Thresholds for Survival of Brown Trout during the Spring Flood Acid Pulse in Streams High in Dissolved Organic Carbon

Abstract

The survival of brown trout Salmo trutta embryos and first-year juveniles was studied using in situ bioassays during the snowmelt-driven spring flood in 12 streams in northern Sweden. Unlike in most previous studies on the impact of acidity on brown trout, the streams in this study were high in dissolved organic carbon (DOC), and as a result organic acids play a primary role in controlling pH. During the spring flood period DOC concentrations increased strongly in most streams and, in combination with dilution of acid-neutralizing capacity, resulted in a decrease in pH and an increase in total and inorganic monomeric aluminum. High mortality of brown trout juveniles occurred during the spring flood and was best correlated to the high H þ concentration. No toxic effect could be directly attributed to measured inorganic aluminum concentrations. An empirical model to predict juvenile brown trout mortality in DOC-rich streams was developed, and based on these predictions a critical chemical threshold of pH 4.8-5.4 is proposed for firstyear juveniles. There was high embryo and yolk sac fry survival during the spring flood, even at sites with pH as low as 4.0, suggesting that the pH threshold in DOC-rich waters is lower than the previously established threshold for low-DOC systems. We discuss the complex role that DOC has in humic-rich surface waters, where it both causes a pH decrease and protects against aluminum toxicity in fish. The results suggest that first-year juveniles are likely to be the stage most vulnerable to the effects of episodic pH depression associated with the snowmelt period in northern boreal systems. This results from asynchrony in the seasonality of the spring flood acid pulse and the seasonality of trout embryo development, which is slow in cold northern waters.

Effect of Transient Acid Spikes on Developmental Stages of <i>Lepomis</i> Fishes

“…In waters where acidification is most likely to occur, the early life stages of many freshwater fish species will be close to their survival threshold and only a slight decline in water quality might result in the loss of a complete year class…" By examining sunfishes at several different scales, we have confirmed this prediction. Our finding that post-swim-up fry are significantly more likely to be killed by transient exposure to acidity than other life stages is consistent with the findings of Reader et al [40] and Serrano et al [41] that brown trout (Salmo trutta) become much more susceptible to episodic exposure to acid plus aluminum after the yolk-sac has been absorbed. Most importantly, this finding completes the evidence showing that the episodic pH changes produced by acid rainstorms cause biological damage, by corroborating the conclusion of Stallsmith et al [22] that day-class gaps in the age distribution of young-of-the-year Lepomis collected at Maquan Pond in Plymouth County, MA resulted from the mortality inflicted on Post-Swim-Up fry by transient acid spikes (pH < 5.3) associated with rainstorms during the years 1990-1992.…”

Riparian zone hydrology and soil water total organic carbon (TOC): implications for spatial variability and upscaling of lateral riparian TOC exports

“…Due to its location at the land-stream interface, the RZ can hydrologically and biogeochemically "buffer" lateral subsurface fluxes (McGlynn and Seibert, 2003;Jencso et al, 2009;Rodhe and Seibert, 2011). The RZ thus controls ecologically-significant short-term variations of surface water quality (Cirmo and McDonnell, 1997;Hooper et al, 1998;McClain et al, 2003;Serrano et al, 2008;Berggren et al, 2009) and quantity (Dunne and Black, 1970;Ocampo et al, 2006;McGlynn and McDonnell, 2003). The RZ often distinguishes itself from the surrounding landscape by characteristic hydromorphic features including different soils (Hill, 1990) and vegetation .…”

Influence of host fish age on a mussel parasite differs among rivers: Implications for conservation

“…The potential for mussel dispersal therefore seems to be higher in the Lärje River. Moreover, the survival rates of YOY brown trout may be lower than that of older brown trout (Serrano et al, 2008), which may also have consequences such as lower mussel recruitment in years when the survival of YOY is low. On the other hand, the abundance of different year classes of brown trout differs between years.…”