Cultural Eutrophication and Pollution


I. Trophic Equilibrium
    A. Natural eutrophication

Natural Eutrophication



        1. Changes over time with the filling in of lakes – the epilimnion volume doesn’t change as fast as the
            hypolimnion – the mixing depth is set by the SA of the lake, the fetch and the wind speed
        2. Increased AHOD – aerial hypolimnetic oxygen deficit
        3. Decreased volume of hypolimnion
    B. Artificial Eutrophication
        1. altered watershed conditions
            a. fire (changes evapotranspiration, water budgets, runoff)
            b. clearcutting – changes runoff
            c. agriculture
        2. addition of nutrients
            a. fertilizers
            b. waste treatment plants
                1) primary treatment – settling
                2) secondary treatment – digest organic matter;
                3) tertiary treatment – any additional treatment of secondary effluent to improve its quality;
                        for example, alum to remove P (expensive)

Pathways between eutrophic lakes and shallow secchi and oligotrophic lakes and deep secchi, and how these can be altered
II. Case Studies of Cultural Eutrophication
    A. Lake Zurich – two basins – Zurichsee and Obersee
 
            whitefish
            1898 first record of Oscillatoria rubescens (an indicator of eutrophication);
                    clarity decreased; oxygen consumption increased; whitefish decreased (Coregonids sensitive to low oxygen);
                    all this was mainly in the Zurichsee
            1918 whitefish disappeared (need cold water and high oxygen)
            Obersee stayed relatively pristine due to fewer people and lower nutrient input
            1940's -- Obersee followed the same course
            Calculated that 54% of the P in the lake was from sewage inputs.

    B. Madison Lakes, Wisconsin
        Mendota, Monona, Waubesa, Keyonsa, Yahara River
        Early 1900’s – settlement, clearcutting, agriculture
      
        1912 – Monona and Mendota eutrophied; to kill algae added CuSO4
        1930’s -- Monona was still so bad that they were diverting sewage to Waubesa
        1962 – so bad that diverted sewage into the Yahara River
        For these lakes 88% of the P and 75% of the N had come from sewage

    C. Lake Washington
        1933 – oligotrophic lake; 65 m deep
        Lake Washington is a monomictic lake in Seattle, with a residence time of ~3 years
        Seattle population in 1865 – 300; 1965 – 1.2 million
        In the 1950’s, the secchi depth was >3 m; lake was dominated by diatoms
        1955 Oscillatoria was found in the lake
        Early 1960’s – “Lake Stinko”
        T. Edmondson at the U. Washington
        At the maximum of eutrophication, Lake Washington was receiving 20 million gallons of secondary effluent each day
        Sewage diversion was started in 1963 and was completed in 1968, with no more effluent entering after that year.
        In 1962, 72% of the phosphorus was brought in by sewage; in 1966 it was 62%, and in 1967 it was 26%
        1962-1964 were even worse algal blooms
        1965-1966 dramatic algal production decline and increase in transparency;
            Food web effects:
                Early on in eutrophication, Daphnia were replaced by Diaptomus (becauseOscillatoria clogs the filtering apparatus)
                In the mid-1970’s Daphnia returns; secchi depth increased to record levels – 12 meters – due to Daphnia grazing

    D. Arctic Lake Example:  Lake N2 – divided lake in the arctic, Fe binding of P, delayed effects of fertilization
 
    E. Tropical Lake Example:  Lake Victoria
 
Year Secchi Chl. a (mg/L) Prim. Prod. 
(g O2/m2/day)
Reference
1960  7 m  3  1  Talling
1990  1-2 m 15  4 Hecky

            Lake had become eutrophied and no one knew what had happened.  The algal species had changed from diatoms to
                blue-green algae.  There were many changes in the system.
        1. Addition of nutrients from basin – now in Lake Victoria there is constant N limitation,
                especially inshore; there have been increases in P loading; N fixation is not enough to relieve N limitation.
                30 years ago the bottom waters were rarely anoxic, today they are often anoxic – 70% less space for the fish to live in.
        2. Food web changes – introduction of Nile Perch (Lates); introduced in the early 1960’s; haplochromines,
                the cichlid fishes, included many guilds and trophic specialists; many of the 300 endemic species have been eaten
                by the Nile Perch.
        3. Climate changes causing different mixing – in the past 50 years the climate has warmed, causing changes in mixing
            and the strength of stratification; affects light, nutrients, oxygen (blue greens need more light and have an advantage
            at shallow mixing depth)

    F. Practice of moving sewage outflows to rivers has improved the nutrient condition of lakes, but caused many
            problems in estuaries and nearshore ocean environments -- lots of Nitrogen loading leads to dead zones

III. Oligotrophication – concern about too low phosphorus levels in the Laurentian Great Lakes – are we actually
        decreasing fish production?

Proposals to start fertilizing lakes in a balanced N:P ratio to increase fisheries production levels.  Some fisheries managers see the issue as a choice between productive ‘greener’ lakes and streams and unproductive aesthetically clear waters.

IV. Other Pollution

    A. Types
        1. Thermal Pollution – power plants; industry
        2. Radioactivity
        3. Toxic contaminants
            a. Types
                1) POPs – persistant organic pollutants -- Pesticides and organic toxins – dioxins, furans, benzopyrene,
                            DDT/DDE, dieldrin/aldrin, hexachlorobenzene, alkylated lead, mirex, mercury, PCB’s, toxaphene,
                            heptachlor, chlordane, endrin
                        i. Nearly 80,000 synthetic organic chemicals are in daily use
                        ii. Endocrine disrupters
                2) Metals – cadmium, mercury, arsenic, lead
            b. Characteristics
                1) Toxicity
                    i. Acute – quick death
                    ii. Sublethal/chronic – impairment of growth, reproduction..
                    iii. Carcinogenicity – impairment of function, death
                    iv. Mutagenicity/teratogenicity – effects on future generations
                2) Bioaccumulation
                    i. Capacity to enter the food chain
                    ii. Biomagnification
                3) Persistence – resist degradation in the environment
                4) Volatility – easily evaporated and transported in the atmosphere

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