Cuyahoga River, 1952 Lake Erie: Progress and Regression Progress 1952 Cuyahoga River goes on fire 1969 Cuyahoga River goes on fire again 1960s and 1970s Canada and the USA agree on and implement a phosphorus control system that adds many new sewage treatment control systems, bans phosphorus detergents and establishes many monitoring locations in 33 rivers and in Lake Erie Introduction

Progress 1970s and 1980s - Lake water quality improves No more algal blooms No more cyanobacteria blooms in the western region of the lake No more “mats” of vegetation washing up on-shore Lake Erie oxygen levels return to normal Lake Erie considered “recovered” from past massive eutrophication due to previous phosphorus overload Progress in 70s and 80s

Regression

In the late 90s, Lake Erie began to show symptoms that had been absent for many years: Dead algal mats and plant material washing up on beaches Birds dying from botulism Walleye population decreased by 66% Toxic chemicals increasing in fish and birds Fish have persistent and increasing numbers of tumours The “dead zone” (the region where the deeper parts of the lake become anaerobic - approximately <1 ppm oxygen levels - during the summer months) increases and continues to spread. Late 90s problems

Possible reasons for Regression 1. PHOSPHORUS LEVELS Inadequate monitoring (only 8 river stations now monitored versus 33 earlier) Voluntary reporting now in effect Reporting of levels of phosphorus may underestimate amounts: Official reported levels of phosphorus are: Prior to 1960 = approximately 30,000 tonnes per year Target after 1960 = 11,000 tonnes 1999 = 7000 tonnes 2000 = 9000 tonnes Sewage plant overflows due to capacity being exceeded due to population increases Storm sewers and sanitary sewers combined (e.g. in Detroit) Industrial releases not reported Farming use of phosphorus fertilizers and consequent runoff increased Reasons - Phosphorus

State of the Lakes

Possible reasons for Regression 2. ZEBRA MUSSEL INVASION Presence in large numbers may generate a lot of organic material that moves to the deeper zones and causes oxygen depletion. May create habitat for Clostridium botulinum, the organism that cases botulism poisoning through the production of botulinum toxin. The transport of the toxin may be helped by the presence of the round gobi, a species of fish from the Black Sea that feeds on the zebra mussel (also from the Black Sea) and may be the carrier of botulinum toxin to the surface layers as it is eaten by larger fish and then birds. Zebra mussel may be “clarifying” the water by its filter feeding systems and making it less suitable for the walleye species of fish (over 60% decline in just a few years - fishing limits have been halved to try and recover the populations). If the walleye population collapses, the lake is then populated by higher numbers of smaller fish species (such as smelt) - the same as in the 1960s ! Reasons - Zebra MUssels

Possible reasons for Regression 3. GLOBAL WARMING Water from the lake entering intake pipes for municipal water systems has shown a consistent yearly increase in temperature since the 1960s This may cause an extension of the period that the lake is stratified during the summer months and this extension may force more oxygen to be utilized and thus extend the “dead zone” in the central basin Global warming may also lead to lower water levels, decreasing the amount of oxygenated water available in the surface layers. Note: The central basin is only about 22 metres deep and the dead zone is 2 or 3 metres at the bottom Reasons – Global warming

Or, it may be a combination of these factors. Or a complex interaction between these and other, unknown, factors ! Conclusion