Rivers and Lakes

Terrestrial freshwater environments are both affected by and contribute to climate change, with highly complex feedback mechanisms. We must look to the records these environments preserve of past periods of climactic upheaval to be able to prepare for an uncertain future.

Rivers and streams are increasingly drying with climate change and biogeochemical impacts may be important. In this comment the authors discuss the challenges to the biogeochemistry of non-perennial rivers and streams, and what can be done to tackle them.

One of the main sources of uncertainty in carbon budgets is that continental landscapes are made up of a heterogeneous mosaic of ecosystems. Here the authors put forward an integrative framework to improve estimates of land-atmosphere carbon exchange based on the accumulation of carbon in the landscape as constrained by its lateral export through rivers.

While over 99% of coastal arctic rivers drain small catchments, future projections of land-ocean fluxes are based on data from large rivers. We encourage inclusion of and increased focus on smaller catchments to support representative assessments of arctic ecosystem change.

Groundwater discharge generates streamflow and influences stream thermal regimes. Classifying more than 1700 streams across the US by using an empirically-based approach the study shows that the vulnerability of streams to stressors depends on the aquifer source-depth of groundwater discharge

Here the authors present a global scale classification of river channel belt extents as a resource for improved ecosystem accounting and river behavior analysis. Moreover, the methods show advances in pattern recognition to define new global landform products.

This work investigates the sensitivity of streamflow simulations to individual hydrologic processes at 3316 locations across North America, revealing common sensitivities across watersheds.

An isotope synthesis of 1257 global lakes revealed on average 20% of inflow is lost to evaporation, but 10% of Earth’s lakes show extreme evaporative losses. Stable water isotope monitoring is an effective way to detect comparative climatic and catchment-scale impacts on lake water-balance budgets.

While the evaporative water loss from global lakes is invisible, the volume is substantial. In recent decades, lake evaporation volume has been significantly increasing due to enhanced evaporation rate, melting lake ice, and expansion of water extent.

Thermal conditions and circulation near glacier fronts are important to understand the recent rapid retreat of calving glaciers. New observations from a glacial lake suggesting a feedback mechanism between atmospheric warming, glacier front melting and calving for freshwater-terminating glaciers.

Antarctic supraglacial lakes (SGLs) have been linked to ice-shelf collapse and the subsequent acceleration of inland ice flow, but observations of SGLs remain relatively scarce and their interannual variability is largely unknown. This new study shows that lake area and volume vary substantially from year-to-year around the East Antarctic Ice Sheet and between ice shelves.

The effect of increasing surface melt on annual discharge is unknown for the Greenland Ice Sheet. Here, the authors find that Greenland’s largest single-glacier contributor to sea-level rise accommodates basal floods following supraglacial lake-drainage events with limited impact on ice flow.

Here the authors show that hyporheic flow, bed morphology, and bed stability are intimately related, and that this relationship is expressed as distinct locked and segregated states of bedform dynamics, which carries implications for river system behavior in general and the storage of carbon, nutrients, and contaminants in particular.

Dams constructed on fine-grained rivers cause an increase in flow resistance downstream, thereby amplifying, rather than reducing, flood stage.

Ultra-high resolution mass spectrometry revealed that plastic bags leach labile compounds. Bioassays performed in Scandinavian lakes indicated that these compounds are incorporated into biomass faster and more efficiently than natural organic matter.

River networks play an important role in biogeochemical processes of the earth system. Here the authors show that cumulative river network function increases faster than watershed size for many biogeochemical processes, particularly at higher river flow, indicating large rivers contribute disproportionately to network function in the Earth System.

Rivers are increasingly plagued by “syndromes”, i.e. salinization, mineralization, desalinization, acidification, alkalization, hardening and softening. A global look at river biogeochemistry reveals dramatically increased flux estimates and anthropogenic drivers of syndromes.

Methane production was thought to be an exclusively anaerobic process. This study shows that methane production occurs in oxygenated surface waters of four pre-alpine lakes and is often the main contributor to their methane emissions

Tropical forest lake sediments are global carbon sinks, representing an important implication for climate change, of which both temperature and forest conservation are key factors in maintaining the carbon burial mechanism in lacustrine ecosystems.

Beaver dams increase water flow gradients and nitrate removal far more than seasonal climate extremes. An expanding beaver range is an ecosystem feedback to climate change which could improve water quality.

Lakes are essential components of the hydrological and biogeochemical cycles. Here, Pi et al develop a global lake dataset called GLAKES via high-resolution satellite images and deep learning to examine global lake changes over four decades.

How lake temperatures are responding to widespread changes in lake ice remains unclear. Here the authors show the excess lake warming during the ice-off and ice-on month due to earlier ice loss and later ice formation across the Northern Hemisphere.

Under continued global warming, lakes will increasingly be covered by white ice, in particular towards the end of the ice cover season when fatal winter drownings occur most often and light limits the growth and reproduction of primary producers.

Many lakes on Earth are covered by seasonal ice, and as lake ice loss has been increasing, it is ever more important to quantify this. Here the authors present a fully coupled lake ice model projection as a part of the new CESM2 large ensemble modelling project and show that unprecedented lake ice loss is emerging globally as a result of anthropogenic-induced warming.

CH₄ inputs to Arctic lakes via groundwater discharge are an important pathway that links CH₄ production in thawing permafrost to emission via lakes. Here the authors unravel the role and drivers of groundwater inflows for CH₄ emissions from Arctic lakes.

The authors combine satellite data with hydrologic models to investigate recent changes in pan-Arctic river discharge magnitude, trends, and seasonality for nearly half a million rivers. They reveal that these rivers likely exported 3-17% more water to the global ocean than previously thought from 1984-2018.

Stratification has a considerable influence on lake ecology, but there is little understanding of past or future changes in its seasonality. Here, the authors use modelling and empirical data to determine that between 1901–2099, climate change causes stratification to start earlier and end later.

This study presents hourly data from a thermistor string in Lake Michigan, inspecting its response at depth to surface warming. Based on the data, the study suggests bottom lake temperatures respond to changes in turnover and re-stratification, with the ultimate possibility of the lake shifting from dimictic to monomictic.

The authors investigate the impacts of wildfires on fluvial networks in the western US. They find that wildfires directly impacted ~6% of the total stream length between 1984 and 2014. When longitudinal propagation was included, they estimate that wildfires affected ~11% of the total stream length.

Rapid sub-daily and weekly fluctuations in streamflow are known as hydropeaking. Here, the authors apply a new “weekly hydropeaking index” (WHI) to streamflow data from 500 gauges across the USA and Canada and find that the strength of WHI peaked in the mid-20th century and has been declining through the 2010s.

This study discovered non-monotonic variations in river flows for seven rivers originating from the Tibetan Plateau at warming levels of 1.5 °C, 2.0 °C, and 3.0 °C, which then resulted in different consequences for riparian countries

This study reports the occurrence of sustained and intensified microbial CH₄ cycling in a giant lake in northwestern China during Early Permian climate warming. Lacustrine CH₄ emissions may have contributed to the end of the Late Paleozoic Ice Age.

A new study reconstructs eight-century streamflow over the South and East Tibetan Plateau, showing that observations underestimate the full range of long-term streamflow variability and revealing contrasting regional variability in streamflow between south and north study regions.

A Gobi Desert megalake system reconstruction enables a quantitative estimate of East Asian Monsoon climate for the last two interglacials and provides insights into dust flux variations across East Asia and northern Pacific

Based on marine multiproxy records, a new study outlines the role of larger heat discharge of the pan-Arctic Rivers in determining the pronounced sea ice retreat over the East Siberian Arctic Shelf in the mid-Holocene.

This study provides evidence for a continental-scale river system that existed in eastern Tibet before the India-Asia collision. The river system developed an extensive low-relief landscape, which was uplifted and dissected during the late Cenozoic.