances from ML to SL and WL. Carbohydrates and N-containing compounds were minor components in both HPOA and TPIA and did not show large variations among the three lakes. The increased relative abundances of CRAM in DOM from ML, SL to WL suggested the selective preservation of CRAM with increased residence time.

Climate‐induced hydrological variation controls the transformation of dissolved organic matter in a subalpine lake

AbstractLakes are an inherent component of the global carbon cycle. They receive dissolved organic matter (DOM) from the catchment, which is stored, transformed and respired, or delivered downstream. In this study, we show that a subalpine lake shifts its role from DOM “transporter” to “transformer” depending on season and climate. We monitored dissolved organic carbon (DOC) concentration and DOM optical properties at the inlet and outlet of subalpine Lake Lunz (Austria) at high frequency during two contrasting years: an extreme drought in 2015, and regular precipitation regime in 2016. During both years, the DOC mass balance revealed that inflowing and outflowing DOC loads were nearly balanced (+6.57% and +1.70% DOC production in 2015 and 2016, respectively). However, DOM optical properties revealed an in‐lake turnover of DOM compounds, so that the terrestrial and aromatic signature of inflowing DOM was modified into autochthonous, protein‐like DOM. The magnitude of this transformation varied seasonally, being maximal in summer and minimal in winter, presumably following periods of high and low primary production and photo‐degradation. Inter‐annually, we found that drought further increased DOM transformation during summer by extending the lake water residence time. Finally, our results demonstrate a rapid response of DOM dynamics to hydrological and meteorological changes at both seasonal and inter‐annual scales, suggesting that carbon cycling in clear‐water mountain lakes may be highly sensitive to hydrological variation.

Arsenic mobility and characterization in lakes impacted by gold ore roasting, Yellowknife, NWT, Canada.

The controls on the mobility and fate of arsenic in lakes impacted by historical gold ore roasting in northern Canada have been examined. A detailed characterization of arsenic solid and aqueous phases in lake waters, lake sediments and sediment porewaters as well as surrounding soils was conducted in three small lakes (<200ha) downwind and within 5km of the historic mining and roasting operations of Giant Mine (Northwest Territories). These lakes are marked by differing limnological characteristics such as area, depth and organic content. Radiometric age-dating shows that the occurrence of arsenic trioxide in lake sediments coincides with the regional onset of roasting activities. Quantification by advanced electron microscopy shows that arsenic trioxide accounts for up to 6wt% of the total arsenic in sediments. The bulk (>80wt%) of arsenic is contained in the form of secondary sulphide precipitates, with iron oxy-hydroxides hosting a minimal amount of arsenic (<1wt%). Soluble arsenic trioxide particles act as the primary source of arsenic into sediment porewaters. Dissolved arsenic in reducing porewaters both precipitates in-situ as secondary sulphides, and diffuses upwards into the overlying lake waters. Geogenic arsenic phases are present in sediments in low concentrations and are not considered a significant source of arsenic to porewaters or lake waters. Sediment-water interface diffusive flux calculations suggest that the diffusion of dissolved arsenic from porewaters, combined with lake water residence time, are the predominant mechanisms controlling arsenic concentrations in lake waters.

Extensive processing of sediment pore water dissolved organic matter during anoxic incubation as observed by high-field mass spectrometry (FTICR-MS)

Dissolved organic matter (DOM) contained in lake sediments is a carbon source for many microbial degradation processes, including aerobic and anaerobic mineralization. During anaerobic degradation, DOM is partially consumed and transformed into new molecules while the greenhouse gases methane (CH4) and carbon dioxide (CO2) are produced. In this study, we used ultrahigh resolution mass spectrometry to trace differences in the composition of solid-phase extractable (PPL resin) pore water DOM (SPE-DOM) isolated from surface sediments of three boreal lakes before and after 40 days of anoxic incubation, with concomitant determination of CH4 and CO2 evolution. CH4 and CO2 production detected by gas chromatography varied considerably among replicates and accounted for fractions of ∼2–4 × 10−4 of sedimentary organic carbon for CO2 and ∼0.8–2.4 × 10−5 for CH4. In contrast, the relative changes of key bulk parameters during incubation, such as relative proportions of molecular series, elemental ratios, average mass and unsaturation, were regularly in the percent range (1–3% for compounds decreasing and 4–10% for compounds increasing), i.e. several orders of magnitude higher than mineralization alone. Computation of the average carbon oxidation state in CHO molecules of lake pore water DOM revealed rather non-selective large scale transformations of organic matter during incubation, with depletion of highly oxidized and highly reduced CHO molecules, and formation of rather non-labile fulvic acid type molecules. In general, proportions of CHO compounds slightly decreased. Nearly saturated CHO and CHOS lipid-like substances declined during incubation: these rather commonplace molecules were less specific indicators of lake sediment alteration than the particular compounds, such as certain oxygenated aromatics and carboxyl-rich alicyclic acids (CRAM) found more abundant after incubation. There was a remarkable general increase in many CHNO compounds during incubation across all lakes. Differences in DOM transformation between lakes corresponded with lake size and water residence time. While in the small lake Svarttjärn, CRAM increased during incubation, lignin-and tannin-like compounds were enriched in the large lake Bisen, suggesting selective preservation of these rather non-labile aromatic compounds rather than recent synthesis. SPE-DOM after incubation may represent freshly synthesized compounds, leftover bulk DOM which is primarily composed of intrinsically refractory molecules and/or microbial metabolites which were not consumed in our experiments. In spite of a low fraction of the total DOM being mineralized to CO2 and CH4, the more pronounced change in molecular DOM composition during the incubation indicates that diagenetic modification of organic matter can be substantial compared to complete mineralization.

Variability in organic carbon reactivity across lake residence time and trophic gradients

The production and consumption of organic carbon in inland waters varies with water residence time and biotic processes, suggest analyses of dissolved organic carbon from Northern Hemisphere water bodies. Inland waters mediate carbon transport between land and ocean.

Numerical Study on the Influences of Hydrodynamic Factors on Water Age in the Liao River Estuary, China

ABSTRACT Liu, R.; Zhang, X.; Liang, B.; Xin, L., and Zhao, Y., 2017. Numerical study on the influences of hydrodynamic factors on water age in the Liao River Estuary, China. In: Zhi, Y. and Guido Aldana, P.A. (eds.), Sustainability of Water Resources and the Development of Coastal Environments: Select Proceedings from the 2016 International Conference on Water Resource and Environment (WRE2016). Journal of Coastal Research, Special Issue No. 80, pp. 98–107. Coconut Creek (Florida), ISSN 0749-0208. The concept of water age (WA) is applied to the Liao River Estuary to estimate the timescale quantifying transport processes. A series of numerical experiments under different hydrodynamic conditions based on a real-time calibrated three-dimensional model have been conducted to investigate the influences of runoff, tide and wind on WA distribution. The model result shows that the WA distribution in a real situation can be estimated roughly by the real-time monitoring runoff with a natural logarithmic function. T...

Investigation of factors affecting the trophic state of a shallow Mediterranean reconstructed lake

In this article, we focus on shallow sub-tropical lakes and study the factors that determine their trophic state and food web structure. We use the model PCLake to simulate lake nutrient dynamics and investigate key factors causing eutrophication, such as in-lake nutrient cycling, long residence time and low depths. Modeling results are validated in a reconstructed lake that is also used as a reservoir located in central Greece. Various operational scenarios and their effect on lake trophic state are explored. A climate change scenario is also presented, showcasing its influence on lake nutrient dynamics and food web structure. Our results confirm that lake residence time, lake depth and nutrient inflows are the factors that determine the lake trophic state, while climate change seems to slightly intensify the mechanisms that establish lake eutrophic conditions.

Modeling Allochthonous Dissolved Organic Carbon Mineralization Under Variable Hydrologic Regimes in Boreal Lakes

Here, we explore the interaction between hydrology and the reactivity of allochthonous dissolved organic carbon (DOCalloch) in determining the potential of DOCalloch to generate CO2 through biological and photo-chemical mineralization in boreal lakes. We developed a mechanistic model that integrates the reactivity continuum (RC) concept to reconstruct in-lake mineralization of DOCalloch under variable hydrologic conditions using empirical measurements of DOCalloch concentrations and reactivity as model inputs. The model predicts lake DOCalloch concentration (L-DOCalloch) and its average overall reactivity $$ \left( {\bar{K}_{\text{alloch}} } \right) $$ , which integrates the distribution of DOCalloch ages within the lake as a function of the DOC loading (DOCin), the initial reactivity of this DOCin (k 0), and the lake water residence time (WRT). The modeled DOCalloch mineralization rates and concentrations were in agreement with expectations based on observed and published values of ambient lake DOC concentrations and reactivity. Results from this modeling exercise reveal that the interaction between WRT and k 0 is a key determinant of the ambient concentration and reactivity of lake DOCalloch, which represents the bulk of DOC in most of these lakes. The steady-state $$ \left( {\bar{K}_{\text{alloch}} } \right) $$ also represents the proportion of CO2 that can be extracted from DOCalloch during its transit through lakes, and partly explains the patterns in surface water pCO2 oversaturation that have been observed across gradients of lake size and volume. We estimate that in-lake DOCalloch mineralization could potentially contribute on average 30–40% of the observed surface carbon dioxide partial pressure (pCO2) across northern lakes. Applying the RC framework to in-lake DOCalloch dynamics improves our understanding of DOCalloch transformation and fate along the aquatic network, and results in a predictable mosaic of DOC reactivity and potential CO2 emissions across lakes within a landscape.