Monomictic lakes francisco muñoz maestre

Warm and cold MonomiCtic Lakes

Structure and function of two different monomictic lakes, San Pablo lake (warm) and

Flakevatn (cold)

By:

Francisco Muñoz Maestre

WARM AND COLD MONOMICTIC LAKES Francisco Muñoz Maestre

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INDEX ABSTRACT .................................................................................................................. 4

WHAT IS A LAKE, CHARACTERISTICS AND MONOMICTIC TYPES ...............................................4

Characteristics and typology..............................................................................................5

Physical/thermal lake types...............................................................................................6

San Pablo Lake.................................................................................................... 8

INTRODUCTION ......................................................................................................... 8

METHOD AND MATERIALS ........................................................................................ 9

STUDY AREA............................................................................................................... 9

LIMNOLOGY OF SAN PABLO LAKE ........................................................................... 10

Limnological classification of the high Andean lakes .............................................................10

Physical and chemical parameters of the San Pablo Lake ......................................................11

Thermal Stratification .....................................................................................................11

Water chemistry .............................................................................................................11

DISCUSSION ............................................................................................................. 12

Flakevatn Lake.................................................................................................. 13

INTRODUCTION ....................................................................................................... 13

MATERIALS AND METHODS..................................................................................... 13

Sampling ............................................................................................................................14

Analysis Methods ...............................................................................................................14

Temperature and Heat Budget ........................................................................................14

Transparency, Color and Turbidity ...................................................................................15

Conductivity ...................................................................................................................15

pH & Alkalinity................................................................................................................15

STUDY AREA............................................................................................................. 15

RESULTS ................................................................................................................... 16

Water column temperature ................................................................................................16

Predicted Thermocline depth ..........................................................................................16

2005 and 2004 water column temperature profiles ..........................................................16

Heat budgets .....................................................................................................................17

Corrections to Strøm 1934 and 1965................................................................................17

Ice cover observations ....................................................................................................18

Heat budgets estimates: 3 strata versus 6 strata...............................................................18


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Transparency, Color and Turbidity .......................................................................................19

Conductivity, pH and Alkalinity............................................................................................19

DISCUSION ............................................................................................................... 20

Meteorology, Stratification and Heat Budgets ......................................................................20

Glacial ooze events, changes in water chemistry and silica content .......................................21

CONCLUSION ........................................................................................................... 22

BIBLIOGRAPHY ......................................................................................................... 23


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ABSTRACT

We are going to study two lakes, one warm and another cold monomictic lakes,

we are going to see the structure and functions if these lakes. Respectively, the first is

the lake San Pablo, in Ecuador and the second is the lake Flakevatn in Norwey.

Lake San Pablo, the largest lake in Ecuador, is a eutrophic lake due to the input of

sewage and other nutrients from the catchment area, which originate from intensive

agriculture and land erosion. Lake San Pablo is a monomictic lake with a short mixing

period during July to September. Stratification of the lake and mixing processes caused

by nocturnal cooling are of great significance for the eutrophication, which occurred

mainly during the last decade.

Flakevatn, a high mountain glacial lake situated in central Norway, has been

investigated for annual heat budgets, minerogenic and biogenic silica content of water

and sediment. This lake belongs in a cold monomictic lake category and is estimated to

have annual heat budget of 15673 cal cm-2 in the year 2004 and 13074 cal cm-2 in the

year 2005.

WHAT IS A LAKE, CHARACTERISTICS AND MONOMICTIC TYPES

A lake may be defined as an enclosed body of water (usually freshwater) totally

surrounded by land and with no direct access to the sea. A lake may also be isolated,

with no observable direct water input and, on occasions, no direct output. In many

circumstances these isolated lakes are saline due to evaporation or groundwater inputs.

Lakes may occur in series, inter-connected by rivers, or as an expansion in water

along the course of a river. In some cases the distinction between a river and a lake may

become vague and the only differences may relate to changes in the residence time of

the water and to a change in water circulation within the system.

Lakes are traditionally under-valued resources to human society. They provide a

multitude of uses and are prime regions for human settlement and habitation.

Good water quality in lakes is essential for maintaining recreation and fisheries

and for the provision of municipal drinking water. These uses are clearly in conflict

with the degradation of water induced by agricultural use and by industrial and

municipal waste disposal practices. The management of lake water quality is usually

directed to the resolution of these conflicts. Nowhere in the world has lake management

been a totally successful activity. However, much progress has been made particularly

with respect to controllable point source discharges of waste. The more pervasive


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impacts of diffuse sources of pollution within the watershed, and from the atmosphere,

are less manageable and are still the subject of intensive investigations in many parts of

the world.

Characteristics and typology

Origins of lakes

In geological terms lakes are ephemeral. They originate as a product of geological

processes and terminate as a result of the loss of the ponding mechanism, by

evaporation caused by changes in the hydrological balance, or by in filling caused by

sedimentation. The mechanisms of origin are numerous differentiated among 11 major

lake types (Hutchinson, 1957):

Glacial lakes: Lakes on or in ice, ponded by ice or occurring in ice-scraped rock

basins. The latter origin (glacial scour lakes) contains the most lakes. Lakes formed by

moraines of all types, and kettle lakes occurring in glacial drift also come under this

category. Lakes of glacial origin are by far the most numerous, occurring in all

mountain regions, in the sub-arctic regions and on Pleistocene surfaces. All of the cold

temperate, and many warm temperate, lakes of the world fall in this category (e.g. in

Canada, Russia, Scandinavia, Patagonia and New Zealand).

Tectonic lakes: Lakes formed by large scale crustal movements separating water

bodies from the sea, e.g. the Aral and Caspian Seas. Lakes formed in rift valleys by

earth faulting, folding or tilting, such as the African Rift lakes and Lake Baikal, Russia.

Lakes in this category may be exceptionally old. For example, the present day Lake

Baikal originated 25 million years ago.

Fluvial lakes: Lakes created by river meanders in flood plains such as oxbow and

levee lakes, and lakes formed by fluvial damming due to sediment deposition by

tributaries, e.g. delta lakes and meres.

Shoreline lakes: Lakes cut off from the sea by the creation of spits caused by

sediment accretion due to long-shore sediment movement, such as for the coastal lakes

of Egypt.

Dammed lakes: Lakes created behind rock slides, mud flows and screes. These are

lakes of short duration but are of considerable importance in mountainous regions.

Volcanic lakes: Lakes occurring in craters and calderas and which include

dammed lakes resulting from volcanic activity. These are common in certain countries,

such as Japan, Philippines, Indonesia, Cameroon and parts of Central America and

Western Europe.


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Solution lakes: Lakes occurring in cavities created by percolating water in water-

soluble rocks such as limestone, gypsum or rock salt. They are normally called Karst

lakes and are very common in the appropriate geological terrain. They tend to be

considered as small, although there is some evidence that some large water bodies may

have originated in this way (e.g. Lake Ohrid, Yugoslavia).

Physical/thermal lake types

The uptake of heat from solar radiation by lake water, and the cooling by

convection loss of heat, results in major physical or structural changes in the water

column. The density of water changes markedly as a function of temperature, with the

highest density in freshwater occurring at 4 °C. The highest density water mass usually

occurs at the bottom of a lake and this may be overlain by colder (0-4 °C) or warmer (4-

30 °C) waters present in the lake. A clear physical separation of the water masses of

different density occurs and the lake is then described as being stratified. When surface

waters cool or warm towards 4 °C, the density separation is either eliminated or reaches

a level where wind can easily induce vertical circulation and mixing of the water masses

producing a constant temperature throughout the water column. In this condition the

lake is termed homothermal and the process is defined as vertical circulation, mixing, or

overturn.

The nomenclature applied to a stratified lake, three strata which are defined like:

The epilimnion or surface waters of constant temperature (usually warm) mixed

throughout by wind and wave circulation, the deeper high density water or

hypolimnion (this is usually much colder, although in Tropical lakes the temperature

difference between surface and bottom water may be only 2-3 °c), and a fairly sharp

gradational zone between the two which is defined as the metalimnion. The name

metalimnion is not commonly used and the gradation is normally referred to as the

thermocline.

Picture made by myself

Hypolimnion


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The thickness of the epilimnion may be quite substantial, and it is dependent on

the lake surface area, solar radiation, air temperature and lateral circulation and

movement of the surface water. Commonly, it extends to about 10 m depth but in large

lakes it can extend up to 30 m depth. Stratification in very shallow lakes is generally

rare since they have warm water mixing throughout their water column due to wind

energy input. However, winter or cold water stratification can occur even in the most

shallow lakes under the right climatic conditions. The interpretation of a shallow lake

has never been satisfactorily defined, although there is a relationship between lake depth

and surface area which controls the maximum depth to which wind induced mixing will

occur. Therefore, an acceptable definition of a shallow lake is one which will overturn

and mix throughout its water column when subjected to an average wind velocity of 20

km h-1 for more than a six hour period. As a general rule, wind exposed lakes of 10 m

depth or less are defined as shallow water lakes.

The thermal characteristics of lakes are a result of climatic conditions that provide

a useful physical classification which is based upon the stratification and mixing

characteristics of the water bodies.

Now we are going to explain shortly the two monomictic, and after that we will

study deeply both:

Warm monomictic lakes occur in temperate latitudes in subtropical

mountains and in areas strongly influenced by oceanic climates. In the same way as

their cold water counterparts, they mix only once during the year with temperatures

that never fall below 4 °C.

Cold monomictic lakes occur in cold areas and at high altitudes (sub-

polar). The water temperature never exceeds 4 °C and they have a vertical

temperature profile close to, or slightly below, 4 °C. They have winter stratification

with a cold water epilimnion, often with ice cover for most of the year, and mixing

occurs only once after ice melt.


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San Pablo Lake

INTRODUCTION

The limnology of tropical lakes is of great interest and has become a main field of

contemporary limnological research to overcome the lack of knowledge. Tropical lakes

are warm water lakes situated in the tropical and subtropical parts of Asia, Africa,

Central and South America. The chemical and physical properties as well as the

biological processes of tropical lakes differ significantly to those of temperate lakes

(LEWIS 1987), due to temperature and thermal stratification, radiation and primary

production, diversity of fauna and flora and metabolic processes in the water body.

Special types of tropical lake are the mountain lakes in the equatorial zone. These

lakes are situated directly on the equator where they receive intensive illumination

without seasonal variation. Such lakes are found in the Andes at about 3,000 to 4,000 m

above sea level. Because of their high elevations these lakes contain cold water at

temperatures less than 20 °C. There are only a few lakes of this type, all situated in the

Andes of Ecuador, Columbia and northern Peru. This lake is situated at 15 ° south

latitude, where a significant seasonal variation of the climate occurs, and cannot be

considered an example of an equatorial high mountain lake.

The radiation input to tropical lakes is very high and the water body heats up

during the daytime and cools at night.

Heat transfer between the water surface and the atmosphere produces convective

nocturnal mixing. Tropical lakes, situated in the lowland, are polymictic at a high

temperature level, and water exchange occurs every night due to divergence and

convergence processes. This intensive water exchange, the high radiation and the

temperature level are parameters, of adequately accounted for in the nutrient loading

concept of Vollenweider (Vollenweider 1968; OECD 1982; TUNDISI 1990). Therefore

a modified nutrient loading concept was developed for tropical South American lakes

by the Centro Panamericano de Ingenieria Sanitaria y Ciencias del Ambiente (CEPIS

1990). However the application of this model to tropical high mountain lakes is

questionable and nothing has been learned about eutrophication processes in this type of

lake.

Investigations are carried out at Lake San Pablo, Ecuador, in the high Andes. The

aim of this study is to describe the limnological processes of this type of lakes under

consideration of the eutrophication processes. This includes the turnover of the

nutrients, the limitation of primary production as well as the succession of phyto- and

zooplankton.


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METHOD AND MATERIALS

Since 1993 there were a lot of investigation in this lake and in these ones, standard

limnological equipment is used and analyses are completed following the US Standard

Methods for the Examination of Water and Wastewater and the German Standard Rules

for Water Analysis (DEV). Chemical analyses are performed by the Subsecretaria

Saneamiento de Quito and the Escuela Politecnica Nacional de Quito (1998-2000),

phyto- and zooplankton analyses are completed by the Technical University of Berlin.

STUDY AREA

Lake San Pablo is a high mountain lake, 2,660 m above sea level (ASL), in the

Andes of Ecuador, South America, situated near Otavalo at 0°12 ' north latitude and

78°13 ' east longitude. It is a natural lake, the largest one of Ecuador.

Lake San Pablo is a nearly circular lake with a shoreline development factor of

1.21 and a steep slope of the shore. The maximum depth is 35.2 m, and the mean depth

is 26.0 m. The lake surface area is 583 hectares, and its volume is 140.106 m3.

The main water source is the Rio

Itambi, which contributes 90% of total

input, a small creek with a 20-years

mean flow of 1.4 m 3 sec 1.

The source of the Rio Itambi is

3,600 m ASL, and its catchment area

extends to 4,000 m ASL. The outlet is

the so called Desaguadera. The water

residence time is about 3.2 years

(Zevallos, 1992).

The catchment area is 14,790

hectares, and the ratio of the catchment

to the lake surface amounts to 1:26.

The catchment area of the Rio

Itambi shows a very high risk of nutrient input from intensive agriculture due to the

slope of the area. Agriculture is practiced up to 3,600 m ASL, and up to this elevation,

crop growing is the main land use with four to six harvests per year. The intensive

cultivation, steep slope of the fields and high precipitation rate results in much erosion

as well as a high input of nutrients into the lake. Intensive land use for the past few

decades led to the destruction of the ancient wet high mountain forests, and we must

Picture took from Limnology of an Equatorial High Mountain Lake in Ecuador, Lago San Pablo by GUNTER GUNKEL


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assume that this is one significant factor for eutrophication processes occurring today in

Lake San Pablo.

About 20,000 people live in the Lake San Pablo area, nearly 5,000 of which

inhabit small settlements, while the rest live in rural areas. The lake is important for

these people, who use its water for irrigation, take animals there to drink, remove

drinking water for themselves, wash clothes there and fish. The sewage from the main

settlement is introduced directly through a pipe into the lake. In addition, sewage flows

into the Rio Itambi from the rural dwellings. Nevertheless, the lake is used for

recreation and boating and is expected to become a centre for tourist activities.

LIMNOLOGY OF SAN PABLO LAKE

Limnological classification of the high Andean lakes

Lake San Pablo can be classified as a cold water lake with a temperature below

20°C. However due to the high heat input from insolation and the lack of seasonal

changes, the hypolimnic temperature is rather high. Consequently, the thermal

stratification of the lake is weak. Mixing processes may be caused by nocturnal cooling

and the development of convergence water currents, which leads to nocturnal mixing.

Besides the evaporation rate is high, and this may lead to a cooling of the surface water.

Another important factor is the lack of coriolis forces in the equatorial. No deflection of

currents produced by the winds occurs under these conditions. Consequently, the effects

of wind are greater than in temperate areas. The stability of the thermal stratification is

very significant for the distribution of oxygen and nutrients. Investigations to quantify

the mixing processes using oxygen isotope concentrations, drifting bodies and

continuous registration of the thermal stratification are planned.

The biology of cold high mountain lakes is also of interest because these are

isolated lakes in the tropics. The colonization of this high mountain area could not have

occurred via Central America, and studies of the vertebrates show that it took place via

southern South America. Therefore, these ecosystems are normally poor in diversity,

and the diversity decreases toward the equator. Another factor that affected the

colonization process is human activity, and many species occurring in these lakes are

introduced. For example trout and bass were released for fish production, while

aquarium plants were accidently introduced. Nothing is known about the succession of

the phyto- and zooplankton in these lakes. Because there are no seasons, a climax state

could be reached through niche building and diversification of species. However, it is

also possible that slight differences in the wind forces and inflow intensity might

influence mixing processes and lead to a seasonal succession of species. Another aspect

of interest is the effect of high UV-radiation at about 3,000 m ASL, which may lead to a

damage of the cells and possibly suppress primary production.


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Physical and chemical parameters of the San Pablo Lake

Thermal Stratification

The water temperature of Lake San Pablo varies between -19°C at the surface and

-17°C in deep water with little seasonal variation. The daytime air temperature does not

change during the whole year; however rain intensity and wind forces vary slightly to

produce a dry and a wet season.

A daily warming to 19.5 °C occurs in a water body of about 5 m depth. Nocturnal

cooling produced a surface temperature of 19 °C, and there was a mixing due to

convective processes to a depth of 15 m, which corresponds to the epilimnion. The

oxygen concentrations revealed that the lake was stratified below 15 m and had an

anoxic hypolimnion. Little temperature change occurred below 15 m. The temperature

isopleths for a whole year show that there is a stratification period from October to June

when the epilimnion is about 12 to 15 m deep. However the temperature differences

only amount to 1 to 2 °C, and a polymixis of the upper 15 m took place. A mixing

period occurs during June to September, promoted by the windy period with little

precipitation. In the Andean region shallow lakes with less than about 20 m depth

should be polymictic. However stability, wind effect, evaporation, nocturnal cooling,

heating by insolation, temperature gradient and absolute temperatures as well as other

factors should be considered to evaluate thermal stability.

Water chemistry

The water of Lake San Pablo is slightly alkaline and has a conductivity of about

250 to 300 μS cm-1. The calcium content is about 20 mg/1. The phosphorus

concentrations were increased by sewage input. During the stratification period, the

soluble reactive phosphorus (SRP) concentration in the epilimnion was about 0.02 to

0.09 mg1-1, but it increases up to 0.15 mg-1 during overturn. In the hypolimnion, very

high concentrations reaching 0.32 mgl-1 were recorded. A significant stratification of the

ortho-phosphate occurs similar to that of the temperature. In the epilimnion, SRP is

available during the whole period of stratification, the concentration of total phosphorus

ranges from 0.14-0.25 mg1-1 in the epilimnion and to 0.5-0.9 mg -1 in the hypolimnion.

During overturn, the mean phosphorus concentration in the epilimnion is

0.36mg1-1. The concentration of nitrogen is lower, which is typical for tropical areas

due to the intensive metabolic processes in the catchment area. The concentratio n of

NH4-N remains below 0.3 mg1-1, and the concentration of NO3-N are usually below

0.5g1-1. However, during overturn, the nitrate-N concentration increases to as much as

3mg1-1. The ratio of nitrogen to phosphorus by weight ranged from 7:1 to 0.5:1.

Therefore, the production in the lake is limited by nitrogen and not by phosphorus. This

limitation by nitrogen should promote a development of blue-green algae because some


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species can use the N2 gas as source of nitrogen. However, no significant amount of

blue-green algae has been reported in the first three months period of investigations.

There may be another factor that is limiting primary production.

The stratification of the lake produces a clinograde oxygen profile with

supersaturation in the epilimnic zone and a lack of oxygen in the hypolimnion below 15

m depth. The decrease in oxygen must be a result of the high load of organic substances

in the inflow from the Rio Itambi, in which the mean oxygen concentration is 5.4 mg 1 -

1, and the mean biological oxygen demand (BOD5) is 12.2 mg1-1. The isopleths for

oxygen confirm that there is a stratification of oxygen and that the hypolimnion of Lake

San Pablo is anoxic. This lack of oxygen is a good indication of the trophic state of the

lake, which is overloaded with organic matter. The primary production and input of

degradable organic substances create a demand for oxygen that the hypolimnion of the

lake cannot meet. After overturn, the oxygen saturation is low in the whole lake,

ranging from 60 to 80% of saturation.

DISCUSSION

Lake San Pablo is loaded with a high input of nutrients, which brought about an

eutrophication of the lake. This has limited the uses of the water as well as impairing the

ecosystem. In Lake San Pablo an increasing rate of decomposition led to a decrease in

the oxygen concentration in the hypolimnion, and the sediments became anaerobic. In

addition, the number of coliform bacteria is very high, due to the input of wastewater

directly into the lake. Using OECD criteria for lake eutrophication, Lake San Pablo

must be classified as a eutrophic lake because of its concentrations of phosphorus and

nitrogen.

Actually, it is not possible to evaluate the trophic level of the lake, and additional

information is needed to determine the eutrophication processes. Therefore, the mixing

processes in the epi- and hypolimnion must be quantified and the internal loading of

phosphorus is of great significance. The first investigations on the fauna and flora in

Lake San Pablo confirm the assumption, that the colonization of high Andean lakes was

obstructed. The Andean equatorial lakes are isolated in the tropical a rea, and few

species arrived via the southern part of South America. This results in low diversity of

the fauna and flora.


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Flakevatn Lake INTRODUCTION

High mountain lakes have recently been focused on by researchers interested in

detecting climate changes and sensing atmospheric-borne pollution (Catalan J et al.

2002, Wright and Cosby 2004). Wright et al. 2005 reports recent reductions in

acidification of central Norwegian mountain lakes and establishes optimistic

atmosphere for the near future. Sensitivity of these remote sites is specifically

exemplified by a glacial lake Flakevatn, deemed biologically near sterile. Flakevatn’s

research record is limited in size, but offers sufficient appeal for further investigation.

This is a semi-arctic lake, since water column temperatures during ‘warm’ years

exceed the temperature of maximum density (Strøm 1940). Summer and winter heat

budget investigations done on Flakevatn in 1933 and 1965, are rough approximations

due to sparse measurements performed on two separate days nearly thirty years apart

(Strøm 1934 and Strøm 1966). These estimates are rooted in the classical works by

Birge on examining and evaluating heat budgets of lakes (Birge 1914). Heat budget

studies are still relevant for investigation, since recent work on Italian lakes links

morphometry to heat budgets (Ambrosetti and Barbanti 2002).

In addition to having ‘peculiar’ aspects of heat budgets, Flakevatn has been

mentioned to occasionally experience late-summer clouding due to heavy runoff of

accumulated glacial clay. Glacial ooze events are common in high mountain lakes

situated next to glaciers. During 1933 expedition, Dr. Kaare M. Strøm observed

Flakevatn to be bluegreen in color and transparent down to 6m depth (Strøm 1934).

pH values of Norwegian mountains were investigated as early as 1925 and highly

alkaline measurements were associated with phyillite dominant localities (Strøm 1925).

MATERIALS AND METHODS

In the period of spring/summer 2005, some expeditions were carried out to

Flakevatn for study transparency depth, turbidity and the temperature changes in the

water column. Sediment samples and water samples were collected for chemical

analysis.

Qualitative observations of snow cover were done in mid March alongside

temperature measurements. Temperature data was obtained using inverting


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thermometer with focus on temperature variation beyond 20m depth.

The results will confirm or disagree with Strøm’s original estimate of

Flakevatn’s annual heat budget. Water samples were collected using standard water

sampler and delivered into 250mL or 1L polypropylene bottles. Duplicate samples

were taken on special occasions to measure alkalinity, pH and conductivity without

disturbing the original sample.

All collected water samples were to be stored in 4 ± 0.1°C cooling room

allowing for maintenance of samples chemical integrity. pH, alkalinity and

conductivity measurements were carried out in a given order. Filtration of the

water samples was performed to detect any measurable changes in the pH,

alkalinity and conductivity.

The study evaluates presence of a glacial ooze event through qualitative

(observation) and quantitative means (turbidity measurements). Changes in pH,

conductivity and alkalinity at 2m and 10m (epilimnion), are quantifiable chemical

aspects of a glacier lake and they test for glacial ooze buffering capacity. Both depths

are epilimnion depths serving for comparative differences.

Sampling

The sampling had two different objectives. Firstly, to measure temperature prior

to and post-melting of ice cover at Flakevatn. Secondly, to detect levels of glacial ooze

at regular intervals and any resulting changes to water chemistry and silica content.

Major constraints on the sampling efficiency were wind, travel and setup time, as

well as short day length.

Analysis Methods

Temperature and Heat Budget

Temperature of the water column was measured directly using reversing

thermometer. Messenger was released down the thermometer line once the

thermometer has reached the desired depth. After 2 minutes, the thermometer was

hoisted up. Temperature was recorded from the main scale and adjusted with readings

from the auxiliary scale (Welch 1948). Summer and winter heat budgets were

determined using reduced thickness method as done in Strøm 1934.


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Transparency, Color and Turbidity

Transparency was determined using a circular Secci disk measuring 20cm in the

diameter. The tabulated depth is the mean between disappearance and reappearance

depths. Eye-sight was the final means of judgment. Color was determined against Secci

disk at the half depth of its reappearance.

The turbidity was measured using highly accurate portable DRT-15CE

turbidimeter against reference standards; 0.02, 0.1, 10, 100 NTU (HF Scientific inc.

2004). All turbidity measurements were carried out in 4°C cooling room. The

turbidimeter was allowed 30 minutes to adjust to temperature before measurements

were carried out.

Conductivity

Conductivity, or electrolyte content, was measured in microsiemens (μS) cm-1

after samples have reached the room temperature. Conductivity meter (CDM 80) was

used for direct measurements.

pH & Alkalinity

Both were measured using Radiometer Copenhagen meters, a multi- function

instrument composed of TT80-Titrator / ABU80- autoburette standard alkalinity meter

and PHM 82 standard pH meter. pH measurements were taken at the first stable reading.

Titration of the water samples during alkalinity analysis was done using dilute 0.02N

HCl. Alkalinity measurements were obtained from slope of titration curves using

standard procedure described in Bøyum and Kaasa 2001.

STUDY AREA

Flakevatn is elevated at 1448m above

sea-level, is sited at North Latitude 60°38’ to

60°40’ and about 7°35’ E of Greenwich. This

lake is positioned approximately 7km from

Finse railway station. It is easily tracked down

by way of a tourist trail. The domed glacier

Hardangerjøkulen to the south and the

mountain range Hallingskarvet to the north,

Picture took from Limnological exploration of Flakevatn, a high mountain lake in central Norway. Annual heat budget and silica content by Nemanja Jevremovic


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are two geomorphological features that qualify Flakevatn. Hallingskarvet is glaciated in

its western part (Strøm 1934).

The Caledonian mountain chain, formed hundreds of millions years ago, is the

geological backbone of Scandinavia. Today we observe only roots of this mountain

chain. The foundation of this massif is archaean rock, minerologically equivalent to

granite or slightly gneissic granite (Fægri 1967). Above this base we find a phyllite

zone, foliated metamorphic rocks consisting of metamorphous shales and schists. This

zone reaches up to 1700m altitude (Strøm 1934). Older archaean rock is found

overlying phyllite zone, at the summits of the highest mountains (Fægri 1967).

Soil formed through disintegration of this parent rock is qualitatively very poor.

Decomposition of plant material introduces humic acids into the soils, further limiting

the survival of plants to only tolerant few. Consequently, this soil is easily removed

through erosion, exposing great parts of the peneplain (Fægri 1967).

RESULTS

Water column temperature

Predicted Thermocline depth

Hanna 1990, Kling 1988, and Baigun and Marione 1995 suggest array of models

for determining the planar thermocline depth (zt) in lakes from different regions.

Poland and Canada region model was found to be the most appropriate one for central

Norway.

The planar thermocline depth, Zt, is equal to mixing depth( Zmix ) ± 2.4m. Zmix, =

4.6 (0.5(Maximum Effective Length + Maximum Effective Width))^0.41. Predicted

range of thermocline according to this model is 5.1-9.9m. Flakevatn has had temporary

stratification at approximately 4-6m in mid august 2005, 8-12m in mid august 2004 and

7-12m in mid august 1933.

2005 and 2004 water column temperature profiles

Winter 2005 temperature profile shows almost no presence of a thermocline

formation. Sinusoidal appearance of April and May temperature curves still suggests a

thermocline at approximately 10m.

Throughout the winter/summer period in 2005 temperature changes have

shown predictable trends as observed in lakes of alpine character (Kalff 2002). In


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July 2005, at the completion of ice melting, Flakevatn had a 0°C surface

temperature and isothermous conditions from 2m downwards. During 2005 summer

period, the temperature did not rise above 4°C. Unstable stratification on almost

daily basis is normal in these conditions. During, thermoclines were developing

around 5m depth. These fluctuations are due to different densities of water layers

being disrupted and rapidly mixing.

In comparison to year 2005, 2004 winter/summer temperature conditions are

quite different. Ice partially disappeared in March 2004, a month earlier than it did in

2005. With surface temperature at about 0°C, a weak thermocline is established at

about 5m. Relatively isothermous conditions are established at the end of July to start

of August (~3.2°C). By mid august, there is a large increase in surface temperatures to

7.2°C and thermocline is positioned at about 10m. Full isothermy appears at the start of

September (~5.4°C), signifying the fall turnover.

Heat budgets

Corrections to Strøm 1934 and 1965

Investigation into Strøm 1934 and 1965 regarding Flakevatn summer and winter

heat budgets has to be corrected due to some discrepances. Calculation of the summer

and the winter heat budgets in these two studies has been based on a simple reduced

thickness method. 4°C is used as a reference temperature. This method is accurate in

estimating heat budgets if large number of depth intervals are available.

Differences among these values reflect on how accurate the estimates of heat

budgets are. The corrected heat budgets show a significant discrepancy in summer and

winter heat budgets from the original estimates, being around 250 cal cm-2 and 1600cal

cm-2 respectively.

Strøm 1934 calculation of summer heat budget was based on seven temperature

measurements from a single day, while 1965 calculation of winter heat budget was

based on temperature measurements from ten depths. Both winter and summer heat

budget calculations were based on temperature averages from three layers, 0-10m, 10-

20m and 20-75m. Summer heat budget estimate (1933), assumed the same temperature

from 30-70m. Furthermore, both summer and winter estimates lack 75m temperature

measurement, and thus 20-75m layer estimate is in fact 20-70m layer.

According to Strøm et al. 1965, the total winter heat budget for Flakevatn is -

22510 cal cm-2 and the summer heat budget is +5792 cal cm-2. Winter heat budget is

the sum of the amount of heat required to melt 150cm thick homogenous ice cover or -


~ 18 ~

12000 cal cm-2 and heat required for the Flakevatn’s water mass or -10510 cal cm-2.

Recalculation of Strøm’s estimate of the latent heat required to melt evenly

distributed 150cm of ice shows a significant ∼1000 cal/cm2 difference, or it changes the

original -12000 cal cm-2 to 10958 cal cm-2. Recalculation of the heat required for the

Flakevatn’s water mass changes the original estimate of -10510 cal cm-2 to 9947 cal cm-

2. Thus Strøm’s original winter heat budget estimate should be -20905 cal cm-2.

Strøm 1934 original summer heat budget estimate is 5792 cal cm-2, but when it

is recalculated, this value is in fact 6051 cal cm-2. By summing these two heat

budgets, the annual Flakevatn heat budget, based on Strøm 1934 and 1965 three strata

and 150cm thick ice, should be 26956 cal cm-2.

Ice cover observations

During year 2004 investigation, the ice disappeared on 27th July and it was

estimated to have reappeared on 31st October. Year 2005 had similar timing of ice

disappearance and reformation, 21st July and October 15th respectively. The total

depth of snow and ice covering Flakevatn is estimated to be 2m. Ice cover was

penetrated using a standard manual ice drill.

The Flakevatn layering in 2005 coincided with layer composition found in 2004.

Two ice layers, with combined 40cm thickness, are drastically different from Strø m’s

single 150cm ice thickness. Latent heat of evenly distributed 40cm thick ice is

calculated to be -2922 cal cm-2. In total, this change in heat reduces Flakevatn’s

original winter heat budget estimate from -20905 cal cm-2 to 13455 cal cm-2, given that

Strøm’s 3 strata method is used.

Heat budgets estimates: 3 strata versus 6 strata

Latent heat of ice is added to the winter heat budgets. 40cm thick ice cover ice

with latent heat of fusion at -2922 cal cm-2 is used in all estimates. Three- layer method

is based on Strøm’s three layers (0-10m, 10-20m and 20-75m) while six- layer method

uses six layers (0-2m, 2-10m, 10-20m, 20-40m, 40-60m, 60-75m).

Winter heat budgets estimated using 3 strata are significantly different from

winter heat budgets estimated using 6 layers. However, summer heat budget

estimates nearly coincide. The annual heat budget for 2004 and 2005 is based on 6

layers method and is 15673 cal cm-2 and 13074 cal cm-2 respectively. Flakevatn’s

annual heat budget is more likely to fluctuate between these two values.


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Transparency, Color and Turbidity

Strøm 1934, speaks of glacial runoff being the source of the milky grey color in

Flakevatn in August 1933. 1933 and 2004 were both warmer years than 2005. Due to

higher average summer temperatures in 1933, the greater amounts of glacial melt

water must have washed out greater amounts of glacial ooze. In 2005 this was not the

case, and most of the water inputs came from the snow melt. On each sampling

occasion, Flakevatn was transparent down to 12m depth.

At the same time, Flakevatn was observed to be bluegreen in color with no

visible glacial ooze. Since Flakevatn is known to receive glacial silt and clay inputs, it

is necessary to investigate turbidity as one of qualifiers of lake’s clay particle content.

All samples for year 2005 have shown an extremely low turbidity, truly characterizing

Flakevatn as a clear-water lake.

Conductivity, pH and Alkalinity

Conductivity, pH and alkalinity were measured before and after filtration of

select set of water samples. Epilimnion depths, 2 and 10m, were examined for any time

changes in these three characteristics. September 20th measurements at 2m depth are

not present in the dataset. August 4th 2005 was the only date that had a full water

column profile. Looking at August 4th 2005 profile, filtration changed very little in the

pH, conductivity and alkalinity. These were the conditions prior to anticipated glacial

milk event.

The time scale of conductivity changes shows an increase in conductivity at the

start of August in both filtered and unfiltered samples at 2 and 10m. It is possible that

this increase in conductivity in epilimnion is due to the initial pulse of airborne

electrolytes trapped within the snow. Stable stratification forming around this time,

levels off the concentration of electrolytes until end of September followed with a

slight increase in conductivity at the start of October. Both depths are following the

same trends, with filtered sample measurements showing only slight deviation from

unfiltered conductivities.

The time scale of pH changes at two depths of filtered and unfiltered samples

shows minor difference in pH. An exception to this is 2m sample measurement at the

start of August, followed by a decrease in difference between filtered and unfiltered

measurements. September 20th measurement at 10m shows a markedly larger

difference with filtration.


~ 20 ~

The time scale of alkalinity changes shows a different situation at two depths.

Filtration at 2m up to end of August, resulted in larger differences in alkalinity than at

10m. This trend reversed at the end of August. September 20th measurement at 10m

shows significantly greater difference in alkalinity, similar to difference observed in

pH measurements. This difference is possibly due to greatest accumulation of glacial

clay in the epilimnion at this time.

DISCUSION

Meteorology, Stratification and Heat Budgets

The analysis of Flakevatn temperature records from 2004 and 2005 shows two

drastically different situations. The Poland and Canada model for predicting the

thermocline position based on lake morphometric characteristics, anticipates the

thermocline in Flakevatn at 5.1 to 9.9m depth.

2005 was a significantly colder year with common isothermous conditions due

to water mass being below 4°C. Recurrent winds and probably night frosts would

contribute to this interchange between stratified and unstratified water column. Year

2004, similar to year 1933, was a warm year with stable stratification developing in

mid august. It would be safe to conclude that F lakevatn is a cold monomictic lake

during ‘warm’ years.

Finse area meterological records show that the monthly temperature trends have

stayed more or less the same over 100 years. In this investigation the mean

temperatures of each stratum are obtained from two temperature measurements at the

borderline of strata. Calculating the mean temperature of each successive stratum is

done by using a lower borderline temperature measurement. This practice introduces

error when the temperature is rapidly declining within water column (Birge 1914).

Annual heat budget for Flakevatn has been overestimated first in the use of low

number of strata for reduced thickness heat budget calculation and second, in the use

of too large of an ice cover thickness in determining winter heat budget. Determining

winter heat budget appears to be more problematic than evaluating summer heat

budget. In the winter months, Flakevatn has a definitive variability in temperatures

from 20-75m. The use of a single layer for 20-75m depth as dictated by three- layer

method overvalues the winter heat budget in 2004 and 2005 at around 3000 cal c m-2.

In the summer months, Flakevatn has a uniform temperature profile from 20-75m. The

differences are measured in hundredths of a degree, allowing for small difference

between summer heat budget estimates using either 3 or 6 layer method.


~ 21 ~

The composition of ice cover is the largest part of the Flakevatn’s winter heat

budget overestimation. By using 150 cm thickness of ice, Flakevatn’s winter heat

budget was estimated to be 9000 cal cm-2 larger than it is likely to be. Both years

2004 and 2005 showed a varied composition of ice cover with combined thickness

being around 40cm. Furthermore, the temperature trends over past century have

shown a relatively the same monthly temperature averages. This high mountain lake

has been evaluated to have an annual heat budget of 15 673 cal cm-2 during ‘warm

2004 year’ and 13074 cal cm-2 during ‘cold 2005 year’. It would be safe to expect

that Flakevatn would continue to have annual heat budget values in between those

two values.

Glacial ooze events, changes in water chemistry and silica content

Glacial ooze events at Flakevatn have been recorded twice in four expeditions

(August 1933, June 1965, 2004 and 2005). These are late summer events. Influx of

glacial ooze is dependant on the melt water washing off the deposits of freshly crushed

bedrock beneath the glacier. In addition to this, precip itation could wash off the deposits

of ground bedrock from former glacier locations. In general, the temperature has been

lower during summer months (June, July and August), seen in Graph 14 (Appendix 1)

2005 than in 2004 and 1933 by 0.7°C and 0.9°C, respectively.

The precipitation in winter months (October-March) has been lower in 2003-

2004 and in 1932-1934, than it was in 2004-2005. On average, these differences

were 42mm and 79mm, respectively.

Glacial ooze events are dependant on the random chance of melt water

encountering significant deposits of ground rock and carrying it off into the lake in a

short period of time. It is likely that in 2005, most of the melt water came from the

melting of snow cover. Snow cover was observed at Flakevatn in 2005 late into the

summer season. Turbidity measurements have shown an upward trend with warming

up, due to the snow melt and inputs of clay particles. Higher turbidity in September is

due to highest inputs of eroded matter to the lake from surrounding tributaries.

Filtration of the epilimnion water samples changed very little in conductivity but

pH and alkalinity showed some visible changes with filtration. These changes were

noted in the larger divergence of filtered samples pH and alkalinity curves from

unfiltered samples later in the season. The statistical significance of these changes was

correlated to the minerogenic silica or quantities of glacial ooze. Water samples

showed a rise in biogenic silica in the early august Total silica or mainly minerogenic

silica at 2m experienced a decrease with formation and reformation of thermocline

while at 10m the highest recorded levels were in mid September. The pH values of


~ 22 ~

epilimnion waters throughout 2005 were measured to be around 6.5 which is

drastically different from Strøm 1934 late August pH of 8.2. It is possible that

Flakevatn experiences alkaline pH only during glacial ooze events.

From conductivity, pH and alkalinity, only alkalinity was found to have a

statistically significant relationship with minerogenic silica. There is a suggestion that

alkalinity is correlated with glacial ooze quantities and that this is not just a chance event, although low number of samples and more conservative statistical testing showed

that support for this relationship is not large enough to confidently claim so.

CONCLUSION

Thanks to researching information for these essay I found that a lake is not only

water, fish, etc, the lake has a lot of characteristics and per this one we can differentiate

among all types, and ecology help us with experiments but is still a recent science, so

there are not to much knowledge about all this and we have to improve more searching

why and how all lake characteristic work, and we will find the relation between the lake

and all that is inside it.

We can see to in these experiments (more in the second one) that methods from

before have been improved rapidly, now we can take the correct results but still we need

improve more to can reach our goal, the knowledge of all the things that are surround

us.


~ 23 ~

BIBLIOGRAPHY

Limnological exploration of Flakevatn, a high mountain lake in

Central Norway. Annual heat budget and silica content, by Nemanja

Jevremovic (2006)

Limnology of an Equatorial High Mountain Lake in Ecuador, Lago

San Pablo by GUNTER GUNKEL (2000)

Stratification of lakes by Bertram Boehrer and Martin Schultze (2008)

Water Quality Assessments - A Guide to Use of Biota, Sediments and

Water in Environmental Monitoring - Second Edition, edited by Deborah

Chapman © 1992, 1996 UNESCO/WHO/UNEP (Chapter 7* - Lakes

prepared by R. Thomas, M. Meybeck and A. Beim)

A revised classification of laked based on mixing, Williams M. Lewis

Jr. (1983).

http://farm8.staticflickr.com/7019/6587163387_44fbf3e8d9_z.jpg

(Blue lake, in the cover)

http://www.hidricosargentina.gov.ar/images/indice_lagos/lacar1.jpg

(second picture in the cover)

http://www.apfanews.com/media/lrgeafp121-canadian-rockies-from-

the-air.jpg (Glaciar lake)

http://lawr.ucdavis.edu/faculty/gpast/tin.jpg (Volcanic lake)

http://enjoyequator.files.wordpress.com/2011/11/sp-see-

5lagosanpablo.jpg (San Pablo lake)

http://folk.uio.no/dagkl/Image214-FinsevatnNett.jpg (Flakevatn lake

without snow)

http://www.finse.uio.no/research/projects/life-science/lake-

finsevatn/pictures/DSC_5930_Finsevatn091009_W400.gif?vrtx=thumbnail

(Flakevatn lake with snow)

Monomictic lakes francisco muñoz maestre

Education