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Ecological Responses of Lakes to Climate Change
Karl Havens 1, * and Erik Jeppesen 2,3
1Florida Sea Grant College Program, University of Florida IFAS, Building 803 McCarty Drive, Gainesville,
FL 32611, USA
2Department of Bioscience, Aarhus University, Vejlsøvej 25, 8600 Silkeborg, Denmark;
3Sino-Danish Centre for Education and Research, University of Chinese Academy of Sciences,
Beijing 100190, China
Received: 14 May 2018; Accepted: 9 July 2018; Published: 11 July 2018
1. Introduction
Lakes around the world are being affected by climate change, and that includes changes in their
physics, chemistry and biology, as well as interactions between their internal compartments and with
their surrounding watersheds [
]. The ecological responses of lakes to climate change will become
more pronounced in the future, with continued global warming, increased evapotranspiration, altered
patterns of rain and drought, and disrupted or amplified climate teleconnections [
]. The continued
ability of lakes to provide habitat to thousands of aquatic species and ecosystem services to society is
threatened as lakes diminish in size, become more saline, and/or have highly altered thermal properties.
At least one of the factors that is occurring with climate change—warming of lake water—is known
to have synergistic effects with nutrient enrichment, by stimulating blooms of toxic cyanobacteria in
eutrophic lakes [
] and by altering food-web structure [
]. Likewise, complex interactions occur when
other physical or chemical properties are altered. Changes in salinity affect composition and diversity
of the various biota and alter trophic structure and dynamics [
]. Changes in thermal stratification or
duration of ice cover affect fishes and, in turn, alter the top-down control of plankton. This can have
cascading effects on the food web [
]. Other synergistic and/or complex effects likely exist and are yet
to be documented as we continue to learn more about the responses of different kinds of lakes to a
warming earth.
Impacts of climate change on lakes are important because lakes play a critical role in the landscape,
providing nesting habitat for birds and foraging habitat and a source of water for many terrestrial
animals, and they play a substantive role as sources and sinks of carbon (C) and nitrogen (N) gases,
as well as oxygen (O). For the human population, lakes are a major source of drinking water, irrigation
water, recreation and fisheries resources, and they can have major cultural and economic significance.
Knowing all of this, it is remarkable that in many nations, funds are being directed away from the
careful assessment of changes in lakes in response to climate change. This is happening at a time when
quantification of the rates of change is most needed to help understand processes and possible tipping
points and to identify measures to increase resilience.
The aim of this special issue is to call attention to contemporary research that has been done to
document how lakes around the world are changing in response to climate change and to provide
insight into the growing body of knowledge about expected future changes. The summary below
provides the highlights of 11 original research papers contained in the issue, in the context of prior
work, and it identifies implications for lake management, for the services that lakes provide to society,
and points to research gaps where further work is needed.
Water 2018,10, 917; doi:10.3390/w10070917
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2. Contributions
2.1. Lake Warming
Lakes around the world are warming at a rapid rate, as documented recently in a survey of 235
lakes [
] showing an increase in the mean surface temperature by 0.34
C per decade between 1985
and 2009. Less is known about the warming that has occurred in water deeper under the lake surface,
where a larger percentage of organisms occur. In this special issue, Richardson et al. [
] quantified
changes in water column temperatures and thermal stratification in 231 lakes in North America over
the period 1975 to 2012. The dataset included lakes varying in their mixing regime, size, trophic state,
and geomorphology.
On average, the lakes displayed an increase in water temperature near the surface, as also
observed by O’Reilly et al. [
] in a global lakes assessment, and most lakes displayed an increase
in the strength of thermal stratification. On average, surface waters warmed 1.7 times faster than
corresponding air temperatures at the lakes. Lakes with high water transparency (Secchi disk depth
> 5 m) had greater warming of surface waters and greater increases in stratification than lakes with
lower transparency. Polymictic lakes displayed the greatest increase in warming throughout their
water columns. The mean change in deep water temperature, the major new focus of this study, was
not significantly different from zero. Approximately half of the lakes warmed and half cooled during
the period of record. Likewise, a study of 20 Danish lakes revealed a warming in the surface water
of ca. 2
C per year and a simultaneous cooling of deep water by ca. 1
C over the period 1989 to
2006 [12].
Certain characteristics were linked to how lakes in North America changed over time. Distance of
the lakes to the coastline was the most important explanatory variable; that is, coastal lakes cooled
and inland lakes warmed in their deeper waters. Elevation, shading by vegetation, duration of ice
cover, input of ground water, and other factors may have contributed to the trend in deep water
temperature changes observed. Two particularly important findings of this study were: (1) that lakes
are an important sentinel of global warming due to their more rapid temperature increase than the
overlying atmosphere; and (2) that there is considerable variability in lake response to climate change,
implying that intensive studies of just prominent lakes will not suffice to understand how lakes in
general will change in future decades.
In addition to long-term synoptic assessment, an approach that is likely to become important
to projecting the future of lake thermal properties in a warming world, is coupled modeling. In this
special issue, Kwak et al. [
] used a model that can simulate hydrological and thermal responses
of water bodies to warming, and coupled it with output from the Coupled Model Inter-Comparison
Project Phase 5 (CMIP5) Global Circulation Models (GCMs). They evaluated the projected effects of
three future climate scenarios on the Fourchue River, Quebec, Canada.
The hydrologic model predicted that under these three scenarios, of global warming by 1.0, 1.8,
and 3.7
C by 2100, the river will experience an increase in water temperature between 0.2 and 0.7
in June and between 0.2 and 1.1
C in September. It is noteworthy that the Fourchue River is a coastal
ecosystem and, as such, warming by a lesser amount than occurs in the atmosphere is consistent
with the findings of the first paper in this issue by Richardson et al. [
]. The model predictions
have ecological and management implications for the river system. This river is a critical habitat for
brook trout (Salvelinus fontinalis) and the predicted increases in temperature could be favorable to
growth. However, the model results also indicated that there will be several days in the summer when
temperatures exceed the upper incipient lethal temperature for this species and that might require
releases of cold water from the reservoir into the river to prevent fish mortality.
To evaluate how altered thermal properties of lakes might affect the structure and function of their
food webs, studies have compared lakes at different latitudes, studied lakes for a long period of time
as they have warmed, and in this special issue Arvola et al. [
] present the results from an experiment
where the mixing regime was artificially altered over a 4-year period. Two small lakes (
4.7 and 4.1 ha
Water 2018,10, 917 3 of 9
in Finland were selected for the study. They were both soft-water lakes of approximately 6 m depth,
with high dissolved organic carbon (DOC) and phytoplankton Chlorophyll-a(Chl-a) of approximately
g L
. In the experiment, one lake was a control, while the other was mixed by placing an
electrically-driven propeller at 1.5 m depth under a raft anchored at the deepest location, pumping
water from the metalimnion into the epilimnion. This artificial mixing occurred from May to September
2005 and again from June to September 2006. The plankton, macro-invertebrates, and fish of both
lakes were sampled weekly from 2004 to 2006 and biweekly in 2007, a year after the mixing ended.
Neither total phytoplankton biomass nor Chl-aconcentrations changed as a result of the artificial
mixing. However, the manipulated lake developed an increase in the relative biomass of diatoms
and cryptophytes. Crustacean zooplankton biomass did not change in the mixed lake compared with
the control; however, biodiversity increased following mixing, but only in the metalimnion. Rotifer
density declined in the mixed lake relative to the control, but only in the hypolimnion where protozoan
density increased. Certain taxa of littoral macroinvertebrates increased after the mixing, while others
declined in density. One food web response, an increase in the growth of perch (
Perca fluviatilis
) in
the mixed lake, was attributed to improved food availability. Another response, the appearance of
ruffe (Gymnocephalus cernuus) in 2006, was attributed to enhanced oxygenation of the benthic habitat
used by this animal. The authors concluded that the response of perch is ‘one of the best indications
that water column manipulation influenced the entire food web and the responses were cascading
to the upper trophic levels’. Another food web effect that was discovered in this experiment was
a decline in the mercury (Hg) concentration in perch. This was explained as being caused by a
mixing-induced reduction of mercury methylation by sulfate-reducing bacteria and an increased
contribution of methane-derived carbon in the food web from enhanced activity of methane-oxidizing
bacteria. In summary, the experiment demonstrated that climate-change induced alterations in the
mixing regime of small humic lakes can have effects on the structure and function of the entire food
web, including processes that influence concentrations of toxic metals at higher trophic levels.
Warming has the potential to greatly alter the rates of C emissions from natural landscapes.
Wetlands, including those that surround lakes, can be major sources of sinks for C, depending on
the conditions [
]. Camacho et al. [
] note that emission of methane (CH
), one of the most potent
greenhouse gases, is enhanced by warming and, as such, climate change could spark a feedback loop
where warming enhances CH
emission and emission contributes to more warming. Those authors
quantified CH
emissions from five saline lakes in central Spain. The lakes varied in their hydroperiod,
salinity, and trophic state. They conducted controlled experiments with intact sediment cores from the
lakes, varying the temperature and salinity, and then used a model to extrapolate the results under
different climate scenarios for 2050 and 2070. In general, and as expected, the rates of CH
from sediment cores were lower in times when sediments were dry and when temperatures were lower.
In the experiments, CH
emission increased in a non-linear manner with warming, especially between
25 and 30
C, and it decreased in a non-linear manner with increasing salinity, dropping quickly from
the maximal value at a conductivity of below 5 mS cm
to 20 mS cm
and then leveling off between
60 and 150 mS cm
. In general, the lakes were predicted to have large increases in CH
emission in
2050 and 2070; however, the outcome depends on sediment flooding vs. drying, with a projection of
the highest rates of CH
emission coming from lakes where the sediments remain flooded throughout
a dry season. To understand the effects that climate change might have on lakes, we therefore also
must consider future changes in hydrology.
2.2. Changes in Hydrology and Land Use
In addition to warming the atmosphere and hydrosphere, global warming is expected to alter
climate cycles, including those that connect oceanic thermal cycles such as the El Niño Southern
Oscillation (ENSO) to multi-year cycles in weather at distant locations around the world [
These teleconnections have major influences on the physics, chemistry and biology of world-wide
lakes [1820]
, and there is increasing evidence that the amplitude of ENSO and other cycles will
Water 2018,10, 917 4 of 9
increase with atmospheric warming [
]. The result of this could be intensified droughts and
concentration of rain into intense shorter-lasting periods of time. Changes like this could have
profound effects on the transfer of nutrients and organic material from the landscape into lakes and
would accentuate cycles of flood and drought that occur in many areas of the world. Intense droughts
might lead to salinization of lakes, concentration of nutrients, and synergistic effects with atmospheric
warming on water temperature increase.
Global warming is also expected to result in intensification of tropical cyclones [
], which can
have major impacts on shallow lowland lakes in the subtropics [
]. An approach to gain insights into
how such changes might affect lakes is to study the responses to contemporary events that are outside
the range of typical conditions. For example, Zhu et al. [
] examined the response of Lake Taihu in
China to repeated hurricane strikes and discussed how storms of greater intensity or frequency of
occurrence could lead to a loss of ecosystem resilience from these catastrophic events, and Ji et al. [
documented long-lasting changes in species composition of plankton in Lake Okeechobee (USA) after
an unusual case of three major hurricanes impacting the lake in two successive years.
In this special issue, Ji et al. [
] examine how a regular cycle of high and low water levels,
linked to the condition of the ENSO, affects water quality and zooplankton in shallow lakes of
central Florida, USA. Water depth, chemistry, phytoplankton, and zooplankton were examined
from a 15-year dataset with monthly samples from 6 shallow (mean depth 1.4 to 3.4 m) eutrophic
Chl-a35 to 65 µg L1
annual mean) polymictic lakes. All of the lakes contained high densities of the
benthivorous gizzard shad (Dorosoma cededianum), a filter-feeding fish that consumes plankton and
also feeds on macro-invertebrates in the sediments, and that can translocate a considerable amount
of soluble P into the water column [
]. In the study period, there was cyclic variation in rainfall
linked to the ENSO, with three droughts and four wet periods. Rainfall was significantly correlated
with lake depth, with the lakes losing as much as 80% of their volume in periods of lowest compared
with highest depth. The result was a concentration of fish and zooplankton in a small volume
of water during droughts and also a large increase in the biomass of filamentous cyanobacteria,
presumably because of greater nutrient availability. During droughts, cladocerans consistently
declined, while copepods were not affected, and the authors concluded that variation in water depth,
driven by the climate cycle, affected both the top-down and the bottom-up factors that control the
zooplankton. Cladocerans were more greatly affected than copepods because: (1) cladocerans are more
susceptible to fish predation [
]; and (2) cladocerans are less able to tolerate high densities of inedible
cyanobacteria—results documented in earlier studies [
]. If, as predicted [
], the amplitude of
the ENSO increases over the next 50 years with further global warming, effects of the associated
teleconnection on lakes may also increase, and in the case of shallow eutrophic lakes this could result in
synergistic adverse effects with nutrient pollution—greater internal loading, more toxic cyanobacteria,
and an altered assemblage of zooplankton.
As noted earlier, lakes themselves can be a substantive contributor to atmospheric C, particularly
if they have large associated wetlands. In addition to warming, hydrologic changes associated with
climate change might affect those C fluxes. Yang et al. [
] quantified emissions of CO
from the
littoral zone of a reservoir in Beijing, China, taking measurements with a dark chamber and gas
chromatography techniques along a transect from a permanently flooded location to a seasonally
flooded location and then to dry land. They also compared emissions from places with different
vegetation types within each hydrographic band. Sampling was done at six different times of the
year to account for seasonal variability. The authors found in general that the littoral wetland was a
much greater source of CO
(averaging 346 mg m
) than the pelagic, based on an average of data
from ten nearby Chinese lakes (pelagic mean, 72 mg m
). A majority of published studies of
the CO
flux from lakes have focused on the pelagic zone, and the results indicate a need for more
measurements of the littoral C flux, especially in lakes with a large littoral to pelagic surface ratio.
With regard to experimental results, there was considerable variation related to location, time of year,
time of day, and biomass of plants in the plots along the hydrologic gradient. The effect of flooding on
Water 2018,10, 917 5 of 9
emission was complex; however, it was noted that in the periodically flooded band, if flooding
resulted in plant growth, this shifted the C balance and the uptake by plants exceeded the loss of C
to the atmosphere, even when taking into account loss from CH
. The regime of flooding vs. water
recession in vegetated shorelines, and the time of year when it happens relative to the growing season,
could have a large influence on the degree to which lakes are sources vs. sinks of C.
As climate continues to change, and sea levels rise, there will likely be mass migration of human
populations away from impacted coastal areas as well as movement in the location where certain kinds
of natural and farmed vegetation exist. An interaction could therefore occur between changes in land
use, warming and the changes in climate cycles just mentioned. For example, if land use changes
to one that exports a higher amount of nutrients into a lake, the synergistic effects of warming and
increased nutrient concentrations could lead to greater prevalence and toxicity of cyanobacteria blooms
in eutrophic lakes as described above. Likewise, if a change in land use transforms a wetland/forest
area into urban, agricultural, or residential use, it will be accompanied by a faster movement of water,
C, and other materials from the watershed to a lake—compared with slow movement through natural
systems. If climate change leads to prolonged droughts interspersed with intense rain events, such a
modified watershed would have very different effects on a lake compared to a non-disturbed one.
However, these are major lasting changes, and there may be some alternations in land use that are of
shorter duration and that do not have these synergistic effects with climate change. In this special issue,
Levesque et al. [
] consider one such example—clear-cut logging in boreal Canada. They examine
the long-term (1991–2003) temporal variation in zooplankton in six lakes to determine how they
are affected by variation in precipitation, limnological conditions, and by factors linked to logging.
Prior studies have documented that clear-cut logging can have significant effects on boreal lakes by
altering nutrient and DOC inputs, transparency, primary productivity, and food web structure [
However, most of the watershed disturbances in those studies were short-term, lasting not more than
three years, and the effects on zooplankton were relatively small.
The aim of the study performed by Levesque et al. [
] was to test whether natural variation
in climate and limnological conditions are more important than the short-term impacts of logging.
To do this, the authors performed whole-lake experiments. They collected zooplankton from the
water column of three experimental lakes during a 5-year period before clear-cut logging and during
an 8-year period after logging. Sampling was twice per month in the ice-free season. Three other
lakes in non-disturbed watersheds were sampled in exactly the same manner and were controls.
There was considerable variation in temperature and precipitation (rain and snow) amongst the years
of study, and this influenced the zooplankton in both experimental and control lakes. In all of the
lakes, there was also temporal variation in the concentrations of major ions, pH, dissolved organic
carbon, total phosphorus, total nitrogen, and Chl-a. Zooplankton experienced a substantive decline
in total abundance over the study period in both the experimental and the control lakes. There were
some subtle interactions between climate variations and logging; however, for the most part, the study
revealed that variability in climate and limnological conditions (depth, residence time) had a stronger
influence on the zooplankton than did logging. The authors note projections of warming in the boreal
shield by 8
C in winter and conclude that this will result in reduced abundance of zooplankton,
in particular calanoid copepods.
While we intuitively expect that, for many other kinds of land use change, particular modifications
that are long-lasting will influence how climate affects lakes, there are no experimental studies like
that done by Levesque et al. [
] to confirm this, because it is not feasible. The gap could be filled
with long-term assessment of lakes with similar limnological characteristics and climate variation but
different land uses, or by scenario modeling. This is a critical research need.
2.3. Related Topics
It is critical that researchers and lake managers be able to track changes in lakes that are occurring
over time and that might be related to climate variability and change. Yet, with diminishing funding
Water 2018,10, 917 6 of 9
for long-term assessment, this is becoming increasingly difficult and the importance of low-cost
yet effective sampling approaches is high. Submerged aquatic plants (SAV) are often a sentinel for
the broader ecological status of lake ecosystems, especially shallow lakes [
] and they are highly
responsive to some of the changes in lakes expected to occur with climate change such as altered
drought severity [
]. Traditional field sampling of SAV is labor-intensive and costly. In this special
issue, Fritz et al. [
] explore the efficacy of a remote sensing method—studying changes in the
SAV community in Lake Starnberg, Germany, in the growing seasons of 2011 to 2015 based on
ground-truthed reflectance spectra. They develop ‘phenologic fingerprints’ for each SAV species and
characterize changes in the plant assemblage with some degree of error that needs to be addressed with
further research. Their study also documented that changes in water temperature had a lesser effect
on an invasive species than two native species. This is yet another issue of climate change—effects on
the relative abundance and biomass of species within particular assemblages in the lake.
One of the prominent effects of global warming is the world-wide melting and retreat of
glaciers [
]. The ecological and societal implications of this phenomenon are tremendous, because while
meltwater may for a period of time be high, once those glaciers are gone, it will disrupt the supply
of freshwater into some of the world’s major rivers that provide water supply, industrial water,
irrigation water, fisheries, and a route for commerce in places with tens of millions of people. At the
present time, melting of glaciers is known to be responsible for transporting organic C to downstream
ecosystems [
], and that C subsequently fuels food webs that are based on bacteria-plankton. One of
the regions experiencing rapid glacial change due to warming is the Tibetan Plateau. In this special
issue, Hu et al. [
] examine the extent to which organic C from glacial runoff subsidizes the plankton
food web in Lake Nam Co, a typical high altitude lake in the Plateau. They did this by focusing on the
zooplankton and using stable C isotope analysis and radio-carbon to determine the basal source of C
in their diets. They concluded that 74% of the C in zooplankton diets is from phytoplankton, 18% is
from a microbial food web fueled by decomposing SAV, and just a small fraction (8%) can be attributed
to allochthonous glacial meltwater C. However, they also note that with enhanced inputs of water and
organic C from glacial runoff, there is a potential to stimulate plankton production in the lakes of the
Tibetan Plateau.
As previously mentioned, if climate change displaces populations and this results in changes in
land-use around lakes, there could be an indirect effect on those aquatic ecosystems, if the changes
result in increased inputs of nutrients, C, or sediments, or a change in the rate at which rainfall over
the watershed makes its way into the lake. Therefore, it is important to understand how the attributes
of lake ecosystems are affected by land use patterns. Xu et al. [
] studied 14 lakes located in the
Yangtze River Basin and quantified recent rates of sediment deposition, and then evaluated their
results in the context of a variety of features of the lakes and their watersheds. Their finding is that
conversion of land to agriculture for growing crops or to urban uses can lead to substantial increases in
the sedimentation rate. High rates of sediment accumulation can lead to reduced depth and ecosystem
services of water bodies, impacts on benthic biota, and degraded water quality. The study reinforces
why it is critical to consider climate change and land use change in tandem when considering future
changes in lakes.
One general question that has been raised amongst limnologists is whether or not climate change
will have different effects on lakes at different latitudes. When considering the zooplankton, a major
focus is on predation, because it often is the major factor determining body size, total biomass,
and taxonomic composition [
], especially in shallow lakes [
]. Changes in the zooplankton
can, in turn, affect the phytoplankton, clarity, and thus indirectly even the submerged vegetation.
Iglesias et al. [41]
carried out controlled experiments using 1000 L in situ enclosures in shallow lakes
in Uruguay and Denmark, in order to compare the effects of presence vs. absence of small omnivorous
and planktivorous fish and/or invertebrate predators on the zooplankton and phytoplankton.
The enclosures contained common artificial plant beds, so that it was possible also to examine effects
on periphyton accumulation. Each treatment (fish, invertebrates, fish+invertebrates, control) was
Water 2018,10, 917 7 of 9
replicated in four enclosures at both study sites. They found that in both climatic zones the addition of
fish resulted in a decline in zooplankton and an increase in the biomass of phytoplankton. In both zones,
macro-invertebrates did not have significant effects. Neither fish nor macro-invertebrates affected the
biomass of periphyton. The results of this study support the view that in shallow lakes, omnivorous and
planktivorous fish may play a critical role in pushing the lakes into a turbid, phytoplankton-dominated
state by facilitating development of phytoplankton when their zooplankton predators are severely
depleted. While this study did not show clear differences in responses between the climate zones,
another study in which fish and invertebrates could move freely between the open water and the
plant beds indicated strong fish-induced differences, resulting in high predation on zooplankton and
macro-invertebrates [
]. The two studies, conducted in the same two countries, collectively identify
the overarching role that change in habitat selection may have in shallow lakes when the climate
gets warmer.
3. Conclusions
Climate change is documented to have major implications for the structure, function, and
ecosystem services provided by lakes. With increasing global warming, climate changes will affect
lakes by warming, by altering the thermal stratification, and by altering the hydrology, and there are
likely to be interactive effects of climate change and substantive changes in land use if people migrate
away from flooded coastal cities into the proximity of lakes. Lakes might display direct effects, such as
increased algal blooms where warming has synergistic effects with high nutrient inputs, and indirect
effects, where changes in fish assemblages have cascading effects that influence plankton, water clarity,
and submerged vegetation. With warming, especially in the littoral zones of lakes, there may be
large-scale changes in the net flux of CO
and CH
to and from the atmosphere, contributing to a
feedback loop where warming causes greater C flux from the natural systems to the atmosphere, which
leads to further warming. Despite a breadth of research, some key uncertainties remain about how
climate change will affect lakes, and it will require continued research and long-term assessment to
fully understand and predict future changes and effects on society.
Author Contributions: K.H. wrote the first draft, and E.J. contributed to the final version.
Erik Jeppesen was supported on this project by a sabbatical grant from Aarhus University and by AU
Centre for Water Technology (WATEC.AU.DK).
The authors are grateful to four anonymous reviewers for comments on an earlier version of
this manuscript.
Conflicts of Interest: The authors declare no conflict of interest.
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2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (
... Not all lake response mechanisms especially to abrupt climate changes are fully understood yet (Havens & Jeppesen 2018;Botta et al. 2019), and different lake systems might also reflect different aspects of climate changes, like for example the impact of extreme events (Adrian et al. 2016). Past lake responses that can be reconstructed from lacustrine sediments include changes in aquatic biota, lake geochemistry, lake salinity, authigenic mineralization, anoxic conditions, water circulation, extreme event layer deposition, catchment vegetation, detrital input, evaporation, water/air temperature, hydrology, and the water level (e.g. ...
... Past lake responses that can be reconstructed from lacustrine sediments include changes in aquatic biota, lake geochemistry, lake salinity, authigenic mineralization, anoxic conditions, water circulation, extreme event layer deposition, catchment vegetation, detrital input, evaporation, water/air temperature, hydrology, and the water level (e.g. Adrian et al. 2009Adrian et al. , 2016Lotter & Anderson 2012;Havens & Jeppesen 2018). Further, multiple stressors can influence lake responses simultaneously, and lake responses can also occur superimposed (Lotter & Anderson 2012). ...
... Adrian et al. 2016). However, there are still synergistic and complex lake response mechanisms that are not fully understood (Havens & Jeppesen 2018). In particular, ecosystem changes to abrupt climate change yet remain elusive (Botta et al. 2019). ...
Different lake systems might reflect different climate elements of climate changes, while the responses of lake systems are also divers, and are not completely understood so far. Therefore, a comparison of lakes in different climate zones, during the high-amplitude and abrupt climate fluctuations of the Last Glacial to Holocene transition provides an exceptional opportunity to investigate distinct natural lake system responses to different abrupt climate changes. The aim of this doctoral thesis was to reconstruct climatic and environmental fluctuations down to (sub-) annual resolution from two different lake systems during the Last Glacial-Interglacial transition (~17 and 11 ka). Lake Gościąż, situated in the temperate central Poland, developed in the Allerød after recession of the Last Glacial ice sheets. The Dead Sea is located in the Levant (eastern Mediterranean) within a steep gradient from sub-humid to hyper-arid climate, and formed in the mid-Miocene. Despite their differences in sedimentation processes, both lakes form annual laminations (varves), which are crucial for studies of abrupt climate fluctuations. This doctoral thesis was carried out within the DFG project PALEX-II (Paleohydrology and Extreme Floods from the Dead Sea ICDP Core) that investigates extreme hydro-meteorological events in the ICDP core in relation to climate changes, and ICLEA (Virtual Institute of Integrated Climate and Landscape Evolution Analyses) that intends to better the understanding of climate dynamics and landscape evolutions in north-central Europe since the Last Glacial. Further, it contributes to the Helmholtz Climate Initiative REKLIM (Regional Climate Change and Humans) Research Theme 3 “Extreme events across temporal and spatial scales” that investigates extreme events using climate data, paleo-records and model-based simulations. The three main aims were to (1) establish robust chronologies of the lakes, (2) investigate how major and abrupt climate changes affect the lake systems, and (3) to compare the responses of the two varved lakes to these hemispheric-scale climate changes. Robust chronologies are a prerequisite for high-resolved climate and environmental reconstructions, as well as for archive comparisons. Thus, addressing the first aim, the novel chronology of Lake Gościąż was established by microscopic varve counting and Bayesian age-depth modelling in Bacon for a non-varved section, and was corroborated by independent age constrains from 137Cs activity concentration measurements, AMS radiocarbon dating and pollen analysis. The varve chronology reaches from the late Allerød until AD 2015, revealing more Holocene varves than a previous study of Lake Gościąż suggested. Varve formation throughout the complete Younger Dryas (YD) even allowed the identification of annually- to decadal-resolved leads and lags in proxy responses at the YD transitions. The lateglacial chronology of the Dead Sea (DS) was thus far mainly based on radiocarbon and U/Th-dating. In the unique ICDP core from the deep lake centre, continuous search for cryptotephra has been carried out in lateglacial sediments between two prominent gypsum deposits – the Upper and Additional Gypsum Units (UGU and AGU, respectively). Two cryptotephras were identified with glass analyses that correlate with tephra deposits from the Süphan and Nemrut volcanoes indicating that the AGU is ~1000 years younger than previously assumed, shifting it into the YD, and the underlying varved interval into the Bølling/Allerød, contradicting previous assumptions. Using microfacies analyses, stable isotopes and temperature reconstructions, the second aim was achieved at Lake Gościąż. The YD lake system was dynamic, characterized by higher aquatic bioproductivity, more re-suspended material and less anoxia than during the Allerød and Early Holocene, mainly influenced by stronger water circulation and catchment erosion due to stronger westerly winds and less lake sheltering. Cooling at the YD onset was ~100 years longer than the final warming, while environmental proxies lagged the onset of cooling by ~90 years, but occurred contemporaneously during the termination of the YD. Chironomid-based temperature reconstructions support recent studies indicating mild YD summer temperatures. Such a comparison of annually-resolved proxy responses to both abrupt YD transitions is rare, because most European lake archives do not preserve varves during the YD. To accomplish the second aim at the DS, microfacies analyses were performed between the UGU (~17 ka) and Holocene onset (~11 ka) in shallow- (Masada) and deep-water (ICDP core) environments. This time interval is marked by a huge but fluctuating lake level drop and therefore the complete transition into the Holocene is only recorded in the deep-basin ICDP core. In this thesis, this transition was investigated for the first time continuously and in detail. The final two pronounced lake level drops recorded by deposition of the UGU and AGU, were interrupted by one millennium of relative depositional stability and a positive water budget as recorded by aragonite varve deposition interrupted by only a few event layers. Further, intercalation of aragonite varves between the gypsum beds of the UGU and AGU shows that these generally dry intervals were also marked by decadal- to centennial-long rises in lake level. While continuous aragonite varves indicate decadal-long stable phases, the occurrence of thicker and more frequent event layers suggests general more instability during the gypsum units. These results suggest a pattern of complex and variable hydroclimate at different time scales during the Lateglacial at the DS. The third aim was accomplished based on the individual studies above that jointly provide an integrated picture of different lake responses to different climate elements of hemispheric-scale abrupt climate changes during the Last Glacial-Interglacial transition. In general, climatically-driven facies changes are more dramatic in the DS than at Lake Gościąż. Further, Lake Gościąż is characterized by continuous varve formation nearly throughout the complete profile, whereas the DS record is widely characterized by extreme event layers, hampering the establishment of a continuous varve chronology. The lateglacial sedimentation in Lake Gościąż is mainly influenced by westerly winds and minor by changes in catchment vegetation, whereas the DS is primarily influenced by changes in winter precipitation, which are caused by temperature variations in the Mediterranean. Interestingly, sedimentation in both archives is more stable during the Bølling/Allerød and more dynamic during the YD, even when sedimentation processes are different. In summary, this doctoral thesis presents seasonally-resolved records from two lake archives during the Lateglacial (ca 17-11 ka) to investigate the impact of abrupt climate changes in different lake systems. New age constrains from the identification of volcanic glass shards in the lateglacial sediments of the DS allowed the first lithology-based interpretation of the YD in the DS record and its comparison to Lake Gościąż. This highlights the importance of the construction of a robust chronology, and provides a first step for synchronization of the DS with other eastern Mediterranean archives. Further, climate reconstructions from the lake sediments showed variability on different time scales in the different archives, i.e. decadal- to millennial fluctuations in the lateglacial DS, and even annual variations and sub-decadal leads and lags in proxy responses during the rapid YD transitions in Lake Gościąż. This showed the importance of a comparison of different lake archives to better understand the regional and local impacts of hemispheric-scale climate variability. An unprecedented example is demonstrated here of how different lake systems show different lake responses and also react to different climate elements of abrupt climate changes. This further highlights the importance of the understanding of the respective lake system for climate reconstructions.
... The sustainability of lakes to support several countless aquatic wildlife and offer ecological services to humanity is challenged by shrinkage, contamination, increasing salinity, and/or significantly changed thermal characteristics (Havens & Jeppesen, 2018). Most fresh waterbodies are under threat of pollution owing to human population expansion and development processes in and around them, which is one of the most pressing concerns harming our ecology (Bordoloi & Baruah, 2014). ...
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Globally, urban waterbodies are continually degrading due to the stresses from both natural and man-made changes. The vulnerability of the water resources system is directly impacted by various threats other than population expansion, such as changes in land use, socio-economic development, and climate change and their sustainability is often challenging. Importance of the natural balance restoration becomes crucial, which would lead to a sustainable development. It is necessary to analyze the environmental deviations in a catchment and their amplitude and decide where one may contribute. This study focuses on assessing the pollution risk index of the urban waterbodies by developing an appropriate extension of WRASTIC (wastewater, recreation, agriculture, size of the watershed, transportation, industrial, and vegetation cover) namely, WRASTIC-HI (WRASTIC-Hazard Index), a novel multi-criteria analysis for identifying potential sources and degree of contamination. The vulnerability assessment of the Upper Lake of city Bhopal to contamination has been computed using WRASTIC-HI and the result indicated that the catchment is at high risk with a high score (71) which is entitled to a three-year waiver illustrating that if the threats continue to increase in and around the catchment, the lake will sooner face more risk. The proposed technique makes use of open-source data as well as field surveys, making it a highly helpful tool for evaluating ecosystems with little time and expense and supporting planners, managers, and administrators for sustainable planning and decision-making with no need for complex computations or the collection of exhaustive scientific data.
... The main benefits of the models include easy development and use, dynamic simulation of the phytoplankton distribution, and explicit description of the interactions between the phytoplankton biomass and the most important environmental variables. The models can be utilized in simulating high phytoplankton biomass due to changing sensitive environmental conditions related to climate change (Havens & Jeppesen, 2018), thus supporting decision-making against potential harmful algal bloom events and allowing sustainable use of water for recreational and drinking purposes, i.e., it can be used for water management purposes. ...
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Phytoplankton represents one of the most important biological components of primary production, trophic interactions, and circulation of organic matter in lakes and reservoirs. To contribute to the understanding of eutrophication processes and ecological status of the small, shallow Butoniga reservoir, a machine learning tool for induction of models in form of decision trees and rule-based models was applied on a dataset comprising physical, chemical, and biological variables measured at four stations. Two types of models were successfully elaborated, i.e., (1) model describing phytoplankton Phylum, which describes and connects phytoplankton Phylum with phytoplankton abundance and biomass, and (2) model simulating phytoplankton biomass according to environmental variables which could be used in management purposes. Such models and their presentation contribute to a better understanding of the Butoniga reservoir ecosystem functioning.
... Steigende Wassertemperaturen und eine verstärkte Sonneinstrahlung im Zuge des Klimawandels, führen sehr wahrscheinlich zu steigenden Trophiewerten vieler Gewässer (Havens & Jeppesen 2018 Karpfen und Wels, bei denen bisher in Mitteleuropa nur unregelmäßige Reproduktion stattfand, können sich künftig häufiger und erfolgreicher vermehren (Britton et al. 2010, KLIWA 2015. Die Austrocknung von Flachseen und Kleingewässern könnte seltene Fischarten direkt im Bestand gefährden (z. ...
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Gewässer und deren Management stehen im Hinblick auf den prognostizierten Klimawandel vor großen Herausforderungen. Intensiver werdende Extremereignisse, wie Hochwasser, Starkregen oder lang anhaltende Trockenphasen mit hohen Temperaturen werden zukünftig verstärkt das sensible ökologische Gleichgewicht der Oberflächengewässer mit deren Flora und Fauna beeinträchtigen. Für eine Aufrechterhaltung der Lebensgrundlage "Wasser" und "biologischen Vielfalt" in Fließgewässern und Seen werden wirksame Anpassungsmaßnahmen benötigt. Demnach stehen sämtliche Akteure der Wasserwirtschaft vor der Herausforderung, die komplexen Wirkungszusammenhänge der vom Menschen beeinflussten Ökosysteme besser zu verstehen und gezielt die Anpassungsfähigkeit aquatischer Ökosysteme zu verbessern. Auf Seiten der Fachinstrumente ist auf EU-Ebene für die Wasserrahmenrichtlinie (EG-WRRL) zu hinterfragen, inwieweit sich deren Methoden und Bewertungssysteme unter sich ändernden klimatischen Randbedingungen als nutzbar erweisen. Zur Untersuchung der Auswirkungen der prognostizierbaren klimatischen Entwicklungen auf die ökologische Beschaffenheit von Oberflächengewässern wurden im Forschungsvorhaben anhand einer umfassenden Literaturrecherche und ergänzenden Expert*inneninterviews zunächst der derzeitige Wissensstandes und bestehende Wissenslücken ermittelt. Anschließend wurde die EG-WRRL als Handlungsinstrument auf ihre künftige Anwendbarkeit überprüft und Vorschläge hinsichtlich einer Anpassung des Methoden- und Bewertungssystems der EG-WRRL abgeleitet. Für die analysierten Wirkungszusammenhänge wurden zudem Verfahrensschritte und derzeitige Umsetzungsgrenzen eines Modellierungskonzeptes beschrieben. Weiterhin erfolgt eine Zuarbeit zur Ermittlung des Indikators "Wasserstress" gemäß der Ziele für nachhaltige Entwicklung der Vereinten Nationen für die Bundesrepublik Deutschland. Im Fokus standen hier die methodischen Ansätze zur Untersuchung des sogenannten "ökologischen Mindestwasserbedarfs" bzw. „Gesamtumweltwasserbedarfs“ für Deutschland. Sämtliche (Zwischen-)Ergebnisse wurden ausgewählten Expert*innen im Rahmen eines Fachworkshops vorgestellt und diskutiert. Die somit identifizierten Kernaussagen und Erfordernisse wurden in Handlungsempfehlungen zusammengefasst und werden über den vorliegenden Bericht Akteuren der Forschung, Verwaltungs- und Fachbehörden, sowie der Planungspraxis bereitgestellt.
... All these factors will lead to a higher evaporation rate throughout the year, and especially in the warmest months. Lakes respond directly to climate change, and some effects in water quality are expected, such as changes in salinity, water level, intensification of eutrophication which favors periodic proliferation by cyanobacteria, an increase of invasive species, increased turbidity, and enhanced vertical stratification, among other effects [4][5][6][7][8][9][10]. Water temperature, which is highly correlated with air temperature, exhibits a rapid and direct response to climatic forcing. ...
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The Alqueva reservoir is essential for water supply in the Alentejo region (south of Portugal). Satellite data are essential to overcome the temporal and spatial limitations of in situ measurements, ensuring continuous and global water quality monitoring. Data between 2017 and 2020, obtained from OLCI (Ocean and Land Color Instrument) aboard Sentinel-3, were explored. Two different methods were used to assess the water quality in the reservoir: K-means to group reflectance spectra into different optical water types (OWT), and empirical algorithms to estimate water quality parameters. Spatial (in five different areas in the reservoir) and temporal (monthly) variations of OWT and water quality parameters were analyzed, namely, Secchi depth, water turbidity, chlorophyll a, and phycocyanin concentrations. One cluster has been identified representing the typical spectra of the presence of microalgae in the reservoir, mainly between July and October and more intense in the northern region of the Alqueva reservoir. An OWT type representing the area of the reservoir with the highest transparency and lowest chlorophyll a concentration was defined. The methodology proposed is suitable to continuously monitor the water quality of Alqueva reservoir, constituting a useful contribution to a potential early warning system for identification of critical areas corresponding to cyanobacterial algae blooms.
The present chapter highlighted the preliminary approach for palaeoclimate studies using lake sediments and discussed the importance of proxy development using modern approach. The purpose of this chapter is to discuss the inportance of field investigation in developing a ‘baseline’ characteristic of individual proxies (e.g., pollen, geochemistry, stable isotopes, grain size, etc.) according to changes in environmental conditions, and utilize those proxies for climate reconstruction. Further, the chapter outlines several preliminary steps such as (i) field investigations – including site and lake selection, understanding geology, and geomorphological parameters in lake catchment; (ii) bathymetric and seismic investigation – to decipher the sediment characteristics and their spatial distribution at the lake bottom; (iii) investigating modern meteorological parameters – for understanding the temporal and spatial variability of real-time modern meteorological conditions; (iv) seasonal measurement of lake parameters such as pH, temperature, dissolved oxygen, etc., to understand the seasonal dynamics of the lake system; and finally (v) samples collection which involves a sequential collection of vegetation, sediments, and water samples.KeywordsProxy calibrationSeismic studiesGround-penetrating radarOpen–Closed Lake basinLake morphometryBathymetric investigationsCore sedimentsGrab samplingsediment trapPhysico-chemical characteristics
The article deals with problem of the fresh waters salinization in view of its relevance for normal functioning of the aquatic ecosystems, development of different branches of industry and agriculture, and human health. Attention is focused on the fact that the fresh waters' salinization inevitably results in decrease of the ecosystem services scope. The main factors and anthropogenic sources of influence on total dissolved solids in the fresh waters and metamorphosis of their ion composition are considered. It is stated that climate changes potentially affect and will affect the surface waters mineralization in future owing to volume and frequency of the atmospheric precipitation, intensity of the rocks and minerals weathering, the ground feeding of the rivers, the marine water penetration into the estuaries along with reducing of the river water yield, etc. The possible impact of mineralization changes on migration of substances from bottom sediments into the water thickness, that is on the intensity of its secondary pollution, is discussed. This impact can be direct and indirect. First of all, it concerns the migration ability of metals in bottom sediments. Elevated content of Na<sup>+</sup>, Ca<sup>2+</sup> and Mg<sup>2+</sup> in water intensifies migration of metals of the exchangeable fraction of bottom sediments. The indirect effect of elevated mineralization is expressed in the oxygen regime of the water bodies, which usually deteriorates in the near-bottom water layers of deep lakes and reservoirs, mouth areas of the rivers and estuaries. The dissolved oxygen deficit becomes usual, anoxic conditions are formed, which favor release of Fe(III) and Mn(IV) from oxyhydroxides or the oxide fraction of the bottom sediments. A review also considers some aspects of potential impact of the fresh waters salinization on survival of the aquatic plants and animals and biodiversity.
Small lakes (< 1 km2) are physically, chemically, and biologically linked to their watersheds through hydrologic, terrestrial, and aerial delivery of materials. Inputs affecting lake function and structure, such as nutrient, energy, sediment, and large wood subsidies, arrive at the lake on three spatial scales, i.e., the lake watershed, lake-inflow streams, and lake riparian areas. Lakes are sinks in the waterscape and integrate cumulative inputs from the landscape. Lakes can therefore react to landscape disturbances such as forest harvesting. Forest harvesting and associated activities can induce changes in watershed water yields, inputs of organic and inorganic materials to lakes, and in lake temperatures and wind. These changes result in stressors that can alter the lake’s physical habitat, water quality, and food webs. Here we review the reported impacts of forest harvesting on small, temperate zone lakes. The magnitude of the lake response to harvesting can depend on factors such as the proportion of the watershed harvested, the intensity of this harvesting, silvicultural practices and other activities, and road construction and density. Other additional factors include the proximity of the lake to harvesting and its impact on hydrological pathways connecting perturbed areas to stream and lake systems. The majority of surveyed studies reported short-term increases in nutrient and energy inputs, increased sedimentation due to harvesting, and increases in wind speeds, where about half reported increases in primary production or decreases in zooplankton biomass. Results on benthic macroinvertebrate, fish, and amphibians were less frequently reported and were geographically variable. Variation in the direction and magnitude of a lake’s food web response is likely due to studies of lakes with differences in watershed characteristics and forestry activities that can affect the magnitude of the lake response (i.e., proportion of watershed harvesting, forestry operations methods, hydrological connections to the lake, and site-specific attributes). We also discuss watershed forestry management and the implementation of lakeshore riparian buffers in the context of reducing forestry impacts on lakes. Most studies have been short-term, and the long-term, cumulative effects of forest harvesting on lake ecosystems remain unclear.
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Climate change can cause drastic changes in lake ecosystems, especially due to the increase in temperature and changes in precipitation, promoting, among other factors, an increase in the nutrients input and, therefore, eutrophication. This paper estimated the projected flow and nutrients load (NO3⁻, PO4–3) at the Mangueira lake — a large subtropical shallow lake, located in southern Brazil. The projections were based on the AR5 products for RCP 2.6, RCP 4.5, and RCP 8.5 scenarios. In each scenario, data from as many as 39 global climate models were used to estimate the projected values of flow and nutrients in two 30-year time intervals centered at 2,030 (near future) and 2,070 (long future). Results show the increase in flow is more likely, with a greater agreement between AR5 products when compared to AR4 products estimated in previous work. The pattern of increase also prevails in the projections of nutrient loads. The nutrients analyzed show an average annual load increase of 9.34% in the near future and RCP 2.6 scenario, while in the long future and RCP 8.5 scenario, this value rises to 22.48%. Mitigation measures should be studied to reduce the nutrient inputs and to preserve a good ecological status of the lake. Keywords: climate change; flow projections; nutrient load projections
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A major attribute of the Earth's climate that may be affected by global warming is the amplitude of variability in teleconnections. These global-scale processes involve links between oceanic conditions in one locale and weather in another, often distant, locale. An example is the El Niño Southern Oscillation (ENSO), which can affect rainfall and then the properties of lakes in Europe, Africa, North and South America. It affects rainfall, droughts and the depth of lakes in Florida, USA. It is predicted that the amplitude of variation in the ENSO will increase with global warming and, therefore, droughts will become more severe and periods of rain more intense. We investigated possible effects of climate on the zooplankton in shallow subtropical lakes by studying 16 years of monthly data from six shallow eutrophic lakes located north of Orlando, Florida. Results indicate that water depth and lake volume are tightly coupled with rainfall, as expected. During droughts, when lake depth and volume were greatly reduced, there were intensified cyanobacterial blooms, and the zooplankton shifted towards greater relative biomass of copepods compared to cladocerans. The change of zooplankton was likely due to the intensified selective fish predation in the reduced water volume, and/or selective adverse effects of cyanobacteria on cladocerans. The greatly reduced volume might lead to a 'perfect storm' of top-down and bottom-up factors that favor copepods over cladocerans. The mechanism needs further study. Regardless, this study documents a direct link between climate variability and zooplankton composition, and suggests how future changes in climate might affect plankton communities.
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In Canada, climate change and forest harvesting may both threaten the ecological integrity of boreal lakes. To disentangle the effects of natural variation in climate and lake environments from those of logging, we evaluated long-term variation (1991–2003) in zooplankton communities of six boreal lakes in Ontario. We monitored concomitantly changes in zooplankton abundance and composition in three undisturbed and three harvested lakes, five years prior and eight years after watershed clearcut logging. We tested the hypothesis that long-term natural variation in climate and lake environments will be more important drivers of zooplankton community changes than short-term impacts of logging. We used space/time interaction tests and asymmetric eigenvector maps to model zooplankton responses to environmental changes and logging. Year-to-year variation in zooplankton abundance and composition were almost an order of magnitude whereas among-lake variation was stable through time. Breakpoints in time series of zooplankton in each lake were not directly related to logging. Climatic and limnological features were the most important drivers of long-term variation in the zooplankton community, shading the effect of logging. These results highlight the need to better understand the pressures exerted by climate change on boreal lake ecosystems in the context of anthropogenic pressure, such as logging.
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Wetlands are among the most biologically active ecosystems on Earth, playing an important role in the global carbon cycle. Methane production in wetlands, resulting from anaerobic respiration of organic matter, accounts for an important part of natural sources of methane. In this work, we have evaluated the methane release rates of saline shallow lakes located in Central Spain, some of which maintain natural conditions, whereas others are hydrologically altered, with lowered salinity, or even presenting trophic alterations. We used sediment core plus water incubations to determine the release of methane from the studied lakes to the atmosphere, integrating both diffusion and ebullition processes, as well as the effects of temperature and salinity on methane production. The studied hypersaline lakes released methane at rates within the lowest range reported for temperate lakes and wetlands, whereas in hydrologically altered lakes that have dropped their salinity these rates were markedly higher. Models built with the specific response of methane release rates to temperature regarding the temperature changes expected according to the RCP climate scenarios predicted significant increases of these rates for the future, which could almost double current methane release for some of the studied lakes under the most pessimistic mitigation scenario (RCP8.5).
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Significantly increased sedimentation rates (SRs) in lakes worldwide in recent decades due to higher inputs of silt and eutrophication have led to significant environmental problems such as lake size diminishment and degraded water quality. Many lakes in the middle and lower reaches of the Yangtze River basin (MLYB) have followed this pattern. For effective lake management, it is essential to understand the pattern and drivers of SRs in these lakes. Fourteen typical lakes in the MLYB were chosen to examine the spatiotemporal patterns of SRs and identify the drivers over different time periods. Since 1900, SRs increased from <0.2 to 0.3–0.6 g·cm −2 ·year −1 , particularly notable during 1930–1990. Combined with climatic factors, SR correlated negatively with lake (catchment) size and abundance of aquatic vegetation, whereas other lake features including nutrient status did not contribute significantly to the variation in SRs, due to the fast decomposition processes of organic matter in shallow lakes. Detrimental land use practices especially reclamation for croplands and rapid urbanization was revealed to elevate SRs pronouncedly. We propose various management strategies aiming to maintain SR reference condition at ~0.16 ± 0.08 g·cm −2 ·year −1 , which is analogous to the SR value between 1850 and 1900.
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Submerged macrophytes are important structural components of freshwater ecosystems that are widely used as long-term bioindicators for the trophic state of freshwater lakes. Climate change and related rising water temperatures are suspected to affect macrophyte growth and species composition as well as the length of the growing season. Alternative to the traditional ground-based monitoring methods, remote sensing is expected to provide fast and effective tools to map submerged macrophytes at short intervals and over large areas. This study analyses interrelations between spectral signature, plant phenology and the length of growing season as influenced by the variable water temperature. During the growing seasons of 2011 and 2015, remote sensing reflectance spectra of macrophytes and sediment were collected systematically in-situ with hyperspectral underwater spectroradiometer at Lake Starnberg, Germany. The established spectral libraries were used to develop reflectance models. The combination of spectral information and phenologic characteristics allows the development of a phenologic fingerprint for each macrophyte species. By inversion, the reflectance models deliver day and daytime specific spectral signatures of the macrophyte populations. The subsequent classification processing chain allowed distinguishing species-specific macrophyte growth at different phenologic stages. The analysis of spectral signatures within the phenologic development indicates that the invasive species Elodea nuttallii is less affected by water temperature oscillations than the native species Chara spp. and Potamogeton perfoliatus.
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The continuous increase in the number of reservoirs globally has raised important questions about the environmental impact of their greenhouse gases emissions. In particular, the littoral zone may be a hotspot for production of greenhouse gases. We investigated the spatiotemporal variation of CO2 flux at the littoral zone of a Chinese reservoir along a wet-to-dry transect from permanently flooded land, seasonally flooded land to non-flooded dry land, using the static dark chamber technique. The mean total CO2 emission was 346 mg m⁻² h⁻¹ and the rate varied significantly by water levels, months and time of day. The spatiotemporal variation of flux was highly correlated with biomass, temperature and water level. Flooding could play a positive role in carbon balance if water recession occurs at the time when carbon gains associated with plant growth overcomes the carbon loss of ecosystem. The overall carbon balance was analysed using cumulative greenhouse gases fluxes and biomass, bringing the data of the present study alongside previously published, simultaneously measured CH4 and N2O fluxes. For the growing season, 12.8 g C m⁻² was absorbed by the littoral zone. Taking CH4 and N2O into the calculation showed that permanently flooded sites were a source of greenhouse gases, rather than a sink. Our study emphasises how water level fluctuation influenced CO2, CH4 and N2O in different ways, which greatly affected the spatiotemporal variation and emission rate of greenhouse gases from the littoral zone.
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In order to simulate food web responses of small boreal lakes to changes in thermal stratification due to global warming, a 4 year whole-lake manipulation experiment was performed. Within that time, period lake mixing was intensified artificially during two successive summers. Complementary data from a nearby lake of similar size and basic water chemistry were used as a reference. Phytoplankton biomass and chlorophyll a did not respond to the greater mixing depth but an increase was observed in the proportional abundance of diatoms, and the proportional abundance of cryptophytes also increased immediately after the onset of mixing. Obligate anoxic green sulphur bacteria vanished at the onset of mixing but gradually recovered after re-establishment of hypolimnetic anoxic conditions. No major effect on crustacean zooplankton was found, but their diversity increased in the metalimnion. During the mixing, the density of rotifers declined but protozoan density increased in the hypolimnion. Littoral benthic invertebrate density increased during the mixing due to Ephemeroptera, Asellus aquaticus and Chironomidae, whereas the density of Chaoborus larvae declined during mixing and lower densities were still recorded one year after the treatment. No structural changes in fish community were found although gillnet catches increased after the onset of the study. The early growth of perch (Perca fluviatilis) increased compared to the years before the mixing and in comparison to the reference lake, suggesting improved food availability in the experimental lake. Although several food web responses to the greater mixing depth were found, their persistence and ecological significancewere strongly dependent on the extent of the disturbance. To better understand the impacts of wind stress on small lakes, long term whole-lake experiments are needed.
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Predators play a key role in the functioning of shallow lakes. Differences between the response of temperate and subtropical systems to fish predation have been proposed, but experimental evidence is scarce. To elucidate cascading effects produced by predators in contrasting climatic zones, we conducted a mesocosm experiment in three pairs of lakes in Uruguay and Denmark. We used two typical planktivorous-omnivorous fish species (Jenynsia multidentata + Cnesterodon decemmaculatus and Gasterosteus aculeatus + Perca fluviatilis) and one littoral omnivorous-predatory macroinvertebrate (Palaemonetes argentinus and Gammarus lacustris), alone and combined, in numbers resembling natural densities. Fish predation on zooplankton increased phytoplankton biomass in both climate zones, whereas the effects of predatory macroinvertebrates on zooplankton and phytoplankton were not significant in either climate zone. Macroinvertebrates (that freely colonized the sampling devices) were diminished by fish in both climate areas; however, periphyton biomass did not vary among treatments. Our experiments demonstrated that fish affected the structure of both planktonic and littoral herbivorous communities in both climate regions, with a visible positive cascading effect on phytoplankton biomass, but no effects on periphyton. Altogether, fish impacts appeared to be a strong driver of turbid water conditions in shallow lakes regardless of climatic zone by indirectly contributing to increasing phytoplankton biomass.
Global environmental change has influenced lake surface temperatures, a key driver of ecosystem structure and function. Recent studies have suggested significant warming of water temperatures in individual lakes across many different regions around the world. However, the spatial and temporal coherence associated with the magnitude of these trends remains unclear. Thus, a global data set of water temperature is required to understand and synthesize global, long-term trends in surface water temperatures of inland bodies of water. We assembled a database of summer lake surface temperatures for 291 lakes collected in situ and/or by satellites for the period 1985–2009. In addition, corresponding climatic drivers (air temperatures, solar radiation, and cloud cover) and geomorphometric characteristics (latitude, longitude, elevation, lake surface area, maximum depth, mean depth, and volume) that influence lake surface temperatures were compiled for each lake. This unique dataset offers an invaluable baseline perspective on global-scale lake thermal conditions as environmental change continues.