Estimating the probability of exceeding elevated pH values critical to fish populations in a hypereutrophic lake

Abstract

Current eutrophication models typically are used to predict seasonal mean conditions. However, the risk of summer fish kills in hypereutrophic lakes is likely to be more closely dependent on periodic extreme events, such as potentially lethal peaks in pH driven by algal photosynthesis. In hypereutrophic Upper Klamath and Agency lakes, Oregon, peak summertime pH values frequently exceed critical levels that can reduce fish growth and survival (pH > 9.50, a likely sublethal tolerance limit for two resident endangered fish species). We developed two empirical models, one parametric and one nonparametric, that predict the likelihood of exceeding user-defined critical values of pH from concentrations of chlorophyll a in these lakes. Separate models were derived to incorporate seasonal dynamics and differences between the two lakes, and the behavior of these models was tested under four different critical pH scenarios. Both parametric and nonparametric models performed similarly, suggesting that management efforts to reduce chlorophyll a in these lakes from 200 to 100 µg·L-1 should decrease the probability of exceeding pH 9.5 by 45%. We suggest that this general approach potentially can be applied to the management of fish populations in other hypereutrophic lakes as well.

Limnological aspects of an Apennine shallow lake

“…In particular the ammonia concentrations along with the pH values detected in the lake easily contributed to the large fish kill observed in the summer of 1997 and 2000. At pH > 9.5 ammonia is present as NH 4 + or NH 4 OH (lethal to fish) with a ratio of 1:1 (Hutchinson 1957) and in lakes with these conditions «summer fish kills» are generally expected (Kann & Smith 1999). On the other hand in May of 1998 and in May of 1999 we probably observed the effects of two «winter fish kills».…”

Modelling ecosystem structure and trophic interactions in a typical cyanobacterial bloom-dominated shallow Lake Dianchi, China

“…In the period of blooms, scums of Microcystis species accumulate on the surface of water and regulate buoyancy for the optimum utilisation of nutrients and light resources (Xiao et al, 2012); this is responsible for water quality deterioration and ecological degradation by severe changes in ecosystem properties (Carpenter et al, 1998;Paerl and Huisman, 2009). Negative impacts of bloom formation and collapse are well known on aquatic ecosystems, including high turbidity and shading the light needed by aquatic plants (Berger, 1989), changing physico-chemical factors (elevated pH and reduced CO 2 ), and producing toxins called microcystins (MCs) that affect the habitats of other biological communities (Kann and Smith, 1999;Hessen et al, 2005). Therefore, some studies have focused on different levels of aquatic organisms along with life cycle of Microcystis (Ke et al, 2008) and even the involved dynamics of the 'microbial loop' (Sommaruga, 1995) to postulate the possible relationship between cyanobacteria and community structure of bacteria and flagellates (Xing et al, 2007;Wilhelm et al, 2011).…”

Status and trends of adult Lost River (<em>Deltistes luxatus</em>) and shortnose (<em>Chasmistes brevirostris</em>) sucker populations in Upper Klamath Lake, Oregon, 2014

“…These conditions lead to massive blooms of the cyanobacterium Aphanizomenon flos-aquae between June and October of each year (Wood and others, 2006;Hoilman and others, 2008;Lindenberg and others, 2009;Eldridge and others, 2012). The algal blooms and their subsequent die-offs produce water quality conditions that are harmful to fish health-low concentrations of dissolved oxygen, elevated concentrations of ammonia, high pH, and high concentrations of toxic microcystins (Kann and Smith, 1999;Eldridge and others, 2013). Poor water quality conditions are thought to have contributed to a number of substantial fish die-offs in the lake, most recently during the summers of 1986, 1995, 1996, and 1997(Perkins and others, 2000National Research Council, 2004), and to a much lesser extent in 2003 (U.S. Geological Survey, unpub.…”