Total Dissolved Gas Supersaturation Biological Effects , Review of Literature 1980-2007

Abstract

This paper supplements a review of total dissolved gas (TDG) supersaturation literature I prepared in 1979 (Weitkamp and Katz 1980). This later review only addresses literature not covered in the original review with a few exceptions. The literature published since 1980 includes a considerable number of field investigations that provide information on the biological effects of TDG supersaturation under conditions that allow substantially greater hydrostatic compensation (depth) than the shallow depth laboratory studies. The recent literature indicates that TDG supersaturation results in little or no gas bubble disease (GBD) at levels up to 120% of saturation when compensating depths (2 m or more) are available. Research has shown that fish have the capacity to rapidly recover from GBD when they reach compensating depths or TDG supersaturation is decreased. Most instances of GBD have reported low incidence and severity, however there have been a few cases of substantial mortalities reported. The reported mortalities and severe cases of GBD are generally attributed to either TDG supersaturation in situations where available depths are shallow (~1 m or less) or the TDG levels are exceptionally high (>130%). Field investigations have not demonstrated population effects resulting from TDG supersaturation. Generally the biological effects of TDG supersaturation appear to be influenced by the depth distribution of the fish or invertebrates resulting from their natural behavior, and there is limited evidence suggesting active avoidance of high TDG levels. Commonly TDG supersaturation occurs during high flows that increase water depths in rivers resulting in greater depths available to fish and over invertebrates, thereby reducing the potential effects. Generally the difference in sensitivity of various life stages is related to differences in behavior. TDG supersaturation is a natural phenomenon that occurs at falls. Niagara Falls has been demonstrated to produce TDG levels of 120-130%. It is likely that natural falls in the Columbia River System and other locations naturally exposed fish populations to substantial TDG levels. TDG levels that were prevalent downstream from many dams in the 1960s to 1980s have been reduced by various measures, however spill required for fish passage frequently results in moderate levels of TDG supersaturation (up to 120% and higher).