Lake Area Ratio Research Articles

Can remotely sensed catchment to lake area ratios predict mercury levels in subarctic fishes?

Mercury concentrations ([Hg]) in fish reflect a complex array of interacting biogeochemical and ecological variables. In northern regions where fish are a critical subsistence food, understanding and predicting fish [Hg] can be particularly difficult, largely due to a paucity of comprehensive data associated with the logistical challenges of field sampling. Building on previous work where we elucidated causal relationships between fish [Hg] and a variety of catchment, water quality, and ecological variables in subarctic lakes, we investigated whether using only ratios of catchment area to lake area (CA:LA) can predict [Hg] in northern freshwater fish species. As CA:LA can be sensed remotely, they may be more feasible and practical to obtain than field data in far northern regions. Our study included thirteen remote lakes that represent a CA:LA gradient of 6.2–423.5 within an ∼66,000 km2 subarctic region of Northwest Territories, Canada. We found that size-standardized [Hg] in three widespread fish species, including Lake Whitefish (Coregonus clupeaformis), Walleye (Sander vitreus), and Northern Pike (Esox lucius), were significantly and positively related to CA:LA (p < 0.007, r2 = 67–80%), indicating higher fish [Hg] in smaller lakes surrounded by relatively larger catchments. Our findings provide compelling evidence that remotely sensed CA:LA can be used to predict [Hg] in northern fishes and aid in prioritizing understudied and subsistence fishing lakes of the Canadian subarctic for [Hg] monitoring programs.

Contamination of depressional wetlands in the Mpumalanga Lake District of South Africa near a global emission hotspot

The Mpumalanga Lake District (MLD) of South Africa hosts a regionally unique cluster of water bodies of great importance for wetland biodiversity. It is also located close to a global hotspot for coal-fired power station emissions but the local impacts from these sources of pollution are poorly understood. Sediment cores from three contrasting wetlands were 210Pb dated and analysed for a range of contaminants linked to fossil fuel combustion, including trace elements, Hg, sulphur and spheroidal carbonaceous fly-ash particles (SCPs). At the two sites with pre-industrial (1900) baseline sediments, Pb, Zn and especially Cr concentrations and fluxes showed significant increases in the impact period (post-1975). Mercury showed the greatest proportional increase in flux (>4-fold) of all trace metals. Mercury and sulphur concentrations and fluxes showed highly significant correlations with emissions over the corresponding periods, while SCPs in sediments also closely tracked emissions. In a global context, levels of sediment contamination are relatively minor compared with other heavily industrialised regions, with only Cr exceeding the sediment Probable Effects Concentration for biological impact post-1975. Despite the relatively large increases in Hg, concentrations do not reach the Threshold Effects Concentration. The unexpectedly low levels of contamination may be due to i) low levels of many trace contaminants in South African coals compared to global averages, ii) prevailing recirculation patterns which transport pollution away from the study area during the wet season, minimising wet deposition, and iii) pollutant remobilisation through desiccation of wetlands or volatilization. The effects of hydrology and sediment accumulation rates lead to differential transport and preservation of organic-associated and more volatile contaminants (e.g. Hg, S) relative to non-volatile trace elements in wetlands of the MLD. The greatest fluxes of Hg and S are recorded in the site with the highest catchment: lake area ratio, lowest salinity and greatest sediment organic matter content.

Influence of hydrological features on CO2 and CH4 concentrations in the surface water of lakes, Southwest China: A seasonal and mixing regime analysis

Due to the large spatiotemporal variability in the processes controlling carbon emissions from lakes, estimates of global lake carbon emission remain uncertain. Identifying the most reliable predictors of CO2 and CH4 concentrations across different hydrological features can enhance the accuracy of carbon emission estimates locally and globally. Here, we used data from 71 lakes in Southwest China varying in surface area (0.01‒702.4 km2), mean depth (< 1‒89.6 m), and climate to analyze differences in CO2 and CH4 concentrations and their driving mechanisms between the dry and rainy seasons and between different mixing regimes. The results showed that the average concentrations of CO2 and CH4 in the rainy season were 23.9 ± 18.8 μmol L−1 and 2.5 ± 4.9 μmol L−1, respectively, which were significantly higher than in the dry season (10.5 ± 10.3 μmol L−1 and 1.8 ± 4.2 μmol L−1, respectively). The average concentrations of CO2 and CH4 at the vertically mixed sites were 24.1 ± 21.8 μmol L−1 and 2.6 ± 5.4 μmol L−1, being higher than those at the stratified sites (14.8 ± 13.4 μmol L−1 and 1.7 ± 3.5 μmol L−1, respectively). Moreover, the environmental factors were divided into four categories, i.e., system productivity (represented by the contents of total nitrogen, total phosphorus, chlorophyll a and dissolved organic matter), physicochemical factors (water temperature, Secchi disk depth, dissolved oxygen and pH value), lake morphology (lake area, water depth and drainage ratio), and geoclimatic factors (altitude, wind speed, precipitation and land-use intensity). In addition to the regression and variance partitioning analyses between the concentrations of CO2 and CH4 and environmental factors, the cascading effects of environmental factors on CO2 and CH4 concentrations were further elucidated under four distinct hydrological scenarios, indicating the different driving mechanisms between the scenarios. Lake morphology and geoclimatic factors were the main direct drivers of the carbon concentrations during the rainy season, while they indirectly affected the carbon concentrations via influencing physicochemical factors and further system productivity during the dry season; although lake morphology and geoclimatic factors directly contributed to the carbon concentrations at the vertically mixed and stratified sites, the direct effect of system productivity was only observed at the stratified sites. Our results emphasize that, when estimating carbon emissions from lakes at broad spatial scales, it is essential to consider the influence of precipitation-related seasons and lake mixing regimes.

Lake Evaporation and Its Effects on Basin Evapotranspiration and Lake Water Storage on the Inner Tibetan Plateau

AbstractEffects of lake evaporation (EW) on basin evapotranspiration (ETB) and lake water storage change (LWSC) at lake‐basin scale have never been reported for most basins on the inner Tibetan Plateau (IB). In this study, EW of 118 large lakes in 95 closed lake‐basins were estimated, and its effects on ETB and LWSC over 2001–2018 were examined using a derivative‐guided framework from the aspects of EW amount, rate, trend slope and inter‐annual variability. We found that EW amount has a high effect (17%) on regional ETB amount compared to the average lake area ratio (α) (∼5%), and the effect has increased significantly (2%/10 a). The spatial pattern of the effect is mainly controlled by α, and the increasing trend of α (0.6%/10 a) also dominated the increasing trend in regional ETB rate (0.30 mm/a) though with large spatial heterogeneity. Variance in α and EW rate have a minor effect (∼3%) on ETB variance, especially for the basins with lower α. The combination of quasi lake inflow (RL, 41%) and lake surface precipitation (PW, 16%) offset the depletion of EW (−43%), resulting in the surplus of regional lake water (LWSC &gt; 0). The increase in EW mount, which is mainly from lake area expansion (90%), caused a decreasing trend in LWSC (i.e., slower growth rate) with a contribution of −59%. This suggests a negative feedback between lake area expansion and EW amount in the IB, and the feedback may continue with the predicted area increases.

Factors related to fish mercury concentrations in Iowa lakes.

Mercury contamination in aquatic ecosystems is a global concern due to the health risks of consuming contaminated fishes. Fish mercury concentrations are influenced by a range of biotic and abiotic factors that vary among regions, but these complex interactions are difficult to disentangle. We collected bluegill (Lepomis macrochirus), white and black crappie (Pomoxis annularis; P. nigromaculatus), largemouth bass (Micropterus salmoides), walleye (Sander vitreus), muskellunge (Esox masquinongy), and northern pike (E. lucius) from waterbodies throughout Iowa and analyzed them for mercury concentrations. We used land use, water chemistry, and fish characteristics to explain variation in mercury concentrations among and within systems. Mercury concentrations were generally low and undetectable (< 0.05mg/kg) in 43% of fish analyzed. Detected mercury concentrations were highest in largemouth bass, muskellunge, northern pike, and walleye, lowest in black and white crappie and bluegill, and positively related to fish length and age. Mean lake depth, pH, watershed area to lake area ratio, and percent of watershed as open water were positively related to fish mercury concentrations whereas lake area and percent of watershed as agriculture, developed, forested, and grassland were negatively related to mercury concentrations. Additionally, mercury concentrations were higher in shallow natural lakes compared to other lake types. Our results indicate fish mercury concentrations are lower in Iowa lakes compared to other regions. Models we developed in this study can be used to identify other waterbodies that may have elevated mercury concentrations that can guide fish mercury monitoring programs.

Relationships between Gizzard Shad, Impoundment Characteristics, and Sympatric Fish Species

AbstractGizzard Shad Dorosoma cepedianum are a widely distributed species that can have detrimental effects on aquatic systems and associated fish populations. As a result, Gizzard Shad populations are often manipulated to improve water quality or benefit recreationally important fish populations. Unfortunately, Gizzard Shad manipulations are expensive and the results are variable. In an attempt to inform management of Gizzard Shad and associated species, we evaluated relationships between Gizzard Shad, impoundment characteristics, and sympatric species in 98 impoundments in Kansas using two‐dimension Kolmogorov–Smirnov tests and multiple regression techniques. Our results indicated that Gizzard Shad abundance had a positive influence on the relative abundance of Largemouth Bass Micropterus salmoides and did not influence other sympatric species. Impoundment characteristics (e.g., watershed : lake area ratio, mean depth, turbidity) were more strongly related to the relative abundance and condition of sympatric species than Gizzard Shad. Our results indicate that manipulation of Gizzard Shad likely has little effect on certain sympatric fish species in Kansas impoundments. Therefore, resources used to manipulate Gizzard Shad populations could be better allocated toward management actions that promote or maintain fisheries in impoundments with characteristics that benefit recreationally important species.

Windows into the past: lake sediment phosphorus trajectories act as integrated archives of watershed disturbance legacies over centennial scales

Historic land alterations and agricultural intensification have resulted in legacy phosphorus (P) accumulations within lakes and reservoirs. Internal loading from such legacy stores can be a major driver of future water quality degradation. Yet, little is known about the magnitude and spatial patterns of legacy P accumulation in lentic systems, and how watershed disturbance trajectories drive these patterns. Here, we used a meta-analysis of 113 paleolimnological studies across 124 lakes and four reservoirs (referred here on as lakes) in 20 countries to quantify the linkages between the 100 year trajectories of P concentrations in lake sediments, watershed inputs, and lake morphology. We find five distinct clusters for lake sediment P trajectories, with lakes in the developing and developed world showing distinctly different patterns. Lakes in the developed world (Europe and North America) with early agricultural intensification had the highest sediment P concentrations (1176–1628 mg kg−1), with a peak between the 1970–1980s and a decline since then, while lakes in the developing world, specifically China, documented monotonically increasing sediment P concentrations (857–1603 mg kg−1). Sediment P trajectories reflected watershed disturbance patterns and were driven by a combination of anthropogenic drivers (fertilizer input and population density) and lake morphology (watershed to lake area ratio). Specifically, we found the largest legacy accumulation rates to occur in shallow lakes experiencing long-term land-use disturbances. These links between land-use change and P accumulation in lentic systems can provide insights about inland water quality response and help to develop robust predictive models useful for resource managers and decision-makers.

Holocene lake phosphorus species and primary producers reflect catchment processes in a small, temperate lake

AbstractThis paleolimnological study aims to investigate how natural processes and anthropogenic land‐use changes have affected sedimentary phosphorus (P) forms and primary producers in a small, temperate lake (Lake Fuglsø, Denmark) throughout the Holocene. Our multi‐proxy approach uses pollen, X‐ray fluorescence scanning, carbon (C) and nitrogen contents and stable isotopes, sequential P extraction, 31P nuclear magnetic resonance spectroscopy, pigments, diatoms, and plant macrofossils from a 14C‐dated sediment record. We found three periods of human impact: (1) low disturbance from domestic grazing during the early/mid Neolithic (~3600 to ~2600 BC), (2) higher disturbance because of animal husbandry and some grain cultivation during the Late Bronze and Pre‐Roman Iron Age (~800 BC to AD ~100), and (3) strong disturbance caused by domestic grazing, intensified crop cultivation and, in particular, by retting of fiber plants during the Middle Ages and Renaissance (AD ~1000 to ~1700). Cultural eutrophication during the latter phase caused unprecedented changes in the lake, including altered species composition, high production, and strongly accelerated sediment accumulation rates. Generally, catchment deforestation was related to elevated proportions of metal (iron, aluminum, calcium)‐bound P forms in the sediment, while high tree cover correlated with elevated proportions of P forms associated with organic material (“organic” P, humic‐bound P, refractory organic P) and loosely bound P. During phases with forest in the catchment, silicon (Si) inputs to the lake were insufficient and diatom frustules were mostly absent in the sediments. In contrast, diatoms thrived in the lake when the landscape was open and erosional Si influx was high. This study is the first to show long‐term (~eight millennia) and recurring Si limitation of diatoms, a finding that may explain the absence of diatoms in sediment records of other sites too. In summary, human land‐use with preceding deforestation accelerated the transport of nutrients and elements from the terrestrial to the aquatic environment, leading to substantial and irreversible changes in Lake Fuglsø. Our study is a good example of the tight links between catchment processes and lake status, indicating that catchment dynamics should be considered in lake restoration projects, particularly for lowland lakes with high catchment : lake area ratios.

Heterogeneous responses of lake CO2 to nutrients and warming in perialpine lakes imprinted in subfossil cladoceran δ13C values

Global change transforms processes regulating carbon dioxide (CO2) concentrations in lakes, yet our understanding of the broad-scale responses of lake CO2 to global and local human perturbation across heterogeneous landscapes and multidecadal time scales is limited. We examined decadal variability in the carbon isotope (δ13C) composition of subfossil zooplankton (Branchiopoda: Cladocera) in seven large clear perialpine lakes, including three previously studied sites, to decipher different patterns in summer surface CO2 concentrations. Generalized additive models were used to examine whether and how these patterns connect to changing nutrient regimes and anthropogenic warming over the past century. In all but one of the lakes shifts in cladoceran δ13C values coincided with turning points in the eutrophication history, broadly implying decreasing summer surface CO2 concentrations driven by phosphorus fertilization of pelagic primary production. Yet where nutrient concentrations remained below mesotrophic levels, the positive relationship between δ13C and phosphorus diminished indicating that the strong biotic control of CO2 concentrations was overwritten, probably by catchment inorganic carbon inputs and internal biochemical processes. Even under extensive nutrient loading, the connection was further weakened in lakes with high catchment to lake area ratio attributable to increased catchment interference and shorter water residence times. Warming of the perialpine region was also imprinted in the isotope records, yet the temperature effects appeared modest and were restricted to three smaller lakes with lower drainage ratios. In these lakes, warming contributed to declining cladoceran δ13C values likely partially driven by epilimnetic deepening increasing CO2 in surface waters. Overall, our results manifest the broad heterogeneity of lake responses to global change and point to the importance of hydrogeomorphic context in shaping the sensitivity and responses of lake CO2 to changing nutrient regimes and warming at the regional scale.

Improving the spatial and temporal monitoring of cyanotoxins in Iowa lakes using a multiscale and multi-modal monitoring approach

Cyanobacterial harmful algal blooms (CyanoHABs) are pervasive and negatively impact lake water quality, resulting in economic losses and public health risks through exposure to cyanotoxins. Therefore, it is critical to better monitor and understand the complexity of CyanoHABs, but current methods do not fully describe the spatial and temporal variability of bloom events. In this work, we developed a framework for a multiscale and multi-modal monitoring approach for CyanoHABs combining drone-based near-range remote sensing with analytical measurements of microcystin cyanotoxins and chlorophyll-a. We analyzed weekly beach monitoring samples from 37 lakes geographically distributed across the state of Iowa (USA) over a 15-week period in the summer of 2019 to quantify ELISA (bioassay), 12 microcystin congeners (LC-MS/MS), and chlorophyll-a. We developed a novel microcystin congener-normalized equivalent toxin metric to compare CyanoHAB impacted waters; this microcystin-LR normalized sum-of-congeners approach yields lower predicted toxicity than parallel ELISA results suggesting ELISA is conservative for assessment. A significant linear relationship existed between chlorophyll-a and microcystin for lakes throughout Iowa (R2 = 0.39, p < 0.001); lakes with low watershed:lake area ratio and long residence times exhibited a stronger correlation. We then developed a novel geometry-based image processing approach to allow for stitching over-water drone images, a previous barrier in photogrammetry. We applied our mutli-modal framework to a case study on Green Valley Lake to assess initial viability and predicted microcystin concentrations within 33%. We concluded that multispectral imaging is possible but may presently be insufficient for predicting microcystin concentrations due to limitations in the spectral capabilities of the multispectral camera, but technologies are quickly advancing, and lightweight hyperspectral imaging could soon become feasible for investigating spatial bloom variability on lakes.

Differences in the Effects of Storms on Dissolved Organic Carbon (DOC) in Boreal Lakes during an Early Summer Storm and an Autumn Storm

In boreal lakes, increased precipitation events have been linked to increased concentrations of dissolved organic carbon (DOC), however the effects of seasonal differences on DOC and how this may impact storm response remain unclear. We evaluated DOC concentration and a set of DOC quality metrics during an early summer storm and an autumn storm on a suite of six lakes in Acadia National Park in Maine, USA. to better understand differences in seasonal storm responses. Our results revealed differences in the response of DOC quality metrics to an early summer versus an autumn storm, with changes in DOC quality metrics varying by storm and lake features. During the early summer storm, we observed greater changes in various DOC quality metrics in deep lakes with longer residence times, whereas during the autumn storm, lakes with large watershed area to lake area ratios experienced the greatest changes. Land cover was highly correlated with changing DOC quality metrics in the early summer storm but did not play a significant role in the autumn storm response. Our research provides evidence of seasonal differences in the effects of storms on boreal lakes, which are ultimately mediated by a combination of lake and watershed characteristics as well as seasonal differences in climate such as solar radiation and antecedent weather conditions.

PCB mass budget in a perialpine lake undergoing natural decontamination in a context of global change

Despite the fact that PCB contamination of the global environment has been extensively studied in the last decades, the fate of these compounds in freshwater ecosystems is not fully understood and an important knowledge gap remains regarding the understanding of PCB dynamics and fate in perialpine lakes. This study relied on both field sampling performed and modeling to accurately identify the main fluxes involved in the PCB dynamics into the French perialpine Lake Bourget from 2013 to 2017. Our results show that the main inputs responsible for the PCB loading of the water column are tributaries inflows (~90%) rather than atmospheric inputs which could be related to the high catchment area over lake surface area ratio (i.e., 13). The main mechanism responsible for the lake natural decontamination was sediment burial (76%) due to the effect of the biological pump coupled with a high sedimentation rate. Volatilization represented 19% of the loss of PCBs from the water column and was mainly controlled by the high PCB concentration in water. These mechanisms are susceptible to be affected by the impact of the global change (increase of temperature, modification of the primary production rate) in the near future.

Reduced Rainfall Increases Metabolic Rates in Upper Mixed Layers of Tropical Lakes

Ecosystem-level metabolism is a good sentinel for human and natural disturbances in freshwater systems, responding from local changes (for example, land use) to regional and global changes (for example, climate). Despite the increasing understanding of metabolic processes in tropical lakes, our knowledge on how morphometric and catchment characteristics affect metabolic responses to those changes in tropical lakes is still very scarce. We investigated how metabolic rates in the upper mixed layer of twelve Brazilian tropical lakes responded to reduced rainfall, considering their lake area and drainage area ratio and the percentage of native forest cover in their drainage area. An 80% reduction in the 2013 rainy season rainfall, compared with 2012, resulted in a reduction of approximated 1 m in the water column depth, a 1–2 m deepening of the upper mixed layer, a 50% reduction in mean light availability, and a doubling in total phosphorus concentrations. These changes were associated with 38% increases in gross primary production (GPP), stimulated by higher nutrient concentrations and reduced photoinhibition. These effects of reduced rainfall were strongest in lakes with a small volume in relation to their catchment areas. Our results show that climatic-related reductions in precipitation in this tropical region will reduce lake volumes, affect temperature, water mixing, and nutrient supply with pronounced effects on lake metabolic processes and carbon cycling in this region.

A comparative study of long-term Hg and Pb sediment archives

Environmental contextLead and mercury are toxic atmospheric pollutants emitted in large quantities since 1850. Accumulating lake and peat sediments capture the pollutants from the atmosphere and indirectly record changes in deposition through time. This study of four long-term sediment records addresses the questions, ‘What proportion of this atmospheric deposition is natural background?’ and ‘Does the archive faithfully represent true rates of atmospheric deposition?’ AbstractAtmospheric phenomena have a large influence on the flux of mercury (Hg) and lead (Pb) to terrestrial and aquatic ecosystems. Some direct phenomena involve high-frequency variations in air movement; other indirect processes involve longer-term changes in climate and associated vegetation and hydrology. Here, we use evidence from sediment cores to explore how these atmospheric and landscape processes produced large natural variations in Hg and Pb deposition over thousands of years before industrial pollution. Cores from Sargent Mountain Pond, coastal Maine, USA (16600 years), Plešné Lake, south-western Czech Republic (15000 years), Lake Tulane, central Florida, USA (45000 years), and Caribou Bog, Orono, Maine, USA (10000 years) each illustrate how long-term local environmental changes influence the deposition and net retention of Hg and Pb. Important natural factors that emerge from comparisons among these four sites include forestation, changing groundwater hydrology, evolution of the watershed and lake system and (watershed area)/(lake area) ratio, all overlain by late-Holocene anthropogenic atmospheric pollution.

Longevity and effectiveness of aluminum addition to reduce sediment phosphorus release and restore lake water quality

114 lakes treated with aluminum (Al) salts to reduce internal phosphorus (P) loading were analyzed to identify factors driving longevity of post-treatment water quality improvements. Lakes varied greatly in morphology, applied Al dose, and other factors that may have affected overall treatment effectiveness. Treatment longevity based on declines in epilimnetic total P (TP) concentration averaged 11 years for all lakes (range of 0–45 years). When longevity estimates were used for lakes with improved conditions through the end of measurements, average longevity increased to 15 years. Significant differences in treatment longevity between deeper, stratified lakes (mean 21 years) and shallow, polymictic lakes (mean 5.7 years) were detected, indicating factors related to lake morphology are important for treatment success. A decision tree developed using a partition model suggested Al dose, Osgood index (OI, a morphological index), and watershed to lake area ratio (related to hydraulic residence time, WA:LA) were the most important variables determining treatment longevity. Multiple linear regression showed that Al dose, WA:LA, and OI explained 47, 32 and 3% respectively of the variation in treatment longevity. Other variables (too data limited to include in the analysis) also appeared to be of importance, including sediment P content to Al dose ratios and the presence of benthic feeding fish in shallow, polymictic lakes.

Lake and watershed influences on the distribution of elemental contaminants in the Rideau Canal System, a UNESCO world heritage site.

Watershed-specific variables such as sediment particle size distribution, water depth, sedimentation rate, focusing factors, and catchment area to lake area ratio can affect the distribution of trace element contaminants to lakes. The aim of this study was to investigate sources of metals to three headwater lakes and to quantify effects of watershed-specific variables on spatial and temporal trends of trace elements (As, Cd, Co, Cr, Cu, Hg, K, Ni, Pb, Rb, and Zn) in sediments and mercury (Hg) concentrations in fish. Surface sediment and water samples were used to characterize spatial patterns, while sediment cores were collected to portray temporal trends. Historical trends of Hg in northern pike (Esox lucius) were assessed in relation to paleolimnological trends of sediment Hg concentrations. Similarity in timing of sediment peak trace element concentrations for the lakes suggests large-scale, atmospheric sources. The lake with highest catchment area-to-lake area ratio was consistently associated with highest sediment elemental concentrations and displayed significant correlations between increased sediment Hg concentrations and decreased pike tissue concentrations over time. This suggests that catchment area-to-lake area ratio is an important factor influencing the concentration of atmospherically derived contaminants within lake sediments and their transfer through the food web.

Burial rates and stoichiometry of sedimentary carbon, nitrogen and phosphorus in Midwestern US reservoirs

Summary Lakes and reservoirs bury large quantities of organic carbon (C) and nutrients (nitrogen, N; phosphorus, P) in their sediments, especially when expressed relative to the small area they occupy. Global estimates of C and nutrient burial rates in reservoirs require a quantitative understanding of the wide variation in the rates and ratios at which C, N and P are sequestered in sediments. We examined how catchment and reservoir characteristics relate to sediment organic C, N and P concentrations, stoichiometric burial ratios (C : P, C : N, N : P) and burial rates in 13 small reservoirs across a catchment land use gradient in the Midwestern United States. Sediment P concentrations were positively correlated with urban catchment land use and negatively correlated with agricultural catchment land use. Stoichiometric burial ratios varied with catchment land use. Both N : P and C : P were positively correlated with agricultural land use, while these ratios were negatively correlated with urban land use and forested land use. In general, rates of C, N and P burial per unit lake area were not related to land use in the catchment, but were all positively correlated with catchment area to lake area ratios. Results from our study reservoirs suggest that reservoir burial rates are more tightly coupled with morphometric catchment characteristics than with land use. Our results suggest that small reservoirs are regionally and globally significant for biogeochemical processing. However, regional variation requires that much more comprehensive sampling is needed for accurate estimates of global element burial rates.

The effects of wildfire on the water chemistry of dilute, acidic lakes in southern Norway

Changes in lake water chemistry were studied for >4 years following a large wildfire in a boreal forest area in Mykland, southern Norway, an area characterized by thin and patchy, base-poor and slow-weathering soils and bedrock. Accordingly, the lakes have low acid neutralizing capacity (ANC), calculated as the difference between the total concentration of base cations ([ΣBC]) and strong acid anions ([SAA]). During the initial post-fire period, and peaking about two months after the fire, the mobilization of SAA from terrestrial to aquatic systems caused a dramatic drop in ANC. In one of the lakes, ANC dropped from about 20 to −80 μeq L−1, while [H+] and inorganic aluminum ([Ali]) increased to 38 μeq L−1 (pH 4.42) and 326 μg Al L−1 (36.2 μeq L−1 as Al3+), respectively. Sulfate and chloride were the predominant anions responsible for this decline in ANC, as the nitrate increase was small. After the severe chemical episode, [SAA] in the lakes declined faster than [ΣBC], and within about one year after the wildfire, ANC was back to almost pre-fire values. However, despite the fact that [SAA] also continued to decline faster than [ΣBC] the following years, no further increase in ANC was documented. The strong ionic strength decline and the increase in TOC during the same period have likely counteracted for the potential ANC increase. There were large lake-to-lake variations in water chemistry of the wildfire affected lakes. Hydrology, geology, lake residence time and the catchment area to lake area ratio are important explanatory factors.

A minimalist model of terminal lakes: Qinghai Lake (China) and Lake Chad (N Africa)

The ratio of the areas of a terminal lake to its total basin provides a geomorphological measure, which characterises the geobotanical state of water limited climates. A minimalist model of this lake area ratio is introduced combining the water balances of lake and land, the Budyko–Schreiber rainfall–runoff chain over land and, as a closure, the land and lake potential evaporation to be of similar magnitude. The following results are analysed. (i) Model diagnostics quantify a dryness threshold separating water from energy limited climate regimes, which coincides with an upper bound for the area ratio of terminal lakes to remain hydrologically closed. (ii) Model validations for Qinghai Lake and Lake Chad demonstrate model and observed water flux budgets to be in close agreement. (iii) Finally, a paleo-climate sensitivity study for Lake Chad demonstrates that the minimalist model appears to be a viable tool for future and paleo-climate estimates based on lake area ratio changes only and a single reference water flux. Furthermore, a stochastic interpretation of the rainfall–runoff chain allows estimates of water flux variability.

Seasonal examination of phytoplankton abundance and assemblages in Myall Lake and Bombah Broadwater, New South Wales, Australia

The Myall Lakes are a series of interconnected, shallow and poorly flushed coastal lakes located within the Myall Lakes National Park in NSW, Australia. The following field study aims to uncover patterns in temporal variability in water quality and phytoplankton abundance, diversity and assemblage structure, in the upper and lower water bodies of the Myall Lakes system. The result showed that the two lakes differ greatly in their catchment to lake area ratios, freshwater inputs, degree of saline intrusion, light attenuation and submerged macrophyte biomass. The broadwater, which receives large inputs of freshwater from the catchment, and is influenced by saline inputs from the Port Stephen’s estuary, exhibited highly variable water quality and dissolved nutrient concentrations, and phytoplankton assemblages with much temporal variation in taxa present, biovolume, cell size and abundance, and taxonomic diversity. In contrast, the upper lake, Myall Lake, shows much greater stability in water chemistry and nutrient availability; the phytoplankton community is diverse, with relatively low and constant biovolume, and is dominated year-round by small-celled cyanobacteria. Differences in phytoplankton between the two lakes were greatest during the autumn and winter, and least during the summer, when the phytoplankton assemblages in both lakes were dominated by similar cyanophyte taxa.