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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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... water temperature warming trend of +0.24°C in the last decade and an anomalously high global and equally weighted lake surface water temperature anomaly of +0.65°C in 2016. This warming trend dramatically affects lake ecosystems with increased algal blooms (Taner, Carleton, and Wellman 2011;Paerl, Hall, and Calandrino 2011) and changes in fish numbers, plankton and submerged vegetation (Havens and Jeppesen 2018;Boeuf and Le Bail 1999). A major concern to water quality is an increase in the occurrence of toxic cyanobacterial blooms (Kosten et al. 2012;Huisman and Hulot 2005), which are linked to the availability of sunlight, carbon dioxide and nutrients such as phosphorus and nitrogen (Dignum et al. 2005). ...
... The OPV cover could have a positive effect on the water quality and the aquatic ecosystem and human health.The material composition of OPVs made up from non-toxic materials(Gaudiana and Brabec 2008) makes OPVs a safe product to be used over water, not polluting the water in case of failure or decomposition of the panels.Climate change has already dramatically influenced terrestrial and aquatic ecosystems (Tkemaladze and Makhashvili 2016): Changes in water transparency, incident sunlight and global warming have led to increased surface water temperatures and thermal stratification in water bodies(Pilla et al. 2018;Havens and Jeppesen 2018).Woolway et al. (2017) reported a global lake surface ...
This paper presents a novel water reservoir cover using semi-transparent Organic Photovoltaics (OPV), that addresses water, energy and land shortages in addition to water quality improvements, by creating a dual-purpose usage of land resources by both generating electricity and reducing evaporation, whilst at the same time preserving or enhancing water quality. A simulation of the effect of the OPV cover on water temperature and evaporation is presented, as well as a discussion on the different variables influencing its viability. The filtering out of parts of the IR spectrum and 400–550 nm parts of the spectrum reduced both water temperatures and evaporation, which could thereby improve water quality.
... 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.
... Deforestation is one of the main problems caused by the overexploitation of land resources and, therefore, forest areas should be monitored and the formation of forests should be promoted [6]. Another very important issue in the face of climate change is the decline in wetlands, water reservoirs, especially in coastal environments [7][8][9]. Reasons that may cause a decrease in the surface area of water reservoirs are smaller precipitation and eutrophication, which can be a serious problem in costal river deltas [9][10][11]. Land cover monitoring is especially important for coastal areas, as they have multiple social functions as a part of the natural environment [12,13]. ...
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The aim of the study is the evaluation of land cover changes in selected areas next to three lagoons (the Curonian Lagoon, the Vistula Lagoon and the Szczecin Lagoon) located on the southern coast of the Baltic Sea (in Lithuania, Russia, Poland and Germany) from 1984 to 2021. The changes are evaluated using multispectral (visible light—RGB and near infrared—NIR) satellite images from the Landsat 5 and Sentinel-2 sensors. Due to their high importance for ecosystem services, two main land cover types are evaluated, i.e., forest area and inland water reservoirs. The classification of the images is performed using a random forest algorithm. Areas of water bodies and forests are evaluated for the years 1984 and 2021. During period 1984–2021, positive changes in land cover are observed in all three regions included in the study. In almost all parts, with the exception of the Polish part of the area located next to the Szczecin Lagoon, of these regions, an increase in forest area is observed. The increase ranges from 0.1% (Poland, area next to the Vistula Lagoon) to 1.2% (Germany, area next to the Szczecin Lagoon). The area of inland water reservoirs has not changed significantly in the long term. Despite the global warming, no reduction in the area of these water reservoirs is observed, even new seminatural reservoirs have been created in some parts of the study area.
... The climate is changing rapidly [3], and lakes are warming with correlated velocity on a global scale and in several regions with different climatic characteristics [4][5][6][7][8][9][10]. The direct or indirect effects of global warming on lake ecosystems has been analyzed in several recent studies [11][12][13]. New research also pointed out that lake heatwaves are becoming more frequent over the years [14]. ...
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Evaluation of the impact of climate change on water bodies has been one of the most discussed open issues of recent years. The exploitation of satellite data for the monitoring of water surface temperatures, combined with ground measurements where available, has already been shown in several previous studies, but these studies mainly focused on large lakes around the world. In this work the water surface temperature characterization during the last few decades of two small–medium Italian lakes, Lake Bracciano and Lake Martignano, using satellite data is addressed. The study also takes advantage of the last space-borne platforms, such as Sentinel-3. Long time series of clear sky conditions and atmospherically calibrated (using a simplified Planck’s Law-based algorithm) images were processed in order to derive the lakes surface temperature trends from 1984 to 2019. The results show an overall increase in water surface temperatures which is more evident on the smallest and shallowest of the two test sites. In particular, it was observed that, since the year 2000, the surface temperature of both lakes has risen by about 0.106 °C/year on average, which doubles the rate that can be retrieved by considering the whole period 1984–2019 (0.053 °C/year on average).
... Climate change is predicted to affect lake ecosystems in various ways (e.g. Havens & Jeppesen 2018). From the perspective of this study, the main effects are an increase in average temperature and length of growing season, an increase in nutrient loading from the catchment area and thus increased sedimentation and lower oxygen concentrations in winter. ...
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Marjomäki, T. J., Valkeajärvi, P. & Karjalainen, J. 2021: Lifting the vendace, Coregonus albula, on the life table: survival, growth and reproduction in different life-stages during very high and low abundance regimes.-Ann. Zool. Fennici 58: 177-189. We analyzed the variability in vendace population parameters in the context of a life table. Parameters related to growth, fecundity and survival were estimated for post-recruitment (age > 1 growing season) life stages of Lake Southern Konnevesi vendace in both very high and low population abundance regimes. Pre-recruitment survival producing population stability was then determined. We found a very strong compensatory density dependence in growth, fecundity and survival: during low abundance, a lifetime reproductive output of a female was almost 20 times that of the abundant regime. To maintain the low abundance regime, pre-recruitment survival must counterbalance it by decreasing to a very low level. Potential drivers of high variability in pre-recruit survival and potential for depensation, Allee effect, are discussed, as well as the implications of the results on fisheries management and risk of extinction due to anthropogenic stressors such as global warming or extensive predator stocking.
... Oversupply of phosphorus is recognized as a trigger of "cultural eutrophication" [4], [5], [6]. Moreover, lakes' function and ecosystem services can also be altered due to the climate change effect [7]. Lake Toba, the largest lake in Indonesia located in North Sumatra Province (Fig. 1), has shown disturbing conditions, especially marked by eutrophication. ...
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Lakes provide various ecosystem services that support biotic habitats and human life. In contrast, many lakes in the world are degraded due to pollutant supply from surrounding areas and human activities in the lake. Lake Toba, which is the largest lake in Indonesia, has indicated a polluted condition. However, the source and load of each pollutant are not yet known. A study has been conducted to determine nutrient and organic load levels entering the lake represented by Total Phosphorus (TP) and Chemical Oxygen Demand (COD), respectively. Observations were carried out in November 2017 at 22 locations, i.e., at 12 inlet rivers debouching to the lake and 10 sites at the lake. The pollutant impact was assessed from water class criteria based on COD, waters trophic status based on TP, and vertical oxygen profile representing cage aquaculture (CA) and non-cage aquaculture (NCA) areas. Based on COD and government regulation number 82/2001, water quality at the lake inlets was class III and IV. In the lake area, water class in NCA was III, while in CA the water class tends to be III and IV. Estimated TP loading from the catchment area was 138 tonnes/yr, while that from cage aquaculture activity was 570.33 tonnes/yr. Pollutants have caused the worsening of water class, increasing water column anoxia in the hypolimnion layer and eutrophication in Lake Toba.
Study region Two giant pockmarks in Lake Banyoles (NE Spain) have been surveyed over the last 35 years. The giant pockmark ‘B1’ has maintained an ‘eruptive’ mode with permanent groundwater discharge, whereas, the giant pockmark ‘B2’ has displayed alternating quiescent and eruptive phases. Study focus Interannual variability of lake-subsurface groundwater discharge in both pockmarks and the main lake aquifer level correlates with changes in the accumulated rainfall during the previous 10 months in the north-east of Spain. In the eruptive phase, the lutocline, marking the top of suspended sediments, is warmer than the ambient lake water and generates a turbid hydrothermal plume. New hydrological insights for the Region: Results show that the permanent hydrothermal plume at pockmark B1 is no longer penetrating the lake's background stratification due to the loss of plume buoyancy. The available data demonstrate that current climate change coupled with a depletion of groundwater resources has strongly impacted the hydrogeology and limnology of the main pockmark of the lake and also the distribution of suspended sediment in the water column.
The ecological status of Pampean shallow lakes is evidenced by Cyanobacteria Harmful Blooms impairing these nutrient enriched, turbid and polymictic water bodies spread along the Central Plains of Argentina. Under the premise that shallow lakes are sentinels of global climate and eutrophication, a 3-year research in ten lakes located across a climatic gradient explored which factors drove the dynamics of cyanobacterial assemblages frequently driving to bloom prevalence. Contrarily to what is expected, the effect of seasonal temperature on cyanobacteria was subordinated to both the light environment of the water column, which was on turn highly affected by water level conditions, and to nutrient concentrations. Monthly samplings evidenced that cyanobacterial assemblages presented a broad-scale temporal dynamics mostly reflecting inter-annual growth patterns driven by water level fluctuations. Both species composition and biovolume gradually changed across a gradient of resources and conditions and hence, the scenario in each individual lake was unique with patterns at different temporal and spatial scales. More than 35 filamentous and colonial morphospecies constituted the assemblages of Pampean lakes: nostocaleans and chroococcaleans were inversely correlated in the prevailing interannual 3-cycled patterns.
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The global surface temperature has increased by about 0.74°C over the past 100 years, and the frequency of extreme weather has increased as well. We used the state-of-the-art complex, dynamic, mechanistic model GOTM-FABM-PCLake to quantify the impacts of extreme summer warming on a summer-stratified temperate Danish lake. Simulated values of all calibrated parameters (water temperature, DO, NO3, NH4, TN, PO4, TP and Chl.-a) agreed well with observed values over the whole calibration and validation period and generally exhibited the same seasonal dynamics and inter-annual variations as the monitoring data. A series of climate scenarios with different summer heat wave frequencies and duration were set up to quantify the effects on the ecosystem state of the lake. Our simulations showed that summer surface mean TN will decrease with rising summer heat wave frequencies, while summer surface mean TP and Chl.-a and the biomass and proportion of cyanobacteria will increase. Following a summer heat wave, the lake approached baseline conditions in the autumn, but with increasing frequency of heatwaves the recovery period increased. Our results suggest that compliance with existing legislation, such as EU’s Water Framework Directive, will become increasingly challenging in a future scenario with increased temperatures and more frequent heatwaves.
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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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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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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.
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.
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.